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Sample records for cr ferritic steels

  1. 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.

  2. 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.

  3. Hot-rolling of reduced activation 8CrODS ferritic steel

    NASA Astrophysics Data System (ADS)

    Wu, Xiaochao; Ukai, Shigeharu; Leng, Bin; Oono, Naoko; Hayashi, Shigenari; Sakasegawa, Hideo; Tanigawa, Hiroyasu

    2013-11-01

    The 8CrODS ferritic steel is based on J1-lot developed for the advanced fusion blanket material to increase the coolant outlet temperature. A hot-rolling was conducted at the temperature above Ar3 of 716 °C, and its effect on the microstructure and tensile strength in 8CrODS ferritic steel was evaluated, comparing together with normalized and tempered specimen. It was confirmed that hot-rolling leads to slightly increased fraction of the ferrite and highly improved tensile strength. This ferrite was formed by transformation from the hot-rolled austenite during cooling due to fine austenite grains induced by hot-rolling. The coarsening of the transformed ferrite in hot-rolled specimen can be attributed to the crystalline rotation and coalescence of the similar oriented grains. The improved strength of hot-rolled specimen was ascribed to the high dislocation density and replacement of easily deformed martensite with the transformed coarse ferrite.

  4. A complex carbonitride of niobium and vanadium in 9% Cr ferritic steels

    SciTech Connect

    Tokuno, K.; Hamada, K.; Takeda, T. ); Uemori, R. ); Itoh, K. )

    1991-01-01

    It has been considered that small additions of Nb and V have striking effects on the creep strength of high Cr ferritic steels which are used for elevated temperature services such as boilers, steam generators etc. Although Nb and V are thought to form complex precipitates which may act as obstacles for the dislocation glide, the distribution and morphology of the precipitates have not been clarified yet. Several examples of simple precipitates of V in low alloy steels were only reported. In this paper, the morphology of the complex carbonitride of Nb and V in 9% Cr ferritic steels was investigated and the role of the carbonitride on the creep strength was discussed.

  5. Analysis of Creep Rupture Behavior of Cr-Mo Ferritic Steels in the Presence of Notch

    NASA Astrophysics Data System (ADS)

    Goyal, Sunil; Laha, K.; Das, C. R.; Mathew, M. D.

    2015-01-01

    Effect of notch on creep rupture behavior of 2.25Cr-1Mo, 9Cr-1Mo, and modified 9Cr-1Mo ferritic steels has been assessed. Creep tests were carried out on smooth and notched specimens of the steels in the stress ranging 90 to 300 MPa at 873 K (600 °C). Creep rupture lives of the steels increased in the presence of notch over those of smooth specimens, thus exhibiting notch strengthening. The strengthening was comparable for the 9Cr-1Mo and 2.25Cr-1Mo steels and appreciably more in modified 9Cr-1Mo steel. The strengthening effect was found to decrease with the decrease in applied stress and increase in rupture life for all the steels. The presence of notch decreased the creep rupture ductility of the steels significantly and the 2.25Cr-1Mo steel suffered more reduction than in the other two 9Cr-steels. Finite element analysis of stress distribution across the notch was carried out to understand the notch strengthening and its variation in the steels. The variation in fracture appearance has also been corroborated based on finite element analysis. Reduction in von-Mises stress across the notch throat plane resulted in strengthening in the steels. Higher reduction in von-Mises stress in modified 9Cr-1Mo steel than that in 2.25Cr-1Mo and 9Cr-1Mo steels induced more strengthening in modified 9Cr-1Mo steel under multiaxial state of stress.

  6. 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.

  7. The influence of Cr content on the mechanical properties of ODS ferritic steels

    NASA Astrophysics Data System (ADS)

    Li, Shaofu; Zhou, Zhangjian; Jang, Jinsung; Wang, Man; Hu, Helong; Sun, Hongying; Zou, Lei; Zhang, Guangming; Zhang, Liwei

    2014-12-01

    The present investigation aimed at researching the mechanical properties of the oxide dispersion strengthened (ODS) ferritic steels with different Cr content, which were fabricated through a consolidation of mechanical alloyed (MA) powders of 0.35 wt.% nano Y2O3 dispersed Fe-12.0Cr-0.5Ti-1.0W (alloy A), Fe-16.0Cr-0.5Ti-1.0W (alloy B), and Fe-18.0Cr-0.5Ti-1.0W (alloy C) alloys (all in wt.%) by hot isostatic pressing (HIP) with 100 MPa pressure at 1150 °C for 3 h. The mechanical properties, including the tensile strength, hardness, and impact fracture toughness were tested by universal testers, while Young's modulus was determined by ultrasonic wave non-destructive tester. It was found that the relationship between Cr content and the strength of ODS ferritic steels was not a proportional relationship. However, too high a Cr content will cause the precipitation of Cr-enriched segregation phase, which is detrimental to the ductility of ODS ferritic steels.

  8. Microstructure of a 14Cr-ODS ferritic steel before and after helium ion implantation

    NASA Astrophysics Data System (ADS)

    Lu, Chenyang; Lu, Zheng; Xie, Rui; Liu, Chunming; Wang, Lumin

    2014-12-01

    A 14Cr-ODS ferritic steel with the nominal compositions of Fe-14Cr-2 W-0.3Ti-0.3Y2O3 (wt.%) was produced by mechanical alloying (MA) and hot isostatic pressing (HIP). Helium ion was implanted into the 14Cr-ODS steel along with Eurofer 97 steel as reference at 400 °C to a fluence of 1 × 1017 He+/cm2. High resolution transmission electron microscopy (HRTEM), high angle annual dark field (HAADF) scanning TEM (STEM) and atom probe tomography (APT) were used to characterize the microstructure of 14Cr-ODS and Eurofer 97 steels before and after helium implantation. High-density Y-Ti-O-rich nanoclusters and Y2Ti2O7 precipitates as well as large Cr-Ti rich oxides were observed in the 14Cr-ODS steel. The average size of Y-Ti-O nanoclusters and Y2Ti2O7 precipitates is 9 nm. After helium implantation, the helium bubbles formed in the 14Cr-ODS steel exhibit the smaller size and the lower volume fraction than that in Eurofer 97 steel, indicating high-density nano-scale precipitates can effectively suppress the coarsening of helium bubbles.

  9. Creep behaviour of modified 9Cr-1Mo ferritic steel

    NASA Astrophysics Data System (ADS)

    Choudhary, B. K.; Isaac Samuel, E.

    2011-05-01

    Creep deformation and fracture behaviour of indigenously developed modified 9Cr-1Mo steel for steam generator (SG) tube application has been examined at 823, 848 and 873 K. Creep tests were performed on flat creep specimens machined from normalised and tempered SG tubes at stresses ranging from 125 to 275 MPa. The stress dependence of minimum creep rate obeyed Norton's power law. Similarly, the rupture life dependence on stress obeyed a power law. The fracture mode remained transgranular at all test conditions examined. The analysis of creep data indicated that the steel obey Monkman-Grant and modified Monkman-Grant relationships and display high creep damage tolerance factor. The tertiary creep was examined in terms of the variations of time to onset of tertiary creep with rupture life, and a recently proposed concept of time to reach Monkman-Grant ductility, and its relationship with rupture life that depends only on damage tolerance factor. SG tube steel exhibited creep-rupture strength comparable to those reported in literature and specified in the nuclear design code RCC-MR.

  10. Role of a complex carbonitride of niobium and vanadium in creep strength of 9% Cr ferritic steels

    SciTech Connect

    Tokuno, K.; Hamada, K.; Takeda, T. ); Uemori, R. ); Itoh, K. )

    1991-08-01

    Complex precipitates of Nb and V in ferritic steels have been considered to act as strong obstacles against dislocation glide. In the previous report, the authors investigated a complex precipitate of Nb and V in 9% Cr ferritic steel and showed that plate-like V-nitrides were formed adhering to spherical Nb (C,N) during tempering. These peculiar shaped precipitates are likely to trap dislocations during high temperature deformation such as creep. In this paper, the effect of the sizes of the complex carbonitrides on the creep strength of 9% Cr ferritic steels was investigated. The sizes of the carbonitrides were varied by changing the amount of N.

  11. Kinetics of isochronal austenization in modified high Cr ferritic heat-resistant steel

    NASA Astrophysics Data System (ADS)

    Liu, Chenxi; Liu, Yongchang; Zhang, Dantian; Yan, Zesheng

    2011-12-01

    Employment of high Cr ferritic steels as a main structural material is considered as a way to achieve economical competitiveness of main steam pipe and nuclear reactors in power plants. Differential dilatometry and microstructure observation were employed to investigate the isochronal austenitic transformation of the modified high Cr ferritic steel. The kinetics of the isochronal austenitic transformation were described by a phase-transformation model involving site saturation (pre-existing nuclei), diffusion-controlled growth, and incorporating an impingement correction. The experimental results and kinetic analysis indicate that an increase of the heating rate promotes the diffusion-controlled austenitic transformation. The dissolving degree of precipitates during the austenization process affects the activation energy for diffusion and the undissolved precipitates lead to an increase of the onset temperature of the subsequent martensite transformation upon cooling.

  12. Influence of Chemical Composition and Heat Treatment Condition on Impact Toughness of 15Cr Ferritic Creep Resistant Steel

    NASA Astrophysics Data System (ADS)

    Toda, Yoshiaki; Tohyama, Hideaki; Kushima, Hideaki; Kimura, Kazuhiro; Abe, Fujio

    Influences of chemical compositions, heat treatment and microstructure on impact toughness of 15Cr ferritic steel have been investigated. Charpy impact values of the furnace cooled steels were lower than 15J/cm2 at room temperature independent of chemical compositions. Drastic improvement in impact toughness has been attained by controlling the carbon and nitrogen contents, by the addition of nickel and by the increase in cooling rate after annealing. However, the effect of nickel on impact toughness strongly depends on carbon and nitrogen contents. Improvement in impact toughness of the 15Cr ferritic steel has not been explained by individual microstructural factors of grain size, distribution of precipitates, volume fraction of martensitic phase. It has been supposed that the increase in Charpy impact toughness of the 15Cr ferritic steel was attained by improvement in toughness of ferrite matrix itself.

  13. Type IV Cracking Susceptibility in Weld Joints of Different Grades of Cr-Mo Ferritic Steel

    NASA Astrophysics Data System (ADS)

    Laha, K.; Chandravathi, K. S.; Parameswaran, P.; Bhanu Sankara Rao, K.

    2009-02-01

    Relative type-IV cracking susceptibility in 2.25Cr-1Mo, 9Cr-1Mo, and 9Cr-1MoVNb ferritic steel weld joint has been assessed. The type-IV cracking was manifested as preferential accumulation of creep deformation and cavitation in the relatively soft intercritical region of heat affected zone of the weld joint. The type-IV cracking susceptibility has been defined as the reduction in creep-rupture strength of weld joint compared to its base metal. The 2.25Cr-1Mo steel exhibited more susceptibility to type-IV cracking at relatively lower temperatures; whereas, at higher temperatures, 9Cr-1MoVNb steel was more susceptible. The relative susceptibility to type-IV cracking in the weld joint of the Cr-Mo steels has been rationalized on the basis of creep-strengthening mechanisms operating in the steels and their venerability to change on intercritical heating during weld thermal cycle, subsequent postweld heat treatment, and creep exposure.

  14. Mechanical Properties and Microstructure of Dissimilar Friction Stir Welds of 11Cr-Ferritic/Martensitic Steel to 316 Stainless Steel

    NASA Astrophysics Data System (ADS)

    Sato, Yutaka S.; Kokawa, Hiroyuki; Fujii, Hiromichi T.; Yano, Yasuhide; Sekio, Yoshihiro

    2015-12-01

    Dissimilar joints between ferritic and austenitic steels are of interest for selected applications in next generation fast reactors. In this study, dissimilar friction-stir welding of an 11 pct Cr ferritic/martensitic steel to a 316 austenitic stainless steel was attempted and the mechanical properties and microstructure of the resulting welds were examined. Friction-stir welding produces a stir zone without macroscopic weld-defects, but the two dissimilar steels are not intermixed. The two dissimilar steels are interleaved along a sharp zigzagging interface in the stir zone. During small-sized tensile testing of the stir zone, this sharp interface did not act as a fracture site. Furthermore, the microstructure of the stir zone was refined in both the ferritic/martensitic steel and the 316 stainless steel resulting in improved mechanical properties over the adjacent base material regions. This study demonstrates that friction-stir welding can produce welds between dissimilar steels that contain no macroscopic weld-defects and display suitable mechanical properties.

  15. 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.

  16. 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.

  17. Dynamic strain aging behavior of modified 9Cr-1Mo and reduced activation ferritic martensitic steels under low cycle fatigue

    NASA Astrophysics Data System (ADS)

    Mariappan, K.; Shankar, Vani; Sandhya, R.; Prasad Reddy, G. V.; Mathew, M. D.

    2013-04-01

    Influence of temperature and strain rate on low cycle fatigue (LCF) behavior of modified 9Cr-1Mo ferritic martensitic steel and 1.4W-0.06Ta reduced activation ferritic martensitic (RAFM) steel in normalized and tempered conditions was studied. Total strain controlled LCF tests between 300 and 873 K on modified 9Cr-1Mo steel and RAFM steel and at various strain rates on modified 9Cr-1Mo steel were performed at total strain amplitude of ±0.6%. Both the steels showed continuous cyclic softening at all temperatures. Whereas manifestations of dynamic strain aging (DSA) were observed in both the steels which decreased fatigue life at intermediate temperatures, at higher temperatures, oxidation played a crucial role in decreasing fatigue life.

  18. Wrought Cr--W--V bainitic/ferritic steel compositions

    DOEpatents

    Klueh, Ronald L.; Maziasz, Philip J.; Sikka, Vinod Kumar; Santella, Michael L.; Babu, Sudarsanam Suresh; Jawad, Maan H.

    2006-07-11

    A high-strength, high-toughness steel alloy includes, generally, about 2.5% to about 4% chromium, about 1.5% to about 3.5% tungsten, about 0.1% to about 0.5% vanadium, and about 0.05% to 0.25% carbon with the balance iron, wherein the percentages are by total weight of the composition, wherein the alloy is heated to an austenitizing temperature and then cooled to produce an austenite transformation product.

  19. High heat flux testing of 12-14Cr ODS ferritic steels

    NASA Astrophysics Data System (ADS)

    Pintsuk, G.; Oksiuta, Z.; Linke, J.; Baluc, N.

    2010-01-01

    The thermal performance of Fe-(12-14)Cr-2W-0.3Ti-0.3Y 2O 3 ODS reduced activation ferritic steels, which are considered as candidate first wall materials for the future fusion power reactors and were manufactured by mechanical alloying in hydrogen and hot isostatic pressing, was assessed by high heat flux (HHF) testing with the electron beam JUDITH facility at the Forschungszentrum Jülich (FZJ), Germany. An analysis of the microhardness and microstructure of the specimens was done before and after HHF tests. In general, both materials present a ferritic (α-Fe, bcc) microstructure with a wide range of grain sizes from 100 to 500 nm up to a few micrometers. The coarse grains are almost dislocation-free, while the smaller ones are surrounded by tangles of dislocations. Oxide and carbide impurities (about a few hundreds nm in size) and a high density of Y-Ti-O nano-clusters, with a mean size of about 5 nm, are also present. The microhardness, density and tensile strength of the 14Cr material are slightly larger than those of the 12Cr material. HHF tests revealed that there is no difference in thermal performance, level of degradation and erosion behaviour of 12Cr and 14Cr ODS steels. The onset of melting of the materials occurs for an energy density between 1 and 1.5 MJ/m 2. Below this value only some kind of thermal etching takes place. This is a significant improvement compared to stainless steel, for which severe plastic deformation at the material surface was observed.

  20. Structure of Oxide Nanoparticles in Fe-16Cr MA/ODS Ferritic Steel

    SciTech Connect

    Hsiung, L; Fluss, M; Kimura, A

    2010-04-06

    Oxide nanoparticles in Fe-16Cr ODS ferritic steel fabricated by mechanical alloying (MA) method have been examined using high-resolution transmission electron microscopy (HRTEM) techniques. A partial crystallization of oxide nanoparticles was frequently observed in as-fabricated ODS steel. The crystal structure of crystalline oxide particles is identified to be mainly Y{sub 4}Al{sub 2}O{sub 9} (YAM) with a monoclinic structure. Large nanoparticles with a diameter larger than 20 nm tend to be incoherent and have a nearly spherical shape, whereas small nanoparticles with a diameter smaller than 10 nm tend to be coherent or semi-coherent and have faceted boundaries. The oxide nanoparticles become fully crystallized after prolonged annealing at 900 C. These results lead us to propose a three-stage formation mechanism of oxide nanoparticles in MA/ODS steels.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  2. Microstructure examination of Fe-14Cr ODS ferritic steels produced through different processing routes

    NASA Astrophysics Data System (ADS)

    Oksiuta, Z.; Hosemann, P.; Vogel, S. C.; Baluc, N.

    2014-08-01

    Various thermo-mechanical treatments were applied to refine and homogenise grain size and improve mechanical properties of hot-isostatically pressed (HIP) 14%Cr ODS ferritic steel. The grain size was reduced, improving mechanical properties, tensile strength and Charpy impact, however bimodal-like distribution was also observed. As a result, larger, frequently elongated grains with size above 1 μm and refined, equiaxed grains with a diameter ranging from 250 to 500 nm. Neutron diffraction measurements revealed that for HIP followed by hydrostatic extrusion material the strongest fiber texture was observed oriented parallel to the extrusion direction. In comparison with hot rolling and hot pressing methods, this material exhibited promising mechanical properties: the ultimate tensile strength of 1350 MPa, yield strength of 1280 MPa, total elongation of 21.7% and Charpy impact energy of 5.8 J. Inferior Charpy impact energy of ∼3.0 J was measured for HIP and hot rolled material, emphasising that parameters of this manufacturing process still have to be optimised. As an alternative manufacturing route, due to the uniform microstructure and simplicity of the process, hot pressing might be a promising method for production of smaller parts of ODS ferritic steels. Besides, the ductile-to-brittle transition temperature of all thermo-mechanically treated materials, in comparison with as-HIPped ODS steel, was improved by more than 50%, the transition temperature ranging from 50 to 70 °C (323 and 343 K) remains still unsatisfactory.

  3. 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.

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

    SciTech Connect

    Tan, Lizhen; Hoelzer, David T; Busby, Jeremy T; Sokolov, Mikhail A; Klueh, Ronald L

    2012-01-01

    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.

  5. Microstructural characterizations of 14Cr ODS ferritic steels subjected to hot torsion

    NASA Astrophysics Data System (ADS)

    Karch, A.; Sornin, D.; Barcelo, F.; Bosonnet, S.; de Carlan, Y.; Logé, R.

    2015-04-01

    Oxide dispersion strengthened (ODS) steels are very promising materials for nuclear applications. In this paper, the hot working behavior of ODS ferritic steels, consolidated by hot extrusion, is studied through torsion tests. Three ODS steels are produced acting on both the quantity of Ti and Y2O3 added to the matrix (wt% Fe-14Cr-1W), and the density and size of the nanoparticles. A temperature range of 1000-1200 °C and strain rates from 5 ṡ 10-2 to 5 s-1 are considered. The microstructures of deformed samples are examined by Electron Back-Scatter Diffraction and X-ray diffraction techniques. It is observed that hot plastic strain leads to an early damage with nucleation and growth of cavities along grain boundaries. Except for the damage, very few microstructural and textural evolutions are noticed. The three tested ODS steels exhibit almost the same behavior under hot torsion straining, regardless of the precipitation state. Overall, the experimental results are interpreted through a mechanism of strain accommodation at grain boundaries, with low dislocation activity in the bulk of the grains.

  6. Microstructure and Charpy impact properties of 12 14Cr oxide dispersion-strengthened ferritic steels

    NASA Astrophysics Data System (ADS)

    Oksiuta, Z.; Baluc, N.

    2008-02-01

    This paper describes the microstructure and Charpy impact properties of 12-14 Cr ODS ferritic steels fabricated by mechanical alloying of pure Fe, Cr, W, Ti and Y 2O 3 powders in a Retsch ball mill in argon atmosphere, followed by hot isostatic pressing at 1100 °C under 200 MPa for 4 h and heat treatment at 850 °C for 1 h. Weak Charpy impact properties were obtained in the case of both types of as-hipped materials. In the case of 14Cr materials, the weak Charpy properties appeared related to a bimodal grain size distribution and a heterogeneous dislocation density between the coarse and fine grains. No changes in microstructure were evidenced after heat treatment at 850 °C. Significant improvement in the transition temperature and upper shelf energy of 12Cr materials was obtained by heat treatment at 850 °C for 1 h, which was attributed to the formation of smaller grains, homogenous in size and containing fewer dislocations, with respect to the as-hipped microstructure. This modified microstructure results in a good compromise between strength and Charpy impact properties.

  7. Cr-W-V bainitic/ferritic steel with improved strength and toughness and method of making

    DOEpatents

    Klueh, Ronald L.; Maziasz, Philip J.

    1994-01-01

    A high strength, high toughness Cr-W-V ferritic steel composition suitable for fast induced-radioactivity (FIRD) decay after irradiation in a fusion reactor comprises 2.5-3.5 wt % Cr, 2. This invention was made with Government support under contract DE-AC05-840R21400 awarded by the U.S. Department of Energy to Martin Marietta Energy Systems, Inc. and the Government has certain rights in this invention.

  8. Non-instantaneous growth characteristics of martensitic transformation in high Cr ferritic creep-resistant steel

    NASA Astrophysics Data System (ADS)

    Liu, Chenxi; Shao, Yi; Chen, Jianguo; Liu, Yongchang

    2016-08-01

    Microstructural observation and high-resolution dilatometry were employed to investigate kinetics of martensitic transformation in high Cr ferritic creep-resistant steel upon different quenching/cooling rates. By incorporating the classical athermal nucleation and impingement correction, a non-instantaneous growth model for martensitic transformation has been developed. The developed model describes austenite/martensite interface mobility during martensite growth. The growth rate of martensite is found to be varied from 1 × 10-6 to 3 × 10-6 m/s. The low interface mobility suggests that it is not appropriate to presume the instantaneous growth behavior of martensite. Moreover, based on the proposed model, nucleation rate of martensite under different cooling rates is found to be nearly the same, while the growth rate of martensite is promoted by increasing the cooling rate.

  9. Resistance spot weldability of 11Cr-ferritic/martensitic steel sheets

    NASA Astrophysics Data System (ADS)

    Uwaba, Tomoyuki; Yano, Yasuhide; Ito, Masahiro

    2012-02-01

    Resistance spot welding of 11Cr-0.4Mo-2W, V, Nb ferritic/martensitic steel sheets with different thicknesses was examined to develop a manufacturing technology for a fast reactor fuel subassembly with an inner duct structure. In the spot welding, welding current, electrode force, welding time and holding time were varied as welding parameters to investigate the appropriate welding conditions. Welding conditions under which spot weld joints did not have either crack or void defects in the nugget could be found when the electrode force was increased to 9.8 kN. It was also found that the electrode cap with a longer tip end length was effective for preventing weld defect formations. Strength of the spot welded joint was characterized from micro hardness and shear tension tests. In addition, the ductile-to-brittle transition temperature of the spot welded joint was measured by Charpy impact tests with specimens that had notches in the welded zone.

  10. 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.

  11. Tensile anisotropy and creep properties of a Fe-14CrWTi ODS ferritic steel

    NASA Astrophysics Data System (ADS)

    Steckmeyer, A.; Rodrigo, Vargas Hideroa; Gentzbittel, J. M.; Rabeau, V.; Fournier, B.

    2012-07-01

    A Fe-14Cr oxide dispersion strengthened (ODS) ferritic steel is studied as a potential material for cladding tube application for the next generation of fast-breeder nuclear reactors. Tensile specimens machined out from a hot extruded round bar in three different orientations are used to evaluate the mechanical anisotropy of this steel for temperatures in the range 20-750 °C. Its anisotropy is discussed both in terms of mechanical strength and fracture mode. At high temperatures (HTs), above 500 °C, the longitudinal direction appears to be the most ductile and most resistant direction. Longitudinal creep tests between 650 °C and 900 °C were also carried out. They show this ODS steel has a high HT creep lifetime and a low creep failure strain. Intergranular cracks aligned along the loading axis were observed on fractured creep specimens. They reveal a particular weakness of prior particle boundaries and suggest to modify the elaboration process through mechanical alloying and hot extrusion.

  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. Effect of Process Parameters on Microstructure and Hardness of Oxide Dispersion Strengthened 18Cr Ferritic Steel

    NASA Astrophysics Data System (ADS)

    Nagini, M.; Vijay, R.; Rajulapati, Koteswararao V.; Rao, K. Bhanu Sankara; Ramakrishna, M.; Reddy, A. V.; Sundararajan, G.

    2016-08-01

    Pre-alloyed ferritic 18Cr steel (Fe-18Cr-2.3W-0.3Ti) powder was milled with and without nano-yttria in high-energy ball mill for varying times until steady-state is reached. The milled powders were consolidated by upset forging followed by hot extrusion. Microstructural changes were examined at all stages of processing (milling, upset forging, and extrusion). In milled powders, crystallite size decreases and hardness increases with increasing milling time reaching a steady-state beyond 5 hours. The size of Y2O3 particles in powders decreases with milling time and under steady-state milling conditions; the particles either dissolve in matrix or form atomic clusters. Upset forged sample consists of unrecrystallized grain structure with few pockets of fine recrystallized grains and dispersoids of 2 to 4 nm. In extruded and annealed rods, the particles are of cuboidal Y2Ti2O7 at all sizes and their size decreased from 15 nm to 5 nm along with significant increase in number density. The oxide particles in ODS6 are of cuboidal Y2Ti2O7 with diamond cubic crystal structure ( Fd bar{3} m) having a lattice parameter of 10.1 Å and are semicoherent with the matrix. The hardness values of extruded and annealed samples predicted by linear summation model compare well with measured values.

  14. Effects of vanadium on polarization of 18% Cr ferritic stainless steel

    SciTech Connect

    Davies, R.D. . Dept. of Metallurgy and Materials Engineering)

    1993-07-01

    Effects of alloying on the anodic polarization of a low interstitial, 18% chromium (Cr) ferritic stainless steel in sulfuric acid (H[sub 2]SO[sub 4]) were examined. Vanadium (V) from 1 to 4% was added alone and with up to 1.5% nickel (Ni), silicon (Si), copper (Cu), and molybdenum (MO). The carbon (C) and nitrogen (N) level varied from 84 to 168 ppm. The alloys were stabilized with titanium (Ti) or niobium (Nb). Increasing V had a variable effect on passivation in 1 N H[sub 2]SO[sub 4]. The critical current density for passivation lowered. The breakdown potential also lowered. Stabilization with Ti prevented lowering of the breakdown potential. Ni addition to Cr-V-Ti alloys broadened the passive region of the alloys and lowered the minimum current density for passivation. Mo and Cu were beneficial, but Si had little effect on passivation. The alloys did not appear to undergo intergranular corrosion in the modified Strauss test.

  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. Effect of Process Parameters on Microstructure and Hardness of Oxide Dispersion Strengthened 18Cr Ferritic Steel

    NASA Astrophysics Data System (ADS)

    Nagini, M.; Vijay, R.; Rajulapati, Koteswararao V.; Rao, K. Bhanu Sankara; Ramakrishna, M.; Reddy, A. V.; Sundararajan, G.

    2016-06-01

    Pre-alloyed ferritic 18Cr steel (Fe-18Cr-2.3W-0.3Ti) powder was milled with and without nano-yttria in high-energy ball mill for varying times until steady-state is reached. The milled powders were consolidated by upset forging followed by hot extrusion. Microstructural changes were examined at all stages of processing (milling, upset forging, and extrusion). In milled powders, crystallite size decreases and hardness increases with increasing milling time reaching a steady-state beyond 5 hours. The size of Y2O3 particles in powders decreases with milling time and under steady-state milling conditions; the particles either dissolve in matrix or form atomic clusters. Upset forged sample consists of unrecrystallized grain structure with few pockets of fine recrystallized grains and dispersoids of 2 to 4 nm. In extruded and annealed rods, the particles are of cuboidal Y2Ti2O7 at all sizes and their size decreased from 15 nm to 5 nm along with significant increase in number density. The oxide particles in ODS6 are of cuboidal Y2Ti2O7 with diamond cubic crystal structure (Fd bar{3} m) having a lattice parameter of 10.1 Å and are semicoherent with the matrix. The hardness values of extruded and annealed samples predicted by linear summation model compare well with measured values.

  17. Effect of Niobium on the Ferrite Continuous-Cooling-Transformation (CCT) Curve of Ultrahigh-Thickness Cr-Mo Steel

    NASA Astrophysics Data System (ADS)

    Lee, Sanghoon; Na, Hyesung; Kim, Byunghoon; Kim, Dongjin; Kang, Chungyun

    2013-06-01

    Pressure vessels made for petrochemical and power plants using Cr-Mo steel must be thick (≥400 mm) and have high tensile strength (≥600 MPa). However, the tensile strength in the middle portion of the vessel is very low as a result of ferrite formation. Therefore, research was performed to study the ferrite transformation that occurs in the middle portion of high-thickness Cr-Mo steel when Nb is added to it. The ferrite-formation start time of the continuous-cooling-transformation (CCT) curve decreased with an increase in Nb content until the latter reached 0.05 pct. On cooling from the austenitizing temperature, some of the NbC present at the austenitizing temperature of 1203 K (930 °C) goes into austenite solution in the temperature range of 1173 K to 1073 K (900 °C to 800 °C). However, the ferrite curve shifted to the left for the alloy containing 0.075 pct Nb. It is postulated that the surplus NbC could act as ferrite nucleation sites despite the lower cooling rate. As a result, the hardenability improved in the order of the following Nb content: 0.05 pct, 0.025 pct, 0 pct, and 0.075 pct.

  18. 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.

  19. 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.

  20. Irradiation effects in ferritic steels

    NASA Astrophysics Data System (ADS)

    Lechtenberg, Thomas

    1985-08-01

    Since 1979 the Alloy Development for Irradiation Performance (ADIP) task funded by the US Department of Energy has been studying the 2-12Cr class of ferritic steels to establish the feasibility of using them in fusion reactor first wall/breeding blanket (FW/B) applications. The advantages of ferritic steels include superior swelling resistance, low thermal stresses compared to austenitic stainless steels, attractive mechanical properties up to 600°C. and service histories exceeding 100 000 h. These steels are commonly used in a range of microstructural conditions which include ferritic, martensitic. tempered martensitic, bainitic etc. Throughout this paper where the term "ferritic" is used it should be taken to mean any of these microstructures. The ADIP task is studying several candidate alloy systems including 12Cr-1MoWV (HT-9), modified 9Cr-1MoVNb, and dual-phased steels such as EM-12 and 2 {1}/{4}Cr-Mo. These materials are ferromagnetic (FM), body centered cubic (bcc), and contain chromium additions between 2 and 12 wt% and molybdenum additions usually below 2%. The perceived issues associated with the application of this class of steel to fusion reactors are the increase in the ductile-brittle transition temperature (DBTT) with neutron damage, the compatibility of these steels with liquid metals and solid breeding materials, and their weldability. The ferromagnetic character of these steels can also be important in reactor design. It is the purpose of this paper to review the current understanding of these bcc steels and the effects of irradiation. The major points of discussion will be irradiation-induced or -enhanced dimensional changes such as swelling and creep, mechanical properties such as tensile strength and various measurements of toughness, and activation by neutron interactions with structural materials.

  1. 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.

  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. Microstructure and mechanical properties of heat-resistant 12% Cr ferritic-martensitic steel EK-181 after thermomechanical treatment

    NASA Astrophysics Data System (ADS)

    Polekhina, N. A.; Litovchenko, I. Yu.; Tyumentsev, A. N.; Astafurova, E. G.; Chernov, V. M.; Leontyeva-Smirnova, M. V.

    2015-10-01

    The effect of high-temperature thermomechanical treatment (TMT) with the deformation in the austenitic region on the features of microstructure, phase transformations and mechanical properties of low-activation 12% Cr ferritic-martensitic steel EK-181 is investigated. It is established, that directly after thermomechanical treatment (without tempering) the sizes and density of V(CN) particles are comparable with those after a traditional heat treatment (air quenching and tempering at 720°C, 3 h), where these particles are formed only during tempering. It causes the increasing of the yield strength of the steel up to ≈1450 MPa at room temperature and up to ≈430 MPa at the test temperature T = 650°C. The potential of microstructure modification by this treatment aimed at improving heat resistance of steel is 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. Tensile properties and deformation mechanisms of a 14Cr ODS ferritic steel

    NASA Astrophysics Data System (ADS)

    Steckmeyer, A.; Praud, M.; Fournier, B.; Malaplate, J.; Garnier, J.; Béchade, J. L.; Tournié, I.; Tancray, A.; Bougault, A.; Bonnaillie, P.

    2010-10-01

    The search for a new cladding material is part of the research studies carried out at CEA to develop a sodium-cooled fast reactor meeting the expectations of the Generation IV International Forum. In this study, the tensile properties of a ferritic oxide dispersion strengthened steel produced by hot extrusion at CEA have been evaluated. They prove the studied alloy to be as resistant as and more ductile than the other nano-reinforced alloys of literature. The effects of the strain rate and temperature on the total plastic strain of the material remind of diffusion phenomena. Intergranular damage and intergranular decohesion are clearly highlighted.

  6. Development of A New Class of Fe-3Cr-W(V)Ferritic Steels for Industrial Process Applications

    SciTech Connect

    Sikka, V.J.; Jawad, M.H.

    2005-06-15

    The project, 'Development of a New Class of Fe-Cr-W(V) Ferritic Steels for Industrial Process Applications', was a Cooperative Research and Development Agreement (CRADA) between Oak Ridge National Laboratory (ORNL) and Nooter Corporation. This project dealt with improving the materials performance and fabrication for the hydrotreating reactor vessels, heat recovery systems, and other components for the petroleum and chemical industries. The petroleum and chemical industries use reactor vessels that can approach the ship weights of approximately 300 tons with vessel wall thicknesses of 3 to 8 in. These vessels are typically fabricated from Fe-Cr-Mo steels with chromium ranging from 1.25 to 12% and molybdenum from 1 to 2%. Steels in this composition have great advantages of high thermal conductivity, low thermal expansion, low cost, and properties obtainable by heat treatment. With all of the advantages of Fe-Cr-Mo steels, several issues are faced in design and fabrication of vessels and related components. These issues include the following: (1) low strength properties of current alloys require thicker sections; (2) increased thickness causes heat-treatment issues related to nonuniformity across the thickness and thus not achieving the optimum properties; (3) fracture toughness (ductile-to-brittle transition ) is a critical safety issue for these vessels, and it is affected in thick sections due to nonuniformity of microstructure; (4) PWHT needed after welding and makes fabrication more time-consuming with increased cost; and (5) PWHT needed after welding also limits any modifications of the large vessels in service. The goal of this project was to reduce the weight of large-pressure vessel components (ranging from 100 to 300 tons) by approximately 25% and reduce fabrication cost and improve in-service modification feasibility through development of Fe-3Cr-W(V) steels with combination of nearly a 50% higher strength, a lower DBTT and a higher upper-shelf energy

  7. 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.

  8. Hot deformation behavior and processing map of a 9Cr ferritic/martensitic ODS steel

    NASA Astrophysics Data System (ADS)

    Zhang, Guangming; Zhou, Zhangjian; Sun, Hongying; Zou, Lei; Wang, Man; Li, Shaofu

    2014-12-01

    The hot deformation behavior of 9Cr oxide-dispersion-strengthened (ODS) steel fabricated through the process of mechanical alloying and hot isostatic pressing (HIP) as investigated through hot compression deformation tests on the Gleeble-1500D simulator in the temperature range of 1050-1200 °C and strain rate range of 0.001 s-1-1 s-1. The relationship between the rheological stress and the strain rate was also studied. The activation energy and the stress and material parameters of the hyperbolic-sine equation were resolved according to the data obtained. The processing map was also proposed. The results show that the flow stress decreases as the temperature increases, and that decreasing of the strain rate of the 9Cr ODS steel results in a positive strain rate sensitivity. It is clear that dynamic recrystallization is influenced by both temperature and strain rate. The results of this study may provide a good reference for the selection of hot working parameters for 9Cr ODS steel. The optimum processing domains are at 1200 °C with a strain rate of 1 s-1 and in the range of 1080-1100 °C with a strain rate between 0.018 s-1 and 0.05 s-1.

  9. High temperature deformation mechanism of 15CrODS ferritic steels at cold-rolled and recrystallized conditions

    NASA Astrophysics Data System (ADS)

    Sugino, Yoshito; Ukai, Shigeharu; Oono, Naoko; Hayashi, Shigenari; Kaito, Takeji; Ohtsuka, Satoshi; Masuda, Hiroshi; Taniguchi, Satoshi; Sato, Eiichi

    2015-11-01

    The ODS ferritic steels realize potentially higher operating temperature due to structural stability by the dispersed nano-size oxide particles. The deformation process and mechanism of 15CrODS ferritic steels were investigated at 1073 K and 1173 K for the cold-rolled and recrystallized conditions. Tensile and creep tests were conducted at the stress in parallel (LD) and perpendicular (TD) directions to the grain boundaries. Strain rate varied from 10-1 to 10-9 s-1. For the LD specimens, deformation in the cold rolled and recrystallized conditions is reinforced by finely dispersed oxide particles. The dominant deformation process for the recrystallized TD specimen is controlled through the grain boundary sliding and stress accommodation via diffusional creep at temperature of 1173 K and lower strain rate less than 10-4 s-1. The grain boundary sliding couldn't be rate-controlling process at 1073 K for the as-cold rolled TD specimen, where a dynamic recovery of the dislocation produced by cold-rolling is related to the deformation process.

  10. Alloy Design and Development of Cast Cr-W-V Ferritic Steels for Improved High-Temperature Strength for Power Generation Applications

    SciTech Connect

    Klueh, R L; Maziasz, P J; Vitek, J M; Evans, N D; Hashimoto, N

    2006-09-23

    Economic and environmental concerns demand that the power-generation industry seek increased efficiency for gas turbines. Higher efficiency requires higher operating temperatures, with the objective temperature for the hottest sections of new systems {approx} 593 C, and increasing to {approx} 650 C. Because of their good thermal properties, Cr-Mo-V cast ferritic steels are currently used for components such as rotors, casings, pipes, etc., but new steels are required for the new operating conditions. The Oak Ridge National Laboratory (ORNL) has developed new wrought Cr-W-V steels with 3-9% Cr, 2-3% W, 0.25% V (compositions are in wt.%), and minor amounts of additional elements. These steels have the strength and toughness required for turbine applications. Since cast alloys are expected to behave differently from wrought material, work was pursued to develop new cast steels based on the ORNL wrought compositions. Nine casting test blocks with 3, 9, and 11% Cr were obtained. Eight were Cr-W-V-Ta-type steels based on the ORNL wrought steels; the ninth was COST CB2, a 9Cr-Mo-Co-V-Nb cast steel, which was the most promising cast steel developed in a European alloy-development program. The COST CB2 was used as a control to which the new compositions were compared, and this also provided a comparison between Cr-W-V-Ta and Cr-Mo-V-Nb compositions. Heat treatment studies were carried out on the nine castings to determine normalizing-and-tempering treatments. Microstructures were characterized by both optical and transmission electron microscopy (TEM). Tensile, impact, and creep tests were conducted. Test results on the first nine cast steel compositions indicated that properties of the 9Cr-Mo-Co-V-Nb composition of COST CB2 were better than those of the 3Cr-, 9Cr-, and 11Cr-W-V-Ta steels. Analysis of the results of this first iteration using computational thermodynamics raised the question of the effectiveness in cast steels of the Cr-W-V-Ta combination versus the Cr

  11. AFM and TEM study of cyclic slip localization in fatigued ferritic X10CrAl24 stainless steel

    SciTech Connect

    Man, J. . E-mail: man@ipm.cz; Petrenec, M.; Obrtlik, K.; Polak, J.

    2004-11-08

    Atomic force microscopy and high resolution scanning electron microscopy were applied to the study of surface relief evolution at emerging persistent slip bands (PSBs) in individual grains of ferritic X10CrAl24 stainless steel cycled with constant plastic strain amplitude. Only the combination of both methods can reveal the true shape and fine details of extrusions and intrusions. Quantitative data on the changes of the surface topography of persistent slip markings and on the kinetics of extrusion growth during the fatigue life were obtained. Transmission electron microscopy of surface foils revealed PSBs with the typical, well-known ladder structure. Experimental data on cyclic slip localization in PSBs are compared with those in fcc metals and discussed in terms of vacancy models of surface relief evolution and fatigue crack initiation.

  12. Microstructure of welded and weld-simulated modified 9Cr-1Mo (P 91) ferritic steel

    SciTech Connect

    Prader, R.; Cerjak, H.; David, S.A.

    1996-12-31

    Within the last 30 years significant advances in materials development have been made which have enhanced the operation temperature of thermal power plants led to an improvement in efficiency. Currently, a great deal of work relating to the modified 9% Cr-1/5 Mo steel (P 91) is in progress. This type of steel was originally considered to be an appropriate candidate for Fast Breeder Applications, and it was designed by Oak Ridge National Laboratory. Up to the present, several modifications of 9% chromium steels have been developed in several labs all over the globe containing different portions of tungsten and molybdenum. This report focuses on the microstructural characterization of a heavy section multi pass weld done on a tube composed of P 91 steel. Weld simulations, using the Gleeble 1500 technology, were successfully applied to aid the microstructural study of the heat affected zone (HAZ). As revealed by the investigations, post weld heat treatment (PWHT) results in a softening of the heat affected zone in an area close to the uninfluenced base metal. According to the observed microstructure and Gleeble simulations, the peak temperature of the soft zone during welding falls within a temperature range between A{sub C1} (= 810 C) and slightly above A{sub C3} typically 900--930 C which was discovered for the first time in a previous investigation.

  13. 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.

  14. Effect of specimen size and nickel content on the impact properties of 12 Cr-1 MoVW ferritic steel

    SciTech Connect

    Corwin, W.R.; Klueh, R.L.; Vitek, J.M.

    1983-01-01

    The ferritic steel 12 Cr-1 MoVW is a candidate material for use in the first wall of magnetic fusion reactors. One of the primary concerns of materials in this application is service-induced embrittlement from aging and irradiation. Unirradiated Charpy impact data have been developed on three typical heats of 12 Cr-1 MoVW steel and on heats that have been modified with nickel and chromium additions for subsequent simulation of helium effects of irradiation. The ductile-to-brittle transition temperature and the upper-shelf energy were reduced by nickel additions. The addition of nickel while simultaneously maintaining a constant net chromium equivalent caused the transition temperature to increase. The use of a subsize specimen is mandated by the small volume and high gamma heating in high-flux research reactors used for very high-fluence irradiation experiments. Therefore, an understanding of the behavior of the subsize specimen is important in predicting corresponding irradiation-induced transition temperature shifts and upper-shelf drops of full-size Charpy specimens. Data are reported from subsize Charpy impact specimens, and the full- and subsize specimens are compared. The effect of specimen size on the upper-shelf energy of this material can be reduced better by volume normalization than by area normalization.

  15. 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.

  16. 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.

  17. 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.

  18. Irradiation embrittlement of neutron-irradiated low activation ferritic steels

    NASA Astrophysics Data System (ADS)

    Kayano, H.; Kimura, A.; Narui, M.; Sasaki, Y.; Suzuki, Y.; Ohta, S.

    1988-07-01

    Effects of neutron irradiation and additions of small amounts of alloying elements on the ductile-brittle transition temperature (DBTT) of three different groups of ferritic steels were investigated by means of the Charpy impact test in order to gain an insight into the development of low-activation ferritic steels suitable for the nuclear fusion reactor. The groups of ferritic steels used in this study were (1) basic 0-5% Cr ferritic steels, (2) low-activation ferritic steels which are FeCrW steels with additions of small amounts of V, Mn, Ta, Ti, Zr, etc. and (3) FeCrMo, Nb or V ferritic steels for comparison. In Fe-0-15% Cr and FeCrMo steels, Fe-3-9% Cr steels showed minimum brittleness and provided good resistance against irradiation embrittlement. Investigations on the effects of additions of trace amounts of alloying elements on the fracture toughness of low-activation ferritic steels made clear the optimum amounts of each alloying element to obtain higher toughness and revealed that the 9Cr-2W-Ta-Ti-B ferritic steel showed the highest toughness. This may result from the refinement of crystal grains and improvement of quenching characteristics caused by the complex effect of Ti and B.

  19. Development of low activation Ferritic steels

    NASA Astrophysics Data System (ADS)

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

    1986-11-01

    Fe-(2-15)%Cr-(0-4)%W-0.1%C and Fe-9%Cr-(0-l)%V-0.1%C steels were prepared on the basis of reduced activation of ferritic steels. Tempering characteristics of these alloys were studied as a preliminary evaluation of mechanical properties. Alloys except for 12-15%Cr, 9%Cr-4%W, and 9%Cr-1%V showed a single phase of martensite. Carbides which precipitated in as-tempered steels are M 23C 6, M 6C, and W 2C for Cr-W steels and M 23C 6 and V 4C 3 for Cr-V steels. The toughness of the alloys was examined with Charpy impact test. The minimum DBTT (ductile-brittle transition temperature) was observed at around 0.25 at% of W or V concentration for 9%Cr steels. 9%Cr-V steels were superior to commercial 9%Cr-2%Mo steel in the point of toughness. The order of alloying element with a low DBTT was V > Mo > W.

  20. Simple bond-order-type interatomic potential for an intermixed Fe-Cr-C system of metallic and covalent bondings in heat-resistant ferritic steels

    SciTech Connect

    Kumagai, Tomohisa Nakamura, Kaoru; Yamada, Susumu; Ohnuma, Toshiharu

    2014-12-28

    It is known that M{sub 23}C{sub 6}(M = Cr/Fe) behavior in heat-resistant ferritic steels affects the strength of the material at high temperature. The ability to garner direct information regarding the atomic motion using classical molecular dynamics simulations is useful for investigating the M{sub 23}C{sub 6} behavior in heat-resistant ferritic steels. For such classical molecular dynamics calculations, a suitable interatomic potential is needed. To satisfy this requirement, an empirical bond-order-type interatomic potential for Fe-Cr-C systems was developed because the three main elements to simulate the M{sub 23}C{sub 6} behavior in heat-resistant ferritic steels are Fe, Cr, and C. The angular-dependent term, which applies only in non-metallic systems, was determined based on the similarity between a Finnis-Sinclair-type embedded-atom-method interatomic potential and a Tersoff-type bond-order potential. The potential parameters were determined such that the material properties of Fe-Cr-C systems were reproduced. These properties include the energy and lattice constants of 89 crystal structures; the elastic constants of four realistic precipitates; the bulk moduli of B1, B2, and B3 crystals; the surface energies of B1 and B2 crystals; and the defect-formation energies and atomic configurations of 66 Fe-Cr-C complexes. Most of these material properties were found to be reproduced by our proposed empirical bond-order potentials. The formation energies and lattice constants of randomly mixed Fe-Cr alloys calculated using the interatomic potentials were comparable to those obtained through experiments and first-principles calculations. Furthermore, the energies and structures of interfaces between Cr carbide and α-Fe as predicted through first-principles calculations were well reproduced using these interatomic potentials.

  1. Articles comprising ferritic stainless steels

    DOEpatents

    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.

  2. Formation Mechanism of Type IV Failure in High Cr Ferritic Heat-Resistant Steel-Welded Joint

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Tsukamoto, S.; Shirane, T.; Abe, F.

    2013-10-01

    The mechanism of type IV failure has been investigated by using a conventional 9Cr ferritic heat-resistant steel Gr.92. In order to clarify the main cause of type IV failure, different heat treatments were performed on the base metal in order to change the prior austenite grain (PAG) size and precipitate distribution after applying the heat-affected zone (HAZ) simulated thermal cycle at the peak temperature of around A c3 ( A c3 HAZ thermal cycle) and postweld heat treatment (PWHT). The microstructural evolution during the A c3 HAZ thermal cycle and PWHT was investigated by means of scanning electron microscope (SEM), electron backscatter diffraction (EBSD), electron probe microanalysis (EPMA), and transmission electron microscope (TEM). It was found that M23C6 carbides were scarcely precipitated at the newly formed fine PAG, block, and lath boundaries in A c3 HAZ-simulated Gr.92, because the carbide forming elements such as Cr and C were segregated at the former PAG and block boundaries of the base metal. On the other hand, if all the boundaries were covered by sufficient M23C6 carbides by homogenization of the alloying elements prior to applying the HAZ thermal cycle, the creep strength was much improved even if the fine PAG was formed. From these results, it is concluded that fine-grained microstructure cannot account for the occurrence of type IV failure, and it only has a small effect during long-term creep. The most important factor is the precipitate formation behavior at various boundaries. Without sufficient boundary strengthening by precipitates, the microstructure of A c3 HAZ undergoes severe changes even during PWHT and causes premature failure during creep.

  3. Creep strengthening by lath boundaries in 9Cr ferritic heat-resistant steel

    NASA Astrophysics Data System (ADS)

    Mitsuhara, Masatoshi; Yamasaki, Shigeto; Miake, Masaki; Nakashima, Hideharu; Nishida, Minoru; Kusumoto, Junichi; Kanaya, Akihiro

    2016-02-01

    The interactions between dislocations and lath boundaries in Grade 91 steel were observed by an in situ transmission electron microscopy tensile test at 973 K. Dislocations glided slowly and bowed out in a martensite lath interior. The ends of the dislocation were connected to the lath boundaries. In a tempered specimen, the pinning stress caused by the lath boundary was estimated to be >70 MPa with a lath width of 0.4 μm. In crept specimens, lath coarsening reduced the pinning effect.

  4. Anomalous surface segregation profiles in ferritic Fe-Cr stainless steel

    NASA Astrophysics Data System (ADS)

    Levesque, Maximilien

    2013-02-01

    The iron-chromium alloy and its derivatives are widely used for their remarkable resistance to corrosion, which only occurs in a narrow concentration range around 9 to 13 atomic percent chromium. Although known to be due to chromium enrichment of a few atoms thick layer at the surfaces, the understanding of its complex atomistic origin has been a remaining challenge. We report an investigation of the thermodynamics of such surfaces at the atomic scale by means of Monte Carlo simulations. We use a Hamiltonian which provides a parametrization of previous ab initio results and successfully describes the alloy's unusual thermodynamics. We report a strong enrichment in Cr of the surfaces for low bulk concentrations, with a narrow optimum around 12 atomic percent chromium, beyond which the surface composition decreases drastically. This behavior is explained by a synergy between (i) the complex phase separation in the bulk alloy, (ii) local phase transitions that tune the layers closest to the surface to an iron-rich state and inhibit the bulk phase separation in this region, and (iii) its compensation by a strong and nonlinear enrichment in Cr of the next few layers. Implications with respect to the design of prospective nanomaterials are briefly discussed.

  5. Relationship Between Grain Boundary Structure and Radiation Induced Segregation in a Neutron Irradiated 9 wt. % Cr Model Ferritic/Martensitic Steel

    SciTech Connect

    Field, Kevin G; Miller, Brandon; Chichester, Heather J.M.; Sridharan, K.; Allen, Todd R.

    2014-01-01

    Ferritic/Martensitic (F/M) steels with high Cr content posses the high temperature strength and low swelling rates required for advanced nuclear reactor designs. Radiation induced segregation (RIS) occurs in F/M steels due to solute atoms preferentially coupling to point defect fluxes to defect sinks, such as grain boundaries (GBs). The RIS response of F/M steels and austenitic steels has been shown to be dependent on the local structure of GBs but has only been demonstrated in ion irradiated specimens. A 9 wt. % Cr model alloy steel was irradiated to 3 dpa using neutrons at the Advanced Test Reactor (ATR) to determine the effect of neutron radiation environment on the RIS-GB structure dependence. This investigation found the relationship between GB structure and RIS is also active for F/M steels irradiated using neutrons. The data generated from the neutron irradiation is also compared to RIS data generated using proton irradiations on the same heat of model alloy.

