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Sample records for ods 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. 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.

  3. 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.

  4. 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.

  5. 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.

  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. 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.

  8. 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.

  9. 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.

  10. 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.

  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. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  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. 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.

  5. 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.

  6. 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.

  7. 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.

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

    PubMed

    Klimiankou, M; Lindau, R; Möslang, A

    2005-01-01

    Oxide-dispersion-strengthened (ODS) ferritic-martensitic steels with yttrium oxide (Y(2)O(3)) have been produced by mechanical alloying and hot isostatic pressing for use as advanced material in fusion power reactors. Argon gas, usually widely used as inert gas during mechanical alloying, was surprisingly detected in the nanodispersion-strengthened materials. Energy-filtered transmission electron microscopy (EFTEM) and electron energy loss spectroscopy (EELS) led to the following results: (i) chemical composition of ODS particles, (ii) voids with typical diameters of 1-6 nm are formed in the matrix, (iii) these voids are filled with Ar gas, and (iv) the high-density nanosized ODS particles serve as trapping centers for the Ar bubbles. The Ar L(3,2) energy loss edge at 245 eV as well as the absorption features of the ODS particle elements were identified in the EELS spectrum. The energy resolution in the EEL spectrum of about 1.0 eV allows to identify the electronic structure of the ODS particles. PMID:15582472

  9. 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.

  10. Joining Techniques for Ferritic ODS Alloys

    SciTech Connect

    V.G. Krishnardula; V.G. Krishnardula; D.E. Clark; T.C. Totemeier

    2005-06-01

    This report presents results of research on advanced joining techniques for ferritic oxide-dispersion strengthened alloys MA956 and PM2000. The joining techniques studied were resistance pressure welding (also known as pressure forge welding), transient liquid phase bonding, and diffusion bonding. All techniques were shown to produce sound joints in fine-grained, unrecrystallized alloys. Post-bond heat treatment to produce a coarse-grained, recrystallized microstructure resulted in grain growth across the bondline for transient liquid phase and diffusion bonds, giving microstructures essentially identical to that of the parent alloy in the recrystallized condition. The effects of bond orientation, boron interlayer thickness, and bonding parameters are discussed for transient liquid phase and diffusion bonding. The report concludes with a brief discussion of ODS joining techniques and their applicability to GEN IV reactor systems.

  11. Investigation on different oxides as candidates for nano-sized ODS particles in reduced-activation ferritic (RAF) steels

    NASA Astrophysics Data System (ADS)

    Hoffmann, Jan; Rieth, Michael; Lindau, Rainer; Klimenkov, Michael; Möslang, Anton; Sandim, Hugo Ricardo Zschommler

    2013-11-01

    Future generation reactor concepts are based on materials that can stand higher temperatures and higher neutron doses in corrosive environments. Oxide dispersion strengthened steels with chromium contents ranging from 9 to 14 wt.% - produced by mechanical alloying - are typical candidate materials for future structural materials in fission and fusion power plants.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Ion-induced swelling of ODS ferritic alloy MA957 tubing to 500 dpa

    NASA Astrophysics Data System (ADS)

    Toloczko, M. B.; Garner, F. A.; Voyevodin, V. N.; Bryk, V. V.; Borodin, O. V.; Mel'nychenko, V. V.; Kalchenko, A. S.

    2014-10-01

    In order to study the potential swelling behavior of the ODS ferritic alloy MA957 at very high dpa levels, specimens were prepared from pressurized tubes that were unirradiated archives of tubes previously irradiated in FFTF to doses as high as 110 dpa. These unirradiated specimens were irradiated with 1.8 MeV Cr+ ions to doses ranging from 100 to 500 dpa and examined by transmission electron microscopy. No co-injection of helium or hydrogen was employed. It was shown that compared to several tempered ferritic/martensitic steels irradiated in the same facility, these tubes were rather resistant to void swelling, reaching a maximum value of only 4.5% at 500 dpa and 450 °C. In this fine-grained material, the distribution of swelling was strongly influenced by the presence of void denuded zones along the grain boundaries.

  18. Ion-induced swelling of ODS ferritic alloy MA957 tubing to 500 dpa

    SciTech Connect

    Toloczko, Mychailo B.; Garner, F. A.; Voyevodin, V.; Bryk, V. V.; Borodin, O. V.; Melnichenko, V. V.; Kalchenko, A. S.

    2014-10-01

    In order to study the potential swelling behavior of the ODS ferritic alloy MA957 at very high dpa levels, specimens were prepared from pressurized tubes that were unirradiated archives of tubes previously irradiated in FFTF to doses as high at 110 dpa. These unirradiated specimens were irradiated with 1.8 MeV Cr+ ions to doses ranging from 100 to 500 dpa and examined by transmission electron microscopy. No coinjection of helium or hydrogen was employed. It was shown that compared to several ferritic/martensitic steels irradiated in the same facility, these tubes were rather resistant to void swelling, reaching a maximum value of only 4.5% at 500 dpa and 450°C. In this fine-grained material, the distribution of swelling was strongly influenced by the presence of void denuded zones along the grain boundaries.

