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Sample records for austenitic chromium-nickel steel

  1. Effect of friction deformation on the structure and properties of a metastable austenitic chromium-nickel steel

    NASA Astrophysics Data System (ADS)

    Baraz, V. R.; Fedorenko, O. N.

    2013-04-01

    The effect of surface friction deformation on the phase composition, structure, and strength properties of a ribbon produced from a chromium-nickel steel with metastable austenite is studied. It is shown that friction processing intensifies the γ-α transformation, creating favorable conditions for the formation of a highly dispersed structure in a thin surface layer and, thus, increasing the microhardness, the elastic limit, the fatigue stability, and the Bauschinger effect.

  2. Forming patterns and mechanical properties of austenitic chromium-nickel steel due to strain aging

    NASA Astrophysics Data System (ADS)

    Kamyshanchenko, N. V.; Krasilnikov, V. V.; Nikulin, I. S.; Gal'tsev, A. V.; Belenko, V. A.; Gal'tseva, I. N.

    2016-02-01

    The work presents the results of studies of forming patterns and mechanical properties of martensite transformation, found in the chromium-nickel steels of 08X18H10T grade, subjected to pre-heat treatment followed by deformation aging. Internal energy state is determined by using acoustic emission. The observed patterns improve the mechanical parameters of steels quenched and plastically deformed at low temperature and then subjected to temper under load in the optimum temperature being associated with obtaining a more stable condition of the structure through the processes of relaxation of internal stresses, high dispersion and uniform distribution of carbides and intermetallic particles, increasing the density of dislocations as well as through other processes occurring during deformation aging martensite. Start your abstract here...

  3. Characterization and Evaluation of Aged Chromium Nickel Niobium Stainless Steels

    NASA Astrophysics Data System (ADS)

    Dewar, Matthew

    20Cr-32Ni-1Nb stainless steel alloys are commonly used in hydrogen reformer manifolds for transporting hot hydrogen by-products at 750-950°C. After long periods of exposure, embrittling secondary carbides and intermetallic phases can precipitate at the grain boundaries which can drastically reduce the ductility, and the repair weldability of the alloy. The intermetallic silicide, G-phase, is commonly observed in 20Cr-32Ni-1Nb stainless steels, and is prone to liquation cracking during welding operations. G-phase is deleterious to the material, where a high degree of G-phase coarsening will render the material unweldable. The present work will investigate various methods in mitigating G-phase precipitation. Variations in casting methods, wall thickness, homogenization treatments, and alloy chemistry will be examined by evaluating their microstructure after periodically aging the samples. Thermodynamic equilibrium modeling using computational thermodynamic tools will be used to optimize the 20Cr-32Ni-1Nb chemistry following ASTM specifications.

  4. Thermophysical Properties of a Chromium Nickel Molybdenum Steel in the Solid and Liquid Phases

    NASA Astrophysics Data System (ADS)

    Wilthan, B.; Reschab, H.; Tanzer, R.; Schützenhöfer, W.; Pottlacher, Gernot

    2008-02-01

    Numerical simulation of vacuum arc re-melting, pressurized or protective electro-slag re-melting, and ingot casting have become quite important in the metal industry. However, a major drawback of these simulation techniques is the lack of accurate thermophysical properties for temperatures above 1,500 K. Heat capacity, heat of fusion, density, and thermal conductivity are important input parameters for the heat transfer equation. Since, direct measurements of thermal conductivity of alloys in the liquid state are almost impossible, its estimation from electrical conductivity using the Wiedemann Franz law is very useful. The afore-mentioned thermophysical properties of several steels are investigated within the context of an ongoing project. Here, we present a full set of thermophysical data for the chromium nickel molybdenum steel meeting the standard DIN 1.4435 (X2CrNiMo18-14-3); these values will be used by our partner to simulate various re-melting and solidification processes. Wire-shaped samples of the steel are resistively volume-heated, as part of a fast capacitor discharge circuit. Time-resolved measurements with sub-μs resolution of current through the specimen are performed with a Pearson probe. The voltage drop across the specimen is measured with knife-edge contacts and ohmic voltage dividers, the temperature of the sample with a pyrometer, and the volumetric expansion of the wire with a fast acting CCD camera. These measurements enable the heat of fusion, the heat capacity, and the electrical resistivity to be determined as a function of temperature in the solid and liquid phases. The thermal conductivity and thermal diffusivity are estimated via the Wiedemann Franz law.

  5. Tensile and pack compressive tests of some sheets of aluminum alloy, 1025 carbon steel, and chromium-nickel steel

    NASA Technical Reports Server (NTRS)

    Atchison, C S; Miller, James A

    1942-01-01

    Tensile and compressive stress-strain curves, stress-deviation curves, and secant modulus-stress curves are given for longitudinal and transverse specimens of 17S-T, 24S-T, and 24S-RT aluminum-alloy sheet in thicknesses from 0.032 to 0.081 inch, 1025 carbon steel sheet in thicknesses of 0.054 and 0.120 inch, and chromium-nickel steel sheet in thicknesses form 0.020 to 0.0275 inch. Significant differences were found between the tensile and the compressive stress-strain curves, and also the corresponding corollary curves; similarly, differences were found between the curves for the longitudinal and transverse directions. These differences are of particular importance in considering the compressive strength of aircraft structures made of thin sheet. They are explored further for the case of compression by giving tangent modulus-stress curves in longitudinal and transverse compression and dimensionless curves of the ratio of tangent modulus to Young's modulus and of the ratio of reduced modulus for a rectangular section to Young's modulus, both plotted against the ratio of stress to secant yield strength.

  6. Phase control of austenitic chrome-nickel steel

    SciTech Connect

    Korkh, M. K. Davidov, D. I. Korkh, J. V. Rigmant, M. B. Nichipuruk, A. P. Kazantseva, N. V.

    2015-10-27

    The paper presents the results of the comparative study of the possibilities of different structural and magnetic methods for detection and visualization of the strain-induced martensitic phase in low carbon austenitic chromium-nickel steel. Results of TEM, SEM, optical microscopy, atomic and magnetic force microscopy, and magnetic measurements are presented. Amount of the magnetic strain-induced martensite was estimated. We pioneered magnetic force microscopic images of the single domain cluster distribution of the strain-induced martensite in austenite-ferrite materials.

  7. Corrosion of some chromium-nickel steels and alloys in sulfuric acid solutions of sodium sulfite

    SciTech Connect

    Kopeliovich, D.K.; Glagolenko, Yu.V.; Ermolinskii, S.P.

    1988-05-01

    Steels 12Kh18N1OT and 10Kh17N13M3T and alloys 06KhN28MDT and 46KhNM were studied in sulfuric acid solutions containing sodium sulfite and sulfur dioxide to determine the effects of different concentrations of the corrosive constituents on the anodic and cathodic active and passive corrosion behavior of the metals. Polarization curves were obtained with a P-5827 M potentiostat. Addition of sulfite facilitated both electrode processes and the region of the reactive state was broadened due to the shift of passivation potentials to more positive values. The activating effect of sulfite reduction products were confirmed by tests of alloys in spent solutions. This increased likelihood of activation and the decrease of the solutions's own corrosion potential were both attributed to retardation of the cathodic process by lower valence sulfur compounds.

  8. Hydrogen isotope transfer in austenitic steels and high-nickel alloy during in-core irradiation

    SciTech Connect

    Polosukhin, B.G.; Sulimov, E.M.; Zyrianov, A.P.; Kalinin, G.M.

    1995-10-01

    The transfer of protium and deuterium in austenitic chromium-nickel steels and in a high-nickel alloy was studied in a specially designed facility. The transfer parameters of protium and deuterium were found to change greatly during in-core irradiation, and the effects of irradiation increased as the temperature decreased. Thus, at temperature T<673K, the relative increase in the permeability of hydrogen isotopes under irradiation can be orders of magnitude higher in these steels. Other radiation effects were also observed, in addition to the changes from the initial values in the effects of protium and deuterium isotopic transfer. 4 refs., 3 figs., 2 tabs.

  9. Standard specification for castings of iron-chromium-nickel-molybdenum corrosion-resistant, duplex (austenitic/ferritic) for general application. ASTM standard

    SciTech Connect

    1998-08-01

    This specification is under the jurisdiction of ASTM Committee A-1 on Steel, Stainless Steel, and Related Alloys and is the direct responsibility of Subcommittee A01.18 on Castings. Current edition approved Nov. 10, 1997 and published August 1998. Originally published as A 890-88. Last previous edition was A 890/A 890M-94a.

  10. High Mn austenitic stainless steel

    DOEpatents

    Yamamoto, Yukinori [Oak Ridge, TN; Santella, Michael L [Knoxville, TN; Brady, Michael P [Oak Ridge, TN; Maziasz, Philip J [Oak Ridge, TN; Liu, Chain-tsuan [Knoxville, TN

    2010-07-13

    An austenitic stainless steel alloy includes, in weight percent: >4 to 15 Mn; 8 to 15 Ni; 14 to 16 Cr; 2.4 to 3 Al; 0.4 to 1 total of at least one of Nb and Ta; 0.05 to 0.2 C; 0.01 to 0.02 B; no more than 0.3 of combined Ti+V; up to 3 Mo; up to 3 Co; up to 1W; up to 3 Cu; up to 1 Si; up to 0.05 P; up to 1 total of at least one of Y, La, Ce, Hf, and Zr; less than 0.05 N; and base Fe, wherein the weight percent Fe is greater than the weight percent Ni, and wherein the alloy forms an external continuous scale including alumina, nanometer scale sized particles distributed throughout the microstructure, the particles including at least one of NbC and TaC, and a stable essentially single phase FCC austenitic matrix microstructure that is essentially delta-ferrite-free and essentially BCC-phase-free.

  11. Standard specification for heat-resisting chromium and chromium-nickel stainless steel plate, sheet, and strip for pressure vessels. ASTM standard

    SciTech Connect

    1998-10-01

    This specification is under the jurisdiction of ASTM Committee A-1 on Steel, Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee A01.17 on Flat Stainless Steel Products. Current edition approved Sep. 10, and Nov. 10, 1997, Apr. 10, and Jun. 10, 1998. Published October 1998. Originally published as A 240-40T. Last previous edition A 240/A 240M-97a.

  12. Tensile behavior of an austenitic stainless steel subjected to multidirectional forging

    NASA Astrophysics Data System (ADS)

    Tikhonova, M.; Sorokopudova, J.; Bondareva, E.; Belyakov, A.; Kaibyshev, R.

    2014-08-01

    The mechanical behavior of a chromium-nickel austenitic stainless steel with submicrocrystalline structures produced by multidirectional forging (MDF) to a total strain of ~ 4 at temperatures of 700 and 600°C was studied. This processing resulted in the formation of uniform ultrafine grained structure with an average crystallite size of 360 and 300 nm, respectively, and high dislocation density. The tensile tests were carried out in a wide temperature range 20-650°C. At ambient temperature, the yield stress (YS) comprised 900 MPa and 730 MPa in the samples subjected to MDF at 600 and 700°C, respectively. It should be noted that this strength was achieved along with elongations of 16% and 22% in the samples subjected to MDF at 600 and 700°C. The YS decreased and elongation-to-failure tends to increase with increasing test temperature and approaching 235 MPa and 51%, respectively, at 650°C. Effect of temperature on mechanical behavior of stainless steel with submicrocrystalline structure is discussed.

  13. Explosive Surface Hardening of Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Kovacs-Coskun, T.

    2016-04-01

    In this study, the effects of explosion hardening on the microstructure and the hardness of austenitic stainless steel have been studied. The optimum explosion hardening technology of austenitic stainless steel was researched. In case of the explosive hardening used new idea mean indirect hardening setup. Austenitic stainless steels have high plasticity and can be easily cold formed. However, during cold processing the hardening phenomena always occurs. Upon the explosion impact, the deformation mechanism indicates a plastic deformation and this deformation induces a phase transformation (martensite). The explosion hardening enhances the mechanical properties of the material, includes the wear resistance and hardness. In case of indirect hardening as function of the setup parameters specifically the flayer plate position the hardening increased differently. It was find a relationship between the explosion hardening setup and the hardening level.

  14. Austenitic stainless steels for cryogenic service

    SciTech Connect

    Dalder, E.N.C.; Juhas, M.C.

    1985-09-19

    Presently available information on austenitic Fe-Cr-Ni stainless steel plate, welds, and castings for service below 77 K are reviewed with the intent (1) of developing systematic relationships between mechanical properties, composition, microstructure, and processing, and (2) of assessing the adequacy of these data bases in the design, fabrication, and operation of engineering systems at 4 K.

  15. Cast alumina forming austenitic stainless steels

    DOEpatents

    Muralidharan, Govindarajan; Yamamoto, Yukinori; Brady, Michael P

    2013-04-30

    An austenitic stainless steel alloy consisting essentially of, in terms of weight percent ranges 0.15-0.5C; 8-37Ni; 10-25Cr; 2.5-5Al; greater than 0.6, up to 2.5 total of at least one element selected from the group consisting of Nb and Ta; up to 3Mo; up to 3Co; up to 1W; up to 3Cu; up to 15Mn; up to 2Si; up to 0.15B; up to 0.05P; up to 1 total of at least one element selected from the group consisting of Y, La, Ce, Hf, and Zr; <0.3Ti+V; <0.03N; and, balance Fe, where the weight percent Fe is greater than the weight percent Ni, and wherein the alloy forms an external continuous scale comprising alumina, and a stable essentially single phase FCC austenitic matrix microstructure, the austenitic matrix being essentially delta-ferrite free and essentially BCC-phase-free. A method of making austenitic stainless steel alloys is also disclosed.

  16. Pitting corrosion resistant austenite stainless steel

    DOEpatents

    van Rooyen, D.; Bandy, R.

    A pitting corrosion resistant austenite stainless steel comprises 17 to 28 wt. % chromium, 15 to 26 wt. % nickel, 5 to 8 wt. % molybdenum, and 0.3 to 0.5 wt. % nitrogen, the balance being iron, unavoidable impurities, minor additions made in the normal course of melting and casting alloys of this type, and may optionally include up to 10 wt. % of manganese, up to 5 wt. % of silicon, and up to 0.08 wt. % of carbon.

  17. Embrittlement of austenitic stainless steel welds

    SciTech Connect

    David, S.A.; Vitek, J.M.; Alexander, D.J.

    1995-06-01

    To prevent hot-cracking, austenitic stainless steel welds generally contain a small percent of delta ferrite. Although ferrite has been found to effectively prevent hot-cracking, it can lead to embrittlement of welds when exposed to elevated temperatures. The aging behavior of type-308 stainless steel weld has been examined over a range of temperatures 475--850 C for times up to 10,000 hrs. Upon aging, and depending on the temperature range, the unstable ferrite may undergo a variety of solid state transformations. These phase changes creep-rupture and Charpy impact properties.

  18. The chemical composition of precipitated austenite in 9Ni steel

    NASA Astrophysics Data System (ADS)

    Fultz, B.; Kim, J. I.; Kim, Y. H.; Morris, J. W.

    1986-06-01

    Analytical scanning transmission electron microscopy and a novel Mössbauer spectrometry technique were used to measure the chemical composition of austenite particles which precipitate during intercritical tempering of 9Ni steel. Both techniques showed an enrichment of Ni, Mn, Cr, and Si in the austenite. A straightforward analysis involving data on both austenite composition and austenite formation kinetics suggests that the growth of austenite particles is controlled by a 3-dimensional diffusion process. The segregation of solutes to the austenite accounts for much of its stability against the martensitic transformation at low temperatures. Composition inhomogeneities develop in austenite particles after long temperings; the central regions of the particles are lean in solutes and are first to undergo the martensitic transformation. However, changes in solute concentrations of the austenite during long temperings seem too small to account for the large changes in austenite stability. It appears that some of the stability of precipitated austenite must be microstructural in origin.

  19. Instabilities in stabilized austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Ayer, Raghavan; Klein, C. F.; Marzinsky, C. N.

    1992-09-01

    The effect of aging on the precipitation of grain boundary phases in three austenitic stainless steels (AISI 347, 347AP, and an experimental steel stabilized with hafnium) was investigated. Aging was performed both on bulk steels as well as on samples which were subjected to a thermal treatment to simulate the coarse grain region of the heat affected zone (HAZ) during welding. Aging of the bulk steels at 866 K for 8000 hours resulted in the precipitation of Cr23C6 carbides, σ, and Fe2Nb phases; the propensity for precipitation was least for the hafnium-stabilized steel. Weld simulation of the HAZ resulted in dissolution of the phases present in the as-received 347 and 347AP steels, leading to grain coarsening. Subsequent aging caused extensive grain boundary Cr23C6 carbides and inhomogeneous matrix precipitation. In addition, steel 347AP formed a precipitate free zone (PFZ) along the grain boundaries. The steel containing hafnium showed the best microstructural stability to aging and welding.

  20. Embrittlement of austenitic stainless steel welds

    SciTech Connect

    David, S.A.; Vitek, J.M.

    1997-12-31

    The microstructure of type-308 austenitic stainless steel weld metal containing {gamma} and {delta} and ferrite is shown. Typical composition of the weld metal is Cr-20.2, Ni-9.4, Mn-1.7, Si-0.5, C-0.05, N-0.06 and balance Fe (in wt %). Exposure of austenitic stainless steel welds to elevated temperatures can lead to extensive changes in the microstructural features of the weld metal. On exposure to elevated temperatures over a long period of time, a continuous network of M{sub 23}C{sub 6} carbide forms at the austenite/ferrite interface. Upon aging at temperatures between 550--850 C, ferrite in the weld has been found to be unstable and transforms to sigma phase. These changes have been found to influence mechanical behavior of the weld metal, in particular the creep-rupture properties. For aging temperatures below 550 C the ferrite decomposes spinodally into {alpha} and {alpha}{prime} phases. In addition, precipitation of G-phase occurs within the decomposed ferrite. These transformations at temperatures below 550 C lead to embrittlement of the weld metal as revealed by the Charpy impact properties.

  1. Weldment for austenitic stainless steel and method

    DOEpatents

    Bagnall, Christopher; McBride, Marvin A.

    1985-01-01

    For making defect-free welds for joining two austenitic stainless steel mers, using gas tungsten-arc welding, a thin foil-like iron member is placed between the two steel members to be joined, prior to making the weld, with the foil-like iron member having a higher melting point than the stainless steel members. When the weld is formed, there results a weld nugget comprising melted and then solidified portions of the joined members with small portions of the foil-like iron member projecting into the solidified weld nugget. The portions of the weld nugget proximate the small portions of the foil-like iron member which project into the weld nugget are relatively rich in iron. This causes these iron-rich nugget portions to display substantial delta ferrite during solidification of the weld nugget which eliminates weld defects which could otherwise occur. This is especially useful for joining austenitic steel members which, when just below the solidus temperature, include at most only a very minor proportion of delta ferrite.

  2. Microstructural studies of advanced austenitic steels

    SciTech Connect

    Todd, J. A.; Ren, Jyh-Ching

    1989-11-15

    This report presents the first complete microstructural and analytical electron microscopy study of Alloy AX5, one of a series of advanced austenitic steels developed by Maziasz and co-workers at Oak Ridge National Laboratory, for their potential application as reheater and superheater materials in power plants that will reach the end of their design lives in the 1990's. The advanced steels are modified with carbide forming elements such as titanium, niobium and vanadium. When combined with optimized thermo-mechanical treatments, the advanced steels exhibit significantly improved creep rupture properties compared to commercially available 316 stainless steels, 17--14 Cu--Mo and 800 H steels. The importance of microstructure in controlling these improvements has been demonstrated for selected alloys, using stress relaxation testing as an accelerated test method. The microstructural features responsible for the improved creep strengths have been identified by studying the thermal aging kinetics of one of the 16Ni--14Cr advanced steels, Alloy AX5, in both the solution annealed and the solution annealed plus cold worked conditions. Time-temperature-precipitation diagrams have been developed for the temperature range 600 C to 900 C and for times from 1 h to 3000 h. 226 refs., 88 figs., 10 tabs.

  3. Wear behavior of austenite containing plate steels

    NASA Astrophysics Data System (ADS)

    Hensley, Christina E.

    As a follow up to Wolfram's Master of Science thesis, samples from the prior work were further investigated. Samples from four steel alloys were selected for investigation, namely AR400F, 9260, Hadfield, and 301 Stainless steels. AR400F is martensitic while the Hadfield and 301 stainless steels are austenitic. The 9260 exhibited a variety of hardness levels and retained austenite contents, achieved by heat treatments, including quench and tempering (Q&T) and quench and partitioning (Q&P). Samples worn by three wear tests, namely Dry Sand/Rubber Wheel (DSRW), impeller tumbler impact abrasion, and Bond abrasion, were examined by optical profilometry. The wear behaviors observed in topography maps were compared to the same in scanning electron microscopy micrographs and both were used to characterize the wear surfaces. Optical profilometry showed that the scratching abrasion present on the wear surface transitioned to gouging abrasion as impact conditions increased (i.e. from DSRW to impeller to Bond abrasion). Optical profilometry roughness measurements were also compared to sample hardness as well as normalized volume loss (NVL) results for each of the three wear tests. The steels displayed a relationship between roughness measurements and observed wear rates for all three categories of wear testing. Nanoindentation was used to investigate local hardness changes adjacent to the wear surface. DSRW samples generally did not exhibit significant work hardening. The austenitic materials exhibited significant hardening under the high impact conditions of the Bond abrasion wear test. Hardening in the Q&P materials was less pronounced. The Q&T microstructures also demonstrated some hardening. Scratch testing was performed on samples at three different loads, as a more systematic approach to determining the scratching abrasion behavior. Wear rates and scratch hardness were calculated from scratch testing results. Certain similarities between wear behavior in scratch testing

  4. Radiation resistant austenitic stainless steel alloys

    DOEpatents

    Maziasz, Philip J.; Braski, David N.; Rowcliffe, Arthur F.

    1989-01-01

    An austenitic stainless steel alloy, with improved resistance to radiation-induced swelling and helium embrittlement, and improved resistance to thermal creep at high temperatures, consisting essentially of, by weight percent: from 16 to 18% nickel; from 13 to 17% chromium; from 2 to 3% molybdenum; from 1.5 to 2.5% manganese; from 0.01 to 0.5% silicon; from 0.2 to 0.4% titanium; from 0.1 to 0.2% niobium; from 0.1 to 0.6% vanadium; from 0.06 to 0.12% carbon; from 0.01% to 0.03% nitrogen; from 0.03 to 0.08% phosphorus; from 0.005 to 0.01% boron; and the balance iron, and wherein the alloy may be thermomechanically treated to enhance physical and mechanical properties.

  5. Radiation resistant austenitic stainless steel alloys

    DOEpatents

    Maziasz, P.J.; Braski, D.N.; Rowcliffe, A.F.

    1987-02-11

    An austenitic stainless steel alloy, with improved resistance to radiation-induced swelling and helium embrittlement, and improved resistance to thermal creep at high temperatures, consisting essentially of, by weight percent: from 16 to 18% nickel; from 13 to 17% chromium; from 2 to 3% molybdenum; from 1.5 to 2.5% manganese; from 0.01 to 0.5% silicon; from 0.2 to 0.4% titanium; from 0.1 to 0.2% niobium; from 0.1 to 0.6% vanadium; from 0.06 to 0.12% carbon; from 0.01 to 0.03% nitrogen; from 0.03 to 0.08% phosphorus; from 0.005 to 0.01% boron; and the balance iron, and wherein the alloy may be thermomechanically treated to enhance physical and mechanical properties. 4 figs.

  6. Austenitic stainless steel for high temperature applications

    DOEpatents

    Johnson, Gerald D.; Powell, Roger W.

    1985-01-01

    This invention describes a composition for an austenitic stainless steel which has been found to exhibit improved high temperature stress rupture properties. The composition of this alloy is about (in wt. %): 12.5 to 14.5 Cr; 14.5 to 16.5 Ni; 1.5 to 2.5 Mo; 1.5 to 2.5 Mn; 0.1 to 0.4 Ti; 0.02 to 0.08 C; 0.5 to 1.0 Si; 0.01 maximum, N; 0.02 to 0.08 P; 0.002 to 0.008 B; 0.004-0.010 S; 0.02-0.05 Nb; 0.01-0.05 V; 0.005-0.02 Ta; 0.02-0.05 Al; 0.01-0.04 Cu; 0.02-0.05 Co; 0.03 maximum, As; 0.01 maximum, O; 0.01 maximum, Zr; and with the balance of the alloy being essentially iron. The carbon content of the alloy is adjusted such that wt. % Ti/(wt. % C+wt. % N) is between 4 and 6, and most preferably about 5. In addition the sum of the wt. % P+wt. % B+wt. % S is at least 0.03 wt. %. This alloy is believed to be particularly well suited for use as fast breeder reactor fuel element cladding.

  7. Weldable, age hardenable, austenitic stainless steel

    DOEpatents

    Brooks, J.A.; Krenzer, R.W.

    1975-07-22

    An age hardenable, austenitic stainless steel having superior weldability properties as well as resistance to degradation of properties in a hydrogen atmosphere is described. It has a composition of from about 24.0 to about 34.0 weight percent (w/o) nickel, from about 13.5 to about 16.0 w/o chromium, from about 1.9 to about 2.3 w/o titanium, from about 1.0 to about 1.5 w/ o molybdenum, from about 0.01 to about 0.05 w/o carbon, from about 0 to about 0.25 w/o manganese, from about 0 to about 0.01 w/o phosphorous and preferably about 0.005 w/o maximum, from about 0 to about 0.010 w/o sulfur and preferably about 0.005 w/o maximum, from about 0 to about 0.25 w/o silicon, from about 0.1 to about 0.35 w/o aluminum, from about 0.10 to about 0.50 w/o vanadium, from about 0 to about 0.0015 w/o boron, and the balance essentially iron. (auth)

  8. Weldability of neutron irradiated austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Asano, Kyoichi; Nishimura, Seiji; Saito, Yoshiaki; Sakamoto, Hiroshi; Yamada, Yuji; Kato, Takahiko; Hashimoto, Tsuneyuki

    1999-01-01

    Degradation of weldability in neutron irradiated austenitic stainless steel is an important issue to be addressed in the planning of proactive maintenance of light water reactor core internals. In this work, samples selected from reactor internal components which had been irradiated to fluence from 8.5 × 10 22 to 1.4 × 10 26 n/m 2 ( E > 1 MeV) corresponding to helium content from 0.11 to 103 appm, respectively, were subjected to tungsten inert gas arc (TIG) welding with heat input ranged 0.6-16 kJ/cm. The weld defects were characterized by penetrant test and cross-sectional metallography. The integrity of the weld was better when there were less helium and at lower heat input. Tensile properties of weld joint containing 0.6 appm of helium fulfilled the requirement for unirradiated base metal. Repeated thermal cycles were found to be very hazardous. The results showed the combination of material helium content and weld heat input where materials can be welded with little concern to invite cracking. Also, the importance of using properly selected welding procedures to minimize thermal cycling was recognized.

  9. Solidification behavior of austenitic stainless steel filler metals

    SciTech Connect

    David, S.A.; Goodwin, G.M.; Braski, D.N.

    1980-02-01

    Thermal analysis and interrupted solidification experiments on selected austenitic stainless steel filler metals provided an understanding of the solidification behavior of austenitic stainless steel welds. The sequences of phase separations found were for type 308 stainless steel filler metal, L + L + delta + L + delta + ..gamma.. ..-->.. ..gamma.. + delta, and for type 310 stainless steel filler metal, L ..-->.. L + ..gamma.. ..-->.. ..gamma... In type 308 stainless steel filler metal, ferrite at room temperature was identified as either the untransformed primary delta-ferrite formed during the initial stages of solidification or the residual ferrite after Widmanstaetten austenite precipitation. Microprobe and scanning transmission electron microscope microanalyses revealed that solute extensively redistributes during the transformation of primary delta-ferrite to austenite, leading to enrichment and stabilization of ferrite by chromium. The type 310 stainless steel filler metal investigated solidifies by the primary crystallization of austenite, with the transformation going to completion at the solidus temperature. In our samples residual ferrite resulting from solute segregation was absent at the intercellular or interdendritic regions.

  10. The mechanical stability of precipitated austenite in 9Ni steel

    NASA Astrophysics Data System (ADS)

    Fultz, B.; Morris, J. W.

    1985-12-01

    The strains inherent to the martensitic transformation of austenite particles in 9Ni steel create dislocation structures in the tempered martensite. These dislocation structures were studied by the complementary techniques of X-ray line profile analysis and transmission electron microscopy. The energy required to form these dislocation structures affects the thermodynamics of the transformation. We propose that changes in these dislocation structures reduce the “mechanical stability” of the austenite particles as they grow larger during isothermal tempering.

  11. Austenite recrystallization and carbonitride precipitation in niobium microalloyed steels

    SciTech Connect

    Speer, J.G.; Hansen, S.S. )

    1989-01-01

    The response of austenite to thermomechanical treatment is investigated in two series of niobium microalloyed steels. Optical and electron metallographic techniques were used to follow the austenite recystallizaiton and carbonitride precipitation reactions in these steels. The first series of steels contained a constant level of 0.05Nb, with carbon levels varying from 0.008 to 0.25 pct. It was found that a lower carbon concentration results in faster austenite recrystallization due to a smaller carbonitride supersaturation which leads to a reduced precipitate nucleation rate. The second series of steels was designed with a constant carbonitride supersaturation by simultaneously varying the Nb and C concentrations while maintaining a constant solubility product. In these steels, the recrystallization kinetics increase as the volume fraction of Nb(C,N) is reduced and/or as the precipitate coarsening rate is increased. The volume fraction of carbonitrides increases as the Nb:(C + 12/14 N) ratio approaches the stoichiometric ratio of approximately 8:1. An experiment to determine whether Nb atoms dissolved in the austenite could exert a significant solute-drag effect on the recrystallization reaction indicated that 0.20Nb in solution could reduce the rate of recrystallization compared to a Nb-free C-Mn steel.

  12. Influence of Martensite Fraction on the Stabilization of Austenite in Austenitic-Martensitic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Huang, Qiuliang; De Cooman, Bruno C.; Biermann, Horst; Mola, Javad

    2016-05-01

    The influence of martensite fraction ( f α') on the stabilization of austenite was studied by quench interruption below M s temperature of an Fe-13Cr-0.31C (mass pct) stainless steel. The interval between the quench interruption temperature and the secondary martensite start temperature, denoted as θ, was used to quantify the extent of austenite stabilization. In experiments with and without a reheating step subsequent to quench interruption, the variation of θ with f α' showed a transition after transformation of almost half of the austenite. This trend was observed regardless of the solution annealing temperature which influenced the martensite start temperature. The transition in θ was ascribed to a change in the type of martensite nucleation sites from austenite grain and twin boundaries at low f α' to the faults near austenite-martensite (A-M) boundaries at high f α'. At low temperatures, the local carbon enrichment of such boundaries was responsible for the enhanced stabilization at high f α'. At high temperatures, relevant to the quenching and partitioning processing, on the other hand, the pronounced stabilization at high f α' was attributed to the uniform partitioning of the carbon stored at A-M boundaries into the austenite. Reduction in the fault density of austenite served as an auxiliary stabilization mechanism at high temperatures.

  13. Bainitic stabilization of austenite in low alloy sheet steels

    NASA Astrophysics Data System (ADS)

    Brandt, Mitchell L.

    The stabilization of retained austenite in 'triple phase' ferrite/bainite/austenite sheet steels by isothermal bainite transformation after intercritical annealing has been studied in 0.27C-1.5Si steels with 0.8 to 2.4Mn. Dilatometric studies show that cooling rates comparable to CAPL processing result in approximately 30% conversion of austenite to epitaxial ferrite, but the reaction can be suppressed by the faster cooling rate of salt bath quenching. Measured isothermal transformation kinetics at 350 to 450sp°C shows a maximum overall rate near 400sp°C. X-ray diffraction shows that the amount of austenite retained from 400sp°C treatment peaks at 3 minutes but the carbon content increases monotonically to a saturation level. The stability of austenite in this type of steel has been quantified for the first time by direct measurement of the characteristic Msbsps{sigma} temperature. With variations in processing conditions and test temperatures, the tensile uniform ductility has been correlated with the amount and stability of retained austenite, while maintaining a constant 3% flow of 83 ksi. Consistent with previous transformations plasticity studies an optimal austenite stability is found at approximately 10 K above the Msbsps{sigma} temperature, demonstrating a maximum uniform ductility of 44% for an austenite content of 16%. Correlations indicate that desired uniform ductility levels of 20 to 25% could be achieved with only approximately 5% austenite if stability is optimized by placing Msbsps{sigma} 10 K below ambient temperature. Measured uniform ductility in plane strain tension shows similar trends with processing conditions, but models predict that stress state effects will shift the Msbsps{sigma} temperature approximately 5 K higher than that for uniaxial tension. The measured dependence of Msbsps{sigma} on austenite composition and particle size has been modeled via heterogeneous nucleation theory. The composition dependence is consistent with

  14. Nanostructured nickel-free austenitic stainless steel/hydroxyapatite composites.

    PubMed

    Tulinski, Maciej; Jurczyk, Mieczyslaw

    2012-11-01

    In this work Ni-free austenitic stainless steels with nanostructure and their nanocomposites with hydroxyapatite are presented and characterized by means of X-ray diffraction and optical profiling. The samples were synthesized by mechanical alloying, heat treatment and nitriding of elemental microcrystalline powders with addition of hydroxyapatite (HA). In our work we wanted to introduce into stainless steel hydroxyapatite ceramics that have been intensively studied for bone repair and replacement applications. Such applications were chosen because of their high biocompatibility and ability to bond to bone. Since nickel-free austenitic stainless steels seem to have better mechanical properties, corrosion resistance and biocompatibility compared to 316L stainless steels, it is possible that composite made of this steel and HA could improve properties, as well. Mechanical alloying and nitriding are very effective technologies to improve the corrosion resistance of stainless steel. Similar process in case of nanocomposites of stainless steel with hydroxyapatite helps achieve even better mechanical properties and corrosion resistance. Hence nanocrystalline nickel-free stainless steels and nickel-free stainless steel/hydroxyapatite nanocomposites could be promising bionanomaterials for use as a hard tissue replacement implants, e.g., orthopedic implants. In such application, the surface roughness and more specifically the surface topography influences the proliferation of cells (e.g., osteoblasts). PMID:23421285

  15. An alternative to the crystallographic reconstruction of austenite in steels

    SciTech Connect

    Bernier, Nicolas; Bracke, Lieven; Malet, Loïc; Godet, Stéphane

    2014-03-01

    An alternative crystallographic austenite reconstruction programme written in Matlab is developed by combining the best features of the existing models: the orientation relationship refinement, the local pixel-by-pixel analysis and the nuclei identification and spreading strategy. This programme can be directly applied to experimental electron backscatter diffraction mappings. Its applicability is demonstrated on both quenching and partitioning and as-quenched lath-martensite steels. - Highlights: • An alternative crystallographic austenite reconstruction program is developed. • The method combines a local analysis and a nuclei identification/spreading strategy. • The validity of the calculated orientation relationship is verified on a Q and P steel. • The accuracy of the reconstructed microtexture is investigated on a martensite steel.

  16. Accurate modelling of anisotropic effects in austenitic stainless steel welds

    SciTech Connect

    Nowers, O. D.; Duxbury, D. J.; Drinkwater, B. W.

    2014-02-18

    The ultrasonic inspection of austenitic steel welds is challenging due to the formation of highly anisotropic and heterogeneous structures post-welding. This is due to the intrinsic crystallographic structure of austenitic steel, driving the formation of dendritic grain structures on cooling. The anisotropy is manifested as both a ‘steering’ of the ultrasonic beam and the back-scatter of energy due to the macroscopic granular structure of the weld. However, the quantitative effects and relative impacts of these phenomena are not well-understood. A semi-analytical simulation framework has been developed to allow the study of anisotropic effects in austenitic stainless steel welds. Frequency-dependent scatterers are allocated to a weld-region to approximate the coarse grain-structures observed within austenitic welds and imaged using a simulated array. The simulated A-scans are compared against an equivalent experimental setup demonstrating excellent agreement of the Signal to Noise (S/N) ratio. Comparison of images of the simulated and experimental data generated using the Total Focusing Method (TFM) indicate a prominent layered effect in the simulated data. A superior grain allocation routine is required to improve upon this.

  17. Accurate modelling of anisotropic effects in austenitic stainless steel welds

    NASA Astrophysics Data System (ADS)

    Nowers, O. D.; Duxbury, D. J.; Drinkwater, B. W.

    2014-02-01

    The ultrasonic inspection of austenitic steel welds is challenging due to the formation of highly anisotropic and heterogeneous structures post-welding. This is due to the intrinsic crystallographic structure of austenitic steel, driving the formation of dendritic grain structures on cooling. The anisotropy is manifested as both a `steering' of the ultrasonic beam and the back-scatter of energy due to the macroscopic granular structure of the weld. However, the quantitative effects and relative impacts of these phenomena are not well-understood. A semi-analytical simulation framework has been developed to allow the study of anisotropic effects in austenitic stainless steel welds. Frequency-dependent scatterers are allocated to a weld-region to approximate the coarse grain-structures observed within austenitic welds and imaged using a simulated array. The simulated A-scans are compared against an equivalent experimental setup demonstrating excellent agreement of the Signal to Noise (S/N) ratio. Comparison of images of the simulated and experimental data generated using the Total Focusing Method (TFM) indicate a prominent layered effect in the simulated data. A superior grain allocation routine is required to improve upon this.

  18. Hardenability of austenite in a dual-phase steel

    SciTech Connect

    Sarwar, M.; Priestner, R.

    1999-06-01

    A low-carbon, low-alloy steel was intercritically heat treated and thermomechanically processed to study the martensitic hardenability of austenite present. Rolling of the two-phase ({alpha} + {gamma}) microstructure elongated austenite particles and reduced their martensitic hardenability because the {alpha}/{gamma} interface where new ferrite forms during cooling was increased by the particle elongation. The martensite particles obtained in rolled material were also elongated or fibered in the rolling direction. Therefore, the thermomechanical processing of a two-phase ({alpha} + {gamma}) mixture has the detrimental effect of increasing the quenching power needed to yield a specific amount of martensite.

  19. Oxidation resistant high creep strength austenitic stainless steel

    DOEpatents

    Brady, Michael P.; Pint, Bruce A.; Liu, Chain-Tsuan; Maziasz, Philip J.; Yamamoto, Yukinori; Lu, Zhao P.

    2010-06-29

    An austenitic stainless steel displaying high temperature oxidation and creep resistance has a composition that includes in weight percent 15 to 21 Ni, 10 to 15 Cr, 2 to 3.5 Al, 0.1 to 1 Nb, and 0.05 to 0.15 C, and that is free of or has very low levels of N, Ti and V. The alloy forms an external continuous alumina protective scale to provide a high oxidation resistance at temperatures of 700 to 800.degree. C. and forms NbC nanocarbides and a stable essentially single phase fcc austenitic matrix microstructure to give high strength and high creep resistance at these temperatures.

  20. Intermetallic strengthened alumina-forming austenitic steels for energy applications

    NASA Astrophysics Data System (ADS)

    Hu, Bin

    In order to achieve energy conversion efficiencies of >50 % for steam turbines/boilers in power generation systems, materials required are strong, corrosion-resistant at high temperatures (>700°C), and economically viable. Austenitic steels strengthened with Laves phase and Ni3Al precipitates, and alloyed with aluminum to improve oxidation resistance, are potential candidate materials for these applications. The creep resistance of these alloys is significantly improved through intermetallic strengthening (Laves-Fe 2Nb + L12-Ni3Al precipitates) without harmful effects on oxidation resistance. This research starts with microstructural and microchemical analyses of these intermetallic strengthened alumina-forming austenitic steels in a scanning electron microscope. The microchemistry of precipitates, as determined by energy-dispersive x-ray spectroscopy and transmission electron microscope, is also studied. Different thermo-mechanical treatments were carried out to these stainless steels in an attempt to further improve their mechanical properties. The microstructural and microchemical analyses were again performed after the thermo-mechanical processing. Synchrotron X-ray diffraction was used to measure the lattice parameters of these steels after different thermo-mechanical treatments. Tensile tests at both room and elevated temperatures were performed to study mechanical behaviors of this novel alloy system; the deformation mechanisms were studied by strain rate jump tests at elevated temperatures. Failure analysis and post-mortem TEM analysis were performed to study the creep failure mechanisms of these alumina-forming austenitic steels after creep tests. Experiments were carried out to study the effects of boron and carbon additions in the aged alumina-forming austenitic steels.

  1. Materials compatibility of hydride storage materials with austenitic stainless steels

    SciTech Connect

    Clark, E.A.

    1992-09-21

    This task evaluated the materials compatibility of LaNi[sub 5-x]Al[sub x] (x= 0.3, 0.75) hydrides and palladium coated kieselguhr with austenitic stainless steel in hydrogen and tritium process environments. Based on observations of retired prototype hydride storage beds and materials exposure testing samples designed for this study, no materials compatibility problem was indicated. Scanning electron microscopy observations of features on stainless steel surfaces after exposure to hydrides are also commonly found on as-received materials before hydriding. These features are caused by either normal heat treating and acid cleaning of stainless steel or reflect the final machining operation.

  2. Materials compatibility of hydride storage materials with austenitic stainless steels

    SciTech Connect

    Clark, E.A.

    1992-09-21

    This task evaluated the materials compatibility of LaNi{sub 5-x}Al{sub x} (x= 0.3, 0.75) hydrides and palladium coated kieselguhr with austenitic stainless steel in hydrogen and tritium process environments. Based on observations of retired prototype hydride storage beds and materials exposure testing samples designed for this study, no materials compatibility problem was indicated. Scanning electron microscopy observations of features on stainless steel surfaces after exposure to hydrides are also commonly found on as-received materials before hydriding. These features are caused by either normal heat treating and acid cleaning of stainless steel or reflect the final machining operation.

  3. Materials compatibility of hydride storage materials with austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Clark, E. A.

    1992-09-01

    This task evaluated the materials compatibility of LaNi(5-x)Al(x) (x= 0.3, 0.75) hydrides and palladium coated kieselguhr with austenitic stainless steel in hydrogen and tritium process environments. Based on observations of retired prototype hydride storage beds and materials exposure testing samples designed for this study, no materials compatibility problem was indicated. Scanning electron microscopy observations of features on stainless steel surfaces after exposure to hydrides are also commonly found on as-received materials before hydriding. These features are caused by either normal heat treating and acid cleaning of stainless steel or reflect the final machining operation.

  4. Characterization of microstructure and texture across dissimilar super duplex/austenitic stainless steel weldment joint by austenitic filler metal

    SciTech Connect

    Eghlimi, Abbas; Shamanian, Morteza; Eskandarian, Masoomeh; Zabolian, Azam; Szpunar, Jerzy A.

    2015-08-15

    The evolution of microstructure and texture across an as-welded dissimilar UNS S32750 super duplex/UNS S30403 austenitic stainless steel joint welded by UNS S30986 (AWS A5.9 ER309LMo) austenitic stainless steel filler metal using gas tungsten arc welding process was evaluated by optical micrography and EBSD techniques. Due to their fabrication through rolling process, both parent metals had texture components resulted from deformation and recrystallization. The weld metal showed the highest amount of residual strain and had large austenite grain colonies of similar orientations with little amounts of skeletal ferrite, both oriented preferentially in the < 001 > direction with cub-on-cube orientation relationship. While the super duplex stainless steel's heat affected zone contained higher ferrite than its parent metal, an excessive grain growth was observed at the austenitic stainless steel's counterpart. At both heat affected zones, austenite underwent some recrystallization and formed twin boundaries which led to an increase in the fraction of high angle boundaries as compared with the respective base metals. These regions showed the least amount of residual strain and highest amount of recrystallized austenite grains. Due to the static recrystallization, the fraction of low degree of fit (Σ) coincident site lattice boundaries, especially Σ3 boundaries, was increased in the austenitic stainless steel heat affected zone, while the formation of subgrains in the ferrite phase increased the content of < 5° low angle boundaries at that of the super duplex stainless steel. - Graphical abstract: Display Omitted - Highlights: • Extensive grain growth in the HAZ of austenitic stainless steel was observed. • Intensification of < 100 > orientated grains was observed adjacent to both fusion lines. • Annealing twins with Σ3 CSL boundaries were formed in the austenite of both HAZ. • Cub-on-cube OR was observed between austenite and ferrite in the weld metal.

  5. Modeling of Austenite Grain Growth During Austenitization in a Low Alloy Steel

    NASA Astrophysics Data System (ADS)

    Dong, Dingqian; Chen, Fei; Cui, Zhenshan

    2016-01-01

    The main purpose of this work is to develop a pragmatic model to predict austenite grain growth in a nuclear reactor pressure vessel steel. Austenite grain growth kinetics has been investigated under different heating conditions, involving heating temperature, holding time, as well as heating rate. Based on the experimental results, the mathematical model was established by regression analysis. The model predictions present a good agreement with the experimental data. Meanwhile, grain boundary precipitates and pinning effects on grain growth were studied by transmission electron microscopy. It is found that with the increasing of the temperature, the second-phase particles tend to be dissolved and the pinning effects become smaller, which results in a rapid growth of certain large grains with favorable orientation. The results from this study provide the basis for the establishment of large-sized ingot heating specification for SA508-III steel.

  6. Magneto-mechanical effects in two steels with metastable austenite

    SciTech Connect

    Fultz, B.; Fior, G.O.; Chang, G.M.; Kopa, R.; Morris, J.W. Jr.

    1985-03-01

    Magneto-mechanical effects, or effects of magnetic fields on mechanical propeties of materials, are reported for two steels containing austenite that undergoes an fcc..-->..bcc martensitic transformation during plastic deformation. Stress-strain curves from tensile tests of AISI 304 stainless steels and 9Ni steels were measured in magnetic fields as large as 18 T at temperatures of 4/sup 0/K, 77/sup 0/K and room temperature. Even in 18 T magnetic fields at cryogenic temperatures the magneto-mechanical effects were small, but they were reproducible and scaled with the strength of the magnetic field and the amount of transformation. Magneto-mechanical effects in steels with metastable austenite provide a unique means of determining how martensitic transformations affect mechanical behavior. The fcc..-->..bcc transformation makes an important contribution to the work hardening of both AISI 304 and 9Ni steel, so the more rapid transformation during magnetic exposure results in a higher strength and a reduced elongation of tensile specimens. In AISI 304 stainless steel a reduced flow stress in the magnetic field was found at small plastic strains.

  7. Manganese-stabilized austenitic stainless steels for fusion applications

    DOEpatents

    Klueh, Ronald L.; Maziasz, Philip J.

    1990-01-01

    An austenitic stainless steel that is comprised of Fe, Cr, Mn, C but no Ni or Nb and minimum N. To enhance strength and fabricability minor alloying additions of Ti, W, V, B and P are made. The resulting alloy is one that can be used in fusion reactor environments because the half-lives of the elements are sufficiently short to allow for handling and disposal.

  8. Manganese-stabilized austenitic stainless steels for fusion applications

    DOEpatents

    Klueh, Ronald L.; Maziasz, Philip J.

    1990-08-07

    An austenitic stainless steel that is comprised of Fe, Cr, Mn, C but no Ni or Nb and minimum N. To enhance strength and fabricability minor alloying additions of Ti, W, V, B and P are made. The resulting alloy is one that can be used in fusion reactor environments because the half-lives of the elements are sufficiently short to allow for handling and disposal.

  9. Grain Boundary Strengthening in High Mn Austenitic Steels

    NASA Astrophysics Data System (ADS)

    Kang, Jee-Hyun; Duan, Shanghong; Kim, Sung-Joon; Bleck, Wolfgang

    2016-05-01

    The Hall-Petch relationship is investigated to find the yield strengths of two high Mn austenitic steels. The Hall-Petch coefficient is found to depend on the overall C concentration and cooling rate, which suggests that the C concentration at the grain boundaries is an important factor. The pile-up model suggests that C raises the stress for the dislocation emission, while the ledge model predicts that C increases the density of ledges which act as dislocation sources.

  10. Evaluation of Microstructure and Mechanical Properties in Dissimilar Austenitic/Super Duplex Stainless Steel Joint

    NASA Astrophysics Data System (ADS)

    Rahmani, Mehdi; Eghlimi, Abbas; Shamanian, Morteza

    2014-10-01

    To study the effect of chemical composition on microstructural features and mechanical properties of dissimilar joints between super duplex and austenitic stainless steels, welding was attempted by gas tungsten arc welding process with a super duplex (ER2594) and an austenitic (ER309LMo) stainless steel filler metal. While the austenitic weld metal had vermicular delta ferrite within austenitic matrix, super duplex stainless steel was mainly comprised of allotriomorphic grain boundary and Widmanstätten side plate austenite morphologies in the ferrite matrix. Also the heat-affected zone of austenitic base metal comprised of large austenite grains with little amounts of ferrite, whereas a coarse-grained ferritic region was observed in the heat-affected zone of super duplex base metal. Although both welded joints showed acceptable mechanical properties, the hardness and impact strength of the weld metal produced using super duplex filler metal were found to be better than that obtained by austenitic filler metal.

  11. Researches upon the cavitation erosion behaviour of austenite steels

    NASA Astrophysics Data System (ADS)

    Bordeasu, I.; Popoviciu, M. O.; Mitelea, I.; Salcianu, L. C.; Bordeasu, D.; Duma, S. T.; Iosif, A.

    2016-02-01

    Paper analyzes the cavitation erosion behavior of two stainless steels with 100% austenitic structure but differing by the chemical composition and the values of mechanical properties. The research is based on the MDE(t) and MDER(t) characteristic curves. We studied supplementary the aspect of the eroded areas by other to different means: observations with performing optical microscopes and roughness measurements. The tests were done in the T2 vibratory facility in the Cavitation Laboratory of the Timisoara Polytechnic University. The principal purpose of the study is the identification of the elements influencing significantly the cavitation erosion resistance. It was established the effect of the principal chemical components (determining the proportion of the structural components in conformity the Schaffler diagram) upon the cavitation erosion resistance. The results of the researches present the influence of the proportion of unstable austenite upon cavitation erosion resistance. The stainless steel with the great proportion of unstable austenite has the best behavior. The obtained conclusion are important for the metallurgists which realizes the stainless steels used for manufacturing the runners of hydraulic machineries (turbines and pumps) with increased resistance to cavitation attack.

  12. Austenite Static Recrystallization Kinetics in Microalloyed B Steels

    NASA Astrophysics Data System (ADS)

    Larrañaga-Otegui, Ane; Pereda, Beatriz; Jorge-Badiola, Denis; Gutiérrez, Isabel

    2016-04-01

    Boron is added to steels to increase hardenability, substituting of more expensive elements. Moreover, B acts as a recrystallization delaying element when it is in solid solution. However, B can interact with N and/or C to form nitrides and carbides at high temperatures, limiting its effect on both phase transformation and recrystallization. On the other hand, other elements like Nb and Ti are added due to the retarding effect that they exert on the austenite softening processes, which results in pancaked austenite grains and refined room microstructures. In B steels, Nb and Ti are also used to prevent B precipitation. However, the complex interaction between these elements and its effect on the austenite microstructure evolution during hot working has not been investigated in detail. The present work is focused on the effect the B exerts on recrystallization when added to microalloyed steels. Although B on its own leads to retarded static recrystallization kinetics, when Nb is added a large delay in the static recrystallization times is observed in the 1273 K to 1373 K (1000 °C to 1100 °C) temperature range. The effect is larger than that predicted by a model developed for Nb-microalloyed steels, which is attributed to a synergistic effect of both elements. However, this effect is not so prominent for Nb-Ti-B steels. The complex effect of the composition on recrystallization kinetics is explained as a competition between the solute drag and precipitation pinning phenomena. The effect of the microalloying elements is quantified, and a new model for the predictions of recrystallization kinetics that accounts for the B and Nb+B synergetic effects is proposed.

  13. Market Opportunities for Austenitic Stainless Steels in SO2 Scrubbers

    NASA Astrophysics Data System (ADS)

    Michels, Harold T.

    1980-10-01

    Recent U.S. federal legislation has created new opportunities for SO2 scrubbers because all coals, even low-sulfur western coals, will probably require scrubbing to remove SO2 from gaseous combustion products. Scrubbing, the chemical absorption of SO2 by vigorous contact with a slurry—usually lime or limestone—creates an aggressive acid-chloride solution. This presents a promising market for pitting-resistant austenitic stainless steels, but there is active competition from rubber and fiberglass-lined carbon steel. Since the latter are favored on a first-cost basis, stainless steels must be justified on a cost/performance or life-cost basis. Nickel-containing austenitic alloys are favored because of superior field fabricability. Ferritic stainless steels have little utility in this application because of limitations in weldability and resulting poor corrosion resistance. Inco corrosion test spools indicate that molybdenum-containing austenitic alloys are needed. The leanest alloys for this application are 316L and 317L. Low-carbon grades of stainless steel are specified to minimize corrosion in the vicinity of welds. More highly alloyed materials may be required in critical areas. At present, 16,000 MW of scrubber capacity is operational and 17,000 MW is under construction. Another 29,000 MW is planned, bringing the total to 62,000 MW. Some 160,000 MW of scrubber capacity is expected to be placed in service over the next 10 years. This could translate into a total potential market of 80,000 tons of alloy plate for new power industry construction in the next decade. Retrofitting of existing power plants plus scrubbers for other applications such as inert gas generators for oil tankers, smelters, municipal incinerators, coke ovens, the pulp and paper industry, sulfuric acid plants, and fluoride control in phosphoric acid plants will add to this large market.

  14. Austenite Static Recrystallization Kinetics in Microalloyed B Steels

    NASA Astrophysics Data System (ADS)

    Larrañaga-Otegui, Ane; Pereda, Beatriz; Jorge-Badiola, Denis; Gutiérrez, Isabel

    2016-06-01

    Boron is added to steels to increase hardenability, substituting of more expensive elements. Moreover, B acts as a recrystallization delaying element when it is in solid solution. However, B can interact with N and/or C to form nitrides and carbides at high temperatures, limiting its effect on both phase transformation and recrystallization. On the other hand, other elements like Nb and Ti are added due to the retarding effect that they exert on the austenite softening processes, which results in pancaked austenite grains and refined room microstructures. In B steels, Nb and Ti are also used to prevent B precipitation. However, the complex interaction between these elements and its effect on the austenite microstructure evolution during hot working has not been investigated in detail. The present work is focused on the effect the B exerts on recrystallization when added to microalloyed steels. Although B on its own leads to retarded static recrystallization kinetics, when Nb is added a large delay in the static recrystallization times is observed in the 1273 K to 1373 K (1000 °C to 1100 °C) temperature range. The effect is larger than that predicted by a model developed for Nb-microalloyed steels, which is attributed to a synergistic effect of both elements. However, this effect is not so prominent for Nb-Ti-B steels. The complex effect of the composition on recrystallization kinetics is explained as a competition between the solute drag and precipitation pinning phenomena. The effect of the microalloying elements is quantified, and a new model for the predictions of recrystallization kinetics that accounts for the B and Nb+B synergetic effects is proposed.

  15. Solidification and solid state transformations of austenitic stainless steel welds

    SciTech Connect

    Brooks, J A; Williams, J C; Thompson, A W

    1982-05-01

    The microstructure of austenitic stainless steel welds can contain a large variety of ferrite morphologies. It was originally thought that many of these morphologies were direct products of solidification. Subsequently, detailed work on castings suggested the structures can solidify either as ferrite or austenite. However, when solidification occurs by ferrite, a large fraction of the ferrite transforms to austenite during cooling via a diffusion controlled transformation. It was also shown by Arata et al that welds in a 304L alloy solidified 70-80% as primary ferrite, a large fraction of which also transformed to austenite upon cooling. More recently it was suggested that the cooling rates in welds were sufficiently high that diffusionless transformations were responsible for several commonly observed ferrite morphologies. However, other workers have suggested that even in welds, delta ..-->.. ..gamma.. transformations are diffusion controlled. A variety of ferrite morphologies have more recently been characterized by Moisio and coworkers and by David. The purpose of this paper is to provide further understanding of the evaluation of the various weld microstructures which are related to both the solidification behavior and the subsequent solid state transformations. To accomplish this, both TEM and STEM (Scanning Transmission Electron Microscopy) techniques were employed.

  16. High temperature properties of an austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Nikulin, I.; Kaibyshev, R.; Skorobogatykh, V.

    2010-07-01

    Tensile properties of the 18Cr-9Ni-W-Nb-V-N austenitic stainless steel were studied at strain rates ranging from 6.7×10-6 to 1.3×10-2 s-1 in the temperature interval 20-740°C. It was found that this steel exhibits jerky flow at temperatures ranging from 530 to 680°C and an initial strain rate of 1.3×10-3 s-1. This phenomenon was interpreted in terms of Portevin-Le Chatelier (PLC) effect occurring due to dynamic strain aging (DSA). PLC yields significant increase in high temperature strength of this steel due to extending of plateau on temperature dependence of yield strength (YS) and ultimate tensile strength (UTS) to higher temperatures. As a result, YS and UTS remain virtually unchanged with increasing temperature from 350 to 740°C. Role of additives of tungsten and vanadium in DSA and high temperatures strength of the austenitic stainless steel is discussed.

  17. Reducing tool wear when machining austenitic stainless steels

    SciTech Connect

    Magee, J.H.; Kosa, T.

    1998-07-01

    Austenitic stainless steels are considered more difficult to machine than carbon steels due to their high work hardening rate, large spread between yield and ultimate tensile strength, high toughness and ductility, and low thermal conductivity. These characteristics can result in a built-up edge or excessive tool wear during machining, especially when the cutting speed is too high. The practical solution is to lower the cutting speed until tool life reaches an acceptable level. However, lower machining speed negatively impacts productivity. Thus, in order to overcome tool wear at relatively high machining speeds for these alloys, on-going research is being performed to improve cutting fluids, develop more wear-resistant tools, and to modify stainless steels to make them less likely to cause tool wear. This paper discusses compositional modifications to the two most commonly machined austenitic stainless steels (Type 303 and 304) which reduced their susceptibility to tool wear, and allowed these grades to be machined at higher cutting speeds.

  18. Corrosion fatigue of iron-chromium-nickel alloys: Fracture mechanics, microstructure and chemistry

    SciTech Connect

    Wei, R.P.

    1992-01-29

    This progress report briefly summarizes the research performed under the referenced grant for the period from 1 December 1990 to 31 December 1991, and contains a cumulative listing of technical presentations and publications dating back to 1 June 1988. Under this grant, a multi-disciplinary research program is undertaken to address certain fundamental issues relating to corrosion fatigue crack growth in structurally important alloys in aqueous environments. The principal goal of the research is to develop and expand the scientific understanding of the processes that control corrosion fatigue crack growth, particularly for ferrous alloys in terms of the controlling mechanical and chemical/electrochemical processes and their interactions with the microstructure. Focus is placed upon the austenitic iron-chromium-nickel (FeCrNi) alloys because of the need to resolve certain mechanistic issues and because of extensive utilization of these alloys in the power generation and chemical industries. Emphasis is given to the growth of short (small) cracks at low growth rates because crack growth in this regime is expected to be more sensitive to changes in external chemical/electrochemical variables.

  19. Effects of Retained Austenite Stability and Volume Fraction on Deformation Behaviors of TRIP Steels

    SciTech Connect

    Choi, Kyoo Sil; Soulami, Ayoub; Liu, Wenning N.; Sun, Xin; Khaleel, Mohammad A.

    2010-10-02

    In this paper, the separate effects of austenite stability and its volume fraction on the deformation behaviors of transformation-induced plasticity (TRIP) steels are investigated based on the microstructure-based finite element modeling method. The effects of austenite stability on the strength, ductility and formability of TRIP steels are first examined based on the microstructure of a commercial TRIP 800 steel. Then, the separate effects of the austenite volume fraction on the overall deformation behaviors of TRIP steels are examined based on the various representative volume elements (RVEs). The computational results suggest that the higher austenite stability is helpful to increase the ductility and formability, but not the UTS. However, the increase of austenite volume fraction alone is not helpful in improving the performance of TRIP steels. This may indicate that various other material factors should also be concurrently adjusted during thermo-mechanical manufacturing process in a way to increase the performance of TRIP steels, which needs further investigation.

  20. Hydrogen vibrations in austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Danilkin, S. A.; Delafosse, D.; Fuess, H.; Gavriljuk, V. G.; Ivanov, A.; Magnin, T.; Wipf, H.

    The vibrational modes of hydrogen in fcc Fe-25Cr-20Ni stainless steel with a hydrogen content of 0.33at.% were studied by neutron spectroscopy. Hydrogen doping was performed at 810K in a hydrogen-gas atmosphere of 190bar. Neutron spectra were taken at 2K and 77K with the spectrometer IN1-BeF (ILL, Grenoble). The spectra show the fundamental hydrogen vibration at 130 meV and the second harmonics at 260 meV. The frequencies are higher than in other fcc hydrides. In spite of the cubic symmetry of the octahedral hydrogen positions and the low hydrogen content, the inelastic hydrogen peak has a relatively large width and an asymmetric shape.

  1. Microstructures of laser deposited 304L austenitic stainless steel

    SciTech Connect

    BROOKS,JOHN A.; HEADLEY,THOMAS J.; ROBINO,CHARLES V.

    2000-05-22

    Laser deposits fabricated from two different compositions of 304L stainless steel powder were characterized to determine the nature of the solidification and solid state transformations. One of the goals of this work was to determine to what extent novel microstructure consisting of single-phase austenite could be achieved with the thermal conditions of the LENS [Laser Engineered Net Shape] process. Although ferrite-free deposits were not obtained, structures with very low ferrite content were achieved. It appeared that, with slight changes in alloy composition, this goal could be met via two different solidification and transformation mechanisms.

  2. Corrosion resistance of kolsterised austenitic 304 stainless steel

    NASA Astrophysics Data System (ADS)

    Abudaia, F. B.; Khalil, E. O.; Esehiri, A. F.; Daw, K. E.

    2015-03-01

    Austenitic stainless suffers from low wear resistance in applications where rubbing against other surfaces is encountered. This drawback can be overcome by surface treatment such as coating by hard materials. Other treatments such as carburization at relatively low temperature become applicable recently to improve hardness and wear resistance. Carburization heat treatment would only be justified if the corrosion resistance is unaffected. In this work samples of 304 stainless steels treated by colossal supersaturation case carburizing (known as Kolsterising) carried out by Bodycote Company was examined for pitting corrosion resistance at room temperature and at 50 °C. Comparison with results obtained for untreated samples in similar testing conditions show that there is no deterioration in the pitting resistance due to the Kolsterising heat treatment. X ray diffraction patterns obtained for Kolsterising sample showed that peaks correspond to the austenite phase has shifted to lower 2θ values compared with those of the untreated sample. The shift is an indication for expansion of austenite unit cells caused by saturation with diffusing carbon atoms. The XRD of Kolsterising samples also revealed additional peaks appeared in the patterns due to formation of carbides in the kolsterised layer. Examination of these additional peaks showed that these peaks are attributed to a type of carbide known as Hagg carbide Fe2C5. The absence of carbides that contain chromium means that no Cr depletion occurred in the layer and the corrosion properties are maintained. Surface hardness measurements showed large increase after Kolsterising heat treatment.

  3. Development of Alumina-Forming Austenitic Stainless Steels

    SciTech Connect

    Brady, Michael P; Yamamoto, Yukinori; Bei, Hongbin; Santella, Michael L; Maziasz, Philip J

    2009-01-01

    This paper presents the results of the continued development of creep-resistant, alumina-forming austenitic (AFA) stainless steel alloys, which exhibit a unique combination of excellent oxidation resistance via protective alumina (Al2O3) scale formation and high-temperature creep strength through the formation of stable nano-scale MC carbides and intermetallic precipitates. Efforts in fiscal year 2009 focused on the characterization and understanding of long-term oxidation resistance and tensile properties as a function of alloy composition and microstructure. Computational thermodynamic calculations of the austenitic matrix phase composition and the volume fraction of MC, B2-NiAl, and Fe2(Mo,Nb) base Laves phase precipitates were used to interpret oxidation behavior. Of particular interest was the enrichment of Cr in the austenitic matrix phase by additions of Nb, which aided the establishment and maintenance of alumina. Higher levels of Nb additions also increased the volume fraction of B2-NiAl precipitates, which served as an Al reservoir during long-term oxidation. Ageing studies of AFA alloys were conducted at 750 C for times up to 2000 h. Ageing resulted in near doubling of yield strength at room temperature after only 50 h at 750 C, with little further increase in yield strength out to 2000 h of ageing. Elongation was reduced on ageing; however, levels of 15-25% were retained at room temperature after 2000 h of total ageing.

  4. Retained austenite thermal stability in a nanostructured bainitic steel

    SciTech Connect

    Avishan, Behzad; Garcia-Mateo, Carlos; Yazdani, Sasan; Caballero, Francisca G.

    2013-07-15

    The unique microstructure of nanostructured bainite consists of very slender bainitic ferrite plates and high carbon retained austenite films. As a consequence, the reported properties are opening a wide range of different commercial uses. However, bainitic transformation follows the T{sub 0} criteria, i.e. the incomplete reaction phenomena, which means that the microstructure is not thermodynamically stable because the bainitic transformation stops well before austenite reaches an equilibrium carbon level. This article aims to study the different microstructural changes taking place when nanostructured bainite is destabilized by austempering for times well in excess of that strictly necessary to end the transformation. Results indicate that while bainitic ferrite seems unaware of the extended heat treatment, retained austenite exhibits a more receptive behavior to it. - Highlights: • Nanostructured bainitic steel is not thermodynamically stable. • Extensive austempering in these microstructures has not been reported before. • Precipitation of cementite particles is unavoidable at longer austempering times. • TEM, FEG-SEM and XRD analysis were used for microstructural characterization.

  5. Corrosion resistance of kolsterised austenitic 304 stainless steel

    SciTech Connect

    Abudaia, F. B. Khalil, E. O. Esehiri, A. F. Daw, K. E.

    2015-03-30

    Austenitic stainless suffers from low wear resistance in applications where rubbing against other surfaces is encountered. This drawback can be overcome by surface treatment such as coating by hard materials. Other treatments such as carburization at relatively low temperature become applicable recently to improve hardness and wear resistance. Carburization heat treatment would only be justified if the corrosion resistance is unaffected. In this work samples of 304 stainless steels treated by colossal supersaturation case carburizing (known as Kolsterising) carried out by Bodycote Company was examined for pitting corrosion resistance at room temperature and at 50 °C. Comparison with results obtained for untreated samples in similar testing conditions show that there is no deterioration in the pitting resistance due to the Kolsterising heat treatment. X ray diffraction patterns obtained for Kolsterising sample showed that peaks correspond to the austenite phase has shifted to lower 2θ values compared with those of the untreated sample. The shift is an indication for expansion of austenite unit cells caused by saturation with diffusing carbon atoms. The XRD of Kolsterising samples also revealed additional peaks appeared in the patterns due to formation of carbides in the kolsterised layer. Examination of these additional peaks showed that these peaks are attributed to a type of carbide known as Hagg carbide Fe{sub 2}C{sub 5}. The absence of carbides that contain chromium means that no Cr depletion occurred in the layer and the corrosion properties are maintained. Surface hardness measurements showed large increase after Kolsterising heat treatment.

  6. Heavy hydrogen isotopes penetration through austenitic and martensitic steels

    NASA Astrophysics Data System (ADS)

    Dolinski, Yu.; Lyasota, I.; Shestakov, A.; Repritsev, Yu.; Zouev, Yu.

    2000-12-01

    Experimental results are presented of deuterium and tritium permeability through samples of nickel, austenitic steel (16Cr-15Ni-3Mo-Ti), and martensitic steel DIN 1.4914 (MANET) exposed to a gaseous phase. Experiments were carried out at the RFNC-VNHTF installation, which has the capability of measuring the permeability of hydrogen isotopes by mass spectrometry over a temperature range of 293-1000 K, hydrogen isotope pressure ranges of 50-1000 Pa. Sample disks (30 and 40 mm diam.) can be assembled in the test chamber by electron-beam welding or mounted (30-mm diam. disks) on gaskets. Diffusion and permeability dependencies on temperature and pressure are determined and corresponding activation energies are presented.

  7. Strength of nanostructured austenitic steel 316LN at cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Czarkowski, P.; Krawczynska, A. T.; Brynk, T.; Nowacki, M.; Lewandowska, M.; Kurzydłowski, K. J.

    2014-12-01

    The aim of this work was to investigate the effect of nano-refinement on the properties of austenitic steel. The material with the initial grain size of 40-50pm was subjected to hydrostatic extrusion at a room temperature to the total accumulated strain exceeding 1. The microstructure developed was investigated by Transmission Electron Microscopy (TEM) and Focus Ion Beam (FIB). The strength of the extruded samples was tested at 293K, 77K and 4.2K by means of cryostat for static tensile tests. The results show that the hydrostatically extruded steel 316LN has excellent strength in cryogenic conditions, which make this material interesting for applications in cryogenic devices.

  8. Ion beam nitriding of single and polycrystalline austenitic stainless steel

    SciTech Connect

    Abrasonis, G.; Riviere, J.P.; Templier, C.; Declemy, A.; Pranevicius, L.; Milhet, X.

    2005-04-15

    Polycrystalline and single crystalline [orientations (001) and (011)] AISI 316L austenitic stainless steel was implanted at 400 deg. C with 1.2 keV nitrogen ions using a high current density of 0.5 mA cm{sup -2}. The nitrogen distribution profiles were determined using nuclear reaction analysis (NRA). The structure of nitrided polycrystalline stainless steel samples was analyzed using glancing incidence and symmetric x-ray diffraction (XRD) while the structure of the nitrided single crystalline stainless steel samples was analyzed using x-ray diffraction mapping of the reciprocal space. For identical treatment conditions, it is observed that the nitrogen penetration depth is larger for the polycrystalline samples than for the single crystalline ones. The nitrogen penetration depth depends on the orientation, the <001> being more preferential for nitrogen diffusion than <011>. In both type of samples, XRD analysis shows the presence of the phase usually called 'expanded' austenite or {gamma}{sub N} phase. The lattice expansion depends on the crystallographic plane family, the (001) planes showing an anomalously large expansion. The reciprocal lattice maps of the nitrided single crystalline stainless steel demonstrate that during nitriding lattice rotation takes place simultaneously with lattice expansion. The analysis of the results based on the presence of stacking faults, residual compressive stress induced by the lattice expansion, and nitrogen concentration gradient indicates that the average lattice parameter increases with the nitrided layer depth. A possible explanation of the anomalous expansion of the (001) planes is presented, which is based on the combination of faster nitriding rate in the (001) oriented grains and the role of stacking faults and compressive stress.

  9. Austenite Formation in a Cold-Rolled Semi-austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Celada Casero, Carola; San Martín, David

    2014-04-01

    The progress of the martensite ( α') to austenite ( γ) phase transformation has been thoroughly investigated at different temperatures during the continuous heating of a cold-rolled precipitation hardening metastable stainless steel at a heating rate of 0.1 K/s. Heat-treated samples have been characterized using different experimental complementary techniques: high-resolution dilatometry, magnetization, and thermoelectric power (TEP) measurements, micro-hardness-Vickers testing, optical/scanning electron microscopy, and tensile testing. The two-step transformation behavior observed is thought to be related to the presence of a pronounced chemical banding in the initial microstructure. This banding has been characterized using electron probe microanalysis. Unexpectedly, dilatometry measurements seem unable to locate the end of the transformation accurately, as this technique does not detect the second step of this transformation (last 20 pct of it). It is shown that once the starting ( A S) and finishing ( A F) transformation temperatures have been estimated by magnetization measurements, the evolution of the volume fractions of austenite and martensite can be evaluated by TEP or micro-hardness measurement quite reliably as compared to magnetization measurements. The mechanical response of the material after being heated to temperatures close to A S, A F, and ( A F - A S)/2 is also discussed.

  10. Hydrogen-related phase transformations in austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Narita, N.; Altstetter, C. J.; Birnbaum, H. K.

    1982-08-01

    The effect of hydrogen and stress (strain) on the stability of the austenite phase in stainless steels was investigated. Hydrogen was introduced by severe cathodic charging and by elevated temperature equilibration with high pressure H2 gas. Using X-ray diffraction and magnetic techniques, the behavior of two “stable” type AISI310 steels and an “unstable” type AISI304 steel was studied during charging and during the outgassing period following charging. Transformation from the fcc γ phase to an expanded fcc phase, γ*, and to the hcp ɛ phase occurred during cathodic charging. Reversion of the γ* and e phases to the original γ structure and formation of the bcc α structure were examined, and the kinetics of these processes was studied. The γ* phase was shown to be ferromagnetic with a subambient Curie temperature. The γ⇆ɛ phase transition was studied after hydrogen charging in high pressure gas, as was the formation of a during outgassing. These results are interpreted as effects of hydrogen and stress (strain) on the stability of the various phases. A proposed psuedo-binary phase diagram for the metal-hydrogen system was proposed to account for the formation of the γ* phase. The relation of these phase changes to hydrogen embrittlement and stress corrosion cracking of stainless steel is discussed.

