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Sample records for martensite ferritic steel

  1. A preliminary ferritic-martensitic stainless steel constitution diagram

    SciTech Connect

    Balmforth, M.C.; Lippold, J.C.

    1998-01-01

    This paper describes preliminary research to develop a constitution diagram that will more accurately predict the microstructure of ferritic and martensitic stainless steel weld deposits. A button melting technique was used to produce a wide range of compositions using mixtures of conventional ferritic and martensitic stainless steels, including types 403, 409, 410, 430, 439 and 444. These samples were prepared metallographically, and the vol-% ferrite and martensite was determined quantitatively. In addition, the hardness and ferrite number (FN) were measured. Using this data, a preliminary constitution diagram is proposed that provides a more accurate method for predicting the microstructures of arc welds in ferritic and martensitic stainless steels.

  2. Two-phase ferritic-martensitic steels

    NASA Astrophysics Data System (ADS)

    Golovanenko, S. A.; Fonshtein, N. M.

    1984-11-01

    The results of laboratory and production experiments showed that the main condition for providing the necessary combination of properties of two-phase ferritic-martensitic steels (high tensile strength, low yield strength, high plasticity and work hardenability) is obtaining the specified quantity of the hardening phase (martensite) in the structure (20-28% M to obtain σt ≥ 550 MPa or 10-18% M for σt ≥ 450 MPa). The specified ratio of the structural constituents under conditions of mass production of two-phase ferritic-martensitic steels may be guaranteed only with the use of steels containing carbon and alloy elements within the necessary limits and also with strict observance of the heat-treatment cycle. Without the use of metallographic measurements as the criteria for obtaining the optimum structural condition in addition to the required values of strength and plasticity it is necessary to use the σ0.2/σt ratio, which must not be greater than 0.5-0.6 with the absence of yield points on the tensile curve (without special temper rolling). As the result of the combination of work done in the Central Scientific-Research Institute of Ferrous Metallurgy together with plants of the Ministries of Ferrous Metallurgy and of the Automobile Industry at present the production is being introduced and experimental production lots of heat-treated two-phase steels of the following types with guaranteed mechanical properties are being supplied: At the Novolipetsk Metallurgical Combine cold-rolled 0.7-2.0-mm sheet of 06KhG(S)Yu and 06G2SYu steels with σ0.2 = 260-320 MPa, σt ≥ 550 MPa, δ4 ≥ 30%, and σ0.2/σt ≤ 0.5-0.6. At the Cherepovets Metallurgical Combine hot-rolled 2-6-mm sheet of 09G2(S) steel with σ0.2 = 260-320 MPa, σt ≥ 550 MPa, δ4 ≥ 25%, and σ0.2/σt ≤ 0.5-0.6. At the Beloretsk Metallurgical Combine (billets melted and rolled at the Cherepovets Metallurgical Combine) heat-treated cold-drawn wire up to 10.5 mm in diameter of 06KhGR steel with

  3. Nitrogen alloying of the 12% Cr martensitic-ferritic steel

    NASA Astrophysics Data System (ADS)

    Kudryavtsev, A. S.; Artem'eva, D. A.; Mikhailov, M. S.

    2017-08-01

    The influence of the nitrogen content on the structure and mechanical properties of heat and corrosion resistant 12% Cr martensitic-ferritic steel developed at the Central Research Institute of Structural Materials Prometey has been studied. Steel containing 0.061 wt % nitrogen possesses a high level of mechanical properties. The decrease in the nitrogen content to 0.017 wt % leads to an increase of structurally free ferrite fraction in the steel, a decrease in the density of dislocations, a decrease of structural dispersity and the absence of finely dispersed precipitates of niobium and vanadium nitrides and carbides. As a result, there is a decrease in the strength properties, especially in the heat resistance.

  4. Microstructural Dependence of Work Hardening Behavior in Martensite-Ferrite Microalloyed Steels

    NASA Astrophysics Data System (ADS)

    Anand, N.; Sankaran, S.; Madhavan, R.; Suwas, Satyam; Venugopal, P.

    2015-01-01

    Martensite-ferrite microstructures were produced in four microalloyed steels A (Fe-0.44C-Cr-V), B (Fe-0.26C-Cr-V), C (Fe-0.34C-Cr-Ti-V), and D (Fe-0.23C-Cr-V) by intercritical annealing. SEM analysis reveals that steels A and C contained higher martensite fraction and finer ferrite when compared to steels B and D which contained coarser ferrite grains and lower martensite fraction. A network of martensite phase surrounding the ferrite grains was found in all the steels. Crystallographic texture was very weak in these steels as indicated by EBSD analysis. The steels contained negligible volume fraction of retained austenite (approx. 3-6%). TEM analysis revealed the presence of twinned and lath martensite in these steels along with ferrite. Precipitates (carbides and nitrides) of Ti and V of various shapes with few nanometers size were found, particularly in the microstructures of steel B. Work hardening behavior of these steels at ambient temperature was evaluated through modified Jaoul-Crussard analysis, and it was characterized by two stages due to presence of martensite and ferrite phases in their microstructure. Steel A displayed large work hardening among other steel compositions. Work hardening behavior of the steels at a warm working temperature of 540 °C was characterized by a single stage due to the decomposition of martensite into ferrite and carbides at this temperature as indicated by SEM images of the steels after warm deformation.

  5. Ferritic, martensitic, and precipitation hardening stainless steel laser weldings

    NASA Astrophysics Data System (ADS)

    Daurelio, Giuseppe; Ludovico, Antonio D.; Panagopoulos, Christos N.; Tundo, Corrado

    1998-07-01

    Even if many steels and alloys have been welded on the last years, nowadays there are some other stainless steel alloys that need a further comprehension when they have to be welded. Typically these alloys are martensitic and precipitation hardening ones that still present some problems to be weld, i.e. hot cracks, fragile beads, an excessive grain size and other surface defects. In this work some martensitic stainless steels of which a AISI 420B, a AISI 440C and a AISI 630 have been studied. The last one is always with a martensitic structure but, in particular, some interesting mechanical properties are reached by a precipitation hardening process. This research has experimented and studied the mechanical and technological properties of the welds obtained on the above cited AISI 420B, AISI 440C and AISI 630, welded by 1.5 kW CO2 laser. The results have also been compared with the ones obtained on ferritic stainless steels AISI 430 and 430F. A technological characterization of the welds has followed as metallographic tests and evaluations, microhardness, tensile and fatigue tests.

  6. Friction Stir Welding of HT9 Ferritic-Martensitic Steel: An Assessment of Microstructure and Properties

    DTIC Science & Technology

    2013-06-01

    report of FSW on a ferritic-martensitic stainless steel is the work of Chung, which applied this approach to a dissimilar weld between F82H (ferritic...January 2007. [43] Y. Chung et al., ―Interface microstructure evolution of dissimilar friction stir butt welded F82H steel and SUS304,‖ Materials... WELDING OF HT9 FERRITIC- MARTENSITIC STEEL: AN ASSESSMENT OF MICROSTRUCTURE AND PROPERTIES by Lara L. Ray June 2013 Thesis Advisor: Luke N

  7. Carbides in a High-Chromium Ferritic/Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Shen, Yin Zhong; Ji, Bo; Zhou, Xiao Ling; Zhu, Jun

    2014-06-01

    The precipitate phases in an 11 pct Cr ferritic/martensitic steel normalized at 1323 K (1050 °C) for 0.5 hour and tempered at 1053 K (780 °C) for 1.5 hours have been investigated. Except for dominant phases, Cr-rich M23C6 carbide and Nb-rich, Ta-Nb-rich, and V-rich MC carbides, needle-like precipitates with a typical size of 70 to 310 and 10 to 30 nm for the length of the long and short axis of the needles, respectively, were also observed on the extraction carbon replica of the steel. The typical metallic element composition of the needle-like precipitates is about 53-82Fe, 14-26Cr, 0.5-18Ta, 1-6W, and 2-5Co in atomic pct. Through energy dispersive X-ray analysis and electron diffraction along with calculations regarding lattice parameter and interplanar spacing, the needle-like precipitates were identified as a Fe-rich M5C2 carbide, which is not known to have been reported previously in high-chromium steels. The M5C2 carbide has a base-centered monoclinic crystal structure with the approximate lattice parameters a/ b/ c = 1.142/0.5186/0.5383 nm and β = 104.68 deg. The formation of the Fe-rich M5C2 carbides in the steel has been discussed. The effect of chromium content in matrix and boron addition on the precipitate phases in ferritic/martensitic steels has also been discussed.

  8. Delta ferrite in the weld metal of reduced activation ferritic martensitic steel

    NASA Astrophysics Data System (ADS)

    Sam, Shiju; Das, C. R.; Ramasubbu, V.; Albert, S. K.; Bhaduri, A. K.; Jayakumar, T.; Rajendra Kumar, E.

    2014-12-01

    Formation of delta(δ)-ferrite in the weld metal, during autogenous bead-on-plate welding of Reduced Activation Ferritic Martensitic (RAFM) steel using Gas Tungsten Arc Welding (GTAW) process, has been studied. Composition of the alloy is such that delta-ferrite is not expected in the alloy; but examination of the weld metal revealed presence of delta-ferrite in the weld metal. Volume fraction of delta-ferrite is found to be higher in the weld interface than in the rest of the fusion zone. Decrease in the volume fraction of delta-ferrite, with an increase in preheat temperature or with an increase in heat input, is observed. Results indicate that the cooling rate experienced during welding affects the volume fraction of delta-ferrite retained in the weld metal and variation in the delta-ferrite content with cooling rate is explained with variation in the time that the weld metal spends in various temperature regimes in which delta-ferrite is stable for the alloy during its cooling from the liquid metal to the ambient temperature. This manuscript will discuss the effect of welding parameters on formation of delta-ferrite and its retention in the weld metal of RAFM steel.

  9. Tritium retention in reduced-activation ferritic/martensitic steels

    SciTech Connect

    Hatano, Y.; Abe, S.; Matsuyama, M.; Alimov, V.K.; Spitsyn, A.V.; Bobyr, N.P.; Cherkez, D.I.; Khripunov, B.I.; Golubeva, A.V.; Ogorodnikova, O.V.; Klimov, N.S.; Chernov, V.M.; Oyaidzu, M.; Yamanishi, T.

    2015-03-15

    Reduced-activation ferritic/martensitic (RAFM) steels are structural material candidates for breeding blankets of future fusion reactors. Therefore, tritium (T) retention in RAFM steels is an important problem in assessing the T inventory of blankets. In this study, specimens of RAFM steels were subjected to irradiation of 20 MeV W ions to 0.54 displacements per atom (dpa), exposure to high flux D plasmas at 400 and 600 K and that to pulsed heat loads. The specimens thus prepared were exposed to DT gas at 473 K. Despite severe modification in the surface morphology, heat loads had negligible effects on T retention. Significant increase in T retention at the surface and/or subsurface was observed after D plasma exposure. However, T trapped at the surface/subsurface layer was easily removed by maintaining the specimens in the air at about 300 K. Displacement damage led to increase in T retention in the bulk due to the trapping effects of defects, and T trapped was stable at 300 K. It was therefore concluded that displacement damages had the largest influence on T retention under the present conditions.

  10. Nanosized MX Precipitates in Ultra-Low-Carbon Ferritic/Martensitic Heat-Resistant Steels

    NASA Astrophysics Data System (ADS)

    Yin, Feng-Shi; Jung, Woo-Sang

    2009-02-01

    Nanosized MX precipitates in ultra-low-carbon ferritic/martensitic heat-resistant 9Cr-W-Mo-VNbTiN steels were characterized by transmission electron microscope (TEM) using carbon film replicas. The steels were prepared by vacuum induction melting followed by hot forging and rolling into plates. The plates were normalized at 1100 °C for 1 hour, cooled in air, and tempered at 700 °C for 1 hour. The results show that bimodal nanosized MX precipitates distribute densely and homogeneously in the matrix within martensitic lath after normalizing-and-tempering heat treatment. The larger nanosized MX precipitates with the size of 30 to 50 nm are rich in Nb, while the smaller ones with the size of about 10 nm contain less Nb but more V. Small addition of Ti causes an increase in the number of the larger nanosized MX precipitates. The total number density of the nanosized MX precipitates in the ultra-low-carbon ferritic/martensitic steels is measured to be over 300/ μm2, much higher than that in conventional ferritic/martensitic steels. Short-term creep test results show that the ultra-low-carbon ferritic/martensitic steels with high dense nanosized MX precipitates have much higher creep rupture strength than conventional ASME-P92 steel. The strength degradation of the ultra-low-carbon ferritic/martensitic heat-resistant steels during creep is also discussed in this article.

  11. Martensitic/ferritic steels as container materials for liquid mercury target of ESS

    SciTech Connect

    Dai, Y.

    1996-06-01

    In the previous report, the suitability of steels as the ESS liquid mercury target container material was discussed on the basis of the existing database on conventional austenitic and martensitic/ferritic steels, especially on their representatives, solution annealed 316 stainless steel (SA 316) and Sandvik HT-9 martensitic steel (HT-9). Compared to solution annealed austenitic stainless steels, martensitic/ferritic steels have superior properties in terms of strength, thermal conductivity, thermal expansion, mercury corrosion resistance, void swelling and irradiation creep resistance. The main limitation for conventional martensitic/ferritic steels (CMFS) is embrittlement after low temperature ({le}380{degrees}C) irradiation. The ductile-brittle transition temperature (DBTT) can increase as much as 250 to 300{degrees}C and the upper-shelf energy (USE), at the same time, reduce more than 50%. This makes the application temperature range of CMFS is likely between 300{degrees}C to 500{degrees}C. For the present target design concept, the temperature at the container will be likely controlled in a temperature range between 180{degrees}C to 330{degrees}C. Hence, CMFS seem to be difficult to apply. However, solution annealed austenitic stainless steels are also difficult to apply as the maximum stress level at the container will be higher than the design stress. The solution to the problem is very likely to use advanced low-activation martensitic/ferritic steels (LAMS) developed by the fusion materials community though the present database on the materials is still very limited.

  12. Proceedings of the IEA Working Group meeting on ferritic/martensitic steels

    SciTech Connect

    Klueh, R.L.

    1996-12-31

    An IEA working group on ferritic/martensitic steels for fusion applications, consisting of researchers from Japan, European Union, USA, and Switzerland, met at the headquarters of the Joint European Torus, Culham, UK. At the meeting, preliminary data generated on the large heats of steels purchased for the IEA program and on other heats of steels were presented and discussed. Second purpose of the meeting was to continue planning and coordinating the collaborative test program in progress on reduced-activation ferritic/martensitic steels. The majority of this report consists of viewographs for the presentations.

  13. Microstructure and Mechanical Properties of a Nitride-Strengthened Reduced Activation Ferritic/Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Zhou, Qiangguo; Zhang, Wenfeng; Yan, Wei; Wang, Wei; Sha, Wei; Shan, Yiyin; Yang, Ke

    2012-12-01

    Nitride-strengthened reduced activation ferritic/martensitic (RAFM) steels are developed taking advantage of the high thermal stability of nitrides. In the current study, the microstructure and mechanical properties of a nitride-strengthened RAFM steel with improved composition were investigated. Fully martensitic microstructure with fine nitrides dispersion was achieved in the steel. In all, 1.4 pct Mn is sufficient to suppress delta ferrite and assure the steel of the full martensitic microstructure. Compared to Eurofer97, the steel showed similar strength at room temperature but higher strength at 873 K (600 °C). The steel exhibited very high impact toughness and a low ductile-to-brittle transition temperature (DBTT) of 243 K (-30 °C), which could be further reduced by purification.

  14. Toughness of 12%Cr ferritic/martensitic steel welds produced by non-arc welding processes

    SciTech Connect

    Ginn, B.J.; Gooch, T.G.

    1998-08-01

    Low carbon 12%Cr steels can offer reduced life cycle costs in many applications. The present work examined the behavior of commercial steels of varying composition when subject to low heat input welding by the electron beam (EB) process and to a forge cycle by linear friction welding (LFW). Charpy impact testing was carried out on the high temperature heat-affected zone (HAZ)/fusion boundary or weld interface, with metallographic examination. With EB welding, the ductile-brittle transition temperature (DBTT) was below 0 C (32 F) only for steel of low ferrite factor giving a fully martensitic weld area. Higher ferrite factor alloys showed predominantly ferritic transformed microstructures and a transition well above room temperature. Grain coarsening was found even with low EB process power, the peak grain size increasing with both heat input and steel ferrite factor. Use of LFW gave a fine weld area structure and DBTTs around 0 C even in high ferrite factor (FF) material.

  15. Elevated-Temperature Ferritic and Martensitic Steels and Their Application to Future Nuclear Reactors

    SciTech Connect

    Klueh, RL

    2005-01-31

    In the 1970s, high-chromium (9-12% Cr) ferritic/martensitic steels became candidates for elevated-temperature applications in the core of fast reactors. Steels developed for conventional power plants, such as Sandvik HT9, a nominally Fe-12Cr-1Mo-0.5W-0.5Ni-0.25V-0.2C steel (composition in wt %), were considered in the United States, Europe, and Japan. Now, a new generation of fission reactors is in the planning stage, and ferritic, bainitic, and martensitic steels are again candidates for in-core and out-of-core applications. Since the 1970s, advances have been made in developing steels with 2-12% Cr for conventional power plants that are significant improvements over steels originally considered. This paper will review the development of the new steels to illustrate the advantages they offer for the new reactor concepts. Elevated-temperature mechanical properties will be emphasized. Effects of alloying additions on long-time thermal exposure with and without stress (creep) will be examined. Information on neutron radiation effects will be discussed as it applies to ferritic and martensitic steels.

  16. Summary of the IEA workshop/working group meeting on ferritic/martensitic steels for fusion

    SciTech Connect

    Klueh, R.L.

    1997-04-01

    An International Energy Agency (IEA) Working Group on Ferritic/Martensitic Steels for Fusion Applications, consisting of researchers from Japan, the European Union, the United States, and Switzerland, met at the headquarters of the Joint European Torus (JET), Culham, United Kingdom, 24-25 October 1996. At the meeting preliminary data generated on the large heats of steel purchased for the IEA program and on other heats of steels were presented and discussed. The second purpose of the meeting was to continue planning and coordinating the collaborative test program in progress on reduced-activation ferritic/martensitic steels. The next meeting will be held in conjunction with the International Conference on Fusion Reactor Materials (ICFRM-8) in Sendai, Japan, 23-31 October 1997.

  17. Metallography studies and hardness measurements on ferritic/martensitic steels irradiated in STIP

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Long, B.; Dai, Y.

    2008-06-01

    In this work metallography investigations and microhardness measurements have been performed on 15 ferritic/martensitic (FM) steels and 6 weld metals irradiated in the SINQ Target Irradiation Program (STIP). The results demonstrate that all the steels have quite similar martensite lath structures. However, the sizes of the prior austenite grain (PAG) of these steels are quite different and vary from 10 to 86 μm. The microstructure in the fusion zones (FZ) of electron-beam welds (EBWs) of 5 steels (T91, EM10, MANET-II, F82H and Optifer-IX) is similar in respect to the martensite lath structure and PAG size. The FZ of the inert-gas-tungsten weld (TIGW) of the T91 steel shows a duplex structure of large ferrite gains and martensite laths. The microhardness measurements indicate that the normalized and tempered FM steels have rather close hardness values. The unusual high hardness values of the EBW and TIGW of the T91 steel were detected, which suggests that these materials are without proper tempering or post-welding heat treatment.

  18. Fatigue strength of low-activation ferritic-martensitic high-chromium EK-181 steel

    NASA Astrophysics Data System (ADS)

    Kolmakov, A. G.; Terent'ev, V. F.; Prosvirnin, D. V.; Chernov, V. M.; Leont'eva-Smirnova, M. V.

    2016-04-01

    The static and cyclic mechanical properties of low-activation ferritic-martensitic EK-181 (Fe‒12Cr-2W-V-Ta-B-C) steel are studied in the temperature range 20-920°C (static tests) and at 20°C (cyclic tests). The fracture mechanisms of the steel under static tension and fatigue fracture conditions are analyzed by scanning electron microscopy.

  19. Microstructural stability of 9-12%Cr ferrite/martensite heat-resistant steels

    NASA Astrophysics Data System (ADS)

    Yan, Wei; Wang, Wei; Shan, Yi-Yin; Yang, Ke

    2013-03-01

    The microstructural evolutions of advanced 9-12%Cr ferrite/martensite heat-resistant steels used for power generation plants are reviewed in this article. Despite of the small differences in chemical compositions, the steels share the same microstructure of the as-tempered martensite. It is the thermal stability of the initial microstructure that matters the creep behavior of these heat-resistant steels. The microstructural evolutions involved in 9-12%Cr ferrite heat-resistant steels are elaborated, including (1) martensitic lath widening, (2) disappearance of prior austenite grain boundary, (32) emergence of subgrains, (4) coarsening of precipitates, and (5) formation of new precipitates, such as Laves-phase and Z-phase. The former three microstructural evolutions could be retarded by properly disposing the latter two. Namely improving the stability of precipitates and optimizing their size distribution can effectively exert the beneficial influence of precipitates on microstructures. In this sense, the microstructural stability of the tempered martensite is in fact the stability of precipitates during the creep. Many attempts have been carried out to improve the microstructural stability of 9-12%Cr steels and several promising heat-resistant steels have been developed.

  20. Effect of constituent phase on mechanical properties of 9Cr-1WVTa reduced activation ferritic-martensitic steels

    NASA Astrophysics Data System (ADS)

    Lee, Chang-Hoon; Moon, Joonoh; Park, Min-Gu; Lee, Tae-Ho; Jang, Min-Ho; Kim, Hyoung Chan; Suh, Dong-Woo

    2014-12-01

    Influence of the formation of ferrite and accompanying carbides in martensite matrix on the tensile and Charpy impact properties was investigated for reduced activation ferritic-martensitic (RAFM) 9Cr-1WVTa steel. As the fractions of ferrite and carbide adjacent to the ferrite grain boundary increase, both tensile and Charpy impact properties deteriorated in as-normalized condition. In particular, the tensile strength and elongation decreased simultaneously, which is believed to be led by the localized deformation in ferrite which is softer than martensite, promoting the formation and growth of voids. In addition, the formation of ferrite was also detrimental to the Charpy impact properties regarding to the absorbed energy because the precipitation of carbides around ferrite were vulnerable to the nucleation and propagation of cleavage cracks. The degradation of tensile properties can be recovered by tempering, but the DBTT temperature still increases with presence of ferrite.

  1. Recent Progress of R&D Activities on Reduced Activation Ferritic/Martensitic Steels

    SciTech Connect

    Huang, Q.; Baluc, N.; Dai, Y.; Jitsukawa, S.; Kimura, A.; Konys, J.; Kurtz, Richard J.; Lindau, R.; Muroga, T.; Odette, George R.; Raj, B.; Stoller, Roger E.; Tan, L.; Tanigawa, Hiroyasu; Tavassoli, A,-A.F.; Yamamoto, Takuya; Wan, F.; Wu, Y.

    2013-01-03

    Several types of reduced activation ferritic/martensitic (RAFM) steel have been developed over the past 30 years in China, Europe, India, Japan, Russia and the USA for application in ITER TBM and future fusion DEMO and power reactors. The progress has been particularly important during the past few years with evaluation of mechanical porperties of these steels before and after irradiation and in contact with different cooling media. This paper presents recent RAFM steel results obtained in ITER partner countries in relation with different TBM and DEMO options

  2. Ultrahigh Charpy impact toughness (~450J) achieved in high strength ferrite/martensite laminated steels

    NASA Astrophysics Data System (ADS)

    Cao, Wenquan; Zhang, Mingda; Huang, Chongxiang; Xiao, Shuyang; Dong, Han; Weng, Yuqing

    2017-02-01

    Strength and toughness are a couple of paradox as similar as strength-ductility trade-off in homogenous materials, body-centered-cubic steels in particular. Here we report a simple way to get ultrahigh toughness without sacrificing strength. By simple alloying design and hot rolling the 5Mn3Al steels in ferrite/austenite dual phase temperature region, we obtain a series of ferrite/martensite laminated steels that show up-to 400–450J Charpy V-notch impact energy combined with a tensile strength as high as 1.0–1.2 GPa at room temperature, which is nearly 3–5 times higher than that of conventional low alloy steels at similar strength level. This remarkably enhanced toughness is mainly attributed to the delamination between ferrite and martensite lamellae. The current finding gives us a promising way to produce high strength steel with ultrahigh impact toughness by simple alloying design and hot rolling in industry.

  3. Ultrahigh Charpy impact toughness (~450J) achieved in high strength ferrite/martensite laminated steels.

    PubMed

    Cao, Wenquan; Zhang, Mingda; Huang, Chongxiang; Xiao, Shuyang; Dong, Han; Weng, Yuqing

    2017-02-02

    Strength and toughness are a couple of paradox as similar as strength-ductility trade-off in homogenous materials, body-centered-cubic steels in particular. Here we report a simple way to get ultrahigh toughness without sacrificing strength. By simple alloying design and hot rolling the 5Mn3Al steels in ferrite/austenite dual phase temperature region, we obtain a series of ferrite/martensite laminated steels that show up-to 400-450J Charpy V-notch impact energy combined with a tensile strength as high as 1.0-1.2 GPa at room temperature, which is nearly 3-5 times higher than that of conventional low alloy steels at similar strength level. This remarkably enhanced toughness is mainly attributed to the delamination between ferrite and martensite lamellae. The current finding gives us a promising way to produce high strength steel with ultrahigh impact toughness by simple alloying design and hot rolling in industry.

  4. Ultrahigh Charpy impact toughness (~450J) achieved in high strength ferrite/martensite laminated steels

    PubMed Central

    Cao, Wenquan; Zhang, Mingda; Huang, Chongxiang; Xiao, Shuyang; Dong, Han; Weng, Yuqing

    2017-01-01

    Strength and toughness are a couple of paradox as similar as strength-ductility trade-off in homogenous materials, body-centered-cubic steels in particular. Here we report a simple way to get ultrahigh toughness without sacrificing strength. By simple alloying design and hot rolling the 5Mn3Al steels in ferrite/austenite dual phase temperature region, we obtain a series of ferrite/martensite laminated steels that show up-to 400–450J Charpy V-notch impact energy combined with a tensile strength as high as 1.0–1.2 GPa at room temperature, which is nearly 3–5 times higher than that of conventional low alloy steels at similar strength level. This remarkably enhanced toughness is mainly attributed to the delamination between ferrite and martensite lamellae. The current finding gives us a promising way to produce high strength steel with ultrahigh impact toughness by simple alloying design and hot rolling in industry. PMID:28150692

  5. Microstructure and properties of pipeline steel with a ferrite/martensite dual-phase microstructure

    SciTech Connect

    Li Rutao Zuo Xiurong Hu Yueyue Wang Zhenwei Hu, Dingxu

    2011-08-15

    In order to satisfy the transportation of the crude oil and gas in severe environmental conditions, a ferrite/martensite dual-phase pipeline steel has been developed. After a forming process and double submerged arc welding, the microstructure of the base metal, heat affected zone and weld metal was characterized using scanning electron microscopy and transmission electron microscopy. The pipe showed good deformability and an excellent combination of high strength and toughness, which is suitable for a pipeline subjected to the progressive and abrupt ground movement. The base metal having a ferrite/martensite dual-phase microstructure exhibited excellent mechanical properties in terms of uniform elongation of 7.5%, yield ratio of 0.78, strain hardening exponent of 0.145, an impact energy of 286 J at - 10 deg. C and a shear area of 98% at 0 deg. C in the drop weight tear test. The tensile strength and impact energy of the weld metal didn't significantly reduce, because of the intragranularly nucleated acicular ferrites microstructure, leading to high strength and toughness in weld metal. The heat affected zone contained complete quenching zone and incomplete quenching zone, which exhibited excellent low temperature toughness of 239 J at - 10 deg. C. - Research Highlights: {yields}The pipe with ferrite/martensite microstructure shows high deformability. {yields}The base metal of the pipe consists of ferrite and martensite. {yields}Heat affected zone shows excellent low temperature toughness. {yields}Weld metal mainly consists of intragranularly nucleated acicular ferrites. {yields}Weld metal shows excellent low temperature toughness and high strength.

  6. Development and characterization of advanced 9Cr ferritic/martensitic steels for fission and fusion reactors

    NASA Astrophysics Data System (ADS)

    Saroja, S.; Dasgupta, A.; Divakar, R.; Raju, S.; Mohandas, E.; Vijayalakshmi, M.; Bhanu Sankara Rao, K.; Raj, Baldev

    2011-02-01

    This paper presents the results on the physical metallurgy studies in 9Cr Oxide Dispersion Strengthened (ODS) and Reduced Activation Ferritic/Martensitic (RAFM) steels. Yttria strengthened ODS alloy was synthesized through several stages, like mechanical milling of alloy powders and yttria, canning and consolidation by hot extrusion. During characterization of the ODS alloy, it was observed that yttria particles possessed an affinity for Ti, a small amount of which was also helpful in refining the dispersoid particles containing mixed Y and Ti oxides. The particle size and their distribution in the ferrite matrix, were studied using Analytical and High Resolution Electron Microscopy at various stages. The results showed a distribution of Y 2O 3 particles predominantly in the size range of 5-20 nm. A Reduced Activation Ferritic/Martensitic steel has also been developed with the replacement of Mo and Nb by W and Ta with strict control on the tramp and trace elements (Mo, Nb, B, Cu, Ni, Al, Co, Ti). The transformation temperatures ( Ac1, Ac3 and Ms) for this steel have been determined and the transformation behavior of the high temperature austenite phase has been studied. The complete phase domain diagram has been generated which is required for optimization of the processing and fabrication schedules for the steel.

  7. Mechanical properties and microstructure of advanced ferritic-martensitic steels used under high dose neutron irradiation

    NASA Astrophysics Data System (ADS)

    Shamardin, V. K.; Golovanov, V. N.; Bulanova, T. M.; Povstianko, A. V.; Fedoseev, A. E.; Goncharenko, Yu. D.; Ostrovsky, Z. E.

    Some results of the study of mechanical properties and structure of ferritic-martensitic chromium steels with 13% and 9% chromium, irradiated in the BOR-60 reactor up to different damage doses are presented in this report. Results concerning the behaviour of commercial steels, containing to molybdenum, vanadium and niobium, and developed for the use in fusion reactors, are compared to low-activation steels in which W and Ta replaced Mo and Nb. It is shown that after irradiation to the dose of ˜10 dpa at 400°C 0.1C-9Cr-1W, V, Ta steels are prone to lower embrittlement as deduced from fracture surface observations of tensile specimens. Peculiarities of fine structure and fracture mode, composition and precipitation reactions in steels during irradiation are discussed.

  8. The Z-Phase in 9Cr Ferritic/martensitic Heat Resistant Steel

    NASA Astrophysics Data System (ADS)

    Yin, Fengshi; Chen, Fuxia; Jiang, Xuebo; Xue, Bing; Zhou, Li; Jung, Woosang

    The precipitation behavior of Z-phase was investigated during long-term aging at 650°C in an ultra low carbon 9Cr ferritic/martensitic heat resistant steel. The steel was prepared by vacuum induction melting followed by hot forging and rolling into a plate. The plate was normalized at 1100°C for 1h, cooled in air and tempered at 700°C for 1h. Bimodal nano-sized MX precipitates distribute densely and homogeneously in the matrix within martensitic lath after normalizing-and-tempering heat treatment. After aging at 650°C for 1200h, the Z-phase was found to nucleate on the larger nano-sized MX. The Z-phase and MX have the following orientation relationship: <112>Z-phase//<001>MX and (1bar 10){Z-phase}//(200){MX} .

  9. Report on thermal aging effects on tensile properties of ferritic-martensitic steels.

    SciTech Connect

    Li, M.; Soppet, W.K.; Rink, D.L.; Listwan, J.T.; Natesan, K.

    2012-05-10

    This report provides an update on the evaluation of thermal-aging induced degradation of tensile properties of advanced ferritic-martensitic steels. The report is the first deliverable (level 3) in FY11 (M3A11AN04030103), under the Work Package A-11AN040301, 'Advanced Alloy Testing' performed by Argonne National Laboratory, as part of Advanced Structural Materials Program for the Advanced Reactor Concepts. This work package supports the advanced structural materials development by providing tensile data on aged alloys and a mechanistic model, validated by experiments, with a predictive capability on long-term performance. The scope of work is to evaluate the effect of thermal aging on the tensile properties of advanced alloys such as ferritic-martensitic steels, mod.9Cr-1Mo, NF616, and advanced austenitic stainless steel, HT-UPS. The aging experiments have been conducted over a temperature of 550-750 C for various time periods to simulate the microstructural changes in the alloys as a function of time at temperature. In addition, a mechanistic model based on thermodynamics and kinetics has been used to address the changes in microstructure of the alloys as a function of time and temperature, which is developed in the companion work package at ANL. The focus of this project is advanced alloy testing and understanding the effects of long-term thermal aging on the tensile properties. Advanced materials examined in this project include ferritic-martensitic steels mod.9Cr-1Mo and NF616, and austenitic steel, HT-UPS. The report summarizes the tensile testing results of thermally-aged mod.9Cr-1Mo, NF616 H1 and NF616 H2 ferritic-martensitic steels. NF616 H1 and NF616 H2 experienced different thermal-mechanical treatments before thermal aging experiments. NF616 H1 was normalized and tempered, and NF616 H2 was normalized and tempered and cold-rolled. By examining these two heats, we evaluated the effects of thermal-mechanical treatments on material microstructures and

  10. Characterization of Ferrite in Tempered Martensite of Modified 9Cr-1Mo Steel Using the Electron Backscattered Diffraction Technique

    NASA Astrophysics Data System (ADS)

    Das, C. R.; Albert, S. K.; Bhaduri, A. K.; Murty, B. S.

    2011-12-01

    Ferrite was identified and characterized in tempered martensitic modified 9Cr-1Mo steel using the electron backscattered diffraction (EBSD) technique. Microstructural examination of the as-received modified 9Cr-1Mo steel revealed the presence of polycrystalline grains without lath morphology having low hardness within a predominantly tempered lath martensitic matrix. These grains were identified as the ferrite phase, and subsequent EBSD data analysis confirmed that the image quality (IQ) index of these grains is higher and boundary line length per unit area is lower than those of martensitic matrix. Therefore, it is proposed that characterization of ferrite phase in martensitic matrix can be carried out using microstructural parameters such as IQ index and boundary line length per unit area obtained from EBSD data analysis.

  11. Reason for high strength and good ductility in dual phase steels composed of soft ferrite and hard martensite

    NASA Astrophysics Data System (ADS)

    Terada, Daisuke; Ikeda, Gosuke; Park, Myeong-heom; Shibata, Akinobu; Tsuji, Nobuhiro

    2017-07-01

    Dual phase (DP) steels in which the microstructures are composed of a soft ferrite phase and a hard martensite phase are known to show good strain-hardening, high strength and large elongation, but reasons for their superior mechanical properties are still unclear. In the present study, two types of DP structures, having either networked martensite or isolated martensite were fabricated in a low-carbon steel by different heat treatment routes, and their tensile deformation behavior was analyzed using the digital image correlation (DIC) technique. It was revealed that the DP specimens having networked martensite microstructures showed a better strength-ductility balance than the DP specimens with isolated martensite structures. The microscopic DIC analysis of identical areas showed that the strain distribution within the DP microstructures was not uniform and the plastic strain was localized in soft ferrite grains. The strain localized regions tended to detour around hard martensite but eventually propagated across the martensite. It was found also from the DIC analysis that the degree of strain partitioning between ferrite and martensite in the networked DP structure was lower than that in the isolated DP structure. The deformation became more homogeneous when the hard phase (martensite) was connected to form a network structure, which could be one of the reasons for the better strength-ductility balance in the networked DP structure compared to that in the isolated DP structure.

  12. Effect of δ-ferrite evolution and high-temperature annealing on mechanical properties of 11Cr3W3Co ferritic/martensitic steel

    NASA Astrophysics Data System (ADS)

    Shang, Zhongxia; Shen, Yinzhong; Ji, Bo; Zhang, Lanting

    2016-03-01

    An 11Cr3W3Co ferritic/martensitic steel was annealed at 1100 °C for different time to gradually dissolve δ-ferrite, and then conducted tensile, hardness, and short-term creep tests in combination with microstructural characterization to study the effect of δ-ferrite on the mechanical properties of high-Cr ferritic/martensitic steels. The amount of δ-ferrite gradually decreased to a minimum value with increasing annealing time up to 10 h, and then tended to an ascending tendency when annealed for 15 and 20 h. Accordingly the tensile strength at 300 and 650 °C, and Vickers hardness of the steel had an increase and a decrease tendency when δ-ferrite amount decreased down to its minimum value and increased again, respectively. The short-term creep property at 210 MPa at 650 °C of the steel exhibited a serious degradation as annealing time gradually increased to 15 h. The morphology and orientation of δ-ferrite grains seriously affected the short-term creep property of the steel. δ-ferrite with a continuously bamboo-like shape parallel to loading direction effectively improved the short-term creep property of the steel at high temperature, while δ-ferrite with a granular or block shape seriously damaged the short-term creep property of the steel. These findings have also been discussed.

  13. Reduction method of DBTT shift due to irradiation for reduced-activation ferritic/martensitic steels

    NASA Astrophysics Data System (ADS)

    Wakai, E.; Okubo, N.; Ando, M.; Yamamoto, T.; Takada, F.

    2010-03-01

    The method for reducing irradiation-induced DBTT shift of reduced-activation ferritic/martensitic steels was examined. F82H-LN (low nitrogen, 20 ppm), F82H+60 ppm 11B+200 ppmN and F82H+60 ppm 10B+200 ppmN steels tempered at 780 °C for 0.5 h were irradiated at 250 °C to 2 dpa, and the results for Charpy impact tests were analyzed. The upper shelf energy of F82H+ 11B+N steel was hardly changed by the irradiation, and DBTT shift was very small. From our research, DBTT shift due to irradiation can be reduced by the control of tempered conditions before irradiation, and it is found to be furthermore reduced by impurity doping with 60 ppm 11B and 200 ppmN to F82H steel.

  14. Mechanical property changes of low activation ferritic/martensitic steels after neutron irradiation

    NASA Astrophysics Data System (ADS)

    Kohno, Y.; Kohyama, A.; Hirose, T.; Hamilton, M. L.; Narui, M.

    Mechanical property changes of Fe- XCr-2W-0.2V,Ta ( X: 2.25-12) low activation ferritic/martensitic steels including Japanese Low Activation Ferritic/martensitic (JLF) steels and F82H after neutron irradiation were investigated with emphasis on Charpy impact property, tensile property and irradiation creep properties. Dose dependence of ductile-to-brittle transition temperature (DBTT) in JLF-1 (9Cr steel) irradiated at 646-700 K increased with irradiation up to 20 dpa and then decreased with further irradiation showing highest DBTT of 260 K at 20 dpa. F82H showed similar dose dependence in DBTT to JLF-1 with higher transition temperature than that of JLF-1 at the same displacement damage. Yield strength in JLF steels and F82H showed similar dose dependence to that of DBTT. Yield strength increased with irradiation up to 15-20 dpa and then decreased to saturate above about 40 dpa. Irradiation hardening in 7-9%Cr steels (JLF-1, JLF-3, F82H) were observed to be smaller than those in steels with 2.25%Cr (JLF-4) or 12%Cr (JLF-5). Dependences of creep strain on applied hoop stress and neutron fluence were measured to be 1.5 and 1, respectively. Temperature dependence of creep coefficient showed a maximum at about 700 K which was caused by irradiation induced void formation or irradiation enhanced creep deformation. Creep coefficient of F82H was larger than those of JLF steels above 750 K. This was considered to be caused by the differences in N and Ta concentration between F82H and JLF steels.

  15. Radiation hardening and deformation behavior of irradiated ferritic-martensitic steels

    SciTech Connect

    Robertson, J.P.; Klueh, R.L.; Rowcliffe, A.F.; Shiba, K.

    1998-03-01

    Tensile data from several 8--12% Cr alloys irradiated in the High Flux Isotope Reactor (HFIR) to doses up to 34 dpa at temperatures ranging from 90 to 600 C are discussed in this paper. One of the critical questions surrounding the use of ferritic-martensitic steels in a fusion environment concerns the loss of uniform elongation after irradiation at low temperatures. Irradiation and testing at temperatures below 200--300 C results in uniform elongations less than 1% and stress-strain curves in which plastic instability immediately follows yielding, implying dislocation channeling and flow localization. Reductions in area and total elongations, however, remain high.

  16. Irradiation-induced grain growth in nanocrystalline reduced activation ferrite/martensite steel

    SciTech Connect

    Liu, W. B.; Chen, L. Q.; Zhang, C. Yang, Z. G.; Ji, Y. Z.; Zang, H.; Shen, T. L.

    2014-09-22

    In this work, we investigate the microstructure evolution of surface-nanocrystallized reduced activation ferrite/martensite steels upon high-dose helium ion irradiation (24.3 dpa). We report a significant irradiation-induced grain growth in the irradiated buried layer at a depth of 300–500 nm, rather than at the peak damage region (at a depth of ∼840 nm). This phenomenon can be explained by the thermal spike model: minimization of the grain boundary (GB) curvature resulting from atomic diffusion in the cascade center near GBs.

  17. Study of martensitic-ferritic dual phase steels produced by hot stamping

    NASA Astrophysics Data System (ADS)

    Erişir, E.; Bilir, O. G.

    2017-02-01

    The effects of heat treatment and initial microstructure on tensile properties of 22MnB5 and 30MnB5 high-strength hot stamping steels with martensite-ferrite matrix were investigated. Hot stamping steels possessed limited elongations of about 5% in a tensile strength ranging from 1300 to 1500 MPa when quenched at temperatures above A3 temperatures. The total elongations were tried to improve by partial austenization between Ac1 and Ac3 temperature and quenching. Ac1 and Ac3 temperatures were calculated via ThermoCalc. Microstructural characterization was made by using Light Microscope and Scanning Electron Microscope. Microstructure is composed of ferrite+martensite. It was seen that annealing temperature affects the volume fraction of phases. It was concluded that initial microstructure is an important parameter for the final microstructure. This method can be used for automobile parts which require higher TE with sufficient yield and tensile strength. Also this process may be a way of using Zn coated steel sheets in hot stamping process.

  18. Low-Cycle Fatigue Properties of P92 Ferritic-Martensitic Steel at Elevated Temperature

    NASA Astrophysics Data System (ADS)

    Zhang, Zhen; Hu, ZhengFei; Schmauder, Siegfried; Mlikota, Marijo; Fan, KangLe

    2016-04-01

    The low-cycle fatigue behavior of P92 ferritic-martensitic steel and the corresponding microstructure evolution at 873 K has been extensively studied. The test results of fatigue lifetime are consistent with the Coffin-Manson relationship over a range of controlled total strain amplitudes from 0.15 to 0.6%. The influence of strain amplitude on the fatigue crack initiation and growth has been observed using optical microscopy and scanning electron microscopy. The formation mechanism of secondary cracks is established according to the observation of fracture after fatigue process and there is an intrinsic relationship between striation spacing, current crack length, and strain amplitude. Transmission electron microscopy has been employed to investigate the microstructure evolution after fatigue process. It indicates the interaction between carbides and dislocations together with the formation of cell structure inhibits the cyclic softening. The low-angle sub-boundary elimination in the martensite is mainly caused by the cyclic stress.

  19. Neutron irradiation effects on the ductile-brittle transition of ferritic/martensitic steels

    SciTech Connect

    Klueh, R.L.; Alexander, D.J.

    1997-08-01

    Ferritic/martensitic steels such as the conventional 9Cr-1MoVNb (Fe-9Cr-1Mo-0.25V-0.06Nb-0.1C) and 12Cr-1MoVW (Fe-12Cr-1Mo-0.25V-0.5W-0.5Ni-0.2C) steels have been considered potential structural materials for future fusion power plants. The major obstacle to their use is embrittlement caused by neutron irradiation. Observations on this irradiation embrittlement is reviewed. Below 425-450{degrees}C, neutron irradiation hardens the steels. Hardening reduces ductility, but the major effect is an increase in the ductile-brittle transition temperature (DBTT) and a decrease in the upper-shelf energy, as measured by a Charpy impact test. After irradiation, DBTT values can increase to well above room temperature, thus increasing the chances of brittle rather than ductile fracture.

  20. Liquid metal embrittlement susceptibility of ferritic martensitic steel in liquid lead alloys

    NASA Astrophysics Data System (ADS)

    Van den Bosch, J.; Bosch, R. W.; Sapundjiev, D.; Almazouzi, A.

    2008-06-01

    The susceptibility of the ferritic-martensitic steels T91 and EUROFER97 to liquid metal embrittlement (LME) in lead alloys has been examined under various conditions. T91, which is currently the most promising candidate material for the high temperature components of the future accelerator driven system (ADS) was tested in liquid lead bismuth eutectic (LBE), whereas the reduced activation steel, EUROFER97 which is under consideration to be the structural steel for fusion reactors was tested in liquid lead lithium eutectic. These steels, similar in microstructure and mechanical properties in the unirradiated condition were tested for their susceptibility to LME as function of temperature (150-450 °C) and strain rate (1 × 10 -3-1 × 10 -6 s -1). Also, the influence of pre-exposure and surface stress concentrators was evaluated for both steels in, respectively, liquid PbBi and PbLi environment. To assess the LME effect, results of the tests in liquid metal environment are compared with tests in air or inert gas environment. Although both unirradiated and irradiated smooth ferritic-martensitic steels do not show any or little deterioration of mechanical properties in liquid lead alloy environment compared to their mechanical properties in gas as function of temperature and strain rate, pre-exposure or the presence of surface stress concentrators does lead to a significant decrease in total elongation for certain test conditions depending on the type of liquid metal environment. The results are discussed in terms of wetting enhanced by liquid metal corrosion or crack initiation processes.

  1. Mechanical Performance of Ferritic Martensitic Steels for High Dose Applications in Advanced Nuclear Reactors

    NASA Astrophysics Data System (ADS)

    Anderoglu, Osman; Byun, Thak Sang; Toloczko, Mychailo; Maloy, Stuart A.

    2013-01-01

    Ferritic/martensitic (F/M) steels are considered for core applications and pressure vessels in Generation IV reactors as well as first walls and blankets for fusion reactors. There are significant scientific data on testing and industrial experience in making this class of alloys worldwide. This experience makes F/M steels an attractive candidate. In this article, tensile behavior, fracture toughness and impact property, and creep behavior of the F/M steels under neutron irradiations to high doses with a focus on high Cr content (8 to 12) are reviewed. Tensile properties are very sensitive to irradiation temperature. Increase in yield and tensile strength (hardening) is accompanied with a loss of ductility and starts at very low doses under irradiation. The degradation of mechanical properties is most pronounced at <0.3 T M ( T M is melting temperature) and up to 10 dpa (displacement per atom). Ferritic/martensitic steels exhibit a high fracture toughness after irradiation at all temperatures even below 673 K (400 °C), except when tested at room temperature after irradiations below 673 K (400 °C), which shows a significant reduction in fracture toughness. Creep studies showed that for the range of expected stresses in a reactor environment, the stress exponent is expected to be approximately one and the steady state creep rate in the absence of swelling is usually better than austenitic stainless steels both in terms of the creep rate and the temperature sensitivity of creep. In short, F/M steels show excellent promise for high dose applications in nuclear reactors.

  2. Current status and recent research achievements in ferritic/martensitic steels

    NASA Astrophysics Data System (ADS)

    Tavassoli, A.-A. F.; Diegele, E.; Lindau, R.; Luzginova, N.; Tanigawa, H.

    2014-12-01

    When the austenitic stainless steel 316L(N) was selected for ITER, it was well known that it would not be suitable for DEMO and fusion reactors due to its irradiation swelling at high doses. A parallel programme to ITER collaboration already had been put in place, under an IEA fusion materials implementing agreement for the development of a low activation ferritic/martensitic steel, known for their excellent high dose irradiation swelling resistance. After extensive screening tests on different compositions of Fe-Cr alloys, the chromium range was narrowed to 7-9% and the first RAFM was industrially produced in Japan (F82H: Fe-8%Cr-2%W-TaV). All IEA partners tested this steel and contributed to its maturity. In parallel several other RAFM steels were produced in other countries. From those experiences and also for improving neutron efficiency and corrosion resistance, European Union opted for a higher chromium lower tungsten grade, Fe-9%Cr-1%W-TaV steel (Eurofer), and in 1997 ordered the first industrial heats. Other industrial heats have been produced since and characterised in different states, including irradiated up to 80 dpa. China, India, Russia, Korea and US have also produced their grades of RAFM steels, contributing to overall maturity of these steels. This paper reviews the work done on RAFM steels by the fusion materials community over the past 30 years, in particular on the Eurofer steel and its design code qualification for RCC-MRx.

  3. Neodymium-rich precipitate phases in a high-chromium ferritic/martensitic steel

    NASA Astrophysics Data System (ADS)

    Shen, Yinzhong; Zhou, Xiaoling; Shang, Zhongxia

    2016-05-01

    Neodymium being considered as nitride forming element has been used in a design of advanced ferritic/martensitic (FM) steels for fossil fired power plants at service temperatures of 630 °C to 650 °C to effectively improve the creep strength of the steels. To fully understand the characteristics of neodymium precipitates in high-Cr FM steels, precipitate phases in an 11Cr FM steel with 0.03 wt% addition of Nd have been investigated by transmission electron microscopy. Three neodymium phases with a face-centered cubic crystal structure and different composition were observed in the steel. They consisted of neodymium carbonitride with an average lattice parameter of 1.0836 nm, Nd-rich carbonitride mainly containing Mn, and Nd-rich MN nitride mainly containing Mn and Co. Other three Nd-rich and Nd-containing phases, which appear to be Nd-Co-Cr/Nd-rich intermetallic compounds and Cr-Fe-rich nitride containing Nd, were also detected in the steel. Nd-relevant precipitates were found to be minor phases compared with M23C6 and Nb/V/Ta-rich MX phases in the steel. The content of Nd in other precipitate phases was very low. Most of added Nd is considered to be present as solid solution in the matrix of the steel.

  4. Diffusive transport parameters of deuterium through China reduced activation ferritic-martensitic steels

    NASA Astrophysics Data System (ADS)

    Wang, Bo; Liu, Lingbo; Xiang, Xin; Rao, Yongchu; Ye, Xiaoqiu; Chen, Chang An

    2016-03-01

    Reduced Activation Ferritic/Martensitic (RAFM) steels have been considered as the most promising candidate structure materials for a fusion reactor. In the recent decades, two new types of RAFM steels, called China Low Activation Martensitic (CLAM) steel and China Low-activation Ferritic (CLF-1) steel, have been developed. The gas evolution permeation technique has been used to investigate diffusive transport parameters of deuterium through CLAM and CLF-1 over the temperature range 623 ∼ 873 K at deuterium pressure of 105 Pa. The resultant transport parameters are: Φ (mol. m-1 s-1 Pa-1/2) = 5.40 × 10-8 exp (-46.8 (kJ. mol-1)/RT), D(m2 s-1) = 3.81 × 10-7 exp(-24.0(kJ. mol-1)/RT) and S (mol. m-3 Pa-1/2) = 1.42 × 10-1 exp(-22.8(kJ. mol-1)/RT) for CLAM; while Φ(mol m-1 s-1 Pa-1/2) = 1.76 × 10-8 exp(-43.9(kJ. mol-1)/RT), D(m2. s-1) = 1.02 × 10-7 exp(-16.9(kJ. mol-1)/RT) and S(mol. m-1 Pa-1/2) = 1.73 × 10-1 exp(-27.0(kJ. mol-1) /RT) for CLF-1. The results show that CLAM is more permeable than CLF-1, thus it is easier for hydrogen isotopes to transport and be removed.

  5. Neutron irradiation effects on the ductile-brittle transition of ferritic/martensitic steels

    SciTech Connect

    Klueh, R.L.; Alexander, D.J.

    1997-06-01

    Ferritic/martensitic steels such as the conventional 9Cr-1MoVNb (Fe-9Cr-1Mo-0.25V-0.06Nb-0.1C) and 12Cr-1MoVW (Fe-12Cr-1Mo-0.25V-0.5W-0.5Ni-0.2C) steels have been considered potential structural materials for future fusion power plants. The major obstacle to their use is embrittlement caused by neutron irradiation. Observations on this irradiation embrittlement will be reviewed. Below 425-450{degrees}C, neutron irradiation hardens the steels. Hardening reduces ductility, but the major effect is an increase in the ductile-brittle transition temperature (DBTT) and a decrease in the upper-shelf energy, as measured by a Charpy impact test. After irradiation, DBTT values can increase to well above room temperature, thus increasing the chances of brittle rather than ductile fracture. In addition to irradiation hardening, neutrons from the fusion reaction will produce large amounts of helium in the steels used to construct fusion power plant components. Tests to simulate the fusion environment indicate that helium can also affect the toughness. Steels are being developed for fusion applications that have a low DBTT prior to irradiation and then show only a small shift after irradiation. A martensitic 9Cr-2WVTa (nominally Fe-9Cr-2W-0.25V-0.07Ta-0.1C) steel had a much lower DBTT than the conventional 9Cr-1MoVNb steel prior to neutron irradiation and showed a much smaller increase in DBTT after irradiation. 27 refs., 5 figs., 1 tab.

  6. Proceedings of the IEA working group meeting on ferritic/martensitic steels

    SciTech Connect

    Klueh, R.L.

    1995-02-01

    An International Energy Agency (IEA) working group consist- ng of researchers from Japan, the European Union (EU), and the United States, met at the Oak Ridge National Laboratory (ORNL) 16 February 1995 to continue planning a collaborative test program on reduced-activation ferritic/martensitic steels for fusion applications. Plates from a 5-ton, a 1-ton, and three 150 kg heats of reduced-activation martensitic steels have been melted and processed to 7.5- and 15-mm plates in Japan. Plates were delivered in 1994 to the three parties that will participate in the test program. A second 5-ton IEA heat of modified F82H steel was produced in Japan in late 1994, and it was processed into 15- and 25-mm plates, which are to be shipped in February, 1995. Weldments will be produced on plates from this heat, and they will be shipped in April, 1995. At the ORNL meeting, a detailed test program and schedule was presented by the EU representatives, and less detailed programs were presented by the Japanese and US representatives. Detailed program schedules are required from the latter two programs to complete the program planning stage. A meeting is planned for 19--20 September 1995 in Switzerland to continue the planning and coordination of the test program and to present the preliminary results obtained in the collaboration.

  7. On the (in)adequacy of the Charpy impact test to monitor irradiation effects of ferritic/martensitic steels

    NASA Astrophysics Data System (ADS)

    Chaouadi, R.

    2007-02-01

    Irradiation embrittlement studies rely very often on Charpy impact data, in particular the ductile-to-brittle transition temperature (DBTT). However, while the DBTT-shift is equivalent to the increase of the fracture toughness transition temperature of ferritic steels, it is not the case for ferritic/martensitic steels. The aim of this study is to critically assess experimental data obtained on a 9%Cr-ferritic/martensitic steel, Eurofer-97, to better understand the underlying mechanisms involved during the fracture process. More specifically, a dedicated analysis using the load diagram approach allows to unambiguously reveal the actual effects of irradiation on physically rather than empirically based parameters. A comparison is made between a ferritic and ferritic/martensitic steel to better identify the possible similarities and differences. Tensile, Charpy impact and fracture toughness tests data are examined in a global approach to assess the actual rather than apparent irradiation effects. The adequacy or inadequacy of the Charpy impact test to monitor irradiation effects is extensively discussed.

  8. Corrosion of ferritic-martensitic steels and nickel-based alloys in supercritical water

    NASA Astrophysics Data System (ADS)

    Ren, Xiaowei

    The corrosion behavior of ferritic/martensitic (F/M) steels and Ni-based alloys in supercritical water (SCW) has been studied due to their potential applications in future nuclear reactor systems, fossil fuel power plants and waste treatment processes. 9˜12% chromium ferritic/martensitic steels exhibit good radiation resistance and stress corrosion cracking resistance. Ni-based alloys with an austenitic face-centered cubic (FCC) structure are designed to retain good mechanical strength and corrosion/oxidation resistance at elevated temperatures. Corrosion tests were carried out at three temperatures, 360°C, 500°C and 600°C, with two dissolved oxygen contents, 25 ppb and 2 ppm for up to 3000 hours. Alloys modified by grain refinement and reactive element addition were also investigated to determine their ability to improve the corrosion resistance in SCW. A duplex oxide structure was observed in the F/M steels after exposure to 25 ppb oxygen SCW, including an outer oxide layer with columnar magnetite grains and an inner oxide layer constituted of a mixture of spinel and ferrite phases in an equiaxed grain structure. An additional outermost hematite layer formed in the SCW-exposed samples when the oxygen content was increased to 2 ppm. Weight gain in the F/M steels increased with exposure temperatures and times, and followed parabolic growth kinetics in most of the samples. In Ni-based alloys after exposure to SCW, general corrosion and pitting corrosion were observed, and intergranular corrosion was found when exposed at 600°C due to formation of a local healing layer. The general oxide structure on the Ni-based alloys was characterized as NiO/Spinel/(CrxFe 1-x)2O3/(Fe,Ni). No change in oxidation mechanism was observed in crossing the critical point despite the large change in water properties. Corrosion resistance of the F/M steels was significantly improved by plasma-based yttrium surface treatment because of restrained outward diffusion of iron by the

  9. Development of new generation reduced activation ferritic-martensitic steels for advanced fusion reactors

    NASA Astrophysics Data System (ADS)

    Tan, L.; Snead, L. L.; Katoh, Y.

    2016-09-01

    International development of reduced activation ferritic-martensitic (RAFM) steels has focused on 9 wt percentage Cr, which primarily contain M23C6 (M = Cr-rich) and small amounts of MX (M = Ta/V, X = C/N) precipitates, not adequate to maintain strength and creep resistance above ∼500 °C. To enable applications at higher temperatures for better thermal efficiency of fusion reactors, computational alloy thermodynamics coupled with strength modeling have been employed to explore a new generation RAFM steels. The new alloys are designed to significantly increase the amount of MX nanoprecipitates, which are manufacturable through standard and scalable industrial steelmaking methods. Preliminary experimental results of the developed new alloys demonstrated noticeably increased amount of MX, favoring significantly improved strength, creep resistance, and Charpy impact toughness as compared to current RAFM steels. The strength and creep resistance were comparable or approaching to the lower bound of, but impact toughness was noticeably superior to 9-20Cr oxide dispersion-strengthened ferritic alloys.

  10. A comparative assessment of the fracture toughness behavior of ferritic-martensitic steels and nanostructured ferritic alloys

    NASA Astrophysics Data System (ADS)

    Byun, Thak Sang; Hoelzer, David T.; Kim, Jeoung Han; Maloy, Stuart A.

    2017-02-01

    The Fe-Cr alloys with ultrafine microstructures are primary candidate materials for advanced nuclear reactor components because of their excellent high temperature strength and high resistance to radiation-induced damage such as embrittlement and swelling. Mainly two types of Fe-Cr alloys have been developed for the high temperature reactor applications: the quenched and tempered ferritic-martensitic (FM) steels hardened primarily by ultrafine laths and carbonitrides and the powder metallurgy-based nanostructured ferritic alloys (NFAs) by nanograin structure and nanoclusters. This study aims at elucidating the differences and similarities in the temperature and strength dependences of fracture toughness in the Fe-Cr alloys to provide a comparative assessment of their high-temperature structural performance. The KJQ versus yield stress plots confirmed that the fracture toughness was inversely proportional to yield strength. It was found, however, that the toughness data for some NFAs were outside the band of the integrated dataset at given strength level, which indicates either a significant improvement or deterioration in mechanical properties due to fundamental changes in deformation and fracture mechanisms. When compared to the behavior of NFAs, the FM steels have shown much less strength dependence and formed narrow fracture toughness data bands at a significantly lower strength region. It appeared that at high temperatures ≥600 °C the NFAs cannot retain the nanostructure advantage of high strength and high toughness either by high-temperature embrittlement or by excessive loss of strength. Irradiation studies have revealed, however, that the NFAs have much stronger radiation resistance than tempered martensitic steels, such as lower radiation-induced swelling, finer helium bubble formation, lower irradiation creep rate and reduced low temperature embrittlement.

  11. A comparative assessment of the fracture toughness behavior of ferritic-martensitic steels and nanostructured ferritic alloys

    DOE PAGES

    Byun, Thak Sang; Hoelzer, David T.; Kim, Jeoung Han; ...

    2016-12-07

    The Fe-Cr alloys with ultrafine microstructures are primary candidate materials for advanced nuclear reactor components because of their excellent high temperature strength and high resistance to radiation-induced damage such as embrittlement and swelling. Mainly two types of Fe-Cr alloys have been developed for the high temperature reactor applications: the quenched and tempered ferritic-martensitic (FM) steels hardened primarily by ultrafine laths and carbonitrides and the powder metallurgy-based nanostructured ferritic alloys (NFAs) by nanograin structure and nanoclusters. This paper aims at elucidating the differences and similarities in the temperature and strength dependences of fracture toughness in the Fe-Cr alloys to provide amore » comparative assessment of their high-temperature structural performance. The KJQ versus yield stress plots confirmed that the fracture toughness was inversely proportional to yield strength. It was found, however, that the toughness data for some NFAs were outside the band of the integrated dataset at given strength level, which indicates either a significant improvement or deterioration in mechanical properties due to fundamental changes in deformation and fracture mechanisms. When compared to the behavior of NFAs, the FM steels have shown much less strength dependence and formed narrow fracture toughness data bands at a significantly lower strength region. It appeared that at high temperatures ≥600 °C the NFAs cannot retain the nanostructure advantage of high strength and high toughness either by high-temperature embrittlement or by excessive loss of strength. Finally, irradiation studies have revealed, however, that the NFAs have much stronger radiation resistance than tempered martensitic steels, such as lower radiation-induced swelling, finer helium bubble formation, lower irradiation creep rate and reduced low temperature embrittlement.« less

  12. A comparative assessment of the fracture toughness behavior of ferritic-martensitic steels and nanostructured ferritic alloys

    SciTech Connect

    Byun, Thak Sang; Hoelzer, David T.; Kim, Jeoung Han; Maloy, Stuart A.

    2016-12-07

    The Fe-Cr alloys with ultrafine microstructures are primary candidate materials for advanced nuclear reactor components because of their excellent high temperature strength and high resistance to radiation-induced damage such as embrittlement and swelling. Mainly two types of Fe-Cr alloys have been developed for the high temperature reactor applications: the quenched and tempered ferritic-martensitic (FM) steels hardened primarily by ultrafine laths and carbonitrides and the powder metallurgy-based nanostructured ferritic alloys (NFAs) by nanograin structure and nanoclusters. This paper aims at elucidating the differences and similarities in the temperature and strength dependences of fracture toughness in the Fe-Cr alloys to provide a comparative assessment of their high-temperature structural performance. The KJQ versus yield stress plots confirmed that the fracture toughness was inversely proportional to yield strength. It was found, however, that the toughness data for some NFAs were outside the band of the integrated dataset at given strength level, which indicates either a significant improvement or deterioration in mechanical properties due to fundamental changes in deformation and fracture mechanisms. When compared to the behavior of NFAs, the FM steels have shown much less strength dependence and formed narrow fracture toughness data bands at a significantly lower strength region. It appeared that at high temperatures ≥600 °C the NFAs cannot retain the nanostructure advantage of high strength and high toughness either by high-temperature embrittlement or by excessive loss of strength. Finally, irradiation studies have revealed, however, that the NFAs have much stronger radiation resistance than tempered martensitic steels, such as lower radiation-induced swelling, finer helium bubble formation, lower irradiation creep rate and reduced low temperature embrittlement.

  13. Influence of high temperature pre-deformation on the dissolution rate of delta ferrites in martensitic heat-resistant steels

    NASA Astrophysics Data System (ADS)

    Li, Junru; Liu, Jianjun; Jiang, Bo; Zhang, Chaolei; Liu, Yazheng

    2017-03-01

    The dissolution process of delta ferrites and the influence of high temperature pre-deformation on the dissolution rate of delta ferrites in martensitic heat-resistant steel 10Cr12Ni3Mo2VN were studied by isothermal heating and thermal simulation experiments. The precipitation temperature of delta ferrites in experimental steel is about 1195 °C. M23C6-type carbides incline to precipitate and coarsen at the boundaries of delta ferrites below 930 °C, and can be rapidly dissolved by heating at 1180 °C. The percentage of delta ferrites gradually decreases with heating time. And a Kolmogorov-Johnson-Mehl-Avrami equation was established to describe the dissolution process of delta ferrites at 1180 °C. High temperature pre-deformation can markedly increase the dissolution rate of delta ferrites. Pre-deformation can largely increase the interface area between delta ferrite and matrix and thus increase the unit-time diffusing quantities of alloying elements between delta ferrites and matrix. In addition, high temperature pre-deformation leads to dynamic recrystallization and increases the number of internal grain boundaries in the delta ferrites. This can also greatly increase the diffusing rate of alloying elements. In these cases, the dissolution of delta ferrites can be promoted.

  14. Influence of high temperature pre-deformation on the dissolution rate of delta ferrites in martensitic heat-resistant steels

    NASA Astrophysics Data System (ADS)

    Li, Junru; Liu, Jianjun; Jiang, Bo; Zhang, Chaolei; Liu, Yazheng

    2017-02-01

    The dissolution process of delta ferrites and the influence of high temperature pre-deformation on the dissolution rate of delta ferrites in martensitic heat-resistant steel 10Cr12Ni3Mo2VN were studied by isothermal heating and thermal simulation experiments. The precipitation temperature of delta ferrites in experimental steel is about 1195 °C. M23C6-type carbides incline to precipitate and coarsen at the boundaries of delta ferrites below 930 °C, and can be rapidly dissolved by heating at 1180 °C. The percentage of delta ferrites gradually decreases with heating time. And a Kolmogorov-Johnson-Mehl-Avrami equation was established to describe the dissolution process of delta ferrites at 1180 °C. High temperature pre-deformation can markedly increase the dissolution rate of delta ferrites. Pre-deformation can largely increase the interface area between delta ferrite and matrix and thus increase the unit-time diffusing quantities of alloying elements between delta ferrites and matrix. In addition, high temperature pre-deformation leads to dynamic recrystallization and increases the number of internal grain boundaries in the delta ferrites. This can also greatly increase the diffusing rate of alloying elements. In these cases, the dissolution of delta ferrites can be promoted.

  15. Studies on A-TIG welding of Low Activation Ferritic/Martensitic (LAFM) steel

    NASA Astrophysics Data System (ADS)

    Vasantharaja, P.; Vasudevan, M.

    2012-02-01

    Low Activation Ferritic-Martensitic steels (LAFM) are chosen as the candidate material for structural components in fusion reactors. The structural components are generally fabricated by welding processes. Activated Tungsten Inert Gas (A-TIG) welding is an emerging process for welding of thicker components. In the present work, attempt was made to develop A-TIG welding technology for LAFM steel plates of 10 mm thick. Activated flux was developed for LAFM steel by carrying out various bead-on-plate TIG welds without flux and with flux. The optimum flux was identified as one which gave maximum depth of penetration at minimum heat input values. With the optimized flux composition, LAFM steel plate of 10 mm thickness was welded in square butt weld joint configuration using double side welding technique. Optical and Scanning Electron Microscopy was used for characterizing the microstructures. Microhardness measurements were made across the weld cross section for as welded and post weld heat treated samples. Tensile and impact toughness properties were determined. The mechanical properties values obtained in A-TIG weld joint were comparable to that obtained in weld joints of LAFM steel made by Electron beam welding process.

  16. Charpy impact tests on martensitic/ferritic steels after irradiation in SINQ target-3

    NASA Astrophysics Data System (ADS)

    Dai, Yong; Marmy, Pierre

    2005-08-01

    Charpy impact tests were performed on martensitic/ferritic (MF) steels T91, F82H, Optifer-V and Optimax-A/-C irradiated in SINQ Target-3 up to 7.5 dpa and 500 appm He in a temperature range of 120-195 °C. Results demonstrate that for all the four kinds of steels, the ductile-to-brittle transition temperature (DBTT) increases with irradiation dose. The difference in the DBTT shifts (ΔDBTT) of the different steels is not significant after irradiation in the SINQ target. The ΔDBTT data from the previous small punch (Δ DBTT SP) and the present Charpy impact (ΔDBTT CVN) tests can be correlated with the expression: Δ DBTT SP = 0.4ΔDBTT CVN. All the ΔDBTT data fall into a linear band when they are plotted versus helium concentration. The results indicate that helium effects on the embrittlement of MF steels are significant, particularly at higher concentrations. It suggests that MF steels may not be very suitable for applications at low temperatures in spallation irradiation environments where helium production is high.

  17. Investigation on the Enhanced Oxidation of Ferritic/Martensitic Steel P92 in Pure Steam.

    PubMed

    Yuan, Juntao; Wu, Ximao; Wang, Wen; Zhu, Shenglong; Wang, Fuhui

    2014-04-03

    Oxidation of ferritic/martensitic steel P92 was investigated in pure oxygen and in pure steam at 600-800 °C by thermogravimetric analysis (TGA), optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results showed that the oxidation of P92 was significantly enhanced and multilayer scale with an outer iron oxides layer formed in pure steam. At 700 °C, the gas switch markedly influenced the scaling kinetics and scale microstructure. It was supposed that the higher affinity of iron to steam would be attributed to the enhanced oxidation of P92 in pure steam, and the much easier transport of hydroxyl would account for the significant difference induced by gas switch.

  18. Investigation on the Enhanced Oxidation of Ferritic/Martensitic Steel P92 in Pure Steam

    PubMed Central

    Yuan, Juntao; Wu, Ximao; Wang, Wen; Zhu, Shenglong; Wang, Fuhui

    2014-01-01

    Oxidation of ferritic/martensitic steel P92 was investigated in pure oxygen and in pure steam at 600–800 °C by thermogravimetric analysis (TGA), optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results showed that the oxidation of P92 was significantly enhanced and multilayer scale with an outer iron oxides layer formed in pure steam. At 700 °C, the gas switch markedly influenced the scaling kinetics and scale microstructure. It was supposed that the higher affinity of iron to steam would be attributed to the enhanced oxidation of P92 in pure steam, and the much easier transport of hydroxyl would account for the significant difference induced by gas switch. PMID:28788592

  19. Effect of mechanical restraint on weldability of reduced activation ferritic/martensitic steel thick plates

    NASA Astrophysics Data System (ADS)

    Serizawa, Hisashi; Nakamura, Shinichiro; Tanaka, Manabu; Kawahito, Yousuke; Tanigawa, Hiroyasu; Katayama, Seiji

    2011-10-01

    As one of the reduced activation ferritic/martensitic steels, the weldability of thick F82H plate was experimentally examined using new heat sources in order to minimize the total heat input energy in comparison with TIG welding. A full penetration of 32 mm thick plate could be produced as a combination of a 12 mm deep first layer generated by a 10 kW fiber laser beam and upper layers deposited by a plasma MIG hybrid welding with Ar + 2%O shielding gas. Also, the effect of mechanical restraint on the weldability under EB welding of thick F82H plate was studied by using FEM to select an appropriate specimen size for the basic test. The appropriate and minimum size for the basic test of weldability under EB welding of 90 mm thick plate might be 200 mm in length and 400 mm in width where the welding length should be about 180 mm.