  19. On the Role of Alloy Composition and Sintering Parameters in the Bimodal Grain Size Distribution and Mechanical Properties of ODS Ferritic Steels

    NASA Astrophysics Data System (ADS)

    García-Junceda, Andrea; Campos, Mónica; García-Rodríguez, Nerea; Torralba, José Manuel

    2016-04-01

    A sintered 14Cr-5Al-3W oxide dispersion strengthened steel was produced by mechanical alloying and consolidated by field-assisted hot pressing. First, a nanostructured powder was developed thanks to the high-energy milling used for introducing 0.4Ti-0.25Y2O3-0.6ZrO2 into the prealloyed Fe-Cr-Al-W powder, and then the processed powders were consolidated under a low diffusive technique to better retain the microstructure inherited from milling. The effect of the addition of zirconia and of the pressure applied during sintering on the final bimodal grain microstructure and mechanical properties is assessed. Both parameters are responsible for the refinement of the microstructure by increasing the volume fraction of the ultrafine grains (0 to 400 nm), leading to an enhancement of the mechanical properties, such as the microhardness and tensile strength.

  20. 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.

  1. 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.

  2. 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.

  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. 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.

  5. ODS steel raw material local structure analysis using X-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Cintins, A.; Anspoks, A.; Purans, J.; Kuzmin, A.; Timoshenko, J.; Vladimirov, P.; Gräning, T.; Hoffmann, J.

    2015-03-01

    Oxide dispersion strengthened (ODS) steels are promising materials for fusion power reactors, concentrated solar power plants, jet engines, chemical reactors as well as for hydrogen production from thermolysis of water. In this study we used X-ray absorption spectroscopy at the Fe and Cr K-edges as a tool to get insight into the local structure of ferritic and austenitic ODS steels around Fe and Cr atoms and its transformation during mechanical alloying process. Using the analysis of X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) we found that for austenitic samples a transformation of ferritic steel to austenitic steel is detectable after 10 hours of milling and proceeds till 40 hours of milling; only small amount of a-phase remains after 80 hours of milling. We found that the Cr K-edge EXAFS can be used to observe distortions inside the material and to get an impression on the formation of chromium clusters. In-situ EXAFS experiments offer a reliable method to investigate the ferritic to austenitic transformation.

  6. 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.

  7. Long-term high temperature oxidation behavior of ODS ferritics

    NASA Astrophysics Data System (ADS)

    Pint, B. A.; Wright, I. G.

    2002-12-01

    Four oxide dispersion strengthened Fe-(13-14 at.%) Cr ferritic compositions were exposed in air and air with 10 vol.% water vapor for up to 10 000 h at 700-1100 °C. At 700-800 °C in air, the reaction rates were very low for all of the alloys compared to stainless steels. At 900 °C, a dispersion of Y 2O 3, compared to Al 2O 3, showed a distinct benefit in improving the oxidation resistance, due to a reactive element effect. However, failure occurred after 7000 h at 900 °C when only 13% Cr was present. The absence of Ti and W in one alloy appeared to result in a thinner reaction product after oxidation at 800 °C. One composition was exposed in 10 vol.% water vapor at 800 and 900 °C and in air at 1000 and 1100 °C. Under both of these conditions, there was a significant increase in the rates of oxidation. With the relatively low Cr contents in these alloys, their corrosion-limited operating temperature in air is near 900 °C.

  8. 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.

  9. 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.

  10. Optimization of the chemical composition and manufacturing route for ODS RAF steels for fusion reactor application

    NASA Astrophysics Data System (ADS)

    Oksiuta, Z.; Baluc, N.

    2009-05-01

    As the upper temperature for use of reduced activation ferritic/martensitic steels is presently limited by a drop in mechanical strength at about 550 °C, Europe, Japan and the US are actively researching steels with high strength at higher operating temperatures, mainly using stable oxide dispersion. In addition, the numerous interfaces between matrix and oxide particles are expected to act as sinks for the irradiation-induced defects. The main R&D activities aim at finding a compromise between good tensile and creep strength and sufficient ductility, especially in terms of fracture toughness. Oxide dispersion strengthened (ODS) reduced activation ferritic (RAF) steels appear as promising materials for application in fusion power reactors up to about 750 °C. Six different ODS RAF steels, with compositions of Fe-(12-14)Cr-2W-(0.1-0.3-0.5)Ti-0.3Y2O3 (in wt%), were produced by powder metallurgy techniques, including mechanical alloying, canning and degassing of the milled powders and compaction of the powders by hot isostatic pressing, using various devices and conditions. The materials have been characterized in terms of microstructure and mechanical properties. The results have been analysed in terms of optimal chemical composition and manufacturing conditions. In particular, it was found that the composition of the materials should lie in the range Fe-14Cr-2W-(0.3-0.4)Ti-(0.25-0.3)Y2O3, as 14Cr ODS RAF steels exhibit higher tensile strength and better Charpy impact properties and are more stable than 12Cr materials (no risk of martensitic transformation), while materials with 0.5% Ti or more should not be further investigated, due to potential embrittlement by large TiO2 particles.