  11. Austenite Grain Growth and the Surface Quality of Continuously Cast Steel

    NASA Astrophysics Data System (ADS)

    Dippenaar, Rian; Bernhard, Christian; Schider, Siegfried; Wieser, Gerhard

    2014-04-01

    Austenite grain growth does not only play an important role in determining the mechanical properties of steel, but certain surface defects encountered in the continuous casting industry have also been attributed to the formation of large austenite grains. Earlier research has seen innovative experimentation, the development of metallographic techniques to determine austenite grain size and the building of mathematical models to simulate the conditions pertaining to austenite grain growth during the continuous casting of steel. Oscillation marks and depressions in the meniscus region of the continuously casting mold lead to retarded cooling of the strand surface, which in turn results in the formation of coarse austenite grains, but little is known about the mechanism and rate of formation of these large austenite grains. Relevant earlier research will be briefly reviewed to put into context our recent in situ observations of the delta-ferrite to austenite phase transition. We have confirmed earlier evidence that very large delta-ferrite grains are formed very quickly in the single-phase region and that these large delta-ferrite grains are transformed to large austenite grains at low cooling rates. At the higher cooling rates relevant to the early stages of the solidification of steel in a continuously cast mold, delta-ferrite transforms to austenite by an apparently massive type of transformation mechanism. Large austenite grains then form very quickly from this massive type of microstructure and on further cooling, austenite transforms to thin ferrite allotriomorphs on austenite grain boundaries, followed by Widmanstätten plate growth, with almost no regard to the cooling rate. This observation is important because it is now well established that the presence of a thin ferrite film on austenite grain boundaries is the main cause of reduction in hot ductility. Moreover, this reduction in ductility is exacerbated by the presence of large austenite grains.

  12. Microstructural evolution in fast-neutron-irradiated austenitic stainless steels

    SciTech Connect

    Stoller, R.E.

    1987-12-01

    The present work has focused on the specific problem of fast-neutron-induced radiation damage to austenitic stainless steels. These steels are used as structural materials in current fast fission reactors and are proposed for use in future fusion reactors. Two primary components of the radiation damage are atomic displacements (in units of displacements per atom, or dpa) and the generation of helium by nuclear transmutation reactions. The radiation environment can be characterized by the ratio of helium to displacement production, the so-called He/dpa ratio. Radiation damage is evidenced microscopically by a complex microstructural evolution and macroscopically by density changes and altered mechanical properties. The purpose of this work was to provide additional understanding about mechanisms that determine microstructural evolution in current fast reactor environments and to identify the sensitivity of this evolution to changes in the He/dpa ratio. This latter sensitivity is of interest because the He/dpa ratio in a fusion reactor first wall will be about 30 times that in fast reactor fuel cladding. The approach followed in the present work was to use a combination of theoretical and experimental analysis. The experimental component of the work primarily involved the examination by transmission electron microscopy of specimens of a model austenitic alloy that had been irradiated in the Oak Ridge Research Reactor. A major aspect of the theoretical work was the development of a comprehensive model of microstructural evolution. This included explicit models for the evolution of the major extended defects observed in neutron irradiated steels: cavities, Frank faulted loops and the dislocation network. 340 refs., 95 figs., 18 tabs.

  13. Retained austenite characteristics in thermomechanically processed Si-Mn transformation-induced plasticity steels

    SciTech Connect

    Hanzaki, A.Z.; Hodgson, P.D.; Yue, S.

    1997-11-01

    It is well known that a significant amount of retained austenite can be obtained in steels containing high additions (>1 pct) of Si, where bainite is the predominant microconstituent. Furthermore, retained austenite with optimum characteristics (volume fraction, composition, morphology, size, and distribution), when present in ferrite plus bainite microstructures, can potentially increase strength and ductility, such that formability and final properties are greatly improved. These beneficial properties can be obtained largely by transformation-induced plasticity (TRIP). In this work, the effect of a microalloy addition (0.035 pct Nb) in a 0.22 pct C-1.55 pct Si-1.55 pct Mn TRIP steel was investigated. Niobium was added to enable the steel to be processed by a variety of thermomechanical processing (TMP) routes, thus allowing the effects of prior austenite grain size, austenite recrystallization temperature, Nb in austenite solid solution, and Nb as a precipitate to be studied. The results, which were compared with those of the same steel without Nb, indicate that the retained austenite volume fraction is strongly influenced by both prior austenite grain size and the state of Nb in austenite. Promoting Nb(CN) precipitation by the change in TMP conditions resulted in a decrease in the V{sub RA}. These findings are rationalized by considering the effects of changes in the TMP conditions on the subsequent transformation characteristics of the parent austenite.

  14. Tailoring plasticity of austenitic stainless steels for nuclear applications: Review of mechanisms controlling plasticity of austenitic steels below 400 °C

    NASA Astrophysics Data System (ADS)

    Meric de Bellefon, G.; van Duysen, J. C.

    2016-07-01

    AISI 304 and 316 austenitic stainless steels were invented in the early 1900s and are still trusted by materials and mechanical engineers in numerous sectors because of their good combination of strength, ductility, and corrosion resistance, and thanks to decades of experience and data. This article is part of an effort focusing on tailoring the plasticity of both types of steels to nuclear applications. It provides a synthetic and comprehensive review of the plasticity mechanisms in austenitic steels during tensile tests below 400 °C. In particular, formation of twins, extended stacking faults, and martensite, as well as irradiation effects and grain rotation are discussed in details.

  15. The stability of precipitated austenite and the toughness of 9Ni steel

    NASA Astrophysics Data System (ADS)

    Fultz, B.; Kim, J. I.; Kim, Y. H.; Kim, H. J.; Fior, G. O.; Morris, J. W.

    1985-12-01

    A correlation was confirmed between the good low temperature Charpy toughness of 9Ni steel and the stability of its precipitated austenite against the martensitic transformation. Changes in the microstructure during isothermal tempering were studied in detail. The austenite/martensite interface is originally quite coherent over ˜100 A distances. With further tempering, however, the dislocation structure at the austenite/martensite interface changes, and this change may be related to the increased instability of the austenite particles. The reduction in austenite carbon concentration does not seem large enough to account for the large reduction in austenite stability with tempering time. The strains inherent to the transformation of austenite particles create dislocation structures in the tempered martensite. The large deterioration of the Charpy toughness of overtempered material is attributed, in part, to these dislocation structures.

  16. Mechanical Properties of Austenitic Stainless Steel Made by Additive Manufacturing.

    PubMed

    Luecke, William E; Slotwinski, John A

    2014-01-01

    Using uniaxial tensile and hardness testing, we evaluated the variability and anisotropy of the mechanical properties of an austenitic stainless steel, UNS S17400, manufactured by an additive process, selective laser melting. Like wrought materials, the mechanical properties depend on the orientation introduced by the processing. The recommended stress-relief heat treatment increases the tensile strength, reduces the yield strength, and decreases the extent of the discontinuous yielding. The mechanical properties, assessed by hardness, are very uniform across the build plate, but the stress-relief heat treatment introduced a small non-uniformity that had no correlation to position on the build plate. Analysis of the mechanical property behavior resulted in four conclusions. (1) The within-build and build-to-build tensile properties of the UNS S17400 stainless steel are less repeatable than mature engineering structural alloys, but similar to other structural alloys made by additive manufacturing. (2) The anisotropy of the mechanical properties of the UNS S17400 material of this study is larger than that of mature structural alloys, but is similar to other structural alloys made by additive manufacturing. (3) The tensile mechanical properties of the UNS S17400 material fabricated by selective laser melting are very different from those of wrought, heat-treated 17-4PH stainless steel. (4) The large discontinuous yielding strain in all tests resulted from the formation and propagation of Lüders bands. PMID:26601037

  17. Laser beam surface melting of high alloy austenitic stainless steel

    SciTech Connect

    Woollin, P.

    1996-12-31

    The welding of high alloy austenitic stainless steels is generally accompanied by a substantial reduction in pitting corrosion resistance relative to the parent, due to microsegregation of Mo and Cr. This prevents the exploitation of the full potential of these steels. Processing to achieve remelting and rapid solidification offers a means of reducing microsegregation levels and improving corrosion resistance. Surface melting of parent UNS S31254 steel by laser beam has been demonstrated as a successful means of producing fine, as-solidified structures with pitting resistance similar to that of the parent, provided that an appropriate minimum beam travel speed is exceeded. The use of N{sub 2} laser trail gas increased the pitting resistance of the surface melted layer. Application of the technique to gas tungsten arc (GTA) melt runs has shown the ability to raise the pitting resistance significantly. Indeed, the use of optimized beam conditions, N{sub 2} trail gas and appropriate surface preparation prior to laser treatment increased the pitting resistance of GTA melt runs to a level approaching that of the parent material.

  18. Mechanical Properties of Austenitic Stainless Steel Made by Additive Manufacturing

    PubMed Central

    Luecke, William E; Slotwinski, John A

    2014-01-01

    Using uniaxial tensile and hardness testing, we evaluated the variability and anisotropy of the mechanical properties of an austenitic stainless steel, UNS S17400, manufactured by an additive process, selective laser melting. Like wrought materials, the mechanical properties depend on the orientation introduced by the processing. The recommended stress-relief heat treatment increases the tensile strength, reduces the yield strength, and decreases the extent of the discontinuous yielding. The mechanical properties, assessed by hardness, are very uniform across the build plate, but the stress-relief heat treatment introduced a small non-uniformity that had no correlation to position on the build plate. Analysis of the mechanical property behavior resulted in four conclusions. (1) The within-build and build-to-build tensile properties of the UNS S17400 stainless steel are less repeatable than mature engineering structural alloys, but similar to other structural alloys made by additive manufacturing. (2) The anisotropy of the mechanical properties of the UNS S17400 material of this study is larger than that of mature structural alloys, but is similar to other structural alloys made by additive manufacturing. (3) The tensile mechanical properties of the UNS S17400 material fabricated by selective laser melting are very different from those of wrought, heat-treated 17-4PH stainless steel. (4) The large discontinuous yielding strain in all tests resulted from the formation and propagation of Lüders bands. PMID:26601037

  19. Modified Monkman-Grant relationship for austenitic stainless steel foils

    NASA Astrophysics Data System (ADS)

    Osman Ali, Hassan; Tamin, Mohd Nasir

    2013-02-01

    Characteristics of creep deformation for austenitic stainless steel foils are examined using the modified Monkman-Grant equation. A series of creep tests are conducted on AISI 347 steel foils at 700 °C and different stress levels ranging from 54 to 221 MPa. Results showed that at lower stress levels below 110 MPa, the creep life parameters ɛ, ɛr, tr can be expressed using the modified Monkman-Grant equation with exponent m'= 0.513. This indicates significant deviation of the creep behavior from the first order reaction kinetics theory for creep (m' = 1.0). The true tertiary creep damage in AISI 347 steel foil begins after 65.9% of the creep life of the foil has elapsed at stress levels above 150 MPa. At this high stress levels, Monkman-Grant ductility factor λ' saturates to a value of 1.3 with dislocation-controlled deformation mechanisms operating. At low stress levels, λ' increases drastically (λ'=190 at 54 MPa) when slow diffusion-controlled creep is dominant.

  20. A new constitutive model for nitrogen austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Fréchard, S.; Lichtenberger, A.; Rondot, F.; Faderl, N.; Redjaïmia, A.; Adoum, M.

    2003-09-01

    Quasi-static, quasi-dynamic and dynamic compression tests have been performed on a nitrogen alloyed austenitic stainless steel. For all strain rates, a high strain hardening rate and a good ductility have been achieved. In addition, this steel owns a great strain rate sensitivity. The temperature sensitivity bas been determined between 20°C and 400°C. Microstructural analysis has been performed after different loading conditions in relation to the behaviour of the material. Johnson-Cook and Zerilli-Armstrong models have been selected to fit the experimental data into constitutive equations. These models do not reproduce properly the behaviour of this type of steel over the complete range. A new constitutive model that fits very well all the experimental data at different strain, strain rate and temperature has been determined. The model is based on empirical considerations on the separated influence of the main parameters. Single Taylor tests have been realized to validate the models. Live observations of the specimen during impact have been achieved using a special CCD camera set-up. The overall profile at different times are compared to numerical predictions using LS-DYNA code.

  1. Welding techniques for high alloy austenitic stainless steel

    SciTech Connect

    Gooch, T.G.; Woollin, P.

    1996-11-01

    Factors controlling corrosion resistance of weldments in high alloy austenitic stainless steel are described, with emphasis on microsegregation, intermetallic phase precipitation and nitrogen loss from the molten pool. The application is considered of a range of welding processes, both fusion and solid state. Autogenous fusion weldments have corrosion resistance below that of the parent, but low arc energy, high travel speed and use of N{sub 2}-bearing shielding gas are recommended for best properties. Conventional fusion welding practice is to use an overalloyed nickel-base filler metal to avoid preferential weld metal corrosion, and attention is given to the effects of consumable composition and level of weldpool dilution by base steel. With non-matching consumables, overall joint corrosion resistance may be limited by the presence of a fusion boundary unmixed zone: better performance may be obtained using solid state friction welding, given appropriate component geometry. Overall, the effects of welding on superaustenitic steels are understood, and the materials have given excellent service in welded fabrications. The paper summarizes recommendations on preferred welding procedure.

  2. Strain oxidation cracking of austenitic stainless steels at 610 C

    SciTech Connect

    Calvar, M. Le; Scott, P.M.; Magnin, T.; Rieux, P.

    1998-02-01

    Strain oxidation cracking of both forged and welded austenitic stainless steels (SS) was studied. Creep and slow strain rate tests (SSRT) were performed in vacuum, air, and a gas furnace environment (air + carbon dioxide [CO{sub 2}] + water [H{sub 2}O]). Results showed cracking was environmentally dependent. Almost no cracking was observed in vacuum, whereas intergranular cracking was observed with increasing severity in passing from an air to a gas furnace environment. The most severe cracking was associated with formation of a less protective film formed in the gas furnace environment (air: haematite-like M{sub 2}O{sub 3} oxide; gas furnace environment: spinel M{sub 3}O{sub 4} oxide). Cracking depended strongly on the carbon content and the sensitization susceptibility of the material: the higher the carbon content, the more susceptible the alloy. This cracking was believed to be similar to other oxidation-induced cracking phenomena.

  3. Formability analysis of austenitic stainless steel-304 under warm conditions

    NASA Astrophysics Data System (ADS)

    Lade, Jayahari; Singh, Swadesh Kumar; Banoth, Balu Naik; Gupta, Amit Kumar

    2013-12-01

    A warm deep drawing process of austenitic stainless steel-304 (ASS-304) of circular blanks with coupled ther mal analysis is studied in this article. 65 mm blanks were deep drawn at different temperatures and thickness distribution is experimentally measured after cutting the drawn component into two halves. The process is simulated using explicit fin ite element code LS-DYNA. A Barlat 3 parameter model is used in the simulation, as the material is anisotropic up to 30 0°C. Material properties for the simulation are determined at different temperatures using a 5 T UTM coupled with a furn ace. In this analysis constant punch speed and variable blank holder force (BHF) is applied to draw cups without wrinkle.

  4. Austenite Formation Kinetics During Rapid Heating in a Microalloyed Steel

    SciTech Connect

    BURNETT,M.E.; DYKHUIZEN,RONALD C.; KELLEY,J. BRUCE; PUSKAR,JOSEPH D.; ROBINO,CHARLES V.

    1999-09-07

    The model parameters for the normalized 1054V1 material were compared to parameters previously generated for 1026 steel, and the transformation behavior was relatively consistent. Validation of the model predictions by heating into the austenite plus undissolved ferrite phase field and rapidly quenching resulted in reasonable predictions when compared to the measured volume fractions from optical metallography. The hot rolled 1054V1 material, which had a much coarser grain size and a non-equilibrium volume fraction of pearlite, had significantly different model parameters and the on heating transformation behavior of this material was less predictable with the established model. The differences in behavior is consistent with conventional wisdom that normalized micro-structure produce a more consistent response to processing, and it reinforces the need for additional work in this area.

  5. Fatigue crack growth in metastable austenitic stainless steels

    SciTech Connect

    Mei, Z.; Chang, G.; Morris, J.W. Jr.

    1988-06-01

    The research reported here is an investigation of the influence of the mechanically induced martensitic transformation on the fatigue crack growth rate in 304-type steels. The alloys 304L and 304LN were used to test the influence of composition, the testing temperatures 298 K and 77 K were used to study the influence of test temperature, and various load ratios (R) were used to determine the influence of the load ratio. It was found that decreasing the mechanical stability of the austenite by changing composition or lowering temperature decreases the fatigue crack growth rate. The R-ratio effect is more subtle. The fatigue crack growth rate increases with increasing R-ratio, even though this change increases the martensite transformation. Transformation-induced crack closure can explain the results in the threshold regime, but cannot explain the R-ratio effect at higher cyclic stress intensities. 26 refs., 6 figs.

  6. Structure and properties of high-temperature austenitic steels for superheater tubes

    NASA Astrophysics Data System (ADS)

    Blinov, V. M.

    2009-12-01

    The structure and properties of high-temperature austenitic steels intended for superheater tubes are analyzed. Widely used Kh18N10T (AISI 304) and Kh16N13M3 (AISI 316) steels are found not to ensure a stable austenitic structure and stable properties during long-term thermal holding under stresses. The hardening of austenitic steels by fine particles of vanadium and niobium carbides and nitrides and γ'-phase and Fe2W and Fe2Mo Laves phase intermetallics is considered. The role of Cr23C6 chromium carbides, the σ phase, and coarse precipitates of an M 3B2 phase and a boron-containing eutectic in decreasing the time to failure and the stress-rupture strength of austenitic steels is established. The mechanism of increasing the stress-rupture strength of steels by boron additions is described. The chemical compositions, mechanical properties, stress-rupture strength, and creep characteristics of Russian and foreign austenitic steels used or designed for superheater tubes intended for operation under stress conditions at temperatures above 600°C are presented. The conditions are found for increasing the strength, plasticity, and thermodeformation stability of austenite in steels intended for superheater tubes operating at 700°C under high stresses for a long time.

  7. Magnetic properties of single crystalline expanded austenite obtained by plasma nitriding of austenitic stainless steel single crystals.

    PubMed

    Menéndez, Enric; Templier, Claude; Garcia-Ramirez, Pablo; Santiso, José; Vantomme, André; Temst, Kristiaan; Nogués, Josep

    2013-10-23

    Ferromagnetic single crystalline [100], [110], and [111]-oriented expanded austenite is obtained by plasma nitriding of paramagnetic 316L austenitic stainless steel single crystals at either 300 or 400 °C. After nitriding at 400 °C, the [100] direction appears to constitute the magnetic easy axis due to the interplay between a large lattice expansion and the expected decomposition of the expanded austenite, which results in Fe- and Ni-enriched areas. However, a complex combination of uniaxial (i.e., twofold) and biaxial (i.e., fourfold) in-plane magnetic anisotropies is encountered. It is suggested that the former is related to residual stress-induced effects while the latter is associated to the in-plane projections of the cubic lattice symmetry. Increasing the processing temperature strengthens the biaxial in-plane anisotropy in detriment of the uniaxial contribution, in agreement with a more homogeneous structure of expanded austenite with lower residual stresses. In contrast to polycrystalline expanded austenite, single crystalline expanded austenite exhibits its magnetic easy axes along basic directions. PMID:24028676

  8. Effect of initial microstructure on austenite formation kinetics in high-strength experimental microalloyed steels

    NASA Astrophysics Data System (ADS)

    López-Martínez, Edgar; Vázquez-Gómez, Octavio; Vergara-Hernández, Héctor Javier; Campillo, Bernardo

    2015-12-01

    Austenite formation kinetics in two high-strength experimental microalloyed steels with different initial microstructures comprising bainite-martensite and ferrite-martensite/austenite microconstituents was studied during continuous heating by dilatometric analysis. Austenite formation occurred in two steps: (1) carbide dissolution and precipitation and (2) transformation of residual ferrite to austenite. Dilatometric analysis was used to determine the critical temperatures of austenite formation and continuous heating transformation diagrams for heating rates ranging from 0.03°C•s-1 to 0.67°C•s-1. The austenite volume fraction was fitted using the Johnson-Mehl-Avrami-Kolmogorov equation to determine the kinetic parameters k and n as functions of the heating rate. Both n and k parameters increased with increasing heating rate, which suggests an increase in the nucleation and growth rates of austenite. The activation energy of austenite formation was determined by the Kissinger method. Two activation energies were associated with each of the two austenite formation steps. In the first step, the austenite growth rate was controlled by carbon diffusion from carbide dissolution and precipitation; in the second step, it was controlled by the dissolution of residual ferrite to austenite.

  9. Austenite Formation from Martensite in a 13Cr6Ni2Mo Supermartensitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Bojack, A.; Zhao, L.; Morris, P. F.; Sietsma, J.

    2016-05-01

    The influence of austenitization treatment of a 13Cr6Ni2Mo supermartensitic stainless steel (X2CrNiMoV13-5-2) on austenite formation during reheating and on the fraction of austenite retained after tempering treatment is measured and analyzed. The results show the formation of austenite in two stages. This is probably due to inhomogeneous distribution of the austenite-stabilizing elements Ni and Mn, resulting from their slow diffusion from martensite into austenite and carbide and nitride dissolution during the second, higher temperature, stage. A better homogenization of the material causes an increase in the transformation temperatures for the martensite-to-austenite transformation and a lower retained austenite fraction with less variability after tempering. Furthermore, the martensite-to-austenite transformation was found to be incomplete at the target temperature of 1223 K (950 °C), which is influenced by the previous austenitization treatment and the heating rate. The activation energy for martensite-to-austenite transformation was determined by a modified Kissinger equation to be approximately 400 and 500 kJ/mol for the first and the second stages of transformation, respectively. Both values are much higher than the activation energy found during isothermal treatment in a previous study and are believed to be effective activation energies comprising the activation energies of both mechanisms involved, i.e., nucleation and growth.

  10. A review on nickel-free nitrogen containing austenitic stainless steels for biomedical applications.

    PubMed

    Talha, Mohd; Behera, C K; Sinha, O P

    2013-10-01

    The field of biomaterials has become a vital area, as these materials can enhance the quality and longevity of human life. Metallic materials are often used as biomaterials to replace structural components of the human body. Stainless steels, cobalt-chromium alloys, commercially pure titanium and its alloys are typical metallic biomaterials that are being used for implant devices. Stainless steels have been widely used as biomaterials because of their very low cost as compared to other metallic materials, good mechanical and corrosion resistant properties and adequate biocompatibility. However, the adverse effects of nickel ions being released into the human body have promoted the development of "nickel-free nitrogen containing austenitic stainless steels" for medical applications. Nitrogen not only replaces nickel for austenitic structure stability but also much improves steel properties. Here we review the harmful effects associated with nickel and emphatically the advantages of nitrogen in stainless steel, as well as the development of nickel-free nitrogen containing stainless steels for medical applications. By combining the benefits of stable austenitic structure, high strength, better corrosion and wear resistance and superior biocompatibility in comparison to the currently used austenitic stainless steel (e.g. 316L), the newly developed nickel-free high nitrogen austenitic stainless steel is a reliable substitute for the conventionally used medical stainless steels. PMID:23910251

  11. HYDROGEN-ASSISTED FRACTURE IN FORGED TYPE 304L AUSTENITIC STAINLESS STEEL

    SciTech Connect

    Switzner, Nathan; Neidt, Ted; Hollenbeck, John; Knutson, J.; Everhart, Wes; Hanlin, R.; Bergen, R.; Balch, D. K.

    2012-09-06

    Austenitic stainless steels generally have good resistance to hydrogen-assisted fracture; however, structural designs for high-pressure gaseous hydrogen are constrained by the low strength of this class of material. Forging is used to increase the low strength of austenitic stainless steels, thus improving the efficiency of structural designs. Hydrogen-assisted racture, however, depends on microstructural details associated with manufacturing. In this study, hydrogen-assisted fracture of forged type 304L austenitic stainless steel is investigated. Microstructural variation in multi-step forged 304L was achieved by forging at different rates and temperatures, and by process annealing. High internal hydrogen content in forged type 304L austenitic stainless steel is achieved by thermal precharging in gaseous hydrogen and results in as much as 50% reduction of tensile ductility.

  12. Microstructural Evolution During Friction Surfacing of Austenitic Stainless Steel AISI 304 on Low Carbon Steel

    NASA Astrophysics Data System (ADS)

    Khalid Rafi, H.; Kishore Babu, N.; Phanikumar, G.; Prasad Rao, K.

    2013-01-01

    Austenitic stainless steel AISI 304 coating was deposited over low carbon steel substrate by means of friction surfacing and the microstructural evolution was studied. The microstructural characterization of the coating was carried out by optical microscopy (OM), electron back scattered diffraction (EBSD), and transmission electron microscopy (TEM). The coating exhibited refined grains (average size of 5 μm) as compared to the coarse grains (average size of 40 μm) in as-received consumable rod. The results from the microstructural characterization studies show that discontinuous dynamic recrystallization (DDRX) is the responsible mechanism for grain evolution as a consequence of severe plastic deformation.

  13. Stress corrosion cracking of austenitic stainless steel core internal welds.

    SciTech Connect

    Chung, H. M.; Park, J.-H.; Ruther, W. E.; Sanecki, J. E.; Strain, R. V.; Zaluzec, N. J.

    1999-04-14

    Microstructural analyses by several advanced metallographic techniques were conducted on austenitic stainless steel mockup and core shroud welds that had cracked in boiling water reactors. Contrary to previous beliefs, heat-affected zones of the cracked Type 304L, as well as 304 SS core shroud welds and mockup shielded-metal-arc welds, were free of grain-boundary carbides, which shows that core shroud failure cannot be explained by classical intergranular stress corrosion cracking. Neither martensite nor delta-ferrite films were present on the grain boundaries. However, as a result of exposure to welding fumes, the heat-affected zones of the core shroud welds were significantly contaminated by oxygen and fluorine, which migrate to grain boundaries. Significant oxygen contamination seems to promote fluorine contamination and suppress thermal sensitization. Results of slow-strain-rate tensile tests also indicate that fluorine exacerbates the susceptibility of irradiated steels to intergranular stress corrosion cracking. These observations, combined with previous reports on the strong influence of weld flux, indicate that oxygen and fluorine contamination and fluorine-catalyzed stress corrosion play a major role in cracking of core shroud welds.

  14. Deuterium retention in ITER-grade austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Nemanič, Vincenc; Žumer, Marko; Zajec, Bojan

    2008-11-01

    In view of the construction of ITER, it is essential to confirm that the retention of tritium by the large interior surface area of stainless steel will not become an issue for safety or operating inventory reasons. Retention of deuterium in ITER-grade austenitic stainless steel samples was studied during t = 24 h exposures to pure gaseous deuterium at p = 0.01 mbar and 0.1 mbar and T = 100 °C, 250 °C and 400 °C, respectively. The required high sensitivity for distinguishing hydrogen isotopes involved in the process (H2, HD and D2) was gained after suppression of the native hydrogen concentration by a thermal treatment at T = 400 °C for t = 200 h. The quantity of retained deuterium was determined by measuring the absolute pressure change during the deuterium exposure and subsequent mass spectrometry revealing an intense isotope exchange reaction. The retained amount of 2.6 × 1016 D cm-2 was the highest at T = 400 °C and p = 0.1 mbar and noticeably less at lower deuterium pressure and temperature. Our results, when compared with similar tritium exposures, do not exceed the limits set in the generic safety analysis for the ITER. They manifest that an extremely high sensitivity for deuterium absorption and release can be gained with a precise pressure measuring technique, otherwise attributed exclusively to tritium scintillation methods.

  15. Hot compression deformation behavior of AISI 321 austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Haj, Mehdi; Mansouri, Hojjatollah; Vafaei, Reza; Ebrahimi, Golam Reza; Kanani, Ali

    2013-06-01

    The hot compression behavior of AISI 321 austenitic stainless steel was studied at the temperatures of 950-1100°C and the strain rates of 0.01-1 s-1 using a Baehr DIL-805 deformation dilatometer. The hot deformation equations and the relationship between hot deformation parameters were obtained. It is found that strain rate and deformation temperature significantly influence the flow stress behavior of the steel. The work hardening rate and the peak value of flow stress increase with the decrease of deformation temperature and the increase of strain rate. In addition, the activation energy of deformation ( Q) is calculated as 433.343 kJ/mol. The microstructural evolution during deformation indicates that, at the temperature of 950°C and the strain rate of 0.01 s-1, small circle-like precipitates form along grain boundaries; but at the temperatures above 950°C, the dissolution of such precipitates occurs. Energy-dispersive X-ray analyses indicate that the precipitates are complex carbides of Cr, Fe, Mn, Ni, and Ti.

  16. The formation of twinned austenite in Fe-10Cr-10Ni-2W maraging steel

    SciTech Connect

    Suk, J.I.; Hong, S.H.; Nam, S.W. )

    1991-12-01

    The precipitation hardening mechanisms in high strength maraging steels have been studied in detail by many investigators, but limited information is available on the formation of austenite during aging. Some investigations have been concerned with the understanding of the effect of reverted austenite formed during aging on the mechanical properties. However, only a few investigations have been reported on the morphology and crystallographic feature of austenite. Shiang and Wayman first reported the twin-related and coupled morphology of Widmanstatten austenite plates which were frequently observed in maraging steel. In addition, Ameyama et al. reported the morphology and crystallographic features of austenite formed in ferrite grain during aging in a two-phase stainless steel, and found that each side of the austenite pair of twins satisfies the Kurdjumov-Sachs (K-S) orientation relationship with the parent phase. The morphology and crystallographic features of the reverted austenite formed during aging of Fe-10Cr-10Ni-2W stainless maraging steel have been investigated in this paper. The major strengthening precipitate in Fe-10Cr-10Ni-2W maraging steels has been identified as the rod-shaped {eta}-Ni{sub 3}Ti phase in our previous study. The peculiar morphology of the austenite, i.e., twinned austenite, also has been found in our studies of maraging steel in the Fe-10Cr-10Ni-2W lath martensite. In addition, computer simulation of the diffraction pattern is used to confirm the orientation relationships, such as the Kurdjumov-Sachs (K-S) relationship, the Nishiyama-Wasserman (N-W) relationship and the twin relationship by comparisons with the experimentaly observed results.

  17. Study of biocompatibility of medical grade high nitrogen nickel-free austenitic stainless steel in vitro.

    PubMed

    Li, Menghua; Yin, Tieying; Wang, Yazhou; Du, Feifei; Zou, Xingzheng; Gregersen, Hans; Wang, Guixue

    2014-10-01

    Adverse effects of nickel ions being released into the living organism have resulted in development of high nitrogen nickel-free austenitic stainless steels for medical applications. Nitrogen not only replaces nickel for austenitic structure stability but also improves steel properties. The cell cytocompatibility, blood compatibility and cell response of high nitrogen nickel-free austenitic stainless steel were studied in vitro. The mechanical properties and microstructure of this stainless steel were compared to the currently used 316L stainless steel. It was shown that the new steel material had comparable basic mechanical properties to 316L stainless steel and preserved the single austenite organization. The cell toxicity test showed no significant toxic side effects for MC3T3-E1 cells compared to nitinol alloy. Cell adhesion testing showed that the number of MC3T3-E1 cells was more than that on nitinol alloy and the cells grew in good condition. The hemolysis rate was lower than the national standard of 5% without influence on platelets. The total intracellular protein content and ALP activity and quantification of mineralization showed good cell response. We conclude that the high nitrogen nickel-free austenitic stainless steel is a promising new biomedical material for coronary stent development. PMID:25175259

  18. Structure and Mechanical Properties of Nitrogen Austenitic Steel after Ultrasonic Forging

    NASA Astrophysics Data System (ADS)

    Narkevich, N. A.; Tolmachev, A. I.; Vlasov, I. V.; Surikova, N. S.

    2016-03-01

    Electron microscopy and X-ray diffraction have been used to investigate a nitrogen 07Kh17AG18 steel with an austenitic structure after the surface deformation treatment—ultrasonic forging. During ultrasonic forging, an austenitic structure transforms into a new structure with an elevated concentration of deformation-induced stacking faults, a lot of deformation microtwins, ɛ-martensite crystals. The austenite lattice parameter is found to be decreased in the surface layer. After ultrasonic forging, nitrided steel exhibits enhanced strength properties with retained high plasticity.

  19. Austenite layer and precipitation in high Co-Ni maraging steel.

    PubMed

    Wang, Chenchong; Zhang, Chi; Yang, Zhigang

    2014-12-01

    In high Co-Ni maraging steel, austenite has a great effect on the fracture toughness of the steel and the precipitated carbides are the main strengthening phase. In this study, both austenite layers and precipitation were observed and their formation theory was analyzed by Thermo-Calc simulation and several reported results. TEM and HRTEM observation results showed that the thickness of the austenite layers was about 5-10 nm and the length of the needle-like precipitated carbides was less than 10nm. The carbides maintained coherent or semi-coherent relation with the matrix. PMID:25129424

  20. Influence of kinetics of supercooled austenite decomposition on structure formation in sparingly-alloyed tool steel

    NASA Astrophysics Data System (ADS)

    Krylova, S. E.; Yakovleva, I. L.; Tereshchenko, N. A.; Priimak, E. Yu.; Kletsova, O. A.

    2013-10-01

    The decomposition of supercooled austenite in 70Kh3G2VTB steel under isothermal conditions and continuous cooling have been studied. The isothermal and continuous cooling tranformation curves of the decomposition of austenite in the experimental steel have been constructed. The effect of alloying elements on phase transformations in the steel under heating and cooling have been established. The features of the formation of a microstructure in the 70Kh3G2VTB steel after different regimes of heat treatment have been described. The optimal parameters of hardening heat treatment have been developed.

  1. Austenite precipitation during tempering in 16Cr-2Ni martensitic stainless steels

    SciTech Connect

    Balan, K.P.; Reddy, A.V.; Sarma, D.S.

    1998-09-04

    The 16Cr-2Ni steel when quenched from austenitizing temperature of 1,323K results in the formation of a complex microstructure consisting of the inherited {delta}-ferrite, martensite and retained austenite with a few undissolved M{sub 23}C{sub 6} carbides. There do not appear to be many reports on tempering behavior of 16Cr-2Ni steel through microstructural characterization using transmission electron microscopy. A comprehensive study is under progress to examine the structure-fracture-property relationship on 16Cr-2Ni steel and the microstructural changes that occur on tempering the steel are dealt with in this paper.

  2. The correlation between swelling and radiation-induced segregation in iron-chromium-nickel alloys.

    SciTech Connect

    Allen, T. R.; Busby, J. T.; Kenik, E. A.; Was, G. S.

    1998-03-05

    The magnitudes of both void swelling and radiation-induced segregation (RIS) in iron-chromium-nickel alloys are dependent on bulk alloy composition. Because the diffusivity of nickel via the vacancy flux is slow relative to chromium, nickel enriches and chromium depletes at void surfaces during irradiation. This local composition change reduces the subsequent vacancy flux to the void, thereby reducing void swelling. In this work, the resistance to swelling from major element segregation is estimated using diffusivities derived from grain boundary segregation measurements in irradiated iron-chromium-nickel alloys. The resistance to void swelling in iron- and nickel-base alloys correlates with the segregation and both are functions of bulk alloy composition. Alloys that display the greatest amount of nickel enrichment and chromium depletion are found to be most resistant to void swelling, as predicted. Additionally, swelling is shown to be greater in alloys in which the RIS profiles are slow to develop.

  3. Long term corrosion resistance of alumina forming austenitic stainless steels in liquid lead

    NASA Astrophysics Data System (ADS)

    Ejenstam, Jesper; Szakálos, Peter

    2015-06-01

    Alumina forming austenitic steels (AFA) and commercial stainless steels have been exposed in liquid lead with 10-7 wt.% oxygen at 550 °C for up to one year. It is known that chromia forming austenitic stainless steels, such as 316L and 15-15 Ti, have difficulties forming protective oxides in liquid lead at temperatures above 500 °C, which is confirmed in this study. By adding Al to austenitic steels, it is in general terms possible to increase the corrosion resistance. However this study shows that the high Ni containing AFA alloys are attacked by the liquid lead, i.e. dissolution attack occurs. By lowering the Ni content in AFA alloys, it is possible to achieve excellent oxidation properties in liquid lead. Following further optimization of the microstructural properties, low Ni AFA alloys may represent a promising future structural steel for lead cooled reactors.

  4. Fundamental study of the austenite formation and decomposition in low-silicon, aluminum added TRIP steels

    NASA Astrophysics Data System (ADS)

    Garcia-Gonzalez, Jose Enrique

    2005-11-01

    TRIP (Transformation Induced Plasticity) steels are under development for automotive applications that require high strength and excellent formability. Conventional TRIP steels consist of a multiphase microstructure comprised of a ferrite matrix with a dispersion of bainite and metastable retained austenite. The high ductility exhibited by these steels results from the transformation of the metastable retained austenite to martensite during straining. In conventional TRIP steel processing, the multiphase microstructure is obtained by controlled cooling from the alpha + gamma region to an isothermal holding temperature. During this holding, bainite forms and carbon is rejected out into the austenite, which lowers the Ms temperature and stabilizes the austenite to room temperature. In this research project, a fundamental study of a low-Si, Mo-Nb added cold rolled TRIP steel with and without Al additions was conducted. In this study, the recrystallization of cold-rolled ferrite, the formation of austenite during intercritical annealing and the characteristics of the decomposition of the intercritically annealed austenite by controlled cooling rates were systematically assessed. Of special interest were: (i) the effect of the initial hot band microstructure, (ii) the formation of epitaxial ferrite during cooling from the intercritical annealing temperature to the isothermal holding temperature, (iii) the influence of the intercritically annealed austenite on the formation of bainite during the isothermal holding temperature, and (iv) the influence of the processing variables on the type, amount, composition and stability of the retained austenite. During this research study, techniques such as OM, SEM, EBSD, TEM, XRD and Magnetometry were used to fully characterize the microstructures. Furthermore, a Gleeble 3500 unit at US Steel Laboratories was used for dilatometry studies and to simulate different CGL processing routes, from which specimens were obtained to evaluate

  5. Amorphous stainless steel coatings prepared by reactive magnetron-sputtering from austenitic stainless steel targets

    NASA Astrophysics Data System (ADS)

    Cusenza, Salvatore; Schaaf, Peter

    2009-01-01

    Stainless steel films were reactively magnetron sputtered in argon/methane gas flow onto oxidized silicon wafers using austenitic stainless-steel targets. The deposited films of about 200 nm thickness were characterized by conversion electron Mössbauer spectroscopy, magneto-optical Kerr-effect, X-ray diffraction, scanning electron microscopy, Rutherford backscattering spectrometry, atomic force microscopy, corrosion resistance tests, and Raman spectroscopy. These complementary methods were used for a detailed examination of the carburization effects in the sputtered stainless-steel films. The formation of an amorphous and soft ferromagnetic phase in a wide range of the processing parameters was found. Further, the influence of the substrate temperature and of post vacuum-annealing were examined to achieve a comprehensive understanding of the carburization process and phase formation.

  6. Numerical simulation and experimental investigation of laser dissimilar welding of carbon steel and austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Nekouie Esfahani, M. R.; Coupland, J.; Marimuthu, S.

    2015-07-01

    This study reports an experimental and numerical investigation on controlling the microstructure and brittle phase formation during laser dissimilar welding of carbon steel to austenitic stainless steel. The significance of alloying composition and cooling rate were experimentally investigated. The investigation revealed that above a certain specific point energy the material within the melt pool is well mixed and the laser beam position can be used to control the mechanical properties of the joint. The heat-affected zone within the high-carbon steel has significantly higher hardness than the weld area, which severely undermines the weld quality. A sequentially coupled thermo-metallurgical model was developed to investigate various heat-treatment methodology and subsequently control the microstructure of the HAZ. Strategies to control the composition leading to dramatic changes in hardness, microstructure and service performance of the dissimilar laser welded fusion zone are discussed.

  7. Influence of boron on void swelling in model austenitic steels

    NASA Astrophysics Data System (ADS)

    Okita, T.; Wolfer, W. G.; Garner, F. A.; Sekimura, N.

    2004-08-01

    Model austenitic steels based on Fe-15Cr-16Ni with additions of 0.25Ti, 500 appm B, or 0.25Ti-500 appm B were irradiated in FFTF/MOTA over a wide range of dose rates at ˜400 °C. In addition to the effect of dose rate on swelling, it was desired to study the effect of boron addition to produce variations in He/dpa ratio. A strong effect of dose rate was observed, so strong that the relatively small distances separating the boron-free and doped alloys introduced a complication into the experiment. For specimens irradiated within the core, boron addition had no significant effect. For irradiations conducted near or outside the core edge, swelling appeared to be either enhanced or decreased by boron. The variability was a consequence of a strong dose rate effect overwhelming the influence of boron and helium. It is shown that helium exerted little influence relative to other important factors in these alloys.

  8. Dislocation loop evolution under ion irradiation in austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Etienne, A.; Hernández-Mayoral, M.; Genevois, C.; Radiguet, B.; Pareige, P.

    2010-05-01

    A solution annealed 304 and a cold worked 316 austenitic stainless steels were irradiated from 0.36 to 5 dpa at 350 °C using 160 keV Fe ions. Irradiated microstructures were characterized by transmission electron microscopy (TEM). Observations after irradiation revealed the presence of a high number density of Frank loops. Size and number density of Frank loops have been measured. Results are in good agreement with those observed in the literature and show that ion irradiation is able to simulate dislocation loop microstructure obtained after neutron irradiation. Experimental results and data from literature were compared with predictions from the cluster dynamic model, MFVIC (Mean Field Vacancy and Interstitial Clustering). It is able to reproduce dislocation loop population for neutron irradiation. Effects of dose rate and temperature on the loop number density are simulated by the model. Calculations for ion irradiations show that simulation results are consistent with experimental observations. However, results also show the model limitations due to the lack of accurate parameters.

  9. Material Parameters for Creep Rupture of Austenitic Stainless Steel Foils

    NASA Astrophysics Data System (ADS)

    Osman, H.; Borhana, A.; Tamin, M. N.

    2014-08-01

    Creep rupture properties of austenitic stainless steel foil, 347SS, used in compact recuperators have been evaluated at 700 °C in the stress range of 54-221 MPa to establish the baseline behavior for its extended use. Creep curves of the foil show that the primary creep stage is brief and creep life is dominated by tertiary creep deformation with rupture lives in the range of 10-2000 h. Results are compared with properties of bulk specimens tested at 98 and 162 MPa. Thin foil 347SS specimens were found to have higher creep rates and higher rupture ductility than their bulk specimen counterparts. Power law relationship was obtained between the minimum creep rate and the applied stress with stress exponent value, n = 5.7. The value of the stress exponent is indicative of the rate-controlling deformation mechanism associated with dislocation creep. Nucleation of voids mainly occurred at second-phase particles (chromium-rich M23C6 carbides) that are present in the metal matrix by decohesion of the particle-matrix interface. The improvement in strength is attributed to the precipitation of fine niobium carbides in the matrix that act as obstacles to the movement of dislocations.

  10. Dissimilar Friction Stir Welding Between UNS S31603 Austenitic Stainless Steel and UNS S32750 Superduplex Stainless Steel

    NASA Astrophysics Data System (ADS)

    Theodoro, Maria Claudia; Pereira, Victor Ferrinho; Mei, Paulo Roberto; Ramirez, Antonio Jose

    2015-02-01

    In order to verify the viability of dissimilar UNS S31603 austenitic and UNS S32750 superduplex stainless steels joined by friction stir welding, 6-mm-thick plates were welded using a PCBN-WRe tool. The welded joints were performed in position control mode at rotational speeds of 100 to 300 rpm and a feed rate of 100 mm/min. The joints performed with 150 and 200 rpm showed good appearance and no defects. The metallographic analysis of both joints showed no internal defects and that the material flow pattern is visible only in the stirred zone (SZ) of the superduplex steel. On the SZ top, these patterns are made of regions of different phases (ferrite and austenite), and on the bottom and central part of the SZ, these patterns are formed by alternated regions of different grain sizes. The ferrite grains in the superduplex steel are larger than those in the austenitic ones along the SZ and thermo-mechanically affected zone, explained by the difference between austenite and ferrite recrystallization kinetics. The amount of ferrite islands present on the austenitic steel base metal decreased near the SZ interface, caused by the dissolving of the ferrite in austenitic matrix. No other phases were found in both joints. The best weld parameters were found to be 200 rpm rotation speed, 100 mm/min feed rate, and tool position control.

  11. Copper modified austenitic stainless steel alloys with improved high temperature creep resistance

    DOEpatents

    Swindeman, R.W.; Maziasz, P.J.

    1987-04-28

    An improved austenitic stainless steel that incorporates copper into a base Fe-Ni-Cr alloy having minor alloying substituents of Mo, Mn, Si, T, Nb, V, C, N, P, B which exhibits significant improvement in high temperature creep resistance over previous steels. 3 figs.

  12. Texture evolution of warm-rolled and annealed 304L and 316L austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Lindell, D.

    2015-04-01

    The brass-to-copper rolling texture transition is observed during warm rolling austenitic stainless steels. In the current paper austenitic stainless steels 304L and 316L have been subjected to warm rolling at 700°C to 90% reduction. The evolution of microstructure and texture during subsequent annealing has been studied using dilatometry and electron backscatter diffraction. Recrystallisation texture for 304L was primarily cube with some retained rolling texture while 316L only had retained rolling texture. The different behaviour between the two steels is believed to originate from differences in molybdenum content.

  13. Stages of austenitization of cold-worked low-carbon steel in intercritical temperature range

    NASA Astrophysics Data System (ADS)

    Panov, D. O.; Simonov, Y. N.; Spivak, L. V.; Smirnov, A. I.

    2015-08-01

    Austenization processes in 10Kh3G3MF low-carbon steel in the initially cold-worked state are investigated during its continuous heating in an intercritical temperature range. The austenization of this steel has three stages, which is shown by dilatometry, differential scanning calorimetry, and transmission electron microscopy. The thermokinetic diagram of the austenite formation in 10Kh3G3MF steel is constructed. Critical points A c1 and A c2 and temperature ranges of austenite formation at every stage of the α → γ transformation at heating rates of 0.6-400 K/s are determined.

  14. Retained Austenite in SAE 52100 Steel Post Magnetic Processing and Heat Treatment

    SciTech Connect

    Pappas, Nathaniel R; Watkins, Thomas R; Cavin, Odis Burl; Jaramillo, Roger A; Ludtka, Gerard Michael

    2007-01-01

    Steel is an iron-carbon alloy that contains up to 2% carbon by weight. Understanding which phases of iron and carbon form as a function of temperature and percent carbon is important in order to process/manufacture steel with desired properties. Austenite is the face center cubic (fcc) phase of iron that exists between 912 and 1394 C. When hot steel is rapidly quenched in a medium (typically oil or water), austenite transforms into martensite. The goal of the study is to determine the effect of applying a magnetic field on the amount of retained austenite present at room temperature after quenching. Samples of SAE 52100 steel were heat treated then subjected to a magnetic field of varying strength and time, while samples of SAE 1045 steel were heat treated then subjected to a magnetic field of varying strength for a fixed time while being tempered. X-ray diffraction was used to collect quantitative data corresponding to the amount of each phase present post processing. The percentage of retained austenite was then calculated using the American Society of Testing and Materials standard for determining the amount of retained austenite for randomly oriented samples and was plotted as a function of magnetic field intensity, magnetic field apply time, and magnetic field wait time after quenching to determine what relationships exist with the amount of retained austenite present. In the SAE 52100 steel samples, stronger field strengths resulted in lower percentages of retained austenite for fixed apply times. The results were inconclusive when applying a fixed magnetic field strength for varying amounts of time. When applying a magnetic field after waiting a specific amount of time after quenching, the analyses indicate that shorter wait times result in less retained austenite. The SAE 1045 results were inconclusive. The samples showed no retained austenite regardless of magnetic field strength, indicating that tempering removed the retained austenite. It is apparent

  15. Effect of nitrogen and vanadium on austenite grain growth kinetics of a low alloy steel

    SciTech Connect

    Stasko, Renata . E-mail: rstasko@ap.Cracow.pl; Adrian, Henryk . E-mail: adrian@uci.agh.edu.pl; Adrian, Anna . E-mail: adrian@metal.agh.edu.pl

    2006-06-15

    Austenite grain growth kinetics in a steel containing 0.4% C, 1.8% Cr with different nitrogen contents (in the range 0.0038-0.0412%) and a micralloying addition of 0.078% V were investigated. The investigations were carried out in an austenitising temperature range of 840-1200 deg. C for 30 min. The results of investigations showed that N promotes the grain growth of austenite. The microalloying addition of vanadium protects the austenite grain growth because of carbonitride V(C,N) precipitation and the grain boundary pinning effect of undissolved particles of V(C,N). Using a thermodynamic model, the carbonitride V(C,N) content, undissolved at the austenitising temperature was calculated. At temperatures when a coarsening and dissolution of carbonitride occurs, the austenite grains start to growth. The effect of nitrogen on the type of chord length distribution of austenite grains was analysed.

  16. A Feasibility Study on Low Temperature Thermochemical Treatments of Austenitic Stainless Steel in Fluidized Bed Furnace

    NASA Astrophysics Data System (ADS)

    Haruman, Esa; Sun, Yong; Triwiyanto, Askar; Manurung, Yupiter H. P.; Adesta, Erry Y.

    2011-04-01

    In this work, the feasibility of using an industrial fluidized bed furnace to perform low temperature thermochemical treatments of austenitic stainless steels has been studied, with the aim to produce expanded austenite layers with combined wear and corrosion resistance, similar to those achievable by plasma and gaseous processes. Several low temperature thermochemical treatments were studied, including nitriding, carburizing, combined nitridingcarburizing (hybrid treatment), and sequential carburizing and nitriding. The results demonstrate that it is feasible to produce expanded austenite layers on the investigated austenitic stainless steel by the fluidized bed heat treatment technique, thus widening the application window for the novel low temperature processes. The results also demonstrate that the fluidized bed furnace is the most effective for performing the hybrid treatment, which involves the simultaneous incorporation of nitrogen and carbon together into the surface region of the component in nitrogen and carbon containing atmospheres. Such hybrid treatment produces a thicker and harder layer than the other three processes investigated.

  17. Mechanical properties of steels with a microstructure of bainite/martensite and austenite islands

    NASA Astrophysics Data System (ADS)

    Syammach, Sami M.

    Advanced high strength steels (AHSS) are continually being developed in order to reduce weight and improve safety for automotive applications. There is need for economic steels with improved strength and ductility combinations. These demands have led to research and development of third generation AHSS. Third generation AHSS include steel grades with a bainitic and tempered martensitic matrix with retained austenite islands. These steels may provide improved mechanical properties compared to first generation AHSS and should be more economical than second generation AHSS. There is a need to investigate these newer types of steels to determine their strength and formability properties. Understanding these bainitic and tempered martensitic steels is important because they likely can be produced using currently available production systems. If viable, these steels could be a positive step in the evolution of AHSS. The present work investigates the effect of the microstructure on the mechanical properties of steels with a microstructure of bainite, martensite, and retained austenite, so called TRIP aided bainitic ferrite (TBF) steels. The first step in this project was creating the desired microstructure. To create a microstructure of bainite, martensite, and austenite an interrupted austempering heat treatment was used. Varying the heat treatment times and temperatures produced microstructures of varying amounts of bainite, martensite, and austenite. Mechanical properties such as strength, ductility, strain hardening, and hole-expansion ratios were then evaluated for each heat treatment. Correlations between mechanical properties and microstructure were then evaluated. It was found that samples after each of the heat treatments exhibited strengths between 1050 MPa and 1350 MPa with total elongations varying from 8 pct to 16 pct. By increasing the bainite and austenite volume fraction the strength of the steel was found to decrease, but the ductility increased. Larger

  18. Precipitation and stability of reversed austenite in 9Ni steel

    NASA Astrophysics Data System (ADS)

    Yang, Yue-Hui; Cai, Qing-Wu; Tang, Di; Wu, Hui-Bin

    2010-10-01

    A new method was used to analyze the factors affecting the precipitation of reversed austenite during tempering. The samples were kept at various tempering temperatures for 10 min and their length changes were recorded. Then, the precipitation of reversed austenite which led to the length reduction was shown by thermal expansion curves. The results show that the effects of process parameters on the precipitation of reversed austenite can be determined more accurately by this method than by X-ray diffraction. When the quenching and tempering process is adopted, both the lower quenching temperature and higher tempering temperature can promote the precipitation of reversed austenite during tempering; and when the quenching, lamellarizing, and tempering process is used, intercritical quenching is considered beneficial to the precipitation of reversed austenite in the subsequent tempering because of Ni segregation during holding at the intercritical temperature.

  19. Heat treatment giving a stable high temperature micro-structure in cast austenitic stainless steel

    DOEpatents

    Anton, Donald L.; Lemkey, Franklin D.

    1988-01-01

    A novel micro-structure developed in a cast austenitic stainless steel alloy and a heat treatment thereof are disclosed. The alloy is based on a multicomponent Fe-Cr-Mn-Mo-Si-Nb-C system consisting of an austenitic iron solid solution (.gamma.) matrix reinforced by finely dispersed carbide phases and a heat treatment to produce the micro-structure. The heat treatment includes a prebraze heat treatment followed by a three stage braze cycle heat treatment.

  20. Recrystallization Behavior of a Heavily Deformed Austenitic Stainless Steel During Iterative Type Annealing

    NASA Astrophysics Data System (ADS)

    Ravi Kumar, B.; Sharma, Sailaja

    2014-09-01

    The study describes evolution of the recrystallization microstructure in an austenitic stainless steel during iterative or repetitive type annealing process. The starting heavily cold deformed microstructure consisted of a dual phase structure i.e., strain-induced martensite (SIM) (43 pct in volume) and heavily deformed large grained retained austenite. Recrystallization behavior was compared with Johnson Mehl Avrami and Kolmogorov model. Early annealing iterations led to reversion of SIM to reversed austenite. The microstructure changes observed in the retained austenite and in the reverted austenite were mapped by electron backscatter diffraction technique and transmission electron microscope. The reversed austenite was characterized by a fine polygonal substructure consisting of low-angle grain boundaries. With an increasing number of annealing repetitions, these boundaries were gradually replaced by high-angle grain boundaries and recrystallized into ultrafine-grained microstructure. On the other hand, recrystallization of retained austenite grains was sluggish in nature. Progress of recrystallization in these grains was found to take place by a gradual evolution of subgrains and their subsequent transformation into fine grains. The observed recrystallization characteristics suggest continuous recrystallization type process. The analysis provided basic insight into the recrystallization mechanisms that enable the processing of ultrafine-grained fcc steels by iterative type annealing. Tensile properties of the processed material showed a good combination of strength and ductility.

  1. Recrystallization Behavior of a Heavily Deformed Austenitic Stainless Steel During Iterative Type Annealing

    NASA Astrophysics Data System (ADS)

    Ravi Kumar, B.; Sharma, Sailaja

    2014-12-01

    The study describes evolution of the recrystallization microstructure in an austenitic stainless steel during iterative or repetitive type annealing process. The starting heavily cold deformed microstructure consisted of a dual phase structure i.e., strain-induced martensite (SIM) (43 pct in volume) and heavily deformed large grained retained austenite. Recrystallization behavior was compared with Johnson Mehl Avrami and Kolmogorov model. Early annealing iterations led to reversion of SIM to reversed austenite. The microstructure changes observed in the retained austenite and in the reverted austenite were mapped by electron backscatter diffraction technique and transmission electron microscope. The reversed austenite was characterized by a fine polygonal substructure consisting of low-angle grain boundaries. With an increasing number of annealing repetitions, these boundaries were gradually replaced by high-angle grain boundaries and recrystallized into ultrafine-grained microstructure. On the other hand, recrystallization of retained austenite grains was sluggish in nature. Progress of recrystallization in these grains was found to take place by a gradual evolution of subgrains and their subsequent transformation into fine grains. The observed recrystallization characteristics suggest continuous recrystallization type process. The analysis provided basic insight into the recrystallization mechanisms that enable the processing of ultrafine-grained fcc steels by iterative type annealing. Tensile properties of the processed material showed a good combination of strength and ductility.

  2. Grain refinement of a nickel and manganese free austenitic stainless steel produced by pressurized solution nitriding

    SciTech Connect

    Mohammadzadeh, Roghayeh Akbari, Alireza

    2014-07-01

    Prolonged exposure at high temperatures during solution nitriding induces grain coarsening which deteriorates the mechanical properties of high nitrogen austenitic stainless steels. In this study, grain refinement of nickel and manganese free Fe–22.75Cr–2.42Mo–1.17N high nitrogen austenitic stainless steel plates was investigated via a two-stage heat treatment procedure. Initially, the coarse-grained austenitic stainless steel samples were subjected to an isothermal heating at 700 °C to be decomposed into the ferrite + Cr{sub 2}N eutectoid structure and then re-austenitized at 1200 °C followed by water quenching. Microstructure and hardness of samples were characterized using X-ray diffraction, optical and scanning electron microscopy, and micro-hardness testing. The results showed that the as-solution-nitrided steel decomposes non-uniformly to the colonies of ferrite and Cr{sub 2}N nitrides with strip like morphology after isothermal heat treatment at 700 °C. Additionally, the complete dissolution of the Cr{sub 2}N precipitates located in the sample edges during re-austenitizing requires longer times than 1 h. In order to avoid this problem an intermediate nitrogen homogenizing heat treatment cycle at 1200 °C for 10 h was applied before grain refinement process. As a result, the initial austenite was uniformly decomposed during the first stage, and a fine grained austenitic structure with average grain size of about 20 μm was successfully obtained by re-austenitizing for 10 min. - Highlights: • Successful grain refinement of Fe–22.75Cr–2.42Mo–1.17N steel by heat treatment • Using the γ → α + Cr{sub 2}N reaction for grain refinement of a Ni and Mn free HNASS • Obtaining a single phase austenitic structure with average grain size of ∼ 20 μm • Incomplete dissolution of Cr{sub 2}N during re-austenitizing at 1200 °C for long times • Reducing re-austenitizing time by homogenizing treatment before grain refinement.

  3. TEM studies of plasma nitrided austenitic stainless steel.

    PubMed

    Stróz, D; Psoda, M

    2010-03-01

    Cross-sectional transmission electron microscopy and X-ray phase analysis were used to study the structure of a layer formed during nitriding the AISI 316L stainless steel at temperature 440 degrees C. It was found that the applied treatment led to the formation of 6-microm-thick layer of the S-phase. There is no evidence of CrN precipitation. The X-ray diffraction experiments proved that the occurred austenite lattice expansion - due to nitrogen atoms - depended on the crystallographic direction. The cross-sectional transmission electron microscopy studies showed that the layer consisted of a single cubic phase that contained a lot of defects such as dislocations, stacking faults, slip bands and twins. The high-resolution electron microscopy observations were applied to study the defect formation due to the nitriding process. It was shown that the presence of great number of stacking faults leads to formation of nanotwins. Weak, forbidden {100} reflections were still another characteristic feature of the S-phase. These were not detected in the X-ray spectra of the phase. Basing on the high-resolution electron microscopy studies it can be suggested that the short-range ordering of the nitrogen atoms in the octahedral sites inside the f.c.c. matrix lattice takes place and gives rise to appearance of these spots. It is suggested that the cubic lattice undergoes not only expansion but also slight rombohedral distortion that explains differences in the lattice expansion for different crystallographic directions. PMID:20500370

  4. Investigation of fatigue behavior of two austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Kalnaus, Sergiy

    2009-12-01

    Fatigue of two stainless steels, AISI 304L and AL6-XN, was systematically investigated. While AISI 304L is well known in industry and has been used in engineering applications over the years, AL6-XN is a relatively new alloy and fatigue properties of this material have not been fully investigated by researchers. Both materials belong to one group of austenitic stainless steels. Tension-compression, torsion, and axial-torsion fatigue experiments were conducted on the two alloys to experimentally investigate the cyclic plasticity behavior and the fatigue behavior. Both materials are found to display significant non-proportional hardening. While AISI 304L exhibits cyclic hardening, the AL6-XN alloy displays overall softening under applied cyclic load. Under tension-compression, the cracking plane is perpendicular to the axial loading direction regardless of the loading amplitude for both alloys. The strain-life curves under fully reversed tension-compression and pure torsion for AISI 304L steel are smooth as expected for most metallic materials and can be described by a three-parameter power equation. However, the shear strain-life curve under pure torsion loading for AL6-XN alloy displays a distinct plateau in the fatigue life range approximately from 20,000 to 60,000 loading cycles. The shear strain amplitude corresponding to the plateau is approximately 1.0%. When the shear strain amplitude is above 1.0% under pure shear, the material displays shear cracking. When the shear strain amplitude is below 1.0%, the material displays tensile cracking. A transition from shear cracking to tensile cracking is associated with the plateau in the shear strain-life curve. Three different multiaxial fatigue criteria were evaluated based upon the experimental results on the material for the capability of the criteria to predict fatigue life and the cracking direction. Despite the difference in theory, all the three multiaxial criteria can reasonably correlate the experiments in

  5. Ferrite and austenite phase identification in duplex stainless steel using SPM techniques

    NASA Astrophysics Data System (ADS)

    Guo, L. Q.; Lin, M. C.; Qiao, L. J.; Volinsky, Alex A.

    2013-12-01

    It can be challenging to properly identify the phases in electro-polished duplex stainless steel using optical microscopy or other characterization techniques. This letter describes magnetic force microscopy to properly identify the phases in electropolished duplex stainless steel. The results are also confirmed with the current sensing atomic force and scanning Kelvin probe force microscopy. The difference in topography heights between the ferrite and austenite phases is attributed to the different etching rates during electropolishing, although these phases have different mechanical properties. The current in the austenite is much higher compared with the ferrite, thus current sensing atomic force microscopy can also be used to properly identify the phases.

  6. Studies on Stress Corrosion Cracking of Super 304H Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Prabha, B.; Sundaramoorthy, P.; Suresh, S.; Manimozhi, S.; Ravishankar, B.

    2009-12-01

    Stress corrosion cracking (SCC) is a common mode of failure encountered in boiler components especially in austenitic stainless steel tubes at high temperature and in chloride-rich water environment. Recently, a new type of austenitic stainless steels called Super304H stainless steel, containing 3% copper is being adopted for super critical boiler applications. The SCC behavior of this Super 304H stainless steel has not been widely reported in the literature. Many researchers have studied the SCC behavior of steels as per various standards. Among them, the ASTM standard G36 has been widely used for evaluation of SCC behavior of stainless steels. In this present work, the SCC behavior of austenitic Fe-Cr-Mn-Cu-N stainless steel, subjected to chloride environments at varying strain conditions as per ASTM standard G36 has been studied. The environments employed boiling solution of 45 wt.% of MgCl2 at 155 °C, for various strain conditions. The study reveals that the crack width increases with increase in strain level in Super 304H stainless steels.

  7. The composition of precipitated austenite in 5.5ni steel

    NASA Astrophysics Data System (ADS)

    Kim, J. I.; Morris, J. W.

    1981-11-01

    Both scanning transmission electron microscopic (STEM) and chemical extraction techniques were used to analyze the chemical content of precipitated austenite in 5.5Ni steel as a function of heat treatment. Austenite was introduced into the steel by tempering at 600 °C for 2 h (QT2) or 100 h (QT100), by tempering for 1 h at 670 °C (QL), or by double tempering 1 h at 670 °C + 1 h at 600 °C (QLT). The two methods of chemical analysis employed for the analysis of this austenite differ quantitatively in the measured austenite composition but are in qualitative agreement; they show an austenite enrichment in Ni, Cr, Mn, and Mo which is most pronounced (and nearly equivalent) for the QT100 and QLT treatments. The similar enrichment of the QT100 and QLT material is interpreted in light of the sequence of reactions leading to the QLT structure. A good correlation is found between the apparent solute enrichment of the precipitated austenite and its thermal stability on cooling to 77 K.

  8. On the measurement of austenite in supermartensitic stainless steel by X-ray diffraction

    SciTech Connect

    Tolchard, Julian Richard; Sømme, Astri; Solberg, Jan Ketil; Solheim, Karl Gunnar

    2015-01-15

    Sections of a 13Cr supermartensitic stainless steel were investigated to determine the optimum sample preparation for measurement of the austenite content by X-ray diffraction. The surface of several samples was mechanically ground or polished using media of grit sizes in the range 1–120 μm. The strained surface layer was afterwards removed stepwise by electropolishing, and the austenite content measured at each step. It was found that any level of mechanical grinding or polishing results in a reduction of the measured austenite fraction relative to the true bulk value, and that coarser grinding media impart greater damage and greater reduction in the measured austenite content. The results thus highlight the importance of the electropolishing step in preparation of such samples, but suggest that the American Society for Testing and Materials standard E975-03 substantially overestimates the amount of material which needs to be removed to recover the true “bulk” content. - Highlights: • Quantitative Rietveld analysis of austenite/martensite ratio in supermartensitic stainless steels • Critical evaluation of sample preparation for residual austenite measurements by X-ray diffraction • Highlighting of the importance of electropolishing as a final preparation step.

  9. The effect of dose rate on the response of austenitic stainless steels to neutron radiaiton

    SciTech Connect

    Allen, T. R.; Cole, J I.; Trybus, Carole L.; Porter, D. L.; Tsai, Hanchung; Garner, Francis A.; Kenik, E A.; Yoshitake, T.; Ohta, Joji

    2006-01-01

    Depending on reactor design and component location, austenitic stainless steels may experience significantly different irradiation dose rates in the same reactor. Understanding the effect of dose rate on radiation performance is important to predicting component lifetime. This study examined the effect of dose rate on swelling, grain boundary segregation, and tensile properties in austenitic stainless steels through the examination of components retrieved from the Experimental Breeder Reactor-II (EBR-II) following its shutdown. Annealed 304 stainless steel, stress-relieved 304 stainless steel, 12% cold-worked 316 stainless steel, and 20% cold-worked 316 stainless steel were irradiated over a dose range of 1-56 dpa at temperatures from 371 to 440 C and dose rates from 0.5 to 5.8 ? 10*7 dpa/s. Density and tensile properties were measured for 304 and 316 stainless steel. Changes in grain boundary composition were examined for 304 stainless steel. Swelling appears to increase at lower dose rates in both 304 and 316 stainless steel, although the effect was not always statistically significant. Grain boundary segregation also appears to increase at lower dose rate in 304 stainless steel. For the range of dose rates examined, no measurable dose rate effect on tensile properties was noted for any of the steels.

  10. Influence of reverted austenite on the texture and magnetic properties of 350 maraging steel

    NASA Astrophysics Data System (ADS)

    Abreu, Hamilton F. G.; Silva, Jean J.; Silva, Manoel R.; Gomes da Silva, Marcelo J.

    2015-11-01

    The aging temperature to improve magnetic properties in Maraging-350 steel (Mar-350) is limited by the onset of austenite reversion. The traditional process of cooling after aging is to remove the piece from the oven and then to air cool it. The purpose of this research was to characterize the reverted austenite and to investigate the effect of cooling below the martensite start temperature (Ms) on the magnetic properties. The Mar350 samples aged at temperatures above 550 °C, and subsequently cooled in liquid nitrogen presented less austenite than samples cooled in air, resulting in higher magnetization saturation and a lower coercive force. A combination of optical microscopy (OM), X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) techniques were used to characterize the presence of reverted austenite. The crystallographic texture of both martensite and reverted austenite were analyzed. The texture of the reverted austenite coincides with the texture of the parent austenite indicating that a phenomenon of texture memory is present.

  11. Microstructural effects on the stability of retained austenite in Transformation Induced Plasticity steels

    NASA Astrophysics Data System (ADS)

    Mark, Alison Fiona Lockie

    Transformation Induced Plasticity (TRIP) steels have both high strength and high ductility. Retained austenite in the microstructure, upon straining, transforms to martensite and this absorbs energy and improves the work hardening of the steel, giving improved elongation. The transformation can be either stress-assisted or strain-induced and the initiation and the mechanism depend on the composition of, the size and shape of, and the phases surrounding, the austenite grains. It is important to understand the relationship between these variables and the properties of the TRIP steel. The aim of this work was to determine how the microstructure of the TRIP steel affects the transformation. Four experimental microstructures were developed, containing austenite grains with different sizes, shapes, and surrounding phases. The Fine microstructure had thin elongated austenite laths between fine bainitic ferrite laths, the Coarse microstructure had elongated austenite grains between coarser bainitic ferrite laths, the Equiaxed microstructure had equiaxed austenite grains in a matrix of equiaxed ferrite and the Acicular microstructure had elongated austenite grains surrounded by recovered ferrite laths. Tensile tests were performed and detailed characterization, using neutron diffraction, was done of samples with the four microstructures. The variation in the amount of austenite during deformation was measured. The tensile tests revealed that the microstructures had different mechanical properties and different transformation behaviours. Fine had the lowest elongation and the highest strength. Acicular and Equiaxed had good elongation but lower strength. Coarse had intermediate strength and Equiaxed had sustained work hardening. The transformation in Fine and Coarse was minimal. Coarse had some slow, steady transformation, but Fine may have had none. The transformation in Equiaxed was larger. It started quickly and then slowed at higher strains. The austenite in Acicular

  12. Characterization of the Carbon and Retained Austenite Distributions in Martensitic Medium Carbon, Low Alloy, Steel

    SciTech Connect

    Sherman, D. H.; Cross, Steven M; Kim, Sangho; Grandjean, F.; Long, G. J.; Miller, Michael K

    2007-01-01

    The retained austenite content and carbon distribution in martensite were determined as a function of cooling rate and temper temperature in steel that contained 1.31 at. pct C, 3.2 at. pct Si, and 3.2 at. pct non-iron metallic elements. Mossbauer spectroscopy, transmission electron microscopy (TEM), transmission synchrotron X-ray diffraction (XRD), and atom probe tomography were used for the microstructural analyses. The retained austenite content was an inverse, linear function of cooling rate between 25 and 560 K/s. The elevated Si content of 3.2 at. pct did not shift the start of austenite decomposition to higher tempering temperatures relative to SAE 4130 steel. The minimum tempering temperature for complete austenite decomposition was significantly higher (>650 C) than for SAE 4130 steel ({approx}300 C). The tempering temperatures for the precipitation of transition carbides and cementite were significantly higher (>400 C) than for carbon steels (100 C to 200 C and 200 C to 350 C), respectively. Approximately 90 pct of the carbon atoms were trapped in Cottrell atmospheres in the vicinity of the dislocation cores in dislocation tangles in the martensite matrix after cooling at 560 K/s and aging at 22 C. The 3.2 at. pct Si content increased the upper temperature limit for stable carbon clusters to above 215 C. Significant autotempering occurred during cooling at 25 K/s. The proportion of total carbon that segregated to the interlath austenite films decreased from 34 to 8 pct as the cooling rate increased from 25 to 560 K/s. Developing a model for the transfer of carbon from martensite to austenite during quenching should provide a means for calculating the retained austenite. The maximum carbon content in the austenite films was 6 to 7 at. pct, both in specimens cooled at 560 K/s and at 25 K/s. Approximately 6 to 7 at. pct carbon was sufficient to arrest the transformation of austenite to martensite. The chemical potential of carbon is the same in martensite

  13. Characterization of the Carbon and Retained Austenite Distributions in Martensitic Medium Carbon, High Silicon Steel

    NASA Astrophysics Data System (ADS)

    Sherman, Donald H.; Cross, Steven M.; Kim, Sangho; Grandjean, Fernande; Long, Gary J.; Miller, Michael K.

    2007-08-01

    The retained austenite content and carbon distribution in martensite were determined as a function of cooling rate and temper temperature in steel that contained 1.31 at. pct C, 3.2 at. pct Si, and 3.2 at. pct noniron metallic elements. Mössbauer spectroscopy, transmission electron microscopy (TEM), transmission synchrotron X-ray diffraction (XRD), and atom probe tomography were used for the microstructural analyses. The retained austenite content was an inverse, linear function of cooling rate between 25 and 560 K/s. The elevated Si content of 3.2 at. pct did not shift the start of austenite decomposition to higher tempering temperatures relative to SAE 4130 steel. The minimum tempering temperature for complete austenite decomposition was significantly higher (>650 °C) than for SAE 4130 steel (˜300 °C). The tempering temperatures for the precipitation of transition carbides and cementite were significantly higher (>400 °C) than for carbon steels (100 °C to 200 °C and 200 °C to 350 °C), respectively. Approximately 90 pct of the carbon atoms were trapped in Cottrell atmospheres in the vicinity of the dislocation cores in dislocation tangles in the martensite matrix after cooling at 560 K/s and aging at 22 °C. The 3.2 at. pct Si content increased the upper temperature limit for stable carbon clusters to above 215 °C. Significant autotempering occurred during cooling at 25 K/s. The proportion of total carbon that segregated to the interlath austenite films decreased from 34 to 8 pct as the cooling rate increased from 25 to 560 K/s. Developing a model for the transfer of carbon from martensite to austenite during quenching should provide a means for calculating the retained austenite. The maximum carbon content in the austenite films was 6 to 7 at. pct, both in specimens cooled at 560 K/s and at 25 K/s. Approximately 6 to 7 at. pct carbon was sufficient to arrest the transformation of austenite to martensite. The chemical potential of carbon is the same in

  14. A role of {delta}-ferrite in edge-crack formation during hot-rolling of austenitic stainless steels

    SciTech Connect

    Czerwinski, F.; Brodtka, A.; Cho, J.Y.; Szpunar, J.A.; Zielinska-Lipiec, A.; Sunwoo, J.H.