  6. Relationship between lath boundary structure and radiation induced segregation in a neutron irradiated 9 wt.% Cr model ferritic/martensitic steel

    SciTech Connect

    Field, Kevin G.; Miller, Brandon D.; Chichester, Heather J. M.; Sridharan, Kumar; Allen, Todd R.

    2014-02-01

    Ferritic/Martensitic (F/M) steels with high Cr content posses the high temperature strength and low swelling rates required for advanced nuclear reactor designs. Radiation induced segregation (RIS) occurs in F/M steels due to solute atoms preferentially coupling to point defect fluxes which migrate to defect sinks, such as grain boundaries (GBs). The RIS response of F/M steels and austenitic steels has been shown to be dependent on the local structure of GBs where low energy structures have suppressed RIS responses. This relationship between local GB structure and RIS has been demonstrated primarily in ion-irradiated specimens. A 9 wt.% Cr model alloy steel was irradiated to 3 dpa using neutrons at the Advanced Test Reactor (ATR) to determine the effect of a neutron radiation environment on the RIS response at different GB structures. This investigation found the relationship between GB structure and RIS is also active for F/M steels irradiated using neutrons. The data generated from the neutron irradiation is also compared to RIS data generated using proton irradiations on the same heat of model alloy.

  7. Development of a New Class of Fe-3Cr-W(V) Ferritic Steels for Industrial Process Applications

    SciTech Connect

    Jawad, Mann; Sikka, Vinod K.

    2005-04-06

    The project described in this report dealt with improving the materials performance and fabrication for hydrotreating reactor vessels, heat recovery systems, and other components for the petroleum and chemical industries. These reactor vessels can approach ship weights of about 300 tons with vessel wall thicknesses of 3 to 8 inches. They are typically fabricated from Fe-Cr-Mo alloy steels, containing 1.25 to 12% chromium and 1 to 2% molybdenum. The goal of this project was to develop Fe-Cr-W(V) steels that can perform similar duties, in terms of strength at high temperatures, but will weigh less and thereby save energy.

  8. 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.

  9. Cr-W-V bainitic/ferritic steel with improved strength and toughness and method of making

    DOEpatents

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

    1994-03-08

    This work describes a high strength, high toughness bainitic/ferritic steel alloy comprising about 2.75% to 4.0% chromium, about 2.0% to 3.5% tungsten, about 0.10% to 0.30% vanadium, and about 0.1% to 0.15% carbon with the balance iron, wherein the percentages are by total weight of the composition, wherein the alloy having been heated to an austenitizing temperature and then cooled at a rate sufficient to produce carbide-free acicular bainite. 15 figures.

  10. Development of ferritic steels for fusion reactor applications

    SciTech Connect

    Klueh, R.L.; Maziasz, P.J.; Corwin, W.R.

    1988-08-01

    Chromium-molybdenum ferritic (martensitic) steels are leading candidates for the structural components for future fusion reactors. However, irradiation of such steels in a fusion environment will produce long-lived radioactive isotopes that will lead to difficult waste-disposal problems. Such problems could be reduced by replacing the elements in the steels (i.e., Mo, Nb, Ni, N, and Cu) that lead to long-lived radioactive isotopes. We have proposed the development of ferritic steels analogous to conventional Cr-Mo steels, which contain molybdenum and niobium. It is proposed that molybdenum be replaced by tungsten and niobium be replaced by tantalum. Eight experimental steels were produced. Chromium concentrations of 2.25, 5, 9, and 12% were used (all concentrations are in wt %). Steels with these chromium compositions, each containing 2% W and 0.25% V, were produced. To determine the effect of tungsten and vanadium, 2.25 Cr steels were produced with 2% W and no vanadium and with 0.25% V and O and 1% W. A 9Cr steel containing 2% W, 0.25 V, and 0.07% Ta was also studied. For all alloys, carbon was maintained at 0.1%. Tempering studies on the normalized steels indicated that the tempering behavior of the new Cr-W steels was similar to that of the analogous Cr-Mo steels. Microscopy studies indicated that 2% tungsten was required in the 2.25 Cr steels to produce 100% bainite in 15.9-mm-thick plate during normalization. The 5Cr and 9Cr steels were 100% martensite, but the 12 Cr steel contained about 75% martensite with the balance delta-ferrite. 33 refs., 35 figs., 5 tabs.

  11. Effect of impurity content on creep crack growth resistance in 1Cr1Mo0.25V ferritic steels

    NASA Astrophysics Data System (ADS)

    Fattorini, F.; Franzoni, U.; Sturlese, S.

    1990-07-01

    The effect of impurity content on creep crack growth (CCG) rate and, more generally, on hot ductility of a typical lCrlMo0.25V ferritic steel was evaluated. Four heats intentionally doped with various amounts of impurities were characterized after heat treatments simulating the industrial thermal cycle taking place in a 1000-mm-diameter high-pressure rotor at two positions: near the outside surface and at the center in the cases of air cooling and oil quenching, respectively. Results indicate that the highest crack growth rates occur in the grade with a low P content (40 ppm) and Sn and Sb values (100 to 200 ppm) comparable with those characteristic of commercial steels. A marked reduction in brittleness is achieved only through a substantial reduction in the amount of Sn and Sb, even when medium-to-high P levels (100 ppm) are present. Creep resistance in terms of both time to rupture and minimum growth rate is not influenced by the impurity content, at least within the range of stresses investigated. Auger analyses on crept specimens demonstrate the presence of a selective segregation of impurity elements similar to that found in other ferritic steels: P is the only segregating element at non-cavitated grain boundaries, while cavitated areas contain Sn, Sb, and Cu in addition to P. The embrittlement at high Sn and Sb levels depends on two factors: at low P levels, cracks rapidly propagate under surface diffusivity control; at high P levels, excess P segregates at the grain boundaries, and crack propagation proceeds by an intergranular decohesion mechanism.

  12. Modelling of the effect of precipitates on work-hardening, ductility and impact behaviour of ferritic-martensitic Cr steels

    NASA Astrophysics Data System (ADS)

    Preininger, D.

    2002-12-01

    The effect of precipitates on work-hardening, tensile ductility and impact behaviour of carbon and high nitrogen martensitic 7-12Cr as well as particle strengthened ODS-(9-13)Cr steels have been analysed by models. A minimum of work-hardening and uniform strain generally appears around 600 °C at onset of dislocation recovery. Pronounced precipitation by increasing nitrogen and carbon content or additionally of fine Y 2O 3-particles distinctly increases work-hardening and uniform ductility. These, however, decrease with increasing strengthening but do not reach a visible level above 1500 MPa for ODS-steels at 20 °C. Minima of total elongation and fracture strain additionally appear in carbon and nitrogen martensitic steels around 300 °C where dynamic strain ageing occurs. Fracture strain and ductile upper shelf energy of Charpy tests in accordance with model predictions also decrease with increasing yield strength more strongly for ODS-steels due to their enhanced work-hardening and localized deformation. The strength-induced increase of ductile-to-brittle transition temperatures of ODS-steels is comparable to that observed by irradiation defect strengthening.

  13. 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.

  14. Effects of W and Co on the Microstructure and Creep Strength of the Precipitation Strengthened 15Cr Ferritic Steels

    NASA Astrophysics Data System (ADS)

    Toda, Yoshiaki; Seki, Kazuhiro; Kimura, Kazuhiro; Abe, Fujio

    Effects of W and Co on microstructure of Co free 0.1C-15Cr-1Mo-3W-0.2V-0.05Nb-0.07N-0.003B (mass%) steel has been investigated, and a correlation between microstructure and creep strength property has been discussed. Time to rupture of 6W-3Co steel, in which W content was increased from 3 to 6mass% and 3mass%Co was added, was about 100 times longer than that of 3W-0Co base steel at 923K-100MPa and was almost the same as that of the conventional tempered martensitic creep resistant steel of NF616 steel. It has been found that the increase in W content and the addition of Co increases a number of coarse block type precipitates and promotes a precipitation of fine particles within grain, respectively. Furthermore, a large number of needle or disk-like fine particles aligned in a certain crystallographic orientation within grain has been observed in the creep ruptured steel containing high W and Co. It has been concluded that a remarkable increase in creep strength by the addition of W and Co is obtained by a combination of increase in an amount of coarse precipitates and a distribution of needle or disk-like fine particles within grain.

  15. A new equation for the Cr equivalent in 9 to 12 pct Cr steels

    SciTech Connect

    Ryu, S.H.; Yu, J.

    1998-06-01

    In advanced 9 to 12 pct Cr steels, the Cr equivalent is used as a measure to check the formation of {delta}-ferrite. In the present analysis, 29 alloys of varying composition were vacuum induction melted, and the amounts of {delta}-ferrite were measured in as-tempered conditions. Based on this and previous results on 9 to 12 pct Cr steels, a new equation for the Cr equivalent is proposed and correlated with the amount of {delta}-ferrite formation. Results indicate that the new Cr equivalent equation shows better correlation than previous equations and predicts the amount of {delta}-ferrite formed reasonably well.

  16. Development of a New Class of Fe-3Cr-W(V)Ferritic STeels for Industrial Process Applications

    SciTech Connect

    Jawad, M.

    2005-03-31

    The project described in this report dealt with improving the materials performance and fabrication for hydrotreating reactor vessels, heat recovery systems, and other components for the petroleum and chemical industries. The petroleum and chemical industries use reactor vessels that can approach ship weights of approximately 300 tons with vessel wall thicknesses of 3-8 in. These vessels are typically fabricated from Fe-Cr-Mo steels with chromium ranging from 1.25 to 12% and molybdenum from 1 to 2%. Steels in this composition range have great advantages of high thermal conductivity, low thermal expansion, low cost, and good properties obtainable by heat treatment. With all of the advantages of Fe-Cr-Mo steels, several issues are faced in design and fabrication of vessels and related components. These issues include the following: 1. The low strengths of current alloys require thicker sections. 2. Increased thickness causes heat-treatment issues related to nonuniformity across the thickness and thus a failure to achieve optimum properties. 3. Fracture toughness (ductile-to-brittle transition) is a critical safety issue for these vessels, especially in thick sections because of the nonuniformity of the microstructure. 4. The postweld heat treatment (PWHT) needed after welding makes fabrication more timeconsuming with increased cost. 5. PWHT needed after welding also limits any modifications of the large vessels in service. The goal of this project was to reduce the weight of large-pressure-vessel components (ranging from 100 to 300 tons) by approximately 25%, reduce fabrication cost, and improve in-service modification feasibility through development of Fe-3Cr-W(V) steels with a combination of nearly a 50% higher strength, a lower ductile-brittle transition temperature (DBTT), a higher upper-shelf energy, ease of heat treating, and a strong potential for not requiring PWHT.

  17. Lattice strain and damage evolution of 9-12/%Cr ferritic/martensitic steel during in situ tensile test by x-ray diffraction and small angle scattering.

    SciTech Connect

    Pan, X.; Wu, X.; Mo, K.; Chen, X,; Almer, J. D.; Ilavsky, J.; Haeffner, D. R.; Stubbins, J. F.; X-Ray Science Division; Univ. of Illinois

    2010-01-01

    In situ X-ray diffraction and small angle scattering measurements during tensile tests were performed on 9-12% Cr ferritic/martensitic steels. The lattice strains in both particle and matrix phases, along two principal directions, were directly measured. The load transfer between particle and matrix was calculated based on matrix/particle elastic mismatch, matrix plasticity and interface decohesion. In addition, the void or damage evolution during the test was measured using small angle X-ray scattering. By combining stress and void evolution during deformation, the critical interfacial strength for void nucleation was determined, and compared with pre-existing void nucleation criteria. These comparisons show that models overestimate the measured critical strength, and require a larger particle size than measured to match the X-ray observations.

  18. 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.

  19. Role of Boundary Strengthening on Prevention of Type IV Failure in High Cr Ferritic Heat-Resistant Steels

    NASA Astrophysics Data System (ADS)

    Liu, Yuan; Tsukamoto, Susumu; Sawada, Kota; Abe, Fujio

    2013-10-01

    Microstructure evolution of newly developed 9Cr-3W-3Co-V, Nb steel with boron addition (B steel) has been analyzed during HAZ thermal cycle at the peak temperature of around Ac3 (Ac3 HAZ) and post-weld heat treatment (PWHT) to elucidate the prevention mechanism of type IV failure by boron addition. It was found that enhancement of the boundary strengthening by precipitates is the main reason for prevention of type IV failure by boron addition. In B steel HAZ, original austenite is reconstituted through martensitic α to γ reverse transformation during the heating and original martensite is reconstituted through martensitic transformation during cooling of the Ac3 HAZ thermal cycle. This process allows M23C6 carbides to precipitate at the prior austenite grain (PAG) and block boundaries during PWHT even if the chemical segregation of carbide forming elements exists. The effect of boundary strengthening on the creep property has also been investigated. Microstructure evolution during creep was compared among Gr.92 with different Ac3 HAZ microstructures prepared by three kinds of heat treatments and B steel. The results revealed that both the boundary length and kernel average misorientation value decreased in all samples during creep. However, this process occurred very rapidly in Ac3 HAZ simulated Gr.92, whereas it was significantly retarded in the other samples with sufficient boundary strengthening by precipitates. This result confirms that the precipitates formed at PAG and block boundaries play the most important role to stabilize the microstructure of Ac3 HAZ simulated samples during creep and prolong the creep life.

  20. Effect of Laves Phase on High-Temperature Deformation and Microstructure Evolution in an 18Cr-2Mo-0.5Nb Ferritic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Ikeda, Ken-ichi; Yamoah, Nana Kwame Gyan; Reynolds, William T.; Hamada, Jun-ichi; Murayama, Mitsuhiro

    2015-08-01

    Niobium-containing ferritic stainless steels are finding new applications in automotive exhaust components because of their oxidation resistance, thermal fatigue resistance, and high-temperature strength. The mechanical behavior of Nb-containing ferritic steels at service temperatures of 973 K (700 °C) and higher results from the convolution of dynamic microstructural changes including precipitation, precipitate coarsening, strain hardening, recovery, and recrystallization. The relative contributions of these competing processes have yet to be clarified. In this study, the high-temperature flow strength of an 18Cr-2Mo-0.5Nb ferritic stainless steel (SUS 444) was correlated with microstructure under different strain and initial precipitate distributions to clarify the relative role of the strengthening and softening processes. High-temperature tensile tests at 1023 K (750 °C) of un-aged (initial microstructure is precipitate-free) and pre-aged (initial microstructure contains precipitates) samples were carried out and transmission electron microscopy was used to assess dislocation distributions and precipitate morphology. The difference in the stress-strain curves between un-aged and pre-aged samples was drastic; the yield strength of the un-aged sample was twice that of the pre-aged sample, and the un-aged sample exhibits a noticeable yield drop. Transmission electron microscopy revealed a Laves phase nucleated and grew during the high-temperature tensile test in the un-aged sample and the majority of the precipitates in the pre-aged sample were the same Laves phase. Furthermore, a strain effect on precipitate growth was recognized in un-aged and pre-aged conditions by comparing grip (no strain) and gage (strained) sections of tensile samples. The dominant strengthening contribution in un-aged samples is initially the precipitate shearing mechanism and it changes to Orowan strengthening beyond the ultimate tensile strength, whereas the dominant contribution in

  1. 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.

  2. 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.

  3. 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.

  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. Corrosion Study of Super Ferritic Stainless Steel UNS S44660 (26Cr-3Ni-3Mo) and Several Other Stainless Steel Grades (UNS S31603, S32101, and S32205) in Caustic Solution Containing Sodium Sulfide

    NASA Astrophysics Data System (ADS)

    Chasse, Kevin R.; Singh, Preet M.

    2013-11-01

    Electrochemical techniques, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) were used in this study to show how the corrosion mechanism of several commercial grades of stainless steel in hot caustic solution is strongly influenced by the presence of sodium sulfide. Experimental results from super ferritic stainless steel UNS S44660 (26Cr-3Ni-3Mo) were compared to austenitic stainless steel UNS S31603, lean duplex stainless steel (DSS) UNS S32101, and standard DSS UNS S32205 in caustic solution, with and without sodium sulfide, at 443 K (170 °C). Weight loss measurements indicated that corrosion rates of UNS44660 were much lower than the other grades of stainless steel in the presence of the sodium sulfide. Potentiodynamic polarization and linear polarization resistance measurements showed that the electrochemical behavior was altered by the adhesion of sulfur species, which reduced the polarization resistances and increased the anodic current densities. SEM and XPS results imply that the surface films that formed in caustic solution containing sodium sulfide were defective due to the adsorption of sulfide, which destabilized the passive film and led to the formation of insoluble metal sulfide compounds.

  6. Formation of delta ferrite in 9 wt.% Cr steel investigated by in-situ X-ray diffraction using synchrotron radiation

    SciTech Connect

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

    2010-01-01

    In situ X-ray diffraction measurements using high energy synchrotron radiation were performed to monitor in real time the formation of delta ferrite in a martensitic 9 wt.% 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 C s-1 heating rate to 1300 C and subsequent cooling to room temperature. At the peak temperature, the delta ferrite concentration rose to a level of 19%, of which 17% transformed back to austenite on subsequent cooling. The final microstructure after this single thermal cycle consisted of newly formed martensite with 4% of retained austenite and 2% of retained delta ferrite.

  7. UNDERSTANDING DAMAGE MECHANISMS IN FERRITIC/MARTENSITIC STEELS

    SciTech Connect

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

    2003-04-22

    Advanced ferritic/martensitic steels are being used extensively in fossil energy applications. New steels such as 2 1/4Cr-W-V (T23, T24), 3Cr-W-V, 9Cr-Mo-V (T91), 7Cr-W-V, 9Cr-W-V (T92 and T911), and 12Cr-W-V (T122, SAVE 12, and NF12) are examples of tubing being used in boilers and heat recovery steam generators (1). Other products for these new steels include piping, plates, and forgings. There is concern about the high-temperature performance of the advanced steels for several reasons. First, they exhibit a higher sensitivity to temperature than the 300 series stainless steels that they often replace. Second, they tend to be metallurgically unstable and undergo significant degradation at service temperatures in the creep range. Third, the experience base is limited in regard to duration. Fourth, they will be used for thick-section, high-pressure components that require high levels of integrity. To better understand the potential limitations of these steels, damage models are being developed that consider metallurgical factors as well as mechanical performance factors. Grade 91 steel was chosen as representative of these steels for evaluation of cumulative damage models since laboratory and service exposures of grade 91 exceed 100,000 hours.

  8. HIGH TEMPERATURE BRAZING ALLOY FOR JOINT Fe-Cr-Al MATERIALS AND AUSTENITIC AND FERRITIC STAINLESS STEELS

    DOEpatents

    Cost, R.C.

    1958-07-15

    A new high temperature brazing alloy is described that is particularly suitable for brazing iron-chromiumaluminum alloys. It consists of approximately 20% Cr, 6% Al, 10% Si, and from 1.5 to 5% phosphorus, the balance being iron.

  9. 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.

  10. The Development of Multi-axial Creep Damage Constitutive Equations for 0.5Cr0.5Mo0.25V Ferritic Steel at 590°C

    NASA Astrophysics Data System (ADS)

    Xu, Qiang; Barrans, Simon

    Within the framework of a phenomenological approach a set of multi-axial creep damage constitutive equations for 0.5Cr0.5Mo0.25V ferritic steel at 590°C is developed in which a new formulation is employed. The deficiency of the previous formulation and the need for improvement became apparent after a critical review of the development of creep damage constitutive equations for 316 stainless steel(1). The need for improvement was further underpinned by a call for modification of the constitutive equations(36). Recently, a specific formulation was proposed and validated(2)-(4). This paper reports the latest developments of the multi-axial creep constitutive equations for 0.5Cr0.5Mo0.25V ferritic steel at 590°C including: 1) the fundamental requirement; 2) formulation; 3) validation; and 4) conclusion. It systematically shows the suitability of this new set of constitutive equations and the incapability of the previous ones. Furthermore, it contributes knowledge to the methodology.

  11. 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.

  12. Chromizing of 3Cr Steel

    SciTech Connect

    Ravi, Vilupanur; Harrison, Bradley; Koch, Jordan; Ly, Alexander; Schissler, Andrew; Pint, Bruce A; Haynes, James A

    2011-01-01

    Grade 315 steel (Fe-2.9 Cr-1.7 W-0.7 Mo-0.3 Mn-0.3 Si-0.2 V-0.1 Ni-0.13 C-0.01 N) was chromized by the halide-activated pack cementation (HAPC) process. Key process parameters, i.e., coating temperatures and pack compositions, were investigated. Ammonium chloride-activated packs in the 700-1000 C range produced coatings nominally in the 1-8 {micro}m range, as determined by optical and scanning electron microscopy (SEM). Coatings applied in the 900-1000 C temperature range resulted in Cr-rich coatings. The predominant phase in the coating was identified as Cr23C6 by X-ray diffraction. In addition, the presence of chromium nitride, Cr2N, was observed in the coating. The power generation industry is faced with an ever-increasing demand for energy while simultaneously having to reduce carbon emissions. These goals can be facilitated by increasing plant efficiency through the use of higher operating temperatures and pressures. Traditional construction materials, e.g., the ferritic Grade 22 high strength low alloy steel, are limited to operations below {approx} 550 C. Therefore, new materials are required for future plants designed to operate up to 650 C and possibly higher. These new materials need to have improved tensile strength, ductility, toughness, corrosion resistance, and creep properties at elevated temperatures. Oak Ridge National Laboratory (ORNL) is investigating the oxidation and creep behavior of various coatings on Grade 315 steel (Fe-2.9 Cr-1.7 W-0.7 Mo-0.3 Mn-0.3 Si-0.2 V-0.1 Ni-0.13 C-0.01 N), a super-bainitic steel developed for superior creep properties. Thin, chemical vapor-deposited (CVD) aluminide coatings were used to compensate for the reduced corrosion and oxidation resistance that resulted from the low chromium content of the alloy. However, the aluminized Grade 315 alloys performed less-than-favorably under conditions relevant to fossil boilers, leading to the conclusion that higher chromium contents are required for the formation of

  13. Screen-printed (La,Sr)CrO3 coatings on ferritic stainless steel interconnects for solid oxide fuel cells using nanopowders prepared by means of ultrasonic spray pyrolysis

    NASA Astrophysics Data System (ADS)

    Brylewski, Tomasz; Dabek, Jaroslaw; Przybylski, Kazimierz; Morgiel, Jerzy; Rekas, Mieczyslaw

    2012-06-01

    In order to protect the cathode from chromium poisoning and improve electrical resistance, a perovskite (La,Sr)CrO3 coating was deposited on the surface of a DIN 50049 ferritic stainless steel by means of the screen-printing method, using a paste composed of an ultra-fine powder prepared via ultrasonic spray pyrolysis. Investigations of the oxidation process of the coated steel in air and the Ar-H2-H2O gas mixture at 1073 K for times up to 820 h showed high compactness of the protective film, good adhesion to the metal substrate, as well as area specific resistance (ASR) at a level acceptable for metallic SOFC interconnect materials. The microstructure, nanostructure, phase composition of the thick film, and in particular the film/substrate interface, were examined via chemical analyses by means of SEM-EDS and TEM-SAD. It was shown that the (La,Sr)CrO3 coating interacts with the steel during long-term thermal oxidation in the afore-mentioned conditions and intermediate, chromia-rich and/or spinel multilayer interfacial zones are formed. Cr-vaporization tests showed that the (La,Sr)CrO3 coating may play the role of barriers that decrease the volatilization rate of chromia species.

  14. Abnormal ferrite in hyper-eutectoid steels

    SciTech Connect

    Chairuangsri, T.; Edmonds, D.V.

    2000-04-19

    The microstructural characteristics of ultra-high carbon hyper-eutectoid Fe-C and Fe-C-Cu experimental steels have been examined after isothermal transformation in a range just beneath the eutectoid temperature. Particular attention was paid to the formation of so-called abnormal ferrite, which refers to coarse ferrite grains which can form, in hyper-eutectoid compositions, on the pro-eutectoid cementite before the pearlite reaction occurs. Thus it is confirmed that the abnormal ferrite is not a result of pearlite coarsening, but of austenite decomposition before the conditions for coupled growth of pearlite are established. The abnormal ferrite formed on both allotriomorphic and Widmanstaetten forms of pro-eutectoid cementite, and significantly, it was observed that the pro-eutectoid cementite continued to grow, despite being enclosed by the abnormal ferrite. Under certain conditions this could lead to the eventual formation of substantially reduced amounts of pearlite. Thus, a model for carbon redistribution that allows the proeutectoid cementite to thicken concurrently with the abnormal ferrite is presented. The orientation relationships between the abnormal ferrite and pro-eutectoid cementite were also determined and found to be close to those which have been reported between pearlitic ferrite and pearlitic cementite.

  15. 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.

  16. Comparison of the mechanical strength properties of several high-chromium ferritic steels

    SciTech Connect

    Booker, M.K.; Sikka, V.K.; Booker, B.L.P.

    1981-01-01

    A modified 9 Cr-1 Mo ferritic steel has been selected as an alternative material for breeder reactors. Different 9 Cr-1 Mo steels are already being used commercially in UK and USA and a 9 Cr-2 Mo steel (EM12) is being used commercially in France. The 12% Cr steel alloy HT9 is also often recommended for high-temperature service. Creep-rupture data for all six seels were analyzed to yield rupture life as a function of stress, temperature, and lot-to-lot variations. Yield and tensile strength data for the three 9 Cr-1 Mo materials were also examined. All results were compared with Type 304 stainless steel, and the tensile and creep properties of the modified and British 9 Cr-1 Mo materials were used to calculate allowable stress values S/sub 0/ per Section VIII, Division 1 and S/sub m/ per code Case N-47 to section III of the ASME Boiler and Pressure Vessel Code. these values were compared with code listings for American commercial 9 Cr-1 Mo steel, 2 1/4 Cr-1 Mo steel, and Type 304 stainless steel. The conclusion is made that the modified 9 Cr-1 Mo steel displays tensile and creep strengths superior to those of the other ferritic materials examined and is at least comparable to Type 304 stainless steel from room temperature to about 625/sup 0/C. 31 figures.

  17. Creep Behavior and Degradation of Subgrain Structures Pinned by Nanoscale Precipitates in Strength-Enhanced 5 to 12 Pct Cr Ferritic Steels

    NASA Astrophysics Data System (ADS)

    Ghassemi Armaki, Hassan; Chen, Ruiping; Maruyama, Kouichi; Igarashi, Masaaki

    2011-10-01

    Creep behavior and degradation of subgrain structures and precipitates of Gr. 122 type xCr-2W-0.4Mo-1Cu-VNb ( x = 5, 7, 9, 10.5, and 12 pct) steels were evaluated during short-term and long-term static aging and creep with regard to the Cr content of steel. Creep rupture life increased from 5 to 12 pct Cr in the short-term creep region, whereas in the long-term creep region, it increased up to 9 pct Cr and then decreased with the addition of Cr from 9 to 12 pct. Behavior of creep rupture life was attributed to the size of elongated subgrains. In the short-term creep region, subgrain size decreased from 5 to 12 pct Cr, corresponding to the longer creep strength. However, in the long-term creep region after 104 hours, subgrain size increased up to 9 pct Cr and then decreased from 9 to 12 pct, corresponding to the behavior of creep rupture life. M23C6 and MX precipitates had the highest number fraction among all of the precipitates present in the studied steels. Cr concentration dependence of spacing of M23C6 and MX precipitates exhibited a V-like shape during short-term as well as long-term aging at 923 K (650 °C), and the minimum spacing of precipitates belonged to 9 pct Cr steel, corresponding to the lowest recovery speed of subgrain structures. In the short-term creep region, subgrain coarsening during creep was controlled by strain and proceeded slower with the addition of Cr, whereas in long-term creep region, subgrain coarsening was controlled by the stability of precipitates rather than due to the creep plastic deformation and took place faster from 9 to 12 pct and 9 to 5 pct Cr. However, M23C6 precipitates played a more important role than MX precipitates in the control of subgrain coarsening, and there was a closer correlation between spacing of M23C6 precipitates and subgrain size during static aging and long-term creep region.

  18. Irradiation creep of low-activation ferritic steels in FFTF/MOTA*1

    NASA Astrophysics Data System (ADS)

    Kohyama, A.; Kohno, Y.; Asakura, K.; Yoshino, M.; Namba, C.; Eiholzer, C. R.

    1994-09-01

    Irradiation creep behavior of low-activation steels, developed as structural materials for fusion reactors (JLF series steels), was investigated to obtain a fundamental understanding of these alloys under fast neutron irradiation in FFTF. (2.25-8)Cr(1-2)W bainitic steels and 12Cr-2W ferritic steels showed superior creep resistance to type-316 stainless steels under fast neutron irradiation up to 520°C. At temperatures below 460°C the creep strain increased with increasing Cr content up to 7 Cr, and further increments of Cr content up to 12% reduced the creep strain. At temperatures between 460 and 600°C, 7-8 Cr ferritic steels showed the largest creep strain. Swelling-enhanced creep, near the peak swelling temperature of 410°C, was also observed. The 9Cr-2W ferritic steel JLF-1 presented excellent properties, suggesting it as a leading candidate alloy for structural components of fusion reactors.

  19. 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.

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

    SciTech Connect

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

    1981-07-01

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

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

    SciTech Connect

    David, S.A.

    1981-04-01

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

  2. 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.

  3. 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.

  4. 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.

  5. Effect of Alloy Composition, Surface Preparation and Exposure Conditions on the Selective Oxidation Behavior of Ferritic Fe-Cr and Fe-Cr-X Alloy

    SciTech Connect

    Meier, G H; Mu, N; Yanar, N M; Pettit, F S; Piron Abellan, J; Olszewski, T; Quadakkers, W J; Holcomb, G R

    2010-09-01

    Abstract Selective oxidation behavior of ferritic martensitic Fe–Cr base alloys, exposed in various atmospheres containing combinations of O2, CO2, and H2O, were studied at various temperatures relevant to oxy-fuel combustion. This paper begins with a discussion of the required Cr content to form a continuous external chromia scale on a simple binary Fe–Cr alloy exposed in oxygen or air based on experiments and calculations using the classic Wagner model. Then, the effects of the exposure environment and Cr content on the selective oxidation of Fe–Cr alloys are evaluated. Finally, the effects produced by alloying additions of Si, commonly present in various groups of commercially available ferritic steels, are described. The discussion compares the oxide scale formation on simple binary and ternary Fe–Cr base model alloys with that on several commercially available ferritic steels.

  6. 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.

  7. 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

    NASA Astrophysics Data System (ADS)

    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 X-ray 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.

  8. Stress-relief cracking of a new ferritic steel

    NASA Astrophysics Data System (ADS)

    Nawrocki, Jesse Gerald

    The mechanism of stress-relief cracking in the coarse-grained heat-affected zone (CGHAZ) of low-alloy ferritic steels was studied through a tempering study, stress-relaxation testing, and detailed microstructural characterization. A new ferritic alloy steel, HCM2S, was used as the model system. Common 2.25Cr-1 Mo steel, which is susceptible to stress-relief cracking, was used for comparison to HCM2S. The CGHAZ was simulated using Gleeble techniques. A dense distribution of small tungsten-rich carbides within the prior austenite grains induced secondary hardening in the CGHAZ of HCM2S. The CGHAZ of 2.25Cr-1 Mo steel exhibited secondary hardening due to the intragranular precipitation of many Fe-rich M3C carbides. The hardness of HCM2S was more stable at longer times and high temperatures than 2.25Cr-1 Mo steel due to the intragranular precipitation of small W and V-rich carbides. The CGHAZs of HCM2S and 2.25Cr-1 Mo steel were susceptible to stress-relief cracking between 575 and 725°C. HCM2S exhibited C-curve behavior with respect to the time to failure as a function of post-weld heat treatment (PWHT) temperature. No segregation of tramp elements to prior austenite grain boundaries was detected in HCM2S. Both intergranular and intragranular carbide precipitation controlled the stress-relief cracking behavior. The amount of intergranular failure increased with test temperature due to the increasing amounts of Fe-rich M3C carbides at the prior austenite grain boundaries. These carbides acted as cavity nucleation sites. The cavities coalesced to form microcracks along prior austenite grain boundaries. Eventually, the remaining uncracked areas could not support the load and failed by ductile rupture. The balance of intergranular and intragranular carbide precipitation resulted in the C-curve behavior. The nose of the C-curve occurred at 675°C. The intragranular regions were strong because of a dense distribution of W/Fe-rich carbides, but the prior austenite grain

  9. 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.

  10. Processing and microstructure characterisation of oxide dispersion strengthened Fe-14Cr-0.4Ti-0.25Y2O3 ferritic steels fabricated by spark plasma sintering

    NASA Astrophysics Data System (ADS)

    Zhang, Hongtao; Huang, Yina; Ning, Huanpo; Williams, Ceri A.; London, Andrew J.; Dawson, Karl; Hong, Zuliang; Gorley, Michael J.; Grovenor, Chris R. M.; Tatlock, Gordon J.; Roberts, Steve G.; Reece, Michael J.; Yan, Haixue; Grant, Patrick S.

    2015-09-01

    Ferritic steels strengthened with Ti-Y-O nanoclusters are leading candidates for fission and fusion reactor components. A Fe-14Cr-0.4Ti + 0.25Y2O3 (14YT) alloy was fabricated by mechanical alloying and subsequently consolidated by spark plasma sintering (SPS). The densification of the 14YT alloys significantly improved with an increase in the sintering temperature. Scanning electron microscopy and electron backscatter diffraction revealed that 14YT SPS-sintered at 1150 °C under 50 MPa for 5 min had a high density (99.6%), a random grain orientation and a bimodal grain size distribution (<500 nm and 1-20 μm). Synchrotron X-ray diffraction patterns showed bcc ferrite, Y2Ti2O7, FeO, and chromium carbides, while transmission electron microscopy and atom probe tomography showed uniformly dispersed Y2Ti2O7 nanoclusters of <5 nm diameter and number density of 1.04 × 1023 m-3. Due to the very much shorter consolidation times and lower pressures used in SPS compared with the more usual hot isostatic pressing routes, SPS is shown to be a cost-effective technique for oxide dispersion strengthened (ODS) alloy manufacturing with microstructural features consistent with the best-performing ODS alloys.

  11. Long-Term SOFC Stability with Coated Ferritic Stainless Steel Interconnect

    SciTech Connect

    Simner, Steve P.; Anderson, Michael D.; Xia, Gordon; Yang, Z Gary; Stevenson, Jeffry W.

    2005-01-25

    This study details long-term performance data for anode-supported thin-film YSZ-based SOFCs utilizing a ferritic stainless steel cathode current collector (Crofer22 APU) coated with a protective (Mn,Co)3O4 spinel to prevent Cr volatilization. Two standard cathode compositions, La(Sr)FeO3 and La(Sr)MnO3, were considered. The coating proved effective in blocking Cr migration, which resulted in long-term stability of the manganite cathode. In contrast the ferrite cathode indicated degradation that could not be attributed to Cr poisoning.

  12. Influence of microstructural changes due to tempering at 923 K and 1,023 K on magnetic Barkhausen noise behavior in normalized 2.25Cr-1Mo ferritic steel

    SciTech Connect

    Raj, B.; Moorthy, V.; Vaidyanathan, S.

    1997-01-01

    Magnetic Barkhausen noise analysis has been used to characterize the microstructural changes in normalized and tempered 2.25 Cr-1Mo steel. It is observed that tempering at 923 K shows a single peak behavior up to 20 h and tempering at 1,023 K shows a two peak behavior. This has been explained on the basis of the two stage process of irreversible domain wall movement during magnetization, associated with two major obstacles to domain wall movement: namely lath/grain boundaries and secondary phase precipitates. At lower fields, existing reverse domain walls at lath/grain boundaries overcome the resistance offered by the grain boundaries and move to a distance before they are pined by the precipitates. Then, at higher field, they overcome these precipitates. These two processes occur over a range of critical field strengths with some mean values. If these two mean values are close to each other, then a single peak in the rms voltage of the magnetic Barkhausen noise, with the associated changes in its shape, is observed. On the other hand, if the mean values of the critical fields for these two barriers are widely separated, then a two peak behavior is the clear possibility. The effect of the microstructural changes due to tempering for different durations at 923 K and 1,023 K in 2.25 Cr-1Mo ferritic steel on magnetic Barkhausen noise is explained based on these two stage processes. The influence of high dislocation density in bainitic structure, dissociation of bainite, and precipitation of different carbides such as Fe{sub 3}C, Mo{sub 2}C, Cr{sub 7}Ce{sub 3}, M{sub 23}C{sub 6}, etc., on magnetic Barkhausen noise behavior has been analyzed in this study.

  13. 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.

  14. 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.

  15. 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.

  16. Mechanical behaviour of ferritic ODS steels - Temperature dependancy and anisotropy

    NASA Astrophysics Data System (ADS)

    Fournier, B.; Steckmeyer, A.; Rouffie, A.-L.; Malaplate, J.; Garnier, J.; Ratti, M.; Wident, P.; Ziolek, L.; Tournie, I.; Rabeau, V.; Gentzbittel, J. M.; Kruml, T.; Kubena, I.

    2012-11-01

    Ferritic 14%Cr and 18%Cr ODS steels produced at CEA in round bars or plates were tested mechanically. The present paper reports results obtained in tension, impact, fatigue, creep and toughness tests. These tests were carried out at various temperatures and in different directions. These materials show a pronounced anisotropy at all tested temperatures. No matter the loading, the transversal direction is always found to be far less resistant than the longitudinal one. This anisotropy is mainly observed in terms of damage mechanisms, with intergranular fracture preferentially occurring along the extrusion direction. This intergranular fracture mode leads to very low and anisotropic toughness values and to the absence of tertiairy creep stage, pointing out the unstable nature of fracture, even at high temperature. The unrealistically high values of the Norton exponent measured in creep suggests the existence of a threshold stress, which is consistent with the mainly kinematic nature of the stress as revealed by fatigue tests.

  17. Calculation of the ferrite volume in some dual phase steels

    SciTech Connect

    Qixun, D.; Ruzeng, Y.

    1997-04-01

    The relation between the {gamma}/{gamma} + {alpha} boundary temperature, T{sub {alpha}}, and the equivalent values of [Cr] and [Ni], as well as the variation of the ferrite volume, V{sub f}, with the temperature in {alpha} + {gamma} dual-phase steels have been studied. With the aid of a computer, the regressive expressions derived from the experimental results are: T{sub {alpha}} (C) = T{sub 3} + 21.2 [Cr] {minus} 15.8 [Ni] + 223; V{sub f} (%) = 0.715 {l_brace}exp [0.015(T-T{sub {delta}})] {minus} exp[0.015(T{sub c}-T{sub {delta}})]{r_brace} + 1.85 exp [0.0083(T{sub {alpha}}-T{sub c})].

  18. 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.

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

    PubMed

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

    2006-09-01

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

  20. 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.

  1. 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.

  2. Design of tough ferritic steels for cryogenic use

    SciTech Connect

    Morris, J.W. Jr.

    1985-10-01

    This paper describes the design of ferritic steels and weldments that combine strength and toughness at cryogenic temperatures. The alloy must have a ductile-brittle transition temperature below the intended service temperature and a high fracture toughness in the ductile mode. Its systematic design uses the microstructure-property relations that govern the transition temperature and fracture toughness to identify a suitable microstructure, and then employs the microstructure-processing relations that govern its thermal response to manipulate the microstructure into the appropriate form. The procedure is illustrated by describing the heat treatments, microstructures and properties of a variety of laboratory and commercial alloys, including conventional ''9Ni'' steel, the low-Ni and Fe-Mn ferritic steels that have been developed as an alternative to 9Ni, the 12Ni steels that are promising for use at 4K, and the welding procedures and ferritic filler metals that are useful for ferritic cryogenic steels.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Microstructural Effects on Fracture Behavior of Ferritic and Martensitic Structural Steels

    NASA Astrophysics Data System (ADS)

    Ibrahim, Omyma H.; Elshazly, Ezzat S.

    2013-02-01

    The effect of microstructure on fracture behavior of 1Cr-0.5Mo and 9Cr-1Mo structural steels was evaluated. 1Cr-0.5Mo steel is used in steam pipes and superheater tubes of power stations. Its microstructure is typically comprised of bainite in a pre-eutectoid ferrite matrix with an average grain size of 10 μm. 9Cr-1Mo steel was developed for applications in steam power stations and as a candidate structural material for first-wall and blanket components of future fusion reactors. Its microstructure consisted of a fully martensitic structure with a prior austenite grain size of 25 μm. The fracture properties were measured using instrumented impact testing at temperatures between -196 and 300 °C. The total impact fracture energy, the crack initiation and propagation energy, the dynamic yield strength, the brittleness temperature, and the cleavage fracture stress were measured. The bainitic-ferritic alloy steel exhibited much higher resistance to ductile fracture at high test temperatures, while its resistance to brittle fracture at low test temperatures was reduced compared to that of the fully martensitic alloy steel. The results were discussed in terms of the chemical composition and microstructure of the two steel types.

  8. 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.

  9. 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.

  10. (Mn,Co)(3)O-4 Spinel Coatings on Ferritic Stainless Steels for SOFC Interconnect Applications

    SciTech Connect

    Yang, Z Gary; Xia, Gordon; Li, Xiaohong S.; Stevenson, Jeffry W.

    2007-11-01

    (Mn,Co)3O4 spinel with a nominal composition of Mn1.5Co1.5O4 demonstrates excellent electrical conductivity, satisfactory thermal and structural stability, as well as good thermal expansion match to ferritic stainless steel interconnects. A slurry-coating technique was developed for fabricating the spinel coatings onto the steel interconnects. Thermally grown layers of Mn1.5Co1.5O4 not only significantly decreased the contact resistance between a LSF cathode and stainless steel interconnect, but also acted as a mass barrier to inhibit scale growth on the stainless steel and to prevent Cr outward migration through the coating. The level of improvement in electrical performance and oxidation resistance (i.e. the scale growth rate) was dependent on the ferritic substrate composition. For E-brite and Crofer22 APU, with a relatively high Cr concentration (27wt% and 23%, respectively) and negligible Si, the reduction of contact ASR and scale growth on the ferritic substrates was significant. In comparison, limited improvement was achieved by application of the Mn1.5Co1.5O4 spinel coating on AISI430, which contains only 17% Cr and a higher amount of residual Si.

  11. 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.

  12. Long term high temperature oxidation characteristics of La and Cu alloyed ferritic stainless steels for solid oxide fuel cell interconnects

    NASA Astrophysics Data System (ADS)

    Swaminathan, Srinivasan; Lee, Young-Su; Kim, Dong-Ik

    2016-09-01

    To ensure the best performance of solid oxide fuel cell metallic interconnects, the Fe-22 wt.% Cr ferritic stainless steels with various La contents (0.006-0.6 wt.%) and Cu addition (1.57 wt.%), are developed. Long-term isothermal oxidation behavior of these steels is investigated in air at 800 °C, for 2700 h. Chemistry, morphology, and microstructure of the thermally grown oxide scale are examined using XPS, SEM-EDX, and XRD techniques. Broadly, all the steels show a double layer consisting of an inner Cr2O3 and outer (Mn, Cr)3O4. Distinctly, in the La-added steels, binary oxides of Cr, Mn and Ti are found at the oxide scale surface together with (Mn, Cr)3O4. Furthermore, all La-varied steels possess the metallic Fe protrusions along with discontinuous (Mn, Cr)3O4 spinel zones at the oxide scale/metal interface and isolated precipitates of Ti-oxides in the underlying matrix. Increase of La content to 0.6 wt.% is detrimental to the oxidation resistance. For the Cu-added steel, Cu is found to segregate strongly at the oxide scale/metal interface which inhibits the ingress of oxygen thereby suppressing the subscale formation of (Mn, Cr)3O4. Thus, Cu addition to the Fe-22Cr ferritic stainless steels benefits the oxidation resistance.

  13. 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.

  14. 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.

  15. Oxidation resistance of novel ferritic stainless steels alloyed with titanium for SOFC interconnect applications

    SciTech Connect

    Jablonski, P.D.; Alman, D.E.

    2008-05-15

    Chromia (Cr2O3) forming ferritic stainless steels are being developed for interconnect application in Solid Oxide Fuel Cells (SOFC). A problem with these alloys is that in the SOFC environment chrome in the surface oxide can evaporate and deposit on the electrochemically active sites within the fuel cell. This poisons and degrades the performance of the fuel cell. The development of steels that can form conductive outer protective oxide layers other than Cr2O3 or (CrMn)3O4 such as TiO2 may be attractive for SOFC application. This study was undertaken to assess the oxidation behavior of ferritic stainless steel containing 1 weight percent (wt.%) Ti, in an effort to develop alloys that form protective outer TiO2 scales. The effect of Cr content (6–22 wt.%) and the application of a Ce-based surface treatment on the oxidation behavior (at 800° C in air+3% H2O) of the alloys was investigated. The alloys themselves failed to form an outer TiO2 scale even though the large negative {delta}G of this compound favors its formation over other species. It was found that in conjunction with the Ce-surface treatment, a continuous outer TiO2 oxide layer could be formed on the alloys, and in fact the alloy with 12 wt.% Cr behaved in an identical manner as the alloy with 22 wt.% Cr.

  16. Microstructure and crack resistance of low carbon Cr-Ni and Cr-Ni-W steel after austempering

    NASA Astrophysics Data System (ADS)

    Avdjieva, Tatyana B.; Tsutsumanova, Gichka G.; Russev, Stoyan N.; Staevski, Konstantin G.

    2013-09-01

    The microstructure of the low carbon Cr-Ni steel after slow cooling from austenization temperature represents a mix of granulated bainite with islands from carbon-rich martensite and carbon-poor austenite. After quick cooling throwing in salt bath from austenization temperature the microstructure is lath bainite. However, in the same treatment conditions, the microstructure of the low carbon Cr-Ni-W steel is different — clusters consist from lath ferrite and retained austenite, disposed in the frame of parent's austenite grains. The cooling velocity has no effect upon the structure making. The impact toughness of the steel with tungsten content is bigger than the steel without tungsten.

  17. Microstructural evolution of delta ferrite in SAVE12 steel under heat treatment and short-term creep

    SciTech Connect

    Li, Shengzhi; Eliniyaz, Zumrat; Zhang, Lanting; Sun, Feng; Shen, Yinzhong; Shan, Aidang

    2012-11-15

    This research focused on the formation and microstructural evolution of delta ferrite phase in SAVE12 steel. The formation of delta ferrite was due to the high content of ferrite forming alloy elements such as Cr, W, and Ta. This was interpreted through either JMatPro-4.1 computer program or Cr{sub eq} calculations. Delta ferrite was found in bamboo-like shape and contained large amount of MX phase. It was surrounded by Laves phases before creep or aging treatment. Annealing treatments were performed under temperatures from 1050 Degree-Sign C to 1100 Degree-Sign C and various time periods to study its dissolution kinetics. The result showed that most of the delta ferrite can be dissolved by annealing in single phase austenitic region. Dissolution process of delta ferrite may largely depend on dissolution kinetic factors, rather than on thermodynamic factors. Precipitation behavior during short-term (1100 h) creep was investigated at temperature of 600 Degree-Sign C under a stress of 180 MPa. The results demonstrated that delta ferrite became preferential nucleation sites for Laves phase at the early stage of creep. Laves phase on the boundary around delta ferrite showed relatively slower growth and coarsening rate than that inside delta ferrite. - Highlights: Black-Right-Pointing-Pointer Delta ferrite is systematically studied under heat treatment and short-term creep. Black-Right-Pointing-Pointer Delta ferrite contains large number of MX phase and is surrounded by Laves phases before creep or aging treatment. Black-Right-Pointing-Pointer Formation of delta ferrite is interpreted by theoretical and empirical methods. Black-Right-Pointing-Pointer Most of the delta ferrite is dissolved by annealing in single phase austenitic region. Black-Right-Pointing-Pointer Delta ferrite becomes preferential nucleation sites for Laves phase at the early stage of creep.

  18. ON QUANTIFICATION OF HELIUM EMBRITTLEMENT IN FERRITIC/MARTENSITIC STEELS

    SciTech Connect

    Gelles, David S.

    2000-12-01

    Helium accumulation due to transmutation has long been considered a potential cause for embrittlement in ferritic/martensitic steels. Three Charpy impact databases involving nickel- and boron-doped alloys are quantified with respect to helium accumulation, and it is shown that all predict a very large effect of helium production on embrittlement. If these predictions are valid, use of Ferritic/Martensitic steels for Fusion first wall applications is highly unlikely. It is therefore necessary to reorient efforts regarding development of these steels for fusion applications to concentrate on the issue of helium embrittlement.

  19. 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.

  20. Ferritic weldment of grain-refined ferritic steels for cryogenic use

    SciTech Connect

    Kim, H.J.; Syn, C.K.; Morris, J.W. Jr.

    1981-08-01

    The problem of welding grain-refined Fe-12Ni-0.25Ti for 4K service was first approached in this laboratory by using high nickel filler metals such as are often specified for ferritic steel weldments at 77K. This approach led to an undesirable brittleness in the fusion zone and a low yield strength in the weld metal. A more promising approach was developed in joint research between the Japanese steel companies, who showed that quench-and-tempered 9Ni steel may be welded for 77K service with a matching ferritic filler if a multipass GTAW technique is employed. The present paper reports the initial resultsof similar studies on ferritic GTA weldments in grain-refined 9Ni steel. Information is included on the preparation of the 9Ni steel and the weld filler metal, on the welding procedure, the microstructure of both the weld metal and the heat affected zone, and on impact toughness and fracture toughness testing at 77/sup 0/K and 4.2/sup 0/K. The results show that it is possible to weld grain-refined 9Ni steel with ferritic weld filler metal so as to retain good toughness at cryogenic temperatures. The results of this work may permit the utilization of retreated commercial grade 9Ni steel in structural applications within helium-cooled cryogenic devices where high strength and good toughness are required. (LCL)

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

    SciTech Connect

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

    1998-09-04

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

  2. Ferritic/martensitic steels - overview of recent results

    NASA Astrophysics Data System (ADS)

    Klueh, R. L.; Gelles, D. S.; Jitsukawa, S.; Kimura, A.; Odette, G. R.; van der Schaaf, B.; Victoria, M.

    2002-12-01

    Considerable research work has been conducted on the ferritic/martensitic steels since the last International Conference on Fusion Reactor Materials in 1999. Since only a limited amount of that work can be reviewed in this paper, four areas will be emphasized: (1) the international collaboration under the auspices of the International Energy Agency (IEA) to address potential problems with ferritic/martensitic steels and to prove their feasibility for fusion, (2) the major uncertainty that remains concerning the effect of transmutation helium on mechanical properties of the steels when irradiated in a fusion neutron environment, (3) development of new reduced-activation steels beyond the F82H and JLF-1 steels studied in the IEA collaboration, and (4) work directed at developing oxide dispersion-strengthened steels for operation above 650 °C.

  3. 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.

  4. Effect of chromium, tungsten, tantalum, and boron on mechanical properties of 5-9Cr-WVTaB steels

    NASA Astrophysics Data System (ADS)

    Klueh, R. L.; Alexander, D. J.; Sokolov, M. A.

    2002-08-01

    The Cr-W-V-Ta reduced-activation ferritic/martensitic steels use tungsten and tantalum as substitutes for molybdenum and niobium in the Cr-Mo-V-Nb steels that the reduced-activation steels replaced as candidate materials for fusion applications. Studies were made to determine the effect of W, Ta, and Cr composition on the tensile and Charpy properties of the Cr-W-V-Ta; steels with 5%, 7%, and 9% Cr with 2% or 3% W and 0%, 0.05%, or 0.10% Ta were examined. Boron has a long history of use in steels to improve properties, and the effect of boron was also examined. Regardless of the chromium concentration, the steels with 2% W and 0.05-0.1% Ta generally had a better combination of tensile and Charpy properties than steels with 3% W. Boron had a negative effect on properties for the 5% and 7% Cr steels, but had a positive effect on the 9% Cr steel. When the 5, 7, and 9Cr steels containing 2% W and 0.05% Ta were compared, the tensile and Charpy properties of the 5 and 9Cr steels were better than those of the 7Cr steel, and overall, the properties of the 5Cr steel were better than those of the 9Cr steel. Such information will be useful if the properties of the reduced-activation steels are to be optimized.