  11. 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

  12. Effects of heat treatment conditions on the microstructure and impact properties of EUROFER 97 ODS steel

    NASA Astrophysics Data System (ADS)

    Di Martino, S. F.; Faulkner, R. G.; Riddle, N. B.; Monge, M. A.; Munoz, A.

    2011-12-01

    Probably the most important range of materials to consider for the blanket material in the tokamak design for fusion reactors such as ITER and DEMO is the high alloy Fe9Cr oxide dispersion strengthened (ODS) ferritic steels. These steels possess exceptional thermal conductivity and low thermal expansion while being strongly resistant to void swelling. Their main drawback is the high ductile-to-brittle transition temperature (DBTT), particularly in the ODS versions of the material. This paper describes attempts that are being made to reduce this DBTT in as yet unirradiated materials by a novel heat treatment procedure. The principle behind this approach is that low DBTT in the unirradiated materials will lead to relatively low DBTT even in He-containing material that has been irradiated with fusion blanket-type irradiations. New batches of high alloy Fe9Cr ODS (EUROFER) ferritic steel have been produced by a powder metallurgical route, and relatively homogeneous material has been produced by a hot isostatic pressing procedure. Mini-Charpy test specimens were made from materials that had been subjected to a matrix of heat treatments designed to show up variations in solution treatment (ST) temperature, cooling rate from the ST temperature and tempering treatment. The initial DBTT was in the range 150-200 °C. Extremely interesting results have been obtained. DBTT downward shifts of up to 200 °C have been observed by using a high 1300 °C ST temperature and a low cooling rate. The paper goes on to describe the microstructure of this material, and discusses the possible microstructural factors needed to produce these very high DBTT downward shifts. Low dissolved carbon and higher proportions of low-angle grain boundaries seem to provide the key to the understanding of the alloy behaviour.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-09-01

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

  20. Friction Stir Welding of ODS and RAFM Steels

    NASA Astrophysics Data System (ADS)

    Yu, Zhenzhen; Feng, Zhili; Hoelzer, David; Tan, Lizhen; Sokolov, Mikhail A.

    2015-09-01

    Advanced structural materials such as oxide dispersion strengthened steels and reduced-activation ferritic/martensitic steels are desired in fusion reactors as primary candidate materials for first wall and blanket structures, due to their excellent radiation and high-temperature creep resistance. However, their poor fusion weldability has been the major technical challenge limiting practical applications. For this reason, solid-state friction stir welding (FSW) has been considered for such applications. In this work, the effect of FSW parameters on joining similar and dissimilar advanced structural steels was investigated. Scanning electron microscopy and electron backscatter diffraction methods were used to reveal the effects of FSW on grain size, micro-texture distribution, and phase stability. Hardness mapping was performed to evaluate mechanical properties. Post weld heat treatment was also performed to tailor the microstructure in the welds in order to match the weld zone mechanical properties to the base material.

  1. Friction Stir Welding of ODS and RAFM Steels

    DOE PAGESBeta

    Yu, Zhenzhen; Feng, Zhili; Hoelzer, David; Tan, Lizhen; Sokolov, Mikhail A.

    2015-09-14

    Advanced structural materials such as oxide dispersion strengthened steels and reduced-activation ferritic/martensitic steels are desired in fusion reactors as primary candidate materials for first wall and blanket structures, due to their excellent radiation and high-temperature creep resistance. However, their poor fusion weldability has been the major technical challenge limiting practical applications. For this reason, solid-state friction stir welding (FSW) has been considered for such applications. In this paper, the effect of FSW parameters on joining similar and dissimilar advanced structural steels was investigated. Scanning electron microscopy and electron backscatter diffraction methods were used to reveal the effects of FSW onmore » grain size, micro-texture distribution, and phase stability. Hardness mapping was performed to evaluate mechanical properties. Finally, post weld heat treatment was also performed to tailor the microstructure in the welds in order to match the weld zone mechanical properties to the base material.« less

  2. Friction Stir Welding of ODS and RAFM Steels

    SciTech Connect

    Yu, Zhenzhen; Feng, Zhili; Hoelzer, David; Tan, Lizhen; Sokolov, Mikhail A.

    2015-09-14

    Advanced structural materials such as oxide dispersion strengthened steels and reduced-activation ferritic/martensitic steels are desired in fusion reactors as primary candidate materials for first wall and blanket structures, due to their excellent radiation and high-temperature creep resistance. However, their poor fusion weldability has been the major technical challenge limiting practical applications. For this reason, solid-state friction stir welding (FSW) has been considered for such applications. In this paper, the effect of FSW parameters on joining similar and dissimilar advanced structural steels was investigated. Scanning electron microscopy and electron backscatter diffraction methods were used to reveal the effects of FSW on grain size, micro-texture distribution, and phase stability. Hardness mapping was performed to evaluate mechanical properties. Finally, post weld heat treatment was also performed to tailor the microstructure in the welds in order to match the weld zone mechanical properties to the base material.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  9. 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.