    1997-10-15

    Austenitic stainless steels are substantially harder during hot-rolling than either ferritic or mild steels. The objective of this study is to verify the possible correlation between the edge-crack formation during hot-rolling and the presence of {delta} ferrite in austenitic stainless steel. Hot-rolled plates of austenitic stainless steels, examined at room temperatures, contain up to 9% of {delta} ferrite in austenitic matrix. The distribution of ferrite in steel plate is inhomogeneous: the highest ferrite content is located in the vicinity of the plate edge. Moreover, the content of {delta} ferrite changes irregularly across the plate thickness. The results obtained from analysis of several plates suggest a correlation between the maximum content of {delta} ferrite in steel microstructure and the length of the edge-crack formed during hot-rolling: the higher the volume fraction of ferrite, the longer the edge-crack.

  15. Effect of austenitizing temperature on microstructure in 16Mn steel treated by cerium

    NASA Astrophysics Data System (ADS)

    Wen, Bin; Song, Bo; Pan, Ning; Hu, Qing-Yun; Mao, Jing-Hong

    2011-12-01

    The change of inclusions and microstructure of 16Mn steel treated by Ce were observed, and the effect of austenitizing temperature on the microstructure was also examined. The results show that the inclusions are transformed from Si-Mn-Al composite oxide and MnS into AlCeO3, Ce2O2S, and MnS composite inclusions after being treated by Ce. Plenty of intragranular ferrites are formed in 16Mn steel containing ˜0.017wt% Ce. A large amount of intragranular acicular ferrites are formed after being austenitized for 20 min at 1473 K. The prior austenite grain size fit for the formation of intragranular acicular ferrites is about 120 μm.

  16. Review of environmental effects on fatigue crack growth of austenitic stainless steels

    SciTech Connect

    Shack, W.J.; Kassner, T.F.

    1994-05-01

    Fatigue and environmentally assisted cracking of piping, pressure vessel cladding, and core components in light water reactors are potential concerns to the nuclear industry and regulatory agencies. The degradation processes include intergranular stress corrosion cracking of austenitic stainless steel (SS) piping in boiling water reactors (BWRs), and propagation of fatigue or stress corrosion cracks (which initiate in sensitized SS cladding) into low-alloy ferritic steels in BWR pressure vessels. Crack growth data for wrought and cast austenitic SSs in simulated BWR water, developed at Argonne National Laboratory under US Nuclear Regulatory Commission sponsorship over the past 10 years, have been compiled into a data base along with similar data obtained from the open literature. The data were analyzed to develop corrosion-fatigue curves for austenitic SSs in aqueous environments corresponding to normal BWR water chemistries, for BWRs that add hydrogen to the feedwater, and for pressurized water reactor primary-system-coolant chemistry.

  17. Solidification behavior and microstructural analysis of austenitic stainless steel laser welds

    SciTech Connect

    David, S.A.; Vitek, J.M.

    1981-01-01

    Solidification behavior of austenitic stainless steel laser welds has been investigated with a high-power laser system. The welds were made at speeds ranging from 13 to 60 mm/s. The welds sowed a wide variety of microstructural features. The ferrite content in the 13-mm/s weld varied from less than 1% at the root of the weld to about 10% at the crown. The duplex structure at the crown of the weld was much finer than the one observed in conventional weld metal. However, the welds made at 25 and 60 mm/s contained an austenitic structure with less than 1% ferrite throughout the weld. Microstructural analysis of these welds used optical microscopy, transmission electron microscopy, and analytical electron microscopy. The austenitic stainless steel welds were free of any cracking, and the results are explained in terms of the rapid solidification conditions during laser welding.

  18. Estimation of fatigue strain-life curves for austenitic stainless steels in light water reactor environments.

    SciTech Connect

    Chopra, O. K.; Smith, J. L.

    1998-02-12

    The ASME Boiler and Pressure Vessel Code design fatigue curves for structural materials do not explicitly address the effects of reactor coolant environments on fatigue life. Recent test data indicate a significant decrease in fatigue lives of austenitic stainless steels (SSs) in light water reactor (LWR) environments. Unlike those of carbon and low-alloy steels, environmental effects on fatigue lives of SSs are more pronounced in low-dissolved-oxygen (low-DO) water than in high-DO water, This paper summarizes available fatigue strain vs. life data on the effects of various material and loading variables such as steel type, DO level, strain range, and strain rate on the fatigue lives of wrought and cast austenitic SSs. Statistical models for estimating the fatigue lives of these steels in LWR environments have been updated with a larger data base. The significance of the effect of environment on the current Code design curve has been evaluated.

  19. The effect of hydrogen on strain hardening and fracture mechanism of high-nitrogen austenitic steel

    NASA Astrophysics Data System (ADS)

    Maier, G. G.; Astafurova, E. G.; Melnikov, E. V.; Moskvina, V. A.; Vojtsik, V. F.; Galchenko, N. K.; Zakharov, G. N.

    2016-07-01

    High-nitrogen austenitic steels are perspective materials for an electron-beam welding and for producing of wear-resistant coatings, which can be used for application in aggressive atmospheres. The tensile behavior and fracture mechanism of high-nitrogen austenitic steel Fe-20Cr-22Mn-1.5V-0.2C-0.6N (in wt.%) after electrochemical hydrogen charging for 2, 10 and 40 hours have been investigated. Hydrogenation of steel provides a loss of yield strength, uniform elongation and tensile strength. The degradation of tensile properties becomes stronger with increase in charging duration - it occurs more intensive in specimens hydrogenated for 40 hours as compared to ones charged for 2-10 hours. Fracture analysis reveals a hydrogen-induced formation of brittle surface layers up to 6 μm thick after 40 hours of saturation. Hydrogenation changes fracture mode of steel from mixed intergranular-transgranular to mainly transgranular one.

  20. Cast heat-resistant austenitic steel with improved temperature creep properties and balanced alloying element additions and methodology for development of the same

    DOEpatents

    Pankiw, Roman I; Muralidharan, Govindrarajan; Sikka, Vinod Kumar; Maziasz, Philip J

    2012-11-27

    The present invention addresses the need for new austenitic steel compositions with higher creep strength and higher upper temperatures. The new austenitic steel compositions retain desirable phases, such as austenite, M.sub.23C.sub.6, and MC in its microstructure to higher temperatures. The present invention also discloses a methodology for the development of new austenitic steel compositions with higher creep strength and higher upper temperatures.

  1. Acoustic Emission Technique for Characterizing Deformation and Fatigue Crack Growth in Austenitic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Raj, Baldev; Mukhopadhyay, C. K.; Jayakumar, T.

    2003-03-01

    Acoustic emission (AE) during tensile deformation and fatigue crack growth (FCG) of austenitic stainless steels has been studied. In AISI type 316 stainless steel (SS), AE has been used to detect micro plastic yielding occurring during macroscopic plastic deformation. In AISI type 304 SS, relation of AE with stress intensity factor and plastic zone size has been studied. In AISI type 316 SS, fatigue crack growth has been characterised using acoustic emission.

  2. Delta ferrite-containing austenitic stainless steel resistant to the formation of undesirable phases upon aging

    SciTech Connect

    Leitnaker, J.M.

    1981-05-05

    Austenitic stainless steel alloys containing delta ferrite, such as are used as weld deposits, are protected against the transformation of delta ferrite to sigma phase during aging by the presence of carbon plus nitrogen in a weight percent 015-0.030 times the volume percent ferrite present in alloy. The formation of chi phase upon aging is controlled by controlling the mo content.

  3. Austenitic stainless steel alloys having improved resistance to fast neutron-induced swelling

    DOEpatents

    Bloom, Everett E.; Stiegler, James O.; Rowcliffe, Arthur F.; Leitnaker, James M.

    1977-03-08

    The present invention is based on the discovery that radiation-induced voids which occur during fast neutron irradiation can be controlled by small but effective additions of titanium and silicon. The void-suppressing effect of these metals in combination is demonstrated and particularly apparent in austenitic stainless steels.

  4. High-Temperature Performance of Cast CF8C-Plus Austenitic Stainless Steel

    SciTech Connect

    Maziasz, Philip J; Pint, Bruce A

    2011-01-01

    Covers and casings of small to medium size gas turbines can be made from cast austenitic stainless steels, including grades such as CF8C, CF3M, or CF10M. Oak Ridge National Laboratory and Caterpillar have developed a new cast austenitic stainless steel, CF8C-Plus, which is a fully austenitic stainless steel, based on additions of Mn and N to the standard Nb-stabilized CF8C steel grade. The Mn addition improves castability, as well as increases the alloy solubility for N, and both Mn and N synergistically act to boost mechanical properties. CF8C-Plus steel has outstanding creep-resistance at 600-900 C, which compares well with Ni-based superalloys such as alloys X, 625, 617, and 230. CF8C-Plus also has very good fatigue and thermal fatigue resistance. It is used in the as-cast condition, with no additional heat-treatments. While commercial success for CF8C-Plus has been mainly for diesel exhaust components, this steel can also be considered for gas turbine and microturbine casings. The purposes of this paper are to demonstrate some of the mechanical properties, to update the long-term creep-rupture data, and to present new data on the high-temperature oxidation behavior of these materials, particularly in the presence of water vapor.

  5. Determination of Proper Austenitization Temperatures for Hot Stamping of AISI 4140 Steel

    NASA Astrophysics Data System (ADS)

    Samadian, Pedram; Parsa, Mohammad Habibi; Shakeri, Amid

    2014-04-01

    High strength steels are desirable materials for use in automobile bodies in order to reduce vehicle weight and increase the safety of car passengers, but steel grades with high strength commonly show poor formability. Recently, steels with controlled microstructures and compositions are used to gain adequate strength after hot stamping while maintaining good formability during processing. In this study, microstructure evolutions and changes in mechanical properties of AISI 4140 steel sheets resulting from the hot stamping process at different austenitization temperatures were investigated. To determine the proper austenitization temperatures, the results were compared with those of the cold-worked and cold-worked plus quench-tempered specimens. Comparisons showed that the austenitization temperatures of 1000 and 1100 °C are proper for hot stamping of 3-mm-thick AISI 4140 steel sheets due to the resultant martensitic microstructure which led to the yield and ultimate tensile strength of 1.3 and 2.1 GPa, respectively. Such conditions resulted in more favorable simultaneous strength and elongation than those of hot-stamped conventional boron steels.

  6. Austenite Grain Growth and Precipitate Evolution in a Carburizing Steel with Combined Niobium and Molybdenum Additions

    NASA Astrophysics Data System (ADS)

    Enloe, Charles M.; Findley, Kip O.; Speer, John G.

    2015-11-01

    Austenite grain growth and microalloy precipitate size and composition evolution during thermal processing were investigated in a carburizing steel containing various additions of niobium and molybdenum. Molybdenum delayed the onset of abnormal austenite grain growth and reduced the coarsening of niobium-rich precipitates during isothermal soaking at 1323 K, 1373 K, and 1423 K (1050 °C, 1100 °C, and 1150 °C). Possible mechanisms for the retardation of niobium-rich precipitate coarsening in austenite due to molybdenum are considered. The amount of Nb in solution and in precipitates at 1373 K (1100 °C) did not vary over the holding times evaluated. In contrast, the amount of molybdenum in (Nb,Mo)C precipitates decreased with time, due to rejection of Mo into austenite and/or dissolution of fine Mo-rich precipitates. In hot-rolled alloys, soaking in the austenite regime resulted in coarsening of the niobium-rich precipitates at a rate that exceeded that predicted by the Lifshitz-Slyozov-Wagner relation for volume-diffusion-controlled coarsening. This behavior is attributed to an initial bimodal precipitate size distribution in hot-rolled alloys that results in accelerated coarsening rates during soaking. Modification of the initial precipitate size distribution by thermal processing significantly lowered precipitate coarsening rates during soaking and delayed the associated onset of abnormal austenite grain growth.

  7. The effect of chemical composition and austenite conditioning on the transformation behavior of microalloyed steels

    SciTech Connect

    Mousavi Anijdan, S.H.; Rezaeian, Ahmad; Yue, Steve

    2012-01-15

    In this investigation, by using continuous cooling torsion (CCT) testing, the transformation behavior of four microalloyed steels under two circumstances of austenite conditioning and non-conditioning was studied. A full scale hot-rolling schedule containing a 13-pass deformation was employed for the conditioning of the austenite. The CCT tests were then employed till temperature of {approx} 540 Degree-Sign C and the flow curves obtained from this process were analyzed. The initial and final microstructures of the steels were studied by optical and electron microscopes. Results show that alloying elements would decrease the transformation temperature. This effect intensifies with the gradual increase of Mo, Nb and Cu as alloying elements added to the microalloyed steels. As well, austenite conditioning increased the transformation start temperature due mainly to the promotion of polygonal ferrite formation that resulted from a pancaked austenite. The final microstructures also show that CCT alone would decrease the amount of bainite by inducing ferrite transformation in the two phase region. In addition, after the transformation begins, the deformation might result in the occurrence of dynamic recrystallization in the ferrite region. This could lead to two different ferrite grain sizes at the end of the CCT. Moreover, the Nb bearing steels show no sign of decreasing the strength level after the transformation begins in the non-conditioned situation and their microstructure is a mix of polygonal ferrite and bainite indicating an absence of probable dynamic recrystallization in this condition. In the conditioned cases, however, these steels show a rapid decrease of the strength level and their final microstructures insinuate that ferrite could have undergone a dynamic recrystallization due to deformation. Consequently, no bainite was seen in the austenite conditioned Nb bearing steels. The pancaking of austenite in the latest cases produced fully polygonal ferrite

  8. Role of Austenite in Brittle Fracture of Bond Region of Super Duplex Stainless Steel

    NASA Astrophysics Data System (ADS)

    Kitagawa, Yoshihiko; Ikeuchi, Kenji; Kuroda, Toshio

    Weld simulation of heat-affected zone (HAZ) was performed to investigate the mechanism by which austenite affects the toughness of super duplex stainless steel. Thermal cycles of various peak temperatures in the range from 1373 K to 1673 K corresponding to the HAZ were applied to SAF2507 super duplex stainless steel specimens. Charpy impact test was carried out using the specimens after the weld simulation, and the fracture surfaces were observed by SEM using three-dimensionally reconstruction technique. Austenite content decreased with increasing the peak temperature when the peak temperature exceeded 1473 K and the impact value decreased with increasing the peak temperature and decreasing the austenite content. The thermal cycle of the peak temperature of 1673 K corresponding to weld bond region caused decreasing of austenite content which was 22% lower than that of the base metal. The ductile-brittle transition temperature was measured. As a result the temperature increased rapidly in the weld bond region, the peak temperature of which exceeded 1623 K by the grain growth of ferrite matrix occurring subsequently to the completely dissolution of austenite. The morphology of the fracture surfaces after impact testing at 77 K showed cleavage fracture of ferrite. The {100} orientations of cleavage fracture facets were measured using three-dimensional images of the fracture surfaces and the results were visualized as the orientation color maps. The results showed that there were cleavage fractures consisting of a few facets parallel to each other. It was considered that a few facets existed in one ferrite grain. It was concluded that Widmanstätten austenite divided the large fracture into smaller cleavage facets in a ferrite grain and then suppressed the degradation of bond toughness of duplex stainless steel.

  9. Corrosion characteristics of ferric and austenitic stainless steels for dental magnetic attachment.

    PubMed

    Endo, K; Suzuki, M; Ohno, H

    2000-03-01

    The corrosion behaviors of four ferric stainless steels and two austenitic stainless steels were examined in a simulated physiological environment (0.9% NaCl solution) to obtain basic data for evaluating the appropriate composition of stainless steels for dental magnetic attachments. The corrosion resistance was evaluated by electrochemical techniques and the analysis of released metal ions by atomic absorption spectrophotometry. The surface of the stainless steels was analyzed by X-ray photoelectron spectroscopy (XPS). The breakdown potential of ferric stainless steels increased and the total amount of released metal ions decreased linearly with increases in the sum of the Cr and Mo contents. The corrosion rate of the ferric stainless steels increased 2 to 6 times when they were galvanically coupled with noble metal alloys but decreased when coupled with commercially pure Ti. For austenitic stainless steels, the breakdown potential of high N-bearing stainless steel was approximately 500 mV higher than that of SUS316L, which is currently used as a component in dental magnetic attachments. The enriched nitrogen at the alloy/passive film interface may be effective in improving the localized corrosion resistance. PMID:11219089

  10. Modelling of Nb influence on phase transformation behaviours from austenite to ferrite in low carbon steels

    NASA Astrophysics Data System (ADS)

    Wang, L.; Parker, S. V.; Rose, A. J.; West, G. D.; Thomson, R. C.

    2016-03-01

    In this paper, a new model has been developed to predict the phase transformation behaviours from austenite to ferrite in Nb-containing low carbon steels. The new model is based on some previous work and incorporates the effects of Nb on phase transformation behaviours, in order to make it applicable for Nb-containing steels. Dissolved Nb atoms segregated at prior austenite grain boundaries increase the critical energy for ferrite nucleation, and thus the ferrite nucleation rate is decreased. Dissolved Nb atoms also apply a solute drag effect to the moving transformation interface, and the ferrite grain growth rate is also decreased. The overall transformation kinetics is then calculated according to the classic Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory. The new model predictions are quite consistent with experimental results for various steels during isothermal transformations or continuous cooling.

  11. A simplified leak-before-break evaluation procedure for austenitic and ferritic steel piping

    SciTech Connect

    Gamble, R.M.; Zahoor, A.; Ghassemi, B.

    1994-10-01

    A simplified procedure has been defined for computing the allowable circumferential throughwall crack length as a function of applied loads in piping. This procedure has been defined to enable leak-before-break (LBB) evaluations to be performed without complex and time consuming analyses. The development of the LBB evaluation procedure is similar to that now used in Section 11 of the ASME Code for evaluation of part-throughwall flaws found in piping. The LBB evaluation procedure was bench marked using experimental data obtained from pipes having circumferential throughwall flaws. Comparisons of the experimental and predicted load carrying capacities indicate that the method has a conservative bias, such that for at least 97% of the experiments the experimental load is equal to or greater than 90% of the predicted load. The procedures described in this report are applicable to pipe and pipe fittings with: (1) wrought austenitic steel (Ni-Cr-Fe alloy) having a specified minimum yield strength less than 45 ksi, and gas metal-arc, submerged arc and shielded metal-arc austenitic welds, and (2) seamless or welded wrought carbon steel having a minimum yield strength not greater than 40 ksi, and associated weld materials. The procedures can be used for cast austenitic steel when adequate information is available to place the cast material toughness into one of the categories identified later in this report for austenitic wrought and weld materials.

  12. Crack growth rates and fracture toughness of irradiated austenitic stainless steels in BWR environments.

    SciTech Connect

    Chopra, O. K.; Shack, W. J.

    2008-01-21

    In light water reactors, austenitic stainless steels (SSs) are used extensively as structural alloys in reactor core internal components because of their high strength, ductility, and fracture toughness. However, exposure to high levels of neutron irradiation for extended periods degrades the fracture properties of these steels by changing the material microstructure (e.g., radiation hardening) and microchemistry (e.g., radiation-induced segregation). Experimental data are presented on the fracture toughness and crack growth rates (CGRs) of wrought and cast austenitic SSs, including weld heat-affected-zone materials, that were irradiated to fluence levels as high as {approx} 2x 10{sup 21} n/cm{sup 2} (E > 1 MeV) ({approx} 3 dpa) in a light water reactor at 288-300 C. The results are compared with the data available in the literature. The effects of material composition, irradiation dose, and water chemistry on CGRs under cyclic and stress corrosion cracking conditions were determined. A superposition model was used to represent the cyclic CGRs of austenitic SSs. The effects of neutron irradiation on the fracture toughness of these steels, as well as the effects of material and irradiation conditions and test temperature, have been evaluated. A fracture toughness trend curve that bounds the existing data has been defined. The synergistic effects of thermal and radiation embrittlement of cast austenitic SS internal components have also been evaluated.

  13. Thermodynamic Calculation Study on Effect of Manganese on Stability of Austenite in High Nitrogen Stainless Steels

    NASA Astrophysics Data System (ADS)

    Wang, Qingchuan; Zhang, Bingchun; Yang, Ke

    2016-07-01

    A series of high nitrogen steels were studied by using thermodynamic calculations to investigate the effect of manganese on the stability of austenite. Surprisingly, it was found that the austenite stabilizing ability of manganese was strongly weakened by chromium, but it was strengthened by molybdenum. In addition, with an increase of manganese content, the ferrite stabilizing ability of chromium significantly increased, but that of molybdenum decreased. Therefore, strong interactions exist between manganese and the other alloying elements, which should be the main reason for the difference among different constituent diagrams.

  14. Thermodynamic Calculation Study on Effect of Manganese on Stability of Austenite in High Nitrogen Stainless Steels

    NASA Astrophysics Data System (ADS)

    Wang, Qingchuan; Zhang, Bingchun; Yang, Ke

    2016-05-01

    A series of high nitrogen steels were studied by using thermodynamic calculations to investigate the effect of manganese on the stability of austenite. Surprisingly, it was found that the austenite stabilizing ability of manganese was strongly weakened by chromium, but it was strengthened by molybdenum. In addition, with an increase of manganese content, the ferrite stabilizing ability of chromium significantly increased, but that of molybdenum decreased. Therefore, strong interactions exist between manganese and the other alloying elements, which should be the main reason for the difference among different constituent diagrams.

  15. Embrittlement Phenomena in an Austenitic Stainless Steel: Influence of Hydrogen and Temperature

    NASA Astrophysics Data System (ADS)

    Lamani, Emil; Jouinot, Patrice

    2007-04-01

    The influence of hydrogen and temperature (up to 650°C) on an austenitic stainless steel is studied by means of two main techniques: the disk pressure embrittlement and the special biaxial tensile tests. The embrittlement index of the steel is determined as the ratio of rupture pressures of the disks tested similarly under helium and hydrogen. Furthermore, we studied the effect of loading speed and temperature on rupture pressures. We show that the mechanical behavior of the steel is strongly influenced by the apparition of a second phase: the deformation induced martensite, α'.

  16. Phase stability in austenitic stainless steels -- New approaches, results, and their relation to properties

    SciTech Connect

    Vitek, J.M.; David, S.A.

    1995-12-31

    In recent years, the phase stability of austenitic stainless steels, and its effect on the mechanical properties of stainless steels, have been the subject of much interest. With the availability of new experimental techniques, new theoretical methods, and new computational procedures, significant advances have been made in understanding, and being able to predict, phase stability and mechanical properties of stainless steel welds. This paper reviews some of these developments, with an emphasis on recent work that has been done at Oak Ridge National Laboratory.

  17. Interim fatigue design curves for carbon, low-alloy, and austenitic stainless steels in LWR environments

    SciTech Connect

    Majumdar, S.; Chopra, O.K.; Shack, W.J.

    1993-01-01

    Both temperature and oxygen affect fatigue life; at the very low dissolved-oxygen levels in PWRs and BWRs with hydrogen water chemistry, environmental effects on fatigue life are modest at all temperatures (T) and strain rates. Between 0.1 and 0.2 ppM, the effect of dissolved-oxygen increases rapidly. In oxygenated environments, fatigue life depends strongly on strain rate and T. A fracture mechanics model is developed for predicting fatigue lives, and interim environmentally assisted cracking (EAC)-adjusted fatigue curves are proposed for carbon steels, low-alloy steels, and austenitic stainless steels.

  18. The Change of Austenitic Stainless Steel Elements Content in the Inner Parts of VVER-440 Reactor during Operation

    NASA Astrophysics Data System (ADS)

    Smutný, Vladimír; Hep, Jaroslav; Novosad, Petr

    2009-08-01

    Neutron activation induces the element transmutation in materials surrounding the reactor active core. The objective of the present paper is to calculate and evaluate the change of austenitic stainless steel 08Ch18N10T elements content through neutron induced activation, in inner parts of VVER-440 - in the baffle and in the barrel. Particularly the content changes of Mn in austenitic stainless steel. The neutron flux density and then the neutron activation of austenitic stainless steel elements in parts at the core are calculated. Neutron activation represents a measure of austenitic stainless steel elements transmutation. The power distribution is determined as an average value of several cycles power distribution in the middle of a cycle for the NPP Dukovany. The power distribution is calculated with the code MOBY-DICK [1]. The neutron flux density is calculated with the code TORT [2]. The neutron activation of austenitic stainless steel elements in the baffle and in the barrel is calculated with the system EASY-2007 containing the code FISPACT-2007 [3]. The calculation of the changing austenitic stainless steel elements content is performed depending on the moment of the supposed end of reactor operation - 40 years. There is also necessary monitoring and benchmarking of steel element content change, because the neutron flux calculation, particularly in thermal region, shows a considerable uncertainty, e.g. [4]. The motivation for this work is the study focused to stress corrosion cracking of austenitic stainless steels induced by radiation inside PWR and BWR, e.g. [5]. The paper could be a suggestion to estimation of austenitic stainless steel corrosion damage induced by neutrons in inner parts of VVER-440 reactor.

  19. Influence of retained austenite on short fatigue crack growth and wear resistance of case carburized steel

    SciTech Connect

    Silva, V.F. da; Canale, L.F.; Spinelli, D.P.; Bose-Filho, W.W.; Crnkovic, O.R.

    1999-10-01

    The influence of the amount of retained austenite on short fatigue crack growth and wear resistance in carburized SAE 8620 steel was studied in this article. Different amounts of retained austenite in the microstructure of the carburized case were obtained through different heat treatment routes applied after the carburizing process. The wear tests were carried out using pin on disk equipment. After every 200 turns the weight loss was registered. Four point bend fatigue tests were carried out at room temperature, using three different levels of stress and R = 0.1. Crack length versus number of cycles and crack growth rate versus mean crack length curves were analyzed. In both tests the results showed that the test pieces with higher levels of retained austenite in the carburized case exhibited longer fatigue life and better wear resistance.

  20. Unraveling the Effect of Thermomechanical Treatment on the Dissolution of Delta Ferrite in Austenitic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Rezayat, Mohammad; Mirzadeh, Hamed; Namdar, Masih; Parsa, Mohammad Habibi

    2016-02-01

    Considering the detrimental effects of delta ferrite stringers in austenitic stainless steels and the industrial considerations regarding energy consumption, investigating, and optimizing the kinetics of delta ferrite removal is of vital importance. In the current study, a model alloy prone to the formation of austenite/delta ferrite dual phase microstructure was subjected to thermomechanical treatment using the wedge rolling test aiming to dissolve delta ferrite. The effect of introducing lattice defects and occurrence of dynamic recrystallization (DRX) were investigated. It was revealed that pipe diffusion is responsible for delta ferrite removal during thermomechanical process, whereas when the DRX is dominant, the kinetics of delta ferrite dissolution tends toward that of the static homogenization treatment for delta ferrite removal that is based on the lattice diffusion of Cr and Ni in austenite. It was concluded that the optimum condition for dissolution of delta ferrite can be defined by the highest rolling temperature and strain in which DRX is not pronounced.

  1. Corrosion of austenitic stainless steels and nickel-base alloys in supercritical water and novel control methods

    SciTech Connect

    Tan, Lizhen; Allen, Todd R.; Yang, Ying

    2012-01-01

    This chapter contains sections titled: (1) Introduction; (2) Thermodynamics of Alloy Oxidation; (3) Corrosion of Austenitic Stainless Steels and Ni-Base Alloys in SCW; (4) Novel Corrosion Control Methods; (5) Factors Influencing Corrosion; (6) Summary; and (7) References.

  2. Effect of Internal Hydrogen on Delayed Cracking of Metastable Low-Nickel Austenitic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Papula, Suvi; Talonen, Juho; Todoshchenko, Olga; Hänninen, Hannu

    2014-10-01

    Metastable austenitic stainless steels, especially manganese-alloyed low-nickel grades, may be susceptible to delayed cracking after forming processes. Even a few wppm of hydrogen present in austenitic stainless steels as an inevitable impurity is sufficient to cause cracking if high enough fraction of strain-induced α'-martensite and high residual tensile stresses are present. The role of internal hydrogen content in delayed cracking of several metastable austenitic stainless steels having different alloying chemistries was investigated by means of Swift cup tests, both in as-supplied state and after annealing at 673 K (400 °C). Hydrogen content of the test materials in each state was analyzed with three different methods: inert gas fusion, thermal analysis, and thermal desorption spectroscopy. Internal hydrogen content in as-supplied state was higher in the studied manganese-alloyed low-nickel grades, which contributed to susceptibility of unstable grades to delayed cracking. Annealing of the stainless steels reduced their hydrogen content by 1 to 3 wppm and markedly lowered the risk of delayed cracking. Limiting drawing ratio was improved from 1.4 to 1.7 in grade 204Cu, from 1.7 to 2.0 in grade 201 and from 1.8 to 2.12 in grade 301. The threshold levels of α'-martensite and residual stress for delayed cracking at different hydrogen contents were defined for the test materials.

  3. Ferrite morphology and variations in ferrite content in austenitic stainless steel welds

    SciTech Connect

    David, S.A.; Hanzelka, S.E.; Haltom, C.P.

    1981-07-01

    Four distinct ferrite morphologies have been identified in type 308 stainless steel multipass welds: vermicular, lacy, acicular, and globular. The first three ferrite types are related to transformations following solidification and the fourth is related to the shape instability of the residual ferrite. An earlier study showed that most of the ferrite observed in austenitic stainless steel welds contaning a duplex structure may be identified as residual primary ferrite resulting from incomplete delta ..-->.. ..gamma.. transformation during solidification and/or residual ferrite after Widmanstaetten austenite precipitation in primary ferrite. These modes of ferrite formation can be used to explain observed ferrite morphologies in austenitic stainless steel welds. Variations in ferrite content within the weld were related to weld metal composition, ferrite morphology, and dissolution of ferrite resulting from thermal cycles during subsequent weld passes. An investigation of the type 308 stainless steel filler metal solidified over cooling rates ranging from 7 to 1600/sup 0/C/s showed that the cooling rate of the weld metal within the freezing range of the alloy affects the amount of ferrite in the microstructure very litte. However, the scale of the solidification substructure associated with various solidification rates may influence the ferrite dissolution kinetics.

  4. Ferrite morphology and variations in ferrite content in austenitic stainless steel welds

    SciTech Connect

    David, S.A.

    1981-04-01

    Four distinct ferrite morphologies have been identified in Type 308 stainless steel multipass welds: vermicular, lacy, acicular, and globular. The first three ferrite types are related to transformations following solidfication and the fourth is related to the shape instability of the residual ferrite. An earlier study showed that most of the ferrite observed in austenitic stainless steel welds containing a duplex structure may be identified as residual primary ferrite resulting from incomplete delta ..-->.. ..gamma.. transformation during solidification and/or residual ferrite after Widmanstatten austenite precipitation in primary ferrite. These modes of ferrite formation can be used to explain observed ferrite morphologies in austenitic stainless steel welds. Variations in ferrite content within the weld were also related to weld metal composition, ferrite morphology, and dissolution of ferrite resulting from thermal cycles during subsequent weld passes. An investigation of the Type 308 stainless steel filler metal solidified over cooling rates ranging from 7 to 1600/sup 0/C/s (44.6 to 2912/sup 0/F/s) showed that the cooling rate of the weld metal within the freezing range of the alloy affects the amount of ferrite in the microstructure very little. However, the scale of the solidification substructure associated with various solidification rates may influence the ferrite dissolution kinetics.

  5. Evaluation of the fabricability of advanced iron aluminide-clad austenitic stainless steel tubing

    SciTech Connect

    Mohn, W.R.; Topolski, M.J.

    1993-07-01

    Researchers at Babcock & Wilcox Alliance Research Center have investigated methods to produce bimetallic tubing consisting of iron aluminide-clad austenitic stainless steel for practical use in fossil fueled energy equipment. In the course of this work, the compatibility of iron aluminide with four candidate austenitic stainless steel substrates was first evaluated using diffusion couples. Based on these results, a combination of iron aluminide and 304 stainless steel was selected for further development. Two composite billets of this combination were then prepared and extruded in separate trails at 2200F and 2000F. Both extrusions yielded 2-inch OD clad tubes, each approximately 18 feet long. Results of the evaluation show that the tube extruded at 2000F had a sound, integrally bonded clad layer throughout its entire length. However, the tube extruded at 2200F exhibited regions of disbonding between the clad layer and the substrate. In supplement to this work, an assessment of the technical and economic merits of iron aluminide-clad austenitic stainless steel components in power generation systems was conducted by B&W Fossil Power Division. Future activities should include an investigation of lower extrusion processing temperatures to optimize the fabrication of high quality iron-aluminide clad tubing.

  6. The critical analysis of austenitic manganese steel T130Mn135 used for castings in the mining industry

    NASA Astrophysics Data System (ADS)

    Josan, A.; Pinca Bretotean, C.; Putan, V.

    2016-02-01

    This paper presents the critical analysis of making technology of austenitic manganese steel T130Mn135, used for castings of the type Mills hammer at a Romanian foundry. Are analyzed 11 charges of steel for castings and is determined the diagram of the heat treatment. After the applying of the heat treatment results a single-phase structure, consisting of homogeneous austenite. For all the 11 charges is presented the variation of chemical composition.

  7. Effect of residual austenite on the tendency of incompletely aged maraging steels to embrittlement during slow deformation

    SciTech Connect

    Kardonskii, V.M.; Gorbunova, N.B.

    1986-03-01

    The authors investigate the high-strength maraging steels (HSMS) N17K10V10MT and N18V10V10MT by cyclic heat treatment and heating to temperatures of the dual-phase (alpha + gamma)-region. Embrittlement during the slow loading of incompletely aged HSMS with titanium can be reduced when approximately 20% of residual austenite is obtained in them. Maraging steel containing residual austenite in the initial state does not tend toward this type of embrittlement.

  8. Effect of martensite to austenite reversion on the formation of nano/submicron grained AISI 301 stainless steel

    SciTech Connect

    Karimi, M.; Najafizadeh, A.; Kermanpur, A.; Eskandari, M.

    2009-11-15

    The martensite to austenite reversion behavior of 90% cold rolled AISI 301 stainless steel was investigated in order to refine the grain size. Cold rolled specimens were annealed at 600-900 deg. C, and subsequently characterized by scanning electron microscopy, X-ray diffraction, Feritscope, and hardness measurements. The effects of annealing parameters on the formation of fully-austenitic nano/submicron grained structure and the mechanisms involved were studied. It was found that annealing at 800 deg. C for 10 s exhibited the smallest average austenite grain size of 240 {+-} 60 nm with an almost fully-austenitic structure.

  9. Austenite decomposition during continuous cooling of an HSLA-80 plate steel

    NASA Astrophysics Data System (ADS)

    Thompson, S. W.; Colvin, D. J.; Krauss, G.

    1996-06-01

    Decomposition of fine-grained austenite (10-µm grain size) during continuous cooling of an HSLA-80 plate steel (containing 0.05C, 0.50Mn, 1.12Cu, 0.88Ni, 0.71Cr, and 0.20Mo) was evaluated by dilatometric measurements, light microscopy, scanning electron microscopy, transmission electron microscopy, and microhardness testing. Between 750 °C and 600 °C, austenite transforms primarily to polygonal ferrite over a wide range of cooling rates, and Widmanstätten ferrite sideplates frequently evolve from these crystals. Carbon-enriched islands of austenite transform to a complex mixture of granular ferrite, acicular ferrite, and martensite (all with some degree of retained austenite) at cooling rates greater than approximately 5 °C/s. Granular and acicular ferrite form at temperatures slightly below those at which polygonal and Widmanstätten ferrite form. At cooling rates less than approximately 5 °C/s, regions of carbon-enriched austenite transform to a complex mixture of upper bainite, lower bainite, and martensite (plus retained austenite) at temperatures which are over 100 °C lower than those at which polygonal and Widmanstätten ferrite form. Interphase precipitates of copper form only in association with polygonal and Widmanstätten ferrite. Kinetic and microstruc-tural differences between Widmanstätten ferrite, acicular ferrite, and bainite (both upper and lower) suggest different origins and/or mechanisms of formation for these morphologically similar austenite transformation products.

  10. Prediction and Validation of the Austenite Phase Fraction upon Intercritical Annealing of Medium Mn Steels

    NASA Astrophysics Data System (ADS)

    Farahani, Hussein; Xu, Wei; van der Zwaag, Sybrand

    2015-11-01

    In this research, the effects of Mn and Si concentration and that of the isothermal intercritical holding temperature on the austenite-to-ferrite ( γ → α) and the martensite-to-austenite ( α' → γ) phase transformations are studied for a series of Fe-C-Mn-Si steels with up to 7 wt pct Mn. The model is based on the local equilibrium (LE) concept. The model predictions are compared to experimental observations. It is found that the austenite volume fraction at the end of intercritical annealing depends significantly on the initial microstructure. For Mn concentrations between 3 and 7 wt pct, the LE model is qualitatively correct. However, at higher Mn levels the discrepancy between the predicted austenite fractions and the experimental values increases, in particular for the α' → γ transformation. Intragrain nucleation is held responsible for the higher austenite fractions observed experimentally. Silicon is found have a much smaller effect on the kinetics of the intercritical annealing than Mn.

  11. Residual Ferrite and Relationship Between Composition and Microstructure in High-Nitrogen Austenitic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Wang, Qingchuan; Ren, Yibin; Yao, Chunfa; Yang, Ke; Misra, R. D. K.

    2015-12-01

    A series of high-nitrogen stainless steels (HNS) containing δ-ferrite, which often retained in HNS, were studied to establish the relationship between composition and microstructure. Both ferrite and nitrogen depletions were found in the center regions of cast ingots, and the depletion of nitrogen in that area was found to be the main reason for the existence of δ-ferrite. Because of the existence of heterogeneity, the variation of microstructure with nitrogen content was detected. Hence, the critical contents of nitrogen (CCN) for the fully austenitic HNS were obtained. Then the effects of elements such as N, Cr, Mn, and Mo on austenite stability were investigated via thermodynamic calculations. The CCN of HNS alloys were also obtained by calculations. Comparing the CCN obtained from experiment and calculation, it was found that the forged microstructure of the HNS was close to the thermodynamic equilibrium. To elucidate the above relationship, by regression analysis using calculated thermodynamic data, nitrogen equivalent and a new constitution diagram were proposed. The constitution diagram accurately distinguishes the austenitic single-phase region and the austenite + ferrite dual-phase region. The nitrogen equivalent and the new constitution diagram can be used for alloying design and microstructural prediction in HNS. According to the nitrogen equivalent, the ferrite stabilizing ability of Mo is weaker than Cr, and with Mn content increases, Mn behaves as a weak austenite stabilizer first and then as a ferrite stabilizer.

  12. Microstructure and Deformation Behavior of Phase-Reversion-Induced Nanograined/Ultrafine-Grained Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Misra, R. D. K.; Nayak, S.; Mali, S. A.; Shah, J. S.; Somani, M. C.; Karjalainen, L. P.

    2009-10-01

    Materials with submicron to nanometer-sized grains by virtue of their high grain boundary area to grain size ratio provide valuable tools for studying deformation behavior in ultrafine-grained structures. In this regard, the well-known strain-induced martensite transformation and its reversal to the parent austenite phase were used to produce nanograins/ultrafine grains via controlled annealing of heavily cold-worked metastable austenite. The results of the electron microscopy study of phase-reversion-induced microstructure and deformation behavior of nanograined/ultrafine-grained (NG/UFG) austenitic stainless steel during tensile straining are described here. The phase-reversion-induced structure was observed to depend on the cold rolling reduction and temperature-time annealing cycle. The optimized structure consisted of nanocrystalline ( d < 100 nm), ultrafine ( d ≈ 100 to 500 nm), and submicron ( d ≈ 500 to 1000 nm) grains and was characterized by a high yield strength (800 to 1000 MPa)-high ductility (30 to 40 pct) combination. Austenite nucleation during phase-reversion annealing occurred in the form of thin plates or as equiaxed grains along the martensite laths. Twinning and dislocation glide were identified as the primary deformation mechanisms, where twinning had a varied character. However, the high elongation seems to be associated with the gradual transformation of metastable austenite, with twinning having only a minor contribution.

  13. Deformation Mechanisms in Austenitic TRIP/TWIP Steel as a Function of Temperature

    NASA Astrophysics Data System (ADS)

    Martin, Stefan; Wolf, Steffen; Martin, Ulrich; Krüger, Lutz; Rafaja, David

    2016-01-01

    A high-alloy austenitic CrMnNi steel was deformed at temperatures between 213 K and 473 K (-60 °C and 200 °C) and the resulting microstructures were investigated. At low temperatures, the deformation was mainly accompanied by the direct martensitic transformation of γ-austenite to α'-martensite (fcc → bcc), whereas at ambient temperatures, the transformation via ɛ-martensite (fcc → hcp → bcc) was observed in deformation bands. Deformation twinning of the austenite became the dominant deformation mechanism at 373 K (100 °C), whereas the conventional dislocation glide represented the prevailing deformation mode at 473 K (200 °C). The change of the deformation mechanisms was attributed to the temperature dependence of both the driving force of the martensitic γ → α' transformation and the stacking fault energy of the austenite. The continuous transition between the ɛ-martensite formation and the twinning could be explained by different stacking fault arrangements on every second and on each successive {111} austenite lattice plane, respectively, when the stacking fault energy increased. A continuous transition between the transformation-induced plasticity effect and the twinning-induced plasticity effect was observed with increasing deformation temperature. Whereas the formation of α'-martensite was mainly responsible for increased work hardening, the stacking fault configurations forming ɛ-martensite and twins induced additional elongation during tensile testing.

  14. RESULTS OF CHARACTERIZATION TESTS OF THE SURFACES OF A COMMERCIALLY CARBURIZED AUSTENITIC STAINLESS STEEL

    SciTech Connect

    Farrell, K

    2004-01-07

    A commercial surface carburization treatment that shows promise for hardening the surfaces of the stainless steel target vessel of the Spallation Neutron Source against cavitation erosion and pitting caused by the action of pulsed pressure waves in the liquid mercury target has been investigated. To verify promotional claims for the treatment and to uncover any factors that might be of concern for the integrity of a carburized target vessel, some characterization tests of the nature of the surface layers of carburized austenitic 316LN stainless steel were conducted. The findings support most of the claims. The carburized layer is about 35 {micro}m thick. Its indentation hardness is about five times larger than that of the substrate steel and declines rapidly with depth into the layer. The surface is distorted by the treatment, and the austenite lattice is enlarged. The corrosion resistance of the carburized layer in an acid medium is greater than that for untreated austenite. The layer is not brittle; it is plastically deformable and is quite resistant to cracking during straining. Contrary to the provider's assertations, the maximum carbon content of the layer is much less than 6-7 wt% carbon, and the carbon is not simply contained in supersaturated solid solution; some of it is present in a previously unreported iron carbide phase located at the very surface. Large variations were found in the thickness of the layer, and they signify that controls may be needed to ensure a uniform thickness for treatment of the SNS target vessel. Inclusion stringers and {delta}-ferrite phase embraced in the treated layer are less resistant to chemical attack than the treated austenite. From a cavitation pitting perspective under SNS bombardment, such non-austenitic phases may provide preferential sites for pitting. The shallow depth of the hardened layer will require use of protection measures to avoid mishandling damage to the layer during assembly and installation of a target

  15. An Investigation on Low-Temperature Thermochemical Treatments of Austenitic Stainless Steel in Fluidized Bed Furnace

    NASA Astrophysics Data System (ADS)

    Haruman, E.; Sun, Y.; Triwiyanto, A.; Manurung, Y. H. P.; Adesta, E. Y.

    2012-03-01

    In this study, the feasibility of using an industrial fluidized bed furnace to perform low-temperature thermochemical treatments of austenitic stainless steels has been studied, with the aim to produce expanded austenite layers with combined wear and corrosion resistance, similar to those achievable by plasma and gaseous processes. Several low-temperature thermochemical treatments were studied, including nitriding, carburizing, combined nitriding-carburizing (hybrid treatment), and sequential carburizing and nitriding. The results demonstrate that it is feasible to produce expanded austenite layers on the investigated austenitic stainless steel by the fluidized bed heat treatment technique, thus widening the application window for the novel low-temperature processes. The results also demonstrate that the fluidized bed furnace is the most effective for performing the hybrid treatment, which involves the simultaneous incorporation of nitrogen and carbon together into the surface region of the component in nitrogen- and carbon-containing atmospheres. Such hybrid treatment produces a thicker and harder layer than the other three processes investigated.

  16. Swelling and swelling resistance possibilities of austenitic stainless steels in fusion reactors

    SciTech Connect

    Maziasz, P.J.

    1983-01-01

    Fusion reactor helium generation rates in stainless steels are intermediate to those found in EBR-II and HFIR, and swelling in fusion reactors may differ from the fission swelling behavior. Advanced titanium-modified austenitic stainless steels exhibit much better void swelling resistance than AISI 316 under EBR-II (up to approx. 120 dpa) and HFIR (up to approx. 44 dpa) irradiations. The stability of fine titanium carbide (MC) precipitates plays an important role in void swelling resistance for the cold-worked titanium-modified steels irradiated in EBR-II. Futhermore, increased helium generation in these steels can (a) suppress void conversion, (b) suppress radiation-induced solute segregation (RIS), and (c) stabilize fine MC particles, if sufficient bubble nucleation occurs early in the irradation. The combined effects of helium-enhanced MC stability and helium-suppressed RIS suggest better void swelling resistance in these steels for fusion service than under EBR-II irradiation.

  17. Hydrogen-induced defects in austenite and ferrite of a duplex steel.

    PubMed

    Głowacka, A; Swiatnicki, W A; Jezierska, E

    2006-09-01

    The influence of hydrogen on the microstructure of two types of austeno-ferritic duplex stainless steel (Cr26-Ni6 model steel and Cr22-Ni5-Mo3 commercial steel), each of them after two thermo-mechanical treatments, was investigated. The aim of this study was to reveal microstructural changes appearing during the hydrogen charging and particularly to clarify the occurrence of phase transformations induced by hydrogen. The specific microstructural changes in the ferrite (alpha) and austenite (gamma) of both types of steel were observed. A strong increase of dislocation density was noticed in the alpha phase. In the case of model steel, longer hydrogen charging times led to significant ferrite grain refinement. In the commercial steel, the strips and twin plates appeared in the ferrite after hydrogenation. The appearance of stacking faults was revealed in the gamma phase. The martensite laths appeared in austenite after longer hydrogenation times. It seems that the microstructural changes gave rise to the formation of microcracks in the alpha and gamma phases as well as on the alpha/gamma interphase boundaries. PMID:17059551

  18. Mechanism and estimation of fatigue crack initiation in austenitic stainless steels in LWR environments.

    SciTech Connect

    Chopra, O. K.; Energy Technology

    2002-08-01

    The ASME Boiler and Pressure Vessel Code provides rules for the construction of nuclear power plant components. Figures I-9.1 through I-9.6 of Appendix I to Section III of the Code specify fatigue design curves for structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. Existing fatigue strain-vs.-life ({var_epsilon}-N) data illustrate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping steels. This report provides an overview of fatigue crack initiation in austenitic stainless steels in LWR coolant environments. The existing fatigue {var_epsilon}-N data have been evaluated to establish the effects of key material, loading, and environmental parameters (such as steel type, strain range, strain rate, temperature, dissolved-oxygen level in water, and flow rate) on the fatigue lives of these steels. Statistical models are presented for estimating the fatigue {var_epsilon}-N curves for austenitic stainless steels as a function of the material, loading, and environmental parameters. Two methods for incorporating environmental effects into the ASME Code fatigue evaluations are presented. The influence of reactor environments on the mechanism of fatigue crack initiation in these steels is also discussed.

  19. An integrated computer model with applications for austenite-to-ferrite transformation during hot deformation of Nb-microalloyed steels

    NASA Astrophysics Data System (ADS)

    Majta, Janusz; Pietrzyk, Maciej; Zurek, Anna K.; Cola, Mark; Hochanadel, Pat

    2002-05-01

    This work presents an austenite decomposition model, based on the thermodynamics of the system and diffusion-controlled nucleation theory, to predict the evolution of microstructure during hot working of niobium-microalloyed steels. The differences in microstructural development of hotdeformed microalloyed steel in the single-phase austenite and two-phase (austenite + ferrite) regions have been effectively described using an integrated computer modeling process. The complete model presented here takes into account the kinetics of recrystallization, recrystallized austenite grain size, precipitation, phase transformation, and the resulting ferrite structure. After considering existing austenite decomposition models, we decided that the method adopted in the present work relies on isothermal transformation kinetics and the principle-of-additivity rule. The thermomechanical part of the modeling process was carried out using the finite-element method. Experimental results at different temperatures, strain rates, and strain levels were obtained using a Gleeble thermomechanical simulator. A comparison of results of the model with experiments shows good agreement.

  20. Correlation Between Microstructure and Mechanical Properties Before and After Reversion of Metastable Austenitic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Fargas, Gemma; Zapata, Ana; Roa, Joan Josep; Sapezanskaia, Ina; Mateo, Antonio

    2015-12-01

    Reversion treatments are a way to improve the mechanical response of metastable austenitic stainless steels by means of grain refinement. To effectively apply those treatments, the steel must be previously deformed to induce a significant amount of martensitic transformation. In this work, the effect of reversion treatments was studied on a commercial AISI 301LN grade subjected to an industrial cold rolling process, with thickness reductions not higher than 40 pct. Microstructural changes and evolution of both monotonic and cyclic mechanical properties were investigated after cold rolling and upon reversion treatments. Results revealed that the finer austenitic microstructure obtained after reversion leads to an interesting combination of properties, with strong increments in hardness and yield strength, and also fatigue limit improvement, as compared to the initial annealed condition.

  1. Study of the Sensitization on the Grain Boundary in Austenitic Stainless Steel Aisi 316

    NASA Astrophysics Data System (ADS)

    Kocsisová, Edina; Dománková, Mária; Slatkovský, Ivan; Sahul, Martin

    2014-12-01

    Intergranular corrosion (IGC) is one of the major problems in austenitic stainless steels. This type of corrosion is caused by precipitation of secondary phases on grain boundaries (GB). Precipitation of the secondary phases can lead to formation of chromium depleted zones in the vicinity of grain boundaries. Mount of the sensitization of material is characterized by the degree of sensitization (DOS). Austenitic stainless steel AISI 316 as experimental material had been chosen. The samples for the study of sensitization were solution annealed on 1100 °C for 60 min followed by water quenching and then sensitization by isothermal annealing on 700 °C and 650 °C with holding time from 15 to 600 min. Transmission electron microscopy (TEM) was used for identification of secondary phases. Electron backscattered diffraction (EBSD) was applied for characterization of grain boundary structure as one of the factors which influences on DOS.

  2. High temperature corrosion of austenitic stainless steel coils in a direct reduction plant in Mexico

    SciTech Connect

    Juarez-Islas, J.A.; Campillo, B.; Chaudhary, N.; Mendoza, R.; Gonzalez, A.

    1996-08-01

    The subject of this study is related to the performance of austenitic steels coils and tubes, in a range of temperatures between 425 to 870 C for the transport of reducing gases, in an installation involving the direct reduction of iron-ore by reforming natural gas. Evidence is presented that metal dusting is not the only unique high temperature corrosion mechanism that caused catastrophic failures of austenitic 304 (UNS S30400) coils and HK-40 (UNS J94204) tubes. Sensitization as well as stress corrosion cracking occurred in 304 stainless steel coils, and metal dusting occurred in tubes of HK-40, a high resistance alloy. The role of a continuous injection of H{sub 2}S to the process is suggested to avoid the high temperature metal dusting corrosion mechanism found in these kind of installations.

  3. Ultrasonic inspection of austenitic stainless steel welds with artificially produced stress corrosion cracks

    SciTech Connect

    Dugan, Sandra; Wagner, Sabine

    2014-02-18

    Austenitic stainless steel welds and nickel alloy welds, which are widely used in nuclear power plants, present major challenges for ultrasonic inspection due to the grain structure in the weld. Large grains in combination with the elastic anisotropy of the material lead to increased scattering and affect sound wave propagation in the weld. This results in a reduced signal-to-noise ratio, and complicates the interpretation of signals and the localization of defects. Mechanized ultrasonic inspection was applied to study austenitic stainless steel test blocks with different types of flaws, including inter-granular stress corrosion cracks (IGSCC). The results show that cracks located in the heat affected zone of the weld are easily detected when inspection from both sides of the weld is possible. In cases of limited accessibility, when ultrasonic inspection can be carried out only from one side of a weld, it may be difficult to distinguish between signals from scattering in the weld and signals from cracks.

  4. Mechanical properties of 15%Mn steel with fine lamellar structure consisting of ferrite and austenite phases

    NASA Astrophysics Data System (ADS)

    Ueji, R.; Okitsu, Y.; Nakamura, T.; Takagi, Y.; Tanaka, Y.

    2010-07-01

    New steel with fine lamellar structure consisting of austenite and ferrite was developed. 15mass%Mn-3%Al-3%Si steel sheet was used in this study. First of all, the effect of the cooling rate on the microstructure was examined. The cooling at the slower speed of 100 deg/hour created the dual phase structure consisting of both austenite and ferrite. The additional rolling developed the fine lamellar duplex structure. Improvement of both the tensile strength and elongation was achieved by rolling. The strength increases furthermore by the rolling up to larger reduction. The 90% rolled sheet shows high tensile strength around 1000MPa with large elongation (15%-20%). These results indicate that the multi-phased structure with controlled lamellar morphology is beneficial for the management of both high strength and large ductility.

  5. A review of compatibility of IFR fuel and austenitic stainless steel

    SciTech Connect

    Keiser, D.D. Jr.

    1996-11-01

    Interdiffusion experiments have been conducted to investigate the compatibility of various austenitic stainless steels with U-Pu-Zr alloys, which are alloys to be employed as fuel for the Integral Fast Reactor being developed by Argonne National Laboratory. These tests have also studied the compatibility of austenitic stainless steels with fission products, like the minor actinides (Np and Am) and lanthanides (Ce and Nd), that are generated during the fission process in an IFR. This paper compares the results of these investigations in the context of fuel-cladding compatibility in IFR fuel elements, specifically focusing on the relative Interdiffusion behavior of the components and the types of phases that develop based on binary phase diagrams. Results of Interdiffusion tests are assessed in the light of observations derived from post-test examinations of actual irradiated fuel elements.

  6. Hydrogen Environment Embrittlement on Austenitic Stainless Steels from Room Temperature to Low Temperatures

    NASA Astrophysics Data System (ADS)

    Ogata, Toshio

    2015-12-01

    Hydrogen environment embrittlement (HEE) on austenitic stainless steels SUS304, 304L, and 316L in the high pressure hydrogen gas was evaluated from ambient temperature to 20 K using a very simple mechanical properties testing procedure. In the method, the high- pressure hydrogen environment is produced just inside the hole in the specimen and the specimen is cooled in a cooled-alcohol dewar and a cryostat with a GM refrigerator. The effect of HEE was observed in tensile properties, especially at lower temperatures, and fatigue properties at higher stress level but almost no effect around the stress level of yield strength where almost no strain-induced martensite was produced. So, no effect of HEE on austenitic stainless steels unless the amount of the ferrite phase is small.

  7. A creep model for austenitic stainless steels incorporating cavitation and wedge cracking

    NASA Astrophysics Data System (ADS)

    Mahesh, S.; Alur, K. C.; Mathew, M. D.

    2011-01-01

    A model of damage evolution in austenitic stainless steels under creep loading at elevated temperatures is proposed. The initial microstructure is idealized as a space-tiling aggregate of identical rhombic dodecahedral grains, which undergo power-law creep deformation. Damage evolution in the form of cavitation and wedge cracking on grain-boundary facets is considered. Both diffusion- and deformation-driven grain-boundary cavity growth are treated. Cavity and wedge-crack length evolution are derived from an energy balance argument that combines and extends the models of Cottrell (1961 Trans. AIME 212 191-203), Williams (1967 Phil. Mag. 15 1289-91) and Evans (1971 Phil Mag. 23 1101-12). The time to rupture predicted by the model is in good agreement with published experimental data for a type 316 austenitic stainless steel under uniaxial creep loading. Deformation and damage evolution at the microscale predicted by the present model are also discussed.

  8. Ultrasonic inspection of austenitic stainless steel welds with artificially produced stress corrosion cracks

    NASA Astrophysics Data System (ADS)

    Dugan, Sandra; Wagner, Sabine

    2014-02-01

    Austenitic stainless steel welds and nickel alloy welds, which are widely used in nuclear power plants, present major challenges for ultrasonic inspection due to the grain structure in the weld. Large grains in combination with the elastic anisotropy of the material lead to increased scattering and affect sound wave propagation in the weld. This results in a reduced signal-to-noise ratio, and complicates the interpretation of signals and the localization of defects. Mechanized ultrasonic inspection was applied to study austenitic stainless steel test blocks with different types of flaws, including inter-granular stress corrosion cracks (IGSCC). The results show that cracks located in the heat affected zone of the weld are easily detected when inspection from both sides of the weld is possible. In cases of limited accessibility, when ultrasonic inspection can be carried out only from one side of a weld, it may be difficult to distinguish between signals from scattering in the weld and signals from cracks.

  9. Improvement of the resistance to stress corrosion cracking in austenitic stainless steels by cyclic prestraining

    SciTech Connect

    Chambreuil-Paret, A.; Magnin, T.

    1999-05-01

    Austenitic stainless steels are known to be sensitive to stress corrosion cracking (SCC) in hot chloride solutions. The aim of the present study is to find improvements in the SCC behavior of 316L-type austenitic stainless steels in 117 C MgCl{sub 2} solutions. Previously, the authors have proposed the corrosion-enhanced plasticity model (CEPM) to describe the discontinuous cracking process which occurs in SCC. This model is based on localized corrosion (anodic dissolution, and hydrogen absorption)-deformation (dislocations) interactions (CDI). From the framework of this model, it is proposed that a prestraining in fatigue at saturation decreases the SCC sensitivity. This idea is experimentally confirmed for both crack initiation and crack propagation, through the analysis of the SCC behavior by slow-strain-rate tests of single and polycrystals after different prestraining conditions.

  10. Effect of Austenitizing Temperature on Microstructure and Mechanical Properties of Semi-High-Speed Steel Cold-Forged Rolls

    NASA Astrophysics Data System (ADS)

    Wu, Qiong; Sun, Da-Le; Liu, Chang-Sheng

    2009-10-01

    The effect of austenitizing temperature on the microstructure and mechanical properties of semi-high-speed steel (S-HSS) cold-forged rolls was investigated. Low-temperature austenitizing below 1313 K induced carbide coarsening during subsequent tempering at 973 K due to the nucleation effect of undissolved M7C3. On the other hand, the heavy dissolution of M7C3 above 1353 K caused the fine carbide formation on lath and plate boundaries, which retarded the subgrain growth during tempering. The increase in strength with increasing austenitizing temperature was attributed to the fine carbide distribution and the high dislocation density. Furthermore, as the austenitizing temperature increased, the impact energy markedly reduced, due to the large prior austenite grain size and the high strength. Finally, based on the microstructure and mechanical properties, an optimal austenitizing temperature range between 1313 and 1333 K was determined.

  11. Cytotoxicity study of plasma-sprayed hydroxyapatite coating on high nitrogen austenitic stainless steels.

    PubMed

    Ossa, C P O; Rogero, S O; Tschiptschin, A P

    2006-11-01

    Stainless steel has been frequently used for temporary implants but its use as permanent implants is restricted due to its low pitting corrosion resistance. Nitrogen additions to these steels improve both mechanical properties and corrosion resistance, particularly the pitting and crevice corrosion resistance. Many reports concerning allergic reactions caused by nickel led to the development of nickel free stainless steel; it has excellent mechanical properties and very high corrosion resistance. On the other hand, stainless steels are biologically tolerated and no chemical bonds are formed between the steel and the bone tissue. Hydroxyapatite coatings deposited on stainless steels improve osseointegration, due their capacity to form chemical bonds (bioactive fixation) with the bone tissue. In this work hydroxyapatite coatings were plasma-sprayed on three austenitic stainless steels: ASTM-F138, ASTM-F1586 and the nickel-free Böhler-P558. The coatings were analyzed by SEM and XDR. The cytotoxicity of the coatings/steels was studied using the neutral red uptake method by quantitative evaluation of cell viability. The three uncoated stainless steels and the hydroxyapatite coated Böhler-P558 did not have any toxic effect on the cell culture. The hydroxyapatite coated ASTM-F138 and ASTM-F1586 stainless steels presented cytotoxicity indexes (IC50%) lower than 50% and high nickel contents in the extracts. PMID:17122924

  12. Effect of Structural Heterogeneity on In Situ Deformation of Dissimilar Weld Between Ferritic and Austenitic Steel

    NASA Astrophysics Data System (ADS)

    Ghosh, M.; Santosh, R.; Das, S. K.; Das, G.; Mahato, B.; Korody, J.; Kumar, S.; Singh, P. K.

    2015-08-01

    Low-alloy steel and 304LN austenitic stainless steel were welded using two types of buttering material, namely 309L stainless steel and IN 182. Weld metals were 308L stainless steel and IN 182, respectively, for two different joints. Cross-sectional microstructure of welded assemblies was investigated. Microhardness profile was determined perpendicular to fusion boundary. In situ tensile test was performed in scanning electron microscope keeping low-alloy steel-buttering material interface at the center of gage length. Adjacent to fusion boundary, low-alloy steel exhibited carbon-depleted region and coarsening of matrix grains. Between coarse grain and base material structure, low-alloy steel contained fine grain ferrite-pearlite aggregate. Adjacent to fusion boundary, buttering material consisted of Type-I and Type-II boundaries. Within buttering material close to fusion boundary, thin cluster of martensite was formed. Fusion boundary between buttering material-weld metal and weld metal-304LN stainless steel revealed unmixed zone. All joints failed within buttering material during in situ tensile testing. The fracture location was different for various joints with respect to fusion boundary, depending on variation in local microstructure. Highest bond strength with adequate ductility was obtained for the joint produced with 309L stainless steel-buttering material. High strength of this weld might be attributed to better extent of solid solution strengthening by alloying elements, diffused from low-alloy steel to buttering material.

  13. Variation of carbon concentration in proeutectoid ferrite during austenitization in hypoeutectoid steel

    SciTech Connect

    Jung, Minsu; Cho, Wontae; Park, Jihye; Jung, Jae-Gil; Lee, Young-Kook

    2014-08-15

    The variation of the C concentration in proeutectoid ferrite (α{sub PF}) during austenitization in hypoeutectoid steels was quantitatively investigated using the massive transformation start temperature (T{sub m}) of α{sub PF} to austenite (γ) measured by high-temperature confocal laser scanning microscopy and hardness of α{sub PF}. The C concentration in α{sub PF} at T{sub m} in hypoeutectoid steels increased with increasing total C concentration up to approximately 0.2 wt.% during heating. The hardness of α{sub PF} with isothermal holding time at 775 °C in S20C steel revealed C enrichment in α{sub PF} at the early stage of isothermal holding and its reduction with further holding. These results explain the redistribution of the C in α{sub PF} during austenitization as follows: free C atoms released from cementite during pearlite decomposition diffuse excessively into neighboring α{sub PF} as well as pearlitic ferrite. The supersaturated C concentration in α{sub PF} is reduced during the long-range diffusive transformation of α{sub PF} to γ. However, some of the excess C atoms still remain in α{sub PF} until α{sub PF} starts to massively transform to γ. - Highlights: • Massive transformation of αPF to γ in hypoeutectoid steels was observed using CLSM. • C content in αPF during austenitization was analyzed by measured Tm and hardness. • Tm decreases and C content in αPF at Tm increases with increasing total C. • C atoms released from θ during formation of P to γ diffuse excessively into αPF. • Supersaturated C content in αPF is reduced during transformation of αPF to γ.

  14. Delta ferrite-containing austenitic stainless steel resistant to the formation of undesirable phases upon aging

    DOEpatents

    Leitnaker, J.M.

    Austenitic stainless steel alloys containing delta ferrite, such as are used as weld deposits, are protected against the transformation of delta ferrite to sigma phase during aging by the presence of carbon plus nitrogen in a weight percent 0.015 to 0.030 times the volume percent ferrite present in the alloy. The formation of chi phase upon aging is controlled by controlling the Mo content.

  15. Delta ferrite-containing austenitic stainless steel resistant to the formation of undesirable phases upon aging

    DOEpatents

    Leitnaker, James M.

    1981-01-01

    Austenitic stainless steel alloys containing delta ferrite, such as are used as weld deposits, are protected against the transformation of delta ferrite to sigma phase during aging by the presence of carbon plus nitrogen in a weight percent 0.015-0.030 times the volume percent ferrite present in the alloy. The formation of chi phase upon aging is controlled by controlling the Mo content.

  16. Effects of a Hydrogen Gas Environment on Fatigue Crack Growth of a Stable Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Kawamoto, Kyohei; Oda, Yasuji; Noguchi, Hiroshi; Higashida, Kenji

    In order to clarify the effects of a hydrogen gas environment on the fatigue crack growth characteristics of stable austenitic stainless steels, bending fatigue tests were carried out in a hydrogen gas, in a nitrogen gas at 1.0 MPa and in air on a SUS316L using the Japanese Industrial Standards (type 316L). Also, in order to discuss the difference in the hydrogen sensitivity between austenitic stainless steels, the fatigue tests were also carried out on a SUS304 using the Japanese Industrial Standards (type 304) metastable austenitic stainless steel as a material for comparison. The main results obtained are as follows. Hydrogen gas accelerates the fatigue crack growth rate of type 316L. The degree of the fatigue crack growth acceleration is low compared to that in type 304. The fracture surfaces of both the materials practically consist of two parts; the faceted area seemed to be brittle and the remaining area occupying a greater part of the fracture surface and seemed to be ductile. The faceted area does not significantly contribute to the fatigue crack growth rate in both austenitic stainless steels. The slip-off mechanism seems to be valid not only in air and in nitrogen, but also in hydrogen. Also, the main cause of the fatigue crack growth acceleration of both materials occurs by variation of the slip behaviour. The difference in the degree of the acceleration, which in type 316L is lower than in type 304, seems to be caused by the difference in the stability of the γ phase.

  17. A simplified LBB evaluation procedure for austenitic and ferritic steel piping

    SciTech Connect

    Gamble, R.M.; Wichman, K.R.

    1997-04-01

    The NRC previously has approved application of LBB analysis as a means to demonstrate that the probability of pipe rupture was extremely low so that dynamic loads associated with postulated pipe break could be excluded from the design basis (1). The purpose of this work was to: (1) define simplified procedures that can be used by the NRC to compute allowable lengths for circumferential throughwall cracks and assess margin against pipe fracture, and (2) verify the accuracy of the simplified procedures by comparison with available experimental data for piping having circumferential throughwall flaws. The development of the procedures was performed using techniques similar to those employed to develop ASME Code flaw evaluation procedures. The procedures described in this report are applicable to pipe and pipe fittings with: (1) wrought austenitic steel (Ni-Cr-Fe alloy) having a specified minimum yield strength less than 45 ksi, and gas metal-arc, submerged arc and shielded metal-arc austentic welds, and (2) seamless or welded wrought carbon steel having a minimum yield strength not greater than 40 ksi, and associated weld materials. The procedures can be used for cast austenitic steel when adequate information is available to place the cast material toughness into one of the categories identified later in this report for austenitic wrought and weld materials.

  18. Development of a robust modeling tool for radiation-induced segregation in austenitic stainless steels

    SciTech Connect

    Yang, Ying; Field, Kevin G; Allen, Todd R.; Busby, Jeremy T

    2015-09-01

    Irradiation-assisted stress corrosion cracking (IASCC) of austenitic stainless steels in Light Water Reactor (LWR) components has been linked to changes in grain boundary composition due to irradiation induced segregation (RIS). This work developed a robust RIS modeling tool to account for thermodynamics and kinetics of the atom and defect transportation under combined thermal and radiation conditions. The diffusion flux equations were based on the Perks model formulated through the linear theory of the thermodynamics of irreversible processes. Both cross and non-cross phenomenological diffusion coefficients in the flux equations were considered and correlated to tracer diffusion coefficients through Manning’s relation. The preferential atomvacancy coupling was described by the mobility model, whereas the preferential atom-interstitial coupling was described by the interstitial binding model. The composition dependence of the thermodynamic factor was modeled using the CALPHAD approach. Detailed analysis on the diffusion fluxes near and at grain boundaries of irradiated austenitic stainless steels suggested the dominant diffusion mechanism for chromium and iron is via vacancy, while that for nickel can swing from the vacancy to the interstitial dominant mechanism. The diffusion flux in the vicinity of a grain boundary was found to be greatly influenced by the composition gradient formed from the transient state, leading to the oscillatory behavior of alloy compositions in this region. This work confirms that both vacancy and interstitial diffusion, and segregation itself, have important roles in determining the microchemistry of Fe, Cr, and Ni at irradiated grain boundaries in austenitic stainless steels.

  19. Radiation-induced segregation of deuterium in austenitic steels and vanadium alloys

    NASA Astrophysics Data System (ADS)

    Arbuzov, V. L.; Raspopova, G. A.; Vykhodets, V. B.

    The accumulation and distribution of implanted deuterium were studied through simultaneous analysis using the nuclear reaction D(d,p)T for some austenitic, austenitic-martensitic steels, Fe-16% Cr, V-4% Ti-4% Cr, V-10% Ti-5% Cr alloys, and vanadium. The implantation was carried out by 700-keV deuteron irradiation at room temperature with a total implantation dose of about 2 × 10 18 cm -2. It is shown that the deuterium segregation induced by ion irradiation in vanadium and the Fe-16% Cr alloy remained unchanged during room temperature holding after implantation. On the other hand, in the two-phase steel and the V-Ti(-Cr) alloys the holding led to a partial elimination of the concentration inhomogeneity of the implant in the irradiated portion, while in the austenitic steel deuterium segregation increased probably due to the migration of deuterium from the unirradiated volume to the irradiation zone. Possible reasons for different behavior of the implanted deuterium in different materials will be briefly discussed.

  20. Effect of material heat treatment on fatigue crack initiation in austenitic stainless steels in LWR environments.

    SciTech Connect

    Chopra, O. K.; Alexandreanu, B.; Shack, W. J.; Energy Technology

    2005-07-31

    The ASME Boiler and Pressure Vessel Code provides rules for the design of Class 1 components of nuclear power plants. Figures I-9.1 through I-9.6 of Appendix I to Section III of the Code specify design curves for applicable structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. The existing fatigue strain-vs.-life ({var_epsilon}-N) data illustrate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping steels. Under certain environmental and loading conditions, fatigue lives of austenitic stainless steels (SSs) can be a factor of 20 lower in water than in air. This report presents experimental data on the effect of heat treatment on fatigue crack initiation in austenitic Type 304 SS in LWR coolant environments. A detailed metallographic examination of fatigue test specimens was performed to characterize the crack morphology and fracture morphology. The key material, loading, and environmental parameters and their effect on the fatigue life of these steels are also described. Statistical models are presented for estimating the fatigue {var_epsilon}-N curves for austenitic SSs as a function of material, loading, and environmental parameters. Two methods for incorporating the effects of LWR coolant environments into the ASME Code fatigue evaluations are presented.

  1. Characterization of the sodium corrosion behavior of commercial austenitic steels

    SciTech Connect

    Shiels, S.A.; Bagnall, C.; Keeton, A.R.; Witkowski, R.E.; Anantatmula, R.P.

    1980-01-01

    During the course of an on-going evaluation of austenitic alloys for potential liquid metal fast breeder reactor (LMFBR) fuel pin cladding application, a series of commercial alloys was selected for study. The data obtained led to the recognition of an underlying pattern of behavior and enabled the prediction of surface chemistry changes. The changes in surface topographical development from alloy to alloy are shown and the important role played by the element molybdenum in this development is indicated. The presentation also illustrates how a total damage equation was evolved to encompass all aspects of weight loss and metal/sodium interactions: wall thinning ferrite layer formation and intergranular attack. The total damage equation represents a significant departure from the classical description of sodium corrosion in which weight loss is simply translated into wall thinning.