  20. Influence of structural-phase state of ferritic-martensitic steels on the helium porosity development

    NASA Astrophysics Data System (ADS)

    Chernov, I. I.; Staltsov, M. S.; Kalin, B. A.; Bogachev, I. A.; Guseva, L. Yu; Dzhumaev, P. S.; Emelyanova, O. V.; Drozhzhina, M. V.; Manukovsky, K. V.; Nikolaeva, I. D.

    2016-04-01

    Transmission electron microscopy (TEM) has been used to study the effect of the initial structural-phase state (SPhS) of ferritic-martensitic steels EK-181, EP-450 and EP-450- ODS (with 0.5 wt.% nanoparticles of Y2O3) on the of helium porosity formation and gas swelling. Different SPhS of steel EK-181 was produced by water quenching, annealing, normalizing plus tempered, intensive plastic deformation by torsion (HPDT). Irradiation was carried out by He+-40 keV ions at 923 K up to fluence of 5-1020 He+/m2. It is shown that the water quenching causes the formation of uniformly distributed small bubbles (d¯ ∼ 2 nm) of the highest density (ρ∼ 1025 m-3). After normalization followed by tempering as well as after annealing bubbles distribution is highly non-uniform both by volume and in size. Very large faceted bubbles (pre-equilibrium gas-filled voids) are formed in ferrite grains resulting in high level of gas swelling of the irradiated layer with S = 4,9 ± 1,2 and 3.8 ± 0.9% respectively. Nano- and microcrystalline structure created by HPDT completely degenerate at irradiation temperature and ion irradiation formed bubbles of the same parameters as in the annealed steel. Bubbles formed in EP-450-ODS steel are smaller in size and density, which led to a decrease of helium swelling by 4 times (S = 0.8 ± 0.2%) as compared to the swelling of the matrix steel EP-450 (S = 3.1 ± 0.7%).

  1. Nano-scale nitride-particle-strengthened high-temperature wrought ferritic and martensitic steels

    SciTech Connect

    Klueh, Ronald L; Hashimoto, Naoyuki; Maziasz, Philip J

    2009-04-21

    A method of making a steel composition includes the steps of: a. providing a steel composition that includes up to 15% Cr, up to 3% Mo, up to 4% W, 0.05-1% V, up to 2% Si, up to 3% Mn, up to 10% Co, up to 3% Cu, up to 5% Ni, up to 0.3% C, 0.02-0.3% N, balance iron, wherein the percentages are by total weight of the composition; b. austenitizing the composition at a temperature in the range of 1000.degree. C. to 1400.degree. C.; c. cooling the composition of steel to a selected hot-working temperature in the range 500.degree. C. to 1000.degree. C.; d. hot-working the composition at the selected hot-working temperature; e. annealing the composition for a time period of up to 10 hours at a temperature in the range of 500.degree. C. to 1000.degree. C.; and f. cooling the composition to ambient temperature to transform the steel composition to martensite, bainite, ferrite, or a combination of those microstructures.

  2. Effect of ultrasonic impact peening on the corrosion of ferritic-martensitic steels in supercritical water

    NASA Astrophysics Data System (ADS)

    Dong, Ziqiang; Liu, Zhe; Li, Ming; Luo, Jing-Li; Chen, Weixing; Zheng, Wenyue; Guzonas, Dave

    2015-02-01

    Ferritic-Martensitic (F/M) steels are important candidate alloys to be used in the next generation (Generation-IV) SCWRs. In this work, two F/M steels with the same Cr content of around 12 wt.% and varied Si content from 0.6 wt.% to 2.2 wt.% were evaluated in supercritical water (SCW) at 500 °C and 25 MPa for up to 1000 h. The effect of ultrasonic shot peening on the oxidation behavior of these F/M steels have been investigated. The results showed that the oxidation was affected by the Si content as well as the surface modification. The F/M steel with low Si concentration exhibited higher corrosion resistance than that of the alloy with high Si content. Shot peening, which could modify the microstructure at the surface, showed significantly beneficial effect to improving the oxidation resistance. A thin, uniform oxide layer formed on the peened sample could be attributed to the enhanced diffusion of Cr induced by the surface modification.

  3. Precipitate phases in normalized and tempered ferritic/martensitic steel P92

    NASA Astrophysics Data System (ADS)

    Shen, Yinzhong; Liu, Huan; Shang, Zhongxia; Xu, Zhiqiang

    2015-10-01

    Ferritic/martensitic steel P92 is a promising candidate for cladding and duct applications in Sodium-Cooled Fast Reactor. The precipitate phases of the P92 steel normalized at 1323 K (1050 °C) for 30 min and tempered at 1038 K (765 °C) for 1 h have been investigated using transmission electron microscopes. Four types of phases consisting of M23C6, MX, M2X and sigma-FeCr were identified in the steel. MX phases consist of Nb-rich M(C,N) carbonitride, Nb-rich MC carbide, V-rich M(C,N) carbonitride, V-rich MC carbide, V-rich MN nitride, and complex MC carbides with Nb-rich MC core and V-rich MC wings. M2X phases consist of Cr-rich M2(C,N) carbonitride, Cr-rich M2C carbide and M2N nitride. Sigma-FeCr has a simple tetragonal lattice and a typical chemical formula of Fe0.45Cr0.45W0.1. M23C6 and MX are the dominant phases, while the sigma-FeCr has the lowest content. The formation of sigma-FeCr and M2X phases in the steel is also discussed.

  4. Load partitioning between ferrite/martensite and dispersed nanoparticles of a 9Cr ferritic/martensitic (F/M) ODS steel at high temperatures

    SciTech Connect

    Zhang, Guangming; Mo, Kun; Miao, Yinbin; Liu, Xiang; Almer, Jonathan; Zhou, Zhangjian; Stubbins, James F.

    2015-06-18

    In this study, a high-energy synchrotron radiation X-ray technique was used to investigate the tensile deformation processes of a 9Cr-ODS ferritic/martensitic (F/M) steel at different temperatures. Two minor phases within the 9Cr-ODS F/M steel matrix were identified as Y2Ti2O7 and TiN by the high-energy X-ray diffraction, and confirmed by the analysis using energy dispersive X-ray spectroscopy (EDS) of scanning transmission electron microscope (STEM). The lattice strains of the matrix and particles were measured through the entire tensile deformation process. During the tensile tests, the lattice strains of the ferrite/martensite and the particles (TiN and Y2Ti2O7) showed a strong temperature dependence, decreasing with increasing temperature. Analysis of the internal stress at three temperatures showed that the load partitioning between the ferrite/martensite and the particles (TiN and Y2Ti2O7) was initiated during sample yielding and reached to a peak during sample necking. At three studied temperatures, the internal stress of minor phases (Y2Ti2O7 and TiN) was about 2 times that of F/M matrix at yielding position, while the internal stress of Y2Ti2O7 and TiN reached about 4.5-6 times and 3-3.5 times that of the F/M matrix at necking position, respectively. It indicates that the strengthening of the matrix is due to minor phases (Y2Ti2O7 and TiN), especially Y2Ti2O7 particles. Although the internal stresses of all phases decreased with increasing temperature from RT to 600 degrees C, the ratio of internal stresses of each phase at necking position stayed in a stable range (internal stresses of Y2Ti2O7 and TiN were about 4.5-6 times and 3-3.5 times of that of F/M matrix, respectively). The difference between internal stress of the F/M matrix and the applied stress at 600 degrees C is slightly lower than those at RI and 300 degrees C, indicating that the nanoparticles still have good strengthening effect at 600 degrees C. (C) 2015 Elsevier B.V. All rights reserved.

  5. 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.

  6. Assessment of Tungsten Content on Tertiary Creep Deformation Behavior of Reduced Activation Ferritic-Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Vanaja, J.; Laha, Kinkar

    2015-10-01

    Tertiary creep deformation behavior of reduced activation ferritic-martensitic (RAFM) steels having different tungsten contents has been assessed. Creep tests were carried out at 823 K (550 °C) over a stress range of 180 to 260 MPa on three heats of the RAFM steel (9Cr-W-0.06Ta-0.22V) with tungsten content of 1, 1.4, and 2.0 wt pct. With creep exposure, the steels exhibited minimum in creep rate followed by progressive increase in creep rate until fracture. The minimum creep rate decreased, rupture life increased, and the onset of tertiary stage of creep deformation delayed with the increase in tungsten content. The tertiary creep behavior has been assessed based on the relationship, , considering minimum creep rate () instead of steady-state creep rate. The increase in tungsten content was found to decrease the rate of acceleration of tertiary parameter ` p.' The relationships between (1) tertiary parameter `p' with minimum creep rate and time spent in tertiary creep deformation and (2) the final creep rate with minimum creep rate revealed that the same first-order reaction rate theory prevailed in the minimum creep rate as well as throughout the tertiary creep deformation behavior of the steel. A master tertiary creep curve of the steels has been developed. Scanning electron microscopic investigation revealed enhanced coarsening resistance of carbides in the steel on creep exposure with increase in tungsten content. The decrease in tertiary parameter ` p' with tungsten content with the consequent decrease in minimum creep rate and increase in rupture life has been attributed to the enhanced microstructural stability of the steel.

  7. Development of benchmark reduced activation ferritic/martensitic steels for fusion energy applications

    NASA Astrophysics Data System (ADS)

    Tanigawa, H.; Gaganidze, E.; Hirose, T.; Ando, M.; Zinkle, S. J.; Lindau, R.; Diegele, E.

    2017-09-01

    Reduced-activation ferritic/martensitic (RAFM) steel is the benchmark structural material for in-vessel components of fusion reactor. The current status of RAFM developments and evaluations is reviewed based on two leading RAFM steels, F82H and EUROFER-97. The applicability of various joining technologies for fabrication of fusion first wall and blanket structures, such as weld or diffusion bonding, is overviewed as well. The technical challenges and potential risks of utilizing RAFM steels as the structural material of in-vessel components are discussed, and possible mitigation methodology is introduced. The discussion suggests that deuterium-tritium fusion neutron irradiation effects currently need to be treated as an ambiguity factor which could be incorporated within the safety factor. The safety factor will be defined by the engineering design criteria which are not yet developed with regard to irradiation effects and some high temperature process, and the operating time condition of the in-vessel component will be defined by the condition at which those ambiguities due to neutron irradiation become too large to be acceptable, or by the critical condition at which 14 MeV fusion neutron irradiation effects is expected to become different from fission neutron irradiation effects.

  8. Microstructure control for high strength 9Cr ferritic-martensitic steels

    NASA Astrophysics Data System (ADS)

    Tan, L.; Hoelzer, D. T.; Busby, J. T.; Sokolov, M. A.; Klueh, R. L.

    2012-03-01

    Ferritic-martensitic (F-M) steels with 9 wt.%Cr are important structural materials for use in advanced nuclear reactors. Alloying composition adjustment, guided by computational thermodynamics, and thermomechanical treatment (TMT) were employed to develop high strength 9Cr F-M steels. Samples of four heats with controlled compositions were subjected to normalization and tempering (N&T) and TMT, respectively. Their mechanical properties were assessed by Vickers hardness and tensile testing. Ta-alloying showed significant strengthening effect. The TMT samples showed strength superior to the N&T samples with similar ductility. All the samples showed greater strength than NF616, which was either comparable to or greater than the literature data of the PM2000 oxide-dispersion-strengthened (ODS) steel at temperatures up to 650 °C without noticeable reduction in ductility. A variety of microstructural analyses together with computational thermodynamics provided rational interpretations on the strength enhancement. Creep tests are being initiated because the increased yield strength of the TMT samples is not able to deduce their long-term creep behavior.

  9. Effect of silicon on the microstructure and mechanical properties of reduced activation ferritic/martensitic steel

    NASA Astrophysics Data System (ADS)

    Chen, Shenghu; Rong, Lijian

    2015-04-01

    The effect of Si in the range of 0.05-0.77 wt.% on the microstructure, tensile properties and impact toughness of reduced activation ferritic/martensitic (RAFM) steels has been investigated. An increase in Si content affected the prior austenite grain size resulting in an increase in the tensile strength at room temperature. The tensile strength of steels tested above 773 K did not change significantly with the addition of Si, which was due to the diminished carbide hardening effect and boundary strengthening effect. Detailed fractographic analysis revealed that tear fractures occurred in the samples tensile tested at room temperature, while cup and cone fractures were found in samples tensile tested at temperatures above 773 K, which were induced by the easing of dislocation pile-ups. The ductile-to-brittle transition temperature (DBTT) decreased when the Si content increased to 0.22 wt.%. However, the DBTT increased when the Si content reached 0.77 wt.% and this was due to the precipitation of Laves phase. The RAFM steel with approximately 0.22 wt.% Si content was found to possess an optimized combination of microstructure, tensile properties and impact toughness.

  10. Microstructure property analysis of HFIR-irradiated reduced-activation ferritic/martensitic steels

    NASA Astrophysics Data System (ADS)

    Tanigawa, H.; Hashimoto, N.; Sakasegawa, H.; Klueh, R. L.; Sokolov, M. A.; Shiba, K.; Jitsukawa, S.; Kohyama, A.

    2004-08-01

    The effects of irradiation on the Charpy impact properties of reduced-activation ferritic/martensitic steels were investigated on a microstructural basis. It was previously reported that the ductile-brittle transition temperature (DBTT) of F82H-IEA and its heat treatment variant increased by about 130 K after irradiation at 573 K up to 5 dpa. Moreover, the shifts in ORNL9Cr-2WVTa and JLF-1 steels were much smaller, and the differences could not be interpreted as an effect of irradiation hardening. The precipitation behavior of the irradiated steels was examined by weight analysis and X-ray diffraction analysis on extraction residues, and SEM/EDS analysis was performed on extraction replica samples and fracture surfaces. These analyses suggested that the difference in the extent of DBTT shift could be explained by (1) smaller irradiation hardening at low test temperatures caused by irradiation-induced lath structure recovery (in JLF-1), and (2) the fracture stress increase caused by the irradiation-induced over-solution of Ta (in ORNL9Cr-2WVTa).

  11. Effect of microstructural evolution by isothermal aging on the mechanical properties of 9Cr-1WVTa reduced activation ferritic/martensitic steels

    NASA Astrophysics Data System (ADS)

    Park, Min-Gu; Lee, Chang-Hoon; Moon, Joonoh; Park, Jun Young; Lee, Tae-Ho; Kang, Namhyun; Chan Kim, Hyoung

    2017-03-01

    The influence of microstructural changes caused by aging condition on tensile and Charpy impact properties was investigated for reduced activation ferritic-martensitic (RAFM) 9Cr-1WVTa steels having single martensite and a mixed microstructure of martensite and ferrite. For the mixed microstructure of martensite and ferrite, the Charpy impact properties deteriorated in both as-normalized and tempered conditions due to the ferrite and the accompanying M23C6 carbides at the ferrite grain boundaries which act as path and initiation sites for cleavage cracks, respectively. However, aging at 550 °C for 20-100 h recovered gradually the Charpy impact toughness without any distinct drop in strength, as a result of the spheroidization of the coarse M23C6 carbides at the ferrite grain boundaries, which makes crack initiation more difficult.

  12. Microstructural analysis of ferritic-martensitic steels irradiated at low temperature in HFIR

    SciTech Connect

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

    1998-09-01

    Disk specimens of ferritic-martensitic steel, HT9 and F82H, irradiated to damage levels of {approximately}3 dpa at irradiation temperatures of either {approximately}90 C or {approximately}250 C have been investigated by using transmission electron microscopy. Before irradiation, tempered HT9 contained only M{sub 23}C{sub 6} carbide. Irradiation at 90 C and 250 C induced a dislocation loop density of 1 {times} 10{sup 22} m{sup {minus}3} and 8 {times} 10{sup 21} m{sup {minus}3}, respectively. in the HT9 irradiated at 250 C, a radiation-induced phase, tentatively identified as {alpha}{prime}, was observed with a number density of less than 1 {times} 10{sup 20} m{sup {minus}3}. On the other hand, the tempered F82H contained M{sub 23}C{sub 6} and a few MC carbides; irradiation at 250 C to 3 dpa caused minor changes in these precipitates and induced a dislocation loop density of 2 {times} 10{sup 22} m{sup {minus}3}. Difference in the radiation-induced phase and the loop microstructure may be related to differences in the post-yield deformation behavior of the two steels.

  13. Void swelling in high dose ion-irradiated reduced activation ferritic-martensitic steels

    NASA Astrophysics Data System (ADS)

    Wang, Xu; Monterrosa, Anthony M.; Zhang, Feifei; Huang, Hao; Yan, Qingzhi; Jiao, Zhijie; Was, Gary S.; Wang, Lumin

    2015-07-01

    To determine the void swelling resistance of reduced-activation ferritic-martensitic steels CNS I and CNS II at high doses, ion irradiation was performed up to 188 dpa (4.6 × 1017 ion/cm2) at 460 °C using 5 MeV Fe++ ions. Helium was pre-implanted at levels of 10 and 100 appm at room temperature to investigate the role of helium on void swelling. Commercial FM steel T91 was also irradiated in this condition and the swelling results are of included in this paper as a reference. Voids were observed in all conditions. The 9Cr CNS I samples implanted with 10 appm helium exhibited lower swelling than 9Cr T91 irradiated at the same condition. The 12Cr CNS II with 10 and 100 appm helium showed significantly lower swelling than CNS I and T91. The swelling rate for CNS I and CNS II were determined to be 0.02%/dpa and 0.003%/dpa respectively. Increasing the helium content from 10 to 100 appm shortened the incubation region and increased the void density but had no effect on the swelling rates.

  14. Parametric study of irradiation effects on the ductile damage and flow stress behavior in ferritic-martensitic steels

    NASA Astrophysics Data System (ADS)

    Chakraborty, Pritam; Biner, S. Bulent

    2015-10-01

    Ferritic-martensitic steels are currently being considered as structural materials in fusion and Gen-IV nuclear reactors. These materials are expected to experience high dose radiation, which can increase their ductile to brittle transition temperature and susceptibility to failure during operation. Hence, to estimate the safe operational life of the reactors, precise evaluation of the ductile to brittle transition temperatures of ferritic-martensitic steels is necessary. Owing to the scarcity of irradiated samples, particularly at high dose levels, micro-mechanistic models are being employed to predict the shifts in the ductile to brittle transition temperatures. These models consider the ductile damage evolution, in the form of nucleation, growth and coalescence of voids; and the brittle fracture, in the form of probabilistic cleavage initiation, to estimate the influence of irradiation on the ductile to brittle transition temperature. However, the assessment of irradiation dependent material parameters is challenging and influences the accuracy of these models. In the present study, the effects of irradiation on the overall flow stress and ductile damage behavior of two ferritic-martensitic steels is parametrically investigated. The results indicate that the ductile damage model parameters are mostly insensitive to irradiation levels at higher dose levels though the resulting flow stress behavior varies significantly.

  15. Effect of V and Ta on the precipitation behavior of 12%Cr reduced activation ferrite/martensite steel

    SciTech Connect

    Xiao, Xiang; Liu, Guoquan; Hu, Benfu; Wang, Jinsan; Ullah, Asad

    2013-08-15

    12%Cr reduced activation ferrite/martensite steels are promising candidate materials for good corrosion and irradiation resistance used for supercritical water-cooled reactor cladding and in-core components. V and Ta are considered to have improved the creep strength of high Cr steels by precipitating as MX phase. In this paper, a series of trial products microalloyed with V and V–Ta are produced, and the microstructure is characterized after quenching at 1050 °C and tempering at 780 °C by using TEM method to investigate the effect of these elements on the precipitation behavior of 12%Cr reduced activation ferrite/martensite steel. The results from both the experimental observations and thermodynamic and kinetic calculations reveal that V and V–Ta can promote the stable MX precipitation instead of M{sub 2}X, thus increasing the volume fraction of M{sub 23}C{sub 6}. Two-phase separation behavior of the (Ta, V)(C, N) carbonitride into a Ta(V)C(N) phase and a V(Ta)N(C) phase in 12Cr3WVTa steel is observed and further discussed. - Highlights: • Microalloyed with V and V-Ta can promote the precipitation of MX instead of M{sub 2}X. • The presence of delta-ferrite in microstructure affects the morphology of MX. • Two-phase separation of MX carbonitride was observed in 12Cr3WVTa steel.

  16. Diffusion Bonding Beryllium to Reduced Activation Ferritic Martensitic Steel: Development of Processes and Techniques

    NASA Astrophysics Data System (ADS)

    Hunt, Ryan Matthew

    Only a few materials are suitable to act as armor layers against the thermal and particle loads produced by magnetically confined fusion. These candidates include beryllium, tungsten, and carbon fiber composites. The armor layers must be joined to the plasma facing components with high strength bonds that can withstand the thermal stresses resulting from differential thermal expansion. While specific joints have been developed for use in ITER (an experimental reactor in France), including beryllium to CuCrZr as well as tungsten to stainless steel interfaces, joints specific to commercially relevant fusion reactors are not as well established. Commercial first wall components will likely be constructed front Reduced Activation Ferritic Martensitic (RAFM) steel, which will need to be coating with one of the three candidate materials. Of the candidates, beryllium is particularly difficult to bond, because it reacts during bonding with most elements to form brittle intermetallic compounds. This brittleness is unacceptable, as it can lead to interface crack propagation and delamination of the armor layer. I have attempted to overcome the brittle behavior of beryllium bonds by developing a diffusion bonding process of beryllium to RAFM steel that achieves a higher degree of ductility. This process utilized two bonding aids to achieve a robust bond: a. copper interlayer to add ductility to the joint, and a titanium interlayer to prevent beryllium from forming unwanted Be-Cu intermetallics. In addition, I conducted a series of numerical simulations to predict the effect of these bonding aids on the residual stress in the interface. Lastly, I fabricated and characterized beryllium to ferritic steel diffusion bonds using various bonding parameters and bonding aids. Through the above research, I developed a process to diffusion bond beryllium to ferritic steel with a 150 M Pa tensile strength and 168 M Pa shear strength. This strength was achieved using a Hot Isostatic

  17. Development of next generation tempered and ODS reduced activation ferritic/martensitic steels for fusion energy applications

    NASA Astrophysics Data System (ADS)

    Zinkle, S. J.; Boutard, J. L.; Hoelzer, D. T.; Kimura, A.; Lindau, R.; Odette, G. R.; Rieth, M.; Tan, L.; Tanigawa, H.

    2017-09-01

    Reduced activation ferritic/martensitic steels are currently the most technologically mature option for the structural material of proposed fusion energy reactors. Advanced next-generation higher performance steels offer the opportunity for improvements in fusion reactor operational lifetime and reliability, superior neutron radiation damage resistance, higher thermodynamic efficiency, and reduced construction costs. The two main strategies for developing improved steels for fusion energy applications are based on (1) an evolutionary pathway using computational thermodynamics modelling and modified thermomechanical treatments (TMT) to produce higher performance reduced activation ferritic/martensitic (RAFM) steels and (2) a higher risk, potentially higher payoff approach based on powder metallurgy techniques to produce very high strength oxide dispersion strengthened (ODS) steels capable of operation to very high temperatures and with potentially very high resistance to fusion neutron-induced property degradation. The current development status of these next-generation high performance steels is summarized, and research and development challenges for the successful development of these materials are outlined. Material properties including temperature-dependent uniaxial yield strengths, tensile elongations, high-temperature thermal creep, Charpy impact ductile to brittle transient temperature (DBTT) and fracture toughness behaviour, and neutron irradiation-induced low-temperature hardening and embrittlement and intermediate-temperature volumetric void swelling (including effects associated with fusion-relevant helium and hydrogen generation) are described for research heats of the new steels.

  18. Development of next generation tempered and ODS reduced activation ferritic/martensitic steels for fusion energy applications

    DOE PAGES

    Zinkle, S. J.; Boutard, J. L.; Hoelzer, D. T.; ...

    2017-06-09

    Reduced activation ferritic/martensitic steels are currently the most technologically mature option for the structural material of proposed fusion energy reactors. Advanced next-generation higher performance steels offer the opportunity for improvements in fusion reactor operational lifetime and reliability, superior neutron radiation damage resistance, higher thermodynamic efficiency, and reduced construction costs. The two main strategies for developing improved steels for fusion energy applications are based on (1) an evolutionary pathway using computational thermodynamics modelling and modified thermomechanical treatments (TMT) to produce higher performance reduced activation ferritic/martensitic (RAFM) steels and (2) a higher risk, potentially higher payoff approach based on powder metallurgy techniquesmore » to produce very high strength oxide dispersion strengthened (ODS) steels capable of operation to very high temperatures and with potentially very high resistance to fusion neutron-induced property degradation. The current development status of these next-generation high performance steels is summarized, and research and development challenges for the successful development of these materials are outlined. In conclusion, material properties including temperature-dependent uniaxial yield strengths, tensile elongations, high-temperature thermal creep, Charpy impact ductile to brittle transient temperature (DBTT) and fracture toughness behaviour, and neutron irradiation-induced low-temperature hardening and embrittlement and intermediate-temperature volumetric void swelling (including effects associated with fusion-relevant helium and hydrogen generation) are described for research heats of the new steels.« less

  19. Irradiation performance of 9--12 Cr ferritic/martensitic stainless steels and their potential for in-core application in LWRs

    SciTech Connect

    Jones, R.H.; Gelles, D.S.

    1993-08-01

    Ferritic-martensitic stainless steels exhibit radiation stability and stress corrosion resistance that make them attractive replacement materials for austenitic stainless steels for in-core applications. Recent radiation studies have demonstrated that 9% Cr ferritic/martensitic stainless steel had less than a 30C shift in ductile-to-brittle transition temperature (DBTT) following irradiation at 365C to a dose of 14 dpa. These steels also exhibit very low swelling rates, a result of the microstructural stability of these alloys during radiation. The 9 to 12% Cr alloys to also exhibit excellent corrosion and stress corrosion resistance in out-of-core applications. Demonstration of the applicability of ferritic/martensitic stainless steels for in-core LWR application will require verification of the irradiation assisted stress corrosion cracking behavior, measurement of DBTT following irradiation at 288C, and corrosion rates measurements for in-core water chemistry.

  20. Ion-irradiation-induced microstructural modifications in ferritic/martensitic steel T91

    NASA Astrophysics Data System (ADS)

    Liu, Xiang; Miao, Yinbin; Li, Meimei; Kirk, Marquis A.; Maloy, Stuart A.; Stubbins, James F.

    2017-07-01

    In this paper, in situ transmission electron microscopy investigations were carried out to study the microstructural evolution of ferritic/martensitic steel T91 under 1 MeV Krypton ion irradiation up to 4.2 × 1015 ions/cm2 at 573 K, 673 K, and 773 K. At 573 K, grown-in defects are strongly modified by black-dot loops, and dislocation networks together with black-dot loops were observed after irradiation. At 673 K and 773 K, grown-in defects are only partially modified by dislocation loops; isolated loops and dislocation segments were commonly found after irradiation. Post irradiation examination indicates that at 4.2 × 1015 ions/cm2, about 51% of the loops were a0 / 2 < 111 > type for the 673 K irradiation, and the dominant loop type was a0 < 100 > for the 773 K irradiation. Finally, a dispersed barrier hardening model was employed to estimate the change in yield strength, and the calculated ion data were found to follow the similar trend as the existing neutron data with an offset of 100-150 MPa.

  1. The development of ferritic-martensitic steels with reduced long-term activation

    NASA Astrophysics Data System (ADS)

    Ehrlich, K.; Kelzenberg, S.; Röhrig, H.-D.; Schäfer, L.; Schirra, M.

    1994-09-01

    Ferritic-martensitic 9-12% CrMoVNb steels of MANET type possess a number of advantageous properties for fusion reactor application. Their optimization has led to improved creep and fracture-toughness properties. New 9-10% CrWVTa alloys have been developed by KfK/IMF in collaboration with the SAARSTAHL GmbH which have a reduced long-term activation and show in addition superior fracture toughness properties. The calculation of dose rate and other radiological parameters with the presently available FISPACT/EAF codes, extended by KfK files for sequential reactions has shown that the long-term dose-rate in these alloys is governed by the remaining 'impurity level' of Nb and the alloying elements W and Ta. Sequential reactions — though relevant for single alloying elements like Cr, Mn, V and N — provide only a second order effect in Fe-based alloys. A challenge for the future materials development is the production of alloys with the desired narrow specification of elements and impurities, which necessitates new ways of steelmaking.

  2. A reassessment of the effects of helium on Charpy impact properties of ferritic/martensitic steels

    SciTech Connect

    Gelles, D.S.; Hamilton, M.L.; Hankin, G.L.

    1998-03-01

    To test the effect of helium on Charpy impact properties of ferritic/martensitic steels, two approaches are reviewed: quantification of results of tests performed on specimens irradiated in reactors with very different neutron spectra, and isotopic tailoring experiments. Data analysis can show that if the differences in reactor response are indeed due to helium effects, then irradiation in a fusion machine at 400 C to 100 dpa and 1000 appm He will result in a ductile to brittle transition temperature shift of over 500 C. However, the response as a function of dose and helium level is unlikely to be simply due to helium based on physical reasoning. Shear punch tests and microstructural examinations also support this conclusion based on irradiated samples of a series of alloys made by adding various isotopes of nickel in order to vary the production of helium during irradiation in HFIR. The addition of nickel at any isotopic balance to the Fe-12Cr base alloy significantly increased the shear yield and maximum strengths of the alloys. However, helium itself, up to 75 appm at over 7 dpa appears to have little effect on the mechanical properties of the alloys. This behavior is instead understood to result from complex precipitation response. The database for effects of helium on embrittlement based on nickel additions is therefore probably misleading and experiments should be redesigned to avoid nickel precipitation.

  3. Using nonlinear ultrasound measurements to track thermal aging in modified 9%Cr ferritic martensitic steel

    NASA Astrophysics Data System (ADS)

    Marino, Daniel; Kim, Jin-Yeon; Jacobs, Laurence J.; Ruiz, Alberto; Joo, Young-Sang

    2015-03-01

    This study investigates early thermal aging in 9%Cr ferritic martensitic (FM) steel, which is caused by the formation of second phases during high temperature exposure. This study employs a recently developed nonlinear ultrasonic technique to explore the sensitivity of the nonlinearity parameter. Experimental results show that the nonlinearity parameter is sensitive to certain changes in material's properties such as thermal embrittlement and hardness changes; therefore, it can be used as an indicator of the thermal damage. The specimens investigated are heat treated for different holding times ranging from 200h to 3000h at 650°C. Nonlinear ultrasonic experiments are conducted for each specimen using a wedge transducer to generate and an air-coupled transducer to detect Raleigh surface waves. The amplitudes of the first and second order harmonics are measured at different propagation distances and these amplitudes are used to obtain the relative nonlinearity parameter for each specimen with a different holding time. The nonlinear ultrasonic results are compared with independent mechanical measurements and metallographic images. This research proposes the nonlinear ultrasonic technique as a nondestructive evaluation tool not only to detect thermal damage in early stages, and also to qualitatively assess the stage of thermal damage.

  4. A review of some effects of helium on charpy impact properties of ferritic/martensitic steels

    NASA Astrophysics Data System (ADS)

    Gelles, D. S.; Hankin, G. L.; Hamilton, M. L.

    1998-10-01

    To evaluate the effect of helium on Charpy impact properties of ferritic/martensitic steels, two approaches are reviewed: quantification of results of earlier tests performed by other researchers on specimens irradiated in reactors with very different neutron spectra, and evaluation of isotopic tailoring experiments. Data analysis can show that if the differences in reactor response are indeed due to helium effects, then irradiation in a fusion machine at 400°C to 100 dpa and 1000 appm He will result in a ductile-to-brittle transition temperature (DBTT) shift of over 500°C. However, it can be shown that the response as a function of dose and helium level is unlikely to be simply due to helium based on physical reasoning. Shear punch tests and microstructural examinations support this conclusion based on irradiated samples of a series of alloys made by adding various isotopes of nickel in order to vary the production of helium during irradiation in High Flux Isotope Reactor (HFIR). The addition of nickel at any isotopic balance to the Fe-12Cr base alloy significantly increased the shear yield and maximum strengths of the alloys. However, helium itself, up to 75 appm at over 7 dpa appears to have little effect on the mechanical properties of the alloys. This behavior is instead understood to result from complex precipitation response. The database for effects of helium on embrittlement based on nickel additions is therefore probably misleading and experiments should be redesigned to avoid nickel precipitation.

  5. In-beam fatigue of a ferritic-martensitic steel. First results

    NASA Astrophysics Data System (ADS)

    Marmy, P.

    1994-09-01

    Due to its pulsed operation mode, a fusion device will have to sustain thermal stresses and at the same time be exposed to a flux of 14 MeV neutrons. In order to simulate this irradiation condition, a new irradiation device has been developed, in which the specimen can be stress and strain-controlled during the irradiation. For the simulation of the fusion neutrons, a 590 MeV proton beam is used. This type of particle produces from spallation reactions the displacement damage and the helium typical of fusion neutrons in the material. The influence of the in situ deformation on the low cycle fatigue of a 12% Cr ferritic-martensitic steel (MANET II) has been investigated. The results are compared with results from non-irradiated specimens and from specimens tested after irradiation to the same end-of-life fluence. The effects of the different conditions are reported for a temperature TTest = TIrr = 573 K and a total imposed strain of 0.7%.

  6. High Strain Fatigue Properties of the F82H Ferritic-Martensitic Steel under Proton Irradiation.

    SciTech Connect

    Marmy, P; Oliver, Brian M. )

    2003-05-15

    During the up and down cycles of a fusion reactor, the first wall is exposed concomitantly to a flux of energetic neutrons that generates radiation defects and to a neutron thermal flux that induces thermal stresses. The resulting strains may exceed the elastic limit and induce a plastic deformation in the material. A similar situation occurs in the window of a spallation liquid source target and results in the same type of damage. This particular loading has been simulated in F82H martensitic ferritic steel, using a device allowing a fatigue test to be carried out during irradiation with 590 MeV protons. All fatigue tests were carried out at 300?C, in a strain controlled test at strain levels around 0.8%. Two different signals have been used: a fully symmetrical triangle wave signal (R=-1) and a triangle ramp with 2 min tension holds. The fatigue was investigated under three different conditions: unirradiated , irradiated and post irradiation tested, and finally in beam tested. The main result is that the in beam tested specimens have the lowest life as compared to the post irradiation tested specimens and unirradiated specimens. Hydrogen is suspected to be the main contributor to the observed embrittlement.

  7. High strain fatigue properties of F82H ferritic martensitic steel under proton irradiation

    NASA Astrophysics Data System (ADS)

    Marmy, P.; Oliver, B. M.

    2003-05-01

    During the up and down cycles of a fusion reactor, the first wall is exposed concomitantly to a flux of energetic neutrons that generates radiation defects and to a thermal flux that induces thermal stresses. The resulting strains may exceed the elastic limit and induce plastic deformation in the material. A similar situation occurs in the window of a spallation liquid source target and results in the same type of damage. This particular loading has been simulated in F82H ferritic-martensitic steel, using a device allowing a fatigue test to be carried out during irradiation with 590 MeV protons. All fatigue tests were carried out in a strain controlled test at strain levels around 0.8% and at 300 °C. Two different signals have been used: a fully symmetrical triangle wave signal ( R=-1) and a triangle ramp with 2 min tension holds. The fatigue was investigated under three different conditions: unirradiated, irradiated and post-irradiation tested, and finally in-beam tested. The main result is that the in-beam tested specimens have the lowest life as compared to the post-irradiation tested specimen and unirradiated specimen. Hydrogen is suspected to be the main contributor to the observed embrittlement.

  8. Formation and Oxidation Performance of Low-Temperature Pack Aluminide Coatings on Ferritic-Martensitic Steels

    SciTech Connect

    Bates, Brian; Wang, Y. Q.; Zhang, Ying; Pint, Bruce A

    2009-01-01

    A pack cementation process was developed to coat commercial 9% Cr ferritic-martensitic steel T91 at temperatures below its normal tempering temperature to avoid any potential detrimental effect on the mechanical properties of the coated alloy. In order to prevent the formation of Fe{sub 2}Al{sub 5} coatings, the Al activity in the pack cementation process was reduced by substituting the pure Al masteralloy with binary Cr-Al masteralloys containing either 15 or 25 wt.% Al. When the Cr-25Al masteralloy was used, a duplex coating was formed at 700 C, consisting of a thin Fe{sub 2}Al{sub 5} outer layer and an inner layer of FeAl. With the Cr-15Al masteralloy, an FeAl coating of {approx} 12 {micro}m thick was achieved at 700 C. The pack aluminide coatings fabricated at 700 C are being evaluated in air + 10 vol.% H{sub 2}O at 650 C and 700 C to determine their long-term oxidation performance.

  9. Microscale deformation of a tempered martensite ferritic steel: Modelling and experimental study of grain and sub-grain interactions

    NASA Astrophysics Data System (ADS)

    Golden, Brian J.; Li, Dong-Feng; Guo, Yina; Tiernan, Peter; Leen, Sean B.; O'Dowd, Noel P.

    2016-01-01

    In this paper, a finite-element modelling framework is presented with explicit representation of polycrystalline microstructure for a tempered martensite ferritic steel. A miniature notched specimen was manufactured from P91 steel with a 20,000 h service history and tested at room temperature under three point bending. Deformation at the microscale is quantified by electron back scattered diffraction (EBSD) before and after mechanical loading. A representative volume element was developed, based on the initial EBSD scan, and a crystal plasticity model used to account for slip-based inelastic deformation in the material. The model showed excellent correlation with the experimental data when the relevant comparisons were made.

  10. Fractographic examination of reduced activation ferritic/martensitic steel charpy specimens irradiated to 30 dpa at 370{degrees}C

    SciTech Connect

    Gelles, D.S.; Hamilton, M.L.; Schubert, L.E.

    1996-10-01

    Fractographic examinations are reported for a series of reduced activation ferritic/Martensitic steel Charpy impact specimens tested following irradiation to 30 dpa at 370{degrees}C in FFTF. One-third size specimens of six low activation steels developed for potential application as structural materials in fusion reactors were examined. A shift in brittle fracture appearance from cleavage to grain boundary failure was noted with increasing manganese content. The results are interpreted in light of transmutation induced composition changes in a fusion environment.

  11. Phase transformation and impact properties in the experimentally simulated weld heat-affected zone of a reduced activation ferritic/martensitic steel

    NASA Astrophysics Data System (ADS)

    Moon, Joonoh; Lee, Chang-Hoon; Lee, Tae-Ho; Jang, Min-Ho; Park, Min-Gu; Han, Heung Nam

    2014-12-01

    In this work, the phase transformation and impact properties in the weld heat-affected zone (HAZ) of a reduced activation ferritic/martensitic (RAFM) steel are investigated. The HAZs were experimentally simulated using a Gleeble simulator. The base steel consisted of tempered martensite through normalizing at 1000 °C and tempering at 750 °C, while the HAZs consisted of martensite, δ-ferrite and a small volume of autotempered martensite. The impact properties using a Charpy V-notch impact test revealed that the HAZs showed poor impact properties due to the formation of martensite and δ-ferrite as compared with the base steel. In addition, the impact properties of the HAZs further deteriorated with an increase in the δ-ferrite fraction caused by increasing the peak temperature. The impact properties of the HAZs could be improved through the formation of tempered martensite after post weld heat treatment (PWHT), but they remained lower than that of the base steel because the δ-ferrite remained in the tempered HAZs.

  12. Effect of Austenization Temperature on the Microstructure and Strength of 9% and 12% Cr Ferritic-Martensitic Steels

    SciTech Connect

    Terry C. Totemeier

    2004-10-01

    The effect of reduced-temperature austenization on the microstructure and strength of two ferritic-martensitic steels was studied. Prototypic 9% and 12% Cr steels, grade 91 (9Cr-1MoVNb) and type 422 stainless (12Cr-1MoVW), respectively, were austenized at 925°C and 1050°C and tempered at 760°C. The reduced austenization temperature was intended to simulate potential inadequate austenization during field construction of large structures and also the thermal cycle experienced in the Type IV region of weld heat affected zones (HAZ). The microstructure, tensile behavior, and creep strength were characterized for both steels treated at each condition. The reduced austenization temperature resulted in general coarsening of carbides in both steels and polygonization of the tempered martensite structure in type 422. For this steel, a marked reduction in microhardness was observed, while there was little change in microhardness for grade 91. Slight reductions in tensile strength were observed for both steels at room temperature and elevated temperatures of 450 and 550°C. The strength reduction was greater for type 422 than for grade 91. At 650°C the tensile strength reduction was minimal for both steels. Marked reductions in creep rupture lives were observed for both steels at 650°C; the reductions were less at 600°C and minimal at 550°C. Overall, the higher Cr content steel was observed to be more sensitive to variations in heat treatment conditions.

  13. Corrosion and Stress Corrosion Cracking of High Cr Ferritic-Martensitic Steels in Supercritical Water

    SciTech Connect

    Jinsung, Jang; Seong Sik, Hwang; Chang Hee, Han; Byung Hak, Lee

    2006-07-01

    Corrosion behavior of the F-M (ferritic-martensitic) steels (T91, T92, T122) and Fe-base ODS (oxide dispersion strengthened) alloy (MA956{sup TM}) were evaluated in an aerated (8 ppm D.O.) SCW (supercritical water) at the temperature range between 300 and 627 deg C under 25 MPa. In aerated SCW the weight change of the F-M steel specimens became greater as the test temperature increased. However, the extent of the weight change at 350 deg C, just below the critical temperature appeared not to be less than those at 550 deg C. And the weight changes of all the F-M steel specimens in the deaerated SCW (for 347 hrs in 100 ppb D.O. for 347 hrs, and in 10 ppb D.O. for 432 hrs) tended to converge to about 1 mgcm{sup -2}. In aerated or deaerated conditions 20Cr Fe-base ODS alloy appeared to be very resistant to a SCW corrosion at all the test temperatures up to 500 hrs. Stress corrosion cracking (SCC) behavior of 9Cr F-M steels (T91 and T92) was investigated by CERT (Constant Extension Rate Test) in SCW at various temperatures and D.O. levels with different strain rates. T91 did not show any evidence of a SCC in a fully deaerated (below 10 ppb D.O.) SCW at 500, 550, and 600 deg C at the test conditions. T92 specimens were tested at 500 deg C in SCW with different D.O. levels. The strain rate did not seem to affect the SCC behavior of the T92 steel, but D.O. in SCW seems to affect the SCC behavior to some extent. The total elongation of T92 in SCW of 100 ppb or of 500 ppb D.O. was significantly smaller than that at a fully deaerated (below 10 ppb D.O.) SCW (about 15 vs. 20%), and it appears to provide a clue to a SCC on the fracture surface after the CERT test. (authors)

  14. HEAT INPUT AND POST WELD HEAT TREATMENT EFFECTS ON REDUCED-ACTIVATION FERRITIC/MARTENSITIC STEEL FRICTION STIR WELDS

    SciTech Connect

    Tang, Wei; Chen, Gaoqiang; Chen, Jian; Yu, Xinghua; Frederick, David Alan; Feng, Zhili

    2015-01-01

    Reduced-activation ferritic/martensitic (RAFM) steels are an important class of structural materials for fusion reactor internals developed in recent years because of their improved irradiation resistance. However, they can suffer from welding induced property degradations. In this paper, a solid phase joining technology friction stir welding (FSW) was adopted to join a RAFM steel Eurofer 97 and different FSW parameters/heat input were chosen to produce welds. FSW response parameters, joint microstructures and microhardness were investigated to reveal relationships among welding heat input, weld structure characterization and mechanical properties. In general, FSW heat input results in high hardness inside the stir zone mostly due to a martensitic transformation. It is possible to produce friction stir welds similar to but not with exactly the same base metal hardness when using low power input because of other hardening mechanisms. Further, post weld heat treatment (PWHT) is a very effective way to reduce FSW stir zone hardness values.

  15. Fracture mechanisms in dual phase steels based on the acicular ferrite + martensite/austenite microstructure

    NASA Astrophysics Data System (ADS)

    Poruks, Peter

    The fracture mechanisms of low carbon microalloyed plate steels based on the acicular ferrite + marten site/austenite microstructure (AF + M/A) are investigated. The final microstructure consists of a dispersed phase of submicron equi-axed martensite particles with a bainitic ferrite matrix. A series of plates with M/A volume fractions of 0.076--0.179 are studied. Brittle fracture is investigated by Instrumented Charpy impact testing of samples at -196°C and subsequent metallography. The M/A particles are identified as the crack nucleation sites and the cleavage fracture stress calculated to be 2400 MPa in a complete AF microstrucuture. This value is significantly larger than in steels that contain significant proportions of conventional bainite. Standard Charpy and Instrumented Charpy impact testing is conducted through a temperature range from -80 to + 22°C to study ductile fracture behaviour. The total absorbed energy is separated into energies of crack nucleation and of crack propagation. It is found that the energy of crack nucleation is weakly dependent on the volume fraction of M/A and completely independent of temperature over the range studied. The crack propagation energy varies significantly with both variables, decreasing with increased volume fraction of M/A and with decreasing temperature. The peak load in the instrumented Charpy data is used to calculate the dynamic fracture toughness, KId, which is found to be 105--120 MPa-m1/2. The void nucleation and void growth stages of ductile fracture are studied by metallographic examination of tensile bars. The sites of void nucleation are identified as inclusions and M/A particles. Voids nucleate at the M/A particles by decohesion of the particle-matrix interface. A constant void nucleation strain of epsilon = 0.90 +/- 0.05 is measured for all of the samples independent of the volume fraction of M/A. A stress-based criterion is used to predict void nucleation and the interface strength is determined to be

  16. Gap Analysis of Material Properties Data for Ferritic/Martensitic HT-9 Steel

    SciTech Connect

    Brown, Neil R.; Serrano De Caro, Magdalena; Rodriguez, Edward A.

    2012-08-28

    The US Department of Energy (DOE), Office of Nuclear Energy (NE), is supporting the development of an ASME Code Case for adoption of 12Cr-1Mo-VW ferritic/martensitic (F/M) steel, commonly known as HT-9, primarily for use in elevated temperature design of liquid-metal fast reactors (LMFR) and components. In 2011, Los Alamos National Laboratory (LANL) nuclear engineering staff began assisting in the development of a small modular reactor (SMR) design concept, previously known as the Hyperion Module, now called the Gen4 Module. LANL staff immediately proposed HT-9 for the reactor vessel and components, as well as fuel clad and ducting, due to its superior thermal qualities. Although the ASME material Code Case, for adoption of HT-9 as an approved elevated temperature material for LMFR service, is the ultimate goal of this project, there are several key deliverables that must first be successfully accomplished. The most important key deliverable is the research, accumulation, and documentation of specific material parameters; physical, mechanical, and environmental, which becomes the basis for an ASME Code Case. Time-independent tensile and ductility data and time-dependent creep and creep-rupture behavior are some of the material properties required for a successful ASME Code case. Although this report provides a cursory review of the available data, a much more comprehensive study of open-source data would be necessary. This report serves three purposes: (a) provides a list of already existing material data information that could ultimately be made available to the ASME Code, (b) determines the HT-9 material properties data missing from available sources that would be required and (c) estimates the necessary material testing required to close the gap. Ultimately, the gap analysis demonstrates that certain material properties testing will be required to fulfill the necessary information package for an ASME Code Case.

  17. Annealing effects on the microstructure and coercive field of two ferritic-martensitic Eurofer steels: A comparative study

    NASA Astrophysics Data System (ADS)

    Oliveira, V. B.; Sandim, M. J. R.; Stamopoulos, D.; Renzetti, R. A.; Santos, A. D.; Sandim, H. R. Z.

    2013-04-01

    Reduced-activation ferritic-martensitic steels are promising candidates for structural applications in future nuclear fusion power plants. Oxide dispersion strengthened ODS-Eurofer and Eurofer 97 steels were cold rolled to 80% reduction in thickness and annealed in vacuum for 1 h from 200 to 1350 °C to evaluate both their thermal stability and magnetic behavior. The microstructural changes were followed by magnetic measurements, in particular the corresponding variation of the coercive field (Hc), as a function of both annealing and tempering treatments. Results show that Y2O3 nanoparticles strongly affect the mechanical properties of ODS-Eurofer steel but leave their magnetic properties fairly unchanged when compared with Eurofer-97 steel.

  18. Oxidation behavior of ferritic/martensitic steels in stagnant liquid LBE saturated by oxygen at 600 °C

    NASA Astrophysics Data System (ADS)

    Shi, Quanqiang; Liu, Jian; Luan, He; Yang, Zhenguo; Wang, Wei; Yan, Wei; Shan, Yiyin; Yang, Ke

    2015-02-01

    Ferritic/martensitic (F/M) steels are primary candidates for application as cladding and structural materials in the Generation IV Nuclear Reactor, especially accelerator driven sub-critical system (ADS). The compatibility of F/M steels with liquid lead-bismuth eutectic (LBE) is a critical issue for development of ADS using liquid LBE as the coolant. In this work, the corrosion tests of two F/M steels, including a novel 9-12 Cr modified F/M steel named SIMP steel and a commercial T91 steel, were conducted in the static oxygen-saturated liquid LBE at 600 °C up to 1000 h, the microstructure of the oxide scale formed on these two steels was analyzed, the relationship between the microstructure and the oxidation behavior was studied, and the reason why the SIMP steel showed better oxidation resistance compared to T91 steel was analyzed. The results of this study confirmed that the oxidation behavior of the F/M steels in liquid metals is influenced by their alloying elements and microstructures.

  19. IRRADIATION CREEP AND MECHANICAL PROPERTIES OF TWO FERRITIC-MARTENSITIC STEELS IRRADIATED IN THE BN-350 FAST REACTOR

    SciTech Connect

    Porollo, S. I.; Konobeev, Yu V.; Dvoriashin, A. M.; Budylkin, N. I.; Mironova, E. G.; Leontyeva-Smirnova, M. V.; Loltukhovsky, A. G.; Bochvar, A. A.; Garner, Francis A.

    2002-09-01

    Russian ferritic/martensitic steels EP-450 and EP-823 were irradiated to 20-60 dpa in the BN-350 fast reactor in the form of pressurized creep tubes and small rings used for mechanical property tests. Data derived from these steels serves to enhance our understanding of the general behavior of this class of steels. It appears that these steels exhibit behavior that is very consistent with that of Western steels. Swelling is relatively low at high neutron exposure and confined to temperatures less then 420 degrees C, but may be camouflaged somewhat by precipitation-related densification. The irradiation creep studies confirm that the creep compliance of F/M steels is about one-half that of austenitic steels, and that the loss of strength at test temperatures above 500 degrees C is a problem generic to all F/M steels. This conclusion is supported by post-irradiation measurement of short-term mechanical properties. At temperatures below 500 degrees C both steels retain their high strength (yield stress 0.2=550-600 MPa), but at higher test temperatures a sharp decrease of strength properties occurs. However, the irradiated steels still retain high post-irradiation ductility at test temperatures in the range of 20-700 degrees C.

  20. Oxidation kinetics and mechanisms in HT-9 ferritic/martensitic stainless steel

    NASA Astrophysics Data System (ADS)

    Benitez Velez, Soraya

    Lead and lead alloys, such as lead bismuth eutectic (LBE), have gained worldwide recognition as potential candidates for coolant and target material in accelerator-driven systems (ADS) due to their excellent chemical, physical, and nuclear properties; however, they are corrosive to stainless steels, which are candidate materials for piping and molten metal containers in ADS applications. The Russians have used LBE as a coolant in their nuclear submarines for more than several decades and their experience has given way to the hypothesis that oxides protect steels from LBE corrosion, thus renewing interest in further understanding the oxidation kinetics and mechanisms of candidate stainless steel alloys. The proposed work will contribute to the ongoing research effort by elucidating the oxidation kinetics and mechanisms, and characterizing the oxides of HT-9, a candidate stainless steel for ADS application. HT-9 (DIN X20CrMoWV12 or Fe-12Cr-MoVW) is a 12 wt% Cr martensitic/ferritic stainless steel alloy developed by Sandvik (Sweden). The approach is to perform thermogravimetric analysis (TGA) to evaluate the oxidation kinetics and assess oxidation rates. Flat bar samples polished to one micron were subjected to non-isothermal and isothermal oxidation scans. Non-isothermal scans were done in dry air from room temperature to 950°C with ramping rates of 2°C/minute and 5°C/minute to obtain preliminary oxidation behavior information. Isothermal scans were done in dry air from 600°C to 800°C for 48 hours, from 800°C to 900°C for 24 hours, and at 950°C for 6 hours. The structure and composition of the oxide film developed during the isothermal scans were characterized using scanning electron microscopy with energy dispersive spectroscopy capabilities (SEM/EDS) and X-ray diffraction (XRD). Oxidation of HT-9 exhibited a complex behavior that does not follow a simple oxidation model and changes as a function of exposure time. At low temperatures (T ≥ 825°C), the

  1. Oxidation behavior of ferritic-martensitic and ODS steels in supercritical water

    NASA Astrophysics Data System (ADS)

    Bischoff, Jeremy

    water corroded much faster than those in steam (1.5 to 2 times faster). Additionally, during these corrosion tests a marker experiment was performed with the deposition of micrometric palladium markers on the surface of some samples prior to oxidation. The markers were found at the outer-inner layer interface, consistent with a corrosion mechanism of outward migration of iron to form the outer layer and inward migration of oxygen to form the inner layer. The discrepancy between the SCW and steam environments suggests that the outward migration of iron may be the rate-limiting step. A detailed study of the oxide advancement was performed using the TEM by analyzing the inner and diffusion layer structure. Energy-filtered TEM images were acquired to analyze the micrometric and nanometric distribution of elements in these layers. Such images from the inner layer revealed the presence of localized chromium enrichment regions associated with the presence of pores. Additionally, an iron-chromium nanometric segregation was observed and may be associated with the mixture of Fe3O4 and FeCr2O4. In the diffusion layer, small nanometric chromium-rich oxide particles were seen within metal grains. The (Fe,Cr)3O4 spinel oxide has an inverse spinel structure as Fe3O4 but becomes normal spinel as FeCr 2O4, thus the structure changes depending on the chromium content. Additionally, the spinel structure was analyzed using the ligand theory and showed that chromium does not migrate and that the main diffusing species is the Fe2+ ion. Calculations of the amount of iron leaving the inner layer showed that this amount accounted for the amount of iron necessary to form the outer layer, thus no dissolution of oxide in SCW is observed. Additionally, the differences in oxidation behavior in steam and SCW suggest that the rate-limiting step for the corrosion of ferritic-martensitic steels is the iron outward migration. The iron migration is driven by the gradient in the Fe2+/Fe 3+ ratio and is

  2. Microstructural Variations Across a Dissimilar 316L Austenitic: 9Cr Reduced Activation Ferritic Martensitic Steel Weld Joint

    NASA Astrophysics Data System (ADS)

    Thomas Paul, V.; Karthikeyan, T.; Dasgupta, Arup; Sudha, C.; Hajra, R. N.; Albert, S. K.; Saroja, S.; Jayakumar, T.

    2016-03-01

    This paper discuss the microstructural variations across a dissimilar weld joint between SS316 and 9Cr-RAFM steel and its modifications on post weld heat treatments (PWHT). Detailed characterization showed a mixed microstructure of austenite and martensite in the weld which is in agreement with the phases predicted using Schaeffler diagram based on composition measurements. The presence of very low volume fraction of δ-ferrite in SS316L has been identified employing state of the art electron back-scattered diffraction technique. PWHT of the ferritic steel did not reduce the hardness in the weld metal. Thermal exposure at 973 K (700 °C) showed a progressive reduction in hardness of weld joint with duration of treatment except in austenitic base metal. However, diffusion annealing at 1073 K (800 °C) for 100 hours resulted in an unexpected increase in hardness of weld metal, which is a manifestation of the dilution effects and enrichment of Ni on the transformation characteristics of the weld zone. Migration of carbon from ferritic steel aided the precipitation of fine carbides in the austenitic base metal on annealing at 973 K (700 °C); but enhanced diffusion at 1073 K (880 °C) resulted in coarsening of carbides and thereby reduction of hardness.

  3. Ar ion irradiation hardening of high-Cr ferritic/martensitic steels at 700 °C

    NASA Astrophysics Data System (ADS)

    Shen, Yinzhong; Zhu, Jun; Huang, Xi

    2016-03-01

    High-Cr ferritic/martensitic (FM) steels are being considered for applications as fuel cladding or core structures for Generation-IV reactors. Because high temperatures approaching 923-973 K (650-700 °C) are envisioned in the designs of Generation IV reactors, irradiation response of high-Cr FM steels at the high temperatures requires investigations. Response of two high-Cr FM steels P92 and 11Cr to irradiation at 973 K (700 °C) was investigated through Ar ion irradiation in combination with damage simulations, nanoindentation measurements and microstructure analyses. Irradiation hardening occurred in both steels after Ar ion irradiation at 973 K (700 °C) to 10 dpa, providing the first evidence that irradiation hardening can occur at a high irradiation temperature of 973 K (700 °C) in high-Cr FM steels. Argon bubbles with a very high number density and an average diameter of about 2.6-3 nm formed in the two steels after the irradiation. The irradiation hardening occurred in the two steels is attributed to the formation of these high-number-density fine argon bubbles produced by the irradiation homogeneously distributed in the matrix. Difference in the magnitude of irradiation hardening between the two steels was also discussed.

  4. Microstructural characterization of weld joints of 9Cr reduced activation ferritic martensitic steel fabricated by different joining methods

    SciTech Connect

    Thomas Paul, V.; Saroja, S.; Albert, S.K.; Jayakumar, T.; Rajendra Kumar, E.

    2014-10-15

    This paper presents a detailed electron microscopy study on the microstructure of various regions of weldment fabricated by three welding methods namely tungsten inert gas welding, electron beam welding and laser beam welding in an indigenously developed 9Cr reduced activation ferritic/martensitic steel. Electron back scatter diffraction studies showed a random micro-texture in all the three welds. Microstructural changes during thermal exposures were studied and corroborated with hardness and optimized conditions for the post weld heat treatment have been identified for this steel. Hollomon–Jaffe parameter has been used to estimate the extent of tempering. The activation energy for the tempering process has been evaluated and found to be corresponding to interstitial diffusion of carbon in ferrite matrix. The type and microchemistry of secondary phases in different regions of the weldment have been identified by analytical transmission electron microscopy. - Highlights: • Comparison of microstructural parameters in TIG, electron beam and laser welds of RAFM steel • EBSD studies to illustrate the absence of preferred orientation and identification of prior austenite grain size using phase identification map • Optimization of PWHT conditions for indigenous RAFM steel • Study of kinetics of tempering and estimation of apparent activation energy of the process.

  5. Thermal Diffusivity of Reduced Activation Ferritic/Martensitic Steel Determined by the Time Domain Photoacoustic Piezoelectric Technique

    NASA Astrophysics Data System (ADS)

    Zhao, Binxing; Wang, Yafei; Gao, Chunming; Sun, Qiming; Wang, Pinghuai

    2015-06-01

    The thermal diffusivity of reduced activation ferritic/martensitic steel (CLF-1), which is recognized as the primary candidate structural material for the test blanket module of the international thermal-nuclear experimental reactor, has been studied by the time-domain (TD) photoacoustic piezoelectric (PAPE) technique. The TD PAPE model based on a simplified thermoelastic theory under square-wave modulated laser excitation is presented, relating the TD PAPE signal to the modulation frequency, thermal diffusivity, and other material parameters. Thermal diffusivities of reference samples such as copper and nickel were measured and analyzed, by which the validity of the technique is verified. The thermal diffusivity of the CLF-1 sample was measured to be , which is at a medium level among the ordinary steel materials ( to and has decent heat-dissipation ability. The results show that the TD PAPE technique can provide a fast and economic way for the investigation of the thermophysical properties of fusion reactor structural materials.

  6. Charpy Impact Properties of Reduced-Activation Ferritic/Martensitic Steels Irradiated in HFIR up to 20 dpa

    SciTech Connect

    Tanigawa, H.; Shiba, K.; Sokolov, M.A.; Klueh, R.L.

    2003-07-15

    The effects of irradiation up to 20 dpa on the Charpy impact properties of reduced-activation ferritic/martensitic steels (RAFs) were investigated. The ductile-brittle transition temperature (DBTT) of F82H-IEA shifted up to around 323K. TIG weldments of F82H showed a fairly small variation on their impact properties. A finer prior austenite grain size in F82H-IEA after a different heat treatment resulted in a 20K lower DBTT compared to F82H-IEA after the standard heat treatment, and that effect was maintained even after irradiation. Helium effects were investigated utilizing Ni-doped F82H, but no obvious evidence of helium effects was obtained. ORNL9Cr-2WVTa and JLF-1 steels showed smaller DBTT shifts compared to F82H-IEA.

  7. Irradiation effects on precipitation and its impact on the mechanical properties of reduced-activation ferritic/martensitic steels

    NASA Astrophysics Data System (ADS)

    Tanigawa, H.; Sakasegawa, H.; Hashimoto, N.; Klueh, R. L.; Ando, M.; Sokolov, M. A.

    2007-08-01

    It was previously reported that reduced-activation ferritic/martensitic steels (RAFs) showed a variety of changes in ductile-brittle transition temperature (DBTT) and yield stress after irradiation at 573 K up to 5 dpa. The precipitation behavior of the irradiated steels was examined and the presence of irradiation induced precipitation which works as if it was forced to reach the thermal equilibrium state at irradiation temperature 573 K. In this study, transmission electron microscopy was performed on extraction replica specimens to analyze the size distribution of precipitates. It turned out that the hardening level multiplied by the square root of the average block size showed a linear dependence on the extracted precipitate weight. This dependence suggests that the difference in irradiation hardening between RAFs was caused by different precipitation behavior on block, packet and prior austenitic grain boundaries during irradiation. The simple Hall-Petch law could be applicable for interpreting this dependence.

  8. Microstructural evolution of ferritic-martensitic steels under heavy ion irradiation

    NASA Astrophysics Data System (ADS)

    Topbasi, Cem

    Ferritic-martensitic steels are primary candidate materials for fuel cladding and internal applications in the Sodium Fast Reactor, as well as first-wall and blanket materials in future fusion concepts because of their favorable mechanical properties and resistance to radiation damage. Since microstructure evolution under irradiation is amongst the key issues for these materials in these applications, developing a fundamental understanding of the irradiation-induced microstructure in these alloys is crucial in modeling and designing new alloys with improved properties. The goal of this project was to investigate the evolution of microstructure of two commercial ferritic-martensitic steels, NF616 and HCM12A, under heavy ion irradiation at a broad temperature range. An in situ heavy ion irradiation technique was used to create irradiation damage in the alloy; while it was being examined in a transmission electron microscope. Electron-transparent samples of NF616 and HCM12A were irradiated in situ at the Intermediate Voltage Electron Microscope (IVEM) at Argonne National Laboratory with 1 MeV Kr ions to ˜10 dpa at temperatures ranging from 20 to 773 K. The microstructure evolution of NF616 and HCM12A was followed in situ by systematically recording micrographs and diffraction patterns as well as capturing videos during irradiation. In these irradiations, there was a period during which no changes are visible in the microstructure. After a threshold dose (˜0.1 dpa between 20 and 573 K, and ˜2.5 dpa at 673 K) black dots started to become visible under the ion beam. These black dots appeared suddenly (from one frame to the next) and are thought to be small defect clusters (2-5 nm in diameter), possibly small dislocation loops with Burgers vectors of either ½ or . The overall density of these defect clusters increased with dose and saturated around 6 dpa. At saturation, a steady-state is reached in which defects are eliminated and created at the same rates so that the

  9. The corrosion product of Cs-Te corrosive compound with 11Cr-Ferritic/Martensitic Steel and 9Cr-Oxide Dispersion Strengthened steel

    NASA Astrophysics Data System (ADS)

    Sasaki, K.; Tanigaki, T.; Fujimura, R.; Fukumoto, K.; Uno, M.

    2015-05-01

    Cs-Te corrosion tests were performed to FBR fuel cladding candidate materials listed below: 11Cr-Ferritic/Martensitic Steel (F/M steel) and 9Cr Oxide Dispersion Strengthened steel (ODS steel). The corrosion products of Cs-Te corrosive compound Cs2Te3 with F/M steel or ODS steel were picked up from the specimens after the corrosion test by focus ion beam method (FIB) and the corrosion products were specified based on element analysis and crystal analysis by transmit electron microscopy (TEM) with electron dispersion X-ray spectrum (EDS). The result of analysis allowed us to presume Cs-Te corrosion reactions in the Fe-Cr based fuel cladding material. The presumable reactions are 4Te + 3/23 Cr23C6 →Cr3Te4 + 18/23 C and 4Te + 3Cr →Cr3Te4 .

  10. Recent status and improvement of reduced-activation ferritic-martensitic steels for high-temperature service

    NASA Astrophysics Data System (ADS)

    Tan, L.; Katoh, Y.; Tavassoli, A.-A. F.; Henry, J.; Rieth, M.; Sakasegawa, H.; Tanigawa, H.; Huang, Q.

    2016-10-01

    Reduced-activation ferritic-martensitic (RAFM) steels, candidate structural materials for fusion reactors, have achieved technological maturity after about three decades of research and development. The recent status of a few developmental aspects of current RAFM steels, such as aging resistance, plate thickness effects, fracture toughness, and fatigue, is updated in this paper, together with ongoing efforts to develop next-generation RAFM steels for superior high-temperature performance. In addition to thermomechanical treatments, including nonstandard heat treatment, alloy chemistry refinements and modifications have demonstrated some improvements in high-temperature performance. Castable nanostructured alloys (CNAs) were developed by significantly increasing the amount of nanoscale MX (M = V/Ta/Ti, X = C/N) precipitates and reducing coarse M23C6 (M = Cr). Preliminary results showed promising improvement in creep resistance and Charpy impact toughness. Limited low-dose neutron irradiation results for one of the CNAs and China low activation martensitic are presented and compared with data for F82H and Eurofer97 irradiated up to ∼70 displacements per atom at ∼300-325 °C.

  11. Recent status and improvement of reduced-activation ferritic-martensitic steels for high-temperature service

    SciTech Connect

    Tan, L.; Katoh, Y.; Tavassoli, A. -A. F.; Henry, J.; Rieth, M.; Sakasegawa, H.; Tanigawa, H.; Huang, Q.

    2016-07-26

    Reduced-activation ferritic-martensitic (RAFM) steels, candidate structural materials for fusion reactors, have achieved technological maturity after about three decades of research and development. The recent status of a few developmental aspects of current RAFM steels, such as aging resistance, plate thickness effects, fracture toughness, and fatigue, is updated in this paper, together with ongoing efforts to develop next-generation RAFM steels for superior high-temperature performance. Additionally, to thermomechanical treatments, including nonstandard heat treatment, alloy chemistry refinements and modifications have demonstrated some improvements in high-temperature performance. Castable nanostructured alloys (CNAs) were developed by significantly increasing the amount of nanoscale MX (M = V/Ta/Ti, X = C/N) precipitates and reducing coarse M23C6 (M = Cr). Preliminary results showed promising improvement in creep resistance and Charpy impact toughness. We present and compare limited low-dose neutron irradiation results for one of the CNAs and China low activation martensitic with data for F82H and Eurofer97 irradiated up to ~70 displacements per atom at ~300–325 °C.

  12. Recent status and improvement of reduced-activation ferritic-martensitic steels for high-temperature service

    SciTech Connect

    Tan, L.; Katoh, Y.; Tavassoli, A. -A. F.; Henry, J.; Rieth, M.; Sakasegawa, H.; Tanigawa, H.; Huang, Q.

    2016-07-26

    Reduced-activation ferritic-martensitic (RAFM) steels, candidate structural materials for fusion reactors, have achieved technological maturity after about three decades of research and development. The recent status of a few developmental aspects of current RAFM steels, such as aging resistance, plate thickness effects, fracture toughness, and fatigue, is updated in this paper, together with ongoing efforts to develop next-generation RAFM steels for superior high-temperature performance. Additionally, to thermomechanical treatments, including nonstandard heat treatment, alloy chemistry refinements and modifications have demonstrated some improvements in high-temperature performance. Castable nanostructured alloys (CNAs) were developed by significantly increasing the amount of nanoscale MX (M = V/Ta/Ti, X = C/N) precipitates and reducing coarse M23C6 (M = Cr). Preliminary results showed promising improvement in creep resistance and Charpy impact toughness. We present and compare limited low-dose neutron irradiation results for one of the CNAs and China low activation martensitic with data for F82H and Eurofer97 irradiated up to ~70 displacements per atom at ~300–325 °C.

  13. Recent status and improvement of reduced-activation ferritic-martensitic steels for high-temperature service

    DOE PAGES

    Tan, L.; Katoh, Y.; Tavassoli, A. -A. F.; ...

    2016-07-26

    Reduced-activation ferritic-martensitic (RAFM) steels, candidate structural materials for fusion reactors, have achieved technological maturity after about three decades of research and development. The recent status of a few developmental aspects of current RAFM steels, such as aging resistance, plate thickness effects, fracture toughness, and fatigue, is updated in this paper, together with ongoing efforts to develop next-generation RAFM steels for superior high-temperature performance. Additionally, to thermomechanical treatments, including nonstandard heat treatment, alloy chemistry refinements and modifications have demonstrated some improvements in high-temperature performance. Castable nanostructured alloys (CNAs) were developed by significantly increasing the amount of nanoscale MX (M = V/Ta/Ti,more » X = C/N) precipitates and reducing coarse M23C6 (M = Cr). Preliminary results showed promising improvement in creep resistance and Charpy impact toughness. We present and compare limited low-dose neutron irradiation results for one of the CNAs and China low activation martensitic with data for F82H and Eurofer97 irradiated up to ~70 displacements per atom at ~300–325 °C.« less

  14. Dependence on grain boundary structure of radiation induced segregation in a 9 wt.% Cr model ferritic/martensitic steel

    NASA Astrophysics Data System (ADS)

    Field, Kevin G.; Barnard, Leland M.; Parish, Chad M.; Busby, Jeremy T.; Morgan, Dane; Allen, Todd R.