  10. 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.

  11. 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.

  12. Past research and fabrication conducted at SCK•CEN on ferritic ODS alloys used as cladding for FBR's fuel pins

    NASA Astrophysics Data System (ADS)

    De Bremaecker, Anne

    2012-09-01

    In the 1960s in the frame of the sodium-cooled fast breeders, SCK•CEN decided to develop claddings made with ferritic stainless materials because of their specific properties, namely a higher thermal conductivity, a lower thermal expansion, a lower tendency to He-embrittlement, and a lower swelling than the austenitic stainless steels. To enhance their lower creep resistance at 650-700 °C arose the idea to strengthen the microstructure by oxide dispersions. This was the starting point of an ambitious programme where both the matrix and the dispersions were optimized. A purely ferritic 13 wt% Cr matrix was selected and its mechanical strength was improved through addition of ferritizing elements. Results of tensile and stress-rupture tests showed that Ti and Mo were the most beneficial elements, partly because of the chi-phase precipitation. In 1973 the optimized matrix composition was Fe-13Cr-3.5Ti-2Mo. To reach creep properties similar to those of AISI 316, different dispersions and methods were tested: internal oxidation (that was not conclusive), and the direct mixing of metallic and oxide powders (Al2O3, MgO, ZrO2, TiO2, ZrSiO4) followed by pressing, sintering, and extrusion. The compression and extrusion parameters were determined: extrusion as hollow at 1050 °C, solution annealing at 1050 °C/15 min, cleaning, cold drawing to the final dimensions with intermediate annealings at 1050 °C, final annealing at 1050 °C, straightening and final aging at 800 °C. The choice of titania and yttria powders and their concentrations were finalized on the basis of their out-of-pile and in-pile creep and tensile strength. As soon as a resistance butt welding machine was developed and installed in a glove-box, fuel segments with PuO2 were loaded in the Belgian MTR BR2. The fabrication parameters were continuously optimized: milling and beating, lubrication, cold drawing (partial and final reduction rates, temperature, duration, atmosphere and furnace). Specific non

  13. Influence of hot rolling and high speed hydrostatic extrusion on the microstructure and mechanical properties of an ODS RAF steel

    NASA Astrophysics Data System (ADS)

    Oksiuta, Z.; Lewandowska, M.; Kurzydlowski, K. J.; Baluc, N.

    2011-02-01

    An argon gas atomized, pre-alloyed Fe-14Cr-2W-0.3Ti (wt.%) reduced activation ferritic (RAF) steel powder was mechanically alloyed with 0.3wt.% Y 2O 3 nano-particles in an attritor ball mill and consolidated by hot isostatic pressing at 1150 °C under a pressure of 200 MPa for 3 h. In the aim to improve its mechanical properties the ODS steel was then submitted to a thermo-mechanical treatment (TMT): hot rolling (HR) at 850 °C or high speed hydrostatic extrusion (HSHE) at 900 °C, followed by heat treatment (HT). Transmission electron microscopy (TEM) observations of the ODS alloys after TMT and heat treatment revealed the presence of elongated grains in the longitudinal direction, with an average width of 8 μm and an average length of 75 μm, and equiaxed grains, a few microns in diameter, in the transverse direction. Two populations of oxide particles were observed by TEM: large Ti-Al-O particles, up to 250 nm in diameter, usually located at the grain boundaries and small Y-Ti-O nanoclusters, about 2.5 nm in diameter, uniformly distributed in the matrix. Charpy impact tests revealed that the HSHE material exhibits a larger upper shelf energy (5.8 J) than the HR material (2.9 J). The ductile-to-brittle transition temperature of both alloys is relatively high, in the range of 55-72 °C. Tensile mechanical properties of both ODS alloys were found satisfactory over the full range of investigated temperatures (23-750 °C). The HSHE material exhibits better tensile strength and ductility than the HR material. These results indicate that HSHE can be considered as a promising TMT method for improving the mechanical properties of ODS RAF steels.

  14. 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.

  15. 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)

  16. 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.

  17. 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.

  18. 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%).

  19. 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...