  2. Alloy Design, Combinatorial Synthesis, and Microstructure-Property Relations for Low-Density Fe-Mn-Al-C Austenitic Steels

    NASA Astrophysics Data System (ADS)

    Raabe, D.; Springer, H.; Gutierrez-Urrutia, I.; Roters, F.; Bausch, M.; Seol, J.-B.; Koyama, M.; Choi, P.-P.; Tsuzaki, K.

    2014-09-01

    We present recent developments in the field of austenitic steels with up to 18% reduced mass density. The alloys are based on the Fe-Mn-Al-C system. Here, two steel types are addressed. The first one is a class of low-density twinning-induced plasticity or single phase austenitic TWIP (SIMPLEX) steels with 25-30 wt.% Mn and <4-5 wt.% Al or even <8 wt.% Al when naturally aged. The second one is a class of κ-carbide strengthened austenitic steels with even higher Al content. Here, κ-carbides form either at 500-600°C or even during quenching for >10 wt.% Al. Three topics are addressed in more detail, namely, the combinatorial bulk high-throughput design of a wide range of corresponding alloy variants, the development of microstructure-property relations for such steels, and their susceptibility to hydrogen embrittlement.

  3. Development of Advanced 9Cr Ferritic-Martensitic Steels and Austenitic Stainless Steels for Sodium-Cooled Fast Reactor

    SciTech Connect

    Sham, Sam; Tan, Lizhen; Yamamoto, Yukinori

    2013-01-01

    Ferritic-martensitic (FM) steel Grade 92, with or without thermomechanical treatment (TMT), and austenitic stainless steels HT-UPS (high-temperature ultrafine precipitate strengthening) and NF709 were selected as potential candidate structural materials in the U.S. Sodium-cooled Fast Reactor (SFR) program. The objective is to develop advanced steels with improved properties as compared with reference materials such as Grade 91 and Type 316H steels that are currently in nuclear design codes. Composition modification and/or processing optimization (e.g., TMT and cold-work) were performed to improve properties such as resistance to thermal aging, creep, creep-fatigue, fracture, and sodium corrosion. Testings to characterize these properties for the advanced steels were conducted by the Idaho National Laboratory, the Argonne National Laboratory and the Oak Ridge National Laboratory under the U.S. SFR program. This paper focuses on the resistance to thermal aging and creep of the advanced steels. The advanced steels exhibited up to two orders of magnitude increase in creep life compared to the reference materials. Preliminary results on the weldment performance of the advanced steels are also presented. The superior performance of the advanced steels would improve reactor design flexibility, safety margins and economics.

  4. Migration and accumulation at dislocations of transmutation helium in austenitic steels upon neutron irradiation

    NASA Astrophysics Data System (ADS)

    Kozlov, A. V.; Portnykh, I. A.

    2016-04-01

    The model of the migration and accumulation at dislocations of transmutation helium and the formation of helium-vacancy pore nuclei in austenitic steels upon neutron irradiation has been proposed. As illustrations of its application, the dependences of the characteristics of pore nuclei on the temperature of neutron irradiation have been calculated. The results of the calculations have been compared with the experimental data in the literature on measuring the characteristics of radiation-induced porosity that arises upon the irradiation of shells of fuel elements of a 16Cr-19Ni-2Mo-2Mn-Si-Ti-Nb-V-B steel in a fast BN600 neutron reactor at different temperatures.

  5. Effect of prior cold work on creep properties of a titanium modified austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Vijayanand, V. D.; Parameswaran, P.; Nandagopal, M.; Panneer Selvi, S.; Laha, K.; Mathew, M. D.

    2013-07-01

    Prior cold worked (PCW) titanium-modified 14Cr-15Ni austenitic stainless steel (SS) is used as a core-structural material in fast breeder reactor because of its superior creep strength and resistance to void swelling. In this study, the influence of PCW in the range of 16-24% on creep properties of IFAC-1 SS, a titanium modified 14Cr-15Ni austenitic SS, at 923 K and 973 K has been investigated. It was found that PCW has no appreciable effect on the creep deformation rate of the steel at both the test temperatures; creep rupture life increased with PCW at 923 K and remained rather unaffected at 973 K. The dislocation structure along with precipitation in the PCW steel was found to change appreciably depending on creep testing conditions. A well-defined dislocation substructure was observed on creep testing at 923 K; a well-annealed microstructure with evidences of recrystallization was observed on creep testing at 973 K. Creep rupture life of the steel increased with the increase in PCW at 923 K. This has been attributed to the partial retention of prior cold work induced dislocations which facilitated the extensive precipitation of secondary Ti(C,N) particles on the stable dislocation substructure. Creep rupture life of the steel did not vary with PCW at 973 K due to softening by recrystallization and absence of secondary Ti(C,N).

  6. Advanced Cast Austenitic Stainless Steels for High Temperature Components

    SciTech Connect

    Maziasz, P.J.; Shingledecker, J.P.; Evans, N.D.; Pollard, M.J.

    2008-10-09

    In July of 2002, a Cooperative Research and Development Agreement (CRADA) was undertaken between Oak Ridge National Laboratory (ORNL) and Caterpillar, Inc. (Caterpillar Technical Center) to develop and commercialize new cast stainless steels invented and initially tested on a prior CRADA. This CRADA is a direct follow-on project to CRADA ORNL-99-0533 for diesel engine exhaust component and gas turbine engine structural component applications. The goal of this new CRADA was to develop and commercialize the newly discovered cast stainless steels (primarily CF8C-Plus) with improved performance and reliability, as lower-cost upgrade alternatives to more costly cast Ni-based superalloys.

  7. Post-irradiation annealing effect on helium diffusivity in austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Katsura, R.; Morisawa, J.; Kawano, S.; Oliver, B. M.

    2004-08-01

    As an experimental basis for helium induced weld cracking of neutron irradiated austenitic stainless steels, helium diffusivity has been evaluated by measuring helium release at high temperature. Isochronal and isothermal experiments were performed at temperatures between 700 and 1300 °C for 304 and 316L stainless steels. In 1 h isochronal experiments, helium was released beginning at ˜900 °C and reaching almost 100% at 1300 °C. No apparent differences in helium release were observed between the two stainless steel types. At temperatures between 900 and 1300 °C, the diffusion rate was calculated from the time dependence of the helium release rate to be: D0=4.91 cm 2/s, E=289 kJ/mol. The observed activation energy suggests that the release of helium from the steels is associated with the removal of helium from helium bubbles and/or from vacancy diffusion.

  8. Post-Irradiation Annealing Effect on Helium Diffusivity in Austenitic Stainless Steels

    SciTech Connect

    Katsura, Ryoei; Morisawa, J; Kawano, S; Oliver, Brian M.

    2004-08-01

    As an experimental basis for helium induced weld cracking of neutron irradiated austenitic stainless steels, helium diffusivity has been evaluated by measuring helium release rates at high temperature. Isochronal and isothermal experiment were performed at temperatures between 700 and 1300 for Type 304 and 316L stainless steels. In 1 hour isochronal experiments, helium was released beginning at {approx}900 and reaching near 100% at 1300. No apparent differences in helium release rate were observed between Type 304 and 316L stainless steels. At temperatures between 1100 and 1300, the diffusion rate was calculated from the time dependence of the helium release rate to be:?D0=3.42?104 cm2/s, E=173.2 kJ/mol. The observed activation energy suggests that the release of helium from the steels is associated with the removal of helium from helium bubbles.

  9. Microstructural changes within similar coronary stents produced from two different austenitic steels.

    PubMed

    Weiss, Sabine; Meissner, Andreas; Fischer, Alfons

    2009-04-01

    Coronary heart disease has become the most common source for death in western industrial countries. Since 1986, a metal vessel scaffold (stent) is inserted to prevent the vessel wall from collapsing [Puel, J., Joffre, F., Rousseau, H., Guermonprez, B., Lancelin, B., Valeix, B., Imbert, G., Bounhoure, J.P, 1987. Endo-prothéses coronariennes autoexpansives dans la Préevention des resténoses apés angioplastie transluminale. Archives des Maladies du Coeur et des Vaisseaux, 1311--1312]. Most of these coronary stents are made from CrNiMo-steel (AISI 316L). Due to its austenitic structure, the material shows strength and ductility combined with corrosion resistance and a satisfactory biocompatibility. However, recent studies indicate that Nickel is under discussion as to its allergenic potential. Other typically used materials like Co-Base L605 or Tantalum alloys are relatively expensive and are not used so often. Newly developed austenitic high-nitrogen CrMnMoN-steels (AHNS) may offer an alternative. Traditional material tests revealed that strength and ductility, as well as corrosion resistance and biocompatibility, are as good as or even better than those of 316L [Vogt, J.B., Degallaix, S., Foct J., 1984. Low cycle fatigue life enhancement of 316L stainless steel by nitrogen alloying. International Journal of Fatigue 6 (4), 211-215, Menzel, J., Stein, G., 1996. High nitrogen containing Ni-free austenitic steels for medical applications. ISIJ Intern 36 (7), 893-900, Gavriljuk, V.G., Berns, H., 1999. High nitrogen steels, Springer Verlag, Berlin, Heidelberg]. However, because of a strut diameter of about 100 microm, the cross section consists of about five to ten crystal grains (oligo-crystalline). Thus very few, or even just one, grain can be responsible for the success or failure of the whole stent. During implantation, the structure of coronary artery stents is subjected to distinct inhomogeneous plastic deformation due to crimping and dilation. PMID:19627825

  10. Sensitivity of the magnetization curves of different austenitic stainless tube and pipe steels to mechanical fatigue

    NASA Astrophysics Data System (ADS)

    Niffenegger, M.; Leber, H. J.

    2008-07-01

    In meta-stable austenitic stainless steels, fatigue is accompanied by a partial strain-induced transformation of paramagnetic austenite to ferromagnetic martensite [G.B. Olsen, M. Cohen, Kinetics of strain induced martensite nucleation, Metall. Trans. 6 (1975) 791-795]. The associated changes of magnetic properties as the eddy current impedance, magnetic permeability or the remanence field may serve as an indication for the degree of fatigue and therefore the remaining lifetime of a component, even though the exact causal relationship between martensite formation and fatigue is not fully understood. However, measuring these properties by magnetic methods may be limited by the low affinity for strain-induced martensite formation. Thus other methods have to be found which are able to detect very small changes of ferromagnetic contents. With this aim the influence of cyclic strain loading on the magnetization curves of the austenitic stainless tube and pipe steels TP 321, 347, 304L and 316L is analysed in the present paper. The measured characteristic magnetic properties, which are the saturation magnetization, residual magnetization, coercive field and the field dependent permeability (AC-magnetization), are sensitive to fatigue and the corresponding material changes (martensitic transformation). In particular, the AC-magnetization was found to be very sensitive to small changes of the amount of strain induced martensite and therefore also to the degree of fatigue. Hence we conclude that applying magnetic minor loops are promising for the non-destructive evaluation of fatigue in austenitic stainless steel, even if a very small amount of strain induced martensite is formed.

  11. Improved ductility of a transformation-induced-plasticity steel by nanoscale austenite lamellae

    SciTech Connect

    Shen, Yongfeng; liu, Yandong; Sun, Xin; Wang, Y. D.; Zuo, Liang; Misra, R. D. K.

    2013-07-02

    TRIP (transformation-induced-plasticity) steel with a chemical composition of 0.19C–0.30Si–1.76Mn–1.52Al (weight percentage, wt.%) have been treated by intercritical annealing and austempering process. The microstructures of the obtained samples consist of the ferrite, the bainite and the retained austenite phase. The volume fractions of the bainite and the retained austenite gradually increase with increasing the temperature of the intercritical annealing. Consequently, significantly different mechanical properties have been observed. The sample annealed at 820°C (for 120s) and partitioned at 400°C (for 300s) has the best combination of ultimate tensile strength (UTS, ~682 MPa) and elongation to failure (~70%) with about 26% of bainitic ferrite plates and 17% retained austenite in its microstructure. The retained austenite has a lamella morphology with 100–300 nm in thickness and 2–5 μm in length. On the contrary, the sample annealed at the same temperature without the partitioning process yields much lower UTS and elongation to failure.

  12. Modelling grain-scattered ultrasound in austenitic stainless-steel welds: A hybrid model

    SciTech Connect

    Nowers, O.; Duxbury, D. J.; Velichko, A.; Drinkwater, B. W.

    2015-03-31

    The ultrasonic inspection of austenitic stainless steel welds can be challenging due to their coarse grain structure, charaterised by preferentially oriented, elongated grains. The anisotropy of the weld is manifested as both a ‘steering’ of the beam and the back-scatter of energy due to the macroscopic granular structure of the weld. However, the influence of weld properties, such as mean grain size and orientation distribution, on the magnitude of scattered ultrasound is not well understood. A hybrid model has been developed to allow the study of grain-scatter effects in austenitic welds. An efficient 2D Finite Element (FE) method is used to calculate the complete scattering response from a single elliptical austenitic grain of arbitrary length and width as a function of the specific inspection frequency. A grain allocation model of the weld is presented to approximate the characteristic structures observed in austenitic welds and the complete scattering behaviour of each grain calculated. This model is incorporated into a semi-analytical framework for a single-element inspection of a typical weld in immersion. Experimental validation evidence is demonstrated indicating excellent qualitative agreement of SNR as a function of frequency and a minimum SNR difference of 2 dB at a centre frequency of 2.25 MHz. Additionally, an example Monte-Carlo study is presented detailing the variation of SNR as a function of the anisotropy distribution of the weld, and the application of confidence analysis to inform inspection development.

  13. Modelling grain-scattered ultrasound in austenitic stainless-steel welds: A hybrid model

    NASA Astrophysics Data System (ADS)

    Nowers, O.; Duxbury, D. J.; Velichko, A.; Drinkwater, B. W.

    2015-03-01

    The ultrasonic inspection of austenitic stainless steel welds can be challenging due to their coarse grain structure, charaterised by preferentially oriented, elongated grains. The anisotropy of the weld is manifested as both a `steering' of the beam and the back-scatter of energy due to the macroscopic granular structure of the weld. However, the influence of weld properties, such as mean grain size and orientation distribution, on the magnitude of scattered ultrasound is not well understood. A hybrid model has been developed to allow the study of grain-scatter effects in austenitic welds. An efficient 2D Finite Element (FE) method is used to calculate the complete scattering response from a single elliptical austenitic grain of arbitrary length and width as a function of the specific inspection frequency. A grain allocation model of the weld is presented to approximate the characteristic structures observed in austenitic welds and the complete scattering behaviour of each grain calculated. This model is incorporated into a semi-analytical framework for a single-element inspection of a typical weld in immersion. Experimental validation evidence is demonstrated indicating excellent qualitative agreement of SNR as a function of frequency and a minimum SNR difference of 2 dB at a centre frequency of 2.25 MHz. Additionally, an example Monte-Carlo study is presented detailing the variation of SNR as a function of the anisotropy distribution of the weld, and the application of confidence analysis to inform inspection development.

  14. Effect of heavy ion irradiation on microstructural evolution in CF8 cast austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Chen, Wei-Ying; Li, Meimei; Kirk, Marquis A.; Baldo, Peter M.; Lian, Tiangan

    2016-04-01

    The microstructural evolution in ferrite and austenitic in cast austenitic stainless steel (CASS) CF8, as received or thermally aged at 400 °C for 10,000 h, was followed under TEM with in situ irradiation of 1 MeV Kr ions at 300 and 350 °C to a fluence of 1.9 × 1015 ions/cm2 (∼3 dpa) at the IVEM-Tandem Facility. For the unaged CF8, the irradiation-induced dislocation loops appeared at a much lower dose in the austenite than in the ferrite. At the end dose, the austenite formed a well-developed dislocation network microstructure, while the ferrite exhibited an extended dislocation structure as line segments. Compared to the unaged CF8, the aged specimen appeared to have lower rate of damage accumulation. The rate of microstructural evolution under irradiation in the ferrite was significantly lower in the aged specimen than in the unaged. This difference is attributed to the different initial microstructures in the unaged and aged specimens, which implies that thermal aging and irradiation are not independent but interconnected damage processes.

  15. Effect of Retained Austenite on the Fracture Toughness of Quenching and Partitioning (Q&P)-Treated Sheet Steels

    NASA Astrophysics Data System (ADS)

    Wu, Riming; Li, Wei; Zhou, Shu; Zhong, Yong; Wang, Li; Jin, Xuejun

    2014-04-01

    Fracture toughness K IC was measured by double edge-notched tension (DENT) specimens with fatigue precracks on quenching and partitioning (Q&P)-treated high-strength (ultimate tensile strength [UTS] superior to 1200 MPa) sheet steels consisting of 4 to 10 vol pct of retained austenite. Crack extension force, G IC, evaluated from the measured K IC, is used to analyze the role of retained austenite in different fracture behavior. Meanwhile, G IC is deduced by a constructed model based on energy absorption by martensite transformation (MT) behavior of retained austenite in Q&P-treated steels. The tendency of the change of two results is in good agreement. The Q&P-treated steel, quenched at 573 K (300 °C), then partitioned at 573 K (300 °C), holding for 60 seconds, has a fracture toughness of 74.1 MPa·m1/2, which is 32 pct higher than quenching and tempering steel (55.9 MPa·m1/2), and 16 pct higher than quenching and austempering (QAT) steel (63.8 MPa·m1/2). MT is found to occur preferentially at the tips of extension cracks on less stable retained austenite, which further improves the toughness of Q&P steels; on the contrary, the MT that occurs at more stable retained austenite has a detrimental effect on toughness.

  16. Isolation, identification and characterization of indigenous fungi for bioremediation of hexavalent chromium, nickel and cobalt

    NASA Astrophysics Data System (ADS)

    Hernahadini, Nelis; Suhandono, Sony; Choesin, Devi N.; Chaerun, Siti K.; Kadarusman, Ade

    2014-03-01

    Waste from nickel mining of Sorowako in South Sulawesi contains hexavalent chromium, nickel and cobalt metals in high concentration and may have a negative impact to the environment. Common waste treatment systems such as chemical treatment using a reducing reagent may still have a negative impact. Bioremediation using fungi or bacteria becomes more popular because it is an environmentally friendly alternative. The purposes of this study are to isolate and identify indigenous fungi that are resistant to heavy metals (hexavalent chromium, nickel, and cobalt) and are capable of reducing the concentration of metals in mining wastes. Ten fungal isolates were successfully isolated from the soils and pond sediments in the area of nickel mining in Sorowako. Selection of superior isolate was carried out by growing all the isolates on PDA medium, which contained all of the three metals. One superior isolate was identified to be able to grow on medium with concentrations of 6400 ppm hexavalent chromium, 200 ppm nickel and 50 ppm cobalt. Molecular identification and phylogenetic studies of the isolate using fungal PCR primers developed to amplify the ITS (internal transcribed spacer) region showed that the isolate sequence was very close to Trichoderma atroviride with 99.8% similarity. Optimum incubation time for the uptake of hexavalent chromium was 3 days, nickel and cobalt was 5 days, respectively, with an optimum pH of 4.

  17. Sensitization of 21% Cr Ferritic Stainless Steel Weld Joints Fabricated With/Without Austenitic Steel Foil as Interlayer

    NASA Astrophysics Data System (ADS)

    Wu, Wenyong; Hu, Shengsun; Shen, Junqi; Ma, Li; Han, Jian

    2015-04-01

    The effects of sensitization heat treatment on the microstructure and electrochemical behavior of 21% Cr ferritic stainless steel weld joints with or without 309L austenite stainless steel as an interlayer were investigated. The joints were processed by pulsed gas tungsten arc welding. With the interlayer, grains in weld bead were refined, and almost fully ferrite. When the joints with the interlayer were maintained at 500 °C for 1 and 4 h, no microstructure changes occurred, whereas Widmanstatten austenite and needle-like austenite formed in the weld bead after sensitization at 815 °C for 1 h. In general, sensitization treatment worsens the corrosion resistance of welds, but the resistance of samples with the 4-h treatment at 500 °C recovered in part compared to those subjected to sensitization at 500 °C for 1 h. This could be due to Cr diffusion from the ferrite that heals the chromium-depletion zone along the grain boundary. However, an increase in temperature does not have the same effect. The corrosion morphology of samples in the weld bead is different from those in base metal after heat treatment at 500 °C for 1 h; in base metal, pitting corrosion occurs, whereas grain boundary corrosion occurs in the weld bead. Corrosion morphology is closely associated with precipitation and segregation along the grain boundary.

  18. Weldability of corrosion-resistant high-nitrogen austenitic Kh22AG16N8M-type steels

    NASA Astrophysics Data System (ADS)

    Bannykh, O. A.; Blinov, V. M.; Kostina, M. V.; Blinov, E. V.; Zvereva, T. N.

    2007-10-01

    The influence of thermal treatment on the structures and mechanical properties of welds of corrosion-resistant high-nitrogen austenitic 05Kh22AG16N8M-type steels is studied. In these steels, austenite is found to be highly resistant to discontinuous precipitation and the formation of σ phase and δ ferrite upon cooling regardless of the temperature of heating for quenching (from 900 to 1250°C) and the cooling conditions (water, air, furnace). Welding of these steels can produce high-strength welds with an enhanced impact toughness.

  19. Effect of carbonitride dissolution on T{sub {delta}} and V{sub {delta}} of austenitic steels

    SciTech Connect

    Yang Ruzeng; Dai Qixun

    1997-03-01

    The authors deal with the effect of carbide dissolution on the {gamma}/{gamma}+{delta} boundary temperature, T{sub {delta}}, and the {delta} phase volume, V{sub {delta}}, as well as the equilibrium relation between the alloying elements at the {gamma}/{gamma}+{delta} boundary of austenitic steels at high temperature, and study the variation of the ferrite volume with temperature in {alpha}+{gamma} dual phase steel. The relevant expressions are derived from many experimental results, which may provide a basis for quantitative calculation, the design of compositions, the determination of working processes and prediction of the mechanical properties and microstructure of the austenitic steels.

  20. Effect of nitrogen on the stabilization of austenite in a tungsten-molybdenum high-speed steel

    SciTech Connect

    Popandopulo, A.N.; Zhukova, L.T.

    1986-05-01

    A study was made of the tendency of steels R6M5 and R6Am5 to austenite stabilization after subzero treatment and high-temperature tempering in hot-rolled bars. Data indicate that in steel R6AM5 during quenching there is almost instantaneous austenite stabilization. The data was derived from a study of phase composition (exposure from a microsection in DRON-2.0 equipment in iron K /SUB alpha/ radiation), microstructure, and hardness. The authors conclude that in view of serious difficulties in metallurgical and tool production, steel R6AM5 should be supplied only at the request of the customer.

  1. Structural factors governing steel resistance during operation in corrosive media under cavitation conditions

    SciTech Connect

    Berezovskaya, V.V.

    1988-05-01

    To evaluate the effect of structural factors on the corrosion resistance of steel under cavitation, a study was made of the effect of cavitation on chromium (95Kh18) and chromium-nickel (12Kh18N9T) corrosion-resistant steels and also on maraging steel 03Kh10N5K5M3KTYuS, specially developed for the loading conditions being studied, together with the austenitic steel 03Kh23N28M3D3T. A study of the effect of martensite content on corrosion and cavitation-corrosion resistance was carried out on steels 12Kh18N9T and 95Kh18 after different treatments. Corrosion tests were conducted in solutions of H/sub 2/SO/sub 4/ and H/sub 3/PO/sub 4/ and scanning electron microscopy was used to assess phase and corrosion behavior. Maraging steels treated for maximum hardness and overaging exhibited high cavitation-corrosion resistance in acid solutions owing to high strength and resistance to microcrack initiation and propagation. It was recommended that under cavitation conditions in corrosive media, high alloy austenitic corrosion-resistant steels are substituted by maraging steels.

  2. Modeling the Ferrite-Austenite Transformation in the Heat-Affected Zone of Stainless Steel Welds

    SciTech Connect

    Vitek, J.M.; David, S.A.

    1997-12-01

    The diffusion-controlled ferrite-austenite transformation in stainless steel welds was modeled. An implicit finite-difference analysis that considers multi-component diffusion was used. The model was applied to the Fe-Cr-Ni system to investigate the ferrite- austenite transformation in the heat-affected zone of stainless steel weld metal. The transformation was followed as a function of time as the heat-affected zone was subjected to thermal cycles comparable to those experienced during gas-tungsten arc welding. The results showed that the transformation behavior and the final microstructural state are very sensitive to the maximum temperature that is experienced by the heat-affected zone. For high maximum exposure temperatures ({approximately} 1300{degree} C), the ferrite formation that occurs at the highest temperatures is not completely offset by the reverse ferrite dissolution at lower temperatures. As a result, for high temperature exposures there is a net increase in the amount of ferrite in the microstructure. It was also found that if compositional gradients are present in the initial ferrite and austenite phases, the extent of the transformation is impacted.

  3. Review of environmental effects on fatigue crack growth of austenitic stainless steels.

    SciTech Connect

    Shack, W. J.; Kassner, T. F.; Energy Technology

    1994-07-11

    Fatigue and environmentally assisted cracking of piping, pressure vessel cladding, and core components in light water reactors are potential concerns to the nuclear industry and regulatory agencies. The degradation processes include intergranular stress corrosion cracking of austenitic stainless steel (SS) piping in boiling water reactors (BWRs), and propagation of fatigue or stress corrosion cracks (which initiate in sensitized SS cladding) into low-alloy ferritic steels in BWR pressure vessels. Crack growth data for wrought and cast austenitic SSs in simulated BWR water, developed at Argonne National Laboratory under US Nuclear Regulatory Commission sponsorship over the past 10 years, have been compiled into a data base along with similar data obtained from the open literature. The data were analyzed to develop corrosion-fatigue curves for austenitic SSs in aqueous environments corresponding to normal BWR water chemistries, for BWRs that add hydrogen to the feedwater, and for pressurized water reactor primary-system-coolant chemistry. The corrosion-fatigue data and curves in water were compared with the air line in Section XI of the ASME Code.

  4. Surface modification of AISI 304 austenitic stainless steel by plasma nitriding

    NASA Astrophysics Data System (ADS)

    Liang, Wang

    2003-04-01

    Plasma nitriding of austenitic stainless steel samples has been carried out using pulse dc glow discharge plasma of NH 3 gas at substrate temperature ranging from 350 to 520 °C. A nitriding time of only 4 h has been found to produce a compact surface nitride layer composed of γN' phase with a thickness of around 7-12 μm as processing temperature remained between 420 and 450 °C. The thickness of γN phase was found to be very thin only about 2 μm after plasma nitriding at temperature below 400 °C. Microhardness measurements showed significant increase in the hardness from 240 HV (for untreated samples) up to 1700 HV (for nitrided samples at temperature of 460 °C). For nitriding at higher temperature, i.e. above 460 °C, the chromium nitrides precipitated in the nitrided layer and caused austenite phase transform into ferrite phase or iron nitrides ( γ' or ɛ). The consequent result of chromium nitride precipitation is the reduction of corrosion resistance of nitrided layer. Compressive residual stresses existed in the nitrided layer due to nitrogen diffusion into austenitic stainless steel.

  5. Determining Experimental Parameters for Thermal-Mechanical Forming Simulation considering Martensite Formation in Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Schmid, Philipp; Liewald, Mathias

    2011-08-01

    The forming behavior of metastable austenitic stainless steel is mainly dominated by the temperature-dependent TRIP effect (transformation induced plasticity). Of course, the high dependency of material properties on the temperature level during forming means the temperature must be considered during the FE analysis. The strain-induced formation of α'-martensite from austenite can be represented by using finite element programs utilizing suitable models such as the Haensel-model. This paper discusses the determination of parameters for a completely thermal-mechanical forming simulation in LS-DYNA based on the material model of Haensel. The measurement of the martensite evolution in non-isothermal tensile tests was performed with metastable austenitic stainless steel EN 1.4301 at different rolling directions between 0° and 90 °. This allows an estimation of the influence of the rolling direction to the martensite formation. Of specific importance is the accuracy of the martensite content measured by magnetic induction methods (Feritscope). The observation of different factors, such as stress dependence of the magnetisation, blank thickness and numerous calibration curves discloses a substantial important influence on the parameter determination for the material models. The parameters obtained for use of Haensel model and temperature-dependent friction coefficients are used to simulate forming process of a real component and to validate its implementation in the commercial code LS-DYNA.

  6. Role of microstructure and heat treatments on the desorption kinetics of tritium from austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Chêne, J.; Brass, A.-M.; Trabuc, P.; Gastaldi, O.

    2007-02-01

    The liquid scintillation counting of solid samples (LSC-SS technique) was successfully used to study the role of microstructure and heat treatments on the behavior of residual tritium in several austenitic stainless steels (as-cast remelted tritiated waste, 316LN and 321 steels). The role of desorption annealing in the 100-600 °C range on the residual amount of tritium in tritiated waste was investigated. The residual tritium concentration computed from surface activity measurements is in good agreement with experimental values measured by liquid scintillation counting after full dissolution of the samples. The kinetics of tritium desorption recorded with the LSC-SS technique shows a significant desorption of residual tritium at room temperature, a strong barrier effect of thermal oxide films on the tritium desorption and a dependance of the tritium release on the steels microstructure. Annealing in the 300-600 °C range allows to desorb a large fraction of the residual tritium. However a significant trapping of tritium is evidenced. The influence of trapping phenomena on the concentration of residual tritium and on its dependance with the annealing temperature was investigated with different recrystallized and sensitized microstructures. Trapping is evidenced mainly below 150 °C and concerns a small fraction of the total amount of tritium introduced in austenitic steels. It presumably occurs preferentially on precipitates such as Ti(CN) or on intermetallic phases.

  7. Development of a System to Measure Austenite Grain Size of Plate Steel Using Laser-Based Ultrasonics

    SciTech Connect

    Lim, C. S.; Hong, S. T.; Yi, J. K.; Choi, S. G.; Oh, K. J.; Nagata, Y.; Yamada, H.; Hamada, N.

    2007-03-21

    A measurement system for austenite grain size of plate steel using laser-based ultrasonics has been developed. At first, the relationship between the ultrasonic attenuation coefficients using longitudinal waves and austenite grain size of samples was investigated in the laboratory experiments. According to the experimental results, the ultrasonic attenuation coefficients showed a good correlation with actual austenite grain sizes. For the next step, the system was installed in a hot rolling pilot plant of plate steel, and it was verified that the austenite grain size could be measured even in the environment of a hot rolling pilot plant. In the experiments, it was also confirmed that the fiber delivery system could deliver Nd:YAG laser beam of 810 mJ/pulse and ultrasonic signals could be obtained successfully.

  8. Static Recrystallized Grain Size of Coarse-Grained Austenite in an API-X70 Pipeline Steel

    NASA Astrophysics Data System (ADS)

    Sha, Qingyun; Li, Guiyan; Li, Dahang

    2013-12-01

    The effects of initial grain size and strain on the static recrystallized grain size of coarse-grained austenite in an API-X70 steel microalloyed with Nb, V, and Ti were investigated using a Gleeble-3800 thermomechanical simulator. The results indicate that the static recrystallized grain size of coarse-grained austenite decreases with decreasing initial grain size and increasing applied strain. The addition of microalloying elements can lead to a smaller initial grain size for hot deformation due to the grain growth inhibition during reheating, resulting in decreasing of static recrystallized grain size. Based on the experimental data, an equation for the static recrystallized grain size was derived using the least square method. The grain sizes calculated using this equation fit well with the measured ones compared with the equations for fine-grained austenite and for coarse-grained austenite of Nb-V microalloyed steel.

  9. Cast, heat-resistant austenitic stainless steels having reduced alloying element content

    DOEpatents

    Muralidharan, Govindarajan [Knoxville, TN; Sikka, Vinod Kumar [Oak Ridge, TN; Maziasz, Philip J [Oak Ridge, TN; Pankiw, Roman I [Greensburg, PA

    2011-08-23

    A cast, austenitic steel composed essentially of, expressed in weight percent of the total composition, about 0.4 to about 0.7 C, about 20 to about 30 Cr, about 20 to about 30 Ni, about 0.5 to about 1 Mn, about 0.6 to about 2 Si, about 0.05 to about 1 Nb, about 0.05 to about 1 W, about 0.05 to about 1.0 Mo, balance Fe, the steel being essentially free of Ti and Co, the steel characterized by at least one microstructural component selected from the group consisting of MC, M.sub.23C.sub.6, and M(C, N).

  10. Cast, heat-resistant austenitic stainless steels having reduced alloying element content

    DOEpatents

    Muralidharan, Govindarajan [Knoxville, TN; Sikka, Vinod Kumar [Oak Ridge, TN; Maziasz, Philip J [Oak Ridge, TN; Pankiw, Roman I [Greensburg, PA

    2010-07-06

    A cast, austenitic steel composed essentially of, expressed in weight percent of the total composition, about 0.4 to about 0.7 C, about 20 to about 30 Cr, about 20 to about 30 Ni, about 0.5 to about 1 Mn, about 0.6 to about 2 Si, about 0.05 to about 1 Nb, about 0.05 to about 1 W, about 0.05 to about 1.0 Mo, balance Fe, the steel being essentially free of Ti and Co, the steel characterized by at least one microstructural component selected from the group consisting of MC, M.sub.23C.sub.6, and M(C, N).

  11. Recrystallization, Precipitation Behaviors, and Refinement of Austenite Grains in High Mn, High Nb Steel

    NASA Astrophysics Data System (ADS)

    Miao, C. L.; Shang, C. J.; Zurob, H. S.; Zhang, G. D.; Subramanian, S. V.

    2012-02-01

    Through a series of experiments conducted on three kinds of high Mn steels with different Nb content, including stress relaxation tests, physical metallurgical modeling, and observation of prior austenite grains and precipitates, the effect of Nb on recrystallization and precipitation behaviors were investigated. The results indicate the existence of a novel deformation temperature range for grain refinement resulting from complete static recrystallization (SRX) in high Mn, high Nb steel, whereas slow SRX kinetics can be accelerated by a finer initial grain size. In this deformation temperature range, the effect of precipitation is too weak to prohibit SRX nucleation efficiently, but solute drag is still large enough to slow down growth rate. As a consequence, shorter incubation and homogeneous recrystallized nucleation can be realized at relative low temperature, and the coarsening rate of grains is much slower because of the high solute drag effect in the rolling of low C high Mn, high Nb line pipe steel.

  12. Quantitative prediction of deformed austenite and transformed ferrite texture in hot-rolled steel sheet

    NASA Astrophysics Data System (ADS)

    Tanaka, Y.; Tomida, T.; Mohles, V.

    2015-04-01

    A model to quantitatively predict ferrite (α) textures in hot-rolled steel sheets has been developed. In this model, the crystal plasticity model, called “Grain Interaction model (GIA)”, and the transformation texture model, called “Double K-S relation (DKS)”, are linked together. The deformed austenite (γ) texture is predicted by GIA with taking not only the standard {111}<110> slip system but also non-octahedral slip systems into account. Then the transformed a texture is calculated by DKS, in which a nucleated α prefers to have orientation relationship near the Kurdjumov-Sachs relation with both of two neighboring γ grains. For validation, single pass hot-rolling tests on a C-Si-Mn steel were carried out. The comparison between the predicted and the experimental textures shows that the linked model (GIA & DKS) can lead to a remarkable reproduction of the texture of hot-rolled steel sheets.

  13. ESD morphology deposition with WZr8 electrode on austenitic stainless steel support

    NASA Astrophysics Data System (ADS)

    Perju, M. C.; Ţugui, C. A.; Nejneru, C.; Axinte, M.; Vizureanu, P.

    2016-06-01

    Stainless steels are used to obtain mechanical parts, working in severe conditions with high dynamic loads in wet, chemically active environments. For this reason, these materials have good corrosion resistance in acidic or basic chemical agents. The main drawback is the relatively low wear and resistance to mechanical stress. This paper proposes a remedy by deposition of the hard thin films of tungsten electrode by spark electro-deposition method (ESD). Tungsten is an alfagen element and causes an increase for the mechanical properties at high and low temperatures for the austenitic stainless steels. Tungsten does not alter the corrosion resistance of stainless steels. The morphology for the obtained layers was analyzed using SEM, in 3D images, and profilographs.

  14. The effects of neutron irradiation on fracture toughness of austenitic stainless steels.

    SciTech Connect

    Chopra, O. K.; Gruber, E. E.; Shack, W. J.

    1999-05-21

    Austenitic stainless steels are used extensively as structural alloys in reactor pressure vessel internal components because of their superior fracture toughness properties. However, exposure to high levels of neutron irradiation for extended periods leads to significant reduction in the fracture resistance of these steels. This paper presents results of fracture toughness J-R curve tests on four heats of Type 304 stainless steel that were irradiated to fluence levels of {approx}0.3 and 0.9 x 10{sup 21} n cm{sup {minus}2} (E >1 MeV) at {approx}288 C in a helium environment in the Halden heavy water boiling reactor. The tests were performed on 1/4-T compact tension specimens in air at 288 C; crack extensions were determined by both DC potential and elastic unloading compliance techniques.

  15. In-situ determination of austenite and martensite formation in 13Cr6Ni2Mo supermartensitic stainless steel

    SciTech Connect

    Bojack, A.; Zhao, L.; Morris, P.F.; Sietsma, J.

    2012-09-15

    In-situ analysis of the phase transformations in a 13Cr6Ni2Mo supermartensitic stainless steel (X2CrNiMoV13-5-2) was carried out using a thermo-magnetic technique, dilatometry and high temperature X-ray diffractometry (HT-XRD). A combination of the results obtained by the three applied techniques gives a valuable insight in the phase transformations during the austenitization treatment, including subsequent cooling, of the 13Cr6Ni2Mo supermartensitic stainless steel, where the magnetic technique offers a high accuracy in monitoring the austenite fraction. It was found by dilatometry that the austenite formation during heating takes place in two stages, most likely caused by partitioning of Ni into austenite. The in-situ evolution of the austenite fraction is monitored by high-temperature XRD and dilatometry. The progress of martensite formation during cooling was described with a Koistinen-Marburger relation for the results obtained from the magnetic and dilatometer experiments. Enhanced martensite formation at the sample surface was detected by X-ray diffraction, which is assumed to be due to relaxation of transformation stresses at the sample surface. Due to the high alloy content and high thermodynamic stability of austenite at room temperature, 4 vol.% of austenite was found to be stable at room temperature after the austenitization treatment. - Highlights: Black-Right-Pointing-Pointer We in-situ analyzed phase transformations and fractions of a 13Cr6Ni2Mo SMSS. Black-Right-Pointing-Pointer Higher accuracy of the austenite fraction was obtained from magnetic technique. Black-Right-Pointing-Pointer Austenite formation during heating takes place in two stages. Black-Right-Pointing-Pointer Enhanced martensite formation at the sample surface detected by X-ray diffraction.

  16. Surface-protein interactions on different stainless steel grades: effects of protein adsorption, surface changes and metal release.

    PubMed

    Hedberg, Y; Wang, X; Hedberg, J; Lundin, M; Blomberg, E; Wallinder, I Odnevall

    2013-04-01

    Implantation using stainless steels (SS) is an example where an understanding of protein-induced metal release from SS is important when assessing potential toxicological risks. Here, the protein-induced metal release was investigated for austenitic (AISI 304, 310, and 316L), ferritic (AISI 430), and duplex (AISI 2205) grades in a phosphate buffered saline (PBS, pH 7.4) solution containing either bovine serum albumin (BSA) or lysozyme (LSZ). The results show that both BSA and LSZ induce a significant enrichment of chromium in the surface oxide of all stainless steel grades. Both proteins induced an enhanced extent of released iron, chromium, nickel and manganese, very significant in the case of BSA (up to 40-fold increase), whereas both proteins reduced the corrosion resistance of SS, with the reverse situation for iron metal (reduced corrosion rates and reduced metal release in the presence of proteins). A full monolayer coverage is necessary to induce the effects observed. PMID:23378148

  17. Synergistic Computational and Microstructural Design of Next- Generation High-Temperature Austenitic Stainless Steels

    SciTech Connect

    Karaman, Ibrahim; Arroyave, Raymundo

    2015-07-31

    The purpose of this project was to: 1) study deformation twinning, its evolution, thermal stability, and the contribution on mechanical response of the new advanced stainless steels, especially at elevated temperatures; 2) study alumina-scale formation on the surface, as an alternative for conventional chromium oxide, that shows better oxidation resistance, through alloy design; and 3) design new generation of high temperature stainless steels that form alumina scale and have thermally stable nano-twins. The work involved few baseline alloys for investigating the twin formation under tensile loading, thermal stability of these twins, and the role of deformation twins on the mechanical response of the alloys. These baseline alloys included Hadfield Steel (Fe-13Mn-1C), 316, 316L and 316N stainless steels. Another baseline alloy was studied for alumina-scale formation investigations. Hadfield steel showed twinning but undesired second phases formed at higher temperatures. 316N stainless steel did not show signs of deformation twinning. Conventional 316 stainless steel demonstrated extensive deformation twinning at room temperature. Investigations on this alloy, both in single crystalline and polycrystalline forms, showed that deformation twins evolve in a hierarchical manner, consisting of micron–sized bundles of nano-twins. The width of nano-twins stays almost constant as the extent of strain increases, but the width and number of the bundles increase with increasing strain. A systematic thermomechanical cycling study showed that the twins were stable at temperatures as high as 900°C, after the dislocations are annealed out. Using such cycles, volume fraction of the thermally stable deformation twins were increased up to 40% in 316 stainless steel. Using computational thermodynamics and kinetics calculations, we designed two generations of advanced austenitic stainless steels. In the first generation, Alloy 1, which had been proposed as an alumina

  18. Assessment of Retained Austenite in AISI D2 Tool Steel Using Magnetic Hysteresis and Barkhausen Noise Parameters

    NASA Astrophysics Data System (ADS)

    Kahrobaee, Saeed; Kashefi, Mehrdad

    2015-03-01

    Inaccurate heat treatment process could result in excessive amount of retained austenite, which degrades the mechanical properties, like strength, wear resistance, and hardness of cold work tool steel parts. Thus, to control the mechanical properties, quantitative measurement of the retained austenite is a critical step in optimizing the heat-treating parameters. X-ray diffraction method is the most frequently used technique for this purpose. This technique is, however, destructive and time consuming. Furthermore, it is not applicable to 100% quality inspection of industrial parts. In the present paper, the influence of austenitizing temperature on the retained austenite content and hardness of AISI D2 tool steel has been studied. Additionally, nondestructive magnetic hysteresis parameters of the samples including coercivity, magnetic saturation, and maximum differential permeability as well as their magnetic Barkhausen noise features (RMS peak voltage and peak position) have been investigated. The results revealed direct relations between magnetic saturation, differential permeability, and MBN peak amplitude with increasing austenitizing temperature due to the retained austenite formation. Besides, both parameters of coercivity and peak position had an inverse correlation with the retained austenite fraction.

  19. Copper, Boron, and Cerium Additions in Type 347 Austenitic Steel to Improve Creep Rupture Strength

    NASA Astrophysics Data System (ADS)

    Laha, Kinkar; Kyono, J.; Shinya, Norio

    2012-04-01

    Type 347 austenitic stainless steel (18Cr-12Ni-Nb) was alloyed with copper (3 wt pct), boron (0.01 to 0.06 wt pct), and cerium (0.01 wt pct) with an aim to increase the creep rupture strength of the steel through the improved deformation and cavitation resistance. Short-term creep rupture strength was found to increase with the addition of copper in the 347 steel, but the long-term strength was inferior. Extensive creep cavitation deprived the steel of the beneficial effect of creep deformation resistance induced by nano-size copper particles. Boron and cerium additions in the copper-containing steel increased its creep rupture strength and ductility, which were more for higher boron content. Creep deformation, grain boundary sliding, and creep cavity nucleation and growth in the steel were found to be suppressed by microalloying the copper-containing steel with boron and cerium, and the suppression was more for higher boron content. An auger electron spectroscopic study revealed the segregation of boron instead of sulfur on the cavity surface of the boron- and cerium-microalloyed steel. Cerium acted as a scavenger for soluble sulfur in the steels through the precipitation of cerium sulfide (CeS). This inhibited the segregation of sulfur and facilitated the segregation of boron on cavity surface. Boron segregation on the nucleated cavity surface reduced its growth rate. Microalloying the copper-containing 347 steel with boron and cerium thus enabled to use the full extent of creep deformation resistance rendered by copper nano-size particle by increase in creep rupture strength and ductility.

  20. Effect of Austenite Stability on Microstructural Evolution and Tensile Properties in Intercritically Annealed Medium-Mn Lightweight Steels

    NASA Astrophysics Data System (ADS)

    Song, Hyejin; Sohn, Seok Su; Kwak, Jai-Hyun; Lee, Byeong-Joo; Lee, Sunghak

    2016-06-01

    The microstructural evolution with varying intercritical-annealing temperatures of medium-Mn ( α + γ) duplex lightweight steels and its effects on tensile properties were investigated in relation to the stability of austenite. The size and volume fraction of austenite grains increased as the annealing temperature increased from 1123 K to 1173 K (850 °C to 900 °C), which corresponded with the thermodynamic calculation data. When the annealing temperature increased further to 1223 K (950 °C), the size and volume fraction were reduced by the formation of athermal α'-martensite during the cooling because the thermal stability of austenite deteriorated as a result of the decrease in C and Mn contents. In order to obtain the best combination of strength and ductility by a transformation-induced plasticity (TRIP) mechanism, an appropriate mechanical stability of austenite was needed and could be achieved when fine austenite grains (size: 1.4 μm, volume fraction: 0.26) were homogenously distributed in the ferrite matrix, as in the 1123 K (850 °C)—annealed steel. This best combination was attributed to the requirement of sufficient deformation for TRIP and the formation of many deformation bands at ferrite grains in both austenite and ferrite bands. Since this medium-Mn lightweight steel has excellent tensile properties as well as reduced alloying costs and weight savings, it holds promise for new automotive applications.

  1. Corrosion fatigue of iron-chromium-nickel alloys: Fracture mechanics, microstructure and chemistry. Progress report, December 1, 1990--December 31, 1992

    SciTech Connect

    Wei, R.P.

    1992-01-29

    This progress report briefly summarizes the research performed under the referenced grant for the period from 1 December 1990 to 31 December 1991, and contains a cumulative listing of technical presentations and publications dating back to 1 June 1988. Under this grant, a multi-disciplinary research program is undertaken to address certain fundamental issues relating to corrosion fatigue crack growth in structurally important alloys in aqueous environments. The principal goal of the research is to develop and expand the scientific understanding of the processes that control corrosion fatigue crack growth, particularly for ferrous alloys in terms of the controlling mechanical and chemical/electrochemical processes and their interactions with the microstructure. Focus is placed upon the austenitic iron-chromium-nickel (FeCrNi) alloys because of the need to resolve certain mechanistic issues and because of extensive utilization of these alloys in the power generation and chemical industries. Emphasis is given to the growth of short (small) cracks at low growth rates because crack growth in this regime is expected to be more sensitive to changes in external chemical/electrochemical variables.

  2. Microstructural evolution and mechanical properties of a low-carbon quenching and partitioning steel after partial and full austenitization

    NASA Astrophysics Data System (ADS)

    Li, Wan-song; Gao, Hong-ye; Nakashima, Hideharu; Hata, Satoshi; Tian, Wen-huai

    2016-08-01

    In this work, low-carbon steel specimens were subjected to the quenching and partitioning process after being partially or fully austenitized to investigate their microstructural evolution and mechanical properties. According to the results of scanning electron microscopy and transmission electron microscopy observations, X-ray diffraction analysis, and tensile tests, upper bainite or tempered martensite appears successively in the microstructure with increasing austenitization temperature or increasing partitioning time. In the partially austenitized specimens, the retained austenite grains are carbon-enriched twice during the heat treatment, which can significantly stabilize the phases at room temperature. Furthermore, after partial austenitization, the specimen exhibits excellent elongation, with a maximum elongation of 37.1%. By contrast, after full austenitization, the specimens exhibit good ultimate tensile strength and high yield strength. In the case of a specimen with a yield strength of 969 MPa, the maximum value of the ultimate tensile strength reaches 1222 MPa. During the partitioning process, carbon partitioning and carbon homogenization within austenite affect interface migration. In addition, the volume fraction and grain size of retained austenite observed in the final microstructure will also be affected.

  3. On the Constitutive Model of Nitrogen-Containing Austenitic Stainless Steel 316LN at Elevated Temperature

    PubMed Central

    Zhang, Lei; Feng, Xiao; Wang, Xin; Liu, Changyong

    2014-01-01

    The nitrogen-containing austenitic stainless steel 316LN has been chosen as the material for nuclear main-pipe, which is one of the key parts in 3rd generation nuclear power plants. In this research, a constitutive model of nitrogen-containing austenitic stainless steel is developed. The true stress-true strain curves obtained from isothermal hot compression tests over a wide range of temperatures (900–1250°C) and strain rates (10−3–10 s−1), were employed to study the dynamic deformational behavior of and recrystallization in 316LN steels. The constitutive model is developed through multiple linear regressions performed on the experimental data and based on an Arrhenius-type equation and Zener-Hollomon theory. The influence of strain was incorporated in the developed constitutive equation by considering the effect of strain on the various material constants. The reliability and accuracy of the model is verified through the comparison of predicted flow stress curves and experimental curves. Possible reasons for deviation are also discussed based on the characteristics of modeling process. PMID:25375345

  4. Intergranular Corrosion Behavior of Low-Nickel and 304 Austenitic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Bansod, Ankur V.; Patil, Awanikumar P.; Moon, Abhijeet P.; Khobragade, Nilay N.

    2016-07-01

    Intergranular corrosion (IGC) susceptibility for Cr-Mn austenitic stainless steel and 304 austenitic stainless steel (ASS) was estimated using electrochemical techniques. Optical and SEM microscopy studies were carried out to investigate the nature of IGC at 700 °C with increasing time (15, 30, 60, 180, 360, 720, 1440 min) according to ASTM standard 262 A. Quantitative analysis was performed to estimate the degree of sensitization (DOS) using double loop electrochemical potentiokinetic reactivation (DLEPR) and EIS technique. DLEPR results indicated that with the increase in thermal aging duration, DOS becomes more severe for both types of stainless steel. The DOS for Cr-Mn ASS was found to be higher (65.12% for 1440 min) than that of the AISI 304 ASS (23% for 1440 min). The higher degree of sensitization resulted in lowering of electrical charge capacitance resistance. Chronoamperometry studies were carried out at a passive potential of 0.4 V versus SCE and was observed to have a higher anodic dissolution of the passive film of Cr-Mn ASS. EDS studies show the formation of chromium carbide precipitates in the vicinity of the grain boundary. The higher Mn content was also observed for Cr-Mn ASS at the grain boundary.

  5. Deformation localization and dislocation channel dynamics in neutron-irradiated austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Gussev, Maxim N.; Field, Kevin G.; Busby, Jeremy T.

    2015-05-01

    The dynamics of deformation localization and dislocation channel formation were investigated in situ in a neutron-irradiated AISI 304 austenitic stainless steel and a model 304-based austenitic alloy by combining several analytical techniques including optic microscopy and laser confocal microscopy, scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy (TEM). Channel formation was observed at ∼70% of the polycrystalline yield stress of the irradiated materials (σ0.2). It was shown that triple junction points do not always serve as a source of dislocation channels; at stress levels below the σ0.2, channels often formed near the middle of the grain boundary. For a single grain, the role of elastic stiffness value (Young's modulus) in channel formation was analyzed; it was shown that in the irradiated 304 steels the initial channels appeared in "soft" grains with a high Schmid factor located near "stiff" grains with high elastic stiffness. The spatial organization of channels in a single grain was analyzed; it was shown that secondary channels operating in the same slip plane as primary channels often appeared at the middle or at one-third of the way between primary channels. The twinning nature of dislocation channels was analyzed for grains of different orientation using TEM. In the AISI 304 steel, channels in grains oriented close to <0 0 1>||TA (tensile axis) and <1 0 1>||TA were twin free and grain with <1 1 1>||TA and grains oriented close to a Schmid factor maximum contained deformation twins.

  6. Deformation localization and dislocation channel dynamics in neutron-irradiated austenitic stainless steels

    DOE PAGESBeta

    Gussev, Maxim N.; Field, Kevin G.; Busby, Jeremy T.

    2015-02-24

    We investigated dynamics of deformation localization and dislocation channel formation in situ in a neutron irradiated AISI 304 austenitic stainless steel and a model 304-based austenitic alloy by combining several analytical techniques including optic microscopy and laser confocal microscopy, scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy. Channel formation was observed at 70% of the formal tensile yield stress for both alloys. It was shown that triple junction points do not always serve as a source of dislocation channels; at stress levels below the yield stress, channels often formed near the middle of the grain boundary. For amore » single grain, the role of elastic stiffness value (Young modulus) in the channel formation was analyzed; it was shown that in the irradiated 304 steels the initial channels appeared in soft grains with a high Schmid factor located near stiff grains with high elastic stiffness. Moreover, the spatial organization of channels in a single grain was analyzed; it was shown that secondary channels operating in the same slip plane as primary channels often appeared at the middle or at one third of the way between primary channels. The twinning nature of dislocation channels was analyzed for grains of different orientation using TEM. Finally, it was shown that in the AISI 304 steel, channels were twin-free in grains oriented close to [001] and [101] of standard unit triangle; [111]-grains and grains oriented close to Schmid factor maximum contained deformation twins.« less

  7. Deformation localization and dislocation channel dynamics in neutron-irradiated austenitic stainless steels

    SciTech Connect

    Gussev, Maxim N.; Field, Kevin G.; Busby, Jeremy T.

    2015-02-24

    We investigated dynamics of deformation localization and dislocation channel formation in situ in a neutron irradiated AISI 304 austenitic stainless steel and a model 304-based austenitic alloy by combining several analytical techniques including optic microscopy and laser confocal microscopy, scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy. Channel formation was observed at 70% of the formal tensile yield stress for both alloys. It was shown that triple junction points do not always serve as a source of dislocation channels; at stress levels below the yield stress, channels often formed near the middle of the grain boundary. For a single grain, the role of elastic stiffness value (Young modulus) in the channel formation was analyzed; it was shown that in the irradiated 304 steels the initial channels appeared in soft grains with a high Schmid factor located near stiff grains with high elastic stiffness. Moreover, the spatial organization of channels in a single grain was analyzed; it was shown that secondary channels operating in the same slip plane as primary channels often appeared at the middle or at one third of the way between primary channels. The twinning nature of dislocation channels was analyzed for grains of different orientation using TEM. Finally, it was shown that in the AISI 304 steel, channels were twin-free in grains oriented close to [001] and [101] of standard unit triangle; [111]-grains and grains oriented close to Schmid factor maximum contained deformation twins.

  8. Ensemble Empirical Mode Decomposition based methodology for ultrasonic testing of coarse grain austenitic stainless steels.

    PubMed

    Sharma, Govind K; Kumar, Anish; Jayakumar, T; Purnachandra Rao, B; Mariyappa, N

    2015-03-01

    A signal processing methodology is proposed in this paper for effective reconstruction of ultrasonic signals in coarse grained high scattering austenitic stainless steel. The proposed methodology is comprised of the Ensemble Empirical Mode Decomposition (EEMD) processing of ultrasonic signals and application of signal minimisation algorithm on selected Intrinsic Mode Functions (IMFs) obtained by EEMD. The methodology is applied to ultrasonic signals obtained from austenitic stainless steel specimens of different grain size, with and without defects. The influence of probe frequency and data length of a signal on EEMD decomposition is also investigated. For a particular sampling rate and probe frequency, the same range of IMFs can be used to reconstruct the ultrasonic signal, irrespective of the grain size in the range of 30-210 μm investigated in this study. This methodology is successfully employed for detection of defects in a 50mm thick coarse grain austenitic stainless steel specimens. Signal to noise ratio improvement of better than 15 dB is observed for the ultrasonic signal obtained from a 25 mm deep flat bottom hole in 200 μm grain size specimen. For ultrasonic signals obtained from defects at different depths, a minimum of 7 dB extra enhancement in SNR is achieved as compared to the sum of selected IMF approach. The application of minimisation algorithm with EEMD processed signal in the proposed methodology proves to be effective for adaptive signal reconstruction with improved signal to noise ratio. This methodology was further employed for successful imaging of defects in a B-scan. PMID:25488024

  9. Quantitative metallographic method for determining delta ferrite content in austenitic stainless steels. Final report

    SciTech Connect

    Pressly, G.A.

    1986-01-01

    Delta ferrite is a magnetic form of iron and has a body centered cubic crystal structure. It is often present as a nonequilibrium phase in austenitic stainless steel welds, castings, and wrought materials. The ferrite content of austenitic stainless steel can directly affect its properties, especially weldability and formability. Therefore, it is highly desirable to be able to predict and/or measure the ferrite content accurately. Current magnetic ferrite measuring methods are not applicable when test materials are geometrically small (less than 2.54 mm thick and 6.35 mm wide). Therefore, a standard metallographic test method STM 00107-A was established to determine delta ferrite content in small weldments and base metals of austenitic stainless steel. This standard test method (STM 00107-A) was then performed on several exemplary metallographic specimens to illustrate its capabilities and applications. The results from the exemplary tests were compared and contrasted to metallographic manual point count measurements, Ferritescope measurements, and predicted values calculated from chemical analyses. By utilizing the manual metallographic point count data, an accuracy of +-16% and a precision of +-0.77% were determined for the standard test method. The comparison of Ferritescope data to standard test method revealed that the results obtained by the two methods are close at low (0 to 3%) ferrite contents and Ferritscope results are substantially greater at higher (6 to 10%) ferrite contents. The standard test method data compiled from the exemplary weld specimens was noted to be very similar to the predicted values calculated from chemical analyses. It was also shown that because the standard test method utilizes optics the morphology of the delta ferrite particles can be determined. This type of determination is possible only with metallographic methods.

  10. Laser etching of austenitic stainless steels for micro-structural evaluation

    NASA Astrophysics Data System (ADS)

    Baghra, Chetan; Kumar, Aniruddha; Sathe, D. B.; Bhatt, R. B.; Behere, P. G.; Afzal, Mohd

    2015-06-01

    Etching is a key step in metallography to reveal microstructure of polished specimen under an optical microscope. A conventional technique for producing micro-structural contrast is chemical etching. As an alternate, laser etching is investigated since it does not involve use of corrosive reagents and it can be carried out without any physical contact with sample. Laser induced etching technique will be beneficial especially in nuclear industry where materials, being radioactive in nature, are handled inside a glove box. In this paper, experimental results of pulsed Nd-YAG laser based etching of few austenitic stainless steels such as SS 304, SS 316 LN and SS alloy D9 which are chosen as structural material for fabrication of various components of upcoming Prototype Fast Breeder Reactor (PFBR) at Kalpakkam India were reported. Laser etching was done by irradiating samples using nanosecond pulsed Nd-YAG laser beam which was transported into glass paneled glove box using optics. Experiments were carried out to understand effect of laser beam parameters such as wavelength, fluence, pulse repetition rate and number of exposures required for etching of austenitic stainless steel samples. Laser etching of PFBR fuel tube and plug welded joint was also carried to evaluate base metal grain size, depth of fusion at welded joint and heat affected zone in the base metal. Experimental results demonstrated that pulsed Nd-YAG laser etching is a fast and effortless technique which can be effectively employed for non-contact remote etching of austenitic stainless steels for micro-structural evaluation.

  11. Creep and precipitation behaviors of AL6XN austenitic steel at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Meng, L. J.; Sun, J.; Xing, H.

    2012-08-01

    Creep behaviors of the solution-treated AL6XN austenitic stainless steel have been investigated at 873-1023 K and 120-260 MPa. The results showed that the creep stress exponent and activation energy of the AL6XN steel are 5 and 395.4 kJ/mol, respectively in the power-law breakdown regime. TEM observations revealed that dislocations distributed homogenously in grains. The creep deformation mechanism is mainly attributed to viscous dislocation glide. Precipitates in the steel after creep deformation were additionally analyzed by TEM, and the results showed that there are four different types of precipitates, such as M23C6, M6C, σ phase and Laves phase. The M23C6 carbides were observed at grain boundaries in the steel after creep at 873 K. The M6C, σ phase and Laves phase precipitates were found when the creep temperature increases to 923-1023 K. Although the AL6XN steel exhibited low steady state creep rates, a high volume fraction of brittle precipitates of σ and Laves phases reduced the creep lifetime of the steel at elevated temperatures.

  12. [Study on electrochemical mechanism of coronary stent used austenitic stainless steel in flowing artificial body fluid].

    PubMed

    Liang, Chenghao; Guo, Liang; Chen, Wan; Wang, Hua

    2005-08-01

    The electrochemical mechanism of austenitic stainless steel (SUS316L and SUS317L) coronary stents in flowing artificial body fluid has been investigated with electrochemical technologies. The results indicated that the flowing medium coursed the samples' pitting potential Eb shift negatively, increased the pitting corrosion sensitivity, accelerated its anodic dissolution, but had little effects on repassivated potential. The flowing environment had great effects on cathodic process. The oxygen reaction on the samples' surface became faster as the cathodic process was not controlled by oxygen diffusion but by mixed diffusion and electrochemical process. With the increase of velocity of solution, the pitting corrosion becomes liable to occur under this circumstance. PMID:16156260

  13. Effect of Nitrogen on Stress Corrosion Behavior of Austenitic Stainless Steels Using Electrochemical Noise Technique

    NASA Astrophysics Data System (ADS)

    Toppo, Anita; Pujar, M. G.; Mallika, C.; Kamachi Mudali, U.; Dayal, R. K.

    2015-03-01

    Stress corrosion cracking (SCC) studies were conducted on austenitic stainless steels with two different nitrogen contents (0.07 and 0.22 wt.% N) in boiling acidified sodium chloride medium using constant load technique. Progress of SCC was monitored using electrochemical noise (EN) technique to understand the effect of nitrogen addition on SCC initiation and propagation. With increase in nitrogen content, the characteristic frequency of corrosion events, f n increased, whereas the characteristic charge, q decreased simultaneously indicating the increased stability of passive film resulting in higher resistance to SCC.

  14. On the Cutting Performance of Coated HSS Taps When Machining of Austenitic Steel

    NASA Astrophysics Data System (ADS)

    Sliwkova, Petra; Piska, Miroslav

    2014-12-01

    The paper deals with a quality of the PVD coated HSS taps when cutting the stainless austenitic chromiumnickel non-stabilized steel DIN 1.4301 (X5CrNi 18-10). The main attention is focused on the analysis of loading (cutting moment, specific energy) of the HSS taps by means of pieso-electrical dynamometer Kistler 9272 and the relation between the quality of duplex and triplex PVD coatings and their effects on the quality of machined thread surfaces and tool life of the taps. The results showed a safe and stabilized cutting with acceptable quality of threads for HSSE with the TiN+TiCN+DLC coating.

  15. Grain Structure Development During Friction Stir Welding of Single-Crystal Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Jeon, Jong Jin; Mironov, Sergey; Sato, Yutaka S.; Kokawa, Hiroyuki; Park, Seung Hwan C.; Hirano, Satoshi

    2013-07-01

    The high-resolution electron backscatter diffraction (EBSD) technique was used to study the grain boundary development and texture evolution during friction stir welding (FSW) in a single-crystal austenitic stainless steel. Strain-induced crystal rotations were found to be induced by simple shear deformation. With the crystal rotations, the single-crystal structure was broken up into a fine-grained polycrystalline aggregate in the stir zone. This process was deduced to be governed by continuous and discontinuous recrystallizations operating during the FSW process. The final texture which evolved in the stir zone was dominated by A/bar{A}\\{ {111} \\} < 110 rangle ideal simple shear orientations.

  16. The calculation of T{sub {delta}} and V{sub {delta}} in austenitic steel

    SciTech Connect

    Dai Qixun; Yang Ruzeng

    1997-03-01

    The relation between the {gamma}/{gamma} + {delta} boundary temperature, T{sub {delta}}, of austenitic steels and the equivalent weights, [Cr] and [Ni], has been studied, as has the law of variation of the {delta} phase volume, V{sub {delta}}, with temperature. With the aid of a computer, the following regression expressions have been derived from the experimental results: T{sub {delta}} ({degree}C) =- T{sub 4} {minus} 21.2[Cr] + 15.8[Ni] {minus} 223; V{sub {delta}} (%) = 0.715 exp [0.015(T {minus} T{sub {delta}})]. Satisfactory results have been obtained by using these regression expressions.

  17. Transition in Failure Mechanism Under Cyclic Creep in 316LN Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Sarkar, Aritra; Nagesha, A.; Parameswaran, P.; Sandhya, R.; Mathew, M. D.

    2014-06-01

    Cyclic creep behavior of a type 316LN austenitic stainless steel was investigated in the temperature range from 823 K to 923 K (550 °C to 650 °C). A transition from fatigue-dominated to creep-dominated failure mode was observed with an increase in the mean stress. The threshold value of mean stress for the transition was seen to be a strong function of the test temperature. Occurrence of dynamic strain aging proved beneficial owing to a substantial reduction in the strain accumulation during cyclic loading.

  18. Fatigue damage evaluation of austenitic stainless steel using nonlinear ultrasonic waves in low cycle regime

    SciTech Connect

    Zhang, Jianfeng; Xuan, Fu-Zhen

    2014-05-28

    The interrupted low cycle fatigue test of austenitic stainless steel was conducted and the dislocation structure and fatigue damage was evaluated subsequently by using both transmission electron microscope and nonlinear ultrasonic wave techniques. A “mountain shape” correlation between the nonlinear acoustic parameter and the fatigue life fraction was achieved. This was ascribed to the generation and evolution of planar dislocation structure and nonplanar dislocation structure such as veins, walls, and cells. The “mountain shape” correlation was interpreted successfully by the combined contribution of dislocation monopole and dipole with an internal-stress dependent term of acoustic nonlinearity.

  19. Nanoscale-twinning-induced strengthening in austenitic stainless steel thin films

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Misra, A.; Wang, H.; Nastasi, M.; Embury, J. D.; Mitchell, T. E.; Hoagland, R. G.; Hirth, J. P.

    2004-02-01

    Magnetron-sputter-deposited austenitic 330 stainless steel (330 SS) films, several microns thick, were found to have a hardness ˜6.5 GPa, about an order of magnitude higher than bulk 330 SS. High-resolution transmission electron microscopy revealed that sputtered 330 SS coatings are heavily twinned on {111} with nanometer scale twin spacing. Molecular dynamics simulations show that, in the nanometer regime where plasticity is controlled by the motion of single rather than pile-ups of dislocations, twin boundaries are very strong obstacles to slip. These observations provide a new perspective to producing ultrahigh strength monolithic metals by utilizing growth twins with nanometer-scale spacing.

  20. Metallographic screening of grain boundary engineered type 304 austenitic stainless steel

    SciTech Connect

    Hanning, F. Engelberg, D.L.

    2014-08-15

    An electrochemical etching method for the identification of grain boundary engineered type 304 austenitic stainless steel microstructures is described. The method can be applied for rapid microstructure screening to complement electron backscatter diffraction analysis. A threshold parameter to identify grain boundary engineered microstructure is proposed, and the application of metallographic etching for characterising the degree of grain boundary engineering discussed. - Highlights: • As-received (annealed) and grain boundary engineered microstructures were compared. • Electro-chemical polarisation in nitric acid solutions was carried out. • A metallographic screening method has been developed. • The screening method complements EBSD analysis for microstructure identification.

  1. Reverse-Martensitic Hardening of Austenitic Stainless Steel upon Up-quenching

    NASA Astrophysics Data System (ADS)

    Sato, Kiminori; Guo, Defeng; Li, Xiaohong; Zhang, Xiangyi

    2016-08-01

    Reverse-martensitic transformation utilizing up-quenching was demonstrated for austenitic stainless steel. Up-quenching was done following the stress-induced phase modification to martensite and then enrichment of the body-centered-cubic ferrite. Transmission-electron-microscopy observation and Vickers hardness test revealed that the reverse-martensitic transformation yields quench hardening owing to an introduction of highly-concentrated dislocation. It is furthermore found that Cr precipitation on grain boundaries caused by isothermal aging is largely suppressed in the present approach.

  2. A new view of the ultrasonic behavior of cast austenitic steels

    SciTech Connect

    Beller, L.S.

    1986-01-01

    A three-dimensionally anisotropic model of the cast austenitics is proposed and tested experimentally. The model predicts unique propagation modes and directions, which are observed experimentally in centrifugally cast stainless steel (CCSS) specimens, but which are not predicted by the single- preferred-axis model. It accounts for a large share of the difficulties noted in ultrasonic inspection of these materials by conventional techniques. The model also suggests a technique for significant improvement in signal/noise ratio (SNR) and in apparent attenuation; this technique is demonstrated experimentally to give striking improvements in SNR. In addition, a number of previously anomalous behaviors are explained by this model. 10 refs., 6 figs.

  3. Structure and properties of a high-temperature austenitic steel at high temperatures

    NASA Astrophysics Data System (ADS)

    Kostina, M. V.; Skorobogatykh, V. N.; Tykochinskaya, T. V.; Nakhabina, M. S.; Nemov, V. V.; Bannykh, I. O.; Korneev, A. E.

    2010-11-01

    The structure of a high-temperature austenitic 12Kh15N16M2TR steel, which is promising for manufacturing steam superheater tubes, is studied after long-term thermal holding under stress. The type, morphology, and matrix arrangement of excess-phase particles that form during thermal holding are found. The structure of the alloy correlates with its high-temperature strength, and the mechanical properties obtained during short-time tensile tests in the temperature range 20-730°C are compared to the results of high-temperature strength tests.

  4. Hydrogen concentration gradients in cathodically charged austenitic stainless steel

    SciTech Connect

    Ulmer, D.G.; Altstetter, C.J.

    1987-05-01

    An x-ray diffraction technique has been developed to make in-situ measurements of hydrogen concentration profiles from which diffusivity and solubility values are calculated. Hydrogen is supplied to the metal surface by cathodically polarizing it in a bath of 1N H/sub 2/SO/sub 4/ electrolyte. The incident x-ray beam penetrates a thin layer of electrolyte solution at the surface of the sample, thus, x-ray diffraction profile changes can be recorded as a function of charging time and temperature. The applied potential prevents outgassing of the specimen during the measurement. The x-ray diffraction profiles are deconvoluted to remove the ..cap alpha../sub 1//..cap alpha../sub 2/ doublet and noncompositional broadening effects. Composition-depth profiles are then obtained from an intensity band transformation of the deconvoluted data. A diffusion coefficient is determined by fitting a solution to Fick's second law to the concentration-depth profile. The technique described here was used to measure hydrogen diffusivity in stainless steel in the temperature range 20/sup 0/--80 /sup 0/C.

  5. Microstructures and Mechanical Properties of Nano/Ultrafine-Grained N-Bearing, Low-Ni Austenitic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Saeedipour, S.; Kermanpur, A.; Najafizadeh, A.; Abbasi, M.

    2015-02-01

    The nitrogen (N)-bearing austenitic stainless steels are new materials with interesting mechanical properties such as high strength and ductility, desirable toughness and work hardening, and good corrosion resistance. This work attempted to investigate the effect of N addition from 0.08 to 0.35 wt.% on grain refinement of the 201L austenitic stainless steel using the martensite thermomechanical process. This process was composed of cold rolling up to the thickness reduction of 90 % followed by reversion annealing at 800 °C for 60 and 1800 s. It was found that increasing N content resulted in an increase in the austenite grain size for short annealing duration (e.g. 60 s), but caused a decrease in the austenite grain size for long annealing duration (e.g. 1800 s). The smallest austenite grain size of about 150 nm was achieved for the 201L steel containing 0.08 wt.% N after reversion annealing at 800 °C for 60 s. The mechanical properties of the reversion-annealed N-bearing steels were enhanced due to both N alloying and grain refinement.

  6. Irradiation assisted stress corrosion cracking of austenitic stainless steels

    SciTech Connect

    Was, G.S.; Atzmon, M.

    1990-06-01

    Samples of ultra high purity stainless steel have been fabricated into 2mm {times} 2mm rectangular bars and irradiated to one dpa ({approximately}l {times} 10{sup 19} p{sup +}/cm{sup 2}) using 3.4 MeV protons (>20{mu}A) while controlling the sample temperature at 400{degree}C. Samples are pressed onto a water-cooled and electrically heated copper block with a thin layer of Sn in between to improve thermal conductivity. The irradiation produced a significant prompt radiation field but sample activation was limited to {beta}-decay and this decayed rapidly in less than 48 h. Samples were hydrogen charged and strained at slow rates at {minus}30{degree}C insitu in the Auger electron spectrometer to successfully fracture several samples intergranularly for grain boundary composition analysis. An ultra-high purity (UHP) alloy of Fe-19Cr-9Ni was irradiated to 1 dpa at 400C {plus minus} 5C and 7 {times} 10{sup {minus}9} torr in the tandem accelerator of the Michigan Ion Beam Laboratory, resulting in a dislocation network density of 1.8 {times} 10{sup 9} cm{sup 2} and a dislocation loop density of 7 {times} 10{sup 16} cm{sup {minus}3} along with the dissolution of small precipitates present in the unirradiated sample. EPR experiments on the UHP irradiated alloy showed no significant increase in charge passed upon reactivation, over an unirradiated sample experiencing the same thermal history. An SCC waterloop and autoclave system has been completed and a sample has been designed to measure the susceptibility of the irradiated microstructure as compared to the unirradiated microstructure.

