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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. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-07-01

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

  4. Development of Oxide Dispersion Strengthened (ODS) Ferritic Steel Through Powder Forging

    NASA Astrophysics Data System (ADS)

    Kumar, Deepak; Prakash, Ujjwal; Dabhade, Vikram V.; Laha, K.; Sakthivel, T.

    2017-02-01

    Oxide dispersion strengthened (ODS) ferritic steels are candidates for cladding tubes in fast breeder nuclear reactors. In this study, an 18%Cr ODS ferritic steel was prepared through powder forging route. Elemental powders with a nominal composition of Fe-18Cr-2 W-0.2Ti (composition in wt.%) with 0 and 0.35% yttria were prepared by mechanical alloying in a Simoloyer attritor under argon atmosphere. The alloyed powders were heated in a mild steel can to 1473 K under flowing hydrogen atmosphere. The can was then hot forged. Steps of sealing, degassing and evacuation are eliminated by using powder forging. Heating ODS powder in hydrogen atmosphere ensures good bonding between alloy powders. A dense ODS alloy with an attractive combination of strength and ductility was obtained after re-forging. On testing at 973 K, a loss in ductility was observed in yttria-containing alloy. The strength and ductility increased with increase in strain rate at 973 K. Reasons for this are discussed. The ODS alloy exhibited a recrystallized microstructure which is difficult to achieve by extrusion. No prior particle boundaries were observed after forging. The forged compacts exhibited isotropic mechanical properties. It is suggested that powder forging may offer several advantages over the traditional extrusion/HIP routes for fabrication of ODS alloys.

  5. 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.

  6. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  8. 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.

  9. 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.

  10. 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.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

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

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

    NASA Astrophysics Data System (ADS)

    Bischoff, Jeremy

    Ferritic-martensitic and ODS alloys are primary candidates for application as cladding and structural material in Generation IV nuclear power plants, especially the supercritical water reactor. One of the main in-service degradation mechanisms for these alloys is uniform corrosion, thus this project focuses on understanding the oxidation behavior of these alloys in the supercritical water (SCW) environment. This understanding is acquired through the analysis of the oxide microstructure using microbeam synchrotron radiation diffraction and fluorescence associated with electron microscopy (both SEM and TEM). The microbeam synchrotron radiation diffraction and fluorescence technique provides unique microstructural data of the oxide. This technique simultaneously probes elemental and phase information step by step with a sub-micron spatial resolution throughout the oxide layers. Thus we were able to locate specific phases, such as Cr2O3, at specific locations in the oxide layer, mainly the interfaces. The electron microscopy complemented this analysis by imaging the oxide layers, to yield detailed information on the oxide morphology. All the alloys studied exhibited the same three-layer structure with an outer layer containing only Fe3O4, an inner layer containing a mixture of Fe3O4 and FeCr2O 4, and a diffusion layer containing a mixture of chromium-rich precipitates (Cr2O3 and FeCr2O4) and metal grains. By analyzing samples with various exposure times, we were able to follow the evolution of the oxide microstructure with exposure time. To obtain the corroded samples, several corrosion experiments were performed: some in supercritical water (at 500°C and 600°C) and one experiment in 500°C steam. The test in steam was undertaken to obtain more data points in the kinetic curves, because we thought the corrosion in steam and supercritical water at the same temperature would result in similar kinetics. This turned out not to be the case and the samples in supercritical

  14. 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.

  15. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-09-01

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

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. Articles comprising ferritic stainless steels

    SciTech Connect

    Rakowski, James M.

    2016-06-28

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

  4. Thermal helium desorption behavior in advanced ferritic steels

    NASA Astrophysics Data System (ADS)

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

    2005-02-01

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

  5. Creep constitutive equation of dual phase 9Cr-ODS steel

    NASA Astrophysics Data System (ADS)

    Sakasegawa, Hideo; Ukai, Shigeharu; Tamura, Manabu; Ohtsuka, Satoshi; Tanigawa, Hiroyasu; Ogiwara, Hiroyuki; Kohyama, Akira; Fujiwara, Masayuki

    2008-02-01

    9Cr-ODS (oxide dispersion strengthened) steels developed by JAEA (Japan Atomic Energy Agency) have superior creep properties compared with conventional heat resistant steels. The ODS steels can enormously contribute to practical applications of fast breeder reactors and more attractive fusion reactors. Key issues are developments of material processing procedures for mass production and creep life prediction methods in present R&D. In this study, formulation of creep constitutive equation was performed against the backdrop. The 9Cr-ODS steel displaying an excellent creep property is a dual phase steel. The ODS steel is strengthened by the δ ferrite which has a finer dispersion of oxide particles and shows a higher hardness than the α' martensite. The δ ferrite functions as a reinforcement in the dual phase 9Cr-ODS steel. Its creep behavior is very unique and cannot be interpreted by conventional theories of heat resistant steels. Alternative qualitative model of creep mechanism was formulated at the start of this study using the results of microstructural observations. Based on the alternative creep mechanism model, a novel creep constitutive equation was formulated using the exponential type creep equation extended by a law of mixture.

  6. Corrosion behavior of oxide dispersion strengthened ferritic steels in supercritical water

    NASA Astrophysics Data System (ADS)

    Gao, Wenhua; Guo, Xianglong; Shen, Zhao; Zhang, Lefu

    2017-04-01

    The corrosion resistance of three different Cr content oxide dispersion strengthened (ODS) ferritic steels in supercritical water (SCW) and their passive films formed on the surface have been investigated. The results show that the dissolved oxygen (DO) and chemical composition have significant influence on the corrosion behavior of the ODS ferritic steels. In 2000 ppb DO SCW at 650 °C, the 14Cr-4Al ODS steel forms a tri-layer oxide film and the surface morphologies have experienced four structures. For the tri-layer oxide film, the middle layer is mainly Fe-Cr spinel and the Al is gradually enriched in the inner layer.

  7. Transient liquid-phase bonding of ODS steels

    NASA Astrophysics Data System (ADS)

    Noto, H.; Ukai, S.; Hayashi, S.

    2011-10-01

    The use of transient liquid-phase bonding of 9CrODS steels using Fe-3B-2Si-0.5C filler was investigated for bonding temperature of 1180 °C and hold times of 0.5-4.0 h. The sequential process, consisting of isothermal melting, solidification and homogenization, was confirmed for bonding the 9CrODS steel. The precipitation of chromium boride found in 19CrODS steel is avoided in 9CrODS steel due to the lower Cr content. Silicon tends to be slightly enriched inside the bonding zone. Agglomeration and coarsening of Y 2O 3 particles in 9CrODS steel lead to softening inside the bonding zone formed by incipient melting of the foil bonding alloy, and in a diffusion affected zone (DAZ) adjacent to the bonding zone.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Influence of microstructure on impact properties of 9-18%Cr ODS steels for fusion/fission applications

    NASA Astrophysics Data System (ADS)

    Hadraba, H.; Fournier, B.; Stratil, L.; Malaplate, J.; Rouffié, A.-L.; Wident, P.; Ziolek, L.; Béchade, J.-L.

    2011-04-01

    The paper describes the influence of the microstructure (coming from the extrusion shape, the chemical composition and the thermo-mechanical treatments) of (9-18%)Cr-W-Ti-Y 2O 3 ODS steels on their impact fracture properties. The extrusion shape plays a major role on the impact properties, materials extruded as a rod present a higher upper shelf energy (USE) and a lower ductile to brittle transition temperature (DBTT) compared to materials extruded as plates. The DBTT for the non-recrystallized 14%Cr ferritic steels was shifted towards higher temperatures compared to the 9%Cr tempered ferritic-martensitic steel. Increasing the W and Ti content in 9%Cr tempered ferritic-martensitic ODS steel leads to a USE and a DBTT shifted towards higher energies and higher temperatures respectively. Increasing the yttria content leads to a drop of the impact energy and a shift of the DBTT of ferritic ODS steel towards higher temperatures. The present study highlights extensive splitting of the fracture surfaces and a dependency of the impact energy on the fracture plane orientation according to the microstructure anisotropy.

  15. Effect of microstructure on low cycle fatigue properties of ODS steels

    NASA Astrophysics Data System (ADS)

    Kubena, Ivo; Fournier, Benjamin; Kruml, Tomas

    2012-05-01

    Low cycle fatigue properties at room temperature, 650 °C and 750 °C of three high chromium steels (9%Cr ferritic-martensitic and two 14%Cr ferritic steels) strengthened by oxide dispersion were studied and compared. Cyclic softening/hardening curves, cyclic deformation curves, S-N curves and Coffin-Manson curves are presented together with microstructural observations. Differences in cyclic response, stress level and fatigue life are attributed to differences in the matrix microstructure. The oxide particles stabilize the cyclic response, even if cyclic softening is detected for some experimental conditions. The strength of these steels is discussed in terms of strengthening mechanisms such as grain size effect, particle-dislocations interaction and dislocation density. Comparing three different ODS steels offers an opportunity to tests the contribution of individual mechanisms to the cyclic strength. The reduction of fatigue life in one of the ferritic steels is explained by the presence of large grains, facilitating the fatigue crack nucleation and the early growth.

  16. 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.

  17. Formation mechanism and the role of nanoparticles in Fe-Cr ODS steels developed for radiation tolerance

    SciTech Connect

    Hsiung, Luke L.; Fluss, Michael J.; Tumey, Scott J.; Choi, B. William; Serruys, Yves; Willaime, Francois; Kimura, Akihiko

    2010-11-01

    Structures of nanoparticles in Fe-16Cr-4.5Al-0.3Ti-2W-0.37Y{sub 2}O{sub 3} (K3) and Fe-20Cr-4.5Al-0.34Ti-0.5Y{sub 2}O{sub 3} (MA956) oxide dispersion strengthened (ODS) ferritic steels produced by mechanical alloying (MA) and followed by hot extrusion have been studied using high-resolution transmission electron microscopy (HRTEM) techniques to understand the formation mechanism of nanoparticles in MA/ODS steels. The observations of Y-Al-O complex-oxide nanoparticles in both ODS steels imply that decomposition of Y{sub 2}O{sub 3} in association with internal oxidation of Al occurred during mechanical alloying. While the majority of oxide nanoparticles formed in both steels is Y{sub 4}Al{sub 2}O{sub 9}, a few oxide particles of YAlO{sub 3} are also observed occasionally. These results reveal that Ti (0.3 wt %) plays an insignificant role in forming oxide nanoparticles in the presence of Al (4.5 wt %). HRTEM observations of crystalline nanoparticles larger than {approx}2 nm and amorphous or disordered cluster domains smaller than {approx}2 nm provide an insight into the formation mechanism of oxide nanoparticle in MA/ODS steels, which we believe from our observations involves solid-state amorphization and recrystallization. The role of nanoparticles in suppressing radiation-induced swelling is revealed through TEM examinations of cavity distributions in ion-irradiated Fe-14Cr and K3-ODS ferritic steels. HRTEM observations of helium-filled cavities (helium bubbles) preferably trapped at nanoscale oxide particles and clusters in ion-irradiated K3-ODS are presented.

  18. Characteristic results and prospects of the 13Cr-1W-0.3Ti-0.3Y 2O 3 ODS steel

    NASA Astrophysics Data System (ADS)

    Eiselt, Ch. Ch.; Klimenkov, M.; Lindau, R.; Möslang, A.

    2009-04-01

    For specific blanket and divertor applications in future fusion power reactors a replacement of presently considered reduced activation ferritic martensitic (RAFM) steels as structural material by suitable oxide dispersion strengthened (ODS) ferritic martensitic steels would allow a substantial increase of the operating temperature from ˜550 °C to about 650 °C. Temperatures above 700 °C in the He cooled modular divertor concept necessitates the use of ferritic (RAF) ODS steels, which are not limited by a phase transition. Therefore a 13Cr-1W-0.3Ti-0.3Y 2O 3 ferritic ODS steel is being developed, using an Attritor with varying milling parameters. Afterwards the mechanically alloyed powders were encapsulated, sealed and consolidated in a hot isostatic press device. In this work, the effects of several parameter variations on the microstructure of the produced ferritic ODS-alloys, analysed by optical microscopy (OM) and high resolution TEM, as well as results of conducted mechanical tests are presented.

  19. Microstructure and impact properties of ferritic ODS ODM401 (14%Cr-ODS of MA957 type)

    NASA Astrophysics Data System (ADS)

    Hadraba, Hynek; Kazimierzak, Bohumil; Stratil, Ludek; Dlouhy, Ivo

    2011-10-01

    The oxide dispersion strengthened (ODS) steel ODM401 is one of the ODS steels developed during the 1960-1970s as a structural tubing material for fast breeder reactors, mainly because of their high-temperature strength and swelling resistance under irradiation. Nowadays, these steels are taken under consideration as a structural material for blanket and heat exchanger components in fusion reactors. The aim of the work was to describe fracture behaviour of ODM401 steel in connection to the microstructure. The microstructure of as-extruded ODM401 steel has fine grains elongated in the extrusion direction. The two population of Y-Ti-O particles sizes were found in the microstructure of size about 10-20 nm and 2-3 nm. Temperature dependence of KLST impact energy was measured and transition temperature tDBTT evaluated about -110 °C. The fracture surface was formed by alternated cleavage areas connected by inclined areas fractured by dimple micro mechanism proportional to the impact energy.

  20. 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.

  1. Mechanical testing of anisotropy in ODS steel tubes

    NASA Astrophysics Data System (ADS)

    Špirit, Z.; Chocholoušek, M.; Šíma, M.

    2017-02-01

    Anisotropy of fuel claddings made from Fe-9Cr and Fe-14Cr ODS (oxide dispersion-strengthened) steel for Generation IV reactors with coolants based on liquid metals was examined. Basic mechanical tests were performed at temperatures of 30 °C, 500 °C and 625 °C on ODS steel thin-walled tubes. Tensile tests were performed in axial and tangential directions in a vacuum to avoid oxidation of the small specimens. A scanning electron microscope with a small in-situ tensile testing device was used to conduct the tests. The result of this paper describes the basic mechanical properties of thin-walled tubes as ultimate tensile strength, yield strength, tensile modulus, etc. depending on the direction of loading.

  2. Effects of mechanical force on grain structures of friction stir welded oxide dispersion strengthened ferritic steel

    NASA Astrophysics Data System (ADS)

    Han, Wentuo; Kimura, Akihiko; Tsuda, Naoto; Serizawa, Hisashi; Chen, Dongsheng; Je, Hwanil; Fujii, Hidetoshi; Ha, Yoosung; Morisada, Yoshiaki; Noto, Hiroyuki

    2014-12-01

    The weldability of oxide dispersion strengthened (ODS) ferritic steels is a critical obstructive in the development and use of these steels. Friction stir welding has been considered to be a promising way to solve this problem. The main purpose of this work was to reveal the effects of mechanical force on grain structures of friction stir welded ODS ferritic steel. The grain appearances and the misorientation angles of grain boundaries in different welded zones were investigated by the electron backscatter diffraction (EBSD). Results showed that the mechanical force imposed by the stir tool can activate and promote the recrystallization characterized by the transformation of boundaries from LABs to HABs, and contribute to the grain refinement. The type of recrystallization in the stir zone can be classified as the continuous dynamic recrystallization (CDRX).

  3. 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

  4. 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.

  5. 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.

  6. Friction Stir Welding of ODS and RAFM Steels

    DOE PAGES

    Yu, Zhenzhen; Feng, Zhili; Hoelzer, David; ...

    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

  7. 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.

  8. Chemical and microstructural evolution on ODS Fe-14CrWTi steel during manufacturing stages

    NASA Astrophysics Data System (ADS)

    Olier, P.; Malaplate, J.; Mathon, M. H.; Nunes, D.; Hamon, D.; Toualbi, L.; de Carlan, Y.; Chaffron, L.

    2012-09-01

    Oxide Dispersion Strengthened (ODS) steels are promising candidate materials for fission and fusion applications thanks to their improved properties related to both their fine grained microstructure and high density of Y-Ti-O nanoscale clusters (NCs). The Fe-14Cr-1 W-0.3Ti-0.3Y2O3 ODS ferritic steel was produced by powder metallurgy: Iron-base gas atomized powders were mechanically alloyed with 0.3% Y2O3 particles in an attritor. Then, the ODS powders were encapsulated in a soft steel can, consolidated by hot extrusion and cold rolled under the shape of tube cladding. The present work investigates the evolution of the chemical composition and the microstructure after each stage of the fabrication route (i.e. mechanical alloying, extrusion and cold rolling). Chemical analysis indicates a significant increase of the carbon content and a moderate increase of oxygen and nitrogen after mechanical alloying compared to initial atomized powders. After extrusion, the measured oxygen content corresponds mainly to the oxygen coming from yttria addition during MA process. In addition, electron microprobe analyses are performed after hot extrusion to determine the concentration and the distribution of the constitutive elements (Cr, Ti, W, Y, O). The microstructure was investigated by transmission electron microscopy (TEM) and small angle neutron scattering (SANS) in order to characterize the size distribution of Y-Ti-O particles. TEM results reveal a fine microstructure (average grain size of 600 nm in the transverse direction) including Y-Ti-O NCs with a mean diameter close to 3 nm after extrusion. A slight coarsening of Y-Ti-O NCs is evidenced by SANS after cold rolling and heat treatments.

  9. Oxide Evolution in ODS Steel Resulting From Friction Stir Welding

    DTIC Science & Technology

    2014-06-01

    Master’s Thesis 4 . TITLE AND SUBTITLE OXIDE EVOLUTION IN ODS STEEL RESULTING FROM FRICTION STIR WELDING 5. FUNDING NUMBERS 6 . AUTHOR(S...temperatures, from [5]. ........... 6   Figure 4 .  The phase diagram for aluminum and yttrium oxide, from [13]. ......................8  Figure 5...millimeters per minute. FSW Conditions RPM IPM MMPM Heat Index 400 7 175 2.3 300 4 100 3 200 2 50 4 400 4 100 4 300 2 50 6 400 2 50 8 500 1 25

  10. 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.

  11. Short Communication on "Coarsening of Y-rich oxide particles in 9%Cr-ODS Eurofer steel annealed at 1350 °C"

    NASA Astrophysics Data System (ADS)

    Sandim, M. J. R.; Souza Filho, I. R.; Bredda, E. H.; Kostka, A.; Raabe, D.; Sandim, H. R. Z.

    2017-02-01

    Oxide-dispersion strengthened (ODS) Eurofer steel is targeted for structural applications in future fusion nuclear reactors. Samples were cold rolled down to 80% reduction in thickness and annealed at 1350 °C up to 8 h. The microstructural characterization was performed using Vickers microhardness testing, electron backscatter diffraction, scanning and scanning transmission electron microscopies. Experimental results provide evidence of coarsening of the Y-rich oxide particles in ODS-Eurofer steel annealed at 1350 °C within delta ferrite phase field.

  12. 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.

  13. 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.

  14. Structural and chemical evolution in neutron irradiated and helium-injected ferritic ODS PM2000 alloy

    NASA Astrophysics Data System (ADS)

    Jung, Hee Joon; Edwards, Dan J.; Kurtz, Richard J.; Yamamoto, Takuya; Wu, Yuan; Odette, G. Robert

    2017-02-01

    An investigation of the influence of helium on damage evolution under neutron irradiation of an 11 at% Al, 19 at% Cr ODS ferritic PM2000 alloy was carried out in the High Flux Isotope Reactor (HFIR) using a novel in situ helium injection (ISHI) technique. Helium was injected into adjacent TEM discs from thermal neutron 58Ni(nth,γ) 59Ni(nth,α) reactions in a thin NiAl layer. The PM2000 undergoes concurrent displacement damage from the high-energy neutrons. The ISHI technique allows direct comparisons of regions with and without high concentrations of helium since only the side coated with the NiAl experiences helium injection. The corresponding microstructural and microchemical evolutions were characterized using both conventional and scanning transmission electron microscopy techniques. The evolutions observed include formation of dislocation loops and associated helium bubbles, precipitation of a variety of phases, amorphization of the Al2YO3 oxides (which also variously contained internal voids), and several manifestations of solute segregation. Notably, high concentrations of helium had a significant effect on many of these diverse phenomena. These results on PM2000 are compared and contrasted to the evolution of so-called nanostructured ferritic alloys (NFA).

  15. Ultra-high temperature tensile properties of ODS steel claddings under severe accident conditions

    NASA Astrophysics Data System (ADS)

    Yano, Y.; Tanno, T.; Oka, H.; Ohtsuka, S.; Inoue, T.; Kato, S.; Furukawa, T.; Uwaba, T.; Kaito, T.; Ukai, S.; Oono, N.; Kimura, A.; Hayashi, S.; Torimaru, T.

    2017-04-01

    Ultra-high temperature ring tensile tests were performed to investigate the tensile behavior of oxide dispersion strengthened (ODS) steel claddings and wrapper materials under severe accident conditions with temperatures ranging from room temperature to 1400 °C which is close to the melting point of core materials. The experimental results showed that the tensile strength of 9Cr-ODS steel claddings was highest in the core materials at ultra-high temperatures of 900-1200 °C, but there was significant degradation in the tensile strength of 9Cr-ODS steel claddings above 1200 °C. This degradation was attributed to grain boundary sliding deformation with γ/δ transformation, which is associated with reduced ductility. By contrast, the tensile strength of recrystallized 12Cr-ODS and FeCrAl-ODS steel claddings retained its high value above 1200 °C, unlike the other tested materials.

  16. 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

  17. 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.

  18. 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.

  19. 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.

  20. Performance of ferritic stainless steels for automobile muffler corrosion

    SciTech Connect

    Tarutani, Y.; Hashizume, T.

    1995-11-01

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

  1. Effects of mechanical alloying time on microstructure and properties of 9Cr-ODS steels

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Pre-alloyed powders of oxide dispersion strengthened (ODS) steels were produced by atomization. The atomized powders without mechanical alloying (MA) and with short-time MA were consolidated by hot isostatic pressing (HIP). The morphology and microstructure of the atomized and the MA powders were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The microstructure of 9Cr-ODS steels with different MA time was characterized by high-resolution transmission electron microscopy (HRTEM), electron backscatter diffraction (EBSD) and atom probe tomography (APT). The results showed that high-density of nanosized precipitates and ultrafine grains are formed in the ODS steels using the processing route, which remarkably reduce MA time. The yield strength and ultimate tensile strength of ODS steels are improved with the increase of MA time.

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  3. Suppression effect of nano-sized oxide particles on helium irradiation hardening in F82H-ODS steel

    NASA Astrophysics Data System (ADS)

    Chen, S.; Wang, Y.; Tadaki, K.; Hashimoto, N.; Ohnuki, S.

    2014-12-01

    Helium implantation was performed to investigate irradiation hardening in ferritic/martensitic steels. Depth dependence of nano-hardness was obtained using a Berkovich nano-indenter, and then nano-hardness was extracted from Nix-Gao model. The correlation between irradiation hardening and the concentration 500-2000 appm of helium was plotted. Nano-hardness increases as a function of helium concentration. F82H-ODS with a higher nano-hardness provides a lower irradiation hardening than F82H-IEA. Cross-sectional transmission electron microscopy (XTEM) revealed that cavities with a uniform distribution were formed after helium implantation at 2000 appm helium concentration, showing a mean size of 1.1 nm with an average number density of 4.9 × 1023 m-3 in F82H-IEA and 1.3 nm with 7.4 × 1023 m-3 in F82H-ODS. Orowan model was applied to evaluate the hardening from dispersed cavities. The significant difference of hardening between calculation and nano-indentation result of F82H-ODS indicates that oxide particles may shield the hardening effect from cavities because of the complex multi-interaction.

  4. 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...

  5. Characterization of Residual Stress as a Function of Friction Stir Welding Parameters in ODS Steel MA956

    DTIC Science & Technology

    2013-06-01

    8  Figure 5.  (a) Residual stress profiles for the FSW of AA 5083. From Peel [15]. (b) The residual stress profile across PM2000, an ODS steel ...solid state technique for joining ODS steels (Figure 2). FSW does not melt the base metal, and preserves many mechanical and microstructural properties...been performed by Baker [5] and Han [12] for fine-grained ODS steels subjected to a variety of FSW conditions. Fine grained material has a grain

  6. 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%).

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

    SciTech Connect

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

    1996-04-01

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

  8. Radiation Stability of Nanoclusters in Nano-structured Oxide Dispersion Strengthened (ODS) Steels

    SciTech Connect

    Certain, Alicia G.; Kuchibhatla, Satyanarayana V N T; Shutthanandan, V.; Hoelzer, D. T.; Allen, T. R.

    2013-03-01

    Nanostructured oxide dispersion strengthened (ODS) steels are considered candidates for nuclear fission and fusion applications at high temperature and dose. The complex oxide nanoclusters in these alloys provide high-temperature strength and are expected to afford better radiation resistance. Proton, heavy ion, and neutron irradiations have been performed to evaluate cluster stability in 14YWT and 9CrODS steel under a range of irradiation conditions. Energy-filtered transmission electron microscopy and atom probe tomography were used in this work to analyze the evolution of the oxide population.

  9. 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.

  10. 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.

  11. 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.

  12. 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)

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

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

  14. Effect of internal nitriding on the fatigue strength of ferritic corrosion-resistant steel

    NASA Astrophysics Data System (ADS)

    Rogachev, S. O.; Nikulin, S. A.; Terent'ev, V. F.; Khatkevich, V. M.; Prosvirnin, D. V.; Savicheva, R. O.

    2015-04-01

    The effect of internal nitriding and subsequent annealing on the mechanical properties of ferritic corrosion-resistance 08Kh17T steel has been studied during static and cyclic loading. Nitriding was shown to increase the static and cyclic strength of ferritic steel substantially and to decrease its plasticity slightly. These changes are confirmed by results of fractographic studies.

  15. 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.''...

  16. 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.

  17. Room temperature texturing of austenite/ferrite steel by electropulsing

    PubMed Central

    Rahnama, Alireza; Qin, Rongshan

    2017-01-01

    The work reports an experimental observation on crystal rotation in a duplex (austenite + ferrite) steel induced by the electropulsing treatment at ambient temperature, while the temperature rising due to ohmic heating in the treatment was negligible. The results demonstrate that electric current pulses are able to dissolve the initial material’s texture that has been formed in prior thermomechanical processing and to produce an alternative texture. The results were explained in terms of the instability of an interface under perturbation during pulsed electromigation. PMID:28195181

  18. Room temperature texturing of austenite/ferrite steel by electropulsing

    NASA Astrophysics Data System (ADS)

    Rahnama, Alireza; Qin, Rongshan

    2017-02-01

    The work reports an experimental observation on crystal rotation in a duplex (austenite + ferrite) steel induced by the electropulsing treatment at ambient temperature, while the temperature rising due to ohmic heating in the treatment was negligible. The results demonstrate that electric current pulses are able to dissolve the initial material’s texture that has been formed in prior thermomechanical processing and to produce an alternative texture. The results were explained in terms of the instability of an interface under perturbation during pulsed electromigation.

  19. Effects of helium on ductile-brittle transition behavior of reduced-activation ferritic steels after high-concentration helium implantation at high temperature

    NASA Astrophysics Data System (ADS)

    Hasegawa, A.; Ejiri, M.; Nogami, S.; Ishiga, M.; Kasada, R.; Kimura, A.; Abe, K.; Jitsukawa, S.

    2009-04-01

    The effects of He on the fracture behavior of reduced-activation ferritic/martensitic steels, including oxide dispersion-strengthened (ODS) steels and F82H, was determined by characterizing the microstructural evolution in and fracture behavior of these steels after He implantation up to 1000 appm at around 550 °C. He implantation was carried out by a cyclotron with a beam of 50 MeV α-particles. In the case of F82H, the ductile-to-brittle transition temperature (DBTT) increase induced by He implantation was about 70 °C and the grain boundary fracture surface was only observed in the He-implanted area of all the ruptured specimens in brittle manner. By contrast, no DBTT shift or fracture mode change was observed in He-implanted 9Cr-ODS and 14Cr-ODS steels. Microstructural characterization suggested that the difference in the bubble formation behavior of F82H and ODS steels might be attributed to the grain boundary rupture of He-implanted F82H.

  20. Precipitation sequence in niobium-alloyed ferritic stainless steel

    NASA Astrophysics Data System (ADS)

    Fujita, Nobuhiro; Bhadeshia, H. K. D. H.; Kikuchi, Masao

    2004-03-01

    Niobium is an important alloying element in the design of heat-resistant ferritic stainless steels for automotive exhaust systems. When in solid solution, it improves both the high temperature strength and the resistance to thermal fatigue. However, it also forms several kinds of precipitates during service. These reactions have been modelled, taking into account the multicomponent nature of the diffusion process and allowing for capillarity effects. It has been possible to estimate not only the volume fractions but also the particle sizes for Fe2Nb (Laves phase) and Fe3Nb3C (M6C) carbide in a 19Cr-0.8Nb steel, with good agreement against experimental data.

  1. 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.

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

    SciTech Connect

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

    1998-08-01

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

  3. Surface modification to improve fireside corrosion resistance of Fe-Cr ferritic steels

    DOEpatents

    Park, Jong-Hee; Natesan, Krishnamurti; Rink, David L.

    2010-03-16

    An article of manufacture and a method for providing an Fe--Cr ferritic steel article of manufacture having a surface layer modification for corrosion resistance. Fe--Cr ferritic steels can be modified to enhance their corrosion resistance to liquid coal ash and other chemical environments, which have chlorides or sulfates containing active species. The steel is modified to form an aluminide/silicide passivating layer to reduce such corrosion.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Sensitization and stabilization of type 409 ferritic stainless steel

    SciTech Connect

    Fritz, J.D.; Franson, I.A.

    1997-08-01

    Type 409 (UNS S40900) ferritic stainless steel, used widely in automotive exhaust systems, can be subject to intergranular corrosion (IGC) of weld heat-affected zones (HAZ), even though ASTM stabilization requirements (Ti = 6 {times} C) are met. A boiling Cu/6% CuSO{sub 4}/0.5% H{sub 2}SO{sub 4} test is shown to be appropriate for detecting IGC of welds and HAZ. This test was used to establish stabilization requirements for type 409, whether dual-stabilized with Ti + Nb or singly stabilized with Ti alone. It was found that the stabilization requirement should be Ti + Nb {ge} 0.08 + 8 (C + N). Benefits of dual stabilization include improved surface quality and formability without sacrifice of mechanical properties or weldability.

  14. New grain formation during warm deformation of ferritic stainless steel

    SciTech Connect

    Belyakov, A.; Sakai, Taku; Kaibyshev, R.

    1998-01-01

    Microstructural evolution accompanied by localization of plastic flow was studied in compression of a ferritic stainless steel with high stacking fault energy (SFE) at 873 K ({approx} 0.5 Tm). The structure evolution is characterized by the formation of dense dislocation walls at low strains and subsequently of microbands and their clusters at moderate strains, followed by the evolution of fragmented structure inside the clusters of microbands at high strains. The misorientations of the fragmented boundaries and the fraction of high-angle grain boundaries increase substantially with increasing strain. Finally, further straining leads to the formation of new fine grains with high-angle boundaries, which become more equiaxed than the previous fragmented structure. The mechanisms operating during such structure changes are discussed in detail.

  15. 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

  16. Development of oxide dispersion strengthened ferritic steels for fusion reactors

    SciTech Connect

    Mukhopadhay, D.K.; Suryanarayana, C.; Froes, F.H.; Hebeisen, J.; Gelles, D.S.

    1996-12-31

    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-13.5Cr-2W-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 C, 900 C, 1,000 C, 1,100 C and 1,200 C showed a minor decrease in the hardness.

  17. 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.

  18. Anisotropic mechanical properties of the MA956 ODS steel characterized by the small punch testing technique

    NASA Astrophysics Data System (ADS)

    Turba, K.; Hurst, R. C.; Hähner, P.

    2012-09-01

    The small punch testing technique was used to assess both creep and fracture properties of the MA956 oxide dispersion strengthened ferritic steel. The anisotropy in mechanical properties was addressed, as well as the alloy's susceptibility to thermal embrittlement. Strong anisotropy was found in the material's creep resistance at 725 °C for longer rupture times. Anisotropic behavior was also observed for the ductile-brittle transition temperature (DBTT). The origin of the anisotropy can be related to the strongly directional microstructure which enables a large amount of intergranular cracking during straining at both high and low temperatures. The DBTT of the alloy is very high, and can be further increased by at least 200 °C after 1000 h of ageing at 475 °C, due to the formation of the Cr-rich α' phase. The particularly high susceptibility of the MA956 to thermal embrittlement is mainly a consequence of its high chromium content.

  19. Radiation induced microstructures in ODS 316 austenitic steel under dual-beam ions

    NASA Astrophysics Data System (ADS)

    Zhang, He Ken; Yao, Zhongwen; Zhou, Zhangjian; Wang, Man; Kaitasov, Odile; Daymond, Mark R.

    2014-12-01

    An ODS 316 austenitic steel was fabricated and irradiated using dual ion beams (1 MeV Kr+ and 15 keV He+) with in-situ transmission electron microscope (TEM) observation. Cavities formed at a low dose in samples irradiated with simultaneous helium injection. It was found that Y-Ti-O particles acted as strong traps for cavity formation at low doses. Helium exhibited a significant effect on cavity development. Cavities were also preferentially nucleated along grain boundaries, phase boundaries and twin boundaries. Irradiation induced lattice defects mainly consisted of small 1/2<1 1 0> perfect loops and 1/3<1 1 1> Frank loops. An increment of helium injection rate also greatly enhanced the Frank loop growth. Small (<10 nm) Y-Ti-O particles were found to be unstable after irradiation to high doses. M23C6 precipitates were observed after irradiation and helium might play a major role in their formation.

  20. 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.

  1. Impact of friction stir welding on the microstructure of ODS steel

    NASA Astrophysics Data System (ADS)

    Dawson, H.; Serrano, M.; Cater, S.; Iqbal, N.; Almásy, L.; Tian, Q.; Jimenez-Melero, E.

    2017-04-01

    We have assessed the impact of the welding parameters on the nano-sized oxide dispersion and the grain size in the matrix of an ODS steel after friction stir welding. Our results, based on combined small angle neutron scattering and electron microscopy, reveal a decrease in the volume fraction of the particles smaller than 80 nm in the welds, mainly due to particle agglomeration. The increase in tool rotation speed or decrease in transverse speed leads to a higher reduction in nano-sized particle fraction, and additionally to the occurrence of particle melting. The dependence of the average grain size in the matrix on the particle volume fraction follows a Zener pinning-type relationship. This result points to the principal role that the particles have in pinning grain boundary movement, and consequently in controlling the grain size during welding.

  2. Production, microstructure and mechanical properties of two different austenitic ODS steels

    NASA Astrophysics Data System (ADS)

    Gräning, T.; Rieth, M.; Hoffmann, J.; Möslang, A.

    2017-04-01

    This article is to summarize and examine processing parameters of novel developed austenitic oxide dispersed strengthened (ODS) steels. Comparing hot-rolled and extruded conditions after the same degree of deformation after and before annealing, are just some examples to give insights into the complex processing of austenitic ODS steels. One of the major drawbacks of the material is the more sophisticated production process. Due to a ductile matrix material with an increased stickiness during milling, a two-step milling procedure with the use of ZrO2 milling balls was applied to raise the production yield and to use the abrasion of the ZrO2 as an additional element to facilitate the formation of nano-sized precipitates. To get a better understanding how the different powder particle sizes after milling affect final properties, sieving was applied and revealed a serious effect in terms of precipitate size, distribution and mechanical properties. Grain sizes in relation to the precipitate size, annealing time and processing parameters were determined and compared to the mechanical properties. Hardness and tensile test have pointed out, that the precipitate size and number are more important in respect to the ultimate tensile strength than the grain size and that in this study hot-rolled material exhibited the better properties. The investigation of the microstructure illustrated the stability of precipitates during annealing at 1100 °C for 40 h. These heat treatments also led to a consistent grain size, due to the pinning effect of the grain boundaries, caused by precipitates.

  3. 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.

  4. Direct correlation between morphology of (Fe,Cr) 23C 6 precipitates and impact behavior of ODS steels

    NASA Astrophysics Data System (ADS)

    Klimiankou, M.; Lindau, R.; Möslang, A.