    2013-04-01

    Ferritic/Martensitic (F/M) steels containing 9 wt.% Cr are candidates for structural and cladding components in the next generation of advanced nuclear fission and fusion reactors. Although it is known these alloys exhibit radiation-induced segregation (RIS) at grain boundaries (GBs) while in-service, little is known about the mechanism behind RIS in F/M steels. The classical understanding of RIS in F/M steels presents a mechanism where point defects migrate to GBs acting as perfect sinks. However, variation in grain boundary structure may influence the sink efficiency and these migration processes. A proton irradiated 9 wt.% Cr model alloy steel was investigated using STEM/EDS spectrum imaging and GB misorientation analysis to determine the role of GB structure on RIS at different GBs. An ab initio based rate theory model was developed and compared to the experimental findings. This investigation found Cr preferentially segregates to specific GB structures. The preferential segregation to specific GB structures suggests GB structure plays a key role in the mechanism behind radiation-induced segregation, showing that not all grain boundaries in F/M steels act as perfect sinks. The study also found how irradiation dose and temperature impact the radiation-induced segregation response in F/M steels.

  15. Precipitation behavior and martensite lath coarsening during tempering of T/P92 ferritic heat-resistant steel

    NASA Astrophysics Data System (ADS)

    Xu, Lin-qing; Zhang, Dan-tian; Liu, Yong-chang; Ning, Bao-qun; Qiao, Zhi-xia; Yan, Ze-sheng; Li, Hui-jun

    2014-05-01

    Tempering is an important process for T/P92 ferritic heat-resistant steel from the viewpoint of microstructure control, as it facilitates the formation of final tempered martensite under serving conditions. In this study, we have gained deeper insights on the mechanism underlying the microstructural evolution during tempering treatment, including the precipitation of carbides and the coarsening of martensite laths, as systematically analyzed by optical microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy. The chemical composition of the precipitates was analyzed using energy dispersive X-ray spectroscopy. Results indicate the formation of M3C (cementite) precipitates under normalized conditions. However, they tend to dissolve within a short time of tempering, owing to their low thermal stability. This phenomenon was substantiated by X-ray diffraction analysis. Besides, we could observe the precipitation of fine carbonitrides (MX) along the dislocations. The mechanism of carbon diffusion controlled growth of M23C6 can be expressed by the Zener's equation. The movement of Y-junctions was determined to be the fundamental mechanism underlying the martensite lath coarsening process. Vickers hardness was estimated to determine their mechanical properties. Based on the comprehensive analysis of both the micro-structural evolution and hardness variation, the process of tempering can be separated into three steps.

  16. Summary Report of Summer Work: High Purity Single Crystal Growth & Microstructure of Ferritic-Martensitic Steels

    SciTech Connect

    Pestovich, Kimberly Shay

    2015-08-18

    Harnessing the power of the nuclear sciences for national security and to benefit others is one of Los Alamos National Laboratory’s missions. MST-8 focuses on manipulating and studying how the structure, processing, properties, and performance of materials interact at the atomic level under nuclear conditions. Within this group, single crystal scintillators contribute to the safety and reliability of weapons, provide global security safeguards, and build on scientific principles that carry over to medical fields for cancer detection. Improved cladding materials made of ferritic-martensitic alloys support the mission of DOE-NE’s Fuel Cycle Research and Development program to close the nuclear fuel cycle, aiming to solve nuclear waste management challenges and thereby increase the performance and safety of current and future reactors.

  17. Evolution of the mechanical properties and microstructure of ferritic-martensitic steels irradiated in the BOR-60 reactor

    NASA Astrophysics Data System (ADS)

    Shamardin, V. K.; Golovanov, V. N.; Bulanova, T. M.; Povstyanko, A. V.; Fedoseev, A. E.; Ostrovsky, Z. E.; Goncharenko, Yu. D.

    2002-12-01

    The effect of neutron irradiation on mechanical properties of low-activation ferritic-martensitic (FM) steels 0.1C-9Cr-1W, V, Ta, B and 0.1C-12Cr-2W, V, Ti, B is studied under tension at temperatures of 330-540 °C and doses of 50 dpa. Steel 0.1C-13Cr-Mo, V, Nb, B was chosen for comparison. At irradiation temperatures of 330-340 °C, the radiation hardening of steel with 9%Cr achieves saturation at a dose of 10 dpa. In this case as compared to steels with 12%Cr, the fracture surface is characterized as ductile without cleavage traces. At irradiation temperatures higher than 420 °C, there is no difference in the behavior of the materials under investigation. The data on radiation creep obtained by direct measurement and from the profilometry data satisfy a model ɛ¯/ σ¯=B 0+D Ṡ, when B0 and D have the values typical for steels of FM type.

  18. Determining the shear fracture properties of HIP joints of reduced-activation ferritic/martensitic steel by a torsion test

    NASA Astrophysics Data System (ADS)

    Nozawa, Takashi; Noh, Sanghoon; Tanigawa, Hiroyasu

    2012-08-01

    Hot isostatic pressing (HIP) is a key technology used to fabricate a first wall with cooling channels for the fusion blanket system utilizing a reduced-activation ferritic/martensitic steel. To qualify the HIPped components, small specimen test techniques are beneficial not only to evaluate the thin-wall cooling channels containing the HIP joint but also to use in neutron irradiation studies. This study aims to develop the torsion test method with special emphasis on providing a reasonable and comprehensive method to determine interfacial shear properties of HIP joints during the torsional fracture process. Torsion test results identified that the torsion process shows yield of the base metal followed by non-elastic deformation due to work hardening of the base metal. By considering this work hardening issue, we propose a reasonable and realistic solution to determine the torsional yield shear stress and the ultimate torsional shear strength of the HIPped interface. Finally, a representative torsion fracture process was identified.

  19. Effect of Carbon Content on Microstructure and Mechanical Properties of 9 to 12 pct Cr Ferritic/Martensitic Heat-Resistant Steels

    NASA Astrophysics Data System (ADS)

    Yin, Feng-Shi; Tian, Li-Qian; Xue, Bing; Jiang, Xue-Bo; Zhou, Li

    2012-07-01

    Two heats of 9 to 12 pct Cr ferritic/martensitic heat-resistant steels were prepared. One has an ultralow carbon content of 0.01 wt pct, whereas another heat has a normal carbon content of 0.09 wt pct. The effect of carbon content on microstructure and mechanical properties of 9 to 12 pct Cr ferritic/martensitic heat-resistant steels was studied. The results show that the ultralow-carbon steel contains bimodal, nanosized MX precipitates with high density in the matrix but few M23C6 carbide particles in the normalized-and-tempered state. The smaller nanosized MX precipitates have two kinds of typical morphology: One is cubic and another is rectangular. The cubic MX precipitate contains Nb, Ti, and V, whereas the rectangular one only contains Nb and V. The normal carbon steel has abundant M23C6 carbide particles along the grain and lath boundaries and much less density of nanosized MX precipitates after the same heat treatments. After long-term aging at 923 K (650 °C) for 10,000 hours, the stress rupture properties of the ultralow carbon content steel degrades more significantly. The strength degradation mechanism of the 9 to 12 pct Cr ferritic/martensitic heat-resistant steels is discussed in this article.

  20. Fatigue crack propagation in dual-phase steels: Effects of ferritic-martensitic microstructures on crack path morphology

    NASA Astrophysics Data System (ADS)

    Dutta, V. B.; Suresh, S.; Ritchie, R. O.

    1984-06-01

    microstructures with maximum resistance to fatigue crack extension while maintaining high strength levels. A wide range of crack growth rates has been examined, from ~10-8 to 10-3 mm per cycle, in a series of duplex microstructures of comparable yield strength and prior austenite grain size where intercritical heat treatments were used to vary the proportion, morphology, and distribution of the ferrite and martensite phases. Results of fatigue crack propagation tests, conducted on “long cracks” in room temperature moist air environments, revealed a very large influence of microstructure over the entire spectrum of growth rates at low load ratios. Similar trends were observed at high load ratio, although the extent of the microstructural effects on crack growth behavior was significantly less marked. Specifically, microstructures containing fine globular or coarse martensite in a coarse-grained ferritic matrix demonstrated exceptionally high resistance to crack growth without loss in strength properties. To our knowledge, these microstructures yielded the highest ambient temperature fatigue threshold stress intensity range ΔK0 values reported to date, and certainly the highest combination of strength and ΔK0 for steels ( i.e., ΔK0 values above 19 MPa√m with yield strengths in excess of 600 MPa). Such unusually high crack growth resistance is attributed primarily to a tortuous morphology of crack path which results in a reduction in the crack driving force from crack deflection and roughness-induced crack closure mechanisms. Quantitative metallography and experimental crack closure measurements, applied to currently available analytical models for the deflection and closure processes, are presented to substantiate such interpretations.

  1. End Closure Joining of Ferritic-Martensitic and Oxide-Dispersion Strengthened Steel Cladding Tubes by Magnetic Pulse Welding

    NASA Astrophysics Data System (ADS)

    Lee, Jung-Gu; Park, Jin-Ju; Lee, Min-Ku; Rhee, Chang-Kyu; Kim, Tae-Kyu; Spirin, Alexey; Krutikov, Vasiliy; Paranin, Sergey

    2015-07-01

    The magnetic pulse welding (MPW) technique was employed for the end closure joining of fuel pin cladding tubes made of ferritic-martensitic (FM) steel and oxide-dispersion strengthened (ODS) steel. The technique is a solid-state impact joining process based on the electromagnetic force, similar to explosive welding. For a given set of optimal process parameters, e.g., the end-plug geometry, the rigid metallurgical bonding between the tube and end plug was obtained by high-velocity impact collision accompanied with surface jetting. The joint region showed a typical wavy morphology with a narrow grain boundary-like bonding interface. There was no evidence of even local melting, and only the limited grain refinement was observed in the vicinity of the bonding interface without destructing the original reinforcement microstructure of the FM-ODS steel, i.e., a fine grain structure with oxide dispersion. No leaks were detected during helium leakage test, and moreover, the rupture occurred in the cladding tube section without leaving any joint damage during internal pressure burst test. All of the results proved the integrity and durability of the MPWed joints and signified the great potential of this method of end closure joining for advanced fast reactor fuel pin fabrication.

  2. Modification in the Microstructure of Mod. 9Cr-1Mo Ferritic Martensitic Steel Exposed to Sodium

    NASA Astrophysics Data System (ADS)

    Prasanthi, T. N.; Sudha, Cheruvathur; Paul, V. Thomas; Bharasi, N. Sivai; Saroja, S.; Vijayalakshmi, M.

    2014-09-01

    Mod. 9Cr-1Mo is used as the structural material in the steam generator circuit of liquid metal-cooled fast breeder reactors. Microstructural modifications on the surface of this steel are investigated after exposing to flowing sodium at a temperature of 798 K (525 °C) for 16000 hours. Sodium exposure results in the carburization of the ferritic steel up to a depth of ~218 µm from the surface. Electron microprobe analysis revealed the existence of two separate zones with appreciable difference in microchemistry within the carburized layer. Differences in the type, morphology, volume fraction, and microchemistry of the carbides present in the two zones are investigated using analytical transmission electron microscopy. Formation of separate zones within the carburized layer is understood as a combined effect of leaching, diffusion of the alloying elements, and thermal aging. Chromium concentration on the surface in the α-phase suggested possible degradation in the corrosion resistance of the steel. Further, concentration-dependent diffusivities for carbon are determined in the base material and carburized zones using Hall's and den Broeder's methods, respectively. These are given as inputs for simulating the concentration profiles for carbon using numerical computation technique based on finite difference method. Predicted thickness of the carburized zone agrees reasonably well with that of experiment.

  3. Small punch tensile/fracture test data and 3D specimen surface data on Grade 91 ferritic/martensitic steel from cryogenic to room temperature.

    PubMed

    Bruchhausen, Matthias; Lapetite, Jean-Marc; Ripplinger, Stefan; Austin, Tim

    2016-12-01

    Raw data from small punch tensile/fracture tests at two displacement rates in the temperature range from -196 °C to room temperature on Grade 91 ferritic/martensitic steel are presented. A number of specimens were analyzed after testing by means of X-ray computed tomography (CT). Based on the CT volume data detailed 3D surface maps of the specimens were established. All data are open access and available from Online Data Information Network (ODIN)https://odin.jrc.ec.europa.eu. The data presented in the current work has been analyzed in the research article "On the determination of the ductile to brittle transition temperature from small punch tests on Grade 91 ferritic-martensitic steel" (M. Bruchhausen, S. Holmström, J.-M. Lapetite, S. Ripplinger, 2015) [1].

  4. Fracture toughness of the IEA heat of F82H ferritic/martensitic stainless steel as a function of loading mode

    SciTech Connect

    Li, Huaxin; Gelles, D.S.; Hirth, J.P.

    1997-04-01

    Mode I and mixed-mode I/III fracture toughness tests were performed for the IEA heat of the reduced activation ferritic/martensitic stainless steel F82H at ambient temperature in order to provide comparison with previous measurements on a small heat given a different heat treatment. The results showed that heat to heat variations and heat treatment had negligible consequences on Mode I fracture toughness, but behavior during mixed-mode testing showed unexpected instabilities.

  5. Effect of heat treatment and irradiation temperature on mechanical properties and structure of reduced-activation Cr-W-V steels of bainitic, martensitic, and martensitic-ferritic classes

    NASA Astrophysics Data System (ADS)

    Gorynin, I. V.; Rybin, V. V.; Kursevich, I. P.; Lapin, A. N.; Nesterova, E. V.; Klepikov, E. Yu

    2000-12-01

    Effects of molybdenum replacement by tungsten in steels of the bainitic, martensitic, and martensitic-ferritic classes containing 2.5%, 8% and 11% Cr, respectively, were investigated. The phase composition and structure of the bainitic steels were varied by changing the cooling rates from the austenitization temperature (from values typical for normalization up to V=3.3 × 10-2°C/s) and then tempering. The steels were irradiated to a fluence of 4×1023 n/m2 (⩾0.5 MeV) at 270°C and to fluences of 1.3×1023 and 1.2×1024 n/m2 (⩾0.5 MeV) at 70°C. The 2.5Cr-1.4WV and 8Cr-1.5WV steels have shown lower values of the shifts in ductile-brittle transition temperature (DBTT) under irradiation in comparison with corresponding Cr-Mo steels. Radiation embrittlement at elevated irradiation temperature was lowest in bainitic 2.5Cr-1.4WV steel and martensitic-ferritic 11Cr-1.5WV steel. The positive effect of molybdenum replacement by tungsten at irradiation temperature ∼300°C is reversed at Tirr=70∘C.

  6. Blister formation on 13Cr2MoNbVB ferritic-martensitic steel exposed to hydrogen plasma

    NASA Astrophysics Data System (ADS)

    Nikitin, A. V.; Tolstolutskaya, G. D.; Ruzhytskyi, V. V.; Voyevodin, V. N.; Kopanets, I. E.; Karpov, S. A.; Vasilenko, R. L.; Garner, F. A.

    2016-09-01

    The influence of pre-irradiation specimen deformation level on surface blister formation and sub-surface cracking of dual-phase 13Cr2MoNbVB ferritic-martensitic steel was studied using glow discharge hydrogen plasma with ion energy of 1 keV to fluences of 2 × 1025 H/m2. Protium was used for most studies, but deuterium was used for measuring the depth dependence of hydrogen diffusion. Formation of blisters was observed in the temperature range 230-340 K. It was found that pre-irradiation deformation caused changes in the threshold fluences of blister formation and also in blister size distribution. Subsurface cracks located on grain boundaries far beyond the implantation zone were formed concurrently with blisters, arising from hydrogen diffusion and trapping at defects. It was observed that cracks as long as 1 mm in length were formed in 95% deformed steel at depths up to 500 μm from surface.

  7. Impact of the use of the ferritic/martensitic ODS steels cladding on the fuel reprocessing PUREX process

    NASA Astrophysics Data System (ADS)

    Gwinner, B.; Auroy, M.; Mas, D.; Saint-Jevin, A.; Pasquier-Tilliette, S.

    2012-09-01

    Some ferritic/martensitic oxide dispersed strengthened (F/M ODS) steels are presently developed at CEA for the fuel cladding of the next generation of sodium fast nuclear reactors. The objective of this work is to study if this change of cladding could have any consequences on the spent fuel reprocessing PUREX process. During the fuel dissolution stage the cladding can actually be corroded by nitric acid. But some process specifications impose not to exceed a limit concentration of the corrosion products such as iron and chromium in the dissolution medium. For that purpose the corrosion behavior of these F/M ODS steels is studied in hot and concentrated nitric acid. The influence of some metallurgical parameters such as the chromium content, the elaboration process and the presence of the yttrium oxides is first discussed. The influence of environmental parameters such as the nitric acid concentration, the temperature and the presence of oxidizing species coming from the fuel is then analyzed. The corrosion rate is characterized by mass loss measurements and electrochemical tests. Analyses of the corroded surface are carried out by X-ray photoelectron spectroscopy.

  8. Deformation Microstructure of a Reduced-Activation Ferritic/Martensitic Steel Irradiated in HFIR

    SciTech Connect

    Hashimoto, N.; Klueh, R.L.; Ando, M.; Tanigawa, H.; Sawai, T.; Shiba, K.

    2003-09-15

    In order to determine the contributions of different microstructural features to strength and to deformation mode, microstructure of deformed flat tensile specimens of irradiated reduced activation F82H (IEA heat) base metal (BM) and its tungsten inert-gas (TIG) weldments (weld metal and weld joint) were investigated by transmission electron microscopy (TEM), following fracture surface examination by scanning electron microscopy (SEM). After irradiation, the fracture surfaces of F82H BM and TIG weldment showed a martensitic mixed quasi-cleavage and ductile-dimple fracture. The microstructure of the deformed region of irradiated F82H BM contained dislocation channels. This suggests that dislocation channeling could be the dominant deformation mechanism in this steel, resulting in the loss of strain-hardening capacity. While, the necked region of the irradiated F82H TIG, where showed less hardening than F82H BM, showed deformation bands only. From these results, it is suggested that the pre-irradiation microstructure, especially the dislocation density, could affect the post-irradiation deformation mode.

  9. Effect of Heat Input on Microstructure Evolution and Mechanical Properties in the Weld Heat-Affected Zone of 9Cr-2W-VTa Reduced Activation Ferritic-Martensitic Steel for Fusion Reactor

    NASA Astrophysics Data System (ADS)

    Moon, Joonoh; Lee, Chang-Hoon; Lee, Tae-Ho; Kim, Hyoung Chan

    2015-01-01

    The phase transformation and mechanical properties in the weld heat-affected zone (HAZ) of a reduced activation ferritic/martensitic steel were explored. The samples for HAZs were prepared using a Gleeble simulator at different heat inputs. The base steel consisted of tempered martensite and carbides through quenching and tempering treatment, whereas the HAZs consisted of martensite, δ-ferrite, and a small volume of autotempered martensite. The prior austenite grain size, lath width of martensite, and δ-ferrite fraction in the HAZs increased with increase in the heat input. The mechanical properties were evaluated using Vickers hardness and Charpy V-notch impact test. The Vickers hardness in the HAZs was higher than that in the base steel but did not change noticeably with increase in the heat input. The HAZs showed poor impact property due to the formation of martensite and δ-ferrite as compared to the base steel. In addition, the impact property of the HAZs deteriorated more with the increase in the heat input. Post weld heat treatment contributed to improve the impact property of the HAZs through the formation of tempered martensite, but the impact property of the HAZs remained lower than that of base steel.

  10. Microstructural evolution in a ferritic-martensitic stainless steel and its relation to high-temperature deformation and rupture models

    SciTech Connect

    DiMelfi, R.J.; Gruber, E.E.; Kramer, J.M.

    1991-01-01

    The ferritic-martensitic stainless steel HT-9 exhibits an anomalously high creep strength in comparison to its high-temperature flow strength from tensile tests performed at moderate rates. A constitutive relation describing its high-temperature tensile behavior over a wide range of conditions has been developed. When applied to creep conditions the model predicts deformation rates orders of magnitude higher than observed. To account for the observed creep strength, a fine distribution of precipitates is postulated to evolve over time during creep. The precipitate density is calculated at each temperature and stress to give the observed creep rate. The apparent precipitation kinetics thereby extracted from this analysis is used in a model for the rupture-time kinetics that compares favorably with observation. Properly austenitized and tempered material was aged over times comparable to creep conditions, and in a way consistent with the precipitation kinetics from the model. Microstructural observations support the postulates and results of the model system. 16 refs., 10 figs.

  11. Microstructure and mechanical property of ferritic-martensitic steel cladding under a 650 °C liquid sodium environment

    NASA Astrophysics Data System (ADS)

    Kim, Jun Hwan; Kim, Sung Ho

    2013-11-01

    A study was carried out to investigate the effect of liquid sodium on the microstructural and mechanical property of ferritic-martensitic steel (FMS) used for a Sodium-cooled Fast Reactor (SFR) cladding tube. A quasi-dynamic device characterized by natural circulation was constructed and a compatibility test between FMS and liquid sodium was performed. HT9 (12Cr-1MoWVN) and Gr.92 (9Cr-2WNbVNB) coupons as well as a Gr.92 cladding tube were immersed in the 650 °C liquid sodium up to 3095 h and a microstructural observation, a mechanical property evaluation such as nanoindentation, and a ring tension test were also done in this study. The results showed that both HT9 and Gr.92 exhibited macroscopic weight loss behavior where pitting and decarburization took place. Weight loss as well as the decarburization process decreased as the chromium content increased. A compatibility test over the cladding tube revealed that a decrease of the mechanical property caused by the aging process governed the whole mechanical property of the cladding tube.

  12. Effect of processing on microstructural features and mechanical properties of a reduced activation ferritic/martensitic EUROFER steel grade

    NASA Astrophysics Data System (ADS)

    Puype, A.; Malerba, L.; De Wispelaere, N.; Petrov, R.; Sietsma, J.

    2017-10-01

    The microstructure of a 9Cr-1W-0.22V-0.09Ta-0.11C reduced activation ferritic/martensitic (RAFM) steel has been investigated after thermo-mechanical rolling with subsequent annealing for 30 min at temperatures of 880 °C, 920 °C, 980 °C and 1050 °C, followed by water quenching. Scanning and transmission electron microscopy investigations and electron backscattered diffraction (EBSD) measurements were performed to determine the microstructural features after the different thermal treatments. Additionally, the microstructure and the mechanical properties of the materials were studied after tempering at 750 °C for 2 h. This study aims to understand microstructural processes that occur in the material during thermo-mechanical treatment and to assess the effect of the microstructure on its strength and toughness, with a view on improving its mechanical performance. Microstructural analysis together with the data from mechanical tests identified the beneficial effect of grain refinement obtained with adequate processing on the ductile-to-brittle transition temperature (DBTT) and on the delay of strength degradation at elevated temperatures.

  13. Triple ion-beam studies of radiation damage in 9Cr2WVTa ferritic/martensitic steel

    SciTech Connect

    Lee, E.H.; Hunn, J.D.; Rao, G.R.; Klueh, R.L.; Mansur, L.K.

    1997-11-01

    To simulate radiation damage under a future Spallation Neutron Source (SNS) environment, irradiation experiments were conducted on a candidate 9Cr-2WVTa ferritic/martensitic steel using the Triple Ion Facility (TIF) at ORNL. Irradiation was conducted in single, dual, and triple ion beam modes using 3.5 MeV Fe{sup ++}, 360 keV He{sup +}, and 180 keV H{sup +} at 80, 200, and 350{degrees}C. These irradiations produced various defects comprising black dots, dislocation loops, line dislocations, and gas bubbles, which led to hardening. The largest increase in hardness, over 63 %, was observed after 50 dpa for triple beam irradiation conditions, revealing that both He and H are augmenting the hardening. Hardness increased less than 30 % after 30 dpa at 200{degrees}C by triple beams, compatible with neutron irradiation data from previous work which showed about a 30 % increase in yield strength after 27.2 dpa at 365{degrees}C. However, the very large concentrations of gas bubbles in the matrix and on lath and grain boundaries after these simulated SNS irradiations make predictions of fracture behavior from fission reactor irradiations to spallation target conditions inadvisable.

  14. Effects of alloying elements and heat treatments on mechanical properties of Korean reduced-activation ferritic-martensitic steel

    NASA Astrophysics Data System (ADS)

    Chun, Y. B.; Kang, S. H.; Noh, S.; Kim, T. K.; Lee, D. W.; Cho, S.; Jeong, Y. H.

    2014-12-01

    As part of an alloy development program for Korean reduced-activation ferritic-martensitic (RAFM) steel, a total of 37 program alloys were designed and their mechanical properties were evaluated with special attention being paid to the effects of alloying elements and heat treatments. A reduction of the normalizing temperature from 1050 °C to 980 °C was found to have a positive effect on the impact resistance, resulting in a decrease in ductile-brittle transition-temperature (DBTT) of the program alloys by an average of 30 °C. The yield strength and creep rupture time are affected strongly by the tempering time at 760 °C but at the expense of ductility. Regarding the effects of the alloying elements, the addition of trace amounts of Zr enhances both the creep and impact resistance: the lowest DBTT was observed for the alloys containing 0.005 wt.% Zr, whereas the addition of 0.01 wt.% Zr extends the creep rupture-time under an accelerated condition. The enhanced impact resistance owing to the normalizing at lower temperature is attributed to a more refined grain structure, which provides more barriers to the propagation of cleavage cracks. Solution softening by Zr addition is suggested as a possible mechanism for enhanced resistance to both impact and creep of the program alloys.

  15. Fabrication and integrity test preparation of HIP-joined W and ferritic-martensitic steel mockups for fusion reactor development

    NASA Astrophysics Data System (ADS)

    Lee, Dong Won; Shin, Kyu In; Kim, Suk Kwon; Jin, Hyung Gon; Lee, Eo Hwak; Yoon, Jae Sung; Choi, Bo Guen; Moon, Se Youn; Hong, Bong Guen

    2014-10-01

    Tungsten (W) and ferritic-martensitic steel (FMS) as armor and structural materials, respectively, are the major candidates for plasma-facing components (PFCs) such as the blanket first wall (BFW) and the divertor, in a fusion reactor. In the present study, three W/FMS mockups were successfully fabricated using a hot isostatic pressing (HIP, 900 °C, 100 MPa, 1.5 hrs) with a following post-HIP heat treatment (PHHT, tempering, 750 °C, 70 MPa, 2 hrs), and the W/FMS joining method was developed based on the ITER BFW and the test blanket module (TBM) development project from 2004 to the present. Using a 10-MHz-frequency flat-type probe to ultrasonically test of the joint, we found no defects in the fabricated mockups. For confirmation of the joint integrity, a high heat flux test will be performed up to the thermal lifetime of the mockup under the proper test conditions. These conditions were determined through a preliminary analysis with conventional codes such as ANSYS-CFX for thermal-hydraulic conditions considering the test facility, the Korea heat load test facility with an electron beam (KoHLT-EB), and its water coolant system at the Korea Atomic Energy Research Institute (KAERI).

  16. Mixed-mode I/III fracture toughness of a ferritic/martensitic stainless steel

    SciTech Connect

    Li, Huaxin; Jones, R.H.; Gelles, D.S.; Hirth, J.P.

    1993-10-01

    The critical J-integrals of mode I (J{sub IC}), mixed-mode I/III (J{sub MC}), and mode III (J{sub IIIC}) were examined for a ferritic stainless steel (F-82H) at ambient temperature. A determination of J{sub MC} was made using modified compact-tension specimens. Different ratios of tension/shear stress were achieved by varying the principal axis of the crack plane between 0 and 55 degrees from the load line. Results showed that J{sub MC} and tearing modulus (T{sub M}) values varied with the crack angles and were lower than their mode I and mode III counterparts. Both the minimum J{sub MC} and T{sub M} values occurred at a crack angle between 40 and 50 degrees, where the load ratio of {sigma}{sub i}/{sigma}{sub iii} was 1.2 to 0.84. The J{sub min} was 240 Kj/M{sup 2}, and ratios of J{sub IC}/J{sub min} and J{sub IIIC}/J{sub min} were 2.1 and 1.9, respectively. The morphology of fracture surfaces was consistent with the change of J{sub MC} and T{sub M} values. While the upper shelf-fracture toughness of F-82H depends on loading mode, the J{sub min} remains very high. Other important considerations include the effect of mixed-mode loading on the DBT temperature, and effects of hydrogen and irradiation on J{sub min}.

  17. New nano-particle-strengthened ferritic/martensitic steels by conventional thermo-mechanical treatment

    NASA Astrophysics Data System (ADS)

    Klueh, R. L.; Hashimoto, N.; Maziasz, P. J.

    2007-08-01

    For increased fusion power plant efficiency, steels for operation at 650 °C and higher are sought. Based on the science of precipitate strengthening, a thermo-mechanical treatment (TMT) was developed that increased the strength from room temperature to 700 °C of commercial nitrogen-containing steels and new steels designed for the TMT. At 700 °C increases in yield stress of 80 and 200% were observed for a commercial steel and a new steel, respectively, compared to commercial normalized-and-tempered steels. Creep-rupture strength was similarly improved. Depending on the TMT, precipitates were up to eight-times smaller at a number density four orders of magnitude greater than those in a conventionally heat treated steel of similar composition.

  18. Radiation induced segregation and precipitation behavior in self-ion irradiated Ferritic/Martensitic HT9 steel

    NASA Astrophysics Data System (ADS)

    Zheng, Ce; Auger, Maria A.; Moody, Michael P.; Kaoumi, Djamel

    2017-08-01

    In this study, Ferritic/Martensitic (F/M) HT9 steel was irradiated to 20 displacements per atom (dpa) at 600 nm depth at 420 and 440 °C, and to 1, 10 and 20 dpa at 600 nm depth at 470 °C using 5 MeV Fe++ ions. The characterization was conducted using ChemiSTEM and Atom Probe Tomography (APT), with a focus on radiation induced segregation and precipitation. Ni and/or Si segregation at defect sinks (grain boundaries, dislocation lines, carbide/matrix interfaces) together with Ni, Si, Mn rich G-phase precipitation were observed in self-ion irradiated HT9 except in very low dose case (1 dpa at 470 °C). Some G-phase precipitates were found to nucleate heterogeneously at defect sinks where Ni and/or Si segregated. In contrast to what was previously reported in the literature for neutron irradiated HT9, no Cr-rich α‧ phase, χ-phases, η phase and voids were found in self-ion irradiated HT9. The difference of observed microstructures is probably due to the difference of irradiation dose rate between ion irradiation and neutron irradiation. In addition, the average size and number density of G-phase precipitates were found to be sensitive to both irradiation temperature and dose. With the same irradiation dose, the average size of G-phase increased whereas the number density decreased with increasing irradiation temperature. Within the same irradiation temperature, the average size increased with increasing irradiation dose.

  19. Influence of helium on deuterium retention in reduced activation ferritic martensitic steel (F82H) under simultaneous deuterium and helium irradiation

    NASA Astrophysics Data System (ADS)

    Yakushiji, K.; Lee, H. T.; Oya, M.; Hamaji, Y.; Ibano, K.; Ueda, Y.

    2016-02-01

    Deuterium and helium retention in Japanese reduced activation ferritic martensitic (RAFM) steel (F82H) under simultaneous D-He irradiation at 500, 625, 750, and 818 K was studied. This study aims to clarify tritium retention behavior in RAFM steels to assess their use as plasma facing materials. The irradiation fluence was kept constant at 1 × 1024 D m-2. Four He desorption peaks were observed with He retention greatest at 625 K. At T > 625 K a monotonic decrease in He retention was observed. At all temperatures a systematic reduction in D retention was observed for the simultaneous D-He case in comparison to D-only case. This suggests that He implanted at the near surface in RAFM steels may reduce the inward penetration of tritium in RAFM steels that would result in lower tritium inventory for a given fluence.

  20. Diffusion Couple Alloying of Refractory Metals in Austenitic and Ferritic/Martensitic Steels

    DTIC Science & Technology

    2012-03-01

    raised in the samples, the main mode was dislocation channeling [8]. b. Irradiation -Induced Precipitation and Grain Boundary Segregation In materials...centered Cubic FIB Focused Ion Beam HTGR High Temperature Gas Reactor IASCC Irradiation -assisted Stress Corrosion Cracking LMFBR Liquid Metal Fast...displacements per atom (dpa) (From [8]). Observations on irradiated austenitic steel determined that two deformation modes were present: dislocation

  1. Irradiation-induced impurity segregation and ductile-to-brittle transition temperature shift in high chromium ferritic/martensitic steels

    NASA Astrophysics Data System (ADS)

    Lu, Z.; Faulkner, R. G.; Flewitt, P. E. J.

    2007-08-01

    A model is presented to predict irradiation-induced impurity segregation and its contribution to the ductile-to-brittle transition temperature (DBTT) shift in high chromium ferritic steels. The hardening contribution (dislocation loops, voids and precipitates) is also considered in this study. The predicted results are compared with the experimental DBTT shifts data for irradiated 9Cr1MoVNb and 12Cr1MoVW steels with different grain sizes.

  2. Boron effect on the microstructure of 9% Cr ferritic-martensitic steels

    NASA Astrophysics Data System (ADS)

    Klimenkov, M.; Materna-Morris, E.; Möslang, A.

    2015-07-01

    The microstructure of reduces-activation 9Cr-WTaV steel alloyed with 83 and 1160 wt. ppm 10B was detailed analysed using transmission electron microscopy. The influence of boron content on the precipitation behaviour of M23C6 and MX (VN and TaC) phases and, hence, on the formation process of steel's grain and lath structure was studied. VN precipitates, which play an important role in the stabilisation of the lath structure, exhibit most sensitive reaction on presence of boron. Their spatial density significantly reduces in the alloy with 83 ppm boron. In the steel with 1160 wt. ppm boron, no formation of VN was detected, whereas TaC particles precipitate at the lath and grain boundaries. These changes in the structure stabilisation mechanism lead to an increasing lath width and a decreasing thermal stability of laths and grains. Analytical investigations of several BN particles reveal their complex multi-phase structure and allow conclusions to be drawn with respect to their precipitation sequence.

  3. Onset of plasticity of helium-implanted ferritic/martensitic steels during nanoindentation

    NASA Astrophysics Data System (ADS)

    Chen, Siwei; Wang, Yongming; Hashimoto, Naoyuki; Ohnuki, Somei

    2014-07-01

    The onset of plasticity during nanoindentation is a new method to investigate the irradiation damage of structural materials in fission and fusion reactors. In this paper, nanoindentation experiment was carried out to helium implanted F82H-IEA and nano-sized oxide dispersion strengthened F82H-ODS steels for studying the elastic-plastic transition at a constant loading rate. The onset of plasticity shifted after helium implantation. By a statistical thermal activation model, activation volume was extracted to discuss the strength of barrier for dislocation motion. The results reveal an increase in the pinning force and number density of effective obstacles for dislocation motion in He-implanted F82H-IEA, and a decrease in the local pinning force without changing the density of effective obstacles in He-implanted F82H-ODS.

  4. Fabrication of 13Cr-2Mo Ferritic/Martensitic Oxide-Dispersion-Strengthened Steel Components by Mechanical Alloying and Spark-Plasma Sintering

    NASA Astrophysics Data System (ADS)

    Bogachev, I.; Grigoryev, E.; Khasanov, O. L.; Olevsky, E.

    2014-06-01

    The outcomes of the mechanical alloying of 13Cr-2Mo ferritic/martensitic steel and yttria (oxide-dispersion-strengthened steel) powders in a ball mill are reported in terms of the powder particle size and morphology evolution. The optimal ball mill rotation speed and the milling time are discussed. The densification kinetics of the mechanically alloyed powder during the process of spark-plasma sintering is analyzed. An optimal set of the compaction processing parameters, including the maximum temperature, the dwell time, and the heating rate, is determined. The specifics of the densification are discussed in terms of the impact of major spark-plasma sintering parameters as well as the possible phase transformations occurring during compaction processing.

  5. Influence of Alloy Content and Prior Microstructure on Evolution of Secondary Phases in Weldments of 9Cr-Reduced Activation Ferritic-Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Thomas Paul, V.; Sudha, C.; Saroja, S.

    2015-08-01

    9Cr-Reduced Activation Ferritic-Martensitic steels with 1 and 1.4 wt pct tungsten are materials of choice for the test blanket module in fusion reactors. The steels possess a tempered martensite microstructure with a decoration of inter- and intra-lath carbides, which undergoes extensive modification on application of heat. The change in substructure and precipitation behavior on welding and subsequent thermal exposure has been studied using both experimental and computational techniques. Changes i.e., formation of various phases, their volume fraction, size, and morphology in different regions of the weldment due to prolonged thermal exposure was influenced not only by the time and temperature of exposure but also the prior microstructure. Laves phase of type Fe2W was formed in the high tungsten steel, on aging the weldment at 823 K (550 °C). It formed in the fine-grained heat-affected zone (HAZ) at much shorter durations than in the base metal. The accelerated kinetics has been understood in terms of enhanced precipitation of carbides at lath/grain boundaries during aging and the concomitant depletion of carbon and chromium and enrichment of tungsten in the vicinity of the carbides. Therefore, the fine-grained HAZ in the weldment was identified as a region susceptible for failure during service.

  6. Analysis of stress-induced Burgers vector anisotropy in pressurized tube specimens of irradiated ferritic-martensitic steel: JLF-1

    SciTech Connect

    Gelles, D.S.; Shibayama, T.

    1998-09-01

    A procedure for determining the Burgers vector anisotropy in irradiated ferritic steels allowing identification of all a<100> and all a/2<111> dislocations in a region of interest is applied to a pressurized tube specimen of JLF-1 irradiated at 430 C to 14.3 {times} 10{sup 22} n/cm{sup 2} (E > 0.1 MeV) or 61 dpa. Analysis of micrographs indicates large anisotropy in Burgers vector populations develop during irradiation creep.

  7. Effects of boron and phosphorus on creep properties of a ferritic/martensitic steel for fast reactor cladding applications

    SciTech Connect

    Not Available

    1994-10-01

    The thermal efficiencies of both conventional and supercritical fossil-fueled power plants can be improved by increasing the operating temperatures and pressures. Increased thermal efficiency would also result in significant fuel cost savings, as well as reduced environmental emissions per megawatt generated. Creep properties of materials currently used as tubes in the hottest areas of the boiler, the superheater and reheater sections, limit the operating temperature. As such, steels with improved creep strength compared to these conventional alloys are needed to increase the operational efficiencies of thermal-electric generating stations. A new class of creep-resistant, 10%Cr martensitic steel has been developed for use as high temperature components, especially in the electric utility, petrochemical & chemical industries. The steel differs from other 9-12%Cr steels in two important ways: It is strengthened by a uniform dispersion of very fine, coarsening-resistant TiC particles rather than chromium-rich, M{sub 23}C{sub 6} precipitates; and the TiC particles are precipitated in austenite prior to the martensitic transformation, not during tempering. By carefully controlling the thermo-mechanical treatment, three TiC sizes were incorporated into the matrix: 4, 12 and 25 nm; grain size and precipitate volume fraction (0.005) were kept constant. Creep tests on these three specimen types were done at 550{degrees}C, 600{degrees}C and 650{degrees}C. Results indicate that reducing the average particle size from 25 to 4 nm (thereby also reducing the average inter-particle spacing) decreases the steady-state creep rate by more than four orders of magnitude. The prototype steel`s composition must now be optimized, and in doing so the effects of boron and phosphorus are investigated.

  8. Silicon-containing ferritic/martensitic steel after exposure to oxygen-containing flowing lead-bismuth eutectic at 450 and 550 °C

    NASA Astrophysics Data System (ADS)

    Schroer, Carsten; Koch, Verena; Wedemeyer, Olaf; Skrypnik, Aleksandr; Konys, Jürgen

    2016-02-01

    A ferritic/martensitic (f/m) steel with 9 and 3 mass% of chromium (Cr) and silicon (Si), respectively, was tested on performance in flowing lead-bismuth eutectic (LBE) at 450 and 550 °C, each at concentrations of solved oxygen of both 10-7 and 10-6 mass%. The 9Cr-3Si steel generally exhibits the same basic corrosion modes as other f/m materials with 9 mass% Cr and typically lower Si content, namely Steel T91. The Si-rich steel shows an overall improved performance in comparison to T91 at 450 °C and 10-7 mass% solved oxygen, but especially at 450 °C and 10-6 mass% solved oxygen. The advantage of higher Si-content in 9Cr steel is less clear at 550 °C. Especially high oxygen content in flowing LBE at 550 °C, between >10-6 mass% and oxygen saturation, seems detrimental for the high-Si material in respect of the initiation and progress of a solution-based corrosion.

  9. Effect of Tungsten on Long-Term Microstructural Evolution and Impression Creep Behavior of 9Cr Reduced Activation Ferritic/Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Thomas Paul, V.; Vijayanand, V. D.; Sudha, C.; Saroja, S.

    2017-01-01

    The present study describes the changes in the creep properties associated with microstructural evolution during thermal exposures to near service temperatures in indigenously developed reduced activation ferritic-martensitic steels with varying tungsten (1 and 1.4 wt pct W) contents. The creep behavior has been studied employing impression creep (IC) test, and the changes in impression creep behavior with tungsten content have been correlated with the observed microstructures. The results of IC test showed that an increase in 0.4 pct W decreases the creep rate to nearly half the value. Creep strength of 1.4 pct W steel showed an increase in steels aged for short durations which decreased as aging time increased. The microstructural changes include coarsening of precipitates, reduction in dislocation density, changes in microchemistry, and formation of new phases. The formation of various phases and their volume fractions have been predicted using the JMatPro software for the two steels and validated by experimental methods. Detailed transmission electron microscopy analysis shows coarsening of precipitates and formation of a discontinuous network of Laves phase in 1.4 W steel aged for 10,000 hours at 823 K (550 °C) which is in agreement with the JMatPro simulation results.

  10. SANS and TEM of ferritic-martensitic steel T91 irradiated in FFTF up to 184 dpa at 413 °C

    NASA Astrophysics Data System (ADS)

    Van den Bosch, J.; Anderoglu, O.; Dickerson, R.; Hartl, M.; Dickerson, P.; Aguiar, J. A.; Hosemann, P.; Toloczko, M. B.; Maloy, S. A.

    2013-09-01

    Ferritic-martensitic steel T91 was previously irradiated in the Materials Open Test Assembly (MOTA) program of the Fast Flux Test Reactor Facility (FFTF) at 413 °C up to 184 dpa. The microstructure was analyzed by small angle neutron scattering (SANS) and transmission electron microscopy (TEM). Both SANS and TEM revealed a large fraction of voids with an average size of 29-32 nm leading to a calculated void swelling of 1.2-1.6% based on the volume fraction of the voids in the sample. SANS gave no indication of second phase particles having formed under irradiation in the material. Using TEM, one zone was found where a few G-phase particles were analyzed. Quantities were however too low to state reliable particle densities. No alpha prime (α') or Laves phase were observed in any of the investigated zones.

  11. Small punch tests on martensitic/ferritic steels F82H, T91 and Optimax-A irradiated in SINQ Target-3

    NASA Astrophysics Data System (ADS)

    Jia, X.; Dai, Y.

    2003-12-01

    Small punch (SP) tests were conducted in a temperature range from -190 to 80 °C on martensitic/ferritic steels F82H, T91 and Optimax-A irradiated in SINQ Target-3 up to 9.4 dpa in a irradiation temperature range of 90-275 °C. Results demonstrate: (a) the irradiation hardening deduced from SP tests is reasonably consistent with the results obtained by tensile tests; (b) with increasing irradiation dose, the SP yield load increases at all test temperatures, while the displacement at the maximum load and the total displacement at failure decrease; (c) the ductile-to-brittle transition temperature (DBTT SP) increases with increasing irradiation dose, and does so more quickly at irradiation doses above ˜6-7 dpa; in addition, the ΔDBTT SP increases linearly with helium content.

  12. Comminuting irradiated ferritic steel

    DOEpatents

    Bauer, Roger E.; Straalsund, Jerry L.; Chin, Bryan A.

    1985-01-01

    Disclosed is a method of comminuting irradiated ferritic steel by placing the steel in a solution of a compound selected from the group consisting of sulfamic acid, bisulfate, and mixtures thereof. The ferritic steel is used as cladding on nuclear fuel rods or other irradiated components.

  13. The Formation of Martensitic Austenite During Nitridation of Martensitic and Duplex Stainless Steels

    NASA Astrophysics Data System (ADS)

    Zangiabadi, Amirali; Dalton, John C.; Wang, Danqi; Ernst, Frank; Heuer, Arthur H.

    2017-01-01

    Isothermal martensite/ferrite-to-austenite phase transformations have been observed after low-temperature nitridation in the martensite and δ-ferrite phases in 15-5 PH (precipitation hardening), 17-7 PH, and 2205 (duplex) stainless steels. These transformations, in the region with nitrogen concentrations of 8 to 16 at. pct, are consistent with the notion that nitrogen is a strong austenite stabilizer and substitutional diffusion is effectively frozen at the paraequilibrium temperatures of our experiments. Our microstructural and diffraction analyses provide conclusive evidence for the martensitic nature of these phase transformations.

  14. Void swelling and microstructure evolution at very high damage level in self-ion irradiated ferritic-martensitic steels

    NASA Astrophysics Data System (ADS)

    Getto, E.; Sun, K.; Monterrosa, A. M.; Jiao, Z.; Hackett, M. J.; Was, G. S.

    2016-11-01

    The void swelling and microstructure evolution of ferritic-martensitic alloys HT9, T91 and T92 were characterized following irradiation with Fe++ ions at 460 °C to damage levels of 75-650 displacements per atom with 10 atom parts per million pre-implanted helium. Steady state swelling rate of 0.033%/ dpa was determined for HT9, the least swelling resistant alloy, and 0.007%/ dpa in T91. In T91, resistance was due to suppression of void nucleation. Swelling resistance was greatest in T92, with a low density (∼1 × 1020 m-3) of small voids that had not grown appreciably, indicating suppression of nucleation and growth. Additional heats of T91 indicated that alloy composition was not the determining factor of swelling resistance. Carbon and chromium-rich M2X precipitates formed at 250 dpa and were correlated with decreased nucleation in T91 and T92, but did not affect void growth in HT9. Dislocation and G-phase microstructure evolution was analyzed up to 650 dpa in HT9.

  15. Residual ferrite formation in 12CrODS steels

    NASA Astrophysics Data System (ADS)

    Ukai, S.; Kudo, Y.; Wu, X.; Oono, N.; Hayashi, S.; Ohtsuka, S.; Kaito, T.

    2014-12-01

    Increasing Cr content from 9 to 12 mass% leads to superior corrosion and high-temperature oxidation resistances, and usually changes microstructure from martensite to a ferrite. To make transformable martensitic type of 12CrODS steels that have superior processing capability by using α/γ phase transformation, alloy design was conducted through varying nickel content. The structure of 12CrODS steels was successfully modified from full ferrite to a transformable martensite-base matrix containing ferrite. This ferrite consists of both equilibrium ferrite and a metastable residual ferrite. It was shown that the fraction of the equilibrium ferrite is predictable by computed phase diagram and formation of the residual ferrite was successfully evaluated through pinning of α/γ interfacial boundaries by oxide particles.

  16. Dependence of mode I and mixed mode I/III fracture toughness on temperature for a ferritic/martensitic stainless steel

    SciTech Connect

    Li, H.; Jones, R.H.; Gelles, D.S.

    1995-04-01

    The objective is to investigate the dependence of mode I and mixed mode I/III fracture toughness on temperature in the range of {minus}95{degrees}C to 25{degrees}C for a low activation ferritic/martensitic stainless steel (F82-H). Mode I and mixed Mode I/III fracture toughnesses were investigated in the range of {minus}95 to 25{degree}C for a F82-H steel heat-treated in the following way; 1000{degree}C/20 h/air-cooled (AC), 1100{degree}C/7 min/AC, and 700{degree}C/2 h/AC. The results indicate that crack tip plasticity was increased by mixed mode loading, and suggest that at low temperature, mode I fracture toughness is the critical design parameter, but at temperatures above room temperature, expecially concerning fatigure and creep-fatigue crack growth rate, a mixed mode loading may be more harmful than a mode I loading for this steel because a mixed mode loading results in lower fracture toughness and higher crack tip plasticity (or dislocation activity).

  17. Effect of sodium environment on the low cycle fatigue properties of modified 9Cr-1Mo ferritic martensitic steel

    NASA Astrophysics Data System (ADS)

    Kannan, R.; Sandhya, R.; Ganesan, V.; Valsan, M.; Bhanu Sankara Rao, K.

    2009-02-01

    Modified 9Cr-1Mo ferritic steel is the material of current interest for the steam generator components of liquid metal cooled fast breeder reactors (LMFBRs). The steam generator has been designed to operate for 30-40 years. It is important to accurately determine the life of the components in the actual environment in order to consider the extension of life beyond the design life. With this objective in view, a programme has been initiated at our laboratory to evaluate the effects of flowing sodium on the LCF behaviour of modified 9Cr-1Mo steel. LCF tests conducted in flowing sodium environment at 823 K and 873 K exhibited cyclic softening behaviour both in air and sodium environments. The fatigue lives are significantly improved in sodium environment when compared to the data obtained in air environment under identical testing conditions. The lack of oxidation in sodium environment is considered to be responsible for the delayed crack initiation and consequent increase in fatigue life. Comparison of experimental lifetimes with RCC-MR design code predictions indicated that the design curve based on air tests is too conservative.

  18. Microstructure evolution of two model ferritic/martensitic steels under in situ ion irradiation at low doses (0-2 dpa)

    NASA Astrophysics Data System (ADS)

    Kaoumi, D.; Adamson, J.; Kirk, M.

    2014-02-01

    Ferritic/martensitic steels are candidate materials for structural and cladding components designed for Generation IV reactors because of their superior resistance to radiation damage at the high operating temperatures envisioned in these reactors. To enable the development and optimization of such advanced alloys for in-reactor use, a fundamental understanding of radiation damage accumulation in materials is required. In this work, two model F/M steels (12Cr model alloy and 9Cr model alloy) were irradiated with 1 MeV Kr ions at 50 K, 180 K, 298 K, 473 K and 573 K in situ in a TEM. The microstructure evolution under irradiation was followed and characterized at successive doses in terms of irradiation-induced defect formation and evolution, defect density, size distribution and interaction with the as-fabricated microstructure (e.g. dislocation networks, lath boundaries) using weak-beam dark-field imaging. The effect of the irradiation temperature on the defect kinetics is assessed at doses up to 2 dpa.

  19. Fatigue tests on a ferritic-martensitic steel at 420$deg;C: Comparison between in-situ and postirradiation properties

    NASA Astrophysics Data System (ADS)

    Lindau, R.; Möslang, A.

    1994-09-01

    Strain-controlled fatigue experiments under simultaneous irradiation have been performed to investigate the specific loadings of structural materials in next-step fusion devices. All irradiations were done on specimens made of the tempered ferritic/martensitic Cr steel MANET-I at 420°C using a 104 MeV α-particle beam. Continuous push-pull cycling ( R = -1) has been applied with total strain ranges Δɛ t between 0.5 and 1.0%. Under in-beam conditions at e.g. Δɛ t = 0.5% a number of cycles to failure of Nt = 42000, a He concentration of 400 appm and a damage dose of 1.6 dpa has been reached. This Nf is by about a factor of two below the average Nf-value of unirradiated reference tests, but seven times higher than Nf of comparable postirradiated specimens. It was found, that at least at 420°C conventional postirradiation tests are a conservative approach to in-situ conditions, and that in strain-controlled tests Nf is mainly governed by the time evolution of the irradiation-induced hardening. Relevant microstructural features like the He-bubble morphology are correlated with the fatigue properties.

  20. Energy-filtered TEM imaging and EELS study of ODS particles and argon-filled cavities in ferritic-martensitic steels.

    PubMed

    Klimiankou, M; Lindau, R; Möslang, A

    2005-01-01

    Oxide-dispersion-strengthened (ODS) ferritic-martensitic steels with yttrium oxide (Y(2)O(3)) have been produced by mechanical alloying and hot isostatic pressing for use as advanced material in fusion power reactors. Argon gas, usually widely used as inert gas during mechanical alloying, was surprisingly detected in the nanodispersion-strengthened materials. Energy-filtered transmission electron microscopy (EFTEM) and electron energy loss spectroscopy (EELS) led to the following results: (i) chemical composition of ODS particles, (ii) voids with typical diameters of 1-6 nm are formed in the matrix, (iii) these voids are filled with Ar gas, and (iv) the high-density nanosized ODS particles serve as trapping centers for the Ar bubbles. The Ar L(3,2) energy loss edge at 245 eV as well as the absorption features of the ODS particle elements were identified in the EELS spectrum. The energy resolution in the EEL spectrum of about 1.0 eV allows to identify the electronic structure of the ODS particles.

  1. Evaluation of mechanically alloyed Cu-based powders as filler alloy for brazing tungsten to a reduced activation ferritic-martensitic steel

    NASA Astrophysics Data System (ADS)

    de Prado, J.; Sánchez, M.; Ureña, A.

    2017-07-01

    80Cu-20Ti powders were evaluated for their use as filler alloy for high temperature brazing of tungsten to a reduced activation ferritic/martensitic steel (Eurofer), and its application for the first wall of the DEMO fusion reactor. The use of alloyed powders has not been widely considered for brazing purposes and could improve the operational brazeability of the studied system due to its narrower melting range, determined by DTA analysis, which enhances the spreading capabilities of the filler. Ti contained in the filler composition acts as an activator element, reacting and forming several interfacial layers at the Eurofer-braze, which enhances the wettability properties and chemical interaction at the brazing interface. Brazing thermal cycle also activated the diffusion phenomena, which mainly affected to the Eurofer alloying elements causing in it a softening band of approximately 400 μm of thickness. However, this softening effect did not degrade the shear strength of the brazed joints (94 ± 23 MPa), because failure during testing was always located at the tungsten-braze interface.

  2. Triple Ion-Beam Studies of Radiation Damage in 9Cr2WVTa Ferritic/Martensitic Steel for a High Power Spallation Neutron Source

    SciTech Connect

    Lee, EH

    2001-08-01

    To simulate radiation damage under a future Spallation Neutron Source (SNS) environment, irradiation experiments were conducted on a candidate 9Cr-2WVTa ferritic/martensitic steel using the Triple Ion Facility (TIF) at ORNL. Irradiation was conducted in single, dual, and triple ion beam modes using 3.5 MeV Fe{sup 2}, 360 keV He{sup +}, and 180 keV H{sup +} at 80, 200, and 350 C. These irradiations produced various defects comprising black dots, dislocation loops, line dislocations, and gas bubbles, which led to hardening. The largest increase in hardness, over 63%, was observed after 50 dpa for triple beam irradiation conditions, revealing that both He and H are augmenting the hardening. Hardness increased less than 30% after 30 dpa at 200 C by triple beams, compatible with neutron irradiation data from previous work which showed about a 30% increase in yield strength after 27.2 dpa at 365 C. However, the very large concentrations of gas bubbles in the matrix and on lath and grain boundaries after these simulated SNS irradiations make predictions of fracture behavior from fission reactor irradiations to spallation target conditions inadvisable.

  3. High heat flux test with HIP-bonded Ferritic Martensitic Steel mock-up for the first wall of the KO HCML TBM

    NASA Astrophysics Data System (ADS)

    Won Lee, Dong; Dug Bae, Young; Kwon Kim, Suk; Yun Shin, Hee; Guen Hong, Bong; Cheol Bang, In

    2011-10-01

    In order for a Korean Helium Cooled Molten Lithium (HCML) Test Blanket Module (TBM) to be tested in the International Thermonuclear Experimental Reactor (ITER), fabrication method for the TBM FW such as Hot Isostatic Pressing (HIP, 1050 °C, 100 MPa, 2 h) has been developed including post HIP heat treatment (PHHT, normalizing at 950 °C for 2 h and tempering at 750 °C for 2 h) with Ferritic Martensitic Steel (FMS). Several mock-ups were fabricated using the developed methods and one of them, three-channel mock-up, was used for performing a High Heat Flux (HHF) test to verify the joint integrity. Test conditions were determined using the commercial code, ANSYS-11, and the test was performed in the Korea Heat Load Test (KoHLT) facility, which was used a radiation heating with a graphite heater. The mock-up survived up to 1000 cycles under 1.0 MW/m 2 heat flux and there is no delamination or failure during the test.

  4. Effect of loading mode on the fracture toughness of a reduced activation ferritic/martensitic stainless steel

    SciTech Connect

    Li, H.; Hirth, J.P.; Jones, R.H.; Gelles, D.S.

    1993-09-01

    The critical J integrals of mode I (J{sub IC}), mixed-mode I/III (J{sub MC}), and mode III (J{sub IIIC}) were examined for a ferritic stainless steel (F-82H) at ambient temperature. A determination of J{sub MC} was made using modified compact-tension specimens. Different ratios of tension/shear stress were achieved by varying the principal axis of the crack plane between 0 and 55 degrees from the load line. The results showed that J{sub MC}s and tearing moduli (T{sub M}) varied with the crack angles and were lower than their mode I and mode III counterparts. Both the minimum J{sub MC} and T{sub M} occurred at a crack angle between 40 and 50 degrees, where {sigma}{sub i}/{sigma}{sub iii} was 1.2 to 0.84. The J{sub min} was 240 kJ/m{sup 2}, and ratios of J{sub IC}/J{sub min} and J{sub IIIC}/J{sub min} were about 2.1 and 1.9, respectively. Morphology of fracture surfaces was consistent with the change of J{sub MC} and T{sub M} values. While the upper shelf-fracture toughness of F-82H depends on loading mode, the J{sub min} remains very high. Other important considerations include the effect of mixed-mode loading on the DBT temperature, and effects of hydrogen and irradiation on J{sub min}.

  5. Influence of Tool Rotational Speed and Post-Weld Heat Treatments on Friction Stir Welded Reduced Activation Ferritic-Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Manugula, Vijaya L.; Rajulapati, Koteswararao V.; Reddy, G. Madhusudhan; Mythili, R.; Bhanu Sankara Rao, K.

    2017-08-01

    The effects of tool rotational speed (200 and 700 rpm) on evolving microstructure during friction stir welding (FSW) of a reduced activation ferritic-martensitic steel (RAFMS) in the stir zone (SZ), thermo-mechanically affected zone (TMAZ), and heat-affected zone (HAZ) have been explored in detail. The influence of post-weld direct tempering (PWDT: 1033 K (760 °C)/ 90 minutes + air cooling) and post-weld normalizing and tempering (PWNT: 1253 K (980 °C)/30 minutes + air cooling + tempering 1033 K (760 °C)/90 minutes + air cooling) treatments on microstructure and mechanical properties has also been assessed. The base metal (BM) microstructure was tempered martensite comprising Cr-rich M23C6 on prior austenite grain and lath boundaries with intra-lath precipitation of V- and Ta-rich MC precipitates. The tool rotational speed exerted profound influence on evolving microstructure in SZ, TMAZ, and HAZ in the as-welded and post-weld heat-treated states. Very high proportion of prior austenitic grains and martensite lath boundaries in SZ and TMAZ in the as-welded state showed lack of strengthening precipitates, though very high hardness was recorded in SZ irrespective of the tool speed. Very fine-needle-like Fe3C precipitates were found at both the rotational speeds in SZ. The Fe3C was dissolved and fresh precipitation of strengthening precipitates occurred on both prior austenite grain and sub-grain boundaries in SZ during PWNT and PWDT. The post-weld direct tempering caused coarsening and coalescence of strengthening precipitates, in both matrix and grain boundary regions of TMAZ and HAZ, which led to inhomogeneous distribution of hardness across the weld joint. The PWNT heat treatment has shown fresh precipitation of M23C6 on lath and grain boundaries and very fine V-rich MC precipitates in the intragranular regions, which is very much similar to that prevailed in BM prior to FSW. Both the PWDT and PWNT treatments caused considerable reduction in the hardness of SZ

  6. Postirradiation thermocyclic loading of ferritic-martensitic structural materials

    NASA Astrophysics Data System (ADS)

    Belyaeva, L.; Orychtchenko, A.; Petersen, C.; Rybin, V.

    Thermonuclear fusion reactors of the Tokamak-type will be unique power engineering plants to operate in thermocyclic mode only. Ferritic-martensitic stainless steels are prime candidate structural materials for test blankets of the ITER fusion reactor. Beyond the radiation damage, thermomechanical cyclic loading is considered as the most detrimental lifetime limiting phenomenon for the above structure. With a Russian and a German facility for thermal fatigue testing of neutron irradiated materials a cooperation has been undertaken. Ampule devices to irradiate specimens for postirradiation thermal fatigue tests have been developed by the Russian partner. The irradiation of these ampule devices loaded with specimens of ferritic-martensitic steels, like the European MANET-II, the Russian 05K12N2M and the Japanese Low Activation Material F82H-mod, in a WWR-M-type reactor just started. A description of the irradiation facility, the qualification of the ampule device and the modification of the German thermal fatigue facility will be presented.

  7. Use of double and triple-ion irradiation to study the influence of high levels of helium and hydrogen on void swelling of 8-12% Cr ferritic-martensitic steels

    NASA Astrophysics Data System (ADS)

    Kupriiyanova, Y. E.; Bryk, V. V.; Borodin, O. V.; Kalchenko, A. S.; Voyevodin, V. N.; Tolstolutskaya, G. D.; Garner, F. A.

    2016-01-01

    In accelerator-driven spallation (ADS) devices, some of the structural materials will be exposed to intense fluxes of very high energy protons and neutrons, producing not only displacement damage, but very high levels of helium and hydrogen. Unlike fission flux-spectra where most helium and hydrogen are generated by transmutation in nickel and only secondarily in iron or chromium, gas production in ADS flux-spectra are rather insensitive to alloy composition, such that Fe-Cr base ferritic alloys also generate very large gas levels. While ferritic alloys are known to swell less than austenitic alloys in fission spectra, there is a concern that high gas levels in fusion and especially ADS facilities may strongly accelerate void swelling in ferritic alloys. In this study of void swelling in response to helium and hydrogen generation, irradiation was conducted on three ferritic-martensitic steels using the Electrostatic Accelerator with External Injector (ESUVI) facility that can easily produce any combination of helium to dpa and/or hydrogen to dpa ratios. Irradiation was conducted under single, dual and triple beam modes using 1.8 MeV Cr+3, 40 keV He+, and 20 keV H+. In the first part of this study we investigated the response of dual-phase EP-450 to variations in He/dpa and H/dpa ratio, focusing first on dual ion studies and then triple ion studies, showing that there is a diminishing influence on swelling with increasing total gas content. In the second part we investigated the relative response of three alloys spanning a range of starting microstructure and composition. In addition to observing various synergisms between He and H, the most important conclusion was that the tempered martensite phase, known to lag behind the ferrite phase in swelling in the absence of gases, loses much of its resistance to void nucleation when irradiated at large gas/dpa levels.

  8. Investigation of a Novel NDE Method for Monitoring Thermomechanical Damage and Microstructure Evolution in Ferritic-Martensitic Steels for Generation IV Nuclear Energy Systems

    SciTech Connect

    Nagy, Peter

    2013-09-30

    The main goal of the proposed project is the development of validated nondestructive evaluation (NDE) techniques for in situ monitoring of ferritic-martensitic steels like Grade 91 9Cr-1Mo, which are candidate materials for Generation IV nuclear energy structural components operating at temperatures up to ~650{degree}C and for steam-generator tubing for sodium-cooled fast reactors. Full assessment of thermomechanical damage requires a clear separation between thermally activated microstructural evolution and creep damage caused by simultaneous mechanical stress. Creep damage can be classified as "negligible" creep without significant plastic strain and "ordinary" creep of the primary, secondary, and tertiary kind that is accompanied by significant plastic deformation and/or cavity nucleation and growth. Under negligible creep conditions of interest in this project, minimal or no plastic strain occurs, and the accumulation of creep damage does not significantly reduce the fatigue life of a structural component so that low-temperature design rules, such as the ASME Section III, Subsection NB, can be applied with confidence. The proposed research project will utilize a multifaceted approach in which the feasibility of electrical conductivity and thermo-electric monitoring methods is researched and coupled with detailed post-thermal/creep exposure characterization of microstructural changes and damage processes using state-of-the-art electron microscopy techniques, with the aim of establishing the most effective nondestructive materials evaluation technique for particular degradation modes in high-temperature alloys that are candidates for use in the Next Generation Nuclear Plant (NGNP) as well as providing the necessary mechanism-based underpinnings for relating the two. Only techniques suitable for practical application in situ will be considered. As the project evolves and results accumulate, we will also study the use of this technique for monitoring other GEN IV

  9. Kinetics of Ferrite Recrystallization and Austenite Formation During Intercritical Annealing of the Cold-Rolled Ferrite/Martensite Duplex Structures

    NASA Astrophysics Data System (ADS)

    Mazaheri, Y.; Kermanpur, A.; Najafizadeh, A.; Kalashami, A. Ghatei

    2016-03-01

    Ultrafine-grained, dual-phase (UFG DP) steels were produced by a new route using an uncommon cold-rolling and subsequent intercritical annealing of ferrite/martensite duplex starting microstructures. The effects of processing parameters such as rolling reduction, intercritical annealing temperature, and time on the microstructural evaluations have been studied. UFG DP steels with an average grain size of about 1 to 2 μm were achieved by short intercritical annealing of the 80 pct cold-rolled duplex microstructures. The kinetics of ferrite recrystallization and austenite formation were studied based on the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model. The proposed model for describing the isothermal austenite formation kinetics was applied successfully to the nonisothermal conditions. It was found that complete recrystallization of ferrite before the austenite formation led to the formation of a large extent randomly distributed austenite in the ferrite matrix and a chain-networked structure.

  10. Articles comprising ferritic stainless steels

    SciTech Connect

    Rakowski, James M.

    2016-06-28

    An article of manufacture comprises a ferritic stainless steel that includes a near-surface region depleted of silicon relative to a remainder of the ferritic stainless steel. The article has a reduced tendency to form an electrically resistive silica layer including silicon derived from the steel when the article is subjected to high temperature oxidizing conditions. The ferritic stainless steel is selected from the group comprising AISI Type 430 stainless steel, AISI Type 439 stainless steel, AISI Type 441 stainless steel, AISI Type 444 stainless steel, and E-BRITE.RTM. alloy, also known as UNS 44627 stainless steel. In certain embodiments, the article of manufacture is a fuel cell interconnect for a solid oxide fuel cell.

  11. Study of MHD Corrosion and Transport of Corrosion Products of Ferritic/Martensitic Steels in the Flowing PbLi and its Application to Fusion Blanket

    NASA Astrophysics Data System (ADS)

    Saeidi, Sheida

    Two important components of a liquid breeder blanket of a fusion power reactor are the liquid breeder/coolant and the steel structure that the liquid is enclosed in. One candidate combination for such components is Lead-Lithium (PbLi) eutectic alloy and advanced Reduced Activation Ferritic/Martensitic (RAFM) steel. The research performed here is aimed at: (1) better understanding of corrosion processes in the system including RAFM steel and flowing PbLi in the presence of a strong magnetic field and (2) prediction of corrosion losses in conditions of a Dual Coolant Lead Lithium (DCLL) blanket, which is at present the key liquid metal blanket concept in the US. To do this, numerical and analytical tools have been developed and then applied to the analysis of corrosion processes. First, efforts were taken to develop a computational suite called TRANSMAG (Transport phenomena in Magnetohydrodynamic Flows) as an analysis tool for corrosion processes in the PbLi/RAFM system, including transport of corrosion products in MHD laminar and turbulent flows. The computational approach in TRANSMAG is based on simultaneous solution of flow, energy and mass transfer equations with or without a magnetic field, assuming mass transfer controlled corrosion and uniform dissolution of iron in the flowing PbLi. Then, the new computational tool was used to solve an inverse mass transfer problem where the saturation concentration of iron in PbLi was reconstructed from the experimental data resulting in the following correlation: CS = e 13.604--12975/T, where T is the temperature of PbLi in K and CS is in wppm. The new correlation for saturation concentration was then used in the analysis of corrosion processes in laminar flows in a rectangular duct in the presence of a strong transverse magnetic field. As shown in this study, the mass loss increases with the magnetic field such that the corrosion rate in the presence of a magnetic field can be a few times higher compared to purely

  12. Lath martensites in low carbon steels

    SciTech Connect

    Sarikaya, M.; Thomas, G.

    1982-01-01

    The morphology and crystallography of lath martensite in low and medium carbon steels have been studied by transmission electron microscopy and diffraction. The steels have microduplex structures of dislocated lath martensite (a < b much less than c) with fairly straight boundaries and continuous interlath thin films of retained austenite. Stacks of laths (i.e., single crystals of martensite) form the packets which are derived from different (111) transformation variants of austenite. Microdiffraction experiments directly allow the determination of the orientation relationships between austenite and martensite. Relative orientations of adjacent individual laths cluster about common orientations from small to large angular differences all around a common <110>M direction. The overall microstructure and orientations result from minimization of the total strain and shape deformation. Considerable accommodation occurs by deformation of laths (sometimes twinned) and austenite (sometimes tripped to twin martensite). In the meantime, microchemical analyses have shown considerable carbon segregation to the martensite-austenite interface. 4 figures.

  13. Comparative Tensile Flow and Work-Hardening Behavior of 9 Pct Chromium Ferritic-Martensitic Steels in the Framework of the Estrin-Mecking Internal-Variable Approach

    NASA Astrophysics Data System (ADS)

    Choudhary, B. K.; Christopher, J.

    2016-06-01

    The comparative tensile flow and work-hardening behavior of P9 steel in two different product forms, normalized and tempered plate and thick section tube plate forging, and P91 steel were investigated in the framework of the dislocation dynamics based Estrin-Mecking (E-M) one-internal-variable approach. The analysis indicated that the flow behavior of P9 and P91 steels was adequately described by the E-M approach in a wide range of temperatures. It was suggested that dislocation dense martensite lath/cell boundaries and precipitates together act as effective barriers to dislocation motion in P9 and P91 steels. At room and intermediate temperatures, the evolution of the internal-state variable, i.e., the dislocation density with plastic strain, exhibited insignificant variations with respect to temperature. At high temperatures, a rapid evolution of dislocation density with plastic strain toward saturation with increasing temperature was observed. The softer P9 steel tube plate forging exhibited higher work hardening in terms of larger gains in the dislocation density and flow stress contribution from dislocations than the P9 steel plate and P91 steel at temperatures ranging from 300 K to 873 K (27 °C to 600 °C). The evaluation of activation energy suggests that the deformation is controlled by cross-slip of dislocations at room and intermediate temperatures, and climb of dislocations at high temperatures. The relative influence of initial microstructure on flow and work-hardening parameters associated with the E-M approach was discussed in the three temperature regimes displayed by P9 and P91 steels.

