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Sample records for meta-stable austenitic steel

  1. Study on stable and meta-stable carbides in a high speed steel for rollers during tempering processes

    NASA Astrophysics Data System (ADS)

    Guo, Jing; Qu, Hong-wei; Liu, Li-gang; Sun, Yan-liang; Zhang, Yue; Yang, Qing-xiang

    2013-02-01

    A high speed steel (HSS) was studied for rollers in this work. The steel was quenched at 1150°C and tempered at 520°C. The phase structures of the steel were determined by X-ray diffraction (XRD), and the hardness of specimens was measured. The volume fraction of carbides was counted by Image-Pro Plus software. The typical microstructures were observed by field emission scanning electron microscope (FESEM). Stable and meta-stable carbides were deduced by removing the existing phases one by one in the Fe-C equilibrium calculation. It is found that the precipitated carbides are bulk-like MC, long stripe-like M2C, fishbone-like M6C, and daisy-like M7C3 during the tempering process. The stable carbides are MC and M6C, but the meta-stable ones are M2C, M7C3, and M3C.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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)

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Detonation of Meta-stable Clusters

    SciTech Connect

    Kuhl, Allen; Kuhl, Allen L.; Fried, Laurence E.; Howard, W. Michael; Seizew, Michael R.; Bell, John B.; Beckner, Vincent; Grcar, Joseph F.

    2008-05-31

    We consider the energy accumulation in meta-stable clusters. This energy can be much larger than the typical chemical bond energy (~;;1 ev/atom). For example, polymeric nitrogen can accumulate 4 ev/atom in the N8 (fcc) structure, while helium can accumulate 9 ev/atom in the excited triplet state He2* . They release their energy by cluster fission: N8 -> 4N2 and He2* -> 2He. We study the locus of states in thermodynamic state space for the detonation of such meta-stable clusters. In particular, the equilibrium isentrope, starting at the Chapman-Jouguet state, and expanding down to 1 atmosphere was calculated with the Cheetah code. Large detonation pressures (3 and 16 Mbar), temperatures (12 and 34 kilo-K) and velocities (20 and 43 km/s) are a consequence of the large heats of detonation (6.6 and 50 kilo-cal/g) for nitrogen and helium clusters respectively. If such meta-stable clusters could be synthesized, they offer the potential for large increases in the energy density of materials.

  20. 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.

  1. 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

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. 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

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Meta-Stable Brane Configurations by Quartic Superpotential for Bifundamentals

    NASA Astrophysics Data System (ADS)

    Ahn, Changhyun

    The type IIA nonsupersymmetric meta-stable brane configuration consisting of three NS5-branes, D4-branes and anti-D4-branes where the electric gauge theory superpotential has a quartic term for the bifundamentals besides a mass term is constructed. By adding the orientifold 4-plane and 6-plane to this brane configuration, we also describe the intersecting brane configurations of type IIA string theory corresponding to the meta-stable nonsupersymmetric vacua of corresponding gauge theories.

  1. 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

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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'.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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).

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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).

  4. 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).

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. [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

  7. 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.

  8. 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.

  9. 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.

  10. 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.