    2007-08-01

    The microstructure of ODS steels was investigated after different thermal and thermo-mechanical treatments by means of transmission electron microscopy (TEM) and analytical TEM techniques, including energy-dispersive X-ray (EDX) mapping of the elemental distribution at the nanometer scale. In 'as-HIPped' first generation ODS-Eurofer steel the grain boundaries were decorated with Cr-rich precipitates of M 23C 6 type. In addition, EDX mapping showed Cr-depleted areas at grain boundaries. Thermal and thermo-mechanical treatments of the ODS material affect the size, composition and spatial distribution of the precipitates. Depending on the treatments, the morphology and density of the M 23C 6 can be systematically varied. A significant decrease in ductile-to-brittle-transition-temperature (DBTT) in impact tests and an improvement in the tensile ductility at high temperature can be directly linked to the changes in precipitate morphology and size.

  5. 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

    ... 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 operation—ferritic steels with properties enhanced by heat treatment (modifies UHT-5(c), UHT-6, UHT-23, and...

  6. 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

    ... 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 operation—ferritic steels with properties enhanced by heat treatment (modifies UHT-5(c), UHT-6, UHT-23, and...

  7. 46 CFR 54.25-10 - Low temperature operation-ferritic steels (replaces UCS-65 through UCS-67).

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 2 2011-10-01 2011-10-01 false Low temperature operation-ferritic steels (replaces UCS... (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS Construction With Carbon, Alloy, and Heat Treated Steels § 54.25-10 Low temperature operation—ferritic steels (replaces UCS-65 through UCS-67). (a) Scope. (1)...

  8. 46 CFR 54.25-20 - Low temperature operation-ferritic steels with properties enhanced by heat treatment (modifies...

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 2 2010-10-01 2010-10-01 false Low temperature operation-ferritic steels with... VESSELS Construction With Carbon, Alloy, and Heat Treated Steels § 54.25-20 Low temperature operation—ferritic steels with properties enhanced by heat treatment (modifies UHT-5(c), UHT-6, UHT-23, and...

  9. 46 CFR 54.25-10 - Low temperature operation-ferritic steels (replaces UCS-65 through UCS-67).

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 2 2010-10-01 2010-10-01 false Low temperature operation-ferritic steels (replaces UCS... (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS Construction With Carbon, Alloy, and Heat Treated Steels § 54.25-10 Low temperature operation—ferritic steels (replaces UCS-65 through UCS-67). (a) Scope. (1)...

  10. 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

    ... 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 operation—ferritic steels with properties enhanced by heat treatment (modifies UHT-5(c), UHT-6, UHT-23, and...

  11. 46 CFR 54.25-10 - Low temperature operation-ferritic steels (replaces UCS-65 through UCS-67).

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 2 2014-10-01 2014-10-01 false Low temperature operation-ferritic steels (replaces UCS... (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS Construction With Carbon, Alloy, and Heat Treated Steels § 54.25-10 Low temperature operation—ferritic steels (replaces UCS-65 through UCS-67). (a) Scope. (1)...

  12. 46 CFR 54.25-10 - Low temperature operation-ferritic steels (replaces UCS-65 through UCS-67).

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 2 2013-10-01 2013-10-01 false Low temperature operation-ferritic steels (replaces UCS... (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS Construction With Carbon, Alloy, and Heat Treated Steels § 54.25-10 Low temperature operation—ferritic steels (replaces UCS-65 through UCS-67). (a) Scope. (1)...

  13. 46 CFR 54.25-10 - Low temperature operation-ferritic steels (replaces UCS-65 through UCS-67).

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 2 2012-10-01 2012-10-01 false Low temperature operation-ferritic steels (replaces UCS... (CONTINUED) MARINE ENGINEERING PRESSURE VESSELS Construction With Carbon, Alloy, and Heat Treated Steels § 54.25-10 Low temperature operation—ferritic steels (replaces UCS-65 through UCS-67). (a) Scope. (1)...

  14. 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

    ... 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 operation—ferritic steels with properties enhanced by heat treatment (modifies UHT-5(c), UHT-6, UHT-23, and...

  15. 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.

  16. 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)

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

    DTIC Science & Technology

    2013-06-01

    development. While high speed steel or WC-Co tools can be used for aluminum and copper alloys, FSW of steel generally requires even more refractory... steel and the microstructure produced by FSW is much more critical than in aluminum alloys. The αγδ phase transformations can cause complex, multi...thesis explores the processing-microstructure-property relationships in friction stir welded ( FSW ) HT9A ferritic-martensitic steel . HT9 has previously

  18. High-Temperature Tensile Properties of Nano-Oxide Dispersion Strengthened Ferritic Steels Produced by Mechanical Alloying and Spark Plasma Sintering

    NASA Astrophysics Data System (ADS)

    Boulnat, Xavier; Fabregue, Damien; Perez, Michel; Mathon, Marie-Hélène; de Carlan, Yann

    2013-06-01

    Oxide-dispersion strengthened (ODS) ferritic steels were produced by mechanical alloying and subsequent spark plasma sintering. Very fast heating rates were used to minimize porosity when controlling grain size and precipitation of dispersoids within a compacted material. Sintering cycles performed at 1373 K (1100 °C) induced heterogeneous, but fine grain size distribution and high density of nano-oxides. Yield strengths at room temperature and at 923 K (650 °C) are 975 MPa and 298 MPa, respectively. Furthermore, high-temperature ductility is much increased: total strain of 28 pct at 923 K (650 °C).

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

    SciTech Connect

    Dai, Y.

    1996-06-01

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

  20. Electrochemical and passivation behavior investigation of ferritic stainless steel in simulated concrete pore media.

    PubMed

    Luo, Hong; Su, Huaizhi; Dong, Chaofang; Xiao, Kui; Li, Xiaogang

    2015-12-01

    The applications of stainless steel are one of the most reliable solutions in concrete structures to reduce chloride-induced corrosion problems and increase the structures service life, however, due to high prices of nickel, especially in many civil engineering projects, the austenitic stainless steel is replaced by the ferritic stainless steels. Compared with austenite stainless steel, the ferritic stainless steel is known to be extremely resistant of stress corrosion cracking and other properties. The good corrosion resistance of the stainless steel is due to the formation of passive film. While, there is little literature about the electrochemical and passive behavior of ferritic stainless steel in the concrete environments. So, here, we present the several corrosion testing methods, such as the potentiodynamic measurements, EIS and Mott-Schottky approach, and the surface analysis methods like XPS and AES to display the passivation behavior of 430 ferritic stainless steel in alkaline solution with the presence of chloride ions. These research results illustrated a simple and facile approach for studying the electrochemical and passivation behavior of stainless steel in the concrete pore environments.

  1. Electrochemical and passivation behavior investigation of ferritic stainless steel in simulated concrete pore media

    PubMed Central

    Luo, Hong; Su, Huaizhi; Dong, Chaofang; Xiao, Kui; Li, Xiaogang

    2015-01-01

    The applications of stainless steel are one of the most reliable solutions in concrete structures to reduce chloride-induced corrosion problems and increase the structures service life, however, due to high prices of nickel, especially in many civil engineering projects, the austenitic stainless steel is replaced by the ferritic stainless steels. Compared with austenite stainless steel, the ferritic stainless steel is known to be extremely resistant of stress corrosion cracking and other properties. The good corrosion resistance of the stainless steel is due to the formation of passive film. While, there is little literature about the electrochemical and passive behavior of ferritic stainless steel in the concrete environments. So, here, we present the several corrosion testing methods, such as the potentiodynamic measurements, EIS and Mott–Schottky approach, and the surface analysis methods like XPS and AES to display the passivation behavior of 430 ferritic stainless steel in alkaline solution with the presence of chloride ions. These research results illustrated a simple and facile approach for studying the electrochemical and passivation behavior of stainless steel in the concrete pore environments. PMID:26501086

  2. TEM and HRTEM study of oxide particles in an Al-alloyed high-Cr oxide dispersion strengthened ferritic steel with Hf addition

    NASA Astrophysics Data System (ADS)

    Dou, Peng; Kimura, Akihiko; Kasada, Ryuta; Okuda, Takanari; Inoue, Masaki; Ukai, Shigeharu; Ohnuki, Somei; Fujisawa, Toshiharu; Abe, Fujio; Jiang, Shan; Yang, Zhigang

    2017-03-01

    The nanoparticles in an Al-alloyed high-Cr oxide dispersion strengthened (ODS) ferritic steel with Hf addition, i.e., SOC-16 (Fe-15Cr-2W-0.1Ti-4Al-0.62Hf-0.35Y2O3), have been examined by transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). Relative to an Al-alloyed high-Cr ODS ferritic steel without Hf addition, i.e., SOC-9 (Fe-15.5Cr-2W-0.1Ti-4Al-0.35Y2O3), the dispersion morphology and coherency of the oxide nanoparticles in SOC-16 were significantly improved. Almost all the small nanoparticles (diameter <10 nm) in SOC-16 were found to be consistent with cubic Y2Hf2O7 oxides with the anion-deficient fluorite structure and coherent with the bcc steel matrix. The larger particles (diameter >10 nm) were also mainly identified as cubic Y2Hf2O7 oxides with the anion-deficient fluorite structure. The results presented here are compared with those of SOC-9 with a brief discussion of the underlying mechanisms of the unusual thermal and irradiation stabilities of the oxides as well as the superior strength, excellent irradiation tolerance and extraordinary corrosion resistance of SOC-16.

  3. 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.

  4. Changes in the fracture strength parameters of ferritic-bainitic and bainitic pipe steels during operation

    NASA Astrophysics Data System (ADS)

    Zikeev, V. N.; Filippov, G. A.; Shabalov, I. P.; Livanova, O. V.; Solov'ev, D. M.

    2016-10-01

    The fracture strength and the sensitivity to delayed fracture of the pipes in oil-trunk pipelines that are made of ferritic-bainitic and bainitic steels are studied. The results of modeling of the delayed brittle fracture of pipe steel during a simultaneous action of mechanical stresses and a corrosive medium are presented.

  5. Prediction of yield stress in highly irradiated ferritic steels

    NASA Astrophysics Data System (ADS)

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

    2008-03-01

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

  6. 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.

  7. Effect of heat treatment on microstructure and hardness of Eurofer 97, Eurofer ODS and T92 steels

    NASA Astrophysics Data System (ADS)

    Lu, Z.; Faulkner, R. G.; Riddle, N.; Martino, F. D.; Yang, K.

    2009-04-01

    Eurofer ODS steel is a potential candidate for fusion reactor application due to its excellent swelling resistance, low thermal expansion coefficient and high temperature properties. One of the main issues is that high fluence neutron irradiation induces a significant increase of ductile-to-brittle transition temperature (DBTT) at temperatures below 400 °C which restricts its application. The aim of this study is to explore the methods to lower the initial DBTT of Eurofer ODS steel by heat treatment optimization. Two heats of Eurofer ODS steels with different C contents are heat-treated at different normalizing temperatures, cooling rates and tempering conditions, and are compared with Eurofer 97 and T92 steels heat-treated with similar conditions. The microstructure is characterized by optical microscopy, FEG-TEM and OIM-EBSD techniques. The effect of normalization, cooling rate and temper on grain size, precipitation, grain boundary misorientation and hardness are investigated. The influences of these properties on DBTT are discussed.

  8. 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.

  9. 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

  10. 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

  11. 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.

  12. 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.

  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. Carbon concentration measurements by atom probe tomography in the ferritic phase of high-silicon steels

    DOE PAGES

    Rementeria, Rosalia; Poplawsky, Jonathan D.; Aranda, Maria M.; ...

    2016-12-19

    Current studies using atom probe tomography (APT) show that bainitic ferrite formed at low temperature contains more carbon than what is consistent with the paraequilibrium phase diagram. However, nanocrystalline bainitic ferrite exhibits a non-homogeneous distribution of carbon atoms in arrangements with specific compositions, i.e. Cottrell atmospheres, carbon clusters, and carbides, in most cases with a size of a few nanometers. The ferrite volume within a single platelet that is free of these carbon-enriched regions is extremely small. Proximity histograms can be compromised on the ferrite side, and a great deal of care should be taken to estimate the carbon contentmore » in regions of bainitic ferrite free from carbon agglomeration. For this purpose, APT measurements were first validated for the ferritic phase in a pearlitic sample and further performed for the bainitic ferrite matrix in high-silicon steels isothermally transformed between 200 °C and 350 °C. Additionally, results were compared with the carbon concentration values derived from X-ray diffraction (XRD) analyses considering a tetragonal lattice and previous APT studies. In conclusion, the present results reveal a strong disagreement between the carbon content values in the bainitic ferrite matrix as obtained by APT and those derived from XRD measurements. Those differences have been attributed to the development of carbon-clustered regions with an increased tetragonality in a carbon-depleted matrix.« less

  15. Carbon concentration measurements by atom probe tomography in the ferritic phase of high-silicon steels

    SciTech Connect

    Rementeria, Rosalia; Poplawsky, Jonathan D.; Aranda, Maria M.; Guo, Wei; Jimenez, Jose A.; Garcia-Mateo, Carlos; Caballero, Francisca G.

    2016-12-19

    Current studies using atom probe tomography (APT) show that bainitic ferrite formed at low temperature contains more carbon than what is consistent with the paraequilibrium phase diagram. However, nanocrystalline bainitic ferrite exhibits a non-homogeneous distribution of carbon atoms in arrangements with specific compositions, i.e. Cottrell atmospheres, carbon clusters, and carbides, in most cases with a size of a few nanometers. The ferrite volume within a single platelet that is free of these carbon-enriched regions is extremely small. Proximity histograms can be compromised on the ferrite side, and a great deal of care should be taken to estimate the carbon content in regions of bainitic ferrite free from carbon agglomeration. For this purpose, APT measurements were first validated for the ferritic phase in a pearlitic sample and further performed for the bainitic ferrite matrix in high-silicon steels isothermally transformed between 200 °C and 350 °C. Additionally, results were compared with the carbon concentration values derived from X-ray diffraction (XRD) analyses considering a tetragonal lattice and previous APT studies. In conclusion, the present results reveal a strong disagreement between the carbon content values in the bainitic ferrite matrix as obtained by APT and those derived from XRD measurements. Those differences have been attributed to the development of carbon-clustered regions with an increased tetragonality in a carbon-depleted matrix.

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

    SciTech Connect

    Rakowski, James M.

    2013-09-10

    A method of reducing the formation of electrically resistive scale on a an article comprising a silicon-containing ferritic stainless subjected to oxidizing conditions in service includes, prior to placing the article in service, subjecting the article to conditions under which silica, which includes silicon derived from the steel, forms on a surface of the steel. Optionally, at least a portion of the silica is removed from the surface to placing the article in service. A ferritic stainless steel alloy having a reduced tendency to form silica on at least a surface thereof also is provided. The steel includes a near-surface region that has been depleted of silicon relative to a remainder of the steel.

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

    DOEpatents

    Rakowski, James M.

    2017-02-28

    A method of reducing the formation of electrically resistive scale on a an article comprising a silicon-containing ferritic stainless subjected to oxidizing conditions in service includes, prior to placing the article in service, subjecting the article to conditions under which silica, which includes silicon derived from the steel, forms on a surface of the steel. Optionally, at least a portion of the silica is removed from the surface to placing the article in service. A ferritic stainless steel alloy having a reduced tendency to form silica on at least a surface thereof also is provided. The steel includes a near-surface region that has been depleted of silicon relative to a remainder of the steel.

  18. 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.

  19. Accumulation and annealing of radiation defects under low-temperature electron and neutron irradiation of ODS steel and Fe-Cr alloys

    NASA Astrophysics Data System (ADS)

    Arbuzov, V. L.; Goshchitskii, B. N.; Sagaradze, V. V.; Danilov, S. E.; Kar'kin, A. E.

    2010-10-01

    The processes of accumulation and annealing of radiation defects at low-temperature (77 K) electron and neutron irradiation and their effect on the physicomechanical properties of Fe-Cr alloys and oxide dispersion strengthened (ODS) steel have been studied. It has been shown that the behavior of radiation defects in ODS steel and Fe-Cr alloys is qualitatively similar. Above 250 K, radiation-induced processes of the solid solution decomposition become conspicuous. These processes are much less pronounced in ODS steel because of specific features of its microstructure. Processes related to the overlapping of displacement cascades under neutron irradiation have been considered. It has been shown that, in this case, it is the increase in the size of vacancy clusters, rather than the growth of their concentration, that is prevailing. Possible mechanisms of the radiation hardening of the ODS steel and the Fe-13Cr alloy upon irradiation and subsequent annealing have been discussed.

  20. Microstructural study of an ODS stainless steel obtained by Hot Uni-axial Pressing

    NASA Astrophysics Data System (ADS)

    Sornin, D.; Grosdidier, T.; Malaplate, J.; Tiba, I.; Bonnaillie, P.; Allain-Bonasso, N.; Nunes, D.

    2013-08-01

    This study focuses on the consolidation of an ODS Fe-14Cr-1W-0.3Ti-0.3Y2O3 alloy obtained by powder metallurgy. The powder was sintered for 1 h at 1100 °C in a soft steel can and compacted by Hot Uni-axial Pressing (HUP) under 900 MPa within less than 5 s before air cooling. The HUPped material microstructure is prospected to determine relative density as well as microstructure and nano-precipitation. The HUP, which mimics the early stage of hot extrusion (HE), produces a fully dense metallurgical state. The HUPped microstructure is shown to be rather similar to the one obtained by HIPping for equivalent dwell time at high temperature. In both cases heterogeneous grain size microstructure was obtained. It is shown that the bigger grains come from static recrystallization occurring during the dwell time in furnace. Compared to HIP, the effect of the HUP is mainly to introduce intra-granular misorientations within these large recrystallized grains. During Hot Unidirectional Pressing the initially loose powder is fully consolidated. The relative density is rather similar to the HE and HIP process. Even with a uni-axial loading the HUPed material is homogeneous and does not presents any gradients of hardness. The obtained microstructure for the HUPed shows a bimodal grain size distribution and precipitates strings at grain boundaries. This material can be compared to HIP of similar composition grades [10]. Large grains are issued from an incomplete static recrystallization. Precipitation of nano-clusters is very similar for HUPed and HE materials. Nanometer scale precipitates are observed both within the large and small grains. One of the effects of the HUP compared to pure heat treatment is that the large grains that recrystallized during the early stages of the heat treatment present significant internal crystallographic misorientations. This is due to the plastic strain generated by the rapid compaction during HUP consolidation process.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

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

  4. Strength of "Light" Ferritic and Austenitic Steels Based on the Fe - Mn - Al - C System

    NASA Astrophysics Data System (ADS)

    Kaputkina, L. M.; Svyazhin, A. G.; Smarygina, I. V.; Kindop, V. E.

    2017-01-01

    The phase composition, the hardness, the mechanical properties at room temperature, and the resistance to hot (950 - 1000°C) and warm (550°C) deformation are studied for cast deformable "light" ferritic and austenitic steels of the Fe - (12 - 25)% Mn - (0 - 15)% Al - (0 - 2)% C system alloyed additionally with about 5% Ni. The high-aluminum high-manganese low-carbon and carbonless ferritic steels at a temperature of about 0.5 T melt have a specific strength close to that of the austenitic steels and may be used as weldable scale-resistant and wear-resistant materials. The high-carbon Fe - (20 - 24)% Mn - (5 - 9)% Al - 5% Ni - 1.5% C austenitic steels may be applied as light high-strength materials operating at cryogenic temperatures after a solution treatment and as scale- and heat-resistant materials in an aged condition.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

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

    PubMed

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

    2017-02-02

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

  11. 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.

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

    PubMed Central

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

    2017-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-06-01

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

  15. Correlation of microstructure and low cycle fatigue properties for 13.5Cr1.1W0.3Ti ODS steel

    NASA Astrophysics Data System (ADS)

    He, P.; Klimenkov, M.; Möslang, A.; Lindau, R.; Seifert, H. J.

    2014-12-01

    Reduced activation oxide dispersion strengthened (ODS) steels are prospective structural materials for the blanket system and first wall components in Tokamak-type fusion reactors. Under the pulsed operation, these components will be predominantly subjected to cyclic thermal-mechanical loading which leads to inevitable fatigue damage. In this work, strain controlled isothermal fatigue tests were conducted for 13.5Cr1.1W0.3Ti ODS steel at 550 °C. The total strain range varied from 0.54% to 0.9%. After thermomechanical processing, 13.5CrWTi-ODS steel exhibits a remarkable lifetime extension with a factor of 10-20 for strain ranges Δε ⩽ 0.7%. 13.5Cr ODS steel shows no cyclic softening at all during the whole testing process irrespective of the strain range. TEM observations reveal ultrastable grain structure and constant dislocation densities around 1014 m-2, independent of the number of cycles or the applied strain amplitude. The presence of the stabilized ultrafine Y-Ti-O dispersoids enhances the microstructural stability and therefore leads to outstanding fatigue resistance for 13.5Cr1.1W0.3Ti-ODS steel.

  16. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

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

    DOE PAGES

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

    2016-12-07

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

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

    SciTech Connect

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

    2016-12-07

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

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

    NASA Astrophysics Data System (ADS)

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

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

  1. Impact toughness of irradiated reduced-activation ferritic steels*1

    NASA Astrophysics Data System (ADS)

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

    1994-09-01

    Eight chromium-tungsten steels ranging from 2.25 to 12 wt% Cr were irradiated at 365°C to 13-14 dpa in the Fast Flux Test Facility. Post irradiation Charpy impact tests showed a loss of toughness for all steels, as measured by an increase in the ductile-brittle transition temperature (DBTT) and a decrease in the upper-shelf energy. The most irradiation-resistant steels were two 9% Cr steels: the DBTT of a 9Cr-2W-0.25V-0.1C steel increased 29°C, and for the same composition with an addition of 0.07% Ta the DBTT increased only 15°C. This is the smallest shift ever observed for such a steel irradiated to these levels. The other steels developed shifts in DBTT of 100 to 300°C. A 2.25% Cr steel with 2% W, 0.25% V, and 0.1% C was less severely affected by irradiation than 2.25% Cr steels with 0.25% V and no tungsten, 2% W and no vanadium, and with 1% W and 0.25% V. Irradiation resistance appears to be associated with microstructure, and microstructural manipulation may lead to improved properties.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Thermal stability study for candidate stainless steels of GEN IV reactors

    NASA Astrophysics Data System (ADS)

    Simeg Veternikova, J.; Degmova, J.; Pekarcikova, M.; Simko, F.; Petriska, M.; Skarba, M.; Mikula, P.; Pupala, M.

    2016-11-01

    Candidate stainless steels for GEN IV reactors were investigated in term of thermal and corrosion stability at high temperatures. New austenitic steel (NF 709), austenitic ODS steel (ODS 316) and two ferritic ODS steels (MA 956 and MA 957) were exposed to around 1000 °C in inert argon atmosphere at pressure of ∼8 MPa. The steels were further studied in a light of vacancy defects presence by positron annihilation spectroscopy and their thermal resistance was confronted to classic AISI steels. The thermal strain supported a creation of oxide layers observed by scanning electron microscopy (SEM).

  9. TEM characterization of 14YWT and 12YWT ODS ferritic alloys neutron irradiated at 500C using in-situ helium injection

    SciTech Connect

    Jung, Hee Joon; Edwards, Danny J.; Kurtz, Richard J.; Odette, G Robert; Wu, Yuan; Yamamoto, Takuya

    2015-03-31

    This report summaries TEM characterization of 14YWT and 12YWT, ODS ferritic alloys with 14 and 12 wt % of Cr respectively, to compare the effect of neutron irradiation with and without concurrent He injection using ISHI. The density and average size of <100>/{100} type dislocation loops are always larger than those of 1/2<111>/{111} type, but this difference is significantly affected by He implantation. The density of dislocation loops of both types ranges from ~1 to 4x1021 m-3 with average size ranging from 5~20 nm. 14YWT has lower density but larger size dislocation loops than 12YWT, while the line dislocation density of 14YWT is 3 times lower than that of 12YWT. Helium bubble densities of both 14YWT and 12YWT are 1.9x1023 m-3, the average He bubbles size of 14YWT and 12YWT are 1.4 and 1.2 nm, respectively. 14YWT exhibits α-α’ phase separation, Y-rich particles and uniformly distributed W. In addition to those features, 12YWT exhibits Y-Ti-O particles (not Y-O rich) and elongated Cr-rich phases.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    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.

  12. 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.

  13. Evaluation of examination techniques for ferritic stainless steel feedwater heater tubing

    SciTech Connect

    Nugent, M.J.; Catapano, M.C.

    1995-12-01

    Ferritic stainless steel has been finding increased application in utility plant feedwater heaters due to good strength and corrosion resistance and absence of potential copper contamination of feedwater system. Ferritic stainless steel is highly magnetic and is generally not inspectable using conventional eddy current testing techniques. A variety of techniques have been developed for inspection of this tubing material used in typical heat exchanger applications. Through a project funded by the Empire State Electric Energy Research Corporation (ESEERCO), the evaluation of data generated by four present state of the art NDE testing techniques were evaluated on a controlled mock-up of the heater tubing with service related defects. The primary objective was to determine the strengths and limitations of each method. The testing of two in service feedwater heaters at the Consolidated Edison Company of New York, Inc. (Con Edison`s) Arthur Kill Generating Station also allowed further evaluations based on actual field conditions.

  14. 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.

  15. 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.

  16. Recent progress in US Japan collaborative research on ferritic steels R&D

    NASA Astrophysics Data System (ADS)

    Kimura, Akihiko; Kasada, Ryuta; Kohyama, Akira; Tanigawa, Hiroyasu; Hirose, Takanori; Shiba, Kiyoyuki; Jitsukawa, Shiro; Ohtsuka, Satoshi; Ukai, Shigeharu; Sokolov, M. A.; Klueh, R. L.; Yamamoto, Takuya; Odette, G. R.

    2007-08-01

    The mechanisms of irradiation embrittlement of two Japanese RAFSs were different from each other. The larger DBTT shift observed in F82H is interpreted by means of both hardening effects and a reduction of cleavage fracture stress by M 23C 6 carbides precipitation along lath block and packet boundaries, while that of JLF-1 is due to only the hardening effect. Dimensional change measurement during in-pile creep tests revealed the creep strain of F82H was limited at 300 °C. Performance of the weld bond under neutron irradiation will be critical to determine the life time of blanket structural components. Application of the ODS steels, which are resistant to corrosion in supercritical pressurized water, to the water-cooled blanket is essential to increase thermal efficiency of the blanket systems beyond DEMO. The coupling of RAFS and ODS steel could be effective to realize a highly efficient fusion blanket.

  17. 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.

  18. 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.

  19. Influence of Co content on the biocompatibility and bio-corrosion of super ferritic stainless steels

    NASA Astrophysics Data System (ADS)

    Yoo, Y. R.; Jang, S. G.; Nam, H. S.; Shim, G. T.; Cho, H. H.; Kim, J. G.; Kim, Y. S.

    2008-12-01

    Bio-metals require high corrosion resistance, because their biocompatibility is closely related to this parameter. Bio-metals release metal ions into the human body, leading to deleterious effects. Allergies, dermatitis, and asthma are the predominant systemic effects resulting in the human body. In particular, Ni is one of the most common causes of allergic contact dermatitis. In the present work, we designed new ferritic stainless steels wherein Ni is replaced with Co under consideration of allergic respondes and microstructural stability. This work focuses on the effect of Co content on the biocompatibility and corrosion resistance of high PRE super ferritic stainless steels in bio-solution and acidic chloride solution. In the case of the acidic chloride solution, with increasing Co content in the ferritic stainless steels, passive current density increased and critical pitting temperature (CPT) decreased. Also, in the passive state, AC impedance and repassivation rate were reduced. These results are attributed to the thermodynamic stability of cobalt ions, as indicated in the EpH diagram for a Co-H2O system. However, in the case of bio-solutions, with increasing Co content of the alloys, the passive current density decreased. AC impedance and repassivation rate meanwhile increased in the passive state. This is due to the increased ratios of Cr2O3/Cr(OH)3 and [Metal Oxide]/Metal + Metal Oxide] of the passive film formed in bio-solution.

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

    DOE PAGES

    Li, Zhangbo; Lo, Wei-Yang; Chen, Yiren; ...

    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

  1. Helium effects on the mechanical properties of neutron-irradiated Cr-Mo ferritic steels

    SciTech Connect

    Klueh, R.L.

    1990-01-01

    In the first wall of a fusion rector, large amounts of transmutation helium will be produced simultaneously with the displacement damage caused by high-energy neutrons from the fusion reaction. One method used to simulate irradiation effects for ferritic steels is to add nickel to the steels and irradiate them in a mixed-spectrum reactor. Fast neutrons in the spectrum produce displacement damage, while transmutation helium is produced by a two-step reaction of {sup 58}Ni with thermal neutrons. This technique has been used to investigate the effect of helium on tensile properties and toughness. Results from these studies are summarized.

  2. 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.

  3. 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.

  4. Recent improvements in size effects correlations for DBTT and upper shelf energy of ferritic steels

    SciTech Connect

    Kumar, A.S.; Louden, B.S. ); Garner, F.A.; Hamilton, M.L. )

    1992-01-01

    Currently available correlations for the effects of specimen size on the USE were developed for relatively ductile steels and will not serve as well when the steels become embrittled. Size effects correlations were developed recently for the impact properties of less ductile HT9 to be applied to other initially more ductile steels as they lose their ductility during irradiation. These new correlations successfully predict the ductile brittle transition temperature (DBTT) and the upper shelf energy (USE) of full size Charpy specimens based on subsize specimen data. The new DBTT and the USE correlations were tested against published experimental data on other ferritic steels and shown to perform successfully at lower USE particularly when both precracked and notched only specimens were employed.

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

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

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

  6. Low cycle fatigue properties of a low activation ferritic steel (JLF-1) at room temperature

    NASA Astrophysics Data System (ADS)

    Nishimura, A.; Nagasaka, T.; Inoue, N.; Muroga, T.; Namba, C.

    2000-12-01

    To investigate fatigue properties of a low activation ferritic steel (9Cr-2W steel, JLF-1), low cycle fatigue tests were performed in air at room temperature under axial strain control for a complete push-pull condition. The strain rate was 0.4% s-1. Cyclic strain-hardening was observed within the initial 20 cycles, and then cyclic strain-softening occurred gradually until the final failure, though the plastic strain range did not change significantly. Tensile peak stresses in hysteresis curves measured at around half the number of cycles to failure depended on the total strain range. The drop in the peak stress by the cyclic strain-softening increased with decreasing total strain range. The regression curve of the total strain range against the fatigue life was formulated using the Manson-Coffin equation and the fatigue life of JLF-1 steel was compared with that of 8Cr-2W steel.

  7. 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.

  8. In-service inspection method for low-finned ferritic stainless steel tubes for new heat exchanger

    SciTech Connect

    Iwai, O.; Goto, M.

    1994-12-31

    Conventional inner eddy current test cannot obtain sufficient evaluation for low finned ferritic stainless steel tube inspection. The authors tried various methods and developed special partial saturation eddy current method. This paper summarizes typical experimental results of fundamental studies and trials, and introduces developed ECT data acquisition and evaluation system. Moisture Separator Heater (MSH) used in ABWR (Advanced Boiling Water Reactor) plant is a new type heat exchanger to increase plant thermal efficiency. There are four single tubesheet heaters in a MSH vessel. Each heater has hundreds of low finned tubes made of ferritic stainless steel. In nuclear power plants, non-magnetic materials (austenitic stainless steel, titanium, aluminum brass, etc.,) are mainly used as heat exchanger tubes such as the tubes of feedwater heater, condenser, evaporator and so on. Conventional ECT (Eddy Current Test) method are easily applied for the inspection of these heat exchanger tubes. In recent years, the authors started using ferritic stainless steel tube for new heat exchangers such as MSH because of its superior heat transfer efficiency. However, high permeability of ferritic stainless steel prevents the inspection of these tubes using conventional ECT method. To inspect MSH tubes periodically is important to confirm and maintain reliability of MSH. They tried applying various inspection methods and have developed special ECT method for low finned ferritic stainless steel tubes.

  9. 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.

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

    NASA Astrophysics Data System (ADS)

    Shen, Yinzhong; Zhou, Xiaoling; Shang, Zhongxia

    2016-05-01

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

  11. 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.

  12. Thermal Growth and Performance of Manganese Cobaltite Spinel Protection Layers on Ferritic Stainless Steel SOFC Interconnects

    SciTech Connect

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

    2005-08-01

    To protect solid oxide fuel cells (SOFCs) from chromium poisoning and improve metallic interconnect stability, manganese cobaltite spinel protection layers with a nominal composition of Mn1.5Co1.5O4 were thermally grown on Crofer22 APU, a ferritic stainless steel. Thermal, electrical and electrochemical investigations indicated that the spinel protection layers not only significantly decreased the contact area specific resistance (ASR) between a LSF cathode and the stainless steel interconnect, but also inhibited the sub-scale growth on the stainless steel by acting as a barrier to the inward diffusion of oxygen. A long-term thermal cycling test demonstrated excellent structural and thermomechanical stability of these spinel protection layers, which also acted as a barrier to outward chromium cation diffusion to the interconnect surface. The reduction in the contact ASR and prevention of Cr migration achieved by application of the spinel protection layers on ferritic stainless steel resulted in improved stability and electrochemical performance of SOFCs.

  13. 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

  14. 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.

  15. Neutron diffraction investigation of lattice microstrain in ferrite steel

    NASA Astrophysics Data System (ADS)

    Camanzi, A.; Moze, O.

    1992-06-01

    The degradation of carbon steels when exposed to H rich environments is well known to result in catastrophic failure. In order to characterize in a comprehensive manner the structural effects of hydrogenation, a series of high resolution neutron powder diffraction measurements were carried out on cross-sections of carbon steel segments used for gas pipelines. Peak positions were measured to an accuracy of 0.001%, whilst line broadening of individual peaks was measured to an accuracy of 0.1%. The ( h k l) dependent peak linewidths were fitted using a pseudo-Voigt peak shape function. Non-hydrogenated materials were found to display a different diffraction linewidth dependence on the crystal elastic anisotropy than hydrogenated materials.

  16. 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.

  17. Formable ferrite-degenerated pearlite steel (FDP-55) for automotive use

    SciTech Connect

    Nagao, N.; Hamamatsu, S.; Kunishige, K.

    1984-01-01

    In order to help the gauge reduction of wheels and chassis parts of automobiles, a formable and weldable hot rolled steel of 550 MPa grade, named FDP-55, has been developed. FDP-55 is an 0.14% C, 0.1% Si, 1.1% Mn and Nb free Alkilled steel obtained by controlled-cooling to a low coiling temperature on a runout table, and it is featured by ferrite-degenerated pearlite microstructure. Results of co-operative works with automotive makers showed that FDP-55 was successful in the application to wheels and chassis parts attaining the large weight reduction. This paper reports the metallurgical features and characteristics of the steel.

  18. High-Temperature Performance of Ferritic Steels in Fireside Corrosion Regimes: Temperature and Deposits

    NASA Astrophysics Data System (ADS)

    Dudziak, T.; Hussain, T.; Simms, N. J.

    2016-11-01

    The paper reports high temperature resistance of ferritic steels in fireside corrosion regime in terms of temperature and deposits aggressiveness. Four candidate power plant steels: 15Mo3, T22, T23 and T91 were exposed under simulated air-fired combustion environment for 1000 h. The tests were conducted at 600, 650 and 700 °C according to deposit-recoat test method. Post-exposed samples were examined via dimensional metrology (the main route to quantify metal loss), and mass change data were recorded to perform the study of kinetic behavior at elevated temperatures. Microstructural investigations using ESEM-EDX were performed in order to investigate corrosion degradation and thickness of the scales. The ranking of the steels from most to the least damage was 15Mo3 > T22 > T23 > T91 in all three temperatures. The highest rate of corrosion in all temperatures occurred under the screening deposit.

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

    SciTech Connect

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

    1997-08-01

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

  20. High-Temperature Performance of Ferritic Steels in Fireside Corrosion Regimes: Temperature and Deposits

    NASA Astrophysics Data System (ADS)

    Dudziak, T.; Hussain, T.; Simms, N. J.