  5. New Economical 19Cr Duplex Stainless Steels

    NASA Astrophysics Data System (ADS)

    Li, Jun; Zhang, Zixing; Chen, Hong; Xiao, Xueshan; Zhao, Junliang; Jiang, Laizhu

    2012-02-01

    New economical duplex stainless steels (DSSs) containing 19Cr-6Mn- xNi-1.0Mo-0.5W-0.5Cu-0.2N ( x = 0.5 to 2.0) were developed, and the microstructure, impact property, and corrosion resistance of the alloys were studied. The ferrite content increases with the solution treatment temperature, but decreases with an increase in nickel. The sigma phase is not found precipitating in the alloys treated with solution from 1023 K to 1523 K (750 °C to 1250 °C). The low-temperature impact energy of the experimental alloys increases first and then decreases rapidly with an increase in nickel, which is mainly due to the martensite transformation with an increase in austenite. The alloys have a better mechanical property and pitting corrosion resistance than AISI 304. Among the designed DSS alloys, 19Cr-6Mn-1.3Ni-1.0Mo-0.5W-0.5Cu-0.2N is found to be an optimum alloy with proper phase proportion, a better combination of mechanical strength and elongation, and higher pitting corrosion resistance compared with those of the other alloys.

  6. 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.

  7. 77 FR 60478 - Control of Ferrite Content in Stainless Steel Weld Metal

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-10-03

    ... COMMISSION Control of Ferrite Content in Stainless Steel Weld Metal AGENCY: Nuclear Regulatory Commission... 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...

  8. 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.

  9. Correlation of Fe/Cr phase decomposition process and age-hardening in Fe-15Cr ferritic alloys

    NASA Astrophysics Data System (ADS)

    Chen, Dongsheng; Kimura, Akihiko; Han, Wentuo

    2014-12-01

    The effects of thermal aging on the microstructure and mechanical properties of Fe-15Cr ferritic model alloys were investigated by TEM examinations, micro-hardness measurements and tensile tests. The materials used in this work were Fe-15Cr, Fe-15Cr-C and Fe-15Cr-X alloys, where X refers to Si, Mn and Ni to simulate a pressure vessel steel. Specimens were isothermally aged at 475 °C up to 5000 h. Thermal aging causes a significant increase in the hardness and strength. An almost twice larger hardening is required for embrittlement of Fe-15Cr-X relative to Fe-15Cr. The age-hardening is mainly due to the formation of Cr-rich α‧ precipitates, while the addition of minor elements has a small effect on the saturation level of age-hardening. The correlation of phase decomposition process and age-hardening in Fe-15Cr alloy was interpreted by dispersion strengthened models.

  10. 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.

  11. The filler powders laser welding of ODS ferritic steels

    NASA Astrophysics Data System (ADS)

    Liang, Shenyong; Lei, Yucheng; Zhu, Qiang

    2015-01-01

    Laser welding was performed on Oxide Dispersion Strengthened (ODS) ferritic steel with the self-designed filler powders. The filler powders were added to weld metal to produce nano-particles (Y-M-O and TiC), submicron particles (Y-M-O) and dislocation rings. The generated particles were evenly distributed in the weld metal and their forming mechanism and behavior were analyzed. The results of the tests showed that the nano-particles, submicron particles and dislocation rings were able to improve the micro-hardness and tensile strength of welded joint, and the filler powders laser welding was an effective welding method of ODS ferritic steel.

  12. 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.

  13. Experimental and Thermokinetic Simulation Studies on the Formation of Deleterious Zones in Dissimilar Ferritic Steel Weldments

    NASA Astrophysics Data System (ADS)

    Anand, R.; Sudha, C.; Saroja, S.; Vijayalakshmi, M.

    2013-05-01

    The methods to predict and prevent the formation of hard and soft zones in dissimilar weldments of 9Cr-1Mo and 2¼Cr-1Mo ferritic steels during high-temperature exposure are examined in this article. The computational studies have been carried out using multicomponent diffusion model incorporated in Dictra and validated by experimental methods using EPMA and TEM. Carbon concentration profiles across the interface of the weld joint between the two ferritic steels were simulated in the temperatures ranging from 823 K to 1023 K (from 550 °C to 750 °C) for various time durations using "diffusion in dispersed phase model" in Dictra. When precipitation and diffusion were incorporated into the calculations simultaneously, the agreement was better between the calculated and the experimentally measured values of carbon concentration profiles, type, and volume fractions of carbides in the hard zone and diffusion zone, width, and the activation energy. Calculation results of thermodynamic potentials of carbon in 2¼Cr-1Mo and 9Cr-1Mo steels suggested that the diffusion is driven by the activity gradient of carbon across the joint. The effectiveness of nickel-based diffusion barrier in suppressing the formation of hard and soft zones is demonstrated using calculations based on the cell model incorporated in Dictra.

  14. Dynamic recrystallization of ferrite in interstitial free steel

    SciTech Connect

    Tsuji, N.; Matsubara, Y.; Saito, Y.

    1997-08-15

    The present study using IF steel confirmed that dynamic recrystallization can occur also in ferrite where it has been generally considered that recovery is an only restoration process during hot deformation. Although the occurrence of DRX has been clarified by microstructural observations and crystallographic determinations, stress-strain curves do not show obvious drop of stress which has been typically reported in the case of DRX of austenite. This result indicates that it is quite difficult to distinguish whether DRX occurs in ferrite only by stress-strain behavior. The noticeable feature of DRX of ferrite is inhomogeneity of recrystallization, i.e., some of the initial grains are hard to recrystallize. This is presumably due to orientation dependence of recrystallization, which is the essential feature of ferrite.

  15. Deuterium Retention and Physical Sputtering of Low Activation Ferritic Steel

    NASA Astrophysics Data System (ADS)

    T, Hino; K, Yamaguchi; Y, Yamauchi; Y, Hirohata; K, Tsuzuki; Y, Kusama

    2005-04-01

    Low activation materials have to be developed toward fusion demonstration reactors. Ferritic steel, vanadium alloy and SiC/SiC composite are candidate materials of the first wall, vacuum vessel and blanket components, respectively. Although changes of mechanical-thermal properties owing to neutron irradiation have been investigated so far, there is little data for the plasma material interactions, such as fuel hydrogen retention and erosion. In the present study, deuterium retention and physical sputtering of low activation ferritic steel, F82H, were investigated by using deuterium ion irradiation apparatus. After a ferritic steel sample was irradiated by 1.7 keV D+ ions, the weight loss was measured to obtain the physical sputtering yield. The sputtering yield was 0.04, comparable to that of stainless steel. In order to obtain the retained amount of deuterium, technique of thermal desorption spectroscopy (TDS) was employed to the irradiated sample. The retained deuterium desorbed at temperature ranging from 450 K to 700 K, in the forms of DHO, D2, D2O and hydrocarbons. Hence, the deuterium retained can be reduced by baking with a relatively low temperature. The fluence dependence of retained amount of deuterium was measured by changing the ion fluence. In the ferritic steel without mechanical polish, the retained amount was large even when the fluence was low. In such a case, a large amount of deuterium was trapped in the surface oxide layer containing O and C. When the fluence was large, the thickness of surface oxide layer was reduced by the ion sputtering, and then the retained amount in the oxide layer decreased. In the case of a high fluence, the retained amount of deuterium became comparable to that of ferritic steel with mechanical polish or SS 316L, and one order of magnitude smaller than that of graphite. When the ferritic steel is used, it is required to remove the surface oxide layer for reduction of fuel hydrogen retention. Ferritic steel sample was

  16. Effect of Weld Intercooling Temperature on the Structure and Impact Strength of Ferritic-Martensitic Steels

    SciTech Connect

    T.C. Totemeier; J.A. Simpson; H. Tian

    2006-06-01

    The effect of inadequate weld intercooling (cooling prior to post-weld heat treatment) on the structure and impact properties of 9Cr-1MoVNb (ASME Grade 91) and 12Cr-1Mo-WV (Type 422 stainless) steels was studied. A range of weld intercooling conditions were simulated by air cooling the two steels from the standard 1050°C normalization temperature to temperatures ranging from 250 to 450°C for Grade 91 and 100 to 300°C for Type 422, and then immediately tempering at 760°C for two hours. For Grade 91 steel, austenite retained at the intercooling temperature transformed to ferrite during tempering; final microstructures were mixtures of ferrite and tempered martensite. For Type 422 steel, austenite retained at the intercooling temperature was stable in the tempering condition and formed martensite upon cooling to room temperature; final microstructures were mixtures of tempered and untempered martensite. Hardness and impact properties of the two steels reflected the changes in microstructure with intercooling temperature.

  17. Creep Strength of Dissimilar Welded Joints Using High B-9Cr Steel for Advanced USC Boiler

    NASA Astrophysics Data System (ADS)

    Tabuchi, Masaaki; Hongo, Hiromichi; Abe, Fujio

    2014-10-01

    The commercialization of a 973 K (700 °C) class pulverized coal power system, advanced ultra-supercritical (A-USC) pressure power generation, is the target of an ongoing research project initiated in Japan in 2008. In the A-USC boiler, Ni or Ni-Fe base alloys are used for high-temperature parts at 923 K to 973 K (650 °C to 700 °C), and advanced high-Cr ferritic steels are planned to be used at temperatures lower than 923 K (650 °C). In the dissimilar welds between Ni base alloys and high-Cr ferritic steels, Type IV failure in the heat-affected zone (HAZ) is a concern. Thus, the high B-9Cr steel developed at the National Institute for Materials Science, which has improved creep strength in weldments, is a candidate material for the Japanese A-USC boiler. In the present study, creep tests were conducted on the dissimilar welded joints between Ni base alloys and high B-9Cr steels. Microstructures and creep damage in the dissimilar welded joints were investigated. In the HAZ of the high B-9Cr steels, fine-grained microstructures were not formed and the grain size of the base metal was retained. Consequently, the creep rupture life of the dissimilar welded joints using high B-9Cr steel was 5 to 10 times longer than that of the conventional 9Cr steel welded joints at 923 K (650 °C).

  18. Cr3+ substituted spinel ferrite nanoparticles with high coercivity

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Zuo, Xudong; Zhang, Dongmei; Wu, Chengwei; Silva, S. Ravi P.

    2016-06-01

    The low coercivity of spinel ferrites is a major barrier that significantly limits their use in high density magnetic recording applications. By controlling the substituting content of Cr3+, in this article we describe how magnetic CoCr x Fe2‑x O4 (0 < x < 1.2) nanoparticles with coercivity of up to 6.4 kOe were successfully obtained by the hydrothermal process. The high coercivity is attributed to the synergetic effects of magnetocrystalline anisotropy and the nanoscale size effect. X-ray diffraction analysis confirmed the spinel structure of the nanoparticles with transmission electron microscopy (TEM) suggesting regular tetragonal morphology. The TEM indicated an edge length ranging from 15 nm to 150 nm, which increases monotonically with increasing Cr content. Raman analyses supported the proposed model on the formation mechanism of the nanoparticles, i.e. heterogeneous and homogeneous nucleation.

  19. Cr(3+) substituted spinel ferrite nanoparticles with high coercivity.

    PubMed

    Zhang, Wei; Zuo, Xudong; Zhang, Dongmei; Wu, Chengwei; Silva, S Ravi P

    2016-06-17

    The low coercivity of spinel ferrites is a major barrier that significantly limits their use in high density magnetic recording applications. By controlling the substituting content of Cr(3+), in this article we describe how magnetic CoCr x Fe2-x O4 (0 < x < 1.2) nanoparticles with coercivity of up to 6.4 kOe were successfully obtained by the hydrothermal process. The high coercivity is attributed to the synergetic effects of magnetocrystalline anisotropy and the nanoscale size effect. X-ray diffraction analysis confirmed the spinel structure of the nanoparticles with transmission electron microscopy (TEM) suggesting regular tetragonal morphology. The TEM indicated an edge length ranging from 15 nm to 150 nm, which increases monotonically with increasing Cr content. Raman analyses supported the proposed model on the formation mechanism of the nanoparticles, i.e. heterogeneous and homogeneous nucleation. PMID:27159283

  20. 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.

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

    DOE PAGESBeta

    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

  2. Steamside Oxidation Behavior of Experimental 9%Cr Steels

    SciTech Connect

    Dogan, O.N.; Holcomb, G.R.; Alman, D.E.; Jablonski, P.D.

    2007-10-01

    Reducing emissions and increasing economic competitiveness require more efficient steam power plants that utilize fossil fuels. One of the major challenges in designing these plants is the availability of materials that can stand the supercritical and ultra-supercritical steam conditions at a competitive cost. There are several programs around the world developing new ferritic and austenitic steels for superheater and reheater tubes exposed to the advanced steam conditions. The new steels must possess properties better than current steels in terms of creep strength, steamside oxidation resistance, fireside corrosion resistance, and thermal fatigue resistance. This paper introduces a series of experimental 9%Cr steels containing Cu, Co, and Ti. Stability of the phases in the new steels is discussed and compared to the phases in the commercially available materials. The steels were tested under both the dry and moist conditions at 650ºC for their cyclical oxidation resistance. Results of oxidation tests are presented. Under the moist conditions, the experimental steels exhibited significantly less mass gain compared to the commercial P91 steel. Microstructural characterization of the scale revealed different oxide compositions.

  3. Irradiation response of delta ferrite in as-cast and thermally aged cast stainless steel

    DOE PAGESBeta

    Li, Zhangbo; Lo, Wei-Yang; Chen, Yiren; Pakarinen, Janne; Wu, Yaqiao; Allen, Todd; Yang, Yong

    2015-08-08

    To enable the life extension of Light Water Reactors (LWRs) beyond 60 years, it is critical to gain adequate knowledge for making conclusive predictions to assure the integrity of duplex stainless steel reactor components, e.g. primary pressure boundary and reactor vessel internal. Microstructural changes in the ferrite of thermally aged, neutron irradiated only, and neutron irradiated after being thermally aged cast austenitic stainless steels (CASS) were investigated using atom probe tomography. The thermal aging was performed at 400 °C for 10,000 h and the irradiation was conducted in the Halden reactor at ~315 °C to 0.08 dpa (5.6 × 1019more » n/cm2 E > 1 MeV). Low dose neutron irradiation at a dose rate of 5 × 10-9 dpa/s was found to induce spinod,al decomposition in the ferrite of as-cast microstructure, and further to enhance the spinodal decomposition in the thermally aged cast alloys. Regarding the G-phase precipitates, the neutron irradiation dramatically increases the precipitate size, and alters the composition of the precipitates with increased, Mn, Ni, Si and Mo and reduced Fe and Cr contents. Lastly, The results have shown that low dose neutron irradiation can further accelerate the degradation of ferrite in a duplex stainless steel at the LWR relevant condition.« less

  4. Irradiation response of delta ferrite in as-cast and thermally aged cast stainless steel

    SciTech Connect

    Li, Zhangbo; Lo, Wei-Yang; Chen, Yiren; Pakarinen, Janne; Wu, Yaqiao; Allen, Todd; Yang, Yong

    2015-08-08

    To enable the life extension of Light Water Reactors (LWRs) beyond 60 years, it is critical to gain adequate knowledge for making conclusive predictions to assure the integrity of duplex stainless steel reactor components, e.g. primary pressure boundary and reactor vessel internal. Microstructural changes in the ferrite of thermally aged, neutron irradiated only, and neutron irradiated after being thermally aged cast austenitic stainless steels (CASS) were investigated using atom probe tomography. The thermal aging was performed at 400 °C for 10,000 h and the irradiation was conducted in the Halden reactor at ~315 °C to 0.08 dpa (5.6 × 1019 n/cm2 E > 1 MeV). Low dose neutron irradiation at a dose rate of 5 × 10-9 dpa/s was found to induce spinod,al decomposition in the ferrite of as-cast microstructure, and further to enhance the spinodal decomposition in the thermally aged cast alloys. Regarding the G-phase precipitates, the neutron irradiation dramatically increases the precipitate size, and alters the composition of the precipitates with increased, Mn, Ni, Si and Mo and reduced Fe and Cr contents. Lastly, The results have shown that low dose neutron irradiation can further accelerate the degradation of ferrite in a duplex stainless steel at the LWR relevant condition.

  5. Irradiation response of delta ferrite in as-cast and thermally aged cast stainless steel

    NASA Astrophysics Data System (ADS)

    Li, Zhangbo; Lo, Wei-Yang; Chen, Yiren; Pakarinen, Janne; Wu, Yaqiao; Allen, Todd; Yang, Yong

    2015-11-01

    To enable the life extension of Light Water Reactors (LWRs) beyond 60 years, it is critical to gain adequate knowledge for making conclusive predictions to assure the integrity of duplex stainless steel reactor components, e.g. primary pressure boundary and reactor vessel internal. Microstructural changes in the ferrite of thermally aged, neutron irradiated only, and neutron irradiated after being thermally aged cast austenitic stainless steels (CASS) were investigated using atom probe tomography. The thermal aging was performed at 400 °C for 10,000 h and the irradiation was conducted in the Halden reactor at ∼315 °C to 0.08 dpa (5.6 × 1019 n/cm2, E > 1 MeV). Low dose neutron irradiation at a dose rate of 5 × 10-9 dpa/s was found to induce spinodal decomposition in the ferrite of as-cast microstructure, and further to enhance the spinodal decomposition in the thermally aged cast alloys. Regarding the G-phase precipitates, the neutron irradiation dramatically increases the precipitate size, and alters the composition of the precipitates with increased, Mn, Ni, Si and Mo and reduced Fe and Cr contents. The results have shown that low dose neutron irradiation can further accelerate the degradation of ferrite in a duplex stainless steel at the LWR relevant condition.

  6. 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

  7. Radiation-induced strengthening and absorption of dislocation loops in ferritic Fe-Cr alloys: the role of Cr segregation.

    PubMed

    Terentyev, D; Bakaev, A

    2013-07-01

    The understanding of radiation-induced strengthening in ferritic FeCr-based steels remains an essential issue in the assessment of materials for fusion and fission reactors. Both early and recent experimental works on Fe-Cr alloys reveal Cr segregation on radiation-induced nanostructural features (mainly dislocation loops), whose impact on the modification of the mechanical response of the material might be key for explaining quantitatively the radiation-induced strengthening in these alloys. In this work, we use molecular dynamics to study systematically the interaction of dislocations with 1/2<111> and <100> loops in all possible orientations, both enriched by Cr atoms and undecorated, for different temperatures, loop sizes and dislocation velocities. The configurations of the enriched loops have been obtained using a non-rigid lattice Monte Carlo method. The study reveals that Cr segregation influences the interaction mechanisms with both 1/2<111> and <100> loops. The overall effect of Cr enrichment is to penalize the mobility of intrinsically glissile 1/2<111> loops, modifying the reaction mechanisms as a result. The following three most important effects associated with Cr enrichment have been revealed: (i) absence of dynamic drag; (ii) suppression of complete absorption; (iii) enhanced strength of small dislocation loops (2 nm and smaller). Overall the effect of the Cr enrichment is therefore to increase the unpinning stress, so experimentally 'invisible' nanostructural features may also contribute to radiation-induced strengthening. The reasons for the modification of the mechanisms are explained and the impact of the loading conditions is discussed. PMID:23756468

  8. 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.

  9. 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.

  10. Anomalous ultrasonic attenuation in ferritic steels at elevated temperatures.

    PubMed

    Hutchinson, Bevis; Lundin, Peter; Lindh-Ulmgren, Eva; Lévesque, Daniel

    2016-07-01

    An unexpected peak in attenuation has been observed at ∼800°C when heating low carbon steels in a laser-ultrasonic instrument. An explanation is given in terms of enhanced crystalline anisotropy with increasing temperature in the bcc ferrite range combined with subsequent transformation to austenite at still higher temperatures. An analysis based on theoretical models of attenuation in the Rayleigh regime is in good agreement with the experimental observations. PMID:27015796

  11. Deposition and Evaluation of Protective PVD Coatings on Ferritic Stainless Steel SOFC Interconnects

    SciTech Connect

    Gorokhovsky, Vladimir I.; Gannon, Paul; Deibert, Max; Smith, Richard J.; Kayani, Asghar N.; Kopczyk, M.; Van Vorous, D.; Yang, Z Gary; Stevenson, Jeffry W.; Visco, s.; jacobson, c.; Kurokawa, H.; Sofie, Stephen W.

    2006-09-21

    Reduced operating temperatures (600-800°C) of Solid Oxide Fuel Cells (SOFCs) may enable the use of inexpensive ferritic steels as interconnects. Due to the demanding SOFC interconnect operating environment, protective coatings are gaining attention to increase longterm stability. In this study, large area filtered arc deposition (LAFAD) and hybrid filtered arc assisted electron beam physical vapor deposition (FA-EBPVD) technologies were used for deposition of two-segment coatings with Cr-Co-Al-O-N based sublayer and Mn-Co-O top layer. Coatings were deposited on ferritic steel and subsequently annealed in air for various time intervals. Surface oxidation was investigated using RBS, SEM and EDS analyses. Cr volatilization was evaluated using a transpiration apparatus and ICP-MS analysis of the resultant condensate. Electrical conductivity (Area Specific Resistance) was studied as a function of time using the four-point technique with Ag electrodes. The oxidation behavior, Cr volatilization rate, and electrical conductivity of the coated and uncoated samples are reported. Transport mechanisms for various oxidizing species and coating diffusion barrier properties are discussed.

  12. The Role of Alloying Elements in Nanostructured Ferritic Steels

    SciTech Connect

    Miller, Michael K; Parish, Chad M

    2010-01-01

    The roles of the alloying elements in three nanostructured ferritic alloys (14YWT, MA957 and Eurofer 97) have been established through the characterisation of the microstructure by atom probe tomography and spectrum imaging in a transmission electron microscope. Cr, W, Mo, Ti and Y were found in the ferrite matrix and contributed to solid solution hardening. Ti, Y, C, O and N were found in high number densities of precipitates and nanoclusters both in the grain interior and on grain boundaries and thereby contributed to precipitation hardening. Cr, W and Mo were enriched at the intraparticle regions of the grain boundaries. The solute segregation and precipitation pinned the grain boundaries and contributed to the excellent creep properties of the alloys.

  13. Effect of composition on the transformation of {delta}-ferrite to {sigma} in type 316 stainless steel weld metals

    SciTech Connect

    Gill, T.P.S.; Shankar, V.; Pujar, M.G.; Rodriguez, P.

    1995-05-15

    A study of the effect of Cr on {delta}-ferrite transformation kinetics has yielded a relationship between the kinetics parameter n{sub 2} and weld metal chromium content. The amount of {sigma}{sub 0.9} formed from {delta}-ferrite has been correlated with weld metal composition. A nomogram is proposed, to predict the amount of {sigma}{sub 0.9} formed after 90% ferrite transformation in a given weld metal, as a function of C, Cr and Mo contents. The nomogram can be employed to optimize the composition for reducing high temperature embrittlement resulting from {sigma} precipitation in type 316 stainless steel weld metals. The nomogram has been developed from data obtained at 650 C but has been shown to be valid in the temperature range 600--700 C.

  14. Atom-probe investigation of precipitation in 12% Cr steel weld metals

    NASA Astrophysics Data System (ADS)

    Cai, Guang-Jun; Lundin, Lars; Andrén, Hans-Olof; Svensson, Lars-Erik

    1994-03-01

    The microstructure of two types of 12% Cr steel weld metals, one with the composition of a common 12% Cr steel and the other with a higher nitrogen content, was studied using TEM (transmission electron microscopy) and APFIM (atom-probe field-ion microscopy) in post-weld heat-treated condition. The microstructure of the 12% Cr weld metals consisted of tempered martensite, retained δ-ferrite, an irregular low-dislocation α-ferrite and precipitates. Precipitates in the weld metals were dominantly M 23C 6 on different boundaries. Plate-like and fine cubic MN and M 2N were found inside the α-ferrite. APFIM analysis showed that M 23C 6 was almost a pure carbide and MN was almost a pure nitride. Carbon and nitrogen in the weld metals mainly existed in the precipitates. High nitrogen content did not change the composition of the precipitates, but increased the quantity of nitrides. Therefore, in the high nitrogen weld metal, the content of strong nitride-forming elements in the matrix decreased. These results are important in order to understand the strengthening mechanism of the high Cr steel weld metals, as well as of other high Cr heat-resistant steels.

  15. 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)

  16. Development of oxide dispersion strengthened ferritic steel prepared by chemical reduction and mechanical milling

    NASA Astrophysics Data System (ADS)

    Sun, Q. X.; Fang, Q. F.; Zhou, Y.; Xia, Y. P.; Zhang, T.; Wang, X. P.; Liu, C. S.

    2013-08-01

    The oxide dispersion strengthened ferritic steel with a nominal composition of Fe-14Cr-2W-0.5Ti-0.06Si-0.2V-0.1Mn-0.05Ta-0.03C-0.3Y2O3 (14Cr-ODS) was fabricated by sol-gel method in combination with hydrogen reduction, mechanical alloying (MA) and hot isostatic pressing (HIP) techniques. Pure Fe-1.5Y2O3 precursor was obtained by a sol-gel process and a reduction process at 650 °C for 3 h and pure 14Cr-ODS alloy powders were obtained from this precursor and the alloying metallic powders by mechanical alloying. The microstructure analysis investigated by transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS) reveal that Y-Ti-O complexes and V-Ti-O complexes with a main particle size of 8 nm are formed in the 14Cr-ODS steel matrix. After HIP sintering the weight and the relative density of the compacted ingots are about 0.8 kg and 99.7%. The uniform elongation and ultimate tensile strength of the ODS steel obtained by HIP after annealing at 1100 °C for 5 h are about 13% and 840 MPa, respectively.

  17. Effect of mechanical alloying atmosphere on the microstructure and Charpy impact properties of an ODS ferritic steel

    NASA Astrophysics Data System (ADS)

    Oksiuta, Z.; Baluc, N.

    2009-04-01

    Two types of oxide dispersion strengthened (ODS) ferritic steels, with the composition of Fe-14Cr-2W-0.3Ti-0.3Y 2O 3 (in weight percent), have been produced by mechanically alloying elemental powders of Fe, Cr, W, and Ti with Y 2O 3 particles either in argon atmosphere or in hydrogen atmosphere, degassing at various temperatures, and compacting the mechanically alloyed powders by hot isostatic pressing. It was found in particular that mechanical alloying in hydrogen yields a significant reduction in oxygen content in the materials, a lower dislocation density, and a strong improvement in the fast fracture properties of the ODS ferritic steels, as measured by Charpy impact tests.

  18. A micro-alloyed ferritic steel strengthened by nanoscale precipitates

    SciTech Connect

    Shen, Yongfeng; Wang, Chong M.; Sun, Xin

    2011-10-25

    A ferritic steel with finely dispersive precipitates was investigated to reveal the fundamental strengthening mechanisms. The steel has a yield strength of 760 MPa, approximately three times higher than that of conventional Ti-bearing high strength hot-rolled sheet steels, and its ultimate tensile strength reaches 850 MPa with an elongation-to-failure value of 18%. Using energy dispersive X-ray spectroscopy (EDXS) and transmission electron microscope (TEM), fine carbides TiC with an average diameter of 10 nm were observed in the ferrite matrix of the 0.08%Ti steel, and some cubic M23C6 precipitates were also observed at the grain boundaries and the interior of the grains. The finely dispersive TiC precipitates in the matrix provide matrix strengthening. The estimated magnitude of precipitation strengthening is around 458 MPa, depending on the average size of the nanoscale precipitates. Dislocation densities increased from 3.42×1013 m-2 to 1.69 × 1014 m-2, respectively, with increasing tensile strain from 5.5% to 22%. The measured work-hardening behavior can be related to the observed dislocation accumulations resulting from the dispersive nano-scale precipitates.

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

    SciTech Connect

    Leitnaker, J.M.

    1981-05-05

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

  20. TiC reinforced cast Cr steels

    SciTech Connect

    Dogan, O.N.; Hawk, J.A.; Schrems, K.K.

    2006-06-01

    A new class of materials, namely TiC-reinforced cast chromium (Cr) steels, was developed for applications requiring high abrasion resistance and good fracture toughness. The research approach was to modify the carbide structure of commercial AISI 440C steel for better fracture resistance while maintaining the already high abrasion resistance. The new alloys contained 12Cr, 2.5–4.5Ti, and 1–1.5C (wt.%) and were melted in a vacuum induction furnace. Their microstructure was composed primarily of a martensitic matrix with a dispersion of TiC precipitates. Modification of TiC morphology was accomplished through changing the cooling rate during solidification. Wear rates of the TiC-reinforced Cr steels were comparable to that of AISI 440C steel, but the impact resistance was much improved.

  1. Process development for 9Cr nanostructured ferritic alloy (NFA) with high fracture toughness

    NASA Astrophysics Data System (ADS)

    Byun, Thak Sang; Yoon, Ji Hyun; Hoelzer, David T.; Lee, Yong Bok; Kang, Suk Hoon; Maloy, Stuart A.

    2014-06-01

    This article is to summarize the process development and key characterization results for the newly-developed Fe-9Cr based nanostructured ferritic alloys (NFAs) with high fracture toughness. One of the major drawbacks from pursuing ultra-high strength in the past development of NFAs is poor fracture toughness at high temperatures although a high fracture toughness is essential to prevent cracking during manufacturing and to mitigate or delay irradiation-induced embrittlement in irradiation environments. A study on fracture mechanism using the NFA 14YWT found that the low-energy grain boundary decohesion in fracture process at a high temperature (>200 °C) resulted in low fracture toughness. Lately, efforts have been devoted to explore an integrated process to enhance grain bonding. Two base materials were produced through mechanical milling and hot extrusion and designated as 9YWTV-PM1 and 9YWTV-PM2. Isothermal annealing (IA) and controlled rolling (CR) treatments in two phase region were used to enhance diffusion across the interfaces and boundaries. The PM2 alloy after CR treatments showed high fracture toughness (KJQ) at represented temperatures: 240-280 MPa √m at room temperature and 160-220 MPa √m at 500 °C, which indicates that the goal of 100 MPa √m over possible nuclear application temperature range has been well achieved. Furthermore, it is also confirmed by comparison that the CR treatments on 9YWTV-PM2 result in high fracture toughness similar to or higher than those of the conventional ferritic-martensitic steels such as HT9 and NF616.

  2. 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

  3. Development of ferritic weldments for grain-refined ferritic steels for 4. 2K service

    SciTech Connect

    Kim, H.J.

    1982-11-01

    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 9 Ni steel were welded with 14 Ni 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 4.2 K. 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. 46 figures.

  4. 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.

  5. Surface Treatments for Improved Performance of Spinel-coated AISI 441 Ferritic Stainless Steel

    SciTech Connect

    Stevenson, Jeffry W.; Riel, Eric M.; Stephens, Elizabeth V.; Khaleel, Mohammad A.

    2013-01-01

    Ferritic stainless steels are promising candidates for IT-SOFC interconnect applications due to their low cost and resistance to oxidation at SOFC operating temperatures. However, steel candidates face several challenges; including long term oxidation under interconnect exposure conditions, which can lead to increased electrical resistance, surface instability, and poisoning of cathodes due to volatilization of Cr. To potentially extend interconnect lifetime and improve performance, a variety of surface treatments were performed on AISI 441 ferritic stainless steel coupons prior to application of a protective spinel coating. The coated coupons were then subjected to oxidation testing at 800 and 850°C in air, and electrical testing at 800°C in air. While all of the surface-treatments resulted in improved surface stability (i.e., increased spallation resistance) compared to untreated AISI 441, the greatest degree of improvement (through 20,000 hours of testing at 800°C and 14,000 hours of testing at 850°C) was achieved by surface blasting.

  6. Effect of Hot Band Annealing on Forming Limit Diagrams of Ultra-Pure Ferritic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Shu, Jun; Bi, Hongyun; Li, Xin; Xu, Zhou

    2014-03-01

    In order to better understand the texture evolution, coincidence site lattice (CSL) and forming limit diagrams (FLDs) of ferritic stainless steels with and without hot band annealing, the texture evolution and CSL of ferritic stainless steels with 15% Cr content were studied by using x-ray diffraction and electron back-scattered diffraction technique. The strain hardening exponent n value, the strength coefficient K value, and Plastic strain ratio r value are the key parameters for the FLD. It was found out that the FLDo of plane strain condition and the stretchability were mainly influenced by their n value and K value, respectively. The higher n value and K value, better was the stretchability of investigated steels. The intensity of the γ-fiber dominated by {111} <112> was improved significantly in the cold rolled and annealed sheets because of a hot band annealing treatment and the sharp increase of Σ13b CSL boundaries. The increase of the formability is attributed to the significantly increase of the r value.

  7. 78 FR 63517 - Control of Ferrite Content in Stainless Steel Weld Metal

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-10-24

    ... Information The NRC published DG-1279 in the Federal Register on October 3, 2012 (77 FR 60479), for a 60-day... COMMISSION Control of Ferrite Content in Stainless Steel Weld Metal AGENCY: Nuclear Regulatory Commission... revision to Regulatory Guide (RG) 1.31, ``Control of Ferrite Content in Stainless Steel Weld Metal.''...

  8. 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.

  9. 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.

  10. Safe Use Limits for Advanced Ferritic Steels in Ultra-Supercritical Power Boilers.

    SciTech Connect

    Swindeman, RW

    2003-11-03

    In 2000, a Cooperative Research and Development Agreement (CRADA) was undertaken between the Oak Ridge National Laboratory (ORNL) and the Babcock & Wilcox Company to examine the databases for advanced ferritic steels and determine the safe limits for operation in supercritical steam power boilers. The materials of interest included the vanadium-modified 9-12% Cr steels with 1-2% Mo or W. The first task involved a review of pertinent information and the down-selection of a steel of special interest. The long-time database for 9Cr-1Mo-V steel was found to be most satisfactory for the examinations, and this steel was taken to be representative of the group. The second task involved the collection of aged and service exposed samples for metallurgical and mechanical testing. Here, aged samples to 75,000 hours, laboratory-tested samples to 83,000 hours, and service-exposed sample with up to 143,000 hours exposure were collected. The third task involved mechanical testing of exposed samples. Creep-rupture testing to long times was undertaken. Variable stress and temperature testing was included. Results were compared against the prediction of damage models. These models seemed to be adequate for life prediction. The fourth task involved the metallurgical examination of exposed specimens. Changes in microstructure were compared against published information on the evolution of microstructures in 9Cr-Mo-V steels and the results were found to be consistent with expectations. The fifth task involved a survey of steam and fireside corrosion. Data from the service-exposed tubing was examined, and a literature survey was undertaken as part of an activity in support of ultra-supercritical steam boiler technology. The corrosion study indicated some concerns about long-time fireside corrosion and suggested temperature limits were needed for corrosive coal ash conditions.

  11. Innovative Powder Processing of Oxide Dispersion Strengthened ODS Ferritic Stainless Steels

    SciTech Connect

    Rieken, Joel; Anderson, Iver; Kramer, Matthew

    2011-04-01

    An innovative gas atomization reaction synthesis technique was employed as a viable method to dramatically lower the processing cost for precursor oxide dispersion forming ferritic stainless steel powders (i.e., Fe-Cr-(Hf,Ti)-Y). During this rapid solidification process the atomized powders were enveloped by a nano-metric Cr-enriched metastable oxide film. Elevated temperature heat treatment was used to dissociate this metastable oxide phase through oxygen exchange reactions with Y-(Hf,Ti) enriched intermetallic compound precipitates. These solid state reactions resulted in the formation of highly stable nano-metric mixed oxide dispersoids (i.e., Y-Ti-O or Y-Hf-O) throughout the alloy microstructure. Subsequent high temperature (1200 C) heat treatments were used to elucidate the thermal stability of each nano-metric oxide dispersoid phase. Transmission electron microscopy coupled with X-ray diffraction was used to evaluate phase evolution within the alloy microstructure.

  12. 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.

  13. 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.

  14. Irradiation hardening of ODS ferritic steels under helium implantation and heavy-ion irradiation

    NASA Astrophysics Data System (ADS)

    Zhang, Hengqing; Zhang, Chonghong; Yang, Yitao; Meng, Yancheng; Jang, Jinsung; Kimura, Akihiko

    2014-12-01

    Irradiation hardening of ODS ferritic steels after multi-energy He-ion implantation, or after irradiation with energetic heavy ions including Xe and Bi-ions was investigated with nano-indentation technique. Three kinds of high-Cr ODS ferritic steels including the commercial MA956 (19Cr-3.5Al), the 16Cr-0.1Ti and the 16Cr-3.5Al-0.1Zr were used. Data of nano-hardness were analyzed with an approach based on Nix-Gao model. The depth profiles of nano-hardness can be understood by the indentation size effect (ISE) in specimens of MA956 implanted with multi-energy He-ions or irradiated with 328 MeV Xe ions, which produced a plateau damage profile in the near-surface region. However, the damage gradient overlaps the ISE in the specimens irradiated with 9.45 Bi ions. The dose dependence of the nano-hardness shows a rapid increase at low doses and a slowdown at higher doses. An 1/2-power law dependence on dpa level is obtained. The discrepancy in nano-hardness between the helium implantation and Xe-ion irradiation can be understood by using the average damage level instead of the peak dpa level. Helium-implantation to a high dose (7400 appm/0.5 dpa) causes an additional hardening, which is possibly attributed to the impediment of motion dislocations by helium bubbles formed in high concentration in specimens.

  15. Effect of cooling parameters on the microstructure and properties of Mo-bearing and Cr-bearing steels

    NASA Astrophysics Data System (ADS)

    Huo, Xiang-Dong; Li, Yu-Qian; Zhao, Yu-Tao; Zhang, Hai-Wang; Li, Zhao-Hui

    2011-10-01

    To develop low-cost low carbon bainitic steel, Mo-bearing and Cr-bearing steels were melted in a vacuum induction furnace and were researched by thermal simulation and hot rolling at the laboratory. As the cooling rate increases from 0.2 to 50°C/s, the transformation temperatures of two steels lie between 650 and 400°C, and the final microstructures of them change from quasi-polygonal ferrite and granular bainite to lath bainite. Compared with cooling in air or by interrupted cooling, Mo-bearing and Cr-bearing steel plates cooled by sprayed water boast higher strength and superior toughness, for large-size islands are responsible for the poor mechanical properties. Compared to Mo, Cr is effective to isolate the bainitic reaction in low carbon steel, and the bainitic microstructure can also be obtained in Cr-bearing steel cooled at a wide range of cooling rate.

  16. Pack cementation Cr-Al coating of steels and Ge-doped silicide coating of Cr-Nb alloy

    SciTech Connect

    He, Y.R.; Zheng, M.H.; Rapp, R.A.

    1995-08-01

    Carbon steels or low-alloy steels used in utility boilers, heat exchangers, petrochemical plants and coal gasification systems are subjected to high temperature corrosion attack such as oxidation, sulfidation and hot corrosion. The pack cementation coating process has proven to be an economical and effective method to enhance the corrosion resistance by modifying the surface composition of steels. With the aid of a computer program, STEPSOL, pack cementation conditions to produce a ferrite Cr-Al diffusion coating on carbon-containing steels by using elemental Cr and Al powders have been calculated and experimentally verified. The cyclic oxidation kinetics for the Cr-Al coated steels are presented. Chromium silicide can maintain high oxidation resistance up to 1100{degrees}C by forming a SiO{sub 2} protective scale. Previous studies at Ohio State University have shown that the cyclic oxidation resistance of MOSi{sub 2} and TiSi{sub 2} can be further improved by Ge addition introduced during coating growth. The halide-activated pack cementation process was modified to produce a Ge-doped silicide diffusion coating in a single processing step for the ORNL-developed Cr-Nb advanced intermetallic alloy. The oxidation behavior of the silicide-coated Cr-Nb alloy was excellent: weight gain of about 1 mg/cm{sup 2} upon oxidation at 1100{degrees}C in air for 100 hours.

  17. Development oxide dispersion strengthened ferritic steels for fusion

    SciTech Connect

    Mukhopadhyay, D.K.; Froes, F.H.; Gelles, D.S.

    1997-04-01

    Uniaxial tension creep response is reported for an oxide dispersion strengthened (ODS) steel, Fe-13.5Cr-2W-0.5Ti-0.25 Y{sub 2}O{sub 3} (in weight percent) manufactured using the mechanical alloying process. Acceptable creep response is obtained at 900{degrees}C.

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

    SciTech Connect

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

    1997-10-15

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

  19. Weld metal hydrogen cracking behavior, toughness, and microstructure in 9% Cr 1% Mo steels

    SciTech Connect

    Barnes, A.M. Panton-Kent, R.; Gooch, T.G.

    1994-12-31

    The use of 9%Cr 1%Mo steels, within various industries is increasing. The modification of the standard composition by the addition of V, Nb, and N improves the high temperature strength and creep properties. Development of welding conditions is dominated by the avoidance of hydrogen cracking while ensuring adequate mechanical properties and minimizing subcritical HAZ softening. This study was designed to evaluate compositional effects on MMA and electron beam (EB) weld metal properties and compare the weld metal hydrogen cracking sensitivity of the modified and standard grades. In comparing the hydrogen cracking sensitivity of the 9% Cr 1%Mo steels, the effect of welding and PWHT conditions on {delta}-ferrite development and SCHAZ softening were studied. An EB weld was incorporated in this study and assessment made of the CTOD behavior and microstructural development. Standard and modified grades exhibited similar hydrogen cracking sensitivity. The {delta}-ferrite content depended on welding conditions and composition. The ferrite factor gave a better indication of final ferrite content than Cr-equivalent. Softening in the SCHAZ was minimized by decreasing arc energy and preheat. The study indicates that modified grades can be welded using the procedures for standard grades. Charpy toughness was unaffected by 0.02{emdash}0.09%Nb or the PWHT schedules employed. increased Nb reduced the fracture toughness following extended PWHT.

  20. Oxidation and electrical behavior of ferritic stainless steel interconnect with Fe-Co-Ni coating by electroplating

    NASA Astrophysics Data System (ADS)

    Geng, Shujiang; Qi, Shaojun; Xiang, Dong; Zhu, Shenglong; Wang, Fuhui

    2012-10-01

    Fe-Co-Ni coating is deposited on ferritic stainless steel using a cost-effective technique of electroplating for intermediate-temperature solid oxide fuel cell (SOFC) interconnects application. The steel with Fe-Co-Ni coating has been evaluated in air at 800 °C corresponding to the cathode environment of SOFC. The results indicate that the steel with Fe-Co-Ni coating experiences an initially large mass gain, and then the mass gain increases slightly after the first-week rapid oxidation stage. After thermal exposure in air at 800 °C, the Fe-Co-Ni coating has been converted into (Fe,Co,Ni)3O4 spinel layer underneath which a Cr2O3 layer is developed from the steel substrate. The outer layer of (Fe,Co,Ni)3O4 spinel has not only suppressed Cr migration outward but also reduced the growth rate of the inner layer of Cr2O3. The steel with Fe-Co-Ni coating exhibits a stable surface oxide scale area specific resistance (ASR) which is much lower than that of the bare steel. (Fe,Co,Ni)3O4 spinel is a promising protective coating for SOFC steel interconnect.

  1. Insight into the microstructural characterization of ferritic steels using micromagnetic parameters

    SciTech Connect

    Moorthy, V.; Vaidyanathan, S.; Raj, B.; Jayakumar, T.; Kashyap, B.P.

    2000-04-01

    The influence of tempering-induced microstructural changes on the micromagnetic parameters such as magnetic Barkhausen emission (MBE), coercive force (H{sub c}), residual induction (B{sub r}), and maximum induction (B{sub max}) has been studied in 0.2 pct carbon steel, 2.25Cr-1Mo steel, and 9Cr-1Mo steel. It is observed that, after short tempering, the micromagnetic parameters show more or less linear correlation with hardness, which is attributed to the reduction in dislocation density, but long-term tempering produces nonlinear behavior. The variation in each of these parameters with tempering time has been explained based on the changes in the size and distribution of ferrite laths/grains and precipitates. It has been shown that the individual variation in the microstructural features such as size and distribution of laths/grains and precipitates during tempering can be clearly identified by the MBE parameters, which is not possible from the hysteresis loop parameters (H{sub c} and B{sub r}). It is also shown that the MBE parameters cannot only be used to identify different stages of tempering but also to quantify the average size of laths/grains and second-phase precipitates.

  2. Hot Ductility Behaviors in the Weld Heat-Affected Zone of Nitrogen-Alloyed Fe-18Cr-10Mn Austenitic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Moon, Joonoh; Lee, Tae-Ho; Hong, Hyun-Uk

    2015-04-01

    Hot ductility behaviors in the weld heat-affected zone (HAZ) of nitrogen-alloyed Fe-18Cr-10Mn austenitic stainless steels with different nitrogen contents were evaluated through hot tension tests using Gleeble simulator. The results of Gleeble simulations indicated that hot ductility in the HAZs deteriorated due to the formation of δ-ferrite and intergranular Cr2N particles. In addition, the amount of hot ductility degradation was strongly affected by the fraction of δ-ferrite.

  3. Thermophysical and mechanical properties of Fe-(8-9)%Cr reduced activation steels

    SciTech Connect

    Zinkle, S.J.; Robertson, J.P.; Klueh, R.L.

    1998-09-01

    The key thermophysical and mechanical properties for 8--9%Cr reduced activation ferritic/martensitic steels are summarized, including temperature-dependent tensile properties in the unirradiated and irradiated conditions, stress-rupture behavior, elastic constants, thermal conductivity, thermal expansion, specific heat, and ductile-to-brittle transition temperature. The estimated lower and upper temperatures limits for structural applications are 250 and 550 C due to radiation hardening/embrittlement and thermal creep considerations, respectively.

  4. 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

  5. A Micro-Alloyed Ferritic Steel Strengthened by Nanoscale Precipitates

    SciTech Connect

    Shen, Yongfeng; Wang, Chong M.; Sun, Xin

    2011-08-04

    A high strength ferritic steel with finely dispersive precipitates was investigated to reveal the fundamental strengthening mechanisms. Using energy dispersive X-ray spectroscopy (EDXS) and transmission electron microscope (TEM), fine carbides with an average diameter of 10 nm were observed in the ferrite matrix of the 0.08%Ti steel, and some cubic M23C6 precipitates were also observed at the grain boundaries and the interior of grains. The dual precipitate structure of finely dispersive TiC precipitates in the matrix and coarse M23C6 at grain boundaries provides combined matrix and grain boundary strengthening. The calculated amount of precipitation strengthening by the carbides was approximately 450 ~ 630 MPa, depending on the average size of nanoscale precipitates. This value is two or three times higher than that of conventional Ti-bearing high strength hot-rolled sheet steels. Dislocation densities increased from 3.42×1013 m-2 to 1.69 × 1014 m-2, espectively, with increasing tensile strain from 5.5% to 22%. The effect of the particle size, particle distribution and intrinsic particle strength have been investigated through dislocation dynamics (DD) simulations and the relationship for resolved shear stress for single crystal under this condition has been presented using simulation data. The results show that the finely dispersive precipitates can strengthen the material by pinning the dislocations up to a certain shear stress and retarding the recovery as well as annihilation of dislocations. The DD results also show that strengthening is not only a function of the density of the nano-scale precipitates but also of their size.

  6. HRTEM Study of the Role of Nanoparticles in ODS Ferritic Steel

    SciTech Connect

    Hsiung, L; Tumey, S; Fluss, M; Serruys, Y; Willaime, F

    2011-08-30

    Structures of nanoparticles and their role in dual-ion irradiated Fe-16Cr-4.5Al-0.3Ti-2W-0.37Y{sub 2}O{sub 3} (K3) ODS ferritic steel produced by mechanical alloying (MA) were studied using high-resolution transmission electron microscopy (HRTEM) techniques. The observation of Y{sub 4}Al{sub 2}O{sub 9} complex-oxide nanoparticles in the ODS steel imply that decomposition of Y{sub 2}O{sub 3} in association with internal oxidation of Al occurred during mechanical alloying. HRTEM observations of crystalline and partially crystalline nanoparticles larger than {approx}2 nm and amorphous cluster-domains smaller than {approx}2 nm provide an insight into the formation mechanism of nanoparticles/clusters in MA/ODS steels, which we believe involves solid-state amorphization and re-crystallization. The role of nanoparticles/clusters in suppressing radiation-induced swelling is revealed through TEM examinations of cavity distributions in (Fe + He) dual-ion irradiated K3-ODS steel. HRTEM observations of helium-filled cavities (helium bubbles) preferably trapped at nanoparticle/clusters in dual-ion irradiated K3-ODS are presented.

  7. Fatigue Crack Growth Behavior of Gas Metal Arc Welded AISI 409 Grade Ferritic Stainless Steel Joints

    NASA Astrophysics Data System (ADS)

    Lakshminarayanan, A. K.; Shanmugam, K.; Balasubramanian, V.

    2009-10-01

    The effect of filler metals such as austenitic stainless steel, ferritic stainless steel, and duplex stainless steel on fatigue crack growth behavior of the gas metal arc welded ferritic stainless steel joints was investigated. Rolled plates of 4 mm thickness were used as the base material for preparing single ‘V’ butt welded joints. Center cracked tensile specimens were prepared to evaluate fatigue crack growth behavior. Servo hydraulic controlled fatigue testing machine with a capacity of 100 kN was used to evaluate the fatigue crack growth behavior of the welded joints. From this investigation, it was found that the joints fabricated by duplex stainless steel filler metal showed superior fatigue crack growth resistance compared to the joints fabricated by austenitic and ferritic stainless steel filler metals. Higher yield strength and relatively higher toughness may be the reasons for superior fatigue performance of the joints fabricated by duplex stainless steel filler metal.

  8. Irradiation creep and microstructural changes of ODS steels of different Cr-contents during helium implantation under stress

    NASA Astrophysics Data System (ADS)

    Chen, J.; Jung, P.; Henry, J.; de Carlan, Y.; Sauvage, T.; Duval, F.; Barthe, M. F.; Hoffelner, W.

    2013-06-01

    Irradiation creep and microstructural changes of two ferritic ODS steels with 12% and 14% Cr have been studied by homogeneously implantation with helium under uniaxial tensile stresses from 40 to 300 MPa. The maximum dose was about 1.2 dpa (5000 appm-He) with displacement damage rates of 1 × 10-5 dpa/s at a temperature of 300 °C. Irradiation creep compliances were measured to be 4.0 × 10-6 dpa-1 MPa-1 and 10 × 10-6 dpa-1 MPa-1 for 12 and 14Cr ODS, respectively. Subsequently, microstructural evolution was studied in detail by TEM observations, showing dislocation loops and bubbles distributed homogenously in the matrix. Some bubbles were attached to ODS particles. Finally, the effects of Cr content on irradiation creep and microstructural changes are discussed, including earlier results of a 19Cr ODS and a PM2000 ferritic steel. Irradiation creep rates of both 12Cr and 14Cr-ODS ferritic steels a temperature of 300 °C show linear stress dependence up to 300 MPa at. Irradiation creep rate per dose rate and stress at a temperature of 300 °C amounts to 4.0 × 10-6 dpa-1 MPa-1 and 10 × 10-6 dpa-1 MPa-1 for 12Cr- and 14Cr-ODS, respectively. Irradiation creep properties are remarkably insensitive to Cr content, grain size and dispersoid size. Dislocation loops and helium bubbles are distributed homogenously in the matrix. In the case of high density fine dispersoids, most bubbles are attached to ODS particles. This may suppress loop formation as well as growth of bubbles, thereby increasing the resistance of ODS ferritic steels against helium embrittlement.

  9. 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.