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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

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

    NASA Astrophysics Data System (ADS)

    Miao, Yinbin

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

  7. Progress in the R and D Project on Oxide Dispersion Strengthened and Precipitation Hardened Ferritic Steels for Sodium Cooled Fast Breeder Reactor Fuels

    SciTech Connect

    Kaito, Takeji; Ohtsuka, Satoshi; Inoue, Masaki

    2007-07-01

    High burnup capability of sodium cooled fast breeder reactor (SFR) fuels depends significantly on irradiation performance of their component materials. Japan Atomic Energy Agency (JAEA) has been developing oxide dispersion strengthened (ODS) ferritic steels and a precipitation hardened (PH) ferritic steel as the most prospective materials for fuel pin cladding and duct tubes, respectively. Technology for small-scale manufacturing is already established, and several hundreds of ODS steel cladding tubes and dozens of PH steel duct tubes were successfully produced. We will step forward to develop manufacturing technology for mass production to supply these steels for future SFR fuels. Mechanical properties of the products were examined by out-of-pile and in-pile tests including material irradiation tests in the experimental fast reactor JOYO and foreign fast reactors. The material strength standards (MSSs) were tentatively compiled in 2005 for ODS steels and in 1993 for PH steel. In order to upgrade the MSSs and to demonstrate high burnup capability of the materials, we will perform a series of irradiation tests in BOR-60 and JOYO until 2015 and contribute to design study for a demonstration SFR of which operation is expected after 2025. (authors)

  8. 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

  9. 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.

  10. 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)

  11. Hydrogen-induced crack nucleation in tensile testing of EUROFER 97 and ODS-EUROFER steels at elevated temperature

    NASA Astrophysics Data System (ADS)

    Malitckii, Evgenii; Yagodzinskyy, Yuriy; Hänninen, Hannu

    2015-11-01

    The effect of continuous hydrogen charging on tensile properties of EUROFER 97 and ODS-EUROFER steels was studied at room and elevated temperatures of 100 °C and 300 °C. The hydrogen effect decreases with increase of the temperature for ODS-EUROFER steel, while susceptibility to hydrogen of EUROFER 97 steel remains approximately the same at all testing temperatures. Continuous hydrogen charging results in a reduction of the grain boundary cohesion of the EUROFER 97 and ODS-EUROFER steels tested at RT. With increase of the testing temperature up to 300 °C EUROFER 97 steel exhibits relatively high amount of micro-cracks which agglomerate in sub-micrometer size cracks, while the hydrogen-induced intergranular crack nucleation in ODS-EUROFER steel is effectively suppressed. Possible mechanism of the hydrogen-induced crack nucleation and propagation under applied external stress is discussed.

  12. 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.

  13. Nanostructure evolution in ODS Eurofer steel under irradiation up to 32 dpa

    NASA Astrophysics Data System (ADS)

    Rogozhkin, S. V.; Orlov, N. N.; Aleev, A. A.; Zaluzhnyi, A. G.; Kozodaev, M. A.; Kuibeda, R. P.; Kulevoy, T. V.; Nikitin, A. A.; Chalykh, B. B.; Lindau, R.; Möslang, A.; Vladimirov, P.

    2015-01-01

    The nanostructure of the ODS Eurofer steel (9% CrWVTa + 0.5% Y2O3) has been studied after irradiation by iron ions to a damaging dose of 32 dpa. This steel in the initial state is characterized by the presence of a significant amount (˜1024 m-3) of nanosized (2-4 nm) clusters containing atoms of V, Y, O, and N. An analysis of the distribution of various chemical elements in the tested volumes has revealed variations in the composition of the matrix and of the nanosized clusters during irradiation. The data obtained were compared with the results for the ODS Eurofer steel subjected to reactor irradiation to a dose of 32 dpa.

  14. Corrosion behavior of a 14Cr-ODS steel in supercritical water

    NASA Astrophysics Data System (ADS)

    Hu, H. L.; Zhou, Z. J.; Liao, L.; Zhang, L. F.; Wang, M.; Li, S. F.; Ge, C. C.

    2013-06-01

    The corrosion behavior of a 14Cr-ODS steel in the supercritical water was investigated using a variety of characterization techniques. Compared with 316L austenitic steel, the 14Cr-ODS steel had better corrosion resistant property. As the increasing of the exposure time, the weight gain increased, but the corrosion rates decreased. The curve of weight gain as a function of time followed a parabolic law. The general weight gain was 0.3476 mg/(dm2 h). A triple layer was observed which consisted of an outer layer, an inner layer and a diffusion layer. The outer layer was iron rich and contained Fe3O4, on which pores were observed. The inner layer and diffusion layer contained mainly (Fe,Cr2)O4. The oxidation mechanism was also discussed.

  15. TEM characterization of simultaneous triple ion implanted ODS Fe12Cr

    NASA Astrophysics Data System (ADS)

    de Castro, Vanessa; Briceno, Martha; Lozano-Perez, Sergio; Trocellier, Patrick; Roberts, Steve G.; Pareja, Ramiro

    2014-12-01

    Understanding the behavior of oxide dispersion strengthened (ODS) ferritic/martensitic steels under irradiation is vital in the design of advanced fusion reactors. In this work, a simultaneous triple ion implanted ODS Fe12Cr steel was investigated by transmission electron microscopy in order to determine the effect of irradiation on the grain and dislocation structures, oxide nanoparticles and other secondary phases present in the steel. The ODS steel was irradiated at RT with Fe8+, He+ and H+ at the JANNUS-Saclay facility to a damage of 4.4 dpa. Results show that ODS nanoparticles appear very stable under these irradiation conditions.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.''...