    2017-01-01

    The paper reports high temperature resistance of ferritic steels in fireside corrosion regime in terms of temperature and deposits aggressiveness. Four candidate power plant steels: 15Mo3, T22, T23 and T91 were exposed under simulated air-fired combustion environment for 1000 h. The tests were conducted at 600, 650 and 700 °C according to deposit-recoat test method. Post-exposed samples were examined via dimensional metrology (the main route to quantify metal loss), and mass change data were recorded to perform the study of kinetic behavior at elevated temperatures. Microstructural investigations using ESEM-EDX were performed in order to investigate corrosion degradation and thickness of the scales. The ranking of the steels from most to the least damage was 15Mo3 > T22 > T23 > T91 in all three temperatures. The highest rate of corrosion in all temperatures occurred under the screening deposit.

  1. Kinetic transition during the growth of proeutectoid ferrite in Fe-C-Mn-Si quaternary steel

    NASA Astrophysics Data System (ADS)

    Zhang, Guo-Hong; Heo, Yoon-Uk; Song, Eun-Ju; Suh, Dong-Woo

    2013-03-01

    The kinetics of ferrite growth in Fe-0.1C-1.5Mn-0.94Si (mass pct) quaternary steel is investigated through the characterization of isothermal growth behavior, the thermodynamic prediction of kinetic boundary and the diffusional growth simulations using DICTRA. The change in microstructural evolution from slow growth to fast one is consistent with the calculated change of interface condition from the partitioning local equilibrium (PLE) to the negligible partitioning local equilibrium (NPLE). Compared with the DICTRA simulation, the observed growth kinetics of ferrite are between the calculated ones assuming local equilibrium (LE) and paraequilibrium (PE) criterions. At temperatures below the PLE/NPLE kinetic boundary, the observed growth behavior can be reasonably described by kinetic transition from PE to NPLE condition as isothermal time elapses, taking into account the critical velocity of interface at which trans-interface diffusion of subsitutional element permits the transition from PE to NPLE growth.

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

    NASA Astrophysics Data System (ADS)

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

    2008-06-01

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

  3. 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.

  4. 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.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

  7. Corrosion and toughness of experimental and commercial super ferritic stainless steels

    SciTech Connect

    Dowling, N.J.E.; Kim, H.; Kim, J.N.; Ahn, S.K.; Lee, Y.D.

    1999-08-01

    The effect of minor alloying in a super ferritic stainless steel 26% Cr-3% Mo matrix was investigated. The corrosion resistance of several experimental heats was examined in terms of their sensitization and intergranular corrosion (IGA) susceptibility following a low-temperature anneal (620 C). Constant potential etching, electrochemical (electropotentiokinetic reactivation [EPR]), and immersion (modified Strauss test) studies showed that the principal corrosion initiation site of heat-treated steels was intergranular even at low [C + N] (< 130 ppm) and relatively high [Nb + Tl] concentrations. Despite the significant contribution of Nb and Ti to the IGA resistance, these elements had a deleterious effect on the notch toughness. Charpy V testing demonstrated increases in the upper shelf energy and ductile-to-brittle transition temperature (DBTT), the latter shifting from {approx} {minus}50 C in the absence of stabilizing elements to > 25 C for the stabilizing ratio [(Nb + Ti)/(C + N)] > 9. Corrosion resistance of the experimental heats was compared with that of several commercial alloys with intermediate stabilization ratios. The interaction of toughness and corrosion resistance in ferritic stainless steel was discussed with respect to the lack of consistency between published evaluation methods and the ideal stabilization ratio at low [C + N] values.

  8. 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.

  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. 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.

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

    SciTech Connect

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

    2016-05-26

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

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

    DOE PAGES

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

    2016-05-26

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

  13. 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.

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

    NASA Astrophysics Data System (ADS)

    Erişir, E.; Bilir, O. G.

    2017-02-01

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

  15. Characterizing microstructural changes in ferritic steels by positron annihilation spectroscopy: Studies on modified 9Cr-1Mo steel

    NASA Astrophysics Data System (ADS)

    Hari Babu, S.; Rajkumar, K. V.; Hussain, S.; Amarendra, G.; Sundar, C. S.; Jayakumar, T.

    2013-01-01

    Applicability of positron annihilation spectroscopy in probing the microstructural changes in ferritic steels has been investigated with thermal treatment studies on modified 9Cr-1Mo steel, during 300-1273 K. Positron lifetime results are compared with those of ultrasonic velocity and hardness techniques with two initial microstructural conditions i.e., normalized and tempered condition as well as only normalized condition. In first case, positron lifetime is found to be sensitive to small changes in metal carbide precipitation which could not be probed by other two techniques. In later case, positron lifetime is found to be sensitive to defect annealing until 673 K and in distinguishing the growth and coarsening of metal carbide precipitation stages during 773-1073 K. The present study suggests that by combining positron lifetime, ultrasonic velocity and hardness measurements, it is possible to distinguish distinct microstructures occurring at different stages.

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

    NASA Astrophysics Data System (ADS)

    Chaouadi, R.

    2007-02-01

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

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

    SciTech Connect

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

    1998-03-01

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

  18. Low-temperature irradiation effects on tensile and Charpy properties of low-activation ferritic steels

    NASA Astrophysics Data System (ADS)

    Shiba, Kiyoyuki; Hishinuma, Akimichi

    2000-12-01

    Tensile and Charpy properties of low-activation ferritic steel, F82H irradiated up to 0.8 dpa at low temperature below 300°C were investigated. The helium effect on these properties was also investigated using the boron isotope doping method. Neutron irradiation increased yield stress accompanied with ductility loss, and it also shifted the ductile-to-brittle transition temperature (DBTT) from -50°C to 0°C. Boron-doped F82H showed larger degradation in DBTT and ductility than boron-free F82H, while they had the same yield stress before and after irradiation.

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

    SciTech Connect

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

    2014-09-22

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

  20. Morphology, structure, and chemistry of nanoclusters in a mechanically alloyed nanostructured ferritic steel

    SciTech Connect

    Brandes, M. C.; Kovarik, Libor; Miller, Michael K.; Mills, M. J.

    2012-01-14

    Nanostructured ferritic steels have excellent high temperature creep properties and radiation tolerance due to the presence of a high density of Ti-Y-O-enriched nanoclusters. The morphology of the nanoclusters is found to be consistent with a truncated rhombic dodecahedron defined by the {l_brace}100{r_brace} and {l_brace}110{r_brace} planes in the Fe matrix. The derived symmetry and the compositional information indicate that the nanoclusters are inconsistent with the cubic Y2Ti2O7 or the polymorphs of Y2TiO5 phase. Possible structural models are discussed.

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

    NASA Astrophysics Data System (ADS)

    Ren, Xiaowei

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

  2. Synergy effects of Cu and Sn on pitting corrosion resistance of ultra-purified medium chromium ferritic stainless steel

    NASA Astrophysics Data System (ADS)

    Zhang, XiangJun; Liu, ZhenYu

    2017-03-01

    The influence of combination of Cu and Sn on pitting resistance of ultra-purified medium chromium ferritic stainless steel in 3.5 wt.% NaCl at 25°C was investigated by using electrochemical method. The results show that there is synergy effect between Cu and Sn, and the strong interaction between Cu and Sn in ferritic stainless steels clearly affects their pitting corrosion behaviour in 3.5% NaCl. A mechanism of the synergy of Cu and Sn was discussed.

  3. Development of brazing foils to join monocrystalline tungsten alloys with ODS-EUROFER steel

    NASA Astrophysics Data System (ADS)

    Kalin, B. A.; Fedotov, V. T.; Sevrjukov, O. N.; Kalashnikov, A. N.; Suchkov, A. N.; Moeslang, A.; Rohde, M.

    2007-08-01

    Results on rapidly solidified filler metals for brazing W with W and monocrystalline W with EUROFER steel (FS) are presented. Rapidly quenched powder-type filler metals based on Ti bal-V-Cr-Be were developed to braze polycrystalline W with monocrystalline W. In addition, Fe bal-Ta-Ge-Si-B-Pd alloys were developed to braze monocrystalline W with FS for helium gas cooled divertors and plasma-facing components. The W to FS brazed joints were fabricated under vacuum at 1150 °C, using a Ta spacer of 0.1 mm in thickness to account for the different thermal expansions. The monocrystalline tungsten as well as the related brazed joints withstood 30 cycles between 750 °C/20 min and air cooling/3-5 min.

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

    SciTech Connect

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

    2014-11-01

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

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

    SciTech Connect

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

    2005-07-05

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

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

    NASA Astrophysics Data System (ADS)

    Dai, Yong; Marmy, Pierre

    2005-08-01

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

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

    NASA Astrophysics Data System (ADS)

    Vasantharaja, P.; Vasudevan, M.

    2012-02-01

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

  8. Kinetic Model of Decarburization and Denitrogenation in Vacuum Oxygen Decarburization Process for Ferritic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Xu, Yingtie; Chen, Zhaoping; Zhang, Ge

    2009-06-01

    The characteristics and classification of decarburization and denitrogenation in the vacuum vessel for stainless steel production are analyzed. Based on the analysis of movements of the liquid steel and bubbles, the kinetics of decarburization and denitrogenation in the vacuum oxygen decarburization (VOD) process has been studied. A kinetic model of decarburization and denitrogenation has been developed to simulate the VOD process, considering each reaction zone as oxygen blowing crater, bottom blowing plume, steel/slag interface, and plume eye. As a result, it is possible to quantify the contribution of each reaction zone in decarburization and denitrogenation rate at a different stage in the VOD process. Specific trials at a vacuum induction furnace were performed to refine stainless steel in vacuum carbon deoxidation (VCD) and VOD style, respectively. The trial results are in good agreement with the model calculation. Combining the trials and the model calculation and the influence of temperature control, critical carbon content selection on the terminal total [C] + [N] content can be discussed further to provide a reasonable proposal for high-quality ferritic stainless steel production.

  9. Fabrication of oxide dispersion strengthened ferritic clad fuel pins

    SciTech Connect

    Zirker, L.R. ); Bottcher, J.H. ); Shikakura, S. ); Tsai, C.L. . Dept. of Welding Engineering); Hamilton, M.L. )

    1991-01-01

    A resistance butt welding procedure was developed and qualified for joining ferritic fuel pin cladding to end caps. The cladding are INCO MA957 and PNC ODS lots 63DSA and 1DK1, ferritic stainless steels strengthened by oxide dispersion, while the end caps are HT9 a martensitic stainless steel. With adequate parameter control the weld is formed without a residual melt phase and its strength approaches that of the cladding. This welding process required a new design for fuel pin end cap and weld joint. Summaries of the development, characterization, and fabrication processes are given for these fuel pins. 13 refs., 6 figs., 1 tab.

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

    SciTech Connect

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

    2016-02-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  12. Improvement of High Temperature Mechanical Property by Precipitation Hardening of Reduced Activation Ferritic/Martensitic Steels

    SciTech Connect

    Sakasegawa, H.; Kohyama, A.; Katoh, Y.; Tamura, M.; Khono, Y.; Kimura, A.

    2003-07-15

    Reduced Activation Ferritic/Martensitic steels (RAFs) are leading candidates for blanket and first wall structures of the D-T fusion reactors. Recently, in order to achieve better efficiency of energy conversion by using RAFs in advanced blanket systems, improvement of high temperature mechanical property of RAFs is desired. In this work, experimental alloys, FETA-series (Fe-Ta-C or N) steels, were prepared to observe precipitation hardening mechanism by MX-type particles at elevated temperatures in detail. According to the results, innovative improvement of creep property can be achieved by applying of precipitation hardening by very fine TaX (X=C, N) particles. With increasing tantalum content, finer dispersion of MX-type particles, dislocation structures and sub-grain structures were observed by TEM (Transmission Electron Microscopy). These fine structures contributed to the improvement of creep property.

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

    SciTech Connect

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

    2014-08-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  15. Inhibited Aluminization of an ODS FeCr Alloy

    SciTech Connect

    Vande Put Ep Rouaix, Aurelie; Pint, Bruce A

    2012-01-01

    Aluminide coatings are of interest for fusion energy applications both for compatibility with liquid Pb-Li and to form an alumina layer that acts as a tritium permeation barrier. Oxide dispersion strengthened (ODS) ferritic steels are a structural material candidate for commercial reactor concepts expected to operate above 600 C. Aluminizing was conducted in a laboratory scale chemical vapor deposition reactor using accepted conditions for coating Fe- and Ni-base alloys. However, the measured mass gains on the current batch of ODS Fe-14Cr were extremely low compared to other conventional and ODS alloys. After aluminizing at two different Al activities at 900 C and at 1100 C, characterization showed that the ODS Fe-14Cr specimens formed a dense, primarily AlN layer that prevented Al uptake. This alloy batch contained a higher (> 5000 ppma) N content than the other alloys coated and this is the most likely reason for the inhibited aluminization. Other factors such as the high O content, small ({approx} 140 nm) grain size and Y-Ti oxide nano-clusters in ODS Fe-14Cr also could have contributed to the observed behavior. Examples of typical aluminide coatings formed on conventional and ODS Fe- and Ni-base alloys are shown for comparison.

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

    SciTech Connect

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

    2006-09-21

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

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

    SciTech Connect

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

    1997-06-01

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

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

    NASA Astrophysics Data System (ADS)

    Vanaja, J.; Laha, Kinkar

    2015-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

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

    SciTech Connect

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

    1996-12-31

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  3. In Situ Synchrotron Tensile Investigations on 14YWT, MA957 and 9-Cr ODS Alloys

    SciTech Connect

    Lin, Jun-Li; Mo, Kun; Yun, Di; Miao, Yinbin; Liu, Xiang; Zhao, Huijuan; Hoelzer, David T; Park, Jun-Sang; Almer, Jonathan; Zhang, Guangming; Zhou, Zhangjian; Stubbins, James; Yacout, Abdellatif

    2016-01-01

    Nanostructured ferritic alloys (NFAs) provide exceptional radiation tolerance and high-temperature mechanical properties when compared to traditional ferritic and ferritic/martensitic (F/M) steels. Their remarkable properties result from ultrahigh density and ultrafine size of Y-Ti-O nanoclusters within the ferritic matrix. In this work, we applied a high-energy synchrotron radiation X-ray to study the deformation process of two NFAs including 14YWT and MA957, and a 9-Cr ODS steel. Only the relatively large nanoparticles in the 9-Cr ODS were observed in the synchrotron X-ray diffraction. The nanoclusters in both 14 YWT and MA957 were invisible in the measurement due to their non-stoichiometric nature. Due to the different sizes of nanoparticles and nanoclusters in the materials, the Orowan looping was considered to be the major strengthening mechanism in the 9-Cr ODS, while the dispersed-barrier-hardening is dominant strengthening mechanism in both 14YWT and MA957, respectively. This analysis was inferred from the different build-up rates of dislocation density when plastic deformation was initiated. Finally, the dislocation densities interpreted from the X-ray measurements were successfully modeled using the Bergstr m s dislocation models.

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

    NASA Astrophysics Data System (ADS)

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

    2007-08-01

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

  5. Effect of crack length-to-width ratio on crack resistance of high Cr-ODS steels at high temperature for fuel cladding application

    NASA Astrophysics Data System (ADS)

    Chaouadi, R.; Ramesh, M.; Gavrilov, S.

    2013-11-01

    Oxide dispersion strengthened (ODS) steels with high Cr-content are extensively investigated in Europe, Japan and United States by the nuclear materials community for application to both advanced fission reactors and fusion systems. In comparison to standard high Cr-steels, the expected operation temperature range can be extended to 650 °C or more because of their improved creep resistance. However, their crack resistance behavior in the high temperature range was less investigated.The aim of the present paper is to provide some insight on their fracture behavior at high temperature and different crack configurations, in particular shallow crack. Crack resistance measurements were performed on a 12%Cr-ODS steel using compact tension specimens at 650 °C considering both shallow and deep crack configurations. Finite element calculations were performed on a typical fuel cladding tube geometry to assess the performances in terms of crack resistance. It is found that the temperature gradient across the wall should be maintained low enough to avoid cracking. After irradiation in corrosive environment, the boundary conditions might be further affected limiting therefore the lifetime of ODS cladding.

  6. Mechanisms of Sticking Phenomenon Occurring during Hot Rolling of Two Ferritic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Son, Chang-Young; Kim, Chang Kyu; Ha, Dae Jin; Lee, Sunghak; Lee, Jong Seog; Kim, Kwang Tae; Lee, Yong Deuk

    2007-11-01

    Mechanisms of sticking phenomenon occurring during hot rolling of two ferritic stainless steels, STS 430J1L and STS 436L, were investigated in the present study. A hot-rolling simulation test was carried out using a high-temperature wear tester capable of controlling rolling speed, load, and temperature. The test results at 900 °C and 1000 °C revealed that the sticking process proceeded with three stages, i.e., nucleation, growth, and saturation, for the both stainless steels, and that STS 430J1L had a smaller number of sticking nucleation sites and slower growth rate than the STS 436L because of higher high-temperature hardness, thereby leading to less serious sticking. When the test was conducted at 1070 °C, the sticking hardly occurred in both stainless steels as Fe-Cr oxide layers were formed on the surface of the rolled materials. Thus, in order to prevent or minimize the sticking, it was suggested to improve high-temperature properties of stainless steels in the case of hot rolling at 900 °C to 1000 °C, and to establish appropriate rolling conditions and alloy compositions for ready formation of oxide layers in the case of hot rolling at higher temperatures than 1000 °C.

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  8. Effect of alloy composition on high-temperature bending fatigue strength of ferritic stainless steels

    NASA Astrophysics Data System (ADS)

    Ahn, Yong-Sik; Song, Jeon-Young

    2011-12-01

    Exhaust manifolds are subjected to an environment in which heating and cooling cycles occur due to the running pattern of automotive engines. This temperature profile results in the repeated bending stress of exhaust pipes. Therefore, among high-temperature characteristics, the bending fatigue strength is an important factor that affects the lifespan of exhaust manifolds. Here, we report on the effect of the alloy composition, namely the weight fraction of the elements Cr, Mo, Nb, and Ti, on the high-temperature bending fatigue strength of the ferritic stainless steel used in exhaust manifolds. Little difference in the tensile strength and bending fatigue strength of the different composition steels was observed below 600 °C, with the exception of the low-Cr steel. However, steels with high Cr, Mo, or Nb fractions showed considerably larger bending fatigue strength at temperatures of 800 °C. After heating, the precipitates from the specimens were extracted electrolytically and analyzed using scanning electron microscopy energy dispersive spectrometry and transmission electron microscopy. Alloying with Cr and Mo was found to increase the bending fatigue strength due to the substitutional solid solution effect, while alloying with Nb enhanced the strength by forming fine intermetallic compounds, including NbC and Fe2Nb.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

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

    NASA Astrophysics Data System (ADS)

    Hunt, Ryan Matthew

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

  11. Electron work functions of ferrite and austenite phases in a duplex stainless steel and their adhesive forces with AFM silicon probe.

    PubMed

    Guo, Liqiu; Hua, Guomin; Yang, Binjie; Lu, Hao; Qiao, Lijie; Yan, Xianguo; Li, Dongyang

    2016-02-12

    Local electron work function, adhesive force, modulus and deformation of ferrite and austenite phases in a duplex stainless steel were analyzed by scanning force microscopy. It is demonstrated that the austenite has a higher electron work function than the ferrite, corresponding to higher modulus, smaller deformation and larger adhesive force. Relevant first-principles calculations were conducted to elucidate the mechanism behind. It is demonstrated that the difference in the properties between austenite and ferrite is intrinsically related to their electron work functions.

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

    SciTech Connect

    Klueh, R.L.

    1995-02-01

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

  13. Test research on sticking mechanism during hot rolling of SUS 430 ferritic stainless steel

    NASA Astrophysics Data System (ADS)

    Liu, Jun-Xian; Zhang, Yong-Jun; Han, Jing-Tao

    2010-10-01

    The sticking phenomenon during hot rolling of SUS 430 ferritic stainless steel was investigated by means of a two-disc type high-temperature wear tester. The test results indicate that sticking particles on the surfaces of high chromium steel (HiCr) and high-speed steel (HSS) rolls undergo nucleation, growth, and saturation stages. Grooves on the roll surface generated by grinding provide nucleation sites for sticking particles. The number of sticking particles on the HiCr roll surface is greater than that on the HSS roll surface. The average surface roughnesses ( R a) of HiCr and HSS rolls change from 0.502 and 0.493 μm at the initial stage to 0.837 and 0.530 μm at the saturation stage, respectively. The test further proves that the sticking behavior is strongly dependent on roll materials, and the HSS roll is more beneficial to prevent particles sticking compared with the HiCr roll under the same hot-rolling conditions.

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

    SciTech Connect

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

    2000-04-01

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

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

    NASA Astrophysics Data System (ADS)

    Chen, Shenghu; Rong, Lijian

    2015-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2004-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

  18. Control of activation levels to simplify waste management of fusion reactor ferritic steel components

    SciTech Connect

    Wiffen, F.W.; Santoro, R. T.

    1983-01-01

    Activation characteristics of a material for service in the neutron flux of a fusion reactor first wall fall into three areas: waste management, reactor maintenance and repair, and safety. Of these, the waste management area is the most likely to impact the public acceptance of fusion reactors for power generation. The decay of the activity in steels within tens of years could lead to simplified waste disposal or possibly even to materials recycle. Whether or not these can be achieved will be controlled by (1) selection of alloying elements, (2) control of critical impurity elements, and (3) control of cross contamination from other reactor components. Several criteria can be used to judge the acceptability of potential alloying elements in iron, and to define the limits on content of critical impurity elements. One approach is to select and limit alloying additions on the basis of the activity. If material recycle is a goal, N, Al, Ni, Cu, Nb, and Mo must be excluded. If simplified waste storage by shallow land burial is the goal, regulations limit the concentration of only a few isotopes. For first-wall material that will be exposed to 9 MW-y/m/sup 2/ service, allowable initial concentration limits include (in at. ppM) Ni < 20,000; Mo < 3650; N < 3650, Cu < 2400; and Nb < 1.0. The other constituent elements of ferritic steels will not be limited. Possible substitutes for the molybdenum normally used to strengthen the steels include W, Ta, Ti, and V.

  19. Interatomic potential to study the formation of NiCr clusters in high Cr ferritic steels

    NASA Astrophysics Data System (ADS)

    Bonny, G.; Bakaev, A.; Olsson, P.; Domain, C.; Zhurkin, E. E.; Posselt, M.

    2017-02-01

    Under irradiation NiSiPCr clusters are formed in high-Cr ferritic martensitic steels as well as in FeCr model alloys. In the literature little is known about the origin and contribution to the hardening of these clusters. In this work we performed density functional theory (DFT) calculations to study the stability of small substitutional NiCr-vacancy clusters and interstitial configurations in bcc Fe. Based on DFT data and experimental considerations a ternary potential for the ferritic FeNiCr system was developed. The potential was applied to study the thermodynamic stability of NiCr clusters by means of Metropolis Monte Carlo (MMC) simulations. The results of our simulations show that Cr and Ni precipitate as separate fractions and suggest only a limited synergetic effect between Ni and Cr. Therefore our results suggest that the NiCrSiP clusters observed in experiments must be the result of other mechanisms than the synergy of Cr and Ni at thermal equilibrium.

  20. Characterization of twin-like structure in a ferrite-based lightweight steel

    NASA Astrophysics Data System (ADS)

    Nezhadfar, Pooriya Dastranjy; Zarei-Hanzaki, Abbas; Sohn, Seok Su; Abedi, Hamid Reza

    2016-09-01

    The present study examined cold to warm compressive deformation behavior of a ferrite- based lightweight steel through characterization of the banded structures. Compression tests were carried out at 25 to 500 °C at a strain rate of 0.01 s-1 up to true strain of 0.6. Analysis of the microstructural evolution using electron back scatter diffraction indicated that the twin-like bands in the large ferrite grains occurred with the {112}[111] system at a 60° misorientation. Density of the twin-like bands is increased by raising the deformation temperature. EBSD results showed that the primary and secondary twins occurred in the [-11-1] and [1-1-1] directions. In addition, the strain at 500 °C distorted the twin-like bands and resulted in wavy boundaries. The strain hardening behavior was also examined using the Crussard-Jaoul (C-J) model and the n-values were calculated for each stage of imposing strain. The results showed high dislocation density in the adjacent of twin-like boundaries intersections which resulted in the n-value increment.

  1. Microstructural origin of the skeletal ferrite morphology of austenitic stainless steel welds

    SciTech Connect

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

    1982-04-01

    Scanning transmission electron microscopy was conducted on welds exhibiting a variety of skeletal, or vermicular ferrite morphologies in addition to one lathy ferrite morphology. These ferrite morphologies result from primary ferrite solidification followed by a solid state transformation upon cooling. During cooling, a large fraction of the ferrite transforms to austenite leaving a variety of ferrite morphologies. Comparison of composition profiles and alloy partitioning showed both the skeletal and lathy ferrite structures result from a diffusion controlled solid state transformation. However, the overall measured composition profiles of the weld structure are a result of partitioning during both solidification and the subsequent solid state transformation.

  2. Assessment of a new fabrication route for Fe-9Cr-1W ODS cladding tubes

    NASA Astrophysics Data System (ADS)

    Toualbi, L.; Cayron, C.; Olier, P.; Malaplate, J.; Praud, M.; Mathon, M.-H.; Bossu, D.; Rouesne, E.; Montani, A.; Logé, R.; de Carlan, Y.

    2012-09-01

    Oxide Dispersion Strengthened ferritic/martensitic steels are developed as future cladding materials for Generation IV Sodium-Cooled Fast Reactors. ODS alloys are elaborated by powder metallurgy, consolidated by hot extrusion and manufactured into tube cladding using cold rolling process. ODS steels present low ductility and high hardness at room temperature which complicate their manufacturing. Cold working leads to the hardening of the tube which needs to be softened by heat treatment. A new high temperature fabrication route performed on a Fe-9Cr-1W-Ti-Y2O3-ODS martensitic steel has been designed by following the hardness values, the morphological and crystallographic anisotropy and the nano-precipitation size evolution at each step of the fabrication route. Observations show that phase transformation from ferrite (α) to austenite (γ) is crucial to reduce the morphological and the crystallographic anisotropy induced by the manufacturing processes. The high temperature heat treatments permit to make the austenitic grain grow leading to an improvement of the cold workability. Ultimate Tensile Strength values obtained in the hoop direction remain about 315 MPa at 650 °C which is slightly lower compared to other Fe-9Cr ODS tubes but the new microstructure could be more favorable for creep properties.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  4. Fracture toughness of low activation ferritic steel (JLF-1) weld joint at room temperature

    NASA Astrophysics Data System (ADS)

    Nishimura, A.; Inoue, N.; Muroga, T.

    1998-10-01

    A low activation ferritic steel has been developed for a candidate of a structural material of nuclear fusion reactors. Since welding must be performed when the support structures are constructed, fracture toughness of the weld joint has to be characterized as well as the base metal in an engineering sense. In this report, 25 mm thick plates of JLF-1, which contains 9% Cr and 2% W, are butt-welded by a tungsten inert gas (TIG) procedure, and the fracture toughness of the base plate and the weld metal is investigated at room temperature using 1T and 0.5T CT specimens. The base metal reveals high fracture toughness of about 430 kJ/m 2. However, the weld metal showed unstable big pop-ins. One sample fractured in a nearly elastic condition and another sample showed a toughness of over 400 kJ/m 2.

  5. Morphology, Structure, and Chemistry of Nanoclusters in a Mechanically-Alloyed Nanostructured Ferritic Steel

    SciTech Connect

    Brandes, Matthew C; Kovarik, L.; Miller, Michael K; Mills, Michael J.

    2012-01-01

    Nanostructured ferritic steels have excellent elevated temperature strengths, creep resistances, and radiation tolerances due to the presence of a high density of Ti-Y-O-enriched nanoclusters. The compositions, morphologies, and structures of the smallest of these nanoclusters with maximum dimensions of {approx}2-4 nm were investigated in alloy 14YWT by high-resolution scanning transmission electron microscopy and atom probe tomography. Nanoclusters are found to be coherent with truncated rhombic dodecahedron morphologies defined by the {l_brace}100{r_brace} and {l_brace}110{r_brace} planes in the Fe matrix. Particles have compositions rich in Ti, O, Y, and Cr that are inconsistent with known oxide structures. The smallest nanoclusters appear to lack an identifiable crystal structure. Both nano-diffraction and focal series imaging through the sample thickness suggest that they are amorphous.

  6. From embryos to precipitates: a study of nucleation and growth in a multicomponent ferritic steel

    SciTech Connect

    Zhang, Zhongwu; Liu, C T; Wang, Xun-Li; Littrell, Ken; Miller, Michael K; An, Ke; Chin, Bryan

    2011-01-01

    The nucleation and growth of nanoscale precipitates in a new class of high-strength, multicomponent, ferritic steels has been studied with complementary state-of-the-art microstructural characterization techniques of atom probe tomography for individual embryos and precipitates and small-angle neutron scattering for their statistical averages. Both techniques revealed a bimodal size distribution, with subnanometer embryos, and nanoscale precipitates. The embryos, which have a radius of {approx}0.4 nm, are enriched in Cu and served as preferential sites for nucleation. The critical radius for nucleation was determined to be {approx}0.7 nm. Subsequent growth of the precipitates is dictated by volumetric diffusion, as predicted by the Lifshitz-Slyozov-Wagner theory.

  7. Effect of deformation on ferrite nucleation and growth in a plain carbon and two microalloyed steels

    NASA Astrophysics Data System (ADS)

    Essadiqi, E.; Jonas, J. J.

    1989-06-01

    Isothermal compression tests were carried out on plain C, Mo, and Mo-Nb-V microalloyed steels in order to study the effect of austenite deformation on the ferrite nucleation and growth rates. The nucleation rate increases with deformation and the degree of supersaturation, Ae3- T; it appears to be reduced by the substitutional elements Mo, Nb, and V through reduction of the austenite grain boundary energy. The growth rate increases with the degree of supersaturation and is also reduced by these elements, apparently through the solute drag-like effect. Under static conditions, increasing the prestraining strain rate increases the nucleation rate, but this increase is small compared to the effect of concurrent deformation. The growth rate under static conditions decreases as the deformation or the strain rate is increased.

  8. Characterization and Modeling of Grain Boundary Chemistry Evolution in Ferritic Steels under Irradiation

    SciTech Connect

    Marquis, Emmanuelle; Wirth, Brian; Was, Gary

    2016-03-28

    Ferritic/martensitic (FM) steels such as HT-9, T-91 and NF12 with chromium concentrations in the range of 9-12 at.% Cr and high Cr ferritic steels (oxide dispersion strengthened steels with 12-18% Cr) are receiving increasing attention for advanced nuclear applications, e.g. cladding and duct materials for sodium fast reactors, pressure vessels in Generation IV reactors and first wall structures in fusion reactors, thanks to their advantages over austenitic alloys. Predicting the behavior of these alloys under radiation is an essential step towards the use of these alloys. Several radiation-induced phenomena need to be taken into account, including phase separation, solute clustering, and radiation-induced segregation or depletion (RIS) to point defect sinks. RIS at grain boundaries has raised significant interest because of its role in irradiation assisted stress corrosion cracking (IASCC) and corrosion of structural materials. Numerous observations of RIS have been reported on austenitic stainless steels where it is generally found that Cr depletes at grain boundaries, consistently with Cr atoms being oversized in the fcc Fe matrix. While FM and ferritic steels are also subject to RIS at grain boundaries, unlike austenitic steels, the behavior of Cr is less clear with significant scatter and no clear dependency on irradiation condition or alloy type. In addition to the lack of conclusive experimental evidence regarding RIS in F-M alloys, there have been relatively few efforts at modeling RIS behavior in these alloys. The need for predictability of materials behavior and mitigation routes for IASCC requires elucidating the origin of the variable Cr behavior. A systematic detailed high-resolution structural and chemical characterization approach was applied to ion-implanted and neutron-irradiated model Fe-Cr alloys containing from 3 to 18 at.% Cr. Atom probe tomography analyses of the microstructures revealed slight Cr clustering and segregation to dislocations and

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

    SciTech Connect

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

    2008-05-30

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  11. Investigation of Iron-Chromium-Niobium-Titanium Ferritic Stainless Steel for Solid Oxide Fuel Cell Interconnect Applications

    SciTech Connect

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

    2008-09-01

    As part of an effort to develop cost-effective ferritic stainless steel-based interconnects for solid oxide fuel cell (SOFC) stacks, AL 441 HPTM was studied in terms of its metallurgical characteristics, oxidation behavior, and electrical performance. Minor alloying elements (Nb and Ti) captured interstitials such as C by forming carbides, stabilizing the ferritic structure and mitigating the risks of sensitization and inter-granular corrosion. Laves phases rich in Nb and Si precipitated along grain boundaries during high temperature exposure, improving the steel’s high temperature mechanical strength. The capture of Si in the Laves phase minimized the Si activity in the steel substrate and prevented formation of an insulating silica layer at the scale/metal interface. However, the relatively high oxidation rate, and thus increasing ASR over time, necessitates the application of a conductive protection layer on the steel. In particular, Mn1.5Co1.5O4 spinel protection layers drastically improved the electrical performance of the ferritic stainless steel 441, acting as barriers to chromium outward and oxygen inward diffusion.

  12. The Influence of the Induced Ferrite and Precipitates of Ti-bearing Steel on the Ductility of Continuous Casting Slab

    NASA Astrophysics Data System (ADS)

    Qian, Guoyu; Cheng, Guoguang; Hou, Zibing

    2015-11-01

    In order to investigate the loss of the ductility of Ti-bearing ship plate steel under 1000 °C, where the ductility begins to reduce rapidly, so the hot ductility of Ti-bearing ship plate steel has been obtained using the Gleeble 1500 thermal-mechanical simulator and also the studies about the effect of grain boundary ferrite films and precipitates containing Ti on the ductility has been carried out. The result showed that the TiN particles precipitating at 950 °C with a larger size and smaller volume fraction cannot effectively suppress the occurrence of recrystallization and the ductility still retains at a high level, although R.A. value presents a certain degree of decline compared with 1000 °C. A large number of smaller Ti(C,N) particles precipitate at 900 °C and can induce the formation of a very small amount of fine grain boundary ferrite, which deteriorates the adhesion strength of the grain boundary, so the R.A. value rapidly reduces to less than 50%. When the temperature falls to close Ae3 (827 °C), the amount of the grain boundary ferrite films increase due to the ferrite phase transformation, but the ferrite film thickness becomes more uneven at the same time, which results in the increase of strain concentration and plays a leading role in causing the decrease of ductility, so the R.A. value has been kept less than 40% as the temperature cooling to 800 °C from 850 °C. When the temperature further decreases, the ductility starts to recover due to the increase of average ferrite film thickness to a greater degree which greatly reduces the strain concentration of the grain boundary.

  13. Dependence of Precipitation Behavior and Creep Strength on Cr Content in High Cr Ferritic Heat Resistant Steels

    NASA Astrophysics Data System (ADS)

    Murata, Yoshinori; Yamashita, Koji; Morinaga, Masahiko; Hara, Toru; Miki, Kazuhiro; Azuma, Tsukasa; Ishiguro, Toru; Hashizume, Ryokichi

    It is known that high temperature tensile strength increases with increasing Cr content in Cr containing heat resistant steels. Recently, however, it was found that long-term creep strength decreased with increasing Cr content in the heat resistant steels containing 8.5-12%Cr. In this study, precipitation behavior of M23C6 carbide and the Z phase after creep tests was investigated using two kinds of high Cr ferritic steels (9Cr and 10.5Cr). As a result, 10.5Cr steel exhibited larger average particle size of M23C6 than 9Cr steel irrespective of creep stress levels, but the amount of M23C6 carbide was almost the same in both steels. On the other hand, the amount of the Z phase became large in 10.5Cr steel compared with 9Cr steel. These experimental results indicate that high level of Cr content accelerates precipitation and coalescence rate of both M23C6 carbide and the Z phase, resulting in degradation of long term creep strength in 10.5 Cr steel compared to 9Cr steel.

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

    SciTech Connect

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

    2002-09-01

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

  15. Development of rapidly quenched brazing foils to join tungsten alloys with ferritic steel

    NASA Astrophysics Data System (ADS)

    Kalin, B. A.; Fedotov, V. T.; Sevrjukov, O. N.; Moeslang, A.; Rohde, M.