  10. Contributions from research on irradiated ferritic/martensitic steels to materials science and engineering

    NASA Astrophysics Data System (ADS)

    Gelles, D. S.

    1990-05-01

    Ferritic and martensitic steels are finding increased application for structural components in several reactor systems. Low-alloy steels have long been used for pressure vessels in light water fission reactors. Martensitic stainless steels are finding increasing usage in liquid metal fast breeder reactors and are being considered for fusion reactor applications when such systems become commercially viable. Recent efforts have evaluated the applicability of oxide dispersion-strengthened ferritic steels. Experiments on the effect of irradiation on these steels provide several examples where contributions are being made to materials science and engineering. Examples are given demonstrating improvements in basic understanding, small specimen test procedure development, and alloy development.

  11. 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.

  12. Mechanical properties of irradiated 9Cr-2WVTa steel

    SciTech Connect

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

    1998-09-01

    An Fe-9Cr-2W-0.25V-0.07Ta-0.1C (9Cr-2WVTa) steel has excellent strength and impact toughness before and after irradiation in the Fast Flux Test Facility and the High Flux Reactor (HFR). The ductile-brittle transition temperature (DBTT) increased only 32 C after 28 dpa at 365 C in FFTF, compared to a shift of {approx}60 C for a 9Cr-2WV steel--the same as the 9Cr-2WVTa steel but without tantalum. This difference occurred despite the two steels having similar tensile but without tantalum. This difference occurred despite the two steels having similar tensile properties before and after irradiation. The 9Cr-2WVTa steel has a smaller prior-austenite grain size, but otherwise microstructures are similar before irradiation and show similar changes during irradiation. The irradiation behavior of the 9Cr-2WVTa steel differs from the 9Cr-2WV steel and other similar steels in two ways: (1) the shift in DBTT of the 9Cr-2WVTa steel irradiated in FFTF does not saturate with fluence by {approx}28 dpa, whereas for the 9Cr-2WV steel and most similar steels, saturation occurs at <10 dpa, and (2) the shift in DBTT for 9Cr-2WVTa steel irradiated in FFTF and HFR increased with irradiation temperature, whereas it decreased for the 9Cr-2WV steel, as it does for most similar steels. The improved properties of the 9Cr-2WVTa steel and the differences with other steels were attributed to tantalum in solution.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  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. Analysis of delta-ferrite data from production stainless steel pipe welds

    SciTech Connect

    Hebble, T.L.; Canonico, D.A.; Edmonds, D.P.; Goodwin, G.M.; Nanstad, R.K.

    1984-01-01

    An American Society of Mechanical Engineers task group on stainless steel weld materials was organized to determine the need for ferrite measurements of production welds required by the US Nuclear Regulatory Commission Regulatory Guide 1.31 (Rev. 1). The task group studied paired ferrite measurements (i.e., calculated and measured ferrite numbers (FNs) for the material qualifications versus measured ferrite numbers for corresponding production welds (PWs)). Our purpose was to compare delta-ferrite content as measured in the filler metal weld qualification pad with that in the resultant PW. Welds made predominantly by three common processes (submerged arc, shielded metal arc, and gas tungsten arc) were included in the study. Weld metals investigated included types 308, 308L, 316, and 316L stainless steel. An initial evaluation of the paired ferrite measurements was made by the task group, and specific conclusions and recommendations were made. We describe the analysis of the data and the conclusions drawn. The data base consisted of a heterogeneous collection of 1449 paired ferrite measurements for several forms and combinations of types 304 and 316 stainless steel pipe qualification pad and production welds. Qualification pad values ranged from 5 to 15 FN, and corresponding values for the PWs ranged from 2.3 to 17.5 FN. Only two PW ferrite numbers were less than 3. For qualification weld ferrite numbers less than 14, the median PW ferrite number was in reasonable agreement. However, the results show a wide scatter. As a result of this analysis and the task group evaluation, we concluded that the requirements of Regulatory Guide 1.31 on the measurement of ferrite in PWs are not necessary and that a ferrite number of 5 in the qualification welds will, in most cases, result in PW ferrite contents greater than 3 FN.

  20. The effect of a tin barrier layer on the permeability of hydrogen through mild steel and ferritic stainless steel

    SciTech Connect

    Bowker, J.; Piercy, G.R.

    1984-11-01

    Experiments were performed to measure the effectiveness of a commercially electroplated tin layer as a barrier to hydrogen, and to see how this altered when the tin layer was converted to FeSn. The authors measured the permeability of hydrogen through AISI 410 ferritic stainless steel and determined the effectiveness of tin as a surface barrier on it. The measured values for the permeability of hydrogen in iron and ferritic stainless steel are shown.

  1. Long-term oxidation behavior of spinel-coated ferritic stainless steel for solid oxide fuel cell interconnect applications

    SciTech Connect

    Stevenson, Jeffry W.; Yang, Zhenguo; Xia, Guanguang; Nie, Zimin; Templeton, Joshua D.

    2013-06-01

    Long-term tests (>8,000 hours) indicate that AISI 441 ferritic stainless steel coated with a Mn-Co spinel protection layer is a promising candidate material system for IT-SOFC interconnect applications. While uncoated AISI 441 showed a substantial increase in area-specific electrical resistance (ASR), spinel-coated AISI 441 exhibited much lower ASR values (11-13 mOhm-cm2). Formation of an insulating silica sublayer beneath the native chromia-based scale was not observed, and the spinel coatings reduced the oxide scale growth rate and blocked outward diffusion of Cr from the alloy substrate. The structure of the scale formed under the spinel coatings during the long term tests differed from that typically observed on ferritic stainless steels after short term oxidation tests. While short term tests typically indicate a dual layer scale structure consisting of a chromia layer covered by a layer of Mn-Cr spinel, the scale grown during the long term tests consisted of a chromia matrix with discrete regions of Mn-Cr spinel distributed throughout the matrix. The presence of Ti in the chromia scale matrix and/or the presence of regions of Mn-Cr spinel within the scale may have increased the scale electrical conductivity, which would explain the fact that the observed ASR in the tests was lower than would be expected if the scale consisted of pure chromia.

  2. Cleavage-quasi cleavage in ferritic and martensitic steels

    SciTech Connect

    Odette, G.R.; Edsinger, K.V.; Lucas, G.E.

    1997-12-31

    Confocal microscopy-fracture reconstruction and SEM were used to characterize the sequence-of-events leading to cleavage in a low alloy pressure vessel steel and two 8--12 Cr martensitic steels as a function of temperature. While differences between the steels were observed, they shared some common characteristics that differ from the conventional view of cleavage. Most notably cleavage does not occur as a single weakest link event; rather it is the consequence of a critical condition when a previously nucleated dispersion of microcracks suddenly coalesce to form a large, rapidly propagating macroscopic crack. It is argued that the critical event can be treated as a bridging instability. The stabilizing effect of the ductile ligaments separating the cleavage facets increases with increasing temperature. Indeed, even in the ductile tearing regime cleavage facets form a significant fraction of nuclei for larger microvoids.

  3. Effect of Nb on high-temperature properties for ferritic stainless steel

    SciTech Connect

    Fujita, N.; Kikuchi, M.; Ohmura, K.; Suzuki, T.; Funaki, S.; Hiroshige, I.

    1996-09-15

    In order to improve the efficiency of automobile engines and to reduce their weight, there is a move toward the use of conventional stainless steel sheets and pipes for exhaust manifolds to replace cast iron, the traditional material for this application. The exhaust manifold is used in an environment that includes engine vibrations as well as heating and cooling cycles caused by the travel pattern. Therefore, among high-temperature characteristics, thermal fatigue resistance is an important one that affects the life span of an exhaust manifold. Generally, austenitic steels have higher strength at high temperature than ferritic steels. However, type 304, a typical austenitic stainless steel, has less thermal fatigue resistance than type 430, a typical ferritic stainless steel. This is because austenitic steels have higher coefficient of thermal expansion than ferritic steels. Therefore, to obtain a material with excellent thermal fatigue resistance, it would conceivably be best to attempt to increase the high temperature strength of ferritic stainless steels. The present study centered on improvement of the high-temperature proof strength of ferritic stainless steels. The mechanism of high temperature strengthening by Nb addition, which was shown to be one of the most effective methods to improve proof strength at high temperature, was discussed.

  4. Comparison of Short-Term Oxidation Behavior of Model and Commercial Chromia-Forming Ferritic Stainless Steels in Air with Water Vapor

    SciTech Connect

    Brady, Michael P; Keiser, James R; More, Karren Leslie; Fayek, Mostafa; Walker, Larry R; Meisner, Roberta Ann; Anovitz, Lawrence {Larry} M; Wesolowski, David J; Cole, David R

    2012-01-01

    A high-purity Fe-20Cr and commercial type 430 ferritic stainless steel were exposed at 700 and 800 C in dry air and air with 10% water vapor (wet air) and characterized by SEM, XRD, STEM, SIMS, and EPMA. The Fe-20Cr alloy formed a fast growing Fe-rich oxide scale at 700 C in wet air after 24 h exposure, but formed a thin chromia scale at 700 C in dry air and at 800 C in both dry air and wet air. In contrast, thin spinel + chromia base scales with a discontinuous silica subscale were formed on 430 stainless steel under all conditions studied. Extensive void formation was observed at the alloy-oxide interface for the Fe-20Cr in both dry and wet conditions, but not for the 430 stainless steel. The Fe-20Cr alloy was found to exhibit a greater relative extent of subsurface Cr depletion than the 430 stainless steel, despite the former's higher Cr content. Depletion of Cr in the Fe-20Cr after 24 h exposure was also greater at 700 C than 800 C. The relative differences in oxidation behavior are discussed in terms of the coarse alloy grain size of the high-purity Fe-20Cr material, and the effects of Mn, Si, and C on the oxide scale formed on the 430 stainless steel.

  5. Structures and properties of rapidly solidified 9Cr-lMo steel

    NASA Astrophysics Data System (ADS)

    Megusar, J.; Lavernia, E.; Domalavage, P.; Harling, O. K.; Grant, N. J.

    1984-05-01

    Irradiation induced shifts of the DBTT and possible hydrogen embrittlement of ferritic steels are currently considered major problems for CTR applications. Rapid solidification and in particular liquid dynamic compaction (LDC) has been studied in developing 9Cr-1Mo steel as a candidate first wall material. Structural refinements such as reduction of segregation, fine grain size and fine size of second phase particles are retained in this process and this will have a favorable effect on fracture properties. LDC has also the potential of preparing first wall components directly from the melt and this would have an economic advantage over conventional ingot technology.

  6. Ferritic weldment of grain-refined ferritic steels for cryogenic service

    SciTech Connect

    Kim, H.J.; Morris, J.W. Jr.; Syn, C.K.

    1982-01-01

    This paper reports the initial results of the development of a weld filler metal and multipass GTA welding process for grain-refined 9Ni steel. The weld filler metal was cast in 4.5-kg ingots of the nominal composition Fe-14Ni-O.2Ti-0.003B, homogenized, hot-rolled, and then swaged into wire of 1.6-mm diameter. The chemical compositions of the base and filler metal are tabulated and the test welding procedure is described. Among the tests that were conducted on the welds are x-ray diffraction analysis for the residual austenite content; the Charpy impact test at 77 and 4.2 K for the fracture toughness; and scanning electron fractography for the weld metal, the HAZ, and the base metal of 9Ni Charpy specimens broken at 4.2 K. The procedure for grain refinement is defined; the retained austenite volume fraction is calculated using the method proposed by Miller. The results indicate that it is possible to weld grain-refined 9Ni steel with a ferritic weld filler metal and retain good toughness at cryogenic liquid helium temperatures.

  7. Effect of neutron irradiation at low temperature on the embrittlement of the reduced-activation ferritic steels

    NASA Astrophysics Data System (ADS)

    Rybin, V. V.; Kursevich, I. P.; Lapin, A. N.

    1998-10-01

    Effects of neutron irradiation to fluence of 2.0 × 10 24 n/m 2 ( E > 0.5 MeV) in temperature range 70-300°C on mechanical properties and structure of the experimental reduced-activation ferritic 0.1%C-(2.5-12)%Cr-(1-2)%W-(0.2-0.7)%V alloys were investigated. The steels were studied in different initial structural conditions obtained by changing the modes of heat treatments. Effect of neutron irradiation estimated by a shift in ductile-brittle transition temperature (ΔDBTT) and reduction of upper shelf energy (ΔUSE) highly depends on both irradiation condition and steel chemical composition and structure. For the steel with optimum chemical composition (9Cr-1.5WV) after irradiation to 2 × 10 24 n/m 2 ( E ⩾ 0.5 MeV) at 280°C the ΔDBTT does not exceed 25°C. The shift in DBTT increased from 35°C to 110°C for the 8Cr-1.5WV steel at a decrease in irradiation temperature from 300°C to 70°C. The CCT diagrams are presented for several reduced-activated steels.

  8. 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.

  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. Microstructural Characteristics of Plasma Nitrided Layer on Hot-Rolled 304 Stainless Steel with a Small Amount of α-Ferrite

    NASA Astrophysics Data System (ADS)

    Xu, Xiaolei; Yu, Zhiwei; Cui, Liying; Niu, Xinjun; Cai, Tao

    2016-02-01

    The hot-rolled 304 stainless steel with γ-austenite and approximately 5 pct α-ferrite elongated along the rolling direction was plasma-nitrided at a low temperature of 693 K (420 °C). X-ray diffraction results revealed that the nitrided layer was mainly composed of the supersaturated solid solution of nitrogen in austenite ( γ N). Transmission electron microscopy (TEM) observations showed that the microstructure of the γ N phase exhibited "fracture factor contrast" reflective of the occurrence of fine pre-precipitations in γ N by the continuous precipitation. The occurrence of a diffuse scattering effect on the electron diffraction spots of γ N indicated that the pre-precipitation took place in γ N in the form of strongly bonded Cr-N clusters or pairs due to a strong attractive interaction of nitrogen with chromium. Scanning electron microscopy and TEM observations indicated that the discontinuous precipitation initiated from the γ/ α interfaces and grew from the austenite boundaries into austenite grains to form a lamellar structure consisting of CrN and ferrite. The orientation relationship between CrN and ferrite corresponded to a Baker-Nutting relationship: (100)CrN//(100) α ; [011]CrN//[001] α . A zigzag boundary line following the banded structure of alternating γ-austenite and elongated α-ferrite was presented between the nitrided layer and the substrate to form a continuous varying layer thickness, which resulted from the difference in diffusivities of nitrogen in α-ferrite and γ-austenite, along the γ/ α interfaces and through the lattice. Microstructural features similar to the γ N were also revealed in the ferrite of the nitrided layer by TEM. It was not excluded that a supersaturated solid solution of nitrogen in ferrite ( α N) formed in the nitrided layer.

  11. 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.

  12. Study on the activated laser welding of ferritic stainless steel with rare earth elements yttrium

    NASA Astrophysics Data System (ADS)

    Wang, Yonghui; Hu, Shengsun; Shen, Junqi

    2015-10-01

    The ferritic stainless steel SUS430 was used in this work. Based on a multi-component activating flux, composed of 50% ZrO2, 12.09 % CaCO3, 10.43 % CaO, and 27.49 % MgO, a series of modified activating fluxes with 0.5%, 1%, 2%, 5%, 10%, 15%, and 20% of rare earth (RE) element yttrium (Y) respectively were produced, and their effects on the weld penetration (WP) and corrosion resistant (CR) property were studied. Results showed that RE element Y hardly had any effects on increasing the WP. In the FeCl3 spot corrosion experiment, the corrosion rates of almost all the samples cut from welded joints turned out to be greater than the parent metal (23.51 g/m2 h). However, there was an exception that the corrosion rate of the sample with 5% Y was only 21.96 g/m2 h, which was even better than parent metal. The further Energy Dispersive Spectrometer (EDS) test showed the existence of elements Zr, Ca, O, and Y in the molten slag near the weld seam while none of them were found in the weld metal, indicating the direct transition of element from activating fluxes to the welding seam did not exist. It was known that certain composition of activating fluxes effectively restrain the loss of Cr element in the process of laser welding, and as a result, the CR of welded joints was improved.

  13. Ferritic-Martensitic steel Test Blanket Modules: Status and future needs for design criteria requirements and fabrication validation

    NASA Astrophysics Data System (ADS)

    Salavy, J.-F.; Aiello, G.; Aubert, P.; Boccaccini, L. V.; Daichendt, M.; De Dinechin, G.; Diegele, E.; Giancarli, L. M.; Lässer, R.; Neuberger, H.; Poitevin, Y.; Stephan, Y.; Rampal, G.; Rigal, E.

    2009-04-01

    The Helium-Cooled Lithium-Lead and the Helium-Cooled Pebble Bed are the two breeding blankets concepts for the DEMO reactor which have been selected by EU to be tested in ITER in the framework of the Test Blanket Module projects. They both use a 9%CrWVTa Reduced Activation Ferritic-Martensitic steel, called EUROFER, as structural material and helium as coolant. This paper gives an overview of the status of the EUROFER qualification program and discusses the future needs for design criteria requirements and fabrication validation.

  14. Effects of transformed ferrite growth on the tensile fracture characteristics of a dual-phase steel

    NASA Astrophysics Data System (ADS)

    Jeong, W. C.; Kim, C. H.

    1988-02-01

    The effects of transformed ferrite growth on the tensile fracture characteristics of a dual-phase steel were investigated by observing crack initiation, propagation, and fracture behaviors. Crack initiation occurred by decohesion between martensite and ferrite. However, cracks propagated along the ferrite-martensite interface in a high temperature quenched specimen, whereas in specimens quenched from lower temperature cracks propagated into the martensite particle. Tensile fracture behaviors were not strongly influenced by the cooling rate. At both cooling rates of 5.6 and 0.1 °C/sec, specimens quenched from high temperature fractured by partially brittle fracture mode, but fracture mode changed to ductile mode as the quenching temperature decreased. The effect of transformed ferrite on the fracture mode was not substantially different from that of retained ferrite. However, the crack initiation and propagation was influenced by the variation in martensite distribution caused by different growth behavior of transformed ferrite.

  15. Field-dependent neutron depolarization study of the ferrite formation in medium-carbon steels

    SciTech Connect

    Te Velthuis, S.G.E.; Van Dijk, N.H.; Rekveldt, M.T.; Sietsma, J.; Van Der Zwaag, S.

    2000-03-14

    Neutron depolarization experiments have been performed on the ferrite and pearlite phase transformations of the medium-carbon C60 and C35 steels. The interaction of the polarized neutron beam with the ferromagnetic ferrite grains gives information on the mean magnetization and the magnetic correlation length. From these parameters the ferrite fraction and the mean ferrite grain size are determined in situ as a function of time and temperature during the phase transformation. The applied magnetic field was varied periodically in order to record a full hysteresis curve of the magnetization, which gives essential information on the microstructure of the ferromagnetic ferrite grains. The field dependence of the mean particle size during the early stages of the pearlite formation is a strong indication of multi-domain behavior, which is absent in the austenite-ferrite transformation and at the end of the pearlite formation.

  16. Development of oxide dispersion strengthened ferritic steels for fusion

    SciTech Connect

    Mukhopadhyay, D.K.; Suryanarayana, C.; Froes, F.H.; Gelles, D.S.

    1996-04-01

    Seven ODS steels, Fe(5-13.5)Cr-2W-0.5Ti-0.25 Y{sub 2}O{sub 3} (in weight percent) were manufactured using the mechanical alloying process. Only the composition Fe-13.5Cr3W-0.5Ti-0.25Y{sub 2}O{sub 3} showed no austenite formation at any temperature using differential thermal analysis and hence was selected as an experimental alloy for the present investigation. Milled powders were consolidated by hot isostatic pressing and hot swaging. Electron microscopy studies indicated high material homogeneity. The hardness of the as-swaged specimen was 65 R{sub c}. Annealing of the as-swaged material at 800, 900, 1000, 1100, and 1200{degrees}C showed a minor decrease in the hardness.

  17. Characterization of nanoscale NiAl-type precipitates in a ferritic steel by electron microscopy and atom probe tomography

    SciTech Connect

    Teng, Zhenke; Miller, Michael K; Ghosh, Gautam; Liu, Chain T; Huang, Shenyan; Russell, Kaye F; Fine, Morris E; Liaw, Peter K

    2010-01-01

    The microstructure of NiAl-type ({beta}{prime}) precipitates in an aged ferritic steel (Fe-12.7Al-9Ni-10.2Cr-1.9Mo, at.%) is characterized by transmission and analytical electron microscopy (AEM) and atom probe tomography (APT). The alloy shows a duplex precipitation of {beta}{prime} particles: primary with an average diameter of 130 nm and secondary with an average diameter of 3 nm. Based on APT, the primary and secondary {beta}{prime} have compositions of Ni{sub 41.2}Al{sub 43.6}Fe{sub 12.7}Cr{sub 0.8}Mo{sub 1.4} and Ni{sub 26.3}Al{sub 41.6}Fe{sub 26.9}Cr{sub 3.3}Mo{sub 1.7}, respectively.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  19. 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.

  20. 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. PMID:26501086

  1. 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

  2. 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

  3. Oxidation behavior of Fe-20Cr steels alloyed with titanium at 1073 K

    NASA Astrophysics Data System (ADS)

    Setiawan, Asep Ridwan; Artono, Tri Juni

    2016-02-01

    In this work, the oxidation behavior of Fe-20 wt%Cr steels alloyed with different titanium contents: 0, 0.5, and 1 wt% are studied as a function of time in air atmosphere. The samples were isothermally oxidized at 1073 K for 86.4, 172.8, and 345.6 ks in a muffle furnace. The mass of specimen were recorded before and after oxidation. After the oxidation, phases in the oxide were identified by X-ray diffraction (XRD). Optical microscopy observation on the chromium base alloys show that the microstructure consist only ferritic phases. The addition of titanium in the Fe-20Cr alloys does not alter the microstructure significantly. The oxidation behavior of Fe-20Cr, Fe-20Cr-0.5Ti and Fe-20Cr-1Ti were followed the classical parabolic relationship with time. XRD analysis indicated that the oxide scales developed on the Fe-20Cr alloys surface during oxidation tests consisted mainly of Cr2O3. On the other hand, the oxide scales developed on the surface of Fe-20Cr-0.5Ti and Fe-20Cr-1Ti alloys comprised of Cr2O3 and TiO2 oxide. The formation of TiO2 oxide in the Ti-containing alloys consequently increases the mass gain of the alloys during oxidation compared to that of Fe-20Cr alloys.

  4. Microstructure and oxidation properties of 16Cr-5Al-ODS steel prepared by sol-gel and spark plasma sintering methods

    NASA Astrophysics Data System (ADS)

    Xia, Y. P.; Wang, X. P.; Zhuang, Z.; Sun, Q. X.; Zhang, T.; Fang, Q. F.; Hao, T.; Liu, C. S.

    2013-01-01

    The 16Cr-5Al oxide dispersion strengthened (ODS) ferritic steel was fabricated by sol-gel method in combination with hydrogen reduction, mechanical alloying (MA) and spark plasma sintering (SPS) techniques. The phase characterization, microstructure and oxidation resistance of the 16Cr-5Al-ODS steel were investigated in comparison with the Al free 16Cr-ODS steel. X-ray diffraction (XRD) patterns showed that the Al free and Al added 16Cr-ODS steels exhibited typical ferritic characteristic structure. The microstructure analysis investigated by transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS) revealed that Y-Ti-O complexes with particle size of 10-30 nm were formed in the Al free matrix and Y-Al-O complexes with particle size of 20-100 nm were formed in the Al contained high-Cr ODS steel matrix. These complexes are homogeneously distributed in the matrices. The fabricated 16Cr-5Al-ODS steel exhibited superior oxidation resistance compared with the Al free 16Cr-ODS steel and the commercial 304 stainless steel owing to the formation of continuous and dense Al2O3 film on the surface.

  5. Investigation of AISI 441 Ferritic Stainless Steel and Development of Spinel Coatings for SOFC Interconnect Applications

    SciTech Connect

    Yang, Zhenguo; Xia, Guanguang; Wang, Chong M.; Nie, Zimin; Templeton, Joshua D.; Singh, Prabhakar; Stevenson, Jeffry W.

    2008-05-30

    As part of an effort to develop cost-effective ferritic stainless steel-based interconnects for solid oxide fuel cell (SOFC) stacks, both bare and spinel coated AISI 441 were studied in terms of metallurgical characteristics, oxidation behavior, and electrical performance. The conventional melt metallurgy used for the bulk alloy fabrication leads to significant processing cost reduction and the alloy chemistry with the presence of minor alloying additions of Nb and Ti facilitate the strengthening by precipitation and formation of Laves phase both inside grains and along grain boundaries during exposure in the intermediate SOFC operating temperature range. The Laves phase formed along the grain boundaries also ties up Si and prevents the formation of an insulating silica layer at the scale/metal interface during prolonged exposure. The substantial increase in ASR during long term oxidation due to oxide scale growth suggested the need for a conductive protection layer, which could also minimize Cr evaporation. In particular, Mn1.5Co1.5O4 based surface coatings on planar coupons drastically improved the electrical performance of the 441, yielding stable ASR values at 800ºC for over 5,000 hours. Ce-modified spinel coatings retained the advantages of the unmodified spinel coatings, and also appeared to alter the scale growth behavior beneath the coating, leading to a more adherent scale. The spinel protection layers appeared also to improve the surface stability of 441 against the anomalous oxidation that has been observed for ferritic stainless steels exposed to dual atmosphere conditions similar to SOFC interconnect environments. Hence, it is anticipated that, compared to unmodified spinel coatings, the Ce-modified coatings may lead to superior structural stability and electrical performance.

  6. 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.

  7. Microstructure and mechanical properties of weld fusion zones in modified 9Cr-1Mo steel

    NASA Astrophysics Data System (ADS)

    Sireesha, M.; Sundaresan, S.; Albert, Shaju K.

    2001-06-01

    Modified 9Cr-1Mo steel finds increasing application in power plant construction because of its excellent high-temperature properties. While it has been shown to be weldable and resistant to all types of cracking in the weld metal and heat-affected zone (HAZ), the achievement of optimum weld metal properties has often caused concern. The design of appropriate welding consumables is important in this regard. In the present work, plates of modified 9Cr-1Mo steel were welded with three different filler materials: standard 9Cr-1Mo steel, modified 9Cr-1Mo, and nickel-base alloy Inconel 182. Post-weld heat treatment (PWHT) was carried out at 730 and 760 °C for periods of 2 and 6 h. The joints were characterized in detail by metallography. Hardness, tensile properties, and Charpy toughness were evaluated. Among the three filler materials used, although Inconel 182 resulted in high weld metal toughness, the strength properties were too low. Between modified and standard 9Cr-1Mo, the former led to superior hardness and strength in all conditions. However, with modified 9Cr-1Mo, fusion zone toughness was low and an acceptable value could be obtained only after PWHT for 6 h at 760 °C. The relatively poor toughness was correlated to the occurrence of local regions of untransformed ferrite in the microstructure.

  8. Evaluation of Interface Boundaries in 9Cr-1Mo Steel After Thermal and Thermomechanical Treatments

    NASA Astrophysics Data System (ADS)

    Karthikeyan, T.; Dash, Manmath Kumar; Saroja, S.; Vijayalakshmi, M.

    2013-04-01

    The grain boundary character distribution (GBCD) and microstructure in 9Cr-1Mo ferritic/martensitic steel subjected to different heat treatments and thermomechanical treatments (TMTs) have been evaluated using electron backscatter diffraction (EBSD) technique. Microstructures obtained through displacive transformation of high-temperature austenite yielded higher amounts of Σ1-29 coincidence site lattice (CSL) boundaries (from 29 to 38 pct) compared with the ferrite grains obtained by diffusional transformation (~16 pct) or by recrystallization process (~14 pct). Specifically, the low-angle (Σ1), Σ3, Σ11, and Σ25b boundaries were enhanced in the tempered martensite substructure, whereas the prior austenite grain boundaries were largely of random type. Misorientation between the product ferrite variants for ideal orientation relationships during austenite transformation was calculated and compared with CSL misorientation to find its proximity based on Brandon's criteria. The observed enhancements in Σ1, Σ3, and Σ11 could be interpreted based on Kurdjumov-Sachs (K-S) relation, but Nishiyama-Wassermann (N-W) relation was needed to understand Σ25b formation. The amounts of CSL boundaries in the tempered martensite structure were not significantly influenced by austenite grain size or the kinetics of martensitic transformation. In mixed microstructures of "polygonal ferrite + tempered martensite", the frequencies of CSL boundaries were found to systematically decrease with increasing amounts of diffusional/recrystallized ferrite.

  9. Microstructural characterization of the HAZ in AISI 444 ferritic stainless steel welds

    SciTech Connect

    Silva, Cleiton C. Farias, Jesualdo P.; Miranda, Helio C.; Guimaraes, Rodrigo F.; Menezes, John W.A.; Neto, Moises A.M.

    2008-05-15

    Ferritic stainless steel is used as a coating for equipment in the petroleum refining industry. Welding is the main manufacturing and maintenance process used. However, little information on the metallurgical alterations caused by welding of these steels is found in the literature, prompting this study. In this study the authors evaluated the HAZ microstructure of AISI 444 ferritic stainless steel welded plates, by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results indicated that a weld thermal cycle caused microphase precipitation in the HAZ of the ferritic stainless steel. Also needle-like Laves phase precipitation occurred in the HAZ, near the partially-melted zone. Other secondary phases such as chi and sigma were observed, as well as nitride, carbide and carbonitride precipitates.

  10. Optical Band Gap Study Of Nanocrystalline NiCr0.8Fe1.2O4 Ferrite

    NASA Astrophysics Data System (ADS)

    Prasad, Arun S.; Dolia, S. N.; Dhawan, M. S.; Predeep, P.

    2008-04-01

    Optical energy band gap of nanocrystalline NiCr0.8Fe1.2O4 ferrite have been studied. The nanocrystalline NiCr0.8Fe1.2O4 ferrite have been synthesized using sol-gel technique. X-ray diffraction pattern confirms the formation of spinel structure in single phase and the average particle size is 4 nm. The energy band gap measurements of nanocrystalline NiCr0.8Fe1.2O4 ferrite in pellet form have been carried out by absorption spectra using double beam spectrophotometer. A pellet of nanoparticle ferrite was made under a load of 10 tons. From the analysis of absorption spectra, nanocrystalline NiCr0.8Fe1.2O4 ferrite have been found to have energy band gap of 3.2 eV at room temperature.

  11. Development and characterisation of a new ODS ferritic steel for fusion reactor application

    NASA Astrophysics Data System (ADS)

    Oksiuta, Z.; Olier, P.; de Carlan, Y.; Baluc, N.

    2009-08-01

    This paper describes the microstructure, tensile properties and Charpy impact resistance of a reduced activation oxide dispersion strengthened ferritic steel Fe-14Cr-2W-0.3Ti-0.3Y 2O 3 produced by mechanical alloying of a pre-alloyed, gas atomised steel powder with Y 2O 3 particles, compaction by hot extrusion at 1100 °C, hot rolling at 700 °C and heat treatment at 1050 °C for 1 h. At room temperature the material exhibits a high ultimate tensile strength of about 1420 MPa and high yield strength of about 1340 MPa in the transverse direction. In the longitudinal direction the values are about 10% lower, due to the anisotropy of the microstructure (elongated grains in the rolling direction). At 750 °C the material still exhibits relatively high yield strengths of about 325 MPa and 305 MPa in the longitudinal and transverse directions, respectively. The material exhibits reasonable uniform and total elongation values over the temperature range 23-750 °C, in both transverse and longitudinal directions. The material exhibits weak Charpy impact properties in the transverse direction. Charpy impact properties are slightly better in the longitudinal direction, with upper shelf energy of about 4.2 J and a ductile-to-brittle transition temperature of about 8.8 °C.

  12. HRTEM Study of Oxide Nanoparticles in K3-ODS Ferritic Steel Developed for Radiation Tolerance

    SciTech Connect

    Hsiung, L; Fluss, M; Tumey, S; Kuntz, J; El-Dasher, B; Wall, M; Choi, W; Kimura, A; Willaime, F; Serruys, Y

    2009-11-02

    Crystal and interfacial structures of oxide nanoparticles and radiation damage in 16Cr-4.5Al-0.3Ti-2W-0.37 Y{sub 2}O{sub 3} ODS ferritic steel have been examined using high-resolution transmission electron microscopy (HRTEM) techniques. Oxide nanoparticles with a complex-oxide core and an amorphous shell were frequently observed. The crystal structure of complex-oxide core is identified to be mainly monoclinic Y{sub 4}Al{sub 2}O{sub 9} (YAM) oxide compound. Orientation relationships between the oxide and the matrix are found to be dependent on the particle size. Large particles (> 20 nm) tend to be incoherent and have a spherical shape, whereas small particles (< 10 nm) tend to be coherent or semi-coherent and have a faceted interface. The observations of partially amorphous nanoparticles and multiple crystalline domains formed within a nanoparticle lead us to propose a three-stage mechanism to rationalize the formation of oxide nanoparticles containing core/shell structures in as-fabricated ODS steels. Effects of nanoparticle size and density on cavity formation induced by (Fe{sup 8+} + He{sup +}) dual-beam irradiation are briefly addressed.

  13. 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.

  14. 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.

  15. Toughening mechanisms of a high-strength acicular ferrite steel heavy plate

    NASA Astrophysics Data System (ADS)

    Cao, Zhi-Qiang; Bao, Yan-Ping; Xia, Zheng-Hai; Luo, Deng; Guo, Ai-Min; Wu, Kai-Ming

    2010-10-01

    An ultra-low carbon acicular ferrite steel heavy plate was obtained with an advanced thermo-mechanical control process-relaxed precipitation controlled transformation (TMCP-RPC) at Xiangtan Steel, Valin Group. The heavy plate has a tensile strength of approximately 600 MPa with a lower yield ratio. The impact toughness of the heavy plate achieves 280 J at -40°C. The fine-grained mixed microstructures of the heavy plate mainly consist of acicular ferrite, granular bainite, and polygonal ferrite. The high strength and excellent toughness of the heavy plate are attributed to the formation of acicular ferrite microstructure. The prevention of blocks of martensite/retained austenite (M/A) and the higher cleanness are also responsible for the superior toughness.

  16. Effects of Grit Blasting and Annealing on the High-Temperature Oxidation Behavior of Austenitic and Ferritic Fe-Cr Alloys

    NASA Astrophysics Data System (ADS)

    Proy, M.; Utrilla, M. V.; Otero, E.; Bouchaud, B.; Pedraza, F.

    2014-08-01

    Grit blasting (corundum) of an austenitic AISI 304 stainless steel (18Cr-8Ni) and of a low-alloy SA213 T22 ferritic steel (2.25Cr-1Mo) followed by annealing in argon resulted in enhanced outward diffusion of Cr, Mn, and Fe. Whereas 3 bar of blasting pressure allowed to grow more Cr2O3 and Mn x Cr3- x O4 spinel-rich scales, higher pressures gave rise to Fe2O3-enriched layers and were therefore disregarded. The effect of annealing pre-oxidation treatment on the isothermal oxidation resistance was subsequently evaluated for 48 h for both steels and the results were compared with their polished counterparts. The change of oxidation kinetics of the pre-oxidized 18Cr-8Ni samples at 850 °C was ascribed to the growth of a duplex Cr2O3/Mn x Cr3- x O4 scale that remained adherent to the substrate. Such a positive effect was less marked when considering the oxidation kinetics of the 2.25Cr-1Mo steel but a more compact and thinner Fe x Cr3- x O4 subscale grew at 650 °C compared to that of the polished samples. It appeared that the beneficial effect is very sensitive to the experimental blasting conditions. The input of Raman micro-spectroscopy was shown to be of ground importance in the precise identification of multiple oxide phases grown under the different conditions investigated in this study.

  17. Effect of Cr content on the corrosion performance of low-Cr alloy steel in a CO2 environment

    NASA Astrophysics Data System (ADS)

    Xu, Lining; Wang, Bei; Zhu, Jinyang; Li, Wei; Zheng, Ziyi

    2016-08-01

    Low-Cr alloy steel demonstrates lower corrosion rate than does C steel in a high-temperature and high-pressure CO2-containing environment. This study aimed to clarify the role of the Cr content in mitigating corrosion and reports the performance of 1%Cr, 2%Cr, 3%Cr, 4%Cr, 5%Cr, and 6.5%Cr steels. The results show that low-Cr alloy steel in CO2 at 80 °C and 0.8 MPa possesses spontaneous prepassivation characteristics when the Cr content is 3% or higher. Furthermore, the formation and peel-off of a prepassivation film on 3%Cr-6.5%Cr steels surfaces during polarization demonstrate that adequate amount of Cr in the steel substrate can cause protective layer. The main component of prepassivation film on 3%Cr steel is Cr(OH)3. Thus, the role of Cr is revealed. An adequate amount of Cr in the steel substrate causes the formation of protective Cr(OH)3 layer, which helps low-Cr steel to possess prepassivation characteristics. Prepassivation is the reason why low-Cr steel has a lower corrosion rate than C steel.

  18. Intragranular ferrite nucleation in medium-carbon vanadium steels

    SciTech Connect

    Ishikawa, Fusao; Takahashi, Toshihiko ); Ochi, Tatsurou . Muroran R D Lab.)

    1994-05-01

    In this study, the mechanism of intragranular ferrite nucleation is investigated. It is found that intragranular ferrite idiomorphs'' nucleate at vanadium nitrides which precipitate at manganese sulfide particles during cooling in the austenite region. It is observed that intragranular ferrite has the Baker-Nutting orientation relationship with vanadium nitride which precipitated at manganese sulfide. According to classical nucleation theory, the proeutectoid ferrite nucleation rate depends on the following factors: (1) the driving free energy for ferrite nucleation, (2) the diffusivity of carbon atoms in austenite, and (3) the increase in the interfacial energy associated with ferrite nucleation. In the Baker-Nutting orientation relationship, the lattice mismatch across the habit planes is likely to be very small. Depleted zones of solute atoms such as vanadium are assumed to be formed in the austenite matrix around precipitates. The effect of the depleted zones on factors (1) and (2) is estimated thermodynamically and it is proved that those effects are negligibly small. Thus, the authors conclude that the most important factor in nucleation kinetics of intragranular ferrite is the formation of precipitates which can develop coherent, low energy interfaces with ferrite.

  19. Measurement of transformation temperatures and specific heat capacity of tungsten added reduced activation ferritic-martensitic steel

    NASA Astrophysics Data System (ADS)

    Raju, S.; Jeya Ganesh, B.; Rai, Arun Kumar; Mythili, R.; Saroja, S.; Mohandas, E.; Vijayalakshmi, M.; Rao, K. B. S.; Raj, Baldev

    2009-06-01

    The on-heating phase transformation temperatures up to the melting regime and the specific heat capacity of a reduced activation ferritic-martensitic steel (RAFM) with a nominal composition (wt%): 9Cr-0.09C-0.56Mn-0.23V-1W-0.063Ta-0.02N, have been measured using high temperature differential scanning calorimetry. The α -ferrite + carbides → γ-austenite transformation start and finish temperatures, namely A c1, and A c3, are found to be 1104 and 1144 K, respectively for a typical normalized and tempered microstructure. It is also observed that the martensite start ( MS) and finish ( Mf) temperatures are sensitive to the austenitising conditions. Typical MS and Mf values for the 1273 K normalized and 1033 K tempered samples are of the order 714 and 614 K, respectively. The heat capacity CP of the RAFM steel has been measured in the temperature range 473-1273 K, for different normalized and tempered samples. In essence, it is found that the CP of the fully martensitic microstructure is found to be lower than that of its tempered counterpart, and this difference begins to increase in an appreciable manner from about 800 K. The heat capacity of the normalized microstructure is found to vary from 480 to 500 J kg -1 K -1 at 500 K, where as that of the tempered steel is found to be higher by about, 150 J kg -1 K -1.

  20. Method for reducing formation of electrically resistive layer on ferritic stainless steels

    DOEpatents

    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.

  1. Effect of copper on active dissolution and pitting corrosion of 25% Cr duplex stainless steels

    SciTech Connect

    Garfias-Mesias, L.F.; Sykes, J.M.

    1998-01-01

    Electrochemical studies were made of the influence of Cu on pitting behavior and active dissolution of 25% Cr duplex stainless steels (DSS) in chloride-containing neutral and acid solutions. Alloys with increased Cu content showed higher pitting potentials (E{sub p}) in 1 M hydrochloric acid (HCl) and 3.5% sodium chloride (NaCl) solutions. In HCl, the current density in the active state also was lower for the Cu-containing alloys. However, the critical pitting temperature (CPT) in ferric chloride (FeCl{sub 3}) was not improved significantly by addition of Cu. Pitting in all environments took place preferentially in the ferrite phase.

  2. A SYNCHROTRON DIFFRACTION STUDY OF TRANSFORMATION BEHAVIOUR IN 9 CR STEELS USING SIMULATED WELD HEAT-AFFECTED ZONE CONDITIONS

    SciTech Connect

    Santella, Michael L; Specht, Eliot D; Shingledecker, John P; Abe, Fujio

    2007-01-01

    Synchrotron diffraction experiments were conducted to examine the real-time transformation behaviours of an ex-perimental 9Cr-3W-3Co-NbV steel with high B and low N (N130B), and the commercial P92 steel under simulated weld heat-affected zone thermal cycles. When heated to peak temperatures near 1100 C, both steels rapidly trans-formed from ferrite to 100% austenite. During cooling, both transformed to martensite near 400 C. Both steels also retained untransformed austenite: 1.7% in N130B, and 5.8% in P92. The N130B was also heated to about 60 C above its A3 of 847 C. About 56% of the original ferrite never transformed to austenite. During cooling an additional 21% of ferrite and 23% of martensite formed. It retained no austenite. The P92 was heated to just above its A3 of 889 C. About 15% of the original ferrite never transformed to austenite. During cooling an additional 22% of ferrite and 60% of martensite formed. This steel retained about 2.3% austenite. Metallographic examina-tions indicated that the M23C6 in N130B was much more stable than that in P92 for heating to the lower peak tem-peratures. Analysis using equilibrium thermodynamics suggested that the more stable M23C6 in N130B could raise its apparent A3 by sequestering C. This could cause the ferrite-austenite transformation to appear sluggish. Ther-modynamic analysis also indicated that the M23C6 in N130B contained about 3.9 at% B compared to about 0.08 at% B in that of P92. In contrast, the refractory metal element content of the M23C6 was predicted to be higher in P92.

  3. Effect of Cr content on the nanostructural evolution of irradiated ferritic/martensitic alloys: An object kinetic Monte Carlo model

    NASA Astrophysics Data System (ADS)

    Chiapetto, M.; Malerba, L.; Becquart, C. S.

    2015-10-01

    Self-interstitial cluster diffusivity in Fe-Cr alloys, model materials for high-Cr ferritic/martensitic steels, is known to be reduced in a non-monotonic way as a function of Cr concentration: it first decreases, then increases. This non-monotonic behaviour is caused by a relatively long-ranged attractive interaction between Cr atoms and crowdions and correlates well with the experimentally observed swelling in these alloys under neutron irradiation, also seen to first decrease and then increase with increasing Cr content, under comparable irradiation conditions. Moreover, recent studies reveal that C atoms dispersed in the Fe matrix form under irradiation complexes with vacancies which, in turn, act as trap for one-dimensionally migrating self-interstitial clusters. The mobility of one-dimensional migrating clusters is considered key to determine swelling susceptibility. However, no model has ever been built that quantitatively describes the dependence of swelling on Cr content, allowing for the presence of C in the matrix. In this work we developed physically-based sets of parameters for object kinetic Monte Carlo (OKMC) simulations intended to study the nanostructure evolution under irradiation in Fe-Cr-C alloys. The nanostructural evolution in Fe-C and in four Fe-Cr-C alloys (containing 2.5, 5, 9 and 12 wt.% Cr) neutron irradiated up to ∼0.6 dpa at 563 K was simulated according to the model and reference experiments were reproduced. Our model shows that the SIA cluster reduced mobility has a major influence on the nanostructural evolution: it increases the number of vacancy-SIA recombinations and thus leads to the suppression of voids formation. This provides a clear framework to interpret the non-monotonic dependence of swelling in Fe-Cr alloys versus Cr content. Our model also suggests that the amount of C in the matrix has an equally important role: high amounts of it may counteract the beneficial effect that Cr has in reducing swelling.

  4. Alloying effect of Ni and Cr on irradiated microstructural evolution of type 304 stainless steels

    NASA Astrophysics Data System (ADS)

    Tan, L.; Busby, J. T.

    2013-11-01

    Life extension of the existing nuclear power plants imposes significant challenges to core structural materials that suffer increased fluences. This paper presents the microstructural evolution of a type 304 stainless steel and its variants alloyed with extra Ni and Cr under neutron irradiation at ˜320 °C for up to 10.2 dpa. Similar to the reported data of type 304 variants, a large amount of Frank loops, ultrafine G-phase/M23C6 particles, and limited amount of cavities were observed in the irradiated samples. The irradiation promoted the growth of pre-existing M23C6 at grain boundaries and resulted in some phase transformation to CrC in the alloy with both extra Ni and Cr. A new type of ultrafine precipitates, possibly (Ti,Cr)N, was observed in all the samples, and its amount was increased by the irradiation. Additionally, α-ferrite was observed in the type 304 steel but not in the Ni or Ni + Cr alloyed variants. The effect of Ni and Cr alloying on the microstructural evolution is discussed.

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

    SciTech Connect

    Pressly, G.A.

    1986-01-01

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

  6. Deuterium and helium trapping at TiC particles in ferritic steel

    NASA Astrophysics Data System (ADS)

    Spitznagel, J. A.; Brenner, S. S.; Miller, M. K.; Choyke, W. J.

    1984-05-01

    First wall and blanket materials in Tokamak machines must accommodate increasing concentrations of helium and hydrogen isotopes. Alloy design principles point to the efficacy of trapping He and hydrogen at finely dispersed precipitates to minimize their impact on mechanical properties. Titanium carbide particles are known to trap He effectively in austenitic stainless steel. Less is known about TiC as a trap for helium and hydrogen isotopes in ferritic steels. This paper demonstrates the feasibility of directly measuring the trapping of helium and deuterium at TiC-ferrite interfaces using atom probe field ion microscopy.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  8. Simultaneous aluminizing and chromizing of steels to form (Fe,Cr){sub 3}Al coatings and Ge-doped silicide coatings of Cr-Zr base alloys

    SciTech Connect

    Zheng, M.; He, Y.R.; Rapp, R.A.

    1997-12-01

    A halide-activated cementation pack involving elemental Al and Cr powders has been used to achieve surface compositions of approximately Fe{sub 3}Al plus several percent Cr for low alloy steels (T11, T2 and T22) and medium carbon steel (1045 steel). A two-step treatment at 925 C and 1150 C yields the codeposition and diffusion of aluminum and chromium to form dense and uniform ferrite coatings of about 400 {micro}m thickness, while preventing the formation of a blocking chromium carbide at the substrate surfaces. Upon cyclic oxidation in air at 700 C, the coated steel exhibits a negligible 0.085 mg/cm{sup 2} weight gain for 1900 one-hour cycles. Virtually no attack was observed on coated steels tested at ABB in simulated boiler atmospheres at 500 C for 500 hours. But coatings with a surface composition of only 8 wt% Al and 6 wt% Cr suffered some sulfidation attack in simulated boiler atmospheres at temperatures higher than 500 C for 1000 hours. Two developmental Cr-Zr based Laves phase alloys (CN129-2 and CN117(Z)) were silicide/germanide coated. The cross-sections of the Ge-doped silicide coatings closely mimicked the microstructure of the substrate alloys. Cyclic oxidation in air at 1100 C showed that the Ge-doped silicide coating greatly improved the oxidation resistance of the Cr-Zr based alloys.

  9. Use of ferritic steels in breeder reactors worldwide

    SciTech Connect

    Patriarca, P.

    1983-01-01

    The performance of LMFBR reactor steam generator materials is reviewed. Tensile properties of stainless steel-304, stainless steel-316, chromium-molybdenum steels, and Incoloy 800H are presented for elevated temperatures.

  10. Effect of silicon contents on the microstructures and mechanical properties of heat affected zones for 9Cr2WVTa steels

    NASA Astrophysics Data System (ADS)

    Wang, Jian; Lu, Shanping; Rong, Lijian; Li, Dianzhong

    2016-03-01

    The weldability of 9Cr2WVTa steels with silicon content varying from 0.30 wt.% to 1.36 wt.% was studied to meet the requirement of Generation-Ⅳ nuclear reactor. Samples of enlarged HAZs were fabricated by a thermal-mechanical simulator based on the simulation and measurement of non-equilibrium phase transformation. The content of δ-ferrite in the HAZs increased with the silicon content and the peak temperature of welding thermal cycle. The impact toughness in the HAZs decreased in different degrees when the δ-ferrite exhibits stripe (lower than 4.82%) or blocky types (higher than 4.82%). Post weld heat treatment (PWHT) has a significant role on improving the toughness. Adding silicon content increased the volume of δ-ferrite and therefore, decreased the tensile strength of the HAZs for 9Cr2WVTa steels. Silicon also as solid solution strengthening element increased the tensile strength. The 9Cr2WVTa steel has good weldability when the silicon content is lower than 0.60 wt.%.

  11. Study of cation magnetic moment directions in Cr (Co) doped nickel ferrites

    NASA Astrophysics Data System (ADS)

    Lang, L. L.; Xu, J.; Qi, W. H.; Li, Z. Z.; Tang, G. D.; Shang, Z. F.; Zhang, X. Y.; Wu, L. Q.; Xue, L. C.

    2014-09-01

    Powder samples of the ferrites MxNi1-xFe2O4 (M = Cr, Co and 0.0 ≤ x ≤ 0.3) were prepared using a chemical co-precipitation method. X-ray diffraction analysis showed that the two series of samples had a single-phase cubic spinel structure. It was found that the magnetic moments (μexp) per formula of samples measured at 10 K decreased when Cr substituted for Ni, but increased when Co substituted for Ni, in spite of the fact that the magnetic moments of Cr2+ (4 μB) and Co2+ (3 μB) are higher than that of Ni2+ (2 μB). With the assumption that the magnetic moments of Cr2+ and Cr3+ lie antiparallel to those of the Fe, Co, and Ni cations in the same sublattices of spinel ferrites, the dependences on the Cr (Co) doping level of the sample magnetic moments at 10 K were fitted successfully, using the quantum-mechanical potential barrier model earlier proposed by our group. For the two series of samples, the fitted magnetic moments are close to the experimental results.

  12. The fatigue crack initiation at the interface between matrix and {delta}-ferrite in 304L stainless steel

    SciTech Connect

    Rho, B.S.; Hong, H.U.; Nam, S.W.

    1998-10-13

    It is well known that austenitic stainless steels have good mechanical properties and good corrosion resistance at high temperatures and are widely used in high temperature application. However, representative 304L stainless steel among austenitic stainless steels has the undesirable {delta}-ferrite in {gamma} matrix unavoidably because of the limitation of the manufacturing process. While large amounts of {delta}-ferrite in the austenitic stainless steels can give rise to a decrease in the hot workability, the absence of {delta}-ferrite in 304L stainless steel can be the cause of longitudinal facial crack and shortness of continuous cast slab. However, there are few reported papers related with the effect of {delta}-ferrite nucleating the initial crack at the interface between matrix and {delta}-ferrite on fatigue properties at high temperature. In the present work, a comparison of fatigue life with the amount of {delta}-ferrite was examined and to find out the mechanism of crack initiation caused by {delta}-ferrite, dislocation behavior near the interface between {delta}-ferrite and matrix during fatigue testing was analyzed. To analyze the dislocation character near the interface between the matrix and {delta}-ferrite during a low cycle fatigue test, trace analysis was applied. Using Burgers vector and dislocation line direction, calculated by trace analysis, it was possible to obtain some characteristic of dislocation behaviors near the interface.

