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Kazuhiro Kimura - One of the best experts on this subject based on the ideXlab platform.
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the formation and dissolution of residual δ ferrite in asme grade 91 steel plates
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: Satoru Kobayashi, Kota Sawada, Hideaki Kushima, Toru Hara, Kazuhiro KimuraAbstract:Abstract This paper investigated the relationship between Creep Strength and the existence of residual δ ferrite in the initial microstructure in three heats of Grade 91 steel plates and examined the origin, the transformation process and the dissolution of the δ ferrite in the steel plates. The Creep Strength of the steel specimens was lower when the δ ferrite was present in the initial microstructure. The δ ferrite showed a disk shape and a bumpy interface, and had MX carbonitride particle arrays inside and coarse M 23 C 6 carbide particles on the bumpy interface. Chromium and molybdenum were found to segregate in/around the δ ferrite disk. The residual δ ferrite dissolved completely after an additional normalizing heat treatment at 1050 °C for 30 min. The results obtained strongly indicate that the presence of δ ferrite is due to insufficient normalizing heat treatment time to remove segregation during solidification. The δ ferrite was also found to grow through a diffusional transformation during cooling from the normalizing heat treatment.
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effect of precipitation behavior on Creep Strength of 15 cr ferritic steels at high temperature between 923 and 1023k
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: M Shibuya, Kota Sawada, Hideaki Kushima, Yoshiaki Toda, Kazuhiro KimuraAbstract:Abstract The effect of precipitation Strengthening on the high-temperature Creep Strength of heat-resistant 15Cr steels with dual phases of ferrite and martensite was investigated. The Creep rupture lifetime of the 15Cr steel at temperatures up to 1023 K was 10 times longer than that of conventional 9Cr steel (ASME Grade T92) with a tempered martensitic microstructure. The Creep rupture Strength of the 15Cr steel after 10,000 h at 973 and 1023 K was approximately two times higher than that of the T92 steel. The precipitates identified in the Creep ruptured 15Cr steels were intermetallic compounds (Laves phase and χ-phase) and carbide (Cr23C6). In the 15Cr steels Creep ruptured at high temperatures of 973 K and above, the Laves phase was precipitated in both ferritic and martensitic grains, and Cr23C6 carbide was precipitated at the grain boundaries. The 15Cr steel exhibited longer Creep rupture lifetime than 9Cr steel with a tempered martensitic microstructure Strengthened by carbides and carbonitrides, due to the precipitation of Laves phase and Cr23C6.
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influence of chemical composition and heat treatment on long term Creep Strength of grade 91 steel
Procedia Engineering, 2013Co-Authors: Kazuhiro Kimura, Kota Sawada, Hideaki Kushima, Yoshiaki TodaAbstract:Abstract Long-term Creep Strength of ASTM/ASME Grade 91 steels was investigated. Two heats of Grade 91 steels indicated lower Creep rupture Strength than the other four heats from short-term to long-term, and presence of delta ferrite phase was observed. In the short-term, no difference in Creep rupture Strength was observed among four heats of Grade 91 steels, however, the large heat-to-heat variation of Creep rupture Strength was observed in the long-term at 600 °C. The higher nickel containing heat indicates lower Creep rupture Strength in the long-term at 600 °C, although nickel concentration was 0.28mass% in maximum. Homogeneously recovered subgrain structure was observed on the specimens Creep ruptured after about 80,000 h at 600 °C for both high nickel low Strength heat and low nickel high Strength one. Only a small number of fine MX carbonitride particles with a large number of coarse Z-phase were observed on the Creep ruptured specimen of high nickel low Strength heat, in contrast to low nickel high Strength heat in which many MX particles were still observed and Z- phase formation was not pronounced. The difference in stability of fine MX carbonitride particles during Creep exposure at the elevated temperatures is a cause of heat-to-heat variation of long-term Creep Strength of the steels. Decrease in phase transformation temperature of Ac1 with increase in nickel content may reduce stability of the precipitates at the elevated temperatures. Nickel content should be reduced in order to suppress a large drop in long-term Creep Strength of Grade 91 steel.