  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. 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.

  5. 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.

  6. 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

  7. 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.

  8. 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.

  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. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

  12. 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.

  13. 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

  14. 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.

  15. 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.

  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. HRTEM Study of Oxide Nanoparticles in 16Cr-4Al-2W-0.3Ti-0.3Y2O3 ODS Steel

    SciTech Connect

    Hsiung, L; Fluss, M; Wall, M; Kimura, A

    2009-11-18

    Crystal and interfacial structures of oxide nanoparticles in 16Cr-4Al-2W-0.3Ti-0.3Y{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 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 lead us to propose three-stage mechanisms to rationalize the formation of oxide nanoparticles containing core/shell structures in as-fabricated ODS steels.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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})].

  4. 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.

  5. Quantitative measurement of argon inside of nano-sized bubbles in ODS steels

    NASA Astrophysics Data System (ADS)

    Klimenkov, M.

    2011-04-01

    Quantitative analysis of Ar gas in nano-sized bubbles in ODS steel was performed using spatially resolved energy-dispersive X-ray spectroscopy. The Ar Kα line was quantified and used for calculation of Ar the concentration (atoms per nm 3) inside 4-38 nm large bubbles. The Ar concentration and pressure inside bubbles were found to depend on the bubble size. The results were compared with a known equilibrium pressure model developed for calculation of He pressure inside nano-sized bubbles. Several investigations were performed to determine the stability of Ar bubbles in the thin TEM foil.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

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

    SciTech Connect

    Klueh, R.L.

    1996-12-31

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

  13. Influence of consolidation methods on the recrystallization kinetics of a Fe-14Cr based ODS steel

    NASA Astrophysics Data System (ADS)

    Dadé, M.; Malaplate, J.; Garnier, J.; De Geuser, F.; Lochet, N.; Deschamps, A.

    2016-04-01

    The recrystallization behavior during thermal annealing with or without prior cold work has been investigated in a 14%Cr ODS steel consolidated by two different methods, hot extrusion (HE) and hot isostatic pressing (HIP). We show that a 1400°C-1 h annealing induces an increase of the oxide nanoparticles radius from 1.3 to 3 nm, however the grain size remain stable despite a recovery of sub-grain boundaries for the hot extruded material. When pre-deformation is applied before annealing, almost full recrystallization can be achieved on the HE ODS steel. In this study, we show recrystallization after 40% cold deformation and annealing 30 min at 1450 °C together with coarsening of oxide particles. At lower temperature and higher pre-deformation (70%-1150 °C/30 min), we show that recrystallization can be achieved without change of the oxide size distribution. We show that due to a lower initial dislocation density, recrystallization is strongly delayed, by at least 250 °C, in the HIP material. Finally, we show that the evolution of the size of the oxide precipitates is controlled by the time and temperature of annealing and are independent on the pre-deformation and occurrence of recrystallization.

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. 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.

  19. 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

  20. 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

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Study of radiation damage in ODS steels by positron annihilation spectroscopy

    NASA Astrophysics Data System (ADS)

    Bartošová, I.; Bouhaddane, A.; Dománková, M.; Slugeň, V.; Wall, D.; Selim, F. A.

    2016-01-01

    Microstructure of various oxide-dispersion-strengthened (ODS) steels with 15% chromium content was studied in term of vacancy defects presence and their accumulation after defined irradiation treatment, respectively. Studied materials originated from Kyoto University and studied via IAEA collaborative project. Samples were characterized “as received” by positron annihilation lifetime spectroscopy and their microstructure was examined by transmission electron microscopy as well. Samples were afterwards irradiated in Washington State University Nuclear Radiation Center via a strong gamma source (6TBq). Damage induced by gamma irradiation was evaluated by positron lifetime measurements in emphasis on defect accumulation in the materials. We have demonstrated strong defect production induced by gamma irradiation which results from positron measurement data.

  7. Response of 9Cr-ODS Steel to Proton Irradiation at 400 °C

    SciTech Connect

    Jianchao He; Farong Wan; Kumar Sridharan; Todd R. Allen; A. Certain; Y. Q. Wu

    2014-09-01

    The stability of Y–Ti–O nanoclusters, dislocation structure, and grain boundary segregation in 9Cr-ODS steels has been investigated following proton irradiation at 400 °C with damage levels up to 3.7 dpa. A slight coarsening and a decrease in number density of nanoclusters were observed as a result of irradiation. The composition of nanoclusters was also observed to change with a slight increase of Y and Cr concentration in the nanoclusters following irradiation. Size, density, and composition of the nanoclusters were investigated as a function of nanocluster size, specifically classified to three groups. In addition to the changes in nanoclusters, dislocation loops were observed after irradiation. Finally, radiation-induced enrichment of Cr and depletion of W were observed at grain boundaries after irradiation.