  13. Transformation Characteristics of Ferrite/Carbide Aggregate in Continuously Cooled, Low Carbon-Manganese Steels

    NASA Astrophysics Data System (ADS)

    Di Martino, S. F.; Thewlis, G.

    2014-02-01

    Transformation characteristics and morphological features of ferrite/carbide aggregate (FCA) in low carbon-manganese steels have been investigated. Work shows that FCA has neither the lamellae structure of pearlite nor the lath structure of bainite and martensite. It consists of a fine dispersion of cementite particles in a smooth ferrite matrix. Carbide morphologies range from arrays of globular particles or short fibers to extended, branched, and densely interconnected fibers. Work demonstrates that FCA forms over similar cooling rate ranges to Widmanstätten ferrite. Rapid transformation of both phases occurs at temperatures between 798 K and 973 K (525 °C and 700 °C). FCA reaction is not simultaneous with Widmanstätten ferrite but occurs at temperatures intermediate between Widmanstätten ferrite and bainite. Austenite carbon content calculations verify that cementite precipitation is thermodynamically possible at FCA reaction temperatures without bainite formation. The pattern of precipitation is confirmed to be discontinuous. CCT diagrams have been constructed that incorporate FCA. At low steel manganese content, Widmanstätten ferrite and bainite bay sizes are significantly reduced so that large amounts of FCA are formed over a wide range of cooling rates.

  14. Effect of Tungsten on Primary Creep Deformation and Minimum Creep Rate of Reduced Activation Ferritic-Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Vanaja, J.; Laha, Kinkar; Mathew, M. D.

    2014-10-01

    Effect of tungsten on transient creep deformation and minimum creep rate of reduced activation ferritic-martensitic (RAFM) steel has been assessed. Tungsten content in the 9Cr-RAFM steel has been varied between 1 and 2 wt pct, and creep tests were carried out over the stress range of 180 and 260 MPa at 823 K (550 °C). The tempered martensitic steel exhibited primary creep followed by tertiary stage of creep deformation with a minimum in creep deformation rate. The primary creep behavior has been assessed based on the Garofalo relationship, , considering minimum creep rate instead of steady-state creep rate . The relationships between (i) rate of exhaustion of transient creep r' with minimum creep rate, (ii) rate of exhaustion of transient creep r' with time to reach minimum creep rate, and (iii) initial creep rate with minimum creep rate revealed that the first-order reaction-rate theory has prevailed throughout the transient region of the RAFM steel having different tungsten contents. The rate of exhaustion of transient creep r' and minimum creep rate decreased, whereas the transient strain ɛ T increased with increase in tungsten content. A master transient creep curve of the steels has been developed considering the variation of with . The effect of tungsten on the variation of minimum creep rate with applied stress has been rationalized by invoking the back-stress concept.

  15. Influence of high-temperature exposure on the microstructure and mechanical properties of dissimilar metal welds between modified 9Cr-1Mo steel and alloy 800

    NASA Astrophysics Data System (ADS)

    Sireesha, M.; Albert, Shaju K.; Sundaresan, S.

    2005-06-01

    Transition joints between ferritic steel and austenitic stainless steel are commonly encountered in high-temperature components of power plants. Service failures in these are known to occur as a result, mainly, of thermal stresses due to expansion coefficient differentials. In order to mitigate the problem, a trimetallic configuration involving an intermediate piece of a material such as Alloy 800 between the ferritic and austenitic steels has been suggested. In our work, modified 9Cr-1Mo steel and 316LN stainless steel are used as the ferritic and austenitic components and the thermal behavior of the joints between modified 9Cr-1Mo steel and Alloy 800 is described in this article. The joints, made using the nickel-base filler material INCONEL 82/182 (INCONEL 82 for the root pass by gas-tungsten arc welding and INCONEL 182 for the filler passes by shielded-metal arc welding), were aged at 625 °C for periods up to 5000 hours. The microstructural changes occurring in the weld metal as well as at the interfaces with the two parent materials are characterized in detail. Results of across-the-weld hardness surveys and cross-weld tension tests and weld metal Charpy impact tests are correlated with the structural changes observed. Principally, the results show that (1) the tendency for carbon to diffuse from the ferritic steel into the weld metal is much less pronounced than when 2.25Cr-1Mo steel is used as the ferritic part; and (2) intermetallic precipitation occurs in the weld metal for aging durations longer than 2000 hours, but the weld metal toughness still remains adequate in terms of the relevant specification.

  16. Evolutions of Microstructure and Properties During Cold Rolling of 19Cr Duplex Stainless Steel

    NASA Astrophysics Data System (ADS)

    Ran, Qingxuan; Xu, Wanjian; Wu, Zhaoyu; Li, Jun; Xu, Yulai; Xiao, Xueshan; Hu, Jincheng; Jiang, Laizhu

    2016-07-01

    Evolutions of microstructure, mechanical, and corrosion properties of 19Cr (Fe-18.9Cr-10.1Mn-0.3Ni-0.261N-0.030C-0.5Si) duplex stainless steel have been investigated during cold rolling at room temperature. Dislocation slip dominated deformation mode of ferrite phase. However, deformation mechanism of austenite phase was different with the increasing cold-rolling reductions. Dislocation slip and strengthening effect of twin boundaries caused pile-up phenomenon at the initial deformation stage. When the amount of cold-rolling reduction attained greater than 50 pct, induced α'-martensite appeared in deformed austenite phase. Hardness of austenite phase was higher than that of the deformed ferrite because of its higher strengthening effect during cold-rolling process. Cold-rolling deformation caused deterioration of the pitting corrosion resistance in 3.5 wt pct NaCl aqueous solution. Pitting corrosion always initiated in the ferrite phase and the phase boundary in the solution-treated alloy. Additional pitting holes appeared in deformed austenite phase because of the decrease in corrosion resistance caused by dislocation accumulation and induced α'-martensite.

  17. Development of Bimodal Ferrite-Grain Structures in Low-Carbon Steel Using Rapid Intercritical Annealing

    NASA Astrophysics Data System (ADS)

    Karmakar, A.; Karani, A.; Patra, S.; Chakrabarti, Debalay

    2013-05-01

    Mixed ferrite grain structures, which have fine- and coarse-grain regions and showing "bimodal" grain size distributions, have been produced by rapid intercritical annealing of warm-rolled (or cold-rolled) samples. Microstructural changes have been analyzed using dilatometric studies, size prediction of transformed and recrystallized grains, and microtexture measurements. Fine austenite grains (<5 μm) developed during rapid annealing and transformed into fine-ferrite grains (2 to 4 μm) after cooling. Coarse-ferrite grains (28 to 42 μm) resulted from the recrystallization and growth of deformed ferrite. The effect of heating rate on microstructural morphologies during intercritical annealing has also been studied. A slow rate of heating (30 K/s) developed a uniform distribution of fine-ferrite grains and austenitic islands, while rapid heating (300 K/s) generated coarse blocks of austenite, elongated along the prior-pearlitic regions, in the ferrite matrix. As expected, bimodal ferrite grain structures or fine-scale dual-phase structures showed superior combination of tensile strength and ductility, compared to the ultrafine-grained steels.

  18. 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.

  19. 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.

  20. Development of high strength ferritic steel for interconnect application in SOFCs

    NASA Astrophysics Data System (ADS)

    Froitzheim, J.; Meier, G. H.; Niewolak, L.; Ennis, P. J.; Hattendorf, H.; Singheiser, L.; Quadakkers, W. J.

    High-Cr ferritic model steels containing various additions of the refractory elements Nb and/or W were studied with respect to oxidation behaviour (hot) tensile properties, creep behaviour and high-temperature electrical conductivity of the surface oxide scales. Whereas W additions of around 2 wt.% had hardly any effect on the oxidation rates at 800 and 900 °C, Nb additions of 1% led to a substantially enhanced growth rate of the protective surface oxide scale. It was found that this adverse effect can be alleviated by suitable Si additions. This is related to the incorporation of Si and Nb into Laves phase precipitates which also contribute to increased creep and hot tensile strength. The dispersion of Laves phase precipitates was greatly refined by combined additions of Nb and W. The high-temperature electrical conductivity of the surface oxide scales was similar to that of the Nb/W-free alloys. Thus the combined additions of Nb, W and Si resulted in an alloy with oxidation resistance, ASR contribution and thermal expansion comparable to the commercial alloy Crofer 22 APU, but with creep strength far greater than that of Crofer 22 APU.

  1. Cr-substituted Ni-Zn ferrites via oxalate decomposition. Structural, electrical and magnetic properties

    NASA Astrophysics Data System (ADS)

    Gabal, M. A.; Al Angari, Y. M.; Al-Agel, F. A.

    2015-10-01

    A series of Cr-substituted Ni-Zn ferrites; Ni0.8Zn0.2CrxFe2-xO4 (x=0.0-1.0) were prepared via oxalate decomposition route to characterize the effect of Cr-substitution on structural, magnetic and electrical properties. The prepared powders were characterized using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and transmission electron microscopy (TEM). XRD indicated single-phase cubic ferrites. The lattice parameters (aExp) exhibited a gradual decrease with increasing chromium, attributed to the smaller ionic radii of Cr3+ substituent. According to the obtained structural data, an appropriate cation distribution was suggested and fortified through FT-IR spectroscopy besides magnetic and electrical measurements. TEM image showed agglomerated cubic crystals with an average size of about 20 nm. Vibrating sample magnetometer (VSM) measurements indicated minimal hysteresis characteristic for soft magnetic material. The decrease in saturation magnetization (Ms) with Cr-substitution was discussed in view of Neel's two sub-lattice model. The change in the coercivity with Cr-content was discussed in view of estimated cation distribution and magnetization values. The obvious fall in the Curie temperature, estimated from molar susceptibility measurements, with increasing Cr-concentrations was assigned to the gradual replacement of Fe3+ ions on the octahedral sites by paramagnetic Cr3+ ions. ac-conductivity as a function of both frequency and absolute temperature exhibited a semi-conducting behavior. The decrease in conductivity with increasing Cr-content was attributed to the preferential occupation of Cr3+ ions by octahedral sites which replacing Fe3+ ions and limiting Fe2+-Fe3+ conduction.

  2. Ni-Cu-Zn Ferrite Powder Prepared from Steel Pickled Liquor and Electroplating Waste Solutions

    NASA Astrophysics Data System (ADS)

    Liu, Chung-Wen; Fu, Yen-Pei; Lin, Cheng-Hsiung

    2007-03-01

    In this study, we propose a new method of synthesizing Ni-Cu-Zn ferrite powder using steel pickled liquor and electroplating waste solutions as starting materials. It was found that the Ni-Cu-Zn ferrite powder prepared by a hydrothermal process from the waste solutions shows the formation of cubic ferrite with a saturation magnetization (Ms) of 31.5 emu/g and an intrinsic coercive force (Hci) of 19.3 Oe. Upon annealing at 750 °C for 2 h, the saturation magnetization increases to 52.6 emu/g and the intrinsic coercive force reaches 42.8 Oe. This useful method can promote the recycling of industrial waste solution and contribute to the preservation of the earth. Moreover, this method decreases the manufacturing cost in the treatment of the industrial waste solution for electroplating and steel industries.

  3. Effect of Mn Addition on Microstructural Modification and Cracking Behavior of Ferritic Light-Weight Steels

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

    In the present study, effects of Mn addition on cracking phenomenon occurring during cold rolling of ferritic light-weight steels were clarified in relation to microstructural modification involving κ-carbide, austenite, and martensite. Four steels were fabricated by varying Mn contents of 3 to 12 wt pct, and edge areas of steel sheets containing 6 to 9 wt pct Mn were cracked during the cold rolling. The steels were basically composed of ferrite and austenite in a band shape, but a considerable amount of κ-carbide or martensite existed in the steels containing 3 to 6 wt pct Mn. Microstructural observation of the deformed region of fractured tensile specimens revealed that cracks which were initiated at ferrite/martensite interfacial κ-carbides readily propagated along ferrite/martensite interfaces or into martensite areas in the steel containing 6 wt pct Mn, thereby leading to the center or edge cracking during the cold rolling. In the steel containing 9 wt pct Mn, edge cracks were found in the final stage of cold rolling because of the formation of martensite by the strain-induced austenite to martensite transformation, whereas they were hardly formed in the steel containing 12 wt pct Mn. To prevent or minimize the cracking, it was recommended that the formation of martensite during the cooling from the hot rolling temperature or during the cold rolling should be suppressed, which could be achieved by the enhancement of thermal or mechanical stability of austenite with decreasing austenite grain size or increasing contents of austenite stabilizers.

  4. 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.

  5. Effect of boron on post irradiation tensile properties of reduced activation ferritic steel (F-82H) irradiated in HFIR

    SciTech Connect

    Shiba, Kiyoyuki; Suzuki, Masahide; Hishinuma, Akimichi; Pawel, J.E.

    1994-12-31

    Reduced activation ferritic/martensitic steel, F-82H (Fe-8Cr-2W-V-Ta), was irradiated in the High Flux Isotope Reactor (HFIR) to doses between 11 and 34 dpa at 400 and 500 C. Post irradiation tensile tests were performed at the nominal irradiation temperature in vacuum. Some specimens included {sup 10}B or natural boron (nB) to estimate the helium effect on tensile properties. Tensile properties including the 0.2% offset yield stress, the ultimate tensile strength, the uniform elongation and the total elongation were measured. The tensile properties were not dependent on helium content in specimens irradiated to 34 dpa, however {sup 10}B-doped specimens with the highest levels of helium showed slightly higher yield strength and less ductility than boron-free specimens. Strength appears to go through a peak, and ductility through a trough at about 11 dpa. The irradiation to more than 21 dpa reduced the strength and increased the elongation to the unirradiated levels. Ferritic steels are one of the candidate alloys for nuclear fusion reactors because of their good thermophysical properties, their superior swelling resistance, and the low corrosion rate in contact with potential breeder and coolant materials.

  6. Interim storage of sodium in ferritic steel tanks at ambient temperature

    SciTech Connect

    Blackburn, L.D.

    1994-09-30

    Sodium tanks originally fabricated for elevated temperature service in the Clinch River Breeder Reactor Plant (CRBRP) will be used to store sodium removed from the Fast Flux Test Facility (FFTF) in the Sodium Storage Facility (SSF) at ambient temperature. This report presents an engineering review to confirm that protection against brittle fracture of the ferritic steel tanks is adequate for the intended service.

  7. 9 Cr-- 1 Mo steel material for high temperature application

    DOEpatents

    Jablonski, Paul D; Alman, David; Dogan, Omer; Holcomb, Gordon; Cowen, Christopher

    2012-11-27

    One or more embodiments relates to a high-temperature, titanium alloyed, 9 Cr-1 Mo steel exhibiting improved creep strength and oxidation resistance at service temperatures up to 650.degree. C. The 9 Cr-1 Mo steel has a tempered martensite microstructure and is comprised of both large (0.5-3 .mu.m) primary titanium carbides and small (5-50 nm) secondary titanium carbides in a ratio of. from about 1:1.5 to about 1.5:1. The 9 Cr-1 Mo steel may be fabricated using exemplary austenizing, rapid cooling, and tempering steps without subsequent hot working requirements. The 9 Cr-1 Mo steel exhibits improvements in total mass gain, yield strength, and time-to-rupture over ASTM P91 and ASTM P92 at the temperature and time conditions examined.

  8. Connection between micro and macro hardness pearlitic-ferritic steel

    NASA Astrophysics Data System (ADS)

    Duka, Edlira; Oettel, Heinrich; Dilo, Teuta

    2012-09-01

    Many physical and mechanical properties of materials are closely related to their microstructure, technologies to control the microstructure of materials have been well developed to obtain suitable properties. We measured the volume fraction of perlite and ferrite, micro Vickers hardness in pearlite and ferrite and macro hardness using different sample with different carbon content. The volume fraction of pearlite increases by increasing carbon content. By increasing carbon content, micro and macro hardness increase. We can conclude that for those conditional the mixing rule can't be use.

  9. 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.

  10. Microscopic impact of creep damage incipience and development on the magnetic properties of ferromagnetic Cr Mo steel

    NASA Astrophysics Data System (ADS)

    Augustyniak, Boleslaw; Piotrowski, Leszek; Chmielewski, Marek; Sablik, Martin J.

    2006-09-01

    Results are presented for magnetoacoustic emission (MAE) and magnetostriction measurements for Cr-Mo P22 steel (2.25Cr-1Mo) in the as-manufactured stage and after service at a power plant. We argue that MAE is correlated with magnetostriction behavior in relation to its derivative. Some quantitative description of precipitate morphology elucidates the as-observed decrease of MAE intensity with creep damage by change of precipitate morphology in the ferrite grain and grain boundary. This is discussed via a simple model for the MAE intensity dependence on microstructural change.

  11. Defect and void evolution in oxide dispersion strengthened ferritic steels under 3.2 MeV Fe + ion irradiation with simultaneous helium injection

    NASA Astrophysics Data System (ADS)

    Kim, I.-S.; Hunn, J. D.; Hashimoto, N.; Larson^1, D. L.; Maziasz, P. J.; Miyahara, K.; Lee, E. H.

    2000-08-01

    In an attempt to explore the potential of oxide dispersion strengthened (ODS) ferritic steels for fission and fusion structural materials applications, a set of ODS steels with varying oxide particle dispersion were irradiated at 650°C, using 3.2 MeV Fe + and 330 keV He + ions simultaneously. The void formation mechanisms in these ODS steels were studied by juxtaposing the response of a 9Cr-2WVTa ferritic/martensitic steel and solution annealed AISI 316LN austenitic stainless steel under the same irradiation conditions. The results showed that void formation was suppressed progressively by introducing and retaining a higher dislocation density and finer precipitate particles. Theoretical analyses suggest that the delayed onset of void formation in ODS steels stems from the enhanced point defect recombination in the high density dislocation microstructure, lower dislocation bias due to oxide particle pinning, and a very fine dispersion of helium bubbles caused by trapping helium atoms at the particle-matrix interfaces.

  12. Microstructures and Type-IV Creep Damage of High Cr Steel Welds

    NASA Astrophysics Data System (ADS)

    Hongo, Hiromichi; Tabuchi, Masaaki; Takahashi, Yukio

    Creep strength of welded joints in high Cr steels decreases due to the formation of Type-IV creep damage in the heat-affected zone (HAZ) during long-term use at high temperatures. This paper aims to elucidate the processes and mechanisms of Type-IV failure. Creep tests for the welded joints with different groove configurations of Mod.9Cr-1Mo steel were conducted. Distributions of Type-IV creep damages in HAZ of these welds were measured quantitatively, and were compared with FEM computations using damage mechanics analysis. For the welded joints with double U groove, creep voids were observed mostly at 20% below the surface of the plate, and scarcely near surfaces and center of thickness. For the welded joints with single U groove, creep voids were observed inside the plate thickness more than 3mm below the surfaces. From the comparison of experimental damage distributions with FEM analysis, it is considered to be important to take the stress triaxiality into account for the prediction of damage location and fracture life of high Cr ferritic steel welds.

  13. 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.

  14. Effect of tempering temperature on properties of 00Cr16Ni5Mo stainless steel

    SciTech Connect

    Qin, B. Wang, Z.Y.; Sun, Q.S.

    2008-08-15

    Specimens of 00Cr16Ni5Mo low carbon martensitic stainless steel were normalized at 1000 deg. C followed by tempering at 525 deg. C, 550 deg. C, 575 deg. C, 600 deg. C and 625 deg. C. After heat treatment, mechanical properties and pitting potential were determined through tensile, impact and electrochemical polarization tests. The results showed that the samples tempered at 550 deg. C and 600 deg. C for 2 h had an excellent combination of tensile strength, elongation, impact energy, hardness and corrosion resistance. Scanning electron microscopy, and X-ray diffraction examinations were conducted. These revealed that the properties of the steel were affected by the structure of the lath martensite, {delta}-ferrite, retained austenite and carbides.

  15. Evaluation on Fatigue Crack Propagation of Reduced Activation Ferritic Steel (JLF-1) at High Temperature

    NASA Astrophysics Data System (ADS)

    Yoon, Han Ki; Kim, Sa Woong; Lee, Sang Pill; Katoh, Yutai; Kohyama, Akira

    Recently, reduced activation ferritic/martensitic steel, vanadium alloy and SiC/SiC composite are embossed for nuclear fusion reactor in accordance with the coolant. Especially, reduced activation ferritic/martensitic steel is very suitable material for nuclear fusion reactor, because it has low coefficient of thermal expansion and excellent heat conductivity. The objective of this study is to investigate fatigue crack propagation behavior in the Reduced Activation Ferritic Steel (JLF-1). The fatigue crack propagation behavior of the JLF-1 steel was investigated by the constant-amplitude loading test for the stress ratios R = 0.1, 0.3 and 0.5 respectively. The fatigue crack growth tests carried out at room temperature and 400°C for base metal and weld metal. The effects of stress ratio, test temperature, specimen size and TIG welding on the fatigue crack propagation behaviors for JLF-1 steel were discussed within the Paris law. Particularly, the fatigue crack propagation rate of a weld metal was similar to that of base metal at the stress ratio of 0.3. Also, the fatigue crack propagation rate of a half size specimen was similar to that of a full size specimen at the stress ratios of 0.1, 0.3 and 0.5 respectively. From this result, we can recognize that the fatigue crack propagation behavior of this material can be evaluated by using the half size specimens.

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

    SciTech Connect

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

    1991-12-01

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

  17. Effect of aluminizing of Cr-containing ferritic alloys on the seal strength of a novel high-temperature solid oxide fuel cell sealing glass

    SciTech Connect

    Chou, Y. S.; Stevenson, Jeffry W.; Singh, Prabhakar

    2008-12-01

    A novel high-temperature alkaline-earth silicate sealing glass was developed for solid oxide fuel cell (SOFC) applications. The glass was used to join two metallic coupons of Cr-containing ferritic stainless steel for seal strength evaluation. In previous work, SrCrO4 was found to form along the glass/steel interface, which led to severe strength degradation. In the present study, aluminization of the steel surface was investigated as a remedy to minimize or prevent the strontium chromate formation. Three different processes for aluminization were evaluated with Crofer22APU stainless steel: pack cementation, vapor phase deposition, and aerosol spraying. It was found that pack cementation resulted in a rough surface with occasional cracks in the Al-diffused region. Vapor phase deposition yielded a smoother surface, but the resulting high Al content increased the coefficient of thermal expansion (CTE), resulting in failure of joined coupons. Aerosol spraying of an Al-containing salt resulted in formation of a thin aluminum oxide layer without any surface damage. The room temperature seal strength was evaluated in the as-fired state and in environmentally aged conditions. In contrast to earlier results with uncoated Crofer22APU, the aluminized samples showed no strength degradation even for samples aged in air. Interfacial and chemical compatibility was also investigated. The results showed aluminization to be a viable candidate approach to minimize undesirable chromate formation between alkaline earth silicate sealing glass and Cr-containing interconnect alloys for SOFC applications.

  18. Effect of aluminizing of Cr-containing ferritic alloys on the seal strength of a novel high-temperature solid oxide fuel cell sealing glass

    NASA Astrophysics Data System (ADS)

    Chou, Yeong-Shyung; Stevenson, Jeffry W.; Singh, Prabhakar

    A novel high-temperature alkaline earth silicate sealing glass was developed for solid oxide fuel cell (SOFC) applications. The glass was used to join two metallic coupons of Cr-containing ferritic stainless steel for seal strength evaluation. In previous work, SrCrO 4 was found to form along the glass/steel interface, which led to severe strength degradation. In the present study, aluminization of the steel surface was investigated as a remedy to minimize or prevent the strontium chromate formation. Three different processes for aluminization were evaluated with Crofer22APU stainless steel: pack cementation, vapor-phase deposition, and aerosol spraying. It was found that pack cementation resulted in a rough surface with occasional cracks in the Al-diffused region. Vapor-phase deposition yielded a smoother surface, but the resulting high Al content increased the coefficient of thermal expansion (CTE), resulting in the failure of joined coupons. Aerosol spraying of an Al-containing salt resulted in the formation of a thin aluminum oxide layer without any surface damage. The room temperature seal strength was evaluated in the as-fired state and in environmentally aged conditions. In contrast to earlier results with uncoated Crofer22APU, the aluminized samples showed no strength degradation even for samples aged in air. Interfacial and chemical compatibility was also investigated. The results showed aluminization to be a viable candidate approach to minimize undesirable chromate formation between alkaline earth silicate sealing glass and Cr-containing interconnect alloys for SOFC applications.

  19. Transformation and Precipitation Kinetics in 30Cr10Ni Duplex Stainless Steel

    NASA Astrophysics Data System (ADS)

    Fazarinc, Matevz; Terčelj, Milan; Bombač, David; Kugler, Goran

    2010-09-01

    To improve the microstructure during casting, hot forming, and heat treatment of 30Cr10Ni duplex stainless steel, accurate data on the precipitation and transformation processes at high temperatures are needed. In this article, the precipitation and transformation processes at various aging times in the temperature range 873 K to 1573 K (600 °C to 1300 °C) were studied. The 30Cr10Ni ferrous alloy contains a relatively large amount of Cr, Ni, and C, which results in a complex microstructure. In addition to the ferrite, austenite, and sigma phase, the M23C6 and MC carbides were also observed in the microstructure. The precipitation of the sigma phase was observed after just 3 minutes of aging, and after 30 minutes of aging at approximately 1053 K (780 °C), its fraction exceeded 40 pct. An intensive austenite-to-ferrite transformation was observed above 1423 K (1150 °C). Optical microscopy, energy-dispersive X-ray spectroscopy (EDS), electron backscattered diffraction (EBSD), and X-ray diffraction (XRD), as well as micro-indentation hardness, hardness, impact toughness, and tensile tests, were carried out to evaluate the obtained microstructures of aged samples.

  20. 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

  1. Nature of anisotropy of impact toughness of structural steels with ferrite-pearlite structure

    NASA Astrophysics Data System (ADS)

    Goritskii, V. M.; Shneyderov, G. R.; Lushkin, M. A.

    2013-10-01

    The anisotropy of the impact toughness of low-alloy steels of various compositions and purities with a ferrite-pearlite structure has been investigated using samples of type 11 according to the Russian Standard GOST 9454-78. It has been established that the anisotropy coefficient of the impact toughness depends on the anisotropy coefficient of the work of crack propagation and is independent of the degree of striation of the ferrite-pearlite structure and the work for nucleation of the ductile crack.

  2. Enabling Inexpensive Metallic Alloys as SOFC Interconnects: An Investigation into Hybrid Coating Technologies to Deposit Nanocomposite Functional Coatings on Ferritic Stainless Steel

    SciTech Connect

    Gannon, Paul; Gorokhovsky, Vladimir I.; Deibert, Max; Smith, Richard J.; Kayani, Asghar N.; White, P T.; Sofie, Stephen W.; Yang, Z Gary; Mccready, David E.; Visco, S.; Jacobson, C.; Kurokawa, H.

    2007-11-01

    Reduced operating temperatures (600-800°C) of Solid Oxide Fuel Cells (SOFCs) may enable the use of inexpensive ferritic steels as interconnects. Due to the demanding SOFC interconnect operating environment, protective coatings are required to increase long-term stability. In this study, large area filtered arc deposition (LAFAD) and hybrid filtered arc-assisted electron beam physical vapor deposition (FA-EBPVD) technologies were used to deposit two-segment coatings with Cr-Al-Y-O nanocomposite bottom segments and Mn-Co-O spinel-based top segments. Coatings were deposited on ferritic steels and subsequently annealed in air for various times. Surface oxidation was investigated using SEM/EDS, XRD and RBS analyses. Cr-volatilization was evaluated by transpiration and ICP-MS analysis of the resultant condensate. Time dependent Area Specific Resistance (ASR) was studied using the four-point technique. The oxidation behavior, Cr volatilization rate, and ASR of coated and uncoated samples are reported. Significant long-term (>1,000 hours) surface stability, low ASR, and dramatically reduced Cr-volatility were observed with the coated specimens. Improvement mechanisms, including the coating diffusion barrier properties and electrical conductivity are discussed.

  3. Influence of Dispersoids on Corrosion Behavior of Oxide Dispersion-Strengthened 18Cr Steels made by High-Energy Milling

    NASA Astrophysics Data System (ADS)

    Nagini, M.; Jyothirmayi, A.; Vijay, R.; Rao, Tata N.; Reddy, A. V.; Rajulapati, Koteswararao V.; Sundararajan, G.

    2016-02-01

    Corrosion behavior of 18Cr ferritic steel with and without yttria produced by high-energy milling followed by hot extrusion was studied in 3.5% NaCl solution using electrochemical and immersion techniques. The cyclic polarization study showed that pitting corrosion is predominant in all the materials. The pitting rate is higher in yttria dispersed steels and also increases with milling time. Impedance analysis revealed the formation of better corrosion resistance film on the surface of the steel without yttria. Potentiodynamic polarization studies indicated that the corrosion rate decreased up to 48 h of exposure time and increased beyond 48 h. The increase in corrosion rate beyond 48 h is due to the porous passive film. The corrosion behavior of all the materials in immersion studies followed the same trend as observed in electrochemical studies. Even though the corrosion rate of yttria dispersed 18Cr ferritic steel is less than that of the base material, the difference is marginal. The presence of dispersoids appears to promote nucleation of pits when compared to the steel without the dispersoids.

  4. 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.

  5. Effect of nickel on the precipitation processes in 12CrMoV steels under creep at 550 C

    SciTech Connect

    Vodarek, V.; Strang, A.

    1997-12-18

    In the course of development of 12 CrMoV steels nickel was added in order to improve impact properties and to suppress the presence of {delta}-ferrite in the microstructure. It was found, however, that excessive amounts of nickel, greater than {approximately}0.6 wt. %, caused an accelerated reduction in the creep rupture strength. This resulted in a downward inflexion in time dependence of creep rupture strength which is known as sigmoidal behavior. This phenomenon was particularly evident when these steels were tested at temperatures of 550 C and greater. In order to improve understanding of the effect of nickel on the microstructural evolution of 12CrMoV steels the metallographic investigation was undertaken on a series of four casts with different contents of nickel, which had been creep tested at 550 C out to durations of around 100,000 hours.

  6. Cr12 steels and the science of tribology

    SciTech Connect

    Beckitt, C.

    1994-12-01

    This articles reviews the use of Cr12 utility stainless steels as a simple means of dramatically improving the profitability and operating efficiency of the British mining industry. The trust of the paper is the use of tribology to determine the correct specification of materials for equipment construction to significantly reduce routine maintenance and extend life cycles. This particular paper addresses the benefits of Cr12 steels to resist abrasion and corrosion and compares it to several other steels to show the benefit of such material selection.

  7. 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.

  8. 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.

  9. Molds for electroslag casting systems. [2-1/4 Cr-1 Mo steel, 9 Cr-1 Mo steel

    SciTech Connect

    Bhat, G.K.

    1985-07-01

    This report describes the basic types of molds used for the manufacture of electroslag castings. The report also provides guidelines for the design of such molds based on heat generation and heat transfer considerations pertaining to the electroslag casting process. The designs of the two-step and three-step molds used for the manufacture of electroslag castings of 2-1/4 Cr-1 Mo steel, 316 stainless steel and 9 Cr-1 Mo steel are provided as examples of cost effective mold construction using cooled copper liners for metal-slag containment. 5 refs., 12 figs.

  10. Structure and hardness of corrosion-resistant ferritic steels subjected to high-temperature nitriding

    NASA Astrophysics Data System (ADS)

    Nikulin, S. A.; Rogachev, S. O.; Khatkevich, V. M.; Rozhnov, A. B.

    2014-02-01

    A comparative study of the effect of high-temperature internal nitriding (at above 1000°C) on the structure formation and hardening of thin-sheet samples of 08Kh17T (0.06% C-17.0% Cr-0.5% Ti) and 15Kh25T (0.10% C-25.0% Cr-0.5% Ti) steels was performed. The high-temperature internal nitriding of the 08Kh17T steel leads to the formation of martensite structure with Cr2N precipitates. The nitriding of 15Kh25T steel results in the formation of a layered structure; in this case, individual layers consist of a mixture of the α and γ phases and Cr2N particles, which are present in different proportions. It was shown that the internal nitriding of both steels with their subsequent annealing leads to their substantial uniform hardening.

  11. Effects of activating fluxes on the weld penetration and corrosion resistant property of laser welded joint of ferritic stainless steel

    NASA Astrophysics Data System (ADS)

    Wang, Yonghui; Hu, Shengsun; Shen, Junqi

    2015-10-01

    This study was based on the ferritic stainless steel SUS430. Under the parallel welding conditions, the critical penetration power values (CPPV) of 3mm steel plates with different surface-coating activating fluxes were tested. Results showed that, after coating with activating fluxes, such as ZrO2, CaCO3, CaF2 and CaO, the CPPV could reduce 100~250 W, which indicating the increases of the weld penetrations (WP). Nevertheless, the variation range of WP with or without activating fluxes was less than 16.7%. Compared with single-component ones, a multi-component activating flux composed of 50% ZrO2, 12.09% CaCO3, 10.43% CaO, and 27.49% MgO was testified to be much more efficient, the WP of which was about 2.3-fold of that without any activating fluxes. Furthermore, a FeCl3 spot corrosion experiment was carried out with samples cut from weld zone to test the effects of different activating fluxes on the corrosion resistant (CR) property of the laser welded joints. It was found that all kinds of activating fluxes could improve the CR of the welded joints. And, it was interesting to find that the effect of the mixed activating fluxes was inferior to those single-component ones. Among all the activating fluxes, the single-component of CaCO3 seemed to be the best in resisting corrosion. By means of Energy Dispersive Spectrometer (EDS) testing, it was found that the use of activating fluxes could effectively restrain the loss of Cr element of weld zone in the process of laser welding, thus greatly improving the CR of welded joints.

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

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

    DOE PAGESBeta

    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,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. Effect of recrystallization on ion-irradiation hardening and microstructural changes in 15Cr-ODS steel

    NASA Astrophysics Data System (ADS)

    Ha, Yoosung; Kimura, Akihiko

    2015-12-01

    The effects of recrystallization on ion-irradiation hardening and microstructural changes were investigated for a 15Cr-ODS ferritic steel. Dual ion-irradiation experiments were performed at 470 °C using 6.4 MeV Fe3+ ions simultaneously with energy-degraded 1 MeV He+ ions. The displacement of damage at 600 nm depth from the specimen surface was 30 dpa. Nano-indentation test with Berkovich type indentation tip was measured by constant stiffness measurement (CSM) technique. Results from nano-indentation tests indicate irradiation hardening in ODS steels even at 470 °C, while it wasn't observed in reduced activation ferritic steel. Recrystallized ODS steel shows a larger irradiation hardening, which is considered to be due to the reduction of grain boundaries and interfaces of matrix/oxide particles. In 20% cold rolled ODS steel after recrystallization, both the hardening and bubble number density were lower than those of recrystallized ODS steel, suggesting that dislocations generated by cold rolling suppress bubble formation. Based on the estimation of irradiation hardening from TEM observation results, it is considered that the bubbles are not the main factor controlling ion-irradiation hardening.

  15. Properties of Cr-substituted M-type barium ferrites prepared by nitrate citrate gel-autocombustion process

    NASA Astrophysics Data System (ADS)

    Ounnunkad, S.; Winotai, P.

    2006-06-01

    The Cr-substituted M-type barium hexaferrites, BaFe 12-xCr xO 19, with x=0.0-0.8 have been successfully prepared by nitrate-citrate auto-combustion process using citric acid as a fuel/reductant and nitrates as oxidants. The resulting precursors were calcined at 1100 °C for 1 h and followed by sintering at 1200 °C for 12 h in oxygen atmosphere. The ferrites were systematically investigated by using powder X-ray diffractometer (XRD), magnetic hysteresis recorder, Mössbauer spectrometer, and scanning electron microscope (SEM). The XRD data show the formation of pure magnetoplumbite phase without any other impurity phases. Both a and c lattice parameters calculated by the Rietveld method systematically decrease with increasing Cr content. The effects of Cr 3+ ions on the barium ferrites were reported and discussed in detail. The site preference of Cr 3+ and magnetic properties of the ferrites have been studied using Mössbauer spectra and hystereses. The results show that the magnetic properties are closely related to the distributions of Cr 3+ ions on the five crystallographic sites. The saturation magnetization systematically decreases, however, the coercivity increases with Cr concentration. The magnetization and Mössbauer results indicate that the Cr 3+ ions preferentially occupy the 2a, 12k, and 4f VI sites. The average size of hexagonal platelets obtained by SEM photographs tends to decrease with respect to Cr content.

  16. 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. PMID:26942534

  17. 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.

  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. 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.

  20. Irradiation creep in austenitic and ferritic steels irradiated in a tailored neutron spectrum to induce fusion reactor levels of helium

    SciTech Connect

    Grossbeck, M.L.; Gibson, L.T.; Jitsukawa, S.

    1996-04-01

    Six austenitic stainless steels and two ferritic alloys were irradiated sequentially in two research reactors where the neutron spectrum was tailored to produce a He production rate typical of a fusion device. Irradiation began in the Oak Ridge Research Reactor where an atomic displacement level of 7.4 dpa was achieved and was then transferred to the High Flux Isotope Reactor for the remainder of the irradiation to a total displacement level of 19 dpa. Temperatures of 60 and 330{degree}C are reported on. At 330{degree}C irradiation creep was found to be linear in stress and fluence with rates in the range of 1.7 - 5.5 x 10{sup -4}% MPa{sup -1} dpa{sup -1}. Annealed and cold-worked materials exhibited similar creep rates. There is some indication that austenitic alloys with TiC or TiO precipitates had a slightly higher irradiation creep rate than those without. The ferritic alloys HT-9 and Fe-16Cr had irradiatoin creep rates about 0.5 x 10{sup -4}% MPa{sup -1} dpa{sup -1}. No meaningful data could be obtained from the tubes irradiated at 60{degree}C because of damage to the tubes.

  1. Finite element residual stress analysis of induction heating bended ferritic steel piping

    SciTech Connect

    Kima, Jong Sung; Kim, Kyoung-Soo; Oh, Young-Jin; Chang, Hyung-Young; Park, Heung-Bae

    2014-10-06

    Recently, there is a trend to apply the piping bended by induction heating process to nuclear power plants. Residual stress can be generated due to thermo-mechanical mechanism during the induction heating bending process. It is well-known that the residual stress has important effect on crack initiation and growth. The previous studies have focused on the thickness variation. In part, some studies were performed for residual stress evaluation of the austenitic stainless steel piping bended by induction heating. It is difficult to find the residual stresses of the ferritic steel piping bended by the induction heating. The study assessed the residual stresses of induction heating bended ferriticsteel piping via finite element analysis. As a result, it was identified that high residual stresses are generated on local outersurface region of the induction heating bended ferritic piping.

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

    NASA Astrophysics Data System (ADS)

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

    2010-07-01

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

  3. Ripple reduction and surface coating tests with ferritic steel on JFT-2M

    NASA Astrophysics Data System (ADS)

    Tsuzuki, K.; Sato, M.; Kawashima, H.; Miura, Y.; Kimura, H.; Abe, T.; Uehara, K.; Ogawa, T.; Akiyama, T.; Shibata, T.; Yamamoto, M.; Koike, T.

    2000-12-01

    Applicability of the low-activation ferritic steel (F82H), which is one of the candidate materials for next generation fusion devices, has been tested in JFT-2M. Ferritic steel boards (FB) were installed between toroidal field coils (TFC) and the vacuum vessel at all toroidal sections. The experiment and the calculation show that the ripple amplitude decreases from 2.2% to 1.1% by the FB installation at R=1.6 m. The ripple reduction results in the reduction of fast ion loss and in the shift of the ripple loss to the outer region. No undesirable effect to the energy confinement and the plasma control was observed. The FB will be installed inside the vacuum vessel in the near future. In preparation, surface coating tests, mainly concerning with an in situ boron coating, are carried out.

  4. Tensile and fracture toughness properties of the nanostructured oxide dispersion strengthened ferritic alloy 13Cr-1W-0.3Ti-0.3Y 2O 3

    NASA Astrophysics Data System (ADS)

    Eiselt, Ch. Ch.; Klimenkov, M.; Lindau, R.; Möslang, A.; Odette, G. R.; Yamamoto, T.; Gragg, D.

    2011-10-01

    The realization of fusion power as an attractive energy source requires advanced structural materials that can cope with ultra-severe thermo-mechanical loads and high neutron fluxes experienced by fusion power plant components, such as the first wall, divertor and blanket structures. Towards this end, two variants of a 13Cr-1W-0.3Ti-0.3Y 2O 3 reduced activation ferritic (RAF-) ODS steel were produced by ball milling phase blended Fe-13Cr-1W, 0.3Y 20 3 and 0.3Ti powders in both argon and hydrogen atmospheres. The milled powders were consolidated by hot isostatic pressing (HIP). The as-HIPed alloys were then hot rolled into 6 mm plates. Microstructural, tensile and fracture toughness characterization of the hot rolled alloys are summarized here and compared to results previously reported for the as-HIPed condition.

  5. Analysis of chemical changes and microstructure characterization during deformation in ferritic stainless steel.

    PubMed

    Núñez, Andrés; Llovet, Xavier; Almagro, Juan F

    2013-08-01

    Uni- and biaxial tension deformation tests, with different degrees of deformation, have been done on AISI 430 (EN 1.4016) ferritic stainless steel samples, which had both different chemical compositions and had undergone different annealing treatments. The initial and deformed materials were characterized by using electron backscatter diffraction and backscatter electron imaging in a scanning electron microscope together with electron probe microanalysis. The correlation observed among the chemical compositions, annealing treatment, and strain level obtained after deformation is discussed. PMID:23628319

  6. Long-term corrosion of Cr-Mo steels in superheated steam at 482 and 538/sup 0/C. [21/4 Cr-1 Mo; 9 Cr-1 Mo; Sumitomo 9 Cr-2 Mo; Sandvik HT-9

    SciTech Connect

    Griess, J.C.; DeVan, J.H.; Maxwell, W.A.

    1980-01-01

    The corrosion of several Cr-Mo ferritic steels was investigated in superheated steam at an operating power plant. Tests were conducted at 482 and 538/sup 0/C (900 and 1000/sup 0/F) in a once-through loop for times up to 28,000 h. Chromium concentrations ranged from 2.0 to 11.3%, and the effect of surface preparation on corrosion was investigated. Only one of many specimens showed evidence of exfoliation at 482/sup 0/C, but at 538/sup 0/C exfoliation occurred on at least some of the specimens of most materials; the exceptions were the alloy with the highest chromium content (Sandvik HT-9), one heat of 9 Cr-1 Mo steel with the highest silicon content, and Sumitomo 9 Cr-2 Mo steel, which was in test for only 19,000 h. Parabolic oxidation kinetics adequately described the corrosion process for about the first year, after which corrosion rates were constant and lower than predicted from extrapolation of the initial part of the penetration versus time curves. With chromium concentrations between 2 and 9%, corrosion behavior was independent of chromium content, and corrosion was only slightly less with Sandvik HT-9. Corrosion was nearly independent of surface preparation, but in two cases the presence of mill scale on the surface prior to steam exposure seemed to retard oxidation in steam. 11 figures, 5 tables.

  7. Dilution and Ferrite Number Prediction in Pulsed Current Cladding of Super-Duplex Stainless Steel Using RSM

    NASA Astrophysics Data System (ADS)

    Eghlimi, Abbas; Shamanian, Morteza; Raeissi, Keyvan

    2013-12-01

    Super-duplex stainless steels have an excellent combination of mechanical properties and corrosion resistance at relatively low temperatures and can be used as a coating to improve the corrosion and wear resistance of low carbon and low alloy steels. Such coatings can be produced using weld cladding. In this study, pulsed current gas tungsten arc cladding process was utilized to deposit super-duplex stainless steel on high strength low alloy steel substrates. In such claddings, it is essential to understand how the dilution affects the composition and ferrite number of super-duplex stainless steel layer in order to be able to estimate its corrosion resistance and mechanical properties. In the current study, the effect of pulsed current gas tungsten arc cladding process parameters on the dilution and ferrite number of super-duplex stainless steel clad layer was investigated by applying response surface methodology. The validity of the proposed models was investigated by using quadratic regression models and analysis of variance. The results showed an inverse relationship between dilution and ferrite number. They also showed that increasing the heat input decreases the ferrite number. The proposed mathematical models are useful for predicting and controlling the ferrite number within an acceptable range for super-duplex stainless steel cladding.

  8. An Investigation of the Massive Transformation from Ferrite to Austenite in Laser-Welded Mo-Bearing Stainless Steels

    NASA Astrophysics Data System (ADS)

    Perricone, M. J.; Dupont, J. N.; Anderson, T. D.; Robino, C. V.; Michael, J. R.

    2011-03-01

    A series of 31 Mo-bearing stainless steel compositions with Mo contents ranging from 0 to 10 wt pct and exhibiting primary δ-ferrite solidification were analyzed over a range of laser welding conditions to evaluate the effect of composition and cooling rate on the solid-state transformation to γ-austenite. Alloys exhibiting this microstructural development sequence are of particular interest to the welding community because of their reduced susceptibility to solidification cracking and the potential reduction of microsegregation (which can affect corrosion resistance), all while harnessing the high toughness of γ-austenite. Alloys were created using the arc button melting process, and laser welds were prepared on each alloy at constant power and travel speeds ranging from 4.2 to 42 mm/s. The cooling rates of these processes were estimated to range from 10 K (°C)/s for arc buttons to 105 K (°C)/s for the fastest laser welds. No shift in solidification mode from primary δ-ferrite to primary γ-austenite was observed in the range of compositions or welding conditions studied. Metastable microstructural features were observed in many laser weld fusion zones, as well as a massive transformation from δ-ferrite to γ-austenite. Evidence of epitaxial massive growth without nucleation was also found when intercellular γ-austenite was already present from a solidification reaction. The resulting single-phase γ-austenite in both cases exhibited a homogenous distribution of Mo, Cr, Ni, and Fe at nominal levels.

  9. Effect of cooling after welding on microstructure and mechanical properties of 12 pct Cr steel weld metals

    SciTech Connect

    Cai, G.J.; Andren, H.O.; Svensson, L.E.

    1997-07-01

    The microstructure of three 12 pct Cr steel weld metals with different nickel and nitrogen contents was studied in as-welded condition and after postweld heat treatment with and without intercooling. Tensile strength and impact toughness of the weld metals were investigated in different postweld heat treatment conditions. In weld metals heat treated without intercooling, austenite decomposed by a eutectoid reaction that resulted in M{sub 23}C{sub 6} aggregates around retained {delta}-ferrite. Two morphologies of M{sub 2}N and MN precipitates were found in a low-dislocation {alpha}-ferrite. It was concluded that these phases were also transformed from austenite. In weld metals heat treated with intercooling, M{sub 23}C{sub 6} precipitates were smaller and more homogeneously distributed. Different MN precipitates were found in the tempered martensite. The fracture mode of the weld metals at room temperature was mainly transgranular cleavage with some fibrous fracture. Intercooling treatment improved Charpy impact toughness of the 12 pct Cr steel weld metals substantially. It was found that the important microstructural factors affecting the impact toughness of the weld metals which were heat treated without intercooling were the sizes of the {alpha}-ferrite grains, nonmetallic inclusions, and M{sub 23}C{sub 6} aggregates. For the weld metals heat treated with intercooling, the factors which affect the toughness of the weld metals were the sizes of martensite packets and nonmetallic inclusions.

  10. An equation-of-state for methane for modeling hydrogen attack in ferritic steels

    NASA Astrophysics Data System (ADS)

    Odette, G. R.; Vagarali, S. S.

    1982-02-01

    A statistical mechanical-based high temperature and high pressure equation-of-state for methane has been developed using the McQuarrie and Katz formulation based on Leonard-Jones (n, 6) intermolecular potential. Fugacity coefficients for methane have been estimated, and it is shown that for plain carbon steels during hydrogen attack the methane pressures are considerably lower than the fugacities and fall into a physically meaningful range (≤2500 MPa). Further, simple, but reasonably accurate, expressions for both the equation-of-state and fugacity coefficient have been developed for the purpose of modeling hydrogen attack kinetics in ferritic steels.

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

    SciTech Connect

    Usui, Makoto; Asano, Shigeru

    1996-06-01

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

  12. Corrosion of Ferritic Steels in High Temperature Molten Salt Coolants for Nuclear Applications

    SciTech Connect

    Farmer, J; El-Dasher, B; de Caro, M S; Ferreira, J

    2008-11-25

    Corrosion of ferritic steels in high temperature molten fluoride salts may limit the life of advanced reactors, including some hybrid systems that are now under consideration. In some cases, the steel may be protected through galvanic coupling with other less noble materials with special neutronic properties such a beryllium. This paper reports the development of a model for predicting corrosion rates for various ferritic steels, with and without oxide dispersion strengthening, in FLiBe (Li{sub 2}BeF{sub 4}) and FLiNaK (Li-Na-K-F) coolants at temperatures up to 800 C. Mixed potential theory is used to account for the protection of steel by beryllium, Tafel kinetics are used to predict rates of dissolution as a function of temperature and potential, and the thinning of the mass-transfer boundary layer with increasing Reynolds number is accounted for with dimensionless correlations. The model also accounts for the deceleration of corrosion as the coolants become saturated with dissolved chromium and iron. This paper also reports electrochemical impedance spectroscopy of steels at their corrosion potentials in high-temperature molten salt environments, with the complex impedance spectra interpreted in terms of the interfacial charge transfer resistance and capacitance, as well as the electrolyte conductivity. Such in situ measurement techniques provide valuable insight into the degradation of materials under realistic conditions.

  13. Shear Punch Properties of Low Activation Ferritic Steels Following Irradiation in ORR

    SciTech Connect

    Ermi, Ruby M.; Hamilton, Margaret L.; Gelles, David S.; Ermi, August M.

    2001-10-01

    Shear punch post-irradiation test results are reported for a series of low activation steels containing Mn following irradiation in the Oak Ridge Reactor at 330 and 400 degrees centigrade to {approx}10 dpa. Alloy compositions included 2Cr, 9Cr and 12Cr steels with V to 1.5% and W to 1.0%. Comparison of results with tensile test results showed good correlations with previously observed trends except where disks were improperly manufactured because they were too thin or because engraving was faulty.

  14. ENABLING THE PRACTICAL APPLICATION OF OXIDE DISPERSION-STRENGTHENED FERRITIC STEELS

    SciTech Connect

    Wright, Ian G; Pint, Bruce A; Dyadko, Dr. Eugene G.; Bornstein, Norman S.; Tatlock, Gordon J

    2007-01-01

    Effort has continued to evaluate joints made in oxide dispersion-strengthened (ODS) FeCrAl by (i) pulsed plasma-assisted diffusion (PPAD) bonding, and (ii) transient liquid phase (TLP) bonding. Creep tests of PPAD-bonded butt joints in air at 1000 C, using small, shoulder-loaded, dog bone-shaped specimens and an incrementally-loaded test technique, indicated that failure occurred at loads of up to 82% of that required to fail the parent alloy in the same test. For high creep-strength ferritic steels joined by conventional welding methods, strength reduction factors of 50-80% are considered to be acceptable. The failures apparently did not initiate along the joints; the observed mode of failure of the joined specimens was the same as observed for monolithic specimens of this alloy, by crack-initiated transgranular brittle fracture, followed by ductile overload failure. The progress of TLP bonding has been slower, with the major effort focused on understanding the behavior of the transient liquid phase and its interaction with the alloy microstructure during the various stages of bonding. Creep testing using the same procedures also has been used to evaluate changes resulting from torsional deformation of ODS-FeCrAl tubes in an attempt to modify their microstructures and increase their hoop strength. Interpretation of the results so far has not shown a clear trend, largely due to difficulties in measuring the effective angle of twist in the specimen gauge lengths. Other issues that have been addressed are the refinement of an approach for prediction of the oxidation-limited service lifetime of alumina scale-forming ODS alloys, and alternative routes for ODS alloy powder processing. Analysis of alloy specimens oxidized to failure (in some cases involving exposures for many thousands of hours) over a range of temperatures has provided an improved basis for calculating the values of parameters required in the lifing model (minimum Al content for protective behavior

  15. The Irradiation Performance and Microstructural Evolution in 9Cr-2W Steel Under Ion Irradiation

    NASA Astrophysics Data System (ADS)

    Alsagabi, Sultan; Charit, Indrajit; Pasebani, Somayeh

    2016-02-01

    Grade 92 steel (9Cr-2W) is a ferritic-martensitic steel with good mechanical and thermal properties. It is being considered for structural applications in Generation IV reactors. Still, the irradiation performance of this alloy needs more investigation as a result of the limited available data. The irradiation performance investigation of Grade 92 steel would contribute to the understanding of engineering aspects including feasibility of application, economy, and maintenance. In this study, Grade 92 steel was irradiated by iron ion beam to 10, 50, and 100 dpa at 30 and 500 °C. In general, the samples exhibited good radiation damage resistance at these testing parameters. The radiation-induced hardening was higher at 30 °C with higher dislocation density; however, the dislocation density was less pronounced at higher temperature. Moreover, the irradiated samples at 30 °C had defect clusters and their density increased at higher doses. On the other hand, dislocation loops were found in the irradiated sample at 50 dpa and 500 °C. Further, the irradiated samples did not show any bubble or void.