  7. Automated GMA welding of austenitic stainless steel pipe

    SciTech Connect

    Tahash, G.J.

    1996-12-31

    The study focused on reducing weld cycle times of rotatable subassemblies (spools) using automated welding equipment. A unique automatic Gas Metal Arc Welding (GMAW) system was used to produce a series of pipe to pipe welds on 141 mm (5 in.) schedule 80 seamless stainless steel pipe. After manual tack welding, the adaptive control system welded the root pass of the argon gas backed open vee groove circumferential butt joints in the IG rotated position with short circuiting transfer GMAW. The fill and cover passes were welded automatically with spray transfer GMAW. Automatic welding cycle times were found to be 50--80 percent shorter than the current techniques of roll welding with Shielded Metal Arc Welding and manual Gas Tungsten Arc Welding. Weld costs ({Brit_pounds}/m), including amortization, for the various systems were compared. The cost of automated GMA welds was virtually equivalent to the most competitive methods while depositing 75% more filler metal per year. Also investigated were metallurgical effects generated by weld thermal cycling, and the associated effects on mechanical properties of the weld joint. Mechanical properties of the welds met or exceeded those of the base metal. Sensitization of the pipe did not occur in the heat affected zone (HAZ), based on the absence of evidence of intergranular attack in modified Strauss corrosion tests and despite the fact of interpass temperatures well above recommended maximums. Cooling rates of 3--5 C/s in the heat affected zone of the four pass welds were measured by thermocouple technique and found to be within the non-sensitizing range for this alloy.

  8. Capabilities of Ultrasonic Phased Arrays for Far-Side Examinations of Austenitic Stainless Steel Piping Welds

    SciTech Connect

    Anderson, Michael T.; Cumblidge, Stephen E.; Doctor, Steven R.

    2006-10-01

    A study was conducted to assess the ability of advanced ultrasonic techniques to detect and accurately determine the size of flaws from the far-side of wrought austenitic piping welds. Far-side inspections of nuclear system austenitic piping welds are currently performed on a “best effort” basis and do not conform to ASME Code Section XI Appendix VIII performance demonstration requirements for near side inspection. For this study, four circumferential welds in 610mm (24inch) diameter, 36mm (1.42inch) thick ASTM A-358, Grade 304 vintage austenitic stainless steel pipe were examined. The welds were fabricated with varied welding parameters; both horizontal and vertical pipe orientations were used, with air and water backing, to simulate field welding conditions. A series of saw cuts, electro-discharge machined (EDM) notches, and implanted fatigue cracks were placed into the heat affected zones of the welds. The saw cuts and notches ranged in depth from 7.5% to 28.4% through-wall. The implanted cracks ranged in depth from 5% through-wall to 64% through-wall. The welds were examined with phased array technology at 2.0 MHz, and compared to conventional ultrasonic techniques as a baseline. The examinations showed that phased-array methods were able to detect and accurately length-size, but not depth size, the notches and flaws through the welds. The ultrasonic results were insensitive to the different welding techniques used in each weld.

  9. Development and Exploratory Scale-Up of Alumina-Forming Austenitic (AFA) Stainless Steels

    SciTech Connect

    Brady, Michael P; Magee, John H; Yamamoto, Yukinori; Maziasz, Philip J; Santella, Michael L; Pint, Bruce A; Bei, Hongbin

    2009-01-01

    This paper presents the results of the continued development of creep-resistant, alumina-forming austenitic (AFA) stainless steel alloys, which exhibit a unique combination of excellent oxidation resistance via protective alumina (Al2O3) scale formation and high-temperature creep strength through the formation of stable nano-scale MC carbides and intermetallic precipitates. Efforts in fiscal year 2009 focused on the characterization and understanding of long-term oxidation resistance and tensile properties as a function of alloy composition and microstructure. Computational thermodynamic calculations of the austenitic matrix phase composition and the volume fraction of MC, B2-NiAl, and Fe2(Mo,Nb) base Laves phase precipitates were used to interpret oxidation behavior. Of particular interest was the enrichment of Cr in the austenitic matrix phase by additions of Nb, which aided the establishment and maintenance of alumina. Higher levels of Nb additions also increased the volume fraction of B2-NiAl precipitates, which served as an Al reservoir during long-term oxidation. Ageing studies of AFA alloys were conducted at 750C for times up to 2000 h. Ageing resulted in near doubling of yield strength at room temperature after only 50 h at 750C, with little further increase in yield strength out to 2000 h of ageing. Elongation was reduced on ageing; however, levels of 15-25% were retained at room temperature after 2000 h of total ageing.

  10. High Nb, Ta, and Al creep- and oxidation-resistant austenitic stainless steel

    DOEpatents

    Brady, Michael P [Oak Ridge, TN; Santella, Michael L [Knoxville, TN; Yamamoto, Yukinori [Oak Ridge, TN; Liu, Chain-tsuan [Oak Ridge, TN

    2010-07-13

    An austenitic stainless steel HTUPS alloy includes, in weight percent: 15 to 30 Ni; 10 to 15 Cr; 2 to 5 Al; 0.6 to 5 total of at least one of Nb and Ta; no more than 0.3 of combined Ti+V; up to 3 Mo; up to 3 Co; up to 1 W; up to 0.5 Cu; up to 4 Mn; up to 1 Si; 0.05 to 0.15 C; up to 0.15 B; up to 0.05 P; up to 1 total of at least one of Y, La, Ce, Hf, and Zr; less than 0.05 N; and base Fe, wherein the weight percent Fe is greater than the weight percent Ni wherein said alloy forms an external continuous scale comprising alumina, nanometer scale sized particles distributed throughout the microstructure, said particles comprising at least one composition selected from the group consisting of NbC and TaC, and a stable essentially single phase fcc austenitic matrix microstructure, said austenitic matrix being essentially delta-ferrite-free and essentially BCC-phase-free.

  11. Control of cryogenic intergranular fracture in high-manganese austenitic steels

    SciTech Connect

    Strum, M.J.

    1986-12-01

    The sources of cryogenic intergranular embrittlement in high-Mn austenitic steels and the conditions necessary for its control are examined. It is shown that the high-Mn alloys are inherently susceptible to intergranular embrittlement due to both their low grain boundary cohesion and heterogeneous deformation characteristics. Extrinsic sources of embrittlement which could account for the transition behavior are not observed. An Auger electron spectroscopy (AES) study shows no indication of impurity-segregation-induced embrittlement. No grain boundary precipitation is observed, and austenite stabilization does not ensure ductile fracture. The influence of chemistry modifications on the ductile-to-brittle transition behavior were also examined through additions of N, Cr, and C to binary Fe-31 Mn. Nitrogen additions increase the 77K yield strength at a rate of 2200 MPa per weight percent N, and increase the austenite stability, but also increase the susceptibility of ternary alloys to intergranular fracture. Quaternary Cr additions are effective in increasing the N solubility, and lower the transition temperature. Carbon additions result in complete suppression of intergranular fracture at 77K. Qualitatively significant changes in the deformation heterogeneity with chemistry modifications are not observed. The temper-toughening of Fe-Mn-Cr-N alloys is associated with the grain boundary segregation of boron and the redistribution of N. Both boron and carbon are expected to inhibit intergranular fracture through increases in grain boundary cohesion.

  12. Mechanical Properties of High Manganese Austenitic Stainless Steel JK2LB for ITER Central Solenoid Jacket Material

    NASA Astrophysics Data System (ADS)

    Saito, Toru; Kawano, Katsumi; Yamazaki, Toru; Ozeki, Hidemasa; Isono, Takaaki; Hamada, Kazuya; Devred, Arnaud; Vostner, Alexander

    A suite of advanced austenitic stainless steels are used for the ITER TF, CS and PF coil systems.These materials will be exposed to cyclic-stress at cryogenic temperature. Therefore, high manganese austenitic stainless steel JK2LB, which has high tensile strength, high ductility and high resistance to fatigue at 4 K has been chosen for the CS conductor. The cryogenic temperature mechanical property data of this material are very important for the ITER magnet design. This study is focused on mechanical characteristics of JK2LB and its weld joint.

  13. Features of structure-phase transformations and segregation processes under irradiation of austenitic and ferritic-martensitic steels

    NASA Astrophysics Data System (ADS)

    Neklyudov, I. M.; Voyevodin, V. N.

    1994-09-01

    The difference between crystal lattices of austenitic and ferritic steels leads to distinctive features in mechanisms of physical-mechanical change. This paper presents the results of investigations of dislocation structure and phase evolution, and segregation phenomena in austenitic and ferritic-martensitic steels and alloys during irradiation with heavy ions in the ESUVI and UTI accelerators and by neutrons in fast reactors BOR-60 and BN-600. The influence of different factors (including different alloying elements) on processes of structure-phase transformation was studied.

  14. In Situ Thermo-magnetic Investigation of the Austenitic Phase During Tempering of a 13Cr6Ni2Mo Supermartensitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Bojack, A.; Zhao, L.; Morris, P. F.; Sietsma, J.

    2014-09-01

    The formation of austenite during tempering of a 13Cr6Ni2Mo supermartensitic stainless steel (X2CrNiMoV13-5-2) was investigated using an in situ thermo-magnetic technique to establish the kinetics of the martensite to austenite transformation and the stability of austenite. The austenite fraction was obtained from in situ magnetization measurements. It was found that during heating to the tempering temperature 1 to 2 vol pct of austenite, retained during quenching after the austenitization treatment, decomposed between 623 K and 753 K (350 °C and 480 °C). The activation energy for martensite to austenite transformation was found by JMAK-fitting to be 233 kJ/mol. This value is similar to the activation energy for Ni and Mn diffusion in iron and supports the assumption that partitioning of Ni and Mn to austenite are mainly rate determining for the austenite formation during tempering. This also indicates that the stability of austenite during cooling after tempering depends on these elements. With increasing tempering temperature the thermal stability of austenite is decreasing due to the lower concentrations of austenite-stabilizing elements in the increased fraction of austenite. After cooling from the tempering temperature the retained austenite was further partially decomposed during holding at room temperature. This appears to be related to previous martensite formation during cooling.

  15. In Situ Thermo-magnetic Investigation of the Austenitic Phase During Tempering of a 13Cr6Ni2Mo Supermartensitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Bojack, A.; Zhao, L.; Morris, P. F.; Sietsma, J.

    2014-12-01

    The formation of austenite during tempering of a 13Cr6Ni2Mo supermartensitic stainless steel (X2CrNiMoV13-5-2) was investigated using an in situ thermo-magnetic technique to establish the kinetics of the martensite to austenite transformation and the stability of austenite. The austenite fraction was obtained from in situ magnetization measurements. It was found that during heating to the tempering temperature 1 to 2 vol pct of austenite, retained during quenching after the austenitization treatment, decomposed between 623 K and 753 K (350 °C and 480 °C). The activation energy for martensite to austenite transformation was found by JMAK-fitting to be 233 kJ/mol. This value is similar to the activation energy for Ni and Mn diffusion in iron and supports the assumption that partitioning of Ni and Mn to austenite are mainly rate determining for the austenite formation during tempering. This also indicates that the stability of austenite during cooling after tempering depends on these elements. With increasing tempering temperature the thermal stability of austenite is decreasing due to the lower concentrations of austenite-stabilizing elements in the increased fraction of austenite. After cooling from the tempering temperature the retained austenite was further partially decomposed during holding at room temperature. This appears to be related to previous martensite formation during cooling.

  16. Characterization of microstructure and texture across dissimilar super duplex/austenitic stainless steel weldment joint by super duplex filler metal

    SciTech Connect

    Eghlimi, Abbas; Shamanian, Morteza; Eskandarian, Masoomeh; Zabolian, Azam; Szpunar, Jerzy A.

    2015-08-15

    In the present paper, microstructural changes across an as-welded dissimilar austenitic/duplex stainless steel couple welded by a super duplex stainless steel filler metal using gas tungsten arc welding process is characterized with optical microscopy and electron back-scattered diffraction techniques. Accordingly, variations of microstructure, texture, and grain boundary character distribution of base metals, heat affected zones, and weld metal were investigated. The results showed that the weld metal, which was composed of Widmanstätten austenite side-plates and allotriomorphic grain boundary austenite morphologies, had the weakest texture and was dominated by low angle boundaries. The welding process increased the ferrite content but decreased the texture intensity at the heat affected zone of the super duplex stainless steel base metal. In addition, through partial ferritization, it changed the morphology of elongated grains of the rolled microstructure to twinned partially transformed austenite plateaus scattered between ferrite textured colonies. However, the texture of the austenitic stainless steel heat affected zone was strengthened via encouraging recrystallization and formation of annealing twins. At both interfaces, an increase in the special character coincident site lattice boundaries of the primary phase as well as a strong texture with <100> orientation, mainly of Goss component, was observed. - Graphical abstract: Display Omitted - Highlights: • Weld metal showed local orientation at microscale but random texture at macroscale. • Intensification of <100> orientated grains was observed adjacent to the fusion lines. • The austenite texture was weaker than that of the ferrite in all duplex regions. • Welding caused twinned partially transformed austenites to form at SDSS HAZ. • At both interfaces, the ratio of special CSL boundaries of the primary phase increased.

  17. Microstructural and Texture Development in Two Austenitic Steels with High-Manganese Content

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Basudev; Ray, Ranjit Kumar; Leffers, Torben

    2015-11-01

    Two austenitic steels, Fe-21.3Mn-3.44Si-3.74Al-0.5C and Fe-29.8Mn-2.96Si-2.73Al-0.52C, were subjected to cold rolling with 30 to 80 pct reduction with an increment of 10 pct and subsequently the development of their microstructures and textures were studied. The overall texture after 80 pct cold reduction was Brass type. A weak Copper component {112}<111> was present at the early stage of deformation, which disappeared completely after 60 pct cold reduction. Extensive shear banding took place in both the steels, right from rather low cold rolling levels, which became more prominent at higher amounts of cold rolling. Formation of twin bands, along with cellular dislocation network, was observed in Steel A after 30 pct cold rolling. In case of Steel B, denser twin bands and dislocation cellular network were observed in early stage of deformation. After 80 pct cold reduction, the development of a strong brass-type texture in both the steels could be attributed predominantly to the formation of shear banding, possibly with some partial contribution coming from micro twinning.

  18. Advanced characterizations of austenitic oxide dispersion-strengthened (ODS) steels for high-temperature reactor applications

    NASA Astrophysics Data System (ADS)

    Miao, Yinbin

    Future advanced nuclear systems involve higher operation temperatures, intenser neutron flux, and more aggressive coolants, calling for structural materials with excellent performances in multiple aspects. Embedded with densely and dispersedly distributed oxide nanoparticles that are capable of not only pinning dislocations but also trapping radiation-induced defects, oxide dispersion-strengthened (ODS) steels provide excellence in mechanical strength, creep resistance, and radiation tolerance. In order to develop ODS steels with qualifications required by advanced nuclear applications, it is important to understand the fundamental mechanisms of the enhancement of ODS steels in mechanical properties. In this dissertation, a series of austenitic ODS stainless steels were investigated by coordinated state-of-the-art techniques. A series of different precipitate phases, including multiple Y-Ti-O, Y-Al-O, and Y-Ti-Hf-O complex oxides, were observed to form during mechanical alloying. Small precipitates are likely to have coherent or cubic-on-cubic orientation relationships with the matrix, allowing the dislocation to shear through. The Orowan looping mechanism is the dominant particle-dislocation interaction mode as the temperature is low, whereas the shearing mechanism and the Hirsch mechanism are also observed. Interactions between the particles and the dislocations result in the load-partitioning phenomenon. Smaller particles were found to have the stronger loading-partitioning effect. More importantly, the load-partitioning of large size particles are marginal at elevated temperatures, while the small size particles remain sustaining higher load, explaining the excellent high temperature mechanical performance of ODS steels.

  19. Effects of LWR coolant environments on fatigue lives of austenitic stainless steels

    SciTech Connect

    Chopra, O.K.; Gavenda, D.J.

    1997-07-01

    The ASME Boiler and Pressure Vessel Code fatigue design curves for structural materials do not explicitly address the effects of reactor coolant environments on fatigue life. Recent test data indicate a significant decrease in fatigue life of pressure vessel and piping materials in light water reactor (LWR) environments. Fatigue tests have been conducted on Types 304 and 316NG stainless steel in air and LWR environments to evaluate the effects of various material and loading variables, e.g., steel type, strain rate, dissolved oxygen (DO) in water, and strain range, on fatigue lives of these steels. The results confirm the significant decrease in fatigue life in water. The environmentally assisted decrease in fatigue life depends both on strain rate and DO content in water. A decrease in strain rate from 0.4 to 0.004%/s decreases fatigue life by a factor of {approx} 8. However, unlike carbon and low-alloy steels, environmental effects are more pronounced in low-DO than in high-DO water. At {approx} 0.004%/s strain rate, reduction in fatigue life in water containing <10 ppb D is greater by a factor of {approx} 2 than in water containing {ge} 200 ppb DO. Experimental results have been compared with estimates of fatigue life based on the statistical model. The formation and growth of fatigue cracks in austenitic stainless steels in air and LWR environments are discussed.

  20. Structure and composition of phases occurring in austenitic stainless steels in thermal and irradiation environments

    SciTech Connect

    Lee, E.H.; Maziasz, P.J.; Rowcliffe, A.F.

    1980-01-01

    Transmission electron diffraction techniques coupled with quantitative x-ray energy dispersive spectroscopy have been used to characterize the phases which develop in austenitic stainless steels during exposure to thermal and to irradiation environments. In AISI 316 and Ti-modified stainless steels some thirteen phases have been identified and characterized in terms of their crystal structure and chemical composition. Irradiation does not produce any completely new phases. However, as a result of radiation-induced segregation principally of Ni and Si, and of enhanced diffusion rates, several major changes in phase relationships occur during irradiation. Firstly, phases characteristic of remote regions of the phase diagram appear unexpectedly and dissolve during postirradiation annealing (radiation-induced phases). Secondly, some phases develop with their compositions significantly altered by the incorporation of Ni or Si (radiation-modified phases).

  1. Tensile properties and damage microstructures in ORR/HFIR-irradiated austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Wakai, E.; Hashimoto, N.; Robertson, J. P.; Jistukawa, S.; Sawai, T.; Hishinuma, A.

    2000-12-01

    The synergistic effect of displacement damage and helium generation under neutron irradiation on tensile behavior and microstructures of austenitic stainless steels was investigated. The steels were irradiated at 400°C in the spectrally-tailored (ST) Oak Ridge research reactor/high flux isotope reactor (ORR/HFIR) capsule to 17 dpa with a helium production of about 200 appm and in the HFIR target capsule to 21 and 34 dpa with 1590 and 2500 appm He, respectively. The increase of yield strength in the target irradiation was larger than that in the ST irradiation because of the high-number density of Frank loops, bubbles, voids, and carbides. Based on the theory of dispersed barrier hardening, the strengths evaluated from these clusters coincide with the measured increase of yield strengths. This analysis suggests that the main factors of radiation hardening in the ST and the target irradiation at 400°C are Frank-type loops and cavities, respectively.

  2. Thick-section Laser and Hybrid Welding of Austenitic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Kujanpää, Veli

    Austenitic stainless steels are generally known to have very good laser weldability, when ordinary grades of sheets are concerned. But it is not necessarily the case, if special grades of fully austenitic structures with e.g. high molybdenum, or thick-section are used. It is also known that hot cracking susceptibility is strictly controlled by composition and welding parameters. If solidification is primary ferritic, hot cracking resistance is dramatically increased. It is also well known that laser welding needs a careful control of weld edge preparation and air gap between the edges. The dependence on edge quality can be decreased by using filler metal, either cold wire, hot wire or hybrid laser-arc welding. An additional role is high molybdenum contents where micro segregation can cause low local contents in weld which can decrease the corrosion properties, if filler metal is not used. Another feature in laser welding is its incomplete mixing, especially in thick section applications. It causes inhomogeneity, which can make uneven microstructure, as well as uneven mechanical and corrosion properties In this presentation the features of laser welding of thick section austenitic stainless steels are highlighted. Thick section (up to 60 mm) can be made by multi-pass laser or laser hybrid welding. In addition to using filler metal, it requires careful joint figure planning, laser head planning, weld parameter planning, weld filler metal selection, non-destructive and destructive testing and metallography to guarantee high-quality welds in practice. In addition some tests with micro segregation is presented. Also some examples of incomplete mixing is presented.

  3. Mechanical and microstructural aspects of severe plastic deformation of austenitic steel

    NASA Astrophysics Data System (ADS)

    Rodak, K.; Pawlicki, J.; Tkocz, M.

    2012-05-01

    The paper presents the effects of severe plastic deformation by multiple compression in the orthogonal directions on the microstructure and the mechanical properties of austenitic steel. Several deformation variants were conducted with different number of passes. FEM simulations were performed in order to evaluate the actual values of the effective strain in the examined, central parts of the compressed samples. The deformed microstructure was investigated by means of the scanning transmission electron microscopy (STEM) and the scanning electron microscopy (SEM) supported by the electron back scattered diffraction (EBSD). X-ray phase analysis was performed to evaluate the martensite volume fraction. The mechanical properties were determined by means of the digital image correlation method and hardness testing. It is shown that the applied forming technique leads to strong grain refinement in the austenitic steel. Moreover, deformation induces the martensitic γ- α' transformation. The microstructural changes cause an improvement in the strength properties. The material exhibits the ultimate tensile strength of 1560 MPa and the yield stress of 1500 MPa after reaching the effective strain of 10.

  4. Estimation of Fatigue Damage for AN Austenitic Stainless Steel (SUS304) Using a Pancake Type Coil

    NASA Astrophysics Data System (ADS)

    Oka, M.; Tsuchida, Y.; Nagato, S.; Yakushiji, T.; Enokizono, M.

    2008-02-01

    There are some fatigue damage estimation methods of an austenitic stainless steel that uses martensitic transformation. For instance, those are the remanent magnetization method, the excitation method, and so on. Those two methods are researched also in our laboratory now. In the remanent magnetization method, it is well known that the relationship between fatigue damage and the remanent magnetization is simple, clear, and reproducible. However, this method has the disadvantage to need a special magnetizer. Then, this method cannot be easily used at the job site such as the factory. On the other hand, as the special magnetizer is unnecessary, the excitation method can be easily used at the job site. But, this method has some disadvantages shown as follows. For instance, the output signal of this method is small. And the surface state of the specimen strongly influences the noise component of the output signal. It is well known that the inductance of a pancake type coil put on the metallic specimen changes according to the electromagnetic properties of the metallic specimen. In this paper, the method of evaluation of fatigue damage of an austenitic stainless steel (SUS304) by using a change of an inductance of a pancake type coil is shown. In addition, the fatigue evaluation performance of this method is described.

  5. Evaluation of Giga-cycle Fatigue Properties of Austenitic Stainless Steels Using Ultrasonic Fatigue Test

    NASA Astrophysics Data System (ADS)

    Takahashi, Kyouhei; Ogawa, Takeshi

    Ultrasonic fatigue tests have been performed in austenitic stainless steel, SUS316NG, in order to investigate giga-cycle fatigue strength of pre-strained materials, i.e. 5, 10 and 20% tensile pre-strains and -20% compressive pre-strain. The pre-strains were applied before specimen machining. The austenitic stainless steels are known to exhibit remarkable self-heating during the fatigue experiment. Therefore, heat radiation method was established by setting fatigue specimens in a low temperature chamber at about -100°C. The self-heating was controlled by intermittent loading condition, which enabled us to maintain the test section of the specimens at about room temperature. The results revealed that the fatigue strength increased with increasing pre-strain levels. Fish-eye fracture was observed for -20% pre-strained specimen fractured at 4.11×107 cycles, while the other specimens exhibited ordinary fatigue fracture surface originated from stage I facet on the specimen surface. The increase in fatigue limit was predicted by Vickers hardness, HV, which depended on the size of indented region. The prediction was successful using HV values obtained by the size of the indented region similar to those of the stage I facets.

  6. Mechanical and metallurgical properties of ion-nitrided austenitic-stainless steel welds

    NASA Astrophysics Data System (ADS)

    Çetinarslan, C. S.; Sahin, M.; Karaman Genç, S.; Sevil, C.

    2012-12-01

    Ion nitriding is an operation widely used in industry to harden materials surface. Nowadays, friction welding is one of the special welding methods used for welding the same or different kinds of materials. Especially in industry, it can be necessary to use materials after having operated them with different techniques or to use materials obtained by different manufacturing techniques. Investigating the mechanical and metallurgical properties of this kind of materials can be crucial. In this study, austenitic-stainless steel was used as an experimental material. Additionally, the samples of austenitic stainless steel with a diameter of 10 mm were joined by friction welding. The samples were subjected to ion nitriding process at 550 °C for 24 and 60 h. Then, tensile, fatigue, notch-impact and hardness tests were applied to the weldless and welded parts, and metallographic examinations were carried out. It was found that chromium and iron nitrides precipitated along the grain boundaries and in the middle of the grains. Spectrum patterns revealed that the most dominant phases resulted from the formation of CrN, Fe4N and Fe3N. However, the tests revealed that high temperature and longer time of ion nitriding caused a decrease in the values of fatigue and tensile strengths as well as in the notch-impact toughness in the ion nitrided joints.

  7. The microstructural, mechanical, and fracture properties of austenitic stainless steel alloyed with gallium

    NASA Astrophysics Data System (ADS)

    Kolman, D. G.; Bingert, J. F.; Field, R. D.

    2004-11-01

    The mechanical and fracture properties of austenitic stainless steels (SSs) alloyed with gallium require assessment in order to determine the likelihood of premature storage-container failure following Ga uptake. AISI 304 L SS was cast with 1, 3, 6, 9, and 12 wt pct Ga. Increased Ga concentration promoted duplex microstructure formation with the ferritic phase having a nearly identical composition to the austenitic phase. Room-temperature tests indicated that small additions of Ga (less than 3 wt pct) were beneficial to the mechanical behavior of 304 L SS but that 12 wt pct Ga resulted in a 95 pct loss in ductility. Small additions of Ga are beneficial to the cracking resistance of stainless steel. Elastic-plastic fracture mechanics analysis indicated that 3 wt pct Ga alloys showed the greatest resistance to crack initiation and propagation as measured by fatigue crack growth rate, fracture toughness, and tearing modulus. The 12 wt pct Ga alloys were least resistant to crack initiation and propagation and these alloys primarily failed by transgranular cleavage. It is hypothesized that Ga metal embrittlement is partially responsible for increased embrittlement.

  8. Carburization behavior of AISI 316LN austenitic stainless steel - Experimental studies and modeling

    NASA Astrophysics Data System (ADS)

    Sudha, C.; Sivai Bharasi, N.; Anand, R.; Shaikh, H.; Dayal, R. K.; Vijayalakshmi, M.

    2010-07-01

    AISI type 316LN austenitic stainless steel was exposed to flowing sodium at 798 K for 16,000 h in the bi-metallic (BIM) sodium loop. A modified surface layer of 10 μm width having a ferrite structure was detected from X-ray diffraction and electron micro probe based analysis. Beneath the modified surface layer a carburized zone of 60 μm width was identified which was found to consist of M 23C 6 carbides. A mathematical model based on finite difference technique was developed to predict the carburization profiles in sodium exposed austenitic stainless steel. In the computation, effect of only chromium on carbon diffusion was considered. Amount of carbon remaining in solution was determined from the solubility parameter. The predicted profile showed a reasonably good match with the experimental profile. Calculations were extended to simulate the thickness of the carburized layer after exposure to sodium for a period of 40 years. Attempt was also made to predict the carburization profiles based on equilibrium calculations using Dictra and Thermocalc which contain both thermodynamic and kinetic databases for the system under consideration.

  9. Analysis of tensile deformation and failure in austenitic stainless steels: Part II - Irradiation dose dependence

    NASA Astrophysics Data System (ADS)

    Kim, Jin Weon; Byun, Thak Sang

    2010-01-01

    Irradiation effects on the stable and unstable deformation and fracture behavior of austenitic stainless steels (SSs) have been studied in detail based on the equivalent true stress versus true strain curves. An iterative finite element simulation technique was used to obtain the equivalent true stress-true strain data from experimental tensile curves. The simulation result showed that the austenitic stainless steels retained high strain hardening rate during unstable deformation even after significant irradiation. The strain hardening rate was independent of irradiation dose up to the initiation of a localized necking. Similarly, the equivalent fracture stress was nearly independent of dose before the damage (embrittlement) mechanism changed. The fracture strain and tensile fracture energy decreased with dose mostly in the low dose range <˜2 dpa and reached nearly saturation values at higher doses. It was also found that the fracture properties for EC316LN SS were less sensitive to irradiation than those for 316 SS, although their uniform tensile properties showed almost the same dose dependencies. It was confirmed that the dose dependence of tensile fracture properties evaluated by the linear approximation model for nominal stress was accurate enough for practical use without elaborate calculations.

  10. Corrosion properties of S-phase layers formed on medical grade austenitic stainless steel.

    PubMed

    Buhagiar, Joseph; Dong, Hanshan

    2012-02-01

    The corrosion properties of S-phase surface layers formed in AISI 316LVM (ASTM F138) and High-N (ASTM F1586) medical grade austenitic stainless steels by plasma surface alloying with nitrogen (at 430°C), carbon (at 500°C) and both carbon and nitrogen (at 430°C) has been investigated. The corrosion behaviour of the S-phase layers in Ringer's solutions was evaluated using potentiodynamic and immersion corrosion tests. The corrosion damage was evaluated using microscopy, hardness testing, inductive coupled plasma mass spectroscopy and X-ray diffraction. The experimental results have demonstrated that low-temperature nitriding, carburising and carbonitriding can improve the localised corrosion resistance of both industrial and medical grade austenitic stainless steels as long as the threshold sensitisation temperature is not reached. Carburising at 500°C has proved to be the best hardening treatment with the least effect on the corrosion resistance of the parent alloy. PMID:22160745

  11. Defect structures before steady-state void growth in austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Yoshiie, T.; Sato, K.; Cao, X.; Xu, Q.; Horiki, M.; Troev, T. D.

    2012-10-01

    In the radiation damage process of austenitic stainless steels, there exists an incubation period before steady-state void growth, and the defect formation behaviors during that period strongly depend on alloy composition. Using the technique of positron annihilation lifetime measurement, the evolution of defect clusters during the incubation period in neutron, electron, and H-ion irradiations was studied for a variety of austenitic stainless steels including commercial and model alloys. The lifetime measurements indicated that in fission neutron irradiation to 0.2 dpa at 363 K, single vacancies were predominantly formed in the commercial alloys, SUS316L and Ti added, modified SUS316, while large voids were formed in Ni and Fe-Cr-Ni. After neutron irradiation at 573 K, stacking fault tetrahedra and/or precipitates were detected in the commercial alloys, while large voids were detected in the model alloys. In the 30 MeV electron irradiation to a dose of 0.012 dpa, the effect of alloying elements on lifetime data was less significant at 353 K, but a significant difference was found between model alloys and commercial alloys at 573 K. The H-ion irradiation at 2 MeV was also performed at room temperature. Defect evolution during the incubation period is discussed on the basis of the neutron, electron and H-ion irradiation results.

  12. A Method to Estimate Residual Stress in Austenitic Stainless Steel Using a Microindentation Test

    NASA Astrophysics Data System (ADS)

    Yonezu, Akio; Kusano, Ryota; Hiyoshi, Tomohiro; Chen, Xi

    2015-01-01

    This study proposed a method to evaluate the residual stress and plastic strain of an austenitic stainless steel using a microindentation test. The austenitic stainless steel SUS316L obeys the Ludwick's work hardening law and is subjected to in-plane equi-biaxial residual stress. A numerical experiment with the finite element method (FEM) was carried out to simulate an indentation test for SUS316L having various plastic strains (pre-strains) and residual stresses. It was found that the indentation force increased with increasing pre-strain as well as with compressive residual stress. Next, a parametric FEM study by changing both residual stress σres and pre-strain ɛpre was conducted to deduce the relationship between the indentation curve and the parameters ɛpre and σres (which were employed for the FEM study). This relationship can be expressed by a dimensionless function with simple formulae. Thus, the present method can estimate both ɛpre and σres, when a single indentation test is applied to SUS316L.

  13. The Effects of Austenitizing Conditions on the Microstructure and Wear Resistance of a Centrifugally Cast High-Speed Steel Roll

    NASA Astrophysics Data System (ADS)

    Kang, Minwoo; Lee, Young-Kook

    2016-04-01

    The influences of austenitizing conditions on the microstructure and wear resistance of a centrifugally cast high-speed steel roll were investigated through thermodynamic calculation, microstructural analysis, and high-temperature wear tests. When the austenitizing temperature was between 1323 K and 1423 K (1050 °C and 1150 °C), coarse eutectic M2C plates were decomposed into a mixture of MC and M6C particles. However, at 1473 K (1200 °C), the M2C plates were first replaced by both new austenite grains and MC particles without M6C particles, and then remaining M2C particles were dissolved during the growth of MC particles. The wear resistance of the HSS roll was improved with increasing austenitizing temperature up to 1473 K (1200 °C) because the coarse eutectic M2C plates, which are vulnerable to crack propagation, changed to disconnected hard M6C and MC particles.

  14. The Effects of Austenitizing Conditions on the Microstructure and Wear Resistance of a Centrifugally Cast High-Speed Steel Roll

    NASA Astrophysics Data System (ADS)

    Kang, Minwoo; Lee, Young-Kook

    2016-07-01

    The influences of austenitizing conditions on the microstructure and wear resistance of a centrifugally cast high-speed steel roll were investigated through thermodynamic calculation, microstructural analysis, and high-temperature wear tests. When the austenitizing temperature was between 1323 K and 1423 K (1050 °C and 1150 °C), coarse eutectic M2C plates were decomposed into a mixture of MC and M6C particles. However, at 1473 K (1200 °C), the M2C plates were first replaced by both new austenite grains and MC particles without M6C particles, and then remaining M2C particles were dissolved during the growth of MC particles. The wear resistance of the HSS roll was improved with increasing austenitizing temperature up to 1473 K (1200 °C) because the coarse eutectic M2C plates, which are vulnerable to crack propagation, changed to disconnected hard M6C and MC particles.

  15. Microstructures and tensile properties of 304 steel with dual nanocrystalline and microcrystalline austenite content prepared by aluminothermic reaction casting

    NASA Astrophysics Data System (ADS)

    La, Peiqing; Wei, Fuan; Lu, Xuefeng; Shi, Ting; Chu, Chenggang; Wei, Yupeng; Wang, Hongding

    2014-08-01

    The microstructures of 304 stainless steels with different amounts of nanocrystalline and microcrystalline austenite prepared by an aluminothermic reaction casting, without and with annealing at 1073 K for 8 h, have been investigated by X-ray diffraction, an electron probe micro-analyser, a transmission electron microscope and a scanning electron microscope. The steels, both without and with annealing, consisted of different dual nanocrystalline and microcrystalline austenite combinations and a little nanocrystalline δ ferrite, while the average grain size of the nanocrystalline austenite increased from 19 to 26 nm and volume fraction of the microcrystalline austenite increased from 17 to 30% after annealing. The tensile strength of the steel was dramatically increased from 500 to 1000 MPa and the tensile elongation ratio increased from 8 to 12% after annealing. However, the tensile strength was decreased to 600 MPa and the tensile elongation ratio increased from 12 to 22% after an annealing at 1273 K. The combination of dual nanocrystalline and microcrystalline austenite obtained after the annealing at 1073 K results in the best tensile properties.

  16. Effect of hydrogen on internal friction and Young`s modulus of Fe-Cr-Mn austenitic stainless steel

    SciTech Connect

    Usui, Makoto; Asano, Shigeru

    1996-06-01

    The internal friction technique has so far been applied to studies on hydrogen behavior in iron and steel. The hydrogen cold-work peak is well known for pure iron and has also been observed in BCC iron alloys such as ferritic stainless steel and maraging steel. It provides important information about the hydrogen- dislocation interaction in the BCC iron lattice. Meanwhile, for FCC iron alloys such as austenitic stainless steel, another characteristic hydrogen internal friction peak has been found by authors` group and confirmed by several other investigators. In the present study, type 205 austenitic stainless steel (Fe-17Cr-15Mn) was chosen as a nickel-free FCC iron alloy, in which manganese is totally substituted for nickel in type 304 steel. This steel has an unstable FCC lattice as is the case of type 304 steel, in which hydrogen-induced phase transformation depends on the austenite stability. However, the present steel was confirmed to form the {var_epsilon}{sub H} phase after cathodic hydrogen charging in a similar manner to the stable FCC lattice of type 310 steel. In addition, the Fe-Cr-Mn alloy shows a marked anomaly in the temperature dependence of Young`s modulus: an abrupt drop near the Neel temperature T{sub N} and successive lowering below T{sub N}, as has been reported in the literature for some antiferromagnetic materials. The effect of hydrogen on Young`s modulus was studied by several investigators, but there was great inconsistency among their experimental results. The purpose of this paper is to confirm the hydrogen peak of internal friction in type 205 steel and to examine the effect of hydrogen on Young`s modulus of this steel.

  17. Characterization of oxide layers grown on D9 austenitic stainless steel in lead bismuth eutectic

    NASA Astrophysics Data System (ADS)

    Hosemann, P.; Hawley, M.; Koury, D.; Swadener, J. G.; Welch, J.; Johnson, A. L.; Mori, G.; Li, N.

    2008-04-01

    Lead bismuth eutectic (LBE) is a possible coolant for fast reactors and targets in spallation neutron sources. Its low melting point, high evaporation point, good thermal conductivity, low reactivity, and good neutron yield make it a safe and high performance coolant in radiation environments. The disadvantage is that it is a corrosive medium for most steels and container materials. This study was performed to evaluate the corrosion behavior of the austenitic stainless steel D9 in oxygen controlled LBE. In order to predict the corrosion behavior of steel in this environment detailed analyses have to be performed on the oxide layers formed on these materials and various other relevant materials upon exposure to LBE. In this study the corrosion/oxidation of D9 stainless steel in LBE was investigated in great detail. The oxide layers formed were characterized using atomic force microscopy, magnetic force microscopy, nanoindentation, and scanning electron microscopy with wavelength-dispersive spectroscopy (WDS) to understand the corrosion and oxidation mechanisms of D9 stainless steel in contact with the LBE. What was previously believed to be a simple double oxide layer was identified here to consist of at least 4 different oxide layers. It was found that the inner most oxide layer takes over the grain structure of what used to be the bulk steel material while the outer oxide layer consists of freshly grown oxides with a columnar structure. These results lead to a descriptive model of how these oxide layers grow on this steel under the harsh environments encountered in these applications.

  18. TEM microscopical examination of the magnetic domain boundaries in a super duplex austenitic-ferritic stainless steel

    SciTech Connect

    Fourlaris, G.; Gladman, T.; Maylin, M.

    1996-12-31

    It has been demonstrated in an earlier publication that significant improvements in the coercivity, maximum induction and remanence values can be achieved, by using a 2205 type Duplex austenitic-ferritic stainless steel (DSS) instead of the low alloy medium carbon steels currently being used. These improvements are achieved in the as received 2205 material, and after small amounts of cold rolling have been applied, to increase the strength. In addition, the modification of the duplex austenitic-ferritic microstructure, via a heat treatment route, results in a finer austenite `island` dispersion in a ferritic matrix and provides an attractive option for further modification of the magnetic characteristics of the material. However, the 2205 type DSS exhibits {open_quotes}marginal{close_quotes} corrosion protection in a marine environment, so that a study has been undertaken to examine whether the beneficial effects exhibited by the 2205 DSS, are also present in a 2507 type super-DSS.

  19. In vitro corrosion resistance of plasma source ion nitrided austenitic stainless steels.

    PubMed

    Le, M K; Zhu, X M

    2001-04-01

    Plasma source ion nitriding has emerged as a low-temperature, low-pressure nitriding approach for low-energy implanting nitrogen ions and then diffusing them into steel and alloy. In this work, a single high nitrogen face-centered-cubic (f.c.c.) phase (gammaN) formed on the 1Cr18Ni9Ti and AISI 316L austenitic stainless steels with a high nitrogen concentration of about 32 at % was characterized using Auger electron spectroscopy, electron probe microanalysis, glancing angle X-ray diffraction, and transmission electron microscopy. The corrosion resistance of the gammaN-phase layer was studied by the electrochemical cyclic polarization measurement in Ringer's solutions buffered to pH from 3.5 to 7.2 at a temperature of 37 degrees C. No pitting corrosion in the Ringer's solutions with pH = 7.2 and 5.5 was detected for the gammaN-phase layers on the two stainless steels. The high pitting potential for the gammaN-phase layers is higher, about 500 and 600 mV, above that of the two original stainless steels, respectively, in the Ringer's solution with pH = 3.5. The corroded surface morphologies of the gammaN-phase layers observed by scanning electron microscopy are consistent with the results of the electrochemical polarization measurement. PMID:11246957

  20. Microstructure and Mechanical Properties of Ultrafine-Grained Austenitic Oxide Dispersion Strengthened Steel

    NASA Astrophysics Data System (ADS)

    Mao, Xiaodong; Kang, Suk Hoon; Kim, Tae Kyu; Kim, Seul Cham; Oh, Kyu Hwan; Jang, Jinsung

    2016-06-01

    316L stainless steel based austenitic oxide dispersion strengthened (AODS) steel was fabricated by mechanical alloying (MA) and hot isostatic pressing (HIP). The AODS sample exhibited an ultrafine-grained (UFG) structure with a bimodal grain size distribution (large grains of about 1200 nm and fine grains of about 260 nm). Two groups of oxide particles were observed; fine Y2Ti2O7 of about 7.7 nm and coarse Cr2O3 particles of about 200 nm in diameter. Tensile tests of the hot-rolled AODS steel samples showed yield strength of up to 890 MPa at room temperature, which is nearly four times higher than that of conventional 316L stainless steel. Micro-indentation and hardness tests indicated even higher yield strength of up to 1200 MPa, which shows a good agreement with the calculated value by combining of the grain refinement strengthening by the Hall-Petch relation and the dispersion strengthening by the Orowan mechanism. The lower strength from tensile tests should be attributed to the formation of micro-cracks at the interfaces between coarse Cr2O3 particles and the matrix. Coarse Cr2O3 particles were also frequently observed inside the fracture surface dimples of the creep ruptured sample at 923 K (650 °C) and 140 MPa. It is thus suggested that the yield strength and elongation could be further improved by controlling the coarse Cr2O3 particles.

  1. On the decomposition of austenite in the heat-affected zone upon welding of high-strength steels

    NASA Astrophysics Data System (ADS)

    Efimenko, L. A.; Ramus', A. A.; Merkulova, A. O.

    2015-05-01

    The kinetics of the decomposition of austenite in the heat-affected zone of welded joints of low-carbon microalloyed high-strength steels has been investigated. A new approach to selecting the parameters of the thermal cycle of welding that ensure the service characteristics of welded joints on a level no lower than the normative requirements is suggested.

  2. Direct estimation of austenitic grain dimensions in heat affected zones of a martensitic steel from EBSD images.

    PubMed

    Altendorf, H; Faessel, M; Jeulin, D; Latourte, F

    2015-05-01

    In the context of automated analyses of electron-backscattered-diffraction images, we present in this paper a novel method to automatically extract morphological properties of prior austenitic grains in martensitic steels based on raw crystallographic orientation maps. This quantification includes the estimation of the mean chord length in specific directions, with in addition the reconstruction of the mean shape of austenitic grains inducing anisotropic shape properties. The approach is based on the morphological measure of covariance on a decision curve of grain fidelity per disorientation angle. These efforts have been motivated by the need of realistic microstructures to perform micromechanical studies of grain boundary localized damage phenomenons in steels, one example being the type IV fracture phenomenon occurring in welded joints of grade P91/P92 steel. This failure is attributed to a change of the microstructure due to thermal gradients arising during the welding process. To precisely capture the relationships between microstructural changes and mechanical fields localization in a polycrystalline aggregate, we first need to achieve a reasonable stochastic model of its microstructure, which relies on a detailed knowledge of the microstructural morphology. As martensitic steels possess multiscale microstructures composed of prior austenitic grains, packets and laths, a relevant modelling strategy has to be proposed to account for the observed hierarchies. With this objective, this paper focuses on the larger scale entities present in the microstructure, namely, the austenitic grains. PMID:25689129

  3. Electron Backscatter Diffraction Analysis of Joints Between AISI 316L Austenitic/UNS S32750 Dual-Phase Stainless Steel

    NASA Astrophysics Data System (ADS)

    Shamanian, Morteza; Mohammadnezhad, Mahyar; Amini, Mahdi; Zabolian, Azam; Szpunar, Jerzy A.

    2015-08-01

    Stainless steels are among the most economical and highly practicable materials widely used in industrial areas due to their mechanical and corrosion resistances. In this study, a dissimilar weld joint consisting of an AISI 316L austenitic stainless steel (ASS) and a UNS S32750 dual-phase stainless steel was obtained under optimized welding conditions by gas tungsten arc welding technique using AWS A5.4:ER2594 filler metal. The effect of welding on the evolution of the microstructure, crystallographic texture, and micro-hardness distribution was also studied. The weld metal (WM) was found to be dual-phased; the microstructure is obtained by a fully ferritic solidification mode followed by austenite precipitation at both ferrite boundaries and ferrite grains through solid-state transformation. It is found that welding process can affect the ferrite content and grain growth phenomenon. The strong textures were found in the base metals for both steels. The AISI 316L ASS texture is composed of strong cube component. In the UNS S32750 dual-phase stainless steel, an important difference between the two phases can be seen in the texture evolution. Austenite phase is composed of a major cube component, whereas the ferrite texture mainly contains a major rotated cube component. The texture of the ferrite is stronger than that of austenite. In the WM, Kurdjumov-Sachs crystallographic orientation relationship is found in the solidification microstructure. The analysis of the Kernel average misorientation distribution shows that the residual strain is more concentrated in the austenite phase than in the other phase. The welding resulted in a significant hardness increase in the WM compared to initial ASS.

  4. Irradiation-Assisted Stress Corrosion Cracking of Austenitic Stainless Steels in BWR Environments

    SciTech Connect

    Chen, Y.; Chopra, O. K.; Gruber, Eugene E.; Shack, William J.

    2010-06-01

    The internal components of light water reactors are exposed to high-energy neutron irradiation and high-temperature reactor coolant. The exposure to neutron irradiation increases the susceptibility of austenitic stainless steels (SSs) to stress corrosion cracking (SCC) because of the elevated corrosion potential of the reactor coolant and the introduction of new embrittlement mechanisms through radiation damage. Various nonsensitized SSs and nickel alloys have been found to be prone to intergranular cracking after extended neutron exposure. Such cracks have been seen in a number of internal components in boiling water reactors (BWRs). The elevated susceptibility to SCC in irradiated materials, commonly referred to as irradiation-assisted stress corrosion cracking (IASCC), is a complex phenomenon that involves simultaneous actions of irradiation, stress, and corrosion. In recent years, as nuclear power plants have aged and irradiation dose increased, IASCC has become an increasingly important issue. Post-irradiation crack growth rate and fracture toughness tests have been performed to provide data and technical support for the NRC to address various issues related to aging degradation of reactor-core internal structures and components. This report summarizes the results of the last group of tests on compact tension specimens from the Halden-II irradiation. The IASCC susceptibility of austenitic SSs and heat-affected-zone (HAZ) materials sectioned from submerged arc and shielded metal arc welds was evaluated by conducting crack growth rate and fracture toughness tests in a simulated BWR environment. The fracture and cracking behavior of HAZ materials, thermally sensitized SSs and grain-boundary engineered SSs was investigated at several doses (≤3 dpa). These latest results were combined with previous results from Halden-I and II irradiations to analyze the effects of neutron dose, water chemistry, alloy compositions, and welding and processing conditions on IASCC

  5. Effect of Composition and Deformation on Coarse-Grained Austenite Transformation in Nb-Mo Microalloyed Steels

    NASA Astrophysics Data System (ADS)

    Isasti, N.; Jorge-Badiola, D.; Taheri, M. L.; López, B.; Uranga, P.

    2011-12-01

    Thermomechanical processing of microalloyed steels containing niobium can be performed to obtain deformed austenite prior to transformation. Accelerated cooling can be employed to refine the final microstructure and, consequently, to improve both strength and toughness. This general rule is fulfilled if the transformation occurs on a quite homogeneous austenite microstructure. Nevertheless, the presence of coarse austenite grains before transformation in different industrial processes is a usual source of concern, and regarding toughness, the coarsest high-angle boundary units would determine its final value. Sets of deformation dilatometry tests were carried out using three 0.06 pct Nb microalloyed steels to evaluate the effect of Mo alloying additions (0, 0.16, and 0.31 pct Mo) on final transformation from both recrystallized and unrecrystallized coarse-grained austenite. Continuous cooling transformation (CCT) diagrams were created, and detailed microstructural characterization was achieved through the use of optical microscopy (OM), field emission gun scanning electron microscopy (FEGSEM), and electron backscattered diffraction (EBSD). The resultant microstructures ranged from polygonal ferrite (PF) and pearlite (P) at slow cooling ranges to bainitic ferrite (BF) accompanied by martensite (M) for fast cooling rates. Plastic deformation of the parent austenite accelerated both ferrite and bainite transformation, moving the CCT curves to higher temperatures and shorter times. However, an increase in the final heterogeneity was observed when BF packets were formed, creating coarse high-angle grain boundary units.

  6. Effect of Treatment Time on the Microstructure of Austenitic Stainless Steel During Low-Temperature Liquid Nitrocarburizing

    NASA Astrophysics Data System (ADS)

    Wang, Jun; Lin, Yuanhua; Zhang, Qiang; Zeng, Dezhi; Fan, Hongyuan

    2014-09-01

    The effect of treatment time on the microstructure of AISI 304 austenitic stainless steel during liquid nitrocarburizing (LNC) at 703 K (430 °C) was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Experimental results revealed that the modified layer was covered with the alloy surface and the modified layer depth increased extensively from 2 to 33.4 μm with increasing treatment time. SEM and XRD showed that when the 304 stainless steel sample was subjected to LNC at 703 K (430 °C) for less than 4 hours, the main phase of the modified layer was expanded austenite. When the treatment time was prolonged to 8 hours, the abundant expanded austenite was formed and it partially transformed into CrN and ferrite subsequently. With the increased treatment time, more and more CrN precipitate transformed in the overwhelming majority zone in the form of a typical dendritic structure in the nearby outer part treated for 40 hours. Still there was a single-phase layer of the expanded austenite between the CrN part and the inner substrate. TEM showed the expanded austenite decomposition into the CrN and ferrite after longtime treatment even at low temperature.

  7. Effect of single and double austenitization treatments on the microstructure and mechanical properties of 16Cr-2Ni steel

    SciTech Connect

    Balan, K.P.; Venugopal Reddy, A.; Sarma, D.S.

    1999-06-01

    Double austenitization (DA) treatment is found to yield the best combination of strength and toughness in both low-temperature as well as high-temperature tempered conditions as compared to single austenitization (SA) treatments. Obtaining the advantages of double austenitization (DA) to permit dissolution of alloy carbides without significant grain coarsening was attempted in AISI 431 type martensitic stainless steel. Structure-property correlation after low-temperature tempering (200 C) as well as high-temperature double tempering (650 + 600 C) was carried out for three austenitization treatments through SA at 1000 C, SA at 1070 C, and DA at 1070 + 1000 C. While the increase in strength after DA treatment and low-temperature tempering at 200 C is due to the increased amount of carbon in solution as a result of dissolution of alloy carbides during first austenitization, the increased toughness is attributable to the increased quantity of retained austenite. After double tempering (650 + 600 C), strength and toughness are mainly found to depend on the precipitation and distribution of carbides in the microstructure and the grain size effect.

  8. Assessment of void swelling in austenitic stainless steel PWR core internals.

    SciTech Connect

    Chung, H. M.; Energy Technology

    2006-01-31

    As many pressurized water reactors (PWRs) age and life extension of the aged plants is considered, void swelling behavior of austenitic stainless steel (SS) core internals has become the subject of increasing attention. In this report, the available database on void swelling and density change of austenitic SSs was critically reviewed. Irradiation conditions, test procedures, and microstructural characteristics were carefully examined, and key factors that are important to determine the relevance of the database to PWR conditions were evaluated. Most swelling data were obtained from steels irradiated in fast breeder reactors at temperatures >385 C and at dose rates that are orders of magnitude higher than PWR dose rates. Even for a given irradiation temperature and given steel, the integral effects of dose and dose rate on void swelling should not be separated. It is incorrect to extrapolate swelling data on the basis of 'progressive compounded multiplication' of separate effects of factors such as dose, dose rate, temperature, steel composition, and fabrication procedure. Therefore, the fast reactor data should not be extrapolated to determine credible void swelling behavior for PWR end-of-life (EOL) or life-extension conditions. Although the void swelling data extracted from fast reactor studies is extensive and conclusive, only limited amounts of swelling data and information have been obtained on microstructural characteristics from discharged PWR internals or steels irradiated at temperatures and at dose rates comparable to those of a PWR. Based on this relatively small amount of information, swelling in thin-walled tubes and baffle bolts in a PWR is not considered a concern. As additional data and relevant research becomes available, the newer results should be integrated with existing data, and the worthiness of this conclusion should continue to be scrutinized. PWR baffle reentrant corners are the most likely location to experience high swelling rates, and

  9. Capabilities of Ultrasonic Techniques for Far-Side Examinations of Austenitic Stainless Steel Piping Welds.

    SciTech Connect

    Anderson, Michael T.; Diaz, Aaron A.; Cumblidge, Stephen E.; Doctor, Steven R.

    2007-01-01

    A study was conducted to assess the ability of advanced ultrasonic techniques to detect and accurately length-size flaws from the far-side of wrought austenitic piping welds. Far-side inspections of nuclear system piping welds are currently performed on a “best effort” basis and do not conform to ASME Code Section XI Appendix VIII performance demonstration requirements. For this study, austenitic stainless steel specimens with flaws located on the far-side of full penetration structural welds were used. The welds were fabricated with varied welding parameters to simulate as-built conditions in the components, and were examined with phased array technology at 2.0 MHz, and low-frequency/Synthetic Aperture Focusing Technique (SAFT) methods in the 250-400 kHz regime. These results were compared to conventional ultrasonic techniques as a baseline. The examinations showed that both phased-array and low-frequency/SAFT were able to reliably detect and length-size, but not depth size, notches and implanted fatigue cracks through the welds.

  10. Crack initiation in smooth fatigue specimens of austenitic stainless steel in light water reactor environments.

    SciTech Connect

    Chopra, O. K.; Smith, J. L.

    1999-04-08

    The fatigue design curves for structural materials specified in Section III of the ASME Boiler and Pressure Vessel Code are based on tests of smooth polished specimens at room temperature in air. The effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves; however, recent test data illustrate the detrimental effects of LWR coolant environments on the fatigue resistance of austenitic stainless steels (SSs). Certain loading and environmental conditions have led to test specimen fatigue lives that are significantly shorter than those obtained in air. Results of fatigue tests that examine the influence of reactor environments on crack initiation and crack growth of austenitic SSs are presented. Block loading was used to mark the fracture surface to determine crack length as a function of fatigue cycles in water environments, Crack lengths were measured by scanning electron microscopy. The mechanism for decreased fatigue life in LWR environments is discussed, and crack growth rates in the smooth fatigue specimens are compared with existing data from studies of crack growth rates.

  11. Flexural Strength and Toughness of Austenitic Stainless Steel Reinforced High-Cr White Cast Iron Composite

    NASA Astrophysics Data System (ADS)

    Sallam, H. E. M.; Abd El-Aziz, Kh.; Abd El-Raouf, H.; Elbanna, E. M.

    2013-12-01

    Flexural behavior of high-Cr white cast iron (WCI) reinforced with different shapes, i.e., I- and T-sections, and volume fractions of austenitic stainless steel (310 SS) were examined under three-point bending test. The dimensions of casted beams used for bending test were (50 × 100 × 500 mm3). Carbon and alloying elements diffusion enhanced the metallurgical bond across the interface of casted beams. Carbon diffusion from high-Cr WCI into 310 SS resulted in the formation of Cr-carbides in 310 SS near the interface and Ni diffusion from 310 SS into high-Cr WCI led to the formation of austenite within a network of M7C3 eutectic carbides in high-Cr WCI near the interface. Inserting 310 SS plates into high-Cr WCI beams resulted in a significant improvement in their toughness. All specimens of this metal matrix composite failed in a ductile mode with higher plastic deformation prior to failure. The high-Cr WCI specimen reinforced with I-section of 310 SS revealed higher toughness compared to that with T-section at the same volume fraction. The presence of the upper flange increased the reinforcement efficiency for delaying the crack growth.

  12. Hydrogen-Assisted Crack Propagation in Austenitic Stainless Steel Fusion Welds

    NASA Astrophysics Data System (ADS)

    Somerday, B. P.; Dadfarnia, M.; Balch, D. K.; Nibur, K. A.; Cadden, C. H.; Sofronis, P.

    2009-10-01

    The objective of this study was to characterize hydrogen-assisted crack propagation in gas-tungsten arc (GTA) welds of the nitrogen-strengthened, austenitic stainless steel 21Cr-6Ni-9Mn (21-6-9), using fracture mechanics methods. The fracture initiation toughness and crack growth resistance curves were measured using fracture mechanics specimens that were thermally precharged with 230 wppm (1.3 at. pct) hydrogen. The fracture initiation toughness and slope of the crack growth resistance curve for the hydrogen-precharged weld were reduced by as much as 60 and 90 pct, respectively, relative to the noncharged weld. A physical model for hydrogen-assisted crack propagation in the welds was formulated from microscopy evidence and finite-element modeling. Hydrogen-assisted crack propagation proceeded by a sequence of microcrack formation at the weld ferrite, intense shear deformation in the ligaments separating microcracks, and then fracture of the ligaments. One salient role of hydrogen in the crack propagation process was promoting microcrack formation at austenite/ferrite interfaces and within the ferrite. In addition, hydrogen may have facilitated intense shear deformation in the ligaments separating microcracks. The intense shear deformation could be related to the development of a nonuniform distribution of hydrogen trapped at dislocations between microcracks, which in turn created a gradient in the local flow stress.

  13. Microstructure, Texture, and Mechanical Property Analysis of Gas Metal Arc Welded AISI 304 Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Saha, Saptarshi; Mukherjee, Manidipto; Pal, Tapan Kumar

    2015-03-01

    The present study elaborately explains the effect of welding parameters on the microstructure, texture, and mechanical properties of gas metal arc welded AISI 304 austenitic stainless steel sheet (as received) of 4 mm thickness. The welded joints were prepared by varying welding speed (WS) and current simultaneously at a fixed heat input level using a 1.2-mm-diameter austenitic filler metal (AISI 316L). The overall purpose of this study is to investigate the effect of the variation of welding conditions on: (i) Microstructural constituents using optical microscope and transmission electron microscope; (ii) Micro-texture evolution, misorientation distributions, and grain boundaries at welded regions by measuring the orientation data from electron back scattered diffraction; and (iii) Mechanical properties such as hardness and tensile strength, and their correlation with the microstructure and texture. It has been observed that the higher WS along with the higher welding current (weld metal W1) can enhance weld metal mechanical properties through alternation in microstructure and texture of the weld metal. Higher δ-ferrite formation and high-angle boundaries along with the <101> + <001> grain growth direction of the weld metal W1 were responsible for dislocation pile-ups, SFs, deformation twinning, and the induced martensite with consequent strain hardening during tensile deformation. Also, fusion boundary being the weakest link in the welded structure, failure took place mainly at this region.

  14. Thermal embrittlement of simulated heat-affected zone in cast austenitic stainless steels

    SciTech Connect

    Mimura, H.; Taniguchi, T.; Horii, Y.; Kume, R.; Uesugi, N.

    1998-08-01

    Metallurgical factors controlling thermal embrittlement in the heat-affected zone (HAZ) of cast austenitic stainless steels were investigated by using the simulated HAZ. It was shown that the simulated HAZ was more susceptible to the thermal embrittlement by aging at 673 K in correspondence with its higher tendency to age hardening and a higher content of ferrite than the parent casting. Electron microprobe analyzer measurement showed that application of the simulated thermal cycle gave a change in the chemical composition of the ferrite, which might be a cause of the higher age hardening of the ferrite in the simulated HAZ. This higher ferrite hardness had a good correlation with fine precipitates of presumably G-phase in the ferrite grain, which existed more in the simulated HAZ than in the parent casting, though it is not clear whether this correlation was only apparent. Ductility of the austenite portion was found to reduce remarkably when surrounded by the hard ferrite of a high fraction. Annealing after aging restored CTOD to some degree. Aging after fatigue cracking gave more embrittlement than a usual procedure for preparation of test specimens, i.e., fatigue cracking after aging.

  15. Damage structure of austenitic stainless steel 316LN irradiated at low temperature in HFIR

    SciTech Connect

    Hashimoto, N.; Robertson, J.P.; Grossbeck, M.L.; Rowcliffe, A.F.; Wakai, E.

    1998-03-01

    TEM disk specimens of austenitic stainless steel 316LN irradiated to damage levels of about 3 dpa at irradiation temperatures of either about 90 C or 250 C have been investigated by using transmission electron microscopy. The irradiation at 90 C and 250 C induced a dislocation loop density of 3.5 {times} 10{sup 22} m{sup {minus}3} and 6.5 {times} 10{sup 22} m{sup {minus}3}, a black dot density of 2.2 {times} 10{sup 23} m{sup {minus}3} and 1.6 {times} 10{sup 23} m{sup {minus}3}, respectively, in the steels, and a high density (<1 {times} 10{sup 22} m{sup {minus}3}) of precipitates in matrix. Cavities could be observed in the specimens after the irradiation. It is suggested that the dislocation loops, the black dots, and the precipitates cause irradiation hardening, an increase in the yield strength and a decrease in the uniform elongation, in the 316LN steel irradiated at low temperature.

  16. Use of plasma arc welding process to combat hydrogen metallic disbonding of austenitic stainless steel claddings

    SciTech Connect

    Alexandrov, O.A. ); Steklov, O.I.; Alexeev, A.V. )

    1993-11-01

    A separation type crack, metallic disbonding, occurred between austenitic stainless steel weld metal cladding and 2 1/4Cr-1Mo base metal in the hydrodesulfurizing reactor of an oil refining plant. For stainless steel cladding, the submerged arc welding (SAW) process with a strip electrode is usually applied, but the authors experimented with the plasma arc welding (PAW) process with hot wire electrode for the cladding. The metallic disbonding is considered to be attributed to hydrogen accumulation at the transition zone and has been generally studied on a laboratory scale using an autoclave. The authors used a electrolytic hydrogen charging technique for the sake of experimental simplicity and made a comparison with the results for gaseous hydrogen charging. The main conclusions obtained were follows: The PAW stainless steel weld metal cladding is more resistant to metallic disbonding with the PAW process is explained by the desirable microstructure and properties of the first layer of weld metal at the transition zone. Electrolytic hydrogen charging pretty well reproduces the results of autoclave gas phase charging.

  17. Austenitic stainless steels and high strength copper alloys for fusion components

    NASA Astrophysics Data System (ADS)

    Rowcliffe, A. F.; Zinkle, S. J.; Stubbins, J. F.; Edwards, D. J.; Alexander, D. J.

    1998-10-01

    An austenitic stainless steel (316LN), an oxide-dispersion-strengthened copper alloy (GlidCop Al25), and a precipitation-hardened copper alloy (Cu-Cr-Zr) are the primary structural materials for the ITER first wall/blanket and divertor systems. While there is a long experience of operating 316LN stainless steel in nuclear environments, there is no prior experience with the copper alloys in neutron environments. The ITER first wall (FW) consists of a stainless steel shield with a copper alloy heat sink bonded by hot isostatic pressing (HIP). The introduction of bi-layer structural material represents a new materials engineering challenge; the behavior of the bi-layer is determined by the properties of the individual components and by the nature of the bond interface. The development of the radiation damage microstructure in both classes of materials is summarized and the effects of radiation on deformation and fracture behavior are considered. The initial data on the mechanical testing of bi-layers indicate that the effectiveness of GlidCop Al25 as a FW heat sink material is compromised by its strongly anisotropic fracture toughness and poor resistance to crack growth in a direction parallel to the bi-layer interface.

  18. Corrosion behavior of austenitic stainless steels in chloride containing ozone solutions

    SciTech Connect

    Pohjanne, P.

    1997-08-01

    Environmental concern about chlorinated organic compounds generated from traditional bleach plants has led to a development of new environmentally friendly bleaching processes. Recently, the development of ozone bleaching has progressed from pilot operations to production scale installations. Ozone is currently used as a bleaching agent of pulp as a replacement for chlorine based bleaching chemicals. Yet, there are few articles which are dealing with ozone and its effect to corrosion resistance of stainless steels or any other construction materials used in bleaching equipment. In this paper corrosion behavior of austenitic stainless steels, grades AISI 316, AISI 317LNM, UNS S31254 and UNS 32654 PM, were studied in simulated ozone bleaching environments. The laboratory tests showed that in ozone environments without chlorides the corrosion resistance of AISI 316 was superior to that of the high-alloyed stainless steels, due to the relatively low amount of alloying elements. The sequence was reversed in ozone environments containing chlorides. In the presence of chlorides AISI 316 was susceptible to localized corrosion whereas the high-alloyed UNS S31254 and UNS S 32654 PM were resistant to localized corrosion in all chloride concentrations examined.

  19. Stress-induced martensitic transformation in metastable austenitic stainless steels: Effect on fatigue crack growth rate

    NASA Astrophysics Data System (ADS)

    Khan, Z.; Ahmed, M.

    1996-04-01

    This paper addresses the influence of cyclic stress-induced martensitic transformation on fatigue crack growth rates in metastable austenitic stainless steels. At low applied stress and mean stress values in AISI type 301 stainless steel, fatigue crack growth rate is substantially retarded due to a cyclic stress-induced γ-α' and γ-ɛ martensitic transformation occurring at the crack-tip plastic zone. It is suggested that the transformation products produce a compressive residual stress at the tip of the fatigue crack, which essentially lowers the effective stress intensity and hence retards the fatigue crack growth rate. At high applied stress or mean stress values, fatigue crack growth rates in AISI type 301 steels become almost equal to those of stable AISI type 302 alloy. As the amount of transformed products increases (with an increase in applied or mean stress), the strain-hardening effect brought about by the transformed martensite phase appears to accelerate fatigue crack growth, offsetting the contribution from the compressive residual stress produced by the positive volume change of γ → α' or ɛ transformation.

  20. Microstructural characterization of dissimilar welds between Incoloy 800H and 321 Austenitic Stainless Steel

    SciTech Connect

    Sayiram, G. Arivazhagan, N.

    2015-04-15

    In this work, the microstructural character of dissimilar welds between Incoloy 800H and 321 Stainless Steel has been discussed. The microscopic examination of the base metals, fusion zones and interfaces was characterized using an optical microscope and scanning electron microscopy. The results revealed precipitates of Ti (C, N) in the austenitic matrix along the grain boundaries of the base metals. Migration of grain boundaries in the Inconel 82 weld metal was very extensive when compared to Inconel 617 weldment. Epitaxial growth was observed in the 617 weldment which increases the strength and ductility of the weld metal. Unmixed zone near the fusion line between 321 Stainless Steel and Inconel 82 weld metal was identified. From the results, it has been concluded that Inconel 617 filler metal is a preferable choice for the joint between Incoloy 800H and 321 Stainless Steel. - Highlights: • Failure mechanisms produced by dissimilar welding of Incoloy 800H to AISI 321SS • Influence of filler wire on microstructure properties • Contemplative comparisons of metallurgical aspects of these weldments • Microstructure and chemical studies including metallography, SEM–EDS • EDS-line scan study at interface.

  1. Phase Transformations of an Fe-0.85 C-17.9 Mn-7.1 Al Austenitic Steel After Quenching and Annealing

    NASA Astrophysics Data System (ADS)

    Cheng, Wei-Chun

    2014-09-01

    Low-density Mn-Al steels could potentially be substitutes for commercial Ni-Cr stainless steels. However, the development of the Mn-Al stainless steels requires knowledge of the phase transformations that occur during the steel making processes. Phase transformations of an Fe-0.85 C-17.9 Mn-7.1 Al (wt.%) austenitic steel, which include spinodal decomposition, precipitation transformations, and cellular transformations, have been studied after quenching and annealing. The results show that spinodal decomposition occurs prior to the precipitation transformation in the steel after quenching and annealing at temperatures below 1023 K and that coherent fine particles of L12-type carbide precipitate homogeneously in the austenite. The cellular transformation occurs during the transformation of high-temperature austenite into lamellae of austenite, ferrite, and kappa carbide at temperatures below 1048 K. During annealing at temperatures below 923 K, the austenite decomposes into lamellar austenite, ferrite, κ-carbide, and M23C6 carbide grains for another cellular transformation. Last, when annealing at temperatures below 873 K, lamellae of ferrite and κ-carbide appear in the austenite.

  2. Formation of Inclusions in Ti-Stabilized 17Cr Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Yin, Xue; Sun, Yanhui; Yang, Yindong; Bai, Xuefeng; Barati, Mansoor; Mclean, Alex

    2016-04-01

    The behavior and formation mechanisms of inclusions in Ti-stabilized, 17Cr Austenitic Stainless Steel produced by the ingot casting route were investigated through systematic sampling of liquid steel and rolled products. Analysis methods included total oxygen and nitrogen contents, optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results indicate that the composition of inclusions was strongly dependent on the types of added alloying agents. During the AOD refining process, after the addition of ferrosilicon alloy and electrolytic manganese, followed by aluminum, the composition of inclusions changed from manganese silicate-rich inclusions to alumina-rich inclusions. After tapping and titanium wire feeding, pure TiN particles and complex inclusions with Al2O3-MgO-TiO x cores containing TiN were found to be the dominant inclusions when [pct Ti] was 0.307 mass pct in the molten steel. These findings were confirmed by thermodynamic calculations which indicated that there was a driving force for TiN inclusions to be formed in the liquid phase due to the high contents of [Ti] and [N] in the molten steel. From the start of casting through to the rolled bar, there was no further change in the composition of inclusions compared to the titanium addition stage. Stringer-shaped TiN inclusions were observed in the rolled bar. These inclusions were elongated along the rolling direction with lengths varying from 17 to 84 µm and could have a detrimental impact on the corrosion resistance as well as the mechanical properties of the stainless steel products.

  3. Implications of radiation-induced reductions in ductility to the design of austenitic stainless steel structures

    SciTech Connect

    Lucas, G.E.; Billone, M.; Pawel, J.E.; Hamilton, M.L.

    1995-12-31

    In the dose and temperature range anticipated for ITER, austenitic stainless steels exhibit significant hardening with a concomitant loss in work hardening and uniform elongation. However, significant post-necking ductility may still be retained. When uniform elongation (e{sub u}) is well defined in terms of a plastic instability criterion, e{sub u} is found to sustain reasonably high values out to about 7 dpa in the temperature range 250-350 C, beyond which it decreases to about 0.3% for 316LN. This loss of ductility has significant implications to fracture toughness and the onset of new failure modes associated with hear instability. However, the retention of a significant reduction in area at failure following irradiation indicates a less severe degradation of low-cycle fatigue life in agreement with a limited amount of data obtained to date. Suggestions are made for incorporating these results into design criteria and future testing programs.

  4. Five-parameter grain boundary analysis of a grain boundary-engineered austenitic stainless steel.

    PubMed

    Jones, R; Randle, V; Engelberg, D; Marrow, T J

    2009-03-01

    Two different grain boundary engineering processing routes for type 304 austenitic stainless steel have been compared. The processing routes involve the application of a small level of strain (5%) through either cold rolling or uni-axial tensile straining followed by high-temperature annealing. Electron backscatter diffraction and orientation mapping have been used to measure the proportions of Sigma3(n) boundary types (in coincidence site lattice notation) and degree of random boundary break-up, in order to gain a measure of the success of the two types of grain boundary engineering treatments. The distribution of grain boundary plane crystallography has also been measured and analyzed in detail using the five-parameter stereological method. There were significant differences between the grain boundary population profiles depending on the type of deformation applied. PMID:19250462

  5. Hydrogen-assisted damage in austenite/martensite dual-phase steel

    NASA Astrophysics Data System (ADS)

    Koyama, Motomichi; Cem Tasan, Cemal; Nagashima, Tatsuya; Akiyama, Eiji; Raabe, Dierk; Tsuzaki, Kaneaki

    2016-01-01

    For understanding the underlying hydrogen embrittlement mechanism in transformation-induced plasticity steels, the process of damage evolution in a model austenite/martensite dual-phase microstructure following hydrogenation was investigated through multi-scale electron channelling contrast imaging and in situ optical microscopy. Localized diffusible hydrogen in martensite causes cracking through two mechanisms: (1) interaction between {1 1 0}M localized slip and {1 1 2}M twin and (2) cracking of martensite-martensite grain interfaces. The former resulted in nanovoids along the {1 1 2}M twin. The coalescence of the nanovoids generated plate-like microvoids. The latter caused shear localization on the specific plane where the crack along the martensite/martensite boundary exists, which led to additional martensite/martensite boundary cracking.