    2004-08-01

    Results on rapidly solidified filler metals for tungsten brazing are presented. A rapidly quenched foil-type filler metal based on Ni bal-15Cr-4Mo-4Fe-(0.5-1.0)V-7.5Si-1.5B was developed to braze tungsten to ferritic/martensitic Crl3Mo2NbVB steel (FS) for helium gas cooled divertors and plasma facing components. Polycrystalline W-2CeO 2 and monocrystalline pure tungsten were brazed to the steel under vacuum at 1150 °C, using a 0.5 mm thick foil spacer made of a 50Fe-50Ni alloy. As a result of thermocycling tests (100 cycles between 700 °C/20 min and air-water cooling/3-5 min) on brazed joints, tungsten powder metallurgically processed W-2CeO 2 failed due to residual stresses, whereas the brazed joint with zone-melted monocrystalline tungsten withstood the thermocycling tests.

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

    SciTech Connect

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

    1998-09-01

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

  17. Effects of proton irradiation on nanocluster precipitation in ferritic steel containing fcc alloying additions

    SciTech Connect

    Zhang, Zhongwu; Liu, C T; Wang, Xun-Li; Miller, Michael K; Ma, Dong; Chen, Guang; Williams, J R; Chin, Bryan

    2012-01-01

    Newly-developed precipitate-strengthened ferritic steels with and without pre-existing nanoscale precipitates were irradiated with 4 MeV protons to a dose of ~5 mdpa at 50 C and subsequently examined by nanoindentation and atom probe tomography (APT). Irradiation-enhanced precipitation and coarsening of pre-existing nanoscale precipitates were observed. Copper partitions to the precipitate core along with a segregation of Ni, Al and Mn to the precipitate/matrix interface after both thermal aging and proton irradiation. Proton irradiation induces the precipitation reaction and coarsening of pre-existing nanoscale precipitates, and these results are similar to a thermal aging process. The precipitation and coarsening of nanoscale precipitates are responsible for the changes in hardness. The observation of the radiation-induced softening is essentially due to the coarsening of the pre-existing Cu-rich nanoscale precipitates. The implication of the precipitation on the embrittlement of reactor-pressure-vessel steels after irradiation is discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

  19. Microstructural changes induced near crack tip during corrosion fatigue tests in austenitic-ferritic steel.

    PubMed

    Gołebiowski, B; Swiatnicki, W A; Gaspérini, M

    2010-03-01

    Microstructural changes occurring during fatigue tests of austenitic-ferritic duplex stainless steel (DSS) in air and in hydrogen-generating environment have been investigated. Hydrogen charging of steel samples during fatigue crack growth (FCG) tests was performed by cathodic polarization of specimens in 0.1M H(2)SO(4) aqueous solution. Microstructural investigations of specimens after FCG tests were carried out using transmission electron microscopy to reveal the density and arrangement of dislocations formed near crack tip. To determine the way of crack propagation in the microstructure, electron backscatter diffraction investigations were performed on fatigue-tested samples in both kinds of environment. To reveal hydrogen-induced phase transformations the atomic force microscopy was used. The above investigations allowed us to define the character of fatigue crack propagation and microstructural changes near the crack tip. It was found that crack propagation after fatigue tests in air is accompanied with plastic deformation; a high density of dislocations is observed at large distance from the crack. After fatigue tests performed during hydrogen charging the deformed zone containing high density of dislocations is narrow compared to that after fatigue tests in air. It means that hydrogenation leads to brittle character of fatigue crack propagation. In air, fatigue cracks propagate mostly transgranularly, whereas in hydrogen-generating environment the cracks have mixed transgranular/interfacial character.

  20. Fretting corrosion resistance and fretting corrosion product cytocompatibility of ferritic stainless steel.

    PubMed

    Xulin, S; Ito, A; Tateishi, T; Hoshino, A

    1997-01-01

    To avoid nickel ion release from SUS317L as an implant material, a new type of nickel, commercially free, of high purity, and high chromium ferritic stainless steel, was developed. The new stainless steel (FJ) was studied for aspects of fretting corrosion and cytocompatibility compared with SUS317L. A pin-on-plate fretting corrosion test in an artificial physiologic solution, and cell culture in media with the addition of the artificial physiologic solution used for fretting was conducted. Resistance to the fretting induced crevice corrosion of FJ was higher than that of SUS317L because of the favorable electrochemical stability of the FJ alloy. The amount of iron ion or colloidal fine particles released from FJ was about a quarter of that from SUS317L, although the weight loss of a pin of FJ was almost 5/3 that of SUS317L. The artificial physiologic solution used for SUS317L fretting was more harmful to the growth of L929 and MC3T3-E1 cells than that used for FJ fretting. FJ was therefore superior to SUS317L as a biomaterial, judging from the resistance to fretting-induced crevice corrosion, electrochemical stability, and the cytocompatibility of fretting corrosion products.

  1. Effect of Proeutectoid Ferrite Morphology on the Microstructure and Mechanical Properties of Hot Rolled 60Si2MnA Spring Steel

    NASA Astrophysics Data System (ADS)

    Yang, Hu; Wei-qing, Chen; Huai-bin, Han; Rui-juan, Bai

    2017-02-01

    The hot rolled 60Si2MnA spring steel was transformed to obtain different proeutectoid ferrite morphologies by different cooling rates after finish rolling through dynamic thermal simulation test. The coexistence relationship between proeutectoid ferrite and pearlite, and the effect of proeutectoid ferrite morphology on mechanical properties were systematically investigated. Results showed that the reticular proeutectoid ferrite could be formed by the cooling rates of 0.5-2 °C/s; the small, dispersed and blocky proeutectoid ferrite could be formed by the increased cooling rates of 3-5 °C/s; and the bulk content of proeutectoid ferrite decreased. The pearlitic colony and interlamellar spacing also decreased, the reciprocal of them both followed a linear relationship with the reciprocal of proeutectoid ferrite bulk content. Besides, the tensile strength, percentage of area reduction, impact energy and microhardness increased, which all follow a Hall-Petch-type relationship with the inverse of square root of proeutectoid ferrite bulk content. The fracture morphologies of tensile and impact tests transformed from intergranular fracture to cleavage and dimple fracture, and the strength and plasticity of spring steel were both improved. The results have been explained on the basis of proeutectoid ferrite morphologies-microstructures-mechanical properties relationship effectively.

  2. Effect of Austenitic and Austeno-Ferritic Electrodes on 2205 Duplex and 316L Austenitic Stainless Steel Dissimilar Welds

    NASA Astrophysics Data System (ADS)

    Verma, Jagesvar; Taiwade, Ravindra V.

    2016-11-01

    This study addresses the effect of different types of austenitic and austeno-ferritic electrodes (E309L, E309LMo and E2209) on the relationship between weldability, microstructure, mechanical properties and corrosion resistance of shielded metal arc welded duplex/austenitic (2205/316L) stainless steel dissimilar joints using the combined techniques of optical, scanning electron microscope, energy-dispersive spectrometer and electrochemical. The results indicated that the change in electrode composition led to microstructural variations in the welds with the development of different complex phases such as vermicular ferrite, lathy ferrite, widmanstatten and intragranular austenite. Mechanical properties of welded joints were diverged based on compositions and solidification modes; it was observed that ferritic mode solidified weld dominated property wise. However, the pitting corrosion resistance of all welds showed different behavior in chloride solution; moreover, weld with E2209 was superior, whereas E309L exhibited lower resistance. Higher degree of sensitization was observed in E2209 weld, while lesser in E309L weld. Optimum ferrite content was achieved in all welds.

  3. Comparison between magnetic force microscopy and electron back-scatter diffraction for ferrite quantification in type 321 stainless steel.

    PubMed

    Warren, A D; Harniman, R L; Collins, A M; Davis, S A; Younes, C M; Flewitt, P E J; Scott, T B

    2015-01-01

    Several analytical techniques that are currently available can be used to determine the spatial distribution and amount of austenite, ferrite and precipitate phases in steels. The application of magnetic force microscopy, in particular, to study the local microstructure of stainless steels is beneficial due to the selectivity of this technique for detection of ferromagnetic phases. In the comparison of Magnetic Force Microscopy and Electron Back-Scatter Diffraction for the morphological mapping and quantification of ferrite, the degree of sub-surface measurement has been found to be critical. Through the use of surface shielding, it has been possible to show that Magnetic Force Microscopy has a measurement depth of 105-140 nm. A comparison of the two techniques together with the depth of measurement capabilities are discussed.

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

    SciTech Connect

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

    1993-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

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

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

    SciTech Connect

    Gelles, D.S.; Shibayama, T.

    1998-09-01

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

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

    DOEpatents

    Klueh, Ronald L.; Maziasz, Philip J.

    1994-01-01

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

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

    SciTech Connect

    Terry C. Totemeier

    2004-10-01

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

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

    NASA Astrophysics Data System (ADS)

    Chakraborty, Pritam; Biner, S. Bulent

    2015-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  11. The role of nitrogen in the preferential chromium segregation on the ferritic stainless steel (1 1 1) surface

    NASA Astrophysics Data System (ADS)

    Yuhara, J.; Matsui, T.

    2010-03-01

    The temperature dependence on the segregation behavior of the ferritic stainless steel single crystal (1 1 1) surface morphology has been examined by scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), and low energy electron diffraction (LEED). AES clearly showed the surface segregations of chromium and nitrogen upon annealing. Nanoscale triangular chromium nitride clusters were formed around 650 °C and were regularly aligned in a hexagonal configuration. In contrast, for the ferritic stainless steel (1 1 1) surface with low-nitrogen content, chromium and carbon were found to segregate on the surface upon annealing and Auger spectra of carbon displayed the characteristic carbide peak. For the low-nitrogen surface, LEED identified a facetted surface with (2 × 2) superstructure at 650 °C. High-resolution STM identified a chromium carbide film with segregated carbon atoms randomly located on the surface. The facetted (2 × 2) superstructure changed into a (3 × 3) superstructure with no faceting upon annealing at 750 °C. Also, segregated sulfur seems to contribute to the reconstruction or interfacial relaxation between the ferritic stainless steel (1 1 1) substrate and chromium carbide film.

  12. Yttria-Stabilized Zirconia Ceramic Deposition on SS430 Ferritic Steel Grown by PLD - Pulsed Laser Deposition Method

    NASA Astrophysics Data System (ADS)

    Khalid Rivai, Abu; Mardiyanto; Agusutrisno; Suharyadi, Edi

    2017-01-01

    Development of high temperature materials are one of the key issues for the deployment of advanced nuclear reactors due to higher temperature operation. One of the candidate materials for that purpose is ceramic-coated ferritic steel that one of the functions is to be a thermal barrier coating (TBC). Thin films of YSZ (Ytrria-Stabilized Zirconia) ceramic have been deposited on a SS430 ferritic steel using Pulsed Laser Deposition (PLD) at Center For Science and Technology of Advanced Materials laboratory – National Nuclear Energy Agency of Indonesia (BATAN). The thin film was deposited with the chamber pressure range of 200-225 mTorr, the substrate temperature of 800oC, and the number of laser shots of 3×104, 6×104 and 9×104. Afterward, the samples were analyzed using Scanning Electron Microscope – Energy Dispersive X-ray Spectroscope (SEM-EDS), X-Ray Diffractometer (XRD), Atomic Force Microscope (AFM) and Vickers hardness tester. The results showed that the YSZ could homogeneously and sticky deposited on the surface of the ferritic steel. The surfaces were very smoothly formed with the surface roughness was in the range of 70 nm. Furthermore, thickness, composition of Zr4+ dan Y3+, the crystallinity, and hardness property was increased with the increasing the number of the shots.

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

    SciTech Connect

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

    1996-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  15. Osteoblast and monocyte responses to 444 ferritic stainless steel intended for a magneto-mechanically actuated fibrous scaffold.

    PubMed

    Malheiro, Vera N; Spear, Rose L; Brooks, Roger A; Markaki, Athina E

    2011-10-01

    The rationale behind this work is to design an implant device, based on a ferromagnetic material, with the potential to deform in vivo promoting osseointegration through the growth of a healthy periprosthetic bone structure. One of the primary requirements for such a device is that the material should be non-inflammatory and non-cytotoxic. In the study described here, we assessed the short-term cellular response to 444 ferritic stainless steel; a steel, with a very low interstitial content and a small amount of strong carbide-forming elements to enhance intergranular corrosion resistance. Two different human cell types were used: (i) foetal osteoblasts and (ii) monocytes. Austenitic stainless steel 316L, currently utilised in many commercially available implant designs, and tissue culture plastic were used as the control surfaces. Cell viability, proliferation and alkaline phosphatase activity were measured. In addition, cells were stained with alizarin red and fluorescently-labelled phalloidin and examined using light, fluorescence and scanning electron microscopy. Results showed that the osteoblast cells exhibited a very similar degree of attachment, growth and osteogenic differentiation on all surfaces. Measurement of lactate dehydrogenase activity and tumour necrosis factor alpha protein released from human monocytes indicated that 444 stainless steel did not cause cytotoxic effects or any significant inflammatory response. Collectively, the results suggest that 444 ferritic stainless steel has the potential to be used in advanced bone implant designs.

  16. Effects of Annealing Treatment Prior to Cold Rolling on Delayed Fracture Properties in Ferrite-Austenite Duplex Lightweight Steels

    NASA Astrophysics Data System (ADS)

    Sohn, Seok Su; Song, Hyejin; Kim, Jung Gi; Kwak, Jai-Hyun; Kim, Hyoung Seop; Lee, Sunghak

    2016-02-01

    Tensile properties of recently developed automotive high-strength steels containing about 10 wt pct of Mn and Al are superior to other conventional steels, but the active commercialization has been postponed because they are often subjected to cracking during formation or to the delayed fracture after formation. Here, the delayed fracture behavior of a ferrite-austenite duplex lightweight steel whose microstructure was modified by a batch annealing treatment at 1023 K (750 °C) prior to cold rolling was examined by HCl immersion tests of cup specimens, and was compared with that of an unmodified steel. After the batch annealing, band structures were almost decomposed as strong textures of {100}<011> α-fibers and {111}<112> γ-fibers were considerably dissolved, while ferrite grains were refined. The steel cup specimen having this modified microstructure was not cracked when immersed in an HCl solution for 18 days, whereas the specimen having unmodified microstructure underwent the delayed fracture within 1 day. This time delayed fracture was more critically affected by difference in deformation characteristics such as martensitic transformation and deformation inhomogeneity induced from concentration of residual stress or plastic strain, rather than the difference in initial microstructures. The present work gives a promise for automotive applications requiring excellent mechanical and delayed fracture properties as well as reduced specific weight.

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

    NASA Astrophysics Data System (ADS)

    Poruks, Peter

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

  18. The effect of cooling speed on the structure and properties of the heat affected zone in welded compounds of ferrite-austenitic steels

    NASA Astrophysics Data System (ADS)

    Gonik, I. L.; Gurulev, D. N.; Bondareva, O. P.

    2017-02-01

    Such parameters as the maximum heating temperature, duration of stay at high temperatures, the rate of cooling influence greatly the structure and properties of the heat-affected zone of welded joints of steels and alloys. In the present work, the effect of different cooling speed upon the impact of the thermal cycle of welding on the structure, the fine structure and toughness of ferrite-austenitic steels is investigated. It is established that the cooling speed after welding has a great influence on the shock impact toughness, the phase composition and the structure of the zone of ferrite-austenitic steels.

  19. High temperature corrosion of welded ferritic stainless steel in flowing CO2 gas

    NASA Astrophysics Data System (ADS)

    Shariff, Nurul Atikah; Othman, Norinsan Kamil; Jalar, Azman; Hamid, Muhammad Azmi Abdul; Rahman, Irman Abdul

    2013-05-01

    The high temperature corrosion of welded structure of Ferritic Stainless Steel (FSS) in flowing Ar-75%CO2 gas at 700°C has been investigated. The welded structure of FSS joint using ER 308L filler metal by GTAW. The soundness of welded joint has been clarified by X-Ray CT Scan. Prior the high temperature exposure, the welded FSS compulsory passed the standard of ASME. The welded structure of FSS was heated in flowing CO2 gas for 50 h at 1 atm. The morphology and microstructure of oxide formation on welded FSS alloy was characterized by using SEM. The result shows that the different oxide morphologies were observed on parent and fusion metal. The formation of different oxide and element properties at the interface were revealed by X-Ray Diffraction. The differences of the physical condition and morphology microstructure of welded and parent metal were observed to respond to different exposure times. This phenomenon perhaps explained due to the differences of the minor alloying elements on both parent and filler metals. The high temperature corrosion behaviour was discussed in details in this paper regarding on the physical properties, morphology and the microstructure.

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

    SciTech Connect

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

    1998-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1998-10-01

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

  3. Substructural changes during hot deformation of an Fe-26Cr ferritic stainless steel

    SciTech Connect

    Gao, F.; Xu, Y.; Song, B.; Xia, K.

    2000-01-01

    Dynamic softening and substructural changes during hot deformation of a ferritic Fe-26Cr stainless steel were studied. The flow stress increased to reach a steady state in all the cases and the steady-state stress decreased with decreasing Z, the Zener-Hollomon parameter. A constant subgrain size was observed to correspond to the steady-state flow and the steady-state subgrain size increased with decreasing Z. Substructure examinations revealed that elongated, pancake-shaped subgrains formed in the early stage of deformation. Straight sub-boundaries and equiaxed subgrains developed progressively with strain, leading eventually to a stable substructure at strains greater than 0.7. During deformation at 1,100 C, dynamic recrystallization occurred by the migration and coalescence of sub-boundaries. Dynamic recovery dominated during deformation at 900 C, resulting in the formation of fine equiaxed subgrains. Based on microstructural observations, the process of substructural changes during hot deformation was described by a schematic diagram.

  4. Prediction of yield stress and Charpy transition temperature in highly neutron irradiated ferritic steels

    NASA Astrophysics Data System (ADS)

    Windsor, Colin; Cottrell, Geoff; Kemp, Richard

    2010-07-01

    Recent predictions have been made of metallurgical properties of low-activation ferritic/martensitic steels alloys at the high irradiation levels (displacements per atom or dpa) needed for a fusion power plant as based on measurements at low irradiation levels where more data are available. These predictions have been published for the yield stress and for the Charpy ductile to brittle transition temperature shift. The neural network model predictions use training data up to a certain dpa level to predict metallurgical properties above this level. This 'extrapolation' mode of neural networks is explored in some detail. Our studies revealed an increasing accuracy of predictions as the test dpa level is increased for both yield stress and Charpy shift predictions. This result suggests that a model exists for these metallurgical properties as a function of dpa level which becomes more accurate as the available irradiation range in the training data is increased. The explanation suggested is that the metallurgical annealing, which occurs as the irradiation level is increased, simplifies the microstructure and makes prediction more reliable.

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

    NASA Astrophysics Data System (ADS)

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

    1994-09-01

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

  6. ECCI observations of dislocation structures around fatigue cracks in ferritic stainless steel single crystals

    NASA Astrophysics Data System (ADS)

    Taniguchi, T.; Kaneko, Y.; Hashimoto, S.

    2009-07-01

    Dislocation structures around the crack tips of ferritic stainless steel single crystals were observed with electron channelling contrast imaging (ECCI) method. The ECCI method enables us to observe dislocations lying near surface using a scanning electron microscope. Fatigue crack growth tests were conducted on compact tension (CT) specimens having loading axes of [221] and [110] directions. In the specimen having the [110] loading axis at which the fatigue crack having Mode I and II component propagated, a thin band-like structure consisting of dislocation wall array was observed ahead of the crack tip. On the other hand, the dislocation structures around the crack having Mode I and III components could be divided into three regions in the specimen with the [221] loading axis: the cell structure, the dislocation wall structure and the vein structure were observed in order of ascending distance from crack tip. Difference between the dislocation structures near the fatigue cracks could be understood from the crack mode by which edge and screw dislocation emissions from the crack tips are strongly affected.

  7. Flow behaviour and constitutive modelling of a ferritic stainless steel at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Zhao, Jingwei; Jiang, Zhengyi; Zu, Guoqing; Du, Wei; Zhang, Xin; Jiang, Laizhu

    2016-05-01

    The flow behaviour of a ferritic stainless steel (FSS) was investigated by a Gleeble 3500 thermal-mechanical test simulator over the temperature range of 900-1100 °C and strain rate range of 1-50 s-1. Empirical and phenomenological constitutive models were established, and a comparative study was made on the predictability of them. The results indicate that the flow stress decreases with increasing the temperature and decreasing the strain rate. High strain rate may cause a drop in flow stress after a peak value due to the adiabatic heating. The Zener-Hollomon parameter depends linearly on the flow stress, and decreases with raising the temperature and reducing the strain rate. Significant deviations occur in the prediction of flow stress by the Johnson-Cook (JC) model, indicating that the JC model cannot accurately track the flow behaviour of the FSS during hot deformation. Both the multiple-linear and the Arrhenius-type models can track the flow behaviour very well under the whole hot working conditions, and have much higher accuracy in predicting the flow behaviour than that of the JC model. The multiple-linear model is recommended in the current work due to its simpler structure and less time needed for solving the equations relative to the Arrhenius-type model.

  8. Characterisation of Laves phase precipitation and its correlation to creep rupture strength of ferritic steels

    SciTech Connect

    Zhu, S.; Yang, M.; Song, X.L.; Tang, S.; Xiang, Z.D.

    2014-12-15

    The Laves phase precipitation process was characterised by means of field emission scanning electron microscopy to demonstrate its effect on creep rupture strength of steels with a fully ferritic matrix. To eliminate the effects of carbide and carbonitride precipitations so that the creep rupture data can be analysed exclusively in relation to the Laves phase precipitation process, an alloy Fe–9Cr–3Co–3W (wt.%) without C and N additions was used for the study. Creep rupture strengths were measured and volume fraction and particle size of Laves phase precipitates in the ruptured specimens were analysed. It was found that the creep rupture strength started to collapse (or decrease more rapidly) long before the Laves phase precipitation reached equilibrium fraction. This was related to the onset of the coarsening of Laves phase particles, which precipitated only on grain boundaries and hence contributed little to precipitation strengthening. Creep deformation had no effect either on the precipitation kinetics or on the growth kinetics of Laves phase particles. - Highlights: • Laves phase precipitation at 650 °C was characterised for Fe–9Cr–3W–3Co alloy. • Laves phase precipitated predominantly on grain boundaries. • Creep deformation had no effect on Laves phase precipitation and growth kinetics. • Creep strength started to collapse long before Laves phase precipitation is ended. • Collapse of creep strength was attributed to the coarsening of Laves phase particles.

  9. Hydrogen Embrittlement Behavior of 430 and 445NF Ferritic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Kim, Sun Mi; Chun, Young Soo; Won, Sung Yeun; Kim, Young Hwan; Lee, Chong Soo

    2013-03-01

    Hydrogen embrittlement behavior of two kinds of commercial ferritic stainless steels (STSs), 430 (UNS S43000) and 445NF (UNS S44536), was investigated by means of a series of cathodical hydrogen charging, slow strain rate tests, bending tests, and thermal desorption spectrometry analyses. The hydrogen concentration in 445NF STS was lower than that of 430 STS under identical hydrogen charging conditions because of the formation of a more passive layer. In addition, 445NF STS exhibited a larger passive range in the potentiodynamic polarization curve. However, resistance to hydrogen embrittlement of 445NF STS was inferior to that of 430 STS because of precipitation of the Laves phase at grain boundaries of the former at annealing temperatures of 873 K to 1123 K (600 °C to 850 °C). Crack propagation was found to occur along the interface between the Laves phase and the matrix. For 445NF STS, dissolution of the Laves phase by solution heat treatment at 1273 K (1000 °C) followed by quenching was effective in terms of suppressing degradation of its mechanical properties and formability, which were related to hydrogen embrittlement.

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

    SciTech Connect

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

    2009-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Marmy, P.

    1994-09-01

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

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

    SciTech Connect

    Marmy, P; Oliver, Brian M. )

    2003-05-15

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

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

    NASA Astrophysics Data System (ADS)

    Marmy, P.; Oliver, B. M.

    2003-05-01

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

  14. Elevated-temperature tensile and creep properties of several ferritic stainless steels

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.

    1977-01-01

    The elevated-temperature mechanical properties of several ferritic stainless steels were determined. The alloys evaluated included Armco 18SR, GE 1541, and NASA-18T-A. Tensile and creep strength properties at 1073 and 1273 K and residual room temperature tensile properties after creep testing were measured. In addition, 1273 K tensile and creep tests and residual property testing were conducted with Armco 18SR and GE 1541 which were exposed for 200 hours to a severe oxidizing environment in automotive thermal reactors. Aside from the residual tensile properties for Armco 18SR, prior exposure did not affect the mechanical properties of either alloy. The 1273 K creep strength parallel to the sheet-rolling direction was similar for all three alloys. At 1073 K, NASA-18T-A had better creep strength than either Armco 18SR or GE 1541. NASA-18T-A possesses better residual properties after creep testing than either Armco 18SR or Ge 1541.

  15. Corrosion behavior of ferritic stainless steel with 15wt% chromium for the automobile exhaust system

    NASA Astrophysics Data System (ADS)

    Li, Hua-bing; Jiang, Zhou-hua; Feng, Hao; Zhu, Hong-chun; Sun, Bin-han; Li, Zhen

    2013-09-01

    The effect of chloride ion concentration, pH value, and grain size on the pitting corrosion resistance of a new ferritic stainless steel with 15wt% Cr was investigated using the anodic polarization method. The semiconducting properties of passive films with different chloride ion concentrations were performed using capacitance measurement and Mott-Schottky analysis methods. The aging precipitation and intergranular corrosion behavior were evaluated at 400-900°C. It is found that the pitting potential decreases when the grain size increases. With the increase in chloride ion concentration, the doping density and the flat-bland potential increase but the thickness of the space charge layer decreases. The pitting corrosion resistance increases rapidly with the decrease in pH value. Precipitants is identified as Nb(C,N) and NbC, rather than Cr-carbide. The intergranular corrosion is attributed to the synergistic effects of Nb(C,N) and NbC precipitates and Cr segregation adjacent to the precipitates.

  16. Microstructural stability of a self-ion irradiated lanthana-bearing nanostructured ferritic steel

    SciTech Connect

    Pasebani, Somayeh; Charit, Indrajit; Burns, Jatuporn; Alsagabi, Sultan; Butt, Darryl P.; Cole, James I.; Price, Lloyd M.; Shao, Lin

    2015-07-01

    Thermally stable nanofeatures with high number density are expected to impart excellent high temperature strength and irradiation stability in nanostructured ferritic steels (NFSs) which have potential applications in advanced nuclear reactors. A lanthana-bearing NFS (14LMT) developed via mechanical alloying and spark plasma sintering was used in this study. The sintered samples were irradiated by Fe2+ ions to 10, 50 and 100 dpa at 30 °C and 500 °C. Microstructural and mechanical characteristics of the irradiated samples were studied using different microscopy techniques and nanoindentation, respectively. Overall morphology and number density of the nanofeatures remained unchanged after irradiation. Average radius of nanofeatures in the irradiated sample (100 dpa at 500 °C) was slightly reduced. A notable level of irradiation hardening and enhanced dislocation activity occurred after ion irradiation except at 30 °C and ≥50 dpa. Other microstructural features like grain boundaries and high density of dislocations also provided defect sinks to assist in defect removal.

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

    SciTech Connect

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

    2016-01-01

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

  18. Tensile Properties of Medium Mn Steel with a Bimodal UFG α + γ and Coarse δ-Ferrite Microstructure

    NASA Astrophysics Data System (ADS)

    Lee, Seonjong; Shin, Sunmi; Kwon, Minhyeok; Lee, Kyooyoung; De Cooman, Bruno C.

    2017-04-01

    While the tensile strength and elongation obtained for medium Mn steel would appear to make it a candidate material in applications which require formable ultra-high strength materials, many secondary aspects of the microstructure-properties relationships have not yet been given enough attention. In this contribution, the microstructural and tensile properties of medium Mn steel with a bimodal microstructure consisting of an ultra-fine grained ferrite + austenite constituent and coarse-grained delta-ferrite are therefore reviewed in detail. The tensile properties of ultra-fine-grained intercritically annealed medium Mn steel reveal a complex dependence on the intercritical annealing temperature. This dependence is related to the influence of the intercritical annealing temperature on the activation of the plasticity-enhancing mechanisms in the microstructure. The kinetics of deformation twinning and strain-induced transformation in the ultra-fine grained austenite play a prominent role in determining the strain hardening of medium Mn steel. While excellent strength-ductility combinations are obtained when deformation twinning and strain-induced transformation occur gradually and in sequence, large elongations are also observed when strain-induced transformation plasticity is not activated. In addition, the localization of plastic flow is observed to occur in samples after intercritical annealing at intermediate temperatures, suggesting that both strain hardening and strain rate sensitivity are influenced by the properties of the ultra-fine-grained austenite.

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

    SciTech Connect

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

    2014-10-15

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

  20. Sensitization Behavior of Type 409 Ferritic Stainless Steel: Confronting DL-EPR Test and Practice W of ASTM A763

    NASA Astrophysics Data System (ADS)

    Scalise, Taís Campos; de Oliveira, Mara Cristina Lopes; Sayeg, Isaac Jamil; Antunes, Renato Altobelli

    2014-06-01

    Stainless steels employed for manufacturing automotive exhaust systems must withstand severe thermal cycles, corrosive environment due to urea decomposition, and welding operations. AISI 409 ferritic stainless steel can be considered a low-cost alternative for this application. However, depending on the manufacturing conditions during welding cycles, this material can be sensitized due to the precipitation of chromium carbides at grain boundaries. In this work, the intergranular corrosion resistances of the AISI 409 ferritic stainless steel were evaluated after annealing at 300, 500, and 700 °C for 2, 4, and 6 h. Solution-annealed samples were also tested for comparison purposes. Two methodologies were used to assess the sensitization behavior of the 409 stainless steel samples: the first one was based on the ASTM A763 (practice W), while the second one was based on the double-loop electrochemical potentiodynamic reactivation test. It was possible to identify that the annealing treatment performed at 500 °C was more critical to the occurrence of intergranular corrosion.

  1. Creep behavior of oxide dispersion strengthened 8Cr-2WVTa and 8Cr-1W steels

    NASA Astrophysics Data System (ADS)

    Shinozuka, K.; Tamura, M.; Esaka, H.; Shiba, K.; Nakamura, K.

    2009-01-01

    Microstructures and creep behavior of two martensitic oxide dispersion strengthened (ODS) steels 8%Cr-2%W-0.2%V-0.1%Ta (J1) and 8%Cr-1%W (J2) with finely dispersed Y 2Ti 2O 7 have been investigated. Creep tests have been carried out at 670, 700 and 730 °C. Creep strength of J1 is stronger than that of any other ODS martensitic steels and the hoop strength of the ferritic ODS steel cladding. At the beginning of creep test, shrinkage was frequently observed for J1. This is one of the reasons for high creep strength of J1. The δ-ferrite, which is untransformed to austenite at hot isostatic press and hot rolling temperatures, was elongated along the rolling direction, and volume fraction of δ-ferrite in J1 is larger than J2. Although the elongated δ-ferrite affects the anisotropy of creep behavior, the extent of anisotropy in J1 is not so large as that of the ferritic ODS steel.

  2. Effect of Coiling Temperature on Microstructure and Tensile Behavior of a Hot-Rolled Ferritic Lightweight Steel

    NASA Astrophysics Data System (ADS)

    Wang, Junfeng; Yang, Qi; Wang, Xiaodong; Wang, Li

    2016-12-01

    Effects of coiling temperature (CT) ranging from 673 K to 973 K (400 °C to 700 °C) on microstructure and tensile property of a hot-rolled ferritic lightweight steel containing 0.35 wt pct C and 4.1 wt pct Al are investigated in the present study. Basically, the microstructure of the hot-rolled steel is composed of δ-ferrite grain bands and secondary phase bands which are originated from the decomposition of antecedent austenite. The secondary phase band is a bainite band at coiling temperatures (CTs) lower than 723 K (450 °C). More specifically, the bainite band mainly consists of lower bainite together with blocky retained austenite at the CT of 673 K (400 °C), while it primarily contains carbide-free bainite being an aggregate of lath-shaped ferrite and austenite at the CT of 723 K (450 °C). The secondary phase band is a carbide band which mainly contains a pearlite structure at CTs higher than 773 K (500 °C). There are three types of carbides in the steel matrix: transitional ɛ-carbide present inside lower bainite, cementite present within carbide bands as well as at the boundaries between carbide bands and δ-ferrite bands, and κ-carbide present at δ-ferrite grain boundaries which is clearly seen at CTs higher than 773 K (500 °C). The volume fraction of retained austenite reaches the peak value of 9.6 pct at the CT of 723 K (450 °C), and abruptly drops to zero when the CTs are higher than 773 K (500 °C). Lath-shaped retained austenite with a higher volume fraction induces significant enhancement of elongation through the TRIP effect, leading to a uniform elongation of 25 pct and an elongation-to-failure of 32 pct at the CT of 723 K (450 °C). Crack initiation and propagation inside the tested specimens are tracked and fracture surface is observed to help understand the deformation and fracture behavior of the hot-rolled steel.

  3. Residual Stress Analysis in Girth-welded Ferritic and Austenitic Steel Pipes Using Neutron and X-Ray Diffraction

    SciTech Connect

    Hempel, Nico; Bunn, Jeffrey R; Nitschke-Pagel, Thomas; Payzant, E Andrew; Dilger, Klaus

    2016-01-01

    This paper is dedicated to the thorough experimental analysis of the residual stresses in the vicinity of tubular welds and the mechanisms involved in their formation. Pipes made of a ferritic-pearlitic structural steel and an austenitic stainless steel are investigated in this study. The pipes feature a similar geometry and are MAG welded with two passes and comparable parameters. Residual strain mappings are carried out using X-ray and neutron diffraction. The combined use of both techniques permits both near-surface and through-wall analyses of the residual stresses. The findings allow for a consistent interpretation of the mechanisms accounting for the formation of the residual stress fields due to the welding process. Since the results are similar for both materials, it can be concluded that residual stresses induced by phase transformations, which can occur in the structural steel, play a minor role in this regard.

  4. Characteristics and Modification of Non-metallic Inclusions in Titanium-Stabilized AISI 409 Ferritic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Kruger, Dirk; Garbers-Craig, Andrie

    2017-02-01

    This study describes an investigation into the improvement of castability, final surface quality and formability of titanium-stabilized AISI 409 ferritic stainless steel on an industrial scale. Non-metallic inclusions found in this industrially produced stainless steel were first characterized using SEM-EDS analyses through the INCA-Steel software platform. Inclusions were found to consist of a MgO·Al2O3 spinel core, which acted as heterogeneous nucleation site for titanium solubility products. Plant-scale experiments were conducted to either prevent the formation of spinel, or to modify it by calcium treatment. Modification to spherical dual-phase spinel-liquid matrix inclusions was achieved with calcium addition, which eliminated submerged entry nozzle clogging for this grade. Complete modification to homogeneous liquid calcium aluminates was achieved at high levels of dissolved aluminum. A mechanism was suggested to explain the extent of modification achieved.

  5. Characterization of precipitates in nano structured 14% Cr ODS alloys for fusion application

    NASA Astrophysics Data System (ADS)

    He, P.; Klimenkov, M.; Lindau, R.; Möslang, A.

    2012-09-01

    Oxide dispersion strengthened (ODS) reduced activation ferritic (RAF) steels, have been considered as promising materials for application in fusion power reactors up to about 750 °C. Four ODS RAF steels, with compositions of Fe-13.5Cr-2W-(0-0.2-0.3-0.4)Ti-0.3Y2O3 (in wt.%) were produced by powder metallurgy technique. For the different Ti-contents, the correlation between microstructure and mechanical properties was analyzed by means of scanning electron microscope (SEM) and transmission electron microscope (TEM) equipped with energy- dispersive X-ray spectrometer (EDX) and electron energy loss spectrometer (EELS). A bimodal grain size distribution was observed in all as-hipped Ti-containing ODS alloys. These alloys consisted of coarse grains typical ranging from 1 μm to 8 μm and fine grains well below 1 μm in diameter. The addition of Ti resulted in the formation of spherical Ti oxides rather than Cr oxides owing to the stronger affinity of Ti. The influence of Ti on particle size refinement was striking and the optimum effect was obtained when adding 0.3% Ti. Generally the hardness increased consistently with increasing in Ti content. The ODS alloying with 0.3% Ti exhibit the highest strength due to the optimum refinement of mean ODS particle size.