  14. Ultrahigh Ductility, High-Carbon Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Qin, Shengwei; Liu, Yu; Hao, Qingguo; Zuo, Xunwei; Rong, Yonghua; Chen, Nailu

    2016-10-01

    Based on the proposed design idea of the anti-transformation-induced plasticity effect, both the additions of the Nb element and pretreatment of the normalization process as a novel quenching-partitioning-tempering (Q-P-T) were designed for Fe-0.63C-1.52Mn-1.49Si-0.62Cr-0.036Nb hot-rolled steel. This high-carbon Q-P-T martensitic steel exhibits a tensile strength of 1890 MPa and elongation of 29 pct accompanied by the excellent product of tensile and elongation of 55 GPa pct. The origin of ultrahigh ductility for high-carbon Q-P-T martensitic steel is revealed from two aspects: one is the softening of martensitic matrix due to both the depletion of carbon in the matensitic matrix during the Q-P-T process by partitioning of carbon from supersaturated martensite to retained austenite and the reduction of the dislocation density in a martensitic matrix by dislocation absorption by retained austenite effect during deformation, which significantly enhances the deformation ability of martensitic matrix; another is the high mechanical stability of considerable carbon-enriched retained austenite, which effectively reduces the formation of brittle twin-type martensite. This work verifies the correctness of the design idea of the anti-TRIP effect and makes the third-generation advanced high-strength steels extend to the field of high-carbon steels from low- and medium-carbon steels.

  15. Effects of alloying and processing modifications on precipitation and strength in 9%Cr ferritic/martensitic steels for fast reactor cladding

    NASA Astrophysics Data System (ADS)

    Tippey, Kristin E.

    P92 was modified with respect to alloying and processing in the attempt to enhance high-temperature microstructural stability and mechanical properties. Alloying effects were modeled in ThermoCalcRTM and analyzed with reference to literature. ThermoCalcRTM modeling was conducted to design two low-carbon P92-like low-carbon alloys with austenite stabilized by alternative alloying; full conversion to austenite allows for a fully martensitic structure. Goals included avoidance of Z-phase, decrease of M23C6 phase fraction and maintained or increased MX phase fraction. Fine carbonitride precipitation was optimized by selecting alloying compositions such that all V and Nb could be solutionized at temperatures outside the delta-ferrite phase field. A low-carbon alloy (LC) and a low-carbon-zero-niobium alloy (0Nb) were identified and fabricated. This low-carbon approach stems from the increased creep resistance reported in several low-carbon alloys, presumably from reduced M23C6 precipitation and maintained MX precipitation [1], although these low-carbon alloys also contained additional tungsten (W) and cobalt (Co) compared to the base P92 alloy. The synergistic effect of Co and W on the microstructure and mechanical properties are difficult to deconvolute. Higher solutionizing temperatures allow more V and Nb into solution and increase prior austenite grain size; however, at sufficiently high temperatures delta-ferrite forms. Optimal solutionizing temperatures to maximize V and Nb in solution, while avoiding the onset of the delta ferrite phase field, were analyzed in ThermoCalcRTM. Optical microscopy showed ThermoCalc RTM predicted higher delta-ferrite onset temperatures of 20 °C in P92 alloys to nearly 50 °C in the designed alloys of the critical temperature. Identifying the balance where maximum fine precipitation is achieved and delta-ferrite avoided is a key factor in the design of an acceptable P92-like alloy for Generation IV reactor cladding. Processing was

  16. Microstructures and Mechanical Properties of High-Mn TRIP Steel Based on Warm Deformation of Martensite

    NASA Astrophysics Data System (ADS)

    Guo, Zhikai; Li, Longfei; Yang, Wangyue; Sun, Zuqing

    2015-04-01

    High-Mn TRIP steel with about 5 wt pct Mn was prepared by a thermo-mechanical treatment based on warm deformation of martensite and subsequent short-time annealing in the intercritical region. The microstructural evolution and the mechanical properties of the used steel during such treatment were investigated. The results indicate that during warm deformation of martensite in the intercritical region, the decomposition of martensite was accelerated by warm deformation and the occurrence of dynamic recrystallization of ferrite led to the formation of equiaxed ferrite grains. Meanwhile, the reverse transformation of austenite was accelerated by warm deformation to some extent. During subsequent annealing in the intercritical region, static recrystallization of ferrite led to the increase in the fraction of equiaxed ferrite grains, and the formation of the reversed austenite was accelerated by the addition of the deformation-stored energy, while the stability of the reversed austenite was improved by the accelerated diffusions of C atoms and Mn atoms. As a whole, the mechanical properties of the used steel by the thermo-mechanical treatment based on warm deformation of martensite and subsequent short-time annealing in the intercritical region were comparable to the steels with similar compositions subjected to intercritical annealing for hours after cold rolling of martensite.

  17. The evolution of internal stress and dislocation during tensile deformation in a 9Cr ferritic/martensitic (F/M) ODS steel investigated by high-energy X-rays

    SciTech Connect

    Zhang, Guangming; Zhou, Zhangjian; Mo, Kun; Miao, Yinbin; Liu, Xiang; Almer, Jonathan; Stubbins, James F.

    2015-12-01

    An application of high-energy wide angle synchrotron X-ray diffraction to investigate the tensile deformation of 9Cr ferritic/martensitic (F/M) ODS steel is presented. With tensile loading and in-situ Xray exposure, the lattice strain development of matrix was determined. The lattice strain was found to decrease with increasing temperature, and the difference in Young's modulus of six different reflections at different temperatures reveals the temperature dependence of elastic anisotropy. The mean internal stress was calculated and compared with the applied stress, showing that the strengthening factor increased with increasing temperature, indicating that the oxide nanoparticles have a good strengthening impact at high temperature. The dislocation density and character were also measured during tensile deformation. The dislocation density decreased with increasing of temperature due to the greater mobility of dislocation at high temperature. The dislocation character was determined by best-fit methods for different dislocation average contrasts with various levels of uncertainty. The results shows edge type dislocations dominate the plastic strain at room temperature (RT) and 300 C, while the screw type dislocations dominate at 600 C. The dominance of edge character in 9Cr F/M ODS steels at RT and 300 C is likely due to the pinning effect of nanoparticles for higher mobile edge dislocations when compared with screw dislocations, while the stronger screw type of dislocation structure at 600 C may be explained by the activated cross slip of screw segments.

  18. Microstructure and cleavage in lath martensitic steels

    NASA Astrophysics Data System (ADS)

    Morris, John W., Jr.; Kinney, Chris; Pytlewski, Ken; Adachi, Y.

    2013-02-01

    In this paper we discuss the microstructure of lath martensitic steels and the mechanisms by which it controls cleavage fracture. The specific experimental example is a 9Ni (9 wt% Ni) steel annealed to have a large prior austenite grain size, then examined and tested in the as-quenched condition to produce a relatively coarse lath martensite. The microstructure is shown to approximate the recently identified ‘classic’ lath martensite structure: prior austenite grains are divided into packets, packets are subdivided into blocks, and blocks contain interleaved laths whose variants are the two Kurjumov-Sachs relations that share the same Bain axis of the transformation. When the steel is fractured in brittle cleavage, the laths in the block share {100} cleavage planes and cleave as a unit. However, cleavage cracks deflect or blunt at the boundaries between blocks with different Bain axes. It follows that, as predicted, the block size governs the effective grain size for cleavage.

  19. Microstructure and cleavage in lath martensitic steels.

    PubMed

    Morris, John W; Kinney, Chris; Pytlewski, Ken; Adachi, Y

    2013-02-01

    In this paper we discuss the microstructure of lath martensitic steels and the mechanisms by which it controls cleavage fracture. The specific experimental example is a 9Ni (9 wt% Ni) steel annealed to have a large prior austenite grain size, then examined and tested in the as-quenched condition to produce a relatively coarse lath martensite. The microstructure is shown to approximate the recently identified 'classic' lath martensite structure: prior austenite grains are divided into packets, packets are subdivided into blocks, and blocks contain interleaved laths whose variants are the two Kurjumov-Sachs relations that share the same Bain axis of the transformation. When the steel is fractured in brittle cleavage, the laths in the block share {100} cleavage planes and cleave as a unit. However, cleavage cracks deflect or blunt at the boundaries between blocks with different Bain axes. It follows that, as predicted, the block size governs the effective grain size for cleavage.

  20. The effect of low dose irradiation on the impact fracture energy and tensile properties of pure iron and two ferritic martensitic steels

    NASA Astrophysics Data System (ADS)

    Belianov, I.; Marmy, P.

    1998-10-01

    Two batches of subsize V-notched impact bend specimens and subsize tensile specimens have been irradiated in the Saphir test reactor of the Paul Scherrer Institute (PSI). The first batch of specimen has been irradiated at 250°C to a dose of 2.65 × 10 19 n/cm 2 (0.042 dpa) and the second batch has been irradiated at 400°C to a dose of 8.12 × 10 19 n/cm 2 (0.13 dpa). Three different materials in three different microstructures were irradiated: pure iron and two ferritic steels, the alloy MANET 2 and a low activation composition CETA. The results of the impact tests and of the corresponding tensile tests are presented. Despite the very low neutron dose, a significant shift of the ductile to brittle transition temperature (DBTT) is observed. The influence of the test temperature on the impact energy is discussed for the irradiated and unirradiated conditions, with special emphasis on the microstructure.

  1. EVALUATION OF SPECIFICATION RANGES FOR CREEP STRENGTH ENHANCED FERRITIC STEELS

    SciTech Connect

    Shingledecker, John P; Santella, Michael L; Wilson, Keely A

    2008-01-01

    Creep Strength Enhanced Ferritic Steels (CSEF) such as Gr. 91, 911, 92, and 122 require a fully martensitic structure for optimum properties, mainly good creep strength. However, broad chemical compositional ranges are specified for these steel grades which can strongly influence the microstructures obtained. In this study, we have produced chemical compositions within the specification ranges for these alloys which intentionally cause the formation of ferrite or substantially alter the lower intercritical temperatures (A1) so as to affect the phase transformation behavior during tempering. Thermodynamic modeling, thermo-mechanical simulation, tensile testing, creep testing, and microstructural analysis were used to evaluate these materials. The results show the usefulness of thermodynamic calculations for setting rational chemical composition ranges for CSEF steels to control the critical temperatures, set heat-treatment temperature limits, and eliminate the formation of ferrite.

  2. Microstructural Evolution and Recrystallization Kinetics of a Cold-Rolled, Ferrite-Martensite Structure During Intercritical Annealing

    NASA Astrophysics Data System (ADS)

    Etesami, S. A.; Enayati, M. H.

    2016-07-01

    The recrystallization behavior of 80 pct, cold-rolled, low-carbon, dual-phase steel during intercritical annealing for different times was studied. The annealed microstructures showed that the recrystallization initially occurred in the deformed martensitic regions. The values of Avrami exponent for recrystallization varied from 3.8 to 4 with an activation energy of 46.9 kJ/mol. This study also introduced a novel method for the production of bimodal grain structures in low-carbon, ferrite-martensite steel.

  3. Microstructure and mechanical properties of dual phase steels, with different martensite morphology, produced during TLP bonding of a low C-Mn steel

    NASA Astrophysics Data System (ADS)

    Fazaeli, Abolfazl; Ekrami, Aliakbar; Kokabi, Amir Hossein

    2016-09-01

    In this research, production of ferrite - martensite dual phase Steels with different martensite morphology was considered during transient liquid phase bonding of a low carbon steel. The steel was bonded using an iron base interlayer with melting point of 1443 K and 40 μm thickness. Bonding process carried out at 1473 K, under pressure of 0.5 MPa, at different holding time of 10, 20, 30 and 40 minutes. Microstructural studies of joint region showed that isothermal solidification completed at the bonding time of 40 minutes. Microstructure of joints made at the bonding time of 10, 20, and 30 minutes consists of two distinct region, athermal and isothermal solidified zones. Microstructure of these zones was studied and chemical composition of these zones was determined by EDS. Joints made with bonding time of 40 minutes were homogenized at 1008 K and then cooled into cold water to produce dual phase ferrite and martensite microstructure with different martensite morphology. According to shear test results, it was found that the shear strength of ferrite - fibrous martensite microstructure is greater than those with ferrite - continuous martensite and ferrite - blocky martensite microstructure.

  4. 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.

  5. Microstructural behavior of 8Cr-ODS martensitic steels during creep deformation

    NASA Astrophysics Data System (ADS)

    Shinozuka, K.; Esaka, H.; Tamura, M.; Tanigawa, H.

    2011-10-01

    Oxide dispersion strengthened (ODS) steels show a high anisotropy in their creep behavior because of the δ-ferrite grain elongated in the hot-rolled direction and the characteristic formation of creep cavities. In this work, the relationship between the δ-ferrite grain and the growth of creep cavities in 8Cr-ODS steels was investigated. The samples of two ODS steels with different δ-ferrite volume fractions were machined parallel and perpendicular to the hot-rolled direction. Creep rupture tests and interrupted tests were performed at 700 °C and about 197 MPa. Cavities formed in the martensite along δ-ferrite grains during creep deformation. The area fraction of the cavities of all specimens increased in proportion to the cube root of test time. When the volume fraction of δ-ferrite was high and δ-ferrite grains elongated parallel to the load direction, δ-ferrite then obstructed the propagation of cracks. However, when the volume fraction of δ-ferrite was low and δ-ferrite grains elongated perpendicular to the load direction, δ-ferrite grains had little effect on crack propagation.

  6. Must we use ferritic steel in TBM?

    SciTech Connect

    Salavy, Jean-Francois; Boccaccini, Lorenzo V.; Chaudhuri, Paritosh; Cho, Seungyon; Enoeda, Mikio; Giancarli, Luciano; Kurtz, Richard J.; Luo, Tian Y.; Rao, K. Bhanu Sankara; Wong, Clement

    2010-12-13

    Mock-ups of DEMO breeding blankets, called Test Blanket Modules (TBMs), inserted and tested in ITER in dedicated equatorial ports directly facing the plasma, are expected to provide the first experimental answers on the necessary performance of the corresponding DEMO breeding blankets. Several DEMO breeding blanket designs have been studied and assessed in the last 20 years. At present, after considering various coolant and breeder combinations, all the TBM concepts proposed by the seven ITER Parties use Reduced-Activation Ferritic/Martensitic (RAFM) steel as the structural material. In order to perform valuable tests in ITER, the TBMs are expected to use the same structural material as corresponding DEMO blankets. However, due to the fact that this family of steels is ferromagnetic, their presence in the ITER vacuum vessel will create perturbations of the ITER magnetic fields that could reduce the quality of the plasma confinement during H-mode. As a consequence, a legitimate question has been raised on the necessity of using RAFM steel for TBMs structural material in ITER. By giving a short description of the main TBM testing objectives in ITER and assessing the consequences of not using such a material, this paper gives a comprehensive answer to this question. According to the working group author of the study, the use of RAFM steel as structural material for TBM is judged mandatory.

  7. Microstructure and toughness of CrW and CrV ferritic steels

    NASA Astrophysics Data System (ADS)

    Abe, F.; Araki, H.; Noda, T.; Okada, M.

    1988-07-01

    In order to obtain an optimum alloy composition of reduced-activation Cr-W-V ferritic steels, the microstructural evolution during thermal aging at 823-973 K and its effect on the toughness were investigated for simple Cr-W and Cr-V steels by means of transmission electron microscopy and Charpy impact testing. The microstructural evolution of the Cr-W steels was similar to that of the conventional CrMo steels. Carbides precipitated in the martensite and the intermetallic compound Fe 2W precipitated in the δ-ferrite of the Cr-W steels. On the other hand, only carbides precipitated in both the martensite and the δ-ferrite of the Cr-V steels. The effect of Cr, W and V on the thermal embrittlement is discussed by taking account of the precipitation behavior.

  8. Influence of displacement damage on deuterium and helium retention in austenitic and ferritic-martensitic alloys considered for ADS service

    NASA Astrophysics Data System (ADS)

    Voyevodin, V. N.; Karpov, S. A.; Kopanets, I. E.; Ruzhytskyi, V. V.; Tolstolutskaya, G. D.; Garner, F. A.

    2016-01-01

    The behavior of ion-implanted hydrogen (deuterium) and helium in austenitic 18Cr10NiTi stainless steel, EI-852 ferritic steel and ferritic/martensitic steel EP-450 and their interaction with displacement damage were investigated. Energetic argon irradiation was used to produce displacement damage and bubble formation to simulate nuclear power environments. The influence of damage morphology and the features of radiation-induced defects on deuterium and helium trapping in structural alloys was studied using ion implantation, the nuclear reaction D(3He,p)4He, thermal desorption spectrometry and transmission electron microscopy. It was found in the case of helium irradiation that various kinds of helium-radiation defect complexes are formed in the implanted layer that lead to a more complicated spectra of thermal desorption. Additional small changes in the helium spectra after irradiation with argon ions to a dose of ≤25 dpa show that the binding energy of helium with these traps is weakly dependent on the displacement damage. It was established that retention of deuterium in ferritic and ferritic-martensitic alloys is three times less than in austenitic steel at damage of ˜1 dpa. The retention of deuterium in steels is strongly enhanced by presence of radiation damages created by argon ion irradiation, with a shift in the hydrogen release temperature interval of 200 K to higher temperature. At elevated temperatures of irradiation the efficiency of deuterium trapping is reduced by two orders of magnitude.

  9. Assessment of martensitic steels as structural materials in magnetic fusion devices

    SciTech Connect

    Rawls, J.M.; Chen, W.Y.K.; Cheng, E.T.; Dalessandro, J.A.; Miller, P.H.; Rosenwasser, S.N.; Thompson, L.D.

    1980-01-01

    This manuscript documents the results of preliminary experiments and analyses to assess the feasibility of incorporating ferromagnetic martensitic steels in fusion reactor designs and to evaluate the possible advantages of this class of material with respect to first wall/blanket lifetime. The general class of alloys under consideration are ferritic steels containing from about 9 to 13 percent Cr with some small additions of various strengthening elements such as Mo. These steels are conventionally used in the normalized and tempered condition for high temperature applications and can compete favorably with austenitic alloys up to about 600/sup 0/C. Although the heat treatment can result in either a tempered martensite or bainite structure, depending on the alloy and thermal treatment parameters, this general class of materials will be referred to as martensitic stainless steels for simplicity.

  10. Fatigue Hardening Behavior of 1.5 GPa Grade Transformation-Induced Plasticity-Aided Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Sugimoto, Koh-Ichi; Hojo, Tomohiko

    2016-11-01

    Low cycle fatigue hardening/softening behavior of a 0.2 pct C-1.5 pct Si-1.5 pct Mn-1.0 pct Cr-0.2 pct Mo-0.05 pct Nb transformation-induced plasticity (TRIP)-aided steel consisting of a wide lath martensite structure matrix and a narrow lath martensite-metastable retained austenite mixture was investigated. The steel exhibited notable fatigue hardening in the same way as TRIP-aided bainitic ferrite steel, although conventional martensitic steel such as SCM420 steel with the same tensile strength exhibited fatigue softening. The considerable fatigue hardening of this steel is believed to be associated mainly with the compressive internal stress that results from a difference in flow stress between the matrix and the martensite-austenite-like phase, with a small contribution from the strain-induced transformation and dislocation hardenings.

  11. Sensitization of Laser-beam Welded Martensitic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Dahmen, Martin; Rajendran, Kousika Dhasanur; Lindner, Stefan

    Ferritic and martensitic stainless steels are an attractive alternative in vehicle production due to their inherent corrosion resistance. By the opportunity of press hardening, their strength can be increased to up to 2000 MPa, making them competitors for unalloyed ultra-high strength steels. Welding, nevertheless, requires special care, especially when it comes to joining of high strength heat treated materials. With an adopted in-line heat treatment of the welds in as-rolled as well as press hardened condition, materials with sufficient fatigue strength and acceptable structural behavior can be produced. Because of microstructural transformations in the base material such as grain coarsening and forced carbide precipitation, the corrosion resistance of the weld zone may be locally impaired. Typically the material in the heat-affected zone becomes sensitive to intergranular cracking in the form of knife-edge corrosion besides the fusion line. The current study comprises of two text scenarios. By an alternating climate test, general response in a corroding environment is screened. In order to understand the corrosion mechanisms and to localize the sensitive zones, sensitisation tests were undertaken. Furthermore, the applicability of a standard test according to ASTM 763-83 was examined. It was found that the alternative climate test does not reveal any corrosion effects. Testing by the oxalic acid test revealed clearly the effect of welding, weld heat treatment and state of thermal processing. Also application of the standard which originally suited for testing ferritic stainless steels could have been justified.

  12. Creep resistant, precipitation-dispersion-strengthened, martensitic stainless steel and method thereof

    DOEpatents

    Buck, Robert F.

    1994-01-01

    An iron-based, corrosion-resistant, precipitation strengthened, martensitic steel essentially free of delta ferrite for use at high temperatures has a nominal composition of 0.05-0.1 C, 8-12 Cr, 1-5 Co, 0.5-2.0 Ni, 0.41-1.0 Mo, 0.1-0.5 Ti, and the balance iron. This steel is different from other corrosion-resistant martensitic steels because its microstructure consists of a uniform dispersion of fine particles, which are very closely spaced, and which do not coarsen at high temperatures. Thus at high temperatures this steel combines the excellent creep strength of dispersion-strengthened steels, with the ease of fabricability afforded by precipitation hardenable steels.

  13. Creep resistant, precipitation-dispersion-strengthened, martensitic stainless steel and method thereof

    DOEpatents

    Buck, R.F.

    1994-05-10

    An iron-based, corrosion-resistant, precipitation strengthened, martensitic steel essentially free of delta ferrite for use at high temperatures has a nominal composition of 0.05--0.1 C, 8--12 Cr, 1--5 Co, 0.5--2.0 Ni, 0.41--1.0 Mo, 0.1--0.5 Ti, and the balance iron. This steel is different from other corrosion-resistant martensitic steels because its microstructure consists of a uniform dispersion of fine particles, which are very closely spaced, and which do not coarsen at high temperatures. Thus at high temperatures this steel combines the excellent creep strength of dispersion-strengthened steels, with the ease of fabricability afforded by precipitation hardenable steels. 2 figures.

  14. Thermal helium desorption behavior in advanced ferritic steels

    NASA Astrophysics Data System (ADS)

    Kimura, Akihiko; Sugano, R.; Matsushita, Y.; Ukai, S.

    2005-02-01

    Thermal helium desorption measurements were performed to investigate the difference in the helium trapping and accumulation behavior among a reduced activation ferritic (RAF) steel and oxide dispersion strengthening (ODS) steels after implantation of He+ ions at room temperature. Thermal helium desorption spectra (THDS) were obtained during annealing to 1200 °C at a heating rate of 1 °C/s. The THDS of the ODS steels are very similar to that of the RAF steel, except for the presence of the peak in the temperature range from 800 to 1000 °C, where the α γ transformation related helium desorption from the γ-phase is considered to occur in the 9Cr-ODS martensitic steels. The fraction of helium desorption becomes larger at higher temperatures, and this trend is increased with the amount of implanted helium. In the 9Cr-ODS steels, the fraction of helium desorption by bubble migration mechanism was smaller than that in the RAF steel. This suggests that the bubble formation was suppressed in the ODS steels. In the 12Cr-ODS steel, the fraction of helium desorption by bubble migration reached more than 90%, suggesting that the trapping capacity of martensite phase in the 9Cr-ODS steel is rather large.

  15. Atomic scale investigation of non-equilibrium segregation of boron in a quenched Mo-free martensitic steel.

    PubMed

    Li, Y J; Ponge, D; Choi, P; Raabe, D

    2015-12-01

    B-added low carbon steels exhibit excellent hardenability. The reason has been frequently attributed to B segregation at prior austenite grain boundaries, which prevents the austenite to ferrite transformation and favors the formation of martensite. The segregation behavior of B at prior austenite grain boundaries is strongly influenced by processing conditions such as austenitization temperatures and cooling rates and by alloying elements such as Mo, Cr, and Nb. Here an local electrode atom probe was employed to investigate the segregation behavior of B and other alloying elements (C, Mn, Si, and Cr) in a Cr-added Mo-free martensitic steel. Similar to our previous results on a Mo-added steel, we found that in both steels B is segregated at prior austenite grain boundaries with similar excess values, whereas B is neither detected in the martensitic matrix nor at martensite-martensite boundaries at the given cooling rate of 30K/s. These results are in agreement with the literature reporting that Cr has the same effect on hardenability of steels as Mo in the case of high cooling rates. The absence of B at martensite-martensite boundaries suggests that B segregates to prior austenite grain boundaries via a non-equilibrium mechanism. Segregation of C at all boundaries such as prior austenite grain boundaries and martensite-martensite boundaries may occur by an equilibrium mechanism.

  16. Effect of ferrite on cast stainless steels

    SciTech Connect

    Nadezhdin, A.; Cooper, K. ); Timbers, G. . Kraft Pulp Division)

    1994-09-01

    Premature failure of stainless steel castings in bleach washing service is attributed to poor casting quality high porosity and to a high ferrite content, which makes the castings susceptible to corrosion by hot acid chloride solutions. A survey of the chemical compositions and ferrite contents of corrosion-resistant castings in bleach plants at three pulp mills found high [delta]-ferrite levels in the austenitic matrix due to the improper balance between austenite and ferrite stabilizers.

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

    NASA Astrophysics Data System (ADS)

    Syammach, Sami M.

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

  18. Notch-Fatigue Properties of Advanced TRIP-Aided Bainitic Ferrite Steels

    NASA Astrophysics Data System (ADS)

    Yoshikawa, Nobuo; Kobayashi, Junya; Sugimoto, Koh-ichi

    2012-11-01

    To develop a transformation-induced plasticity (TRIP)-aided bainitic ferrite steel (TBF steel) with high hardenability for a common rail of the next generation diesel engine, 0.2 pct C-1.5 pct Si-1.5 pct Mn-0.05 pct Nb TBF steels with different contents of Cr, Mo, and Ni were produced. The notch-fatigue strength of the TBF steels was investigated and was related to the microstructural and retained austenite characteristics. If Cr, Mo, and/or Ni were added to the base steel, then the steels achieved extremely higher notch-fatigue limits and lower notch sensitivity than base TBF steel and the conventional structural steels. This was mainly associated with (1) carbide-free and fine bainitic ferrite lath structure matrix without proeutectoid ferrite, (2) a large amount of fine metastable retained austenite, and (3) blocky martensite phase including retained austenite, which may suppress a fatigue crack initiation and propagation.

  19. Ferritic steel melt and FLiBe/steel experiment : melting ferritic steel.

    SciTech Connect

    Troncosa, Kenneth P.; Smith, Brandon M.; Tanaka, Tina Joan

    2004-11-01

    In preparation for developing a Z-pinch IFE power plant, the interaction of ferritic steel with the coolant, FLiBe, must be explored. Sandia National Laboratories Fusion Technology Department was asked to drop molten ferritic steel and FLiBe in a vacuum system and determine the gas byproducts and ability to recycle the steel. We tried various methods of resistive heating of ferritic steel using available power supplies and easily obtained heaters. Although we could melt the steel, we could not cause a drop to fall. This report describes the various experiments that were performed and includes some suggestions and materials needed to be successful. Although the steel was easily melted, it was not possible to drip the molten steel into a FLiBe pool Levitation melting of the drop is likely to be more successful.

  20. Experimental investigation of the transformation texture in hotrolled ferritic stainless steel using single orientation determination

    NASA Astrophysics Data System (ADS)

    Raabe, D.; Ylitalo, M.

    1996-01-01

    Two ferritic stainless steels (≈16.5 mass pct Cr) were hot-rolled using seven subsequent passes. The first sample was rolled within the range 1280 °C to 750 °C, i.e., the deformation started in the ferritic region. The second sample was rolled within the range 1080 °C to 770 °C, i.e., the deformation started in the ferritic-austenitic region. In both cases, up to 40 vol pct of the ferrite transformed into austenite during hot rolling. During the last passes, the austenite transformed into cubic martensite. After hot rolling, these former austenitic regions were identified using a selective etching technique and examined using single orientation determination in the scanning electron microscope. The regions which remained ferritic throughout the hot-rolling process were investigated as well. Whereas the texture of the martensite considerably depended on the hot-rolling conditions, especially on the temperature and on the intervals between the rollings, the texture of the ferrite was less affected. The textures of the martensite were interpreted in terms of the crystallographic transformation rules between austenite and martensite. The textures of the ferrite were discussed in terms of recovery and recrystallization.

  1. Diffusion bonding between ODS ferritic steel and F82H steel for fusion applications

    NASA Astrophysics Data System (ADS)

    Noh, Sanghoon; Kim, Byungjun; Kasada, Ryuta; Kimura, Akihiko

    2012-07-01

    Diffusion bonding techniques were employed to join high Cr oxide dispersion strengthened (ODS) ferritic steel (Fe-15Cr-2W-0.2Ti-0.35Y2O3) and F82H steel under uni-axial hydrostatic pressure using a high vacuum hot press, and the microstructure and mechanical properties of the joints were investigated. The dissimilar joints were bonded by solid-state diffusion bonding (SSDB) and liquid phase diffusion bonding (LPDB). After bonding process, heat treatments were conducted to utilize the phase transformation of F82H steel for recovering the martensitic structure. Tensile tests with miniaturized specimens were carried out to investigate and compare the bonding strengths of each joint. Microstructure was observed for the bonding interface, and fracture mode was investigated after the tensile tests. LPDB joint of interfacial F82H steel fully recovered to martensite phase by post-joining heat treatments, while SSDB joint had ferrite phases at the interface even after heat treatment, which is considered to be due to decarburization of F82H steel during the bonding process. Therefore it is considered that the insert material plays a role as diffusion barrier of carbon during LPDB process. Microstructure observations and tensile tests of the joints revealed that the LPDB joints possess suitable tensile properties which are comparable to that of F82H steel. This indicates that LPDB is more promising method to bond ODS-FS and F82H steel than SSDB.

  2. Creep behavior of pack cementation aluminide coatings on Grade 91 ferritic martensitic alloy

    SciTech Connect

    Bates, Brian; Zhang, Ying; Dryepondt, Sebastien N; Pint, Bruce A

    2014-01-01

    The creep behavior of various pack cementation aluminide coatings on Grade 91 ferritic-martensitic steel was investigated at 650 C in laboratory air. The coatings were fabricated in two temperature regimes, i.e., 650 or 700 C (low temperature) and 1050 C(high temperature), and consisted of a range of Al levels and thicknesses. For comparison, uncoated specimens heat-treated at 1050 C to simulate the high temperature coating cycle also were included in the creep test. All coated specimens showed a reduction in creep resistance, with 16 51% decrease in rupture life compared to the as-received bare substrate alloy. However, the specimens heat-treated at 1050 C exhibited the lowest creep resistance among all tested samples, with a surprisingly short rupture time of < 25 h, much shorter than the specimen coated at 1050 C. Factors responsible for the reduction in creep resistance of both coated and heat-treated specimens were discussed.

  3. Creep resistant high temperature martensitic steel

    DOEpatents

    Hawk, Jeffrey A.; Jablonski, Paul D.; Cowen, Christopher J.

    2015-11-13

    The disclosure provides a creep resistant alloy having an overall composition comprised of iron, chromium, molybdenum, carbon, manganese, silicon, nickel, vanadium, niobium, nitrogen, tungsten, cobalt, tantalum, boron, and potentially additional elements. In an embodiment, the creep resistant alloy has a molybdenum equivalent Mo(eq) from 1.475 to 1.700 wt. % and a quantity (C+N) from 0.145 to 0.205. The overall composition ameliorates sources of microstructural instability such as coarsening of M.sub.23C.sub.6 carbides and MX precipitates, and mitigates or eliminates Laves and Z-phase formation. A creep resistant martensitic steel may be fabricated by preparing a melt comprised of the overall composition followed by at least austenizing and tempering. The creep resistant alloy exhibits improved high-temperature creep strength in the temperature environment of around 650.degree. C.

  4. Creep resistant high temperature martensitic steel

    DOEpatents

    Hawk, Jeffrey A.; Jablonski, Paul D.; Cowen, Christopher J.

    2017-01-31

    The disclosure provides a creep resistant alloy having an overall composition comprised of iron, chromium, molybdenum, carbon, manganese, silicon, nickel, vanadium, niobium, nitrogen, tungsten, cobalt, tantalum, boron, copper, and potentially additional elements. In an embodiment, the creep resistant alloy has a molybdenum equivalent Mo(eq) from 1.475 to 1.700 wt. % and a quantity (C+N) from 0.145 to 0.205. The overall composition ameliorates sources of microstructural instability such as coarsening of M.sub.23C.sub.6carbides and MX precipitates, and mitigates or eliminates Laves and Z-phase formation. A creep resistant martensitic steel may be fabricated by preparing a melt comprised of the overall composition followed by at least austenizing and tempering. The creep resistant alloy exhibits improved high-temperature creep strength in the temperature environment of around 650.degree. C.

  5. Multiscale Modeling of the Deformation of Advanced Ferritic Steels for Generation IV Nuclear Energy

    SciTech Connect

    Nasr M. Ghoniem; Nick Kioussis

    2009-04-18

    The objective of this project is to use the multi-scale modeling of materials (MMM) approach to develop an improved understanding of the effects of neutron irradiation on the mechanical properties of high-temperature structural materials that are being developed or proposed for Gen IV applications. In particular, the research focuses on advanced ferritic/ martensitic steels to enable operation up to 650-700°C, compared to the current 550°C limit on high-temperature steels.

  6. Stress-Corrosion Cracking in Martensitic PH Stainless Steels

    NASA Technical Reports Server (NTRS)

    Humphries, T.; Nelson, E.

    1984-01-01

    Precipitation-hardening alloys evaluated in marine environment tests. Report describes marine-environment stress-corrosion cracking (SCC) tests of three martensitic precipitation hardening (PH) stainless-steel alloys.

  7. Effect of Microstructure on Torsional Fatigue Endurance of Martensitic Carbon Steel

    NASA Astrophysics Data System (ADS)

    Toyoda, Shunsuke; Ishiguro, Yasuhide; Kawabata, Yoshikazu; Sakata, Kei; Sato, Akio; Sakai, Jun'ichi

    The microstructural influence of martensitic carbon steel on torsional fatigue endurance was investigated, taking into consideration the application of high strength steel electric resistance welded (ERW) tubes to automotive structural parts. The chemical composition of the base steel alloy was 0.1-0.2%C-0.2-1.5%Si-1.3-1.9%Mn-0.01%P-0.001%S-(Cr, Mo, Ti, Nb, B). Laboratory vacuum-fused ingots were hot-rolled, heated to 1023 or 1223 K in a salt bath, and then water-quenched and tempered at 473 K. Consequently, three types of microstructure, martensite (M), martensite and ferrite (M+F), and ferrite and pearlite (F+P), were prepared. Fully reversed torsional fatigue testing was conducted with 6 mm diameter round bar specimens. Torsional fatigue endurance was found to monotonously increase with increases in the tensile strength of the specimen from 540 to 1380 MPa. The martensitic single structure and the M+F dual-phase structure showed a similar level of fatigue endurance at a tensile strength of approximately 950 MPa. However, fatigue micro-crack morphology varied slightly between them. At the surface of the M+F specimen, many small cracks were observed in addition to the main crack. Conversely, in the martensitic specimen, these small cracks were rarely observed. ΔK decreasing/increasing crack growth testing with compact tension (CT)-type specimens was also conducted. Based on these experimental results, the effect of microstructure and stress level on the initiation/propagation cycle ratio is discussed. In addition to fatigue properties, some practical properties, such as low-temperature toughness and hydrogen embrittlement resistance, were also evaluated in view of actual applications for automotive structural parts.

  8. Effect of heat treatment and irradiation temperature on impact properties of Cr-W-V ferritic steels

    NASA Astrophysics Data System (ADS)

    Klueh, R. L.; Alexander, D. J.

    Charpy impact tests were conducted on eight normalized-and-tempered ferritic and martensitic steels irradiated in two different normalized conditions. Irradiation was conducted in the Fast Flux Test Facility (FFTF) at 393°C to ≈14 dpa on eight steels with 2.25%, 5%, 9%, and 12% Cr (0.1% C) with varying amounts of W, V, and Ta. The different normalization treatments involved changing the cooling rate after austenitization. The faster cooling rate produced 100% bainite in the 2.25Cr steels, compared to duplex structures of bainite and polygonal ferrite for the slower cooling rate. For both cooling rates, martensite formed in the 5% and 9% Cr steels, and martensite with ≈25% δ-ferrite formed in the 12% Cr steel. Irradiation caused an increase in the ductile-brittle transition temperature (DBTT) and a decrease in the upper-shelf energy (USE). The difference in microstructure in the low-chromium steels due to the different heat treatments had little effect on properties. For the high-chromium martensitic steels, only the 5Cr steel was affected by heat treatment. When the results at 393°C were compared with previous results at 365°C, all but a 5Cr and a 9Cr steel showed the expected decrease in the shift in DBTT with increasing temperature.

  9. Materials design data for reduced activation martensitic steel type EUROFER

    NASA Astrophysics Data System (ADS)

    Tavassoli, A.-A. F.; Alamo, A.; Bedel, L.; Forest, L.; Gentzbittel, J.-M.; Rensman, J.-W.; Diegele, E.; Lindau, R.; Schirra, M.; Schmitt, R.; Schneider, H. C.; Petersen, C.; Lancha, A.-M.; Fernandez, P.; Filacchioni, G.; Maday, M. F.; Mergia, K.; Boukos, N.; Baluc; Spätig, P.; Alves, E.; Lucon, E.

    2004-08-01

    Materials design limits derived so far from the data generated in Europe for the reduced activation ferritic/martensitic (RAFM) steel type Eurofer are presented. These data address the short-term needs of the ITER Test Blanket Modules and a DEMOnstration fusion reactor. Products tested include plates, bars, tubes, TIG and EB welds, as well as powder consolidated blocks and solid-solid HIP joints. Effects of thermal ageing and low dose neutron irradiation are also included. Results are sorted and screened according to design code requirements before being introduced in reference databases. From the physical properties databases, variations of magnetic properties, modulus of elasticity, density, thermal conductivity, thermal diffusivity, specific heat, mean and instantaneous linear coefficients of thermal expansion versus temperature are derived. From the tensile and creep properties databases design allowable stresses are derived. From the instrumented Charpy impact and fracture toughness databases, ductile to brittle transition temperature, toughness and behavior of materials in different fracture modes are evaluated. From the fatigue database, total strain range versus number of cycles to failure curves are plotted and used to derive fatigue design curves. Cyclic curves are also derived and compared with monotonic hardening curves. Finally, irradiated and aged materials data are compared to ensure that the safety margins incorporated in unirradiated design limits are not exceeded.

  10. Hot-Deformation Behavior and Hot-Processing Maps of AISI 410 Martensitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Qi, Rong-Sheng; Jin, Miao; Guo, Bao-Feng; Liu, Xin-Gang; Chen, Lei

    2016-10-01

    The compressive deformation behaviors of 410 martensitic stainless steel were investigated on a Gleeble-1500 thermomechanical simulator, and the experimental stress-strain data were obtained. The measured flow stress was corrected for friction and temperature. A constitutive equation that accounts for the influence of strain was established, and the hot-processing maps at different strain were plotted. The microstructure evolution of the hot-deformation process was studied on the basis of microstructural observations at high temperatures. Phase-transformation experiments on 410 steel were conducted at high temperatures to elucidate the effects of temperature on the delta-ferrite content. The initial forging temperature and optimum process parameters were obtained on the basis of the processing map and the changes in the delta-ferrite content at high temperatures.

  11. Influence of PWHT on Toughness of High Chromium and Nickel Containing Martensitic Stainless Steel Weld Metals

    NASA Astrophysics Data System (ADS)

    Divya, M.; Das, Chitta Ranjan; Mahadevan, S.; Albert, S. K.; Pandian, R.; Kar, Sujoy Kumar; Bhaduri, A. K.; Jayakumar, T.

    2015-06-01

    Commonly used 12.5Cr-5Ni consumable specified for welding of martensitic stainless steels is compared with newly designed 14.5Cr-5Ni consumable in terms of their suitability for repair welding of 410 and 414 stainless steels by gas tungsten arc welding process. Changes in microstructure and austenite evolution were investigated using optical, scanning electron microscopy, X-ray diffraction techniques and Thermo-Calc studies. Microstructure of as-welded 12.5Cr-5Ni weld metal revealed only lath martensite, whereas as-welded 14.5Cr-5Ni weld metal revealed delta-ferrite, retained austenite, and lath martensite. Toughness value of as-welded 12.5Cr-5Ni weld metal is found to be significantly higher (216 J) than that of the 14.5Cr-5Ni weld metal (15 J). The welds were subjected to different PWHTs: one at 923 K (650 °C) for 1, 2, 4 hours (single-stage PWHT) and another one at 923 K (650 °C)/4 h followed by 873 K (600 °C)/2 h or 873 K (600 °C)/4 h (two-stage heat treatment). Hardness and impact toughness of the weld metals were measured for these weld metals and correlated with the microstructure. The study demonstrates the importance of avoiding formation of delta-ferrite in the weld metal.

  12. Crystallographic analysis of the martensitic transformation in medium-carbon steel with packet martensite

    NASA Astrophysics Data System (ADS)

    Gundyrev, V. M.; Zel'dovich, V. I.; Schastlivtsev, V. M.

    2016-10-01

    Based on X-ray diffraction studies of the martensite texture in a single martensite packet, exact orientation relationships between the orientations of martensite crystallites and the original austenite single crystal in medium-carbon steel 37KhN3A have been determined to be as follows: (011)α||(1; 0.990; 1.009)γ to an accuracy of ± 0.15°, [ {01overline 1 } ]_α ||{[ {1;1.163; - 2.133} ]_γ } to an accuracy of ±0.15°. It has been shown that the orientation relationships proved to be almost the same as in the Fe-31% Ni alloy with a twinned martensite with close lattice parameters. Therefore, the conclusion has been drawn that the mechanism of the lattice deformation upon the martensitic transformation is the same in both alloys. It is described as follows. The lattice deformation occurs by shear on the (111) plane in the {[ {11overline 2 } ]_{_γ }} direction and is accompanied by an additional change in the dimensions in the mutually perpendicular directions {[ {11overline 2 } ]_{_γ }},[ {111} ],and{[ {1overline 1 0} ]_{_γ }}. The invariantlattice deformation is implemented by slip in martensite on the planes of the (112)α type in the direction {[ {overline 1 overline 1 1} ]_α }. One of the 24 crystallographically equivalent variants of the transformation mechanism has been considered. Apart from this type of deformation, an additional deformation of martensite is possible that does not change its orientation. It has been shown that the orientation of the martensite crystallite calculated via the phenomenological theory of the martensitic transformations (PTMT) differs by approximately 1° from the experimentally determined orientation. This refers to both the lath and twinned martensite. In the twinned martensite, the invariant plane obtained in the PTMT calculations and the habit plane coincide. In lath martensite of 37KhN3A steel, the invariant plane of the martensite crystal obtained in PTMT calculations deviates by 25° from the orientation of the

  13. Characterization and comparative analysis of the tensile properties of five tempered martensitic steels and an oxide dispersion strengthened ferritic alloy irradiated at ≈295 °C to ≈6.5 dpa

    NASA Astrophysics Data System (ADS)

    Maloy, S. A.; Saleh, T. A.; Anderoglu, O.; Romero, T. J.; Odette, G. R.; Yamamoto, T.; Li, S.; Cole, J. I.; Fielding, R.

    2016-01-01

    Tensile test results at 25 and 300 °C on five 9-12Cr tempered martensitic steels and one 14Cr oxide dispersion strengthened alloy, that were side-by side irradiated to 6.5 dpa at 295 °C in the Advanced Test Reactor (ATR), are reported. The engineering stress-strain curves are analyzed to provide true stress-strain constitutive σ(ɛ) laws for all of these alloys. In the irradiated condition, the σ(ɛ) fall into categories of: strain softening, nearly perfectly plastic and strain hardening. Increases in yield stress (Δσy) and reductions in uniform strain ductility (eu) are observed, where the latter can be understood in terms of the alloy's σ(ɛ) behavior. Increases in the average σ(ɛ) in the range of 0-10% strain are smaller than the corresponding Δσy, and vary more from alloy to alloy. The data are also analyzed to establish relations between Δσy and coupled changes in the ultimate stresses as well as the effects of both test temperature and the unirradiated yield stress (σyu). The latter shows that higher σyu correlates with lower Δσy. In five out of six cases the effects of irradiation are generally consistent with previous observations on these alloys. However, the particular heat of the 12Cr HT-9 tempered martensitic steel in this study has a much higher eu than observed for earlier heats. The reasons for this improved behavior are not understood and may be microstructural in origin. However, it is noted that the new heat of HT-9, which was procured under modern quality assurance standards, has lower interstitial nitrogen than previous heats. Notably lower interstitial solute contents correlate with improved ductility and homogenous deformation in broadly similar steels.

  14. Characterization and comparative analysis of the tensile properties of five tempered martensitic steels and an oxide dispersion strengthened ferritic alloy irradiated at ≈295 °C to ≈6.5 dpa

    DOE PAGES

    Maloy, Stuart A.; Saleh, Tarik A.; Anderoglu, Osman; ...

    2015-08-06

    Tensile test results at 25 and 300 °C on five 9-12Cr tempered martensitic steels and one 14Cr oxide dispersion strengthened alloy, that were side-by side irradiated to 6.5 dpa at 295 °C in the Advanced Test Reactor (ATR), are reported. The engineering stress–strain curves are analyzed to provide true stress–strain constitutive σ(ε) laws for all of these alloys. In the irradiated condition, the σ(ε) fall into categories of: strain softening, nearly perfectly plastic and strain hardening. Increases in yield stress (Δσy) and reductions in uniform strain ductility (eu) are observed, where as the latter can be understood in terms ofmore » the alloy's σ(ε) behavior. Increases in the average σ(ε) in the range of 0–10% strain are smaller than the corresponding Δσy, and vary more from alloy to alloy. The data are analyzed to establish relations between Δσy and coupled changes in the ultimate stresses as well as the effects of both test temperature and the unirradiated yield stress (σyu). The latter shows that higher σyu correlates with lower Δσy. In five out of six cases the effects of irradiation are generally consistent with previous observations on these alloys. However, the particular heat of the 12Cr HT-9 tempered martensitic steel in this study has a much higher eu than observed for earlier heats. The reasons for this improved behavior are not understood and may be microstructural in origin. However, it is noted that the new heat of HT-9, which was procured under modern quality assurance standards, has lower interstitial nitrogen than previous heats. As a result, notably lower interstitial solute contents correlate with improved ductility and homogenous deformation in broadly similar steels.« less

  15. A correlative approach to segmenting phases and ferrite morphologies in transformation-induced plasticity steel using electron back-scattering diffraction and energy dispersive X-ray spectroscopy.

    PubMed

    Gazder, Azdiar A; Al-Harbi, Fayez; Spanke, Hendrik Th; Mitchell, David R G; Pereloma, Elena V

    2014-12-01

    Using a combination of electron back-scattering diffraction and energy dispersive X-ray spectroscopy data, a segmentation procedure was developed to comprehensively distinguish austenite, martensite, polygonal ferrite, ferrite in granular bainite and bainitic ferrite laths in a thermo-mechanically processed low-Si, high-Al transformation-induced plasticity steel. The efficacy of the ferrite morphologies segmentation procedure was verified by transmission electron microscopy. The variation in carbon content between the ferrite in granular bainite and bainitic ferrite laths was explained on the basis of carbon partitioning during their growth.

  16. Nanotribological behavior of deep cryogenically treated martensitic stainless steel

    PubMed Central

    Bakoglidis, Konstantinos D; Tuckart, Walter R; Broitman, Esteban

    2017-01-01

    Cryogenic treatments are increasingly used to improve the wear resistance of various steel alloys by means of transformation of retained austenite, deformation of virgin martensite and carbide refinement. In this work the nanotribological behavior and mechanical properties at the nano-scale of cryogenically and conventionally treated AISI 420 martensitic stainless steel were evaluated. Conventionally treated specimens were subjected to quenching and annealing, while the deep cryogenically treated samples were quenched, soaked in liquid nitrogen for 2 h and annealed. The elastic–plastic parameters of the materials were assessed by nanoindentation tests under displacement control, while the friction behavior and wear rate were evaluated by a nanoscratch testing methodology that it is used for the first time in steels. It was found that cryogenic treatments increased both hardness and elastic limit of a low-carbon martensitic stainless steel, while its tribological performance was enhanced marginally. PMID:28904837

  17. Microstructure and mechanical properties of newly developed low activation martensitic steels

    NASA Astrophysics Data System (ADS)

    Victoria, M.; Gavillet, D.; Spätig, P.; Rezai-Aria, F.; Rossmann, S.

    1996-10-01

    The reference ferritic-martensitic steel of the European Fusion Technology Program, the 10CrMoNbV MANET cast, has been modified by replacing the elements that result in long term residual radioactivity when irradiated under a fusion neutron spectra by others which have shorter activation periods. A base composition of a 9CrWVTa steel has been so defined. Two different compositions of the base alloy have been cast from high purity components, which the Mn and N contents have been varied. The extracted carbide types and their size distribution have been studied under the electron microscope. The mechanical properties of both compositions have been determined. Both steel compositions have a ductile-brittle transition temperature (DBTT) well below room temperature while their tensile properties are comparable to those of the parent (MANET) steel.

  18. Optimization and testing results of Zr-bearing ferritic steels

    SciTech Connect

    Tan, Lizhen; Yang, Ying; Tyburska-Puschel, Beata; Sridharan, K.

    2014-09-01

    The mission of the Nuclear Energy Enabling Technologies (NEET) program is to develop crosscutting technologies for nuclear energy applications. Advanced structural materials with superior performance at elevated temperatures are always desired for nuclear reactors, which can improve reactor economics, safety margins, and design flexibility. They benefit not only new reactors, including advanced light water reactors (LWRs) and fast reactors such as sodium-cooled fast reactor (SFR) that is primarily designed for management of high-level wastes, but also life extension of the existing fleet when component exchange is needed. Developing and utilizing the modern materials science tools (experimental, theoretical, and computational tools) is an important path to more efficient alloy development and process optimization. Ferritic-martensitic (FM) steels are important structural materials for nuclear reactors due to their advantages over other applicable materials like austenitic stainless steels, notably their resistance to void swelling, low thermal expansion coefficients, and higher thermal conductivity. However, traditional FM steels exhibit a noticeable yield strength reduction at elevated temperatures above ~500°C, which limits their applications in advanced nuclear reactors which target operating temperatures at 650°C or higher. Although oxide-dispersion-strengthened (ODS) ferritic steels have shown excellent high-temperature performance, their extremely high cost, limited size and fabricability of products, as well as the great difficulty with welding and joining, have limited or precluded their commercial applications. Zirconium has shown many benefits to Fe-base alloys such as grain refinement, improved phase stability, and reduced radiation-induced segregation. The ultimate goal of this project is, with the aid of computational modeling tools, to accelerate the development of a new generation of Zr-bearing ferritic alloys to be fabricated using conventional

  19. Microstructure and high temperature properties of the dissimilar weld between ferritic stainless steel and carbon steel

    NASA Astrophysics Data System (ADS)

    Kim, Jeong Kil; Hong, Seung Gab; Kang, Ki Bong; Kang, Chung Yun

    2009-10-01

    Dissimilar joints between STS441, a ferritic stainless steel, and SS400, a carbon steel, were welded by GMAW (Gas Metal Arc Welding) using STS430LNb as a welding wire. The fracture behavior of the dissimilar weld was analyzed by a microstructural observation and thermo-mechanical tests. Martensite was formed at the region between SS400 and the weld metal because the Cr and Nb content in this region decreased due to the dilution of SS400 carbon steel during welding. According to results from a high temperature tensile test with a specimen aged at 900 °C, it was found that the tensile strength of the dissimilar weld at high temperature was equal to that of STS441 base metal and the formation of martensite had little influence on tensile strength of the dissimilar weld at high temperature. However, in the case of thermal fatigue resistance, the dissimilar weld had an inferior thermal fatigue life to STS441 because of the presence of martensite and the softened region around the interface between the dissimilar weld metal and SS400.

  20. Effect of heat treatment and irradiation temperature on impact behavior of irradiated reduced-activation ferritic steels

    SciTech Connect

    Klueh, R.L.; Alexander, D.J.

    1998-03-01

    Charpy tests were conducted on eight normalized-and-tempered reduced-activation ferritic steels irradiated in two different normalized conditions. Irradiation was conducted in the Fast Flux Test Facility at 393 C to {approx}14 dpa on steels with 2.25, 5, 9, and 12% Cr (0.1% C) with varying amounts of W, V, and Ta. The different normalization treatments involved changing the cooling rate after austenitization. The faster cooling rate produced 100% bainite in the 2.25 Cr steels, compared to duplex structures of bainite and polygonal ferrite for the slower cooling rate. For both cooling rates, martensite formed in the 5 and 9% Cr steels, and martensite with {approx}25% {delta}-ferrite formed in the 12% Cr steel. Irradiation caused an increase in the ductile-brittle transition temperature (DBTT) and a decrease in the upper-shelf energy. The difference in microstructure in the low-chromium steels due to the different heat treatments had little effect on properties. For the high-chromium martensitic steels, only the 5 Cr steel was affected by heat treatment. When the results at 393 C were compared with previous results at 365 C, all but a 5 Cr and a 9 Cr steel showed the expected decrease in the shift in DBTT with increasing temperature.

  1. Characterization and comparative analysis of the tensile properties of five tempered martensitic steels and an oxide dispersion strengthened ferritic alloy irradiated at ≈295 °C to ≈6.5 dpa

    SciTech Connect

    Maloy, Stuart A.; Saleh, Tarik A.; Anderoglu, Osman; Romero, Tobias J.; Odette, G. Robert; Yamamoto, Takuya; Li, S.; Cole, James I.; Fielding, Randall

    2015-08-06

    Tensile test results at 25 and 300 °C on five 9-12Cr tempered martensitic steels and one 14Cr oxide dispersion strengthened alloy, that were side-by side irradiated to 6.5 dpa at 295 °C in the Advanced Test Reactor (ATR), are reported. The engineering stress–strain curves are analyzed to provide true stress–strain constitutive σ(ε) laws for all of these alloys. In the irradiated condition, the σ(ε) fall into categories of: strain softening, nearly perfectly plastic and strain hardening. Increases in yield stress (Δσy) and reductions in uniform strain ductility (eu) are observed, where as the latter can be understood in terms of the alloy's σ(ε) behavior. Increases in the average σ(ε) in the range of 0–10% strain are smaller than the corresponding Δσy, and vary more from alloy to alloy. The data are analyzed to establish relations between Δσy and coupled changes in the ultimate stresses as well as the effects of both test temperature and the unirradiated yield stress (σyu). The latter shows that higher σyu correlates with lower Δσy. In five out of six cases the effects of irradiation are generally consistent with previous observations on these alloys. However, the particular heat of the 12Cr HT-9 tempered martensitic steel in this study has a much higher eu than observed for earlier heats. The reasons for this improved behavior are not understood and may be microstructural in origin. However, it is noted that the new heat of HT-9, which was procured under modern quality assurance standards, has lower interstitial nitrogen than previous heats. As a result, notably lower interstitial solute contents correlate with improved ductility and homogenous deformation in broadly similar steels.

  2. Radiation embrittlement of manganese-stabilized martensitic stainless steel

    SciTech Connect

    Gelles, D.S.; Hu, W.L.

    1986-12-01

    Fractographic examination has been performed on selected Charpy specimens of manganese stabilized martensitic stainless steels in order to identify the cause of irradiation embrittlement. Embrittlement was found to be partly due to enhanced failure at grain boundaries arising from precipitation. Microstructural examination of a specimen irradiated at higher temperature has demonstrated the presence of Fe-Cr-Mn chi phase, a body centered cubic intermetallic phase known to cause embrittlement. This work indicated that manganese stabilized martensitic stainless steels are prone to intermetallic phase formation which is detrimental to mechanical properties.

  3. Tensile properties of the modified 13Cr martensitic stainless steels

    NASA Astrophysics Data System (ADS)

    Mabruri, Efendi; Anwar, Moch. Syaiful; Prifiharni, Siska; Romijarso, Toni B.; Adjiantoro, Bintang

    2016-04-01

    This paper reports the influence of Mo and Ni on the tensile properties of the modified 13Cr martensitic stainless steels in tempered condition. Four steels with different content of Mo and Ni were prepared by induction melting followed by hot forging, quenching and tempering. The experimental results showed that the addition of about 1% and 3% Mo has a beneficial effect to increase both the tensile strength and the elongation of the steels. On the contrary, the addition of about 3% Ni into the martensitic stainless steel results in decreasing of both the tensile strength and the elongation. Among the alloys investigated the 13Cr3Mo type steel exhibited largest tensile strength of 1348 MPa and largest elongation of 12%. The observation on the tensile fractured surfaces by using scanning electron microscope supported these findings.

  4. Tensile properties of the modified 13Cr martensitic stainless steels

    SciTech Connect

    Mabruri, Efendi Anwar, Moch Syaiful Prifiharni, Siska Romijarso, Toni B.; Adjiantoro, Bintang

    2016-04-19

    This paper reports the influence of Mo and Ni on the tensile properties of the modified 13Cr martensitic stainless steels in tempered condition. Four steels with different content of Mo and Ni were prepared by induction melting followed by hot forging, quenching and tempering. The experimental results showed that the addition of about 1% and 3% Mo has a beneficial effect to increase both the tensile strength and the elongation of the steels. On the contrary, the addition of about 3% Ni into the martensitic stainless steel results in decreasing of both the tensile strength and the elongation. Among the alloys investigated the 13Cr3Mo type steel exhibited largest tensile strength of 1348 MPa and largest elongation of 12%. The observation on the tensile fractured surfaces by using scanning electron microscope supported these findings.

  5. Twinning and martensite in a 304 austenitic stainless steel

    SciTech Connect

    Shen, Yongfeng; Li, Xi; Sun, Xin; Wang, Y. D.; Zuo, Liang

    2012-08-30

    The microstructure characteristics and deformation behavior of 304L stainless steel during tensile deformation at two different strain rates have been investigated by means of interrupted tensile tests, electron-backscatter-diffraction (EBSD) and transmission electron microscopy (TEM) techniques. The volume fractions of transformed martensite and deformation twins at different stages of the deformation process were measured using X-ray diffraction method and TEM observations. It is found that the volume fraction of martensite monotonically increases with increasing strain but decreases with increasing strain rate. On the other hand, the volume fraction of twins increases with increasing strain for strain level less than 57%. Beyond that, the volume fraction of twins decreases with increasing strain. Careful TEM observations show that stacking faults (SFs) and twins preferentially occur before the nucleation of martensite. Meanwhile, both {var_epsilon}-martensite and {alpha}{prime}-martensite are observed in the deformation microstructures, indicating the co-existence of stress induced- transformation and strain-induced-transformation. We also discussed the effects of twinning and martensite transformation on work-hardening as well as the relationship between stacking faults, twinning and martensite transformation.

  6. Abnormal grain growth in Eurofer-97 steel in the ferrite phase field

    NASA Astrophysics Data System (ADS)

    Oliveira, V. B.; Sandim, H. R. Z.; Raabe, D.

    2017-03-01

    Reduced-activation ferritic-martensitic (RAFM) Eurofer-97 steel is a candidate material for structural applications in future fusion reactors. Depending on the amount of prior cold rolling strain and annealing temperature, important solid-state softening reactions such as recovery, recrystallization, and grain growth occur. Eurofer-97 steel was cold rolled up to 70, 80 and 90% reductions in thickness and annealed in the ferrite phase field (below ≈ 800 °C). Changes in microstructure, micro-, and mesotexture were followed by orientation mappings provided by electron backscatter diffraction (EBSD). Eurofer-97 steel undergoes abnormal grain growth above 650 °C and this solid-state reaction seems to be closely related to the high mobility of a few special grain boundaries that overcome pinning effects caused by fine particles. This solid-state reaction promotes important changes in the microstructure and microtexture of this steel. Abnormal grain growth kinetics for each condition was determined by means of quantitative metallography.

  7. Effect of grain refinement on mechanical properties of martensitic steel

    NASA Astrophysics Data System (ADS)

    Islamgaliev, R. K.; Nikitina, M. A.; Ganeev, A. V.; Karavaeva, M. V.

    2017-05-01

    Microstructure and strength of commercial martensitic steel processed by equal channel angular pressing (ECAP) has been investigated using transmission electron microscopy and tensile tests. Application of ECAP led to significant grain refinement to a grain size of 0.8 µm and precipitation of particles with a size of 90 nm. Impact of annealing on thermal stability of ultrafine-grained structure was investigated. The contribution of various strengthening mechanisms to strength of steel was discussed.

  8. Microstructural evolution and examination of α'-martensite during a multi-pass dissimilar stainless steel GTAW process

    NASA Astrophysics Data System (ADS)

    Hsieh, Chih-Chun; Lin, Dong-Yih; Wu, Weite

    2008-10-01

    This study discusses the microstructural evolution and examination of α'-martensite in fusion zones and heat-affected zones under multi-pass dissimilar stainless steels welding. The morphology, quantity, grain size, and chemical composition of the α'-martensite and δ-ferrite were analyzed using optical microscopy (OM), an image analyzer (IA), a ferritscope (FS), field emission scanning electron microscopy (FESEM), energy dispersive spectrometry (EDS), respectively. Recrystallization induced grain refinement of α'-martensite in over-lapping heat-affected zones (HAZ1 > 2 and HAZ2 > 3) after the second and third pass of welding. The Creq, Nieq, and K-factor values were calculated in an elemental analysis according to the Kaltenhauser equation. The higher Nieq (8.0-9.26) and lower K-factor (7.73-9.50) were examined for α'-martensite in the second pass fusion zone (FZ-2) as opposed to δ-ferrite. Comparatively, the ä-ferrite indicated higher Creq (22.30-22.91) and K-factor (15.72-16.68) values.

  9. 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.

  10. On the Processing of Martensitic Steels in Continuous Galvanizing Lines: Part II

    NASA Astrophysics Data System (ADS)

    Song, Taejin; Kwak, Jaihyun; de Cooman, B. C.

    2012-01-01

    The conventional continuous hot-dip galvanizing (GI) and galvannealing (GA) processes can be applied to untransformed austenite to produce Zn and Zn-alloy coated low-carbon ultra-high-strength martensitic steel provided specific alloying additions are made. The most suitable austenite decomposition behavior results from the combined addition of boron, Cr, and Mo, which results in a pronounced transformation bay during isothermal transformation. The occurrence of this transformation bay implies a considerable retardation of the austenite decomposition in the temperature range below the bay, which is close to the stages in the continuous galvanizing line (CGL) thermal cycle related to the GI and GA processes. After the GI and GA processes, a small amount of granular bainite, which consists of bainitic ferrite and discrete islands of martensite/austenite (M/A) constituents embedded in martensite matrix, is present in the microstructure. The ultimate tensile strength (UTS) of the steel after the GI and GA cycle was over 1300 MPa, and the stress-strain curve was continuous without any yielding phenomena.

  11. Formation of Delta Ferrite in 9 Wt Pct Cr Steel Investigated by In-Situ X-Ray Diffraction Using Synchrotron Radiation

    NASA Astrophysics Data System (ADS)

    Mayr, P.; Palmer, T. A.; Elmer, J. W.; Specht, E. D.; Allen, S. M.

    2010-10-01

    In-situ X-ray diffraction (XRD) measurements using high energy synchrotron radiation were performed to monitor in real time the formation of delta ferrite in a martensitic 9 wt pct chromium steel under simulated weld thermal cycles. Volume fractions of martensite, austenite, and delta ferrite were measured as a function of temperature at a 10 K/s heating rate to 1573 K (1300 °C) and subsequent cooling. At the peak temperature, the delta ferrite concentration rose to 19 pct, of which 17 pct transformed back to austenite on subsequent cooling.

  12. Influences of cyclic loading on martensite transformation of TRIP steels

    NASA Astrophysics Data System (ADS)

    Dan, W. J.; Hu, Z. G.; Zhang, W. G.

    2013-03-01

    While austenite transformation into martensite induces increasing of the crack initiation life and restraining of the growth of fatigue cracks in cyclic-loading processes, TRIP-assisted steels have a better fatigue life than the AHSS (Advance High Strength Steels). As two key parameters in the cyclic loading process, strain amplitude and cyclic frequency are used in a kinetic transformation model to reasonably evaluate the phase transformation from austenite into martensite with the shear-band intersections theory, in which strain amplitude and cyclic frequency are related to the rate of shear-band intersection formation and the driving force of phase transformation. The results revealed that the martensite volume fraction increased and the rate of phase transformation decrease while the number of cycles increased, and the martensite volume fraction was almost constant after the number of cycles was more than 2000 times. Higher strain amplitude promotes martensite transformation and higher cyclic frequency impedes phase transformation, which are interpreted by temperature increment, the driving force of phase transformation and the rate of shearband intersection formation.

  13. 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.

  14. Direct observation of phase transformations in the simulated heat-affected zone of a 9Cr martensitic steel

    SciTech Connect

    Mayr, Peter; Palmer, T. A.; Elmer, J. W.; Specht, Eliot D

    2008-01-01

    An experimental test melt of a boron alloyed 9Cr-3W-3Co-V,Nb steel for high temperature applications in the thermal power generation industry was produced by vacuum induction melting. This grade of steel typically displays a homogeneous tempered martensitic microstructure in the as-received condition. However, after welding, this microstructure is significantly altered, resulting in a loss of its desired properties. The phase transformations during simulated thermal cycles typical of those experienced in the weld heat-affected zone (HAZ) were directly observed by in situ X-ray diffraction experiments using synchrotron radiation. Heating rates of 10 C s-1 and 100 C s-1 up to a peak temperature of 1300 C are investigated here. The final microstructures observed after both simulated weld thermal cycles are primarily composed of martensite with approximately 4% retained delta ferrite and 4% retained austenite, by volume. With the temporal resolution of the in situ X-ray diffraction technique, phase transformations from tempered martensite to austenite to delta ferrite during heating and to martensite during cooling were monitored. With this technique, the evolution of the final microstructure through both heating and cooling is monitored, providing additional context to the microstructural observations.

  15. AM363 martensitic stainless steel: A multiphase equation of state

    NASA Astrophysics Data System (ADS)

    De Lorenzi-Venneri, Giulia; Crockett, Scott D.

    2017-01-01

    A multiphase equation of state for stainless steel AM363 has been developed within the Opensesame approach and has been entered as material 4295 in the LANL-SESAME Library. Three phases were constructed separately: the low pressure martensitic phase, the austenitic phase and the liquid. Room temperature data and the explicit introduction of a magnetic contribution to the free energy determined the martensitic phase, while shock Hugoniot data was used to determine the austenitic phase and the phase boundaries. More experimental data or First Principles calculations would be useful to better characterize the liquid.

  16. Martensitic transformations in high-strength steels at aging

    NASA Astrophysics Data System (ADS)

    Berezovskaya, V. V.; Bannykh, O. A.

    2011-04-01

    The effect of heat treatment and elastic stresses on the texture of maraging NiTi-steels is studied. The interruption of the decomposition of martensite at the early stages is shown to be accompanied by the γ → α transformation, which proceeds upon cooling from the aging temperature and under elastic (σ < σ0.2) tensile stresses. The martensite has a crystallographic texture, which is caused by the evolution of hot-deformation texture as a result of quenching and decomposition of a supersaturated α solid solution.

  17. A phenomenological approach to micromagnetics in martensitic steels

    NASA Astrophysics Data System (ADS)

    Tomka, G. J.; Gore, J. G.; Earl, J.; Murray, N.; Maylin, M. G.; Squire, P. T.

    2000-09-01

    A series of applied field measurements have been done on rods of martensitic steel using a BH-permeameter incorporated into a stress-strain apparatus. Zero stress measurements have been cross-checked using a VSM. For the unstressed steel, it is shown that it is necessary to adapt the Jiles-Atherton model to account for a significant departure in the virgin and demagnetisation curves from that predicted in the standard model. The adapted model gives a good description of magnetisation changes for points on the curve and provides an insight into the reversal mechanism in martensitic steel. Measurements under stress indicate that the nature of the reversal mechanism is stress dependent.

  18. Laser Beam Welding of Ultra-high Strength Chromium Steel with Martensitic Microstructure

    NASA Astrophysics Data System (ADS)

    Dahmen, Martin; Janzen, Vitalij; Lindner, Stefan; Wagener, Rainer

    A new class of steels is going to be introduced into sheet manufacturing. Stainless ferritic and martensitic steels open up opportunities for sheet metal fabrication including hot stamping. Strengths of up to 2 GPa at fracture elongations of 15% can be attained through this. Welding of these materials, as a result, became a challenge. Energy-reduced welding methods with in-situ heat treatment are required in order to ensure the delicate and complex heat control. Laser beam welding is the joining technique of choice to supply minimum heat input to the fusion process and to apply efficient heat control. For two application cases, tailored blank production in as-rolled condition and welding during assembly in hot stamped condition, welding processes have been developed. The welding suitability is shown through metallurgical investigations of the welds. Crash tests based on the KS-II concept as well as fatigue tests prove the applicability of the joining method.

  19. Analysis of factors responsible for the accelerated creep rupture of 12% Cr martensitic steel weld joints

    NASA Astrophysics Data System (ADS)

    Kudryavtsev, A. S.; Okhapkin, K. A.; Mikhailov, M. S.; Skutin, V. S.; Zubova, G. E.; Fedotov, B. V.

    2016-06-01

    In the process of the investigation of the heat resistance of a 0.07C-12Cr-Ni-Mo-V-Nb steel of the martensitic-ferritic class, a reduction was revealed in the long-term strength of its welded joints to below the level of the strength of the base metal. To establish the causes for the accelerated failure of the welded joints, an imitation of the thermal cycles was carried out that produce the structure of the heataffected zone using a dilatometer. In the samples with the structure that corresponds to that of the heataffected zone, a local zone of softening was revealed. The investigations of the metal structure using transmission electron microscopy have shown that the reduction in the creep rupture strength was caused by structural changes under the conditions of the thermal cycle of welding upon the staying of the steel in the temperature range between the Ac 1 and Ac 3 points.