  6. Effect of Laser Peening without Coating on 316L austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Sathyajith, S.; kalainathan, S.

    2015-02-01

    Laser Peening without Coating (LPwC) is an innovative surface modification technique used for the in-suit preventive maintenance of nuclear reactor components using frequency doubled (green) laser. The advantage of LPwC is that the laser required for this technique is in milli joule range and the processes can perform in aqueous environment. This paper discussed the effect of LPwC on 316L austenitic stainless steel using low energy Nd: YAG laser with various laser pulse density. The base specimen and laser peened specimen were subjected to surface residual stress, surface morphology, micro hardness and potentiodynamic polarization studies. The laser peened surface exhibit significant improvement in surface compressive residual stress. The depth profile of micro hardness revealed higher strain hardening on laser peened specimens. Though corrosion potential reported an anodic shift,current density is found to be increased after LPwC for the specimen peened with higher pulse density.

  7. Deformation analysis on F138 austenitic stainless steel: ECAE and rolling

    NASA Astrophysics Data System (ADS)

    De Vincentis, N. S.; Avalos, M. C.; Kliauga, A. M.; Sordi, V. L.; Schell, N.; Brokmeier, H.-G.; Bolmaro, R. E.

    2014-08-01

    Twinning is an alternative mechanism to achieve ultra-fine grain structures through severe plastic deformation. The properties induced in a plastically deformed material are highly dependent on the degree of deformation, accumulated deformation energy and details on grain sizes and microstructure, which are on the scale of some tens of nanometers; therefore it is very important to understand misorientation distributions and dislocation arrays developed in the samples. In this work an F138 austenitic stainless steel was solution heat treated, deformed by Equal Channel Angular Extrusion (ECAE) at room temperature up to four passes, and rolled up to 70% thickness reduction at room temperature. The microstructure evolution was analyzed by x-ray diffraction and domain sizes calculated by Convolutional Multiple Whole Profile (CMWP) model, the misorientation boundaries were measured by electron backscattered diffraction (EBSD), and transmission electron microscopy. Mechanical behavior was tested by tensile tests.

  8. Influence of localized plasticity on oxidation behaviour of austenitic stainless steels under primary water reactor

    NASA Astrophysics Data System (ADS)

    Cissé, Sarata; Laffont, Lydia; Lafont, Marie-Christine; Tanguy, Benoit; Andrieu, Eric

    2013-02-01

    The sensitivity of precipitation-strengthened A286 austenitic stainless steel to stress corrosion cracking was studied by means of slow-strain-rate tests. First, alloy cold working by low cycle fatigue (LCF) was investigated. Fatigue tests under plastic strain control were performed at different strain levels (Δɛp/2 = 0.2%, 0.5%, 0.8% and 2%) to establish correlations between stress softening and the deformation microstructure resulting from the LCF tests. Deformed microstructures were identified through TEM investigations. The interaction between oxidation and localized deformation bands was also studied and it resulted that localized deformation bands are not preferential oxide growth channels. The pre-cycling of the alloy did not modify its oxidation behaviour. However, intergranular oxidation in the subsurface under the oxide layer formed after exposure to PWR primary water was shown.

  9. Influence of sulfate-reducing bacteria on alloy 625 and austenitic stainless steel weldments

    SciTech Connect

    Enos, D.G.; Taylor, S.R.

    1996-11-01

    A series of welded austenitic stainless steel and alloy 625 clad specimens were exposed to natural lake water inoculated with a mixed culture of anaerobic organisms high in sulfate-reducing bacteria. Total exposure was 300 days. The water and bacteria were taken from an actual service water system. Electrochemical testing included electrochemical impedance spectroscopy, monitoring of open-circuit potential (E{sub oc}), and zero resistance ammetry tests. Comparison of electrochemical and visual observations to sterile controls indicated electrochemical behavior of all materials in the test matrix was influenced by the bacteria. Polarization resistance and E{sub oc} values were reduced dramatically. Attack was along the fusion line of the weld. The magnitude of these effects followed a trend predicted by the pitting index for each material.

  10. Ultrasonic Sound Field Mapping Through Coarse Grained Cast Austenitic Stainless Steel Components

    SciTech Connect

    Crawford, Susan L.; Prowant, Matthew S.; Cinson, Anthony D.; Larche, Michael R.; Diaz, Aaron A.

    2014-08-01

    The Pacific Northwest National Laboratory (PNNL) has been involved with nondestructive examination (NDE) of coarse-grained cast austenitic stainless steel (CASS) components for over 30 years. More recent work has focused on mapping the ultrasonic sound fields generated by low-frequency phased array probes that are typically used for the evaluation of CASS materials for flaw detection and characterization. The casting process results in the formation of large grained material microstructures that are nonhomogeneous and anisotropic. The propagation of ultrasonic energy for examination of these materials results in scattering, partitioning and redirection of these sound fields. The work reported here provides an assessment of sound field formation in these materials and provides recommendations on ultrasonic inspection parameters for flaw detection in CASS components.

  11. Correlation between locally deformed structure and oxide film properties in austenitic stainless steel irradiated with neutrons

    NASA Astrophysics Data System (ADS)

    Chimi, Yasuhiro; Kitsunai, Yuji; Kasahara, Shigeki; Chatani, Kazuhiro; Koshiishi, Masato; Nishiyama, Yutaka

    2016-07-01

    To elucidate the mechanism of irradiation-assisted stress corrosion cracking (IASCC) in high-temperature water for neutron-irradiated austenitic stainless steels (SSs), the locally deformed structures, the oxide films formed on the deformed areas, and their correlation were investigated. Tensile specimens made of irradiated 316L SSs were strained 0.1%-2% at room temperature or at 563 K, and the surface structures and crystal misorientation among grains were evaluated. The strained specimens were immersed in high-temperature water, and the microstructures of the oxide films on the locally deformed areas were observed. The appearance of visible step structures on the specimens' surface depended on the neutron dose and the applied strain. The surface oxides were observed to be prone to increase in thickness around grain boundaries (GBs) with increasing neutron dose and increasing local strain at the GBs. No penetrative oxidation was observed along GBs or along surface steps.

  12. TEM, XRD and nanoindentation characterization of Xenon ion irradiation damage in austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Huang, H. F.; Li, J. J.; Li, D. H.; Liu, R. D.; Lei, G. H.; Huang, Q.; Yan, L.

    2014-11-01

    Cross-sectional and bulk specimens of a 20% cold-worked 316 austenitic stainless steel (CW 316 SS) has been characterized by TEM, XRD and nanoindentation to determine the microstructural evolution and mechanical property changes of 316 SS after irradiation with 7 MeV Xe26+ ions. TEM results reveal the presence of dislocation loops with a number density of approximately 3 × 1022 m-3 and sizes between 3 to 10 nm due to the collapse of vacancy rich cores inside displacement cascades. Peak broadening observed in XRD diffraction patters reveal systematic changes to lattice parameters due to irradiation. The calculated indentation values in irradiated 316 SS were found to be much higher in comparison to the unirradiated specimen, indicating the dose dependent effect of irradiation on hardness. The relationship between irradiation induced microstructural evolution and the changes to the mechanical properties of CW 316 SS are discussed in the context of fluence and irradiation temperature.

  13. Development of corrosion-resistant improved Al-doped austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Kondo, Keietsu; Miwa, Yukio; Okubo, Nariaki; Kaji, Yoshiyuki; Tsukada, Takashi

    2011-10-01

    Aluminum-doped type 316L SS (316L/Al) has been developed for the purpose of suppressing the degradation of corrosion resistance induced by irradiation in austenitic stainless steels (SSs). The electrochemical corrosion properties of this material were estimated after Ni-ion irradiation at a temperature range from 330 °C to 550 °C. When irradiated at 550 °C up to 12 dpa, 316L/Al showed high corrosion resistance in the vicinity of grain boundaries (GBs) and in grains, while severe GB etching and local corrosion in grains were observed in irradiated 316L and 316 SS. It is supposed that aluminum enrichment was enhanced by high-temperature irradiation at GBs and in grains, to compensate for lost corrosion resistance induced by chromium depletion.

  14. Noncontact nonlinear resonant ultrasound spectroscopy to evaluate creep damage in an austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Ohtani, T.; Kusanagi, Y.; Ishii, Y.

    2013-01-01

    In this paper, we described an evaluating technique of creep damage in an austenitic stainless steel by the combination with an electromagnetic acoustic transducer (EMAT) and the nonlinear resonant ultrasound spectroscopy (NRUS), which was a resonance-based technique exploiting the significant nonlinear behavior of damaged materials. In NRUS, the resonant frequency of an object is studied as a function of the excitation level. As the excitation level increases, the elastic nonlinearity was manifest by a shift in the resonance frequency. The nonlinearity with NRUS showed a peak at 50 % and a minimum at 70 % of the total creep life. This nonlinearity measurement has a potential to assess creep damage advance and predict the creep remaining life of metals.

  15. Effects of low temperature neutron irradiation on deformation behavior of austenitic stainless steels

    SciTech Connect

    Pawel, J.E.; Rowcliffe, A.F.; Alexander, D.J.; Grossbeck, M.L.; Shiba, K.

    1996-04-01

    An austenitic stainless steel, designated 316LN-IG, has been chosen for the first wall/shield (FW/S) structure for the International Thermonuclear Experimental Reactor (ITER). The proposed operational temperature range for the structure (100 to 250{degree}C) is below the temperature regimes for void swelling (400-600{degree}C) and for helium embrittlement (500-700{degree}C). However, the proposed neutron dose is such that large changes in yield strength, deformation mode, and strain hardening capacity could be encountered which could significantly affect fracture properties. Definition of the irradiation regimes in which this phenomenon occurs is essential to the establishment of design rules to protect against various modes of failure.

  16. A study on corrosion behavior of austenitic stainless steel in liquid metals at high temperature

    NASA Astrophysics Data System (ADS)

    Shin, Sang Hun; Kim, Jong Jin; Jung, Ju Ang; Choi, Kyoung Joon; Bang, In Cheol; Kim, Ji Hyun

    2012-03-01

    The purpose of this study is to investigate the interaction between austenitic stainless steel, AISI 316L, and gallium liquid metal at a high temperature, for the potential application to advanced fast reactor coolants. Test specimens of AISI 316L were exposed to static gallium at 500 °C for up to 700 h in two different cover-gas conditions, including air and vacuum. Similar experimental tests were conducted in gallium alloy liquid metal environments, including Ga-14Sn-6Zn and Ga-8Sn-6Zn, in order to study the effect of addition of alloying elements. The results have shown that the weight change and metal loss of specimens were generally reduced in Ga-14Sn-6Zn and Ga-8Sn-6Zn compared to those in pure gallium at a high temperature.

  17. Composite model of microstructural evolution in austenitic stainless steel under fast neutron irradiation

    SciTech Connect

    Stoller, R.E.; Odette, G.R.

    1986-01-01

    A rate-theory-based model has been developed which includes the simultaneous evolution of the dislocation and cavity components of the microstructure of irradiated austenitic stainless steels. Previous work has generally focused on developing models for void swelling while neglecting the time dependence of the dislocation structure. These models have broadened our understanding of the physical processes that give rise to swelling, e.g., the role of helium and void formation from critically-sized bubbles. That work has also demonstrated some predictive capability by successful calibration to fit the results of fast reactor swelling data. However, considerable uncertainty about the values of key parameters in these models limits their usefulness as predictive tools. Hence the use of such models to extrapolate fission reactor swelling data to fusion reactor conditions is compromised.

  18. Microstructure and Nanoindentation Characterization of Low Temperature Hybrid Treated layer on Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Triwiyanto, Askar; Hussain, Patthi; Che Ismail, Mokhtar

    2013-06-01

    In this work, the hybrid treated layer on austenitic AISI 316L stainless steels were characterized to investigate the improvement on its surface properties. Characterization of this resulting layer was performed by FESEM (Field Emission Scanning Electron Microscope), USPM (Universal Scanning Probe Microscope) and nanoindentation. By using these methods, changes in the mechanical properties due to the diffusion of carbon and nitrogen at low temperature treatments have been traced. This hybrid treated sample has confirmed a considerable increase in hardness and a small rise in the elastic modulus compared to the untreated sample. It is found that all treated samples have enhance E/H ratio which exhibited the decreasing tendency to plastic deformation and reduced the mismatch of properties, while keeping deformation within the elastic range.

  19. Microstructural observations of HFIR-irratiated austenitic stainless steels including welds from JP9-16

    SciTech Connect

    Sawai, T.; Shiba, K.; Hishinuma, A.

    1996-04-01

    Austenitic stainless steels, including specimens taken from various electron beam (EB) welds, have been irradiated in HFIR Phase II capsules, JP9-16. Fifteen specimens irradiated at 300, 400, and 500{degrees}C up to 17 dpa are so far examined by a transmission electron microscope (TEM). In 300{degrees}C irradiation, cavities were smaller than 2nm and different specimens showed little difference in cavity microstructure. At 400{degrees}C, cavity size was larger, but still very small (<8 nm). At 500{degrees}C, cavity size reached 30 nm in weld metal specimens of JPCA, while cold worked JPCA contained a small (<5 nm) cavities. Inhomogeneous microstructural evolution was clearly observed in weld-metal specimens irradiated at 500{degrees}C.

  20. Evaluation of the biocompatibility of S-phase layers on medical grade austenitic stainless steels.

    PubMed

    Buhagiar, Joseph; Bell, Thomas; Sammons, Rachel; Dong, Hanshan

    2011-05-01

    S-phase surface layers were formed in AISI 316LVM (ASTM F138) and High-N (ASTM F1586) medical grade austenitic stainless steels by plasma surface alloying with nitrogen (at 430°C), carbon (at 500°C) and both carbon and nitrogen (at 430°C). The presence of the S-phase was confirmed by microscopy, hardness testing, depth-profile analysis of chemical composition and X-ray Diffraction. Attachment and proliferation of mouse osteoblast MC3T3-E1 cells were tested on S-phase and untreated controls and the results demonstrated that all the S-phase layers formed were biocompatible under the conditions used. Cells adhered equally well to all samples but proliferation was enhanced on the treated materials. PMID:21437638

  1. Bauschinger Effect in an Austenitic Steel: Neutron Diffraction and a Multiscale Approach

    NASA Astrophysics Data System (ADS)

    Fajoui, Jamal; Gloaguen, David; Legrand, Vincent; Oum, Guy; Kelleher, Joe; Kockelmann, Winfried

    2016-05-01

    The generation of internal stresses/strains arising from mechanical deformations in single-phase engineering materials was studied. Neutron diffraction measurements were performed to study the evolution of intergranular strains in austenitic steel during sequential loadings. Intergranular strains expand due to incompatibilities between grains and also resulting from single-crystal elastic and plastic anisotropy. A two-level homogenization approach was adopted in order to predict the mechanical state of deformed polycrystals in relation to the microstructure during Bauschinger tests. A mechanical description of the grain was developed through a micro-meso transition based on the Kröner model. The meso-macro transition using a self-consistent approach was applied to deduce the global behavior. Mechanical tests and neutron diffraction measurements were used to validate and assess the model.

  2. Formation of dislocations, precipitates and cavities in He-implanted Mn-Cr austenitic steels

    NASA Astrophysics Data System (ADS)

    Ruedl, E.; Valdrè, G.

    1991-03-01

    Solution-annealed discs of three Mn-Cr austenitic steels containing different amounts of C and N were uniformly implanted at 310 K with 1000 appm He corresponding to ~ 0.2 dpa. The samples were subsequently aged at temperatures from 923 to 1073 K for various times and, after electropolishing, examined by TEM, EDS and EELS. A study was made of the dislocation loops developing on aging and of the compositional changes in their neighbourhood. The formation and growth of precipitates and He-filled cavities was also investigated together with the elemental segregation to the cavity surfaces. It was found that the microstructural evolution in the three materials can take various forms depending on many parameters.

  3. Evolution of secondary phases in austenitic stainless steels during long-term exposures at 600, 650 and 800 deg. C

    SciTech Connect

    Vach, Marian Kunikova, Terezia; Domankova, Maria; Sevc, Peter; Caplovic, Lubomir; Gogola, Peter; Janovec, Jozef

    2008-12-15

    Three austenitic steels (18Cr-8Ni, 18Cr-10Ni, 21Cr-30Ni), used for long-term applications at temperatures between 600 and 800 deg. C were investigated. In the investigation, metallography, transmission electron microscopy, selected area electron diffraction, energy dispersive X-ray spectroscopy, and scanning electron microscopy were used. In additional to the experimental measurements, thermodynamic predictions were done using the ThermoCalc software and the non-commercial database STEEL16F. Various combinations of M{sub 23}C{sub 6}, sigma, and MC phases were identified in the austenite matrix of these steels. It was confirmed experimentally that extra large particles (up to 10 {mu}m) observed in the 21Cr-30Ni steel are M{sub 23}C{sub 6}, even though this carbide was not predicted as the equilibrium carbide at service temperature (800 deg. C). The analytical-experimental approach, combining thermodynamic predictions and experimental measurements, was found to be reliable for the characterization of austenitic steels.

  4. The Effects of Cold Work on the Microstructure and Mechanical Properties of Intermetallic Strengthened Alumina-Forming Austenitic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Hu, B.; Trotter, G.; Baker, Ian; Miller, M. K.; Yao, L.; Chen, S.; Cai, Z.

    2015-08-01

    In order to achieve energy conversion efficiencies of >50 pct for steam turbines/boilers in power generation systems, materials are required that are both strong and corrosion-resistant at >973 K (700 °C), and economically viable. Austenitic steels strengthened with Laves phase, NiAl and Ni3Al precipitates, and alloyed with aluminum to improve oxidation resistance, are potential candidate materials for these applications. The microstructure and microchemistry of recently developed alumina-forming austenitic stainless steels have been characterized by scanning electron microscopy, transmission electron microscopy, and synchrotron X-ray diffraction. Different thermo-mechanical treatments were performed on these steels to improve their mechanical performance. These reduced the grain size significantly to the nanoscale (~100 nm) and the room temperature yield strength to above 1000 MPa. A solutionizing anneal at 1473 K (1200 °C) was found to be effective for uniformly redistributing the Laves phase precipitates that form upon casting.

  5. Alumina-Forming Austenitic Stainless Steels Strengthened by Laves Phase and MC Carbide Precipitates

    NASA Astrophysics Data System (ADS)

    Yamamoto, Y.; Brady, M. P.; Lu, Z. P.; Liu, C. T.; Takeyama, M.; Maziasz, P. J.; Pint, B. A.

    2007-11-01

    Creep strengthening of Al-modified austenitic stainless steels by MC carbides or Fe2Nb Laves phase was explored. Fe-20Cr-15Ni-(0-8)Al and Fe-15Cr-20Ni-5Al base alloys (at. pct) with small additions of Nb, Mo, W, Ti, V, C, and B were cast, thermally-processed, and aged. On exposure from 650 °C to 800 °C in air and in air with 10 pct water vapor, the alloys exhibited continuous protective Al2O3 scale formation at an Al level of only 5 at. pct (2.4 wt pct). Matrices of the Fe-20Cr-15Ni-5Al base alloys consisted of γ (fcc) + α (bcc) dual phase due to the strong α-Fe stabilizing effect of the Al addition and exhibited poor creep resistance. However, adjustment of composition to the Fe-15Cr-20Ni-5Al base resulted in alloys that were single-phase γ-Fe and still capable of alumina scale formation. Alloys that relied solely on Fe2Nb Laves phase precipitates for strengthening exhibited relatively low creep resistance, while alloys that also contained MC carbide precipitates exhibited creep resistance comparable to that of commercially available heat-resistant austenitic stainless steels. Phase equilibria studies indicated that NbC precipitates in combination with Fe2Nb were of limited benefit to creep resistance due to the solution limit of NbC within the γ-Fe matrix of the alloys studied. However, when combined with other MC-type strengtheners, such as V4C3 or TiC, higher levels of creep resistance were obtained.

  6. Effect of lower bainite/martensite/retained austenite triplex microstructure on the mechanical properties of a low-carbon steel with quenching and partitioning process

    NASA Astrophysics Data System (ADS)

    Li, Wan-song; Gao, Hong-ye; Li, Zhong-yi; Nakashima, Hideharu; Hata, Satoshi; Tian, Wen-huai

    2016-03-01

    We present a study concerning Fe-0.176C-1.31Si-1.58Mn-0.26Al-0.3Cr (wt%) steel subjected to a quenching and partitioning (Q&P) process. The results of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and tensile tests demonstrate that the microstructures primarily consist of lath martensite, retained austenite, lower bainite (LB), and a small amount of tempered martensite; moreover, few twin austenite grains were observed. In the microstructure, three types of retained austenite with different sizes and morphologies were observed: blocky retained austenite (~300 nm in width), film-like retained austenite (80-120 nm in width), and ultra- fine film-like retained austenite (30-40 nm in width). Because of the effect of the retained austenite/martensite/LB triplex microstructure, the specimens prepared using different quenching temperatures exhibit high ultimate tensile strength and yield strength. Furthermore, the strength effect of LB can partially counteract the decreasing strength effect of martensite. The formation of LB substantially reduces the amount of retained austenite. Analyses of the retained austenite and the amount of blocky retained austenite indicated that the carbon content is critical to the total elongation of Q&P steel.

  7. Accelerated corrosion of stainless steel in thiocyanate-containing solutions

    SciTech Connect

    Pistorius, P Chris; Li, Wen

    2012-09-19

    It is known that reduced sulfur compounds (such as thiocyanate and thiosulfate) can accelerate active corrosion of austenitic stainless steel in acid solutions, but before we started this project the mechanism of acceleration was largely unclear. This work combined electrochemical measurements and analysis using scanning electron microscopy (SEM) and X-ray photo-electron spectroscopy (XPS), which provided a comprehensive understanding of the catalytic effect of reduced sulfur species on the active corrosion of stainless steel. Both the behavior of the pure elements and the steel were studied and the work focused on the interaction between the pure elements of the steel, which is the least understood area. Upon completion of this work, several aspects are now much clearer. The main results from this work can be summarized as follows: The presence of low concentrations (around 0.1 mM) of thiocyanate or tetrathionate in dilute sulfuric acid greatly accelerates the anodic dissolution of chromium and nickel, but has an even stronger effect on stainless steels (iron-chromium-nickel alloys). Electrochemical measurements and surface analyses are in agreement with the suggestion that accelerated dissolution really results from suppressed passivation. Even well below the passivation potential, the electrochemical signature of passivation is evident in the electrode impedance; the electrode impedance shows clearly that this pre-passivation is suppressed in the presence of thiocyanate. For the stainless steels, remarkable changes in the morphology of the corroded metal surface and in the surface concentration of chromium support the suggestion that pre-passivation of stainless steels is suppressed because dissolution of chromium is accelerated. Surface analysis confirmed that adsorbed sulfur / sulfide forms on the metal surfaces upon exposure to solutions containing thiocyanate or thiosulfate. For pure nickel, and steels containing nickel (and residual copper), bulk sulfide

  8. Synthesis of chromium-nickel nanoparticles prepared by a microemulsion method and mechanical milling.

    PubMed

    Ban, Irena; Stergar, Janja; Drofenik, Miha; Ferk, Gregor; Makovec, Darko

    2013-01-01

    A chemical and a physical method have been applied for the preparation of chromium-nickel alloy nanoparticles. These particles were designed to be used for controlled magnetic hyperthermia applications. Microemulsions with Ni2+ and Cr3+ and/or NaBH4 as precursors were prepared using the isooctane/CTAB, n-butanol/H2O system. The samples of CrxNi1-x nanoparticles with the desired composition were obtained after the reduction of their salts with NaBH4 and afterwards heat treated in a TGA in a N2 atmosphere at various temperatures. The CrxNi1-x materials were also prepared by mechanical milling. Utilizing a ball-to-powder mass ratio of 20 : 1 and selecting the proper alloy compositions we were able to obtain nanocrystalline CrxNi1-x particles. Thermal demagnetization in the vicinity of the Curie temperature of the nanoparticles was studied using a modified TGA-SDTA method. The alloy's phase composition, size and morphology were determined with XRD measurements and TEM analyses. PMID:24362977

  9. [On deffect of cobalt-chromium-nickel alloy for dental castings (author's transl)].

    PubMed

    Nasu, T; Hikichi, H; Noguchi, H

    1978-01-01

    We studied about castability and microporosity of cobalt-chromium-nickel alloy for dental casting in various methods of fusion and casting. The combinations of fusion and casting were induction fusion and centrifugal casting, arc discharge fusion and argon gas pressure casting and oxy-acetylene flame fusion and centrifugal casting. The following results were obtained. 1. The amount of microposity was smaller, when only mold temperature was low, and as mold temperature and casting temperature were high, castability was better. 2. The arc discharge fusion and argon gas pressure casting was the best method about castability and microporosity in three methods. Second method was the induction fusion and centrifugal casting. 3. In the induction fusion and centrifugal casting, blowing arong gas of 1 l/min to molten metal to protect the metal from oxidization improved the castability the best, but amount of microporosity was large, so that it was needed to lower the mold temperature in this condition. 4. The oxyacetylene flame fusion and centrifugal casting was not suitable for the casting of Co-Cr alloy "Regalloy No. 3", for the alloy was made for the induction fusion casting. PMID:366039

  10. Preferred Crystallographic Orientation Development in Nano/Ultrafine-Grained 316L Stainless Steel During Martensite to Austenite Reversion

    NASA Astrophysics Data System (ADS)

    Eskandari, M.; Mohtadi-Bonab, M. A.; Basu, R.; Nezakat, M.; Kermanpur, A.; Szpunar, J. A.; Nahar, S.; Baghpanah, A. H.

    2015-02-01

    The crystallographic orientation of cold-rolled 316L stainless steel is investigated during reversion of strain-induced ά-martensite to nano/ultrafine-grained austenite upon annealing at 750 °C for different holding times; 1, 5, 15, and 30 min. The texture of nanoscale reverted austenite reveals a Brass ({110}<112>) and a Goss ({110}<100>) textures after annealing for 1 min. No new texture component is appeared through the completion of martensite to austenite reversion for 5 min, but the intensity of Brass and Goss textures are increased. Further annealing for 30 min results in a stronger texture with higher intensity for Brass compared to Goss.

  11. Coupled Model for Carbon Partitioning from Martensite into Austenite During the Quenching Process in Fe-C Steels

    NASA Astrophysics Data System (ADS)

    Liu, Peixing; Zhu, Bin; Wang, Yilin; Zhang, Yisheng

    2016-08-01

    In this paper, a coupled model for carbon partitioning from martensite into austenite during the quenching process in Fe-C steels is constructed where the carbon is permitted to partition while the martensite is continuously forming. A diffusion model of carbon at the `martensite/austenite interface' is created where the interface does not move during the carbon partitioning process, and the driving force for carbon partitioning originates from the chemical potential difference. The results show that the martensitic transformation and carbon partitioning affect each other, and that the cooling rate between the martensite start temperature ( M s) and room temperature has a major effect on the volume fraction of the final retained austenite. The simulation results are shown to be in good agreement with experiments.

  12. Microstructural Evolutions During Annealing of Plastically Deformed AISI 304 Austenitic Stainless Steel: Martensite Reversion, Grain Refinement, Recrystallization, and Grain Growth

    NASA Astrophysics Data System (ADS)

    Naghizadeh, Meysam; Mirzadeh, Hamed

    2016-06-01

    Microstructural evolutions during annealing of a plastically deformed AISI 304 stainless steel were investigated. Three distinct stages were identified for the reversion of strain-induced martensite to austenite, which were followed by the recrystallization of the retained austenite phase and overall grain growth. It was shown that the primary recrystallization of the retained austenite postpones the formation of an equiaxed microstructure, which coincides with the coarsening of the very fine reversed grains. The latter can effectively impair the usefulness of this thermomechanical treatment for grain refinement at both high and low annealing temperatures. The final grain growth stage, however, was found to be significant at high annealing temperatures, which makes it difficult to control the reversion annealing process for enhancement of mechanical properties. Conclusively, this work unravels the important microstructural evolution stages during reversion annealing and can shed light on the requirements and limitations of this efficient grain refining approach.

  13. Microstructural Evolutions During Annealing of Plastically Deformed AISI 304 Austenitic Stainless Steel: Martensite Reversion, Grain Refinement, Recrystallization, and Grain Growth

    NASA Astrophysics Data System (ADS)

    Naghizadeh, Meysam; Mirzadeh, Hamed

    2016-08-01

    Microstructural evolutions during annealing of a plastically deformed AISI 304 stainless steel were investigated. Three distinct stages were identified for the reversion of strain-induced martensite to austenite, which were followed by the recrystallization of the retained austenite phase and overall grain growth. It was shown that the primary recrystallization of the retained austenite postpones the formation of an equiaxed microstructure, which coincides with the coarsening of the very fine reversed grains. The latter can effectively impair the usefulness of this thermomechanical treatment for grain refinement at both high and low annealing temperatures. The final grain growth stage, however, was found to be significant at high annealing temperatures, which makes it difficult to control the reversion annealing process for enhancement of mechanical properties. Conclusively, this work unravels the important microstructural evolution stages during reversion annealing and can shed light on the requirements and limitations of this efficient grain refining approach.

  14. Coupled Model for Carbon Partitioning from Martensite into Austenite During the Quenching Process in Fe-C Steels

    NASA Astrophysics Data System (ADS)

    Liu, Peixing; Zhu, Bin; Wang, Yilin; Zhang, Yisheng

    2016-05-01

    In this paper, a coupled model for carbon partitioning from martensite into austenite during the quenching process in Fe-C steels is constructed where the carbon is permitted to partition while the martensite is continuously forming. A diffusion model of carbon at the `martensite/austenite interface' is created where the interface does not move during the carbon partitioning process, and the driving force for carbon partitioning originates from the chemical potential difference. The results show that the martensitic transformation and carbon partitioning affect each other, and that the cooling rate between the martensite start temperature (M s) and room temperature has a major effect on the volume fraction of the final retained austenite. The simulation results are shown to be in good agreement with experiments.

  15. Microstructural characterization of high-manganese austenitic steels with different stacking fault energies

    SciTech Connect

    Sato, Shigeo; Kwon, Eui-Pyo; Imafuku, Muneyuki; Wagatsuma, Kazuaki; Suzuki, Shigeru

    2011-08-15

    Microstructures of tensile-deformed high-manganese austenitic steels exhibiting twinning-induced plasticity were analyzed by electron backscatter diffraction pattern observation and X-ray diffraction measurement to examine the influence of differences in their stacking fault energies on twinning activity during deformation. The steel specimen with the low stacking fault energy of 15 mJ/m{sup 2} had a microstructure with a high population of mechanical twins than the steel specimen with the high stacking fault energy (25 mJ/m{sup 2}). The <111> and <100> fibers developed along the tensile axis, and mechanical twinning occurred preferentially in the <111> fiber. The Schmid factors for slip and twinning deformations can explain the origin of higher twinning activity in the <111> fiber. However, the high stacking fault energy suppresses the twinning activity even in the <111> fiber. A line profile analysis based on the X-ray diffraction data revealed the relationship between the characteristics of the deformed microstructures and the stacking fault energies of the steel specimens. Although the variation in dislocation density with the tensile deformation is not affected by the stacking fault energies, the effect of the stacking fault energies on the crystallite size refinement becomes significant with a decrease in the stacking fault energies. Moreover, the stacking fault probability, which was estimated from a peak-shift analysis of the 111 and 200 diffractions, was high for the specimen with low stacking fault energy. Regardless of the difference in the stacking fault energies of the steel specimens, the refined crystallite size has a certain correlation with the stacking fault probability, indicating that whether the deformation-induced crystallite-size refinement occurs depends directly on the stacking fault probability rather than on the stacking fault energies in the present steel specimens. - Highlights: {yields} We studied effects of stacking fault energies on

  16. Effects of fluoride and other halogen ions on the external stress corrosion cracking of Type 304 austenitic stainless steel

    SciTech Connect

    Whorlow, K.M.; Hutto, F.B. Jr.

    1997-07-01

    The drip procedure from the Standard Test Method for Evaluating the Influence of Thermal Insulation on External Stress Corrosion Cracking Tendency of Austenitic Stainless Steel (ASTM C 692-95a) was used to research the effect of halogens and inhibitors on the External Stress Corrosion Cracking (ESCC) of Type 304 stainless steel as it applies to Nuclear Regulatory Commission Regulatory Guide 1.36, Nonmetallic Thermal Insulation for Austenitic Stainless Steel. The solutions used in this research were prepared using pure chemical reagents to simulate the halogens and inhibitors found in insulation extraction solutions. The results indicated that sodium silicate compounds that were higher in sodium were more effective for preventing chloride-induced ESCC in Type 304 austenitic stainless steel. Potassium silicate (all-silicate inhibitor) was not as effective as sodium silicate. Limited testing with sodium hydroxide (all-sodium inhibitor) indicated that it may be effective as an inhibitor. Fluoride, bromide, and iodide caused minimal ESCC which could be effectively inhibited by sodium silicate. The addition of fluoride to the chloride/sodium silicate systems at the threshold of ESCC appeared to have no synergistic effect on ESCC. The mass ratio of sodium + silicate (mg/kg) to chloride (mg/kg) at the lower end of the NRC RG 1.36 Acceptability Curve was not sufficient to prevent ESCC using the methods of this research.

  17. Effect of Vanadium Nitride Precipitation on Martensitic Transformation and Mechanical Properties of CrMnNi Cast Austenitic Steels

    NASA Astrophysics Data System (ADS)

    Wendler, Marco; Reichel, Benedikt; Eckner, Ralf; Fabrichnaya, Olga; Krüger, Lutz; Weiß, Andreas; Mola, Javad

    2016-01-01

    The microstructural evolution and mechanical properties of two cast Fe-15Cr-6Mn-3Ni-0.5Si-0.2N-0.1C (concentrations in wt pct) steels containing no vanadium and 0.65 wt pct vanadium were investigated under uniaxial tensile loading for room temperature (RT) and 373 K (100 °C). The alloy development was focused on the formation of nanosized vanadium nitride precipitates in the austenite to serve as obstacles to dislocation motion. The austenitic steels exhibited transformation- and twinning-induced plasticity (TRIP/TWIP) effects and the planar glide of dislocations in the austenite. The triggering stress for the RT strain-induced σ γ→ α' formation increased by 190 MPa, and the transformation occurred at higher strain levels due to the presence of VN precipitates. The occurrence of the TWIP effect during tensile testing at 373 K (100 °C) of both steels resulted in engineering strains above 50 pct. The yield strength (YS) of the VN-containing steel was 420 MPa at RT, 52 MPa higher than the vanadium-free alloy. The difference increased to 59 MPa at 373 K (100 °C) with the VN-containing alloy exhibiting a YS of 311 MPa.

  18. EFFECT OF MINOR ADDITIONS OF HYDROGEN TO ARGON SHIELDING GAS WHEN WELDING AUSTENITIC STAINLESS STEEL WITH THE GTAW PROCESS

    SciTech Connect

    CANNELL, G.R.

    2004-12-15

    This paper provides the technical basis to conclude that the use of hydrogen containing shielding gases during welding of austenitic stainless steels will not lead to hydrogen induced cracking (HIC) of the weld or weld heat affected zone. Argon-hydrogen gas mixtures, with hydrogen additions up to 35% [1], have been successfully used as the shielding gas in gas tungsten arc welding (GTAW) of austenitic stainless steels. The addition of hydrogen improves weld pool wettability, bead shape control, surface cleanliness and heat input. The GTAW process is used extensively for welding various grades of stainless steel and is preferred when a very high weld quality is desired, such as that required for closure welding of nuclear materials packages. The use of argon-hydrogen gas mixtures for high-quality welding is occasionally questioned, primarily because of concern over the potential for HIC. This paper was written specifically to provide a technical basis for using an argon-hydrogen shielding gas in conjunction with the development, at the Savannah River Technology Center (SRTC), of an ''optimized'' closure welding process for the DOE standardized spent nuclear fuel canister [2]. However, the basis developed here can be applied to other applications in which the use of an argon-hydrogen shielding gas for GTAW welding of austenitic stainless steels is desired.

  19. Irradiation-assisted stress corrosion cracking behavior of austenitic stainless steels applicable to LWR core internals.

    SciTech Connect

    Chung, H. M.; Shack, W. J.; Energy Technology

    2006-01-31

    This report summarizes work performed at Argonne National Laboratory on irradiation-assisted stress corrosion cracking (IASCC) of austenitic stainless steels that were irradiated in the Halden reactor in simulation of irradiation-induced degradation of boiling water reactor (BWR) core internal components. Slow-strain-rate tensile tests in BWR-like oxidizing water were conducted on 27 austenitic stainless steel alloys that were irradiated at 288 C in helium to 0.4, 1.3, and 3.0 dpa. Fractographic analysis was conducted to determine the fracture surface morphology. Microchemical analysis by Auger electron spectroscopy was performed on BWR neutron absorber tubes to characterize grain-boundary segregation of important elements under BWR conditions. At 0.4 and 1.4 dpa, transgranular fracture was mixed with intergranular fracture. At 3 dpa, transgranular cracking was negligible, and fracture surface was either dominantly intergranular, as in field-cracked core internals, or dominantly ductile or mixed. This behavior indicates that percent intergranular stress corrosion cracking determined at {approx}3 dpa is a good measure of IASCC susceptibility. At {approx}1.4 dpa, a beneficial effect of a high concentration of Si (0.8-1.5 wt.%) was observed. At {approx}3 dpa, however, such effect was obscured by a deleterious effect of S. Excellent resistance to IASCC was observed up to {approx}3 dpa for eight heats of Types 304, 316, and 348 steel that contain very low concentrations of S. Susceptibility of Types 304 and 316 steels that contain >0.003 wt.% S increased drastically. This indicates that a sulfur related critical phenomenon plays an important role in IASCC. A sulfur content of <0.002 wt.% is the primary material factor necessary to ensure good resistance to IASCC. However, for Types 304L and 316L steel and their high-purity counterparts, a sulfur content of <0.002 wt.% alone is not a sufficient condition to ensure good resistance to IASCC. This is in distinct contrast to

  20. Effect of Intercritical Thermomechanical Processing on Austenite Retention and Mechanical Properties in a Multiphase TRIP-Assisted Steel

    NASA Astrophysics Data System (ADS)

    Mohamadizadeh, Alireza; Zarei-Hanzaki, Abbas; Mehtonen, Saara; Porter, David; Moallemi, Mohammad

    2016-01-01

    The effect of dynamic microstructural evolution on austenite retention was investigated in a transformation-induced plasticity-assisted multiphase steel by compressive deformation between 993 K and 1233 K (720 °C and 960 °C) covering the intercritical two-phase region. Based on optical microscopy and electron backscatter diffraction observations, extensive dynamic recovery of ferrite occurred below 1113 K (840 °C), i.e., lower part of two-phase region, due to strain concentration in the ferrite. Deformation-induced ferrite formation occurred at temperatures between 1113 K and 1153 K (840 °C to 880 °C), i.e., upper part of two-phase region, providing up to 27 pct additional fine ferrite grains compared to the undeformed state. Dynamic recrystallization of austenite took place at temperatures above 1173 K (900 °C), above Ac3. The dynamic restoration phenomena were found to have no positive influence on austenite retention; however, shear punch test results indicated that the specimens processed at 1113 K to 1153 K (840 °C to 880 °C) had a very good combination of strength and elongation, which was attributed to the synergic effects of the transformation of retained austenite and the fine ferrite structure generated through deformation-induced ferrite formation. X-ray diffraction analysis and scanning electron microscopy showed that deformation-induced ferrite might have rejected the excess carbon to the boundaries, thereby promoting the austenite formation in these regions. The present findings suggest that austenite can be dynamically stabilized as the result of deformation-induced ferrite formation. The effect is referred to as dynamic transformation-assisted austenite retention.

  1. Effects of welding on weldment mechanical performance in two austenitic steels

    SciTech Connect

    Strum, M.J.

    1982-06-01

    The effect of autogenous gas-tungsten arc-welding on the mechanical performance of two austenitic steels has been evaluated for cable jackets of force-cooled superconductor coils. The original candidate material was Nitronic 40, a nitrogen-strengthened stainless steel. The in-situ reaction heat treatment at 700/sup 0/C necessary for the formation of the superconducting A15 phase results in severe degradation of the cryogenic tensile ductility in the weld metal. The search for an alternate material led to JBK-75, a modified A-286 type ..gamma..' precipitation hardening iron-based superalloy. Observations of a tensile strength mismatch between base metal and the weaker weld metal in JBK-75 prompted a study into the aging response in weldments of this alloy. Localized strain through slip step traces show an easy path of deformation within the solidification structure. Weldment strength varies with grain size. It was found that through post-weld annealing treatments at 950/sup 0/C, prior to aging, weldment hardness levels can be matched. However, although increased strength levels are obtained in the weld metal, concomitant decreases in base metal strengths are suffered, presumably due to observed grain growth. 24 figures, 9 tables.

  2. Strengthening of σ phase in a Fe20Cr9Ni cast austenite stainless steel

    SciTech Connect

    Wang, Y.Q.; Han, J.; Yang, B.; Wang, X.T.

    2013-10-15

    The strengthening mechanism of σ phase in a Fe20Cr9Ni cast austenite stainless steel used for primary coolant pipes of nuclear power plants has been investigated. The yield and ultimate tensile strengths of aged specimens increased comparing with those of the unaged ones. It was found that the increase of strengths is due to the hard and brittle (σ + γ{sub 2}) structure which decomposed from α phase in the steel. Fracture surfaces of specimens after in situ tensile test showed that the inhibition of (σ + γ{sub 2}) structure on the dislocation movements was more significant than ferrite although cracks started predominately at σ/γ{sub 2} interfaces. The (σ + γ{sub 2}) structure behaves like a fiber reinforced composite material. - Highlights: • The strengthening mechanism of σ phase in a Fe20Cr9Ni CASS is investigated. • The yield and ultimate tensile strengths increase with increasing of σ phase. • The increase of strengths is due to hard and brittle (σ + γ{sub 2}) structure. • The (σ + γ{sub 2}) structure in CASS behaves like a fibre reinforced composite material. • The σ/γ{sub 2} and α/σ/γ{sub 2} boundaries hinder the movement of dislocation.

  3. A Comparison of Ultrasonic Flaw Responses as Observed through Austenitic Stainless Steel Piping Welds

    SciTech Connect

    Anderson, Michael T.; Crawford, Susan L.; Cumblidge, Stephen E.; Diaz, Aaron A.; Doctor, Steven R.

    2008-01-01

    A study was conducted to assess ultrasonic techniques for detection and sizing of flaws from the opposite side of wrought austenitic piping welds. A series of stainless steel specimens with implanted flaws were examined using phased-array ultrasonic probes. These examinations were conducted from both sides of the full-penetration structural piping welds, with emphasis on comparing the responses from the far-side inspection. The types of flaws examined include thermal fatigue cracks, saw cuts, and service-induced intergranular stress corrosion cracks (IGSCC). The flaws were examined using three phased-array probes: a 2-MHz shear-wave probe, a 1.5-MHz longitudinal-wave probe, and a “mini” 2-MHz longitudinal-wave probe. The sound fields for each probe were modeled in stainless steel to assure proper insonification at the depths and angles used in the tests. This paper describes the results of the sound field modeling, and compares the responses of the various flaws from the near and far side of the welds.

  4. Welding of 316L Austenitic Stainless Steel with Activated Tungsten Inert Gas Process

    NASA Astrophysics Data System (ADS)

    Ahmadi, E.; Ebrahimi, A. R.

    2015-02-01

    The use of activating flux in TIG welding process is one of the most notable techniques which are developed recently. This technique, known as A-TIG welding, increases the penetration depth and improves the productivity of the TIG welding. In the present study, four oxide fluxes (SiO2, TiO2, Cr2O3, and CaO) were used to investigate the effect of activating flux on the depth/width ratio and mechanical property of 316L austenitic stainless steel. The effect of coating density of activating flux on the weld pool shape and oxygen content in the weld after the welding process was studied systematically. Experimental results indicated that the maximum depth/width ratio of stainless steel activated TIG weld was obtained when the coating density was 2.6, 1.3, 2, and 7.8 mg/cm2 for SiO2, TiO2, Cr2O3, and CaO, respectively. The certain range of oxygen content dissolved in the weld, led to a significant increase in the penetration capability of TIG welds. TIG welding with active fluxes can increase the delta-ferrite content and improves the mechanical strength of the welded joint.

  5. Crack growth rates of irradiated austenitic stainless steel weld heat affected zone in BWR environments.

    SciTech Connect

    Chopra, O. K.; Alexandreanu, B.; Gruber, E. E.; Daum, R. S.; Shack, W. J.; Energy Technology

    2006-01-31

    Austenitic stainless steels (SSs) are used extensively as structural alloys in the internal components of reactor pressure vessels because of their superior fracture toughness. However, exposure to high levels of neutron irradiation for extended periods can exacerbate the corrosion fatigue and stress corrosion cracking (SCC) behavior of these steels by affecting the material microchemistry, material microstructure, and water chemistry. Experimental data are presented on crack growth rates of the heat affected zone (HAZ) in Types 304L and 304 SS weld specimens before and after they were irradiated to a fluence of 5.0 x 10{sup 20} n/cm{sup 2} (E > 1 MeV) ({approx} 0.75 dpa) at {approx}288 C. Crack growth tests were conducted under cycling loading and long hold time trapezoidal loading in simulated boiling water reactor environments on Type 304L SS HAZ of the H5 weld from the Grand Gulf reactor core shroud and on Type 304 SS HAZ of a laboratory-prepared weld. The effects of material composition, irradiation, and water chemistry on growth rates are discussed.

  6. Microstructural changes induced near crack tip during corrosion fatigue tests in austenitic-ferritic steel.

    PubMed

    Gołebiowski, B; Swiatnicki, W A; Gaspérini, M

    2010-03-01

    Microstructural changes occurring during fatigue tests of austenitic-ferritic duplex stainless steel (DSS) in air and in hydrogen-generating environment have been investigated. Hydrogen charging of steel samples during fatigue crack growth (FCG) tests was performed by cathodic polarization of specimens in 0.1M H(2)SO(4) aqueous solution. Microstructural investigations of specimens after FCG tests were carried out using transmission electron microscopy to reveal the density and arrangement of dislocations formed near crack tip. To determine the way of crack propagation in the microstructure, electron backscatter diffraction investigations were performed on fatigue-tested samples in both kinds of environment. To reveal hydrogen-induced phase transformations the atomic force microscopy was used. The above investigations allowed us to define the character of fatigue crack propagation and microstructural changes near the crack tip. It was found that crack propagation after fatigue tests in air is accompanied with plastic deformation; a high density of dislocations is observed at large distance from the crack. After fatigue tests performed during hydrogen charging the deformed zone containing high density of dislocations is narrow compared to that after fatigue tests in air. It means that hydrogenation leads to brittle character of fatigue crack propagation. In air, fatigue cracks propagate mostly transgranularly, whereas in hydrogen-generating environment the cracks have mixed transgranular/interfacial character. PMID:20500395

  7. Partial transient liquid phase diffusion bonding of Zircaloy-4 to stabilized austenitic stainless steel 321

    SciTech Connect

    Atabaki, M. Mazar; Hanzaei, A. Talebi

    2010-10-15

    An innovative method was applied for bonding Zircaloy-4 to stabilized austenitic stainless steel 321 using an active titanium interlayer. Specimens were joined by a partial transient liquid phase diffusion bonding method in a vacuum furnace at different temperatures under 1 MPa dynamic pressure of contact. The influence of different bonding temperatures on the microstructure, microindentation hardness, joint strength and interlayer thickness has been studied. The diffusion of Fe, Cr, Ni and Zr has been investigated by scanning electron microscopy and energy dispersive spectroscopy elemental analyses. Results showed that control of the heating and cooling rate and 20 min soaking at 1223 K produces a perfect joint. However, solid-state diffusion of the melting point depressant elements into the joint metal causes the solid/liquid interface to advance until the joint is solidified. The tensile strength of all the bonded specimens was found around 480-670 MPa. Energy dispersive spectroscopy studies indicated that the melting occurred along the interface of the bonded specimens as a result of the transfer of atoms between the interlayer and the matrix during bonding. This technique provides a reliable method of bonding zirconium alloy to stainless steel.

  8. Analysis of the strain induced martensitic transformation in austenitic steel subjected to dynamic perforation

    NASA Astrophysics Data System (ADS)

    Rodríguez-Martínez, J. A.; Rusinek, A.; Pesci, R.; Zaera, R.

    2012-08-01

    An experimental and numerical analysis on the martensitic transformation in AISI 304 steel sheets subjected to perforation by conical and hemispherical projectiles is reported. Two target thicknesses are considered, 0.5 and 1.0 mm, and impact velocities range from 35 to 200 m/s. The perforation mechanisms are identified and the effect of the projectile nose-shape on the ability of the target for energy absorption is evaluated. Martensite has been detected in all the impacted samples and the role played by the projectile nose-shape on the transformation is highlighted. A 3D model implemented in ABAQUS/Explicit allowed to simulate the perforation tests. The material is defined through a constitutive description developed by the authors to describe the strain induced martensitic transformation taking place in metastable austenitic steels at high strain rates. The numerical results are compared with the experimental evidence and satisfactory matching is obtained. The numerical model succeeds in describing the perforation mechanisms associated to each projectile-target configuration analysed.

  9. Investigation of thermal spray coatings on austenitic stainless steel substrate to enhance corrosion protection

    NASA Astrophysics Data System (ADS)

    Rogers, Daniel M.

    The research is aimed to evaluate thermal spray coatings to address material issues in supercritical and ultra-supercritical Rankine cycles. The primary purpose of the research is to test, evaluate, and eventually implement a coating to improve corrosion resistance and increase efficiency of coal fired power plants. The research is performed as part of a comprehensive project to evaluate the ability of titanium, titanium carbide, or titanium diboride powders to provide fireside corrosion resistance in supercritical and ultra-supercritical steam boilers, specifically, coal driven boilers in Illinois that must utilize high sulfur and high chlorine content coal. [1] The powder coatings that were tested are nano-sized titanium carbide (TiC) and titanium di-boride (TiB2) powders that were synthesized by a patented process at Southern Illinois University. The powders were then sent to Gas Technology Institute in Chicago to coat steel coupons by HVOF (High Velocity Oxy-Fuel) thermal spray technique. The powders were coated on an austenitic 304H stainless steel substrate which is commonly found in high temperature boilers, pipelines, and heat exchangers. The samples then went through various tests for various lengths of time under subcritical, supercritical, and ultra-supercritical conditions. The samples were examined using a scanning electron microscope and x-ray diffraction techniques to study microstructural changes and then determined which coating performed best.

  10. Compatibility of martensitic/austenitic steel welds with liquid lead bismuth eutectic environment

    NASA Astrophysics Data System (ADS)

    Van den Bosch, J.; Almazouzi, A.

    2009-04-01

    The high-chromium ferritic/martensitic steel T91 and the austenitic stainless steel 316L are to be used in contact with liquid lead-bismuth eutectic (LBE), under high irradiation doses. Both tungsten inert gas (TIG) and electron beam (EB) T91/316L welds have been examined by means of metallography, scanning electron microscopy (SEM-EDX), Vickers hardness measurements and tensile testing both in inert gas and in LBE. Although the T91/316L TIG weld has very good mechanical properties when tested in air, its properties decline sharply when tested in LBE. This degradation in mechanical properties is attributed to the liquid metal embrittlement of the 309 buttering used in TIG welding of T91/316L welds. In contrast to mixed T91/316L TIG welding, the mixed T91/316L EB weld was performed without buttering. The mechanical behaviour of the T91/316L EB weld was very good in air after post weld heat treatment but deteriorated when tested in LBE.

  11. Attachment of Listeria monocytogenes to an austenitic stainless steel after welding and accelerated corrosion treatments.

    PubMed

    Mai, Tam L; Sofyan, Nofrijon I; Fergus, Jeffrey W; Gale, William F; Conner, Donald E

    2006-07-01

    Austenitic stainless steels, widely used in food processing, undergo microstructural changes during welding, resulting in three distinctive zones: weld metal, heat-affected zone, and base metal. This research was conducted to determine the attachment of Listeria monocytogenes in these three zones before and after exposure to a corrosive environment. All experiments were done with tungsten inert gas welding of type 304 stainless steel. The four welding treatments were large or small beads with high or low heat. After welding, all surfaces were polished to an equivalent surface finish. A 10-microl droplet of an L. monocytogenes suspension was placed on the test surfaces. After 3 h at 23 degrees C, the surfaces were washed and prepared for scanning electron microscopy, which was used to determine attachment of L. monocytogenes by counting cells remaining on each test surface. In general, bacteria were randomly distributed on each surface type. However, differences in surface area of inoculum due to differences in interfacial energy (as manifested by the contact angle) were apparent and required normalization of bacterial count data. There were no differences (P > 0.05) in numbers of bacteria on the three surface zones. However, after exposure to the corrosive medium, numbers of bacteria on the three zones were higher (P < 0.05) than those on the corresponding zones of noncorroded surfaces. For the corroded surfaces, bacterial counts on the base metal were lower (P < 0.05) than those on heat-affected and weld zones. PMID:16865881

  12. Investigation on the Behavior of Austenite and Ferrite Phases at Stagnation Region in the Turning of Duplex Stainless Steel Alloys

    NASA Astrophysics Data System (ADS)

    Nomani, J.; Pramanik, A.; Hilditch, T.; Littlefair, G.

    2016-06-01

    This paper investigates the deformation mechanisms and plastic behavior of austenite and ferrite phases in duplex stainless steel alloys 2205 and 2507 under chip formation from a machine turning operation. SEM images and EBSD phase mapping of frozen chip root samples detected a build-up of ferrite bands in the stagnation region, and between 65 and 85 pct, more ferrite was identified in the stagnation region compared to austenite. SEM images detected micro-cracks developing in the ferrite phase, indicating ferritic build-up in the stagnation region as a potential triggering mechanism to the formation of built-up edge, as transgranular micro-cracks found in the stagnation region are similar to micro-cracks initiating built-up edge formation. Higher plasticity of austenite due to softening under high strain is seen responsible for the ferrite build-up. Flow lines indicate that austenite is plastically deforming at a greater rate into the chip, while ferrite shows to partition most of the strain during deformation. The loss of annealing twins and activation of multiple slip planes triggered at high strain may explain the highly plastic behavior shown by austenite.

  13. Investigation on the Behavior of Austenite and Ferrite Phases at Stagnation Region in the Turning of Duplex Stainless Steel Alloys

    NASA Astrophysics Data System (ADS)

    Nomani, J.; Pramanik, A.; Hilditch, T.; Littlefair, G.

    2016-04-01

    This paper investigates the deformation mechanisms and plastic behavior of austenite and ferrite phases in duplex stainless steel alloys 2205 and 2507 under chip formation from a machine turning operation. SEM images and EBSD phase mapping of frozen chip root samples detected a build-up of ferrite bands in the stagnation region, and between 65 and 85 pct, more ferrite was identified in the stagnation region compared to austenite. SEM images detected micro-cracks developing in the ferrite phase, indicating ferritic build-up in the stagnation region as a potential triggering mechanism to the formation of built-up edge, as transgranular micro-cracks found in the stagnation region are similar to micro-cracks initiating built-up edge formation. Higher plasticity of austenite due to softening under high strain is seen responsible for the ferrite build-up. Flow lines indicate that austenite is plastically deforming at a greater rate into the chip, while ferrite shows to partition most of the strain during deformation. The loss of annealing twins and activation of multiple slip planes triggered at high strain may explain the highly plastic behavior shown by austenite.

  14. Structural Transformations in Austenitic Stainless Steel Induced by Deuterium Implantation: Irradiation at 295 K.

    PubMed

    Morozov, Oleksandr; Zhurba, Volodymir; Neklyudov, Ivan; Mats, Oleksandr; Progolaieva, Viktoria; Boshko, Valerian

    2016-12-01

    Deuterium thermal desorption spectra were investigated on the samples of austenitic steel 18Cr10NiTi pre-implanted at 295 K with deuterium ions in the dose range from 8 × 10(14) to 2.7 × 10(18) D/cm(2). The kinetics of structural transformation development in the steel layer was traced from deuterium thermodesorption spectra as a function of deuterium concentration. Three characteristic regions with different low rates of deuterium amount desorption as the implantation dose increases were revealed: I-the linear region of low implantation doses (up to 1 × 10(17) D/cm(2)); II-the nonlinear region of medium implantation doses (1 × 10(17) to 8 × 10(17) D/cm(2)); III-the linear region of high implantation doses (8 × 10(17) to 2.7 × 10(18) D/cm(2)). During the process of deuterium ion irradiation, the coefficient of deuterium retention in steel varies in discrete steps. Each of the discrete regions of deuterium retention coefficient variation corresponds to different implanted-matter states formed during deuterium ion implantation. The low-dose region is characterized by formation of deuterium-vacancy complexes and solid-solution phase state of deuterium in the steel. The total concentration of the accumulated deuterium in this region varies between 2.5 and 3 at.%. The medium-dose region is characterized by the radiation-induced action on the steel in the presence of deuterium with the resulting formation of the energy-stable nanosized crystalline structure of steel, having a developed network of intercrystalline boundaries. The basis for this developed network of intercrystalline boundaries is provided by the amorphous state, which manifests itself in the thermodesorption spectra as a widely temperature-scale extended region of deuterium desorption (structure formation with a varying activation energy). The total concentration of the accumulated deuterium in the region of medium implantation doses makes 7 to 8 at.%. The

  15. Structural Transformations in Austenitic Stainless Steel Induced by Deuterium Implantation: Irradiation at 295 K

    NASA Astrophysics Data System (ADS)

    Morozov, Oleksandr; Zhurba, Volodymir; Neklyudov, Ivan; Mats, Oleksandr; Progolaieva, Viktoria; Boshko, Valerian

    2016-02-01

    Deuterium thermal desorption spectra were investigated on the samples of austenitic steel 18Cr10NiTi pre-implanted at 295 K with deuterium ions in the dose range from 8 × 1014 to 2.7 × 1018 D/cm2. The kinetics of structural transformation development in the steel layer was traced from deuterium thermodesorption spectra as a function of deuterium concentration. Three characteristic regions with different low rates of deuterium amount desorption as the implantation dose increases were revealed: I—the linear region of low implantation doses (up to 1 × 1017 D/cm2); II—the nonlinear region of medium implantation doses (1 × 1017 to 8 × 1017 D/cm2); III—the linear region of high implantation doses (8 × 1017 to 2.7 × 1018 D/cm2). During the process of deuterium ion irradiation, the coefficient of deuterium retention in steel varies in discrete steps. Each of the discrete regions of deuterium retention coefficient variation corresponds to different implanted-matter states formed during deuterium ion implantation. The low-dose region is characterized by formation of deuterium-vacancy complexes and solid-solution phase state of deuterium in the steel. The total concentration of the accumulated deuterium in this region varies between 2.5 and 3 at.%. The medium-dose region is characterized by the radiation-induced action on the steel in the presence of deuterium with the resulting formation of the energy-stable nanosized crystalline structure of steel, having a developed network of intercrystalline boundaries. The basis for this developed network of intercrystalline boundaries is provided by the amorphous state, which manifests itself in the thermodesorption spectra as a widely temperature-scale extended region of deuterium desorption (structure formation with a varying activation energy). The total concentration of the accumulated deuterium in the region of medium implantation doses makes 7 to 8 at.%. The resulting structure shows stability against the action of

  16. Effect of double vacuum melting and retained austenite on rolling-element fatigue life of AMS 5749 bearing steel

    NASA Technical Reports Server (NTRS)

    Parker, R. J.; Hodder, R. S.

    1977-01-01

    AMS 5749 steel combines the tempering, hot hardness, and hardness retention characteristics of AISI M-50 steel with the corrosion and oxidation resistance of AISI 440C stainless steel. The five-ball fatigue tester was used to evaluate the rolling-element fatigue life of AMS 5749. Double vacuum melting (vacuum induction melting plus vacuum arc remelting, VIM-VAR) produced AMS 5749 material with a rolling-element fatigue life at least 14 times that of vacuum induction melting alone. The VIM-VAR AMS 5749 steel balls gave lives from 6 to 12 times greater than VIM-VAR AISI M-50 steel balls. The highest level of retained austenite, 14.6 percent, was significantly detrimental to rolling-element fatigue life relative to the intermediate level of 11.1 percent.

  17. On the formation of stacking fault tetrahedra in irradiated austenitic stainless steels - A literature review

    NASA Astrophysics Data System (ADS)

    Schibli, Raluca; Schäublin, Robin

    2013-11-01

    Irradiated austenitic stainless steels, because of their low stacking fault energy and high shear modulus, should exhibit a high ratio of stacking fault tetrahedra relative to the overall population of radiation induced nanometric defects. Experimental observations of stacking fault tetrahedra by transmission electron microscopy in commercial-purity stainless steels are however scarce, while they abundantly occur in high-purity or model austenitic alloys irradiated at both low and high temperatures, but not at around 673 K. In commercial alloys, the little evidence of stacking fault tetrahedra does not follow such a trend. These contradictions are reviewed and discussed. Reviewing the three possible formation mechanisms identified in the literature, namely the Silcox and Hirsch Frank loop dissociation, the void collapse and the stacking fault tetrahedra growth, it seems that the later dominates under irradiation. Black dots, are very small defect clusters, smaller than 1 nm in diameter, which cannot be resolved in TEM being below its spatial resolution in diffraction contrast. They can be created directly from the collapse of the cascade as undefined 3D clusters of point defects, namely vacancies, interstitials or impurities, or could be already well-defined nanometric voids, vacancy or interstitial dislocation loops [7]. Dislocation loops, either Frank or perfect dislocation loops, are generated by vacancies or interstitials coalescing as platelets between two adjacent {1 1 1} close-packed planes. Perfect loops are scarcer than Frank loops. For irradiation temperatures below 573 K some authors identified that Frank loops are of interstitial nature, while black dots are predominantly of vacancy nature [8-11]. More recent studies [12] contradict this statement and conclude that Frank loops with sizes in the range of 1-30 nm can be either vacancy or interstitial type. Stacking fault tetrahedra (SFT) are three-dimensional stacking fault configurations in the shape of

  18. [Methodology and evaluation of exposure to fumes formed during welding of chromium-nickel steel].

    PubMed

    Matczak, W; Chmielnicka, J

    1988-01-01

    Using various methods for determination of welding fumes components and taking into account a simultaneous determination of soluble compounds of chromium III and IV, hygienic evaluation in two working places employing different systems of MMA/SS welding, TIG/SS welding and padding was carried out. As it is indicated by the results, proper hygienic evaluation of working conditions is possible owing to the measurements of individual exposure of workers in the breathing zone, allowing for determination of chromium manganese, nickel, and, while applying low-hydrogen electrodes, also fluorides, in every test. PMID:3226286

  19. Tensile elastic properties of 18:8 chromium-nickel steel as affected by plastic deformation

    NASA Technical Reports Server (NTRS)

    Mcadam, D J; Mebs, R W

    1939-01-01

    The relationship between stress and strain, and between stress and permanent set, for 18:8 alloy as affected by prior plastic deformation is discussed. Hysteresis and creep and their effects on the stress-strain and stress-set curves are also considered, as well as the influence of duration of the rest interval after cold work and the influence of plastic deformation on proof stresses, on the modulus of elasticity at zero stress, and on the curvature of the stress-strain line. A constant (c sub 1) is suggested to represent the variation of the modulus of elasticity with stress.

  20. Nitrogen containing shielding gases for GTAW duplex stainless steels

    SciTech Connect

    Creffield, G.K.; Cole, M.H.; Paciej, R.; Huang, W.; Urmston, S.

    1993-12-31

    The duplex stainless steel are alloys characterized as consisting of two phases; austenite and ferrite. As such, they combine the benefits of both phases i.e. good ductility and general corrosion resistance of austenite, but with improved stress corrosion cracking resistance and strength associate with ferrite. Carefully controlled manufacturing techniques are employed to produce this combination in roughly equal proportions to ensure optimum properties. The range of duplex alloys studied in this work covered both the standard grade (2205) and the latest generation of super duplex (2507) alloys; typical compositions are shown in Table 1. Although the standard duplex is the most commonly available and widely used, super duplexes, which are characterized by higher chromium, nickel, molybdenum and nitrogen contents, have even better corrosion properties and are finding increasing applications in the offshore industry. To benefit from the superior properties of duplex, it is vital that these alloys can be welded effectively and that the properties of the welded joint match those of the parent weld. The objective of the current investigation was to study the effect of nitrogen, in both the shielding and purge gas, on the weld metal nitrogen content, microstructure and corrosion resistance, with the eventual aim of recommending an effective shielding gas mixture for duplex stainless steels.

  1. High temperature oxidation behavior of austenitic stainless steel AISI 304 in steam of nanofluids contain nanoparticle ZrO2

    SciTech Connect

    Prajitno, Djoko Hadi Syarif, Dani Gustaman

    2014-03-24

    The objective of this study is to evaluate high temperature oxidation behavior of austenitic stainless steel SS 304 in steam of nanofluids contain nanoparticle ZrO{sub 2}. The oxidation was performed at high temperatures ranging from 600 to 800°C. The oxidation time was 60 minutes. After oxidation the surface of the samples was analyzed by different methods including, optical microscope, scanning electron microscope (SEM) and X-ray diffraction (XRD). X-ray diffraction examination show that the oxide scale formed during oxidation of stainless steel AISI 304 alloys is dominated by iron oxide, Fe{sub 2}O{sub 3}. Minor element such as Cr{sub 2}O{sub 3} is also appeared in the diffraction pattern. Characterization by optical microscope showed that cross section microstructure of stainless steel changed after oxidized with the oxide scale on the surface stainless steels. SEM and x-ray diffraction examination show that the oxide of ZrO{sub 2} appeared on the surface of stainless steel. Kinetic rate of oxidation of austenite stainless steel AISI 304 showed that increasing oxidation temperature and time will increase oxidation rate.

  2. High temperature oxidation behavior of austenitic stainless steel AISI 304 in steam of nanofluids contain nanoparticle ZrO2

    NASA Astrophysics Data System (ADS)

    Prajitno, Djoko Hadi; Syarif, Dani Gustaman

    2014-03-01

    The objective of this study is to evaluate high temperature oxidation behavior of austenitic stainless steel SS 304 in steam of nanofluids contain nanoparticle ZrO2. The oxidation was performed at high temperatures ranging from 600 to 800°C. The oxidation time was 60 minutes. After oxidation the surface of the samples was analyzed by different methods including, optical microscope, scanning electron microscope (SEM) and X-ray diffraction (XRD). X-ray diffraction examination show that the oxide scale formed during oxidation of stainless steel AISI 304 alloys is dominated by iron oxide, Fe2O3. Minor element such as Cr2O3 is also appeared in the diffraction pattern. Characterization by optical microscope showed that cross section microstructure of stainless steel changed after oxidized with the oxide scale on the surface stainless steels. SEM and x-ray diffraction examination show that the oxide of ZrO2 appeared on the surface of stainless steel. Kinetic rate of oxidation of austenite stainless steel AISI 304 showed that increasing oxidation temperature and time will increase oxidation rate.

  3. Capabilities of Ultrasonic Techniques for the Far-Side Examination of Austenitic Stainless Steel Piping Welds.

    SciTech Connect

    Anderson, Michael T.; Diaz, Aaron A.; Cumblidge, Stephen E.; Doctor, Steven R.

    2006-02-01

    A study was conducted to assess the ability of advanced ultrasonic techniques to detect and accurately determine the size of flaws from the far-side of wrought austenitic piping welds. Far-side inspections of nuclear system piping welds are currently performed on a “best effort” basis and do not conform to ASME Code Section XI Appendix VIII performance demonstration requirements. For this study, four circumferential welds in 610mm diameter, 36mm thick ASTM A-358, Grade 304 vintage austenitic stainless steel pipe were examined. The welds were fabricated with varied welding parameters; both horizontal and vertical pipe orientations were used, with air and water backing, to simulate field welding conditions. A series of saw cuts, electro-discharge machined (EDM) notches, and implanted fatigue cracks were placed into the heat affected zones of the welds. The saw cuts and notches ranged in depth from 7.5% to 28.4% through-wall. The implanted cracks ranged in depth from 5% through-wall to 64% through-wall. The welds were examined with phased array technology at 2.0 MHz, and with low-frequency/Synthetic Aperture Focusing Technique (SAFT) methods in the 250-400 kHz regime. These results were compared to conventional ultrasonic techniques as a baseline. The examinations showed that both phased-array and low-frequency/SAFT were able to detect and accurately length-size, but not depth size, the notches and flaws through the welds. The ultrasonic results were insensitive to the different welding techniques used in each weld.

  4. Improvement of ultrasonic characteristics in butt-welded joint of austenitic stainless steel using magnetic stirring method

    SciTech Connect

    Tanosaki, M.; Yoshikawa, K.; Arakawa, T.

    1995-08-01

    Magnetic Stirring Method of Tungsten Inert Gas(TIG) Welding are applied to butt-welded joint of austenitic stainless steel. The purpose of this method is to refine the welded structure and to improve the ultrasonic characteristics. In the conventional method of ultrasonic test in austenitic stainless steel weldments, dendritic solidification structure of weldment prevents smooth ultrasonic beam transmission. The tests are performed in three welding conditions; One is conventional TIG welding (without magnetic stirring), the other two are TIG welding using magnetic stirring method. Each test piece is evaluated by observing macro structure of cross section and by several ultrasonic tests examining pulse amplitudes, beam path length and proceeding beam direction. The detectability of artificial notches in weldment is also investigated and compared.

  5. Influence of nitrogen on the sensitization, corrosion, mechanical, and microstructural properties of austenitic stainless steels. First annual progress report

    SciTech Connect

    Clark, W.A.T.; Macdonald, D.D.

    1982-04-01

    During this first year of the project, the research effort has concentrated on the electrochemical aspects of the effect of nitrogen on austenitic steels. The status of all the individual project tasks are outlined briefly, and then more detailed results of the electrochemical studies conducted so far are reported. Highlights of this quarter are: (1) nitrogen additions of up to 0.16 wt % retard sensitization of 18Cr-8Ni austenitic stainless steels. However, nitrogen additions to levels above approx. 0.25 wt % promote sensitization; (2) the retardation of sensitization by nitrogen can possibly be explained as being due to retardation of the nucleation or rate of growth of chromium carbides; and (3) polarization studies in high temperature 0.01 M Na/sub 2/SO/sub 4/ solutions at 250/sup 0/C demonstrate that the sensitized alloys are electrochemically more active than the solution annealed materials thereby indicating that they are susceptible to intergranular attack.

  6. A review of irradiation effects on LWR core internal materials - IASCC susceptibility and crack growth rates of austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Chopra, O. K.; Rao, A. S.

    2011-02-01

    Austenitic stainless steels (SSs) are used extensively as structural alloys in the internal components of light water reactor (LWR) pressure vessels because of their relatively high strength, ductility, and fracture toughness. However, exposure to neutron irradiation for extended periods changes the microstructure (radiation hardening) and microchemistry (radiation-induced segregation) of these steels, and degrades their fracture properties. Irradiation-assisted stress corrosion cracking (IASCC) is another degradation process that affects LWR internal components exposed to neutron radiation. The existing data on irradiated austenitic SSs were reviewed to evaluate the effects of key parameters such as material composition, irradiation dose, and water chemistry on IASCC susceptibility and crack growth rates of these materials in LWR environments. The significance of microstructural and microchemistry changes in the material on IASCC susceptibility is also discussed. The results are used to determine (a) the threshold fluence for IASCC and (b) the disposition curves for cyclic and IASCC growth rates for irradiated SSs in LWR environments.

  7. A guide for the ASME code for austenitic stainless steel containment vessels for high-level radioactive materials

    SciTech Connect

    Raske, D.T.

    1995-06-01

    The design and fabrication criteria recommended by the US Department of Energy (DOE) for high-level radioactive materials containment vessels used in packaging is found in Section III, Division 1, Subsection NB of the ASME Boiler and Pressure Vessel Code. This Code provides material, design, fabrication, examination, and testing specifications for nuclear power plant components. However, many of the requirements listed in the Code are not applicable to containment vessels made from austenitic stainless steel with austenitic or ferritic steel bolting. Most packaging designers, engineers, and fabricators are intimidated by the sheer volume of requirements contained in the Code; consequently, the Code is not always followed and many requirements that do apply are often overlooked during preparation of the Safety Analysis Report for Packaging (SARP) that constitutes the basis to evaluate the packaging for certification.