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

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

  7. High Temperature Strengthening in 12Cr-W-Mo Steels by Controlling the Formation of Delta Ferrite

    NASA Astrophysics Data System (ADS)

    Wang, Shushen; Chang, Li; Lin, Deye; Chen, Xiaohua; Hui, Xidong

    2014-09-01

    Novel 12Cr-W-Mo-Co heat resistance steels (HRSs) with excellent mechanical properties have been developed for ultra-supercritical (USC) applications above 923 K (650 °C). The thermal analysis of the present steels indicates that the remelting temperature of secondary phases is increased by Co alloying, resulting in the improvement of microstructural stability. Delta ferrite in these HRSs is completely suppressed as the content of Co is increased up to 5 pct. The room temperature tensile strength (TS), yield strength (YS), and the elongation (EL) of the HRS with 5 pct Co reach 887.9, 652.6 MPa, and 21.07 pct, respectively. At 948 K (675 °C), the TS and YS of the HRS with 5 pct Co attain 360 and 290 MPa, respectively, which are higher than those of T/P122 steel by 27.4 and 22.1 pct, respectively. TEM study of the microstructure confirmed that the strengthening effects for these 12Cr-W-Mo-Co HRSs are attributed to the suppression of delta ferrite, the formation of fine martensitic laths with substructure, dislocation networks and walls, and the precipitation of second nanoscale phases.

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

    DOE PAGES

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

    2016-03-03

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

  9. Variation in Mechanical Properties and Heterogeneity in Microstructure of High-Strength Ferritic Steel During Mill Trial

    NASA Astrophysics Data System (ADS)

    Ghosh, M.; Barat, K.; Das, S. K.; Ravi Kumar, B.; Pramanick, A. K.; Chakraborty, J.; Das, G.; Hadas, S.; Bharathy, S.; Ray, S. K.

    2014-06-01

    HS600 and HS800 are two new generation, high-strength advanced ferritic steels that find widespread application in automobiles. During commercial production of the same grades with different thicknesses, it has been found that mechanical properties like tensile strength and stretchability varied widely and became inconsistent. In the current endeavor, two different thicknesses have been chosen from a mill trial sample of HS600 and HS800. An in-depth structural characterization was carried out for all four alloys to explain the variation in their respective mechanical and shear punch properties. The carbon content was smaller and Ti + Mo quantity was higher in case of HS800 with respect to HS600. The microstructure of both steels consisted of the dispersion of (Ti,Mo)C in a ferrite matrix. The grain size of HS800 was little larger than HS600 due to an increased coiling temperature (CT) of the former in comparison to the latter. It was found that in case of same grade of steel with a different thickness, a variation in microstructure occurred due to change in strain, CT, and cooling rate. The strength and stretch formability of these two alloys were predominantly governed by a microalloyed carbide. In this respect, carbides with a size range above 5 nm were responsible for loosing coherency with ferrite matrix. In case of HS600, both ≤5 and >5-nm size (Ti,Mo)C precipitates shared a nearly equal fraction of microalloyed precipitates. However, for HS800, >5-nm size (Ti,Mo)C carbide was substantially higher than ≤5-nm size alloy carbides. The ultimate tensile strength and yield strength of HS800 was superior to that of HS600 owing to a higher quantity of microalloyed carbide with a decreased column width and interparticle distance. A higher degree of in-coherency of HS800 made the alloy prone to crack formation with low stretchability.

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

    SciTech Connect

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

    2012-08-28

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

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

    SciTech Connect

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

    1993-10-01

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

  12. Morphological Stability of δ-Ferrite/γ Interphase Boundary in Carbon Steel

    NASA Astrophysics Data System (ADS)

    Chang, Guowei; Chen, Shuying; Yue, Xudong; Li, Qingchun

    2017-01-01

    The morphological changes of the δ-ferrite/γ interphase boundary have been observed in situ with a high-temperature confocal scanning laser microscope (HTCSLM) during δ/γ transformations (δ → γ and γ → δ) of Fe-0.06 wt pct C-0.6 wt pct Mn alloy, and a kinetic equation of morphological stability of δ-ferrite/γ interphase boundary has been established. Thereafter, the criterion expression for morphological stability of δ-ferrite/γ interphase boundary was established and discussed, and the critical migration speeds of δ-ferrite/γ interphase boundaries are calculated in Fe-C, Fe-Ni, and Fe-Cr alloys. The results indicate that the δ-ferrite/γ interphase boundary is very stable and nearly remains absolute planar all the time during γ → δ transformation in Fe-C alloy. The δ-ferrite/γ interphase boundary remains basically planar during δ → γ transformation when the migration speed is lower than 0.88 μm/s, and the interphase boundary will be unstable and exhibit a finger-like morphology when the migration speed is higher than 0.88 μm/s. The morphological stability of δ-ferrite/γ interphase boundary is primarily controlled by the interface energy and the solute concentration gradient at the front of the boundary. During the constant temperature phase transformation, an opposite temperature gradient on both sides of δ-ferrite/γ interphase boundary weakens the steady effect of the temperature gradient on the boundary. The theoretical analysis of the morphological stability of the δ-ferrite/γ interphase boundary is coincident with the observed experimental results utilizing the HTCSLM. There is a good agreement between the theoretical calculation of the critical moving velocities of δ-ferrite/γ interphase boundaries and the experimental results.

  13. Morphological Stability of δ-Ferrite/ γ Interphase Boundary in Carbon Steel

    NASA Astrophysics Data System (ADS)

    Chang, Guowei; Chen, Shuying; Yue, Xudong; Li, Qingchun

    2017-04-01

    The morphological changes of the δ-ferrite/ γ interphase boundary have been observed in situ with a high-temperature confocal scanning laser microscope (HTCSLM) during δ/ γ transformations ( δ → γ and γ → δ) of Fe-0.06 wt pct C-0.6 wt pct Mn alloy, and a kinetic equation of morphological stability of δ-ferrite/ γ interphase boundary has been established. Thereafter, the criterion expression for morphological stability of δ-ferrite/ γ interphase boundary was established and discussed, and the critical migration speeds of δ-ferrite/ γ interphase boundaries are calculated in Fe-C, Fe-Ni, and Fe-Cr alloys. The results indicate that the δ-ferrite/ γ interphase boundary is very stable and nearly remains absolute planar all the time during γ → δ transformation in Fe-C alloy. The δ-ferrite/ γ interphase boundary remains basically planar during δ → γ transformation when the migration speed is lower than 0.88 μm/s, and the interphase boundary will be unstable and exhibit a finger-like morphology when the migration speed is higher than 0.88 μm/s. The morphological stability of δ-ferrite/ γ interphase boundary is primarily controlled by the interface energy and the solute concentration gradient at the front of the boundary. During the constant temperature phase transformation, an opposite temperature gradient on both sides of δ-ferrite/ γ interphase boundary weakens the steady effect of the temperature gradient on the boundary. The theoretical analysis of the morphological stability of the δ-ferrite/ γ interphase boundary is coincident with the observed experimental results utilizing the HTCSLM. There is a good agreement between the theoretical calculation of the critical moving velocities of δ-ferrite/ γ interphase boundaries and the experimental results.

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

    DOEpatents

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

    1994-03-08

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

  15. Effect of deformation on the austenite-to-ferrite transformation in a plain carbon and two microalloyed steels

    NASA Astrophysics Data System (ADS)

    Essadiqi, E.; Jonas, J. J.

    1988-03-01

    Isothermal compression tests were carried out on three steels: (i) a plain C, (ii) a Mo, and (iii) a Mo-Nb-V microalloyed grade in order to study the effect of deformation on the austenite-to-ferrite transformation. Dynamic TTT (DTTT) curves were determined, which show clearly the extent to which deformation accelerates the decomposition of austenite. The latter effect is diminished by the addition of the alloying elements Mo, Nb, and V and is further reduced as the temperature is increased. The substitutional elements Mo, Nb, and V appear to reduce the nucleation rate through reduction of the austenite grain boundary energy. The growth rate is also reduced by these elements, apparently through the solute drag-like effect. The microstructural results indicate that the ferrite formed under dynamic conditions becomes more homogeneous and finer when the strain rate or the temperature is increased. Under static conditions, increasing the prestrain or the prestraining strain rate accelerates the γ-to-α transformation and reduces the mean grain size of the ferrite, although the highest transformation rate is still associated with the dynamic case.

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

    NASA Astrophysics Data System (ADS)

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

    1998-10-01

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

  17. Corrosion of ferritic steels by molten lithium: Influence of competing thermal gradient mass transfer and surface product reactions

    SciTech Connect

    Tortorelli, P.F.

    1987-10-01

    An Fe-12Cr-1MoVW steel was exposed to thermally convective lithium for 6962 h. Results showed that the weight change profile of Fe-12Cr-1MoVW steel changed substantially as the maximum loop temperature was raised from 500 to 600/sup 0/C. Furthermore, for a particular loop experiment, changes in the structure and composition of the exposed surfaces did not reflect typical thermal gradient mass transfer effects for all elements: the surface concentration of chromium was often a maximum at intermediate temperatures, while nickel (present at low concentrations in the starting material) tended to be transported to the coldest part of the loop. Such data were interpreted in terms of a qualitative model in which there are different dominant reactions or the various constituents of the ferritic steels (surface product formation involving nitrogen and/or carbon and solubility-driven elemental transport). This competition among different reactions is important in evaluating overall corrosion behavior and the effects of temperature. The overall corrosion rate of the 12Cr-1MoVW steel was relatively low when compared to that for austenitic stainless steel exposed under similar conditions.

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

    NASA Astrophysics Data System (ADS)

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

    2002-12-01

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

  19. Influence of grain refinement on the electrochemical behavior of AISI 430 ferritic stainless steel in an alkaline solution

    NASA Astrophysics Data System (ADS)

    Fattah-alhosseini, A.; Vafaeian, S.

    2016-01-01

    In this paper, the effect of grain refinement on the electrochemical behavior of AISI 430 ferritic stainless steel in 0.1 M NaOH solution was investigated. Potentiodynamic polarization curves showed that fine-grained samples have less corrosion potential, higher corrosion current density, and less protective passive film in comparison to coarse-grained samples. Electrochemical impedance spectroscopy (EIS) analysis revealed that implementing the thermomechanical operation led to lower polarization resistance. Also, Mott-Schottky analysis revealed that the passive films on both fine-grained and coarse-grained samples behave as n-type and p-type semiconductors and the semiconductor character of the passive films did not change by grain refinement. Moreover, it was found that the calculated donor and acceptor densities increased with grain refinement. Thus, the presented results indicated that grain refinement weakens the corrosion and passivation behavior of AISI 430 stainless steel in this alkaline solution.

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

    SciTech Connect

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2007-08-01

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

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

    SciTech Connect

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

    2003-07-15

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

  3. Dual and Triple Ion-Beam Irradiations of Fe, Fe(Cr) and Fe(Cr)-ODS Final Report: IAEA SMoRE CRP

    SciTech Connect

    Fluss, M J; Hsiung, L L; Marian, J

    2011-11-20

    Structures of nanoparticles in Fe-16Cr-4.5Al-0.3Ti-2W-0.37Y2O3 (K3) and Fe-20Cr-4.5Al-0.34Ti-0.5Y2O3 (MA956) oxide dispersion strengthened (ODS) ferritic steels produced by mechanical alloying (MA) and followed by hot extrusion have been studied using high-resolution transmission electron microscopy (HRTEM) techniques to gain insight about the formation mechanism of nanoparticles in MA/ODS steels. The observations of Y-Al-O complex-oxide nanoparticles in both ODS steels imply that decomposition of Y2O3 in association with internal oxidation of Al occurred during mechanical alloying. While the majority of oxide nanoparticles formed in both steels is Y4Al2O9, a few oxide particles of YAlO3 are also occasionally observed. These results reveal that Ti (0.3 wt %) plays an insignificant role in forming oxide nanoparticles in the presence of Al (4.5 wt %). HRTEM observations of crystalline nanoparticles larger than {approx}2 nm and amorphous or disordered cluster domains smaller than {approx}2 nm provide an insight into the formation mechanism of oxide nanoparticle in MA/ODS steels, which we believe from our observations involves a solid-state amorphous precursor followed by recrystallization. Dual ion-beam irradiations using He{sup +} + Fe{sup +8} ions were employed to gain more detailed insight about the role of nanoparticles in suppressing radiation-induced swelling. This is elaborated through TEM examinations of cavity distributions in ion-irradiated Fe-14Cr and K3-ODS ferritic steels. HRTEM observations of helium-filled cavities (helium bubbles) preferably trapped at nanoscale oxide particles and clusters in ion-irradiated K3-ODS are presented. Finally, we describe the results from triple ion-beam irradiations using H{sup +} + He{sup +} + Fe{sup +8} ions to emulate fusion first wall radiation effects. Preliminary work is reported that confirms the existence of significant hydrogen synergistic effects described earlier by Tanaka et al., for Fe(Cr) and by Wakai et al

  4. Parametric Optimization Of Gas Metal Arc Welding Process By Using Grey Based Taguchi Method On Aisi 409 Ferritic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Ghosh, Nabendu; Kumar, Pradip; Nandi, Goutam

    2016-10-01

    Welding input process parameters play a very significant role in determining the quality of the welded joint. Only by properly controlling every element of the process can product quality be controlled. For better quality of MIG welding of Ferritic stainless steel AISI 409, precise control of process parameters, parametric optimization of the process parameters, prediction and control of the desired responses (quality indices) etc., continued and elaborate experiments, analysis and modeling are needed. A data of knowledge - base may thus be generated which may be utilized by the practicing engineers and technicians to produce good quality weld more precisely, reliably and predictively. In the present work, X-ray radiographic test has been conducted in order to detect surface and sub-surface defects of weld specimens made of Ferritic stainless steel. The quality of the weld has been evaluated in terms of yield strength, ultimate tensile strength and percentage of elongation of the welded specimens. The observed data have been interpreted, discussed and analyzed by considering ultimate tensile strength ,yield strength and percentage elongation combined with use of Grey-Taguchi methodology.

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

    SciTech Connect

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

    2013-06-01

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

  6. Characterization of Residual Stress as a Function of Friction Stir Welding Parameters in Oxide Dispersion Strengthened (ODS) Steel MA956

    SciTech Connect

    Brewer, Luke N.; Bennett, Martin S.; Baker, B. W.; Payzant, E. Andrew; Kolbus, Lindsay M.

    2015-09-08

    This article characterizes the residual stresses generated by friction stir welding of oxide dispersion strengthened steel MA956 over a series of welding conditions. A plate of MA956 steel was friction stir welded at three conditions: 500 rpm/25 millimeters per minute (mmpm), 400 rpm/50 mmpm and 400 rpm/100 mmpm. The residual stresses across these welds were measured using both x-ray and neutron diffraction techniques. Longitudinal residual stresses up to eighty percent of the yield strength were observed for the 400 rpm/100 mmpm condition. Increasing the traverse rate while holding the rotational speed fixed increased the residual stress levels in the stir zone and at the stir zone-thermomechanically affected zone interface. The stress profiles displayed the characteristic M shape, and the asymmetry between advancing and retreating stress peaks was limited, occurring mainly on the root side of the weld. The large magnitude of the stresses was maintained throughout the thickness of the plates.

  7. Factors Affecting the Inclusion Potency for Acicular Ferrite Nucleation in High-Strength Steel Welds

    NASA Astrophysics Data System (ADS)

    Kang, Yongjoon; Jeong, Seonghoon; Kang, Joo-Hee; Lee, Changhee

    2016-06-01

    Factors affecting the inclusion potency for acicular ferrite nucleation in high-strength weld metals were investigated and the contribution of each factor was qualitatively evaluated. Two kinds of weld metals with different hardenabilities were prepared, in both, MnTi2O4-rich spinel formed as the predominant inclusion phase. To evaluate the factors determining the inclusion potency, the inclusion characteristics of size, phase distribution in the multiphase inclusion, orientation relationship with ferrite, and Mn distribution near the inclusion were analyzed. Three factors affecting the ferrite nucleation potency of inclusions were evaluated: the Baker-Nutting (B-N) orientation relationship between ferrite and the inclusion; the formation of an Mn-depleted zone (MDZ) near the inclusion; and the strain energy around the inclusion. Among these, the first two factors were found to be the most important. In addition, it was concluded that the increased chemical driving force brought about by the formation of an MDZ contributed more to the formation of acicular ferrite in higher-strength weld metals, because the B-N orientation relationship between ferrite and the inclusion was less likely to form as the transformation temperature decreased.

  8. Studies on oxidation and deuterium permeation behavior of a low temperature α-Al2O3-forming Fesbnd Crsbnd Al ferritic steel

    NASA Astrophysics Data System (ADS)

    Xu, Yu-Ping; Zhao, Si-Xiang; Liu, Feng; Li, Xiao-Chun; Zhao, Ming-Zhong; Wang, Jing; Lu, Tao; Hong, Suk-Ho; Zhou, Hai-Shan; Luo, Guang-Nan

    2016-08-01

    To evaluate the capability of Fesbnd Crsbnd Al ferritic steels as tritium permeation barrier in fusion systems, the oxidation behavior together with the permeation behavior of a Fesbnd Crsbnd Al steel was investigated. Gas driven permeation experiments were performed. The permeability of the oxidized Fesbnd Crsbnd Al steel was obtained and a reduced activation ferritic/martensitic steel CLF-1 was used as a comparison. In order to characterize the oxide layer, SEM, XPS, TEM, HRTEM were used. Al2O3 was detected in the oxide film by XPS, and HRTEM showed that Al2O3 in the α phase was found. The formation of α-Al2O3 layer at a relatively low temperature may result from the formation of Cr2O3 nuclei.

  9. Dislocation structures in the bands of localized cyclic plastic strain in austenitic 316L and austenitic-ferritic duplex stainless steels

    SciTech Connect

    Kruml, T.; Polak, J.; Obrtlik, K.; Degallaix, S.

    1997-12-01

    Dislocation structures in bands corresponding to cyclic strain localization have been studied in two types of stainless steels, single phase austenitic 316L steel and two-phase austenitic-ferritic duplex steel. Dislocation structures are documented in thin foils oriented approximately perpendicular to the active slip plane of individual grains and parallel to the primary Burgers vector. Persistent slip bands, with the structure more or less reminiscent of the well-known ladder structure, were found in austenitic grains of both steels. These bands can be correlated with the distinct surface relief consisting of extrusions, intrusions and shallow surface cracks in austenitic grains were found. The distribution of the wall and labyrinth structure embedded in the matrix structure in ferritic grains, which was proposed to be responsible for the localization of the cyclic strain, however, does not correspond to the distribution of the distinct surface slip lines on the surface.

  10. Evaluation by the Double Loop Electrochemical Potentiokinetic Reactivation Test of Aged Ferritic Stainless Steel Intergranular Corrosion Susceptibility

    NASA Astrophysics Data System (ADS)

    Sidhom, H.; Amadou, T.; Braham, C.

    2010-12-01

    An experimental design method was used to determine the effect of factors that significantly affect the response of the double loop-electrochemical potentiokinetic reactivation (DL-EPR) test in controlling the susceptibility to intergranular corrosion (IGC) of UNS S43000 (AISI 430) ferritic stainless steel. The test response is expressed in terms of the reactivation/activation current ratio ( I r / I a pct). Test results analysed by the analysis of variance (ANOVA) method show that the molarity of the H2SO4 electrolyte and the potential scanning rate have a more significant effect on the DL-EPR test response than the temperature and the depassivator agent concentration. On the basis of these results, a study was conducted in order to determine the optimal operating conditions of the test as a nondestructive technique for evaluating IGC resistance of ferritic stainless steel components. Three different heat treatments are considered in this study: solution annealing (nonsensitized), aging during 3 hours at 773 K (500 °C) (slightly sensitized), and aging during 2 hours at 873 K (600 °C) (highly sensitized). The aim is to find the operating conditions that simultaneously ensure the selectivity of the attack (intergranular and chromium depleted zone) and are able to detect the effect of low dechromization. It is found that a potential scanning rate of 2.5 mV/s in an electrolyte composed of H2SO4 3 M solution without depassivator, at a temperature around 293 K (20 °C), is the optimal operating condition for the DL-EPR test. Using this condition, it is possible to assess the degree of sensitization (DOS) to the IGC of products manufactured in ferritic stainless steels rapidly, reliably, and quantitatively. A time-temperature-start of sensitization (TTS) diagram for the UNS S43000 (France Inox, Villepinte, France) stainless steel was obtained with acceptable accuracy by this method when the IGC sensitization criterion was set to I r / I a > 1 pct. This diagram is in

  11. Investigation of iron-chromium-niobium-titanium ferritic stainless steel for solid oxide fuel cell interconnect applications

    NASA Astrophysics Data System (ADS)

    Yang, Zhenguo; Xia, Guan-Guang; Wang, Chong-Min; Nie, Zimin; Templeton, Joshua; Stevenson, Jeffry W.; Singh, Prabhakar

    As part of an effort to develop cost-effective ferritic stainless steel-based interconnects for solid oxide fuel cell (SOFC) stacks, both bare AISI441 and AISI441 coated with (Mn,Co) 3O 4 protection layers were studied in terms of its metallurgical characteristics, oxidation behavior, and electrical performance. The addition of minor alloying elements, in particular Nb, led to formation of Laves phases both inside grains and along grain boundaries. In particular, the Laves phase which precipitated out along grain boundaries during exposure at intermediate SOFC operating temperatures was found to be rich in both Nb and Si. The capture of Si in the Laves phase minimized the Si activity in the alloy matrix and prevented formation of an insulating silica layer at the scale/metal interface, resulting in a reduction in area-specific electrical resistance (ASR). However, the relatively high oxidation rate of the steel, which leads to increasing ASR over time, and the need to prevent volatilization of chromium from the steel necessitates the application of a conductive protection layer on the steel. In particular, the application of a Mn 1.5Co 1.5O 4 spinel protection layer substantially improved the electrical performance of the 441 by reducing the oxidation rate.

  12. Characterization of Residual Stress as a Function of Friction Stir Welding Parameters in Oxide Dispersion Strengthened (ODS) Steel MA956

    DOE PAGES

    Brewer, Luke N.; Bennett, Martin S.; Baker, B. W.; ...

    2015-09-08

    This article characterizes the residual stresses generated by friction stir welding of oxide dispersion strengthened steel MA956 over a series of welding conditions. A plate of MA956 steel was friction stir welded at three conditions: 500 rpm/25 millimeters per minute (mmpm), 400 rpm/50 mmpm and 400 rpm/100 mmpm. The residual stresses across these welds were measured using both x-ray and neutron diffraction techniques. Longitudinal residual stresses up to eighty percent of the yield strength were observed for the 400 rpm/100 mmpm condition. Increasing the traverse rate while holding the rotational speed fixed increased the residual stress levels in the stirmore » zone and at the stir zone-thermomechanically affected zone interface. The stress profiles displayed the characteristic M shape, and the asymmetry between advancing and retreating stress peaks was limited, occurring mainly on the root side of the weld. The large magnitude of the stresses was maintained throughout the thickness of the plates.« less

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

    NASA Astrophysics Data System (ADS)

    Topbasi, Cem

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

  14. The effects of oxide evolution on mechanical properties in proton- and neutron-irradiated Fe-9%Cr ODS steel

    NASA Astrophysics Data System (ADS)

    Swenson, M. J.; Dolph, C. K.; Wharry, J. P.

    2016-10-01

    The objective of this study is to evaluate the effect of irradiation on the strengthening mechanisms of a model Fe-9%Cr oxide dispersion strengthened steel. The alloy was irradiated with protons or neutrons to a dose of 3 displacements per atoms at 500 °C. Nanoindentation was used to measure strengthening due to irradiation, with neutron irradiation causing a greater increase in yield strength than proton irradiation. The irradiated microstructures were characterized using transmission electron microscopy and atom probe tomography (APT). Cluster analysis reveals solute migration from the Y-Ti-O-rich nanoclusters to the surrounding matrix after both irradiations, though the effect is more pronounced in the neutron-irradiated specimen. Because the dissolved oxygen atoms occupy interstitial sites in the iron matrix, they contribute significantly to solid solution strengthening. The dispersed barrier hardening model relates microstructure evolution to the change in yield strength, but is only accurate if solid solution contributions to strengthening are considered simultaneously.

  15. Microstructure investigation of 13Cr-2Mo ODS steel components obtained by high voltage electric discharge compaction technique

    SciTech Connect

    Bogachev, Igor; Yudin, Artem; Grigoryev, Evgeniy; Chernov, Ivan; Staltsov, Maxim; Khasanov, Oleg; Olevsky, Eugene

    2015-11-02

    Refractory oxide dispersion strengthened 13Cr-2Mo steel powder was successfully consolidated to near theoretical density using high voltage electric discharge compaction. Cylindrical samples with relative density from 90% to 97% and dimensions of 10 mm in diameter and 10–15 mm in height were obtained. Consolidation conditions such as pressure and voltage were varied in some ranges to determine the optimal compaction regime. Three different concentrations of yttria were used to identify its effect on the properties of the samples. It is shown that the utilized ultra-rapid consolidation process in combination with high transmitted energy allows obtaining high density compacts, retaining the initial structure with minimal grain growth. The experimental results indicate some heterogeneity of the structure which may occur in the external layers of the tested samples due to various thermal and electromagnetic in-processing effects. As a result, the choice of the optimal parameters of the consolidation enables obtaining samples of acceptable quality.

  16. High-resolution electron microscopy observation and dislocation reaction mechanism of fivefold twinning in a Cu-rich precipitate in a cold rolled ferritic steel containing copper

    SciTech Connect

    Wang, Ling; Wang, Wei; Chen, Bolin; Zhou, Xiying; Li, Zhongwen; Zhou, Bangxin; Wang, Lumin

    2014-09-15

    Ferritic steels containing copper have been studied as model systems for clusters/precipitate formation in reactor pressure vessel steels. The samples were aged at 400 °C for 4000 h and subsequently cold rolled to 30% reduction at room temperature. The microstructural characteristics of the samples were analyzed using high-resolution transmission electron microscopy. Direct evidence was found that the fivefold twinning occurs via simultaneous emission of two Shockley partial dislocations from two particular α-Fe/Cu interfaces, and then the pileup tips of the twofold twin. - Highlights: • Fivefold twin is observed in a Cu-rich precipitate in cold rolled ferritic steels. • A dislocation reaction mechanism for the fivefold twin formation is proposed. • Two particular mismatching α-Fe/Cu-rich precipitate interfaces play a critical role.

  17. The comparison of microstructure and nanocluster evolution in proton and neutron irradiated Fe-9%Cr ODS steel to 3 dpa at 500 °C

    NASA Astrophysics Data System (ADS)

    Swenson, M. J.; Wharry, J. P.

    2015-12-01

    A model Fe-9%Cr oxide dispersion strengthened (ODS) steel was irradiated with protons or neutrons to a dose of 3 displacements per atom (dpa) at a temperature of 500 °C, enabling a direct comparison of ion to neutron irradiation effects at otherwise fixed irradiation conditions. The irradiated microstructures were characterized using transmission electron microscopy and atom probe tomography including cluster analysis. Both proton and neutron irradiations produced a comparable void and dislocation loop microstructure. However, the irradiation response of the Ti-Y-O oxide nanoclusters varied. Oxides remained stable under proton irradiation, but exhibited dissolution and an increase in Y:Ti composition ratio under neutron irradiation. Both proton and neutron irradiation also induced varying extents of Si, Ni, and Mn clustering at existing oxide nanoclusters. Protons are able to reproduce the void and loop microstructure of neutron irradiation carried out to the same dose and temperature. However, since nanocluster evolution is controlled by both diffusion and ballistic impacts, protons are rendered unable to reproduce the nanocluster evolution of neutron irradiation at the same dose and temperature.

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

    SciTech Connect

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

    2005-06-15

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

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

    DOE PAGES

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

    2016-07-26

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

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

    SciTech Connect

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

    2016-07-26

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

  2. Dynamic finite element modeling of the effects of size on the upper shelf energy of ferritic steels

    SciTech Connect

    Sidener, S.E.; Kumar, A.S.; Schubert, L.E.; Hamilton, M.L.; Rosinski, S.T.

    1996-04-01

    Both the fusion and light water reactor program require the use of the subsize specimens to obtain sufficient irradiation data on neutron-induced embrittlement of ferritic steels. While the development of fusion-relevant size effects correlations can proceed analytically, it is more cost-effective at this time to use data currently being obtained on embrittlement of pressure vessel steels to test and expand the correlations developed earlier using fusion relevant steels. Dynamic finite elements modeling of the fracture behavior of fatigue-precracked Charpy Specimens was performed to determine the effect of single variable changes in ligament size, width, span, and thickness on the upper shelf energy. A method based on tensile fracture strain was used for modeling crack initiation and propagation. It was found that the upper shelf energy of precracked specimens (USE{sub p}) is proportional to b{sup n}, where b is ligament size and n varies from about 1.6 for subsize to 1.9 for full size specimens. The USE{sub p} was found to be proportional to width according to W{sup 25}. The dependence on thickness was found to be linear for all cases studied. Some of the data from the FEM analysis were compared with experimental data and were found to be in reasonable agreement.

  3. Microstructure investigation of 13Cr-2Mo ODS steel components obtained by high voltage electric discharge compaction technique

    DOE PAGES

    Bogachev, Igor; Yudin, Artem; Grigoryev, Evgeniy; ...

    2015-11-02

    Refractory oxide dispersion strengthened 13Cr-2Mo steel powder was successfully consolidated to near theoretical density using high voltage electric discharge compaction. Cylindrical samples with relative density from 90% to 97% and dimensions of 10 mm in diameter and 10–15 mm in height were obtained. Consolidation conditions such as pressure and voltage were varied in some ranges to determine the optimal compaction regime. Three different concentrations of yttria were used to identify its effect on the properties of the samples. It is shown that the utilized ultra-rapid consolidation process in combination with high transmitted energy allows obtaining high density compacts, retaining themore » initial structure with minimal grain growth. The experimental results indicate some heterogeneity of the structure which may occur in the external layers of the tested samples due to various thermal and electromagnetic in-processing effects. As a result, the choice of the optimal parameters of the consolidation enables obtaining samples of acceptable quality.« less

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

    SciTech Connect

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

    1996-04-01

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

  5. Residual stresses in a ferritic steel welded pipe: an experimental comparison between reactor and pulsed neuron sources

    NASA Astrophysics Data System (ADS)

    Albertini, Gianni; Brugnami, D.; Bruno, Giovanni; Ceretti, M.; Cernuschi, F. M.; Edwards, Lyndon

    1997-02-01

    Residual stresses induced by welding processes can affect the integrity of structural components like tubes and pipes of thermoelectric power plants. In order to reduce or cancel these stresses, welded components are often heat treated. The residual stress field in an arc-welded 2.25Cr1Mo ferritic steel pipe was measured using neutron diffraction both before and after stress relieving heat treatment. In the first stage stresses were measured using two different kinds of neutron sources: a reactor and a pulsed one. A comparison between results obtained using G5.2 diffractometer at LLB and ENGIN equipment at ISIS will be outlined and the effectiveness of heat treatment will be shown.

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

    SciTech Connect

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

    2004-11-08

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

  7. Study for corrosion characteristics of ferritic stainless steel weld metal with respect to added contents of Ti and Nb

    NASA Astrophysics Data System (ADS)

    Kim, JongMin; Lee, HaeWoo

    2014-03-01

    This paper identified the effects of Ti and Nb on pitting and intergranular corrosion resistance in a ferritic stainless steel weld metal of the automobile exhaust system. We fabricated 4 flux cored wires designed with 0-0.2 wt% Ti and 0-1.0 wt% Nb and performed Flux Cored Arc Welding. Through the potentiodynamic polarization test in 0.5M NaCl, we evaluated pitting resistance. And in order to evaluate the intergranular corrosion resistance, we observed microstructure after we performed DL-EPR test in 0.5M H2SO4+0.01M KSCN. As a result of the test, the specimen added with 0.2%Ti+1.0%Nb showed the highest pitting resistance. From observing the degree of sensitization and microstructure, the intergranular corrosion resistance was higher as the contents of Ti and Nb increased. And through EBSD we observed Cr carbide which affects the corrosion resistance.

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

    NASA Astrophysics Data System (ADS)

    Nozawa, Takashi; Noh, Sanghoon; Tanigawa, Hiroyasu

    2012-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2007-08-01

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

  10. Influence of alloy content and a cerium surface treatment on the oxidation behavior of Fe-Cr ferritic stainless steels

    SciTech Connect

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

    2006-01-01

    The cost of solid oxide fuel cells (SOFC) can be significantly reduced by using interconnects made from ferritic stainless steels. In fact, several alloys have been developed specifically for this application (Crofer 22APU and Hitachi ZMG323). However, these steels lack environmental stability in SOFC environments, and as a result, degrade the performance of the SOFC. A steel interconnect can contribute to performance degradation through: (i) Cr poisoning of electrochemically active sites within the cathode; (ii) formation of non-conductive oxides, such as SiO2 or Al2O3 from residual or minor alloying elements, at the base metal-oxide scale interface; and/or (iii) excessive oxide scale growth, which may also retard electrical conductivity. Consequently, there has been considerable attention on developing coatings to protect steel interconnects in SOFC environments and controlling trace elements during alloy production. Recently, we have reported on the development of a Cerium surface treatment that improves the oxidation behavior of a variety alloys, including Crofer 22APU [1-5]. Initial results indicated that the treatment may improve the performance of Crofer 22APU for SOFC application by: (i) retarding scale growth resulting in a thinner oxide scale; and (ii) suppressing the formation of a deleterious continuous SiO2 layer that can form at the metal-oxide scale interface in materials with high residual Si content [5]. Crofer 22 APU contains Fe-22Cr-0.5Mn-0.1Ti (weight percent). Depending on current market prices and the purity of raw materials utilized for ingot production, Cr can contribute upwards of 90 percent of the raw materials cost. The present research was undertaken to determine the influence of Cr content and minor element additions, especially Ti, on the effectiveness of the Ce surface treatment. Particular emphasis is placed on the behavior of low Cr alloys.

  11. Elevated temperature tensile properties of P9 steel towards ferritic steel wrapper development for sodium cooled fast reactors

    NASA Astrophysics Data System (ADS)

    Choudhary, B. K.; Mathew, M. D.; Isaac Samuel, E.; Christopher, J.; Jayakumar, T.

    2013-11-01

    Tensile deformation and fracture behaviour of the three developmental heats of P9 steel for wrapper applications containing varying silicon in the range 0.24-0.60% have been examined in the temperature range 300-873 K. Yield and ultimate tensile strengths in all the three heats exhibited gradual decrease with increase in temperature from room to intermediate temperatures followed by rapid decrease at high temperatures. A gradual decrease in ductility to a minimum at intermediate temperatures followed by an increase at high temperatures has been observed. The fracture mode remained transgranular ductile. The steel displayed signatures of dynamic strain ageing at intermediate temperatures and dominance of recovery at high temperatures. No significant difference in the strength and ductility values was observed for varying silicon in the range 0.24-0.60% in P9 steel. P9 steel for wrapper application displayed strength and ductility values comparable to those reported in the literature.

  12. Static Recrystallization Kinetics and Crystallographic Texture of Nb-Stabilized Ferritic Stainless Steel Based on Orientation Imaging Microscopy

    NASA Astrophysics Data System (ADS)

    Malta, Paula Oliveira; Alves, Davi Silva; Ferreira, Aline Oliveira Vasconcelos; Moutinho, Iane Dutra; Dias, Carolina Arriel Pedroso; Santos, Dagoberto Brandão

    2017-01-01

    In the present study, Nb-stabilized ferritic stainless steel was prepared with annealing (430-A) and without annealing (430-NA) annealing, and the microstructure of the resulting samples was examined. The steel was then subjected to cold rolling and isothermal annealing in order to analyze its recrystallization kinetics and texture evolution. Microstructural characterization was performed by scanning and transmission electron microscopies. Recrystallization kinetics were evaluated by measuring the microhardness of the samples, and analyzing their kernel average misorientation and grain orientation spread via electron backscatter diffraction. The Avrami exponent data revealed that one-dimensional grain growth occurred owing to the migration of high-angle grain boundaries. The mean activation energies for recrystallization for 430-NA and 430-A was found to be 365 and 419 kJ mol-1, respectively. The recrystallization texture was influenced by oriented nucleation and selected growth mechanisms, as well as by the Nb carbonitride distribution and grain boundary energy. The recrystallized and growing grains with the {554}<225> orientation showed a dimensional advantage over the other recrystallized components. The coincident site lattice boundaries were attributed to the progression of recrystallization since the CSL numeric fraction increased as the temperature increased. The {554}<225> component was associated with the ∑19a boundary, which exerted a significant control on the selective growth during the recrystallization.