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evaluation of long term Creep Strength of asme grades 91 92 and 122 type steels
ASME 2012 Pressure Vessels and Piping Conference, 2012Co-Authors: Kazuhiro Kimura, Yukio TakahashiAbstract:Creep rupture data of ASME Grades 91, 92 and 122 type steels have been collected and long-term Creep rupture Strength of the steels has been evaluated. Similar study was conducted by the SHC committee in 2004 and 2005, therefore, the evaluation of long-term Creep rupture Strength was conducted with emphasis on the long-term Creep rupture data obtained after the previous study. Creep rupture Strength was analyzed by means of region splitting analysis method in consideration of 50% of 0.2% offset yield Strength, in the same way as the previous study. Almost the same results were obtained on base metal of Grade 92 as the previous study, however, evaluated 100,000 hours Creep rupture Strength of base metal of Grades 91 and 122 were lower than the previous results. For Grades 91 and 122 type steels, moreover, Creep rupture Strength of the plate steel were lower than those of pipe and forging steels. Tendency to decrease with increase in nickel content was observed on long-term Creep rupture Strength of tube steel of Grade 91 at 600°C. According to the evaluation of long-term Creep Strength of the steels, allowable tensile stress was reviewed and proposed revision was concluded.Copyright © 2012 by ASME
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Creep rupture ductility of Creep Strength enhanced ferritic steels
Journal of Pressure Vessel Technology-transactions of The Asme, 2012Co-Authors: Kazuhiro Kimura, Kota Sawada, Hideaki KushimaAbstract:Creep rupture Strength and ductility of Creep Strength enhanced ferritic steels of Grades 23, 91, 92, and 122 was investigated with particular emphasis on remarkable drop in the long-term. Large difference in Creep rupture Strength and ductility was observed on three heats of Grade 23 steels. Remarkable drop of Creep rupture Strength in the long-term of T91 was comparable to those of Grades 92 and 122. Remarkable drop in Creep rupture ductility in a stress regime below 50% of 0.2% offset yield stress was observed on Grade T23 steel, however, that of Grade P23 steel did not indicate any degradation of Creep rupture ductility. Higher Creep rupture ductility of Grade P23 steel was considered to be caused by its lower Creep Strength than that of T23 steels. Creep rupture ductility of Grades 92 and 122 steels indicated rapid and drastic decrease with decrease in stress at 50% of 0.2% offset yield stress. Stress dependence of Creep rupture ductility of Grades 92 and 122 steels was well described by a ratio of stress to 0.2% offset yield stress, regardless of temperature. On the other hand, large drop in Creep rupture ductility of Grade 91 steel was observed only in the very low-stress regime at 650 °C. Alloying elements including impurities and changes in precipitates may influence on Creep rupture ductility, however, remarkable drop in ductility of the steels cannot be explained by chemical composition and precipitates. High ductility in the high-stress regime above 50% of 0.2% offset yield stress should be provided by easy plastic deformation, and it has been concluded that a remarkable drop in ductility in the low-stress regime is derived from a concentration of Creep deformation into a tiny recovered region formed at the vicinity of grain boundary.
Fujio Abe - One of the best experts on this subject based on the ideXlab platform.
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Creep Strength of dissimilar welded joints using high b 9cr steel for advanced usc boiler
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2014Co-Authors: Masaaki Tabuchi, Hiromichi Hongo, Fujio AbeAbstract:The commercialization of a 973 K (700 °C) class pulverized coal power system, advanced ultra-supercritical (A-USC) pressure power generation, is the target of an ongoing research project initiated in Japan in 2008. In the A-USC boiler, Ni or Ni-Fe base alloys are used for high-temperature parts at 923 K to 973 K (650 °C to 700 °C), and advanced high-Cr ferritic steels are planned to be used at temperatures lower than 923 K (650 °C). In the dissimilar welds between Ni base alloys and high-Cr ferritic steels, Type IV failure in the heat-affected zone (HAZ) is a concern. Thus, the high B-9Cr steel developed at the National Institute for Materials Science, which has improved Creep Strength in weldments, is a candidate material for the Japanese A-USC boiler. In the present study, Creep tests were conducted on the dissimilar welded joints between Ni base alloys and high B-9Cr steels. Microstructures and Creep damage in the dissimilar welded joints were investigated. In the HAZ of the high B-9Cr steels, fine-grained microstructures were not formed and the grain size of the base metal was retained. Consequently, the Creep rupture life of the dissimilar welded joints using high B-9Cr steel was 5 to 10 times longer than that of the conventional 9Cr steel welded joints at 923 K (650 °C).