  8. High temperature stability of a 316 austenitic stainless steel coated with cerium oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Mendoza Del Angel, Humberto

    Cerium oxide (CeO2-x) nanoparticles were used for coating protection on a 316 Austenitic Stainless Steel (Aust. SS) to enhance the thermal stability of the oxide films formed at high temperatures. Three simple coating methods were used, dipping, spraying and spinning in order to explore the coating film morphology, nanoparticle distribution and its effect on thermal stability of the steel substrates. Experimentally, the selected steel was exposed to 800°C/1000°C under dry air conditions. Weight changes (DeltaW/A) were monitored as a function of time and the results were compared with uncoated alloys tested under similar conditions. The cerium oxide nanoparticles used on the three methods were synthesized in the laboratory obtaining nanoparticles in the range of 3.5 to 6.2 nanometers. It was found that cerium oxide particle size is affected by temperature. In this case, the activation energy for particle growth was estimated to be around 21,1 kJ/mol. Characterization of the film morphologies before and after oxidation were carried out using Atomic Force Microscopy (AFM), Surface Profilometry, Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). A comparison of the three coating methods was carried out for the particular case of the 316 Aust. SS coupons. In addition, the oxidation kinetics was experimentally investigated for the coated samples. For this purpose thermal gravimetric determinations were made at 800°C, 900°C, and 1000°C and oxidation rate constants were calculated at each temperature.

  9. Influence of deposition rate on the formation of growth twins in sputter-deposited 330 austenitic stainless steel films

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Anderoglu, O.; Misra, A.; Wang, H.

    2007-04-01

    The authors have studied the influence of deposition rate on the formation of growth twins in sputter-deposited 330 austenitic stainless steel thin films. Transmission electron microscopy shows that the volume fraction of twinned grains increases with increasing deposition rate, whereas the average columnar grain size and twin spacing stay approximately unchanged. These experimental results agree qualitatively with their analytical model that predicts deposition rate dependent formation of growth twins. The film hardness increases monotonically with increasing volume fraction of twinned grains.

  10. Influence of deposition rate on the formation of growth twins in sputter-deposited 330 austenitic stainless steel films

    SciTech Connect

    Zhang, X.; Anderoglu, O.; Misra, A.; Wang, H.

    2007-04-09

    The authors have studied the influence of deposition rate on the formation of growth twins in sputter-deposited 330 austenitic stainless steel thin films. Transmission electron microscopy shows that the volume fraction of twinned grains increases with increasing deposition rate, whereas the average columnar grain size and twin spacing stay approximately unchanged. These experimental results agree qualitatively with their analytical model that predicts deposition rate dependent formation of growth twins. The film hardness increases monotonically with increasing volume fraction of twinned grains.

  11. The influence of fine ferrite formation on the γ/α interface, fine bainite and retained austenite in a thermomechanically-processed transformation induced plasticity steel

    DOE PAGESBeta

    Timokhina, Ilana B.; Miller, Michael K.; Beladi, Hossein; Hodgson, Peter D.

    2016-03-03

    We subjected a Fe–0.26C–1.96Si–2Mn with 0.31Mo (wt%) steel to a novel thermomechanical processing route to produce fine ferrite with different volume fractions, bainite, and retained austenite. In two types of fine ferrites were found to be: (i) formed along prior austenite grain boundaries, and (ii) formed intragranularly in the interior of austenite grains. An increase in the volume fraction of fine ferrite led to the preferential formation of blocky retained austenite with low stability, and to a decrease in the volume fraction of bainite with stable layers of retained austenite. Moreover, the difference in the morphology of the bainitic ferritemore » and the retained austenite after different isothermal ferrite times was found to be responsible for the deterioration of the mechanical properties. The segregation of Mn, Mo, and C at distances of 2–2.5 nm from the ferrite and retained austenite/martensite interface on the retained austenite/martensite site was observed after 2700 s of isothermal hold. Finally, it was suggested that the segregation occurred during the austenite-to-ferrite transformation, and that this would decrease the interface mobility, which affects the austenite-to-ferrite transformation and ferrite grain size.« less

  12. The effect of high pressure torsion on structural refinement and mechanical properties of an austenitic stainless steel.

    PubMed

    Krawczynska, Agnieszka Teresa; Lewandowska, Malgorzata; Pippan, Reinhard; Kurzydlowski, Krzysztof Jan

    2013-05-01

    In the present study, the high pressure torsion (HPT) was used to refine the grain structure down to the nanometer scale in an austenitic stainless steel. The principles of HPT lay on torsional deformation under simultaneous high pressure of the specimen, which results in substantial reduction in the grain size. Disks of the 316LVM austenitic stainless steel of 10 mm in diameter were subjected to equivalent strains epsilon of 32 at RT and 450 degrees C under the pressure of 4 GPa. Furthermore, two-stage HPT processes, i.e., deformation at room temperature followed by deformation at 450 degrees C, were performed. The resulting microstructures were investigated in TEM observations. The mechanical properties were measured in terms of the microhardness and in tensile tests. HPT performed at two-stage conditions (firstly at RT next at 450 degrees C) gives similar values of microhardness to the ones obtained after deforming only at 450 degrees C but performed to higher values of the overall equivalent strain epsilon. The effect of high pressure torsion on structural refinement and mechanical properties of an austenitic stainless steel was evaluated. PMID:23858838

  13. Influence of the PM-Processing Route and Nitrogen Content on the Properties of Ni-Free Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Lefor, Kathrin; Walter, M.; Weddeling, A.; Hryha, E.; Huth, S.; Weber, S.; Nyborg, L.; Theisen, W.

    2015-03-01

    Ni-free austenitic steels alloyed with Cr and Mn are an alternative to conventional Ni-containing steels. Nitrogen alloying of these steel grades is beneficial for several reasons such as increased strength and corrosion resistance. Low solubility in liquid and δ-ferrite restricts the maximal N-content that can be achieved via conventional metallurgy. Higher contents can be alloyed by powder-metallurgical (PM) production via gas-solid interaction. The performance of sintered parts is determined by appropriate sintering parameters. Three major PM-processing routes, hot isostatic pressing, supersolidus liquid phase sintering (SLPS), and solid-state sintering, were performed to study the influence of PM-processing route and N-content on densification, fracture, and mechanical properties. Sintering routes are designed with the assistance of thermodynamic calculations, differential thermal analysis, and residual gas analysis. Fracture surfaces were studied by X-ray photoelectron spectroscopy, secondary electron microscopy, and energy dispersive X-ray spectroscopy. Tensile tests and X-ray diffraction were performed to study mechanical properties and austenite stability. This study demonstrates that SLPS process reaches high densification of the high-Mn-containing powder material while the desired N-contents were successfully alloyed via gas-solid interaction. Produced specimens show tensile strengths >1000 MPa combined with strain to fracture of 60 pct and thus overcome the other tested production routes as well as conventional stainless austenitic or martensitic grades.

  14. Microstructure of austenitic stainless steels irradiated at 400°C in the ORR and the HFIR spectral tailoring experiment

    NASA Astrophysics Data System (ADS)

    Hashimoto, N.; Wakai, E.; Robertson, J. P.; Sawai, T.; Hishinuma, A.

    2000-07-01

    Microstructural evolution in solution-annealed Japanese-PCA (JPCA-SA) and four other austenitic stainless steels, irradiated at 400°C to 17.3 dpa in the ORR and the high flux isotope reactor (HFIR) spectrally tailored experiment, were investigated by transmission electron microscopy (TEM). The mean He/dpa ratio throughout the irradiation fell between 12 and 16 appm He/dpa , which is close to the He/dpa values expected for fusion. In all the specimens, a bi-modal size distribution of cavities was observed and the number densities were about 1.0×10 22 m -3. There was no significant difference between the number densities in the different alloys, although the root mean cubes of the cavity radius are quite different for each alloy. Precipitates of the MC type were also observed in the matrix and on grain boundaries in all alloys except a high-purity (HP) ternary alloy. The JPCA-SA (including 0.06% carbon and 0.027% phosphorus) and standard type 316 steel (including 0.06% carbon and 0.028% phosphorus) showed quite low-swelling values of about 0.016 and 0.015%, respectively, while a HP ternary austenitic alloy showed the highest swelling value of 2.9%. This suggests that the existence of impurities affects the cavity growth in austenitic stainless steels even at 400°C.

  15. Microstructural Variations Across a Dissimilar 316L Austenitic: 9Cr Reduced Activation Ferritic Martensitic Steel Weld Joint

    NASA Astrophysics Data System (ADS)

    Thomas Paul, V.; Karthikeyan, T.; Dasgupta, Arup; Sudha, C.; Hajra, R. N.; Albert, S. K.; Saroja, S.; Jayakumar, T.

    2016-03-01

    This paper discuss the microstructural variations across a dissimilar weld joint between SS316 and 9Cr-RAFM steel and its modifications on post weld heat treatments (PWHT). Detailed characterization showed a mixed microstructure of austenite and martensite in the weld which is in agreement with the phases predicted using Schaeffler diagram based on composition measurements. The presence of very low volume fraction of δ-ferrite in SS316L has been identified employing state of the art electron back-scattered diffraction technique. PWHT of the ferritic steel did not reduce the hardness in the weld metal. Thermal exposure at 973 K (700 °C) showed a progressive reduction in hardness of weld joint with duration of treatment except in austenitic base metal. However, diffusion annealing at 1073 K (800 °C) for 100 hours resulted in an unexpected increase in hardness of weld metal, which is a manifestation of the dilution effects and enrichment of Ni on the transformation characteristics of the weld zone. Migration of carbon from ferritic steel aided the precipitation of fine carbides in the austenitic base metal on annealing at 973 K (700 °C); but enhanced diffusion at 1073 K (880 °C) resulted in coarsening of carbides and thereby reduction of hardness.

  16. Crack growth behavior of warm-rolled 316L austenitic stainless steel in high-temperature hydrogenated water

    NASA Astrophysics Data System (ADS)

    Choi, Kyoung Joon; Yoo, Seung Chang; Jin, Hyung-Ha; Kwon, Junhyun; Choi, Min-Jae; Hwang, Seong Sik; Kim, Ji Hyun

    2016-08-01

    To investigate the effects of warm rolling on the crack growth of 316L austenitic stainless steel, the crack growth rate was measured and the oxide structure was characterized in high-temperature hydrogenated water. The warm-rolled specimens showed a higher crack growth rate compared to the as-received specimens because the slip bands and dislocations produced during warm rolling served as paths for corrosion and cracking. The crack growth rate increased with the dissolved hydrogen concentration. This may be attributed to the decrease in performance and stability of the protective oxide layer formed on the surface of stainless steel in high-temperature water.

  17. An Investigation of the Massive Transformation from Ferrite to Austenite in Laser-Welded Mo-Bearing Stainless Steels

    NASA Astrophysics Data System (ADS)

    Perricone, M. J.; Dupont, J. N.; Anderson, T. D.; Robino, C. V.; Michael, J. R.

    2011-03-01

    A series of 31 Mo-bearing stainless steel compositions with Mo contents ranging from 0 to 10 wt pct and exhibiting primary δ-ferrite solidification were analyzed over a range of laser welding conditions to evaluate the effect of composition and cooling rate on the solid-state transformation to γ-austenite. Alloys exhibiting this microstructural development sequence are of particular interest to the welding community because of their reduced susceptibility to solidification cracking and the potential reduction of microsegregation (which can affect corrosion resistance), all while harnessing the high toughness of γ-austenite. Alloys were created using the arc button melting process, and laser welds were prepared on each alloy at constant power and travel speeds ranging from 4.2 to 42 mm/s. The cooling rates of these processes were estimated to range from 10 K (°C)/s for arc buttons to 105 K (°C)/s for the fastest laser welds. No shift in solidification mode from primary δ-ferrite to primary γ-austenite was observed in the range of compositions or welding conditions studied. Metastable microstructural features were observed in many laser weld fusion zones, as well as a massive transformation from δ-ferrite to γ-austenite. Evidence of epitaxial massive growth without nucleation was also found when intercellular γ-austenite was already present from a solidification reaction. The resulting single-phase γ-austenite in both cases exhibited a homogenous distribution of Mo, Cr, Ni, and Fe at nominal levels.

  18. The Effect of Constant and Pulsed Current Gas Tungsten Arc Welding on Joint Properties of 2205 Duplex Stainless Steel to 316L Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Neissi, R.; Shamanian, M.; Hajihashemi, M.

    2016-05-01

    In this study, dissimilar 316L austenitic stainless steel/2205 duplex stainless steel (DSS) joints were fabricated by constant and pulsed current gas tungsten arc welding process using ER2209 DSS as a filler metal. Microstructures and joint properties were characterized using optical and electron scanning microscopy, tensile, Charpy V-notch impact and micro-hardness tests, and cyclic polarization measurements. Microstructural observations confirmed the presence of chromium nitride and delta ferrite in the heat-affected zone of DSS and 316L, respectively. In addition, there was some deviation in the austenite/ferrite ratio of the surface welding pass in comparison to the root welding pass. Besides having lower pitting potential, welded joints produced by constant current gas tungsten arc welding process, consisted of some brittle sigma phase precipitates, which resulted in some impact energy reduction. The tensile tests showed high tensile strength for the weld joints in which all the specimens were broken in 316L base metal.

  19. The Effect of Constant and Pulsed Current Gas Tungsten Arc Welding on Joint Properties of 2205 Duplex Stainless Steel to 316L Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Neissi, R.; Shamanian, M.; Hajihashemi, M.

    2016-04-01

    In this study, dissimilar 316L austenitic stainless steel/2205 duplex stainless steel (DSS) joints were fabricated by constant and pulsed current gas tungsten arc welding process using ER2209 DSS as a filler metal. Microstructures and joint properties were characterized using optical and electron scanning microscopy, tensile, Charpy V-notch impact and micro-hardness tests, and cyclic polarization measurements. Microstructural observations confirmed the presence of chromium nitride and delta ferrite in the heat-affected zone of DSS and 316L, respectively. In addition, there was some deviation in the austenite/ferrite ratio of the surface welding pass in comparison to the root welding pass. Besides having lower pitting potential, welded joints produced by constant current gas tungsten arc welding process, consisted of some brittle sigma phase precipitates, which resulted in some impact energy reduction. The tensile tests showed high tensile strength for the weld joints in which all the specimens were broken in 316L base metal.

  20. Design and Optimization of an Austenitic TRIP Steel for Blast and Fragment Protection

    NASA Astrophysics Data System (ADS)

    Feinberg, Zechariah Daniel

    In light of the pervasive nature of terrorist attacks, there is a pressing need for the design and optimization of next generation materials for blast and fragment protection applications. Sadhukhan used computational tools and a systems-based approach to design TRIP-120---a fully austenitic transformation-induced plasticity (TRIP) steel. Current work more completely evaluates the mechanical properties of the prototype, optimizes the processing for high performance in tension and shear, and builds models for more predictive power of the mechanical behavior and austenite stability. Under quasi-static and dynamic tension and shear, the design exhibits high strength and high uniform ductility as a result of a strain hardening effect that arises with martensitic transformation. Significantly more martensitic transformation occurred under quasi-static loading conditions (69% in tension and 52% in shear) compared to dynamic loading conditions (13% tension and 5% in shear). Nonetheless, significant transformation occurs at high-strain rates which increases strain hardening, delays the onset of necking instability, and increases total energy absorption under adiabatic conditions. Although TRIP-120 effectively utilizes a TRIP effect to delay necking instability, a common trend of abrupt failure with limited fracture ductility was observed in tension and shear at all strain rates. Further characterization of the structure of TRIP-120 showed that an undesired grain boundary cellular reaction (η phase formation) consumed the fine dispersion of the metastable gamma' phase and limited the fracture ductility. A warm working procedure was added to the processing of TRIP-120 in order to eliminate the grain boundary cellular reaction from the structure. By eliminating η formation at the grain boundaries, warm-worked TRIP-120 exhibits a drastic improvement in the mechanical properties in tension and shear. In quasi-static tension, the optimized warm-worked TRIP-120 with an Mssigma

  1. Development of Stronger and More Reliable Cast Austenitic Stainless Steels (H-Series) Based on Scientific and Design Methodology

    SciTech Connect

    Pankiw, Roman I; Muralidharan, G.; Sikka, Vinod K.

    2006-06-30

    The goal of this project was to increase the high-temperature strength of the H-Series of cast austenitic stainless steels by 50% and the upper use temperature by 86 to 140 degrees fahrenheit (30 to 60 degrees celsius). Meeting this goal is expected to result in energy savings of 35 trillion Btu/year by 2020 and energy cost savings of approximately $230 million/year. The higher-strength H-Series cast stainless steels (HK and HP type) have applications for the production of ethylene in the chemical industry, for radiant burner tubes and transfer rolls for secondary processing of steel in the steel industry, and for many applications in the heat treating industry, including radiant burner tubes. The project was led by Duraloy Technologies, Inc., with research participation by Oak Ridge National Laboratory (ORNL) and industrial participation by a diverse group of companies.

  2. Austenitic and duplex stainless steels in simulated physiological solution characterized by electrochemical and X-ray photoelectron spectroscopy studies.

    PubMed

    Kocijan, Aleksandra; Conradi, Marjetka; Schön, Peter M

    2012-04-01

    A study of oxide layers grown on 2205 duplex stainless steel (DSS) and AISI 316L austenitic stainless steel in simulated physiological solution is presented here in order to establish the possibility of replacement of AISI 316 L with 2205 DSS in biomedical applications. The results of the potentiodynamic measurements show that the extent of the passive range significantly increased for DSS 2205 compared to AISI 316L stainless steel. Cyclic voltammetry was used to investigate electrochemical processes taking place on the steel surfaces. Oxide layers formed by electrochemical oxidation at different oxidation potentials were studied by X-ray photoelectron spectroscopy, and their compositions were analyzed as a function of depth. The main constituents on both the investigated materials were Cr- and Fe-oxides. Atomic force microscopy topography studies revealed the higher corrosion resistance of the DSS 2205 compared to the AISI 316L under the chosen experimental conditions. PMID:22331841

  3. Characterization of a nitrogen-rich austenitic stainless steel used for osteosynthesis devices.

    PubMed

    Ornhagen, C; Nilsson, J O; Vannevik, H

    1996-05-01

    Two laboratory melts of the standardized nitrogen-rich austenitic stainless steel specified in ISO 5832-9:1992(E) have been characterized with respect to corrosion properties, mechanical properties, and microstructure. The two melts differ essentially in nitrogen concentration, namely, 0.42 and 0.46 wt %, respectively. Both melts were found to fulfill the requirements in the ISO standard for corrosion and mechanical properties. The resistance to pitting corrosion in a solution of 0.9% NaCl, intended to simulate the conditions in the human body, was demonstrated by a critical pitting temperature of about 70 degrees C for both alloys, which should be compared with 40 degrees C for the biocompatible reference steel AISI 316. While no difference in corrosion resistance was observed between the two alloys, a significantly higher mechanical strength and lower toughness were observed for the nitrogen-rich melt. Using electron diffraction Z-phase was identified in unaged material. These were present as primary precipitates, most likely precipitated in the liquid state owing to the high concentration of nitrogen in combination with the presence of the strong nitride former niobium. However, the influence of Z-phase on pitting corrosion is believed to be of minor importance. The ageing behavior was studied indirectly in terms of toughness as a function of ageing. Formation of the intermetallic phase--chi-phase--was observed, particularly during prolonged ageing at 800 degrees C. The total absence of chi-phase in forged bar condition shows that the cooling rates during production are sufficient to suppress the formation of chi-phase. PMID:8731154

  4. Micro-mechanical investigation for effects of helium on grain boundary fracture of austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Miura, Terumitsu; Fujii, Katsuhiko; Fukuya, Koji

    2015-02-01

    Effects of helium (He) on grain boundary (GB) fracture of austenitic stainless steel were investigated by micro-tensile tests. Micro-bicrystal tensile specimens were fabricated for non-coincidence site lattice boundaries of He ion-irradiated 316 stainless steel by focused ion beam (FIB) micro-processing. Micro-tensile tests were conducted in a vacuum at room temperature in the FIB system. Specimens containing more than 2 at.% He fractured at GBs. The criteria for brittle fracture occurrence on GBs were: (1) He concentrations higher than 2 at.%; (2) formation of He bubbles on the GBs with less than a 5 nm spacing; and (3) matrix hardening to more than 4.6 GPa (nano-indentation hardness). The fracture stress of GB brittle fracture was lower for a specimen with higher He concentration while the size and areal density of the GB He bubbles were the same. The specimens that contained 10 at.% He and had been annealed at 923 K after irradiation fractured at the GB nominally in a brittle manner; however the inter-bubble matrix at the GB experienced ductile fracture. The annealing caused He bubbles to grow but decreased the areal density so that the spacing of the GB He bubbles widened and the hardness decreased, therefore the fracture mode changed from brittle to ductile. The findings revealed that He promotes GB fracture by weakening the GB strength and hardening the matrix due to the formation of He bubbles both on GBs and in the matrix. In addition, the findings suggested that GB segregated He atoms may have a role in GB fracture.

  5. Tensile flow and work-hardening behavior of a Ti-modified austenitic stainless steel

    SciTech Connect

    Sivaprasad, P.V.; Venugopal, S.; Venkadesan, S.

    1997-01-01

    The flow-stress data of a 15Cr-15Ni-2.2Mo-Ti modified austenitic stainless steel in the temperature range 300 to 1,023 K was analyzed in terms of Ludwigson and Voce equations. The parameters of these equations were critically examined with respect to the effect of Ti/C ratio and test temperature. It was found that the Ludwigson equation described the flow behavior adequately up to the test temperature of 923 K, whereas the Voce equation could be employed in the full temperature range. The peaks/plateaus observed in the variation of these parameters as a function of temperature in the intermediate temperature range have been identified as one of the manifestations of dynamic strain aging (DSA). Also, the variation of these parameters with temperature clearly could bring out the different domains of DSA observed in this alloy. The work-hardening analysis of the flow-stress data revealed that in the DSA regime, the onset of stage III hardening is athermal.

  6. Evolution of magnetic properties of cladding austenitic steel under irradiation in a reactor

    NASA Astrophysics Data System (ADS)

    Chukalkin, Yu. G.; Kozlov, A. V.; Evseev, M. V.

    2014-03-01

    Magnetic properties of samples of austenitic steel ChS-68 cut from the cladding of a fuel element, which was irradiated in a BN-600 fast-neutron reactor to a maximal damage dose of ˜80 displacements per atom (dpa) at temperatures of 370-587°C, have been investigated. It has been established that irradiation with fast neutrons leads to the formation of ferromagnetic microregions, the effective sizes and concentration of which depend on the damage dose. It has been shown that, at damage doses higher than ˜55 dpa, small spontaneous magnetization and magnetization hysteresis, which are characteristic of the ferromagnetic state, appear in the samples. It is assumed that the ferromagnetic microregions are the nuclei of the α' phase and the radiation-induced segregation microregions, in which the spacing between the nearest iron atoms exceeds the critical distance that determines the change in the sign of exchange interaction. Arguments in favor of this assumption are presented.

  7. Grain boundary engineering in a thermo-mechanically processed Nb-stabilized austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Yunquera, A.; Jorge-Badiola, D.; Gutiérrez, I.; Iza-Mendia, A.

    2015-04-01

    Three different thermo-mechanical strategies—annealing, strain recrystallization and strain annealing—were applied to a Nb-stabilized 304H austenitic stainless steel in order to study their effects on grain boundary character distribution (GBCD). An Electron Backscatter Diffraction (EBSD) analysis revealed specific combinations of cold reduction-temperature-time that favor annealing twinning. A uniform increase in microstructural size and special boundaries (particularly for Σ3, Σ9 and Σ27 boundaries) was achieved under strain annealing conditions (low cold reductions) and long times at high temperatures (≥ 990°C). These conditions provide a high fraction of special boundaries (about 80%), which replace the random grain boundary network and thus optimize the GBCD. The profuse presence of Σ3n boundaries is attributed to the geometric interaction of twin-related variants during grain boundary migration. In addition to all this, precipitation takes place at the temperature range where optimum GBCD is achieved. The significance of precipitation in the different strategies was also tackled.

  8. Tensile properties of a titanium modified austenitic stainless steel and the weld joints after neutron irradiation

    SciTech Connect

    Shiba, Kiyoyuki; Ioka, Ikuo; Jitsukawa, Shiro; Hamada, Shozo; Hishinuma, Atkinichi; Robertson, J.P.

    1999-10-01

    Tensile specimens of a titanium modified austenitic stainless steel and its weldments fabricated with Tungsten Inert Gas (TIG) and Electron Beam (EB) welding techniques were irradiated to a peak dose of 19 dpa and a peak helium level of 250 appm in the temperature range between 200 and 400 C in spectrally tailored capsules in the Oak Ridge Research Reactor (ORR) and the High Flux Isotope Reactor (HFIR). The He/dpa ratio of about 13 appm/dpa is similar to the typical helium/.dpa ratio of a fusion reactor environment. The tensile tests were carried out at the irradiation temperature in vacuum. The irradiation caused an increase in yield stress to levels between 670 and 800 MPa depending on the irradiation temperature. Total elongation was reduced to less than 10%, however the specimens failed in a ductile manner. The results were compared with those of the specimens irradiated using irradiation capsules producing larger amount of He. Although the He/dpa ratio affected the microstructural change, the impact on the post irradiation tensile behavior was rather small not only for base metal specimens but also for the weld joint and the weld metal specimens.

  9. Superior radiation-resistant nanoengineered austenitic 304L stainless steel for applications in extreme radiation environments

    DOE PAGESBeta

    Sun, C.; Zheng, S.; Wei, C. C.; Wu, Y.; Shao, L.; Yang, Y.; Hartwig, K. T.; Maloy, S. A.; Zinkle, S. J.; Allen, T. R.; et al

    2015-01-15

    Nuclear energy provides more than 10% of electrical power internationally, and the increasing engagement of nuclear energy is essential to meet the rapid worldwide increase in energy demand. A paramount challenge in the development of advanced nuclear reactors is the discovery of advanced structural materials that can endure extreme environments, such as severe neutron irradiation damage at high temperatures. It has been known for decades that high dose radiation can introduce significant void swelling accompanied by precipitation in austenitic stainless steel (SS). Here we report, however, that through nanoengineering, ultra-fine grained (UFG) 304L SS with an average grain size ofmore » ~100 nm, can withstand Fe ion irradiation at 500°C to 80 displacements-per-atom (dpa) with moderate grain coarsening. Compared to coarse grained (CG) counterparts, swelling resistance of UFG SS is improved by nearly an order of magnitude and swelling rate is reduced by a factor of 5. M₂₃C₆ precipitates, abundant in irradiated CG SS, are largely absent in UFG SS. This study provides a nanoengineering approach to design and discover radiation tolerant metallic materials for applications in extreme radiation environments.« less

  10. Cracking behavior of thermally aged and irradiated CF-8 cast austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Chen, Y.; Alexandreanu, B.; Chen, W.-Y.; Natesan, K.; Li, Z.; Yang, Y.; Rao, A. S.

    2015-11-01

    To assess the combined effect of thermal aging and neutron irradiation on the cracking behavior of CF-8 cast austenitic stainless steel, crack growth rate (CGR) and fracture toughness J-R curve tests were carried out on compact-tension specimens in high-purity water with low dissolved oxygen. Both unaged and thermally aged specimens were irradiated at ∼320 °C to 0.08 dpa. Thermal aging at 400 °C for 10,000 h apparently had no effect on the corrosion fatigue and stress corrosion cracking behavior in the test environment. The cracking susceptibility of CF-8 was not elevated significantly by neutron irradiation at 0.08 dpa. Transgranular cleavage-like cracking was the main fracture mode during the CGR tests, and a brittle morphology of delta ferrite was often seen on the fracture surfaces at the end of CGR tests. The fracture toughness J-R curve tests showed that both thermal aging and neutron irradiation can induce significant embrittlement. The loss of fracture toughness due to neutron irradiation was more pronounced in the unaged than aged specimens. After neutron irradiation, the fracture toughness values of the unaged and aged specimens were reduced to a similar level. G-phase precipitates were observed in the aged and irradiated specimens with or without prior aging. The similar microstructural changes resulting from thermal aging and irradiation suggest a common microstructural mechanism of inducing embrittlement in CF-8.

  11. Analysis of Tensile Deformation and Failure in Austenitic Stainless Steels: Part II- Irradiation Dose Dependence

    SciTech Connect

    Kim, Jin Weon; Byun, Thak Sang

    2010-01-01

    Irradiation effects on stable and unstable deformations and fracture behaviors in irradiated austenitic stainless steels (SSs) have been studied in detail based on the equivalent true stress versus true strain curves. An iterative technique in finite element simulation was used to obtain the equivalent true stress-true strain data from experimental tensile curves. It was shown that the strain hardening rate was retained at a high level on unstable deformation after significant irradiation and was independent of the irradiation dose up to the initiation of a localized necking. The equivalent fracture stress was nearly independent of irradiation dose before the damage (embrittlement) mechanism changed. In low dose range (< ~ 2dpa), the fracture strain and tensile fracture energy decreased rapidly with dose and at higher doses they decreased gradually to saturated levels, which were still high for irradiated materials. It was also found that the fracture properties for EC316LN SS were less sensitive to irradiation dose than those for 316 SS, although their uniform tensile properties showed almost the same dose dependencies. It was confirmed that the dose dependence of tensile fracture properties evaluated by the linear approximation model for nominal stress was accurate enough for practical use without elaborate calculations.

  12. Analysis of Tensile Deformation and Failure in Austenitic Stainless Steels: Part I- Temperature Dependence

    SciTech Connect

    Kim, Jin Weon; Byun, Thak Sang

    2010-01-01

    This paper describes the temperature dependence of deformation and failure behaviors in the austenitic stainless steels (annealed 304, 316, 316LN, and 20% cold-worked 316LN) in terms of equivalent true stress-true strain curves. The true stress-true strain curves up to the final fracture were calculated from the tensile test data obtained at -150 ~ 450oC using an iterative technique of finite element simulation. Analysis was largely focused on the necking deformation and fracture: Key parameters such as the strain hardening rate, equivalent fracture stress, fracture strain, and tensile fracture energy were evaluated, and their temperature dependencies were investigated. It was shown that a significantly high strain hardening rate was still retained during unstable deformation although overall strain hardening rate beyond the onset of necking was lower than that of the uniform deformation. The values of the parameters except for fracture strain decreased with temperature up to 200oC and were saturated as the temperature came close to the maximum test temperature 450oC. The fracture strain increased and had a maximum at -50oC to 20oC before decreasing with temperature. It was explained that these temperature dependencies of fracture properties were associated with a change in the dominant strain hardening mechanism with test temperature. Also, it was seen that the pre-straining of material has little effect on the strain hardening rate during necking deformation and on fracture properties.

  13. Residual Stresses Due to Circumferential Girth Welding of Austenitic Stainless Steel Pipes

    NASA Astrophysics Data System (ADS)

    Tarak, Farzan

    Welding, as a joining method in fabrication of engineering products and structural elements, has a direct influence on thermo-mechanical behavior of components in numerous structural applications. Since these thermo-mechanical behaviors have a major role in the life of welding components, predicting thermo-mechanical effects of welding is a major factor in designing of welding components. One of the major of these effects is generation of residual stresses due to welding. These residual stresses are not the causes of failure in the components solely, but they will add to external loads and stresses in operating time. Since, experimental methods are time consuming and expensive, computational simulation of welding process is an effective method to calculate these residual stresses. This investigation focuses on the evaluation of residual stresses and distortions due to circumferential girth welding of austenitic stainless steel pipes using the commercial finite element software ESI Visual-Environment and SYSWELDRTM to simulate welding process. Of particular importance is the comparison of results from three different types of mechanics models: 1) Axisymmetric, 2) Shell, and 3) Full 3-D.

  14. Superior radiation-resistant nanoengineered austenitic 304L stainless steel for applications in extreme radiation environments

    PubMed Central

    Sun, C.; Zheng, S.; Wei, C. C.; Wu, Y.; Shao, L.; Yang, Y.; Hartwig, K. T.; Maloy, S. A.; Zinkle, S. J.; Allen, T. R.; Wang, H.; Zhang, X.

    2015-01-01

    Nuclear energy provides more than 10% of electrical power internationally, and the increasing engagement of nuclear energy is essential to meet the rapid worldwide increase in energy demand. A paramount challenge in the development of advanced nuclear reactors is the discovery of advanced structural materials that can endure extreme environments, such as severe neutron irradiation damage at high temperatures. It has been known for decades that high dose radiation can introduce significant void swelling accompanied by precipitation in austenitic stainless steel (SS). Here we report, however, that through nanoengineering, ultra-fine grained (UFG) 304L SS with an average grain size of ~100 nm, can withstand Fe ion irradiation at 500°C to 80 displacements-per-atom (dpa) with moderate grain coarsening. Compared to coarse grained (CG) counterparts, swelling resistance of UFG SS is improved by nearly an order of magnitude and swelling rate is reduced by a factor of 5. M23C6 precipitates, abundant in irradiated CG SS, are largely absent in UFG SS. This study provides a nanoengineering approach to design and discover radiation tolerant metallic materials for applications in extreme radiation environments. PMID:25588326

  15. Computational design and analysis of high strength austenitic TRIP steels for blast protection applications

    NASA Astrophysics Data System (ADS)

    Sadhukhan, Padmanava

    Recent assessment of material property requirements for blast resistant applications, especially for the naval ship hulls, has defined the need to design steels with high stretch ductility and fragment penetration resistance, along with high strength and adequate toughness. Using a system based computational materials design approach, two series of austenitic (gamma) steels have been designed -- BA120 to exhibit high uniform ductility in tension (>20%) and SA120 to exhibit high tensile (>20%) and shear strains (>50%), with both alloys maintaining high levels of yield strength (120 ksi/827 MPa) at room temperature under Tensile and Shear stress states. BA120 is low chromium (4 wt %) high nickel (23.5 wt %) alloy while the SA120 is a high chromium design (10 wt %), both designed for non-magnetic behavior. The Thermo-Calc computational thermodynamics software in conjunction with a Ni-DATA 7 thermodynamic database has been used to model precipitation strengthening of the alloy, by quantifying the dependence of yield stress of austenitic steels on the mole fraction of the precipitated gamma' (Gamma Prime) Ni3(Ti, Al) phase. The required high strength has been achieved by the precipitation of spheroidal intermetallic gamma' -- phase of optimum diameter (15 nm) in equilibrium with the matrix at the standard aging temperature. Adequate Al and Ti with respect 5 to the Ni in the matrix ensure enough gamma' phase fraction and number density of precipitates to provide the necessary strength. The predicted gamma' precipitation strengthening to 120-130 ksi for both BA120 and SA120 has been validated through both microhardness as well as static and dynamic tensile and shear tests conducted at room temperature. 3-D LEAP analysis of the aged specimens has shown the expected size and distribution of gamma' -- precipitates with good compositional accuracy of predicted values from the thermodynamic models, for both matrix austenite and gamma'. Metastable austenitic steels have been

  16. Interface segregation behavior in thermal aged austenitic precipitation strengthened stainless steel.

    PubMed

    Li, Hui; Song, Hui; Liu, Wenqing; Xia, Shuang; Zhou, Bangxin; Su, Cheng; Ding, Wenyan

    2015-12-01

    The segregation of various elements at grain boundaries, precipitate/matrix interfaces were analyzed using atom probe tomography in an austenitic precipitation strengthened stainless steel aged at 750 °C for different time. Segregation of P, B and C at all types of interfaces in all the specimens were observed. However, Si segregated at all types of interfaces only in the specimen aged for 16 h. Enrichment of Ti at grain boundaries was evident in the specimen aged for 16 h, while Ti did not segregate at other interfaces. Mo varied considerably among interface types, e.g. from segregated at grain boundaries in the specimens after all the aging time to never segregate at γ'/γ phase interfaces. Cr co-segregated with C at grain boundaries, although carbides still did not nucleate at grain boundaries yet. Despite segregation tendency variations in different interface types, the segregation tendency evolution variation of different elements depending aging time were analyzed among all types of interfaces. Based on the experimental results, the enrichment factors, Gibbs interface excess and segregation free energies of segregated elements were calculated and discussed. PMID:26142697

  17. Microsegregation in high-molybdenum austenitic stainless steel laser beam and gas tungsten arc welds

    SciTech Connect

    Kujanpaeae, V.P.; David, S.A.

    1986-01-01

    An austenitic stainless steel with 6% molybdenum (thickness 6 mm) was welded using laser beam (LB) and gas tungsten arc (GTA) processes at various welding speeds. Depending on the welding speed the primary dendrite spacing ranged from 12 to 17 ..mu..m and from 2 to 7 ..mu..m for the GTA and LB welds, respectively. Extensive segregation of molybdenum was observed in the GTA welds. The segregation ratio for molybdenum, C/sub ID//C/sub D/, was found to be 1.9 in the GTA weld, and 1.2 in the LB weld. Distribution of iron, chromium and nickel was found nearly uniform in both welds. A recovered microstructure was observed after a post-weld annealing heat treatment. Annealing had a profound effect on the molybdenum segregation ratio in the laser weld. The critical pitting temperature (CPT) determined by a standard test was 55/sup 0/C for welds made using both processes, whereas it was 75/sup 0/C for the base metal. Upon homogenization the CPT of the laser beam weld increased to the base metal value, while that of the gas tungsten arc weld remained at 60/sup 0/C.

  18. Superior radiation-resistant nanoengineered austenitic 304L stainless steel for applications in extreme radiation environments

    SciTech Connect

    Sun, C.; Zheng, S.; Wei, C. C.; Wu, Y.; Shao, L.; Yang, Y.; Hartwig, K. T.; Maloy, S. A.; Zinkle, S. J.; Allen, T. R.; Wang, H.; Zhang, X.

    2015-01-15

    Nuclear energy provides more than 10% of electrical power internationally, and the increasing engagement of nuclear energy is essential to meet the rapid worldwide increase in energy demand. A paramount challenge in the development of advanced nuclear reactors is the discovery of advanced structural materials that can endure extreme environments, such as severe neutron irradiation damage at high temperatures. It has been known for decades that high dose radiation can introduce significant void swelling accompanied by precipitation in austenitic stainless steel (SS). Here we report, however, that through nanoengineering, ultra-fine grained (UFG) 304L SS with an average grain size of ~100 nm, can withstand Fe ion irradiation at 500°C to 80 displacements-per-atom (dpa) with moderate grain coarsening. Compared to coarse grained (CG) counterparts, swelling resistance of UFG SS is improved by nearly an order of magnitude and swelling rate is reduced by a factor of 5. M₂₃C₆ precipitates, abundant in irradiated CG SS, are largely absent in UFG SS. This study provides a nanoengineering approach to design and discover radiation tolerant metallic materials for applications in extreme radiation environments.

  19. Welding-induced mechanical properties in austenitic stainless steels before and after neutron irradiation

    NASA Astrophysics Data System (ADS)

    Stoenescu, R.; Schäublin, R.; Gavillet, D.; Baluc, N.

    2007-03-01

    The effects of neutron irradiation on the mechanical properties of welded joints made of austenitic stainless steels have been investigated. The materials are welded AISI 304 and AISI 347, so-called test weld materials, irradiated with neutrons at 573 K to doses of 0.3 and 1.0 dpa. In addition, an AISI 304 from a decommissioned pressurised water reactor, so-called in-service material, which had accumulated a maximum dose of 0.35 dpa at about 573 K, was investigated. The mechanical properties of heat-affected zones and base materials were analysed before and after irradiation. Tensile parameters were determined at room temperature and at 573 K, for all materials and irradiation conditions. In the test weld materials it is found that radiation hardening is lower and loss of ductility is higher in the heat-affected zone than in the base material. In the in-service material radiation hardening is about the same in heat-affected zone and base material. After irradiation, deformation takes place by stacking faults and twins, at both room temperature and high temperature, contrary to unirradiated materials, where deformation takes place by twinning at room temperature and by dislocation cells at high temperature. No defect free channels are observed.

  20. Welding-induced microstructure in austenitic stainless steels before and after neutron irradiation

    NASA Astrophysics Data System (ADS)

    Stoenescu, R.; Schäublin, R.; Gavillet, D.; Baluc, N.

    2007-02-01

    The effects of neutron irradiation on the microstructure of welded joints made of austenitic stainless steels have been investigated. The materials were welded AISI 304 and AISI 347, so-called test weld materials, and irradiated with neutrons at 300 °C to 0.3 and 1.0 dpa. In addition, an AISI 304 type from a decommissioned pressurised water reactor, so-called in-service material, which had accumulated a maximum dose of 0.35 dpa at about 300 °C, was investigated. The microstructure of heat-affected zones and base materials was analysed before and after irradiation, using transmission electron microscopy. Neutron diffraction was performed for internal stress measurements. It was found that the heat-affected zone contains, relative to the base material, a higher dislocation density, which relates well to a higher residual stress level and, after irradiation, a higher irradiation-induced defect density. In both materials, the irradiation-induced defects are of the same type, consisting in black dots and Frank dislocation loops. Careful analysis of the irradiation-induced defect contrast was performed and it is explained why no stacking fault tetrahedra could be identified.

  1. Flux effect on the ion-beam nitriding of austenitic stainless-steel AISI 304L

    SciTech Connect

    Abrasonis, G.; Riviere, J.P.; Templier, C.; Pranevicius, L.; Barradas, N.P.

    2005-06-15

    The effect of flux and Ar pretreatment during ion-beam nitriding of austenitic stainless steel is investigated. The ion energy and temperature were 1.2 keV and 400 deg. C, respectively, the ion current densities were 0.5, 0.67, and 0.83 mA cm{sup -2}. The nitrogen distribution profiles were measured using nuclear reaction analysis. The obtained nitrogen distribution profiles were analyzed by the means of the nitrided layer thickness evolution due to sputtering and diffusion and the model of trapping-detrapping. Both approaches could fit well the experimental results, however, different diffusion coefficients have to be assumed for each current density. In addition, the diffusion coefficients are higher for higher current densities. On the other hand, it is shown that the pretreatment with Ar-ion beam at nitriding temperatures produces only a thermal effect without any other influence on the following nitrogen diffusion. The results are discussed in relation with surface and temperature effects and atomic transport mechanisms.

  2. Irradiation testing of 316L(N)-IG austenitic stainless steel for ITER

    NASA Astrophysics Data System (ADS)

    van Osch, E. V.; Horsten, M. G.; de Vries, M. I.

    1998-10-01

    In the frame work of the European Fusion Technology Programme and the International Thermonuclear Experimental Reactor (ITER), ECN is investigating the irradiation behaviour of the structural materials for ITER. The main structural material for ITER is austenitic stainless steel Type 316L(N)-IG. The operating temperatures of (parts of) the components are envisaged to range between 350 and 700 K. A significant part of the dose-temperature domain of irradiation conditions relevant for ITER has already been explored, there is, however, very little data at about 600 K. Available data tend to indicate a maximum in the degradation of the mechanical properties after irradiation at this temperature, e.g. a minimum in ductility and a maximum of hardening. Therefore an irradiation program for plate material 316L(N)-IG, its Electron Beam (EB) weld and Tungsten Inert Gas (TIG) weld metal, and also including Hot Isostatically Pressed (HIP) 316L(N) powder and solid-solid joints, was set up in 1995. Irradiations have been carried out in the High Flux Reactor (HFR) in Petten at a temperature of 600 K, at dose levels from 1 to 10 dpa. The paper presents the currently available post-irradiation test results. Next to tensile and fracture toughness data on plate, EB and TIG welds, first results of powder HIP material are included.

  3. Melt expulsion during ultrasonic vibration-assisted laser surface processing of austenitic stainless steel.

    PubMed

    Alavi, S Habib; Harimkar, Sandip P

    2015-05-01

    Simultaneous application of ultrasonic vibrations during conventional materials processing (casting, welding) and material removal processes (machining) has recently been gaining widespread attention due to improvement in metallurgical quality and efficient material removal, respectively. In this paper, ultrasonic vibration-assisted laser surface melting of austenitic stainless steel (AISI 316) is reported. While the application of ultrasonic vibrations during laser processing delays the laser interaction with material due to enhancement of surface convection, it resulted in expulsion of melt from the irradiated region (forming craters) and transition from columnar to equiaxed dendritic grain structure in the resolidified melt films. Systematic investigations on the effect of ultrasonic vibrations (with vibrations frequency of 20 kHz and power output in the range of 20-40%) on the development of microstructure during laser surface melting (with laser power of 900 W and irradiation time in the range of 0.30-0.45 s) are reported. The results indicate that the proposed ultrasonic vibration-assisted laser processing can be designed for efficient material removal (laser machining) and improved equiaxed microstructure (laser surface modifications) during materials processing. PMID:25670412

  4. Tensile properties of a titanium modified austenitic stainless steel and the weld joints after neutron irradiation

    SciTech Connect

    Shiba, K.; Ioka, I.; Jitsukawa, S.; Hamada, A.; Hishinuma, A.

    1996-10-01

    Tensile specimens of a titanium modified austenitic stainless steel and its weldments fabricated with Tungsten Inert Gas (TIG) and Electron Beam (EB) welding techniques were irradiated to a peak dose of 19 dpa and a peak helium level of 250 appm in the temperature range between 200 and 400{degrees}C in spectrally tailored capsules in the Oak Ridge Research Reactor (ORR) and the High Flux Isotope Reactor (HFIR). The He/dpa ratio of about 13 appm/dpa is similar to the typical helium/dpa ratio of a fusion reactor environment. The tensile tests were carried out at the irradiation temperature in vacuum. The irradiation caused an increase in yield stress to levels between 670 and 800 MPa depending on the irradiation temperature. Total elongation was reduced to less than 10%, however the specimens failed in a ductile manner. The results were compared with those of the specimens irradiated using irradiation capsules producing larger amount of He. Although the He/dpa ratio affected the microstructural change, the impact on the post irradiation tensile behavior was rather small for not only base metal specimens but also for the weld joint and the weld metal specimens.

  5. Hydrogen emission in fatigue process of hydrogen-charged austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Hayashida, Katsuya; Matsunaga, Hisao; Endo, Masahiro

    2010-03-01

    The acceleration of hydrogen diffusion in the fatigue process of AISI type 304 and 316L meta-stable austenitic stainless steels was studied by paying attention to the relation between fatigue slip bands and hydrogen emission. Slip bands were formed in tension-compression fatigue tests of round specimens in ambient air, and then the specimens were cathodically charged with hydrogen. The location of hydrogen emission was microscopically visualized by means of the hydrogen microprint technique (HMT). Hydrogen was mainly emitted from slip bands on the surface of fatigued specimens. The depth of hydrogen diffusion into the specimens was also observed on the fatigue fracture surfaces by the HMT. The depth for a specimen hydrogen-charged before fatigue testing was about 50 μm at a maximum, whereas the depth for a specimen that was hydrogen-charged after slip bands had been formed in a preliminary fatigue test was about 300 μm. Those results suggested that slip bands act as a pathway where hydrogen will move preferentially.

  6. Hydrogen emission in fatigue process of hydrogen-charged austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Hayashida, Katsuya; Matsunaga, Hisao; Endo, Masahiro

    2009-12-01

    The acceleration of hydrogen diffusion in the fatigue process of AISI type 304 and 316L meta-stable austenitic stainless steels was studied by paying attention to the relation between fatigue slip bands and hydrogen emission. Slip bands were formed in tension-compression fatigue tests of round specimens in ambient air, and then the specimens were cathodically charged with hydrogen. The location of hydrogen emission was microscopically visualized by means of the hydrogen microprint technique (HMT). Hydrogen was mainly emitted from slip bands on the surface of fatigued specimens. The depth of hydrogen diffusion into the specimens was also observed on the fatigue fracture surfaces by the HMT. The depth for a specimen hydrogen-charged before fatigue testing was about 50 μm at a maximum, whereas the depth for a specimen that was hydrogen-charged after slip bands had been formed in a preliminary fatigue test was about 300 μm. Those results suggested that slip bands act as a pathway where hydrogen will move preferentially.

  7. Material Modeling and Springback Prediction of Ultra Thin Austenitic Stainless Steel Sheet

    NASA Astrophysics Data System (ADS)

    Verma, Rahul K.; Murakoso, Satoko; Chung, Kwansoo; Kuwabara, Toshihiko

    2010-06-01

    The constitutive model with combined isotropic-kinematic hardening along with hardening stagnation (or permanent softening) [Verma, Kuwabara, Chung, Haldar: Int. J. Plasticity (submitted)] was used here for modeling the tension-compression behaviors of a 0.1 mm thick austenitic stainless steel sheet (SUS304), which was observed in a recent work [Kuwabara and Murakoso: Proc. CIRP 2010 Conf. (submitted)]. Springback was also experimentally measured for a shallow drawn rectangular cup here and it was verified using the above model. It was found that this model can successfully predict the Bauschinger effect and hardening stagnation. As for springback, it was found that in this particular case it depends on, other than the material model, factors like boundary conditions, in the finite element analysis (FEA), during unloading. It was also observed that incorporation of the Bauschinger effect and permanent softening is a key for accurate springback prediction and, therefore, the present model performs better than the one which is based only on isotropic hardening without any hardening stagnation.

  8. Methods for the In-Situ Characterization of Cast Austenitic Stainless Steel Microstructures

    SciTech Connect

    Ramuhalli, Pradeep; Good, Morris S.; Harris, Robert V.; Bond, Leonard J.; Ruud, Clayton O.; Diaz, Aaron A.; Anderson, Michael T.

    2011-06-29

    Cast austenitic stainless steel (CASS) that was commonly used in U.S. nuclear power plants is a coarse-grained, elastically anisotropic material. Its engineering properties made it a material of choice for selected designs of nuclear power reactor systems. However, the fabrication processes result in a variety of coarse-grain microstructures that make current ultrasonic in-service inspection of components quite challenging. To address inspection needs, new ultrasonic inspection approaches are being sought. However, overcoming the deleterious and variable effects of the microstructure on the interrogating ultrasonic beam may require knowledge of the microstructure, for potential optimization of inspection parameters to enhance the probability of detection (POD). The ability to classify microstructure type (e.g. polycrystalline or columnar) has the potential to guide selection of optimal NDE approaches. This paper discusses the application of ultrasonic and electromagnetic methods for classifying CASS microstructures, when making measurements from the outside surface of the component. Results to date demonstrate the potential of these measurements to discriminate between two consistent microstructures - equiaxed-grain material versus columnar-grain material. The potential for fusion of ultrasonic and electromagnetic measurements for in-situ microstructure characterization in CASS materials will be explored.

  9. Superior radiation-resistant nanoengineered austenitic 304L stainless steel for applications in extreme radiation environments.

    PubMed

    Sun, C; Zheng, S; Wei, C C; Wu, Y; Shao, L; Yang, Y; Hartwig, K T; Maloy, S A; Zinkle, S J; Allen, T R; Wang, H; Zhang, X

    2015-01-01

    Nuclear energy provides more than 10% of electrical power internationally, and the increasing engagement of nuclear energy is essential to meet the rapid worldwide increase in energy demand. A paramount challenge in the development of advanced nuclear reactors is the discovery of advanced structural materials that can endure extreme environments, such as severe neutron irradiation damage at high temperatures. It has been known for decades that high dose radiation can introduce significant void swelling accompanied by precipitation in austenitic stainless steel (SS). Here we report, however, that through nanoengineering, ultra-fine grained (UFG) 304 L SS with an average grain size of ~100 nm, can withstand Fe ion irradiation at 500 °C to 80 displacements-per-atom (dpa) with moderate grain coarsening. Compared to coarse grained (CG) counterparts, swelling resistance of UFG SS is improved by nearly an order of magnitude and swelling rate is reduced by a factor of 5. M(23)C(6) precipitates, abundant in irradiated CG SS, are largely absent in UFG SS. This study provides a nanoengineering approach to design and discover radiation tolerant metallic materials for applications in extreme radiation environments. PMID:25588326

  10. Residual stress variation due to piping processes of austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Ihara, R.; Hashimoto, T.; Mochizuki, M.

    2012-08-01

    In nuclear power plants, stress corrosion cracking (SCC) has been observed near the heat affected zone (HAZ) of the primary loop recirculation pipes made of austenitic stainless steel type 316L. Residual stress is a major cause of SCC. In the joining process of pipes, butt-welding is conducted after machining. Machining is performed to match the inside pipe diameter. Residual stress is generated by both machining and welding. In the case of welding after machining in manufacturing processes of pipes, it appears that residual stress due to machining is varied by the welding thermal cycle. In this study, residual stress variation caused by manufacturing processes was investigated. Residual stress variation was examined by the X-ray diffraction method. The residual stress distribution generated by welding after machining has a local maximum point in the HAZ. The Vickers hardness distribution also has a local maximum point. By the EBSD method, it is clarified that recovery and recrystallization due to welding heat do not occurred in the local maximum point. Residual stress distribution results from the superposition effect of hardening due to machining and welding. The location and value of the local maximum stress are varied by welding conditions. The region of the local maximum stress corresponds to the region where SCC has been observed. Therefore, in addition to a part of the manufacturing processes such as welding or machining, evaluation of all parts of the processes is important to investigate the effect of residual stress distribution on SCC.

  11. Evaluation of Alumina-Forming Austenitic Stainless Steel Alloys in Microturbines

    SciTech Connect

    Brady, M.P.; Matthews, W.J.

    2010-09-15

    Oak Ridge National Laboratory (ORNL) and Capstone Turbine Corporation (CTC) participated in an in-kind cost share cooperative research and development agreement (CRADA) effort under the auspices of the Energy Efficiency and Renewable Energy (EERE) Technology Maturation Program to explore the feasibility for use of developmental ORNL alumina-forming austenitic (AFA) stainless steels as a material of construction for microturbine recuperator components. ORNL delivered test coupons of three different AFA compositions to CTC. The coupons were exposed in steady-state elevated turbine exit temperature (TET) engine testing, with coupons removed for analysis after accumulating ~1,500, 3,000, 4,500, and 6,000 hours of operation. Companion test coupons were also exposed in oxidation testing at ORNL at 700-800°C in air with 10% H2O. Post test assessment of the coupons was performed at ORNL by light microscopy and electron probe microanalysis. The higher Al and Nb containing AFA alloys exhibited excellent resistance to oxidation/corrosion, and thus show good promise for recuperator applications.

  12. Improved austenitic stainless steel for high temperature applications. [Improved stress-rupture properties

    DOEpatents

    Not Available

    This invention describes a composition for an austenitic stainless steel which has been found to exhibit improved high temperature stress rupture properties. The composition of this alloy is about (in wt. %): 12.5 to 14.5 Cr; 14.5 to 16.5 Ni; 1.5 to 2.5 Mo; 1.5 to 2.5 Mn; 0.1 to 0.4 Ti; 0.02 to 0.08 C; 0.5 to 1.0 Si; 0.01 maximum, N; 0.02 to 0.08 P; 0.002 to 0.008 B; 0.004-0.010 S; 0.02-0.05 Nb; .01-.05 V; 0.005-0.02 Ta; 0.02-0.05 Al; 0.01-0.04 Cu; 0.02-0.05 Co; .03 maximum, As; 0.01 maximum, 0; 0.01 maximum, Zr; and with the balance of the alloy being essentially iron. The carbon content of the alloy is adjusted such that wt. % Ti/(wt. % C+wt. % N) is between 4 and 6, and most preferably about 5. In addition the sum of the wt. % P + wt. % B + wt. % S is at least 0.03 wt. %. This alloy is believed to be particularly well suited for use as fast breeder reactor fuel element cladding.

  13. Multi-response optimization of CO 2 laser-welding process of austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Benyounis, K. Y.; Olabi, A. G.; Hashmi, M. S. J.

    2008-02-01

    Recently, laser welding of austenitic stainless steel has received great attention in industry. This is due to its widespread application in petroleum refinement stations, power plants, the pharmaceutical industry and also in households. Therefore, mechanical properties should be controlled to obtain good welded joints. The welding process should be optimized by the proper mathematical models. In this research, the tensile strength and impact strength along with the joint-operating cost of laser-welded butt joints made of AISI304 was investigated. Design-expert software was used to establish the design matrix and to analyze the experimental data. The relationships between the laser-welding parameters (laser power, welding speed and focal point position) and the three responses (tensile strength, impact strength and joint-operating cost) were established. Also, the optimization capabilities in design-expert software were used to optimize the welding process. The developed mathematical models were tested for adequacy using analysis of variance and other adequacy measures. In this investigation, the optimal welding conditions were identified in order to increase the productivity and minimize the total operating cost. Overlay graphs were plotted by superimposing the contours for the various response surfaces. The process parameters effect was determined and the optimal welding combinations were tabulated.

  14. Superior radiation-resistant nanoengineered austenitic 304L stainless steel for applications in extreme radiation environments

    NASA Astrophysics Data System (ADS)

    Sun, C.; Zheng, S.; Wei, C. C.; Wu, Y.; Shao, L.; Yang, Y.; Hartwig, K. T.; Maloy, S. A.; Zinkle, S. J.; Allen, T. R.; Wang, H.; Zhang, X.

    2015-01-01

    Nuclear energy provides more than 10% of electrical power internationally, and the increasing engagement of nuclear energy is essential to meet the rapid worldwide increase in energy demand. A paramount challenge in the development of advanced nuclear reactors is the discovery of advanced structural materials that can endure extreme environments, such as severe neutron irradiation damage at high temperatures. It has been known for decades that high dose radiation can introduce significant void swelling accompanied by precipitation in austenitic stainless steel (SS). Here we report, however, that through nanoengineering, ultra-fine grained (UFG) 304L SS with an average grain size of ~100 nm, can withstand Fe ion irradiation at 500°C to 80 displacements-per-atom (dpa) with moderate grain coarsening. Compared to coarse grained (CG) counterparts, swelling resistance of UFG SS is improved by nearly an order of magnitude and swelling rate is reduced by a factor of 5. M23C6 precipitates, abundant in irradiated CG SS, are largely absent in UFG SS. This study provides a nanoengineering approach to design and discover radiation tolerant metallic materials for applications in extreme radiation environments.

  15. Cryogenic strength and microstructure of a hydrostatically extruded austenitic steel 1.4429 (AISI 316LN)

    NASA Astrophysics Data System (ADS)

    Czarkowski, P.; Krawczyńska, A. T.; Brynk, T.; Nowacki, M.; Lewandowska, M.; Kurzydłowski, K. J.

    2014-11-01

    The as-received material with the average equivalent grain diameter of 45 μm was subjected to a hydrostatic extrusion process to a total true strain of 0.25, 0.84 and 1.36. Static tensile tests of the extruded material, performed at the room temperature, in liquid nitrogen and liquid helium. The material extruded to the strain of 1.36 and tested in liquid helium revealed ultimate strength 2.6 GPa. The results obtained for strengthened material were compared with the properties of as-received state. The effect of extrusion on the structure of this material was examined by transmission and scanning electron microscopy. The presence of necking and the nature of fracture surfaces in the specimens subjected to tensile tests confirm ductile behaviour of the extruded material even at liquid helium temperature, despite limited ductility. The results show that the hydrostatically extruded austenitic stainless steel is a promising material for relatively small, heavy loaded components working at cryogenic conditions.

  16. Precipitation kinetics during aging of an alumina-forming austenitic stainless steel

    DOE PAGESBeta

    Trotter, Geneva; Hu, Bin; Sun, Annie Y.; Harder, Reed; Miller, Michael K.; Baker, Ian; Yao, Lan

    2016-04-28

    The microstructural evolution of DAFA26, an alumina-forming austenitic (AFA) stainless steel, was investigated during aging. The effect of aging at 750 °C and 800 °C on the growth of spherical γ’-Ni3(Al, Ti) particles present in the as-processed state was studied extensively using X-ray diffraction, microhardness testing, scanning electron microscopy, transmission electron microscopy, and atom probe tomography. The γ’ particles had a cube-on-cube orientation relationship with the matrix (i.e. ((010)(010)m//(010)(010)p, [100][100]m//[100][100]p)). The coarsening kinetics of γ’-Ni3Al particles were in agreement with the Lifshitz, Slyozof-Wagner theory. Coarse Laves phase particles were also present in the as-processed state, and during the aging processmore » both smaller Laves phase precipitates and B2-NiAl precipitates formed on both the grain boundaries and in the matrix. As a result, the γ’ precipitates were determined to have the most impact on the room temperature hardness.« less

  17. Void Swelling and Microstructure of Austenitic Stainless Steels Irradiated in the BOR - 60 Reactor

    SciTech Connect

    Chen, Y.; Yang, Yong; Huang, Yina; Allen, T.; Alexandreanu, B.; Natesan, K.

    2012-11-01

    As nuclear power plants age and neutron fluence increases, detrimental effects resulting from radiation damage have become an increasingly important issue for the operational safety and structural integrity of core internal components. In this study, irradiated specimens of reactor core internal components were characterized by transmission electron microscopy. The specimens had been irradiated to 5.5-45 dpa in the BOR-60 reactor at a dose rate close to 10-6 dpa/s and temperature of about 320°C. No voids were observed in the austenitic stainless steels and nickel alloys at all doses. Despite the possibility that fine voids below the TEM resolution limit may be present, it was clear that void swelling was insignificant in all examined alloys up to 45 dpa. Irradiated microstructures of the studied alloys were dominated by a high density of Frank loops. The mean size and density of the Frank loops varied from one material to another, but saturated with increasing dose above ~10 dpa. While no irradiation-induced precipitations were present below 24.5 dpa, fine precipitates were evident in several alloys at 45 dpa.

  18. On the Mechanical Stability of Austenite Matrix After Martensite Formation in a Medium Mn Steel

    NASA Astrophysics Data System (ADS)

    He, B. B.; Huang, M. X.

    2016-07-01

    The present work employs the nanoindentation technique to investigate the effect of prior martensite formation on the mechanical stability of a retained austenite matrix. It is found that the small austenite grains that were surrounded by martensite laths have higher mechanical stability than the large austenite grains that were free of martensite laths. The higher mechanical stability of small austenite grains is due to its higher amount of defects resulting from the prior martensite formation. These defects act as barriers for the later martensite formation and therefore contribute to the higher mechanical stability of small austenite grains. As a result, the present work suggests that the formation of martensite tends to stabilize the surrounding austenite matrix. Therefore, it may explain the lower transformed amount of martensite after quenching as compared to the theoretical calculation using the Koistinen and Marburger (K-M) equation.

  19. On the Mechanical Stability of Austenite Matrix After Martensite Formation in a Medium Mn Steel

    NASA Astrophysics Data System (ADS)

    He, B. B.; Huang, M. X.

    2016-04-01

    The present work employs the nanoindentation technique to investigate the effect of prior martensite formation on the mechanical stability of a retained austenite matrix. It is found that the small austenite grains that were surrounded by martensite laths have higher mechanical stability than the large austenite grains that were free of martensite laths. The higher mechanical stability of small austenite grains is due to its higher amount of defects resulting from the prior martensite formation. These defects act as barriers for the later martensite formation and therefore contribute to the higher mechanical stability of small austenite grains. As a result, the present work suggests that the formation of martensite tends to stabilize the surrounding austenite matrix. Therefore, it may explain the lower transformed amount of martensite after quenching as compared to the theoretical calculation using the Koistinen and Marburger (K-M) equation.

  20. Characterization of Low Temperature Ferrite/Austenite Transformations in the Heat Affected Zone of 2205 Duplex Stainless Steel Arc Welds

    SciTech Connect

    Palmer, T A; Elmer, J W; Babu, S S; Vitek, J M

    2003-08-20

    Spatially Resolved X-Ray Diffraction (SRXRD) has been used to identify a previously unobserved low temperature ferrite ({delta})/austenite({gamma}) phase transformation in the heat affected zone (HAZ) of 2205 Duplex Stainless Steel (DSS) welds. In this ''ferrite dip'' transformation, the ferrite transforms to austenite during heating to peak temperatures on the order of 750 C, and re-transforms to ferrite during cooling, resulting in a ferrite volume fraction equivalent to that in the base metal. Time Resolved X-Ray Diffraction (TRXRD) and laser dilatometry measurements during Gleeble{reg_sign} thermal simulations are performed in order to verify the existence of this low temperature phase transformation. Thermodynamic and kinetic models for phase transformations, including both local-equilibrium and para-equilibrium diffusion controlled growth, show that diffusion of substitutional alloying elements does not provide a reasonable explanation for the experimental observations. On the other hand, the diffusion of interstitial alloying elements may be rapid enough to explain this behavior. Based on both the experimental and modeling results, two mechanisms for the ''ferrite dip'' transformation, including the formation and decomposition of secondary austenite and an athermal martensitic-type transformation of ferrite to austenite, are considered.

  1. Determination of the temperature range of recrystallization based on structural studies of an austenitic high-nitrogen Cr-Mn-Mo steel

    NASA Astrophysics Data System (ADS)

    Sokolovskaya, Yu. A.; Berezovskaya, V. V.

    2015-03-01

    The effect of thermoplastic treatment, which includes cold plastic deformation by rolling, on the microstructure of a high-nitrogen 07Kh16AG13M3 steel has been studied. The temperature range of recrystallization is determined by three methods. An equation is proposed for calculating the melting temperature of the high-nitrogen austenitic steel

  2. Low-Temperature Nitriding of Deformed Austenitic Stainless Steels with Various Nitrogen Contents Obtained by Prior High-Temperature Solution Nitriding

    NASA Astrophysics Data System (ADS)

    Bottoli, Federico; Winther, Grethe; Christiansen, Thomas L.; Dahl, Kristian Vinter; Somers, Marcel A. J.

    2016-08-01

    In the past decades, high nitrogen steels (HNS) have been regarded as substitutes for conventional austenitic stainless steels because of their superior mechanical and corrosion properties. However, the main limitation to their wider application is their expensive production process. As an alternative, high-temperature solution nitriding has been applied to produce HNS from three commercially available stainless steel grades (AISI 304L, AISI 316, and EN 1.4369). The nitrogen content in each steel alloy is varied and its influence on the mechanical properties and the stability of the austenite investigated. Both hardness and yield stress increase and the alloys remain ductile. In addition, strain-induced transformation of austenite to martensite is suppressed, which is beneficial for subsequent low-temperature nitriding of the surface of deformed alloys. The combination of high- and low-temperature nitriding results in improved properties of both bulk and surface.

  3. Biocompatibility studies of low temperature nitrided and collagen-I coated AISI 316L austenitic stainless steel.

    PubMed

    Martinesi, M; Stio, M; Treves, C; Borgioli, F

    2013-06-01

    The biocompatibility of austenitic stainless steels can be improved by means of surface engineering techniques. In the present research it was investigated if low temperature nitrided AISI 316L austenitic stainless steel may be a suitable substrate for bioactive protein coating consisting of collagen-I. The biocompatibility of surface modified alloy was studied using as experimental model endothelial cells (human umbilical vein endothelial cells) in culture. Low temperature nitriding produces modified surface layers consisting mainly of S phase, the supersaturated interstitial solid solution of nitrogen in the austenite lattice, which allows to enhance surface microhardness and corrosion resistance in PBS solution. The nitriding treatment seems to promote the coating with collagen-I, without chemical coupling agents, in respect of the untreated alloy. For biocompatibility studies, proliferation, lactate dehydrogenase levels and secretion of two metalloproteinases (MMP-2 and MMP-9) were determined. Experimental results suggest that the collagen protection may be favourable for endothelial cell proliferation and for the control of MMP-2 release. PMID:23471501

  4. Modelling the evolution of composition-and stress-depth profiles in austenitic stainless steels during low-temperature nitriding

    NASA Astrophysics Data System (ADS)

    Jespersen, Freja N.; Hattel, Jesper H.; Somers, Marcel A. J.

    2016-02-01

    Nitriding of stainless steel causes a surface zone of expanded austenite, which improves the wear resistance of the stainless steel while preserving the stainless behaviour. During nitriding huge residual stresses are introduced in the treated zone, arising from the volume expansion that accompanies the dissolution of high nitrogen contents in expanded austenite. An intriguing phenomenon during low-temperature nitriding is that the residual stresses evoked by dissolution of nitrogen in the solid state, affect the thermodynamics and the diffusion kinetics of nitrogen dissolution. In the present paper solid mechanics was combined with thermodynamics and diffusion kinetics to simulate the evolution of composition-depth and stress-depth profiles resulting from nitriding. The model takes into account a composition-dependent diffusion coefficient of nitrogen in expanded austenite, short range ordering (trapping) of nitrogen atoms by chromium atoms, and the effect of composition-induced stress on surface concentration and diffusive flux. The effect of plasticity and concentration-dependence of the yield stress was also included.

  5. Overview of strategies for high-temperature creep and oxidation resistance of alumina-forming austenitic stainless steels

    SciTech Connect

    Yamamoto, Yukinori; Brady, Michael P; Santella, Michael L; Bei, Hongbin; Maziasz, Philip J; Pint, Bruce A

    2011-01-01

    A family of creep-resistant, alumina-forming austenitic (AFA) stainless steel alloys is under development for structural use in fossil energy conversion and combustion system applications. The AFA alloys developed to date exhibit comparable creep-rupture lives to state-of-the-art advanced austenitic alloys, and superior oxidation resistance in the {approx}923 K to 1173 K (650 C to 900 C) temperature range due to the formation of a protective Al{sub 2}O{sub 3} scale rather than the Cr{sub 2}O{sub 3} scales that form on conventional stainless steel alloys. This article overviews the alloy design approaches used to obtain high-temperature creep strength in AFA alloys via considerations of phase equilibrium from thermodynamic calculations as well as microstructure characterization. Strengthening precipitates under evaluation include MC-type carbides or intermetallic phases such as NiAl-B2, Fe{sub 2}(Mo,Nb)-Laves, Ni{sub 3}Al-L1{sub 2}, etc. in the austenitic single-phase matrix. Creep, tensile, and oxidation properties of the AFA alloys are discussed relative to compositional and microstructural factors.

  6. DCEMS Study of Thin Oxide Layers and Interface of Stainless Steel Films Deposited by Sputtering Austenitic AISI304

    NASA Astrophysics Data System (ADS)

    Nomura, K.; Takahashi, K.; Takeda, M.; Shimizu, K.; Habasaki, H.; Kuzmann, E.

    2004-12-01

    Thin stainless steel films were deposited on surface oxidized Si plate using austenitic AISI304 stainless steel as target with a RF magnetron Ar sputtering method. The deposited films and the oxidized films with about 15 nm in thickness were characterized by depth selective conversion electron Mössbauer spectroscopy (DCEMS) using a 2π gas proportional counter. The as-deposited film consisted of ferromagnetic phase. The average hyperfine magnetic fields increased from 25 to 28 T by heating. A relative large amount of iron oxide (Fe2O3) was produced on the top surface layer upon heating at 400°C. After heating at 500°C the relative amount of iron oxide decreased and chromium oxide layers grew in the interface between the iron oxide and substrate layers. The ferromagnetic phase in the deposited stainless steel film was partially converted into austenitic phase at 500°C and largely at 600°C. DCEMS is effective for non-destructive characterization of both surface and interface layers of thin stainless steel films with several 10 nm thickness.

  7. The grain coarsening and subsequent transformation of austenite in the HSLA steel during high temperature thermomechanical processing

    NASA Astrophysics Data System (ADS)

    Al-Hajeri, Khaled F.

    In heavy steel sections, fundamental properties such as strength and toughness are improved remarkably by refining and homogenizing the final ferrite microstructure. Conventionally, the microstructural refinement of the final ferrite depends mainly on the austenite grain size, morphology and composition prior to the phase transformation as well as the cooling rate during the transformation. The production of heavy sections by universal-type rolling mills takes place at elevated temperature (above 1200°C) followed by low cooling rates (<0.1°C/sec). These processing conditions produce coarse austenite grains and subsequently coarse ferrite grains in addition to other undesirable low temperature transformation products. In heavy steel sections, therefore, the refinement of the ferrite microstructure through modern TMP techniques is not feasible. The main objective of this study is to investigate the feasibility of refining the ferrite microstructure and eliminate the high-carbon low transformation products in heavy steel sections using the particle-stimulated nucleation, PSN, mechanism to enhance the nucleation of the intragranular ferrite, IGF. In this investigation, the MnS and Ti-oxide inclusions were used to promote the intragranular ferrite (IGF) nucleation mechanism in a typical ASTM A572 grade 50 Steel. This work included the study of the decomposition behavior of coarse grained austenite and nucleation of the IGF as a function of very slow cooling rate. In addition, the effects of the inclusions type, size and volume fraction on the kinetics (nucleation and growth) of IGF were investigated. The main findings of this research were that the refining of ferrite microstructure is achieved, successfully, through enhancing the IGF nucleation with implementing of the PSN mechanism. Additionally, the efficiency of the inclusion as an IGF nucleation site is mainly related to the inclusion size and type.