  20. Assessment of mechanical properties of the martensitic steel EUROFER97 by means of punch tests

    NASA Astrophysics Data System (ADS)

    Ruan, Y.; Spätig, P.; Victoria, M.

    2002-12-01

    The ball punch test technique was used to evaluate the conventional tensile and impact properties of the tempered martensitic steel EUROFER97 from room temperature down to liquid nitrogen temperature. The testing was carried out on unirradiated material only with small disks, 3 mm in diameter and 0.25 mm in thickness. For comparison, tensile tests were also performed over the same temperature range. Correlations between the load at the plastic bending initiation and the maximum load of the punch tests with the yield stress and the ultimate tensile stress of the tension tests could be established. The temperature dependence of the specific fracture energy of the punch test was used to define a ductile-brittle transition temperature (DBTT) and to correlate this with the DBTT measured from impact Charpy on KLST specimens. The results are compared with other available correlations done in the past on other ferritic steels.

  1. New martensitic steels for fossil power plant: Creep resistance

    NASA Astrophysics Data System (ADS)

    Kaybyshev, R. O.; Skorobogatykh, V. N.; Shchenkova, I. A.

    2010-02-01

    In this paper, we consider the origin of high-temperature strength of heat-resistant steels belonging to martensitic class developed on the basis of the Fe—9%Cr alloy for the boiler pipes and steam pipelines of power plants at steam temperatures of up to 620°C and pressures to 300 atm. In addition, we give a brief information on the physical processes that determine the creep strength and consider the alloying philosophy of traditional heat-resistant steels. The effect of the chemical and phase composition of heat-resistant steels and their structure on creep strength is analyzed in detail. It is shown that the combination of the solid-solution alloying by elements such as W and Mo, as well as the introduction of carbides of the MX type into the matrix with the formation of a dislocation structure of tempered martensite, ensures a significant increase in creep resistance. The steels of the martensitic class withstand creep until an extensive polygonization starts in the dislocation structure of the tempered martensite(“troostomartensite”), which is suppressed by V(C,N) and Nb(C,N) dispersoids. Correspondingly, the service life of these steels is determined by the time during which the dispersed nanocarbonitrides withstand coalescence, while tungsten and molybdenum remain in the solid solution. The precipitation of the Laves phases Fe2(W,Mo) and the coalescence of carbides lead to the development of migration of low-angle boundaries, and the steel loses its ability to resist creep.

  2. High-strength economically alloyed corrosion-resistant steels with the structure of nitrogen martensite

    NASA Astrophysics Data System (ADS)

    Bannykh, O.; Blinov, V.; Lukin, E.

    2016-04-01

    The use of nitrogen as the main alloying element allowing one both to increase the corrosion resistance and mechanical properties of steels and to improve their processability is a new trend in physical metallurgy of high-strength corrosion resistant steels. The principles of alloying, which are developed for high-nitrogen steel in IMET RAS, ensure the formation of the structure, which contains predetermined amounts of martensite (70-80%) and austenite (20-30%) and is free from δ-ferrite, σ-phase, and Cr23C6 carbide. These principles were used as the base for the creation of new high-strength corrosion-resistant weldable and deformable 0Kh16AN5B, 06Kh16AN4FD, 08Kh14AN4MDB, 09Kh16AN3MF, 27Kh15AN3MD2, 40Kh13AN3M2, and 19Kh14AMB steels, which are operative at temperatures ranging from - 70 to 400°C. The developed nitrogen-containing steels compared with similar carbon steels are characterized by a higher resistance to pitting and crevice corrosion and are resistant to stress corrosion cracking. The new steels successfully passed trial tests as heavy duty articles.

  3. Ferritic steels for sodium-cooled fast reactors: Design principles and challenges

    NASA Astrophysics Data System (ADS)

    Raj, Baldev; Vijayalakshmi, M.

    2010-09-01

    An overview of the current status of development of ferritic steels for emerging fast reactor technologies is presented in this paper. The creep-resistant 9-12Cr ferritic/martensitic steels are classically known for steam generator applications. The excellent void swelling resistance of ferritic steels enabled the identification of their potential for core component applications of fast reactors. Since then, an extensive knowledge base has been generated by identifying the empirical correlations between chemistry of the steels, heat treatment, structure, and properties, in addition to their in-reactor behavior. A few concerns have also been identified which pertain to high-temperature irradiation creep, embrittlement, Type IV cracking in creep-loaded weldments, and hard zone formation in dissimilar joints. The origin of these problems and the methodologies to overcome the limitations are highlighted. Finally, the suitability of the ferritic steels is re-evaluated in the emerging scenario of the fast reactor technology, with a target of achieving better breeding ratio and improved thermal efficiency.

  4. Influence of Temperature on Fatigue-Induced Martensitic Phase Transformation in a Metastable CrMnNi-Steel

    NASA Astrophysics Data System (ADS)

    Biermann, Horst; Glage, Alexander; Droste, Matthias

    2016-01-01

    Metastable austenitic steels can exhibit a fatigue-induced martensitic phase transformation during cyclic loading. It is generally agreed that a certain strain amplitude and a threshold of the cumulated plastic strain must be exceeded to trigger martensitic phase transformation under cyclic loading. With respect to monotonic loading, the martensitic phase transformation takes place up to a critical temperature—the so-called M d temperature. The goal of the present investigation is to determine an M d,c temperature which would be the highest temperature at which a fatigue-induced martensitic phase transformation can take place. For this purpose, fatigue tests controlled by the total strain were performed at different temperatures. The material investigated was a high-alloy metastable austenitic steel X3CrMnNi16.7.7 (16.3Cr-7.2Mn-6.6Ni-0.03C-0.09N-1.0Si) produced using the hot pressing technique. The temperatures were set in the range of 283 K (10 °C) ≤ T ≤ 473 K (200 °C). Depending on the temperature and strain amplitude, the onset of the martensitic phase transformation shifted to different values of the cumulated plastic strain, or was inhibited completely. Moreover, it is known that metastable austenitic CrMnNi steels with higher nickel contents can exhibit the deformation-induced twinning effect. Thus, at higher temperatures and strain amplitudes, a transition from the deformation-induced martensitic transformation to deformation-induced twinning takes place. The fatigue-induced martensitic phase transformation was monitored during cyclic loading using a ferrite sensor. The microstructure after the fatigue tests was examined using the back-scattered electrons, the electron channeling contrast imaging and the electron backscatter diffraction techniques to study the temperature-dependent dislocation structures and phase transformations.

  5. The morphology and ageing behaviour of δ-ferrite in a modified 9Cr-1Mo steel

    NASA Astrophysics Data System (ADS)

    Kishore, R.; Singh, R. N.; Sinha, T. K.; Kashyap, B. P.

    1992-10-01

    Dual phase (martensite + δ-ferrite) microstructures were developed in a modified 9Cr-1Mo steel, by austenitising at 1523-1623 K, followed by water-quenching. These duplex structures were thermally aged at 973 K for ageing periods varying from 30 min to 21 h. Morphological aspects of δ-ferrite phase and its response to age-hardening were studied by optical, scanning electron and transmission electron microscopy, X-ray diffraction, electron probe microanalysis and microhardness testing. It was observed that austenitizing at 1523 K produced fine, acicular δ-ferrite while the δ-ferrite formed by austenitising at higher temperatures (1573-1623 K) were massive, irregular-shaped and banded. Moreover the presence of 8-ferrite caused an abnormally strong (110) reflection, observed in X-ray diffraction patterns of martensite plus δ-ferrite structures. This behaviour is thought to be due to development of (110) texture in δ-ferrite phase. Thermal ageing at 973 K caused age-hardening of δ-ferrite with a peak hardness attained after 3.6 ks of ageing. Electron microscopic results suggest that the observed hardening was caused by the formation of Fe 2Mo Laves phase.

  6. Previous heat treatment inducing different plasma nitriding behaviors in martensitic stainless steels

    SciTech Connect

    Figueroa, C. A.; Alvarez, F.; Mitchell, D. R. G.; Collins, G. A.; Short, K. T.

    2006-09-15

    In this work we report a study of the induced changes in structure and corrosion behavior of martensitic stainless steels nitrided by plasma immersion ion implantation (PI{sup 3}) at different previous heat treatments. The samples were characterized by x-ray diffraction and glancing angle x-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy, and potentiodynamic measurements. Depending on the proportion of retained austenite in the unimplanted material, different phase transformations are obtained at lower and intermediate temperatures of nitrogen implantation. At higher temperatures, the great mobility of the chromium yields CrN segregations like spots in random distribution, and the {alpha}{sup '}-martensite is degraded to{alpha}-Fe (ferrite). The nitrided layer thickness follows a fairly linear relationship with the temperature and a parabolic law with the process time. The corrosion resistance depends strongly on chromium segregation from the martensitic matrix, as a result of the formation of CrN during the nitrogen implantation process and the formation of Cr{sub x}C during the heat treatment process. Briefly speaking, the best results are obtained using low tempering temperature and low implantation temperature (below 375 deg. ) due to the increment of the corrosion resistance and nitrogen dissolution in the structure with not too high diffusion depths (about 5-10 {mu}m)

  7. Characteristics of Laser Beam and Friction Stir Welded AISI 409M Ferritic Stainless Steel Joints

    NASA Astrophysics Data System (ADS)

    Lakshminarayanan, A. K.; Balasubramanian, V.

    2012-04-01

    This article presents the comparative evaluation of microstructural features and mechanical properties of friction stir welded (solid-state) and laser beam welded (high energy density fusion welding) AISI 409M grade ferritic stainless steel joints. Optical microscopy, microhardness testing, transverse tensile, and impact tests were performed. The coarse ferrite grains in the base material were changed to fine grains consisting duplex structure of ferrite and martensite due to the rapid cooling rate and high strain induced by severe plastic deformation caused by frictional stirring. On the other hand, columnar dendritic grain structure was observed in fusion zone of laser beam welded joints. Tensile testing indicates overmatching of the weld metal relative to the base metal irrespective of the welding processes used. The LBW joint exhibited superior impact toughness compared to the FSW joint.

  8. Cast Stainless Steel Ferrite and Grain Structure

    SciTech Connect

    Ruud, Clayton O.; Ramuhalli, Pradeep; Meyer, Ryan M.; Mathews, Royce; Diaz, Aaron A.; Anderson, Michael T.

    2012-09-01

    In-service inspection requirements dictate that piping welds in the primary pressure boundary of light-water reactors be subject to a volumetric examination based on the rules contained within the American Society of Mechanical Engineers Boiler and Pressure Vessel Code, Section XI. The purpose of the inspection is the reliable detection and accurate sizing of service-induced degradation and/or material flaws introduced during fabrication. The volumetric inspection is usually carried out using ultrasonic testing (UT) methods. However, the varied metallurgical macrostructures and microstructures of cast austenitic stainless steel piping and fittings, including statically cast stainless steel and centrifugally cast stainless steel (CCSS), introduce significant variations in the propagation and attenuation of ultrasonic energy. These variations complicate interpretation of the UT responses and may compromise the reliability of UT inspection. A review of the literature indicated that a correlation may exist between the microstructure and the delta ferrite content of the casting alloy. This paper discusses the results of a recent study where the goal was to determine if a correlation existed between measured and/or calculated ferrite content and grain structure in CCSS pipe.

  9. Deformation behavior of duplex austenite and ε-martensite high-Mn steel.

    PubMed

    Kwon, Ki Hyuk; Suh, Byeong-Chan; Baik, Sung-Il; Kim, Young-Woon; Choi, Jong-Kyo; Kim, Nack J

    2013-02-01

    Deformation and work hardening behavior of Fe-17Mn-0.02C steel containing ε-martensite within the austenite matrix have been investigated by means of in situ microstructural observations and x-ray diffraction analysis. During deformation, the steel shows the deformation-induced transformation of austenite → ε-martensite → α'-martensite as well as the direct transformation of austenite → α'-martensite. Based on the calculation of changes in the fraction of each constituent phase, we found that the phase transformation of austenite → ε-martensite is more effective in work hardening than that of ε-martensite → α'-martensite. Moreover, reverse transformation of ε-martensite → austenite has also been observed during deformation. It originates from the formation of stacking faults within the deformed ε-martensite, resulting in the formation of 6H-long periodic ordered structure.

  10. Impurity content of reduced-activation ferritic steels and a vanadium alloy

    SciTech Connect

    Klueh, R.L.; Grossbeck, M.L.; Bloom, E.E.

    1997-04-01

    Inductively coupled plasma mass spectrometry was used to analyze a reduced-activation ferritic/martensitic steel and a vanadium alloy for low-level impurities that would compromise the reduced-activation characteristics of these materials. The ferritic steel was from the 5-ton IEA heat of modified F82H, and the vanadium alloy was from a 500-kg heat of V-4Cr-4Ti. To compare techniques for analysis of low concentrations of impurities, the vanadium alloy was also examined by glow discharge mass spectrometry. Two other reduced-activation steels and two commercial ferritic steels were also analyzed to determine the difference in the level of the detrimental impurities in the IEA heat and steels for which no extra effort was made to restrict some of the tramp impurities. Silver, cobalt, molybdenum, and niobium proved to be the tramp impurities of most importance. The levels observed in these two materials produced with present technology exceeded the limits for low activation for either shallow land burial or recycling. The chemical analyses provide a benchmark for the improvement in production technology required to achieve reduced activation; they also provide a set of concentrations for calculating decay characteristics for reduced-activation materials. The results indicate the progress that has been made and give an indication of what must still be done before the reduced-activation criteria can be achieved.

  11. Effect of irradiation temperature on void swelling of China Low Activation Martensitic steel (CLAM)

    SciTech Connect

    Zhao Fei; Qiao Jiansheng; Huang Yina; Wan Farong Ohnuki, Soumei

    2008-03-15

    CLAM is one composition of a Reduced Activation Ferritic/Martensitic steel (RAFM), which is being studied in a number of institutes and universities in China. The effect of electron-beam irradiation temperature on irradiation swelling of CLAM was investigated by using a 1250 kV High Voltage Electron Microscope (HVEM). In-situ microstructural observations indicated that voids formed at each experimental temperature - 723 K, 773 K and 823 K. The size and number density of voids increased with increasing irradiation dose at each temperature. The results show that CLAM has good swelling resistance. The maximum void swelling was produced at 723 K; the swelling was about 0.3% when the irradiation damage was 13.8 dpa.

  12. Robust Passivation of Martensitic Stainless Steel for Water Cleaning Compatibility

    NASA Astrophysics Data System (ADS)

    Prater, Walter; Chung, Wendy; Loop, Ken; Powell, Mark; Shatz, Tom

    Corrosion of hardened martensitic stainless steels used in magnetic disk drives is problematic because the rusting surface becomes a source of particulate contamination that can compromise the operational performance and reliability of the file. Corrosion of the stainless steels can be initiated by either atmospheric moisture or during aqueous based cleaning of the parts that typically occurs during their manufacturing steps or prior to file build. Aqueous based cleaning is commonplace since CFC cleaning solvents are losing favor because they are expensive and are discouraged by the EPA for their environmentally "unfriendly" nature. Passivation of the stainless stees can be accomplished by thermal treatment or chemical means, using nitric acid. Four techniques (1 thermal and 3 chemical) were evaluated in this study on two base materials, 440C and X105CrMo17. Natural passivation initiated by abrasive polishing was also tested. Corrosion tests were performed on specimens made of 440C and X105CrMo17 rails, the martensitic type, using electropotential in a basic electrolyte and electropotential in an acidic electrolyte. To understand the importance of metallurgical, physical and chemical variables and how they could influence the rail's corrosion resistance, three measurements were taken: 1. Grain size and carbide distribution using EDS. 2. Surface morphology. 3. Auger electron spectroscopy to determine the iron/chrome ratio and the chrome oxide layer thickness. When properly done, thermal and chemical passivation are excellent methods to make martensitic stainless steels corrosion resistant and water cleanable. Natural passivation when initiated by abrasive polishing does not perform well. Passivation is imparted to the stainless steel by the high chromium/low iron content at the surface and by a thin, chrome oxide layer at the surface.

  13. Prediction of yield stress in highly irradiated ferritic steels

    NASA Astrophysics Data System (ADS)

    Windsor, Colin G.; Cottrell, Geoff; Kemp, Richard

    2008-03-01

    The design of any fusion power plant requires information on the irradiation hardening of low-activation ferritic/martensitic steels beyond the range of most present measurements. Neural networks have been used by Kemp et al (J. Nucl. Mater. 348 311-28) to model the yield stress of some 1811 irradiated alloys. The same dataset has been used in this study, but has been divided into a training set containing the majority of the dataset with low irradiation levels, and a test set which contains just those alloys which have been irradiated above a given level. For example some 4.5% of the alloys were irradiated above 30 displacements per atom. For this 'prediction' problem it is found that simpler networks with fewer inputs are advantageous. By using target-driven dimensionality reduction, linear combinations of the atomic inputs reduce the test residual below that achievable by adding inputs from single atoms. It is postulated that these combinations represent 'mechanisms' for the prediction of irradiated yield stress.

  14. Development of Advanced Ods Ferritic Steels for Fast Reactor Fuel Cladding

    NASA Astrophysics Data System (ADS)

    Ukai, S.; Oono, N.; Ohtsuka, S.; Kaito, T.

    Recent progress of the 9CrODS steel development is presented focusing on their microstructure control to improve sufficient high-temperature strength as well as cladding manufacturing capability. The martensitic 9CrODS steel is primarily candidate cladding materials for the Generation IV fast reactor fuel. They are the attractive composite-like materials consisting of the hard residual ferrite and soft tempered martensite, which are able to be easily controlled by α-γ phase transformation. The residual ferrite containing extremely nanosized oxide particles leads to significantly improved creep rupture strength in 9CrODS cladding. The creep strength stability at extended time of 60,000 h at 700 ºC is ascribed to the stable nanosized oxide particles. It was also reviewed that 9CrODS steel has well irradiation stability and fuel pin irradiation test was conducted up to 12 at% burnup and 51 dpa at the cladding temperature of 700ºC.

  15. Physical metallurgy of BATMAN II Ti-bearing martensitic steels

    NASA Astrophysics Data System (ADS)

    Pilloni, L.; Attura, F.; Calza-Bini, A.; De Santis, G.; Filacchioni, G.; Carosi, A.; Amato, S.

    1998-10-01

    Seven laboratory experimental casts of 7-9% Cr Ti-bearing martensitic steels were obtained via VIM process. Plates of 25 mm thickness were produced by hot rolling. On each cast CCT diagrams and critical temperatures were determined. Several austenitizing treatments were performed to study the grain size evolution. The effect of microstructure on impact properties were finally investigated. This paper discusses the role of chemical composition on microstructural and physical properties and shows the beneficial effect either of low-temperature austenitizing or double-austenitizing steps on impact properties.

  16. Characterization of Irradiated Nanostructured Ferritic Steels

    SciTech Connect

    Bentley, James; Hoelzer, David T; Tanigawa, H.; Yamamoto, T.; Odette, George R.

    2007-01-01

    The past decade has seen the development of a new class of mechanically alloyed (MA) ferritic steels with outstanding mechanical properties that come, at least in part, from the presence of high concentrations (>10{sup 23} m{sup -3}) of Ti-, Y-, and O-enriched nanoclusters (NC). From the outset, there has been much interest in their potential use for applications to fission and proposed fusion reactors, not only because of their attractive high-temperature strength, but also because the presence of NC may result in a highly radiation-resistant material by efficiently trapping point defects to enhance recombination. Of special interest for fusion applications is the potential of NC to trap transmutation-produced He in high concentrations of small cavities, rather than in fewer but larger cavities that lead to greater radiation-induced swelling and other degraded properties.

  17. Reversed austenite for enhancing ductility of martensitic stainless steel

    NASA Astrophysics Data System (ADS)

    Dieck, S.; Rosemann, P.; Kromm, A.; Halle, T.

    2017-03-01

    The novel heat treatment concept, “quenching and partitioning” (Q&P) has been developed for high strength steels with enhanced formability. This heat treatment involves quenching of austenite to a temperature between martensite start and finish, to receive a several amount of retained austenite. During the subsequent annealing treatment, the so called partitioning, the retained austenite is stabilized due to carbon diffusion, which results in enhanced formability and strength regarding strain induced austenite to martensite transformation. In this study a Q&P heat treatment was applied to a Fe-0.45C-0.65Mn-0.34Si-13.95Cr stainless martensite. Thereby the initial quench end temperature and the partitioning time were varied to characterize their influence on microstructural evolution. The microstructural changes were analysed by dilatometer measurements, X-ray diffraction and scanning electron microscopy, including electron back-scatter diffraction. Compression testing was made to examine the mechanical behaviour. It was found that an increasing partitioning time up to 30 min leads to an enhanced formability without loss in strength due to a higher amount of stabilized retained and reversed austenite as well as precipitation hardening.

  18. 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.

  19. An atom probe study of carbon distribution in martensite in 2[1/4]Cr1Mo steel

    SciTech Connect

    Thomson, R.C. . Dept. of Materials Science and Metallurgy); Miller, M.K. . Metals and Ceramics Division)

    1995-01-15

    2[1/4]Cr1Mo steel is used widely for superheater tubing in power plants, and as a filler material for joining [1/2]Cr[1/2]Mo[1/4]V steam piping. Components in power plants can be massive and therefore differences in cooling rates can result in a mixed microstructure of allotriomorphic ferrite, bainite and martensite. The creep strength of the steel is critically dependent on the carbide distribution within the microstructure. The position and nature of carbides within the microstructure is itself a critical function of the movement of carbon through the microstructure during the early stages of tempering. In this paper, atom probe field ion microscopy has been used to examine carbon segregation to lath boundaries in martensite in 2[1/4]Cr1Mo steel. Significant carbon enrichment was observed at the lath boundaries. This enrichment is consistent with the observation of retained austenite films at the lath boundaries in the transmission electron microscope, and with carbon levels previously found in retained austenite in low alloy ferrous martensites.

  20. Controlled ferrite content improves weldability of corrosion-resistant steel

    NASA Technical Reports Server (NTRS)

    Malin, C. O.

    1967-01-01

    Corrosion-resistant steel that adds restrictions on chemical composition to ensure sufficient ferrite content decreases the tendency of CRES to develop cracks during welding. The equations restricting composition are based on the Schaeffler constitution diagram.

  1. Investigation of Magnetic Signatures and Microstructures for Heat-Treated Ferritic/Martensitic HT-9 Alloy

    SciTech Connect

    Henager, Charles H.; McCloy, John S.; Ramuhalli, Pradeep; Edwards, Danny J.; Hu, Shenyang Y.; Li, Yulan

    2013-05-01

    There is increased interest in improved methods for in-situ nondestructive interrogation of materials for nuclear reactors in order to ensure reactor safety and quantify material degradation (particularly embrittlement) prior to failure. Therefore, a prototypical ferritic/martensitic alloy, HT-9, of interest to the nuclear materials community was investigated to assess microstructure effects on micromagnetics measurements – Barkhausen noise emission, magnetic hysteresis measurements, and first-order reversal curve analysis – for samples with three different heat-treatments. Microstructural and physical measurements consisted of high-precision density, resonant ultrasound elastic constant determination, Vickers microhardness, grain size, and texture. These were varied in the HT-9 alloy samples and related to various magnetic signatures. In parallel, a meso-scale microstructure model was created for alpha iron and effects of polycrystallinity and demagnetization factor were explored. It was observed that Barkhausen noise emission decreased with increasing hardness and decreasing grain size (lath spacing) while coercivity increased. The results are discussed in terms of the use of magnetic signatures for nondestructive interrogation of radiation damage and other microstructural changes in ferritic/martensitic alloys.

  2. Hydrogen-assisted damage in austenite/martensite dual-phase steel

    NASA Astrophysics Data System (ADS)

    Koyama, Motomichi; Cem Tasan, Cemal; Nagashima, Tatsuya; Akiyama, Eiji; Raabe, Dierk; Tsuzaki, Kaneaki

    2016-01-01

    For understanding the underlying hydrogen embrittlement mechanism in transformation-induced plasticity steels, the process of damage evolution in a model austenite/martensite dual-phase microstructure following hydrogenation was investigated through multi-scale electron channelling contrast imaging and in situ optical microscopy. Localized diffusible hydrogen in martensite causes cracking through two mechanisms: (1) interaction between {1 1 0}M localized slip and {1 1 2}M twin and (2) cracking of martensite-martensite grain interfaces. The former resulted in nanovoids along the {1 1 2}M twin. The coalescence of the nanovoids generated plate-like microvoids. The latter caused shear localization on the specific plane where the crack along the martensite/martensite boundary exists, which led to additional martensite/martensite boundary cracking.

  3. Performance of ferritic stainless steels for automobile muffler corrosion

    SciTech Connect

    Tarutani, Y.; Hashizume, T.

    1995-11-01

    Corrosion behavior of ferritic stainless steels was studied in artificial exhaust gas condensates containing corrosive ions such as Cl{sup {minus}} and SO{sub 3}{sup 2{minus}}. Continuous immersion tests in flasks and Dip and Dry tests by using the alternate corrosion tester with a heating system clarified the effects of chromium and molybdenum additions on the corrosion resistance of a ferritic stainless steel in the artificial exhaust gas condensates. Effects of surface oxidation on the corrosion behavior were investigated in a temperature range of 573K to 673K. Oxidation of 673K reduced the corrosion resistance of the ferritic stainless steels in the artificial environment of the automobile muffler. Particulate matter deposited on the muffler inner shell from the automobile exhaust gas was also examined. Deposited particulate matter increased the corrosion rate of the ferritic stainless steel. Finally, the authors also investigated the corrosion of the automobile mufflers made of Type 436L ferritic stainless steel with 18% chromium-1.2% molybdenum after 24 months, in Japan. The sets of results clarified that Type 436L ferritic stainless steel as the material for the automobile muffler exhibited acceptable corrosion resistance.

  4. Thermal Desorption Analysis of Hydrogen in High Strength Martensitic Steels

    NASA Astrophysics Data System (ADS)

    Enomoto, M.; Hirakami, D.; Tarui, T.

    2012-02-01

    Thermal desorption analyses (TDA) were conducted in high strength martensitic steels containing carbon from 0.33 to 1.0 mass pct, which were charged with hydrogen at 1223 K (950 °C) under hydrogen of one atmospheric pressure and quenched to room temperature. In 0.33C steel, which had the highest M s temperature, only one desorption peak was observed around 373 K (100 °C), whereas two peaks, one at a similar temperature and the other around and above 573 K (300 °C), were observed in the other steels, the height of the second peak increasing with carbon content. In 0.82C steel, both peaks disappeared during exposure at room temperature in 1 week, whereas the peak heights decreased gradually over 2 weeks in specimens electrolytically charged with hydrogen and aged for varying times at room temperature. From computer simulation, by means of the McNabb-Foster theory coupled with theories of carbon segregation, these peaks are likely to be due to trapping of hydrogen in the strain fields and cores of dislocations, and presumably to a lesser extent in prior austenite grain boundaries. The results also indicate that carbon atoms prevent and even expel hydrogen from trapping sites during quenching and aging in these steels.

  5. Process for making a martensitic steel alloy fuel cladding product

    DOEpatents

    Johnson, Gerald D.; Lobsinger, Ralph J.; Hamilton, Margaret L.; Gelles, David S.

    1990-01-01

    This is a very narrowly defined martensitic steel alloy fuel cladding material for liquid metal cooled reactors, and a process for making such a martensitic steel alloy material. The alloy contains about 10.6 wt. % chromium, about 1.5 wt. % molybdenum, about 0.85 wt. % manganese, about 0.2 wt. % niobium, about 0.37 wt. % silicon, about 0.2 wt. % carbon, about 0.2 wt. % vanadium, 0.05 maximum wt. % nickel, about 0.015 wt. % nitrogen, about 0.015 wt. % sulfur, about 0.05 wt. % copper, about 0.007 wt. % boron, about 0.007 wt. % phosphorous, and with the remainder being essentially iron. The process utilizes preparing such an alloy and homogenizing said alloy at about 1000.degree. C. for 16 hours; annealing said homogenized alloy at 1150.degree. C. for 15 minutes; and tempering said annealed alloy at 700.degree. C. for 2 hours. The material exhibits good high temperature strength (especially long stress rupture life) at elevated temperature (500.degree.-760.degree. C.).

  6. Mechanical Properties of Laser Beam Welded Ultra-high Strength Chromium Steel with Martensitic Microstructure

    NASA Astrophysics Data System (ADS)

    Dahmen, Martin; Janzen, Vitalij; Lindner, Stefan; Wagener, Rainer

    A new class of steels is going to be introduced into sheet manufacturing. Stainless ferritic and martensitic steels open up opportunities for sheet metal fabrication including hot stamping. A strength of up to 2 GPa at a fracture strain of 15% can be attained. Welding of these materials became apparently a challenge. Energy-reduced welding methods with in-situ heat treatment are required in order to ensure the delicate and complex heat control. Laser beam welding is the joining technique of choice to supply minimum heat input to the fusion process and to apply an efficient heat control. For two application cases, production of tailored blanks in as-rolled condition and welding in assembly in hot stamped conditions, welding processes have been developed. The welding suitability is shown in metallurgical investigations of the welds. Crash tests based on the KSII concept as well as fatigue tests prove the applicability of the joining method. For the case of assembly also joining with deep drawing and manganese boron steel was taken into consideration. The strength of the joint is determined by the weaker partner but can benefit from its ductility.

  7. Microstructure and Mechanical Properties of a Tempered High Cr Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Guerra-Fuentes, L.; Hernandez-Rodriguez, M. A. L.; Zambrano-Robledo, P.; Salinas-Rodriguez, A.; Garcia-Sanchez, E.

    2017-07-01

    Microstructural and mechanical studies have been performed in a high Cr martensitic steel Firth-Vickers (FV535) to analyze the tempering of martensite. Nanoindentation technique was used to determine the hardness and elastic modulus through systematic measurements on martensite and tempered martensite. On the other hand, microscopic studies were carried out to analyze the material in the same condition as received and subsequently observe the microstructural modifications after heat treatment. The precipitation presented in the last stage of tempering was observed by transmission electron microscopy. The results showed the effect of the martensite decomposition on the mechanical and nanomechanical properties of FV535.

  8. Hydrogen-Induced Delayed Cracking in TRIP-Aided Lean-Alloyed Ferritic-Austenitic Stainless Steels.

    PubMed

    Papula, Suvi; Sarikka, Teemu; Anttila, Severi; Talonen, Juho; Virkkunen, Iikka; Hänninen, Hannu

    2017-06-03

    Susceptibility of three lean-alloyed ferritic-austenitic stainless steels to hydrogen-induced delayed cracking was examined, concentrating on internal hydrogen contained in the materials after production operations. The aim was to study the role of strain-induced austenite to martensite transformation in the delayed cracking susceptibility. According to the conducted deep drawing tests and constant load tensile testing, the studied materials seem not to be particularly susceptible to delayed cracking. Delayed cracks were only occasionally initiated in two of the materials at high local stress levels. However, if a delayed crack initiated in a highly stressed location, strain-induced martensite transformation decreased the crack arrest tendency of the austenite phase in a duplex microstructure. According to electron microscopy examination and electron backscattering diffraction analysis, the fracture mode was predominantly cleavage, and cracks propagated along the body-centered cubic (BCC) phases ferrite and α'-martensite. The BCC crystal structure enables fast diffusion of hydrogen to the crack tip area. No delayed cracking was observed in the stainless steel that had high austenite stability. Thus, it can be concluded that the presence of α'-martensite increases the hydrogen-induced cracking susceptibility.

  9. Hydrogen-Induced Delayed Cracking in TRIP-Aided Lean-Alloyed Ferritic-Austenitic Stainless Steels

    PubMed Central

    Papula, Suvi; Sarikka, Teemu; Anttila, Severi; Talonen, Juho; Virkkunen, Iikka; Hänninen, Hannu

    2017-01-01

    Susceptibility of three lean-alloyed ferritic-austenitic stainless steels to hydrogen-induced delayed cracking was examined, concentrating on internal hydrogen contained in the materials after production operations. The aim was to study the role of strain-induced austenite to martensite transformation in the delayed cracking susceptibility. According to the conducted deep drawing tests and constant load tensile testing, the studied materials seem not to be particularly susceptible to delayed cracking. Delayed cracks were only occasionally initiated in two of the materials at high local stress levels. However, if a delayed crack initiated in a highly stressed location, strain-induced martensite transformation decreased the crack arrest tendency of the austenite phase in a duplex microstructure. According to electron microscopy examination and electron backscattering diffraction analysis, the fracture mode was predominantly cleavage, and cracks propagated along the body-centered cubic (BCC) phases ferrite and α’-martensite. The BCC crystal structure enables fast diffusion of hydrogen to the crack tip area. No delayed cracking was observed in the stainless steel that had high austenite stability. Thus, it can be concluded that the presence of α’-martensite increases the hydrogen-induced cracking susceptibility. PMID:28772975

  10. Hybrid Laser-Arc Welding of 10-mm-Thick Cast Martensitic Stainless Steel CA6NM: As-Welded Microstructure and Mechanical Properties

    NASA Astrophysics Data System (ADS)

    Mirakhorli, Fatemeh; Cao, Xinjin; Pham, Xuan-Tan; Wanjara, Priti; Fihey, Jean-Luc

    2016-07-01

    Cast CA6NM martensitic stainless steel plates, 10 mm in thickness, were welded using hybrid laser-arc welding. The effect of different welding speeds on the as-welded joint integrity was characterized in terms of the weld bead geometry, defects, microstructure, hardness, ultimate tensile strength, and impact energy. Significant defects such as porosity, root humping, underfill, and excessive penetration were observed at a low welding speed (0.5 m/min). However, the underfill depth and excessive penetration in the joints manufactured at welding speeds above 0.75 m/min met the specifications of ISO 12932. Characterization of the as-welded microstructure revealed untempered martensite and residual delta ferrite dispersed at prior-austenite grain boundaries in the fusion zone. In addition, four different heat-affected zones in the weldments were differentiated through hardness mapping and inference from the Fe-Cr-Ni ternary phase diagram. The tensile fracture occurred in the base metal for all the samples and fractographic analysis showed that the crack path is within the martensite matrix, along primary delta ferrite-martensite interfaces and within the primary delta ferrite. Additionally, Charpy impact testing demonstrated slightly higher fracture energy values and deeper dimples on the fracture surface of the welds manufactured at higher welding speeds due to grain refinement and/or lower porosity.

  11. Effects of neutron irradiation on microstructural evolution in candidate low activation ferritic steels

    NASA Astrophysics Data System (ADS)

    Kohno, Yutaka; Kohyama, Akira; Yoshino, Masahiko; Asakura, Kentaro

    1994-09-01

    Fe-(2.25-12)Cr-2W-V, Ta low activation ferritic steels (JLF series steels) were developed in the fusion materials development program of Japanese universities. Microstructural observations, including precipitation response, were performed after neutron irradiation in the FFTF/MOTA. The preirradiation microstructure was stable after irradiation at low temperature (< 683 K). Recovery of martensitic lath structure and coarsening of precipitates took place above 733 K. Precipitates observed after irradiation were the same as those in unirradiated materials in 7-9Cr steels, and no irradiation induced phase was identified. The irradiation induced shift in DBTT in the 9Cr-2W steel proved to be very small which is a reflection of stable precipitation response in these steels. A high density of fine α' precipitates was observed in the 12Cr steel which might be responsible for the large irradiation hardening found in the 12Cr steel. Void formation was observed in 7-9Cr steels irradiated at 683 K, but the amount of void swelling was very small.

  12. Modeling Hardenable Stainless Steels Using Calculated Martensite Start Temperatures in Thermodynamic Equilibrium Calculations

    NASA Astrophysics Data System (ADS)

    Seifert, Merlin; Theisen, Werner

    2016-12-01

    In this work, martensite start temperatures of several martensitic stainless steels containing different amounts and types of carbides were calculated by means of thermodynamic equilibrium calculations. Two different equations were introduced into the Thermo-Calc® software. The calculations were performed for the respective compositions at austenitization temperature and compared to martensite start temperatures measured using a quenching dilatometer. The purpose was to estimate hardenability and hardness of newly developed steels. Even though the equations used were determined empirically for specific alloying systems, general trends for the investigated steels were found to be reproduced very well. Thus, the comparison of martensite start temperatures of different steels in comparable alloying systems is highly effective for modeling new steels and for predicting their hardenability.

  13. Influence of the Martensitic Transformation on the Microscale Plastic Strain Heterogeneities in a Duplex Stainless Steel

    NASA Astrophysics Data System (ADS)

    Lechartier, Audrey; Martin, Guilhem; Comby, Solène; Roussel-Dherbey, Francine; Deschamps, Alexis; Mantel, Marc; Meyer, Nicolas; Verdier, Marc; Veron, Muriel

    2017-01-01

    The influence of the martensitic transformation on microscale plastic strain heterogeneity of a duplex stainless steel has been investigated. Microscale strain heterogeneities were measured by digital image correlation during an in situ tensile test within the SEM. The martensitic transformation was monitored in situ during tensile testing by high-energy synchrotron X-ray diffraction. A clear correlation is shown between the plasticity-induced transformation of austenite to martensite and the development of plastic strain heterogeneities at the phase level.

  14. Laser milling of martensitic stainless steels using spiral trajectories

    NASA Astrophysics Data System (ADS)

    Romoli, L.; Tantussi, F.; Fuso, F.

    2017-04-01

    A laser beam with sub-picosecond pulse duration was driven in spiral trajectories to perform micro-milling of martensitic stainless steel. The geometry of the machined micro-grooves channels was investigated by a specifically conceived Scanning Probe Microscopy instrument and linked to laser parameters by using an experimental approach combining the beam energy distribution profile and the absorption phenomena in the material. Preliminary analysis shows that, despite the numerous parameters involved in the process, layer removal obtained by spiral trajectories, varying the radial overlap, allows for a controllable depth of cut combined to a flattening effect of surface roughness. Combining the developed machining strategy to a feed motion of the work stage, could represent a method to obtain three-dimensional structures with a resolution of few microns, with an areal roughness Sa below 100 nm.

  15. Stress corrosion cracking evaluation of martensitic precipitation hardening stainless steels

    NASA Technical Reports Server (NTRS)

    Humphries, T. S.; Nelson, E. E.

    1980-01-01

    The resistance of the martensitic precipitation hardening stainless steels PH13-8Mo, 15-5PH, and 17-4PH to stress corrosion cracking was investigated. Round tensile and c-ring type specimens taken from several heats of the three alloys were stressed up to 100 percent of their yield strengths and exposed to alternate immersion in salt water, to salt spray, and to a seacoast environment. The results indicate that 15-5PH is highly resistant to stress corrosion cracking in conditions H1000 and H1050 and is moderately resistant in condition H900. The stress corrosion cracking resistance of PH13-8Mo and 17-4PH stainless steels in conditions H1000 and H1050 was sensitive to mill heats and ranged from low to high among the several heats included in the tests. Based on a comparison with data from seacoast environmental tests, it is apparent that alternate immersion in 3.5 percent salt water is not a suitable medium for accelerated stress corrosion testing of these pH stainless steels.

  16. Cold Spray Repair of Martensitic Stainless Steel Components

    NASA Astrophysics Data System (ADS)

    Faccoli, M.; Cornacchia, G.; Maestrini, D.; Marconi, G. P.; Roberti, R.

    2014-12-01

    The possibility of using cold spray as repair technique of martensitic stainless steel components was evaluated through laboratory investigations. An austenitic stainless steel feedstock powder was chosen, instead of soft metals powders like nickel, copper, or aluminum, used for repairing components made in light alloy or cast iron. The present study directly compares the microstructure, the residual stresses, and the micro-hardness of repairs obtained by cold spray and by TIG welding, that is commonly used as repair technique in large steel components. XRD and optical metallographic analysis of the repairs showed that cold spray offers some advantages, inducing compressive residual stresses in the repair and avoiding alterations of the interface between repair and base material. For these reasons, a heat treatment after the cold spray repair is not required to restore the base material properties, whereas a post-weld heat treatment is needed after the welding repair. Cold spray repair also exhibits a higher micro-hardness than the welding repair. In addition, the cavitation erosion resistance of a cold spray coating was investigated through ultrasonic cavitation tests, and the samples worn surfaces were observed by scanning electron microscopy.

  17. Effect of Strain-Induced Age Hardening on Yield Strength Improvement in Ferrite-Austenite Duplex Lightweight Steels

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

    Ferrite-austenite lightweight steels showing TRansformation-induced plasticity were developed by varying the aging temperature with or without prestraining, and their effects on tensile properties were investigated in relation with microstructural evolution of carbide formation. The aged steels contained austenite, pearlite, and martensite in the ferrite matrix, and the austenite volume fraction decreased with the increasing aging temperature because some austenite grains decomposed to pearlites. This austenite decomposition to pearlite was favorable for the improvement of yield strength, but negatively influenced overall tensile properties. The prestraining promoted the austenite decomposition by a diffusion-controlled phase transformation, and changed the morphology of the cementite from a long lamellar shape to a densely agglomerated particle shape. In order to obtain the large increase in yield strength as well as excellent combination of strength and ductility, the strain-induced aging treatment, i.e., prestraining followed by aging, is important like in the prestrained and 673 K (400 °C)-aged steel. This large increase in yield strength, in spite of a reduction of elongation (65 to 43 pct), was basically attributed to an appropriate amount of decomposition of austenite to pearlite ( e.g., 4 vol pct), while having sufficient austenite to martensite transformation ( e.g., 14.5 vol pct martensite).

  18. Identification, size classification and evolution of Laves phase precipitates in high chromium, fully ferritic steels.

    PubMed

    Lopez Barrilao, Jennifer; Kuhn, Bernd; Wessel, Egbert

    2017-10-01

    To fulfil the new challenges of the German "Energiewende" more efficient, sustainable, flexible and cost-effective energy technologies are strongly needed. For a reduction of consumed primary resources higher efficiency steam cycles with increased operating parameters, pressure and temperature, are mandatory. Therefore advanced materials are needed. The present study focuses on a new concept of high chromium, fully ferritic steels. These steels, originally designed for solid oxide fuel cell applications, provide favourable steam oxidation resistance, creep and thermomechanical fatigue behaviour in comparison to conventional ferritic-martensitic steels. The strength of this type of steel is achieved by a combination of solid-solution hardening and precipitation strengthening by intermetallic Laves phase particles. The effect of alloy composition on particle composition was measured by energy dispersive X-ray spectroscopy and partly verified by thermodynamic modelling results. Generally the Laves phase particles demonstrated high thermodynamic stability during long-term annealing up to 40,000h at 600°C. Variations in chemical alloy composition influence Laves phase particle formation and consequently lead to significant changes in creep behaviour. For this reason particle size distribution evolution was analysed in detail and associated with the creep performance of several trial alloys. Copyright © 2017 Elsevier Ltd. All rights reserved.

  19. Surface modification of ferritic steels using MEVVA and duoplasmatron ion sources

    SciTech Connect

    Kulevoy, Timur V. Orlov, Nikolay N.; Rogozhkin, Sergey V.; Bogachev, Alexey A.; Nikitin, Alexander A.; Iskandarov, Nasib A.; Golubev, Alexander A.; Chalyhk, Boris B.; Fedin, Petr A.; Sitnikov, Alexey L.; Kozlov, Alexander V.; Kuibeda, Rostislav P.; Andrianov, Stanislav L.; Kravchuk, Konstantin S.; Useinov, Alexey S.; Oks, Efim M.

    2016-02-15

    Metal Vapor Vacuum Arc (MEVVA) ion source (IS) is a unique tool for production of high intensity metal ion beam that can be used for material surface modification. From the other hand, the duoplasmatron ion source provides the high intensity gas ion beams. The MEVVA and duoplasmatron IS developed in Institute for Theoretical and Experimental Physics were used for the reactor steel surface modification experiments. Response of ferritic-martensitic steel specimens on titanium and nitrogen ions implantation and consequent vacuum annealing was investigated. Increase in microhardness of near surface region of irradiated specimens was observed. Local chemical analysis shows atom mixing and redistribution in the implanted layer followed with formation of ultrafine precipitates after annealing.

  20. Oxide dispersion strengthened ferritic steels: a basic research joint program in France

    NASA Astrophysics Data System (ADS)

    Boutard, J.-L.; Badjeck, V.; Barguet, L.; Barouh, C.; Bhattacharya, A.; Colignon, Y.; Hatzoglou, C.; Loyer-Prost, M.; Rouffié, A. L.; Sallez, N.; Salmon-Legagneur, H.; Schuler, T.

    2014-12-01

    AREVA, CEA, CNRS, EDF and Mécachrome are funding a joint program of basic research on Oxide Dispersion Strengthened Steels (ODISSEE), in support to the development of oxide dispersion strengthened 9-14% Cr ferritic-martensitic steels for the fuel element cladding of future Sodium-cooled fast neutron reactors. The selected objectives and the results obtained so far will be presented concerning (i) physical-chemical characterisation of the nano-clusters as a function of ball-milling process, metallurgical conditions and irradiation, (ii) meso-scale understanding of failure mechanisms under dynamic loading and creep, and, (iii) kinetic modelling of nano-clusters nucleation and α/α‧ unmixing.

  1. ODS Ferritic/martensitic alloys for Sodium Fast Reactor fuel pin cladding

    NASA Astrophysics Data System (ADS)

    Dubuisson, Philippe; Carlan, Yann de; Garat, Véronique; Blat, Martine

    2012-09-01

    The development of ODS materials for the cladding for Sodium Fast Reactors is a key issue to achieve the objectives required for the GEN IV reactors. CEA, AREVA and EDF have launched in 2007 an important program to determine the optimal fabrication parameters, and to measure and understand the microstructure and properties before, under and after irradiation of such cladding materials. The aim of this paper is to present the French program and the major results obtained recently at CEA on Fe-9/14/18Cr1WTiY2O3 ferritic/martensitic ODS materials. The first step of the program was to consolidate Fe-9/14/18Cr ODS materials as plates and bars to study the microstructure and the mechanical properties of the new alloys. The second step consists in producing tubes at a geometry representative of the cladding of new Sodium Fast Reactors. The optimization of the fabrication route at the laboratory scale is conducted and different tubes were produced. Their microstructure depends on the martensitic (Fe-9Cr) or ferritic (Fe-14Cr) structure. To join the plug to the tube, the reference process is the welding resistance. A specific approach is developed to model the process and support the development of the welds performed within the "SOPRANO" facility. The development at CEA of Fe-9/14/18Cr new ODS materials for the cladding for GENIV Sodium Fast Reactors is in progress. The first microstructural and mechanical characterizations are very encouraging and the full assessment and qualification of this new alloys and products will pass through the irradiation of specimens, tubes, fuel pins and subassemblies up to high doses.

  2. The influence of fine ferrite formation on the γ/α interface, fine bainite and retained austenite in a thermomechanically-processed transformation induced plasticity steel

    DOE PAGES

    Timokhina, Ilana B.; Miller, Michael K.; Beladi, Hossein; ...

    2016-03-03

    We subjected a Fe–0.26C–1.96Si–2Mn with 0.31Mo (wt%) steel to a novel thermomechanical processing route to produce fine ferrite with different volume fractions, bainite, and retained austenite. In two types of fine ferrites were found to be: (i) formed along prior austenite grain boundaries, and (ii) formed intragranularly in the interior of austenite grains. An increase in the volume fraction of fine ferrite led to the preferential formation of blocky retained austenite with low stability, and to a decrease in the volume fraction of bainite with stable layers of retained austenite. Moreover, the difference in the morphology of the bainitic ferritemore » and the retained austenite after different isothermal ferrite times was found to be responsible for the deterioration of the mechanical properties. The segregation of Mn, Mo, and C at distances of 2–2.5 nm from the ferrite and retained austenite/martensite interface on the retained austenite/martensite site was observed after 2700 s of isothermal hold. Finally, it was suggested that the segregation occurred during the austenite-to-ferrite transformation, and that this would decrease the interface mobility, which affects the austenite-to-ferrite transformation and ferrite grain size.« less

  3. Superstrength of nanograined steel with nanoscale intermetallic precipitates transformed from shock-compressed martensitic steel

    NASA Astrophysics Data System (ADS)

    Yu, Hailiang; Yan, Ming; Lu, Cheng; Tieu, Anh Kiet; Li, Huijun; Zhu, Qiang; Godbole, Ajit; Li, Jintao; Su, Lihong; Kong, Charlie

    2016-11-01

    An increasing number of industrial applications need superstrength steels. It is known that refined grains and nanoscale precipitates can increase strength. The hardest martensitic steel reported to date is C0.8 steel, whose nanohardness can reach 11.9 GPa through incremental interstitial solid solution strengthening. Here we report a nanograined (NG) steel dispersed with nanoscale precipitates which has an extraordinarily high hardness of 19.1 GPa. The NG steel (shock-compressed Armox 500T steel) was obtained under these conditions: high strain rate of 1.2 μs-1, high temperature rise rate of 600 Kμs-1 and high pressure of 17 GPa. The mean grain size achieved was 39 nm and reinforcing precipitates were indexed in the NG steel. The strength of the NG steel is expected to be ~3950 MPa. The discovery of the NG steel offers a general pathway for designing new advanced steel materials with exceptional hardness and excellent strength.

  4. Superstrength of nanograined steel with nanoscale intermetallic precipitates transformed from shock-compressed martensitic steel

    PubMed Central

    Yu, Hailiang; Yan, Ming; Lu, Cheng; Tieu, Anh Kiet; Li, Huijun; Zhu, Qiang; Godbole, Ajit; Li, Jintao; Su, Lihong; Kong, Charlie

    2016-01-01

    An increasing number of industrial applications need superstrength steels. It is known that refined grains and nanoscale precipitates can increase strength. The hardest martensitic steel reported to date is C0.8 steel, whose nanohardness can reach 11.9 GPa through incremental interstitial solid solution strengthening. Here we report a nanograined (NG) steel dispersed with nanoscale precipitates which has an extraordinarily high hardness of 19.1 GPa. The NG steel (shock-compressed Armox 500T steel) was obtained under these conditions: high strain rate of 1.2 μs−1, high temperature rise rate of 600 Kμs−1 and high pressure of 17 GPa. The mean grain size achieved was 39 nm and reinforcing precipitates were indexed in the NG steel. The strength of the NG steel is expected to be ~3950 MPa. The discovery of the NG steel offers a general pathway for designing new advanced steel materials with exceptional hardness and excellent strength. PMID:27892460

  5. Strain-induced martensite to austenite reverse transformation in an ultrafine-grained Fe-Ni-Mn martensitic steel

    NASA Astrophysics Data System (ADS)

    Ghasemi-Nanesa, H.; Nili-Ahmadabadi, M.; Koohdar, H. R.; Habibi-Parsa, M.; Nedjad, S. Hossein; Alidokht, S. A.; Langdon, Terence G.

    2014-05-01

    Research was conducted to evaluate the effect of heavy cold rolling on microstructural evolution in an Fe-10Ni-7Mn (wt.%) martensitic steel. The chemical driving force for the strain-induced martensite to austenite reverse transformation was calculated using thermodynamic principles and a model was developed for estimating the effect of applied stress on the driving force of the martensite to austenite reverse transformation through heavy cold rolling. These calculations show that, in order to make a reverse transformation feasible, the applied stress on the material should supply the total driving force, both chemical and non-chemical, for the transformation. It is demonstrated that after 60% cold rolling the required driving force for the reverse transformation may be provided. Experimental results, including cold rolling and transmission electron microscopy images, are utilized to verify the thermodynamic calculations.

  6. Microstructure and texture of Nb + Ti stabilized ferritic stainless steel

    SciTech Connect

    Yan Haitao Bi Hongyun; Li Xin; Xu Zhou

    2008-12-15

    The microstructure, texture and grain boundary character distribution of Nb + Ti stabilized ferritic stainless steel were analyzed using scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The addition of alloying elements such as Ti and Nb to ferritic stainless steel causes the formation of TiN, NbC and Fe{sub 2}Nb. The textures of cold rolled samples were dominated by the {alpha}-fiber, while the textures of annealed samples exhibit a very strong {gamma}-fiber. The changes in texture are closely related to the grain boundary characteristics.

  7. Low-chromium reduced-activation ferritic steels for fusion

    SciTech Connect

    Klueh, R.L.; Alexander, D.J.; Kenik, E.A.

    1996-04-01

    Development of reduced-activation ferritic steels has concentrated on high-chromium (8-10 wt% Cr) steels. However, there are advantages for a low-chromium steel, and initial ORNL studies on reduced-activation steels were on compositions with 2.25 to 12% Cr. Those studies showed an Fe-2.25Cr-2W-0.25V-0.1C (2 1/4Cr-2WV) steel to have the highest strenglth of the steels studied. Although this steel had the best strength, Charpy impact properties were inferior to those of an Fe-9Cr-2W-0.25V-0.07Ta-0.1C (9Cr-2WVTa) and an Fe-2.25Cr-2W-0.1C (2 1/4Cr-2W) steel. Therefore, further development of the low-chromium Cr-W steels was required. These results indicate that it is possible to develop low-chromium reduced-activation ferritic steels that have tensile and impact properties as good or better than those of high-chromium (7-9% Cr) steels. Further improvement of properties should be possible by optimizing the composition.

  8. Isothermal formation of martensite in a 12Cr-9Ni-4Mo maraging stainless steel

    SciTech Connect

    Holmquist, M.

    1995-11-01

    The present paper is concerned with the nature of the martensite, which provides the basis for the maraging treatment. Rather than forming martensite during cooling, 1RK91 develops martensite when held at a constant temperature in a range from room temperature and below. Isothermal martensite formation showing C-curve kinetics was found to occur in the maraging steel 1RK91, the nose temperature being about {minus}40 C. The kinetics was found to be enhanced for higher austenitizing treatment temperatures, presumably through a combination of larger grain size and a larger number of quenched in nuclei for isothermal martensite transformation. Experiments involving different cooling rates showed that fast cooling enhanced the transformation kinetics. Based on this observation it is suggested that quenched-in vacancy clusters provide suitable strain embryos for isothermal martensite nucleation.

  9. Investigation of Steels for Improved Weldability in Ship Construction.

    DTIC Science & Technology

    1984-05-01

    transformation products from Widmanstatten ferrite, pearlite, and bainite to a more equiaxed ferrite and pearlite microstructure. Additions of residuals (Cu + Ni...ferrite and the type of AL.. microconstituents present (pearlite, bainite , or martensite). Microstructures of the HAZ’s of all the steels after simulated...martensite and bainite . The final group of steels all contained vanadium. Th’. plain vanadium steel V1 had a slightly higher CVN transition temperature

  10. Development of new generation reduced activation ferritic-martenstic steels for advanced fusion reactors

    SciTech Connect

    Tan, Lizhen; Snead, Lance Lewis; Katoh, Yutai

    2016-05-26

    International development of reduced activation ferritic-martensitic (RAFM) steels has focused on 9 wt percentage Cr, which primarily contain M23C6 (M = Cr-rich) and small amounts of MX (M = Ta/V, X = C/N) precipitates, not adequate to maintain strength and creep resistance above ~500 °C. To enable applications at higher temperatures for better thermal efficiency of fusion reactors, computational alloy thermodynamics coupled with strength modeling have been employed to explore a new generation RAFM steels. The new alloys are designed to significantly increase the amount of MX nanoprecipitates, which are manufacturable through standard and scalable industrial steelmaking methods. Preliminary experimental results of the developed new alloys demonstrated noticeably increased amount of MX, favoring significantly improved strength, creep resistance, and Charpy impact toughness as compared to current RAFM steels. Furthermore, the strength and creep resistance were comparable or approaching to the lower bound of, but impact toughness was noticeably superior to 9–20Cr oxide dispersion-strengthened ferritic alloys.

  11. Development of new generation reduced activation ferritic-martenstic steels for advanced fusion reactors

    DOE PAGES

    Tan, Lizhen; Snead, Lance Lewis; Katoh, Yutai

    2016-05-26

    International development of reduced activation ferritic-martensitic (RAFM) steels has focused on 9 wt percentage Cr, which primarily contain M23C6 (M = Cr-rich) and small amounts of MX (M = Ta/V, X = C/N) precipitates, not adequate to maintain strength and creep resistance above ~500 °C. To enable applications at higher temperatures for better thermal efficiency of fusion reactors, computational alloy thermodynamics coupled with strength modeling have been employed to explore a new generation RAFM steels. The new alloys are designed to significantly increase the amount of MX nanoprecipitates, which are manufacturable through standard and scalable industrial steelmaking methods. Preliminary experimentalmore » results of the developed new alloys demonstrated noticeably increased amount of MX, favoring significantly improved strength, creep resistance, and Charpy impact toughness as compared to current RAFM steels. Furthermore, the strength and creep resistance were comparable or approaching to the lower bound of, but impact toughness was noticeably superior to 9–20Cr oxide dispersion-strengthened ferritic alloys.« less

  12. Development of new generation reduced activation ferritic-martenstic steels for advanced fusion reactors

    SciTech Connect

    Tan, Lizhen; Snead, Lance Lewis; Katoh, Yutai

    2016-05-26

    International development of reduced activation ferritic-martensitic (RAFM) steels has focused on 9 wt percentage Cr, which primarily contain M23C6 (M = Cr-rich) and small amounts of MX (M = Ta/V, X = C/N) precipitates, not adequate to maintain strength and creep resistance above ~500 °C. To enable applications at higher temperatures for better thermal efficiency of fusion reactors, computational alloy thermodynamics coupled with strength modeling have been employed to explore a new generation RAFM steels. The new alloys are designed to significantly increase the amount of MX nanoprecipitates, which are manufacturable through standard and scalable industrial steelmaking methods. Preliminary experimental results of the developed new alloys demonstrated noticeably increased amount of MX, favoring significantly improved strength, creep resistance, and Charpy impact toughness as compared to current RAFM steels. Furthermore, the strength and creep resistance were comparable or approaching to the lower bound of, but impact toughness was noticeably superior to 9–20Cr oxide dispersion-strengthened ferritic alloys.

  13. Structure and mechanical properties of hot-deformed low-carbon martensitic steel

    NASA Astrophysics Data System (ADS)

    Romanov, I. D.; Shatsov, A. A.; Zakirova, M. G.; Berezin, S. K.

    2016-03-01

    The structural changes in low-carbon martensitic 15Kh2G2NMFBA steel induced by its hot forging in the temperature range 1150-850°C have been studied. The calculated cracking resistance parameter I c is in agreement with its experimental value. A relation is found between the lath sizes in the martensite structure and the change in the impact toughness characteristics. A combined regime of hot deformation and hot treatment of the low-carbon martensitic steel is proposed to form submicrometer-sized structural elements and high strength and impact toughness characteristics.

  14. PERFORMANCE IMPROVEMENT OF CREEP-RESISTANT FERRITIC STEEL WELDMENTS THROUGH THERMO-MECHANICAL TREATMENT AND ALLOY DESIGN

    SciTech Connect

    Yamamoto, Yukinori; Babu, Prof. Sudarsanam Suresh; Shassere, Benjamin; Yu, Xinghua

    2016-01-01

    Two different approaches have been proposed for improvement of cross-weld creep properties of the high temperature ferrous structural materials for fossil-fired energy applications. The traditional creep strength-enhanced ferritic (CSEF) steel weldments suffer from Type IV failures which occur at the fine-grained heat affected zone (FGHAZ). In order to minimize the premature failure at FGHAZ in the existing CSEF steels, such as modified 9Cr-1Mo ferritic-martensitic steels (Grade 91), a thermo-mechanical treatment consisting of aus-forging/rolling and subsequent aus-aging is proposed which promotes the formation of stable MX carbonitrides prior to martensitic transformation. Such MX remains undissolved during welding process, even in FGHAZ, which successfully improves the cross-weld creep properties. Another approach is to develop a new fully ferrtic, creep-resistant FeCrAl alloy which is essentially free from Type IV failure issues. Fe-30Cr-3Al base alloys with minor alloying additions were developed which achieved a combination of good oxidation/corrosion resistance and improved tensile and creep performance comparable or superior to Grade 92 steel.

  15. Formation of nano-size oxide particles and δ-ferrite at elevated temperature in 9Cr-ODS steel

    NASA Astrophysics Data System (ADS)

    Kim, Sawoong; Ohtsuka, Satoshi; Kaito, Takeji; Yamashita, Shinichiro; Inoue, Masaki; Asayama, Tai; Shobu, Takahisa

    2011-10-01

    Excellent high-temperature strength and resistance to radiation damage of 9Cr Oxide Dispersion Strengthened (9Cr-ODS) martensitic steel have been realized by nano-size Y-Ti-O complex oxide particles dispersed in the matrix and a dual phase structure consisting of α'-martensite and δ-ferrite. These are produced by mechanically alloying Fe-Cr-Ti powders with Y 2O 3 followed by a hot-consolidation process. Therefore, the hot-consolidation process is the issue to be clarified for the formation of nano-size oxide particle and δ-ferrite. The temperature dependence of the formation and development of nano-size oxide particles and δ-ferrite using mechanically alloyed 9Cr-ODS raw powder were investigated applying X-ray Diffraction and Small Angle X-ray Scattering measurement at SPring-8 and by Electron Probe Micro Analysis. In situ heating measurement techniques with XRD and SAXS enabled real-time observation of phase transformations and allowed correlation between formation of nano-size oxide particle and δ-ferrite.

  16. Helium effects on microstructural evolution in tempered martensitic steels: In situ helium implanter studies in HFIR

    SciTech Connect

    Yamamoto, Takuya; Odette, George R.; Miao, Pifeng; Edwards, Danny J.; Kurtz, Richard J.

    2009-04-30

    Microstructural evolutions in tempered martensitic steels (TMS) under neutron-irradiation, at fusion relevant He/dpa ratios and dpa rates, were characterized using a novel in situ He-implanter technique. F82H-mod3 was irradiated at 500 C in HFIR to a nominal 9 dpa and 190 or 380 appm He in both in the as-tempered (AT) and 20% cold-worked (CW) conditions. In all cases, a high number density of 1-2 nm He-bubbles were observed, along with fewer but larger 10 nm void-like faceted cavities. The He-bubbles form preferentially on dislocations and various interfaces. A slightly larger number of smaller He bubbles were observed in the CW condition. The lower He/dpa ratio produced slightly smaller and fewer He-bubbles. Comparisons of these observations to the results in nano-structured ferritic alloy (NFA) MA957 provide additional evidence that TMS may be susceptible to He-embrittlement as well as void swelling at fusion relevant He concentrations, while NFA are much more resistant to these degradation phenomena.

  17. Microstructural Features Controlling Ductile-to-Brittle Transition Behavior in High-Strength, Martensitic Steel Weld Metals

    DTIC Science & Technology

    1990-10-01

    Development Report Microstructural Features Controlling Ductile-to- Brittle Transition Behavior in High-Strength, Martensitic Steel Weld Metals C 0by...Martensitic Steel Weld Metals PERSONAL AUTHOR(S) .J. DeLoach, Jr. .TYPE OF REPORT 13b TIME COVERED 114 DATE OF REPORT (Year, Month, Day) 1S PAGE COUNT I...if necessary and identify by block number) FIELD GROUP SUB-GROUP High strength steel , Ductile-brittle transition Martensitic Mechanical proper ties

  18. Simulation Computation of 430 Ferritic Stainless Steel Solidification

    NASA Astrophysics Data System (ADS)

    Pang, Ruipeng; Li, Changrong; Wang, Fuming; Hu, Lifu

    The solidification structure of 430 ferritic stainless steel has been calculated in the solidification process by using 3D-CAFE model under the condition of water cooling. The calculated results consistent with those obtained from experiment. Under watercooling condition, the solidification structure consists of chilled layer, columnar grain zone, transition zone and equiaxed grain zone.

  19. Response of ferritic steels to nonsteady loading at elevated temperatures

    SciTech Connect

    Swindeman, R.W.

    1984-04-01

    High-temperature operating experience is lacking in pressure vessel materials that have strength levels above 586 MPa. Because of their tendency toward strain softening, we have been concerned about their behavior under nonsteady loading. Testing was undertaken to explore the extent of softening produced by monotonic and cyclic strains. The specific materials included bainitic 2 1/4Cr-1Mo steel, a micro-alloyed version of 2 1/4Cr-1Mo steel, a micro-alloyed version of 2 1/4Cr-1Mo steel containing vanadium, titanium, and boron, and a martensitic 9Cr-1Mo-V-Nb steel. Tests included tensile, creep, variable stress creep, relaxation, strain cycling, stress cycling, and non-isothermal creep ratchetting experiments. We found that these steels had very low uniform elongation and exhibited small strains to the onset of tertiary creep compared to annealed 2 1/4Cr-1Mo steel. Repeated relaxation test data also indicated a limited capacity for strain hardening. Reversal strains produced softening. The degree of softening increased with increased initial strength level. We concluded that the high strength bainitic and martensitic steels should perform well when used under conditions where severe cyclic operation does not occur.

  20. Characterization of a Laser Surface-Treated Martensitic Stainless Steel

    PubMed Central

    Al-Sayed, S. R.; Hussein, A. A.; Nofal, A. A.; Hassab Elnaby, S. I.; Elgazzar, H.

    2017-01-01

    Laser surface treatment was carried out on AISI 416 machinable martensitic stainless steel containing 0.225 wt.% sulfur. Nd:YAG laser with a 2.2-KW continuous wave was used. The aim was to compare the physical and chemical properties achieved by this type of selective surface treatment with those achieved by the conventional treatment. Laser power of different values (700 and 1000 W) with four corresponding different laser scanning speeds (0.5, 1, 2, and 3 m·min−1) was adopted to reach the optimum conditions for impact toughness, wear, and corrosion resistance for laser heat treated (LHT) samples. The 0 °C impact energy of LHT samples indicated higher values compared to the conventionally heat treated (CHT) samples. This was accompanied by the formation of a hard surface layer and a soft interior base metal. Microhardness was studied to determine the variation of hardness values with respect to the depth under the treated surface. The wear resistance at the surface was enhanced considerably. Microstructure examination was characterized using optical and scanning electron microscopes. The corrosion behavior of the LHT samples was also studied and its correlation with the microstructures was determined. The corrosion data was obtained in 3.5% NaCl solution at room temperature by means of a potentiodynamic polarization technique. PMID:28772955

  1. Characterization of Hydrogen-Related Fracture Behavior in As-Quenched Low-Carbon Martensitic Steel and Tempered Medium-Carbon Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Shibata, Akinobu; Murata, Tamotsu; Takahashi, Hiroshi; Matsuoka, Takahiro; Tsuji, Nobuhiro

    2015-12-01

    Hydrogen-related fracture behaviors in low-carbon (Fe-0.1wtpctC) and medium-carbon (Fe-0.4wtpctC) martensitic steels were characterized through crystallographic orientation analysis using electron backscattering diffraction. The martensitic steels with lower strength (Fe-0.1C specimen or Fe-0.4C specimen tempered at higher temperature) exhibited transgranular fracture, where fractured surfaces consisted of dimples and quasi-cleavage patterns. Crystallographic orientation analysis revealed that several of the micro-cracks that formed around the prior austenite grain boundaries propagated along {011} planes. In contrast, fracture surface morphologies of the martensitic steels with higher strength (Fe-0.4C specimen tempered at lower temperature) appeared to be intergranular-like. Crystallographic orientation analysis demonstrated that, on a microscopic level, the fracture surfaces comprised the facets parallel to {011} planes. These results suggest that the hydrogen-related fractures in martensitic steels with higher strength are not exactly intergranular at the prior austenite grain boundaries, but they are transgranular fractures propagated along {011} planes close to the prior austenite grain boundaries. A description of the mechanism of hydrogen-related fracture is proposed based on the results.

  2. Twinning and martensitic transformations in nickel-enriched 304 austenitic steel during tensile and indentation deformations

    SciTech Connect

    Gussev, Maxim N; Busby, Jeremy T; Byun, Thak Sang; Parish, Chad M

    2013-01-01

    Twinning and martensitic transformation have been investigated in nickel-enriched AISI 304 stainless steel subjected to tensile and indentation deformation. Using electron backscatter diffraction (EBSD), the morphology of alpha- and epsilon-martensite and the effect of grain orientation to load axis on phase and structure transformations were analyzed in detail. It was found that the twinning occurred less frequently under indentation than under tension; also, twinning was not observed in [001] and [101] grains. In tensile tests, the martensite particles preferably formed at the deformation twins, intersections between twins, or at twin-grain boundary intersections. Conversely, martensite formation in the indentation tests was not closely associated with twinning; instead, the majority of martensite was concentrated in the dense colonies near grain boundaries. Martensitic transformation seemed to be obstructed in the [001] grains in both tensile and indentation test cases. Under a tensile stress of 800 MPa, both alpha- and epsilon-martensite were found in the microstructure, but at 1100 MPa only -martensite presented in the specimen. Under indentation, alpha- and epsilon-martensite were observed in the material regardless of stress level.

  3. Ferritic steel for use in nuclear energy — A report of the snowbird conference

    NASA Astrophysics Data System (ADS)

    Davis, J. W.

    1984-05-01

    This international conference on ferritic or martensitic steels consisted of a planary session with all invited papers and several parallel sessions of contributed papers. The conference was sponsored by the Metallurgical Society of the American Institute of Mining, Metallurgical, and Petroleum Engineers (AIME) as well as several industrial organizations. The technical program chairmen were J. W. Davis of MDAC and D. J. Michel of the U.S. Naval Research Laboratory. The Program committee was composed of representatives from the Federal Republic of Germany, France, Japan, the UK, and the USA. The conference proceedings will be published as a hard bound book by the AIME. Consequently, the present paper is intended to highlight the results of the conference prior to the publication of the proceedings.

  4. Effect of W-addition on low cycle fatigue behavior of high Cr ferritic steels

    NASA Astrophysics Data System (ADS)

    Park, Joon Sik; Lee, Kee Ahn; Lee, Chong Soo

    1999-12-01

    A study was done to investigate the effect of tungsten (W) addition on the microstructure, tensile properties and low cycle fatigue (LCF) properties of 9Cr-lMo steels at 298K and 873K. Four steels containing different amounts of W (0W, 1.2W, 1.8W and 2.7W) were normalized at 1323K for 1 hour and tempered at 1023K for 1 hour. Microstructural analysis revealed that no significant differences wete observed in their tempered martensitic microstructure of 0W, 1.2W and 1.8W alloys, but d-ferrite was observed to form at the prior austenite grain boundaries of the 2.7W alloy. With the increase in W content, yield and tensile strength increased at both temperatures. Low cycle fatigue life also increased with the W content up to 1.8%, but decreased in the 2.7W alloy, which was primarily due to the presence of soft d-ferrite acting as the crack initiation site. The fatigue life at 873K was reduced compared to that at 298K, due not only to the decrease in strength at high temperature but also to the formation of oxide layers along the slip bands, which increases slip irre-versibility during cyclic deformation.