  8. Corrosion property of 9Cr-ODS steel in nitric acid solution for spent nuclear fuel reprocessing

    SciTech Connect

    Takeuchi, M.; Koizumi, T.; Inoue, M.; Koyama, S.I.

    2013-07-01

    Corrosion tests of oxide dispersion strengthened with 9% Cr (9Cr-ODS) steel, which is one of the desirable materials for cladding tube of sodium-cooled fast reactors, in pure nitric acid solution, spent FBR fuel solution, and its simulated solution were performed to understand the corrosion behavior in a spent nuclear fuel reprocessing. In this study, the 9Cr-ODS steel with lower effective chromium content was evaluated to understand the corrosion behavior conservatively. As results, the tube-type specimens of the 9Cr-ODS steels suffered severe weight loss owing to active dissolution at the beginning of the immersion test in pure nitric acid solution in the range from 1 to 3.5 M. In contrast, the weight loss was decreased and they showed a stable corrosion in the higher nitric acid concentration, the dissolved FBR fuel solution, and its simulated solution by passivation. The corrosion rates of the 9Cr-ODS steel in the dissolved FBR fuel solution and its simulated solution were 1-2 mm/y and showed good agreement with each other. The passivation was caused by the shift of corrosion potential to noble side owing to increase in nitric acid concentration or oxidative ions in the dissolved FBR fuel solution and the simulated spent fuel solution. (authors)

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  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. 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

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Microstructure of HIPed and SPSed 9Cr-ODS steel and its effect on helium bubble formation

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    Two 9Cr-ODS steels with the same nominal composition were consolidated by hot isostatic pressing (HIP, named COS-1) and spark plasma sintering (SPS, named COS-2). Helium ions were implanted into COS-1, COS-2 and non-ODS Eurofer 97 steels up at 673 K. Microstructures before and after helium ion implantations were carefully characterized. The results show a bimodal grain size distribution in COS-2 and a more uniform grain size distribution in COS-1. Nanoscale clusters of GP-zone type Y-Ti-O and Y2Ti2O7 pyrochlore as well as large spinel Mn(Ti)Cr2O4 particles are all observed in the two ODS steels. The Y-Ti-enriched nano-oxides in COS-1 exhibit higher number density and smaller size than in COS-2. The Y-Ti-enriched nano-oxides in fine grains of COS-2 show higher number density and smaller size than that in coarse grains of COS-2. Nano-oxides effectively trap helium atoms and lead to the formation of high density and ultra-fine helium bubbles.

  14. Helium effects on creep properties of Fe-14CrWTi ODS steel at 650 °C

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    In the present paper, the effects of helium on creep properties of Fe-14CrWTi ODS steel were studied by in-beam and post He-implantation creep tests. In-situ creep was performed in an in-beam creep device under uniaxial tensile stresses from 350 to 370 MPa during homogeneous helium implantation. Helium ions of energies varying from 0 to 25 MeV were implanted at a rate of 6 × 10-3 appm/s (corresponding to a displacement dose rate of 1.5 × 10-6 dpa/s). The average temperature was controlled to 650 °C within ±2 °C. In addition, post He-implantation creep tests were conducted at 650 °C as well. Subsequently, fracture surfaces and helium bubble evolution were studied in detail by SEM and TEM observations, respectively. Preliminary creep results show that helium slightly shortens the creep life time of ODS steel at 650 °C. Fracture surfaces of reference as well as implanted specimens, show areas with various grades of deformation. Areas of highest deformation can be interpreted as necking, while areas of low deformation show in helium implanted specimens a more granular structure. The results are discussed in terms of possible embrittlement of ODS steels by helium.

  15. Microstructure of HIPed and SPSed 9Cr-ODS steel and its effect on helium bubble formation

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    Two 9Cr-ODS steels with the same nominal composition were consolidated by hot isostatic pressing (HIP, named COS-1) and spark plasma sintering (SPS, named COS-2). Helium ions were implanted into COS-1, COS-2 and non-ODS Eurofer 97 steels up at 673 K. Microstructures before and after helium ion implantations were carefully characterized. The results show a bimodal grain size distribution in COS-2 and a more uniform grain size distribution in COS-1. Nanoscale clusters of GP-zone type Y-Ti-O and Y2Ti2O7 pyrochlore as well as large spinel Mn(Ti)Cr2O4 particles are all observed in the two ODS steels. The Y-Ti-enriched nano-oxides in COS-1 exhibit higher number density and smaller size than in COS-2. The Y-Ti-enriched nano-oxides in fine grains of COS-2 show higher number density and smaller size than that in coarse grains of COS-2. Nano-oxides effectively trap helium atoms and lead to the formation of high density and ultra-fine helium bubbles.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

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

    SciTech Connect

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

    2013-01-03

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

  2. 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.

  3. 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.

  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. 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.

  6. 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.

  7. 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.