  13. Static Recrystallization Kinetics and Crystallographic Texture of Nb-Stabilized Ferritic Stainless Steel Based on Orientation Imaging Microscopy

    NASA Astrophysics Data System (ADS)

    Malta, Paula Oliveira; Alves, Davi Silva; Ferreira, Aline Oliveira Vasconcelos; Moutinho, Iane Dutra; Dias, Carolina Arriel Pedroso; Santos, Dagoberto Brandão

    2017-03-01

    In the present study, Nb-stabilized ferritic stainless steel was prepared with annealing (430-A) and without annealing (430-NA) annealing, and the microstructure of the resulting samples was examined. The steel was then subjected to cold rolling and isothermal annealing in order to analyze its recrystallization kinetics and texture evolution. Microstructural characterization was performed by scanning and transmission electron microscopies. Recrystallization kinetics were evaluated by measuring the microhardness of the samples, and analyzing their kernel average misorientation and grain orientation spread via electron backscatter diffraction. The Avrami exponent data revealed that one-dimensional grain growth occurred owing to the migration of high-angle grain boundaries. The mean activation energies for recrystallization for 430-NA and 430-A was found to be 365 and 419 kJ mol-1, respectively. The recrystallization texture was influenced by oriented nucleation and selected growth mechanisms, as well as by the Nb carbonitride distribution and grain boundary energy. The recrystallized and growing grains with the {554}<225> orientation showed a dimensional advantage over the other recrystallized components. The coincident site lattice boundaries were attributed to the progression of recrystallization since the CSL numeric fraction increased as the temperature increased. The {554}<225> component was associated with the ∑19a boundary, which exerted a significant control on the selective growth during the recrystallization.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  15. New Ferritic Steels with Combined Optimal Creep Resistance and Ductility by Coupling Thermodynamic Calculations with Focused Experiments

    SciTech Connect

    Teng, Zhenke; Zhang, F; Miller, Michael K; Liu, Chain T; Huang, Shenyan; Chou, Y; Tien, R; Chang, Y A; Liaw, Peter K

    2012-01-01

    Two critical issues restricting the applications of NiAl precipitate-strengthened ferritic steels are their poor room temperature ductility and insufficient creep resistance at temperatures higher than 600 C. In this study, a thermodynamic modeling approach is integrated with experiments focused on investigating the ductility and creep resistance of steel alloys based on the Fe-Ni-Al-Cr-Mo multi-component system. The mechanical property studies showed that the creep resistance increases with increasing the volume fraction of B2-ordered precipitates, while the opposite trend was observed for the ductility. Low solubility of Al in the {alpha}-Fe matrix was found to favor a ductility increase. Thermodynamic calculations were used to predict the volume fraction of B2-ordered precipitate and the elemental partitioning to guide the selection of alloy compositions that might exhibit the balanced creep resistance and ductility. Key experiments were then conducted to validate the prediction. This integrated approach was found to be very effective in the alloy development.

  16. Extending the boundaries of mechanical properties of Ti-Nb low-carbon steel via combination of ultrafast cooling and deformation during austenite-to-ferrite transformation

    NASA Astrophysics Data System (ADS)

    Deng, Xiangtao; Fu, Tianliang; Wang, Zhaodong; Liu, Guohuai; Wang, Guodong; Misra, R. D. K.

    2017-01-01

    We underscore here a novel approach to extend the boundaries of mechanical properties of Ti-Nb low-carbon steel via combination of ultrafast cooling and deformation during austenite-to-ferrite transformation. The proposed approach yields a refined microstructure and high density nano-sized precipitates, with consequent increase in strength. Steels subjected to ultra-fast cooling during austenite-to-ferrite transformation led to 145 MPa increase in yield strength, while the small deformation after ultra-fast cooling process led to increase in strength of 275 MPa. The ultra-fast cooling refined the ferrite and pearlite constituents and enabled uniform dispersion, while the deformation after ultra-fast cooling promoted precipitation and broke the lamellar pearlite to spherical cementite and long thin strips of FexC. The contribution of nano-sized precipitates to yield strength was estimated to be 247.9 MPa and 358.3 MPa for ultrafast cooling and deformation plus ultrafast cooling processes. The nano precipitates carbides were identified to be (Ti, Nb)C and had a NaCl-type crystal structure, and obeyed the Baker-Nutting orientation relationship with the ferrite matrix.

  17. Effect of particle size, fraction and carbide banding on deformation and damage behavior of ferrite-cementite steel under tensile/shear loads

    NASA Astrophysics Data System (ADS)

    Zhuang, Xincun; Ma, Siming; Zhao, Zhen

    2017-01-01

    Deformation and damage behavior of ferrite-cementite steel was investigated using microstructure-based representative volume element (RVE) methodology. A series of automatically generated 2D RVEs with ferrite matrix and globular cementite particles were generated as representative of various microstructures. The geometrically necessary dislocation (GND) accumulation at the ferrite-cementite interphase was also studied by introducing an intermediate layer around the cementite particles. Damage mechanisms such as ductile fracture in ferrite matrix, brittle fracture in cementite, and decohesion at ferrite-cementite interphase were considered to study the fracture modes. The relationships between interface strength and particle size were estimated according to the modified Argon criterion and showed satisfactory agreement with related works. The influences of microstructural features, such as particle size, particle fraction and carbide banding, on deformation and damage evolution were investigated under tensile and shear loads. Simulation results indicated that small particle size and particle fraction could postpone the initial decohesion under both tensile and shear loads, while carbide banding can lead to early fracture due to local stress concentration, which has potential to cause the loss of ductility and premature failure. These adverse effects become more severe when more cementite particles remain in the band or the gather density of the cementite particles in the band becomes higher.

  18. Mn1.5Co1.5O4 Spinel Protection Layers on Ferritic Stainless Steels for SOFC Interconnect Applications

    SciTech Connect

    Yang, Z Gary; Xia, Gordon; Stevenson, Jeffry W.

    2005-01-26

    In intermediate solid oxide fuel cells, the use of cost effective chromia forming alloy interconnects such as ferritic stainless steels can lead to severe degradation in cell performance due to chromium migration into the cells at the cathode side. To protect cells from chromium poisoning and improve their performance, a Mn1.5Co1.5O4 spinel barrier layer has been developed and tested on the ferritic stainless steel Crofer22 APU. Thermal and electrical tests confirmed the effectiveness of the spinel protection layer as a means of stopping chromium migration and decreasing oxidation, while promoting electrical contact and minimizing cathode/interconnect interfacial resistance. The thermally grown spinel protection layer was well-bonded to the Crofer22 APU substrate and demonstrated stable performance under thermal cycling.

  19. Impact behavior of 9-Cr and 12-Cr ferritic steels after low-temperature irradiation

    SciTech Connect

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

    1987-01-01

    Miniature Charpy impact specimens of 9Cr-1MoVNb and 12Cr-1MoVW steels and these steels with 1 and 2% Ni were irradiated in the High-Flux Isotope Reactor (HFIR) at 50/sup 0/C to displacement damage levels of up to 9 dpa. Nickel was added to study the effect of transmutation helium. Irradiation caused an increase in the ductile-brittle transition temperature (DBTT). The 9Cr-1MoVNb steels, with and without nickel, showed a larger shift than the 12Cr-1MoVW steels, with and without nickel. The results indicated that helium also increased the DBTT. The same steels were previously irradiated at higher temperatures. From the present and past tests, the effect of irradiation temperature on the DBTT behavior can be evaluated. For the 9Cr-1MoVNb steel, there is a continuous decrease in the magnitude of the DBTT increase up to an irradiation temperature of about 400/sup 0/C, after which the shift drops rapidly to zero at about 450/sup 0/C. The DBTT of the 12Cr-1MoVW steel shows a maximum increase at an irradiation temperature of about 400/sup 0/C and less of an increase at either higher or lower irradiation temperatures.

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

    SciTech Connect

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

    1997-04-01

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

  1. Microstructure and mechanical behavior of neutron irradiated ultrafine grained ferritic steel

    SciTech Connect

    Ahmad Alsabbagh; Apu Sarkar; Brandon Miller; Jatuporn Burns; Leah Squires; Douglas Porter; James I. Cole; K. L. Murty

    2014-10-01

    Neutron irradiation effects on ultra-fine grain (UFG) low carbon steel prepared by equal channel angular pressing (ECAP) has been examined. Counterpart samples with conventional grain (CG) sizes have been irradiated alongside with the UFG ones for comparison. Samples were irradiated in the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) to 1.24 dpa. Atom probe tomography revealed manganese, silicon-enriched clusters in both ECAP and CG steel after neutron irradiation. X-ray quantitative analysis showed that dislocation density in CG increased after irradiation. However, no significant change was observed in UFG steel revealing better radiation tolerance.

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

    NASA Astrophysics Data System (ADS)

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

    1984-06-01

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

  3. Effect of aging temperature on the microstructures and mechanical properties of ZG12Cr9Mo1Co1NiVNbNB ferritic heat-resistant steel

    NASA Astrophysics Data System (ADS)

    Yang, Xue; Sun, Lan; Xiong, Ji; Zhou, Ping; Fan, Hong-yuan; Liu, Jian-yong

    2016-02-01

    The effect of aging on the mechanical properties and microstructures of a new ZG12Cr9Mo1Co1NiVNbNB ferritic heat resistant steel was investigated in this work to satisfy the high steam parameters of the ultra-supercritical power plant. The results show that the main precipitates during aging are Fe(Cr, Mo)23C6, V(Nb)C, and (Fe2Mo) Laves in the steel. The amounts of the precipitated phases increase during aging, and correspondingly, the morphologies of phases are similar to be round. Fe(Cr, Mo)23C6 appears along boundaries and grows with increasing temperature. In addition, it is revealed that the martensitic laths are coarsened and eventually happen to be polygonization. The hardness and strength decrease gradually, whereas the plasticity of the steel increases. What's more, the hardness of this steel after creep is similar to that of other 9%-12%Cr ferritic steels. Thus, ZG12Cr9Mo1Co1NiVNbNB can be used in the project.

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

    SciTech Connect

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

    1996-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

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

    SciTech Connect

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

    1996-10-01

    Tensile tests were conducted on 8 reduced-activation Cr-W steels after irradiation to 15-17 and 26-29 dpa, and Charpy impact tests were conducted on steels irradiated to 26-29 dpa. Irradiation was in Fast Flux Test Facility at 365 C on steels containing 2.25-12% Cr, varying amounts of W, V, and Ta, and 0.1%C. Previously, tensile specimens were irradiated to 6-8 dpa and Charpy specimens to 6-8, 15- 17, and 20-24 dpa. Tensile and Charpy specimens were also thermally aged to 20,000 h at 365 C. Thermal aging had little effect on tensile properties or ductile-brittle transition temperature (DBTT), but several steels showed a slight increase in upper-shelf energy (USE). After 7 dpa, strength increased (hardened) and then remained relatively unchanged through 26-29 dpa (ie, strength saturated with fluence). Post-irradiation Charpy impact tests after 26-29 dpa showed that the loss of impact toughness (increased DBTT, decreased USE) remained relatively unchanged from the values after 20-24 dpa, which had been relatively unchanged from the earlier irradiations. As before, the two 9Cr steels had the most irradiation resistance.

  7. The influence of ferrite volume fraction on Rayleigh wave propagation in A572 grade 50 steel

    NASA Astrophysics Data System (ADS)

    Abbasi, Zeynab; Tehrani, Niloofar; Ozevin, Didem; Indacochea, J. E.

    2017-02-01

    The acoustoelastic effect is the interaction between ultrasonic wave velocity and stress. To estimate the stress a perturbation signal is introduced and the shift in time of flight is measured at the receiving location. In addition to the stress, the wave velocity can be affected by the volume fraction of the phases in the material's microstructure. This study investigates the changes in Rayleigh wave velocity as a function of stress and microstructure obtained in A572 grade 50 steel following heat treatments. The steel was heat treated to homogenize the microstructure of as-received steel that showed banding; the samples are heat treated at 970 °C for 0.5, 1, and 4 hours, furnace cooled and metallographically characterized. The acoustoelastic coefficient for 1 MHz perturbation frequency is calculated by uniaxial loading of each heat treated plate while measuring ultrasonic wave velocity. The results are discussed in relation to the reduction of banding obtained from optical microscopy.

  8. Tensile Properties, Ferrite Contents, and Specimen Heating of Stainless Steels in Cryogenic Gas Tests

    SciTech Connect

    Ogata, T.; Yuri, T.; Ono, Y.

    2006-03-31

    We performed tensile tests at cryogenic temperatures below 77 K and in helium gas environment for SUS 304L and SUS 316L in order to obtain basic data of mechanical properties of the materials for liquid hydrogen tank service. We evaluate tensile curves, tensile properties, ferrite contents, mode of deformation and/or fracture, and specimen heating during the testing at 4 to 77 K. For both SUS 304L and 316L, tensile strength shows a small peak around 10 K, and specimen heating decreases above 30 K. The volume fraction of {alpha}-phase increases continuously up to 70 % with plastic strain, at approximately 15 % plastic strain for 304L and up to 35 % for 316L. There was almost no clear influence of testing temperature on strain-induced martensitic transformation at the cryogenic temperatures.

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

    SciTech Connect

    Pestovich, Kimberly Shay

    2015-08-18

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

  10. MICROSTRUCTURAL EXAMINATION OF LOW ACTIVATION FERRITIC STEELS FOLLOWING IRRADIATION IN ORR

    SciTech Connect

    Gelles, David S.

    2002-09-01

    Microstructural examinations are reported for a series of low activation steels containing Mn following irradiation in the Oak Ridge Reactor at 330 and 400 degrees C to approximately 10 dpa. Alloy compositions included 2Cr, 9Cr and 12Cr steels with V to 1.5 percent and W to 1.0 percent. Results include compositional changes in precipitates and microstructural changes as a function of composition and irradiation temperature. It is concluded that temperatures in ORR are on the order of 50 degrees C higher than anticipated.

  11. Short-term in vitro responses of human peripheral blood monocytes to ferritic stainless steel fiber networks.

    PubMed

    Spear, Rose L; Brooks, Roger A; Markaki, Athina E

    2013-05-01

    Beneficial effects on bone-implant bonding may accrue from ferromagnetic fiber networks on implants which can deform in vivo inducing controlled levels of mechanical strain directly in growing bone. This approach requires ferromagnetic fibers that can be implanted in vivo without stimulating undue inflammatory cell responses or cytotoxicity. This study examines the short-term in vitro responses, including attachment, viability, and inflammatory stimulation, of human peripheral blood monocytes to 444 ferritic stainless steel fiber networks. Two types of 444 networks, differing in fiber cross section and thus surface area, were considered alongside austenitic stainless steel fiber networks, made of 316L, a widely established implant material. Similar high percent seeding efficiencies were measured by CyQuant® on all fiber networks after 48 h of cell culture. Extensive cell attachment was confirmed by fluorescence and scanning electron microscopy, which showed round monocytes attached at various depths into the fiber networks. Medium concentrations of lactate dehydrogenase (LDH) and tumor necrosis factor alpha (TNF-α) were determined as indicators of viability and inflammatory responses, respectively. Percent LDH concentrations were similar for both 444 fiber networks at all time points, whereas significantly lower than those of 316L control networks at 24 h. All networks elicited low-level secretions of TNF-α, which were significantly lower than that of the positive control wells containing zymosan. Collectively, the results indicate that 444 networks produce comparable responses to medical implant grade 316L networks and are able to support human peripheral blood monocytes in short-term in vitro cultures without inducing significant inflammatory or cytotoxic effects.

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

    NASA Astrophysics Data System (ADS)

    Wang, Yonghui; Hu, Shengsun; Shen, Junqi

    2015-10-01

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

  13. Low cycle fatigue behavior of a ferritic reactor pressure vessel steel

    NASA Astrophysics Data System (ADS)

    Sarkar, Apu; Kumawat, Bhupendra K.; Chakravartty, J. K.

    2015-07-01

    The cyclic stress-strain response and the low cycle fatigue (LCF) behavior of 20MnMoNi55 pressure vessel steel were studied. Tensile strength and LCF properties were examined at room temperature (RT) using specimens cut from rolling direction of a rolled block. The fully reversed strain-controlled LCF tests were conducted at a constant total strain rate with different axial strain amplitude levels. The cyclic strain-stress relationships and the strain-life relationships were obtained through the test results, and related LCF parameters of the steel were calculated. The studied steel exhibits cyclic softening behavior. Furthermore, analysis of stabilized hysteresis loops showed that the steel exhibits non-Masing behavior. Complementary scanning electron microscopy examinations were also carried out on fracture surfaces to reveal dominant damage mechanisms during crack initiation, propagation and fracture. Multiple crack initiation sites were observed on the fracture surface. The investigated LCF behavior can provide reference for pressure vessel life assessment and fracture mechanisms analysis.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  15. Probing Formability Improvement of Ultra-thin Ferritic Stainless Steel Bipolar Plate of PEMFC in Non-conventional Forming Process

    NASA Astrophysics Data System (ADS)

    Bong, Hyuk Jong; Barlat, Frédéric; Lee, Myoung-Gyu

    2016-08-01

    Formability increase in non-conventional forming profiles programmed in the servo-press was investigated using finite element analysis. As an application, forming experiment on a 0.15-mm-thick ferritic stainless steel sheet for a bipolar plate, a primary component of a proton exchange membrane fuel cell, was conducted. Four different forming profiles were considered to investigate the effects of forming profiles on formability and shape accuracy. The four motions included conventional V motion, holding motion, W motion, and oscillating motion. Among the four motions, the holding motion, in which the slide was held for a certain period at the bottom dead point, led to the best formability. Finite element simulations were conducted to validate the experimental results and to probe the formability improvement in the non-conventional forming profiles. A creep model to address stress relaxation effect along with tool elastic recovery was implemented using a user-material subroutine, CREEP in ABAQUS finite element software. The stress relaxation and variable contact conditions during the holding and oscillating profiles were found to be the main mechanism of formability improvement.

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

    SciTech Connect

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

    1991-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Kim, Jun Hwan; Kim, Sung Ho

    2013-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  19. Fracture and the formation of sigma phase, M[sub 23]C[sub 6], and austenite from delta-ferrite in an AISI 304L stainless steel

    SciTech Connect

    Tseng, C.C.; Shen, Y.; Thompson, S.W.; Krauss, G. . Dept. of Metallurgical and Materials Engineering); Mataya, M.C. )

    1994-06-01

    The decomposition of delta-ferrite and its effects on tensile properties and fracture of a hot-rolled AISI 304L stainless steel plate were studied. Magnetic response measurements of annealed specimens showed that the transformation rate of delta-ferrite was highest at 720 C. Transformation behavior was characterized by light microscopy, transmission electron microscopy, scanning electron microscopy, and energy-dispersive spectroscopy on thin foils. The initial transformation of delta-ferrite ([delta]) to austenite ([gamma]) and a chromium-rich carbide (M[sub 23]C[sub 6]) occurred by a lamellar eutectoid reaction, [sigma] [r reversible] M[sub 23]C[sub 6] + [gamma]. The extent of the reaction was limited by the low carbon content of the 304L plate, and the numerous, fine M[sub 23]C[sub 6] particles of the eutectoid structure provide microvoid nucleation sites in tensile specimens annealed at 720 C for short times. Sigma phase ([sigma]) formed as a result of a second eutectoid reaction, [delta] [r reversible] [sigma] + [gamma]. Brittle fracture associated with the plate-shaped sigma phase of the second eutectoid structure resulted in a significant decrease in reduction of area (RA) in the transverse tensile specimens. The RA for longitudinal specimens was not affected by the formation of sigma phase. Tensile strengths were little affected by delta-ferrite decomposition products in either longitudinal or transverse orientations.

  20. Preparation and performances of Co-Mn spinel coating on a ferritic stainless steel interconnect material for solid oxide fuel cell application

    NASA Astrophysics Data System (ADS)

    Zhang, H. H.; Zeng, C. L.

    2014-04-01

    Ferritic stainless steels have become the candidate materials for interconnects of intermediate temperature solid oxide fuel cell (SOFC). The present issues to be solved urgently for the application of ferritic stainless steel interconnects are their rapid increase in contact resistance and Cr poisoning. In the present study, a chloride electrolyte suspension has been developed to electro-deposit a Co-Mn alloy on a type 430 stainless steel, followed by heat treatment at 750 °C in argon and at 800 °C in air to obtain Co-Mn spinel coatings. The experimental results indicate that an adhesive and compact Co-Mn alloy layer can be deposited in the chloride solution. After heat treatment, a complex coating composed of an external MnCo2O4 layer and an inner Cr-rich oxide layer has been formed on 430SS. The coating improves the oxidation resistance of the steel at 800 °C in air, especially in wet air, and inhibits the outward diffusion of Cr from the Cr-rich scale. Moreover, a low contact resistance has been achieved with the application of the spinel coatings.

  1. Fatigue performance and cyclic softening of F82H, a ferritic martensic steel

    SciTech Connect

    Stubbins, J.F.; Gelles, D.S.

    1996-04-01

    The room temperature fatigue performance of F82H has been examined. The fatigue life was determined in a series of strain-controlled tests where the stress level was monitored as a function of the number of accrued cycles. Fatigue lives in the range of 10{sup 3} to 10{sup 6} cycles to failure were examined. The fatigue performance was found to be controlled primarily by the elastic strain range over most of the range of fatigue lives examined. Only at low fatigue lives did the plastic strain range contribute to the response. However, when the significant plastic strain did contribute, the material showed a tendency to cyclically soften. That is the load carrying capability of the material degrades with accumulated fatigue cycles. The overall fatigue performance of the F82H alloy was found to be similiar to other advanced martensitic steels, but lower than more common low alloy steels which possess lower yield strengths.

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

    SciTech Connect

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

    1997-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

  4. Accelerated development of Zr-containing new generation ferritic steels for advanced nuclear reactors

    SciTech Connect

    Tan, Lizhen; Yang, Ying; Sridharan, K.

    2015-12-01

    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 the 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. The ultimate goal of this project is, with the aid of computational modeling tools, to accelerate the development of Zr-bearing ferritic alloys that can be fabricated using conventional steelmaking methods. The new alloys are expected to have superior high-temperature creep performance and excellent radiation resistance as compared to Grade 91. The designed alloys were fabricated using arc-melting and drop-casting, followed by hot rolling and conventional heat treatments. Comprehensive experimental studies have been conducted on the developed alloys to evaluate their hardness, tensile properties, creep resistance, Charpy impact toughness, and aging resistance, as well as resistance to proton and heavy ion (Fe2+) irradiation.

  5. Characterization of TiN, TiC and Ti(C,N) in titanium-alloyed ferritic chromium steels focusing on the significance of different particle morphologies

    SciTech Connect

    Michelic, S.K.; Loder, D.; Reip, T.; Ardehali Barani, A.; Bernhard, C.

    2015-02-15

    Titanium-alloyed ferritic chromium steels are a competitive option to classical austenitic stainless steels owing to their similar corrosion resistance. The addition of titanium significantly influences their final steel cleanliness. The present contribution focuses on the detailed metallographic characterization of titanium nitrides, titanium carbides and titanium carbonitrides with regard to their size, morphology and composition. The methods used are manual and automated Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy as well as optical microscopy. Additional thermodynamic calculations are performed to explain the precipitation procedure of the analyzed titanium nitrides. The analyses showed that homogeneous nucleation is decisive at an early process stage after the addition of titanium. Heterogeneous nucleation gets crucial with ongoing process time and essentially influences the final inclusion size of titanium nitrides. A detailed investigation of the nuclei for heterogeneous nucleation with automated Scanning Electron Microscopy proved to be difficult due to their small size. Manual Scanning Electron Microscopy and optical microscopy have to be applied. Furthermore, it was found that during solidification an additional layer around an existing titanium nitride can be formed which changes the final inclusion morphology significantly. These layers are also characterized in detail. Based on these different inclusion morphologies, in combination with thermodynamic results, tendencies regarding the formation and modification time of titanium containing inclusions in ferritic chromium steels are derived. - Graphical abstract: Display Omitted - Highlights: • The formation and modification of TiN in the steel 1.4520 was examined. • Heterogeneous nucleation essentially influences the final steel cleanliness. • In most cases heterogeneous nuclei in TiN inclusions are magnesium based. • Particle morphology provides important information

  6. Long-term microstructural stability of oxide-dispersion strengthened Eurofer steel annealed at 800 °C

    NASA Astrophysics Data System (ADS)

    Zilnyk, K. D.; Sandim, H. R. Z.; Bolmaro, R. E.; Lindau, R.; Möslang, A.; Kostka, A.; Raabe, D.

    2014-05-01

    Oxide-dispersion strengthened ferritic martensitic steels such as ODS-Eurofer grade are good candidates for structural applications in future fusion power reactors. Long-term annealing treatments in vacuum were carried out in cold-rolled samples (80% reduction in thickness) from 1 h up to 4320 h (6 months) at 800 °C, i.e. the maximum temperature in the ferritic phase field, to follow its softening behavior. The microstructural stability of this steel was mapped using several characterization techniques including scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction, Vickers microhardness testing, X-ray diffraction texture measurements, low-temperature electrical resistivity, and magnetic coercive field measurements. ODS-Eurofer steel displays good microstructural stability. Discontinuous recrystallization occurs at the early stages of annealing resulting in a low volume fraction of recrystallized grains. Extended recovery is the predominant softening mechanism at this temperature for longer times.

  7. Size-dependent characteristics of ultra-fine oxygen-enriched nanoparticles in austenitic steels

    NASA Astrophysics Data System (ADS)

    Miao, Yinbin; Mo, Kun; Zhou, Zhangjian; Liu, Xiang; Lan, Kuan-Che; Zhang, Guangming; Miller, Michael K.; Powers, Kathy A.; Stubbins, James F.

    2016-11-01

    Here, a coordinated investigation of the elemental composition and morphology of ultra-fine-scale nanoparticles as a function of size within a variety of austenitic oxide dispersion-strengthened (ODS) steels is reported. Atom probe tomography was utilized to evaluate the elemental composition of these nanoparticles. Meanwhile, the crystal structures and orientation relationships were determined by high-resolution transmission electron microscopy. The nanoparticles with sufficient size (>4 nm) to maintain a Y2Ti2-xO7-2x stoichiometry were found to have a pyrochlore structure, whereas smaller YxTiyOz nanoparticles lacked a well-defined structure. The size-dependent characteristics of the nanoparticles in austenitic ODS steels differ from those in ferritic/martensitic ODS steels.

  8. On the shape of the magnetic Barkhausen noise profile for better revelation of the effect of microstructures on the magnetisation process in ferritic steels

    NASA Astrophysics Data System (ADS)

    Vashista, M.; Moorthy, V.

    2015-11-01

    The shape of the Magnetic Barkhausen Noise (MBN) profiles has been compared for two different methods of MBN measurements in order to reveal the true extent of the influence of different carbon-content related microstructures on the magnetisation process. The MBN profiles were measured using high frequency and low frequency MBN measurement systems on samples from low carbon 18CrNiMo5 steel and high carbon 42CrMo4 steel heat treated by isothermal annealing, spheroidising annealing and quenching and tempering processes. The high frequency MBN (HFMBN) profile shows only a single peak for all the samples due to insufficient applied magnetic field strength and shallow skin-depth of detection of HFMBN signals. The low frequency MBN (LFMBN) profile shows two peaks for all the samples due to larger magnetisation range revealing the difference in the interaction of domain walls with different microstructural features such as ferrite, pearlite, martensite and carbides. The shape of the LFMBN profile shows systematic and distinct variation in the magnetisation process with respect to carbon content and different microstructures. This study shows that the LFMBN profile reveals distinct changes in shape which could be successfully used for characterisation of different microstructural phases in ferritic steels.

  9. High-temperature degradation and protection of ferritic and austenitic steels in steam generators

    NASA Astrophysics Data System (ADS)

    Martínez-Villafañe, A.; Almeraya-Calderón, M. F.; Gaona-Tiburcio, C.; Gonzalez-Rodriguez, J. G.; Porcayo-Calderón, J.

    1998-02-01

    The useful life of superheaters and reheaters of power stations which use heavy fuel oil is shortened and their continuous service is inhibited by corrosion (fireside) and creep-type problems. The increase of corrosion attack on boilers is caused by the presence of fuel ash deposits containing mainly vanadium, sodium, and sulfur which form low-melting-point compounds. The tubes are exposed to the action of high stresses and high temperatures, producing the so-called “creep damage.” In this work, two kinds of results are reported: lab and field studies using a 2.25Cr-1Mo steel. The laboratory work was in turn divided into two parts. In the first, the steel was exposed to the action of natural ash deposits in oxidant atmospheres at 600 ° for 24 h. In the second part, tensile specimens were creep tested in Na2SO4, V2O5, and their mixture over a temperature range of 580 to 620 °. In the field work, components of a power station were coated with different types of nickel-and iron-base coatings containing chromium, Fe-Cr, and Fe-Si using the powder flame spraying technique. After testing, the coated tubes were analyzed using electron microscopy. The results showed that all the coating systems had good corrosion resistance, especially those containing silicon or chromium.

  10. In Situ Observation of Phase Transformation and Structure Evolution of a 12 pct Cr Ferritic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Song, Changjiang; Guo, Yuanyi; Li, Kefeng; Sun, Fengmei; Han, Qingyou; Zhai, Qijie

    2012-10-01

    This work focuses on an in situ observation of phase transformation of a 12 pct Cr ferritic stainless steel using high-temperature laser scanning confocal microscopy. α→ γ→ δ phase transformation temperatures are determined to be approximately 1073 K and 1423 K (800 °C and 1150 °C), respectively. The onset of phase transformation is found to occur at grain boundaries. When the temperature is beyond 1518 K (1245 °C), the grain growth rate suddenly becomes very high, and the grain growth is related to the self-organizing of adjacent grains. δ→ γ phase transformation has been mostly restrained when cooling rates are in the range of 22.4 K/s to 13.3 K/s (22.4 °C/s to 13.3 °C/s) except for at grain boundaries. Martensitic phase transformation, rather than γ→ α phase transformation, occurs when the cooling rates are in the range of 8.5 K/s to 2.2 K/s (8.5 °C/s to 2.2 °C/s). The starting temperature of martensitic phase transformation is approximately 697 K to 728 K (424 °C to 455 °C) for specimens heated to 1373 K (1100 °C) ( i.e., γ phase field), which is 50 K to 100 K (50 °C to 100 °C) higher than that of specimens heated to 1723 K (1450 °C) ( i.e., δ phase field). Many bulges remain on the surfaces of the specimen heated to 1723 K (1450 °C), and their formation mechanism is analyzed.

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

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

    SciTech Connect

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

    1993-09-01

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

  13. Evolution of microstructure at hot band annealing of ferritic FeSi steels

    NASA Astrophysics Data System (ADS)

    Schneider, Jürgen; Li, Guangqiang; Franke, Armin; Zhou, Bowen

    2017-02-01

    The magnetic properties of the finally fabricated nonoriented FeSi steels critically depend on the microstructure and on the occurring crystallographic texture. The fabrication route comprises hot rolling, coiling and cooling, hot band annealing before cold rolling (optional), cold rolling and the final thermal treatment. As well known there is an interplay between the microstructure and texture during the various processing steps. For that reason, it is of interest to know more on the evolution of the microstructure at hot band annealing of hot band prepared in different ways. In this paper we will summarize our recent results on the evolution of microstructure during thermal annealing of hot band: thermal treatment following immediately the last pass of hot rolling or a hot band annealing as a separate processing step before cold rolling.

  14. Room temperature ductility of NiAl-strengthened ferritic steels: Effects of precipitate microstructure

    SciTech Connect

    Teng, Z.K.; Liu, C.T.; Miller, M.K.; Ghosh, G.; Kenik, E.A.; Huang, S.; Liaw, P.K.

    2012-04-11

    The effects of precipitate microstructure on the room temperature ductility of a series of carefully designed Fe-Al-Ni-Cr-Mo steels were investigated. Transmission electron microscopy (TEM), ultra small angle X-ray scattering (USAXS), and atom probe tomography (APT) were conducted to quantify the nano-scaled precipitates. The accuracy of the characterization results was verified by a numerical analysis. Three point bending tests results demonstrated that ductility was a function of the precipitate volume fraction and the Al and Ni concentrations in the Fe matrix, these relationships were discussed in terms of possible mechanisms. The ductility was also found to be independent of the precipitate size and inter-particle spacing in the studied range, which was validated by a theoretical model.

  15. Surface modification and deuterium retention in reduced-activation steels under low-energy deuterium plasma exposure. Part I: undamaged steels

    NASA Astrophysics Data System (ADS)

    Ogorodnikova, O. V.; Zhou, Z.; Sugiyama, K.; Balden, M.; Gasparyan, Yu.; Efimov, V.

    2017-03-01

    In this paper, reduced-activation ferritic/martensitic (RAFM) steels including Eurofer (9Cr) and oxide dispersion strengthening (ODS) steels by the addition of Y2O3 particles with different amounts of Cr, namely, (9-16)Cr were exposed to low energy deuterium (D) plasma (~20-200 eV per D) up to a fluence of 2.9  ×  1025 D m-2 in the temperature range from 290 K to 700 K. The depth profile of D in steels was measured up to 8 µm depth by nuclear reaction analysis (NRA) and the total retained amount of D in those materials was determined by thermal desorption spectroscopy (TDS). It was found that the D retention in ODS steels is higher compared to Eurofer due to the much higher density of fine dispersoids and finer grain size. This work shows that in addition to the sintering temperature and time, the type, size and concentration of the doping particles have an enormous effect on the increase in the D retention. The D retention in undamaged ODS steels strongly depends on the Cr content: ODS with 12Cr has a minimum and the D retention in the case of ODS with (14-16)Cr is higher compared to (9-12)Cr. The replacing of Ti by Al in ODS-14Cr steels reduces the D retention. The formation of nano-structure surface roughness enriched in W or Ta due to combination of preferential sputtering of light elements and radiation-induced segregation was observed at incident D ion energy of 200 eV for both Eurofer and ODS steels. Both the surface roughness and the eroded layer enhance with increasing the temperature. The surface modifications result in a reduction of the D retention near the surface due to increasing the desorption flux and can reduce the overall D retention.

  16. Investigation of the Kinetics of the Ferrite/Austenite Phase Transformation in the HAZ of a 2205 Duplex Stainless Steel Weldment

    SciTech Connect

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

    2002-03-14

    A semi-quantitative map based on a series of spatially resolved X-ray diffraction (SRXRD) scans shows the progression of the ferrite ({delta})/austenite ({gamma}) phase balance throughout the HAZ during GTA welding of a 2205 duplex stainless steel (DSS). This map shows an unexpected decrease in the ferrite fraction on heating, followed by a recovery to the original ferrite fraction on cooling at locations within the HAZ. Even though such behavior is supported by thermodynamic calculations, it has not been confirmed by either experimental methods or have the kinetics been evaluated. Both Gleeble thermal simulations and time resolved x-ray diffraction measurements on spot welds in the 2205 DSS provide further evidence for this rather low-temperature transformation. On the other hand, calculations of the diffusion of alloying elements across the 6/y interface under a variety of conditions shed no further light on the driving force for this transformation. Further work on the mechanisms and driving forces for this transformation is on-going.