  5. A Shear Strain Route Dependency of Martensite Formation in 316L Stainless Steel.

    PubMed

    Kang, Suk Hoon; Kim, Tae Kyu; Jang, Jinsung; Oh, Kyu Hwan

    2015-06-01

    In this study, the effect of simple shearing on microstructure evolution and mechanical properties of 316L austenitic stainless steel were investigated. Two different shear strain routes were obtained by twisting cylindrical specimens in the forward and backward directions. The strain-induced martensite phase was effectively obtained by alteration of the routes. Formation of the martensite phase clearly resulted in significant hardening of the steel. Grain-size reduction and strain-induced martensitic transformation within the deformed structures of the strained specimens were characterized by scanning electron microscopy - electron back-scattered diffraction, X-ray diffraction, and the TEM-ASTAR (transmission electron microscopy - analytical scanning transmission atomic resolution, automatic crystal orientation/phase mapping for TEM) system. Significant numbers of twin networks were formed by alteration of the shear strain routes, and the martensite phases were nucleated at the twin interfaces.

  6. Effect of Quenching Process on the Microstructure and Hardness of High-Carbon Martensitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Zhu, Qin-tian; Li, Jing; Shi, Cheng-bin; Yu, Wen-tao

    2015-11-01

    The microstructure and hardness of high-carbon martensitic stainless steel (HMSS) were investigated using thermal expansion analyzer, Thermo-calc, scanning electron microscope, x-ray diffraction, and Ultra-high temperature confocal microscope. The results indicate that the experimental steel should be austenitized in the temperature range of 1025-1075 °C, which can give a maximum hardness of 62 HRc with the microstructure consisting of martensite, retained austenite, and some undissolved carbides. With increasing austenitizing temperature, the amount of retained austenite increases, while the volume fraction of carbides increases first and then decreases. The starting temperature and finish temperature of martensite formation decrease with increasing cooling rates. Air-quenched samples can obtain less retained austenite, more compact microstructure, and higher hardness, compared with that of oil-quenched samples. For HMSS, the martensitic transformation takes place at some isolated areas with a slow nucleation rate.

  7. HYDROGEN EFFECTS ON STRAIN-INDUCED MARTENSITE FORMATION IN TYPE 304L STAINLESS STEEL

    SciTech Connect

    Morgan, M; Ps Lam, P

    2008-12-11

    Unstable austenitic stainless steels undergo a strain-induced martensite transformation. The effect of hydrogen on this transformation is not well understood. Some researchers believe that hydrogen makes the transformation to martensite more difficult because hydrogen is an austenite stabilizer. Others believe that hydrogen has little or no effect at all on the transformation and claim that the transformation is simply a function of strain and temperature. Still other researchers believe that hydrogen should increase the ability of the metal to transform due to hydrogen-enhanced dislocation mobility and slip planarity. While the role of hydrogen on the martensite transformation is still debated, it has been experimentally verified that this transformation does occur in hydrogen-charged materials. What is the effect of strain-induced martensite on hydrogen embrittlement? Martensite near crack-tips or other highly strained regions could provide much higher hydrogen diffusivity and allow for quicker hydrogen concentration. Martensite may be more intrinsically brittle than austenite and has been shown to be severely embrittled by hydrogen. However, it does not appear to be a necessary condition for embrittlement since Type 21-6-9 stainless steel is more stable than Type 304L stainless steel but susceptible to hydrogen embrittlement. In this study, the effect of hydrogen on strain-induced martensite formation in Type 304L stainless steel was investigated by monitoring the formation of martensite during tensile tests of as-received and hydrogen-charged samples and metallographically examining specimens from interrupted tensile tests after increasing levels of strain. The effect of hydrogen on the fracture mechanisms was also studied by examining the fracture features of as-received and hydrogen-charged specimens and relating them to the stress-strain behavior.

  8. Large-strain cyclic response and martensitic transformation of austenitic stainless steel at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Hamasaki, H.; Nakano, T.; Ishimaru, E.; Yoshida, F.

    2016-08-01

    Cyclic tension-compression tests were carried out for austenitic stainless steel (SUS304) at elevated temperatures. The significant Bauschinger effect was found in the obtained stress-strain curve. In addition, stagnation of deformation induced martensitic transformation was observed just after stress reversal until the equivalent stress reached the maximum value in the course of experiment. The constitutive model for SUS304 at room temperature was developed, in which homogenized stress of SUS304 was expressed by the weighed summation of stresses of austenite and martensite phases. The calculated stress-strain curves and predicted martensite volume fraction were well correlated with those experimental results.

  9. Studies on oxidation and deuterium permeation behavior of a low temperature α-Al2O3-forming Fesbnd Crsbnd Al ferritic steel

    NASA Astrophysics Data System (ADS)

    Xu, Yu-Ping; Zhao, Si-Xiang; Liu, Feng; Li, Xiao-Chun; Zhao, Ming-Zhong; Wang, Jing; Lu, Tao; Hong, Suk-Ho; Zhou, Hai-Shan; Luo, Guang-Nan

    2016-08-01

    To evaluate the capability of Fesbnd Crsbnd Al ferritic steels as tritium permeation barrier in fusion systems, the oxidation behavior together with the permeation behavior of a Fesbnd Crsbnd Al steel was investigated. Gas driven permeation experiments were performed. The permeability of the oxidized Fesbnd Crsbnd Al steel was obtained and a reduced activation ferritic/martensitic steel CLF-1 was used as a comparison. In order to characterize the oxide layer, SEM, XPS, TEM, HRTEM were used. Al2O3 was detected in the oxide film by XPS, and HRTEM showed that Al2O3 in the α phase was found. The formation of α-Al2O3 layer at a relatively low temperature may result from the formation of Cr2O3 nuclei.

  10. The Investigation of Strain-Induced Martensite Reverse Transformation in AISI 304 Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Cios, G.; Tokarski, T.; Żywczak, A.; Dziurka, R.; Stępień, M.; Gondek, Ł.; Marciszko, M.; Pawłowski, B.; Wieczerzak, K.; Bała, P.

    2017-07-01

    This paper presents a comprehensive study on the strain-induced martensitic transformation and reversion transformation of the strain-induced martensite in AISI 304 stainless steel using a number of complementary techniques such as dilatometry, calorimetry, magnetometry, and in-situ X-ray diffraction, coupled with high-resolution microstructural transmission Kikuchi diffraction analysis. Tensile deformation was applied at temperatures between room temperature and 213 K (-60 °C) in order to obtain a different volume fraction of strain-induced martensite (up to 70 pct). The volume fraction of the strain-induced martensite, measured by the magnetometric method, was correlated with the total elongation, hardness, and linear thermal expansion coefficient. The thermal expansion coefficient, as well as the hardness of the strain-induced martensitic phase was evaluated. The in-situ thermal treatment experiments showed unusual changes in the kinetics of the reverse transformation (α' → γ). The X-ray diffraction analysis revealed that the reverse transformation may be stress assisted—strains inherited from the martensitic transformation may increase its kinetics at the lower annealing temperature range. More importantly, the transmission Kikuchi diffraction measurements showed that the reverse transformation of the strain-induced martensite proceeds through a displacive, diffusionless mechanism, maintaining the Kurdjumov-Sachs crystallographic relationship between the martensite and the reverted austenite. This finding is in contradiction to the results reported by other researchers for a similar alloy composition.

  11. The Investigation of Strain-Induced Martensite Reverse Transformation in AISI 304 Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Cios, G.; Tokarski, T.; Żywczak, A.; Dziurka, R.; Stępień, M.; Gondek, Ł.; Marciszko, M.; Pawłowski, B.; Wieczerzak, K.; Bała, P.

    2017-10-01

    This paper presents a comprehensive study on the strain-induced martensitic transformation and reversion transformation of the strain-induced martensite in AISI 304 stainless steel using a number of complementary techniques such as dilatometry, calorimetry, magnetometry, and in-situ X-ray diffraction, coupled with high-resolution microstructural transmission Kikuchi diffraction analysis. Tensile deformation was applied at temperatures between room temperature and 213 K (-60 °C) in order to obtain a different volume fraction of strain-induced martensite (up to 70 pct). The volume fraction of the strain-induced martensite, measured by the magnetometric method, was correlated with the total elongation, hardness, and linear thermal expansion coefficient. The thermal expansion coefficient, as well as the hardness of the strain-induced martensitic phase was evaluated. The in-situ thermal treatment experiments showed unusual changes in the kinetics of the reverse transformation (α' → γ). The X-ray diffraction analysis revealed that the reverse transformation may be stress assisted—strains inherited from the martensitic transformation may increase its kinetics at the lower annealing temperature range. More importantly, the transmission Kikuchi diffraction measurements showed that the reverse transformation of the strain-induced martensite proceeds through a displacive, diffusionless mechanism, maintaining the Kurdjumov-Sachs crystallographic relationship between the martensite and the reverted austenite. This finding is in contradiction to the results reported by other researchers for a similar alloy composition.

  12. Phase composition and hardening of steels of the Fe-Cr-Ni-Co-Mo system with martensite-austenite structure

    NASA Astrophysics Data System (ADS)

    Tarasenko, L. V.; Shal'kevich, A. B.

    2007-03-01

    The phase composition and mechanical properties of maraging steels of the Fe-Cr-Ni-Co-Mo system are studied as a function of the alloying and of the temperatures of quenching and aging. The intermetallic phases strengthening martensite in different aging stages are determined. The degree of the hardening and the variation of the impact toughness at cryogenic temperatures are compared for steels with different structures (martensite and martensite-austenite) in the stages of maximum hardening and overaging. The effect of retained and reverted austenite on the resistance to crack propagation under impact loading is determined for steels with martensite of a different nature and amount of hardening phases.

  13. Effects of Microalloying on the Impact Toughness of Ultrahigh-Strength TRIP-Aided Martensitic Steels

    NASA Astrophysics Data System (ADS)

    Kobayashi, Junya; Ina, Daiki; Nakajima, Yuji; Sugimoto, Koh-ichi

    2013-11-01

    The effects of the addition of Cr, Mo, and/or Ni on the Charpy impact toughness of a 0.2 pct C-1.5 pct Si-1.5 pct Mn-0.05 pct Nb transformation-induced plasticity (TRIP)-aided steel with a lath-martensite structure matrix ( i.e., a TRIP-aided martensitic steel or TM steel) were investigated with the aim of using the steel in automotive applications. In addition, the relationship between the toughness of the various alloyed steels and their metallurgical characteristics was determined. When Cr, Cr-Mo, or Cr-Mo-Ni was added to the base steel, the TM steel exhibited a high upper-shelf Charpy impact absorbed value that ranged from 100 to 120 J/cm2 and a low ductile-brittle fracture appearance transition temperature that ranged from 123 K to 143 K (-150 °C to -130 °C), while also exhibiting a tensile strength of about 1.5 GPa. This impact toughness of the alloyed steels was far superior to that of conventional martensitic steel and was caused by the presence of (i) a softened wide lath-martensite matrix, which contained only a small amount of carbide and hence had a lower carbon concentration, (ii) a large amount of finely dispersed martensite-retained austenite complex phase, and (iii) a metastable retained austenite phase of 2 to 4 vol pct in the complex phase, which led to plastic relaxation via strain-induced transformation and played an important role in the suppression of the initiation and propagation of voids and/or cleavage cracks.

  14. Magnetic Study of Martensitic Transformation in Austenitic Stainless Steel by Low Field Hysteresis Loops Analysis

    SciTech Connect

    Zhang Lefu; Takahashi, Seiki; Kamada, Yasuhiro; Kikuchi, Hiroaki; Mumtaz, Khalid; Ara, Katsuyuki; Sato, Masaya

    2005-04-09

    Magnetic method has been used to evaluate the volume percentage of {alpha}' martensitic phase in austenitic stainless steels by measuring saturation magnetization, and it is said to be a candidate NDE method. However, nondestructive detection of saturation magnetization without high magnetic field is difficult. In the current work, we present a NDE method for evaluating the magnetic properties of strain induced {alpha}' martensitic phase. Low field hysteresis loops of an austenitic stainless steels type SUS 304 after cold rolling were measured by using a yoke sensor. The results show that the initial permeability {mu}i and the relative coercive field Hcl calculated by low field hysteresis loop analysis keep monotonic relation with saturation magnetization and coercive force measured by VSM, respectively. By this method, it is possible to characterize the volume content and particle properties of {alpha}' martensitic phase in stainless steels.

  15. Gas Metal Arc Welding Process Modeling and Prediction of Weld Microstructure in MIL A46100 Armor-Grade Martensitic Steel

    DTIC Science & Technology

    2013-06-01

    most of the commercially available metallic materials, in particular steels (including stainless steels ), super alloys, aluminum alloys, etc., can...REPORT Gas Metal Arc Welding Process Modeling and Prediction of Weld Microstructure in MIL A46100 Armor-Grade Martensitic Steel 14. ABSTRACT 16...Welding Process Modeling and Prediction of Weld Microstructure in MIL A46100 Armor-Grade Martensitic Steel Report Title ABSTRACT A conventional gas metal

  16. On the Prediction of α-Martensite Temperatures in Medium Manganese Steels

    NASA Astrophysics Data System (ADS)

    Field, Daniel M.; Baker, Daniel S.; Van Aken, David C.

    2017-02-01

    A new composition-based method for calculating the α-martensite start temperature in medium manganese steel is presented and uses a regular solution model to accurately calculate the chemical driving force for α-martensite formation, Δ G_{Chem}^{γ to α } . In addition, a compositional relationship for the strain energy contribution during martensitic transformation was developed using measured Young's moduli (E) reported in literature and measured values for steels produced during this investigation. An empirical relationship was developed to calculate Young's modulus using alloy composition and was used where dilatometry literature did not report Young's moduli. A comparison of the Δ G_{Chem}^{γ to α } normalized by dividing by the product of Young's modulus, unconstrained lattice misfit squared (δ 2), and molar volume (Ω) with respect to the measured α-martensite start temperatures, M_{S}^{α } , produced a single linear relationship for 42 alloys exhibiting either lath or plate martensite. A temperature-dependent strain energy term was then formulated as Δ G_{str}^{γ to α } ( {{J}/{mol}} ) = EΩ δ2 (14.8 - 0.013T) , which opposed the chemical driving force for α-martensite formation. M_{S}^{α } was determined at a temperature where Δ G_{Chem}^{γ to α } + Δ G_{str}^{γ to α } = 0 . The proposed M_{S}^{α } model shows an extended temperature range of prediction from 170 K to 820 K (-103 °C to 547 °C). The model is then shown to corroborate alloy chemistries that exhibit two-stage athermal martensitic transformations and two-stage TRIP behavior in three previously reported medium manganese steels. In addition, the model can be used to predict the retained γ-austenite in twelve alloys, containing ɛ-martensite, using the difference between the calculated M_{S}^{ɛ} and M_{S}^{α }.

  17. On the Prediction of α-Martensite Temperatures in Medium Manganese Steels

    NASA Astrophysics Data System (ADS)

    Field, Daniel M.; Baker, Daniel S.; Van Aken, David C.

    2017-05-01

    A new composition-based method for calculating the α-martensite start temperature in medium manganese steel is presented and uses a regular solution model to accurately calculate the chemical driving force for α-martensite formation, Δ G_{{Chem}}^{γ \\to α } . In addition, a compositional relationship for the strain energy contribution during martensitic transformation was developed using measured Young's moduli ( E) reported in literature and measured values for steels produced during this investigation. An empirical relationship was developed to calculate Young's modulus using alloy composition and was used where dilatometry literature did not report Young's moduli. A comparison of the Δ G_{{Chem}}^{γ \\to α } normalized by dividing by the product of Young's modulus, unconstrained lattice misfit squared ( δ 2), and molar volume ( Ω) with respect to the measured α-martensite start temperatures, M_{{S}}^{α } , produced a single linear relationship for 42 alloys exhibiting either lath or plate martensite. A temperature-dependent strain energy term was then formulated as Δ G_{{str}}^{γ \\to α } ( {{{J}}/{{mol}}} ) = EΩ δ2 (14.8 - 0.013T) , which opposed the chemical driving force for α-martensite formation. M_{{S}}^{α } was determined at a temperature where Δ G_{{Chem}}^{γ \\to α } + Δ G_{{str}}^{γ \\to α } = 0 . The proposed M_{{S}}^{α } model shows an extended temperature range of prediction from 170 K to 820 K (-103 °C to 547 °C). The model is then shown to corroborate alloy chemistries that exhibit two-stage athermal martensitic transformations and two-stage TRIP behavior in three previously reported medium manganese steels. In addition, the model can be used to predict the retained γ-austenite in twelve alloys, containing ɛ-martensite, using the difference between the calculated M_{{S}}^{ɛ} and M_{{S}}^{α }.

  18. Composite Behavior of Lath Martensite Steels Induced by Plastic Strain, a New Paradigm for the Elastic-Plastic Response of Martensitic Steels

    NASA Astrophysics Data System (ADS)

    Ungár, Tamás; Harjo, Stefanus; Kawasaki, Takuro; Tomota, Yo; Ribárik, Gábor; Shi, Zengmin

    2017-01-01

    Based on high-resolution neutron diffraction experiments, we will show that in lath martensite steels, the initially homogeneous dislocation structure, i.e., homogeneous on the length scale of grain size, is disrupted by plastic deformation, which, in turn, produces a composite on the length scale of martensite lath packets. The diffraction patterns of plastically strained martensitic steel reveal characteristically asymmetric peak profiles in the same way as has been observed in materials with heterogeneous dislocation structures. The quasi homogeneous lath structure, formed by quenching, is disrupted by plastic deformation producing a composite structure. Lath packets oriented favorably or unfavorably for dislocation glide become soft or hard. Two lath packet types develop by work softening or work hardening in which the dislocation densities become smaller or larger compared to the initial average dislocation density. The decomposition into soft and hard lath packets is accompanied by load redistribution and the formation of long-range internal stresses between the two lath packet types. The composite behavior of plastically deformed lath martensite opens a new way to understand the elastic-plastic response in this class of materials.

  19. Fine structure characterization of martensite/austenite constituent in low-carbon low-alloy steel by transmission electron forward scatter diffraction.

    PubMed

    Li, C W; Han, L Z; Luo, X M; Liu, Q D; Gu, J F

    2016-11-01

    Transmission electron forward scatter diffraction and other characterization techniques were used to investigate the fine structure and the variant relationship of the martensite/austenite (M/A) constituent of the granular bainite in low-carbon low-alloy steel. The results demonstrated that the M/A constituents were distributed in clusters throughout the bainitic ferrite. Lath martensite was the main component of the M/A constituent, where the relationship between the martensite variants was consistent with the Nishiyama-Wassermann orientation relationship and only three variants were found in the M/A constituent, suggesting that the variants had formed in the M/A constituent according to a specific mechanism. Furthermore, the Σ3 boundaries in the M/A constituent were much longer than their counterparts in the bainitic ferrite region. The results indicate that transmission electron forward scatter diffraction is an effective method of crystallographic analysis for nanolaths in M/A constituents. © 2016 The Authors Journal of Microscopy © 2016 Royal Microscopical Society.

  20. Effects of Annealing Treatment Prior to Cold Rolling on Delayed Fracture Properties in Ferrite-Austenite Duplex Lightweight Steels

    NASA Astrophysics Data System (ADS)

    Sohn, Seok Su; Song, Hyejin; Kim, Jung Gi; Kwak, Jai-Hyun; Kim, Hyoung Seop; Lee, Sunghak

    2016-02-01

    Tensile properties of recently developed automotive high-strength steels containing about 10 wt pct of Mn and Al are superior to other conventional steels, but the active commercialization has been postponed because they are often subjected to cracking during formation or to the delayed fracture after formation. Here, the delayed fracture behavior of a ferrite-austenite duplex lightweight steel whose microstructure was modified by a batch annealing treatment at 1023 K (750 °C) prior to cold rolling was examined by HCl immersion tests of cup specimens, and was compared with that of an unmodified steel. After the batch annealing, band structures were almost decomposed as strong textures of {100}<011> α-fibers and {111}<112> γ-fibers were considerably dissolved, while ferrite grains were refined. The steel cup specimen having this modified microstructure was not cracked when immersed in an HCl solution for 18 days, whereas the specimen having unmodified microstructure underwent the delayed fracture within 1 day. This time delayed fracture was more critically affected by difference in deformation characteristics such as martensitic transformation and deformation inhomogeneity induced from concentration of residual stress or plastic strain, rather than the difference in initial microstructures. The present work gives a promise for automotive applications requiring excellent mechanical and delayed fracture properties as well as reduced specific weight.

  1. Mechanical alloying of lanthana-bearing nanostructured ferritic steels

    SciTech Connect

    Somayeh Paseban; Indrajit Charit; Yaqiao Q. Wu; Jatuporn Burns; Kerry N. Allahar; Darryl P. Butt; James I. Cole

    2013-09-01

    A novel nanostructured ferritic steel powder with the nominal composition Fe–14Cr–1Ti–0.3Mo–0.5La2O3 (wt.%) was developed via high energy ball milling. La2O3 was added to this alloy instead of the traditionally used Y2O3. The effects of varying the ball milling parameters, such as milling time, steel ball size and ball to powder ratio, on the mechanical properties and micro structural characteristics of the as-milled powder were investigated. Nanocrystallites of a body-centered cubic ferritic solid solution matrix with a mean size of approximately 20 nm were observed by transmission electron microscopy. Nanoscale characterization of the as-milled powder by local electrode atom probe tomography revealed the formation of Cr–Ti–La–O-enriched nanoclusters during mechanical alloying. The Cr:Ti:La:O ratio is considered “non-stoichiometric”. The average size (radius) of the nanoclusters was about 1 nm, with number density of 3.7 1024 m3. The mechanism for formation of nanoclusters in the as-milled powder is discussed. La2O3 appears to be a promising alternative rare earth oxide for future nanostructured ferritic steels.

  2. SELECTIVE SEPARATION OF URANIUM FROM FERRITIC STAINLESS STEELS

    DOEpatents

    Beaver, R.J.; Cherubini, J.H.

    1963-05-14

    A process is described for separating uranium from a nuclear fuel element comprising a uranium-containing core and a ferritic stainless steel clad by heating said element in a non-carburizing atmosphere at a temperature in the range 850-1050 un. Concent 85% C, rapidly cooling the heated element through the temperature range 815 un. Concent 85% to 650 EC to avoid annealing said steel, and then contacting the cooled element with an aqueous solution of nitric acid to selectively dissolve the uranium. (AEC)

  3. Effects of strain-induced martensite and its reversion on the magnetic properties of AISI 201 austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Souza Filho, I. R.; Sandim, M. J. R.; Cohen, R.; Nagamine, L. C. C. M.; Hoffmann, J.; Bolmaro, R. E.; Sandim, H. R. Z.

    2016-12-01

    Strain-induced martensite (SIM) and its reversion in a cold-rolled AISI 201 austenitic stainless steel was studied by means of magnetic properties, light optical (LOM) and scanning electron (SEM) microscopy, electron backscatter diffraction (EBSD), texture measurements, and Vickers microhardness testing. According to Thermo-calc© predictions, the BCC phase (residual δ-ferrite and SIM) is expected to be stable until 600 °C. The current material was cold rolled up to 60% thickness reduction and submitted to both isothermal and stepwise annealing up to 800 °C. Magnetic measurements were taken during annealing (in situ) of the samples and also for their post mortem conditions. The Curie temperatures (Tc) of residual δ-ferrite and SIM have similar values between 550 and 600 °C. Besides Tc, the focused magnetic parameters were saturation magnetization (Ms), remanent magnetization (MR), and coercive field (Hc). SIM reversion was found to occur in the range of 600-700 °C in good agreement with Thermo-calc© predictions. The microstructures of the material, annealed at 600 and 700 °C for 1 h, were investigated via EBSD. Microtexture measurements for these samples revealed that the texture components were mainly those found for the 60% cold rolled material. This is an evidence that the SIM reversion occurred by an athermal mechanism.

  4. Comprehensive microstructural characterization in modified 9Cr-1Mo ferritic steel by ultrasonic measurements

    NASA Astrophysics Data System (ADS)

    Kumar, Anish; Laha, K.; Jayakumar, T.; Rao, K. Bhanu Sankaro; Raj, Baldev

    2002-06-01

    Modified 9Cr-1Mo ferritic steel (T91/P91) has been subjected to a series of heat treatments consisting of soaking for 5 minutes at the selected temperatures, starting from the α-phase region (1073 K) to the γ + δ-phase region (1623 K), followed by oil quenching. Hardness measurements, microstructural features, and grain-size measurements by the linear-intercept method have been used for correlating them with the ultrasonic parameters. Ultrasonic velocity and attenuation measurements, and spectral analysis of the first backwall echo have been used for characterization of the microstructures obtained by various heat treatments. As the soaking temperature increased above Ac 1, the ultrasonic velocity decreased because of the increase in the volume fraction of martensite in the structure. There were sharp changes in the ultrasonic velocities corresponding to the two critical temperatures, Ac 1 and Ac 3. Ultrasonic longitudinal- and shear-wave velocities were found to be useful in identifying the Ac 1 and Ac 3 temperatures and for the determination of hardness in the intercritical region. However, ultrasonic attenuation and spectral analysis of the first backwall echo were found to be useful to characterize the variation in the prior-austenitic grain size and formation of δ ferrite above the Ac 4 temperature. The scattering coefficients have been experimentally determined for various microstructures and compared with the theoretically calculated value of the scattering coefficients for iron reported in literature.

  5. Interatomic potential to study the formation of NiCr clusters in high Cr ferritic steels

    NASA Astrophysics Data System (ADS)

    Bonny, G.; Bakaev, A.; Olsson, P.; Domain, C.; Zhurkin, E. E.; Posselt, M.

    2017-02-01

    Under irradiation NiSiPCr clusters are formed in high-Cr ferritic martensitic steels as well as in FeCr model alloys. In the literature little is known about the origin and contribution to the hardening of these clusters. In this work we performed density functional theory (DFT) calculations to study the stability of small substitutional NiCr-vacancy clusters and interstitial configurations in bcc Fe. Based on DFT data and experimental considerations a ternary potential for the ferritic FeNiCr system was developed. The potential was applied to study the thermodynamic stability of NiCr clusters by means of Metropolis Monte Carlo (MMC) simulations. The results of our simulations show that Cr and Ni precipitate as separate fractions and suggest only a limited synergetic effect between Ni and Cr. Therefore our results suggest that the NiCrSiP clusters observed in experiments must be the result of other mechanisms than the synergy of Cr and Ni at thermal equilibrium.

  6. Processing of Ultrafine-Grained Twinning-Induced Plasticity Steel Using Martensite Treatment

    NASA Astrophysics Data System (ADS)

    Dini, Ghasem; Zamani, Davood

    2017-07-01

    For the first time, martensite treatment was used to fabricate an ultrafine-grained (UFG) twinning-induced plasticity (TWIP) steel. The effects of cold rolling with 70 pct reduction at the liquid nitrogen temperature and subsequently annealing at 973 K (700 °C) for 5 to 20 minutes on the microstructure and mechanical properties of Fe-22Mn-0.4C-1.5Al-1Si TWIP steel were investigated. The results showed that a fully recrystallized UFG TWIP steel with a mean grain size of about 400 to 600 nm can be produced by the designed martensite treatment. The UFG TWIP steel exhibited high yield and tensile strengths and relatively high ductility.

  7. Strength and cracking resistance of hot-deformed steel with a low-carbon martensite structure

    NASA Astrophysics Data System (ADS)

    Romanov, I. D.; Shatsov, A. A.; Kleiner, L. M.

    2013-10-01

    Effect of the structure of the low-carbon martensitic steel air-quenched from the temperature of the end of the hot deformation on the strength and impact-toughness characteristics has been studied. A connection between the sizes of typical structure elements and the level of mechanical properties was established.

  8. Tensile and impact behaviour of BATMAN II steels, Ti-bearing reduced activation martensitic alloys

    NASA Astrophysics Data System (ADS)

    Filacchioni, G.; Casagrande, E.; De Angelis, U.; De Santis, G.; Ferrara, D.; Pilloni, L.

    Two series of Reduced Activation Ferrous alloys (RAF) have been produced and studied by Casaccia's Laboratories. These martensitic alloys are named BATMAN steels. They are among the few presently developed RAF materials to exploit Ti as a carbide forming and grain size stabilizing element instead of Ta. In this work their mechanical properties are illustrated.

  9. Super-strong dislocation-structured high-carbon martensite steel.

    PubMed

    Sun, Jun-Jie; Liu, Yong-Ning; Zhu, Yun-Tian; Lian, Fu-Liang; Liu, Hong-Ji; Jiang, Tao; Guo, Sheng-Wu; Liu, Wen-Qing; Ren, Xiao-Bing

    2017-07-26

    High-carbon martensite steels (with C > 0.5 wt.%) are very hard but at the same time as brittle as glass in as-quenched or low-temperature-tempered state. Such extreme brittleness, originating from a twin microstructure, has rendered these steels almost useless in martensite state. Therefore, for more than a century it has been a common knowledge that high-carbon martensitic steels are intrinsically brittle and thus are not expected to find any application in harsh loading conditions. Here we report that these brittle steels can be transformed into super-strong ones exhibiting a combination of ultrahigh strength and significant toughness, through a simple grain-refinement treatment, which refines the grain size to ~4 μm. As a result, an ultra-high tensile strength of 2.4~2.6 GPa, a significant elongation of 4~10% and a good fracture toughness (K1C) of 23.5~29.6 MPa m(1/2) were obtained in high-carbon martensitic steels with 0.61-0.65 wt.% C. These properties are comparable with those of "the king of super-high-strength steels"-maraging steels, but achieved at merely 1/30~1/50 of the price. The drastic enhancement in mechanical properties is found to arise from a transition from the conventional twin microstructure to a dislocation one by grain refinement. Our finding may provide a new route to manufacturing super-strong steels in a simple and economic way.

  10. High-strength state of ultrafine-grained martensitic steel produced by high pressure torsion

    NASA Astrophysics Data System (ADS)

    Karavaeva, M. V.; Nikitina, M. A.; Ganeev, A. V.; Islamgaliev, R. K.

    2017-02-01

    The paper presents the study results on the effect of severe plastic deformation (SPD) via high pressure torsion (HPT) on the structure and properties of martensitic steel. The contribution of different strengthening mechanisms in the strength of steel has been analyzed. It is shown that independently of the deformation temperature the main contribution in hardening belongs to grain boundaries (about 50 %), whereas the dislocation and solid solution components achieve 15 and 25 %, respectively.

  11. The effects of laser welding parameters on the microstructure of ferritic and duplex stainless steels welds

    NASA Astrophysics Data System (ADS)

    Pekkarinen, J.; Kujanpää, V.

    This study is focused to determine empirically, which microstructural changes occur in ferritic and duplex stainless steels when heat input is controlled by welding parameters. Test welds were done autogenously bead-on-plate without shielding gas using 5 kW fiber laser. For comparison, some gas tungsten arc welds were made. Used test material were 1.4016 (AISI 430) and 1.4003 (low-carbon ferritic) type steels in ferritic steels group and 1.4162 (low-alloyed duplex, LDX2101) and 1.4462 (AISI 2205) type steels in duplex steels group. Microstructural changes in welds were identified and examined using optical metallographic methods.

  12. Effect of shot peening on the residual stress and mechanical behaviour of low-temperature and high-temperature annealed martensitic gear steel 18CrNiMo7-6

    NASA Astrophysics Data System (ADS)

    Yang, R.; Zhang, X.; Mallipeddi, D.; Angelou, N.; Toftegaard, H. L.; Li, Y.; Ahlström, J.; Lorentzen, L.; Wu, G.; Huang, X.

    2017-07-01

    A martensitic gear steel (18CrNiMo7-6) was annealed at 180 °C for 2h and at ∼ 750 °C for 1h to design two different starting microstructures for shot peening. One maintains the original as-transformed martensite while the other contains irregular-shaped sorbite together with ferrite. These two materials were shot peened using two different peening conditions. The softer sorbite + ferrite microstructure was shot peened using 0.6 mm conditioned cut steel shots at an average speed of 25 m/s in a conventional shot peening machine, while the harder tempered martensite steel was shot peened using 1.5 mm steel shots at a speed of 50 m/s in an in-house developed shot peening machine. The shot speeds in the conventional shot peening machine were measured using an in-house lidar set-up. The microstructure of each sample was characterized by optical and scanning electron microscopy, and the mechanical properties examined by microhardness and tensile testing. The residual stresses were measured using an Xstress 3000 G2R diffractometer equipped with a Cr Kα x-ray source. The correspondence between the residual stress profile and the gradient structure produced by shot peening, and the relationship between the microstructure and strength, are analyzed and discussed.

  13. Significance of Delta Ferrite Content to Fatigue Crack Growth Resistance of Austenitic Stainless Steel Weld Deposits

    DTIC Science & Technology

    1978-03-01

    Compositions of AISI Type 308 Shielded Metal Arc Weld Series With Variable Delta Ferrite Content NRL Weld Delta Ferrite T Chemical Composition (wt%) b Code...3 NRL Report201 Significance of Delta Ferrite Content to Fatigue Crack Growth Resistance of Austentic Stainless Steel We!d Deposits J, R. HAWTHORNE...RIults for the preirradlatlon (as-welded) condition show that delta ferrite content a’id tempera. ture variations in the ranges studied do not exert

  14. Hybrid/Tandem Laser-Arc Welding of Thick Low Carbon Martensitic Stainless Steel Plates =

    NASA Astrophysics Data System (ADS)

    Mirakhorli, Fatemeh

    High efficiency and long-term life of hydraulic turbines and their assemblies are of utmost importance for the hydropower industry. Usually, hydroelectric turbine components are made of thick-walled low carbon martensitic stainless steels. The assembly of large hydroelectric turbine components has been a great challenge. The use of conventional welding processes involves typical large groove design and multi-pass welding to fill the groove which exposes the weld to a high heat input creating relatively large fusion zone and heat affected zone. The newly-developed hybrid/tandem laser-arc welding technique is believed to offer a highly competitive solution to improve the overall hydro-turbine performance by combining the high energy density and fast welding speed of the laser welding technology with the good gap bridging and feeding ability of the gas metal arc welding process to increase the productivity and reduce the consumable material. The main objective of this research work is to understand different challenges appearing during hybrid laser-arc welding (HLAW) of thick gauge assemblies of low carbon 13%Cr- 4%Ni martensitic stainless steel and find a practical solution by adapting and optimizing this relatively new welding process in order to reduce the number of welding passes necessary to fill the groove gap. The joint integrity was evaluated in terms of microstructure, defects and mechanical properties in both as-welded and post-welded conditions. A special focus was given to the hybrid and tandem laser-arc welding technique for the root pass. Based on the thickness of the low carbon martensitic stainless steel plates, this work is mainly focused on the following two tasks: • Single pass hybrid laser-arc welding of 10-mm thick low carbon martensitic stainless steel. • Multi-pass hybrid/tandem laser-arc welding of 25-mm thick martensitic stainless steel.

  15. Effect of martensitic transformation on springback behavior of 304L austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Fathi, H.; Mohammadian Semnani, H. R.; Emadoddin, E.; Sadeghi, B. Mohammad

    2017-09-01

    The present paper studies the effect of martensitic transformation on the springback behavior of 304L austenitic stainless steel. Martensite volume fraction was determined at the bent portion under various strain rates after bending test. Martensitic transformation has a significant effect on the springback behavior of this material. The findings of this study indicated that the amount of springback was reduced under a situation of low strain rate, while a higher amount of springback was obtained with a higher strain rate. The reason for this phenomenon is that higher work hardening occurs during the forming process with the low strain rate due to the higher martensite volume fraction, therefore the formability of the sheet is enhanced and it leads to a decreased amount of springback after the bending test. Dependency of the springback on the martensite volume fraction and strain rate was expressed as formulas from the results of the experimental tests and simulation method. Bending tests were simulated using LS-DYNA software and utilizing MAT_TRIP to determine the martensite volume fraction and strain under various strain rates. Experimental result reveals good agreement with the simulation method.

  16. Development of oxide dispersion strengthened ferritic steels for fusion

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, D. K.; Froes, F. H.; Gelles, D. S.

    1998-10-01

    An oxide dispersion strengthened (ODS) ferritic steel with high temperature strength has been developed in line with low activation criteria for application in fusion power systems. The composition Fe-13.5Cr-2W-0.5Ti-0.25Y 2O 3 was chosen to provide a minimum chromium content to insure fully delta-ferrite stability. High temperature strength has been demonstrated by measuring creep response of the ODS alloy in uniaxial tension at 650°C and 900°C in an inert atmosphere chamber. Results of tests at 900°C demonstrate that this alloy has creep properties similar to other alloys of similar design and can be considered for use in high temperature fusion power system designs. The alloy selection process, materials production, microstructural evaluation and creep testing are described.

  17. Development of oxide dispersion strengthened ferritic steels for fusion

    SciTech Connect

    Mukhopadhyay, D.K.; Froes, F.H.; Gelles, D.S.

    1998-03-01

    An oxide dispersion strengthened (ODS) ferritic steel with high temperature strength has been developed in line with low activation criteria for application in fusion power systems. The composition Fe-13.5Cr-2W-0.5Ti-0.25Y{sub 2}O{sup 3} was chosen to provide a minimum chromium content to insure fully delta-ferrite stability. High temperature strength has been demonstrated by measuring creep response of the ODS alloy in uniaxial tension at 650 and 900 C in an inert atmosphere chamber. Results of tests at 900 C demonstrate that this alloy has creep properties similar to other alloys of similar design and can be considered for use in high temperature fusion power system designs. The alloy selection process, materials production, microstructural evaluation and creep testing are described.

  18. 77 FR 60478 - Control of Ferrite Content in Stainless Steel Weld Metal

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-10-03

    ...The U.S. Nuclear Regulatory Commission (NRC or the Commission) is issuing for public comment draft regulatory guide (DG), DG-1279, ``Control of Ferrite Content in Stainless Steel Weld Metal.'' This guide describes a method that the NRC staff considers acceptable for controlling ferrite content in stainless steel weld metal. Revision 4 updates the guide to remove references to outdated......

  19. Effect of internal nitriding on the fatigue strength of ferritic corrosion-resistant steel

    NASA Astrophysics Data System (ADS)

    Rogachev, S. O.; Nikulin, S. A.; Terent'ev, V. F.; Khatkevich, V. M.; Prosvirnin, D. V.; Savicheva, R. O.

    2015-04-01

    The effect of internal nitriding and subsequent annealing on the mechanical properties of ferritic corrosion-resistance 08Kh17T steel has been studied during static and cyclic loading. Nitriding was shown to increase the static and cyclic strength of ferritic steel substantially and to decrease its plasticity slightly. These changes are confirmed by results of fractographic studies.

  20. Effect of Boron on the Kinetics of Low-Temperature Decomposition of Martensite in Quenched Medium-Carbon Steel

    NASA Astrophysics Data System (ADS)

    Alekseev, A. A.; Grinberg, E. M.

    2016-03-01

    The effect of boron on the microstructure, microhardness, and kinetics of low-temperature decomposition of martensite in the 40Kh and 30KhRA steels quenched at different cooling rates has been studied. It has been shown that the low-temperature decomposition of martensite in the boron-containing steel after quenching from 1050°C at a high cooling rate is strongly decelerated at the initial stage of decomposition. At low quenching cooling rates, the martensite decomposition in the steels under investigation is characterized by a similar kinetics.

  1. Development of rapidly quenched brazing foils to join tungsten alloys with ferritic steel

    NASA Astrophysics Data System (ADS)

    Kalin, B. A.; Fedotov, V. T.; Sevrjukov, O. N.; Moeslang, A.; Rohde, M.

    2004-08-01

    Results on rapidly solidified filler metals for tungsten brazing are presented. A rapidly quenched foil-type filler metal based on Ni bal-15Cr-4Mo-4Fe-(0.5-1.0)V-7.5Si-1.5B was developed to braze tungsten to ferritic/martensitic Crl3Mo2NbVB steel (FS) for helium gas cooled divertors and plasma facing components. Polycrystalline W-2CeO 2 and monocrystalline pure tungsten were brazed to the steel under vacuum at 1150 °C, using a 0.5 mm thick foil spacer made of a 50Fe-50Ni alloy. As a result of thermocycling tests (100 cycles between 700 °C/20 min and air-water cooling/3-5 min) on brazed joints, tungsten powder metallurgically processed W-2CeO 2 failed due to residual stresses, whereas the brazed joint with zone-melted monocrystalline tungsten withstood the thermocycling tests.

  2. Micromagnetic and Moessbauer spectroscopic investigation of strain-induced martensite in austenitic stainless steel

    SciTech Connect

    Meszaros, I.; Kaldor, M.; Hidasi, B.; Vertes, A.; Czako-Nagy, I.

    1996-08-01

    Strain-induced martensite in 18/8 austenitic stainless steel was studied. Magnetic measurements and Moessbauer spectroscopic investigations were performed to characterize the amount of {alpha}{prime}-martensite due to room-temperature plastic tensile loading. The effects of cold work and annealing heat treatment were explored using magnetic Barkhausen noise, saturation polarization, coercive force, hardness, and conversion electron Moessbauer spectroscopy. The suggested Barkhausen noise measurement technique proved to be a useful quantitative and nondestructive method for determining the ferromagnetic phase ratio of the studied alloy.

  3. An Investigation Into 6-Fold Symmetry in Martensitic Steels

    NASA Astrophysics Data System (ADS)

    Kinney, Christopher; Pytlewski, Ken; Qi, Liang; Khachaturyan, Armen G.; Morris, J. W.

    2016-11-01

    Austenite grains that have undergone a martensitic transformation are typically composed of 24 variants that can be categorized by their Bain axis of transformation. There are 3 <001> axes for Bain transformations, therefore the (001) pole figure of a prior austenite grain displays 3-fold symmetry. However, we observed superficially similar prior austenite grains containing 6-fold symmetry in the (001) pole figure. This paper introduces evidence of this 6-fold symmetry and explores the crystallographic origins.

  4. R&D of low activation ferritic steels for fusion in japanese universities*1

    NASA Astrophysics Data System (ADS)

    Kohyama, Akira; Kohno, Yutaka; Asakura, Kentaro; Kayano, Hideo

    1994-09-01

    Following the brief review of the R&D of low activation ferritic steels in Japanese universities, the status of 9Cr-2W type ferritic steels development is presented. The main emphasis is on mechanical property changes by fast neutron irradiation in FFTF. Bend test, tensile test, CVN test and in-reactor creep results are provided including some data about low activation ferritic steels with Cr variation from 2.25 to 12%. The 9Cr-2W ferritic steel, denoted as JLF-1, showed excellent mechanical properties under fast neutron irradiation as high as 60 dpa. As potential materials for DEMO and beyond, innovative oxide dispersion strengthened (ODS) quasi-amorphous low activation ferritic steels are introduced. The baseline properties, microstructural evolution under ion irradiation and the recent progress of new processes are provided.

  5. Development of ferritic weldments for grain-refined ferritic steels for 4. 2K service

    SciTech Connect

    Kim, H.J.

    1982-01-01

    The weldability of grain-refined ferritic nickel steels designed for structural use in liquid helium was investigated. Plates of interstitial-free Fe-12Ni-0.25Ti alloy and carbon-containing 9Ni steel were welded with 14Ni ferritic fillers using a gas tungsten arc welding (GTAW) process with pure argon gas shielding. The ferritic weldments made have a strength closely matching those of the base plates without a significant loss in base metal toughness at temperatures as low as 4.2K. The comparable toughness obtained in the welded region is attributed to three factors; the defect-free weldment, the chemical cleanliness of the GTAW weld deposit, and the in-process formation of an appropriate microstructure in the welded region. Special emphasis in this study was placed on changes in microstructures with respect to the characteristic of the weld thermal cycles and the effect of the resultant microstructures on low temperature toughness. In the heat-affected zone (HAZ) of multipass welded 9Ni steel, the retained (or precipitated) austenite is removed by the weld heat cycles but the sequential rapid heat cycles to successively lower peak temperatures associated with succeeding weld passes re-establish high toughness by sequentially refining the grain size and gettering carbon in the form of cementite precipitates. On the other hand, the high toughness in the HAZ of the 12Ni alloy and in the weld deposit is a direct consequence of repeated grain refinement through the overlapped austenitizing cycles and is not affected by the tempering cycles because of the carbon-free nature of these materials.

  6. Effect of Nb on Delayed Fracture Resistance of Ultra-High Strength Martensitic Steels

    NASA Astrophysics Data System (ADS)

    Song, Rongjie; Fonstein, Nina; Pottore, Narayan; Jun, Hyun Jo; Bhattacharya, Debanshu; Jansto, Steve

    Ultra-high strength steels are materials of considerable interest for automotive and structural applications and are increasingly being used in those areas. Higher strength, however, makes steels more prone to hydrogen embrittlement (HE). The effects of Nb and other alloying elements on the hydrogen-induced delayed fracture resistance of cold rolled martensitic steels with ultra-high strength 2000 MPa were studied using an acid immersion test, thermal desorption analysis (TDA) and measuring of permeation. The microstructure was characterized by high resolution field emission Scanning Electron Microscopy (SEM) with Electron Backscattered Diffraction (EBSD) and Transmission Electron Microscopy (TEM). It was shown that the combined addition of Nb significantly improved the delayed fracture resistance of investigated steel. The addition of Nb to alloyed martensitic steels resulted in very apparent grain refinement of the prior austenite grain size. The Nb microalloyed steel contained a lower diffusible hydrogen content during thermal desorption analysis as compared to the base steel and had a higher trapped hydrogen amount after charging. The reason that Nb improved the delayed fracture resistance of steels can be attributed mostly to both hydrogen trapping and grain refinement.

  7. Stress Induce Martensitic Transformations in Hydrogen Embrittlement of Austenitic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Rozenak, Paul

    2013-04-01

    In austenitic type stainless steels, hydrogen concentration gradients formed during electrochemical charging and followed by hydrogen loss during aging, at room temperature, surface stresses, and martensitic phases α'-BCC and ɛ-HCP developed. The basic relationship between the X-ray diffraction peak broadening and the hydrogen gradients, formed during charging and aging at room temperature in such austenitic stainless steels, were analyzed. The results demonstrate that the impact of stresses must be considered in the discussion of phase transformations due to hydrogenation. Austenitic stainless steels based on iron-nickel-chromium, have relatively low stacking fault energy γSFE and undergo: quenching to low temperatures, plastic deformation, sensitization heat treatments, high pressure (≥3-5 × 109 Pa) by hydrogen or other gases, electrochemical charging (when the sample is cathode) and when is irradiation by various ions the samples in vacuum. All the above mentioned induce formation of ɛ and α' in the face-centered cubic (FCC) austenite γ matrix. The highest stresses cause formation of mainly α' phase and ɛ-martensite, and both are involved in plastic deformation processes and promoting crack propagation at the surface. In 310 steel, the crack propagation is based on deformation processes following ɛ-martensitic formation only. Formations of ɛ- and α'-martensites were noted along the fracture surfaces and ahead of the crack tip. The cracks propagated through the ɛ-martensitic plates, which formed along the active slip planes, while α' phase was always found in the high-stress region on the ends of the ligaments from both sides of the crack surfaces undergoing propagation.

  8. Stress Induce Martensitic Transformations in Hydrogen Embrittlement of Austenitic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Rozenak, Paul

    2014-01-01

    In austenitic type stainless steels, hydrogen concentration gradients formed during electrochemical charging and followed by hydrogen loss during aging, at room temperature, surface stresses, and martensitic phases α'-BCC and ɛ-HCP developed. The basic relationship between the X-ray diffraction peak broadening and the hydrogen gradients, formed during charging and aging at room temperature in such austenitic stainless steels, were analyzed. The results demonstrate that the impact of stresses must be considered in the discussion of phase transformations due to hydrogenation. Austenitic stainless steels based on iron-nickel-chromium, have relatively low stacking fault energy γSFE and undergo: quenching to low temperatures, plastic deformation, sensitization heat treatments, high pressure (≥3-5 × 109 Pa) by hydrogen or other gases, electrochemical charging (when the sample is cathode) and when is irradiation by various ions the samples in vacuum. All the above mentioned induce formation of ɛ and α' in the face-centered cubic (FCC) austenite γ matrix. The highest stresses cause formation of mainly α' phase and ɛ-martensite, and both are involved in plastic deformation processes and promoting crack propagation at the surface. In 310 steel, the crack propagation is based on deformation processes following ɛ-martensitic formation only. Formations of ɛ- and α'-martensites were noted along the fracture surfaces and ahead of the crack tip. The cracks propagated through the ɛ-martensitic plates, which formed along the active slip planes, while α' phase was always found in the high-stress region on the ends of the ligaments from both sides of the crack surfaces undergoing propagation.

  9. Room temperature texturing of austenite/ferrite steel by electropulsing

    PubMed Central

    Rahnama, Alireza; Qin, Rongshan

    2017-01-01

    The work reports an experimental observation on crystal rotation in a duplex (austenite + ferrite) steel induced by the electropulsing treatment at ambient temperature, while the temperature rising due to ohmic heating in the treatment was negligible. The results demonstrate that electric current pulses are able to dissolve the initial material’s texture that has been formed in prior thermomechanical processing and to produce an alternative texture. The results were explained in terms of the instability of an interface under perturbation during pulsed electromigation. PMID:28195181

  10. Corrosion Performance of Ferritic Steel for SOFC Interconnect Applications

    SciTech Connect

    Ziomek-Moroz, M.; Holcomb, G.R.; Covino, B.S., Jr.; Bullard, S.J.; Jablonski, P.D.; Alman, D.E.

    2006-11-01

    Ferritic stainless steels have been identified as potential candidates for interconnects in planar-type solid oxide fuel cells (SOFC) operating below 800ºC. Crofer 22 APU was selected for this study. It was studied under simulated SOFC-interconnect dual environment conditions with humidified air on one side of the sample and humidified hydrogen on the other side at 750ºC. The surfaces of the oxidized samples were studied by scanning electron microscopy (SEM) equipped with microanalytical capabilities. X-ray diffraction (XRD) analysis was also used in this study.

  11. Room temperature texturing of austenite/ferrite steel by electropulsing

    NASA Astrophysics Data System (ADS)

    Rahnama, Alireza; Qin, Rongshan

    2017-02-01

    The work reports an experimental observation on crystal rotation in a duplex (austenite + ferrite) steel induced by the electropulsing treatment at ambient temperature, while the temperature rising due to ohmic heating in the treatment was negligible. The results demonstrate that electric current pulses are able to dissolve the initial material’s texture that has been formed in prior thermomechanical processing and to produce an alternative texture. The results were explained in terms of the instability of an interface under perturbation during pulsed electromigation.

  12. The features of microstructure and mechanical properties of austenitic steel after direct and reverse martensitic transformations

    NASA Astrophysics Data System (ADS)

    Litovchenko, I. Yu.; Akkuzin, S. A.; Polekhina, N. A.; Tyumentsev, A. N.; Naiden, E. P.

    2015-10-01

    The features of structural states of metastable austenitic steel after thermomechanical treatments, including low-temperature deformation, warm deformation and subsequent annealing are investigated. It is shown that under these conditions the direct (γ → α') and reverse (α' → γ) martensitic transformations occur and submicrocrystalline structural states are formed. The proposed thermomechanical treatment allows varying the strength and plastic properties of austenitic steel in a wide range. The strength of steel in submicrocrystalline state is 4-6 times higher than its original value.

  13. Structure and Mechanical Properties of Maraging and Low-Carbon Martensitic Steels

    NASA Astrophysics Data System (ADS)

    Shvetsov, V. V.; Simonov, Yu. N.; Kleiner, L. M.

    2005-01-01

    The structure, mechanical properties, and crack resistance after tempering of maraging steel 03Kh11N10M2T (EP-678) and low-carbon martensitic steel 12Kh2G2NMFT are studied. The range of tempering temperatures ensuring the combination of properties required for massive parts (σr #x2265; 1300 MPa, σ0.2 ≥ 1100 MPa, KCT ≥ 0.2 MJ/m2) is determined. It is shown that steel 12Kh2G2NMFT is better adaptable to manufacture because it is hardened by air-cooling.

  14. Cup-Drawing Behavior of High-Strength Steel Sheets Containing Different Volume Fractions of Martensite

    SciTech Connect

    Choi, Shi-Hoon; Kim, Dae-Wan; Yang, Hoe-Seok; Han, Seong-Ho; Yoon, Jeong Whan

    2010-06-15

    Planar anisotropy and cup-drawing behavior were investigated for high-strength steel sheets containing different volume fractions of martensite. Macrotexture analysis using XRD was conducted to capture the effect of crystallographic orientation on the planar anisotropy of high-strength steel sheets. A phenomenological yield function, Yld96, which accounts for the anisotropy of yield stress and r-values, was implemented into ABAQUS using the user subroutine UMAT. Cup drawing of high-strength steel sheets was simulated using the FEM code. The profiles of earing and thickness strain were compared with the experimentally measured results.

  15. Direct Observations of Austenite, Bainite and Martensite Formation During Arc Welding of 1045 Steel using Time Resolved X-Ray Diffraction

    SciTech Connect

    Elmer, J; Palmer, T; Babu, S; Zhang, W; DebRoy, T

    2004-02-17

    In-situ Time Resolved X-Ray Diffraction (TRXRD) experiments were performed during stationary gas tungsten arc (GTA) welding of AISI 1045 C-Mn steel. These synchrotron-based experiments tracked, in real time, phase transformations in the heat-affected zone of the weld under rapid heating and cooling conditions. The diffraction patterns were recorded at 100 ms intervals, and were later analyzed using diffraction peak profile analysis to determine the relative fraction of ferrite ({alpha}) and austenite ({gamma}) phases in each diffraction pattern. Lattice parameters and diffraction peak widths were also measured throughout the heating and cooling cycle of the weld, providing additional information about the phases that were formed. The experimental results were coupled with a thermofluid weld model to calculate the weld temperatures, allowing time-temperature transformation kinetics of the {alpha} {yields} {gamma} phase transformation to be evaluated. During heating, complete austenitization was observed in the heat affected zone of the weld and the kinetics of the {alpha} {yields} {gamma} phase transformation were modeled using a Johnson-Mehl-Avrami (JMA) approach. The results from the 1045 steel weld were compared to those of a 1005 low carbon steel from a previous study. Differences in austenitization rates of the two steels were attributed to differences in the base metal microstructures, particularly the relative amounts of pearlite and the extent of the allotriomorphic ferrite phase. During weld cooling, the austenite transformed to a mixture of bainite and martensite. In situ diffraction was able to distinguish between these two non-equilibrium phases based on differences in their lattice parameters and their transformation rates, resulting in the first real time x-ray diffraction observations of bainite and martensite formation made during welding.

  16. High Temperature Strengthening in 12Cr-W-Mo Steels by Controlling the Formation of Delta Ferrite

    NASA Astrophysics Data System (ADS)

    Wang, Shushen; Chang, Li; Lin, Deye; Chen, Xiaohua; Hui, Xidong

    2014-09-01

    Novel 12Cr-W-Mo-Co heat resistance steels (HRSs) with excellent mechanical properties have been developed for ultra-supercritical (USC) applications above 923 K (650 °C). The thermal analysis of the present steels indicates that the remelting temperature of secondary phases is increased by Co alloying, resulting in the improvement of microstructural stability. Delta ferrite in these HRSs is completely suppressed as the content of Co is increased up to 5 pct. The room temperature tensile strength (TS), yield strength (YS), and the elongation (EL) of the HRS with 5 pct Co reach 887.9, 652.6 MPa, and 21.07 pct, respectively. At 948 K (675 °C), the TS and YS of the HRS with 5 pct Co attain 360 and 290 MPa, respectively, which are higher than those of T/P122 steel by 27.4 and 22.1 pct, respectively. TEM study of the microstructure confirmed that the strengthening effects for these 12Cr-W-Mo-Co HRSs are attributed to the suppression of delta ferrite, the formation of fine martensitic laths with substructure, dislocation networks and walls, and the precipitation of second nanoscale phases.

  17. M5C2 carbide precipitates in a high-Cr martensitic steel

    NASA Astrophysics Data System (ADS)

    Shen, Yinzhong; Ji, Bo; Zhou, Xiaoling

    2014-05-01

    The precipitate phases in an advanced 11% Cr martensitic steel, expected to be used at 650 °C, have been investigated to understand the effect of precipitates on the creep-rupture strength of the steel. M23C6 and MX precipitates were dominant phases in this steel. Needle-like precipitates with a typical length of 180 nm and width of 20 nm; and metallic-element compositions of 53-74Fe, 16-26Cr, 3-18Ta, 2-8W, and 2-4Co (at%); were observed mainly within the martensite laths of the normalized-and-tempered steel. The needle-like precipitates have been identified as monoclinic carbide M5C2, which is not known to have been reported previously in high chromium steels, or in heat-resistant steels those have been normalized-and-tempered. This indicates that the formation of M5C2 carbides can occur in heat-resistant steels produced under appropriate tempering conditions, and that this does not require long-term isothermal aging or creep testing, in all cases.

  18. Residual Stress Determination for A Ferritic Steel Weld Plate

    SciTech Connect

    Wang, D.-Q.; Hubbard, C.R.; Spooner, S.

    1999-10-01

    The primary objective of this experiment is to demonstrate the capability of neutron diffraction technique to reproducibly map residual strains in a ferritic steel weld. The objective includes the identification of corrections for variations in metal composition due to the welding process which produces changes in lattice parameter that are not due to mechanical effects. The second objective is to develop and demonstrate a best practice for neutron diffraction strain mapping of steel welds. The appropriate coordinate system for the measurement of a weld, which is strongly distorted from planar geometry, has to be defined. The coordinate system is important in determining the procedures for mounting and positioning of the weld so that mapping details, especially in regions of high gradients, can be conveniently inter-compared between laboratories.

  19. Precipitation sequence in niobium-alloyed ferritic stainless steel

    NASA Astrophysics Data System (ADS)

    Fujita, Nobuhiro; Bhadeshia, H. K. D. H.; Kikuchi, Masao

    2004-03-01

    Niobium is an important alloying element in the design of heat-resistant ferritic stainless steels for automotive exhaust systems. When in solid solution, it improves both the high temperature strength and the resistance to thermal fatigue. However, it also forms several kinds of precipitates during service. These reactions have been modelled, taking into account the multicomponent nature of the diffusion process and allowing for capillarity effects. It has been possible to estimate not only the volume fractions but also the particle sizes for Fe2Nb (Laves phase) and Fe3Nb3C (M6C) carbide in a 19Cr-0.8Nb steel, with good agreement against experimental data.

  20. Relationship between acoustic emission energy and the kinetics of martensite formation in plain carbon steels

    NASA Astrophysics Data System (ADS)

    van Bohemen, S. M. C.

    2015-01-01

    The kinetics of the martensitic transformation in Fe-0.80C determined on the basis of dilatometry data is compared to the acoustic emission (AE) energy accompanying the transformation in the same steel reported in a previous study. The discrepancy between the AE energy and the volume fraction of martensite indicates that the mechanism for the generation of AE during the martensitic transformation is not solely dependent on the kinetics and the associated moving interfaces as suggested in previous studies. During the growth of martensite, slip takes place in order to relieve internal stresses, and dislocations are thought to be mainly introduced in the relatively soft austenite matrix. The quantitative analysis in this study demonstrates that the AE energy generated per unit time is a function of both the transformation kinetics and the volume fraction of remaining austenite. This strongly indicates that the moving dislocations associated with the plastic deformation of the austenite surrounding the as-formed martensite are the dominant sources of the generated acoustic waves. This improved AE source model is consistent with the well-accepted mechanism of AE during conventional plastic deformation due to an external load.

  1. 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.

  2. Microstructure and mechanical properties of China low activation martensitic steel joint by TIG multi-pass welding with a new filler wire

    NASA Astrophysics Data System (ADS)

    Huang, Bo; Zhang, Junyu; Wu, Qingsheng

    2017-07-01

    Tungsten Inner Gas (TIG) welding is employed for joining of China low activation martensitic (CLAM) steel. A new filler wire was proposed, and the investigation on welding with various heat input and welding passes were conducted to lower the tendency towards the residual of δ ferrite in the joint. With the optimized welding parameters, a butt joint by multi-pass welding with the new filler wire was prepared to investigate the microstructure and mechanical properties. The microstructure of the joint was observed by optical microscope (OM) and scanning electron microscope (SEM). The hardness, Charpy impact and tensile tests of the joint were implemented at room temperature (25 °C). The results revealed that almost full martensite free from ferrite in the joints were obtained by multipass welding with the heat input of 2.26 kJ/mm. A certain degree of softening occurred at the heat affected zone of the joint according to the results of tensile and hardness tests. The as welded joints showed brittle fracture in the impact tests. However, the joints showed toughness fracture after tempering and relatively better comprehensive performance were achieved when the joints were tempered at 740 °C for 2 h.

  3. Surface modification to improve fireside corrosion resistance of Fe-Cr ferritic steels

    DOEpatents

    Park, Jong-Hee; Natesan, Krishnamurti; Rink, David L.

    2010-03-16

    An article of manufacture and a method for providing an Fe--Cr ferritic steel article of manufacture having a surface layer modification for corrosion resistance. Fe--Cr ferritic steels can be modified to enhance their corrosion resistance to liquid coal ash and other chemical environments, which have chlorides or sulfates containing active species. The steel is modified to form an aluminide/silicide passivating layer to reduce such corrosion.

  4. Investigation of Parent Austenite Grains from Martensite Structure Using EBSD in a Wear Resistant Steel

    PubMed Central

    Gyhlesten Back, Jessica; Engberg, Göran

    2017-01-01

    Crystallographic reconstruction of parent austenite grain boundaries from the martensitic microstructure in a wear resistant steel was carried out using electron backscattered diffraction (EBSD). The present study mainly aims to investigate the parent austenite grains from the martensitic structure in an as-rolled (reference) steel sample and samples obtained by quenching at different cooling rates with corresponding dilatometry. Subsequently, this study is to correlate the nearest cooling rate by the dilatometer which yields a similar orientation relationship and substructure as the reference sample. The Kurdjumov-Sachs orientation relationship was used to reconstruct the parent austenite grain boundaries from the martensite boundaries in both reference and dilatometric samples using EBSD crystallographic data. The parent austenite grain boundaries were successfully evaluated from the EBSD data and the corresponding grain sizes were measured. The parent austenite grain boundaries of the reference sample match the sample quenched at 100 °C/s (CR100). Also the martensite substructures and crystallographic textures are similar in these two samples. The results from hardness measurements show that the reference sample exhibits higher hardness than the CR100 sample due to the presence of carbides in the reference sample. PMID:28772813

  5. Investigation of Parent Austenite Grains from Martensite Structure Using EBSD in a Wear Resistant Steel.

    PubMed

    Gyhlesten Back, Jessica; Engberg, Göran

    2017-04-26

    Crystallographic reconstruction of parent austenite grain boundaries from the martensitic microstructure in a wear resistant steel was carried out using electron backscattered diffraction (EBSD). The present study mainly aims to investigate the parent austenite grains from the martensitic structure in an as-rolled (reference) steel sample and samples obtained by quenching at different cooling rates with corresponding dilatometry. Subsequently, this study is to correlate the nearest cooling rate by the dilatometer which yields a similar orientation relationship and substructure as the reference sample. The Kurdjumov-Sachs orientation relationship was used to reconstruct the parent austenite grain boundaries from the martensite boundaries in both reference and dilatometric samples using EBSD crystallographic data. The parent austenite grain boundaries were successfully evaluated from the EBSD data and the corresponding grain sizes were measured. The parent austenite grain boundaries of the reference sample match the sample quenched at 100 °C/s (CR100). Also the martensite substructures and crystallographic textures are similar in these two samples. The results from hardness measurements show that the reference sample exhibits higher hardness than the CR100 sample due to the presence of carbides in the reference sample.

  6. Characterization of strain-induced martensite phase in austenitic stainless steel using a magnetic minor-loop scaling relation

    SciTech Connect

    Kobayashi, Satoru; Saito, Atsushi; Takahashi, Seiki; Kamada, Yasuhiro; Kikuchi, Hiroaki

    2008-05-05

    We propose a combined magnetic method using a scaling power-law rule and initial permeability in magnetic minor hysteresis loops for characterization of ferromagnetic {alpha}{sup '} martensites in austenitic stainless steel. The scaling power law between the hysteresis loss and remanence is universal, being independent of volume fraction of strain-induced {alpha}{sup '} martensites. A coefficient of the power law largely decreases with volume fraction, while the initial permeability linearly increases, reflecting a change in the morphology and quantity of martensites, respectively. The present method is highly effective for integrity assessment of austenitic stainless steels because of the sensitivity and extremely low measurement field.

  7. Laser-based welding of 17-4 PH martensitic stainless steel in a tubular butt joint configuration with a built-in backing bar

    NASA Astrophysics Data System (ADS)

    Ma, Junjie; Atabaki, Mehdi Mazar; Liu, Wei; Pillai, Raju; Kumar, Biju; Vasudevan, Unnikrishnan; Kovacevic, Radovan

    2016-08-01

    Laser-based welding of thick 17-4 precipitation hardening (PH) martensitic stainless steel (SS) plates in a tubular butt joint configuration with a built-in backing bar is very challenging because the porosity and cracks are easily generated in the welds. The backing bar blocked the keyhole opening at the bottom surface through which the entrapped gas could escape, and the keyhole was unstable and collapsed overtime in a deep partially penetrated welding conditions resulting in the formation of pores easily. Moreover, the fast cooling rate prompted the ferrite transform to austenite which induced cracking. Two-pass welding procedure was developed to join 17-4 PH martensitic SS. The laser welding assisted by a filler wire, as the first pass, was used to weld the groove shoulder. The added filler wire could absorb a part of the laser beam energy; resulting in the decreased weld depth-to-width ratio and relieved intensive restraint at the weld root. A hybrid laser-arc welding or a gas metal arc welding (GMAW) was used to fill the groove as the second pass. Nitrogen was introduced to stabilize the keyhole and mitigate the porosity. Preheating was used to decrease the cooling rate and mitigate the cracking during laser-based welding of 17-4 PH martensitic SS plates.

  8. New ferritic steels increase the thermal efficiency of steam turbines

    SciTech Connect

    Mayer, K.H.; Bakker, W.T.

    1996-12-31

    The further development of ferritic high-temperature-resistant 9--11%Cr steels has paved the way for fossil-fired power stations to be operated at turbine steam inlet temperatures of up to around 600 C and high supercritical steam pressures with a distinct improvement in thermal efficiency, a significant contribution towards reducing the environmental impact of SO{sub 2}, NO{sub x} and CO{sub 2} emissions and to a more economical utilization of fossil fuels. Advances in the development of these steels are primarily attributable to joint research projects undertaken by the manufacturers and operators of power stations in Japan (EPDC), in the USA (EPRI) and in Europe (COST 501). The report gives details on the results achieved under EPRI Research Project RP 140 3-15/23 on the creep behavior of modified 9%CrMo cast steel used in the manufacture of steam turbines for coal-fired power plants. The modified 9%CrMo cast steel also offers great benefits as regards improving the useful life and thermal efficiency of existing power plants.

  9. Strengthening and toughening mechanisms in low-c microalloyed martensitic steel as influenced by austenite conditioning

    NASA Astrophysics Data System (ADS)

    Kennett, Shane C.

    Three low-carbon ASTM A514 microalloyed steels were used to assess the effects of austenite conditioning on the microstructure and mechanical properties of martensite. A range of prior austenite grain sizes with and without thermomechanical processing were produced in a Gleeble RTM 3500 and direct-quenched. Samples in the as-quenched, low temperature tempered, and high temperature tempered conditions were studied. The microstructure was characterized with scanning electron microscopy, electron backscattered diffraction, transmission electron microscopy, and x-ray diffraction. The uniaxial tensile properties and Charpy V-notch properties were measured and compared with the microstructural features (prior austenite grain size, packet size, block size, lath boundaries, and dislocation density). For the equiaxed prior austenite grain conditions, prior austenite grain size refinement decreases the packet size, decreases the block size, and increases the dislocation density of as-quenched martensite. However, after high temperature tempering the dislocation density decreases with prior austenite grain size refinement. Thermomechanical processing increases the low angle substructure, increases the dislocation density, and decreases the block size of as-quenched martensite. The dislocation density increase and block size refinement is sensitive to the austenite grain size before ausforming. The larger prior austenite grain size conditions have a larger increase in dislocation density, but the small prior austenite grain size conditions have the largest refinement in block size. Additionally, for the large prior austenite grain size conditions, the packet size increases with thermomechanical processing. The strength of martensite is often related to an effective grain size or carbon concentration. For the current work, it was concluded that the strength of martensite is primarily controlled by the dislocation density and dislocation substructure; which is related to a grain

  10. Study of electroless Ni-W-P alloy coating on martensitic stainless steel

    NASA Astrophysics Data System (ADS)

    Nikitasari, Arini; Mabruri, Efendi

    2016-04-01

    Electroless nickel phospor (Ni-P) is widely used in many industries due to their corrosion and wear resistance, coating uniformity, and ability to coat non-conductive surfaces. The unique properties of tungsten such as high hardness, higher melting point, lower coefficient of linear thermal expansion, and high tensile strength have created a lot of interest in developing ternary Ni-W-P alloys. This article presents the study of electroless Ni-W-P alloys coating using acid or alkaline bath on martensitic stainless steel. Nickel sulfate and sodium tungstate were used as nickel and tungsten sources, respectively, and sodium hypophosphite was used as a reducing agent. Acid or alkaline bath refer to bath pH condition was adjusted by adding sulfuric acid. Martensitic stainless steel was immersed in Ni-W-P bath for 15, 30, and 60 minutes. The substrate of martensitic stainless steel was subjected to pre-treatment (polishing and cleaning) and activation prior to electroless plating. The plating characteristics were investigated for concentration ratio of nickel and hypophosphite (1:3), sodium tungstate concentration 0,1 M, immersion time (15 min, 30 min, 60 min), and bath condition (acid, alkaline). The electroless Ni-W-P plating was heat treated at 400°C for 1 hour. Deposits were characterized using scanning electron microscope (SEM) and corrosion measurement system (CMS).