  8. Precipitation sensitivity to alloy composition in Fe-Cr-Mn austenitic steels developed for reduced activation for fusion application

    SciTech Connect

    Maziasz, P.J.; Klueh, R.L.

    1988-01-01

    Special austenitic steels are being designed in which alloying elements like Mo, Nb, and Ni are replaced with Mn, W, V, Ti, and/or Ta to reduce the long-term radioactivity induced by fusion reactor irradiation. However, the new steels still need to have properties otherwise similar to commercial steels like type 316. Precipitation strongly affects strength and radiation-resistance in austenitic steels during irradiation at 400--600/degree/C, and precipitation is also usually quite sensitive to alloy composition. The initial stage of development was to define a base Fe-Cr-Mn-C composition that formed stable austenite after annealing and cold-working, and resisted recovery or excessive formation of coarse carbide and intermetallic phases during elevated temperature annealing. These studies produced a Fe-12Cr-20Mn-0.25C base alloy. The next stage was to add the minor alloying elements W, Ti, V, P, and B for more strength and radiation-resistance. One of the goals was to produce fine MC precipitation behavior similar to the Ti-modified Fe-Cr-Ni prime candidate alloy (PCA). Additions of Ti+V+P+B produced fine MC precipitation along network dislocations and recovery/recrystallization resistance in 20% cold worked material aged at 800/degree/C for 166h, whereas W, Ti, W+Ti, or Ti+P+B additions did not. Addition of W+Ti+V+P+B also produced fine MC, but caused some sigma phase formation and more recrystallization as well. 29 refs., 14 figs., 9 tabs.

  9. Influence of Plastic Deformation on Low-Temperature Surface Hardening of Austenitic Stainless Steel by Gaseous Nitriding

    NASA Astrophysics Data System (ADS)

    Bottoli, Federico; Winther, Grethe; Christiansen, Thomas L.; Somers, Marcel A. J.

    2015-06-01

    This article addresses an investigation of the influence of plastic deformation on low-temperature surface hardening by gaseous nitriding of two commercial stainless steels: EN 1.4369 and AISI 304. The materials were plastically deformed to several levels of equivalent strain by conventional tensile straining, plane strain compression, and shear. Gaseous nitriding of the strained material was performed in ammonia gas at atmospheric pressure at various temperatures. Microstructural characterization of the as-deformed state and the nitrided case produced included X-ray diffraction analysis, reflected-light microscopy, and microhardness testing. The results demonstrate that a case of expanded austenite develops and that the presence of plastic deformation has a significant influence on the morphology of the nitrided case. The presence of strain-induced martensite favors the formation of CrN, while a high dislocation density in a fully austenitic structure does not lead to such premature nucleation of CrN.

  10. The Mechanical and material properties of 316LN austenitic stainless steel for the fusion application in cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Sas, J.; Weiss, K.-P.; Jung, A.

    2015-12-01

    Due to the constant increase of claims for all materials used in superconducting magnets in "magnetic fusion reactors", the article deals with the possibilities of increasing the mechanical properties of austenitic stainless steel tested at cryogenic conditions that ensure the transport of Helium to magnets. The aim of the experimental plan was to increase the mechanical properties of the steel grade 316LN tested at 4.2K from the original value Steel A: YS = 1045 MPa, UTS = 1528 MPa, A = 33% to the value of YS = 1204 MPa,UTS = 1642 MPa, A = 34% and Steel B: YS = 1173 MPa, UTS = 1541 MPa, A = 28% to the value of YS = 1351 MPa, UTS = 1645 MPa, A = 17%. The increase in mechanical properties of the steel grade under examination has been made by means of heat processing in the conditions of annealing: Th1 = 625 ° C / th1 = 696 h. The mechanical properties of steel were evaluated using static tension tests at 4,2 K. The samples were placed in a cryostat filled with liquid helium. Except for the mechanical properties, there were also evaluated structural changes depending on the conditions of heat processing by light optical microscopy and EBSD (Electron Backscatter Diffraction). The increase of steel properties used in low temperatures was achieved by heat processing.

  11. Development of 18Cr-9Ni-W-Nb-V-N Austenitic Stainless Steel Tube for Thermal Power Boilers

    NASA Astrophysics Data System (ADS)

    Ishitsuka, Tetsuo; Mimura, Hiroyuki

    An 18Cr-9Ni-W-Nb-V-N austenitic stainless steel tube for thermal power boilers has been newly developed. The high temperature mechanical properties and corrosion resistance of the steel were investigated. The creep rupture strength of the developed steel is about 1.5 times as high as that of SUS347HTB, and is almost the same as that of Ka-SUS310J2TB at 650°C. This excellent creep strength of the steel is mainly due to solid solution strengthening by tungsten and nitrogen, and precipitation strengthening by nitrides of niobium and vanadium. The carbon content of the steel is reduced to 0.03% to improve intergranular corrosion resistance. The steam oxidation resistance and the high temperature corrosion resistance of the tube are almost the same as those of SUS347HTB. Weldability of the developed steel is superior to that of SUS304HTB and SUS310TB. Thus the developed steel is suitable for use as a material for superheater and reheater tubes of thermal power boilers.

  12. Microstructure and Mechanical Properties of a Low-Carbon Mn-Si Multiphase Steel Based on Dynamic Transformation of Undercooled Austenite

    NASA Astrophysics Data System (ADS)

    Li, Longfei; Zhang, Xiaojing; Yang, Wangyue; Sun, Zuqing

    2013-09-01

    The microstructure evolution of 0.20C-2.00Mn-2.00Si steel treated by the thermomechanical process to manufacture hot-rolled, transformation-induced plasticity (TRIP) steel based on dynamic transformation of undercooled austenite was investigated using a Gleeble 1500 (Dynamic Systems, Inc., Poestenkill, NY) hot simulation test machine in combination with light microscope (LM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The mechanical properties of this steel with different multiphase microstructures were also analyzed using room-temperature tensile tests. The results indicated that the multi-phase microstructures consisting of fine-grained ferrite with a size of 1-3 μm, bainite packets, and retained austenite and martensite were formed for the used steel by a thermo-mechanical process involving dynamic transformation of undercooled austenite, controlled cooling, isothermal bainite treatment and water-quenching. With the increase in the strain of hot deformation of undercooled austenite, the fraction of ferrite increased, that of bainite decreased, and that of martensite increased. At the same time, the fraction of retained austenite (RA), as well as the carbon content of RA, first increased and then decreased. For the used steel treated by such process, the tensile strength is about 1200 MPa with a total elongation of about 20 pct, and the product of tensile strength and total elongation can be up to 25,000 MPa × pct.

  13. Creep and rupture strength of pearlitic and austenitic steels under active proportional loading in a plane stress state

    SciTech Connect

    Mozharovskaya, T.N.

    1985-04-01

    The authors conducted creep and creep-rupture tests of materials on a modernized DST-5 unit with allowance for the type of stress state. Steel 15Kh2MFA was subjected to creep tests at 823/sup 0/K, as was steel 08Kh18N9. It is shown that the minimum creep rate and rupture strength of materials depend significantly on the type of stress state. A universal relation is established between the minimum creep rate and stress intensity under long-term proportional loading with a plane stress state. A generalized rupture-strength criterion is proposed for plane stress under proportional loading and is substantiated on pearlitic and austenitic steels.

  14. A Comparison of Creep Rupture Strength of Ferritic/Austenitic Dissimilar Weld Joints of Different Grades of Cr-Mo Ferritic Steels

    NASA Astrophysics Data System (ADS)

    Laha, K.; Chandravathi, K. S.; Parameswaran, P.; Goyal, Sunil; Mathew, M. D.

    2012-04-01

    Evaluations of creep rupture properties of dissimilar weld joints of 2.25Cr-1Mo, 9Cr-1Mo, and 9Cr-1MoVNb steels with Alloy 800 at 823 K were carried out. The joints were fabricated by a fusion welding process employing an INCONEL 182 weld electrode. All the joints displayed lower creep rupture strength than their respective ferritic steel base metals, and the strength reduction was greater in the 2.25Cr-1Mo steel joint and less in the 9Cr-1Mo steel joint. Failure location in the joints was found to shift from the ferritic steel base metal to the intercritical region of the heat-affected zone (HAZ) of the ferritic steel (type IV cracking) with the decrease in stress. At still lower stresses, the failure in the joints occurred at the ferritic/austenitic weld interface. The stress-life variation of the joints showed two-slope behavior and the slope change coincided with the occurrence of ferritic/austenitic weld interface cracking. Preferential creep cavitation in the soft intercritical HAZ induced type IV failure, whereas creep cavitation at the interfacial particles induced ferritic/austenitic weld interface cracking. Micromechanisms of the type IV failure and the ferritic/austenitic interface cracking in the dissimilar weld joint of the ferritic steels and relative cracking susceptibility of the joints are discussed based on microstructural investigation, mechanical testing, and finite element analysis (FEA) of the stress state across the joint.

  15. Recent developments in the study of phase stability of austenitic stainless steels and its relation to properties

    SciTech Connect

    Vitek, J.M.; David, S.A.

    1995-12-31

    Much work has been done over the years in alloy development of stainless steels and in the characterization of stainless steel microstructures and properties. However, in recent years there have been significant new advances made, and insights gained, into the physical metallurgy of these materials. In particular, advanced techniques have led to new information on the phase stability of stainless steels and the influence of the phase stability on mechanical properties. This paper will highlight some of these new advances, with an emphasis on work that has been done at ORNL on these alloys. For stainless steel alloys, the phase stability can be influenced by several factors. They include solidification behavior, the ferrite/austenite solid-state transformation, other high temperature phase transformations, and low temperature phase transformations. Recent advances in theoretical and experimental methods have led to new developments in understanding and characterizing these factors. Advanced solidification theory has been applied to understand the influence of rapid solidification on phase formation during solidification. New thermodynamic evaluation methods have shown great potential in providing details on the overall phase stability, including details on the influence of composition on phase stability. finite-difference techniques have been applied to the stainless steel alloy system to gain much insight into the ferrite/austenite transformation behavior. Finally, advanced techniques such as analytical electron microscopy, atom probe field ion microscopy, nano-indentation techniques, and specimen miniaturization techniques have provided valuable information on the response of stainless steel microstructures and properties to thermal treatment. All of these new methods and approaches are described in detail in this presentation.

  16. Electron work functions of ferrite and austenite phases in a duplex stainless steel and their adhesive forces with AFM silicon probe.

    PubMed

    Guo, Liqiu; Hua, Guomin; Yang, Binjie; Lu, Hao; Qiao, Lijie; Yan, Xianguo; Li, Dongyang

    2016-01-01

    Local electron work function, adhesive force, modulus and deformation of ferrite and austenite phases in a duplex stainless steel were analyzed by scanning force microscopy. It is demonstrated that the austenite has a higher electron work function than the ferrite, corresponding to higher modulus, smaller deformation and larger adhesive force. Relevant first-principles calculations were conducted to elucidate the mechanism behind. It is demonstrated that the difference in the properties between austenite and ferrite is intrinsically related to their electron work functions. PMID:26868719

  17. Electron work functions of ferrite and austenite phases in a duplex stainless steel and their adhesive forces with AFM silicon probe

    PubMed Central

    Guo, Liqiu; Hua, Guomin; Yang, Binjie; Lu, Hao; Qiao, Lijie; Yan, Xianguo; Li, Dongyang

    2016-01-01

    Local electron work function, adhesive force, modulus and deformation of ferrite and austenite phases in a duplex stainless steel were analyzed by scanning force microscopy. It is demonstrated that the austenite has a higher electron work function than the ferrite, corresponding to higher modulus, smaller deformation and larger adhesive force. Relevant first-principles calculations were conducted to elucidate the mechanism behind. It is demonstrated that the difference in the properties between austenite and ferrite is intrinsically related to their electron work functions. PMID:26868719

  18. Gigacycle fatigue behaviour of austenitic stainless steels used for mercury target vessels

    NASA Astrophysics Data System (ADS)

    Naoe, Takashi; Xiong, Zhihong; Futakawa, Masatoshi

    2016-01-01

    A mercury enclosure vessel for the pulsed spallation neutron source manufactured from a type 316L austenitic stainless steel, a so-called target vessel, suffers the cyclic loading caused by the proton beam induced pressure waves. A design criteria of the JSNS target vessel which is defined based on the irradiation damage is 2500 h at 1 MW with a repetition rate of 25 Hz, that is, the target vessel suffers approximately 109 cyclic loading while in operation. Furthermore, strain rate of the beam window of the target vessel reaches 50 s-1 at the maximum, which is much higher than that of the conventional fatigue. Gigacycle fatigue strength up to 109 cycles for solution annealed 316L (SA) and cold-worked 316L (CW) were investigated through the ultrasonic fatigue tests. Fatigue tests were performed under room temperature and 250 °C which is the maximum temperature evaluated at the beam window in order to investigate the effect of temperature on fatigue strength of SA and CW 316L. The results showed that the fatigue strength at 250 °C is clearly reduced in comparison with room temperature, regardless of cold work level. In addition, residual strength and microhardness of the fatigue tested specimen were measured to investigate the change in mechanical properties by cyclic loading. Cyclic hardening was observed in both the SA and CW 316L, and cyclic softening was observed in the initial stage of cyclic loading in CW 316L. Furthermore, abrupt temperature rising just before fatigue failure was observed regardless of testing conditions.

  19. Corrosion behavior of cold-worked austenitic stainless steels in liquid lead-bismuth eutectic

    NASA Astrophysics Data System (ADS)

    Kurata, Yuji

    2014-05-01

    The effect of cold working on the corrosion behavior of austenitic stainless steels in liquid lead-bismuth eutectic (LBE) was studied to develop accelerator-driven systems for the transmutation of long-lived radioactive wastes and lead-bismuth cooled fast reactors. Corrosion tests on solution-treated, 20% cold-worked and 50% cold-worked 316SS and JPCA (15Cr-15Ni-Ti) were conducted in oxygen-controlled LBE. Slight ferritization caused by Ni dissolution and Pb-Bi penetration were observed for all specimens in the corrosion test conducted at 500 °C for 1000 h in liquid LBE with an intermediate oxygen concentration (1.4 × 10-7 wt.%). In the corrosion test performed at 550 °C for 1000 h in liquid LBE with a low oxygen concentration (4.2 × 10-9 wt.%), the depth of the ferritization of 316SS and JPCA increased with the extent of cold working. Only oxidation was observed in the corrosion test that was performed at 550 °C for 1000 h in liquid LBE with a high oxygen concentration (approximately 10-5 wt.%). Cold working accelerated the formation of the double layer oxide and increased the thickness of the oxide layer slightly. In contrast, the ferritization accompanied by Pb-Bi penetration was widely observed with oxidation for all specimens corrosion tested at 550 °C for 3000 h under the high-oxygen condition. Cold working increased the depth of the ferritization of 316SS and JPCA. It is considered that cold working accelerated the ferritization and Pb-Bi penetration through the enhanced dissolution of Ni into LBE due to an increase in the dislocation density under conditions in which the protective oxide layer was not formed in liquid LBE.

  20. Mechanisms of hydrogen-assisted fracture in austenitic stainless steel welds.

    SciTech Connect

    Balch, Dorian K.; Sofronis, Petros; Somerday, Brian P.; Novak, Paul

    2005-03-01

    The objective of this study was to quantify the hydrogen-assisted fracture susceptibility of gas-tungsten arc (GTA) welds in the nitrogen-strengthened, austenitic stainless steels 21Cr-6Ni-9Mn (21-6-9) and 22Cr-13Ni-5Mn (22-13-5). In addition, mechanisms of hydrogen-assisted fracture in the welds were identified using electron microscopy and finite-element modeling. Elastic-plastic fracture mechanics experiments were conducted on hydrogen-charged GTA welds at 25 C. Results showed that hydrogen dramatically lowered the fracture toughness from 412 kJ/m{sup 2} to 57 kJ/m{sup 2} in 21-6-9 welds and from 91 kJ/m{sup 2} to 26 kJ/m{sup 2} in 22-13-5 welds. Microscopy results suggested that hydrogen served two roles in the fracture of welds: it promoted the nucleation of microcracks along the dendritic structure and accelerated the link-up of microcracks by facilitating localized deformation. A continuum finite-element model was formulated to test the notion that hydrogen could facilitate localized deformation in the ligament between microcracks. On the assumption that hydrogen decreased local flow stress in accordance with the hydrogen-enhanced dislocation mobility argument, the finite-element results showed that deformation was localized in a narrow band between two parallel, overlapping microcracks. In contrast, in the absence of hydrogen, the finite-element results showed that deformation between microcracks was more uniformly distributed.

  1. Hot Ductility Characterization of Sanicro-28 Super-Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Mirzaei, A.; Zarei-Hanzaki, A.; Abedi, H. R.

    2016-05-01

    The hot ductility behavior of a super-austenitic stainless steel has been studied using tensile testing method in the temperature range from 1073 K to 1373 K (800 °C to 1100 °C) under the strain rates of 0.1, 0.01, and 0.001 s-1. The hot compression tests were also performed at the same deformation condition to identify the activated restoration mechanisms. At lower temperatures [ i.e., 1073 K and 1173 K (800 °C and 900 °C)], the serration of initial grain boundaries confirms the occurrence of dynamic recovery as the predominant restoration process. However, in the course of applied deformation, the initial microstructure is recrystallized at higher temperatures [ i.e., 1273 K and 1373 K (1000 °C and 1100 °C)]. In this respect, annealing the twin boundaries could well stimulate the recrystallization kinetic through initiation new annealing twins on prior annealing twin boundaries. The hot tensile results show that there is a general trend of increasing ductility by temperature. However, two regions of ductility drop are recognized at 1273 K and 1373 K (1000°C)/0.1s-1 and (1100°C)/0.01s-1. The ductility variations at different conditions of temperature and strain rate are discussed in terms of simultaneous activation of grain boundary sliding and restoration processes. The observed ductility troughs are attributed to the occurrence of grain boundary sliding and the resulting R-type and W-type cracks. The occurrence of dynamic recrystallization is also considered as the main factor increasing the ductility at higher temperatures. The enhanced ductility is primarily originated from the post-uniform elongation behavior, which is directly associated with the strain rate sensitivity of the experimental material.

  2. Defocusing Techniques for Multi-pass Laser Welding of Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Karhu, Miikka; Kujanpää, Veli

    This study introduces an experimental work carried out in multi-pass laser welding with cold filler wire and laser-arc hybrid welding of thick section austenitic stainless steel. As it has been demonstrated earlier, hybrid and cold wire welding with a keyhole-mode can offer very efficient way to produce multi-pass welds in narrow gap thick section joints. However, when multi-pass welding is applied to one pass per layer method without e.g. scanning or defocusing, the used groove width needs to be very narrow in order to ensure the proper melting of groove side walls and thus to avoid lack of fusion/cold-run defects. As a consequence of the narrow groove, particularly in thick section joints, the accessibility of an arc torch or a wire nozzle into the very bottom of a groove in root pass welding can be considerably restricted. In an alternative approach described in this paper, a power density of a laser beam spot was purposely dispersed by using a defocusing technique. In groove filling experiments, a power density of defocused laser beam was kept in the range, which led the welding process towards to conduction limited regime and thus enabled to achieve broader weld cross-sections. The object was to study the feasibility of defocusing as a way to fill and bridge wider groove geometries than what can be welded with focused keyhole-mode welding with filler addition. The paper covers the results of multi-pass welding of up to 60 mm thick joints with single side preparations.

  3. Improvement in the Corrosion Resistance of Austenitic Stainless Steel 316L by Ion Implantation

    NASA Astrophysics Data System (ADS)

    Cai, Xun; Feng, Kai

    In the present work, austenitic stainless steel 316L (SS316L) samples were implanted with Ni and Ni-Cr. A nickel-rich layer about 100 nm in thickness and a Ni-Cr enriched layer about 60 nm thick are formed on the surface of SS316L. The effects of ion implantation on the corrosion performance of SS316L are investigated in a 0.5 M H2SO4 with 2 ppm HF solution at 80°C by open circuit potential (OCP), potentiodynamic and potentiostatic tests. The samples after the potentiostatic test are analyzed by XPS. The results indicate that the composition of the passive film change from a mixture of Fe oxides and Cr oxide to a Cr oxide dominated passive film after the potentiostatic test. The solutions after the potentiostatic test are analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES). The results reveal that Fe is selectively dissolved in all cases and a proper Ni and Ni-Cr implant fluence can greatly improve the corrosion resistance of SS316L in the simulated polymer electrolyte membrane fuel cells (PEMFCS) environment. They are in agreement with the electrochemical test results that the bare SS316L has the highest dissolution rate in both cathode and anode environments and the Ni and Ni-Cr implantation reduce markedly the dissolution rate. After the potentiostatic test the interfacial contact resistance (ICR) values are also measured. Ni and Ni-Cr are enriched in the passive film formed in the simulated PEMFC cathode environment after ion implantation thereby providing better conductivity than that formed in the anode one. A significant improvement of ICR is achieved for the SS316L implanted with Ni and Ni-Cr as compared to the bare SS316L, which is attributed to the reduction in passive layer thickness caused by Ni and Ni-Cr implantation. The ICR values for implanted specimens increase with increasing dose.

  4. Irradiation-assisted stress corrosion cracking of model austenitic stainless steel.

    SciTech Connect

    Chung, H. M.; Ruther, W. E.; Strain, R. V.; Shack, W. J.; Karlsen, T. M.

    1999-10-26

    Slow-strain-rate tensile (SSRT) tests were conducted on model austenitic stainless steel (SS) alloys that were irradiated at 289 C in He. After irradiation to {approx}0.3 x 10{sup 21} n {center_dot} cm{sup 2} and {approx} 0.9 x 10{sup 21} n {center_dot} cm{sup -2} (E > 1 MeV), significant heat-to-heat variations in the degree of intergranular and transgranular stress corrosion cracking (IGSCC and TGSCC) were observed. At {approx}0.3 x 10{sup 21} n {center_dot} cm{sup -2}, a high-purity heat of Type 316L SS that contains a very low concentration of Si exhibited the highest susceptibility to IGSCC. In unirradiated state, Types 304 and 304L SS did not exhibit a systematic effect of Si content on alloy strength. However, at {approx}0.3 x 10{sup 21} n {center_dot} cm{sup -2}, yield and maximum strengths decreased significantly as Si content was increased to >0.9 wt.%. Among alloys that contain low concentrations of C and N, ductility and resistance to TGSCC and IGSCC were significantly greater for alloys with >0.9 wt.% Si than for alloys with <0.47 wt.% Si. Initial data at {approx}0.9 x 10{sup 21} n {center_dot} cm{sup -2} were also consistent with the beneficial effect of high Si content. This indicates that to delay onset of and reduce susceptibility to irradiation-assisted stress corrosion cracking (IASCC), at least at low fluence levels, it is helpful to ensure a certain minimum concentration of Si. High concentrations of Cr were also beneficial; alloys that contain <15.5 wt.% Cr exhibited greater susceptibility to IASCC than alloys with {approx}18 wt.% Cr, whereas an alloy that contains >21 wt.% Cr exhibited less susceptibility than the lower-Cr alloys under similar conditions.

  5. Stress corrosion cracking behavior of irradiated model austenitic stainless steel alloys.

    SciTech Connect

    Chung, H. M.; Karlsen, T. M.; Ruther, W. E.; Shack, W. J.; Strain, R. V.

    1999-07-16

    Slow-strain-rate tensile tests (SSRTs) and posttest fractographic analyses by scanning electron microscopy were conducted on 16 austenitic stainless steel (SS) alloys that were irradiated at 289 C in He. After irradiation to {approx}0.3 x 10{sup 21} n{center_dot}cm{sup {minus}2} and {approx}0.9 x 10{sup 21} n{center_dot}cm{sup {minus}2} (E >1 MeV), significant heat-to-heat variations in the degree of intergranular and transgranular stress corrosion cracking (IGSCC and TGSCC) were observed. Following irradiation to a fluence of {approx}0.3 x 10{sup 21} n{center_dot}cm{sup {minus}2}, a high-purity laboratory heat of Type 316L SS (Si {approx} 0.024 wt%) exhibited the highest susceptibility to IGSCC. The other 15 alloys exhibited negligible susceptibility to IGSCC at this low fluence. The percentage of TGSCC on the fracture surfaces of SSRT specimens of the 16 alloys at {approx}0.3 x 10{sup 21} n{center_dot}cm{sup {minus}2} (E > 1 MeV) could be correlated well with N and Si concentrations; all alloys that contained <0.01 wt.% N and <1.0 wt. % Si were susceptible, whereas all alloys that contained >0.01 wt.% N or >1.0 wt.% Si were relatively resistant. High concentrations of Cr were beneficial. Alloys that contain <15.5 wt.% Cr exhibited greater percentages of TGSCC and IGSCC than those alloys with {approx}18 wt.% Cr, whereas an alloy that contains >21 wt.% Cr exhibited less susceptibility than the lower-Cr alloys under similar conditions.

  6. Thermo-mechanical processing of austenitic steel to mitigate surface related degradation

    NASA Astrophysics Data System (ADS)

    Idell, Yaakov Jonathan

    Thermo-mechanical processing plays an important role in materials property optimization through microstructure modification, required by demanding modern materials applications. Due to the critical role of austenitic stainless steels, such as 316L, as structural components in harsh environments, e.g. in nuclear power plants, improved degradation resistance is desirable. A novel two-dimensional plane strain machining process has shown promise achieving significant grain size refinement through severe plastic deformation (SPD) and imparting large strains in the surface and subsurface regions of the substrate in various metals and alloys. The deformation process creates a heavily deformed 20 -- 30 micron thick nanocrystalline surface layer with increased hardness and minimal martensite formation. Post-deformation processing annealing treatments have been applied to assess stability of the refined scale microstructures and the potential for obtaining grain boundary engineered microstructures with increased fraction of low-energy grain boundaries and altered grain boundary network structure. Varying the deformation and heat treatment process parameters, allows for development of a full understanding of the nanocrystalline layer and cross-section of the surface substrate created. Micro-characterization was performed using hardness measurements, magnetometry, x-ray diffraction, scanning and transmission electron microscopy to assess property and microstructural changes. This study provides a fundamental understanding of two-dimensional plane strain machining as a thermo-mechanical processing technique, which may in the future deliver capabilities for creating grain boundary engineered surface modified components, typified by a combination of grain refinement with improved grain boundary network interconnectivity attributes suitable for use in harsh environments, such as those in commercial nuclear power plants where improved resistance to irradiation stress corrosion

  7. Manufacture of Alumina-Forming Austenitic Steel Alloys by Conventional Casting and Hot-Working Methods

    SciTech Connect

    Brady, M.P.; Yamamoto, Y.; Magee, J.H.

    2009-03-10

    Oak Ridge National Laboratory (ORNL) and Carpenter Technology Corporation (CarTech) participated in an in-kind cost share cooperative research and development agreement (CRADA) effort under the auspices of the Energy Efficiency and Renewable Energy (EERE) Technology Maturation Program to explore the feasibility for scale up of developmental ORNL alumina-forming austenitic (AFA) stainless steels by conventional casting and rolling techniques. CarTech successfully vacuum melted 301b heats of four AFA alloy compositions in the range of Fe-(20-25)Ni-(12-14)Cr-(3-4)Al-(l-2.5)Nb wt.% base. Conventional hot/cold rolling was used to produce 0.5-inch thick plate and 0.1-inch thick sheet product. ORNL subsequently successfully rolled the 0.1-inch sheet to 4 mil thick foil. Long-term oxidation studies of the plate form material were initiated at 650, 700, and 800 C in air with 10 volume percent water vapor. Preliminary results indicated that the alloys exhibit comparable (good) oxidation resistance to ORNL laboratory scale AFA alloy arc casting previously evaluated. The sheet and foil material will be used in ongoing evaluation efforts for oxidation and creep resistance under related CRADAs with two gas turbine engine manufacturers. This work will be directed to evaluation of AFA alloys for use in gas turbine recuperators to permit higher-temperature operating conditions for improved efficiencies and reduced environmental emissions. AFA alloy properties to date have been obtained from small laboratory scale arc-castings made at ORNL. The goal of the ORNL-CarTech CRADA was to establish the viability for producing plate, sheet and foil of the AFA alloys by conventional casting and hot working approaches as a first step towards scale up and commercialization of the AFA alloys. The AFA alloy produced under this effort will then be evaluated in related CRADAs with two gas turbine engine manufacturers for gas turbine recuperator applications.

  8. Austenite stabilization and high strength-elongation product of a low silicon aluminum-free hot-rolled directly quenched and dynamically partitioned steel

    SciTech Connect

    Tan, Xiao-Dong; Xu, Yun-Bo; Yang, Xiao-Long; Hu, Zhi-Ping; Peng, Fei; Ju, Xiao-Wei; Wu, Di

    2015-06-15

    Microstructures composed of lath martensite and retained austenite with volume fraction between 8.0 vol.% and 12.0 vol.% were obtained in a low-C low-Si Al-free steel through hot-rolling direct quenching and dynamical partitioning (HDQ&DP) processes. The austenite stabilization mechanism in the low-C low-Si Al-free steel under the special dynamical partitioning processes is investigated by analyzing the carbon partition behavior from martensite to austenite and the carbide precipitation-coarsening behavior in martensite laths combining with the possible hot rolling deformation inheritance. Results show that the satisfying retained austenite amount in currently studied low-Si Al-free HDQ&DP steel is caused by the high-efficiency carbon enrichment in the 30–80 nm thick regions of austenite near the interfaces in the hot-rolled ultra-fast cooled structure and the avoidance of serious carbides coarsening during the continuous cooling procedures. The excellent strength-elongation product reaching up to 26,000 MPa% shows that the involved HDQ&DP process is a promising method to develop a new generation of advanced high strength steel. - Highlights: • HDQ&DP processes were applied to a low-C low-Si Al-free steel. • Effective partitioning time during the continuous cooling processes is 1–220 s. • Retained austenite with volume fraction between 8.0 vol. % and 12.0 vol. % has been obtained. • The special austenite stabilization mechanism has been expounded.

  9. The effects of cold work on the microstructure and mechanical properties of intermetallic strengthened alumina-forming austenitic stainless steels

    DOE PAGESBeta

    Hu, Bin; Baker, Ian; Miller, Michael K.; Yao, Lan; Chen, Si; Cai, Z.; Trotter, G.

    2015-06-12

    In order to achieve energy conversion efficiencies of >50 pct for steam turbines/boilers in power generation systems, materials are required that are both strong and corrosion-resistant at >973 K (700 °C), and economically viable. Austenitic steels strengthened with Laves phase, NiAl and Ni3Al precipitates, and alloyed with aluminum to improve oxidation resistance, are potential candidate materials for these applications. The microstructure and microchemistry of recently developed alumina-forming austenitic stainless steels have been characterized by scanning electron microscopy, transmission electron microscopy, and synchrotron X-ray diffraction. Different thermo-mechanical treatments were performed on these steels to improve their mechanical performance. These reduced themore » grain size significantly to the nanoscale (~100 nm) and the room temperature yield strength to above 1000 MPa. Lastly, a solutionizing anneal at 1473 K (1200 °C) was found to be effective for uniformly redistributing the Laves phase precipitates that form upon casting.« less

  10. The effects of cold work on the microstructure and mechanical properties of intermetallic strengthened alumina-forming austenitic stainless steels

    SciTech Connect

    Hu, Bin; Baker, Ian; Miller, Michael K.; Yao, Lan; Chen, Si; Cai, Z.; Trotter, G.

    2015-06-12

    In order to achieve energy conversion efficiencies of >50 pct for steam turbines/boilers in power generation systems, materials are required that are both strong and corrosion-resistant at >973 K (700 °C), and economically viable. Austenitic steels strengthened with Laves phase, NiAl and Ni3Al precipitates, and alloyed with aluminum to improve oxidation resistance, are potential candidate materials for these applications. The microstructure and microchemistry of recently developed alumina-forming austenitic stainless steels have been characterized by scanning electron microscopy, transmission electron microscopy, and synchrotron X-ray diffraction. Different thermo-mechanical treatments were performed on these steels to improve their mechanical performance. These reduced the grain size significantly to the nanoscale (~100 nm) and the room temperature yield strength to above 1000 MPa. Lastly, a solutionizing anneal at 1473 K (1200 °C) was found to be effective for uniformly redistributing the Laves phase precipitates that form upon casting.

  11. Effect of Strain and Strain Path on Texture and Twin Development in Austenitic Steel with Twinning-Induced Plasticity

    NASA Astrophysics Data System (ADS)

    Mishra, Sushil K.; Tiwari, Shashank M.; Kumar, Arun M.; Hector, Louis G.

    2012-05-01

    High-manganese (15 to 30 wt pct) austenitic steels exhibit extreme strain hardening because of twinning with increased strain. Twinning in these low stacking fault materials promotes retention of the austenitic microstructure and impedes dislocation motion. A dearth of information is available concerning the extent to which strain path influences twinning in so-called twinning-induced plasticity (TWIP) steels. The present study focuses on the influence of strain level and strain path on texture and twinning in a high-Mn content TWIP steel (Fe17.2Mn0.6C). Electron back-scatter diffraction was employed to measure the twin fraction, twin deviation, twin boundary length, grain misorientation, and volume fraction of different texture components as a function of both uniaxial and biaxial deformation. This information, which is part of the necessary first step toward linking crystallographic texture and twinning to mechanical properties, was used to quantitatively assess the extent to which these critical metallurgical features depend on the amount of straining and the strain path.

  12. The Effects of Cold Work on the Microstructure and Mechanical Properties of Intermetallic Strengthened Alumina-Forming Austenitic Stainless Steels

    SciTech Connect

    Hu, B.; Trotter, G.; Baker, Ian; Miller, M. K.; Yao, L.; Chen, S.; Cai, Z.

    2015-08-01

    In order to achieve energy conversion efficiencies of > 50 pct for steam turbines/boilers in power generation systems, materials are required that are both strong and corrosion-resistant at > 973 K (700 A degrees C), and economically viable. Austenitic steels strengthened with Laves phase, NiAl and Ni3Al precipitates, and alloyed with aluminum to improve oxidation resistance, are potential candidate materials for these applications. The microstructure and microchemistry of recently developed alumina-forming austenitic stainless steels have been characterized by scanning electron microscopy, transmission electron microscopy, and synchrotron X-ray diffraction. Different thermo-mechanical treatments were performed on these steels to improve their mechanical performance. These reduced the grain size significantly to the nanoscale (similar to 100 nm) and the room temperature yield strength to above 1000 MPa. A solutionizing anneal at 1473 K (1200 A degrees C) was found to be effective for uniformly redistributing the Laves phase precipitates that form upon casting. (C) The Minerals, Metals & Materials Society and ASM International 2015

  13. Digital Processing of Ultrasound Signals Backscattered from Coarse Grained Austenitic Stainless Steel.

    NASA Astrophysics Data System (ADS)

    Hargreaves, Martin Lawrence

    Available from UMI in association with The British Library. In this thesis, the characteristics of individual pulse-echo ultrasound signals received from a cast block of coarse grained austenitic stainless steel (ASS) are considered. Such signals are renowned for beam skewing effects and being rich in backscattered acoustic noise due to the nature of the material. Cast ASS is used for its mechanical properties in critical applications such as nuclear reactor systems and the acoustic noise is known to be detrimental to the pulse-echo non-destructive testing (NDT) of this form of steel. After a review of these subjects, this thesis describes the application of one-dimensional (1-D) time sequence analysis techniques to the digitally recorded ultrasound data in order to assess their ability to discriminate between data characteristics due to the material and that due to a reflection from the back surface of the block. This is seen as a first step in the evaluation of improving ultrasonic NDT of these materials by use of standard equipment in conjunction with digital signal processing techniques. Two data sets are examined; one from a broad band 5MHz centre frequency compression wave transducer and the other from a similar 1MHz transducer. Numerous 1-D signal processing techniques are applied to the data and their insensitivity to the effect of the material characteristics on the data is noted. Many techniques have not previously been applied to this type of ultrasound data. Cepstrum techniques have shown to be inappropriate when analysing such data and adaptive techniques were generally unsuccessful except for one variant when applied to the 5MHz data. Modern spectrum analysis techniques and a l_4 norm deconvolution technique have been shown to be promising in the analysis of such data but further work in this area is recommended, especially time-space processing in order to improve the statistics of the techniques. Also contained in this thesis is a description of a

  14. Fracture mechanisms in dual phase steels based on the acicular ferrite + martensite/austenite microstructure

    NASA Astrophysics Data System (ADS)

    Poruks, Peter

    The fracture mechanisms of low carbon microalloyed plate steels based on the acicular ferrite + marten site/austenite microstructure (AF + M/A) are investigated. The final microstructure consists of a dispersed phase of submicron equi-axed martensite particles with a bainitic ferrite matrix. A series of plates with M/A volume fractions of 0.076--0.179 are studied. Brittle fracture is investigated by Instrumented Charpy impact testing of samples at -196°C and subsequent metallography. The M/A particles are identified as the crack nucleation sites and the cleavage fracture stress calculated to be 2400 MPa in a complete AF microstrucuture. This value is significantly larger than in steels that contain significant proportions of conventional bainite. Standard Charpy and Instrumented Charpy impact testing is conducted through a temperature range from -80 to + 22°C to study ductile fracture behaviour. The total absorbed energy is separated into energies of crack nucleation and of crack propagation. It is found that the energy of crack nucleation is weakly dependent on the volume fraction of M/A and completely independent of temperature over the range studied. The crack propagation energy varies significantly with both variables, decreasing with increased volume fraction of M/A and with decreasing temperature. The peak load in the instrumented Charpy data is used to calculate the dynamic fracture toughness, KId, which is found to be 105--120 MPa-m1/2. The void nucleation and void growth stages of ductile fracture are studied by metallographic examination of tensile bars. The sites of void nucleation are identified as inclusions and M/A particles. Voids nucleate at the M/A particles by decohesion of the particle-matrix interface. A constant void nucleation strain of epsilon = 0.90 +/- 0.05 is measured for all of the samples independent of the volume fraction of M/A. A stress-based criterion is used to predict void nucleation and the interface strength is determined to be

  15. Gas porosity evolution and ion-implanted helium behavior in reactor ferritic/martensitic and austenitic steels

    NASA Astrophysics Data System (ADS)

    Chernov, I. I.; Kalin, B. A.; Staltsov, M. S.; Oo, Kyi Zin; Binyukova, S. Yu.; Staltsova, O. S.; Polyansky, A. A.; Ageev, V. S.; Nikitina, A. A.

    2015-04-01

    The peculiarities of gas porosity formation and helium retention and release in reactor ferritic/martensitic EP-450 and EP-450-ODS and austenitic ChS-68 steels are investigated by transmission electron microscopy and helium thermal desorption spectrometry (HTDS). The samples were irradiated by 40 keV He+ ions up to a fluence of 5 · 1020 m-2 at 293 and 923 K. An nonuniform distribution of helium bubbles and high-level gas swelling in ferritic/martensitic steels were found at high-temperature helium implantation. The same irradiation conditions result in formation of uniformly distributed helium bubbles and low-level swelling in ChS-68 steel. Temperature range of helium release from EP-450-ODS steel was considerably wider in comparison to HTDS-spectra of the EP-450 steel. A considerable quantity of helium is released from ODS steel in the high-temperature range after the main peak of the HTDS-spectrum.

  16. AN ULTRASONIC PHASED ARRAY EVALUATION OF INTERGRANULAR STRESS CORROSION CRACK (IGSCC) DETECTION IN AUSTENITIC STAINLESS STEEL PIPING WELDS

    SciTech Connect

    Diaz, Aaron A.; Anderson, Michael T.; Cinson, Anthony D.; Crawford, Susan L.; Cumblidge, Stephen E.

    2010-07-22

    Research is being conducted for the U.S. Nuclear Regulatory Commission at the Pacific Northwest National Laboratory to assess the effectiveness and reliability of advanced nondestructive examination (NDE) methods for the inspection of light water reactor (LWR) components and challenging material/component configurations. This study assessed the effectiveness of far-side inspections on wrought stainless steel piping with austenitic welds, as found in thin-walled, boiling water reactor (BWR) component configurations, for the detection and characterization of intergranular stress corrosion cracks (IGSCC).

  17. Effect of deformation in the intercritical area on the grain refinement of retained austenite of 0.4C TRIP steel

    SciTech Connect

    Basuki, A.; Aernoudt, E.

    1999-04-09

    Producing steels with higher strength without loss of formability has been the subject of many recent investigations. The combination of high strength and high formability of steels can be achieved using the concept of Transformation Induced Plasticity (TRIP). Developing TRIP steels along the hot rolling route has not been studied extensively. This route opens an opportunity for improving the properties of TRIP steel by deformation in the intercritical area. No study about the influences of deformation in the intercritical area has been made systematically. Such deformation in the intercritical area has a substantial effect on microstructures and mechanical properties of TRIP steel. It increases dislocation density, refines retained austenite grain and enriches the carbon content of retained austenite. All of those properties significantly improve the stability of retained austenite, which on its turn enhances the strength and work hardening behavior of the steel. The present study shows that deformation in the intercritical area influences the size and the morphology of the different phases -- ferrite, bainite and retained austenite -- of the resulting microstructure.

  18. Effect of Alloying Element Partition in Pearlite on the Growth of Austenite in High-Carbon Low Alloy Steel

    NASA Astrophysics Data System (ADS)

    Yang, Z. N.; Xia, Y.; Enomoto, M.; Zhang, C.; Yang, Z. G.

    2016-03-01

    The growth of austenite from pearlite in high-carbon low alloy steel occurs with and without alloy element redistribution depending on the amount of superheating above the eutectoid temperature. The transition temperature of austenite growth (denoted PNTT) is calculated as a function of pearlite transformation temperature and subsequent holding time, which affect the degree of partitioning in pearlite, using experimental partition coefficients k θ/ α of Mn, Cr, Co, Si, and Ni reported in the literature. PNTT is the highest in Cr-containing alloys which have the largest k θ/ α in pearlite. Post-transformation aging, usually accompanied by cementite spheroidization, leads to a marked increase of PNTT in Mn and Cr alloys. PNTT of Ni alloy does not depend on pearlite transformation temperature because practically the formation of partitioned pearlite is severely limited in this alloy for kinetic reasons. Above PNTT, austenite growth occurs fast initially, but slows down in the order of ten seconds when the ferrite disappears, and the remaining small carbide particles dissolve very slowly under the control of alloy element diffusion.

  19. The Impact of Retained Austenite Characteristics on the Two-Body Abrasive Wear Behavior of Ultrahigh Strength Bainitic Steels

    NASA Astrophysics Data System (ADS)

    Narayanaswamy, Balaji; Hodgson, Peter; Timokhina, Ilana; Beladi, Hossein

    2016-08-01

    In the current study, a high-carbon, high-alloy steel (0.79 pct C, 1.5 pct Si, 1.98 pct Mn, 0.98 pct Cr, 0.24 pct Mo, 1.06 pct Al, and 1.58 pct Co in wt pct) was subjected to an isothermal bainitic transformation at a temperature range of 473 K to 623 K (200 °C to 350 °C), resulting in different fully bainitic microstructures consisting of bainitic ferrite and retained austenite. With a decrease in the transformation temperature, the microstructure was significantly refined from ~300 nm at 623 K (350 °C) to less than 60 nm at 473 K (200 °C), forming nanostructured bainitic microstructure. In addition, the morphology of retained austenite was progressively altered from film + blocky to an exclusive film morphology with a decrease in the temperature. This resulted in an enhanced wear resistance in nanobainitic microstructures formed at low transformation temperature, e.g., 473 K (200 °C). Meanwhile, it gradually deteriorated with an increase in the phase transformation temperature. This was mostly attributed to the retained austenite characteristics (i.e., thin film vs blocky), which significantly altered their mechanical stability. The presence of blocky retained austenite at high transformation temperature, e.g., 623 K (350 °C) resulted in an early onset of TRIPing phenomenon during abrasion. This led to the formation of coarse martensite with irregular morphology, which is more vulnerable to crack initiation and propagation than that of martensite formed from the thin film austenite, e.g., 473 K (200 °C). This resulted in a pronounced material loss for the fully bainitic microstructures transformed at high temperature, e.g., 623 K (350 °C), leading to distinct sub-surface layer and friction coefficient curve characteristics. A comparison of the abrasive behavior of the fully bainitic microstructure formed at 623 K (350 °C) and fully pearlitic microstructure demonstrated a detrimental effect of blocky retained austenite with low mechanical stability on the

  20. A comparative study of the in vitro corrosion behavior and cytotoxicity of a superferritic stainless steel, a Ti-13Nb-13Zr alloy, and an austenitic stainless steel in Hank's solution.

    PubMed

    Assis, S L; Rogero, S O; Antunes, R A; Padilha, A F; Costa, I

    2005-04-01

    In this study, the in vitro corrosion resistance of a superferritic stainless steel in naturally aerated Hank's solution at 37 degrees C has been determined to evaluate the steel for use as a biomaterial. The potentiodynamic polarization method and electrochemical impedance spectroscopy (EIS) were used to determine the corrosion resistance. The polarization results showed very low current densities at the corrosion potential and electrochemical behavior typical of passive metals. At potentials above 0.75 V (SCE), and up to that of the oxygen evolution reaction, the superferritic steel exhibited transpassive behavior followed by secondary passivation. The superferritic stainless steel exhibited high pitting resistance in Hank's solution. This steel did not reveal pits even after polarization to 3000 mV (SCE). The EIS results indicated high impedance values at low frequencies, supporting the results obtained from the polarization measurements. The results obtained for the superferritic steel have been compared with those of the Ti-13Nb-13Zr alloy and an austenitic stainless steel, as Ti alloys are well known for their high corrosion resistance and biocompatibility, and the austenitic stainless steel is widely used as an implant material. The cytotoxicity tests indicated that the superferritic steel, the austenitic steel, and the Ti-13Nb-13Zr alloy were not toxic. Based on corrosion resistance and cytotoxicity results, the superferritic stainless steel can be considered as a potential biomaterial. PMID:15660438

  1. Hot and cold rolling of high nitrogen Cr-Ni and Cr-Mn austenitic stainless steels

    SciTech Connect

    Iiola, R.; Hanninen, H.; Kauppi, T.

    1998-10-01

    Behavior of austenitic Cr-Ni-(0.14--0.50)N and Cr-Mn-(0.78--1.00)N steels in hot and cold rolling was investigated by rolling experiments and mechanical testing. Structure of the steels in the as-cast condition and fracture surfaces after the rolling experiments were investigated using optical and scanning electron microscopy (SEM). Resistance to deformation was calculated using rolling forces in hot rolling. Increase in strength in the rolling experiments was related to the nitrogen content of the steels. Resistance to deformation during hot rolling increased with decreasing rolling temperature and with increasing nitrogen content. In some steels, hot rolling led to edge cracking, which was more a function of impurity than nitrogen content. Microscopy revealed that the edge cracking occurred along grain boundaries and second phase particles. For the cold-rolled steels, the highest achievable reductions were limited due to a crocodiling phenomenon, that is, opening of the strip end. Fracture type at the opened strip end was a brittle-like fracture.

  2. Effects of Annealing Treatment Prior to Cold Rolling on Delayed Fracture Properties in Ferrite-Austenite Duplex Lightweight Steels

    NASA Astrophysics Data System (ADS)

    Sohn, Seok Su; Song, Hyejin; Kim, Jung Gi; Kwak, Jai-Hyun; Kim, Hyoung Seop; Lee, Sunghak

    2016-02-01

    Tensile properties of recently developed automotive high-strength steels containing about 10 wt pct of Mn and Al are superior to other conventional steels, but the active commercialization has been postponed because they are often subjected to cracking during formation or to the delayed fracture after formation. Here, the delayed fracture behavior of a ferrite-austenite duplex lightweight steel whose microstructure was modified by a batch annealing treatment at 1023 K (750 °C) prior to cold rolling was examined by HCl immersion tests of cup specimens, and was compared with that of an unmodified steel. After the batch annealing, band structures were almost decomposed as strong textures of {100}<011> α-fibers and {111}<112> γ-fibers were considerably dissolved, while ferrite grains were refined. The steel cup specimen having this modified microstructure was not cracked when immersed in an HCl solution for 18 days, whereas the specimen having unmodified microstructure underwent the delayed fracture within 1 day. This time delayed fracture was more critically affected by difference in deformation characteristics such as martensitic transformation and deformation inhomogeneity induced from concentration of residual stress or plastic strain, rather than the difference in initial microstructures. The present work gives a promise for automotive applications requiring excellent mechanical and delayed fracture properties as well as reduced specific weight.

  3. The electrochemical behaviour of 316L austenitic stainless steel in Cl- containing environment under different H2S partial pressures

    NASA Astrophysics Data System (ADS)

    Ding, Jinhui; Zhang, Lei; Lu, Minxu; Wang, Jing; Wen, Zhibin; Hao, Wenhui

    2014-01-01

    In oil-gas production environments, presence of H2S-Cl- can induce deterioration of the passive film, leading to pitting corrosion of stainless steels. In this paper, by using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and capacitance measurements (Mott-Schottky analysis), the electrochemical behaviour of AISI 316L austenitic stainless steel was investigated in Cl- solutions under different H2S partial pressures (from 0 to 1.0 bar). The results indicated that presence of H2S in Cl- solution can accelerate both the cathodic and anodic current density, leading to a metastable passive state in higher passive potential range, changing the semiconductor behaviour from p-type to n-type, increasing its susceptibility to corrosion. XPS analysis was employed to characterize the surface film after potentiostatic polarization, whose results provide good evidences for the electrochemical measurements.

  4. Thermal characterization of austenite stainless steel (304) and CNT films of varying thickness using micropipette thermal sensors

    NASA Astrophysics Data System (ADS)

    Dangol, Ashesh

    Thermal transport behavior of austenite stainless steel stripe (304) and the carbon nano-tubes (CNTs) films of varying thickness are studied using a micropipette thermal sensor. Micropipette sensors of various tip sizes were fabricated and tested for the sensitivity and reliability. The sensitivity deviated by 0.11 for a batch of pipette coated under same physical vapor deposition (PVD) setting without being affected by a tip size. Annealing, rubber coating and the vertical landing test of the pipette sensor proved to be promising in increasing the reliability and durability of the pipette sensors. A micro stripe (80microm x 6microm x 0.6microm) of stainless steel, fabricated using focused ion beam (FIB) machining, was characterized whose thermal conductivity was determined to be 14.9 W/m-K at room temperature. Similarly, the thermal characterization of CNT films showed the decreasing tendency in the thermal transport behavior with the increase in the film thickness.

  5. Effect of Specimen Diameter on Tensile Properties of Austenitic Stainless Steels in Liquid Hydrogen and Gaseous Helium at 20K

    NASA Astrophysics Data System (ADS)

    Fujii, H.; Ohmiya, S.; Shibata, K.; Ogata, T.

    2006-03-01

    Tensile tests using round bar type specimens of 3, 5 and 7 mm in diameter were conducted at 20K in liquid hydrogen and also in gaseous helium at the same temperature for three major austenitic stainless steels, JIS SUS304L, 316L and 316LN, extensively used for cryogenic applications including liquid hydrogen transportation and storage vessels. Stress-strain curves were considerably different between circumstances and also specimen diameter, resulting in differences of strength and ductility. In liquid hydrogen, serrated deformation appeared after considerable work hardening and more active in specimens with larger diameter. Meanwhile serrated deformation was observed from the early stage of plastic deformation in gaseous helium at 20 K and serration was more frequent in specimens with smaller diameter. The serrated deformation behaviors were numerically simulated for 304L steel with taking thermal properties such as thermal conductivity, specific heat, heat transfer from specimens to cryogenic media into account, and some agreement with the experiments was obtained.

  6. The PISC parametric study on the effect of cast austenitic steel macrostructure on the capability of ultrasonic examination

    SciTech Connect

    Maes, G.; Hansoul, B.; Dombret, P.

    1994-12-31

    Within the framework of Action 4 (Austenitic Steel Testing) of PISC 3, a parametric study was carried out on a set of centrifugically cast stainless steel samples, representative of the main coolant piping of pressurized water nuclear reactors. The samples are obtained from different manufacturers, and feature various grain structures and dimensions. Artificial and realistic flaws were used to assess the detection and sizing capability of ultrasonic examination techniques. The paper analyzes the data as a function of the metal structure and of the main parameters of the testing techniques, which include TRL contact probes and immersion focusing transducers. Guidelines are deduced as to the selection of inspection techniques, in relation with the metallurgical structure of each specimen. In addition, the influence of the presence of a weld across the wavepath is evaluated, as well as the similarity, between the responses obtained from crack-like machined reflectors and mechanical fatigue cracks.

  7. Effect of Specimen Diameter on Tensile Properties of Austenitic Stainless Steels in Liquid Hydrogen and Gaseous Helium at 20K

    SciTech Connect

    Fujii, H.; Ohmiya, S.; Shibata, K.; Ogata, T.

    2006-03-31

    Tensile tests using round bar type specimens of 3, 5 and 7 mm in diameter were conducted at 20K in liquid hydrogen and also in gaseous helium at the same temperature for three major austenitic stainless steels, JIS SUS304L, 316L and 316LN, extensively used for cryogenic applications including liquid hydrogen transportation and storage vessels. Stress-strain curves were considerably different between circumstances and also specimen diameter, resulting in differences of strength and ductility. In liquid hydrogen, serrated deformation appeared after considerable work hardening and more active in specimens with larger diameter. Meanwhile serrated deformation was observed from the early stage of plastic deformation in gaseous helium at 20 K and serration was more frequent in specimens with smaller diameter. The serrated deformation behaviors were numerically simulated for 304L steel with taking thermal properties such as thermal conductivity, specific heat, heat transfer from specimens to cryogenic media into account, and some agreement with the experiments was obtained.

  8. Effects of surface preparation on pitting resistance, residual stress, and stress corrosion cracking in austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Rhouma, A. Ben; Sidhom, H.; Braham, C.; Lédion, J.; Fitzpatrick, M. E.

    2001-10-01

    Surface finishing treatments such as shot blasting and wire brushing can be beneficial in improving the integrity of machined surfaces of austenitic stainless steels. These operations optimize in-service properties such as resistance to pitting corrosion and stress corrosion cracking (SCC). In this study, ground steel surfaces were subjected to a series of sand blasting and wire brushing treatments. The surfaces were then characterized by their hardness, surface residual stress state, and resistance to stress corrosion and pitting corrosion. Some samples were selected for depth profiling of residual stress. It is found that surface hardening and the generation of near-surface compressive residual stress are the benefits that can be introduced by sand blasting and brushing operations.

  9. Hydrogen Absorption into Austenitic Stainless Steels Under High-Pressure Gaseous Hydrogen and Cathodic Charge in Aqueous Solution

    NASA Astrophysics Data System (ADS)

    Enomoto, Masato; Cheng, Lin; Mizuno, Hiroyuki; Watanabe, Yoshinori; Omura, Tomohiko; Sakai, Jun'ichi; Yokoyama, Ken'ichi; Suzuki, Hiroshi; Okuma, Ryuji

    2014-12-01

    Type 316L and Type 304 austenitic stainless steels, both deformed and non-deformed, were hydrogen charged cathodically in an aqueous solution as well as by exposure to high-pressure gaseous hydrogen in an attempt to identify suitable conditions of cathodic charge for simulating hydrogen absorption from gaseous hydrogen environments. Thermal desorption analysis (TDA) was conducted, and the amount of absorbed hydrogen and the spectrum shape were compared between the two charging methods. Simulations were performed by means of the McNabb-Foster model to analyze the spectrum shape and peak temperature, and understand the effects of deformation on the spectra. It was revealed that the spectrum shape and peak temperature were dependent directly upon the initial distribution of hydrogen within the specimen, which varied widely according to the hydrogen charge condition. Deformation also had a marked effect on the amount of absorbed hydrogen in Type 304 steel due to the strain-induced martensitic transformation.

  10. Automated Flaw Detection Scheme For Cast Austenitic Stainless Steel Weld Specimens Using Hilbert Huang Transform Of Ultrasonic Phased Array Data

    SciTech Connect

    Khan, T.; Majumdar, Shantanu; Udpa, L.; Ramuhalli, Pradeep; Crawford, Susan L.; Diaz, Aaron A.; Anderson, Michael T.

    2012-01-01

    The objective of this work is to develop processing algorithms to detect and localize the flaws using NDE ultrasonic data. Data was collected using cast austenitic stainless steel (CASS) weld specimens on-loan from the U.S. nuclear power industry’s Pressurized Water Reactor Owners Group (PWROG) specimen set. Each specimen consists of a centrifugally cast stainless steel (CCSS) pipe section welded to a statically cast (SCSS) or wrought (WRSS) section. The paper presents a novel automated flaw detection and localization scheme using low frequency ultrasonic phased array inspection signals in the weld and heat affected zone of the base materials. The major steps of the overall scheme are preprocessing and region of interest (ROI) detection followed by the Hilbert Huang transform (HHT) of A-scans in the detected ROIs. HHT offers time-frequency-energy distribution for each ROI. The accumulation of energy in a particular frequency band is used as a classification feature for the particular ROI.

  11. Effect of Shot Peening on the Intergranular Corrosion Susceptibility of a Novel Super304H Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Wang, Rui Kun; Zheng, Zhi Jun; Gao, Yan

    2016-01-01

    The surface phase constituent of Super304H austenitic stainless steel, after shot peening and sensitization treatment at 600, 650, and 700 °C for 2 h, was characterized using x-ray diffraction method. The degree of sensitization (DOS) was investigated by means of double-loop electrochemical potentiokinetic reactivation (DL-EPR) test, and the morphology after DL-EPR test was observed by scanning electron microscopy (SEM). The results showed that nano-sized grains and strain-induced martensite together with compressive residual stress formed on the surface of Super304H steel after shot peening. Surface compressive residual stresses relaxed greatly after being sensitized at 600-700 °C for 2 h, and no systematic correlation was observed between the compressive residual stresses developed and the intergranular corrosion susceptibility (IGCS). Because of the occurrence of strain-induced martensite in the shot-peened specimens, their IGCS is much higher than that of the as-received specimen when being sensitized at 600-650 °C for 2 h. Besides, the DOS increased with the increasing of shot peening time and the content of strain-induced martensite. On the contrary, the IGCS of Super304H stainless steels subjected to shot peening was eliminated when being sensitized at 700 °C for 2 h because of the reverse transformation of strain-induced martensite and faster diffusion rate of Cr at higher temperature in ultrafine-grained austenite which had helped healing the chromium depletion zone in a very short time. In a word, shot peening promoted desensitization of Super304H steel in a time shorter than 2 h at higher temperature up to 700 °C.

  12. Low Temperature Nitriding of 304 Austenitic Stainless Steel Using RF-ICP Method: the Role of Ion Beam Flux Density

    NASA Astrophysics Data System (ADS)

    Wang, Qing; Ba, Dechun; Ming, Yue; Xu, Lin; Guo, Deyu

    2014-10-01

    The significant role of ion beam flux during nitriding 304 austenitic stainless steel has been investigated by using a radio frequency inductively-coupled plasma reactor into which a sample with negative bias voltage was inserted. A milliammeter is used to detect the current of ions which collide with the sample and optical emission spectroscopy is used to discern the reactive species included in the nitrogen plasma. The nitriding efficiency is indicated by X-ray diffraction and the microhardness test. The reported data reveal that the ion beam flux density as well as the deposition pressure, bias voltage and time can strongly affect the nitriding of stainless steel via the expanded multiphase microstructure inside the nitrided layer. The increase in the density of ion flux results in an ascent in the intensity of the expanded peak and a simultaneous decline in the intensity of the γ austenite peak. The evolution trend of ion beam flux density is described as a function of the operating pressure and the bias voltage. The maximum ion flux density has been achieved at 10 Pa pressure and -500 V bias voltage. A reasonable nitriding region has been, consequently, suggested after comparing this work with previously reported results.

  13. The effects of water vapor on the oxidation behavior of alumina forming austenitic stainless steels

    DOE PAGESBeta

    Yanar, N. M.; Lutz, B. S.; Garcia-Fresnillo, L.; Brady, Michael P.; Meier, G. H.

    2015-08-19

    The isothermal oxidation behavior of three alumina forming austenitic (AFA) stainless steels with varying composition was studied at 650 and 800 °C in dry air and gases which contained water vapor. The AFA alloys exhibited better oxidation resistance than a “good chromia former” at 650 °C, particularly in H2O-containing atmospheres by virtue of alumina-scale formation. Although the AFA alloys were more resistant than chromia formers, their oxidation resistance was degraded at 650 °C in the presence of water vapor. In dry air the AFA alloys formed, thin continuous alumina scales, whereas in Ar–4%H2–3%H2O the areas of continuous alumina were reducedmore » and Fe oxide-rich nodules and regions of Cr, Mn-rich oxides formed. In some regions internal oxidation of the aluminum occurred in the H2O-containing gas. The alloy OC8 had slightly better resistance than OC4 or OC5 in this atmosphere. The alumina-forming capability of the AFA alloys decreases with increasing temperature and, at 800 °C, they are borderline alumina formers, even in dry air. The oxidation resistance of all three alloys was degraded at 800 °C in atmospheres, which contained water vapor (Air–10%H2O, Ar–3%H2O and Ar–4%H2–3%H2O). The areas, which formed continuous alumina, were reduced in these atmospheres and areas of internal oxidation occurred. However, as a result of the borderline alumina-forming capability of the AFA alloys it was not possible to determine which of the H2O-containing atmospheres was more severe or to rank the alloys in terms of their performance. The experimental results indicate that the initial microstructure of the AFA alloys also plays a role in their oxidation performance. Less protective oxides formed at 800 °C when alloy OC8 was equilibrated before exposure rather than being exposed in the as-processed condition. As a result, the reason for this is the presence of different phases in the bulk of the two specimens.« less

  14. Biocompatibility evaluation of surface-treated AISI 316L austenitic stainless steel in human cell cultures.

    PubMed

    Martinesi, M; Bruni, S; Stio, M; Treves, C; Bacci, T; Borgioli, F

    2007-01-01

    The effects of AISI 316L austenitic stainless steel, tested in untreated state or subjected to glow-discharge nitriding (at 10 or 20 hPa) and nitriding + post-oxidizing treatments, on human umbilical vein endothelial cells (HUVEC) and on peripheral blood mononuclear cells (PBMC) were evaluated. All the treated samples showed a better corrosion resistance in PBS and higher surface hardness in comparison with the untreated alloy. In HUVEC put in contact for 72 h with the sample types, proliferation and apoptosis decreased and increased, respectively, in the presence of the nitrided + post-oxidized samples, while only slight differences in cytokine (TNF-alpha, IL-6, and TGF-beta1) release were registered. Intercellular adhesion molecule-1 (ICAM-1) increased in HUVEC incubated with all the treated samples, while vascular cell adhesion molecule-1 (VCAM-1) and E-selectin increased in the presence of all the sample types. PBMC incubated for 48 h with the samples showed a decrease in proliferation and an increase in apoptosis in the presence of the untreated samples and the nitrided + post-oxidized ones. All the sample types induced a remarkable increase in TNF-alpha and IL-6 release in PBMC culture medium, while only the untreated sample and the nitrided at 10 hPa induced an increase in ICAM-1 expression. In HUVEC cocultured with PBMC, previously put in contact with the treated AISI 316L samples, increased levels of ICAM-1 were detected. In HUVEC coincubated with the culture medium of PBMC, previously put in contact with the samples under study, a noteworthy increase in ICAM-1, VCAM-1, and E-selectin levels was always registered, with the exception of VCAM-1, which was not affected by the untreated sample. In conclusion, even if the treated samples do not show a marked increase in biocompatibility in comparison with the untreated alloy, their higher corrosion resistance may suggest a better performance as the contact with physiological environment becomes longer. PMID

  15. Mechanical behavior and structure of passive films on austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Al-Amr, Abdulaziz

    2005-07-01

    The Taguchi analysis method was used in conjunction with ex-situ and in-situ nanoindentation tests to study the effects of alloy chemistry, solution pH, and halide ion concentrations on the mechanical fracture of electrochemically grown passive films formed at passive and metastable pitting potentials. Three austenitic stainless steels, SS, 304, 316, and 904L were anodically polarized in hydrochloric acid solutions for this study. The ex-situ study indicated that the alloy chemistry is the dominant factor of the mechanical fracture of the film formed at a stable passive potential; the average load to fracture the films using a 450 nm radius diamond tip was 52 muN. The films formed on 904L were the strongest, while the films on 316 SS were the weakest. The fracture load of the films formed at a metastable pitting potential, on the other hand, was equally influenced by the chloride ion concentration and the alloy chemistry. The load at fracture of films formed in the metastable pitting region was 64% of the fracture load of passive films formed at a stable potential. The fracture load of the passive films was depended on the degree of crystallinity of the passive film. The passive film on 316SS with lower density of crystalline islands than that of 304 SS had the lowest fracture load. In contrast, when the film was epitaxial, the fracture load was the largest. The dichromate treatment results indicate that the increase in degree of crystallinity of the passive films is associated with the increase in the chromium content of the substrate. In-situ measurements during anodic polarization led to similar behavior and results. The measured strength of films measured in ambient conditions after removal from the electrolyte was greater than when the films were measured in situ. However, the trends in film strength as a function of environment are the same between in situ and ex situ testing, suggesting the two tests are both feasible methods of analyzing environmental

  16. Stress Corrosion Cracking—Crevice Interaction in Austenitic Stainless Steels Characterized By Acoustic Emission

    NASA Astrophysics Data System (ADS)

    Leinonen, H.; Schildt, T.; Hänninen, H.

    2011-02-01

    Stress corrosion cracking (SCC) susceptibility of austenitic EN1.4301 (AISI 304) and EN1.4404 (AISI 316L) stainless steels was studied using the constant load method and polymer (PTFE) crevice former in order to study the effects of crevice on SCC susceptibility. The uniaxial active loading tests were performed in 50 pct CaCl2 at 373 K (100 °C) and in 0.1 M NaCl at 353 K (80 °C) under open-circuit corrosion potential (OCP) and electrochemical polarization. Pitting, crevice, and SCC corrosion were characterized and identified by acoustic emission (AE) analysis using ∆ t filtering and the linear locationing technique. The correlation of AE parameters including amplitude, duration, rise time, counts, and energy were used to identify the different types of corrosion. The stages of crevice corrosion and SCC induced by constant active load/crevice former were monitored by AE. In the early phase of the tests, some low amplitude AE activity was detected. In the steady-state phase, the AE activity was low, and toward the end of the test, it increased with the increasing amplitude of the impulses. AE allowed a good correlation between AE signals and corrosion damage. Although crevice corrosion and SCC induced AE signals overlapped slightly, a good correlation between them and microscopical characterization and stress-strain data was found. Especially, the activity of AE signals increased in the early and final stages of the SCC experiment under constant active load conditions corresponding to the changes in the measured steady-state creep strain rate of the specimen. The results of the constant active load/crevice former test indicate that a crevice can initiate SCC even in the mild chloride solution at low temperatures. Based on the mechanistic model of SCC, the rate determining step in SCC is thought to be the generation of vacancies by selective dissolution, which is supported by the low activity phase of AE during the steady-state creep strain rate region.

  17. The effects of water vapor on the oxidation behavior of alumina forming austenitic stainless steels

    SciTech Connect

    Yanar, N. M.; Lutz, B. S.; Garcia-Fresnillo, L.; Brady, Michael P.; Meier, G. H.

    2015-08-19

    The isothermal oxidation behavior of three alumina forming austenitic (AFA) stainless steels with varying composition was studied at 650 and 800 °C in dry air and gases which contained water vapor. The AFA alloys exhibited better oxidation resistance than a “good chromia former” at 650 °C, particularly in H2O-containing atmospheres by virtue of alumina-scale formation. Although the AFA alloys were more resistant than chromia formers, their oxidation resistance was degraded at 650 °C in the presence of water vapor. In dry air the AFA alloys formed, thin continuous alumina scales, whereas in Ar–4%H2–3%H2O the areas of continuous alumina were reduced and Fe oxide-rich nodules and regions of Cr, Mn-rich oxides formed. In some regions internal oxidation of the aluminum occurred in the H2O-containing gas. The alloy OC8 had slightly better resistance than OC4 or OC5 in this atmosphere. The alumina-forming capability of the AFA alloys decreases with increasing temperature and, at 800 °C, they are borderline alumina formers, even in dry air. The oxidation resistance of all three alloys was degraded at 800 °C in atmospheres, which contained water vapor (Air–10%H2O, Ar–3%H2O and Ar–4%H2–3%H2O). The areas, which formed continuous alumina, were reduced in these atmospheres and areas of internal oxidation occurred. However, as a result of the borderline alumina-forming capability of the AFA alloys it was not possible to determine which of the H2O-containing atmospheres was more severe or to rank the alloys in terms of their performance. The experimental results indicate that the initial microstructure of the AFA alloys also plays a role in their oxidation performance. Less protective oxides formed at 800 °C when alloy OC8 was equilibrated before exposure rather than being exposed in the as-processed condition. As a result, the reason for this is the presence of different

  18. The Effect of Aging Heat Treatment on the Microstructure and Mechanical Properties of 10Cr20Ni25Mo1.5NbN Austenitic Steel

    NASA Astrophysics Data System (ADS)

    Liang, Zhiyuan; Sha, Wanhua; Zhao, Qinxin; Wang, Chongbin; Wang, Jianyong; Jiang, Weiwei

    2016-01-01

    The effect of aging heat treatment on the microstructure and mechanical properties of 10Cr20Ni25Mo1.5NbN austenitic steel was investigated in this article. The microstructure was characterized by scanning electron microscopy, energy dispersive spectrometry and transmission electron microscopy. Results show that the microstructure of 10Cr20Ni25Mo1.5NbN austenitic is composed of austenite. This steel was strengthened by precipitates of secondary phases that were mainly M23C6 carbides and NbCrN nitrides. As aging treatment time increased, the tensile strength first rose (0-3,000 h) and then fell (3,000-5,000 h) due to the decrease of high density of dislocations. The impact absorbed energy decreased sharply, causing the sulfides to precipitate at the grain boundary. Therefore, the content of sulfur should be strictly controlled in the steelmaking process.

  19. Calculation of the Ti(C y N1- y )-Ti4C2S2-MnS-austenite equilibrium in Ti-bearing steels

    NASA Astrophysics Data System (ADS)

    Liu, W. J.; Jonas, J. J.

    1989-08-01

    A thermodynamic model is presented for the equilibria among various precipitates (Ti(C y N1- y ), Ti4C2S2, and MnS) and austenite containing six alloying elements (C, Mn, N, S, Si, and Ti). This model is applied to four microalloyed steels with Ti levels of 0.05, 0.11, 0.18, and 0.25 pct. The calculations show that the Ti in these steels cannot be completely dissolved over the austenite temperature range. However, the compositions of the undissolved Ti carbonitrides differ significantly from pure TiN, as 10 to 40 pct of the nitrogen is replaced by carbon. An expression for the Gibbs energy for the formation of Ti4C2S2 in austenite is estimated. The present predictions are compared with those of the Hudd, Jones, and Kale (HJK) model; considerable differences are observed at temperatures below 1250°C.

  20. Development of Stronger and More Reliable Cast Austenitic Stainless Steels (H-Series) Based on Scientific Design Methodology

    SciTech Connect

    Muralidharan, G.; Sikka, V.K.; Pankiw, R.I.

    2006-04-15

    The goal of this program was to increase the high-temperature strength of the H-Series of cast austenitic stainless steels by 50% and upper use temperature by 86 to 140 F (30 to 60 C). Meeting this goal is expected to result in energy savings of 38 trillion Btu/year by 2020 and energy cost savings of $185 million/year. The higher strength H-Series of cast stainless steels (HK and HP type) have applications for the production of ethylene in the chemical industry, for radiant burner tubes and transfer rolls for secondary processing of steel in the steel industry, and for many applications in the heat-treating industry. The project was led by Duraloy Technologies, Inc. with research participation by the Oak Ridge National Laboratory (ORNL) and industrial participation by a diverse group of companies. Energy Industries of Ohio (EIO) was also a partner in this project. Each team partner had well-defined roles. Duraloy Technologies led the team by identifying the base alloys that were to be improved from this research. Duraloy Technologies also provided an extensive creep data base on current alloys, provided creep-tested specimens of certain commercial alloys, and carried out centrifugal casting and component fabrication of newly designed alloys. Nucor Steel was the first partner company that installed the radiant burner tube assembly in their heat-treating furnace. Other steel companies participated in project review meetings and are currently working with Duraloy Technologies to obtain components of the new alloys. EIO is promoting the enhanced performance of the newly designed alloys to Ohio-based companies. The Timken Company is one of the Ohio companies being promoted by EIO. The project management and coordination plan is shown in Fig. 1.1. A related project at University of Texas-Arlington (UT-A) is described in Development of Semi-Stochastic Algorithm for Optimizing Alloy Composition of High-Temperature Austenitic Stainless Steels (H-Series) for Desired