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

  20. Ferrite Formation Dynamics and Microstructure Due to Inclusion Engineering in Low-Alloy Steels by Ti2O3 and TiN Addition

    NASA Astrophysics Data System (ADS)

    Mu, Wangzhong; Shibata, Hiroyuki; Hedström, Peter; Jönsson, Pär Göran; Nakajima, Keiji

    2016-08-01

    The dynamics of intragranular ferrite (IGF) formation in inclusion engineered steels with either Ti2O3 or TiN addition were investigated using in situ high temperature confocal laser scanning microscopy. Furthermore, the chemical composition of the inclusions and the final microstructure after continuous cooling transformation was investigated using electron probe microanalysis and electron backscatter diffraction, respectively. It was found that there is a significant effect of the chemical composition of the inclusions, the cooling rate, and the prior austenite grain size on the phase fractions and the starting temperatures of IGF and grain boundary ferrite (GBF). The fraction of IGF is larger in the steel with Ti2O3 addition compared to the steel with TiN addition after the same thermal cycle has been imposed. The reason for this difference is the higher potency of the TiO x phase as nucleation sites for IGF formation compared to the TiN phase, which was supported by calculations using classical nucleation theory. The IGF fraction increases with increasing prior austenite grain size, while the fraction of IGF in both steels was the highest for the intermediate cooling rate of 70 °C/min, since competing phase transformations were avoided, the structure of the IGF was though refined with increasing cooling rate. Finally, regarding the starting temperatures of IGF and GBF, they decrease with increasing cooling rate and the starting temperature of GBF decreases with increasing grain size, while the starting temperature of IGF remains constant irrespective of grain size.

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

    SciTech Connect

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

    2007-11-01

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

  2. Nondestructive and Localized Measurements of Stress-Strain Curves and Fracture Toughness of Ferritic Steels at Various Temperatures Using Innovative Stress-Strain Microprobe Technology. Final Report for Period 8/13/1996--06/16/1999

    SciTech Connect

    Fahmy M. Haggag

    1999-10-29

    The results presented in this report demonstrate the capabilities of Advanced Technology Corporation's patented Portable/In Situ Stress-Strain Microprobe (TM) (SSM) System and its Automated Ball Indentation (ABI) test techniques to nondestructively measure the yield strength, the stress-strain curve, and the fracture toughness of ferritic steel samples and components in a reliable and accurate manner.

  3. Stress relaxation behavior of nanocluster-strengthened ferritic alloy at high temperatures

    SciTech Connect

    Kim, Jeoung H; Byun, Thak Sang; Hoelzer, David T

    2012-01-01

    Stress relaxation behavior was investigated for the nanoclusters/dispersoids-strengthened steels including the nanostructured ferritic alloy 14YWT (SM10), oxide-dispersion strengthened (ODS) Eurofer97, and commercial ODS steel PM2000. The stress relaxation tests were carried out at high temperatures ranging from 600 to 1000 degrees C. Overall, the relaxation rates of 14YWT and ODS-Eurofer97 were lower than that of PM2000. To analyze the strain rate sensitivity of the alloys, the load drop-time curves were converted to the stress-strain rate curves. In the log-log plots of these curves, no significant change in slope was observed in the strain rate range of 2 x 10(-5)-1 x 10(-3)s(-1). At 600 degrees C, 14YWT and ODS-Eurofer97 have similar activation values of similar to 50b(3) while PM2000 has similar to 100b(3). Above 700 degrees C, the differences of the activation energy among alloys become more noticeable with increasing temperature. The activation energies of the three alloys were derived and compared. The rate-controlling mechanisms in the stress relaxation of the three nanoclusters/dispersoids-hardened alloys include dislocation glide and climb, and further study is necessary to clarify detailed contributing mechanisms.

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

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

    SciTech Connect

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

    1995-04-01

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

  6. Study of the synergistic effect of 2-methoxy-4-formylphenol and sodium molybdenum oxide on the corrosion inhibition of 3CR12 ferritic steel in dilute sulphuric acid

    NASA Astrophysics Data System (ADS)

    Loto, Roland Tolulope

    The synergistic effect of the corrosion inhibition properties of 2-methoxy-4-formylphenol and sodium molybdenum oxide on the electrochemical property of 3CR12 ferritic stainless steel in 2M H2SO4 acid solution was assessed through coupon analysis, potentiodynamic polarization technique, IR spectroscopy and micro-analytical technique. Experimental data showed the combined admixture effectively inhibited the steel corrosion at the concentrations analyzed with a maximum inhibition efficiency of 94.47% and 89.71% from coupon analysis and potentiodynamic polarization due to the electrochemical action and inhibition of the steel by the ionized molecules of the inhibiting compound which influenced the mechanism of the redox reactions responsible to corrosion and surface deterioration. Results from corrosion thermodynamic calculations showed chemisorption adsorption mechanism. Infrared spectroscopic images exposed the functional groups of the molecules involved for the corrosion inhibition reaction. Micro-analytical images showed sharp contrast in surface morphology between the inhibited and corroded test specimens under study. Cracks, intergranular and pitting corrosion in addition to severe surface deterioration was observed in the uninhibited samples. Inhibitor adsorption fits the Langmuir isotherm model.

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

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

    NASA Astrophysics Data System (ADS)

    Jia, X.; Dai, Y.

    2003-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2000-12-01

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

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

    SciTech Connect

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

    1999-12-15

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

  11. ODS iron aluminides

    SciTech Connect

    Wright, I.G.; Pint, B.A.; Ohriner, E.K.; Tortorelli, P.F.

    1996-08-01

    The overall goal of this program is to develop an oxide dispersion-strengthened (ODS) version of Fe{sub 3}Al that has sufficient creep strength and resistance to oxidation at temperatures in the range 1000 to 1200{degrees}C to be suitable for application as heat exchanger tubing in advanced power generation cycles. The program has two main thrusts: (a) alloy processing, which involves mechanical alloying and thermomechanical processing to achieve the desired size and distribution of the oxide dispersoid, and (b) optimization of the oxidation behavior to provide increased service life compared to ODS-FeCrAl alloys intended for the same applications. Control of the grain size and shape in the final alloy is very dependent on the homogeneity of the alloy powder, in terms of the size and distribution of the dispersed oxide particles, and on the level of strain and temperature applied in the recrystallization step. Studies of the effects of these variables are being made using mechanically-alloyed powder from two sources: a commercial powder metallurgy alloy vendor and an in-house, controlled environment high-energy mill. The effects of milling parameters on the microstructure and composition of the powder and consolidated alloy are described. Comparison of the oxidation kinetics of ODS-Fe{sub 3}Al alloys with commercial ODS-FeCrAl alloys in air at 1000-1300{degrees}C indicated that the best Fe{sub 3}Al-based alloys oxidized isothermally at the same rate as the ODS-FeCrAl alloys but, under thermal cycling conditions, the oxidation rate of ODS-Fe{sub 3}Al was faster. The main difference was that the ODS-Fe{sub 3}Al experienced significantly more scale spallation above 1000{degrees}C. The differences in oxidation behavior were translated into expected lifetimes which indicated that, for an alloy section thickness of 2.5 mm, the scale spallation of ODS-Fe{sub 3}Al leads to an expected service lifetime similar to that for the INCO alloy MA956 at 1100 to 1300{degrees}C.

  12. A comparative study of the mechanical properties and the behavior of carbon and boron in stainless steel cladding tubes fabricated by PM HIP and traditional technologies

    NASA Astrophysics Data System (ADS)

    Shulga, A. V.

    2013-03-01

    The ring tensile test method was optimized and successfully used to obtain precise data for specimens of the cladding tubes of AISI type 316 austenitic stainless steels and ferritic-martensitic stainless steel. The positive modifications in the tensile properties of the stainless steel cladding tubes fabricated by powder metallurgy and hot isostatic pressing of melt atomized powders (PM HIP) when compared with the cladding tubes produced by traditional technology were found. Presently, PM HIP is also used in the fabrication of oxide dispersion strengthened (ODS) ferritic-martensitic steels. The high degree of homogeneity of the distribution of carbon and boron as well the high dispersivity of the phase-structure elements in the specimens manufactured via PM HIP were determined by direct autoradiography methods. These results correlate well with the increase of the tensile properties of the specimens produced by PM HIP technology.

  13. ODS iron aluminides

    SciTech Connect

    Wright, I.G.; Pint, B.A.; Tortorelli, P.F.; Ohriner, E.K.

    1996-06-01

    Interest in advanced cycles that involve indirectly-fired gas turbines, in which coal- or gas-fired high-temperature heat exchangers are used to heat a working fluid in a closed system, has led to investigation of materials for heat exchangers capable of operation at temperatures of the order of 1200 to 1300{degrees}C. The candidate materials are ceramics and, possibly, oxide dispersion-strengthened (ODS) alloys. An ODS FeCrAl alloy was found to meet the strength requirements for such an application, in which the working fluid at 0.9 MPa was to be heated from 800 to 1100{degrees}C over a tube length of 4 m. The oxidation life of ODS FeCrAl alloys is determined by their ability to form or reform a protective alumina scale, and can be related to the time for the aluminum content of the alloy to be depleted to some minimum level. As a result, the service life is a function of the available aluminum content of the alloys and the minimum aluminum level at which breakaway oxidation occurs, hence there is a limit on the minimum cross section which can be safely employed at temperatures above 1200{degrees}C. Because of their significantly higher aluminum content ({ge}28 atom %/{ge}16 wt. percent compared to {approx}9 atom %15 wt. percent), alloys based on Fe{sub 3}Al afford a potentially larger reservoir of aluminum to sustain oxidation resistance at higher temperatures and, therefore, offer a possible improvement over the currently-available ODS FeCrAl alloys, providing they can be strengthened in a similar manner.

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

    NASA Astrophysics Data System (ADS)

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

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

  15. Low activation ferritic alloys

    DOEpatents

    Gelles, David S.; Ghoniem, Nasr M.; Powell, Roger W.

    1986-01-01

    Low activation ferritic alloys, specifically bainitic and martensitic stainless steels, are described for use in the production of structural components for nuclear fusion reactors. They are designed specifically to achieve low activation characteristics suitable for efficient waste disposal. The alloys essentially exclude molybdenum, nickel, nitrogen and niobium. Strength is achieved by substituting vanadium, tungsten, and/or tantalum in place of the usual molybdenum content in such alloys.

  16. Low activation ferritic alloys

    DOEpatents

    Gelles, D.S.; Ghoniem, N.M.; Powell, R.W.

    1985-02-07

    Low activation ferritic alloys, specifically bainitic and martensitic stainless steels, are described for use in the production of structural components for nuclear fusion reactors. They are designed specifically to achieve low activation characteristics suitable for efficient waste disposal. The alloys essentially exclude molybdenum, nickel, nitrogen and niobium. Strength is achieved by substituting vanadium, tungsten, and/or tantalum in place of the usual molybdenum content in such alloys.

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

    SciTech Connect

    Not Available

    1994-10-01

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

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

    SciTech Connect

    Jawad, Mann; Sikka, Vinod K.

    2005-04-06

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

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

    NASA Astrophysics Data System (ADS)

    Belianov, I.; Marmy, P.

    1998-10-01

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

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

    SciTech Connect

    Lee, EH

    2001-08-01

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

  1. Mn1.4Co1.4Cu0.2O4 spinel protective coating on ferritic stainless steels for solid oxide fuel cell interconnect applications

    NASA Astrophysics Data System (ADS)

    Chen, Guoyi; Xin, Xianshuang; Luo, Ting; Liu, Leimin; Zhou, Yuchun; Yuan, Chun; Lin, Chucheng; Zhan, Zhongliang; Wang, Shaorong

    2015-03-01

    In an attempt to reduce the oxidation and Cr evaporation rates of solid oxide fuel cells (SOFCs), Mn1.4Co1.4Cu0.2O4 spinel coating is developed on the Crofer22 APU ferritic stainless steel substrate by a powder reduction technique. Doping of Cu into Mn-Co spinels improves electrical conductivity as well as thermal expansion match with the Crofer22 APU interconnect. Good adhesion between the coating and the alloy substrate is achieved by the reactive sintering process using the reduced powders. Long-term isothermal oxidation experiment and area specific resistance (ASR) measurement are investigated. The ASR is less than 4 mΩ cm2 even though the coated alloy undergoes oxidation at 800 °C for 530 h and four thermal cycles from 800 °C to room temperature. The Mn1.4Co1.4Cu0.2O4 spinel coatings demonstrate excellent anti-oxidation performance and long-term stability. It exhibits a promising prospect for the practical application of SOFC alloy interconnect.

  2. Development of Cu1.3Mn1.7O4 spinel coating on ferritic stainless steel for solid oxide fuel cell interconnects

    NASA Astrophysics Data System (ADS)

    Hosseini, N.; Abbasi, M. H.; Karimzadeh, F.; Choi, G. M.

    2015-01-01

    To protect solid oxide fuel cells (SOFCs) from chromium poisoning and to improve area specific resistance (ASR), Cu1.3Mn1.7O4 is thermally grown on AISI 430 ferritic stainless steel. The samples are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy equipped with energy dispersive spectroscopy (FESEM-EDS) and 4-probe ASR tests. The results show that the coating not only decreases the ASR considerably, but also acts as a barrier to mitigate the sub-scale growth and to prevent chromium migration through the coating and the cathode. The EDS analysis reveals that a mixed spinel region is formed between the coating and oxide scale after 500 h oxidation at 750 °C causing a noticeable decrease in oxygen diffusivity through this layer and subsequent decline in sub-scale growth rate. The ASR of uncoated sample is measured to be 63.5 mΩ cm2 after 500 h oxidation, while the Cu1.3Mn1.7O4 spinel coated sample shows a value of 19.3 mΩ cm2 representing ∼70% reduction compared to the uncoated sample. It is proposed that the high electrical conductivity of Cu1.3Mn1.7O4 (140 S cm-1), reduction of oxide scale growth, and good bonding between the coating and substrate contribute to the substantial ASR reduction for the coated sample.

  3. Simultaneous Investigation of the Effect of Advanced Thermomechanical Treatment and Repetitive Cyclic Voltammetry on the Electrochemical Behavior of AISI 430 Ferritic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Vafaeian, Saeed; Fattah-alhosseini, Arash; Keshavarz, Mohsen K.; Mazaheri, Yousef

    2017-02-01

    In this study, it was revealed that the electrochemical behavior of AISI 430 ferritic stainless steel can be modified and improved to a large extent by the application of repetitive cyclic voltammetry in the anodic polarization branch of the alloy. The efficiency of this method was evaluated on the basis of the alloy grain size which is of great importance in corrosion studies. In fact, a coarse grain structure versus a fine grain structure was the subject of the used surface treatment method. Coarsening and refining of the grain size were conducted through a heat treatment and an advanced thermomechanical process. On the basis of cyclic voltammetry tests and also the electrochemical tests performed after that, it was shown that cyclic voltammetry had a significant improving effect on the passive behavior of both fine- and coarse-grained samples. Moreover, superior behavior of fine-grained sample in comparison with coarse-grained one was distinguished by its smaller cyclic voltammogram loops, more noble free potentials, larger capacitive arcs in the Nyquist plots, and less charge carrier densities within the passive film.

  4. Influence of M-TIG and A-TIG Welding Process on Microstructure and Mechanical Behavior of 409 Ferritic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Vidyarthy, R. S.; Dwivedi, D. K.; Vasudevan, M.

    2017-02-01

    The current study investigates the effects of activating flux tungsten inert gas welding (A-TIG) and multipass tungsten inert gas welding (M-TIG) on the weld morphology, angular distortion, microstructures and mechanical properties when welding 8-mm-thick 409 ferritic stainless steel (FSS). SiO2 was used as activating flux for A-TIG welding, while SUPERTIG ER309L was used as filler for M-TIG welding. Bead-on-plate weld trials were carried out to obtain the full penetration by using different combinations of flux coating density, welding speed and welding current. An optical microscope, field emission scanning microscope (FESEM), and x-ray diffractometer were used for the metallurgical characterizations. Vickers hardness, tensile test, Charpy toughness test, and creep behavior test were carried out to evaluate the mechanical properties of the base and weld metals. Experimental results indicate that the A-TIG process can increase the joint penetration and tends to reduce the angular distortion of the 409 FSS weldment. The A-TIG welded joint also exhibited greater mechanical strength. However, a critically low Charpy toughness was measured for the A-TIG weld fusion zone, which was later sufficiently improved after post weld heat treatment (PWHT). It was concluded that PWHT is mandatory for A-TIG welded 409 FSS.

  5. A Qualitative Comparison of the C-Ring Test and the Jones Test as Standard Practice Test Methods for Studying Stress Corrosion Cracking in Ferritic Steels

    SciTech Connect

    Thomson, Jeffery K; Pawel, Steven J

    2015-01-01

    Creep-strength-enhanced-ferritic (CSEF) steels have been widely implemented as water wall alloy materials in the coal-fired power industry for many years. The stress corrosion cracking (SCC) behavior of this class of materials is currently of significant interest to the industry due to recent failures. To better understand the test methods used to characterize SCC behavior in the laboratory, three representative CSEF alloys (T23, T24, and T92) were subjected to two SCC test protocols: the Jones Test set forth in DIN 50915, and the C-ring SCC test set forth in ASTM G38-01. Samples were tested in either the as-received (normalized + tempered) condition or in the normalized condition (quenched from 1065 C). Samples were exposed to aerated water in one test case and de-aerated water in a second test case for a period of 7 days at 200 C. It was found that for both test protocols, the normalized condition with aerated water led to severe cracking for all three alloys, whereas no evidence of cracking was found for the other conditions.

  6. Simultaneous Investigation of the Effect of Advanced Thermomechanical Treatment and Repetitive Cyclic Voltammetry on the Electrochemical Behavior of AISI 430 Ferritic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Vafaeian, Saeed; Fattah-alhosseini, Arash; Keshavarz, Mohsen K.; Mazaheri, Yousef

    2017-01-01

    In this study, it was revealed that the electrochemical behavior of AISI 430 ferritic stainless steel can be modified and improved to a large extent by the application of repetitive cyclic voltammetry in the anodic polarization branch of the alloy. The efficiency of this method was evaluated on the basis of the alloy grain size which is of great importance in corrosion studies. In fact, a coarse grain structure versus a fine grain structure was the subject of the used surface treatment method. Coarsening and refining of the grain size were conducted through a heat treatment and an advanced thermomechanical process. On the basis of cyclic voltammetry tests and also the electrochemical tests performed after that, it was shown that cyclic voltammetry had a significant improving effect on the passive behavior of both fine- and coarse-grained samples. Moreover, superior behavior of fine-grained sample in comparison with coarse-grained one was distinguished by its smaller cyclic voltammogram loops, more noble free potentials, larger capacitive arcs in the Nyquist plots, and less charge carrier densities within the passive film.

  7. Influence of M-TIG and A-TIG Welding Process on Microstructure and Mechanical Behavior of 409 Ferritic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Vidyarthy, R. S.; Dwivedi, D. K.; Vasudevan, M.

    2017-03-01

    The current study investigates the effects of activating flux tungsten inert gas welding (A-TIG) and multipass tungsten inert gas welding (M-TIG) on the weld morphology, angular distortion, microstructures and mechanical properties when welding 8-mm-thick 409 ferritic stainless steel (FSS). SiO2 was used as activating flux for A-TIG welding, while SUPERTIG ER309L was used as filler for M-TIG welding. Bead-on-plate weld trials were carried out to obtain the full penetration by using different combinations of flux coating density, welding speed and welding current. An optical microscope, field emission scanning microscope (FESEM), and x-ray diffractometer were used for the metallurgical characterizations. Vickers hardness, tensile test, Charpy toughness test, and creep behavior test were carried out to evaluate the mechanical properties of the base and weld metals. Experimental results indicate that the A-TIG process can increase the joint penetration and tends to reduce the angular distortion of the 409 FSS weldment. The A-TIG welded joint also exhibited greater mechanical strength. However, a critically low Charpy toughness was measured for the A-TIG weld fusion zone, which was later sufficiently improved after post weld heat treatment (PWHT). It was concluded that PWHT is mandatory for A-TIG welded 409 FSS.

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

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

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

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

    SciTech Connect

    Jawad, M.

    2005-03-31

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

  10. Synthesis of atom probe experiments on irradiation-induced solute segregation in French ferritic pressure vessel steels

    NASA Astrophysics Data System (ADS)

    Auger, P.; Pareige, P.; Welzel, S.; Van Duysen, J.-C.

    2000-08-01

    Microstructural changes due to neutron irradiation cause an evolution of the mechanical properties of reactor pressure vessels (RPV) steels. This paper aims at identifying and characterising the microstructural changes which have been found to be responsible in part for the observed embrittlement. This intensive work relies principally on an atom probe (AP) study of a low Cu-level French RPV steel (Chooz A). This material has been irradiated in in-service conditions for 0-16 years in the frame of the surveillance program. Under this aging condition, solute clustering occurs (Cu, Ni, Mn, Si, P, …). In order to identify the role of copper, experiments were also carried out on Fe-Cu model alloys submitted to different types of irradiations (neutron, electron, ion). Cu-cluster nucleation appears to be directly related to the presence of displacement cascades during neutron (ion) irradiation. The operating basic physical process is not clearly identified yet. A recovery of the mechanical properties of the irradiated material can be achieved by annealing treatments (20 h at 450°C in the case of the RPV steel under study, following microhardness measurements). It has been shown that the corresponding microstructural evolution was a rapid dissolution of the high number density of irradiation-induced solute clusters and the precipitation of a very low number density of Cu-rich particles.

  11. ODS iron aluminides

    SciTech Connect

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

    1995-06-01

    There has been a recent increase of interest in advanced cycles that involve indirectly-fired gas turbines, in which coal- or gas-fired high-temperature heat exchangers are used to heat a working fluid in a closed system. In a program conducted as part of the European COST-501 Concerted Action Project, available alloys based on FeCrAl-Y{sub 2}O{sub 3} were evaluated for use in the main heat exchanger in a similar closed-cycle gas turbine application. One of the currently available ODS FeCrAl alloys was found to meet the strength requirements for this application, in which the working fluid at 0.9 MPa (131 psi) flowing at 5,889 kg/hr (12,955 lb/hr) was to be heated from 800 to 1100{degrees}C (1472 to 2012{degrees}F) over a tube length of 4 m (13 ft).

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  13. Effect of precipitated austenite on the fracture of a ferritic cryogenic steel. [Fe-8Ni-2Mn-0. 1Ti

    SciTech Connect

    Frear, D.R.

    1984-05-01

    The effect of precipitated austenite on the fracture of an Fe-8Ni-2Mn-0.1Ti steel was investigated. To understand the effect an attempt was made to correlate the microstructure, mechanical properties, and the fracture surface appearance of specimens heat treated to contain austenite or be austenite-free. The fracture surfaces were quantitatively studied using a 3D imaging technique in the SEM. It was found that the presence of austenite had a beneficial influence on mechanical properties by lowering the DBTT. Part of this decrease was found to be due to the austenite gettering deleterious elements off the grain boundaries. Specimens that contained precipitated austenite were also found to have a smaller median facet size, when fractured in a brittle transgranular mode, than specimens with no austenite. The decrease in DBTT and change in fracture surface appearance is related to the austenite transforming to martensite of a different variant than the matrix which effectively grain refines the steel and raises the cleavage stress.

  14. In vitro osteoblast response to ferritic stainless steel fiber networks for magneto-active layers on implants.

    PubMed

    Malheiro, V N; Skepper, J N; Brooks, R A; Markaki, A E

    2013-06-01

    The use of a porous coating on prosthetic components to encourage bone ingrowth is an important way of improving uncemented implant fixation. Enhanced fixation may be achieved by the use of porous magneto-active layers on the surface of prosthetic implants, which would deform elastically on application of a magnetic field, generating internal stresses within the in-growing bone. This approach requires a ferromagnetic material able to support osteoblast attachment, proliferation, differentiation, and mineralization. In this study, the human osteoblast responses to ferromagnetic 444 stainless steel networks were considered alongside those to nonmagnetic 316L (medical grade) stainless steel networks. While both networks had similar porosities, 444 networks were made from coarser fibers, resulting in larger inter-fiber spaces. The networks were analyzed for cell morphology, distribution, proliferation, and differentiation, extracellular matrix production and the formation of mineralized nodules. Cell culture was performed in both the presence of osteogenic supplements, to encourage cell differentiation, and in their absence. It was found that fiber size affected osteoblast morphology, cytoskeleton organization and proliferation at the early stages of culture. The larger inter-fiber spaces in the 444 networks resulted in better spatial distribution of the extracellular matrix. The addition of osteogenic supplements enhanced cell differentiation and reduced cell proliferation thereby preventing the differences in proliferation observed in the absence of osteogenic supplements. The results demonstrated that 444 networks elicited favorable responses from human osteoblasts, and thus show potential for use as magnetically active porous coatings for advanced bone implant applications.

  15. Co- and Ce/Co-coated ferritic stainless steel as interconnect material for Intermediate Temperature Solid Oxide Fuel Cells

    NASA Astrophysics Data System (ADS)

    Falk-Windisch, Hannes; Claquesin, Julien; Sattari, Mohammad; Svensson, Jan-Erik; Froitzheim, Jan

    2017-03-01

    Chromium species volatilization, oxide scale growth, and electrical scale resistance were studied at 650 and 750 °C for thin metallic Co- and Ce/Co-coated steels intended to be utilized as the interconnect material in Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC). Mass gain was recorded to follow oxidation kinetics, chromium evaporation was measured using the denuder technique and Area Specific Resistance (ASR) measurements were carried out on 500 h pre-exposed samples. The microstructure of thermally grown oxide scales was characterized using Scanning Electron Microscopy (SEM), Scanning Transmission Electron Microscopy (STEM), and Energy Dispersive X-Ray Analysis (EDX). The findings of this study show that a decrease in temperature not only leads to thinner oxide scales and less Cr vaporization but also to a significant change in the chemical composition of the oxide scale. Very low ASR values (below 10 mΩ cm2) were measured for both Co- and Ce/Co-coated steel at 650 and 750 °C, indicating that the observed change in the chemical composition of the Co spinel does not have any noticeable influence on the ASR. Instead it is suggested that the Cr2O3 scale is expected to be the main contributor to the ASR, even at temperatures as low as 650 °C.

  16. Room Temperature Ductility of NiAl-strengthened Ferritic Steels: Effects of Precipitate Microstructure and Hot Rolling

    SciTech Connect

    Teng, Zhenke; Liu, Chain T; Miller, Michael K; Ghosh, Gautam; Kenik, Edward A; Huang, Shenyan; Liaw, Peter K

    2012-01-01

    The effects of precipitate microstructure on the room temperature ductility of a series of carefully designed Fe-Al-Ni-Cr-Mo steels were investigated. Transmission electron microscopy (TEM), ultra small angle X-ray scattering (USAXS), and atom probe tomography (APT) were conducted to quantify the nano-scaled precipitates. The accuracy of the characterization results was verified by a numerical analysis. Three point bending tests results demonstrated that ductility was a function of the precipitate volume fraction and the Al and Ni concentrations in the Fe matrix, these relationships were discussed in terms of possible mechanisms. The ductility was also found to be independent of the precipitate size and inter-particle spacing in the studied range, which was validated by a theoretical model.

  17. Evaluation of Pb-17Li compatibility of ODS Fe-12Cr-5Al alloys

    NASA Astrophysics Data System (ADS)

    Unocic, Kinga A.; Hoelzer, David T.

    2016-10-01

    The Dual Coolant Lead Lithium (DCLL: eutectic Pb-17Li and He) blanket concept requires improved Pb-17Li compatibility with ferritic steels in order to demonstrate acceptable performance in fusion reactors. As an initial step, static Pb-17at.%Li (Pb-17Li) capsule experiments were conducted on new oxide dispersion strengthened (ODS) FeCrAl alloys ((1) Y2O3 (125Y), (2) Y2O3 + ZrO2 (125YZ), (3) Y2O3 + HfO2 (125YH), and (4) Y2O3 + TiO2 (125YT)) produced at ORNL via mechanical alloying (MA). Tests were conducted in static Pb-17Li for 1000 h at 700 °C. Alloys showed promising compatibility with Pb-17Li with small mass change after testing for 125YZ, 125YH and 125YT, while the 125Y alloy experienced the highest mass loss associated with some oxide spallation and subsequent alloy dissolution. X-ray diffraction methods identified the surface reaction product as LiAlO2 on all four alloys. A small decrease (∼1 at.%) in Al content beneath the oxide scale was observed in all four ODS alloys, which extended 60 μm beneath the oxide/metal interface. This indicates improvements in alloy dissolution by decreasing the amount of Al loss from the alloy. Scales formed on 125YZ, 125YH and 125YT were examined via scanning transmission electron microscopy (S/TEM) and revealed incorporation of Zr-, Hf-, and Ti-rich precipitates within the LiAlO2 product, respectively. This indicates an inward scale growth mechanism. Future work in flowing Pb-17Li is needed to further evaluate the effectiveness of this strategy in a test blanket module.

  18. Evaluation of Pb-17Li compatibility of ODS Fe-12Cr-5Al alloys

    DOE PAGES

    Unocic, Kinga A.; Hoelzer, David T.

    2016-07-09

    The Dual Coolant Lead Lithium (DCLL: eutectic Pb–17Li and He) blanket concept requires improved Pb–17Li compatibility with ferritic steels in order to demonstrate acceptable performance in fusion reactors. As an initial step, static Pb-17at.%Li (Pb-17Li) capsule experiments were conducted on new oxide dispersion strengthened (ODS) FeCrAl alloys ((1) Y2O3 (125Y), (2) Y2O3+ZrO2 (125YZ), (3) Y2O3+HfO2 (125YH), and (4) Y2O3+TiO2 (125YT)) produced at ORNL via mechanical alloying (MA). Tests were conducted in static Pb–17Li for 1000 h at 700°C. Alloys showed promising compatibility with Pb–17Li with small mass change after testing for 125YZ, 125YH and 125YT, while the 125Y alloy experiencedmore » the highest mass loss associated with some oxide spallation and subsequent alloy dissolution. X-ray diffraction methods identified the surface reaction product as LiAlO2 on all four alloys. A small decrease (~1 at.%) in Al content beneath the oxide scale was observed in all 4 ODS alloys, which extended through 60 μm beneath the oxide/metal interface. This indicates improvements in alloy dissolution by decreasing the amount of Al loss from the alloy. Scales formed on 125YZ, 125YH and 125YT were examined via scanning transmission electron microscopy (S/TEM) and revealed incorporation of Zr-, Hf-, and Ti-rich precipitates within the LiAlO2 product, respectively. This indicates an inward scale growth mechanism. Future work in flowing Pb–17Li is needed to further evaluate the effectiveness of this strategy in a test blanket module.« less

  19. Evaluation of Pb-17Li compatibility of ODS Fe-12Cr-5Al alloys

    SciTech Connect

    Unocic, Kinga A.; Hoelzer, David T.

    2016-07-09

    The Dual Coolant Lead Lithium (DCLL: eutectic Pb–17Li and He) blanket concept requires improved Pb–17Li compatibility with ferritic steels in order to demonstrate acceptable performance in fusion reactors. As an initial step, static Pb-17at.%Li (Pb-17Li) capsule experiments were conducted on new oxide dispersion strengthened (ODS) FeCrAl alloys ((1) Y2O3 (125Y), (2) Y2O3+ZrO2 (125YZ), (3) Y2O3+HfO2 (125YH), and (4) Y2O3+TiO2 (125YT)) produced at ORNL via mechanical alloying (MA). Tests were conducted in static Pb–17Li for 1000 h at 700°C. Alloys showed promising compatibility with Pb–17Li with small mass change after testing for 125YZ, 125YH and 125YT, while the 125Y alloy experienced the highest mass loss associated with some oxide spallation and subsequent alloy dissolution. X-ray diffraction methods identified the surface reaction product as LiAlO2 on all four alloys. A small decrease (~1 at.%) in Al content beneath the oxide scale was observed in all 4 ODS alloys, which extended through 60 μm beneath the oxide/metal interface. This indicates improvements in alloy dissolution by decreasing the amount of Al loss from the alloy. Scales formed on 125YZ, 125YH and 125YT were examined via scanning transmission electron microscopy (S/TEM) and revealed incorporation of Zr-, Hf-, and Ti-rich precipitates within the LiAlO2 product, respectively. This indicates an inward scale growth mechanism. Future work in flowing Pb–17Li is needed to further evaluate the effectiveness of this strategy in a test blanket module.

  20. Study of the deformation mechanisms in a Fe-14% Cr ODS alloy

    NASA Astrophysics Data System (ADS)

    Praud, M.; Mompiou, F.; Malaplate, J.; Caillard, D.; Garnier, J.; Steckmeyer, A.; Fournier, B.

    2012-09-01

    In this present work, the plasticity of a rod bar of a 14% Cr ferritic ODS steel is examined through a multiscale approach based on both macroscopic and microscopic results. This bar was elaborated at CEA by powder metallurgy and consolidated by hot extrusion. The microstructure of the material has been characterized. First, the tensile behavior of this material is studied in a wide range of temperatures. Thereafter, through in situ Transmission Electron Microscopy (TEM) straining experiments, dislocation/dislocation and dislocation/precipitates interactions are observed. The collapse of the tensile properties noticed from 400 °C can be explained by a change in the deformation mechanism. At lower temperatures, the hardening seems to be due to the precipitates, dislocations are pinned on oxides. At higher temperatures, the hardening role of the precipitates is still observed, but the dislocations seem to move in a more steady way, thermal activation of dislocations sources is observed and leads to formation of cavities at the grain boundaries.

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

    SciTech Connect

    Nagy, Peter

    2013-09-30

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

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

    NASA Astrophysics Data System (ADS)

    Saeidi, Sheida

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

  3. Evaluation of Oxide Dispersion Strengthened (ODS) Molybdenum Alloys

    DTIC Science & Technology

    1997-01-01

    containing 4 parts concentrated sulfuric acid and 1 part distilled water using a Type 304 stainless steel cathode and a direct current accelerating...Ductile-to-Brittle Transition Temperature ( DBTT ): The following mechanical properties were measured from the ODS molybdenum alloy rods: (a) 0.2...and to determine the DBTT . Elevated Temperature Tensile Tests: Elevated temperature tensile specimens of each as- swaged alloy were equilibrated

  4. Latent tracks of swift heavy ions in Сr23C6 and Y-Ti-O nanoparticles in ODS alloys

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    The radiation stability of dielectric nanoparticles embedded into a metallic matrix is of considerable practical value due to the growing interest in oxide dispersion strengthened (ODS) steels as promising nuclear reactor materials. In this report the results of a TEM study of structural changes in Cr23C6 and Y-Ti-O nanoparticles in several ODS alloys irradiated with 1.2 MeV/amu Xe and 3.4 MeV/amu Bi ions is presented. It was found that swift heavy ion irradiation leads to the formation of amorphous latent tracks in both materials. The upper limit of the threshold electronic stopping power for track formation in carbides is estimated to be around 35 keV/nm. Multiple ion track overlapping leads to complete amorphization of carbide and Y-Ti oxide nanoparticles. Microstructural analysis have revealed a strong influence of the ferritic matrix on track morphology in Y2Ti2O7 nanoparticles in pre-thinned TEM targets after postradiation annealing and irradiation at elevated temperatures.

  5. Influence of Heat Input on the Content of Delta Ferrite in the Structure of 304L Stainless Steel GTA Welded Joints

    NASA Astrophysics Data System (ADS)

    Sejč, Pavol; Kubíček, Rastislav

    2011-12-01

    Welding of austenitic stainless steel has its specific issues, even when the weldability is considered good. The main problems of austenitic stainless steel welding are connected with its metallurgical weldability. The amount of the components presented in the structure of stainless steel welded joint affect its properties, therefore the understanding of the behavior of stainless steel during its welding is important for successful processing and allows the fabricators the possibility to manage the resulting issues. This paper is focused on the influence of heat input on the structural changes in GTA welded joints of austenitic stainless steel designated: ASTM SA TP 304L.