  8. (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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Swift heavy ion tracks in Y2Ti2O7 nanoparticles in EP450 ODS steel

    NASA Astrophysics Data System (ADS)

    Skuratov, V. A.; Sohatsky, A. S.; O'Connell, J. H.; Kornieieva, K.; Nikitina, A. A.; Neethling, J. H.; Ageev, V. S.

    2015-01-01

    Structural changes induced by 1.2 MeV/amu xenon, krypton and argon ion irradiation in Y2Ti2O7 pyrochlore nanoparticles in EP450 ODS steel have been studied using high resolution transmission electron microscopy. It was found that diameters of amorphous latent tracks formed by Kr and Xe ions are in the range 3-7 nm when electronic stopping powers vary from 10 to 24 keV/nm. The threshold for track formation is estimated to be between 7.4 keV/nm and 9.7 keV/nm.

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  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. 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.

  18. Hot rolling and annealing effects on the microstructure and mechanical properties of ODS austenitic steel fabricated by electron beam selective melting

    NASA Astrophysics Data System (ADS)

    Gao, Rui; Ge, Wen-jun; Miao, Shu; Zhang, Tao; Wang, Xian-ping; Fang, Qian-feng

    2016-03-01

    The grain morphology, nano-oxide particles and mechanical properties of oxide dispersion strengthened (ODS)-316L austenitic steel synthesized by electron beam selective melting (EBSM) technique with different post-working processes, were explored in this study. The ODS-316L austenitic steel with superfine nano-sized oxide particles of 30-40 nm exhibits good tensile strength (412 MPa) and large total elongation (about 51%) due to the pinning effect of uniform distributed oxide particles on dislocations. After hot rolling, the specimen exhibits a higher tensile strength of 482 MPa, but the elongation decreases to 31.8% owing to the introduction of high-density dislocations. The subsequent heat treatment eliminates the grain defects induced by hot rolling and increases the randomly orientated grains, which further improves the strength and ductility of EBSM ODS-316L steel.

  19. 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...

  20. 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...

  1. 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...

  2. 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...

  3. 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.

  4. 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.

  5. Corrosion properties of oxide dispersion strengthened steels in super-critical water environment

    NASA Astrophysics Data System (ADS)

    Cho, H. S.; Kimura, A.; Ukai, S.; Fujiwara, M.

    2004-08-01

    The effects of alloying elements on corrosion resistance in super critical pressurized water (SCPW) have been investigated to develop corrosion resistant oxide dispersion strengthened (ODS) steels. Corrosion tests were performed in a SCPW (783 K, 25 MPa) environment. Weight gain was measured after exposure to the SCPW. For the improvement of corrosion-resistance, the effects of chromium, aluminum, and yttrium on the corrosion behavior were investigated. The 9-12 wt%Cr ODS steels showed almost similar corrosion behavior with the ordinary ferritic/martensitic steel in the SCPW. However, the addition of high chromium (>13 wt%) and aluminum (4.5 wt%) are very effective to suppress the corrosion in the SCPW. Anodic polarization experiments revealed that the passive current of the ODS steels are lower than the ordinary ferritic/martensitic steels. Addition of aluminum improves the Charpy impact property of the ODS steels.

  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. 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.

  8. 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.

  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. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  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. 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.

  20. 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.

  1. Atom probe characterization of nano-scaled features in irradiated ODS Eurofer steel

    NASA Astrophysics Data System (ADS)

    Rogozhkin, S. V.; Aleev, A. A.; Zaluzhnyi, A. G.; Nikitin, A. A.; Iskandarov, N. A.; Vladimirov, P.; Lindau, R.; Möslang, A.

    2011-02-01

    Our previous investigations of unirradiated ODS Eurofer by tomographic atom probe (TAP) revealed numerous nano-scaled features (nanoclusters) enriched in vanadium, yttrium and oxygen. In this work the effect of neutron irradiation on nanostructure behaviour of ODS Eurofer (9%-CrWVTa) was investigated. The irradiation was performed in the research reactor BOR-60 (Dimitrovgrad, Russia) where materials were irradiated at 330 °С to 32 dpa. TAP studies were performed on the needles prepared from parts of broken Charpy specimens. For all specimens except one, which was tested at 500 °C, the Charpy tests were performed at temperatures not exceeding the irradiation temperature. A high number density 2-4 × 10 24 m -3 of ultra fine 1-3 nm diameter nanoclusters enriched in yttrium, oxygen, manganese and chromium was observed in the irradiated state. The composition of detected clusters differs from that for unirradiated ODS Eurofer. It was observed in this work that after neutron irradiation vanadium atoms had left the clusters, moving from the core into solid solution. The concentrations of yttrium and oxygen in the matrix, as it was detected, increase several times under irradiation. In the samples tested at 500 °C both the number density of clusters and the yttrium concentration in the matrix decrease by a factor of two.

  2. 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.

  3. 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.

  4. 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.

  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. 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.

  7. 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

  8. 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.

  9. 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.

  10. 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.