  11. Study of electroless Ni-W-P alloy coating on martensitic stainless steel

    SciTech Connect

    Nikitasari, Arini Mabruri, Efendi

    2016-04-19

    Electroless nickel phospor (Ni-P) is widely used in many industries due to their corrosion and wear resistance, coating uniformity, and ability to coat non-conductive surfaces. The unique properties of tungsten such as high hardness, higher melting point, lower coefficient of linear thermal expansion, and high tensile strength have created a lot of interest in developing ternary Ni-W-P alloys. This article presents the study of electroless Ni-W-P alloys coating using acid or alkaline bath on martensitic stainless steel. Nickel sulfate and sodium tungstate were used as nickel and tungsten sources, respectively, and sodium hypophosphite was used as a reducing agent. Acid or alkaline bath refer to bath pH condition was adjusted by adding sulfuric acid. Martensitic stainless steel was immersed in Ni-W-P bath for 15, 30, and 60 minutes. The substrate of martensitic stainless steel was subjected to pre-treatment (polishing and cleaning) and activation prior to electroless plating. The plating characteristics were investigated for concentration ratio of nickel and hypophosphite (1:3), sodium tungstate concentration 0,1 M, immersion time (15 min, 30 min, 60 min), and bath condition (acid, alkaline). The electroless Ni-W-P plating was heat treated at 400°C for 1 hour. Deposits were characterized using scanning electron microscope (SEM) and corrosion measurement system (CMS).

  12. Structural and mechanical properties of welded joints of reduced activation martensitic steels

    NASA Astrophysics Data System (ADS)

    Filacchioni, G.; Montanari, R.; Tata, M. E.; Pilloni, L.

    2002-12-01

    Gas tungsten arc welding and electron beam welding methods were used to realise welding pools on plates of reduced activation martensitic steels. Structural and mechanical features of these simulated joints have been investigated in as-welded and post-welding heat-treated conditions. The research allowed to assess how each welding technique affects the original mechanical properties of materials and to find suitable post-welding heat treatments. This paper reports results from experimental activities on BATMAN II and F82H mod. steels carried out in the frame of the European Blanket Project - Structural Materials Program.

  13. Stability of the strengthening nanoprecipitates in reduced activation ferritic steels under Fe2+ ion irradiation

    NASA Astrophysics Data System (ADS)

    Tan, L.; Katoh, Y.; Snead, L. L.

    2014-02-01

    The stability of MX-type precipitates is critical to retain mechanical properties of both reduced activation ferritic-martensitic (RAFM) and conventional FM steels at elevated temperatures. Radiation resistance of TaC, TaN, and VN nanoprecipitates irradiated up to ∼49 dpa at 500 °C using Fe2+ is investigated in this work. Transmission electron microscopy (TEM) utilized in standard and scanning mode (STEM) reveals the non-stoichiometric nature of the nanoprecipitates. Irradiation did not alter their crystalline nature. The radiation resistance of these precipitates, in an order of reduced resistance, is TaC, VN, and TaN. Particle dissolution, growth, and reprecipitation were the modes of irradiation-induced instability. Irradiation also facilitated formation of Fe2W type Laves phase limited to the VN and TaN bearing alloys. This result suggests that nitrogen level should be controlled to a minimal level in alloys to gain greater radiation resistance of the MX-type precipitates at similar temperatures as well as postpone the formation and subsequent coarsening of Laves phase.

  14. Prediction of yield stress and Charpy transition temperature in highly neutron irradiated ferritic steels

    NASA Astrophysics Data System (ADS)

    Windsor, Colin; Cottrell, Geoff; Kemp, Richard

    2010-07-01

    Recent predictions have been made of metallurgical properties of low-activation ferritic/martensitic steels alloys at the high irradiation levels (displacements per atom or dpa) needed for a fusion power plant as based on measurements at low irradiation levels where more data are available. These predictions have been published for the yield stress and for the Charpy ductile to brittle transition temperature shift. The neural network model predictions use training data up to a certain dpa level to predict metallurgical properties above this level. This 'extrapolation' mode of neural networks is explored in some detail. Our studies revealed an increasing accuracy of predictions as the test dpa level is increased for both yield stress and Charpy shift predictions. This result suggests that a model exists for these metallurgical properties as a function of dpa level which becomes more accurate as the available irradiation range in the training data is increased. The explanation suggested is that the metallurgical annealing, which occurs as the irradiation level is increased, simplifies the microstructure and makes prediction more reliable.

  15. Microstructure of HFIR-irradiated 12-Cr 1 MoVW ferritic steel

    SciTech Connect

    Vitek, J.M.; Klueh, R.L.

    1983-01-01

    As part of the fusion materials development program in the United States, a 12 Cr-1 MoVW ferritic steel was irradiated in the High Flux Isotope Reactor (HFIR) to a damage level of 36 dpa at 300, 400, 500, and 600/sup 0/C. During irradiation in HFIR, a transmutation reaction of nickel results in the production of helium, to a level of 99 at. ppM in the present experiment. The microstructures were evaluated after irradiation and the results are presented. Cavities were found at all temperatures. Small cavities (3 to 9 nm) were observed after irradiation at 300, 500 and 600/sup 0/C. At 500 and 600/sup 0/C, the cavities were found preferentially at dislocations, lath boundaries, and prior austenite grain boundaries. After irradiation at 400/sup 0/C, larger cavities (4 to 30 nm) were observed homogeneously distributed throughout the tempered martensite structure. The maximum swelling was 0.07% after irradiation at 400/sup 0/C. Comparision of the results with other studies in which helium was not present at such high levels indicated helium enhances the swelling of 12 Cr-1 MoVW.

  16. Application of nitrogen-alloyed martensitic stainless steels in the aviation industry

    SciTech Connect

    Stein, G.; Kirschner, W.; Lueg, J.

    1997-12-31

    Nitrogen in stainless martensitic steels has a beneficial influence on the mechanical as well as on the chemical properties. However the effect of nitrogen is limited due to the rather low solubility of this element. A special alloy development in combination with a pressurized melting technique lead to distinctly higher nitrogen contents. Stainless martensitic steels containing high nitrogen contents are manufactured by VSG today on an industrial scale using the PESR-process (Pressurized Electroslag Remelting). Depending on special applications these steels are available with different chemical analysis under the trademark CRONIDUR. The basic composition of all CRONIDUR-alloys consists of about 15% Chromium, 1% Molybdenum, 0.15 to 0.35% Carbon and 0.20 to 0.40% Nitrogen. The combination of Cr + Mo + N leads to a superior corrosion resistance of these HNS-steels (HNS: High Nitrogen Steels) in comparison to similar carbon based alloys. Focused on applications with a required minimum hardness of 58 HRC, like stainless bearings or screw shafts, the C+N-content is tuned between 0.60 and 0.80% (Brand: CRONIDUR 30). Additions of max. 0.3% Vanadium and 0.1% Niobium qualifies the brand CRONIDUR 20 for enhanced temperature applications like turbine disks or blades.

  17. 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.

  18. 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.

  19. Probing the characteristic deformation behavior of TRIP steels

    SciTech Connect

    Cheng, Sheng; Wang, Xun-Li; Feng, Zhili; Clausen, Bjorn; Choo, Hahn; Liaw, Peter K

    2008-01-01

    Tensile behavior of two TRIP steels was investigated by in situ neutron diffraction. In the sample with a higher fraction of retained-austenite, the first load transfer was observed from the soft ferrite matrix to the hard retained austenite prior to martensitic transformation, while a second load transfer occurred from the austenite to the harder martensite as martensitic transformation was induced. In the sample with less retained-austenite, the martensitic transformation was limited, leading to significantly less tensile ductility.

  20. Observation on Formation of Fresh Martensite from the Reversed Austenite During Water-Quenching Process in Fe-0.2C-5Mn Steel

    NASA Astrophysics Data System (ADS)

    Zhao, Chuan; Zhang, Chi; Cao, Wen-Quan; Yang, Zhi-Gang; Weng, Yu-Qing

    2015-09-01

    Phase transformation behavior during intercritical annealing in Fe-0.2C-5Mn was studied. Austenite lath formed and transformed at martensite lath during annealing. XRD revealed that retained austenite amount did not always increase with time. TEM result may firstly demonstrate that reversed austenite partly changed into fresh martensite during quenching while the remained part was retained as retained austenite. The final structure consisted of ferrite, retained austenite and fresh martensite. Simulation was done by DICTRA to support TEM result.

  1. Mechanical properties of low activating martensitic 8?10% CrWVTa steels of type OPTIFER

    NASA Astrophysics Data System (ADS)

    Schäfer, L.; Schirra, M.; Ehrlich, K.

    1996-10-01

    A series of low activating steels (OPTIFER-Ia, Ib, II, III and IV) has been developed as materials for the first wall and blanket structures of a future fusion device. The steels have been characterized by metallurgical examinations and by tests of the mechanical properties using tensile, impact bending and creep rupture tests. In comparison with conventional martensitic 9-12% CrMoVNb steels (e.g., MANET and P91 steels) a strong improvement of upper shelf impact energy and a remarkable shift to lower DBTT = -118°C was obtained, whereas other mechanical data are similar. Fracture toughness can be optimized by proper selection of austenitization temperature, quenching and tempering treatment with a preference of a lower austenitizing temperature.

  2. Low-temperature mechanical and magnetic properties of the reduced activation martensitic steel

    NASA Astrophysics Data System (ADS)

    Ding, Hui-Li; Zhang, Tao; Gao, Rui; Wang, Xian-Ping; Fang, Qian-Feng; Liu, Chang-Song; Suo, Jin-Ping

    2015-09-01

    Mechanical and magnetic properties as well as their relationship in the reduced activation martensitic (RAM) steel were investigated in the temperature range from -90°C to 20°C. Charpy impact tests show that the ductile-to-brittle transition temperature (DBTT) of the RAM steel is about -60°C. Low-temperature tensile tests show that the yield strength, ultimate tensile strength and total elongation values increase as temperature decreases, indicating that the strength and plasticity below the DBTT are higher than those above the DBTT. The coercive field ( H C) in the scale of logarithm decreases linearly with the increasing temperature and the absolute value of the slope of ln H C versus temperature above the DBTT is obviously larger than that below the DBTT, also confirmed in the T91 steel. The results indicate that the non-destructive magnetic measurement is a promising candidate method for the DBTT detection of ferromagnetic steels.

  3. Characterization and Modeling of Grain Boundary Chemistry Evolution in Ferritic Steels under Irradiation

    SciTech Connect

    Marquis, Emmanuelle; Wirth, Brian; Was, Gary

    2016-03-28

    Ferritic/martensitic (FM) steels such as HT-9, T-91 and NF12 with chromium concentrations in the range of 9-12 at.% Cr and high Cr ferritic steels (oxide dispersion strengthened steels with 12-18% Cr) are receiving increasing attention for advanced nuclear applications, e.g. cladding and duct materials for sodium fast reactors, pressure vessels in Generation IV reactors and first wall structures in fusion reactors, thanks to their advantages over austenitic alloys. Predicting the behavior of these alloys under radiation is an essential step towards the use of these alloys. Several radiation-induced phenomena need to be taken into account, including phase separation, solute clustering, and radiation-induced segregation or depletion (RIS) to point defect sinks. RIS at grain boundaries has raised significant interest because of its role in irradiation assisted stress corrosion cracking (IASCC) and corrosion of structural materials. Numerous observations of RIS have been reported on austenitic stainless steels where it is generally found that Cr depletes at grain boundaries, consistently with Cr atoms being oversized in the fcc Fe matrix. While FM and ferritic steels are also subject to RIS at grain boundaries, unlike austenitic steels, the behavior of Cr is less clear with significant scatter and no clear dependency on irradiation condition or alloy type. In addition to the lack of conclusive experimental evidence regarding RIS in F-M alloys, there have been relatively few efforts at modeling RIS behavior in these alloys. The need for predictability of materials behavior and mitigation routes for IASCC requires elucidating the origin of the variable Cr behavior. A systematic detailed high-resolution structural and chemical characterization approach was applied to ion-implanted and neutron-irradiated model Fe-Cr alloys containing from 3 to 18 at.% Cr. Atom probe tomography analyses of the microstructures revealed slight Cr clustering and segregation to dislocations and

  4. Investigations of low-temperature neutron embrittlement of ferritic steels

    SciTech Connect

    Farrell, K.; Mahmood, S.T.; Stoller, R.E.; Mansur, L.K.

    1992-12-31

    Investigations were made into reasons for accelerated embrittlement of surveillance specimens of ferritic steels irradiated at 50C at the High Flux Isotope Reactor (HFIR) pressure vessel. Major suspects for the precocious embrittlement were a highly thermalized neutron spectrum,a low displacement rate, and the impurities boron and copper. None of these were found guilty. A dosimetry measurement shows that the spectrum at a major surveillance site is not thermalized. A new model of matrix hardening due to point defect clusters indicates little effect of displacement rate at low irradiation temperature. Boron levels are measured at 1 wt ppM or less, inadequate for embrittlement. Copper at 0.3 wt % and nickel at 0.7 wt % are shown to promote radiation strengthening in iron binary alloys irradiated at 50 to 60C, but no dependence on copper and nickel was found in steels with 0.05 to 0.22% Cu and 0.07 to 3.3% Ni. It is argued that copper impurity is not responsible for the accelerated embrittlement of the HFIR surveillance specimens. The dosimetry experiment has revealed the possibility that the fast fluence for the surveillance specimens may be underestimated because the stainless steel monitors in the surveillance packages do not record an unexpected component of neutrons in the spectrum at energies just below their measurement thresholds of 2 to 3 MeV.

  5. Precipitates and boundaries interaction in ferritic ODS steels

    NASA Astrophysics Data System (ADS)

    Sallez, Nicolas; Hatzoglou, Constantinos; Delabrouille, Fredéric; Sornin, Denis; Chaffron, Laurent; Blat-Yrieix, Martine; Radiguet, Bertrand; Pareige, Philippe; Donnadieu, Patricia; Bréchet, Yves

    2016-04-01

    In the course of a recrystallization study of Oxide Dispersion Strengthened (ODS) ferritic steels during extrusion, particular interest was paid to the (GB) Grain Boundaries interaction with precipitates. Complementary and corresponding characterization experiments using Transmission Electron Microscopy (TEM), Energy Dispersive X-ray spectroscopy (EDX) and Atom Probe Tomography (APT) have been carried out on a voluntarily interrupted extrusion or extruded samples. Microscopic observations of Precipitate Free Zones (PFZ) and precipitates alignments suggest precipitate interaction with migrating GB involving dissolution and Oswald ripening of the precipitates. This is consistent with the local chemical information gathered by EDX and APT. This original mechanism for ODS steels is similar to what had been proposed in the late 80s for similar observation made on Ti alloys reinforced by nanosized yttrium oxides: An interaction mechanism between grain boundaries and precipitates involving a diffusion controlled process of precipitates dissolution at grain boundaries. It is believed that this mechanism can be of primary importance to explain the mechanical behaviour of such steels.

  6. Hydrogen Environment Assisted Cracking of Modern Ultra-High Strength Martensitic Steels

    NASA Astrophysics Data System (ADS)

    Pioszak, Greger L.; Gangloff, Richard P.

    2017-07-01

    Martensitic steels (Aermet®100, Ferrium®M54™, Ferrium®S53®, and experimental CrNiMoWV at ultra-high yield strength of 1550 to 1725 MPa) similarly resist hydrogen environment assisted cracking (HEAC) in aqueous NaCl. Cracking is transgranular, ascribed to increased steel purity and rare earth addition compared to intergranular HEAC in highly susceptible 300M. Nano-scale precipitates ((Mo,Cr)2C and (W,V)C) reduce H diffusivity and the K-independent Stage II growth rate by 2 to 3 orders of magnitude compared to 300M. However, threshold K TH is similarly low (8 to 15 MPa√m) for each steel at highly cathodic and open circuit potentials. Transgranular HEAC likely occurs along martensite packet and {110}α'-block interfaces, speculatively governed by localized plasticity and H decohesion. Martensitic transformation produces coincident site lattice interfaces; however, a connected random boundary network persists in 3D to negate interface engineering. The modern steels are near-immune to HEAC when mildly cathodically polarized, attributed to minimal crack tip H production and uptake. Neither reduced Co and Ni in M54 and CrNiMoWV nor increased Cr in S53 broadly degrade HEAC resistance compared to baseline AM100. The latter suggests that crack passivity dominates acidification to widen the polarization window for HEAC resistance. Decohesion models predict the applied potential dependencies of K TH and da/dt II with a single-adjustable parameter, affirming the importance of steel purity and trap sensitive H diffusivity.

  7. Hydrogen Environment Assisted Cracking of Modern Ultra-High Strength Martensitic Steels

    NASA Astrophysics Data System (ADS)

    Pioszak, Greger L.; Gangloff, Richard P.

    2017-09-01

    Martensitic steels (Aermet®100, Ferrium®M54™, Ferrium®S53®, and experimental CrNiMoWV at ultra-high yield strength of 1550 to 1725 MPa) similarly resist hydrogen environment assisted cracking (HEAC) in aqueous NaCl. Cracking is transgranular, ascribed to increased steel purity and rare earth addition compared to intergranular HEAC in highly susceptible 300M. Nano-scale precipitates ((Mo,Cr)2C and (W,V)C) reduce H diffusivity and the K-independent Stage II growth rate by 2 to 3 orders of magnitude compared to 300M. However, threshold K TH is similarly low (8 to 15 MPa√m) for each steel at highly cathodic and open circuit potentials. Transgranular HEAC likely occurs along martensite packet and {110}α'-block interfaces, speculatively governed by localized plasticity and H decohesion. Martensitic transformation produces coincident site lattice interfaces; however, a connected random boundary network persists in 3D to negate interface engineering. The modern steels are near-immune to HEAC when mildly cathodically polarized, attributed to minimal crack tip H production and uptake. Neither reduced Co and Ni in M54 and CrNiMoWV nor increased Cr in S53 broadly degrade HEAC resistance compared to baseline AM100. The latter suggests that crack passivity dominates acidification to widen the polarization window for HEAC resistance. Decohesion models predict the applied potential dependencies of K TH and d a/d t II with a single-adjustable parameter, affirming the importance of steel purity and trap sensitive H diffusivity.

  8. Prediction of diffusion assisted hydrogen embrittlement failure in high strength martensitic steels

    NASA Astrophysics Data System (ADS)

    Wu, Q.; Zikry, M. A.

    2015-12-01

    A stress assisted hydrogen diffusion transport model, a dislocation-density-based multiple-slip crystalline plasticity formulation, and an overlapping fracture method were used to investigate hydrogen diffusion and embrittlement in lath martensitic steels with distributions of M23C6 carbide precipitates. The formulation accounts for variant morphologies based on orientation relationships (ORs) that are uniquely inherent to lath martensitic microstructures. The interrelated effects of martensitic block and packet boundaries and carbide precipitates on hydrogen diffusion, hydrogen assisted crack nucleation and growth, are analyzed to characterize the competition between cleavage fracture and hydrogen diffusion assisted fracture along preferential microstructural fracture planes. Stresses along the three cleavage planes and the six hydrogen embrittlement fracture planes are monitored, such that crack nucleation and growth can nucleate along energetically favorable planes. High pressure gradients result in the accumulation of hydrogen, which embrittles martensite, and results in crack nucleation and growth along {110} planes. Cleavage fracture occurs along {100} planes when there is no significant hydrogen diffusion. The predictions indicate that hydrogen diffusion can suppress the emission and accumulation of dislocation density, and lead to fracture with low plastic strains.

  9. Post-weld Tempered Microstructure and Mechanical Properties of Hybrid Laser-Arc Welded Cast Martensitic Stainless Steel CA6NM

    NASA Astrophysics Data System (ADS)

    Mirakhorli, Fatemeh; Cao, Xinjin; Pham, Xuan-Tan; Wanjara, Priti; Fihey, Jean-Luc

    2016-12-01

    Manufacturing of hydroelectric turbine components involves the assembly of thick-walled stainless steels using conventional multi-pass arc welding processes. By contrast, hybrid laser-arc welding may be an attractive process for assembly of such materials to realize deeper penetration depths, higher production rates, narrower fusion, and heat-affected zones, and lower distortion. In the present work, single-pass hybrid laser-arc welding of 10-mm thick CA6NM, a low carbon martensitic stainless steel, was carried out in the butt joint configuration using a continuous wave fiber laser at its maximum power of 5.2 kW over welding speeds ranging from 0.75 to 1.2 m/minute. The microstructures across the weldment were characterized after post-weld tempering at 873 K (600 °C) for 1 hour. From microscopic examinations, the fusion zone was observed to mainly consist of tempered lath martensite and some residual delta-ferrite. The mechanical properties were evaluated in the post-weld tempered condition and correlated to the microstructures and defects. The ultimate tensile strength and Charpy impact energy values of the fully penetrated welds in the tempered condition were acceptable according to ASTM, ASME, and industrial specifications, which bodes well for the introduction of hybrid laser-arc welding technology for the manufacturing of next generation hydroelectric turbine components.

  10. Low activation ferritic alloys

    DOEpatents

    Gelles, D.S.; Ghoniem, N.M.; Powell, R.W.

    1985-02-07

    Low activation ferritic alloys, specifically bainitic and martensitic stainless steels, are described for use in the production of structural components for nuclear fusion reactors. They are designed specifically to achieve low activation characteristics suitable for efficient waste disposal. The alloys essentially exclude molybdenum, nickel, nitrogen and niobium. Strength is achieved by substituting vanadium, tungsten, and/or tantalum in place of the usual molybdenum content in such alloys.

  11. Low activation ferritic alloys

    DOEpatents

    Gelles, David S.; Ghoniem, Nasr M.; Powell, Roger W.

    1986-01-01

    Low activation ferritic alloys, specifically bainitic and martensitic stainless steels, are described for use in the production of structural components for nuclear fusion reactors. They are designed specifically to achieve low activation characteristics suitable for efficient waste disposal. The alloys essentially exclude molybdenum, nickel, nitrogen and niobium. Strength is achieved by substituting vanadium, tungsten, and/or tantalum in place of the usual molybdenum content in such alloys.

  12. New grain formation during warm deformation of ferritic stainless steel

    SciTech Connect

    Belyakov, A.; Sakai, Taku; Kaibyshev, R.

    1998-01-01

    Microstructural evolution accompanied by localization of plastic flow was studied in compression of a ferritic stainless steel with high stacking fault energy (SFE) at 873 K ({approx} 0.5 Tm). The structure evolution is characterized by the formation of dense dislocation walls at low strains and subsequently of microbands and their clusters at moderate strains, followed by the evolution of fragmented structure inside the clusters of microbands at high strains. The misorientations of the fragmented boundaries and the fraction of high-angle grain boundaries increase substantially with increasing strain. Finally, further straining leads to the formation of new fine grains with high-angle boundaries, which become more equiaxed than the previous fragmented structure. The mechanisms operating during such structure changes are discussed in detail.

  13. Sensitization and stabilization of type 409 ferritic stainless steel

    SciTech Connect

    Fritz, J.D.; Franson, I.A.

    1997-08-01

    Type 409 (UNS S40900) ferritic stainless steel, used widely in automotive exhaust systems, can be subject to intergranular corrosion (IGC) of weld heat-affected zones (HAZ), even though ASTM stabilization requirements (Ti = 6 {times} C) are met. A boiling Cu/6% CuSO{sub 4}/0.5% H{sub 2}SO{sub 4} test is shown to be appropriate for detecting IGC of welds and HAZ. This test was used to establish stabilization requirements for type 409, whether dual-stabilized with Ti + Nb or singly stabilized with Ti alone. It was found that the stabilization requirement should be Ti + Nb {ge} 0.08 + 8 (C + N). Benefits of dual stabilization include improved surface quality and formability without sacrifice of mechanical properties or weldability.

  14. The effect of martensitic stainless steel microstructure on the ultrasonic inspection of turbine runner joints

    NASA Astrophysics Data System (ADS)

    Boukani, Hamid Habibzadeh; Chentouf, Samir Mourad; Viens, Martin; Tahan, Antoine; Gagnon, Martin

    2015-03-01

    Martensitic stainless steel runners are widely used in the hydroelectric turbine industry because of their good mechanical properties, cavitation and corrosion resistance. The high downtime cost and limited in-service inspection possibility of these turbine runners increase the need for accurate fatigue models to estimate the life of these equipment. One of the key inputs of these models is the distribution of flaw size and their location near highly stressed area. The critical area is generally located near the welded joint and flaw sizes are estimated using the outcome of nondestructive inspection. In such case, more reliable NDT results will lead to less uncertainty in the life estimation and hence unfavorable consequences, such as unexpected failure during service or non-essential down time for unnecessary inspections, are avoided. Turbine runner welded joints are inspected using ultrasonic refracted shear waves. Considering the dependence of the refracted angle to the shear wave velocity in the material as well as the role of this angle in the precision of defects' localization, the martensitic microstructure effect on sound wave velocity needs to be accurately known. Furthermore, attenuation coefficient, which affects reflected signal amplitude, is an essential data for the evaluation of defect size which is also dependent on microstructure. In this context, dependence of ultrasonic shear wave properties on metallurgical characteristics of martensitic stainless steel was studied. Our objective is to obtain better POD from a more accurate characterization of received indications.

  15. Martensitic transformation of austenitic stainless steel orthodontic wires during intraoral exposure.

    PubMed

    Izquierdo, Paula P; de Biasi, Ronaldo S; Elias, Carlos N; Nojima, Lincoln I

    2010-12-01

    Our purpose was to study the mechanical properties and phase transformations of orthodontic wires submitted to in-vivo exposure in the mouth for different periods of time. Stainless steel wires were tied to fixed orthodontic appliances of 30 patients from the orthodontics clinic of Universidade Federal do Rio de Janeiro School of Dentistry in Brazil. According to the duration of the clinical treatment, the patients were divided into 3 groups. After in-vivo exposure, the samples were studied by mechanical testing (torsion) and ferromagnetic resonance. Statistical analyses were carried out to evaluate the correlation between time of exposure, mechanical properties, and austenite-to-martensite transformation among the groups. The results were compared with as-received control samples. The torque values increased as time in the mouth increased. The increase in torque resistance showed high correlations with time of exposure (P = 0.005) and austenite-martensite phase transformation. The resistance of stainless steel orthodontic wires increases as the time in the mouth increases; this effect is attributed to the austenite-to-martensite transformation. Copyright © 2010 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.

  16. Atomistically Informed Extended Gibbs Energy Description for Phase-Field Simulation of Tempering of Martensitic Steel

    PubMed Central

    Shchyglo, Oleg; Hammerschmidt, Thomas; Čak, Miroslav; Drautz, Ralf; Steinbach, Ingo

    2016-01-01

    In this study we propose a unified multi-scale chemo-mechanical description of the BCT (Body-Centered Tetragonal) to BCC (Body-Centered Cubic) order-disorder transition in martensitic steel by adding the mechanical degrees of freedom to the standard CALPHAD (CALculation of PHAse Diagrams) type Gibbs energy description. The model takes into account external strain, the effect of carbon composition on the lattice parameter and elastic moduli. The carbon composition effect on the lattice parameters and elastic constants is described by a sublattice model with properties obtained from DFT (Density Functional Theory) calculations; the temperature dependence of the elasticity parameters is estimated from available experimental data. This formalism is crucial for studying the kinetics of martensite tempering in realistic microstructures. The obtained extended Gibbs energy description opens the way to phase-field simulations of tempering of martensitic steel comprising microstructure evolution, carbon diffusion and lattice symmetry change due to the ordering/disordering of carbon atoms under multiaxial load. PMID:28773790

  17. 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

  18. 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

  19. 78 FR 63517 - Control of Ferrite Content in Stainless Steel Weld Metal

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-10-24

    ...The U.S. Nuclear Regulatory Commission (NRC) is issuing a revision to Regulatory Guide (RG) 1.31, ``Control of Ferrite Content in Stainless Steel Weld Metal.'' This guide (Revision 4) describes a method that the NRC staff considers acceptable for controlling ferrite content in stainless steel weld metal. It updates the guide to remove references to outdated standards and to remove an appendix......

  20. Hybrid Laser-arc Welding of 17-4 PH Martensitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Liu, Wei; Ma, Junjie; Atabaki, Mehdi Mazar; Pillai, Raju; Kumar, Biju; Vasudevan, Unnikrishnan; Sreshta, Harold; Kovacevic, Radovan

    2015-06-01

    17-4 PH stainless steel has wide applications in severe working conditions due to its combination of good corrosion resistance and high strength. The weldability of 17-4 PH stainless steel is challenging. In this work, hybrid laser-arc welding was developed to weld 17-4 PH stainless steel. This method was chosen based on its advantages, such as deep weld penetration, less filler materials, and high welding speed. The 17-4 PH stainless steel plates with a thickness of 19 mm were successfully welded in a single pass. During the hybrid welding, the 17-4 PH stainless steel was immensely susceptible to porosity and solidification cracking. The porosity was avoided by using nitrogen as the shielding gas. The nitrogen stabilized the keyhole and inhibited the formation of bubbles during welding. Solidification cracking easily occurred along the weld centerline at the root of the hybrid laser-arc welds. The microstructural evolution and the cracking susceptibility of 17-4 PH stainless steel were investigated to remove these centerline cracks. The results showed that the solidification mode of the material changed due to high cooling rate at the root of the weld. The rapid cooling rate caused the transformation from ferrite to austenite during the solidification stage. The solidification cracking was likely formed as a result of this cracking-susceptible microstructure and a high depth/width ratio that led to a high tensile stress concentration. Furthermore, the solidification cracking was prevented by preheating the base metal. It was found that the preheating slowed the cooling rate at the root of the weld, and the ferrite-to-austenite transformation during the solidification stage was suppressed. Delta ferrite formation was observed in the weld bead as well no solidification cracking occurred by optimizing the preheating temperature.

  1. A Comparison of Creep Rupture Strength of Ferritic/Austenitic Dissimilar Weld Joints of Different Grades of Cr-Mo Ferritic Steels

    NASA Astrophysics Data System (ADS)

    Laha, K.; Chandravathi, K. S.; Parameswaran, P.; Goyal, Sunil; Mathew, M. D.

    2012-04-01

    Evaluations of creep rupture properties of dissimilar weld joints of 2.25Cr-1Mo, 9Cr-1Mo, and 9Cr-1MoVNb steels with Alloy 800 at 823 K were carried out. The joints were fabricated by a fusion welding process employing an INCONEL 182 weld electrode. All the joints displayed lower creep rupture strength than their respective ferritic steel base metals, and the strength reduction was greater in the 2.25Cr-1Mo steel joint and less in the 9Cr-1Mo steel joint. Failure location in the joints was found to shift from the ferritic steel base metal to the intercritical region of the heat-affected zone (HAZ) of the ferritic steel (type IV cracking) with the decrease in stress. At still lower stresses, the failure in the joints occurred at the ferritic/austenitic weld interface. The stress-life variation of the joints showed two-slope behavior and the slope change coincided with the occurrence of ferritic/austenitic weld interface cracking. Preferential creep cavitation in the soft intercritical HAZ induced type IV failure, whereas creep cavitation at the interfacial particles induced ferritic/austenitic weld interface cracking. Micromechanisms of the type IV failure and the ferritic/austenitic interface cracking in the dissimilar weld joint of the ferritic steels and relative cracking susceptibility of the joints are discussed based on microstructural investigation, mechanical testing, and finite element analysis (FEA) of the stress state across the joint.

  2. Strain-Induced Martensite Formation and Recrystallization Behavior in 304 Stainless Steel

    NASA Astrophysics Data System (ADS)

    Al-Fadhalah, Khaled J.

    2015-04-01

    The effect of recrystallization on the evolution of microstructure, texture, and mechanical properties has been examined in an AISI 304 stainless steel, subjected to strain-induced α '-martensite transformation and subsequent annealing. Samples were processed by cold rolling and subzero rolling to induce different amounts of α '-martensite, using three reductions of 20, 40, and 60%, and later solution annealed to ensure complete recrystallization. Large transformation to α '-martensite occurred for subzero-rolled samples at low reduction (20%), while only a gradual increase of α '-martensite in cold-rolled samples took place with the increasing rolling reduction. Results from electron back-scattered diffraction indicate that annealing of cold-rolled samples produces finer recrystallized grains with increasing rolling reduction, while the predominant formation of α '-martensite in subzero-rolled microstructures is believed to have strong effect on the production of similar grain size upon annealing. Twin-related Σ3 boundaries were formed during annealing with maximum fraction of 53%. These boundaries become longer, straighter, and less incorporated into grain boundary network with the increasing rolling reduction and/or using subzero rolling, demonstrating an indirect mechanism of grain boundary engineering. Also, annealing caused scattering around the rolling texture components (Brass, Goss, S, and Copper) and the recrystallization textures become more random with the increasing rolling reduction and/or using subzero rolling. Nevertheless, recrystallization textures of samples reduced by 60% show formation of Cube and Dillamore orientations and strengthening of Brass orientation. This is thought to contribute to the enhancement of the tensile strength and microhardness of annealed samples.

  3. Optimizing Heat Treatment Process of Fe-13Cr-3Mo-3Ni Martensitic Stainless of Steel

    NASA Astrophysics Data System (ADS)

    Anwar, M. S.; Prifiharni, S.; Mabruri, E.

    2017-05-01

    The Fe-13Cr-3Mo-3Ni stainless steels are modified into martensitic stainless steels for steam turbine blades application. The working temperature of steam turbine was around 600 - 700 °C. The improvement properties of turbine blade material is necessary to maintain steam turbine work. The previous research revealed that it has corrosion resistance of Fe-13Cr-3Mo-3Ni which is better than 13Cr stainless steels in the chloride environment. In this work, the effect of heat treatment on microstructure and hardness of Fe-13Cr-3Mo-3Ni stainless steels has been studied. The steel was prepared by induction melting followed by hot forging. The steels were austenitized at 1000, 1050, and 1100 °C for 1 hour and were tempered at 600, 650, and 700 °C for 1 hour. The steels were then subjected to metallographic observation and hardness test of Rockwell C. The optimal heat treatment of Fe-13Cr-3Mo-3Ni was carried out austenitized in 1050 °C and tempered in 600 - 700 °C.

  4. The microstructural stability and mechanical properties of two low activation martensitic steels

    SciTech Connect

    Victoria, M.; Marmy, P.; Batawi, E.; Peters, J.; Briguet, C.; Rezai-Aria, F.; Gavillet, D.

    1996-12-31

    A desirable feature of future magnetically confined fusion reactors is the prospect of producing low level radioactive waste. In order to minimize the volume of radioactive material, in particular from the first wall and blanket structures, reduced long term activation alloys are being developed. Here, a low activation composition of a martensitic 9% Cr steel has been studied, based on the DIN (Deutsches Inst. fuer Normung) 1.4914 composition (MANET) but replacing Ni, Mo and Nb by the low activation elements W, V and Ta. Two casts were produced from high purity components, in which the effects of controlled additions of Mn (0.58 and 0.055 wt. %) and N (7 and 290 wt. ppm) were studied, so that the final compositions resulted in one cast with high Mn and low N (steel A) and the other with the opposite conditions (steel B). The two steels were evaluated in terms of structural stability and mechanical properties under tensile, fatigue and fracture toughness tests. It has been found that both alloys have a DBTT below room temperature, which in the case of the steel A is 70 K below that of MANET. Although the tensile strength is somewhat below that of the parent steel, both steels have longer fatigue life.

  5. Nanoscale Analyses of High-Nickel Concentration Martensitic High-Strength Steels

    NASA Astrophysics Data System (ADS)

    Isheim, Dieter; Hunter, Allen H.; Zhang, Xian J.; Seidman, David N.

    2013-07-01

    Austenite reversion in martensitic steels is known to improve fracture toughness. This research focuses on characterizing mechanical properties and the microstructure of low-carbon, high-nickel steels containing 4.5 and 10 wt pct Ni after a QLT-type austenite reversion heat treatment: first, martensite is formed by quenching ( Q) from a temperature in the single-phase austenite field, then austenite is precipitated by annealing in the upper part of the intercritical region in a lamellarization step ( L), followed by a tempering ( T) step at lower temperatures. For the 10 wt pct Ni steel, the tensile strength after the QLT heat treatment is 910 MPa (132 ksi) at 293 K (20 °C), and the Charpy V-notch impact toughness is 144 J (106 ft-lb) at 188.8 K (-84.4 °C, -120 °F). For the 4.5 wt pct Ni steel, the tensile strength is 731 MPa (106 ksi) at 293 K (20 °C) and the impact toughness is 209 J (154 ft-lb) at 188.8 K (-84.4 °C, -120 °F). Light optical microscopy, scanning electron and transmission electron microscopies, synchrotron X-ray diffraction, and local-electrode atom-probe tomography (APT) are utilized to determine the morphologies, volume fractions, and local chemical compositions of the precipitated phases with sub-nanometer spatial resolution. The austenite lamellae are up to 200 nm in thickness, and up to several micrometers in length. In addition to the expected partitioning of Ni to austenite, APT reveals a substantial segregation of Ni at the austenite/martensite interface with concentration maxima of 10 and 23 wt pct Ni for the austenite lamellae in the 4.5 and 10 wt pct Ni steels, respectively. Copper-rich and M2C-type metal carbide precipitates were detected both at the austenite/martensite interface and within the bulk of the austenite lamellae. Thermodynamic phase stability, equilibrium compositions, and volume fractions are discussed in the context of Thermo-Calc calculations.

  6. Effect of aging temperature on the microstructures and mechanical properties of ZG12Cr9Mo1Co1NiVNbNB ferritic heat-resistant steel

    NASA Astrophysics Data System (ADS)

    Yang, Xue; Sun, Lan; Xiong, Ji; Zhou, Ping; Fan, Hong-yuan; Liu, Jian-yong

    2016-02-01

    The effect of aging on the mechanical properties and microstructures of a new ZG12Cr9Mo1Co1NiVNbNB ferritic heat resistant steel was investigated in this work to satisfy the high steam parameters of the ultra-supercritical power plant. The results show that the main precipitates during aging are Fe(Cr, Mo)23C6, V(Nb)C, and (Fe2Mo) Laves in the steel. The amounts of the precipitated phases increase during aging, and correspondingly, the morphologies of phases are similar to be round. Fe(Cr, Mo)23C6 appears along boundaries and grows with increasing temperature. In addition, it is revealed that the martensitic laths are coarsened and eventually happen to be polygonization. The hardness and strength decrease gradually, whereas the plasticity of the steel increases. What's more, the hardness of this steel after creep is similar to that of other 9%-12%Cr ferritic steels. Thus, ZG12Cr9Mo1Co1NiVNbNB can be used in the project.

  7. Electrochemical and passivation behavior investigation of ferritic stainless steel in simulated concrete pore media.

    PubMed

    Luo, Hong; Su, Huaizhi; Dong, Chaofang; Xiao, Kui; Li, Xiaogang

    2015-12-01

    The applications of stainless steel are one of the most reliable solutions in concrete structures to reduce chloride-induced corrosion problems and increase the structures service life, however, due to high prices of nickel, especially in many civil engineering projects, the austenitic stainless steel is replaced by the ferritic stainless steels. Compared with austenite stainless steel, the ferritic stainless steel is known to be extremely resistant of stress corrosion cracking and other properties. The good corrosion resistance of the stainless steel is due to the formation of passive film. While, there is little literature about the electrochemical and passive behavior of ferritic stainless steel in the concrete environments. So, here, we present the several corrosion testing methods, such as the potentiodynamic measurements, EIS and Mott-Schottky approach, and the surface analysis methods like XPS and AES to display the passivation behavior of 430 ferritic stainless steel in alkaline solution with the presence of chloride ions. These research results illustrated a simple and facile approach for studying the electrochemical and passivation behavior of stainless steel in the concrete pore environments.

  8. Electrochemical and passivation behavior investigation of ferritic stainless steel in simulated concrete pore media

    PubMed Central

    Luo, Hong; Su, Huaizhi; Dong, Chaofang; Xiao, Kui; Li, Xiaogang

    2015-01-01

    The applications of stainless steel are one of the most reliable solutions in concrete structures to reduce chloride-induced corrosion problems and increase the structures service life, however, due to high prices of nickel, especially in many civil engineering projects, the austenitic stainless steel is replaced by the ferritic stainless steels. Compared with austenite stainless steel, the ferritic stainless steel is known to be extremely resistant of stress corrosion cracking and other properties. The good corrosion resistance of the stainless steel is due to the formation of passive film. While, there is little literature about the electrochemical and passive behavior of ferritic stainless steel in the concrete environments. So, here, we present the several corrosion testing methods, such as the potentiodynamic measurements, EIS and Mott–Schottky approach, and the surface analysis methods like XPS and AES to display the passivation behavior of 430 ferritic stainless steel in alkaline solution with the presence of chloride ions. These research results illustrated a simple and facile approach for studying the electrochemical and passivation behavior of stainless steel in the concrete pore environments. PMID:26501086

  9. {225}γ habit planes in martensitic steels: from the PTMC to a continuous model

    PubMed Central

    Baur, Annick P.; Cayron, Cyril; Logé, Roland E.

    2017-01-01

    Fine twinned microstructures with {225}γ habit planes are commonly observed in martensitic steels. The present study shows that an equibalanced combination of twin-related variants associated to the Kurdjumov-Sachs orientation relationship is equivalent to the Bowles and Mackenzie’s version of the PTMC for this specific {225}γ case. The distortion associated to the Kurdjumov-Sachs orientation relationship results from a continuous modeling of the FCC-BCC transformation. Thus, for the first time, an atomic path can be associated to the PTMC. PMID:28106127

  10. {225}γ habit planes in martensitic steels: from the PTMC to a continuous model.

    PubMed

    Baur, Annick P; Cayron, Cyril; Logé, Roland E

    2017-01-20

    Fine twinned microstructures with {225}γ habit planes are commonly observed in martensitic steels. The present study shows that an equibalanced combination of twin-related variants associated to the Kurdjumov-Sachs orientation relationship is equivalent to the Bowles and Mackenzie's version of the PTMC for this specific {225}γ case. The distortion associated to the Kurdjumov-Sachs orientation relationship results from a continuous modeling of the FCC-BCC transformation. Thus, for the first time, an atomic path can be associated to the PTMC.

  11. Demonstration of a high burnup heterogeneous core using ferritic/martensitic materials

    SciTech Connect

    Lovell, A J; Fox, G L; Sutherland, W H; Hecht, S L

    1986-04-11

    The purpose of the Core Demonstration Experiment (CDE) is to demonstrate the capability of a mixed-oxide fuel system to achieve a three year life in a prototypic LMR heterogeneous reactor environment. The CDE assemblies are fabricated using wire-wrapped, large-diameter, advanced-oxide fuel and blanket pins with tempered martensitic HT9 cladding, wire wrap, and duct. The highest power fuel assembly operates with a Beginning of Life (BOL) peak linear pin power of 445 W/cm and a peak cladding temperature of 615C. The fuel and blanket assembly irradiation will start in FFTF Cycle 9 and continue for about 900 Equivalent Full Power Days (EFPD). The successful utilization of the tempered martensitic HT9 alloy in an FFTF test assembly is fully anticipated. The low swelling, observed at intermediate neutron fluence and projected to higher fluences, together with reasonable creep behavior gives acceptable mechanical performance for fuel pins, blanket pins and ducts. Duct length increase, dilation and bow; plus fuel and blanket pin diameter increases remain within specified tolerances. In addition, stress rupture data from unirradiated HT9 imply cumulative damage fractions for the nominal fuel and blanket pins that are low.

  12. Formation quality optimization of laser hot wire cladding for repairing martensite precipitation hardening stainless steel

    NASA Astrophysics Data System (ADS)

    Wen, Peng; Feng, Zhenhua; Zheng, Shiqing

    2015-01-01

    Laser cladding is an advantaged repairing technology due to its low heat input and high flexibility. With preheating wire by resistance heat, laser hot wire cladding shows better process stability and higher deposition efficiency compared to laser cold wire/powder cladding. Multi-pass layer were cladded on the surface of martensite precipitation hardening stainless steel FV520B by fiber laser with ER410NiMo wire. Wire feed rate and preheat current were optimized to obtain stable wire transfer, which guaranteed good formation quality of single pass cladding. Response surface methodology (RSM) was used to optimize processing parameters and predict formation quality of multi-pass cladding. Laser power P, scanning speed Vs, wire feed rate Vf and overlap ratio η were selected as the input variables, while flatness ratio, dilution and incomplete fusion value as the responses. Optimal clad layer with flat surface, low dilution and no incomplete fusion was obtained by appropriately reducing Vf, and increasing P, Vs and η. No defect like pore or crack was found. The tensile strength and impact toughness of the clad layer is respectively 96% and 86% of those of the substrate. The clad layer showed nonuniform microstructure and was divided into quenched areas with coarse lath martensite and tempered areas with tempered martensite due to different thermal cycles in adjacent areas. The tempered areas showed similar hardness to the substrate.

  13. Effect of tin addition on the microstructure and properties of ferritic stainless steel

    NASA Astrophysics Data System (ADS)

    Li, Yang; Han, Ji-peng; Jiang, Zhou-hua; He, Pan

    2015-01-01

    This article reports the effects of Sn on the inclusions as well as the mechanical properties and hot workability of ferritic stainless steel. Precipitation phases and inclusions in Sn-bearing ferritic stainless steel were observed, and the relationship between the workability and the microstructure of the steel was established. Energy-dispersive X-ray spectroscopic analysis of the steel reveals that an almost pure Sn phase forms and MnS-Sn compound inclusions appear in the steel with a higher Sn content. Little Sn segregation was observed in grain boundaries and in the areas around sulfide inclusions; however, the presence of Sn does not adversely affect the workability of the steel containing 0.4wt% Sn. When the Sn content is 0.1wt%-0.4wt%, Sn improves the tensile strength and the plastic strain ratio and also improves the plasticity with increasing temperature. A mechanism of improving the workability of ferritic stainless steel induced by Sn addition was discussed: the presence of Sn lowers the defect concentration in the ultra-pure ferritic lattice and the good distribution of tin in the lattice overcomes the problem of hot brittleness that occurs in low-carbon steel as a result of Sn segregation.

  14. Changes in the fracture strength parameters of ferritic-bainitic and bainitic pipe steels during operation

    NASA Astrophysics Data System (ADS)

    Zikeev, V. N.; Filippov, G. A.; Shabalov, I. P.; Livanova, O. V.; Solov'ev, D. M.

    2016-10-01

    The fracture strength and the sensitivity to delayed fracture of the pipes in oil-trunk pipelines that are made of ferritic-bainitic and bainitic steels are studied. The results of modeling of the delayed brittle fracture of pipe steel during a simultaneous action of mechanical stresses and a corrosive medium are presented.

  15. Corrosion behavior of oxide dispersion strengthened ferritic steels in supercritical water

    NASA Astrophysics Data System (ADS)

    Gao, Wenhua; Guo, Xianglong; Shen, Zhao; Zhang, Lefu

    2017-04-01

    The corrosion resistance of three different Cr content oxide dispersion strengthened (ODS) ferritic steels in supercritical water (SCW) and their passive films formed on the surface have been investigated. The results show that the dissolved oxygen (DO) and chemical composition have significant influence on the corrosion behavior of the ODS ferritic steels. In 2000 ppb DO SCW at 650 °C, the 14Cr-4Al ODS steel forms a tri-layer oxide film and the surface morphologies have experienced four structures. For the tri-layer oxide film, the middle layer is mainly Fe-Cr spinel and the Al is gradually enriched in the inner layer.

  16. TRIP effect in austenitic-martensitic VNS9-Sh steel at various strain rates

    NASA Astrophysics Data System (ADS)

    Terent'ev, V. F.; Slizov, A. K.; Prosvirnin, D. V.

    2016-10-01

    The mechanical properties of austenitic-martensitic VNS9-Sh (23Kh15N5AM3-Sh) steel are studied at a static strain rate from 4.1 × 10-5 to 17 × 10-3 s-1 (0.05-20 mm/min). It is found that, as the strain rate increases, the ultimate tensile strength decreases and the physical yield strength remains unchanged (≈1400 MPa). As the strain rate increases, the yield plateau remains almost unchanged and the relative elongation decreases continuously. Because of high microplastic deformation, the conventional yield strength is lower than the physical yield strength over the entire strain rate range under study. The influence of the TRIP effect on the changes in the mechanical properties of VNS9-Sh steel at various strain rates is discussed.

  17. Research and development on the China low activation martensitic steel (CLAM)

    NASA Astrophysics Data System (ADS)

    Yu, Jinnan; Huang, Qunying; Wan, Farong

    2007-08-01

    Chinese low activation martensitic steel (CLAM) has been designed with improved composition, and its performance, such as tensile properties, ductile-brittle transition temperature (DBTT 41J), creep and thermal physical properties, has been determined. The interaction experiments between CLAM and plasma were carried out in the HT-7 tokamak facility and the activities, afterheat and gamma dose rate for CLAM as a function of cooling time (CT) were calculated to obtain the required control levels of impurities in CLAM. The insulator coatings on CLAM steel prepared by the CVD process at 700 °C and 740 °C have pure Al 2O 3 and Al 2O 3 with an oxygen deficiency layer on surface about 1 μm thick. The electrical resistivity of the coating reaches about 10 4 Ωm 2 on the surface.

  18. Corrosion of austenitic and martensitic stainless steels in flowing 17Li83Pb alloy

    NASA Astrophysics Data System (ADS)

    Broc, M.; Flament, T.; Fauvet, P.; Sannier, J.

    1988-07-01

    With regard to the behaviour of 316 L stainless steel at 400°C in flowing anisothermal 17Li83Pb the mass transfer suffered by this steel appears to be quite important without noticeable influence of constant or cyclic stress. Evaluation made from solution-annealed specimens leads to a corrosion rate of approximately 30 μm yr -1 at steady state to which a depth of 25 μm has to be added to take into account the initial period phenomena. On the other hand, with semi-stagnant 17Li83Pb at 400° C, the mass transfer of 316 L steel appears to be lower and more acceptable after a 3000-h exposure; but long-time kinetics data have to be achieved in order to see if that better behaviour is persistent and does not correspond to a longer incubation period. As for the martensitic steels their corrosion rate at 450°C in the thermal convection loop TULIP is constant up to 3000 h and five times lower than that observed for 316 L steel in the same conditions.

  19. Lanthana-bearing nanostructured ferritic steels via spark plasma sintering

    NASA Astrophysics Data System (ADS)

    Pasebani, Somayeh; Charit, Indrajit; Wu, Yaqiao; Burns, Jatuporn; Allahar, Kerry N.; Butt, Darryl P.; Cole, James I.; Alsagabi, Sultan F.

    2016-03-01

    A lanthana-containing nanostructured ferritic steel (NFS) was processed via mechanical alloying (MA) of Fe-14Cr-1Ti-0.3Mo-0.5La2O3 (wt.%) and consolidated via spark plasma sintering (SPS). In order to study the consolidation behavior via SPS, sintering temperature and dwell time were correlated with microstructure, density, microhardness and shear yield strength of the sintered specimens. A bimodal grain size distribution including both micron-sized and nano-sized grains was observed in the microstructure of specimens sintered at 850, 950 and1050 °C for 45 min. Significant densification occurred at temperatures greater than 950 °C with a relative density higher than 98%. A variety of nanoparticles, some enriched in Fe and Cr oxides and copious nanoparticles smaller than 10 nm with faceted morphology and enriched in La and Ti oxides were observed. After SPS at 950 °C, the number density of Cr-Ti-La-O-enriched nanoclusters with an average radius of 1.5 nm was estimated to be 1.2 × 1024 m-3. The La + Ti:O ratio was close to 1 after SPS at 950 and 1050 °C; however, the number density of nanoclusters decreased at 1050 °C. With SPS above 950 °C, the density improved but the microhardness and shear yield strength decreased due to partial coarsening of the grains and nanoparticles.

  20. Precipitation Kinetics in a Nb-stabilized Ferritic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Labonne, M.; Graux, A.; Cazottes, S.; Danoix, F.; Cuvilly, F.; Chassagne, F.; Perez, M.; Massardier, V.

    2017-08-01

    The precipitation occurring in a Nb-stabilized ferritic stainless steel, containing initially Nb(C, N) carbonitrides and Fe3Nb3X precipitates, was investigated during aging treatments performed between 923 K and 1163 K (650 °C and 890 °C) by combining different techniques, (thermoelectric power (TEP), scanning/transmission electron microscopy (SEM/TEM), and atom probe tomography (APT)), in order to determine the precipitation kinetics, the nature and morphology of the newly formed precipitates as well as the chemistry of the initial Fe3Nb3X precipitates, where X stands for C or N. The following composition was proposed for these precipitates: (Fe0.81 Cr0.19)3 (Nb0.85 Si0.08 Mo0.07)3 (N0.8 C0.2), highlighting the simultaneous presence of N and C in the precipitates. With regard to the precipitation in the investigated temperature range, two main phenomena, associated with a hardness decrease, were clearly identified: (i) the precipitation of Fe2Nb precipitates from the niobium initially present in solution or coming from the progressive dissolution of the Fe3Nb3X precipitates and (ii) the precipitation of the χ-phase at grain boundaries for longer aging times. From the TEP kinetics, a time-temperature-precipitation diagram has been proposed.

  1. Evaluation of misindexing of EBSD patterns in a ferritic steel.

    PubMed

    Karthikeyan, T; Dash, M K; Saroja, S; Vijayalakshmi, M

    2013-01-01

    The systematic misindexing caused by pseudo-symmetry Kikuchi diffraction patterns in automated Electron Backscatter Diffraction analysis has been studied in a 9Cr-1Mo ferritic steel. Grains with its [1 1 1] directed towards detector centre were found to be prone to misindexing, and the solutions exhibit a relative orientation of ±30° and 60° about the common [1 1 1] axis (as compared to the true orientation). Fictitious boundaries were detected within such grains, which satisfy the Σ3 or Σ13b type coincidence site lattice boundary criteria. Misindexing rate was reduced with more than six detected bands, but 30° rotated solution was comparatively more persistent, as the additional bands of (3 1 0)-type exhibited a nearly good pattern match. Increase in detector collection angle to 0.96 sr or number of detected bands to nine were found to be beneficial in preventing the misindexing problem. © 2012 The Authors Journal of Microscopy © 2012 Royal Microscopical Society.

  2. On the Processing of Martensitic Steels in Continuous Galvanizing Lines: Part 1

    NASA Astrophysics Data System (ADS)

    Song, Taejin; Kwak, Jaihyun; de Cooman, B. C.

    2012-01-01

    Whereas low-carbon (<0.2 mass pct) martensitic grades can be produced easily in continuous annealing processing lines equipped with the required cooling capacity, the thermal cycles in continuous galvanizing lines make it difficult to produce hot-dip Zn or Zn-alloy coated high-strength martensitic grades. This is because of the tempering processes occurring during dipping of the strip in the liquid Zn bath and, in the case of galvannealed sheet steel, the short thermal treatment required to achieve the alloying between the Zn and the steel. These short additional thermal treatments last less than 30 seconds but severely degrade the mechanical properties. Using a combination of internal friction, X-ray diffraction, and transmission electron microscopy, it is shown that the ultrafine-grained lath microstructure allows for a rapid dislocation recovery and carbide formation during the galvanizing processes. In addition, the effective dislocation pinning occurring during the galvannealing process results in strain localization and the suppression of strain hardening.

  3. Effects of strain and strain-induced α'-martensite on passive films in AISI 304 austenitic stainless steel.

    PubMed

    Lv, Jinlong; Luo, Hongyun

    2014-01-01

    In this paper, the effects of strain and heat treatment on strain-induced α'-martensite of AISI 304 stainless steel tubes were measured by X-ray diffraction. Moreover, the effects of strain and content of α'-martensite on passivated property on the surface of the material in borate buffer solution were evaluated by electrochemical technique. The results showed that the volume fraction of α'-martensite increased gradually with the increase of tensile strain for as-received and solid solution samples. However, α'-martensite in as-received sample was more than that in the solid solution sample. The electrochemical impedance spectroscopy results showed that the solid solution treatment improved corrosion resistance of the steel, especially for samples with small strain. Moreover, acceptor densities were always higher than donor densities for as-received and solid solution samples. With the increase of strain, the increase tendency of acceptor density was more significant than that of donor density. We also found that the total density of the acceptor and donor almost increased linearly with the increase of α'-martensite. The present results indicated that the increased acceptor density might lead to the decreased corrosion resistance of the steel. © 2013.

  4. Characterization of friction stir welded joint of low nickel austenitic stainless steel and modified ferritic stainless steel

    NASA Astrophysics Data System (ADS)

    Mondal, Mounarik; Das, Hrishikesh; Ahn, Eun Yeong; Hong, Sung Tae; Kim, Moon-Jo; Han, Heung Nam; Pal, Tapan Kumar

    2017-09-01

    Friction stir welding (FSW) of dissimilar stainless steels, low nickel austenitic stainless steel and 409M ferritic stainless steel, is experimentally investigated. Process responses during FSW and the microstructures of the resultant dissimilar joints are evaluated. Material flow in the stir zone is investigated in detail by elemental mapping. Elemental mapping of the dissimilar joints clearly indicates that the material flow pattern during FSW depends on the process parameter combination. Dynamic recrystallization and recovery are also observed in the dissimilar joints. Among the two different stainless steels selected in the present study, the ferritic stainless steels shows more severe dynamic recrystallization, resulting in a very fine microstructure, probably due to the higher stacking fault energy.

  5. Effect of Long-Term Service on Microstructure and Mechanical Properties of Martensitic 9% Cr Steel

    NASA Astrophysics Data System (ADS)

    Golański, Grzegorz; Zielińska-Lipiec, Anna; Zieliński, Adam; Sroka, Marek

    2017-03-01

    The paper presents the results of research on the X10CrMoVNbN9-1 (T91) steel after long-term service. The material for testing was taken from a pipe section of a boiler superheater coil serviced for around 105,000 h at the temperature of 540 °C, at the pressure of 12.5 MPa. A quantitative analysis including the measurement of mean diameter of subgrains and precipitates as well as the density of dislocations of the examined steel was performed by means of TEM. The microscopic tests of T91 steel were complemented with the results of tests on mechanical properties which included also the short creep tests. After service, the investigated steel was characterized by a retained lath microstructure of tempered martensite with fine subgrain and quite large density of dislocations as well as numerous precipitates. In the microstructure, apart from the particles of M23C6 and MX (VX, NbC, V-wings), the precipitates of Laves phase and single particles of Z phase were revealed. It has been shown that the extent of degradation of the T91 steel microstructure was minor, which resulted from its low temperature of service. Performed tests of mechanical properties showed that these properties fulfilled the minimum requirements for this steel in the as-received condition. A favorable influence of fine precipitates of Laves phase on mechanical properties was observed. Moreover, an insignificant influence of single precipitates of Z phase on the creep resistance of the examined steel was stated.

  6. Role of Tungsten in the Tempered Martensite Embrittlement of a Modified 9 Pct Cr Steel

    NASA Astrophysics Data System (ADS)

    Fedoseeva, Alexandra; Dudova, Nadezhda; Kaibyshev, Rustam

    2017-03-01

    The effect of tempering on the mechanical properties and fracture behavior of two 3 pct Co-modified 9 pct Cr steels with 2 and 3 wt pct W was examined. Both steels were ductile in tension tests and tough under impact tests in high-temperature tempered conditions. At T ≤ 923 K (650 °C), the addition of 1 wt pct W led to low toughness and pronounced embrittlement. The 9Cr2W steel was tough after low-temperature tempering up to 723 K (450 °C). At 798 K (525 °C), the decomposition of retained austenite induced the formation of discontinuous and continuous films of M23C6 carbides along boundaries in the 9Cr2W and the 9Cr3W steels, respectively, which led to tempered martensite embrittlement (TME). In the 9Cr2W steel, the discontinuous boundary films played a role of crack initiation sites, and the absorption energy was 24 J cm-2. In the 9Cr3W steel, continuous films provided a fracture path along the boundaries of prior austenite grains (PAG) and interlath boundaries in addition that caused the drop of impact energy to 6 J cm-2. Tempering at 1023 K (750 °C) completely eliminated TME by spheroidization and the growth of M23C6 carbides, and both steels exhibited high values of adsorbed energy of ≥230 J cm-2. The addition of 1 wt pct W extended the temperature domain of TME up to 923 K (650 °C) through the formation of W segregations at boundaries that hindered the spheroidization of M23C6 carbides.

  7. Effect of Long-Term Service on Microstructure and Mechanical Properties of Martensitic 9% Cr Steel

    NASA Astrophysics Data System (ADS)

    Golański, Grzegorz; Zielińska-Lipiec, Anna; Zieliński, Adam; Sroka, Marek

    2017-02-01

    The paper presents the results of research on the X10CrMoVNbN9-1 (T91) steel after long-term service. The material for testing was taken from a pipe section of a boiler superheater coil serviced for around 105,000 h at the temperature of 540 °C, at the pressure of 12.5 MPa. A quantitative analysis including the measurement of mean diameter of subgrains and precipitates as well as the density of dislocations of the examined steel was performed by means of TEM. The microscopic tests of T91 steel were complemented with the results of tests on mechanical properties which included also the short creep tests. After service, the investigated steel was characterized by a retained lath microstructure of tempered martensite with fine subgrain and quite large density of dislocations as well as numerous precipitates. In the microstructure, apart from the particles of M23C6 and MX (VX, NbC, V-wings), the precipitates of Laves phase and single particles of Z phase were revealed. It has been shown that the extent of degradation of the T91 steel microstructure was minor, which resulted from its low temperature of service. Performed tests of mechanical properties showed that these properties fulfilled the minimum requirements for this steel in the as-received condition. A favorable influence of fine precipitates of Laves phase on mechanical properties was observed. Moreover, an insignificant influence of single precipitates of Z phase on the creep resistance of the examined steel was stated.

  8. Grain Refinement and Toughening of Low Carbon Low Alloy Martensitic Steel with Yield Strength 900 MPa Grade by Ausforming

    NASA Astrophysics Data System (ADS)

    Li, Zhaodong; Sun, Xinjun; Yang, Zhigang; Yong, Qilong

    Instead of off-line quenching and tempering (QT), on-line ausforming (non-recrystallization controlled roling) and direct quenching (DQ) was employed to improve the toughness of low alloy steel with yield strength of 900 MPa Grade. Low carbon content ensured a high level of upper shelf energy, while the fine-grained martensite substructures decreased the ductile-to-brittle transition temperature and compensated the strength loss due to carbon reduction. Two mechanisms for the refinement of martensite substructure were proposed: one was the austenite grain refinement in the thickness direction, and the other was the self-accommodation of martensite variants due to austenite grain hardening. More than 200 J of Charpy V-notch impact absorbed energy at 233 K was obtained in the industrial ausformed plate, which was about the double in the traditional QT steel with the same strength grade.

  9. Development of nano-structured duplex and ferritic stainless steels by pulverisette planetary milling followed by pressureless sintering

    SciTech Connect

    R, Shashanka Chaira, D.

    2015-01-15

    Nano-structured duplex and ferritic stainless steel powders are prepared by planetary milling of elemental Fe, Cr and Ni powder for 40 h and then consolidated by conventional pressureless sintering. The progress of milling and the continuous refinement of stainless steel powders have been confirmed by means of X-ray diffraction and scanning electron microscopy. Activation energy for the formation of duplex and ferritic stainless steels is calculated by Kissinger method using differential scanning calorimetry and is found to be 159.24 and 90.17 KJ/mol respectively. Both duplex and ferritic stainless steel powders are consolidated at 1000, 1200 and 1400 °C in argon atmosphere to study microstructure, density and hardness. Maximum sintered density of 90% and Vickers microhardness of 550 HV are achieved for duplex stainless steel sintered at 1400 °C for 1 h. Similarly, 92% sintered density and 263 HV microhardness are achieved for ferritic stainless steel sintered at 1400 °C. - Highlights: • Synthesized duplex and ferritic stainless steels by pulverisette planetary milling • Calculated activation energy for the formation of duplex and ferritic stainless steels • Studied the effect of sintering temperature on density, hardness and microstructure • Duplex stainless steel exhibits 90% sintered density and microhardness of 550 HV. • Ferritic stainless steel shows 92% sintered density and 263 HV microhardness.

  10. Interdiffusion Behavior of Al-Rich Oxidation Resistant Coatings on Ferritic-Martensitic Alloys

    SciTech Connect

    Velraj, S.; Zhang, Ying; Hawkins, W. E.; Pint, Bruce A.

    2012-06-21

    We investigated interdiffusion of thin Al-rich coatings synthesized by chemical vapor deposition (CVD) and pack cementation on 9Cr ferritic–martensitic alloys in the temperature range of 650–700°C. The compositional changes after long-term exposures in laboratory air and air + 10 vol% H2O were examined experimentally. Interdiffusion was modeled by a modified coating oxidation and substrate interdiffusion model (COSIM) program. The modification enabled the program to directly input the concentration profiles of the as-deposited coating determined by electron probe microanalysis (EPMA). Reasonable agreement was achieved between the simulated and experimental Al profiles after exposures. Moreover, the model was also applied to predict coating lifetime at 650–700°C based on a minimum Al content (Cb) required at the coating surface to re-form protective oxide scale. In addition to a Cb value established from the failure of a thin CVD coating at 700°C, values reported for slurry aluminide coatings were also included in lifetime predictions.

  11. High performance corrosion-resistant structural steels

    SciTech Connect

    Fletcher, F.B.; Ferry, B.N.; Beblo, D.G.

    1995-12-31

    A new corrosion-resistant structural steel named Duracorr was developed for low maintenance when compared to conventional structural steels. The new stainless steel is a dual phase composition between the established 12% Cr, ferritic T409 and martensitic T410 grades. Attractive combinations of hardness, strength, toughness, weldability and formability are derived from a microstructure that is a dual phase mixture of ferrite and martensite. The Duracorr composition, UNS S41003, provides for a microstructure of ferrite and austenite to be present throughout the hot rolling process. Cooling to room temperature causes transformation of the austenite to martensite. Subsequent tempering of the steel creates minimum mechanical properties of 275 MPa (40 ksi) yield strength and 455 MPa (66 ksi) tensile strength with room temperature longitudinal Charpy impact values typically greater than 34 J (25 ft-lbs).

  12. Cr segregation at the FeCr surface and the origin of corrosion resistance in ferritic steels

    SciTech Connect

    De Caro, M S; Morse, B; Egiebor, N; Farmer, J; Caro, A

    2008-11-22

    Structural materials in Gen-IV nuclear reactors will face severe conditions of high operating temperatures, high neutron flux exposure, and corrosive environment. Radiation effects and corrosion and chemical compatibility issues are factors that will limit the materials lifetime. Low-chromium (9-12 Cr wt.%) ferritic martensitic (F/M) steels are being considered as possible candidates because they offer good swelling resistance and good mechanical properties under extreme conditions of radiation dose and irradiation temperature. The surface chemistry of FeCr alloys, responsible for the corrosion properties, is complex. It exists today a controversy between equilibrium thermodynamic calculations, which suggest Cr depletion at the surface driven by the higher surface energy of Cr, and experimental data which suggest the oxidation process occurs in two stages, first forming a Fe-rich oxide, followed by a duplex oxide layer, and ending with a Cr-rich oxide. Moreover, it has been shown experimentally that corrosion resistance of F/M steels depends significantly on Cr content, increasing with increasing Cr content and with a threshold around 10% Cr, below which, the alloy behaves as pure Fe. In an attempt to rationalize these two contradicting observations and to understand the physical mechanism behind corrosion resistance in these materials we perform atomistic simulations using our FeCr empirical potential and analyze Cr equilibrium distributions at different compositions and temperatures in single and polycrystalline samples. We analyze the controversy in terms of thermodynamic and kinetic considerations.

  13. Influence of traps on the deuterium behaviour in the low activation martensitic steels F82H and Batman

    NASA Astrophysics Data System (ADS)

    Serra, E.; Perujo, A.; Benamati, G.

    1997-06-01

    A time dependent permeation method is used to measure the permeability, diffusivity and solubility of deuterium in the low activation martensitic steels F82H and Batman. The measurements cover the temperature range from 373 to 743 K which includes the onset of deuterium trapping effects on diffusivity and solubility. The results are interpreted using a trapping model. The number of trap sites and their average energies for deuterium in F82H and Batman steels are determined.

  14. Effect of microstructure on static and dynamic mechanical properties of high strength steels

    NASA Astrophysics Data System (ADS)

    Qu, Jinbo

    The high speed deformation behavior of a commercially available dual phase (DP) steel was studied by means of split Hopkinson bar apparatus in shear punch (25m/s) and tension (1000s-1) modes with an emphasis on the influence of microstructure. The cold rolled sheet material was subjected to a variety of heat treatment conditions to produce several different microstructures, namely ferrite plus pearlite, ferrite plus bainite and/or acicular ferrite, ferrite plus bainite and martensite, and ferrite plus different fractions of martensite. Static properties (0.01mm/s for shear punch and 0.001s -1 for tension) of all the microstructures were also measured by an MTS hydraulic machine and compared to the dynamic properties. The effects of low temperature tempering and bake hardening were investigated for some ferrite plus martensite microstructures. In addition, two other materials, composition designed as high strength low alloy (HSLA) steel and transformation induced plasticity (TRIP) steel, were heat treated and tested to study the effect of alloy chemistry on the microstructure and property relationship. A strong effect of microstructure on both static and dynamic properties and on the relationship between static and dynamic properties was observed. According to the variation of dynamic factor with static strength, three groups of microstructures with three distinct behaviors were identified, i.e. classic dual phase (ferrite plus less than 50% martensite), martensite-matrix dual phase (ferrite plus more than 50% martensite), and non-dual phase (ferrite plus non-martensite). Under the same static strength level, the dual phase microstructure was found to absorb more dynamic energy than other microstructures. It was also observed that the general dependence of microstructure on static and dynamic property relationship was not strongly influenced by chemical composition, except the ferrite plus martensite microstructures generated by the TRIP chemistry, which exhibited

  15. Effects of W on microstructure and high-temperature oxidation behavior of ferritic stainless steel weldment

    NASA Astrophysics Data System (ADS)

    Ji, Yijie; Xie, Yuye; Zhu, Shuangchun; Yan, Biao

    2017-07-01

    With the promotion of fuel economy policy and automobile lightweight concept, ferritic stainless steels applied in vehicles’ exhaust hot end systems have been developed. This paper simulated the high-temperature environment at which the automobile exhaust system serviced in for high-temperature corrosion. Kinetic curves were conducted in isothermal environments at 1000∘C. X-ray diffraction, scanning electron microscope and energy dispersive spectrometer were used to study the oxidation behavior of ferritic stainless steels and the effects of tungsten (W) addition. The results show that, with increasing oxidation time, the rate of weight gains increase and the main failure is spalling of surface oxide layer. The addition of W has a complicated effect on the oxidation behavior of ferritic stainless steel weldment.