  6. Enhanced Radiation-tolerant Oxide Dispersion Strengthened Steel and its Microstructure Evolution under Helium-implantation and Heavy-ion Irradiation

    PubMed Central

    Lu, Chenyang; Lu, Zheng; Wang, Xu; Xie, Rui; Li, Zhengyuan; Higgins, Michael; Liu, Chunming; Gao, Fei; Wang, Lumin

    2017-01-01

    The world eagerly needs cleanly-generated electricity in the future. Fusion reactor is one of the most ideal energy resources to defeat the environmental degradation caused by the consumption of traditional fossil energy. To meet the design requirements of fusion reactor, the development of the structural materials which can sustain the elevated temperature, high helium concentration and extreme radiation environments is the biggest challenge for the entire material society. Oxide dispersion strengthened steel is one of the most popular candidate materials for the first wall/blanket applications in fusion reactor. In this paper, we evaluate the radiation tolerance of a 9Cr ODS steel developed in China. Compared with Ferritic/Martensitic steel, this ODS steel demonstrated a significantly higher swelling resistance under ion irradiation at 460 °C to 188 displacements per atom. The role of oxides and grain boundaries on void swelling has been explored. The results indicated that the distribution of higher density and finer size of nano oxides will lead a better swelling resistance for ODS alloy. The original pyrochlore-structured Y2Ti2O7 particles dissolved gradually while fine Y-Ti-O nano clusters reprecipitated in the matrix during irradiation. The enhanced radiation tolerance is attributed to the reduced oxide size and the increased oxide density. PMID:28079191

  7. Enhanced Radiation-tolerant Oxide Dispersion Strengthened Steel and its Microstructure Evolution under Helium-implantation and Heavy-ion Irradiation

    NASA Astrophysics Data System (ADS)

    Lu, Chenyang; Lu, Zheng; Wang, Xu; Xie, Rui; Li, Zhengyuan; Higgins, Michael; Liu, Chunming; Gao, Fei; Wang, Lumin

    2017-01-01

    The world eagerly needs cleanly-generated electricity in the future. Fusion reactor is one of the most ideal energy resources to defeat the environmental degradation caused by the consumption of traditional fossil energy. To meet the design requirements of fusion reactor, the development of the structural materials which can sustain the elevated temperature, high helium concentration and extreme radiation environments is the biggest challenge for the entire material society. Oxide dispersion strengthened steel is one of the most popular candidate materials for the first wall/blanket applications in fusion reactor. In this paper, we evaluate the radiation tolerance of a 9Cr ODS steel developed in China. Compared with Ferritic/Martensitic steel, this ODS steel demonstrated a significantly higher swelling resistance under ion irradiation at 460 °C to 188 displacements per atom. The role of oxides and grain boundaries on void swelling has been explored. The results indicated that the distribution of higher density and finer size of nano oxides will lead a better swelling resistance for ODS alloy. The original pyrochlore-structured Y2Ti2O7 particles dissolved gradually while fine Y-Ti-O nano clusters reprecipitated in the matrix during irradiation. The enhanced radiation tolerance is attributed to the reduced oxide size and the increased oxide density.

  8. Enhanced Radiation-tolerant Oxide Dispersion Strengthened Steel and its Microstructure Evolution under Helium-implantation and Heavy-ion Irradiation.

    PubMed

    Lu, Chenyang; Lu, Zheng; Wang, Xu; Xie, Rui; Li, Zhengyuan; Higgins, Michael; Liu, Chunming; Gao, Fei; Wang, Lumin

    2017-01-12

    The world eagerly needs cleanly-generated electricity in the future. Fusion reactor is one of the most ideal energy resources to defeat the environmental degradation caused by the consumption of traditional fossil energy. To meet the design requirements of fusion reactor, the development of the structural materials which can sustain the elevated temperature, high helium concentration and extreme radiation environments is the biggest challenge for the entire material society. Oxide dispersion strengthened steel is one of the most popular candidate materials for the first wall/blanket applications in fusion reactor. In this paper, we evaluate the radiation tolerance of a 9Cr ODS steel developed in China. Compared with Ferritic/Martensitic steel, this ODS steel demonstrated a significantly higher swelling resistance under ion irradiation at 460 °C to 188 displacements per atom. The role of oxides and grain boundaries on void swelling has been explored. The results indicated that the distribution of higher density and finer size of nano oxides will lead a better swelling resistance for ODS alloy. The original pyrochlore-structured Y2Ti2O7 particles dissolved gradually while fine Y-Ti-O nano clusters reprecipitated in the matrix during irradiation. The enhanced radiation tolerance is attributed to the reduced oxide size and the increased oxide density.

  9. Small fatigue crack propagation in Y2O3 strengthened steels

    NASA Astrophysics Data System (ADS)

    Hutař, P.; Kuběna, I.; Ševčík, M.; Šmíd, M.; Kruml, T.; Náhlík, L.

    2014-09-01

    This paper is focused on two type of Y2O3 strengthened steels (Fe-14Cr ODS and ODS-EUROFER). Small fatigue crack propagation was experimentally measured using special small cylindrical specimens (diameter 2 and 2.6 mm) with shallow notch grinded in the gauge length. In the middle of this notch, a pre-crack of length of 50 μm was fabricated using a focused ion beam technique. Fatigue crack growth rate was measured for different applied total strain amplitudes and described using plastic part of the J-integral. Obtained results were compared with published data of EUROFER 97. The effect of the oxide dispersion on small fatigue crack propagation was found rather insignificant. Ferritic Fe-14Cr ODS steel shows more brittle behaviour, i.e. for the same cyclic plasticity, characterised by the plastic part of the J-integral, the small cracks grow faster. A new methodology for residual lifetime prediction of structures containing physically small cracks, based on plastic part of the J-integral, is presented.

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

    NASA Astrophysics Data System (ADS)

    Choudhary, B. K.; Christopher, J.

    2016-06-01

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

  11. Characterization of physico-mechanical properties of Z-phase strengthened ferritic steels using internal friction measurements in the range 25 ÷ 750°C

    NASA Astrophysics Data System (ADS)

    Kutelia, E. R.; Dzigrashvili, T. A.; Kukava, T. G.; Darsavelidze, G. Sh.; Kurashvili, I. R.; Riedel, H.; Donth, B.

    2017-02-01

    The present research is dealing with the comparative study of inelastic/elastic behavior of reference ˜12%Cr steel ZL3 and three new trial steels ZU1, ZU2, ZU3, with different ratio of alloying elements and equal content of Cr, using internal friction measurements. The samples were examined in "as-received" condition and after additional electric current tempering at 700˚C under different fixed external mechanical tensions. The values of deformation critical amplitudes for dislocation breakaway (ɛ1) and for microplastic deformation beginning (ɛ2) were determined in addition to the activation energies of relaxation processes in the investigated steels. It is shown that all the three trial steel samples in "as-received" condition exhibit considerably higher values of ɛ2 in comparison to those of reference ZL3 steel. Among them the ZU3 steel has the highest values of ɛ1 and ɛ2, and demonstrates the visible (˜40%) increase in strength characteristics at elevated temperatures (600÷750˚C), achieved by the additional electric current tempering under mechanical tension.

  12. Development of Austenitic ODS Strengthened Alloys for Very High Temperature Applications

    SciTech Connect

    Stubbins, James; Heuser, Brent; Robertson, Ian; Sehitoglu, Huseyin; Sofronis, Petros; Gewirth, Andrew

    2015-04-22

    This “Blue Sky” project was directed at exploring the opportunities that would be gained by developing Oxide Dispersion Strengthened (ODS) alloys based on the Fe-Cr-Ni austenitic alloy system. A great deal of research effort has been directed toward ferritic and ferritic/martensitic ODS alloys which has resulted in reasonable advances in alloy properties. Similar gains should be possible with austenitic alloy which would also take advantage of other superior properties of that alloy system. The research effort was aimed at the developing an in-depth understanding of the microstructural-level strengthening effects of ODS particles in austentic alloys. This was accomplished on a variety of alloy compositions with the main focus on 304SS and 316SS compositions. A further goal was to develop an understanding other the role of ODS particles on crack propagation and creep performance. Since these later two properties require bulk alloy material which was not available, this work was carried out on promising austentic alloy systems which could later be enhanced with ODS strengthening. The research relied on a large variety of micro-analytical techniques, many of which were available through various scientific user facilities. Access to these facilities throughout the course of this work was instrumental in gathering complimentary data from various analysis techniques to form a well-rounded picture of the processes which control austenitic ODS alloy performance. Micromechanical testing of the austenitic ODS alloys confirmed their highly superior mechanical properties at elevated temperature from the enhanced strengthening effects. The study analyzed the microstructural mechanisms that provide this enhanced high temperature performance. The findings confirm that the smallest size ODS particles provide the most potent strengthening component. Larger particles and other thermally- driven precipitate structures were less effective contributors and, in some cases, limited

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

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

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

  14. The oxidation and corrosion of ODS alloys

    NASA Technical Reports Server (NTRS)

    Lowell, Carl E.; Barrett, Charles A.

    1990-01-01

    The oxidation and hot corrosion of high temperature oxide dispersion strengthened (ODS) alloys are reviewed. The environmental resistance of such alloys are classified by oxide growth rate, oxide volatility, oxide spalling, and hot corrosion limitations. Also discussed are environmentally resistant coatings for ODS materials. It is concluded that ODS NiCrAl and FeCrAl alloys are highly oxidation and corrosion resistant and can probably be used uncoated.

  15. Monte Carlo simulation of spinodal decomposition in a ternary alloy within a three-phases field: comparison to phase transformation of ferrite in duplex stainless steels

    NASA Astrophysics Data System (ADS)

    Emo, Jonathan; Pareige, Cristelle; Saillet, Sébastien; Domain, Christophe; Pareige, Philippe

    2014-06-01

    This work proposes to model phase transformations occurring in duplex stainless steels using atomistic kinetic Monte Carlo in a ternary model alloy. Kinetics are simulated in the three-phase field of a ternary system. Influence of the precipitation of the third phase on the kinetic of spinodal decomposition between the two other phases is studied in order to understand the synergy between spinodal decomposition and G-phase precipitation which exists in duplex stainless steels. Simulation results are compared to experimental data obtained with atom probe tomography.

  16. Quantifying the composition of yttrium and oxygen rich nanoparticles in oxide dispersion strengthened steels.

    PubMed

    Williams, C A; Smith, G D W; Marquis, E A

    2013-02-01

    Atom probe tomography (APT) is used to investigate the composition of oxygen rich nanoparticles within a ferritic matrix in Fe-14Cr-2W-0.1Ti oxide-dispersion-strengthened (ODS) steel. This study investigates whether artifacts associated with APT analysis are the cause of a sub-stoichiometric oxide composition measurement. Bulk Y₂O₃ is analyzed by APT, thus demonstrating the ability of the technique to measure near-stoichiometric composition measurements in insulating oxides. Through analysis of the sequence of ion hits on the detector during APT data acquisition, it is shown that a proportion of yttrium hits are spatially correlated but oxygen hits are not. Y-O based nanoparticles in a ferritic matrix are analyzed by APT using voltage pulsing and a laser pulsing with a range of laser energies from 0.3-0.8 nJ. When the material is analyzed using a high effective evaporation field, this influences the effect of trajectory aberrations, and the apparent size of the nanoparticles is reduced. Some reduction in Y:O ratio is observed, caused by high instances of multiple-ion evaporation events. From a detailed comparison between the results of APT analysis of the bulk Y₂O₃ the nanoparticles in the ODS material are concluded to have an approximate Y:O ratio of 1:1.

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

    SciTech Connect

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

    1997-01-01

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

  18. Influence of Gaseous Media Flow in the Dual Ar-H2-H2O/air Atmosphere Setup on the Scale Growth Kinetics of Crofer 22APU Ferritic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Stygar, Mirosław; Dąbrowa, Juliusz; Dziembaj, Piotr; Brylewski, Tomasz

    2017-02-01

    The problem of gaseous media distribution within the metallic interconnects in solid oxide fuel cells (SOFCs) and its influence on the oxidation resistance of the applied materials is currently of great interest. In the presented work, an influence of gas flow within the dual Ar-H2-H2O/air atmosphere experimental setup on the oxidation behavior of the Crofer 22APU ferritic stainless steel was investigated. Examination of the sample oxidized for 1000 h in temperature of 800 °C revealed the presence of coaxial regions on the scale surface, with the differences in scale's thicknesses in those regions being clearly visible. Additionally, the morphology of the surface changed significantly in a function of the radial distance from the sample's center. To further examine the phenomena of uneven gas distribution, a model of the dual-atmosphere setup was created, using Ansys Workbench software. Obtained results suggest that the correlation between scale morphology and distribution of temperature and pressure on the sample's surface, created by gas flow in the system, can be justified.

  19. Influence of Gaseous Media Flow in the Dual Ar-H2-H2O/air Atmosphere Setup on the Scale Growth Kinetics of Crofer 22APU Ferritic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Stygar, Mirosław; Dąbrowa, Juliusz; Dziembaj, Piotr; Brylewski, Tomasz

    2016-12-01

    The problem of gaseous media distribution within the metallic interconnects in solid oxide fuel cells (SOFCs) and its influence on the oxidation resistance of the applied materials is currently of great interest. In the presented work, an influence of gas flow within the dual Ar-H2-H2O/air atmosphere experimental setup on the oxidation behavior of the Crofer 22APU ferritic stainless steel was investigated. Examination of the sample oxidized for 1000 h in temperature of 800 °C revealed the presence of coaxial regions on the scale surface, with the differences in scale's thicknesses in those regions being clearly visible. Additionally, the morphology of the surface changed significantly in a function of the radial distance from the sample's center. To further examine the phenomena of uneven gas distribution, a model of the dual-atmosphere setup was created, using Ansys Workbench software. Obtained results suggest that the correlation between scale morphology and distribution of temperature and pressure on the sample's surface, created by gas flow in the system, can be justified.

  20. Oxidation behaviour of ferritic stainless steel grade Crofer 22 APU at 700 °C in flowing Ar−75%CO{sub 2}−12%H{sub 2}O

    SciTech Connect

    Shariff, Nurul Atikah; Othman, Norinsan Kamil; Jalar, Azman

    2013-11-27

    The oxidation of Ferritic Stainless Steel (FSS) grade Crofer 22 APU has been investigated. FSS alloys were exposed to isothermal conditions in a horizontal tube furnace at a 700 °C in flowing Ar−75%CO{sub 2}−12%H{sub 2}O at a pressure of approximately 1 atm. The results showed that the growth of non protective Fe{sub 2}O{sub 3} and spinel was observed after 50 h exposure in the presence of 12% H{sub 2}O. The weight was increased significantly with time of exposure. The formation of different oxides is presented on the interface of the specimen such as MnCr{sub 2}O{sub 4}, Fe{sub 3}O{sub 4} and Fe{sub 2}O{sub 3} were revealed by X-ray diffraction and supported by EDAX analysis. FSS did not form a protective Cr{sub 2}O{sub 3} layer due to water vapour accelerates the kinetics oxidation. Data of microstructure observation is presented and discussed in this paper in term of water vapour effects.

  1. Investigation of microstructure changes in ODS-EUROFER after hydrogen loading

    NASA Astrophysics Data System (ADS)

    Emelyanova, O. V.; Ganchenkova, M. G.; Malitskii, E.; Yagodzinskyy, Y. N.; Klimenkov, M.; Borodin, V. A.; Vladimirov, P. V.; Lindau, R.; Möslang, A.; Hänninen, H.

    2016-01-01

    The effect of hydrogen on the microstructure of mechanically tested ODS-EUROFER steel was investigated by means of transmission electron microscopy, thermal desorption spectroscopy, and atomistic simulations. The presence of yttrium oxide particles notably increases hydrogen uptake in ODS-EUROFER steel as compared to ODS-free EUROFER 97. Under tensile loading, hydrogen accumulation promotes the loss of cohesion at the oxide particle interfaces. First-principles molecular dynamics simulations indicate that hydrogen can be trapped at nanoparticle/matrix interface, creating OH-groups. The accumulation of hydrogen atoms at the oxide particle surface can be the reason for the observed hydrogen-induced oxide/matrix interface weakening and de-cohesion under the action of external tensile stress.

  2. ODS Characterization Progress Report 06/27/08

    SciTech Connect

    El-Dasher, B

    2008-11-25

    This progress report is intended to help keep track of the work that has been performed in characterizing ODS steels for the LIFE project. This specific report details the current status of the characterization of a 24% Cr, 1% Y{sub 2}O{sub 3} ODS steel obtained from Wayne King via Geoff Campbell. Since no pedigree of the material could be obtained, a baseline characterization was necessary prior to studying processing, welding, and corrosion behavior. This document details the results obtained from analysis performed using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and energy dispersive spectroscopy (EDS). At the time of writing, transmission electron microscopy (TEM) and microhardness measurements have not been completed, and will be included in a future report. The results are presented in two sections: microstructure, and phase identification. As the names suggest, the first section will report on the microstructure in the general sense and include details such as grain size and texture, and the second section will include the identification of the phases present in the baseline material.

  3. High resolution Transmission Electron Microscopy characterization of a milled oxide dispersion strengthened steel powder

    NASA Astrophysics Data System (ADS)

    Loyer-Prost, M.; Merot, J.-S.; Ribis, J.; Le Bouar, Y.; Chaffron, L.; Legendre, F.

    2016-10-01

    Oxide Dispersion Strengthened (ODS) steels are promising materials for generation IV fuel claddings as their dense nano-oxide dispersion provides good creep and irradiation resistance. Even if they have been studied for years, the formation mechanism of these nano-oxides is still unclear. Here we report for the first time a High Resolution Transmission Electron Microscopy and Energy Filtered Transmission Electron Microscopy characterization of an ODS milled powder. It provides clear evidence of the presence of small crystalline nanoclusters (NCs) enriched in titanium directly after milling. Small NCs (<5 nm) have a crystalline structure and seem partly coherent with the matrix. They have an interplanar spacing close to the (011) bcc iron structure. They coexist with larger crystalline spherical precipitates of 15-20 nm in size. Their crystalline structure may be metastable as they are not consistent with any Y-Ti-O or Ti-O structure. Such detailed observations in the as-milled grain powder confirm a mechanism of Y, Ti, O dissolution in the ferritic matrix followed by a NC precipitation during the mechanical alloying process of ODS materials.

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

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

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

  5. Progress in ODS Alloys: A Synopsis of a 2010 Workshop on Fe- Based ODS Alloys

    SciTech Connect

    Kad, Bimal; Dryepondt, Sebastien N; Jones, Andy R.; Vito, Cedro III; Tatlock, Gordon J; Pint, Bruce A; Tortorelli, Peter F; Rawls, Patricia A.

    2012-01-01

    In Fall 2010, a workshop on the role and future of Fe-based Oxide Dispersion Strengthened (ODS) alloys gathered together ODS alloy suppliers, potential industrial end-users, and technical experts in relevant areas. Presentations and discussions focused on the current state of development of these alloys, their availability from commercial suppliers, past major evaluations of ODS alloy components in fossil and nuclear energy applications, and the technical and economic issues attendant to commercial use of ODS alloys. Significant progress has been achieved in joining ODS alloys, with creep resistant joints successfully made by inertia welding, friction stir welding and plasma-assisted pulse diffusion bonding, and in improving models for the prediction of lifetime components. New powder and alloy fabrication methods to lower cost or improve endproduct properties were also described. The final open discussion centered on challenges and pathways for further development and large-scale use of ODS alloys.

  6. Corrosion behavior of magnetic ferrite coating prepared by plasma spraying

    SciTech Connect

    Liu, Yi; Wei, Shicheng Tong, Hui; Tian, Haoliang; Liu, Ming; Xu, Binshi

    2014-12-15

    Graphical abstract: The saturation magnetization (M{sub s}) of the ferrite coating is 34.417 emu/g while the M{sub s} value of the ferrite powder is 71.916 emu/g. It can be seen that plasma spray process causes deterioration of the room temperature soft magnetic properties. - Highlights: • Spinel ferrite coatings have been prepared by plasma spraying. • The coating consists of nanocrystalline grains. • The saturation magnetization of the ferrite coating is 34.417 emu/g. • Corrosion behavior of the ferrite coating was examined in NaCl solution. - Abstract: In this study, spray dried spinel ferrite powders were deposited on the surface of mild steel substrate through plasma spraying. The structure and morphological studies on the ferrite coatings were carried out using X-ray diffraction, scanning electron microscope and Raman spectroscopy. It was showed that spray dried process was an effective method to prepare thermal spraying powders. The coating showed spinel structure with a second phase of LaFeO{sub 3}. The magnetic property of the ferrite samples were measured by vibrating sample magnetometer. The saturation magnetization (M{sub s}) of the ferrite coating was 34.417 emu/g. The corrosion behavior of coating samples was examined by electrochemical impedance spectroscopy. EIS diagrams showed three corrosion processes as the coating immersed in 3.5 wt.% NaCl solution. The results suggested that plasma spraying was a promising technology for the production of magnetic ferrite coatings.

  7. XXIst Century Ferrites

    NASA Astrophysics Data System (ADS)

    Mazaleyrat, F.; Zehani, K.; Pasko, A.; Loyau, V.; LoBue, M.

    2012-05-01

    Ferrites have always been a subject of great interest from point of view of magnetic application, since the fist compass to present date. In contrast, the scientific interest for iron based magnetic oxides decreased after Ørsted discovery as they where replaced by coil as magnetizing sources. Neel discovery of ferrimagnetism boosted again interest and leads to strong developments during two decades before being of less interest. Recently, the evolution of power electronics toward higher frequency, the downsizing of ceramics microstucture to nanometer scale, the increasing price of rare-earth elements and the development of magnetocaloric materials put light again on ferrites. A review on three ferrite families is given herein: harder nanostructured Ba2+Fe12O19 magnet processed by spark plasma sintering, magnetocaloric effect associated to the spin transition reorientation of W-ferrite and low temperature spark plasma sintered Ni-Zn-Cu ferrites for high frequency power applications.

  8. MHD Effects of a Ferritic Wall on Tokamak Plasmas

    NASA Astrophysics Data System (ADS)

    Hughes, Paul E.

    It has been recognized for some time that the very high fluence of fast (14.1MeV) neutrons produced by deuterium-tritium fusion will represent a major materials challenge for the development of next-generation fusion energy projects such as a fusion component test facility and demonstration fusion power reactor. The best-understood and most promising solutions presently available are a family of low-activation steels originally developed for use in fission reactors, but the ferromagnetic properties of these steels represent a danger to plasma confinement through enhancement of magnetohydrodynamic instabilities and increased susceptibility to error fields. At present, experimental research into the effects of ferromagnetic materials on MHD stability in toroidal geometry has been confined to demonstrating that it is still possible to operate an advanced tokamak in the presence of ferromagnetic components. In order to better quantify the effects of ferromagnetic materials on tokamak plasma stability, a new ferritic wall has been installated in the High Beta Tokamak---Extended Pulse (HBT-EP) device. The development, assembly, installation, and testing of this wall as a modular upgrade is described, and the effect of the wall on machine performance is characterized. Comparative studies of plasma dynamics with the ferritic wall close-fitting against similar plasmas with the ferritic wall retracted demonstrate substantial effects on plasma stability. Resonant magnetic perturbations (RMPs) are applied, demonstrating a 50% increase in n = 1 plasma response amplitude when the ferritic wall is near the plasma. Susceptibility of plasmas to disruption events increases by a factor of 2 or more with the ferritic wall inserted, as disruptions are observed earlier with greater frequency. Growth rates of external kink instabilities are observed to be twice as large in the presence of a close-fitting ferritic wall. Initial studies are made of the influence of mode rotation frequency

  9. SCC and corrosion evaluations of the F/M steels for a supercritical water reactor

    NASA Astrophysics Data System (ADS)

    Hwang, Seong Sik; Lee, Byung Hak; Kim, Jung Gu; Jang, Jinsung

    2008-01-01

    As one of the Generation IV nuclear reactors, a supercritical water cooled reactor (SCWR) is being considered as a candidate reactor due to its high thermal efficiency and simple reactor design without steam generators and steam separators. For the application of a structural material to a core's internals and a fuel cladding, the material should be evaluated in terms of its corrosion and stress corrosion cracking susceptibility. Stress corrosion cracking and general corrosion tests of ferritic-martensitic (F/M) steels, high Ni alloys and an oxide dispersion strengthened (ODS) alloy were performed. Stress corrosion cracking (SCC) was not observed on the fractured surface of the T 91 steel in the supercritical water at 500, 550 and 600 °C. As the test temperature increased, the ultimate tensile strength (UTS) and yield strength (YS) of T 91 decreased, and a high dissolved oxygen level induced corrosion and low ductility. The F/M steels showed a high corrosion rate whereas the Ni base alloys showed a little corrosion at 500 and 550 °C. Corrosion rate of the F/M steels at 600 °C test was up to three times larger than that at 500 °C. A thin layer composed of Mo and Ni seems to retard the Cr diffusion into the out layer of the corrosion product of T 92 and T 122.

  10. Epitaxial Garnets and Hexagonal Ferrites.

    DTIC Science & Technology

    1983-12-01

    Ferrites Lithium Ferrite Magnetostatic Wave Garnets Epitaxy Yttrium Iron Garnet Liquid Phase Epitaxy Hexagonal Ferrite Microwave Signal Processing...epitaxial ferrit ( materials for use in microwave and millirreter-wave signal processing devices. The major emphasis has been on multiple layer...overall objective of this research is to develop epitaxial single crystal ferrite films suitable for microwave and millimeter-wave signal processing at

  11. Ferritic Fe-Mn alloy for cryogenic applications

    DOEpatents

    Hwang, Sun-Keun; Morris, Jr., John W.

    1979-01-01

    A ferritic, nickel-free alloy steel composition, suitable for cryogenic applications, which consists essentially of about 10-13% manganese, 0.002-0.01% boron, 0.1-0.5% titanium, 0-0.05% aluminum, and the remainder iron and incidental impurities normally associated therewith.

  12. SEDS Tether M/OD Damage Analyses

    NASA Technical Reports Server (NTRS)

    Hayashida, K. B.; Robinson, J. H.; Hill, S. A.

    1997-01-01

    The Small Expendable Deployer System (SEDS) was designed to deploy an endmass at the end of a 20-km-long tether which acts as an upper stage rocket, and the threats from the meteoroid and orbital debris (M/OD) particle environments on SEDS components are important issues for the safety and success of any SEDS mission. However, the possibility of severing the tether due to M/OD particle impacts is an even more serious concern, since the SEDS tether has a relatively large exposed area to the M/OD environments although its diameter is quite small. The threats from the M/OD environments became a very important issue for the third SEDS mission, since the project office proposed using the shuttle orbiter as a launch platform instead of the second stage of a Delta II expendable rocket, which was used for the first two SEDS missions. A series of hyper-velocity impact tests were performed at the Johnson Space Center and Arnold Engineering Development Center to help determine the critical particle sizes required to sever the tether. The computer hydrodynamic code or hydrocode called CTH, developed by the Sandia National Laboratories, was also used to simulate the damage on the SEDS tether caused by both the orbital debris and test particle impacts. The CTH hydrocode simulation results provided the much needed information to help determine the critical particle sizes required to sever the tether. The M/OD particle sizes required to sever the tether were estimated to be less than 0.1 cm in diameter from these studies, and these size particles are more abundant in low-Earth orbit than larger size particles. Finally, the authors performed the M/OD damage analyses for the three SEDS missions; i.e., SEDS-1, -2, and -3 missions, by using the information obtained from the hypervelocity impact test and hydrocode simulations results.

  13. Stability of nanoclusters in 14YWT oxide dispersion strengthened steel under heavy ion-irradiation by atom probe tomography

    SciTech Connect

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

    2014-12-01

    14YWT oxide dispersion strengthened (ODS) ferritic steel was irradiated with of 5 MeV Ni2+ ions, at 300 C, 450 C, and 600 C to a damage level of 100 dpa. The stability of Ti–Y–O nanoclusters was investigated by applying atom probe tomography (APT) in voltage mode, of the samples before and after irradiations. The average size and number density of the nanoclusters was determined using the maximum separation method. These techniques allowed for the imaging of nanoclusters to sizes well below the resolution limit of conventional transmission electron microscopy techniques. The most significant changes were observed for samples irradiated at 300 C where the size (average Guinier radius) and number density of nanoclusters were observed to decrease from 1.1 nm to 0.8 nm and 12 1023 to 3.6 1023, respectively. In this study, the nanoclusters are more stable at higher temperature.

  14. Ferritic Alloys with Extreme Creep Resistance via Coherent Hierarchical Precipitates

    NASA Astrophysics Data System (ADS)

    Song, Gian; Sun, Zhiqian; Li, Lin; Xu, Xiandong; Rawlings, Michael; Liebscher, Christian H.; Clausen, Bjørn; Poplawsky, Jonathan; Leonard, Donovan N.; Huang, Shenyan; Teng, Zhenke; Liu, Chain T.; Asta, Mark D.; Gao, Yanfei; Dunand, David C.; Ghosh, Gautam; Chen, Mingwei; Fine, Morris E.; Liaw, Peter K.

    2015-11-01

    There have been numerous efforts to develop creep-resistant materials strengthened by incoherent particles at high temperatures and stresses in response to future energy needs for steam turbines in thermal-power plants. However, the microstructural instability of the incoherent-particle-strengthened ferritic steels limits their application to temperatures below 900 K. Here, we report a novel ferritic alloy with the excellent creep resistance enhanced by coherent hierarchical precipitates, using the integrated experimental (transmission-electron microscopy/scanning-transmission-electron microscopy, in-situ neutron diffraction, and atom-probe tomography) and theoretical (crystal-plasticity finite-element modeling) approaches. This alloy is strengthened by nano-scaled L21-Ni2TiAl (Heusler phase)-based precipitates, which themselves contain coherent nano-scaled B2 zones. These coherent hierarchical precipitates are uniformly distributed within the Fe matrix. Our hierarchical structure material exhibits the superior creep resistance at 973 K in terms of the minimal creep rate, which is four orders of magnitude lower than that of conventional ferritic steels. These results provide a new alloy-design strategy using the novel concept of hierarchical precipitates and the fundamental science for developing creep-resistant ferritic alloys. The present research will broaden the applications of ferritic alloys to higher temperatures.

  15. Ferritic Alloys with Extreme Creep Resistance via Coherent Hierarchical Precipitates

    PubMed Central

    Song, Gian; Sun, Zhiqian; Li, Lin; Xu, Xiandong; Rawlings, Michael; Liebscher, Christian H.; Clausen, Bjørn; Poplawsky, Jonathan; Leonard, Donovan N.; Huang, Shenyan; Teng, Zhenke; Liu, Chain T.; Asta, Mark D.; Gao, Yanfei; Dunand, David C.; Ghosh, Gautam; Chen, Mingwei; Fine, Morris E.; Liaw, Peter K.

    2015-01-01

    There have been numerous efforts to develop creep-resistant materials strengthened by incoherent particles at high temperatures and stresses in response to future energy needs for steam turbines in thermal-power plants. However, the microstructural instability of the incoherent-particle-strengthened ferritic steels limits their application to temperatures below 900 K. Here, we report a novel ferritic alloy with the excellent creep resistance enhanced by coherent hierarchical precipitates, using the integrated experimental (transmission-electron microscopy/scanning-transmission-electron microscopy, in-situ neutron diffraction, and atom-probe tomography) and theoretical (crystal-plasticity finite-element modeling) approaches. This alloy is strengthened by nano-scaled L21-Ni2TiAl (Heusler phase)-based precipitates, which themselves contain coherent nano-scaled B2 zones. These coherent hierarchical precipitates are uniformly distributed within the Fe matrix. Our hierarchical structure material exhibits the superior creep resistance at 973 K in terms of the minimal creep rate, which is four orders of magnitude lower than that of conventional ferritic steels. These results provide a new alloy-design strategy using the novel concept of hierarchical precipitates and the fundamental science for developing creep-resistant ferritic alloys. The present research will broaden the applications of ferritic alloys to higher temperatures. PMID:26548303

  16. Ferritic Alloys with Extreme Creep Resistance via Coherent Hierarchical Precipitates

    DOE PAGES

    Song, Gian; Sun, Zhiqian; Li, Lin; ...

    2015-11-09

    There have been numerous efforts to develop creep-resistant materials strengthened by incoherent particles at high temperatures and stresses in response to future energy needs for steam turbines in thermal-power plants. However, the microstructural instability of the incoherent-particle-strengthened ferritic steels limits their application to temperatures below 900 K. Here, we report a novel ferritic alloy with the excellent creep resistance enhanced by coherent hierarchical precipitates, using the integrated experimental (transmission-electron microscopy/scanning-transmission-electron microscopy, in-situ neutron diffraction, and atom-probe tomography) and theoretical (crystal-plasticity finite-element modeling) approaches. This alloy is strengthened by nano-scaled L21-Ni2TiAl (Heusler phase)-based precipitates, which themselves contain coherent nano-scaled B2 zones.more » These coherent hierarchical precipitates are uniformly distributed within the Fe matrix. Our hierarchical structure material exhibits the superior creep resistance at 973 K in terms of the minimal creep rate, which is four orders of magnitude lower than that of conventional ferritic steels. These results provide a new alloy-design strategy using the novel concept of hierarchical precipitates and the fundamental science for developing creep-resistant ferritic alloys. Finally, the present research will broaden the applications of ferritic alloys to higher temperatures.« less

  17. Ferritic Alloys with Extreme Creep Resistance via Coherent Hierarchical Precipitates

    SciTech Connect

    Song, Gian; Sun, Zhiqian; Li, Lin; Xu, Xiandong; Rawlings, Michael; Liebscher, Christian H.; Clausen, Bjørn; Poplawsky, Jonathan; Leonard, Donovan N.; Huang, Shenyan; Teng, Zhenke; Liu, Chain T.; Asta, Mark D.; Gao, Yanfei; Dunand, David C.; Ghosh, Gautam; Chen, Mingwei; Fine, Morris E.; Liaw, Peter K.

    2015-11-09

    There have been numerous efforts to develop creep-resistant materials strengthened by incoherent particles at high temperatures and stresses in response to future energy needs for steam turbines in thermal-power plants. However, the microstructural instability of the incoherent-particle-strengthened ferritic steels limits their application to temperatures below 900 K. Here, we report a novel ferritic alloy with the excellent creep resistance enhanced by coherent hierarchical precipitates, using the integrated experimental (transmission-electron microscopy/scanning-transmission-electron microscopy, in-situ neutron diffraction, and atom-probe tomography) and theoretical (crystal-plasticity finite-element modeling) approaches. This alloy is strengthened by nano-scaled L21-Ni2TiAl (Heusler phase)-based precipitates, which themselves contain coherent nano-scaled B2 zones. These coherent hierarchical precipitates are uniformly distributed within the Fe matrix. Our hierarchical structure material exhibits the superior creep resistance at 973 K in terms of the minimal creep rate, which is four orders of magnitude lower than that of conventional ferritic steels. These results provide a new alloy-design strategy using the novel concept of hierarchical precipitates and the fundamental science for developing creep-resistant ferritic alloys. Finally, the present research will broaden the applications of ferritic alloys to higher temperatures.

  18. Reduction in Defect Content of ODS Alloys

    SciTech Connect

    Ritherdon, J

    2001-05-15

    The work detailed within this report is a continuation of earlier work carried out under contract number 1DX-SY382V. The earlier work comprises a literature review of the sources and types of defects found principally in Fe-based ODS alloys as well as experimental work designed to identify defects in the prototype ODS-Fe{sub 3}Al alloy, deduce their origins and to recommend methods of defect reduction. The present work is an extension of the experimental work already reported and concentrates on means of reduction of defects already identified rather than the search for new defect types. This report also includes results gathered during powder separation trials, conducted by the University of Groningen, Netherlands and coordinated by the University of Liverpool, involving the separation of different metallic powders in terms of their differing densities. The scope and objectives of the present work were laid out in the technical proposal ''Reduction in Defect Content in ODS Alloys-III''. All the work proposed in the ''Statement of Work'' section of the technical proposal has been carried out and all work extra to the ''Statement of Work'' falls within the context of an ODS-Fe{sub 3}Al alloy of improved overall quality and potential creep performance in the consolidated form. The outturn of the experimental work performed is reported in the following sections.

  19. CASS Ferrite and Grain Structure Relationship

    SciTech Connect

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

    2016-07-13

    This document summarizes the results of research conducted at Pacific Northwest National Laboratory (PNNL) to determine whether, based on experimental measurements, a correlation existed between grain structure in cast austenitic stainless steel (CASS) piping and ferrite content of the casting alloy. The motivation for this research lies in the fact that ultrasonic testing (UT) is strongly influenced by CASS grain structure; knowledge of this grain structure may help improve the ability to interpret UT responses, thereby improving the overall reliability of UT inspections of CASS components.

  20. Impedance calculation for ferrite inserts

    SciTech Connect

    Breitzmann, S.C.; Lee, S.Y.; Ng, K.Y.; /Fermilab

    2005-01-01

    Passive ferrite inserts were used to compensate the space charge impedance in high intensity space charge dominated accelerators. They study the narrowband longitudinal impedance of these ferrite inserts. they find that the shunt impedance and the quality factor for ferrite inserts are inversely proportional to the imaginary part of the permeability of ferrite materials. They also provide a recipe for attaining a truly passive space charge impedance compensation and avoiding narrowband microwave instabilities.