  16. 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.

  17. 46 CFR 54.25-20 - Low temperature operation-ferritic steels with properties enhanced by heat treatment (modifies...

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... section VIII of the ASME Boiler and Pressure Vessel Code (incorporated by reference; see 46 CFR 54.01-1... 46 Shipping 2 2014-10-01 2014-10-01 false Low temperature operation-ferritic steels with... VESSELS Construction With Carbon, Alloy, and Heat Treated Steels § 54.25-20 Low temperature...

  18. 46 CFR 54.25-20 - Low temperature operation-ferritic steels with properties enhanced by heat treatment (modifies...

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... section VIII of the ASME Boiler and Pressure Vessel Code (incorporated by reference; see 46 CFR 54.01-1... 46 Shipping 2 2011-10-01 2011-10-01 false Low temperature operation-ferritic steels with... VESSELS Construction With Carbon, Alloy, and Heat Treated Steels § 54.25-20 Low temperature...

  19. 46 CFR 54.25-20 - Low temperature operation-ferritic steels with properties enhanced by heat treatment (modifies...

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... section VIII of the ASME Boiler and Pressure Vessel Code (incorporated by reference; see 46 CFR 54.01-1... 46 Shipping 2 2012-10-01 2012-10-01 false Low temperature operation-ferritic steels with... VESSELS Construction With Carbon, Alloy, and Heat Treated Steels § 54.25-20 Low temperature...

  20. 46 CFR 54.25-20 - Low temperature operation-ferritic steels with properties enhanced by heat treatment (modifies...

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... section VIII of the ASME Boiler and Pressure Vessel Code (incorporated by reference; see 46 CFR 54.01-1... 46 Shipping 2 2013-10-01 2013-10-01 false Low temperature operation-ferritic steels with... VESSELS Construction With Carbon, Alloy, and Heat Treated Steels § 54.25-20 Low temperature...

  1. Influence of delta ferrite and dendritic carbides on the impact and tensile properties of a martensitic chromium steel

    NASA Astrophysics Data System (ADS)

    Schäfer, L.

    1998-10-01

    Martensitic chrome steels with a high content of chromium incline to form delta ferrite frequently accompanied by massive dendritic carbide precipitations. Both phases mostly influence the mechanical properties of this steel in countercurrent manner. The relatively soft delta ferrite causes an increase of ductility and toughness, whilst the brittle dendritic carbides decreases both. Both phases mostly decrease the strength of the steel. One or the other influence will be dominant in dependence of the quantitative relation of the two phases. This is the cause for very different statements in the literature. The dendritic carbides should be avoided using a cooling rate of more than 10 3 K/min after the austenitization, because this phase mostly impairs the mechanical properties of the steel. However, the delta ferrite without dendritic carbides can be tolerated mostly.

  2. Characterization of ferritic G. M. A. weld deposits in 9% Ni steel for cryogenic applications

    SciTech Connect

    Mahin, K.W.

    1980-04-01

    Low temperature containment vessels of 9% Ni are normally fabricated using the shielded metal arc (S.M.A.W.) or the gas metal arc (G.M.A.W.) welding processes. Available filler metals compatible with these processes are highly alloyed austenitics, whose strength levels undermatch those of the base plate. A more efficient weld joint would be a low alloy ferritic deposit. Although acceptable matching ferritic gas tungsten arc weld (G.T.A.W.) wires have been developed, similar progress has not been made in the area of ferritic G.M.A. weld wires. Most of the prior work in this area has focused on correlating composition with mechanical properties, without a corresponding evaluation of resultant microstructure. The study presented focused on establishing correlations between chemistry, microstructure and mechanical properties for four different ferritic G.M.A. weld deposits in 9% Ni steel, with the purpose of developing a better understanding of the factors controlling the 77K (-196/sup 0/C) toughness behavior of these weld metals. Microstructural characterization was carried out using standard optical and scanning electron microscopes, as well as a variety of advanced analytical techniques, including transmission electron microscopy (T.E.M.), scanning T.E.M., Moessbauer spectroscopy and Auger electron spectroscopy.

  3. Effect of thermo-mechanical treatments on the microstructure and mechanical properties of an ODS ferritic steel

    NASA Astrophysics Data System (ADS)

    Oksiuta, Z.; Mueller, P.; Spätig, P.; Baluc, N.

    2011-05-01

    The Fe-14Cr-2W-0.3Ti-0.3Y 2O 3 oxide dispersion strengthened (ODS) reduced activation ferritic (RAF) steel was fabricated by mechanical alloying of a pre-alloyed, gas atomised powder with yttria nano-particles, followed by hot isostatic pressing and thermo-mechanical treatments (TMTs). Two kinds of TMT were applied: (i) hot pressing, or (ii) hot rolling, both followed by annealing in vacuum at 850 °C. The use of a thermo-mechanical treatment was found to yield strong improvement in the microstructure and mechanical properties of the ODS RAF steel. In particular, hot pressing leads to microstructure refinement, equiaxed grains without texture, and an improvement in Charpy impact properties, especially in terms of the upper shelf energy (about 4.5 J). Hot rolling leads to elongated grains in the rolling direction, with a grain size ratio of 6:1, higher tensile strength and reasonable ductility up to 750 °C, and better Charpy impact properties, especially in terms of the ductile-to-brittle transition temperature (about 55 °C).

  4. Compatibility of ferritic steels with sintered Li/sub 2/O pellets in a flowing-helium environment

    SciTech Connect

    Chopra, O.K.; Kurasawa, T.; Smith, D.L.

    1983-01-01

    The compatibility of ferritic HT-9 alloy and Fe-9Cr-1Mo steel with Li/sub 2/O pellets has been investigated at 823 K (550/sup 0/C) in flowing helium containing 93 or 1 ppM H/sub 2/O and 1 ppM H/sub 2/. The results indicate that the alloy specimens gain weight whereas the Li/sub 2/O pellets lose weight after exposure. There is a net loss in weight of the total reaction couple. Both steels develop an iron-rich outer scale and chromium-rich subscale. The reaction rates in helium containing 93 ppM H/sub 2/O are greater than in helium containing 1 ppM H/sub 2/O. The depth of internal penetration for specimens exposed in helium with 1 ppM H/sub 2/O reaches a constant value after approx. 3.6 Ms. The specimens exposed in helium containing 93 ppM H/sub 2/O show a gradual increase in penetration up to 7.2 Ms. For both moisture contents, the total scale thickness follows a power law and the reaction rates decrease with time. The weight losses for Li/sub 2/O pellets follow a linear law and yield values of 12.2 and 3.8%/year in helium with 93 and 1 ppM H/sub 2/O, respectively.

  5. 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.

  6. Microstructure and mechanical properties of friction stir processed ODS ferritic steels

    NASA Astrophysics Data System (ADS)

    Noh, Sanghoon; Kasada, Ryuta; Kimura, Akihiko; Park, Seung Hwan C.; Hirano, Satoshi

    2011-10-01

    Oxide dispersion strengthened (ODS) steels are considered to be one of the candidate structural materials for advanced blanket systems because of its excellent properties in fusion environments. For more applications of the ODS steels to fusion systems with a huge and complex structure, development of joining technologies is a key issue to be solved. To reserve nano-oxide particles in the matrix homogeneously, the friction stir welding (FSW) is a suitable way to get good welding characteristics as a solid-state processing technique. In this research, effects of friction stir processing (FSP) on microstructure and mechanical properties of a ODS steel were studied to apply FSW process to ODS steels. The microstructure of FSPed ODS steel consists of stirred zone (SZ) and base metal (BM), as reported for other ferritic steels. Although equiaxed grain coarsening occurred through dynamic recrystallization during FSP, the nano-oxide particles in SZ showed fewer change in the size distribution. This resulted that FSP is effective to suppress the anisotropy and minimize the change of nano-oxide particles dispersion morphologies of ODS steel.

  7. Gas atomized precursor alloy powder for oxide dispersion strengthened ferritic stainless steel

    SciTech Connect

    Rieken, Joel

    2011-12-13

    Gas atomization reaction synthesis (GARS) was employed as a simplified method for producing precursor powders for oxide dispersion strengthened (ODS) ferritic stainless steels (e.g., Fe-Cr-Y-(Ti,Hf)-O), departing from the conventional mechanical alloying (MA) process. During GARS processing a reactive atomization gas (i.e., Ar-O2) was used to oxidize the powder surfaces during primary break-up and rapid solidification of the molten alloy. This resulted in envelopment of the powders by an ultra-thin (t < 150 nm) metastable Cr-enriched oxide layer that was used as a vehicle for solid-state transport of O into the consolidated microstructure. In an attempt to better understand the kinetics of this GARS reaction, theoretical cooling curves for the atomized droplets were calculated and used to establish an oxidation model for this process. Subsequent elevated temperature heat treatments, which were derived from Rhines pack measurements using an internal oxidation model, were used to promote thermodynamically driven O exchange reactions between trapped films of the initial Cr-enriched surface oxide and internal Y-enriched intermetallic precipitates. This novel microstructural evolution process resulted in the successful formation of nano-metric Y-enriched dispersoids, as confirmed using high energy X-ray diffraction and transmission electron microscopy (TEM), equivalent to conventional ODS alloys from MA powders. The thermal stability of these Y-enriched dispersoids was evaluated using high temperature (1200°C) annealing treatments ranging from 2.5 to 1,000 hrs of exposure. In a further departure from current ODS practice, replacing Ti with additions of Hf appeared to improve the Y-enriched dispersoid thermal stability by means of crystal structure modification. Additionally, the spatial distribution of the dispersoids was found to depend strongly on the original rapidly solidified microstructure. To exploit this, ODS microstructures were engineered from

  8. Gas atomized precursor alloy powder for oxide dispersion strengthened ferritic stainless steel

    NASA Astrophysics Data System (ADS)

    Rieken, Joel Rodney

    Gas atomization reaction synthesis (GARS) was employed as a simplified method for producing precursor powders for oxide dispersion strengthened (ODS) ferritic stainless steels (e.g., Fe-Cr-Y-(Ti,Hf)-O), departing from the conventional mechanical alloying (MA) process. During GARS processing a reactive atomization gas (i.e., Ar-O2) was used to oxidize the powder surfaces during primary break-up and rapid solidification of the molten alloy. This resulted in envelopment of the powders by an ultra-thin (t < 150 nm) metastable Cr-enriched oxide layer that was used as a vehicle for solid-state transport of O into the consolidated microstructure. In an attempt to better understand the kinetics of this GARS reaction, theoretical cooling curves for the atomized droplets were calculated and used to establish an oxidation model for this process. Subsequent elevated temperature heat treatments, which were derived from Rhines pack measurements using an internal oxidation model, were used to promote thermodynamically driven O exchange reactions between trapped films of the initial Cr-enriched surface oxide and internal Y-enriched intermetallic precipitates. This novel microstructural evolution process resulted in the successful formation of nano-metric Y-enriched dispersoids, as confirmed using high energy X-ray diffraction and transmission electron microscopy (TEM), equivalent to conventional ODS alloys from MA powders. The thermal stability of these Y-enriched dispersoids was evaluated using high temperature (1200°C) annealing treatments ranging from 2.5 to 1,000 hrs of exposure. In a further departure from current ODS practice, replacing Ti with additions of Hf appeared to improve the Y-enriched dispersoid thermal stability by means of crystal structure modification. Additionally, the spatial distribution of the dispersoids was found to depend strongly on the original rapidly solidified microstructure. To exploit this, ODS microstructures were engineered from different

  9. The Coexistence of Two Different Pearlites, Lamellae of (Ferrite + M3C), and Lamellae of (Ferrite + M23C6) in a Mn-Al Steel

    NASA Astrophysics Data System (ADS)

    Cheng, Wei-Chun; Li, Yu-Cheng

    2012-06-01

    Two different pearlites after two separate eutectoid reactions were observed in an Fe-19.8 Mn-1.64 Al-1.03 C (wt pct) steel. The steel specimens were processed under solution heat treatment at 1373 K (1100 °C) and received isothermal holding at temperatures from 1073 K to 773 K (800 °C to 500 °C). The constituent phase of the steel is single austenite at temperatures between 1373 K and 1073 K (1100 °C and 800 °C). At temperatures below 1048 K (775 °C), M3C and M23C6 carbides coprecipitate at the austenitic grain boundaries. Two different pearlites appear in the austenite matrix simultaneously at temperatures below 923 K (650 °C). One is lamellae of ferrite and M3C carbide, and the other is lamellae of ferrite and M23C6 carbide. These two pearlites are product phases from two separate eutectoid reactions, i.e., austenite → ferrite + cementite and austenite → ferrite + M23C6. Therefore, the supersaturated austenite has decomposed into two different pearlites, separately.

  10. A Study on Factors Influencing Toughness of Basic Flux-Cored Weld of Modified 9Cr-1Mo Steel

    NASA Astrophysics Data System (ADS)

    Arivazhagan, B.; Kamaraj, M.

    2011-10-01

    Flux-cored arc welding (FCAW) is relatively a new process for joining of modified 9Cr-1Mo (P91) steel. In this study, effect of shielding gas composition, inclusion content, gas tungsten-arc welding (GTAW) surface remelting, and postweld heat treatment (PWHT) on toughness were investigated. The high amount of silicon resulted in the formation of δ-ferrite in basic flux-cored weld. A mixture of 80% argon + 20% (80A) carbon dioxide shielding gas during welding resulted in the required toughness of 47 J at room temperature. The 95% argon + 5% carbon dioxide (95A) gas-shielded welds have lower toughness due to higher amount of δ-ferrite (4%) than 80% argon + 20% carbon dioxide welds (2%). In essence, most desirable shielding gas medium to achieve optimum toughness was 80% argon + 20% carbon dioxide in basic flux-cored arc welding.

  11. A High-Strength High-Ductility Ti- and Mo-Bearing Ferritic Steel

    NASA Astrophysics Data System (ADS)

    Huang, Yao; Zhao, Aimin; Wang, Xiaopei; Wang, Xuming; Yang, Jingbo; Han, Junke; Yang, Fengli

    2016-01-01

    This study reports the development of a Ti- and Mo-bearing ferritic steel precipitation-strengthened by nanometer-sized carbides. The steel showed an ultimate tensile strength of 995 MPa, a tensile elongation of 20 pct, and a hole-expanding ratio of 44 pct. The precipitation of nanometer-sized carbides in this steel during isothermal transformation at 873 K, 898 K, and 973 K (600 °C, 625 °C, and 700 °C) for 60 minutes was investigated in detail. The contributions of various strengthening mechanisms were analyzed, and the maximum contribution from the nanometer-sized carbide precipitates was estimated to be about 430 MPa.

  12. Development of Reduced Activation Ferritic-Martensitic Steels and fabrication technologies for Indian test blanket module

    NASA Astrophysics Data System (ADS)

    Raj, Baldev; Jayakumar, T.

    2011-10-01

    For the development of Reduced Activation Ferritic-Martensitic Steel (RAFMS), for the Indian Test Blanket Module for ITER, a 3-phase programme has been adopted. The first phase consists of melting and detailed characterization of a laboratory scale heat conforming to Eurofer 97 composition, to demonstrate the capability of the Indian industry for producing fusion grade steel. In the second phase which is currently in progress, the chemical composition will be optimized with respect to tungsten and tantalum for better combination of mechanical properties. Characterization of the optimized commercial scale India-specific RAFM steel will be carried out in the third phase. The first phase of the programme has been successfully completed and the tensile, impact and creep properties are comparable with Eurofer 97. Laser and electron beam welding parameters have been optimized and welding consumables were developed for Narrow Gap - Gas Tungsten Arc welding and for laser-hybrid welding.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  14. Tensile and creep properties of reduced activation ferritic-martensitic steel for fusion energy application

    NASA Astrophysics Data System (ADS)

    Mathew, M. D.; Vanaja, J.; Laha, K.; Varaprasad Reddy, G.; Chandravathi, K. S.; Bhanu Sankara Rao, K.

    2011-10-01

    Tensile and creep properties of a reduced activation ferritic-martensitic (RAFM) steel for Indian Test Blanket Module (TBM) to be tested in ITER have been evaluated. The tensile strength was found to decrease with temperature; the rate of decrease being slower in the intermediate temperature range of 450-650 K. Tensile ductility of the steel decreased with increase in temperature up to 650 K, followed by a rapid increase beyond 650 K. Creep studies have been carried out at 773, 823 and 873 K over a stress range of 100-300 MPa. The variation of minimum creep rate with applied stress followed a power law, ɛ = Aσ n. The ' n' value decreased with increase in temperature. The creep rupture life was found to relate inversely with minimum creep rate through the Monkman-Grant relation, t r · ɛ = constant. The tensile and creep properties of the steel were comparable with those of Eurofer 97.

  15. Microstructural probing of ferritic/martensitic steels using internal transmutation-based positron source

    NASA Astrophysics Data System (ADS)

    Krsjak, Vladimir; Dai, Yong

    2015-10-01

    This paper presents the use of an internal 44Ti/44Sc radioisotope source for a direct microstructural characterization of ferritic/martensitic (f/m) steels after irradiation in targets of spallation neutron sources. Gamma spectroscopy measurements show a production of ∼1MBq of 44Ti per 1 g of f/m steels irradiated at 1 dpa (displaced per atom) in the mixed proton-neutron spectrum at the Swiss spallation neutron source (SINQ). In the decay chain 44Ti → 44Sc → 44Ca, positrons are produced together with prompt gamma rays which enable the application of different positron annihilation spectroscopy (PAS) analyses, including lifetime and Doppler broadening spectroscopy. Due to the high production yield, long half-life and relatively high energy of positrons of 44Ti, this methodology opens up new potential for simple, effective and inexpensive characterization of radiation induced defects in f/m steels irradiated in a spallation target.

  16. Interfacial interactions between an alkali-free borosilicate viscous sealing glass and aluminized ferritic stainless steel

    NASA Astrophysics Data System (ADS)

    Hsu, Jen-Hsien; Kim, Cheol-Woon; Brow, Richard K.

    2014-03-01

    An alkali-free, alkaline earth borosilicate glass (designated G73) has been developed as a viscous sealant for use with solid oxide fuel cells (SOFC). In this work, the interfacial interactions that occur between this viscous sealant and aluminized ferritic stainless steel (SS441) under SOFC operational conditions are described. YSZ/glass/aluminized SS441 sandwich seals were held at 800 °C in air for up to 1000 h, and the interfaces were analyzed using analytical scanning electron microscopy (ASEM). Interfacial reactions were also characterized by X-ray diffraction (XRD) analyses of heat-treated mixtures of glass and alumina powders. The results show that the glass reacted with aluminum from the steel to form BaAl2Si2O8 crystals at the glass/metal interface and that the aluminum concentration in the aluminized steel was significantly depleted with time.

  17. Substructural phase transitions during intense plastic deformation of low-carbon ferrite-perlite steel

    NASA Astrophysics Data System (ADS)

    Kozlov, É. V.; Zakirov, D. M.; Popova, N. A.; Ivanov, Yu. F.; Gromov, V. E.; Ignatenko, L. N.; Tsellermaer, V. Y.

    1998-03-01

    We have studied the evolution of the defect structure and phase composition of low-carbon ferrite-perlite steel subjected to intense plastic deformation using diffraction electron microscopy. It has been shown that a high degree of deformation is accompanied by disruption of the perlite columns. We have found and described two perlite decay mechanisms: decay of the carbide plates by a path of their granulation due to dislocation slip and dissolution of cementite arising from the outflow of carbon atoms from the carbide phase into ferrite crystal lattice defects. We have described the phenomenon of morphological reconstruction of the cementite-phase particles (a transition from layers to spheres) under plastic deformation conditions.

  18. 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. PMID:25126753

  19. Strengthening of σ phase in a Fe20Cr9Ni cast austenite stainless steel

    SciTech Connect

    Wang, Y.Q.; Han, J.; Yang, B.; Wang, X.T.

    2013-10-15

    The strengthening mechanism of σ phase in a Fe20Cr9Ni cast austenite stainless steel used for primary coolant pipes of nuclear power plants has been investigated. The yield and ultimate tensile strengths of aged specimens increased comparing with those of the unaged ones. It was found that the increase of strengths is due to the hard and brittle (σ + γ{sub 2}) structure which decomposed from α phase in the steel. Fracture surfaces of specimens after in situ tensile test showed that the inhibition of (σ + γ{sub 2}) structure on the dislocation movements was more significant than ferrite although cracks started predominately at σ/γ{sub 2} interfaces. The (σ + γ{sub 2}) structure behaves like a fiber reinforced composite material. - Highlights: • The strengthening mechanism of σ phase in a Fe20Cr9Ni CASS is investigated. • The yield and ultimate tensile strengths increase with increasing of σ phase. • The increase of strengths is due to hard and brittle (σ + γ{sub 2}) structure. • The (σ + γ{sub 2}) structure in CASS behaves like a fibre reinforced composite material. • The σ/γ{sub 2} and α/σ/γ{sub 2} boundaries hinder the movement of dislocation.

  20. Irradiation-induced precipitation modelling of ferritic steels

    NASA Astrophysics Data System (ADS)

    Yin, You Fa; Faulkner, Roy G.; Lu, Zheng

    2009-06-01

    In high strength low alloy (HSLA) steels typically used in reactor pressure vessels (RPV), irradiation-induced microstructure changes affect the performance of the components. One such change is precipitation hardening due to the formation of solute clusters and/or precipitates which form as a result of irradiation-enhanced solute diffusion and thermodynamic stability changes. The other is irradiation-enhanced tempering which is a result of carbide coarsening due to irradiation-enhanced carbon diffusion. Both effects have been studied using a recently developed Monte Carlo based precipitation kinetics simulation technique and modelling results are compared with experimental measurements. Good agreements have been achieved.

  1. Electrical properties of In3+ and Cr3+ substituted magnesium manganese ferrites

    NASA Astrophysics Data System (ADS)

    Lakshman, A.; Subba Rao, P. S. V.; Parvatheeswara Rao, B.; Rao, K. H.

    2005-03-01

    Two series of magnesium-manganese ferrites, viz. Mg0.9Mn0.1InxFe2 - xO4 and Mg0.9Mn0.1CryFe2-yO4 have been prepared by the conventional ceramic process. The effects of In3+ and Cr3+ ions on the dc resistivity, dielectric constant and dielectric loss factor are presented in this paper. The resistivity increases with increasing concentrations of In3+ and Cr3+ ions. The observed variations in resistivity have been explained by Verwey's hopping mechanism. The activation energy, deduced from the temperature variation of resistivity, was found to increase with increasing concentrations of In3+ and Cr3+ ions. The room temperature dielectric constant at 100 kHz decreases with successive addition of trivalent ions in both the series. The observed variation in dielectric constant has been explained on the basis of space charge polarization. The dielectric loss tangent (tanδ) values measured at 100 kHz and 13 MHz are found to be very low for the samples with a higher concentration. The low values of the loss factor even at a high frequency indicate that the prepared materials may have great potential for use in microwave devices.

  2. Structural and magnetic studies of Cr doped nickel ferrite thin films

    NASA Astrophysics Data System (ADS)

    Panwar, Kalpana; Heda, N. L.; Tiwari, Shailja; Bapna, Komal; Choudhary, R. J.; Phase, D. M.; Ahuja, B. L.

    2016-05-01

    We have studied the structural and magnetic properties of Cr doped nickel ferrite thin films deposited on Si (100) and Si (111) using pulsed laser deposition technique. The films were deposited under vacuum and substrate temperature was kept at 700˚C. X-ray diffraction analysis revealed that films on both substrates have single phase cubic spinel structure. However, the film grown on Si (111) shows better crystalline behavior. Fourier transform infrared spectroscopy suggests that films on both substrates have mixed spinel structure. These films show magnetic hysteresis behavior and magnetization value of film on Si (100) is larger than that on Si (111). It turns out that structural and magnetic properties of these two films are correlated.

  3. Dynamical interaction of helium bubbles with cascade damage in Fe-9Cr ferritic alloy.

    SciTech Connect

    Ono, K.; Miyamoto, M.; Arakawa, K.; Birtcher, R. C.; Materials Science Division; Shimane Univ.; Osaka Univ.

    2008-12-01

    Dynamic interaction of helium bubble with cascade damage in Fe-9Cr ferritic alloy has been studied using in situ irradiation and electron microscopy. During the irradiation of the alloy by 400 keV Fe{sup +} ions at temperatures where no thermal motion takes place, induced displacement of small helium bubbles was observed: the bubbles underwent sporadic and instant displacement. The displacement was of the order of a few nanometers. The experimentally determined displacement probability of helium bubbles is consistent with the calculated probability of their dynamic interaction with sub-cascades introduced by the irradiation. Furthermore, during the irradiation of the alloy at higher temperatures, both retarded and accelerated Brownian type motions were observed. These results are discussed on the basis of dynamic interaction of helium bubbles with point defects that survive through high-energy self-ion irradiation.

  4. Fracture behavior of 9Cr nanostructured ferritic alloy with improved fracture toughness

    NASA Astrophysics Data System (ADS)

    Byun, Thak Sang; Yoon, Ji Hyun; Wee, Sung Hun; Hoelzer, David T.; Maloy, Stuart A.

    2014-06-01

    Nanostructured ferritic alloys (NFAs) have been considered as primary candidate materials for both fission and fusion reactors because of their excellent creep and irradiation resistances. It has been shown that high temperature fracture toughness could be significantly improved by appropriate thermo-mechanical treatments (TMTs). This article focuses on the static fracture behaviors of newly developed 9Cr NFAs with improved toughness. Optimal TMTs resulted in high fracture toughness at room temperature (>250 MPa √m) and in retaining higher than 100 MPa √m over a wide temperature range of 22-700 °C. Significant differences were found in fracture surfaces and fracture resistance (J-R) curves after different TMTs. Unique fracture surface features such as shallow nanoscale facets decorated with shear lips and flake-like grains were observed in high toughness specimens.

  5. Precipitation and mechanical properties of Nb-modified ferritic stainless steel during isothermal aging

    SciTech Connect

    Yan Haitao Bi Hongyun; Li Xin; Xu Zhou

    2009-03-15

    The influence of isothermal aging on precipitation behavior and mechanical properties of Nb-modified ferritic stainless steel was investigated using Thermo-calc software, scanning electron microscopy and transmission electron microscopy. It was observed that TiN, NbC and Fe{sub 2}Nb formed in the investigated steel and the experimental results agreed well with the results calculated by Thermo-calc software. During isothermal aging at 800 deg. C, the coarsening rate of Fe{sub 2}Nb is greater than that of NbC, and the calculated average sizes of NbC and Fe{sub 2}Nb of the aged specimen agreed with the experimental results. In addition, the tensile strength and micro-hardness of the ferritic stainless steel increased with increased aging time from 24 h to 48 h. But aging at 800 deg. C for 96 h caused the coarsening of the precipitation, which led to a decrease of tensile strength and micro-hardness.

  6. Tensile and charpy impact properties of irradiated reduced-activation ferritic steels

    SciTech Connect

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

    1996-10-01

    Tensile tests were conducted on eight reduced-activation Cr-W steels after irradiation to 15-17 and 26-29 dpa, and Charpy impact tests were conducted on the steels irradiated to 26-29 dpa. Irradiation was in the Fast Flux Test Facility at 365{degrees}C on steels containing 2.25-12% Cr, varying amounts of W, V, and Ta, and 0.1%C. Previously, tensile specimens were irradiated to 6-8 dpa and Charpy specimens to 6-8, 15-17, and 20-24 dpa. Tensile and Charpy specimens were also thermally aged to 20000 h at 365{degrees}C. Thermal aging had little effect on the tensile behavior or the ductile-brittle transition temperature (DBTT), but several steels showed a slight increase in the upper-shelf energy (USE). After {approx}7 dpa, the strength of the steels increased and then remained relatively unchanged through 26-29 dpa (i.e., the strength saturated with fluence). Post-irradiation Charpy impact tests after 26-29 dpa showed that the loss of impact toughness, as measured by an increase in DBTT and a decrease in the USE, remained relatively unchanged from the values after 20-24 dpa, which had been relatively unchanged from the earlier irradiations. As before, the two 9Cr steels were the most irradiation resistant.

  7. Structural and electromagnetic characterization of Cr-substituted Ni-Zn ferrites synthesized via Egg-white route

    NASA Astrophysics Data System (ADS)

    Gabal, M. A.; Bayoumy, W. A.; Saeed, A.; Al Angari, Y. M.

    2015-10-01

    Nano-crystalline ferrites with formula Ni0.8Zn0.2CrxFe2-xO4 (x = 0.0-1.0) was synthesized using Egg-white auto-combustion method. An appropriate mechanism for complexation and ferrite formation was suggested. X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Transmission electron microscopy (TEM), vibrating sample magnetometer (VSM) and a.c. electrical conductivity measurements were utilized to study the effect of Cr-substitution and its impact on particle size and electro-magnetic properties of the investigated ferrite. X-ray diffraction revealed single-phase cubic structure. The decrease in lattice parameter with increasing chromium was discussed in the view of ionic radii. TEM exhibited cubic agglomerated crystals with sizes between 10 and 20 nm. The decrease in the saturation magnetization and coercivity estimated through VSM measurements with increasing Cr-content indicated the preferential occupation of Cr3+ ions in the octahedral sites. Ac-conductivity measurements revealed semiconducting behavior of the entire investigated samples at high temperature and revealed a magnetic transition from ferromagnetic to paramagnetic for the samples with Cr-content up to 0.2. The conductivity values as well as the conduction activation energies indicated that the Cr3+ ions do not participate in the conduction and thus limit the Fe2+-Fe3+ conduction by blocking up Fe2+-Fe3+ transformation.

  8. Heat-treatment effect on impact properties of reduced-activation steels*1

    NASA Astrophysics Data System (ADS)

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

    1991-03-01

    The effect of heat treatment on the impact behavior of eight experimental heats of reduced-activation ferritic steels was investigated. Steels with 2 {1}/{4}, 5, 9, and 12 wt% Cr and containing tungsten, vanadium, and tantalum were examined. Impact properties of steels with 2 {1}/{4} wt% Cr depended on microstructure, which was affected by cooling rate after austenitization. By heat-treating the 2 {1}/{4} wt% Cr steels to change the microstructure from a bainitic structure containing ferrite to one without ferrite, the ductile-brittle transition temperatures were reduced substantially. The cooling rate had essentially no effect on the high-chromium martensitic steels.

  9. 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%).

  10. Mantle region accommodating two-dimensional grain boundary sliding in ODS ferritic steel

    NASA Astrophysics Data System (ADS)

    Masuda, Hiroshi; Tobe, Hirobumi; Sato, Eiichi; Sugino, Yoshito; Ukai, Shigeharu

    2015-07-01

    Two-dimensional grain-boundary sliding (GBS) was achieved microscopically in an oxide-dispersion-strengthened ferritic steel with an elongated and aligned grain structure, which was deformed perpendicular to the long axis. At the border between superplastic regions II and III, microscopic deformation was observed using sub-micron grids drawn on the material surface using a focused ion beam. GBS was accommodated by intragranular deformations in narrow areas around grain boundaries, which has been predicted by earlier researchers as characteristics of the core-mantle model. These observations suggest that dislocations slip only in the mantle regions around wavy boundaries to relax the stress concentration caused by GBS during superplasticity.

  11. 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.

  12. Some microstructural characterisations in a friction stir welded oxide dispersion strengthened ferritic steel alloy

    NASA Astrophysics Data System (ADS)

    Legendre, F.; Poissonnet, S.; Bonnaillie, P.; Boulanger, L.; Forest, L.

    2009-04-01

    The goal of this study is to characterize microstructure of a friction stir welded oxide dispersion strengthened alloy. The welded material is constituted by two sheets of an yttria-dispersion-strengthened PM 2000 ferritic steel. Different areas of the friction stir welded product were analyzed using field emission gun secondary electron microscopy (FEG-SEM) and electron microprobe whereas nanoindentation was used to evaluate mechanical properties. The observed microstructural evolution, including distribution of the yttria dispersoids, after friction stir welding process is discussed and a correlation between the microstructure and the results of nanoindentation tests is established.

  13. The Stress-Relief Cracking Susceptibility of a New Ferritic Steel - Part I: Single-Pass Heat-Affected Zone Simulations

    SciTech Connect

    NAWROCKI,J.G.; DUPONT,J.N.; ROBINO,CHARLES V.; MARDER,A.R.

    1999-12-15

    The stress-relief cracking susceptibility of single-pass welds in a new ferritic steel, HCM2S, has been evaluated and compared to 2.25Cr-1Mo steel using Gleeble techniques. Simulated coarse-grained heat-affected zones (CGHAZ) were produced under a range of energy inputs and tested at various post-weld heat treatment (PWHT) temperatures. Both alloys were tested at a stress of 325 MPa. The 2.25 Cr-1Mo steel was also tested at 270 MPa to normalize for the difference in yield strength between the two materials. Light optical and scanning electron microscopy were used to characterize the CGHAZ microstructure. The ''as-welded'' CGHAZ of each alloy consisted of lath martensite or bainite and had approximately equal prior austenite grain sizes. The as-welded hardness of the 2.25Cr-1Mo steel CGHAZ was significantly higher than that of the HCM2S alloy. Over the range studied energy input had no effect on the as-welded microstructure or hardness of either alloy. The energy input also had no effect on the stress-relief cracking susceptibility of either material. Both alloys failed intergranularly along prior austenite grain boundaries under all test conditions. The 2.25Cr-1Mo steel samples experienced significant macroductility and some microductility when tested at 325 MPa. The ductility decreased significantly when tested at 270 MPa but was still higher that than of HCM2S at each test condition. The time to failure decreased with increasing PWHT Temperature for each material. There was no significant difference in the times to failure between the two materials. Varying energy input and stress had no effect on the time-to failure. The ductility, as measured by reduction in are% increased with increasing PWHT temperature for 2.25 Cr-1Mo steel tested at both stresses. However, PWHT temperature had no effect on the ductility of HCM2S. The hardness of the CGHAZ for 2.25Cr-1Mo steel decreased significantly after PWHT, but remained constant for HCM2S. The differences in stress

  14. Influence of Ni-Cr substitution on the magnetic and electric properties of magnesium ferrite nanomaterials

    SciTech Connect

    Iqbal, Muhammad Javed; Ahmad, Zahoor; Meydan, Turgut; Nlebedim, Ikenna Cajetan

    2012-02-15

    . Moreover, the results of the present study provide sufficient evidence to show that the electric and magnetic properties of Mg-ferrite have been improved significantly by substituting low contents of Ni-Cr.

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

    NASA Astrophysics Data System (ADS)

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

    1994-09-01

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

  16. Technical Letter Report on the Cracking of Irradiated Cast Stainless Steels with Low Ferrite Content

    SciTech Connect

    Chen, Y.; Alexandreanu, B.; Natesan, K.

    2014-11-01

    Crack growth rate and fracture toughness J-R curve tests were performed on CF-3 and CF-8 cast austenite stainless steels (CASS) with 13-14% of ferrite. The tests were conducted at ~320°C in either high-purity water with low dissolved oxygen or in simulated PWR water. The cyclic crack growth rates of CF-8 were higher than that of CF-3, and the differences between the aged and unaged specimens were small. No elevated SCC susceptibility was observed among these samples, and the SCC CGRs of these materials were comparable to those of CASS alloys with >23% ferrite. The fracture toughness values of unirradiated CF-3 were similar between unaged and aged specimens, and neutron irradiation decreased the fracture toughness significantly. The fracture toughness of CF-8 was reduced after thermal aging, and declined further after irradiation. It appears that while lowering ferrite content may help reduce the tendency of thermal aging embrittlement, it is not very effective to mitigate irradiation-induced embrittlement. Under a combined condition of thermal aging and irradiation, neutron irradiation plays a dominant role in causing embrittlement in CASS alloys.

  17. Development of (Mn,Co)3O4 Protection Layers for Ferritic Stainless Steel Interconnects

    SciTech Connect

    Yang, Zhenguo; Simner, Steven P.; Singh, Prabhakar; Xia, Guanguang; Stevenson, Jeffry W.

    2005-07-05

    A spinel-based surface protection layer has been developed for alloy SOFC current collectors and bi-polar gas separators. The (Mn,Co)3O4 spinel with a nominal composition of Mn1.5Co1.5O4 demonstrates an excellent electrical conductivity and thermal expansion match to ferritic stainless steel interconnects. A slurry-coating technique provides a viable approach for fabricating protective layers of the spinel onto the steel interconnects. Thermally grown protection layers of Mn1.5Co1.5O4 have been found not only to significantly decrease the contact resistance between a LSF cathode and stainless steel interconnect, but also inhibits the sub-scale growth on the stainless steel. The combination of the inhibited sub-scale growth, good thermal expansion matching between the spinel and the stainless steel, and the closed-pore structure contribute to the excellent structural and thermomechanical stability of these spinel protection layers, which was verified by a long-term thermal-cycling test. The spinel protection layers can also act effectively to prevent outward diffusion of chromium from the interconnect alloy, preventing subsequent chromium migration into the cathode and contact materials. PNNL is currently engaged in studies intended to optimize the composition, microstructure, and fabrication procedure for the spinel protection layers.

  18. 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.

  19. Influence of Prior Fatigue Cycling on Creep Behavior of Reduced Activation Ferritic-Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Sarkar, Aritra; Vijayanand, V. D.; Parameswaran, P.; Shankar, Vani; Sandhya, R.; Laha, K.; Mathew, M. D.; Jayakumar, T.; Rajendra Kumar, E.

    2014-06-01

    Creep tests were carried out at 823 K (550 °C) and 210 MPa on Reduced Activation Ferritic-Martensitic (RAFM) steel which was subjected to different extents of prior fatigue exposure at 823 K at a strain amplitude of ±0.6 pct to assess the effect of prior fatigue exposure on creep behavior. Extensive cyclic softening that characterized the fatigue damage was found to be immensely deleterious for creep strength of the tempered martensitic steel. Creep rupture life was reduced to 60 pct of that of the virgin steel when the steel was exposed to as low as 1 pct of fatigue life. However, creep life saturated after fatigue exposure of 40 pct. Increase in minimum creep rate and decrease in creep rupture ductility with a saturating trend were observed with prior fatigue exposures. To substantiate these findings, detailed transmission electron microscopy studies were carried out on the steel. With fatigue exposures, extensive recovery of martensitic-lath structure was distinctly observed which supported the cyclic softening behavior that was introduced due to prior fatigue. Consequently, prior fatigue exposures were considered responsible for decrease in creep ductility and associated reduction in the creep rupture strength.

  20. 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.

  1. NEGLIGIBLE CREEP CONDITIONS FOR MOD 9 CR 1 MO STEEL

    SciTech Connect

    Ren, Weiju; Riou, Bernard; Escaravage, Claude; Swindeman, Robert W; Cabrillat, Marie-Th�r�se; Allais, Lucien

    2006-01-01

    Mod 9 Cr 1 Mo Steel (grade 91) is one of the materials envisaged for the Reactor Pressure Vessel of Very High Temperature Reactors. To avoid the implementation of a surveillance program covering the monitoring of the creep damage throughout the whole life of the reactor, it is recommended to operate the Reactor Pressure Vessel in the negligible creep regime. In this paper, the background of negligible creep criteria available in nuclear Codes is first recalled and their limitations were analyzed. Then, guidance for deriving criteria more appropriate for mod 9 Cr 1 Mo steel is provided. Finally, R&D actions in the U. S. and France to support the new approaches are discussed and recommended.

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

    PubMed

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

    2016-02-01

    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. PMID:26932112

  3. Effects of Annealing Treatment Prior to Cold Rolling on the Edge Cracking Phenomenon of Ferritic Lightweight Steel

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    Effects of annealing treatment from 923 K to 1023 K (650 °C to 750 °C) prior to cold rolling on the edge cracking phenomenon of a ferritic lightweight steel were investigated. The edge cracking was severely found in the hot-rolled and 923 K (650 °C)-annealed steels after cold rolling, whereas it hardly occurred in the 1023 K (750 °C)-annealed steel. As the annealing temperature increased, lamellar κ-carbides were dissolved and coarsened, and most of the κ-carbides continuously formed along boundaries between ferrite and κ-carbide bands disappeared. Microstructural observation of the deformed region of tensile specimens revealed that the removal of band boundary κ-carbides reduced the difference in tensile elongation along the longitudinal direction (LD) and transverse direction (TD), which consequently led to the reduction in edge cracking. The 1023 K (750 °C)-annealed steel showed fine ferrite grain size, weak texture, and decomposed band structure after subsequent cold rolling and intercritical annealing, because κ-carbides actively worked as nucleation sites of ferrite and austenite. The present annealing treatment prior to cold rolling, which was originally adopted to prevent edge cracking, also beneficially modified the final microstructure of lightweight steel.

  4. The phases and magnetic properties of (Ti, Co), and Cr doped Zn 2Y-type hexagonal ferrite

    NASA Astrophysics Data System (ADS)

    Chang, Y. H.; Wang, C. C.; Chin, T. S.; Yen, F. S.

    1988-04-01

    The phases and magnetic properties of Y-type hexagonal ferrite, Ba 2Zn 2 (Ti, Co) yFe 12-2 yO 22 doped with two sets of ions, (Ti, Co) and Cr were studied. In (Ti, Co) - doped ferrites the second phase appears at y ⩾ 0.6, which is a spinel type with the formula of (Zn 1-ηCo η)(Fe 2-δCo δ)O 4. Two resonant peaks are observed in ESR studies at the fields of 1020 and 2430 Oe, respectively, at a frequency of 9.684 GHz. The linewidth increases with the addition of the dopants. In chromium doped ferrite, two phases are identified as the amount of chromium is up to 0.2: spinel type of Zn(Fe 2-ɛCr ɛ)O 4 and orthorhombic BaCr 2O 4. Although the amount of Cr used does not influence the resonant field of the unique peak of the derivative curves from ESR, it eventually enlarges the linewidth.

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

    SciTech Connect

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

    2014-08-15

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

  6. 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.

  7. Hot Ductility Behavior of an 8 Pct Cr Roller Steel

    NASA Astrophysics Data System (ADS)

    Wang, Zhenhua; Sun, Shuhua; Shi, Zhongping; Wang, Bo; Fu, Wantang

    2015-04-01

    The hot ductility of an 8 pct Cr roller steel was determined between 1173 K and 1473 K (900 °C and 1200 °C) at strain rates of 0.01 to 10 s-1 through tensile testing. The fracture morphology was observed using scanning electron microscopy, and the microstructure was examined through optical microscopy and transmission electron microscopy. The dependence of the hot ductility behavior on the deformation conditions, grain size, and precipitation was analyzed. The relationship between the reduction in area and the natural logarithm of the Zener-Hollomon parameter (ln Z) was found to be a second-order polynomial. When ln Z was greater than 40 s-1, the hot ductility was poor and fracture was mainly caused by incompatible deformation between the grains. When ln Z was between 32 and 40 s-1, the hot ductility was excellent and the main fracture mechanism was void linking. When ln Z was below 32 s-1, the hot ductility was poor and fracture was mainly caused by grain boundary sliding. A fine grain structure is beneficial for homogenous deformation and dynamic recrystallization, which induces better hot ductility. The effect of M7C3 carbide particles dispersed in the matrix on the hot ductility was small. The grain growth kinetics in the 8 pct Cr steel were obtained between 1373 K and 1473 K (1100 °C and 1200 °C). Finally, optimized preheating and forging procedures for 8 pct Cr steel rollers are provided.

  8. Effect of welding parameters on the heat-affected zone of AISI409 ferritic stainless steel

    NASA Astrophysics Data System (ADS)

    Ranjbarnodeh, Eslam; Hanke, Stefanie; Weiss, Sabine; Fischer, Alfons

    2012-10-01

    One of the main problems during the welding of ferritic stainless steels is severe grain growth within the heat-affected zone (HAZ). In the present study, the microstructural characteristics of tungsten inert gas (TIG) welded AISI409 ferritic stainless steel were investigated by electron backscattered diffraction (EBSD), and the effects of welding parameters on the grain size, local misorientation, and low-angle grain boundaries were studied. A 3-D finite element model (FEM) was developed to predict the effects of welding parameters on the holding time of the HAZ above the critical temperature of grain growth. It is found that the base metal is not fully recrystallized. During the welding, complete recrystallization is followed by severe grain growth. A decrease in the number of low-angle grain boundaries is observed within the HAZ. FEM results show that the final state of residual strains is caused by competition between welding plastic strains and their release by recrystallization. Still, the decisive factor for grain growth is heat input.

  9. Investigation of microstructure and thermal stability of pulsed plasma processed chromium ferritic-martensitic steels

    NASA Astrophysics Data System (ADS)

    Emelyanova, O.; Dzhumaev, P.; Yakushin, V.; Polsky, V.

    2016-04-01

    This paper presents results of the microstructural evolution and thermal stability of the promising Russian ferritic-martensitic steels (EP 823, EP 900, EK 181 and ChS 139) for the nuclear and fusion application after surface modification by high temperature pulsed plasma flows (HTPPF) treatment. Investigations of microstructure, topography and elemental content changes associated with irradiation by nitrogen plasma with energy density 19-28 J/ cm2 and pulse duration 20 μs were carried out. Changes in microstructure and elemental content occurring in the modified surface layer were characterized by means of scanning electron microscopy (SEM) and X-ray microanalysis (EDS and WDS). It was shown that independently of initial microstructure and phase composition, HTPPF treatment of ferritic- martensitic steels leads to formation of ultrafine homogeneous structure in the near surface layers with typical grain size ∼100 nm. Results of microstructure investigations after annealing during 1 hour demonstrates significant thermal stability of nanostructure formed by HTPPF treatment.

  10. Effects of Partial Phase Transformation on Characteristics of 9Cr Nanostructured Ferritic Alloy

    SciTech Connect

    Ji Hyun, Yoon; Byun, Thak Sang; Hoelzer, David T

    2014-01-01

    The core structures of future nuclear systems require tolerance to extreme irradiation, and some critical components, for example, the fuel cladding in Sodium-cooled Fast Reactors (SFRs), have to maintain mechanical integrity to very high doses of 200 -400 dpa at high temperatures up to 700 degrees C. The high Cr nanostructured ferritic alloys (NFAs) are under intense research worldwide as a candidate core material. Although the NFAs have some admirable characteristics for high-temperature applications, their crack sensitivity is very high at high temperatures. The fracture toughness of high strength NFAs is unacceptably low above 300 degrees C. The objective of this study is to develop processes and microstructures with improved high temperature fracture toughness and ductility. To optimize the afterextrusion heat treatment condition, both the computational simulation technique on phase equilibrium and the basic microstructural and mechanical characterization have been carried out. 9 Cr-NFA was produced by the mechanical alloying of pre-alloyed Fe-9Cr base metallic powder and yttria particles, and subsequent extrusion. The post-extrusion heat-treatments of various conditions were applied to the asextruded NFA. The tensile and fracture toughness tests were conducted for as-extruded and heat-treated samples at up to 700 degrees C. Fracture toughness of the NFA has increased by more than 40% at every testing temperature after heat-treatment in the inter-critical temperature range. The increment of fracture toughness of the NFA after post-extrusion heat-treatment is attributed to the increased strength at below 500 degrees C, and an increased ductility at 700 degrees C.

  11. Microstructural development under irradiation in European ODS ferritic/martensitic steels

    NASA Astrophysics Data System (ADS)

    Schäublin, R.; Ramar, A.; Baluc, N.; de Castro, V.; Monge, M. A.; Leguey, T.; Schmid, N.; Bonjour, C.

    2006-06-01

    Oxide dispersion strengthened steels based on the ferritic/martensitic steel EUROFER97 are promising candidates for a fusion reactor because of their improved high temperature mechanical properties and their potential higher radiation resistance relative to the base material. Several EUROFER97 based ODS F/M steels are investigated in this study. There are the Plansee ODS steels containing 0.3 wt% yttria, and the CRPP ODS steels, whose production route is described in detail. The reinforcing particles represent 0.3-0.5% weight and are composed of yttria. The effect of 0.3 wt% Ti addition is studied. ODS steel samples have been irradiated with 590 MeV protons to 0.3 and 1.0 dpa at room temperature and 350 °C. Microstructure is investigated by transmission electron microscopy and mechanical properties are assessed by tensile and Charpy tests. While the Plansee ODS presents a ferritic structure, the CRPP ODS material presents a tempered martensitic microstructure and a uniform distribution of the yttria particles. Both materials provide a yield stress higher than the base material, but with reduced elongation and brittle behaviour. Ti additions improve elongation at high temperatures. After irradiation, mechanical properties of the material are only slightly altered with an increase in the yield strength, but without significant decrease in the total elongation, relative to the base material. Samples irradiated at room temperature present radiation induced defects in the form of blacks dots with a size range from 2 to 3 nm, while after irradiation at 350 °C irradiation induced a0<1 0 0>{1 0 0} dislocation loops are clearly visible along with nanocavities. The dispersed yttria particles with an average size of 6-8 nm are found to be stable for all irradiation conditions. The density of the defects and the dispersoid are measured and found to be about 2.3 × 10 22 m -3 and 6.2 × 10 22 m -3, respectively. The weak impact of irradiation on mechanical properties of ODS F

  12. Investigation on the Behavior of Austenite and Ferrite Phases at Stagnation Region in the Turning of Duplex Stainless Steel Alloys

    NASA Astrophysics Data System (ADS)

    Nomani, J.; Pramanik, A.; Hilditch, T.; Littlefair, G.

    2016-06-01

    This paper investigates the deformation mechanisms and plastic behavior of austenite and ferrite phases in duplex stainless steel alloys 2205 and 2507 under chip formation from a machine turning operation. SEM images and EBSD phase mapping of frozen chip root samples detected a build-up of ferrite bands in the stagnation region, and between 65 and 85 pct, more ferrite was identified in the stagnation region compared to austenite. SEM images detected micro-cracks developing in the ferrite phase, indicating ferritic build-up in the stagnation region as a potential triggering mechanism to the formation of built-up edge, as transgranular micro-cracks found in the stagnation region are similar to micro-cracks initiating built-up edge formation. Higher plasticity of austenite due to softening under high strain is seen responsible for the ferrite build-up. Flow lines indicate that austenite is plastically deforming at a greater rate into the chip, while ferrite shows to partition most of the strain during deformation. The loss of annealing twins and activation of multiple slip planes triggered at high strain may explain the highly plastic behavior shown by austenite.

  13. Investigation on the Behavior of Austenite and Ferrite Phases at Stagnation Region in the Turning of Duplex Stainless Steel Alloys

    NASA Astrophysics Data System (ADS)

    Nomani, J.; Pramanik, A.; Hilditch, T.; Littlefair, G.