  16. Low temperature embrittlement behaviour of different ferritic-martensitic alloys for fusion applications

    NASA Astrophysics Data System (ADS)

    Rieth, M.; Dafferner, B.

    1996-10-01

    In the last few years a lot of different low activation CrWVTa steels have been developed world-wide. Without irradiation some of these alloys show clearly a better low temperature embrittlement behaviour than commercial CrNiMoV(Nb) alloys. Within the MANITU project a study was carried out to compare, prior to the irradiation program, the embrittlement behaviour of different alloys in the unirradiated condition performing instrumented Charpy impact bending tests with sub-size specimens. The low activation materials (LAM) considered were different OPTIFER alloys (Forschungszentrum Karlsruhe), F82H (JAERI), 9Cr2WVTa (ORNL), and GA3X (PNL). The modified commercial 10-11% CrNiMoVNb steels were MANET and OPTIMAR. A meaningful comparison between these alloys could be drawn, since the specimens of all materials were manufactured and tested under the same conditions.

  17. Carbon concentration measurements by atom probe tomography in the ferritic phase of high-silicon steels

    SciTech Connect

    Rementeria, Rosalia; Poplawsky, Jonathan D.; Aranda, Maria M.; Guo, Wei; Jimenez, Jose A.; Garcia-Mateo, Carlos; Caballero, Francisca G.

    2016-12-19

    Current studies using atom probe tomography (APT) show that bainitic ferrite formed at low temperature contains more carbon than what is consistent with the paraequilibrium phase diagram. However, nanocrystalline bainitic ferrite exhibits a non-homogeneous distribution of carbon atoms in arrangements with specific compositions, i.e. Cottrell atmospheres, carbon clusters, and carbides, in most cases with a size of a few nanometers. The ferrite volume within a single platelet that is free of these carbon-enriched regions is extremely small. Proximity histograms can be compromised on the ferrite side, and a great deal of care should be taken to estimate the carbon content in regions of bainitic ferrite free from carbon agglomeration. For this purpose, APT measurements were first validated for the ferritic phase in a pearlitic sample and further performed for the bainitic ferrite matrix in high-silicon steels isothermally transformed between 200 °C and 350 °C. Additionally, results were compared with the carbon concentration values derived from X-ray diffraction (XRD) analyses considering a tetragonal lattice and previous APT studies. In conclusion, the present results reveal a strong disagreement between the carbon content values in the bainitic ferrite matrix as obtained by APT and those derived from XRD measurements. Those differences have been attributed to the development of carbon-clustered regions with an increased tetragonality in a carbon-depleted matrix.

  18. Carbon concentration measurements by atom probe tomography in the ferritic phase of high-silicon steels

    DOE PAGES

    Rementeria, Rosalia; Poplawsky, Jonathan D.; Aranda, Maria M.; ...

    2016-12-19

    Current studies using atom probe tomography (APT) show that bainitic ferrite formed at low temperature contains more carbon than what is consistent with the paraequilibrium phase diagram. However, nanocrystalline bainitic ferrite exhibits a non-homogeneous distribution of carbon atoms in arrangements with specific compositions, i.e. Cottrell atmospheres, carbon clusters, and carbides, in most cases with a size of a few nanometers. The ferrite volume within a single platelet that is free of these carbon-enriched regions is extremely small. Proximity histograms can be compromised on the ferrite side, and a great deal of care should be taken to estimate the carbon contentmore » in regions of bainitic ferrite free from carbon agglomeration. For this purpose, APT measurements were first validated for the ferritic phase in a pearlitic sample and further performed for the bainitic ferrite matrix in high-silicon steels isothermally transformed between 200 °C and 350 °C. Additionally, results were compared with the carbon concentration values derived from X-ray diffraction (XRD) analyses considering a tetragonal lattice and previous APT studies. In conclusion, the present results reveal a strong disagreement between the carbon content values in the bainitic ferrite matrix as obtained by APT and those derived from XRD measurements. Those differences have been attributed to the development of carbon-clustered regions with an increased tetragonality in a carbon-depleted matrix.« less

  19. Method for reducing formation of electrically resistive layer on ferritic stainless steels

    SciTech Connect

    Rakowski, James M.

    2013-09-10

    A method of reducing the formation of electrically resistive scale on a an article comprising a silicon-containing ferritic stainless subjected to oxidizing conditions in service includes, prior to placing the article in service, subjecting the article to conditions under which silica, which includes silicon derived from the steel, forms on a surface of the steel. Optionally, at least a portion of the silica is removed from the surface to placing the article in service. A ferritic stainless steel alloy having a reduced tendency to form silica on at least a surface thereof also is provided. The steel includes a near-surface region that has been depleted of silicon relative to a remainder of the steel.

  20. Method for reducing formation of electrically resistive layer on ferritic stainless steels

    DOEpatents

    Rakowski, James M.

    2017-02-28

    A method of reducing the formation of electrically resistive scale on a an article comprising a silicon-containing ferritic stainless subjected to oxidizing conditions in service includes, prior to placing the article in service, subjecting the article to conditions under which silica, which includes silicon derived from the steel, forms on a surface of the steel. Optionally, at least a portion of the silica is removed from the surface to placing the article in service. A ferritic stainless steel alloy having a reduced tendency to form silica on at least a surface thereof also is provided. The steel includes a near-surface region that has been depleted of silicon relative to a remainder of the steel.

  1. γ→α‧ Martensitic transformation and magnetic property of cold rolled Fe-20Mn-4Al-0.3C steel

    NASA Astrophysics Data System (ADS)

    Ma, Biao; Li, Changsheng; Han, Yahui; Wang, Jikai

    2016-12-01

    Direct γ→α‧ martensitic transformation during cold rolling deformation was investigated for a high-Mn non-magnetic steel. Its influence on magnetic property was also analyzed. The magnetization under rolling reduction less than 50% almost presents a linear increase with the applied magnetic field. With deformation up to 73% and 93% thickness reductions, strain induced α‧-martensite transformation starts to occur, causing the steel to be slightly magnetized. The α‧-martensite prefers to nucleate directly at either microband-microband or microband-twin intersections without participation of intermediate ε-martensite. The volume fraction of α‧-martensite is estimated as 0.070% and 0.17%, respectively, based on the magnetic hysteresis loops. Such a small fraction of ferromagnetic α‧-martensite shows little influence on the magnetic induction intensity and low relative permeability.

  2. High resolution studies in martensite

    SciTech Connect

    Sarikaya, M.; Easterling, K.; Thomas, G.

    1980-03-01

    Detailed microstructural studies were performed on the lath martensite in steels containing 0.1 and 0.3 wt %-low alloy structural steels by lattice imaging. This method is providing information on the fine substructural details of dislocated martensite.

  3. Characterization of the carbides and the martensite phase in powder-metallurgy high-speed steel

    SciTech Connect

    Godec, Matjaz; Batic, Barbara Setina; Mandrino, Djordje; Nagode, Ales; Leskovsek, Vojteh; Skapin, Sreco D.; Jenko, Monika

    2010-04-15

    A microstructural characterization of the powder-metallurgy high-speed-steel S390 Microclean was performed based on an elemental distribution of the carbide phase as well as crystallographic analyses. The results showed that there were two types of carbides present: vanadium-rich carbides, which were not chemically homogeneous and exhibited a tungsten-enriched or tungsten-depleted central area; and chemically homogeneous tungsten-rich M{sub 6}C-type carbides. Despite the possibility of chemical inhomogenities, the crystallographic orientation of each of the carbides was shown to be uniform. Using electron backscatter diffraction the vanadium-rich carbides were determined to be either cubic VC or hexagonal V{sub 6}C{sub 5}, while the tungsten-rich carbides were M{sub 6}C. The electron backscatter diffraction results were also verified using X-ray diffraction. Several electron backscatter diffraction pattern maps were acquired in order to define the fraction of each carbide phase as well as the amount of martensite phase. The fraction of martensite was estimated using band-contrast images, while the fraction of carbides was calculated using the crystallographic data.

  4. Formation Wear Resistant Coatings on Martensite Steel Hardox 450 by Welding Methods

    NASA Astrophysics Data System (ADS)

    Konovalov, S. V.; Kormyshev, V. E.; Nevskii, S. A.; Ivanov, Yu F.; Gromov, V. E.

    2016-08-01

    By methods of modern physical materials science the investigations analysis of phase composition, defect substructure, mechanical and tribological properties of Cr-Nb-C-V containing coatings formed in surfacing on martensitic wear resistant steel Hardox 450 were carried out. It was shown that surfacing resulted in the formation of high strength surface layer 6 mm in thinness. This layer had wear resistance 138 times greater than that of the base and friction coefficient 2.5 times less. Having analyzed the deflected mode of the deposited material in conditions of friction, a conclusion is drawn that plastic shear deformation is localized in the surface layer due to the high friction factor, as the result, scratches are formed. The maximum of tangential stress is deflected deep into the material provided that friction factor is low. On the basis of the investigations by methods of X-ray structural analysis and transmission diffraction electron microscopy it was shown that increase strength and tribological properties of surfacing metal were caused by its phase composition and state of defect substructure, namely, availability of interstitial phases (more than 36%) and martensitic type of a-phase structure.

  5. On the shape of the magnetic Barkhausen noise profile for better revelation of the effect of microstructures on the magnetisation process in ferritic steels

    NASA Astrophysics Data System (ADS)

    Vashista, M.; Moorthy, V.

    2015-11-01

    The shape of the Magnetic Barkhausen Noise (MBN) profiles has been compared for two different methods of MBN measurements in order to reveal the true extent of the influence of different carbon-content related microstructures on the magnetisation process. The MBN profiles were measured using high frequency and low frequency MBN measurement systems on samples from low carbon 18CrNiMo5 steel and high carbon 42CrMo4 steel heat treated by isothermal annealing, spheroidising annealing and quenching and tempering processes. The high frequency MBN (HFMBN) profile shows only a single peak for all the samples due to insufficient applied magnetic field strength and shallow skin-depth of detection of HFMBN signals. The low frequency MBN (LFMBN) profile shows two peaks for all the samples due to larger magnetisation range revealing the difference in the interaction of domain walls with different microstructural features such as ferrite, pearlite, martensite and carbides. The shape of the LFMBN profile shows systematic and distinct variation in the magnetisation process with respect to carbon content and different microstructures. This study shows that the LFMBN profile reveals distinct changes in shape which could be successfully used for characterisation of different microstructural phases in ferritic steels.

  6. Fracture toughness master-curve analysis of the tempered martensitic steel Eurofer97

    NASA Astrophysics Data System (ADS)

    Mueller, Pablo; Spätig, P.; Bonadé, R.; Odette, G. R.; Gragg, D.

    2009-04-01

    We report fracture toughness data for the reduced activation tempered martensitic steel Eurofer97 in the lower to middle transition region. The fracture toughness was measured from tests carried out on 0.35 T and 0.87 T pre-cracked compact tension specimens. The data were first analyzed using the ASTM E1921 standard. The toughness-temperature behavior and scatter were shown to deviate from the ASTM E1921 standard predictions near the lower shelf. Using the method of maximum likelihood, the athermal component of the master-curve was calculated to better fit the data from the lower to the middle transition region. We showed that these master-curve adjustments are necessary to make the To values obtained near the lower shelf with 0.35 TC( T) specimens consistent with those obtained in the middle transition region with 0.87 TC( T) specimens.

  7. Effects of vanadium carbides on hydrogen embrittlement of tempered martensitic steel

    NASA Astrophysics Data System (ADS)

    Lee, Junmo; Lee, Taekyung; Kwon, Young Jin; Mun, Dong-Jun; Yoo, Jang-Yong; Lee, Chong Soo

    2016-05-01

    Precipitation of V carbides is known to suppress the hydrogen-embrittlement (HE) phenomenon as well as to increase material strength. Despite increasing attention to V carbides, there have been few systematic and quantitative investigations on their effects on HE resistance. This study reveals the role of V carbides on the HE behavior of tempered martensitic steel while eliminating other factors, such as chemical composition of other elements, mechanical strength, and dislocation density. The amount of trapped hydrogen increased with increasing V content, whereas the best HE resistance was attained at 0.2 wt% V and it decreased with further V addition. V carbide was considered as a non-diffusible hydrogen-trapping site in this study. However, excessive V content led to the formation of large undissolved carbides that gave rise to brittle fracture and decreased HE resistance. This study suggests that improved HE resistance can be achieved by minimizing the size and amount of undissolved V carbides.

  8. Process improvement in laser hot wire cladding for martensitic stainless steel based on the Taguchi method

    NASA Astrophysics Data System (ADS)

    Huang, Zilin; Wang, Gang; Wei, Shaopeng; Li, Changhong; Rong, Yiming

    2016-09-01

    Laser hot wire cladding, with the prominent features of low heat input, high energy efficiency, and high precision, is widely used for remanufacturing metal parts. The cladding process, however, needs to be improved by using a quantitative method. In this work, volumetric defect ratio was proposed as the criterion to describe the integrity of forming quality for cladding layers. Laser deposition experiments with FV520B, one of martensitic stainless steels, were designed by using the Taguchi method. Four process variables, namely, laser power ( P), scanning speed ( V s), wire feed rate ( V f), and wire current ( I), were optimized based on the analysis of signal-to-noise (S/N) ratio. Metallurgic observation of cladding layer was conducted to compare the forming quality and to validate the analysis method. A stable and continuous process with the optimum parameter combination produced uniform microstructure with minimal defects and cracks, which resulted in a good metallurgical bonding interface.

  9. Corrosion behaviour of aluminized martensitic and austenitic steels in liquid Pb-Bi

    NASA Astrophysics Data System (ADS)

    Deloffre, Ph.; Balbaud-Célérier, F.; Terlain, A.

    2004-11-01

    The Pb-Bi liquid alloy is under consideration as a spallation target material in the hybrid systems due to its suitable nuclear and physical properties. In order to limit the risks of corrosion of the structural elements in contact with the liquid Pb-Bi, protection by means of aluminized coatings was investigated for 316L austenitic steel and T91 martensitic steel. For both steels, no damages were observed after immersions in static Pb-Bi up to 500 °C for low oxygen concentrations and long durations. However, at 600 °C in the same conditions, a non-uniform degradation of the coatings was observed. Only coated 316L was tested in dynamic conditions. The results were generally satisfying for temperatures from 350 to 600 °C and for fluid velocities up to 2.3 m s -1. However, in both the IPPE loops and the CICLAD device, some localized damage of the coatings, attributed to erosion, was observed.

  10. Thermal Stability Study of Ultrafine Grained 304L Stainless Steel Produced by Martensitic Process

    NASA Astrophysics Data System (ADS)

    Sabooni, S.; Karimzadeh, F.; Enayati, M. H.

    2014-05-01

    An ultrafine grain 304L stainless steel with average grain size of about 650 nm was produced by martensitic process. 10 mm as-received sheets were 80% cold rolled in the temperature of -15 °C and then annealed at 700 °C for 300 min to obtain ultrafine grained microstructure. The results showed that the ultrafine grained 304L steel has yield strength of 720 MPa, tensile strength of about 920 MPa, and total elongation of 47% which is about twice that of coarse grain structure. The effect of annealing temperature (750-900 °C) on the grain growth kinetics was modeled by isothermal kinetics equation which resulted in the grain growth exponent ( n) and activation energy for grain growth of 4.8 and 455 KJ/mol, respectively. This activation energy was also compared with those for other austenitic steels to better understanding of the nature of grain growth and atoms mobility during annealing. It was found that activation energy for grain growth is about twice higher than self-diffusion activation energy of austenite that is related to the Zener pinning effects of the second phase particles.

  11. Effect of the strain rate on the mechanical properties of a sheet TRIP steel with a high martensite content

    NASA Astrophysics Data System (ADS)

    Eliseev, E. A.; Terent'ev, V. F.; Voznesenskaya, N. M.; Slizov, A. K.; Sirotinkin, V. P.; Baikin, A. S.; Seval'nev, G. S.

    2017-04-01

    The laws of changing the mechanical properties of sheet austenitic-martensitic VNS9-Sh (23Kh15N5AM3-Sh) TRIP steel are studied when the static strain rate changes in the range 0.1-20 mm/min (8.3 × 10-5-17 × 10-3 s-1). The 0.35-mm strip under study is characterized by a high martensite content (≈100%) in the surface layer at an average content of 80-85%. The transformation induced plasticity effect is maximal at a strain rate of 0.1 mm/min (8.3 × 10-5 s-1).

  12. 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.

  13. Radial Distribution of Martensitic Phase Transformation in a Metastable Stainless Steel under Torsional Deformation: A Synchrotron X-ray Diffraction Study

    SciTech Connect

    Cakmak, Ercan; Choo, Hahn; An, Ke; Ren, Yang

    2011-01-01

    The strain-induced martensitic phase transformation in a metastable 304 L stainless steel under torsional deformation was investigated using synchrotron X-ray diffraction. The measured radial distribution of the martensite phase fraction in a solid cylindrical specimen agrees well with the prediction based on a combination of transformation kinetics and a radial plastic strain distribution equation.

  14. Microstructure and Mechanical Properties of High Copper HSLA-100 Steel in 2-inch Plate Form

    DTIC Science & Technology

    1992-06-01

    solution strengthening was caused by dissolved carbon in the bainite ferrite. It was shown by experimental evidence that a residual super -saturation of...quenched plate indicated that the microstructure was a mixture of lath martensite/fretained austenite and bainitic ferrite, which is typical of these... bainitic ferrite, which is typical of these steels. On aging this microstructure developed the tempered structures usually encountered in HSLA steels. This

  15. Strength of "Light" Ferritic and Austenitic Steels Based on the Fe - Mn - Al - C System

    NASA Astrophysics Data System (ADS)

    Kaputkina, L. M.; Svyazhin, A. G.; Smarygina, I. V.; Kindop, V. E.

    2017-01-01

    The phase composition, the hardness, the mechanical properties at room temperature, and the resistance to hot (950 - 1000°C) and warm (550°C) deformation are studied for cast deformable "light" ferritic and austenitic steels of the Fe - (12 - 25)% Mn - (0 - 15)% Al - (0 - 2)% C system alloyed additionally with about 5% Ni. The high-aluminum high-manganese low-carbon and carbonless ferritic steels at a temperature of about 0.5 T melt have a specific strength close to that of the austenitic steels and may be used as weldable scale-resistant and wear-resistant materials. The high-carbon Fe - (20 - 24)% Mn - (5 - 9)% Al - 5% Ni - 1.5% C austenitic steels may be applied as light high-strength materials operating at cryogenic temperatures after a solution treatment and as scale- and heat-resistant materials in an aged condition.

  16. Effect of N on Phase Transformations During Martensite Thermomechanical Processing of the Nano/Ultrafine-Grained 201L Steel

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    Effect of N addition on microstructural evolutions and mechanical properties of a 201L austenitic stainless steel during the martensite thermomechanical treatment was investigated. The as-homogenized samples were cold-rolled by 90% thickness reduction followed by reversion annealing at 800-900 °C for different times of 15-1800 s. The microstructures were characterized by optical and scanning electron microscopy and magnetic measurement, while mechanical properties were determined by hardness and shear punch tests. It was found that N addition retards the kinetics of strain-induced martensitic transformation, but accelerates the martensite reversion. The hardness, yield and ultimate shear strengths were increased by N alloying at the expense of elongation in both solution-annealed and reversion-annealed specimens.

  17. In Situ Observation of Phase Transformation and Structure Evolution of a 12 pct Cr Ferritic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Song, Changjiang; Guo, Yuanyi; Li, Kefeng; Sun, Fengmei; Han, Qingyou; Zhai, Qijie

    2012-10-01

    This work focuses on an in situ observation of phase transformation of a 12 pct Cr ferritic stainless steel using high-temperature laser scanning confocal microscopy. α→ γ→ δ phase transformation temperatures are determined to be approximately 1073 K and 1423 K (800 °C and 1150 °C), respectively. The onset of phase transformation is found to occur at grain boundaries. When the temperature is beyond 1518 K (1245 °C), the grain growth rate suddenly becomes very high, and the grain growth is related to the self-organizing of adjacent grains. δ→ γ phase transformation has been mostly restrained when cooling rates are in the range of 22.4 K/s to 13.3 K/s (22.4 °C/s to 13.3 °C/s) except for at grain boundaries. Martensitic phase transformation, rather than γ→ α phase transformation, occurs when the cooling rates are in the range of 8.5 K/s to 2.2 K/s (8.5 °C/s to 2.2 °C/s). The starting temperature of martensitic phase transformation is approximately 697 K to 728 K (424 °C to 455 °C) for specimens heated to 1373 K (1100 °C) ( i.e., γ phase field), which is 50 K to 100 K (50 °C to 100 °C) higher than that of specimens heated to 1723 K (1450 °C) ( i.e., δ phase field). Many bulges remain on the surfaces of the specimen heated to 1723 K (1450 °C), and their formation mechanism is analyzed.

  18. Precipitates and Particles Coarsening of 9Cr-1.7W-0.4Mo-Co Ferritic Heat-Resistant Steel after Isothermal Aging.

    PubMed

    Gao, Qiuzhi; Zhang, Yanan; Zhang, Hailian; Li, Huijun; Qu, Fu; Han, Jian; Lu, Cheng; Wu, Bintao; Lu, Yao; Ma, Yan

    2017-07-19

    The precipitates obtained by EPE technology from the 9Cr-1.7W-0.4Mo-Co ferritic heat-resistant steel subject to isothermal aging were investigated using SEM, TEM and XRD. The particle size distribution and the coarsening kinetics of M23C6 with duration of isothermal aging were also analyzed with or without consideration of Laves phase. The results show that the isolated dislocations were detected in delta ferrite interior, and the precipitates on delta ferrite and martensite boundaries are obviously larger than other locations. Fe2W-Laves phase can only be found as duration of aging time to 2000 h, and is preferential to form adjacent to M23C6 particles. The small M23C6 particles firstly coarsen, but the large M23C6 are relatively stable during short aging. The total coarsening rate of M23C6 precipitates is 9.75 × 10(-28)m(3)s(-1), and the coarsening of M23C6 depends on the formation of Laves phase.

  19. Z phase precipitation in martensitic 12CrMoVNb steels

    NASA Astrophysics Data System (ADS)

    Vodarek, V.; Strang, A.

    2003-10-01

    Precipitation of Z phase contributes significantly to degradation of creep properties of 12CrMoVNb steels because its precipitation is accompanied by dissolution offinely dispersed nitrides and carbonitrides of M2X and/or MX type. The orientation relationship between Z phase and the ferritic matrix was determined as: (001)_z// (001)_{α}, [010]_z // [010]_{α}. Prolonged thcrmal/creep exposure is accompanied by recrystallisation of the matrix and this orientation relationship is destroyed. Nevertheless Z phase particles preserve the form of thin plates. Z phase is a nitride which is rich in vanadium, niobium and chromium and its composition depends on both the temperature of precipitation and the initial chemical composition of steels. The composition of Z phase does not change during long term exposure at the original precipitation temperature. A relationship between the composition of Z phase and its temperature of formation may be able to be used as a temperature exposure indicator of steels. However it is also necessary to know the Z phase composition for a given cast of material.

  20. Effects of helium on ductile-brittle transition behavior of reduced-activation ferritic steels after high-concentration helium implantation at high temperature

    NASA Astrophysics Data System (ADS)

    Hasegawa, A.; Ejiri, M.; Nogami, S.; Ishiga, M.; Kasada, R.; Kimura, A.; Abe, K.; Jitsukawa, S.

    2009-04-01

    The effects of He on the fracture behavior of reduced-activation ferritic/martensitic steels, including oxide dispersion-strengthened (ODS) steels and F82H, was determined by characterizing the microstructural evolution in and fracture behavior of these steels after He implantation up to 1000 appm at around 550 °C. He implantation was carried out by a cyclotron with a beam of 50 MeV α-particles. In the case of F82H, the ductile-to-brittle transition temperature (DBTT) increase induced by He implantation was about 70 °C and the grain boundary fracture surface was only observed in the He-implanted area of all the ruptured specimens in brittle manner. By contrast, no DBTT shift or fracture mode change was observed in He-implanted 9Cr-ODS and 14Cr-ODS steels. Microstructural characterization suggested that the difference in the bubble formation behavior of F82H and ODS steels might be attributed to the grain boundary rupture of He-implanted F82H.

  1. Application of electron backscatter diffraction techniques to quenched and partitioned steels.

    PubMed

    Thomas, Grant; Speer, John; Matlock, David; Michael, Joseph

    2011-06-01

    Electron backscatter diffraction (EBSD) techniques were used to characterize "hot-rolled" quenched and partitioned microstructures produced via Gleeble thermal simulations representing a hot-strip cooling practice for steel. In particular, EBSD was utilized to positively identify the morphology and location of retained austenite, to qualitatively distinguish martensite from ferrite, and in an attempt to identify transition carbides. Large pools of retained austenite and some thin films were accurately indexed; however, there was some disparity between austenite volume fractions measured by EBSD and those measured by X-ray diffraction. Due to similarities between the crystal structures of martensite and ferrite (body centered tetragonal versus body centered cubic, respectively), martensite could not be distinguished from ferrite by indexing of diffraction patterns; however, martensite could qualitatively be distinguished from ferrite by regions of low image quality based on the very high dislocation density of martensite.

  2. Electron backscattered diffraction study of ɛ/α' martensitic variants induced by plastic deformation in 304 stainless steel

    NASA Astrophysics Data System (ADS)

    Gey, N.; Petit, B.; Humbert, M.

    2005-12-01

    The electron backscattered diffraction (EBSD) technique has been used to assess crystallographic features of the residual γ phase and the strain-induced ɛ/α' martensites in a 304 stainless steel, tensile tested to 10 pct strain at T=-60 °C. The martensitic transformation rate varies according to the γ-grain orientation against the applied stress and the γ-grain size. The α'-transformation textures as well as the γ-misorientation spreads observed in specific γ-grain orientations have been analyzed. Large misorientation spreads are observed in the less-transformed γ grains. This reveals an important crystallographic slip activity, even if less strain-induced martensite has been formed. A strong γ → α' variant selection was detected in the cube- and Goss-oriented γ grains for which the transformation is less developed. For the {110} <1-11> and copper-oriented γ grains, the amount of α' martensite is significantly higher and the γ → α' variant selection is less pronounced. This variant selection is then analyzed on at a local scale and is related to the presence of {111} γ localized deformation bands on which further ɛ/α' martensites have nucleated.

  3. A comparison of dilatometry and in-situ neutron diffraction in tracking bulk phase transformations in a martensitic stainless steel

    SciTech Connect

    Christien, F.; Telling, M.T.F.; Knight, K.S.

    2013-08-15

    Phase transformations in the 17-4PH martensitic stainless steel have been studied using different in-situ techniques, including dilatometry and high resolution neutron diffraction. Neutron diffraction patterns were quantitatively processed using the Rietveld refinement method, allowing the determination of the temperature-dependence of martensite (α′, bcc) and austenite (γ, fcc) phase fractions and lattice parameters on heating to 1000 °C and then cooling to room temperature. It is demonstrated in this work that dilatometry doesn't permit an accurate determination of the end temperature (Ac3) of the α′ → γ transformation which occurs upon heating to high temperature. The analysis of neutron diffraction data has shown that the respective volumes of the two phases become very close to each other at high temperature, thus making the dilatometric technique almost insensitive in that temperature range. However, there is a very good agreement between neutron diffraction and dilatometry at lower temperature. The martensitic transformation occurring upon cooling has been analysed using the Koistinen–Marburger equation. The thermal expansion coefficients of the two phases have been determined in addition. A comparison of the results obtained in this work with data from literature is presented. - Highlights: • Martensite is still present at very high temperature (> 930 °C) upon heating. • The end of austenitisation cannot be accurately monitored by dilatometry. • The martensite and austenite volumes become similar at high temperature (> ∼ 850 °C)

  4. Phase transformation and long-term service of high-temperature martensitic chromium steels

    NASA Astrophysics Data System (ADS)

    Kalashnikov, I. S.; Tarasenko, L.; Acselrad, O.; Pereira, L. C.; Shalkevich, A.; Soboleva, G.

    2000-02-01

    Martensitic high Cr (10 - 16%) steels alloyed with Ni (Co), Mo, W, V, and N are widely used in constructions subjected to cyclic loads at temperatures up to 600 degrees Celsius, in general after quenching from 1100 - 1150 degrees Celsius followed by tempering at 650 - 690 degrees Celsius. Due to long term service exposure at high temperatures, different microstructural changes take place, such as second-phases precipitation, formation of low-angle grain boundaries, as well as internal damage caused by cyclic loads and creep. Specific phase diagrams are presented that can be used to define time periods for reliable operation of parts with given composition, based on the time required for the appearance of second phase particles known to be detrimental to mechanical strength and performance. Restoring thermal treatments to be applied after long time exposure at service conditions, aiming at increasing service life, are also presented and discussed. The combined use of the diagrams and the restoring treatment ensures prediction of a reliable service-life period for components made of these steels.

  5. Phase transformation and long-term service of high-temperature martensitic chromium steels

    NASA Astrophysics Data System (ADS)

    Kalashnikov, I. S.; Tarasenko, L.; Acselrad, O.; Pereira, L. C.; Shalkevich, A.; Soboleva, G.

    2001-02-01

    Martensitic high Cr (10 - 16%) steels alloyed with Ni (Co), Mo, W, V, and N are widely used in constructions subjected to cyclic loads at temperatures up to 600 degrees Celsius, in general after quenching from 1100 - 1150 degrees Celsius followed by tempering at 650 - 690 degrees Celsius. Due to long term service exposure at high temperatures, different microstructural changes take place, such as second-phases precipitation, formation of low-angle grain boundaries, as well as internal damage caused by cyclic loads and creep. Specific phase diagrams are presented that can be used to define time periods for reliable operation of parts with given composition, based on the time required for the appearance of second phase particles known to be detrimental to mechanical strength and performance. Restoring thermal treatments to be applied after long time exposure at service conditions, aiming at increasing service life, are also presented and discussed. The combined use of the diagrams and the restoring treatment ensures prediction of a reliable service-life period for components made of these steels.

  6. Dependence of Microelastic-plastic Nonlinearity of Martensitic Stainless Steel on Fatigue Damage Accumulation

    NASA Technical Reports Server (NTRS)

    Cantrell, John H.

    2006-01-01

    Self-organized substructural arrangements of dislocations formed in wavy slip metals during cyclic stress-induced fatigue produce substantial changes in the material microelastic-plastic nonlinearity, a quantitative measure of which is the nonlinearity parameter Beta extracted from acoustic harmonic generation measurements. The contributions to Beta from the substructural evolution of dislocations and crack growth for fatigued martensitic 410Cb stainless steel are calculated from the Cantrell model as a function of percent full fatigue life to fracture. A wave interaction factor f(sub WI) is introduced into the model to account experimentally for the relative volume of material fatigue damage included in the volume of material swept out by an interrogating acoustic wave. For cyclic stress-controlled loading at 551 MPa and f(sub WI) = 0.013 the model predicts a monotonic increase in Beta from dislocation substructures of almost 100 percent from the virgin state to roughly 95 percent full life. Negligible contributions from cracks are predicted in this range of fatigue life. However, over the last five percent of fatigue life the model predicts a rapid monotonic increase of Beta by several thousand percent that is dominated by crack growth. The theoretical predictions are in good agreement with experimental measurements of 410Cb stainless steel samples fatigued in uniaxial, stress-controlled cyclic loading at 551 MPa from zero to full tensile load with a measured f(sub WI) of 0.013.

  7. Effect of electroslag remelting on carbides in 8Cr13MoV martensitic stainless steel

    NASA Astrophysics Data System (ADS)

    Zhu, Qin-tian; Li, Jing; Shi, Cheng-bin; Yu, Wen-tao

    2015-11-01

    The effect of electroslag remelting (ESR) on carbides in 8Cr13MoV martensitic stainless steel was experimentally studied. Phases precipitated from liquid steel during solidification were calculated using the Thermo-Calc software. The carbon segregation was analyzed by original position analysis (OPA), and the carbides were analyzed by optical microscopy (OM), scanning electron microscopy (SEM), energy- dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The results indicated that more uniform carbon distribution and less segregation were obtained in the case of samples subjected to the ESR process. After ESR, the amount of netty carbides decreased significantly, and the chromium and vanadium contents in the grain-boundary carbides was reduced. The total area and average size of carbides were obviously smaller after the ESR process. In the sample subjected to ESR, the morphology of carbides changed from lamellar and angular to globular or lump, whereas the types of carbides did not change; both M23C6 and M7C3 were present before and after the ESR process.

  8. Hot Deformation Behavior of 1Cr12Ni3Mo2VN Martensitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    He, Xiaomao; Jiang, Peng; Zhou, Leyu; Chen, Chao; Deng, Xiaochun

    2017-08-01

    1Cr12Ni3Mo2VN is a new type of martensitic stainless steel for the last-stage blades of large-capacity nuclear and thermal power turbines. The deformation behavior of this steel was studied by thermal compression experiments that performed on a Gleeble-3500 thermal simulator at a temperature range of 850°C to 1200°C and a strain rate of 0.01s-1 to 20s-1. When the deformation was performed at high temperature and low strain rate, a necklace type of microstructures was observed, the plastic deformation mechanism is grain boundary slip and migration, when at low temperature and lower strain rate, the slip bands were observed, the mechanism is intracrystalline slips, and when at strain rate of 20s-1, twins were observed, the mechanism are slips and twins. The Arrhenius equation was applied to describe the constitutive equation of the flow stress. The accuracy of the equation was verified by using the experimental data and the correlation coefficient R2 = 0.9786, and the equation can provide reasonable data for the design and numerical simulation of the forging process.

  9. Static Recrystallization Behavior of Z12CN13 Martensite Stainless Steel

    NASA Astrophysics Data System (ADS)

    Luo, Min; Zhou, Bing; Li, Rong-bin; Xu, Chun; Guo, Yan-hui

    2017-08-01

    In order to increase the hot workability and provide proper hot forming parameters of forging Z12CN13 martensite stainless steel for the simulation and production, the static recrystallization behavior has been studied by double-pass hot compression tests. The effects of deformation temperature, strain rate and inter-pass time on the static recrystallization fraction by the 2% offset method are extensively studied. The results indicate that increasing the inter-pass time and the deformation temperature as well as strain rate appropriately can increase the fraction of static recrystallization. At the temperature of 1050-1150 °C, inter-pass time of 30-100 s and strain rate of 0.1-5 s-1, the static recrystallization behavior is obvious. In addition, the kinetics of static recrystallization behavior of Z12CN13 steel has been established and the activation energy of static recrystallization is 173.030 kJ/mol. The substructure and precipitates have been studied by TEM. The results reveal that the nucleation mode is bulging at grain boundary. Undissolved precipitates such as MoNi3 and Fe3C have a retarding effect on the recrystallization kinetics. The effect is weaker than the accelerating effect of deformation temperature.

  10. Distribution of C Cr associates and mechanical stability of Cr martensitic steels

    NASA Astrophysics Data System (ADS)

    Gondi, P.; Montanari, R.; Tata, M. E.

    1998-10-01

    Structural and mechanical stability of two martensitic steels with different Cr content (MANET and modified F82H) has been studied by means of internal friction (IF) and dynamic modulus ( Md) measurements, X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) observations with EDS microanalysis and mechanical tests (hardness, Charpy). Following thermal treatments at 700°C, MANET samples cooled from the austenitic field at a rate of 150°C/min, exhibit Cr segregation both inside the grains and in the zones near grain boundaries. The Cr segregation induces internal stresses, which influence the mechanical properties, in particular the fracture mode, ductile-brittle transition temperature (DBTT) and upper shelf energy (USE). The material is not stable: DBTT changes depending on the time of the treatment and after 20 h at 700°C a mixed fracture mode (quasi-cleavage plus intercrystalline) is observed. Cr segregation is very weak in modified F82H steel submitted to the same treatments and a greater mechanical stability has been observed. The different behaviour of MANET and modified F82H is discussed on the basis of IF and Md results, which show that the stability of the distribution of C-Cr associates in as-quenched materials is a factor of great importance to avoid the Cr segregation.

  11. Stress-induced martensitic transformation and impact toughness of cast irons and high-carbon Fe-Ni-C steel

    NASA Astrophysics Data System (ADS)

    Zhang, M.-X.; Kelly, P. M.

    2001-11-01

    The relationship between the impact toughness and stress-induced martensitic transformation, which occurs during the impact process, has been studied in white cast irons and an Fe-Ni-C alloy at different temperatures. The experimental results have shown that in the brittle white cast irons, the stress-induced martensitic transformation makes a positive contribution to the impact toughness, and lowering the stability of austenite increases the toughness. In contrast, the transformation makes a negative contribution to the toughness of high-carbon austenitic steels, and lowering the stability of austenite decreases the toughness. The present work supports the early theory[1] that the magnitude of the toughness change depends on the fracture properties of the new phase and the energy being dissipated during the transformation process. Using the crystallographic model for the stress-induced martensitic transformation, which was originally developed in ceramics and was then refined and extended to irons and steels, the effect of the stress-induced martensitic transformation on the impact toughness can be predicted.

  12. Role of Different Kinds of Boundaries Against Cleavage Crack Propagation in Low-Temperature Embrittlement of Low-Carbon Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Tsuboi, Mizuki; Shibata, Akinobu; Terada, Daisuke; Tsuji, Nobuhiro

    2017-07-01

    The present paper investigated the relationship between low-temperature embrittlement and microstructure of lath martensite in a low-carbon steel from both microstructural and crystallographic points of view. The fracture surface of the specimen after the miniaturized Charpy impact test at 98 K (-175 °C) mainly consisted of cleavage fracture facets parallel to crystallographic {001} planes of martensite. Through the crystallographic orientation analysis of micro-crack propagation, we found that the boundaries which separated different martensite variants having large misorientation angles of {001} cleavage planes could inhibit crack propagation. It was then concluded that the size of the aggregations of martensite variants belonging to the same Bain deformation group could control the low-temperature embrittlement of martensitic steels.

  13. Effects of mechanical force on grain structures of friction stir welded oxide dispersion strengthened ferritic steel

    NASA Astrophysics Data System (ADS)

    Han, Wentuo; Kimura, Akihiko; Tsuda, Naoto; Serizawa, Hisashi; Chen, Dongsheng; Je, Hwanil; Fujii, Hidetoshi; Ha, Yoosung; Morisada, Yoshiaki; Noto, Hiroyuki

    2014-12-01

    The weldability of oxide dispersion strengthened (ODS) ferritic steels is a critical obstructive in the development and use of these steels. Friction stir welding has been considered to be a promising way to solve this problem. The main purpose of this work was to reveal the effects of mechanical force on grain structures of friction stir welded ODS ferritic steel. The grain appearances and the misorientation angles of grain boundaries in different welded zones were investigated by the electron backscatter diffraction (EBSD). Results showed that the mechanical force imposed by the stir tool can activate and promote the recrystallization characterized by the transformation of boundaries from LABs to HABs, and contribute to the grain refinement. The type of recrystallization in the stir zone can be classified as the continuous dynamic recrystallization (CDRX).

  14. Evolution of microstructure and residual stress during annealing of austenitic and ferritic steels

    SciTech Connect

    Wawszczak, R.; Baczmański, A.; Marciszko, M.; Wróbel, M.; Czeppe, T.; Sztwiertnia, K.; Braham, C.; Berent, K.

    2016-02-15

    In this work the recovery and recrystallization processes occurring in ferritic and austenitic steels were studied. To determine the evolution of residual stresses during material annealing the nonlinear sin{sup 2}ψ diffraction method was used and an important relaxation of the macrostresses as well as the microstresses was found in the cold rolled samples subjected to heat treatment. Such relaxation occurs at the beginning of recovery, when any changes of microstructure cannot be detected using other experimental techniques. Stress evolution in the annealed steel samples was correlated with the progress of recovery process, which significantly depends on the value of stacking fault energy. - Highlights: • X-ray diffraction was used to determine the first order and second order stresses. • Diffraction data were analyzed using scale transition elastoplastic models model. • Stress relaxation in annealed ferritic and austenitic steels was correlated with evolution of microstructure. • Influence of stacking fault energy on thermally induced processes was discussed.

  15. 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.

  16. Atom probe tomography investigation of assisted precipitation of secondary hardening carbides in a medium carbon martensitic steels.

    PubMed

    Danoix, F; Danoix, R; Akre, J; Grellier, A; Delagnes, D

    2011-12-01

    A medium carbon martensitic steel containing nanometer scale secondary hardening carbides and intermetallic particles is investigated by field ion microscopy and atom probe tomography. The interaction between the concomitant precipitations of both types of particles is investigated. It is shown that the presence of the intermetallic phase affects the nucleation mechanism and the spatial distribution of the secondary hardening carbides, which shifts from heterogeneous on dislocations to heterogeneous on the intermetallic particles.

  17. Decomposition Kinetics of Ferrite in Isothermally Aged SAF 2507-Type Duplex Stainless Steel

    NASA Astrophysics Data System (ADS)

    Berecz, Tibor; Fazakas, Éva; Mészáros, István; Sajó, István

    2015-12-01

    Decomposition of the ferritic phase is studied in isothermally aged SAF 2507 superduplex stainless steel (SDSS) by means of different examination methods. The ferritic phase ( δ) undergoes an eutectoid transformation into secondary austenite ( γ 2) and σ-phase between 650 and 1000 °C. Samples were treated at 900 °C because the incubation time of this transformation is the shortest at this temperature. In order to follow the microstructural changes, x-ray diffraction analysis (XRD), automated electron backscatter diffraction (EBSD), applied magnetic investigation [vibrating sample magnetometer (VSM)], micro-hardness tests, and differential thermal analysis (DTA) were used. The results of XRD and EBSD methods for phase quantification showed nearly the same amounts for all three phases. The results of applied magnetic investigation for the fraction of ferritic phase were also in good agreement with the corresponding results of XRD and EBSD methods. Decomposition of ferrite is similarly well-traceable on EBSD phase maps where the coherent ferritic areas gradually broke into pieces with increasing time of heat treatment. According to the EBSD measurements the σ-phase grains appeared and started to grow after 2 min aging time in the ferritic-austenitic matrix, usually on the boundaries of ferritic and austenitic grains. After 15 min treating time, the microstructure consisted of mainly σ- and austenitic (primary and secondary) phases with negligible amount of ferrite. Chemical composition of the σ-phase was measured by energy-dispersive x-ray spectroscopy (EDS) at different aging times. Activation energies of σ-phase precipitation and α'-phase formation were determined by the Kissinger plot, through DTA measurements; they are 243 and 261 kJ/mol, respectively. Using the results of phase quantifications, the Johnson-Mehl-Avrami equation was fitted.

  18. Fast Salt Bath Heat Treatment for a Bainitic/Martensitic Low-Carbon Low-Alloyed Steel

    NASA Astrophysics Data System (ADS)

    Urbanec, Julia; Saastamoinen, Ari; Kivivuori, Seppo; Louhenkilpi, Seppo

    2015-11-01

    The mechanical properties of a low-alloyed steel with 0.06 wt pct C were investigated after a series of heat treatment processes using salt bath followed by quenching into water in order to obtain bainitic/martensitic steel. Salt bath holding time varied from 30 to 330 seconds. Hardness, tensile properties and toughness have been examined. The results show the obtained microstructure significantly enhances the impact strength (up to 187 J) and toughness (up to 71.4 pct critical reduction) with good hardness (239 ± 4 HV) and tensile strength (720 to 800 MPa) compared to direct quenching heat treatment without salt bath holding.

  19. Refinement of the magnetic composite model of type 304 stainless steel by considering misoriented ferromagnetic martensite particles

    NASA Astrophysics Data System (ADS)

    Kinoshita, Katsuyuki

    2017-05-01

    We improved a magnetic composite model that combines the Jiles-Atherton model and Eshelby's equivalent inclusion method to consider misoriented martensite particles. The magnetic permeability of type 304 stainless steel were analyzed by using both experimental data on the orientation distribution of type 304 stainless steel specimens and the improved model. We found that the model is able to qualitatively explain the variation of permeability with the orientation angle and orientation distribution, an effect that depends on the direction of the excitation magnetic field.

  20. Passivation and Corrosion Behavior of Modified Ferritic-Pearlitic Railway Axle Steels

    NASA Astrophysics Data System (ADS)

    Moon, A. P.; Sangal, S.; Srivastav, Simant; Gajbhiye, N. S.; Mondal, K.

    2015-01-01

    Electrochemical polarization behavior of two newly developed ferritic-pearlitic railway axle steels (MS3 and MS6) and the standard Indian conventional axle steel has been studied in sodium borate buffer solution of pH 8.4 with and without the presence of NaCl. The polarization behavior of both the new axle steels shows close resemblance, whereas, different polarization behavior has been observed for the conventional axle steel. Electrochemical impedance spectroscopy measurements have clearly reflected significantly improved passivation behavior for the newly developed steels compared to that of the conventional axle steel. NaCl salt fog exposure tests have also shown superior corrosion resistance of the newly developed axle steels as compared to the conventional axle steel. Higher surface roughness on the corroded conventional axle steel has also been observed compared to the smoother surface in case of the new axle steels. Higher corrosion resistance of the new axle steels has been attributed to their finer microstructure and strongly adherent protective rusts.

  1. The production of ultrafine ferrite in low-carbon steel by strain-induced transformation

    NASA Astrophysics Data System (ADS)

    Hickson, M. R.; Hurley, P. J.; Gibbs, R. K.; Kelly, G. L.; Hodgson, P. D.

    2002-04-01

    An investigation into the production of ultrafine (1 µm) equiaxed ferrite (UFF) grains in low-carbon steel was made using laboratory rolling, compression dilatometry, and hot torsion techniques. It was found that the hot rolling of thin strip, with a combination of high shear strain and high undercooling, provided the conditions most suitable for the formation of this type of microstructure. Although high strains could be applied in compression and torsion experiments, large volume fractions of UFF were not observed in those samples, possibly due to the lower level of undercooling achieved. It is thought that ferrite refinement was due to a strain-induced transformation process, and that ferrite grains nucleated on parallel and linear deformation bands that traversed austenite grains. These bands formed during the deformation process, and the undercooling provided by the contact between the strip and the work rolls was sufficient to drive the transformation to homogeneous UFF grains.

  2. Impact toughness of irradiated reduced-activation ferritic steels*1

    NASA Astrophysics Data System (ADS)

    Klueh, R. L.; Alexander, D. J.

    1994-09-01

    Eight chromium-tungsten steels ranging from 2.25 to 12 wt% Cr were irradiated at 365°C to 13-14 dpa in the Fast Flux Test Facility. Post irradiation Charpy impact tests showed a loss of toughness for all steels, as measured by an increase in the ductile-brittle transition temperature (DBTT) and a decrease in the upper-shelf energy. The most irradiation-resistant steels were two 9% Cr steels: the DBTT of a 9Cr-2W-0.25V-0.1C steel increased 29°C, and for the same composition with an addition of 0.07% Ta the DBTT increased only 15°C. This is the smallest shift ever observed for such a steel irradiated to these levels. The other steels developed shifts in DBTT of 100 to 300°C. A 2.25% Cr steel with 2% W, 0.25% V, and 0.1% C was less severely affected by irradiation than 2.25% Cr steels with 0.25% V and no tungsten, 2% W and no vanadium, and with 1% W and 0.25% V. Irradiation resistance appears to be associated with microstructure, and microstructural manipulation may lead to improved properties.

  3. Mechanosynthesis of A Ferritic ODS (Oxide Dispersion Strengthened) Steel Containing 14% Chromium and Its Characterization

    NASA Astrophysics Data System (ADS)

    Rivai, A. K.; Dimyati, A.; Adi, W. A.

    2017-05-01

    One of the advanced materials for application at high temperatures which is aggressively developed in the world is ODS (Oxide Dispersion strengthened) steel. ODS ferritic steels are one of the candidate materials for future nuclear reactors in the world (Generation IV reactors) because it is able to be used in the reactor above 600 °C. ODS ferritic steels have also been developed for the interconnect material of SOFC (Solid Oxide Fuel Cell) which will be exposed to about 800 °C of temperature. The steel is strengthened by dispersing homogeneously of oxide particles (ceramic) in nano-meter sized in the matrix of the steel. Synthesis of a ferritic ODS steel by dispersion of nano-particles of yttrium oxide (yttria: Y2O3) as the dispersion particles, and containing high-chromium i.e. 14% has been conducted. Synthesis of the ODS steels was done mechanically (mechanosynthesis) using HEM (High Energy ball Milling) technique for 40 and 100 hours. The resulted samples were characterized using SEM-EDS (Scanning Electron Microscope-Energy Dispersive Spectroscope), and XRD (X-ray diffraction) to analyze the microstructure characteristics. The results showed that the crystal grains of the sample with 100 hours milling time was much smaller than the sample with 40 hours milling time, and some amount of alloy was formed during the milling process even for 40 hours milling time. Furthermore, the structure analysis revealed that some amount of iron atom substituted by a slight amount of chromium atom as a solid solution. The quantitative analysis showed that the phase mostly consisted of FeCr solid-solution with the structure was BCC (body-centered cubic).

  4. Rapid Tempering of Martensitic Stainless Steel AISI420: Microstructure, Mechanical and Corrosion Properties

    NASA Astrophysics Data System (ADS)

    Abbasi-Khazaei, Bijan; Mollaahmadi, Akbar

    2017-03-01

    In this research, the effect of rapid tempering on the microstructure, mechanical properties and corrosion resistance of AISI 420 martensitic stainless steel has been investigated. At first, all test specimens were austenitized at 1050 °C for 1 h and tempered at 200 °C for 1 h. Then, the samples were rapidly reheated by a salt bath furnace in a temperature range from 300 to 1050 °C for 2 min and cooled in air. The tensile tests, impact, hardness and electrochemical corrosion were carried out on the reheated samples. Scanning electron microscopy was used to study the microstructure and fracture surface. To investigate carbides, transmission electron microscopy and also scanning electron microscopy were used. X-ray diffraction was used for determination of the retained austenite. The results showed that the minimum properties such as the tensile strength, impact energy, hardness and corrosion resistance were obtained at reheating temperature of 700 °C. Semi-continuous carbides in the grain boundaries were seen in this temperature. Secondary hardening phenomenon was occurred at reheating temperature of 500 °C.

  5. Microstructural investigation, using polarized neutron scattering, of a martensitic steel for fusion reactors

    SciTech Connect

    Coppola, R.; Kampmann, R.; Staron, P.; Magnani, M.

    1998-09-18

    Small- and wide-angle polarized neutron scattering has been used to investigate the microstructure of modified martensitic steel DIN 1.4914 (MANET-type) developed as a potential candidate for the first wall of future fusion reactors. The nuclear-magnetic interference term and the comparison of the size distribution functions, obtained from the nuclear and from the magnetic scattering components, show that for quench temperatures lower than 1200 C three kinds of microstructural inhomogeneities can be identified: (a) tiny C-Cr elementary aggregates (1 nm or less in size), (b) larger (1--25 nm) Fe-carbides, (c) much larger inhomogeneities arising either from M{sub 23}C{sub 6} precipitates or from fluctuations in the Cr distribution. The scattering data are also compared with those previously obtained on the same samples from a conventional SANS instrument and the influence of the available Q-range on the accuracy of the obtained size distribution functions is discussed.

  6. Interdiffusion behaviors of iron aluminide coatings on China low activation martensitic steel

    NASA Astrophysics Data System (ADS)

    Zhu, X. X.; Yang, H. G.; Yuan, X. M.; Zhao, W. W.; Zhan, Q.

    2014-12-01

    The iron aluminide coating on China Low Activation Martensitic (CLAM) steel was prepared by pack cementation and subsequent heat treatment. A surface Fe2Al5 layer was formed on CLAM substrate by pack cementation process with Fe2Al5 donor powder and NH4Cl activator. Diffusion heat treatment was performed in order to allow the phase transformation from Fe2Al5 to a phase with lower aluminum content. Morphology and composition of the coatings were characterized by optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), glow discharge optical emission spectroscopy (GDOES) and X-ray diffraction (XRD). There is a need to study the interdiffusion behaviors in these Al containing systems, as a basis for controlling the formation and subsequent degradation of the coating. In this paper, a predictive model was developed to describe the phase transformation of Fe2Al5 as a function of processing parameters. The Wagner's equation was used to calculate the interdiffusion coefficients based on the analysis of the Al concentration profiles. The results showed that the interdiffusion coefficients in the FeAl and α-Fe(Al) phase strongly depends on Al content and showed a maximum at about 28 at.% Al.

  7. Rapid Tempering of Martensitic Stainless Steel AISI420: Microstructure, Mechanical and Corrosion Properties

    NASA Astrophysics Data System (ADS)

    Abbasi-Khazaei, Bijan; Mollaahmadi, Akbar

    2017-04-01

    In this research, the effect of rapid tempering on the microstructure, mechanical properties and corrosion resistance of AISI 420 martensitic stainless steel has been investigated. At first, all test specimens were austenitized at 1050 °C for 1 h and tempered at 200 °C for 1 h. Then, the samples were rapidly reheated by a salt bath furnace in a temperature range from 300 to 1050 °C for 2 min and cooled in air. The tensile tests, impact, hardness and electrochemical corrosion were carried out on the reheated samples. Scanning electron microscopy was used to study the microstructure and fracture surface. To investigate carbides, transmission electron microscopy and also scanning electron microscopy were used. X-ray diffraction was used for determination of the retained austenite. The results showed that the minimum properties such as the tensile strength, impact energy, hardness and corrosion resistance were obtained at reheating temperature of 700 °C. Semi-continuous carbides in the grain boundaries were seen in this temperature. Secondary hardening phenomenon was occurred at reheating temperature of 500 °C.

  8. Microhardness and Stress Analysis of Laser-Cladded AISI 420 Martensitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Alam, Mohammad K.; Edrisy, Afsaneh; Urbanic, Jill; Pineault, James

    2017-03-01

    Laser cladding is a surface treatment process which is starting to be employed as a novel additive manufacturing. Rapid cooling during the non-equilibrium solidification process generates non-equilibrium microstructures and significant amounts of internal residual stresses. This paper investigates the laser cladding of 420 martensitic stainless steel of two single beads produced by different process parameters (e.g., laser power, laser speed, and powder feed rate). Metallographic sample preparation from the cross section revealed three distinct zones: the bead zone, the dilution zone, and the heat-affected zone (HAZ). The tensile residual stresses were in the range of 310-486 MPa on the surface and the upper part of the bead zone. The compressive stresses were in the range of 420-1000 MPa for the rest of the bead zone and the dilution zone. The HAZ also showed tensile residual stresses in the range of 140-320 MPa for both samples. The post-cladding heat treatment performed at 565 °C for an hour had significantly reduced the tensile stresses at the surface and in the subsurface and homogenized the compressive stress throughout the bead and dilution zones. The microstructures, residual stresses, and microhardness profiles were correlated for better understanding of the laser-cladding process.

  9. Microhardness and Stress Analysis of Laser-Cladded AISI 420 Martensitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Alam, Mohammad K.; Edrisy, Afsaneh; Urbanic, Jill; Pineault, James

    2017-02-01

    Laser cladding is a surface treatment process which is starting to be employed as a novel additive manufacturing. Rapid cooling during the non-equilibrium solidification process generates non-equilibrium microstructures and significant amounts of internal residual stresses. This paper investigates the laser cladding of 420 martensitic stainless steel of two single beads produced by different process parameters (e.g., laser power, laser speed, and powder feed rate). Metallographic sample preparation from the cross section revealed three distinct zones: the bead zone, the dilution zone, and the heat-affected zone (HAZ). The tensile residual stresses were in the range of 310-486 MPa on the surface and the upper part of the bead zone. The compressive stresses were in the range of 420-1000 MPa for the rest of the bead zone and the dilution zone. The HAZ also showed tensile residual stresses in the range of 140-320 MPa for both samples. The post-cladding heat treatment performed at 565 °C for an hour had significantly reduced the tensile stresses at the surface and in the subsurface and homogenized the compressive stress throughout the bead and dilution zones. The microstructures, residual stresses, and microhardness profiles were correlated for better understanding of the laser-cladding process.

  10. Linear Friction Welding Process Model for Carpenter Custom 465 Precipitation-Hardened Martensitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Grujicic, M.; Yavari, R.; Snipes, J. S.; Ramaswami, S.; Yen, C.-F.; Cheeseman, B. A.

    2014-06-01

    An Arbitrary Lagrangian-Eulerian finite-element analysis is combined with thermo-mechanical material constitutive models for Carpenter Custom 465 precipitation-hardened martensitic stainless steel to develop a linear friction welding (LFW) process model for this material. The main effort was directed toward developing reliable material constitutive models for Carpenter Custom 465 and toward improving functional relations and parameterization of the workpiece/workpiece contact-interaction models. The LFW process model is then used to predict thermo-mechanical response of Carpenter Custom 465 during LFW. Specifically, temporal evolutions and spatial distribution of temperature within, and expulsion of the workpiece material from, the weld region are examined as a function of the basic LFW process parameters, i.e., (a) contact-pressure history, (b) reciprocation frequency, and (c) reciprocation amplitude. Examination of the results obtained clearly revealed the presence of three zones within the weld, i.e., (a) Contact-interface region, (b) Thermo-mechanically affected zone, and (c) heat-affected zone. While there are no publicly available reports related to Carpenter Custom 465 LFW behavior, to allow an experiment/computation comparison, these findings are consistent with the results of our ongoing companion experimental investigation.

  11. Laser surface melting of Martensitic stainless steel 440C for enhancing corrosion resistance

    NASA Astrophysics Data System (ADS)

    Kwok, Chi-Tat; Lo, Ka-Hing; Cheng, Fai-Tsun; Man, Hau-Chung

    2003-03-01

    Surface modification of martensitic stainless steel 440C was achieved by laser surface melting using a 2-kW continuous wave Nd:YAG laser. The corrosion characteristics of laser-melted specimens fabricated under different processing parameters in 3.5% NaCl solution at 23°C were studied by potentiodynamic polarization technique. The pitting corrosion resistance of all laser-melted specimens was significantly improved, as evidenced by a shift of the pitting potential in the noble direction, a wider passive range, and a lower passive current density. The pitting potential of the laser-melted specimen fabricated under a power density of 4.2 kW/cm2 and a scanning speed of 25 mm/s (specimen P12-440C-25) was increased to 200 mV (SCE), which was much higher than that of annealed and conventionally heat-treated 440C. The pitting corrosion characteristics of the laser-melted specimens were strongly dependent on the processing conditions which resulted in different microstructures. The enhanced pitting resistance resulted from the combined effect of dissolution or refinement of carbide particles and the presence of retained austenite. By using different processing parameters, it was found that the pitting resistance of the laser-melted specimen P12-440C-25 was the highest by virtue of a high volume fraction of retained austenite and a small amount of precipitated carbide.

  12. An energetic approach to abrasive wear of a martensitic stainless steel

    SciTech Connect

    Pamuk, U.; Baydogan, M.; Niluefer, B.; Cimenoglu, H.

    2000-04-01

    Abrasive wear is the most common type of wear that causes failure of machine elements. Examinations of abraded surfaces revealed presence of embedded particles and grooves elongated along the sliding direction. This indicates that, there are two sequential stages of an abrasion process. In the first stage, asperities on the hard surface and/or hard abrasive grains penetrate into the soft material surface and then in the second stage, they grind the surface in the sliding direction. Therefore, indentation and scratching of an indenter, which can be realized by hardness and scratch tests, can simulate the damage produced on the abraded surface. On the basis of this simulation, an energetic model is proposed for abrasive wear in the present study. In this study, abrasive wear behavior of a martensitic stainless steel is examined by hardness and scratch tests. The results of tests were evaluated to estimate the work done during abrasion and to find out the dimensional wear coefficient according to the model proposed above.

  13. Weld microstructure development and properties of precipitation-strengthened martensitic stainless steels

    SciTech Connect

    Brooks, J.

    1994-12-31

    Precipitation-strengthened martensitic stainless steels provide excellent strength (170--220 ksi Y.S.) with high corrosion resistance. However, upon aging, a large reduction in toughness may also occur. The gas tungsten arc (GTA) cold wire feed process was used to weld half inch thick plates of PH 13-8 Mo and Custom 450 from which both tensile and Charpy specimens were machined. A fundamental understanding of the details of weld microstructural evolution was developed by liquid tin quenching GTA welds in which the solidification behavior, primary phase of solidification, microsegregation, and solid-state transformations could be followed. For both alloys studied, the as-welded yield strengths were similar to those of the unaged base material, 130 ksi. Weld properties were very similar to those of the base materials for both alloy systems. Weld strength increases significantly upon aging and achieves a maximum at intermediate aging temperatures. The increase in strength is accompanied by a large decrease in Charpy impact energy; however, the minimum in toughness occurs at aging temperatures slightly less than those resulting in peak strengths. The evolution of the weld microstructure was found to support predictions of microstructural modeling. Although a high degree of alloying partitioning occurs during solidification, a large degree of homogenization occurs upon further solidification and cooling as a result of solid-state diffusion.

  14. Mechanical behavior and brittle-ductile transition of high-chromium martensitic steel

    NASA Astrophysics Data System (ADS)

    Odnobokova, M. V.; Kipelova, A. Yu.; Belyakov, A. N.; Kaibyshev, R. O.

    2016-04-01

    The article presents data on the static tensile tests and dynamic impact-toughness tests of a highchromium martensitic 10Kh9V1M1FBR steel (0.12 wt % C, 9.8 wt % Cr, 0.93 wt % W, 1.01 wt % Mo, 0.2 wt % V, 0.05 wt % Nb, 0.05 wt % N, 0.003 wt % B, 0.36 wt % Mn, 0.2 wt % Ni, 0.06 wt % Si, 0.01 wt % P, 0.008 wt % S, 0.02 wt % Cu, 0.1 wt % Co, 0.015 wt % Al, and the remainder is Fe) in the temperature range from 20 to-196°C. In the case of static loading, a reduction in the temperature leads to an increase in the strength characteristics; upon a drop in the temperature from 20 to-100°C, the plasticity also increases. This is connected with the fact that the ductile fracture remains the basic mechanism down to cryogenic temperatures. The brittle-ductile transition related to the transition from ductile intragranular fracture to quasibrittle one is observed at-45°C. The steel exhibits high impact toughness to the temperature of-60°C ( KCV -60 = 95 J/cm2), at which the fraction of the ductile component in fracture is equal to 20%. At 80°C, the impact toughness decreases down to critical values (30 J/cm2), which correlates with the decrease in the fraction of the ductile component on the fracture surface down to 1%. The further decrease in the impact toughness down to 10 J/cm2 at-196°C is related to the transition from intragranular to intergranular brittle fracture.

  15. Ion irradiation effects on a martensitic stainless steel designed for reduced long-life radioactivity

    SciTech Connect

    Griffin, R.D. . Fusion Technology Inst.); Zinkle, S.J. ); Dodd, R.A.; Kulcinski, G.L. ); Gelles, D.S. )

    1990-04-01

    Alloys with reduced long-life radioactivity (low activation alloys) are being developed to increase the acceptability of fusion power. The phase stability and swelling resistance of a 12Cr-6.5Mn-1W-0.3V-0.1C martensitic steel were evaluated by transmission electron microscopy following 3.8 MeV Fe{sup ++} ion irradiation with and without He coimplantation. Ion irradiations were performed at 450{degree}C, 550{degree}C, and 650{degree}C to approximately 10, 20, and 40 dpa. At 550{degree}C, approximately 20 appm He/dpa was coimplanted with the 3.8 MeV Fe{sup ++} ions. The specimens were examined at a depth approximately halfway between the surface and the mean ion range in order to minimize the influence of the surface and of injected ions. At all temperatures, M{sub 23}C{sub 6}, also present in the unirradiated structure, was the only precipitate present. A nonuniform distribution of loops also formed at all temperatures. After the 450{degree}C and 650{degree}C irradiations, no voids were present. At 550{degree}C, the helium did not appear to have much effect. Very few faceted voids formed. At 20 and 40 dpa some bubbles were found but their density was very low. At 650{degree}C, a structure similar to a heavily over-tempered steel was produced by the irradiation. At 550{degree}C recovery was seen to a lesser extent. Little to no recovery was seen at 450{degree}C.

  16. Nano- and microvoid formation in ultrafine-grained martensitic Fe-Ni-Mn steel after severe cold rolling

    NASA Astrophysics Data System (ADS)

    Ghasemi-Nanesa, Hadi; Nili-Ahmadabadi, Mahmoud; Mirsepasi, Arya; Zamani, Cyrus

    2014-03-01

    Severe cold-rolling was applied on solution annealed Fe-Ni-Mn steel with fully lath martensite structure to obtain ultrafine-grained structure. Field emission scanning electron microscopy and high resolution transmission electron microscopy (HRTEM) were employed to investigate the microstructural evolution after severe cold-rolling. HRTEM images showed the typical deformed structure consisting of lamellar dislocation cell blocks. HRTEM study also revealed strain-induced reverse martensitic transformation (activated during grain refinement). It was assumed that severe plastic deformation route and related deformation mode were responsible for microstructural evolutions. X-ray diffraction (XRD) diagram revealed 7% (volume fraction) reverted austenite after final deformation pass. Moreover, HRTEM images revealed nano-void nucleation at the interface of severely deformed martensite and reverted austenite presumably due to high strain energy of misfit and molar volume difference between the austenite and the martensite. It seems that the coalescence of nano-voids could lead to the formation of microvoids in the microstructure.

  17. High yttria ferritic ODS steels through powder forging

    NASA Astrophysics Data System (ADS)

    Kumar, Deepak; Prakash, Ujjwal; Dabhade, Vikram V.; Laha, K.; Sakthivel, T.

    2017-05-01

    Oxide dispersion strengthened (ODS) steels are being developed for future nuclear reactors. ODS Fe-18%Cr-2%W-0.2%Ti steels with 0, 0.35, 0.5, 1 and 1.5% Y2O3 (all compositions in weight%) dispersion were fabricated by mechanical alloying of elemental powders. The powders were placed in a mild steel can and forged in a stream of hydrogen gas at 1473 K. The steels were forged again to final density. The strength of ODS steel increased with yttria content. Though this was accompanied by a decrease in tensile elongation, all the steels showed significant ductility. The ductility in high yttria alloys may be attributed to improved inter-particle bonding between milled powders due to reduction of surface oxides by hydrogen. This may permit development of ODS steels with yttria contents higher than the conventional limit of 0.5%. It is suggested that powder forging is a promising route to fabricate ODS steels with high yttria contents and improved ductility.

  18. Ferrite Measurement in Austenitic and Duplex Stainless Steel Castings - Final Report

    SciTech Connect

    Lundin, C.D.; Zhou, G.; Ruprecht, W.

    1999-08-01

    The ability to determine ferrite rapidly, accurately and directly on a finished casting, in the solution annealed condition, can enhance the acceptance, save on manufacturing costs and ultimately improve service performance of duplex stainless steel cast products. If the suitability of a non-destructive ferrite determination methodology can be demonstrated for standard industrial measurement instruments, the production of cast secondary standards for calibration of these instruments is a necessity. With these concepts in mind, a series of experiments were carried out to demonstrate, in a non-destructive manner, the proper methodology for determining ferrite content. The literature was reviewed, with regard to measurement techniques and vagaries, an industrial ferrite measurement round-robin was conducted, the effects of casting surface finish, preparation of the casting surface for accurate measurement and the evaluation of suitable means for the production of cast secondary standards for calibration were systematically investigated. The data obtained from this research program provide recommendations to ensure accurate, repeatable, and reproducible ferrite measurement and qualifies the Feritscope for field use on production castings.

  19. Ferrite Measurement in Austenitic and Duplex Stainless Steel Castings - Literature Review

    SciTech Connect

    Lundin, C.D.; Zhou, G.; Ruprecht, W.

    1999-08-01

    The ability to determine ferrite rapidly, accurately and directly on a finished casting, in the solution annealed condition, can enhance the acceptance, save on manufacturing costs and ultimately improve service performance of duplex stainless steel cast products. If the suitability of a non-destructive ferrite determination methodology can be demonstrated for standard industrial measurement instruments, the production of cast secondary standards for calibration of these instruments is a necessity. With these concepts in mind, a series of experiments were carried out to demonstrate, in a non-destructive manner, the proper methodology for determining ferrite content. The literature was reviewed, with regard to measurement techniques and vagaries, an industrial ferrite measurement round-robin was conducted, the effects of casting surface finish, preparation of the casting surface for accurate measurement and the evaluation of suitable means for the production of cast secondary standards for calibration were systematically investigated. The data obtained from this research program provides recommendations to insure accurate, repeatable and reproducible ferrite measurement and qualifies the Feritscope for field use on production castings.

  20. Adsorption of Pb(2+) from aqueous solution using spinel ferrite prepared from steel pickling sludge.

    PubMed

    Fang, Binbin; Yan, Yubo; Yang, Yang; Wang, Fenglian; Chu, Zhen; Sun, Xiuyun; Li, Jiansheng; Wang, Lianjun

    2016-01-01

    In this paper, spinel ferrite with high crystallinity and high saturation magnetization was successfully prepared from steel pickling sludge by adding iron source and precipitator in the hydrothermal condition. The obtained spinel ferrite was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), vibrating sample magnetometer (VSM), and Zeta potential methods and investigated as an adsorbent for removal of Pb(2+) from aqueous solution. Batch experiments were performed by varying the pH values, contact time, temperature and initial metal concentration. The result of pH impact showed that the adsorption of Pb(2+) was a pH dependent process, and the pH 5.8 ± 0.2 was found to be the optimum condition. The achieved experimental data were analyzed with various kinetic and isotherm models. The kinetic studies revealed that Pb(2+) adsorption onto spinel ferrite followed a pseudo-second order model, and the Langmuir isotherm model provided the perfect fit to the equilibrium experimental data. At different temperatures, the maximum Pb(2+) adsorption capacities calculated from the Langmuir equation were in the range of 126.5-175.4 mg/g, which can be in competition with other adsorbents. The thermodynamic results showed that the spinel ferrite could spontaneously and endothermically adsorb Pb(2+) from aqueous solution. The regeneration studies showed that spinel ferrite could be used five times (removal efficiency (%) >90%) by desorption with HNO3 reagent.