    2016-04-01

    This paper investigates the deformation mechanisms and plastic behavior of austenite and ferrite phases in duplex stainless steel alloys 2205 and 2507 under chip formation from a machine turning operation. SEM images and EBSD phase mapping of frozen chip root samples detected a build-up of ferrite bands in the stagnation region, and between 65 and 85 pct, more ferrite was identified in the stagnation region compared to austenite. SEM images detected micro-cracks developing in the ferrite phase, indicating ferritic build-up in the stagnation region as a potential triggering mechanism to the formation of built-up edge, as transgranular micro-cracks found in the stagnation region are similar to micro-cracks initiating built-up edge formation. Higher plasticity of austenite due to softening under high strain is seen responsible for the ferrite build-up. Flow lines indicate that austenite is plastically deforming at a greater rate into the chip, while ferrite shows to partition most of the strain during deformation. The loss of annealing twins and activation of multiple slip planes triggered at high strain may explain the highly plastic behavior shown by austenite.

  14. Characterization of Low Temperature Ferrite/Austenite Transformations in the Heat Affected Zone of 2205 Duplex Stainless Steel Arc Welds

    SciTech Connect

    Palmer, T A; Elmer, J W; Babu, S S; Vitek, J M

    2003-08-20

    Spatially Resolved X-Ray Diffraction (SRXRD) has been used to identify a previously unobserved low temperature ferrite ({delta})/austenite({gamma}) phase transformation in the heat affected zone (HAZ) of 2205 Duplex Stainless Steel (DSS) welds. In this ''ferrite dip'' transformation, the ferrite transforms to austenite during heating to peak temperatures on the order of 750 C, and re-transforms to ferrite during cooling, resulting in a ferrite volume fraction equivalent to that in the base metal. Time Resolved X-Ray Diffraction (TRXRD) and laser dilatometry measurements during Gleeble{reg_sign} thermal simulations are performed in order to verify the existence of this low temperature phase transformation. Thermodynamic and kinetic models for phase transformations, including both local-equilibrium and para-equilibrium diffusion controlled growth, show that diffusion of substitutional alloying elements does not provide a reasonable explanation for the experimental observations. On the other hand, the diffusion of interstitial alloying elements may be rapid enough to explain this behavior. Based on both the experimental and modeling results, two mechanisms for the ''ferrite dip'' transformation, including the formation and decomposition of secondary austenite and an athermal martensitic-type transformation of ferrite to austenite, are considered.

  15. Experimental study of the distribution of alloying elements after the formation of epitaxial ferrite upon cooling in a low-carbon steel

    SciTech Connect

    Santofimia, M.J.; Kwakernaak, C.; Sloof, W.G.; Zhao, L.; Sietsma, J.

    2010-10-15

    The distributions of carbon and substitutional elements in a low-carbon steel during the formation of epitaxial ferrite on cooling after intercritical annealing have been studied by electron probe microanalysis (EPMA). The analysis has shown that the formation of epitaxial ferrite takes place with a partial redistribution of alloying elements between the epitaxial ferrite and the austenite. This redistribution of alloying elements causes compositional gradients in the epitaxial ferrite that lead to a different etching behaviour with respect to the intercritical ferrite. Contrary to Thermo-Calc predictions, a distinct partitioning behaviour of silicon has been observed.

  16. Experimental and Numerical Study on the Effect of ZDDP Films on Sticking During Hot Rolling of Ferritic Stainless Steel Strip

    NASA Astrophysics Data System (ADS)

    Hao, Liang; Jiang, Zhengyi; Wei, Dongbin; Gong, Dianyao; Cheng, Xiawei; Zhao, Jingwei; Luo, Suzhen; Jiang, Laizhu

    2016-08-01

    The aim of this study is to investigate the effect of zinc dialkyl dithio phosphate (ZDDP) films on sticking during hot rolling of a ferritic stainless steel strip. The surface characterization and crack propagation of the oxide scale are very important for understanding the mechanism of the sticking. The high-temperature oxidation of one typical ferritic stainless was conducted at 1373 K (1100 °C) for understanding its microstructure and surface morphology. Hot-rolling tests of a ferritic stainless steel strip show that no obvious cracks among the oxide scale were observed with the application of ZDDP. A finite element method model was constructed with taking into consideration different crack size ratios among the oxide scale, surface profile, and ZDDP films. The simulation results show that the width of the crack tends to be reduced with the introduction of ZDDP films, which is beneficial for improving sticking.

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

    SciTech Connect

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

    1996-12-31

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

  18. Mechanical properties and characteristics of nanometer-sized precipitates in hot-rolled low-carbon ferritic steel

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-pei; Zhao, Ai-min; Zhao, Zheng-zhi; Huang, Yao; Li, Liang; He, Qing

    2014-03-01

    The microstructures and properties of hot-rolled low-carbon ferritic steel have been investigated by optical microscopy, field-emission scanning electron microscopy, transmission electron microscopy, and tensile tests after isothermal transformation from 600°C to 700°C for 60 min. It is found that the strength of the steel decreases with the increment of isothermal temperature, whereas the hole expansion ratio and the fraction of high-angle grain boundaries increase. A large amount of nanometer-sized carbides were homogeneously distributed throughout the material, and fine (Ti, Mo)C precipitates have a significant precipitation strengthening effect on the ferrite phase because of their high density. The nanometer-sized carbides have a lattice parameter of 0.411-0.431 nm. After isothermal transformation at 650°C for 60 min, the ferrite phase can be strengthened above 300 MPa by precipitation strengthening according to the Ashby-Orowan mechanism.

  19. Microstructural Investigation of Fe-Ni-Mn-Mo-V-C-N Ferritic Steels by Neutron Diffraction

    NASA Astrophysics Data System (ADS)

    Baeva, M.; Beskrovnyi, A. I.; Parshorov, I.; Vassilovskii, S. G.

    2010-01-01

    The design of alloys, that economize strategic element as chromium requires detailed physical investigations of their structure and phase composition. In the search for new materials in the last two decades a new class of Fe alloys was composed—the so-called nitrogen steels. The contemporary achievements in the casting technology—the use of nitrogen under high preasure above the melt—made possible the production of Fe alloys with nitrogen concentration even above 0.4 wt%. The wide application of investigated alloy system is connected with creation of alloys without presence of strong carbides-forming elements. The microstructure and phase formation of these new materials are insufficiently studied. The aim of this work is to characterize the microstructure and phase composition of two series Fe-alloys casted with and without nitrogen pressure above the melt. The so cast steels appear as experimental ones and they are directed to demonstrate the possibility for nitrogen doping of steels without presence of Chromium in them. The latter is technologically difficult to fulfil at usual conditions. Six samples [with lower nitrogen, N = 0.0111 wt%] are cast at normal pressure, and six samples [with higher nitrogen, N0.2121 wt%] are cast at pressure of 10.106 Pa. The results of Rietveld structure analysis of Time-Of-Flight neutron diffraction data show that studied steels consist of purely ferritic crystal phase (Body Centered Cubic crystal lattice).

  20. Constitutive modeling of the mechanical behavior of high strength ferritic steels for static and dynamic applications

    NASA Astrophysics Data System (ADS)

    Abed, Farid H.

    2010-11-01

    A constitutive relation is presented in this paper to describe the plastic behavior of ferritic steel over a broad range of temperatures and strain rates. The thermo-mechanical behavior of high strength low alloy (HSLA-65) and DH-63 naval structural steels is considered in this study at strains over 40%. The temperatures and strain rates are considered in the range where dynamic strain aging is not effective. The concept of thermal activation analysis as well as the dislocation interaction mechanism is used in developing the flow model for both the isothermal and adiabatic viscoplastic deformation. The flow stresses of the two steels are very sensitive to temperature and strain rate, the yield stresses increase with decreasing temperatures and increasing strain rates. That is, the thermal flow stress is mainly captured by the yield stresses while the hardening stresses are totally pertained to the athermal component of the flow stress. The proposed constitutive model predicts results that compare very well with the measured ones at initial temperature range of 77 K to 1000 K and strain rates between 0.001 s-1 and 8500 s-1 for both steels.

  1. High temperature tensile properties and fracture characteristics of bimodal 12Cr-ODS steel

    NASA Astrophysics Data System (ADS)

    Chauhan, Ankur; Litvinov, Dimitri; Aktaa, Jarir

    2016-01-01

    This article describes the tensile properties and fracture characteristics of a 12Cr oxide dispersion strengthened (ODS) ferritic steel with unique elongated bimodal grain size distribution. The tensile tests were carried out at four different temperatures, ranging from room temperature to 700 °C, at a nominal strain rate of 10-3 s-1. At room temperature the material exhibits a high tensile strength of 1294 MPa and high yield strength of 1200 MPa. At 700 °C, the material still exhibits relatively high tensile strength of 300 MPa. The total elongation-to-failure exceeds 18% over the whole temperature range and has a maximum value of 29% at 600 °C. This superior ductility is attributed to the material's bimodal grain size distribution. In comparison to other commercial, as well as experimental, ODS steels, the material shows an excellent compromise between strength and ductility. The fracture surface studies reveal a change in fracture behavior from a mixed mode fracture at room temperature to fully ductile fracture at 600 °C. At 700 °C, the fracture path changes from intragranular to intergranular fracture, which is associated with a reduced ductility.

  2. Residual stresses in oxide scale formed on Fe-17Cr stainless steel

    NASA Astrophysics Data System (ADS)

    Li, Ning; Xiao, Ji; Prud'homme, Nathalie; Chen, Zhe; Ji, Vincent

    2014-10-01

    The purpose of this work was to investigate residual stresses in the oxide scale formed on ferritic stainless steel, which is proposed to be used as interconnector in the planar solid oxide fuel cells (SOFCs). The oxidation of the alloy has been conducted at 700 °C, 800 °C and 900 °C for 12-96 h by thermal gravimetric analysis (TGA) system. The oxide surface morphology, cross-section microstructure and the chemical composition of the oxide scale were studied after oxidation, and the residual stresses distribution of the oxide scale were determined at room temperature. It has been found that the oxide scale composed of an inner Cr2O3 layer and an outer Mn1.5Cr1.5O4 spinel layer, the residual stresses in both oxide layers are compressive and the growth stresses plays an important role. The competition of the stresses generation and relaxation during oxidation and cooling affects the residual stresses level. The evolution of residual stresses in the two layers is different according to the oxidation temperature, and the stresses in the two layers are interactional.

  3. Effect of micro-alloy elements (Ti, Nb, Al and Ca) on corrosion resistance of 26%Cr-2%Mo stainless steel in chloride solutions

    SciTech Connect

    Kim, H.; Lee, Y.D.

    1999-11-01

    Ferritic stainless steels have higher corrosion and stress corrosion cracking resistance in chloride environments than austenitic stainless steels. The production mat of ferritic stainless steels is lower than austenitic stainless steels. However, the application of highly alloyed ferritic stainless steels is limited due to low toughness and intergranular corrosion attack. Corrosion resistance of 26%Cr-2%Mo ferritic steels was evaluated using polarization test in 20% NaCl solution and the ferric chloride test. In addition, TEM and SEM were employed to analyze the secondary phases around the matrix where pitting corrosion occurred. In ferric chloride test the crevice corrosion resistance of non-stabilized alloy and Ca added alloy was lower than that of stabilized alloy and the crevice corrosion resistance of stabilized alloys was independent of stabilizing element such as Ti and Nb. The pitting corrosion resistance in chloride solution depended on micro-alloying elements as well as the surface treatment such as pickling and polishing. The effect of micro-alloy element and surface treatment on corrosion properties was explained with the aid of SEM observations. Among the polished alloys, the addition of Nb was the most effective for pitting corrosion resistance but the addition of Ti or Ca decreased the corrosion resistance. The pickling increased the corrosion resistance in all alloys except alloy No. 4 (Ti + Nb + Al). Pickling effectively increased corrosion resistance of the alloy containing Ti or Ca, due to removal of pit initiation sites associated with TiN inclusions or unstable phase (i.e., CaS, TiN).

  4. Creep deformation mechanisms in modified 9Cr-1Mo steel

    NASA Astrophysics Data System (ADS)

    Shrestha, Triratna; Basirat, Mehdi; Charit, Indrajit; Potirniche, Gabriel P.; Rink, Karl K.; Sahaym, Uttara

    2012-04-01

    Modified 9Cr-1Mo (Grade 91) steel is currently considered as a candidate material for reactor pressure vessels (RPVs) and reactor internals for the Very High Temperature Reactor (VHTR). The tensile creep behavior of modified 9Cr-1Mo steel (Grade 91) was studied in the temperature range of 873-1023 K and stresses between 35 MPa and 350 MPa. Analysis of creep results yielded stress exponents of ∼9-11 in the higher stress regime and ∼1 in the lower stress regime. The high stress exponent in the power-law creep regime was rationalized by invoking the concept of threshold stress, which represents the lattice diffusion controlled dislocation climb process. Without threshold stress compensation, the activation energy was 510 ± 51 kJ/mol, while after correcting for the threshold stress, the activation energy decreased to 225 ± 24 kJ/mol. This value is close to the activation energy for lattice self-diffusion in α-Fe. Threshold stress calculations were performed for the high stress regime at all test temperatures. The calculated threshold stress showed a strong dependence on temperature. The creep behavior of Grade 91 steel was described by the modified Bird-Mukherjee-Dorn relation. The rate controlling creep deformation mechanism in the high stress regime was identified as the edge dislocation climb with a stress exponent of n = 5. On the other hand, the deformation mechanism in the Newtonian viscous creep regime (n = 1) was identified as the Nabarro-Herring creep.

  5. Physical, electrical and magnetic properties of nano-sized Co-Cr substituted magnesium ferrites

    NASA Astrophysics Data System (ADS)

    Javed Iqbal, Muhammad; Ahmad, Zahoor; Meydan, Turgut; Melikhov, Yevgen

    2012-02-01

    Co-Cr substituted magnesium ferrite nanomaterials (Mg1-xCoxCrxFe2-xO4 with x = 0.0-0.5) have been prepared by the polyethylene glycol assisted micro emulsion method. X-ray diffraction analysis confirms the single-phase cubic close-packed lattice formation of synthesized materials. Hysteresis loops are measured up to field of 4 MA/m and high field region of these loops are modeled using the Law of Approach to saturation to calculate the magnetocrystalline anisotropy constant. The saturation magnetization of the samples increases initially from 148 kA/m for x = 0.0 to 299 kA/m (x = 0.3) and then decreases to 187 kA/m (x = 0.5). Curie temperature for this series is found to be in the range of 618-766 K. Room temperature resistivity increases gradually from 7.5 × 108 Ω cm (x = 0.0) to 3.47 × 109 Ω cm (x = 0.5). Additionally, dielectric measurements are carried out at room temperature in a frequency range of 100 Hz to 3 MHz. With improvement in the values of the above-mentioned properties, the synthesized materials could be suitable for potential application in some magnetic and microwave devices.

  6. TEM examination of microstructural evolution during processing of 14CrYWTi nanostructured ferritic alloys

    NASA Astrophysics Data System (ADS)

    Kishimoto, H.; Alinger, M. J.; Odette, G. R.; Yamamoto, T.

    2004-08-01

    A transmission electron microscopy (TEM) study was carried out on the co-evolution of the coarser-scale microstructural features in mechanically alloyed (MA) powders and hot isostatic press (HIP) consolidated Fe-14Cr-3W-0 and 0.4Ti-0.25Y 2O 3 nanostructured ferritic alloys (NFAs). The pancake shaped nanoscale grains in the as-MA powders are textured and elongated parallel to the particle surface. Powder annealing results in re-crystallization at 850 °C and grain growth at 1150 °C. The grains also recrystallize and may grow in the alloys HIPed at 850 °C, but appear to retain a polygonized sub-grain structure. The grains are larger and more distinct in the alloys HIPed at 1000 and 1150 °C. However, annealing resulted in bi-modal grain size distribution. Finer grains retained a significant dislocation density and populations of small precipitates with crystal structures distinct form the matrix. The grains and precipitates were much larger in alloys without Ti.

  7. Application of sol-gel technique to synthesis of copper-cobalt spinel on the ferritic stainless steel used for solid oxide fuel cell interconnects

    NASA Astrophysics Data System (ADS)

    Paknahad, Pouyan; Askari, Masoud; Ghorbanzadeh, Milad

    2014-11-01

    The conductive CuCo2O4 spinel coating is applied on the surface of the AISI 430 ferritic stainless steel by the dip-coating sol-gel process and it is evaluated in terms of the microstructure, oxidation resistance and electrical conductivity. The results show that the CuCO2O4 coating forms a double-layer scale consisting of a Cr, Fe-rich subscale and Cu-Co spinel top layer after 500 h in air at 800 °C. This scale is protective, acts as an effective barrier against Cr migration into the outer oxide layer and alleviates the cathode Cr-poisoning. The oxidation resistance is significantly enhanced by the protective coating with a parabolic rate constant of 5.8 × 10-13 gr2 cm-4 s-1, meanwhile the electrical conductivity is considerably improved due to inhibited growth of resistive Cr2O3 oxide scale. The area specific resistance at temperatures between 550 and 800 °C is in the range of 11.5 and 22.2 mΩ cm2.

  8. 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.

  9. Radiation damage in ferritic/martensitic steels for fusion reactors: a simulation point of view

    NASA Astrophysics Data System (ADS)

    Schäublin, R.; Baluc, N.

    2007-12-01

    Low activation ferritic/martensitic steels are good candidates for the future fusion reactors, for, relative to austenitic steels, their lower damage accumulation and moderate swelling under irradiation by the 14 MeV neutrons produced by the fusion reaction. Irradiation of these steels, e.g. EUROFER97, is known to produce hardening, loss of ductility, shift in ductile to brittle transition temperature and a reduction of fracture toughness and creep resistance starting at the lowest doses. Helium, produced by transmutation by the 14 MeV neutrons, is known to impact mechanical properties, but its effect at the microstructure level is still unclear. The mechanisms underlying the degradation of mechanical properties are not well understood, despite numerous studies on the evolution of the microstructure under irradiation. This impedes our ability to predict materials' behaviour at higher doses for use in the future fusion reactors. Simulations of these effects are now essential. An overview is presented on molecular dynamics simulations of the primary state of damage in iron and of the mobility of a dislocation, vector of plasticity, in the presence of a defect.

  10. Upper acicular ferrite formation in a medium-carbon microalloyed steel by isothermal transformation: Nucleation enhancement by CuS

    NASA Astrophysics Data System (ADS)

    Madariaga, I.; Romero, J. L.; Gutiérrez, I.

    1998-03-01

    The isothermal transformation vs time of a medium-carbon microalloyed steel at 450°C, following austenitization at 1250°C for 45 minutes, has been investigated using optical microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). At short times, the fine microstructure of acicular ferrite is nucleated at MnS inclusions, which are covered by a shell of a hexagonal CuS phase. The special orientation between MnS and the CuS crystals of this shell enables the formation of a low-energy interface between the ferrite and the inclusion with, at the same time, the ferrite satisfying one of the 24 variants of the orientation relationship into the Bain region with austenite. As the treatment times are increased, the increase in the volume fraction of acicular ferrite being formed raises the carbon concentration of the austenite, such that some retained austenite instead of martensite is observed for these intermediate treatment times. This retained austenite transforms to ferrite plus carbides at long treatment times, resulting in a final microstructure of acicular ferrite, very similar in nature to those encountered in the case of upper bainite formation.

  11. Acoustic emission-microstructural relationships in ferritic steels. Part 1: The effect of cooling rate

    NASA Astrophysics Data System (ADS)

    Wadley, H. N. G.; Scruby, C. B.

    1985-06-01

    Acoustic emission is controlled during deformation and fracture by the dynamics of dislocation motion and crack advance. The nature of the relationship between defect dynamics and acoustic emission in tensile samples of specially prepared low alloy steels containing 3.25 wt.% Ni, 1 wt.% Mn and a variable carbon content from 0.06 to 0.49 wt.% is studied. The most energetic signals are from microstructures with an initially low dislocation density and a ferrite dimension of approx. 10 microns, indicating the propagation of high velocity dislocations in ferrite to be the origin of acoustic emission during deformation. This is consistent with a model in which the product of glide distance and velocity (which are both controlled by microstructure) determines the amplitude of the acoustic emission. During subcritical micro-fracture, intergranular and alternating shear modes of microcracking in high strength conditions generate detectable signals. Both involve the rapid growth of cracks over distances of 10 to 100 micron. The ductile dimple mode of fracture is found to generate no detectable signals despite wide variations in dimple spacing and fracture stress. This is consistent with the recognized view that such fracture occurs under essentially static conditions.

  12. TIG and HIP joining of Reduced Activation Ferrite/Martensitic steel for the Korean ITER-TBM

    NASA Astrophysics Data System (ADS)

    Ku, Duck Young; Oh, Seungjin; Ahn, Mu-Young; Yu, In-Keun; Kim, Duck-Hoi; Cho, Seungyon; Choi, Im-Sub; Kwon, Ki-Bum

    2011-10-01

    Korea is developing a Helium Cooled Solid Breeder Test Blanket Module for ITER. The primary candidate structural material is a Reduced Activation Ferritic/Martensitic steel. The complex TBM structure requires developing joining technologies for successful fabrication. The characteristics of Tungsten Inert Gas welding and Hot Isostatic Pressing joining of RAFM steel were investigated. Metallurgical examinations showed that the steel grain size was increased after HIP joining and recovered by post joining heat treatment. Both TIG welding and HIP joining are found to be acceptable for ITER TBM based on mechanical tests and microstructure examination.

  13. The role of molybdenum additions and prior deformation on acicular ferrite formation in microalloyed Nb-Ti low-carbon line-pipe steels

    SciTech Connect

    Tang Zhenghua Stumpf, Waldo

    2008-06-15

    Microstructures in Nb-Ti-microalloyed line-pipe steels with various molybdenum additions, consisted mostly of acicular ferrite plus polygonal ferrite after hot rolling and rapid cooling. Structure-sensitive surface relief after etching on shadowed extraction replicas, allowed quantification of the acicular and polygonal ferrite contents. Continuous cooling transformation diagrams of two alloys, one Mo-free and the other containing 0.22% Mo, were determined for cooling rates from 0.1 to 40 deg. C s{sup -1} without and with prior deformation of the austenite below the nil-recrystallisation temperature. Molybdenum additions slightly enhanced the acicular ferrite formation in the strain-free austenite whereas prior deformation had a much greater effect, and strongly promoted acicular ferrite formation in both alloys. Thin foil electron microscopy of acicular ferrite in these low-inclusion content alloys showed a preference for parallel acicular ferrite laths with less 'chaotically' nucleated laths.

  14. Friction Stir Welding Of Ma957 Oxide Dispersion Strengthened Ferritic Steel

    SciTech Connect

    Howard, Stanley M.; Jasthi, Bharat K.; Arbegast, William J.; Grant, Glenn J.; Koduri, Santhosh K.; Herling, Darrell R.; Gelles, David S.

    2005-04-02

    A 1-in. (25.4 mm) diameter yttria-dispersion-strengthened MA957 ferritic steel alloy tube with a 0.125" (3.18 mm) wall thickness was successfully plasticized by friction stir welding. The pin tool was a W-Re tool with 0.125" (3.17 mm) diameter tip. It showed no discernable wear for the total 12" (305 mm) of weld. Weld conditions were 1000 and 1400 RPM, 4 in/min (101 mm/min), with and without preheating to 135ºC. Metallographic analysis of the post friction-stir welded material showed a decrease in material hardness to 225±22 HV compared to the parent material at 373±21 HV. All weld conditions produced plasticization; however, improved plasticization was observed for preheated samples

  15. 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.

  16. 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.

  17. 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.

  18. From embryos to precipitates: A study of nucleation and growth in a multicomponent ferritic steel

    NASA Astrophysics Data System (ADS)

    Zhang, Z. W.; Liu, C. T.; Wang, X.-L.; Littrell, K. C.; Miller, M. K.; An, K.; Chin, B. A.

    2011-11-01

    The nucleation and growth of nanoscale precipitates in a new class of high-strength, multicomponent, ferritic steels has been studied with complementary state-of-the-art microstructural characterization techniques of atom probe tomography for individual embryos and precipitates and small-angle neutron scattering for their statistical averages. Both techniques revealed a bimodal size distribution, with subnanometer embryos, and nanoscale precipitates. The embryos, which have a radius of ˜0.4 nm, are enriched in Cu and served as preferential sites for nucleation. The critical radius for nucleation was determined to be ˜0.7 nm. Subsequent growth of the precipitates is dictated by volumetric diffusion, as predicted by the Lifshitz-Slyozov-Wagner theory.

  19. Nonequilibrium grain-boundary cosegregation of nitrogen and chromium in NiCrMoV steel

    NASA Astrophysics Data System (ADS)

    Zheng, Lei; Xu, Tingdong

    2005-12-01

    It is concluded in this article that nonequilibrium grain-boundary cosegregation (NCGS) of nitrogen and chromium occurs in NiCrMoV steel. That conclusion is reached from experimental observations of the parallel segregation isotherms and the maximum coverage of Cr and N at grain boundaries during the isotherms. This means that the nonequilibrium segregation of Cr induces that of N, in NiCrMoV steel.

  20. Characterization of modified 9 Cr-1 Mo steel extruded pipe

    SciTech Connect

    Sikka, V.K.; Hart, M.D.

    1985-04-01

    The fabrication of hot-extruded pipe of modified 9 Cr-1 Mo steel at Cameron Iron Works is described. The report also deals with the tempering response; tensile, Charpy impact, and creep properties; and microstructure of the hot-extruded pipe. The tensile properties of the pipe are compared with the average and average -1.65 standard error of estimate curves for various product forms of several commercial heats of this alloy. The creep-rupture properties are compared with the average curve for various product forms of the commercial heats.

  1. The magnetic and magneto-optical properties of Co, Cr, Mn, and Ni substituted barium ferrite films

    NASA Astrophysics Data System (ADS)

    Carey, R.; Gago-Sandoval, P. A.; Newman, D. M.; Thomas, B. W. J.

    1994-05-01

    Using rapid thermal processing (RTP) we recently demonstrated the production of high quality well ordered barium ferrite films in times much shorter than those required by a conventional annealing process. Influence over the magnetic and structural properties developed in annealed samples was also achieved by variation of the RTP heating profile (R. Carey, P. A. Gago-Sandoval, D. M. Newman, and B. W. J. Thomas, presented at Intermag-93, Stockholm, April 13-16, 1993). It is known that the magneto-optic properties of barium ferrite can be enhanced by selective substitution of some of the Fe by Co2+ and Ti4+ albeit at the expense of reducing the magnetic anisotropy. A multitarget scanning cosputtering process has been used in conjunction with rapid thermal processing to produce a series of barium ferrite films in which Co, Cr, Mn, Ni are selectively introduced to substitute for between 5 and 20 at. % of the Fe. A corresponding percentage of Ti is also added to maintain charge compensation. The magnetic and magneto-optic properties of these films are presented and discussed with reference to their composition and treatment respect to the properties of barium ferrite.

  2. Impurity effects on reduced-activation ferritic steels developed for fusion applications

    NASA Astrophysics Data System (ADS)

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

    2000-08-01

    Reduced-activation steels are being developed for fusion applications by restricting alloying elements that produce long-lived radioactive isotopes when irradiated in the fusion neutron environment. Another source of long-lived isotopes is the impurities in the steel. To examine this, three heats of reduced-activation martensitic steel were analyzed by inductively coupled plasma mass spectrometry for low-level impurities that compromise the reduced-activation characteristics: a 5-ton heat of modified F82H (F82H-Mod) for which an effort was made during production to reduce detrimental impurities, a 1-ton heat of JLF-1, and an 18-kg heat of ORNL 9Cr-2WVTa. Specimens from commercial heats of modified 9Cr-1Mo and Sandvik HT9 were also analyzed. The objective was to determine the difference in the impurity levels in the F82H-Mod and steels for which less effort was used to ensure purity. Silver, molybdenum, and niobium were found to be the tramp impurities of most importance. The F82H-Mod had the lowest levels, but in some cases the levels were not much different from the other heats. The impurity levels in the F82H-Mod produced with present technology did not achieve the low-activation limits for either shallow land burial or recycling. The results indicate the progress that has been made and what still must be done before the reduced-activation criteria can be achieved.

  3. Fatigue behavior of irradiated helium-containing ferritic steels for fusion reactor applications*1

    NASA Astrophysics Data System (ADS)

    Grossbeck, M. L.; Vitek, J. M.; Liu, K. C.

    1986-11-01

    The martensitic alloys 12Cr-1MoVW and 9Cr-1MoVNb have been irradiated in the High Flux Isotope Reactor (HFIR) and subsequently tested in fatigue. In order to achieve helium levels characteristic of fusion reactors, the 12Cr-1MoVW was doped with 1 and 2% Ni, resulting in helium levels of 210 and 410 appm at damage levels of 25 dpa. The 9Cr-1MoVNb was irradiated to a damage level of 3 dpa and contained less than 5 appm He. Irradiations were carried out at 55°C and testing at 22°C. No significant changes were found in 9Cr-1MoVNb upon irradiation at this damage level, but effects that could possibly be attributed to helium were found in 12Cr-1MoVW. Levels of 210 and 410 appm He produced cyclic strengthening of 29 and 34% over unirradiated nickel-doped materials, respectively. This cyclic hardening, attributable largely to helium, resulted in degradation of the cyclic life. However, the fatigue life remained comparable to or better than unirradiated 20%-cold-worked 316 stainless steel.

  4. Influences of Cr content and PWHT on microstructure and oxidation behavior of stainless steel weld overlay cladding materials in high temperature water

    NASA Astrophysics Data System (ADS)

    Cao, X. Y.; Ding, X. F.; Lu, Y. H.; Zhu, P.; Shoji, T.

    2015-12-01

    Influences of Cr content and post weld heat treatment (PWHT) on microstructure and oxidation behavior of stainless steel cladding materials in high temperature water were investigated. The amounts of metal oxidized and dissolved were estimated to compare the oxidation behaviors of cladding materials with different Cr contents and PWHT. The results indicated that higher Cr content led to formation of more ferrite content, and carbides were found along δ/γ phase interface after PWHT. Higher Cr content enhanced the pitting resistance and compactness of the oxide film to reduce metal amount oxidized and dissolved, which mitigated the weight changes and the formation of Fe-rich oxides. PWHT promoted more and deeper pitting holes along the δ/γ phase interface due to formation of carbides, which resulted in an increase in metal amount oxidized and dissolved, and were also responsible for more Fe-rich oxides and higher weight changes.

  5. Microstructural evolution of P92 ferritic/martensitic steel under Ar{sup +} ion irradiation at elevated temperature

    SciTech Connect

    Jin Shuoxue; Guo Liping; Li Tiecheng; Chen Jihong; Yang Zheng; Luo Fengfeng; Tang Rui; Qiao Yanxin; Liu Feihua

    2012-06-15

    Irradiation damage in P92 ferritic/martensitic steel irradiated by Ar{sup +} ion beams to 7 and 12 dpa at elevated temperatures of 290 Degree-Sign C, 390 Degree-Sign C and 550 Degree-Sign C has been investigated by transmission electron microscopy, scanning electron microscopy and atomic force microscopy. The precipitate periphery (the matrix/carbide interface) was amorphized only at 290 Degree-Sign C, while higher irradiation temperature could prevent the amorphization. The formation of the small re-precipitates occurred at 290 Degree-Sign C after irradiation to 12 dpa. With the increase of irradiation temperature and dose, the phenomenon of re-precipitation became more severe. The voids induced by irradiation were observed after irradiation to 7 dpa at 550 Degree-Sign C, showing that high irradiation temperature ({>=} 550 Degree-Sign C) was a crucial factor which promoted the irradiation swelling. Energy dispersive X-ray analysis revealed that segregation of Cr and W in the voids occurred under irradiation, which may influence mechanical properties of P92 F/M steel. - Graphical Abstract: High density of small voids, about 2.5 nm in diameter, was observed after irradiation to 12 dpa at 550 Degree-Sign C, which was shown in panel a (TEM micrograph). As shown in panel b (SEM image), a large number of nanometer-sized hillocks were formed in the surface irradiated at 550 Degree-Sign C, and the mean size was {approx} 30 nm. The formation of the nanometer-sized hillocks might be due to the voids that appeared as shown in TEM images (panel a). High irradiation temperature ({>=} 550 Degree-Sign C) was a crucial factor for the formation of void swelling. Highlights: Black-Right-Pointing-Pointer Small carbides re-precipitated in P92 matrix irradiated to 12 dpa at 290 Degree-Sign C. Black-Right-Pointing-Pointer High density of voids was observed at 550 Degree-Sign C. Black-Right-Pointing-Pointer Segregation of Cr and W in voids occurred under irradiation.

  6. 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.

  7. Effects of Mo, Cr, and V Additions on Tensile and Charpy Impact Properties of API X80 Pipeline Steels

    NASA Astrophysics Data System (ADS)

    Han, Seung Youb; Shin, Sang Yong; Seo, Chang-Hyo; Lee, Hakcheol; Bae, Jin-Ho; Kim, Kisoo; Lee, Sunghak; Kim, Nack J.

    2009-08-01

    In this study, four API X80 pipeline steels were fabricated by varying Mo, Cr, and V additions, and their microstructures and crystallographic orientations were analyzed to investigate the effects of their alloying compositions on tensile properties and Charpy impact properties. Because additions of Mo and V promoted the formation of fine acicular ferrite (AF) and granular bainite (GB) while prohibiting the formation of coarse GB, they increased the strength and upper-shelf energy (USE) and decreased the energy transition temperature (ETT). The addition of Cr promoted the formation of coarse GB and hard secondary phases, thereby leading to an increased effective grain size, ETT, and strength, and a decreased USE. The addition of V resulted in a higher strength, a higher USE, a smaller effective grain size, and a lower ETT, because it promoted the formation of fine and homogeneous of AF and GB. The steel that contains 0.3 wt pct Mo and 0.06 wt pct V without Cr had the highest USE and the lowest ETT, because its microstructure was composed of fine AF and GB while its maintained excellent tensile properties.

  8. Precipitation in 9Ni-12Cr-2Cu maraging steels

    SciTech Connect

    Stiller, K.; Haettestrand, M.; Danoix, F.

    1998-11-02

    Two maraging steels with the compositions 9Ni-12Cr-2Cu-4Mo (wt%) and 9Ni-12Cr-2Cu and with small additions of Al and Ti were investigated using atom probe field ion microscopy. Tomographic atom probe investigations were performed to clarify the spatial distribution of elements in and close to the precipitates. Materials heat treated at 475 C for 5, 25 min, 1, 2, 4 and 400 h were analyzed. Precipitates in the Mo-rich material were observed already after 5 min of aging, while in the material without MO, precipitation started later. In both materials precipitation begins with the formation of Cu-rich particles which work as nucleation sites for a Ni-rich phase of type Ni{sub 3}(Ti,Al). A Mo-rich phase was detected in the Mo-rich steel after 2 h of aging. The distribution of alloying elements in the precipitates, their role in the precipitation process, and the mechanism of hardening in the two materials are discussed.

  9. Investigation of Iron-Chromium-Niobium-Titanium Ferritic Stainless Steel for Solid Oxide Fuel Cell Interconnect Applications

    SciTech Connect

    Yang, Zhenguo; Xia, Guanguang; Wang, Chong M.; Nie, Zimin; Templeton, Joshua D.; Stevenson, Jeffry W.; Singh, Prabhakar

    2008-09-01

    As part of an effort to develop cost-effective ferritic stainless steel-based interconnects for solid oxide fuel cell (SOFC) stacks, AL 441 HPTM was studied in terms of its metallurgical characteristics, oxidation behavior, and electrical performance. Minor alloying elements (Nb and Ti) captured interstitials such as C by forming carbides, stabilizing the ferritic structure and mitigating the risks of sensitization and inter-granular corrosion. Laves phases rich in Nb and Si precipitated along grain boundaries during high temperature exposure, improving the steel’s high temperature mechanical strength. The capture of Si in the Laves phase minimized the Si activity in the steel substrate and prevented formation of an insulating silica layer at the scale/metal interface. However, the relatively high oxidation rate, and thus increasing ASR over time, necessitates the application of a conductive protection layer on the steel. In particular, Mn1.5Co1.5O4 spinel protection layers drastically improved the electrical performance of the ferritic stainless steel 441, acting as barriers to chromium outward and oxygen inward diffusion.

  10. Effect of Hot Coiling Under Accelerated Cooling on Development of Non-equiaxed Ferrite in Low Carbon Steel

    NASA Astrophysics Data System (ADS)

    Lanjewar, H. A.; Tripathi, Pranavkumar

    2016-06-01

    Strengthening mechanisms dominant in non-equiaxed ferrite structures are not so familiar and well measured. In present study, non-equiaxed ferritic structures were generated and perceived to be strengthened by grain/crystal refinement, presence of varying substructures, solid solution strengthening, and textural hardening. A Nb-V microalloyed steel was modeled under various accelerated cooling and coiling temperature conditions in a thermo-mechanical simulator. Decrease in coiling temperature in conjunction with accelerated cooling resulted in non-equiaxed ferrite structures with array of phase morphologies. Intermediate transformation conditions produced increase in strength concurrent with observed smallness in crystallite size and high amount of microstrain in the matrix phase indicative of high dislocation densities and crystal imperfections. Increase in strength is partially attributed to solid solution and texture hardening owing to increase in (111) pole intensity in structure.

  11. Effect of Hot Coiling Under Accelerated Cooling on Development of Non-equiaxed Ferrite in Low Carbon Steel

    NASA Astrophysics Data System (ADS)

    Lanjewar, H. A.; Tripathi, Pranavkumar

    2016-04-01

    Strengthening mechanisms dominant in non-equiaxed ferrite structures are not so familiar and well measured. In present study, non-equiaxed ferritic structures were generated and perceived to be strengthened by grain/crystal refinement, presence of varying substructures, solid solution strengthening, and textural hardening. A Nb-V microalloyed steel was modeled under various accelerated cooling and coiling temperature conditions in a thermo-mechanical simulator. Decrease in coiling temperature in conjunction with accelerated cooling resulted in non-equiaxed ferrite structures with array of phase morphologies. Intermediate transformation conditions produced increase in strength concurrent with observed smallness in crystallite size and high amount of microstrain in the matrix phase indicative of high dislocation densities and crystal imperfections. Increase in strength is partially attributed to solid solution and texture hardening owing to increase in (111) pole intensity in structure.

  12. A new approach to improve creep resistance of high Cr martensitic steel

    NASA Astrophysics Data System (ADS)

    Tamura, Manabu; Kumagai, Takuya; Sakai, Kazuhisa; Shinozuka, Kei; Esaka, Hisao

    2011-10-01

    A modified 9Cr-1Mo steel was cooled to 200 °C from the normalizing temperature and then directly heated to the tempering temperature. It was found that the time to rupture at 650-700 °C for the steel heat-treated at 200 °C increased three times over than that of the modified 9Cr-1Mo steel conventionally normalized and tempered. The microstructure of the improved steel was tempered martensite and the size of martensite blocks was larger than for the conventional treatment. The hardness of the improved steel was adequately recovered after tempering. Aging tests showed that the particle sizes of Cr 23C 6 and VN type carbonitride in the improved steel were finer in the conventional steel. The above-mentioned heat treatment was applied to the reduced activation martensitic steel F-82H and the improvement was confirmed.

  13. The Influence of the Induced Ferrite and Precipitates of Ti-bearing Steel on the Ductility of Continuous Casting Slab

    NASA Astrophysics Data System (ADS)

    Qian, Guoyu; Cheng, Guoguang; Hou, Zibing

    2015-11-01

    In order to investigate the loss of the ductility of Ti-bearing ship plate steel under 1000 °C, where the ductility begins to reduce rapidly, so the hot ductility of Ti-bearing ship plate steel has been obtained using the Gleeble 1500 thermal-mechanical simulator and also the studies about the effect of grain boundary ferrite films and precipitates containing Ti on the ductility has been carried out. The result showed that the TiN particles precipitating at 950 °C with a larger size and smaller volume fraction cannot effectively suppress the occurrence of recrystallization and the ductility still retains at a high level, although R.A. value presents a certain degree of decline compared with 1000 °C. A large number of smaller Ti(C,N) particles precipitate at 900 °C and can induce the formation of a very small amount of fine grain boundary ferrite, which deteriorates the adhesion strength of the grain boundary, so the R.A. value rapidly reduces to less than 50%. When the temperature falls to close Ae3 (827 °C), the amount of the grain boundary ferrite films increase due to the ferrite phase transformation, but the ferrite film thickness becomes more uneven at the same time, which results in the increase of strain concentration and plays a leading role in causing the decrease of ductility, so the R.A. value has been kept less than 40% as the temperature cooling to 800 °C from 850 °C. When the temperature further decreases, the ductility starts to recover due to the increase of average ferrite film thickness to a greater degree which greatly reduces the strain concentration of the grain boundary.

  14. Effects of proton irradiation on nanocluster precipitation in ferritic steel containing fcc alloying additions

    SciTech Connect

    Zhang, Zhongwu; Liu, C T; Wang, Xun-Li; Miller, Michael K; Ma, Dong; Chen, Guang; Williams, J R; Chin, Bryan

    2012-01-01

    Newly-developed precipitate-strengthened ferritic steels with and without pre-existing nanoscale precipitates were irradiated with 4 MeV protons to a dose of ~5 mdpa at 50 C and subsequently examined by nanoindentation and atom probe tomography (APT). Irradiation-enhanced precipitation and coarsening of pre-existing nanoscale precipitates were observed. Copper partitions to the precipitate core along with a segregation of Ni, Al and Mn to the precipitate/matrix interface after both thermal aging and proton irradiation. Proton irradiation induces the precipitation reaction and coarsening of pre-existing nanoscale precipitates, and these results are similar to a thermal aging process. The precipitation and coarsening of nanoscale precipitates are responsible for the changes in hardness. The observation of the radiation-induced softening is essentially due to the coarsening of the pre-existing Cu-rich nanoscale precipitates. The implication of the precipitation on the embrittlement of reactor-pressure-vessel steels after irradiation is discussed.

  15. Microstructural changes induced near crack tip during corrosion fatigue tests in austenitic-ferritic steel.

    PubMed

    Gołebiowski, B; Swiatnicki, W A; Gaspérini, M

    2010-03-01

    Microstructural changes occurring during fatigue tests of austenitic-ferritic duplex stainless steel (DSS) in air and in hydrogen-generating environment have been investigated. Hydrogen charging of steel samples during fatigue crack growth (FCG) tests was performed by cathodic polarization of specimens in 0.1M H(2)SO(4) aqueous solution. Microstructural investigations of specimens after FCG tests were carried out using transmission electron microscopy to reveal the density and arrangement of dislocations formed near crack tip. To determine the way of crack propagation in the microstructure, electron backscatter diffraction investigations were performed on fatigue-tested samples in both kinds of environment. To reveal hydrogen-induced phase transformations the atomic force microscopy was used. The above investigations allowed us to define the character of fatigue crack propagation and microstructural changes near the crack tip. It was found that crack propagation after fatigue tests in air is accompanied with plastic deformation; a high density of dislocations is observed at large distance from the crack. After fatigue tests performed during hydrogen charging the deformed zone containing high density of dislocations is narrow compared to that after fatigue tests in air. It means that hydrogenation leads to brittle character of fatigue crack propagation. In air, fatigue cracks propagate mostly transgranularly, whereas in hydrogen-generating environment the cracks have mixed transgranular/interfacial character. PMID:20500395

  16. 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.

  17. Gas porosity evolution and ion-implanted helium behavior in reactor ferritic/martensitic and austenitic steels

    NASA Astrophysics Data System (ADS)

    Chernov, I. I.; Kalin, B. A.; Staltsov, M. S.; Oo, Kyi Zin; Binyukova, S. Yu.; Staltsova, O. S.; Polyansky, A. A.; Ageev, V. S.; Nikitina, A. A.

    2015-04-01

    The peculiarities of gas porosity formation and helium retention and release in reactor ferritic/martensitic EP-450 and EP-450-ODS and austenitic ChS-68 steels are investigated by transmission electron microscopy and helium thermal desorption spectrometry (HTDS). The samples were irradiated by 40 keV He+ ions up to a fluence of 5 · 1020 m-2 at 293 and 923 K. An nonuniform distribution of helium bubbles and high-level gas swelling in ferritic/martensitic steels were found at high-temperature helium implantation. The same irradiation conditions result in formation of uniformly distributed helium bubbles and low-level swelling in ChS-68 steel. Temperature range of helium release from EP-450-ODS steel was considerably wider in comparison to HTDS-spectra of the EP-450 steel. A considerable quantity of helium is released from ODS steel in the high-temperature range after the main peak of the HTDS-spectrum.

  18. Effect of nano-sized precipitates on the crystallography of ferrite in high-strength strip steel

    NASA Astrophysics Data System (ADS)

    Yang, Jing-jing; Wu, Run; Liang, Wen; Tang, Meng-xia

    2014-05-01

    For strip steel with the thickness of 1.6 mm, the yield and tensile strengths as high as 760 and 850 MPa, respectively, were achieved using the compact strip production technology. Precipitates in the steel were characterized by scanning and transmission electron microscopy to elucidate the strengthening mechanism. In addition, intragranular misorientation, Kernel average misorientation, and stored energy were measured using electron backscatter diffraction for crystallographic analysis of ferrite grains containing precipitates and their neighbors without precipitates. It is found that precipitates in specimens primarily consist of TiC and Ti4C2S2. Ferrite grains containing precipitates exhibit the high Taylor factor as well as the crystallographic orientations with {012}, {011}, {112}, or {221} plane parallel to the rolling plane. Compared with the intragranular orientation of adjoining grains, the intragranular misorientation of grains containing precipitates fluctuates more frequently and more mildly as a function of distance. Moreover, the precipitates can induce ferrite grains to store a relatively large amount of energy. These results suggest that a correlation exists between precipitation in ferrite grains and grain crystallographic properties.

  19. Multi-stage Modeling of Lüders Elongation and Work-Hardening Behaviors of Ferrite Steels Under Tension

    NASA Astrophysics Data System (ADS)

    Zhang, Zhongyang; Liao, Yiliang

    2016-04-01

    For structural and engineering steels, accurate modeling of stress-strain relation of ferrite phase is of particular importance, since the modeling results could benefit new material system design and process-microstructure-property analysis. Several modeling efforts have been made to achieve this target. However, few efforts have been put on the Lüders elongation behavior of ferrite. As a result, the modeling results from proposed models do not match well with experimental data, particularly at a relatively low-strain range. Furthermore, without the consideration of yield point elongation due to the formation of Lüders bands, additional calibration parameters are required to capture the stress level of stress-strain curves. In this work, a multi-stage model is developed to predict the stress-strain relation of ferrite phase steel under room temperature tension. This model is capable of capturing the grain size effect on both Lüders elongation and work-hardening behaviors of ferrite. The modeling results are extensively validated by experimental data.

  20. Kinetics and formation mechanisms of intragranular ferrite in V-N microalloyed 600 MPa high strength rebar steel

    NASA Astrophysics Data System (ADS)

    Zhang, Jing; Wang, Fu-ming; Li, Chang-rong

    2016-04-01

    To systematically investigate the kinetics and formation mechanisms of intragranular ferrite (IGF), isothermal heat treatment in the temperature range of 450°C to 600°C with holding for 30 s to 300 s, analysis of the corresponding microstructures, and observation of the precipitated particles were conducted in V-N microalloyed 600 MPa high strength rebar steel. The potency of V(C,N) for IGF nucleation was also analyzed statistically. The results show that the dominant microstructure transforms from bainite (B) and acicular ferrite (AF) to grain boundary ferrite (GBF), intragranular polygonal ferrite (IPF), and pearlite (P) as the isothermal temperature increases from 450°C to 600°C. When the holding time at 600°C is extended from 30 s to 60 s, 120 s, and 300 s, the GBF content ranges from 6.0vol% to 6.5vol% and the IPF content increases from 0.5vol% to 2.8vol%, 13.1vol%, and 13.5vol%, respectively, because the ferrite transformation preferentially occurs at the grain boundaries and then occurs at the austenite grains. Notably, V(C,N) particles are the most effective nucleation site for the formation of IPF, accounting for 51% of the said formation.

  1. Investigation on Mechanical Properties of 9%Cr/CrMoV Dissimilar Steels Welded Joint

    NASA Astrophysics Data System (ADS)

    Liu, Xia; Lu, Fenggui; Yang, Renjie; Wang, Peng; Xu, Xiaojin; Huo, Xin

    2015-04-01

    Advanced 9%Cr steel with good heat resistance and CrMoV with good toughness were chosen as candidate materials to fabricate combined rotor for steam turbine operating at over 620 °C. But the great difference in base metals properties presents a challenge in achieving sound defect-free joint with optimal properties in dissimilar welded rotor. In this paper, appropriate selection of filler metal, welding parameters, and post-weld heat treatment was combined to successfully weld 1100-mm-diameter 9%Cr/CrMoV dissimilar experimental rotor through ultra-narrow gap submerge arc welding. Some properties such as hardness, low-cycle fatigue (LCF), and high-cycle fatigue (HCF) combined with microstructural characterization qualify the integrity of the weld. Microstructural analysis indicated the presence of high-temperature tempered martensite as the phase responsible for the improved properties obtained in the weld. The Coffin-Manson parameters were obtained by fitting the data in LCF test, while the conditional fatigue strength was derived from the HCF test based on S-N curve. Analysis of hardness profile showed that the lowest value occurred at heat-affected zone adjacent to base metal which represents the appropriate location of fracture for the samples after LCF and HCF tests.

  2. Changes in Microstructural and Mechanical Properties of AISI Type 316LN Stainless Steel and Modified 9Cr-1Mo Steel on Long-Term Exposure to Flowing Sodium in a Bi-Metallic Sodium Loop

    NASA Astrophysics Data System (ADS)

    Sivai Bharasi, N.; Pujar, M. G.; Thyagarajan, K.; Mallika, C.; Kamachi Mudali, U.; Dhaul, Anuradha; Nandagopal, M.; Moitra, A.; Chandramouli, S.; Rajan, K. K.

    2015-12-01

    AISI Type 316LN stainless steel (SS) and modified 9Cr-1Mo steel were exposed to flowing sodium at 798 K (525 °C) for 30000 hours in a bi-metallic sodium loop. The changes in microchemical, microstructural, and mechanical properties were evaluated and compared with the as-received and thermally aged specimens. Effective carbon diffusion coefficient {( {D_{C}^{eff} } )} was calculated to be 6.8 × 10-19 m2/s. Depth of carburization analyzed by secondary ion mass spectroscopy technique was around 100 µm for sodium-exposed 316LN SS. Selective leaching of nickel occurred across depth from the surface of sodium-exposed 316LN SS with the formation of 10 µm ferrite layer, and it showed an increase in yield strength by 15 pct, reduction in ductility by 60 pct, and a decrease in impact energy by 15 pct vis-a-vis the as-received and thermally aged specimens. This reduction in ductility occurred due to extensive precipitation of sigma phase as a result of long-term thermal aging. No significant changes were observed in the sodium/modified 9Cr-1Mo steel interfacial microstructure as well as tensile properties of sodium-exposed modified 9Cr-1Mo steel. Although modified 9Cr-1Mo neither showed carburization nor decarburization on sodium exposure, it showed a drastic reduction in the impact strength, which was attributed to the presence of Laves phase, observed in X-ray diffraction patterns.

  3. Pros and cons of nickel- and boron-doping to study helium effects in ferritic/martensitic steels

    NASA Astrophysics Data System (ADS)

    Hashimoto, N.; Klueh, R. L.; Shiba, K.

    2002-12-01

    In the absence of a 14 MeV neutron source, the effect of helium on structural materials for fusion must be simulated using fission reactors. Helium effects in ferritic/martensitic steels have been studied by adding nickel and boron and irradiating in a mixed-spectrum reactor. Although the nickel- and boron-doping techniques have limitations and difficulties to estimate helium effects on the ferritic/martensitic steels, past irradiation experiments using these techniques have demonstrated similar effects on the swelling and Charpy impact properties that are indicative of a helium effect. Although both techniques have disadvantages, it should be possible to plan experiments using the nickel- and boron-doping techniques to develop an understanding of the effects of helium on mechanical properties.

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

    NASA Astrophysics Data System (ADS)

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

    2002-05-01

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

  5. Evidence of zinc ferrite formation on carbon steel in primary-side coolant with added soluble zinc

    NASA Astrophysics Data System (ADS)

    Sawicki, Jerzy A.; Allsop, Heather A.

    1996-12-01

    Conversion electron and X-ray backscattering Mössbauer spectroscopy was used to identify iron compounds that were formed on carbon steel in simulated CANDU® reactor coolant containing 15 to 60 ppb (μg/L H 2O) soluble zinc. Analyses of the coupons exposed to coolant in the absence of zinc indicated the formation of magnetite, whereas, in the presence of zinc, the formation of a layer of zinc-bearing ferrite Zn xFe 3- xO 4 (with x > 0.8 was observed. The role of the high electrical resistivity of zinc ferrite in reducing corrosion rates, corrosion-product release rates, and 60Co activity buildup on carbon steel is briefly discussed.

  6. On the mobility of vacancy clusters in reduced activation steels: an atomistic study in the Fe-Cr-W model alloy.

    PubMed

    Bonny, G; Castin, N; Bullens, J; Bakaev, A; Klaver, T C P; Terentyev, D

    2013-08-01

    Reduced activation steels are considered as structural materials for future fusion reactors. Besides iron and the main alloying element chromium, these steels contain other minor alloying elements, typically tungsten, vanadium and tantalum. In this work we study the impact of chromium and tungsten, being major alloying elements of ferritic Fe-Cr-W-based steels, on the stability and mobility of vacancy defects, typically formed under irradiation in collision cascades. For this purpose, we perform ab initio calculations, develop a many-body interatomic potential (EAM formalism) for large-scale calculations, validate the potential and apply it using an atomistic kinetic Monte Carlo method to characterize the lifetime and diffusivity of vacancy clusters. To distinguish the role of Cr and W we perform atomistic kinetic Monte Carlo simulations in Fe-Cr, Fe-W and Fe-Cr-W alloys. Within the limitation of transferability of the potentials it is found that both Cr and W enhance the diffusivity of vacancy clusters, while only W strongly reduces their lifetime. The cluster lifetime reduction increases with W concentration and saturates at about 1-2 at.%. The obtained results imply that W acts as an efficient 'breaker' of small migrating vacancy clusters and therefore the short-term annealing process of cascade debris is modified by the presence of W, even in small concentrations. PMID:23838265

  7. 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.

  8. The segregation behavior of manganese and silicon at the coherent interfaces of copper precipitates in ferritic steels

    NASA Astrophysics Data System (ADS)

    Xie, Yao-Ping; Zhao, Shi-Jin

    2014-02-01

    We have performed first-principles calculations to study the segregation behavior of Mn and Si at the interfaces of Cu precipitates in ferritic steels. We find that both the segregation energies of substitutional Mn and Si at the interfaces of the Cu precipitates are negligible. However, the energetics indicate that the self-interstitial dumbbells containing Mn or Si (Mn@SI or Si@SI)

  9. Use of DL-EPR Test to Assess Sensitization Resistance of AISI 409M Grade Ferritic Stainless Steel Joints

    NASA Astrophysics Data System (ADS)

    Lakshminarayanan, A. K.; Balasubramanian, V.

    2013-08-01

    The susceptibility of 409M grade ferritic stainless steels to sensitization due to welding was investigated. Joints were fabricated by gas tungsten arc welding, friction stir welding, laser beam welding, and electron beam welding processes. Double loop electrochemical potentiokinetic reactivation test was carried out for determining the degree of sensitization of welded joints. The experimental result reveals that, the friction stir welded joint is less prone to sensitization, when compared to the other joints.

  10. The Influence of Shielding Gas and Heat Input on the Mechanical Properties of Laser Welds in Ferritic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Keskitalo, M.; Sundqvist, J.; Mäntyjärvi, K.; Powell, J.; Kaplan, A. F. H.

    Laser welding of ferritic steel in normal atmosphere gives rise to weld embrittlement and poor formability. This paper demonstrates that the addition of an argon gas shield to the welding process results in tough, formable welds. Post weld heat treatment and microscopic analysis has suggested that the poor ductility of welds produced without a gas shield is, to some extent, the result of the presence of oxides in the weld metal.

  11. R&D of ferritic-martensitic steel EP450 ODS for fuel pin claddings of prospective fast reactors

    NASA Astrophysics Data System (ADS)

    Nikitina, A. A.; Ageev, V. S.; Chukanov, A. P.; Tsvelev, V. V.; Porezanov, N. P.; Kruglov, O. A.

    2012-09-01

    Present paper performs research results of structure and mechanical properties of the ODS steel on the base of steel EP450 (Fe-13Cr-2Mo-Nb-V-B-0,12C) on all stages of producing: from powders to thin-walled tubes. Also, the results of research on method of sealing thin-walled tubes from steel EP450 ODS by pressurized resistance welding are shown.

  12. 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.

  13. Laser surface modification of carburized and borocarburized 15CrNi6 steel

    SciTech Connect

    Kulka, M. . E-mail: coolka@sol.put.poznan.pl; Pertek, A.

    2007-05-15

    The paper presents the results of laser heat treatment (LHT) of carburized and borocarburized 15CrNi6 low-carbon steel. Laser tracks were arranged by CO{sub 2} laser beam as multiple tracks formed in the shape of a helical line. The microstructure and properties of these diffusion layers were compared with those obtained after through-hardening. The microstructure after carburizing and LHT consists of adjacent characteristic zones: re-melted zone (coarse-grained martensite), carburized layer with heat affected zone (fine acicular martensite), carburized layer without heat treatment and the substrate (ferrite and pearlite). The highest measured microhardness (about 820 HV) was observed in re-melted and heat affected zones. The increase of distance from the surface was accompanied by a gradual decrease of microhardness up to 400 HV beneath the HAZ and up to 250 HV in the core of steel. The carburized layer after LHT exhibited a higher resistance to frictional wear compared to a carburized layer after through-hardening. The microstructure after borocarburizing and LHT consists of the following characteristic zones: iron borides of laser-modified morphology (FeB and Fe{sub 2}B), carburized layer with heat affected zone (martensite and alloyed cementite), carburized layer without heat treatment and the substrate (ferrite and pearlite). The highest microhardness was obtained in the iron boride zone. The microhardness of FeB boride extended up to 2200 HV and for the Fe{sub 2}B boride up to about 1300-1600 HV. With increased distance from the surface, the microhardness gradually decreases to 800 HV in HAZ, 400-450 HV in the carburized layer without heat treatment and to 250 HV in low-carbon substrate. The iron borides after LHT assume a globular shape, which leads to a lower texture and porosity of the borided layers. The increased resistance to friction wear of the borocarburized layers is certified in comparison with the borided layer after conventional heat treatment

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. 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.

  19. High-temperature degradation and protection of ferritic and austenitic steels in steam generators

    SciTech Connect

    Martinez-Villafane, A.; Almeraya-Calderon, M.F.; Gaona-Tiburcio, C.; Gonzalez-Rodriguez, J.G.; Porcayo-Calderon, J.

    1998-02-01

    The useful life of superheaters and reheaters of power stations which use heavy fuel oil is shortened and their continuous service is inhibited by corrosion (fireside) and creep-type problems. The increase of corrosion attack on boilers is caused by the presence of fuel ash deposits containing mainly vanadium, sodium, and sulfur which form low-melting-point compounds. The tubes are exposed to the action of high stresses and high temperatures, producing the so-called creep damage. In this work, two kinds of results are reported: lab and field studies using a 2.25Cr-1Mo steel. The laboratory work was in turn divided into two parts. In the first, the steel was exposed to the action of natural ash deposits in oxidant atmospheres at 600 C for 24 h. In the second part, tensile specimens were creep tested in Na{sub 2}SO{sub 4}, V{sub 2}O{sub 5}, and their mixture over a temperature range of 580 to 620 C. In the field work, components of a power station were coated with different types of nickel- and iron-base coatings containing chromium, Fe-Cr, and Fe-Si using the powder flame spraying technique. After testing, the coated tubes were analyzed using electron microscopy. The results showed that all the coating systems had good corrosion resistance, especially those containing silicon or chromium.

  20. Room and elevated temperature Mechanical Behavior of 9-12% Cr Steels

    SciTech Connect

    Dogan, Omer N.; Hawk, Jeffrey A.; Schrems, Karol K.

    2005-02-01

    The mechanical properties of medium Cr steels used in fossil fired power plants are very good because of their excellent high temperature microstructural stability. However, as the desire to increase the operating temperature (>650C) of the plant goes up, the need for steels that maintain their strength at these temperatures also increases. The mechanical properties of three medium Cr steels (0.08C-(9-12)Cr-1.2Ni-0.7Mo-3.0Cu-3.0Co-0.5Ti) were investigated through hardness, hot hardness and tensile measurements. The strength of the 9-12%Cr steels at room temperature after long-term isothermal aging (750C; 1000 hours) compares favorably with that of other power plant steels (e.g., P91). In addition, the elevated temperature strength and hot hardness also behave similarly. The mechanical behavior will be discussed in terms of the strength, elongation and tensile fracture characteristics.

  1. The resistance to cavitation erosion of CrMnN stainless steels

    SciTech Connect

    Fu, W.T.; Jing, T.F.; Zheng, Y.Z.; Yang, Y.B.; Yao, M.

    1998-12-01

    The resistance to cavitation erosion (CE) was measured using a magnetostrictive device and a rotating disk device for some CrMnN stainless steels (Chinese patent ZL 90 1 02197.0). The microstructural changes in the surface layer before and after CE were analyzed by use of Mossbauer spectra. Results show that the resistance to CE of duplex austenitic-martensitic CrMnN stainless steels is much better than that of ZG0Cr13Ni4-6Mo and ZG0Cr16Ni5Mo steel, which are in common use for hydraulic turbine runners. The metastable austenite and its changes in the process of CE are the key factors why the CrMnN stainless steels have excellent resistance to cavitation erosion.

  2. Microstructural stability of a self-ion irradiated lanthana-bearing nanostructured ferritic steel

    SciTech Connect

    Pasebani, Somayeh; Charit, Indrajit; Burns, Jatuporn; Alsagabi, Sultan; Butt, Darryl P.; Cole, James I.; Price, Lloyd M.; Shao, Lin

    2015-07-01

    Thermally stable nanofeatures with high number density are expected to impart excellent high temperature strength and irradiation stability in nanostructured ferritic steels (NFSs) which have potential applications in advanced nuclear reactors. A lanthana-bearing NFS (14LMT) developed via mechanical alloying and spark plasma sintering was used in this study. The sintered samples were irradiated by Fe2+ ions to 10, 50 and 100 dpa at 30 °C and 500 °C. Microstructural and mechanical characteristics of the irradiated samples were studied using different microscopy techniques and nanoindentation, respectively. Overall morphology and number density of the nanofeatures remained unchanged after irradiation. Average radius of nanofeatures in the irradiated sample (100 dpa at 500 °C) was slightly reduced. A notable level of irradiation hardening and enhanced dislocation activity occurred after ion irradiation except at 30 °C and ≥50 dpa. Other microstructural features like grain boundaries and high density of dislocations also provided defect sinks to assist in defect removal.

  3. Effect of Imposing Temperature Gradient in Stretch Forming Process for Ferritic Stainless Steel Sheets

    NASA Astrophysics Data System (ADS)

    Iguchi, Takaaki; Ujiro, Takumi

    2010-06-01

    A new stamping method developed by the authors, in which a temperature gradient is imposed on the workpiece during stamping, is capable of improving stretch formability in stamping of ferritic stainless steel sheets. Unlike the conventional warm stamping method, the temperature gradient is utilized in order to diffuse the strain distribution induced in the material. Basically, the portions of the sheets which are in contact with the top of the punch and die face are heated, while simultaneously, the portions in contact with the punch corners and die corners are intensively cooled The authors developed a finite element simulation model of stamping which analyzes mechanical and thermal behaviors simultaneously utilizing LS-DYNA3D. The numerical analysis, combined with a numerical model which evaluates the ductile fracture limit of the material in the high temperature region, confirmed that the new stamping method improves stretch formability and the optimal temperature gradient is given. In order to verify the numerical analysis, an experimental apparatus was constructed, comprising a set of stamping tools containing heaters and cooling circuits. The experiments demonstrated the correctness of the numerical analysis and the effectiveness of the new stamping method.

  4. 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.

  5. High temperature corrosion of welded ferritic stainless steel in flowing CO2 gas

    NASA Astrophysics Data System (ADS)

    Shariff, Nurul Atikah; Othman, Norinsan Kamil; Jalar, Azman; Hamid, Muhammad Azmi Abdul; Rahman, Irman Abdul

    2013-05-01

    The high temperature corrosion of welded structure of Ferritic Stainless Steel (FSS) in flowing Ar-75%CO2 gas at 700°C has been investigated. The welded structure of FSS joint using ER 308L filler metal by GTAW. The soundness of welded joint has been clarified by X-Ray CT Scan. Prior the high temperature exposure, the welded FSS compulsory passed the standard of ASME. The welded structure of FSS was heated in flowing CO2 gas for 50 h at 1 atm. The morphology and microstructure of oxide formation on welded FSS alloy was characterized by using SEM. The result shows that the different oxide morphologies were observed on parent and fusion metal. The formation of different oxide and element properties at the interface were revealed by X-Ray Diffraction. The differences of the physical condition and morphology microstructure of welded and parent metal were observed to respond to different exposure times. This phenomenon perhaps explained due to the differences of the minor alloying elements on both parent and filler metals. The high temperature corrosion behaviour was discussed in details in this paper regarding on the physical properties, morphology and the microstructure.

  6. Elevated-temperature tensile and creep properties of several ferritic stainless steels

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.

    1977-01-01

    The elevated-temperature mechanical properties of several ferritic stainless steels were determined. The alloys evaluated included Armco 18SR, GE 1541, and NASA-18T-A. Tensile and creep strength properties at 1073 and 1273 K and residual room temperature tensile properties after creep testing were measured. In addition, 1273 K tensile and creep tests and residual property testing were conducted with Armco 18SR and GE 1541 which were exposed for 200 hours to a severe oxidizing environment in automotive thermal reactors. Aside from the residual tensile properties for Armco 18SR, prior exposure did not affect the mechanical properties of either alloy. The 1273 K creep strength parallel to the sheet-rolling direction was similar for all three alloys. At 1073 K, NASA-18T-A had better creep strength than either Armco 18SR or GE 1541. NASA-18T-A possesses better residual properties after creep testing than either Armco 18SR or Ge 1541.

  7. Microstructural stability of a self-ion irradiated lanthana-bearing nanostructured ferritic steel

    NASA Astrophysics Data System (ADS)

    Pasebani, Somayeh; Charit, Indrajit; Burns, Jatuporn; Alsagabi, Sultan; Butt, Darryl P.; Cole, James I.; Price, Lloyd M.; Shao, Lin

    2015-07-01

    Thermally stable nanofeatures with high number density are expected to impart excellent high temperature strength and irradiation stability in nanostructured ferritic steels (NFSs) which have potential applications in advanced nuclear reactors. A lanthana-bearing NFS (14LMT) developed via mechanical alloying and spark plasma sintering was used in this study. The sintered samples were irradiated by Fe2+ ions to 10, 50 and 100 dpa at 30 °C and 500 °C. Microstructural and mechanical characteristics of the irradiated samples were studied using different microscopy techniques and nanoindentation, respectively. Overall morphology and number density of the nanofeatures remained unchanged after irradiation. Average radius of nanofeatures in the irradiated sample (100 dpa at 500 °C) was slightly reduced. A notable level of irradiation hardening and enhanced dislocation activity occurred after ion irradiation except at 30 °C and ⩾50 dpa. Other microstructural features like grain boundaries and high density of dislocations also provided defect sinks to assist in defect removal.

  8. Characterisation of Laves phase precipitation and its correlation to creep rupture strength of ferritic steels

    SciTech Connect

    Zhu, S.; Yang, M.; Song, X.L.; Tang, S.; Xiang, Z.D.

    2014-12-15

    The Laves phase precipitation process was characterised by means of field emission scanning electron microscopy to demonstrate its effect on creep rupture strength of steels with a fully ferritic matrix. To eliminate the effects of carbide and carbonitride precipitations so that the creep rupture data can be analysed exclusively in relation to the Laves phase precipitation process, an alloy Fe–9Cr–3Co–3W (wt.%) without C and N additions was used for the study. Creep rupture strengths were measured and volume fraction and particle size of Laves phase precipitates in the ruptured specimens were analysed. It was found that the creep rupture strength started to collapse (or decrease more rapidly) long before the Laves phase precipitation reached equilibrium fraction. This was related to the onset of the coarsening of Laves phase particles, which precipitated only on grain boundaries and hence contributed little to precipitation strengthening. Creep deformation had no effect either on the precipitation kinetics or on the growth kinetics of Laves phase particles. - Highlights: • Laves phase precipitation at 650 °C was characterised for Fe–9Cr–3W–3Co alloy. • Laves phase precipitated predominantly on grain boundaries. • Creep deformation had no effect on Laves phase precipitation and growth kinetics. • Creep strength started to collapse long before Laves phase precipitation is ended. • Collapse of creep strength was attributed to the coarsening of Laves phase particles.

  9. Critical level of intergranular fracture to affect the toughness of embrittled 2.25Cr-1Mo steels

    NASA Astrophysics Data System (ADS)

    Islam, M. A.; Knott, J. F.; Bowen, P.

    2004-10-01

    In general, the low-temperature brittle fracture mode of unembrittled ferritic steel is transgranular cleavage. During temper embrittlement, impurity elements, such as sulfur (S), phosphorus (P), antimony (Sb), arsenic (As), and tin (Sn), segregate to prior austenite grain boundaries, which results in a decrease in the grain boundary cohesive strength. As a result, the brittle transgranular cleavage fracture mode changes to intergranular decohesion in association with the decrease in the critical fracture (stress (σ F) as well as the fracture toughness (K). However, the appearance of intergranular facets on the fracture surface does not cause a decrease in the K and σ F values. In this work, quenched and fully tempered 2.25Cr-1Mo steel (in an unembrittled condition that exhibits almost 100% brittle transgranular cleavage fracture) has been embrittled for 24, 96, and 210 h at 520 °C to produce different proportions of intergranular fracture. These unembrittled and embrittled steel specimens were tested to measure K (at -120 and -196 °C) and σ F (at -196 °C). The experimental results and detailed fractographic observations show that the K and σ F values decrease with an increase in the area fraction of intergranular fracture, provided that the area fraction of the intergranular facet on the brittle fracture surface exceeded a certain critical level, approximately 20 22%.

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

    SciTech Connect

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

    1997-04-01

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

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

    SciTech Connect

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

    1994-10-01

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

  12. Effects of aging temperature on G-phase precipitation and ferrite-phase decomposition in duplex stainless steel

    NASA Astrophysics Data System (ADS)

    Hamaoka, T.; Nomoto, A.; Nishida, K.; Dohi, K.; Soneda, N.

    2012-12-01

    G-phase precipitation and ferrite-phase decomposition in a cast duplex stainless steel (DSS) aged at 623-723 K for up to 8000 h were investigated using atom probe tomography (APT). Large sample volume was observed in every APT experiment, which yielded significantly statistical results. The number density of G-phase precipitates tended to be high and their sizes were small at lower aging temperatures. G-phase precipitates grew during prolonged isothermal aging. The concentrations of nickel, silicon, manganese and molybdenum in G-phase precipitates tended to increase as the precipitates grew. Heterogeneous distributions of alloying elements within G-phase precipitates were observed. An interesting positional relationship of G-phase precipitates with dislocations was revealed. Regarding the ferrite-phase decomposition, local chromium concentrations in the ferrite phase varied fast at higher aging temperatures. Good correlation between the variation of local chromium concentrations and aging conditions was revealed, which indicates that the variation can be estimated for arbitrary aging conditions. Representative distances between chromium-enriched and chromium-diluted regions were long at higher aging temperatures. Time exponent of the representative distances of ferrite-phase decomposition as well as the size of G-phase precipitates increased with aging temperatures.

  13. Improved ferrite number prediction in stainless steel arc welds using artificial neural networks -- Part 2: Neural network results

    SciTech Connect

    Vitek, J.M.; Iskander, Y.S.; Oblow, E.M.

    2000-02-01

    The development of a neural network model, named FNN-1999, for predicting Ferrite Number in arc welds as a function of alloy composition is described in Part 1. In this paper, the results of the model are compared to other means of predicting Ferrite Number in stainless steel welds. It was found the accuracy of the FNN-1999 model in predicting Ferrite Number is superior to that of the WRC-1992 diagram, the Function Fit model and a preliminary neural network model developed earlier. The error in fitting the current model to the training set was 40% less than that for the WRC-1992 diagram. In addition, the FNN-1999 model removes the restriction found in WRC-1992 and many other constitution diagrams that each element's contribution to the Ferrite Number is constant, regardless of the overall composition. Examples are given that show that with this added flexibility of the FNN-1999 model, the impact of alloying additions varies as a function of concentration, and in some cases the variation can be quite significant.

  14. Sensitization Behavior of Type 409 Ferritic Stainless Steel: Confronting DL-EPR Test and Practice W of ASTM A763

    NASA Astrophysics Data System (ADS)

    Scalise, Taís Campos; de Oliveira, Mara Cristina Lopes; Sayeg, Isaac Jamil; Antunes, Renato Altobelli

    2014-06-01

    Stainless steels employed for manufacturing automotive exhaust systems must withstand severe thermal cycles, corrosive environment due to urea decomposition, and welding operations. AISI 409 ferritic stainless steel can be considered a low-cost alternative for this application. However, depending on the manufacturing conditions during welding cycles, this material can be sensitized due to the precipitation of chromium carbides at grain boundaries. In this work, the intergranular corrosion resistances of the AISI 409 ferritic stainless steel were evaluated after annealing at 300, 500, and 700 °C for 2, 4, and 6 h. Solution-annealed samples were also tested for comparison purposes. Two methodologies were used to assess the sensitization behavior of the 409 stainless steel samples: the first one was based on the ASTM A763 (practice W), while the second one was based on the double-loop electrochemical potentiodynamic reactivation test. It was possible to identify that the annealing treatment performed at 500 °C was more critical to the occurrence of intergranular corrosion.

  15. Conditions for the Efficient Crushing of the As-Cast Microstructure of 30Cr10Ni Duplex Stainless Steel

    NASA Astrophysics Data System (ADS)

    Terčelj, Milan; Fazarinc, Matevz; Bombač, David; Kugler, Goran

    2010-12-01

    The hot-deformation behavior of as-cast 30Cr10Ni duplex stainless steel was investigated with the aim to understand the conditions better that lead to the occurrence of cracking. Because of the increased content of Cr, Ni, and C, the 30Cr10Ni ferrous alloy exhibits a complex microstructure, especially in the as-cast state in which, in addition to the ferrite, austenite, and sigma phases, carbides also are present; this leads to a very complex hot-deformation behavior. Hot-compression tests on specimens with an as-cast initial microstructure in the temperature range 1223 K (950 °C) to1573 K (1300 °C) and strain rates of 0.1 to 5.0 s-1 were carried out. To find the most appropriate sequence of initial hot-deformation steps for the effective crushing of the as-cast microstructure, a special experimental procedure was developed. The results indicate that in the temperature range 1423 K (1150 °C) to 1523 K (1250 °C), the as-cast microstructure exhibits increased workability, whereas below this temperature, the microstructure is prone to cracking. As such, the as-cast microstructure should be crushed in the high-temperature range to avoid the occurrence of cracking.

  16. Low-temperature synthesis of nanocrystalline NiCuZn ferrite and the effect of Cr substitution on its electrical properties

    NASA Astrophysics Data System (ADS)

    Gabal, M. A.; Al Angari, Y. M.

    2010-10-01

    In this study, nano-sized ferrites of compositions (Ni 0.6Cu 0.20Zn 0.20Fe 2- xCr xO 4), where x=0-1.0, were synthesized through nitrate-citrate auto-combustion method at relatively low temperature. XRD revealed the formation of nano-sized ferrite particles with cubic spinel structure. An exception was obtained for samples with Cr content ≤0.2, where weak diffraction peaks attributed to the presence of CuO and Fe 2O 3 were appeared. The average crystallite sizes are much dependent on the chromium content and were found to decrease with its increase. The lattice parameter ( a) slightly decreases with Cr substitution, which can be explained on the basis of the relative ionic radii of Cr 3+ and Fe 3+ ions. X-ray density was found also to decrease slightly with increase in chromium content, which indicates lower densification by the addition of Cr. FT-IR measurements show the characteristic ferrite bands. The Mössbauer spectra varied from Zeeman sextets to a relaxed doublet by increase in Cr content, which indicates a decrease in the hyperfine field at the octahedral site. Electrical property measurements revealed that Cr 3+ ions do not participate in conduction process but limit the degree of Fe 3+-O 2--Fe 3+ conduction resulting in a decrease in the conductivity and increase in conduction activation energy.

  17. Exploring the Cr2+ doping effect on structural, vibrational and dielectric properties of Mn-Zn ferrites

    NASA Astrophysics Data System (ADS)

    Choudhary, Pankaj; Tyagi, Tarun; Dar, M. A.; Varshney, Dinesh

    2016-05-01

    A series of Cr doped Mn-Zn ferrites with compositional formula Mn0.5Zn0.5-xCrxFe2O4 (x = 0, 0.3, 0.5) were prepared by solid-state reaction route. X-ray diffraction (XRD) analysis reveals that the samples prepared are polycrystalline cubic spinel in structure (Fd3m) with some secondary phase of α-Fe2O3. Slight variation in the lattice parameter of Cr doped Mn0.5Zn0.5Fe2O4 has been observed due to difference in ionic radii of cations. Small shift in Raman modes towards higher wave number has been observed. Further the line width decreases with the doping ions. A giant dielectric constant ~104 is observed for parent Mn0.5Zn0.5Fe2O4 which is found to decrease with increase in Cr2+ doping. Low dielectric loss is observed for Mn0.5Zn0.5Fe2O4 and improves with Cr2+ doping at Zn2+ site.

  18. Influence of volumic heat treatments upon cavitation erosion resistance of duplex X2CrNiMoN 22-5-3 stainless steels

    NASA Astrophysics Data System (ADS)

    Micu, L. M.; Bordeasu, I.; Popoviciu, M. O.; Popescu, M.; Bordeaşu, D.; Salcianu, L. C.

    2015-06-01

    The stainless steels Duplex 2205 with austenite and ferrite structure have mechanical characteristics close to those of martensite stainless steels but a better corrosion resistance; these steels are very sensitive on the heat treatments. Present work studies the cavitation erosion for those steels for three different heat treatments: simply quenched, annealed at 475°C post quenching and annealed at 875°C. The researches were undertaken at Timisoara “Politehnica” University in the Laboratory of Material Science and the Laboratory of Cavitation, using the T2 facility which integrally respects the recommendation of ASTM G32- 10 Standard. The best results were obtained with the specimens annealed at 875°C. In comparison with the stainless steel 41Cr4, with very good cavitation erosion qualities, all tested steels presented also good erosion resistance. So, Duplex 2205 steels can be used for details subjected to cavitation. The best results are obtained by increasing both the hardness and the quantity of the structure constituent with better cavitation erosion resistance, in our case the alloyed austenite.

  19. Oxidation behaviour of ferritic stainless steel grade Crofer 22 APU at 700 °C in flowing Ar-75%CO2-12%H2O

    NASA Astrophysics Data System (ADS)

    Shariff, Nurul Atikah; Othman, Norinsan Kamil; Jalar, Azman

    2013-11-01

    The oxidation of Ferritic Stainless Steel (FSS) grade Crofer 22 APU has been investigated. FSS alloys were exposed to isothermal conditions in a horizontal tube furnace at a 700 °C in flowing Ar-75%CO2-12%H2O at a pressure of approximately 1 atm. The results showed that the growth of non protective Fe2O3 and spinel was observed after 50 h exposure in the presence of 12% H2O. The weight was increased significantly with time of exposure. The formation of different oxides is presented on the interface of the specimen such as MnCr2O4, Fe3O4 and Fe2O3 were revealed by X-ray diffraction and supported by EDAX analysis. FSS did not form a protective Cr2O3 layer due to water vapour accelerates the kinetics oxidation. Data of microstructure observation is presented and discussed in this paper in term of water vapour effects.

  20. Qualification of welded super 13%Cr martensitic stainless steels for sour service applications

    SciTech Connect

    Enerhaug, J.; Eliassen, S.L.; Kvaale, P.E.

    1997-08-01

    A test program has been carried out to qualify welded super 13%Cr stainless steels for sour service applications. The test program included weldability trials, weld simulations, mechanical testing and corrosion testing of 13%Cr steels from five different steel mills. Two of the tested steels have been qualified for use as flowline materials in some parts of new sour service fields. The result shows excellent weldability properties and acceptable corrosion properties. Post weld heat treatment (PWHT) of the welds improved the resistance towards sulfide stress corrosion cracking significantly.

  1. Nanocluster-associated vacancies in nanocluster-strengthened ferritic steel as seen via positron-lifetime spectroscopy

    NASA Astrophysics Data System (ADS)

    Xu, Jun; Liu, C. T.; Miller, M. K.; Chen, Hongmin

    2009-01-01

    Nanocluster-strengthened ferritic alloys are promising as structural materials because of their excellent high-temperature strength and radiation-damage resistance. Recently, Fu [Phys. Rev. Lett. 99, 225502 (2007)] predicted that vacancies play an essential role in the formation and stabilization of nanoclusters in these materials. Positron-lifetime spectroscopy has been used to test this theoretical prediction in a nanocluster-strengthened Fe-based alloy. Nanoclusters (2-4 nm in diameter) containing Ti, Y, and O have been observed in a mechanically alloyed ferritic steel by atom-probe tomography. Vacancy clusters containing four to six vacancies have also been found in this material. In contrast, no vacancy clusters were detected in similar alloys containing no nanoclusters. These results indicate that vacancies are a vital component of the nanoclusters in these alloys.

  2. Joining techniques for a reduced activation 12Cr steel for inertial fusion energy

    SciTech Connect

    Hunt, R. M.; El-Dasher, B.; Choi, B. W.; Torres, S. G.

    2014-10-01

    At Lawrence Livermore National Laboratory, we are developing a reduced activation ferritic martensitic steel that is based on the ferritic martensitic steel HT-9. As a part of the development of this steel, we tested a series of welding processes for characterization, including conventional welds (electron beam, tungsten inert gas, and laser) as well as solid-state welds (hot isostatic pressing). We also heat treated the joints at various temperatures between 750 °C and 1050 °C to find a suitable normalization scheme. The modified HT-9 reduced activation ferritic martensitic steel appears highly suitable to welding and diffusion bonding. All welds showed good quality fusion zones with insignificant cracking or porosity. Additionally, a heat treatment schedule of 950 °C for one hour caused minimal grain growth while still converging the hardness of the base metal with that of the fusion and heat-affected zones. Also, modified HT-9 diffusion bonds that were created at temperatures of at least 950 °C for two hours at 103 MPa had interface tensile strengths of greater than 600 MPa. The diffusion bonds showed no evidence of increased hardness nor void formation at the diffusion bonded interface.

  3. Probing Pulsed Current Gas Metal Arc Welding for Modified 9Cr-1Mo Steel

    NASA Astrophysics Data System (ADS)

    Krishnan, S.; Kulkarni, D. V.; De, A.

    2015-04-01

    Modified 9Cr-1Mo steels are commonly welded using gas tungsten arc welding process for its superior control over the rate of heat input and vaporization loss of the key alloying elements although the rate electrode deposition remains restricted. Recent developments in pulsed current gas metal arc welding have significantly improved its ability to enhance the rate of electrode deposition with a controlled heat input rate while its application for welding of modified 9Cr-1Mo steels is scarce. The present work reports a detailed experimental study on the pulsed current gas metal arc welding of modified 9Cr-1Mo steels. The effect of the shielding gas, welding current, and speed on the weld bead profile, microstructure and mechanical properties are examined. The results show that the pulsed current gas metal arc welding with appropriate welding conditions can provide acceptable bead profile and mechanical properties in welds of modified 9Cr-1Mo steels.

  4. Kinetics of borided 31CrMoV9 and 34CrAlNi7 steels

    SciTech Connect

    Efe, Goezde Celebi; Ipek, Mediha; Ozbek, Ibrahim; Bindal, Cuma

    2008-01-15

    In this study, kinetics of borides formed on the surface of 31CrMoV9 and 34CrAlNi7 steels borided in solid medium consisting of Ekabor II at 850-900-950 deg. C for 2, 4, 6 and 8 h were investigated. Scanning electron microscopy and optical microscopy examinations showed that borides formed on the surface of borided steels have columnar morphology. The borides formed in the coating layer confirmed by X-ray diffraction analysis are FeB, Fe{sub 2}B, CrB, and Cr{sub 2}B. The hardnesses of boride layers are much higher than that of matrix. It was found that depending on process temperature and time the fracture toughness of boride layers ranged from 3.93 to 4.48 MPa m{sup 1/2} for 31CrMoV9 and from 3.87 to 4.40 MPa m{sup 1/2} for 34CrAlNi7 steel. Activation energy, growth rate and growth acceleration of boride layer calculated according to these kinetic studies revealed that lower activation energy results in the fast growth rate and high growth acceleration.

  5. Electron work functions of ferrite and austenite phases in a duplex stainless steel and their adhesive forces with AFM silicon probe.

    PubMed

    Guo, Liqiu; Hua, Guomin; Yang, Binjie; Lu, Hao; Qiao, Lijie; Yan, Xianguo; Li, Dongyang

    2016-01-01

    Local electron work function, adhesive force, modulus and deformation of ferrite and austenite phases in a duplex stainless steel were analyzed by scanning force microscopy. It is demonstrated that the austenite has a higher electron work function than the ferrite, corresponding to higher modulus, smaller deformation and larger adhesive force. Relevant first-principles calculations were conducted to elucidate the mechanism behind. It is demonstrated that the difference in the properties between austenite and ferrite is intrinsically related to their electron work functions. PMID:26868719

  6. Electron work functions of ferrite and austenite phases in a duplex stainless steel and their adhesive forces with AFM silicon probe

    PubMed Central

    Guo, Liqiu; Hua, Guomin; Yang, Binjie; Lu, Hao; Qiao, Lijie; Yan, Xianguo; Li, Dongyang

    2016-01-01

    Local electron work function, adhesive force, modulus and deformation of ferrite and austenite phases in a duplex stainless steel were analyzed by scanning force microscopy. It is demonstrated that the austenite has a higher electron work function than the ferrite, corresponding to higher modulus, smaller deformation and larger adhesive force. Relevant first-principles calculations were conducted to elucidate the mechanism behind. It is demonstrated that the difference in the properties between austenite and ferrite is intrinsically related to their electron work functions. PMID:26868719

  7. Microstructure, Texture, and Deep Drawability Under Two Different Cold-Rolling Processes in Ferritic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Gao, Fei; Yu, Fu-xiao; Misra, R. D. K.; Zhang, Xiang-jun; Zhang, Shu-min; Liu, Zhen-yu

    2015-10-01

    In the present study, the through-thickness texture evolution and grain colony distribution in ferritic stainless steel under two different cold-rolling processes have been investigated with the aim to enhance deep drawability. It was shown that in the case of conventional cold-rolling process, at the surface, mid-thickness between the surface and the center, and center layers, all the textures consisted of very sharp α-fiber and weak γ-fiber with a peak at {111}<110> after cold rolling, and non-uniform γ-fiber recrystallization textures were formed after final annealing. In case of two-step cold-rolling process, by contrast, all the textures were dominated by sharp α-fiber and weak γ-fiber after cold rolling to 50% reduction, and {111}<112> became the prominent component after subsequent annealing. The α-fiber and γ-fiber with a peak at {111}<112> were intensified after cold rolling to 60% reduction, resulting in the formation of uniform γ-fiber recrystallization textures after final annealing. Furthermore, after two-step cold-rolling process, the final sheet exhibited a more homogeneous distribution of grain colonies. Therefore, the deep drawability of final sheet was significantly improved after two-step cold-rolling process. It was elucidated that the selective growth mechanism was responsible for the characteristics of γ-fiber recrystallization texture under conventional cold-rolling process, whereas γ-fiber recrystallization texture development was controlled by the oriented nucleation mechanism in the two-step cold-rolling process.

  8. Embrittlement of Cr-Mo steels after low fluence irradiation in HFIR

    SciTech Connect

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

    1995-04-01

    The goal of this work is the determination of the possible effect of the simultaneous formation of helium and displacement damage during irradiation on the Charpy impact behavior. Subsize Charpy impact specimens of 9Cr-1MoVNb (modified 9Cr-1Mo) and 12Cr-1MoVW (Sandvik HT9) steels and 12Cr-1MoVW with 2%Ni (12Cr-1MOVW-2Ni) were irradiated in the High Flux Isotope Reactor (HFIR) at 300 and 400{degree}C to damage levels up to 2.5 dpa. The objective was to study the effect of the simultaneous formation of displacement damage and transmutation helium on impact toghness. Despite the low fluence relative to previous irradiations of these steels, significant increases in the ductile-brittle transition temperature (DBTT) occurred. The 12Cr-1MoVW-2Ni steel irradiated at 400{degree}C had the largest increase in DBTT and displayed indications of intergranular fracture. A mechanism is proposed to explain how helium can affect the fracture behaviour of this latter steel in the present tests, and how it affected all three steels in previous experiments, where the steels were irradiated to higher fluences.

  9. High-Power Diode Laser-Treated 13Cr4Ni Stainless Steel for Hydro Turbines

    NASA Astrophysics Data System (ADS)

    Mann, B. S.

    2014-06-01

    The cast martensitic chromium nickel stainless steels such as 13Cr4Ni, 16Cr5Ni, and 17Cr4Ni PH have found wide application in hydro turbines. These steels have adequate corrosion resistance with good mechanical properties because of chromium content of more than 12%. The 13Cr4Ni stainless steel is most widely used among these steels; however, lacks silt, cavitation, and water impingement erosion resistances (SER, CER, and WIER). This article deals with characterizing 13Cr4Ni stainless steel for silt, cavitation, and water impingement erosion; and studying its improved SER, CER, and WIER behavior after high-power diode laser (HPDL) surface treatment. The WIER and CER have improved significantly after laser treatment, whereas there is a marginal improvement in SER. The main reason for improved WIER and CER is due to its increased surface hardness and formation of fine-grained microstructure after HPDL surface treatment. CER and WIER of HPDL-treated 13Cr4Ni stainless steel samples have been evaluated as per ASTM G32-2003 and ASTM G73-1978, respectively; and these were correlated with microstructure and mechanical properties such as ultimate tensile strength, modified ultimate resilience, and microhardness. The erosion damage mechanism, compared on the basis of scanning electron micrographs and mechanical properties, is discussed and reported in this article.

  10. Master Curve and Conventional Fracture Toughness of Modified 9Cr-1Mo Steel

    SciTech Connect

    Ji-Hyun, Yoon; Sung-Ho, Kim; Bong-Sang, Lee; Woo-Seog, Ryu; Jonghwa, Chang

    2006-07-01

    Modified 9Cr-1Mo steel is a primary candidate material for reactor pressure vessel of Very High Temperature Gas-Cooled Reactor (VHTR) in Korean Nuclear Hydrogen Development and Demonstration (NHDD) program. In this study, T0 reference temperature, J-R fracture resistance and Charpy impact properties were evaluated for commercial Grade 91 steel as preliminary tests for the selection of the RPV material for VHTR. The fracture toughness of the modified 9Cr-1Mo steel was compared with those of SA508-Gr.3. The objective of this study was to obtain pre-irradiation fracture toughness properties of modified 9Cr-1Mo steel as reference data for the radiation effects investigation. The results are as follows. Charpy impact properties of the modified 9Cr-1Mo steel were similar to those of SA508-Gr.3. T0 reference temperatures were measured as -67.7 deg C and -72.4 deg C from the tests with standard PCVN (pre-cracked Charpy V-notch) and half sized PCVN specimens respectively, which were similar to results for SA508-Gr.3. The K{sub Jc} values of modified 9Cr-1Mo with test temperatures are successfully expressed with the Master Curve. The J-R fracture resistance of modified 9Cr-1Mo steel at room temperature was almost the same as that of SA508-Gr.3. On the other hand it was a little bit higher at an elevated temperature. (authors)

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

    DOE PAGESBeta

    Timokhina, Ilana B.; Miller, Michael K.; Beladi, Hossein; Hodgson, Peter D.

    2016-03-03

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

  12. 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.

  13. 55Fe effect on enhancing ferritic steel He/dpa ratio in fission reactor irradiations to simulate fusion conditions

    SciTech Connect

    Liu, Haibo; Abdou, Mohamed A.; Greenwood, Lawrence R.

    2013-11-01

    How to increase the ferritic steel He(appm)/dpa ratio in a fission reactor neutron spectrum is an important question for fusion reactor material testing. An early experiment showed that the accelerated He(appm)/dpa ratio of about 2.3 was achieved for 96% enriched 54Fe in iron with 458.2 effective full power days (EFPD) irradiation in the High Flux Isotope Reactor (HFIR), ORNL. Greenwood suggested that the transmutation produced 55Fe has a thermal neutron helium production cross section which may have an effect on this result. In the current work, the ferritic steel He(appm)/dpa ratio is studied in the neutron spectrum of HFIR with 55Fe thermal neutron helium production taken into account. The available ENDF-b format 55Fe incident neutron cross section file from TENDL, Netherlands, is first input into the calculation model. A benchmark calculation for the same sample as used in the aforementioned experiment was used to adjust and evaluate the TENDL 55Fe (n, a) cross section values. The analysis shows a decrease of a factor of 6700 for the TENDL 55Fe (n, a) cross section in the intermediate and low energy regions is required in order to fit the experimental results. The best fit to the cross section value at thermal neutron energy is about 27 mb. With the adjusted 55Fe (n, a) cross sections, calculation show that the 54Fe and 55Fe isotopes can be enriched by the isotopic tailoring technique in a ferritic steel sample irradiated in HFIR to significantly enhance the helium production rate. The results show that a 70% enriched 54Fe and 30% enriched 55Fe ferritic steel sample would produce a He(appm)/dpa ratio of about 13 initially in the HFIR peripheral target position (PTP). After one year irradiation, the ratio decreases to about 10. This new calculation can be used to guide future isotopic tailoring experiments designed to increase the He(appm)/dpa ratio in fission reactors. A benchmark experiment is suggested to be performed to evaluate the 55Fe (n, a) cross section

  14. The effect of chloride ions on the corroded surface layer of 00Cr22Ni5Mo3N duplex stainless steel under cavitation.

    PubMed

    Wan, Tong; Xiao, Ning; Shen, Hanjie; Yong, Xingyue

    2016-11-01

    The effects of Cl(-) on the corroded surface layer of 00Cr22Ni5Mo3N duplex stainless steel under cavitation in chloride solutions were investigated using nanoindentation in conjunction with XRD and XPS. The results demonstrate that Cl(-) had a strong effect on the nano-mechanical properties of the corroded surface layer under cavitation, and there was a threshold Cl(-) concentration. Furthermore, a close relationship between the nano-mechanical properties and the cavitation corrosion resistance of 00Cr22Ni5Mo3N duplex stainless steel was observed. The degradation of the nano-mechanical properties of the corroded surface layer was accelerated by the synergistic effect between cavitation erosion and corrosion. A key factor was the adsorption of Cl(-), which caused a preferential dissolution of the ferrous oxides in the passive film layer on the corroded surface layer. Cavitation further promoted the preferential dissolution of the ferrous oxides in the passive film layer. Simultaneously, cavitation accelerated the erosion of the ferrite in the corroded surface layer, resulting in the degradation of the nano-mechanical properties of the corroded surface layer on 00Cr22Ni5Mo3N duplex stainless steel under cavitation. PMID:27245950

  15. Mechanical Properties and Microstructures of the HAZs of 11Cr F/M Steel for Gen-IV Nuclear Power Station

    NASA Astrophysics Data System (ADS)

    Li, Yongkui; Wang, Jian; Lu, Shanping; Rong, Lijian; Li, Dianzhong

    2015-02-01

    The weldability of a newly developed 11Cr ferritic/martensitic (F/M) steel to be used in Pb-Bi liquid cooled ADS for the fourth generation nuclear power station was studied by experiments and numerical simulation. In this work, an appropriate method for obtaining simulated heat-affected zones (HAZs) was developed. HAZs, including CG-HAZ, FG-HAZ, and IC-HAZ, were successfully simulated by Gleeble at heating rates of 209, 176, and 149 °C/s and peak temperatures of 1314, 1138, and 998 °C, respectively. Results of tension and impact tests indicated that the simulated HAZs had much higher strength and poorer toughness than the base metal. The poor toughness is caused by high carbon, silicon contents, and quenched martensitic microstructures. The tempering treatment is necessary for the developed steel before application in nuclear reactor.

  16. Microstructural Study Of Fusion Welds in 304L and 21Cr-6Ni-9Mn Stainless Steels (U)

    SciTech Connect

    MICHAEL, TOSTEN

    2005-03-01

    Light-optical and transmission electron microscopy (TEM) have been employed to characterize the microstructures of a series of fusion welds made on 304L and 21-6-9 stainless steels. The materials investigated in this study included high-energy-rate-forged 304L, conventionally forged 21-6-9, and 304L weld critical plate (higher ferrite potential). The weld critical plate contained an electron beam weld (no filler wire) while other specimens were welded with various combinations of 308L, 309L modified (MOD) and 312 MOD stainless steel filler wires to produce samples with a range of delta ferrite contents (4 to 33 percent) in the resulting welds. TEM specimens were prepared from broken arc-shaped, mechanical property test specimens that had been used to measure fracture toughness of the fusion welds. Specimens were prepared from regions of the weld heat-affected zones as well as from areas within the weld metal, including areas close to the fracture surface (plastically deformed regions). The observed microstructures varied according to the amount of ferrite in each weld. At the lowest ferrite levels the microstructure consisted of austenite and skeletal ferrite with austenite being the majority (matrix) phase. At intermediate levels of ferrite, lathy austenite/ferrite was observed and the ferrite became continuous throughout the specimens examined. In the weld with the most ferrite, many austenite morphologies were observed and ferrite was the matrix phase. Closest to the fracture surface an increase in dislocation density in both the ferrite and austenite were observed in all welds. Deformation twinning was also observed in the austenite. Many of the welds contained a large number of non-metallic inclusions (oxide particles) which most likely originated from impurities in the weld wires.

  17. Corrosion resistance of duplex and gradient CrN x coated H13 steel

    NASA Astrophysics Data System (ADS)

    Zhou, Q. G.; Bai, X. D.; Chen, X. W.; Peng, D. Q.; Ling, Y. H.; Wang, D. R.

    2003-04-01

    The electrochemical behavior of H13 steel coated with duplex and gradient CrN x coatings deposited by cathodic arc deposition has been studied. The substrate material was coated with CrN by cathodic arc deposition technique. Duplex layers of CrN x, which normally include an interlayer approximately 100-200 nm of Cr under the main CrN coating, were prepared; gradient CrN x coating were produced with continuous elevated nitrogen pressure. The X-ray photoelectron spectroscopy (XPS) was applied to characterize the chemical composition, and the glancing angle X-ray diffraction (GAXRD) was used to examine the crystallographic structure. The potentiodynamic polarization was examined by Zahner IM6e electrochemical workstation in a 0.5 M H 2SO 4 solution at ambient temperature, and the corrosive surface was detected by scanning electron microscopy (SEM). It was shown that the gradient coating could enhance the corrosion performance of CrN x coated H13 steel. The corrosion resistance improvement was not only attributed to the increase in thickness, but also to the internal microstructure and phase composition. Gradient CrN x coating produced in this work was proved to be particularly promising in terms of corrosion resistance, owing to its incontinuous pinholes and different composition: Cr, Cr 2N in inner part and CrN in surface. The results showed that the gradient coating had an improved electrochemical performance than duplex CrN coating.

  18. Effect of Tempering and Strain on Decomposition of Metastable Austenite in X210CrW12 Thixo-Cast Steel

    NASA Astrophysics Data System (ADS)

    Rogal, Ł.; Bonarski, J. T.; Bobrowski, P.

    2016-03-01

    Thixoforming of hot rolled X210CrW12tool steel led to the formation of globular austenitic grains (82.4 vol.%) surrounded by eutectic mixture (α-Fe and M7C3 carbides). The thixo-cast steel reached compression strength 4.8 GPa at plastic strain 34%. The analysis of pole figures after deformation indicated distinct texturization of microstructure in comparison with undeformed steel. Main texture components for austenite were {101}, <010>, while ferrite did not reveal clearly formed orientation. DSC analysis confirmed that austenitic structure in the X210CrW12 steel was metastable and temperature of decomposition depended on the strain applied at 634 °C for the un-deformed sample and at 599 °C for sample compressed up to 4.8 GPa. Discontinuous transformation of austenite into perlite, that started mainly at grain boundaries and proceeded to the center, was the predominant mechanism responsible for the decomposition of globular grains in thixoformed X210CrW12 steel. The decomposition caused by tempering of supersaturated and severely strained steel led to obtaining characteristic product of transformation of higher hardness in comparison with only tempered sample. In the deformed sample the reaction started on slip bands and twins which revealed high density of defects, promoting precipitation of carbides, followed by local depletion in carbon as a result of α'- Fe formation. In contrast to non-deformed state they covered the area of grains. Two fronts of reaction α-Fe plate +M3C → mixture of α-Fe and M7C3 carbides were also observed.

  19. Release of helium from irradiation damage in Fe?9Cr ferritic alloy

    NASA Astrophysics Data System (ADS)

    Ono, K.; Arakawa, K.; Shibasaki, H.; Kurata, H.; Nakamichi, I.; Yoshida, N.

    2004-08-01

    Thermal desorption of helium from Fe-9Cr and pure Fe which were irradiated with 5 keV He + ions at 85 or 473 K have been studied by thermal desorption spectrometry (TDS) at temperatures from room temperature to 1270 K and related microstructure changes by TEM. It is found that five TDS peaks appear in Fe-9Cr specimen and these peaks are well correlated with microstructure changes. From these results, the five peaks I Cr, II Cr, III Cr, IV Cr and V Cr may be attributed to release of trapped helium atoms by the break-up of vacancy-helium-self-interstitial atom complexes or very tiny loops, glide to the specimen surface or coalescence of interstitial type dislocation loops, shrinkage of dislocation loops, bubble migration to the specimen surface and α-γ phase transformation, respectively. Precipitation of Cr around the loops and bubbles in Fe-9Cr is revealed by STEM-EELS and this could shift the related TDS peaks to higher temperatures.

  20. Annealing effects on the microstructure and mechanical properties of hot-rolled 14Cr-ODS steel

    NASA Astrophysics Data System (ADS)

    Gao, R.; Zhang, T.; Ding, H. L.; Jiang, Y.; Wang, X. P.; Fang, Q. F.; Liu, C. S.

    2015-10-01

    The oxide dispersion strengthened ferritic steels with nominal composition (weight percent) of Fe-14Cr-2W-0.5Ti-0.06Si-0.2V-0.1Mn-0.05Ta-0.03C-0.3Y2O3 were fabricated by sol-gel method, mechanical alloying, and hot isostatic pressing techniques. The evolution of microstructure and mechanical properties of the hot-rolled specimens with heat treatment was investigated. Tensile strength and hardness of hot-rolled ODS steel are significantly enhanced due to the formation of mechanical twins and high density dislocations. Uniformly dispersed oxide particles (10-40 nm) and fine-grained structure (200-400 nm) are responsible for the superior mechanical properties of the hot-rolled specimen annealed between 650 °C and 850 °C. With further increasing annealing temperature, the grain size of the hot-rolled specimens increases while the size of oxide particles decreases, which leads to lower strength and hardness but better ductility. The tensile strength and total elongation of samples in the rolling direction are higher than those in the transverse direction after the same treatments owing to the grain anisotropy induced by the large mechanical deformation.