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grade 91 heat resistant martensitic steel
Coal Power Plant Materials and Life Assessment#R##N#Developments and Applications, 2014Co-Authors: Fujio AbeAbstract:Abstract: Key issues for application of Grade 91 (Gr.91) to power plants, such as long-term Creep Strength of base metal and welded joints, microstructure evolution during exposure at elevated temperature, degradation in welded joints due to type IV fracture, Creep–fatigue properties and steam oxidation behaviour, are comprehensively described, together with chemical, heat treatment, tensile and process requirements for Gr.91. Greater attention will be paid to technical issues on estimation of 100 000 h Creep rupture Strength, Creep life prediction by Creep strain analysis, and microstructure degradation causing a loss of Creep Strength at long times, which have been extensively investigated for Gr.91.
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precipitate design for Creep Strengthening of 9 cr tempered martensitic steel for ultra supercritical power plants
Science and Technology of Advanced Materials, 2008Co-Authors: Fujio AbeAbstract:AbstractIt is crucial for the carbon concentration of 9% Cr steel to be reduced to a very low level, so as to promote the formation of MX nitrides rich in vanadium as very fine and thermally stable particles to enable prolonged periods of exposure at elevated temperatures and also to eliminate Cr-rich carbides M23C6. Sub-boundary hardening, which is inversely proportional to the width of laths and blocks, is shown to be the most important Strengthening mechanism for Creep and is enhanced by the fine dispersion of precipitates along boundaries. The suppression of particle coarsening during Creep and the maintenance of a homogeneous distribution of M23C6 carbides near prior austenite grain boundaries, which precipitate during tempering and are less fine, are effective for preventing the long-term degradation of Creep Strength and for improving long-term Creep Strength. This can be achieved by the addition of boron. The steels considered in this paper exhibit higher Creep Strength at 650 °C than existing hig...
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precipitate design for Creep Strengthening of 9 cr tempered martensitic steel for ultra supercritical power plants
Science and Technology of Advanced Materials, 2008Co-Authors: Fujio AbeAbstract:It is crucial for the carbon concentration of 9% Cr steel to be reduced to a very low level, so as to promote the formation of MX nitrides rich in vanadium as very fine and thermally stable particles to enable prolonged periods of exposure at elevated temperatures and also to eliminate Cr-rich carbides M23C6. Sub-boundary hardening, which is inversely proportional to the width of laths and blocks, is shown to be the most important Strengthening mechanism for Creep and is enhanced by the fine dispersion of precipitates along boundaries. The suppression of particle coarsening during Creep and the maintenance of a homogeneous distribution of M23C6 carbides near prior austenite grain boundaries, which precipitate during tempering and are less fine, are effective for preventing the long-term degradation of Creep Strength and for improving long-term Creep Strength. This can be achieved by the addition of boron. The steels considered in this paper exhibit higher Creep Strength at 650 °C than existing high-Strength steels used for thick section boiler components.
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suppression of type iv fracture and improvement of Creep Strength of 9cr steel welded joints by boron addition
International Journal of Pressure Vessels and Piping, 2007Co-Authors: Fujio Abe, Masaaki Tabuchi, Masayuki Kondo, Susumu TsukamotoAbstract:Abstract The microstructure and Creep Strength of simulated heat-affected zone (HAZ) specimens and welded joints have been investigated for advanced 9–12% Cr steels in order to make clear the mechanisms responsible for Type IV fracture and to improve the Creep Strength of welded joints at elevated temperature. Creep and Creep rupture tests were carried out at 650 °C (923 K) for up to about 2×10 4 h. The Creep rupture time of simulated HAZ specimens has its minimum after heating to A C3 temperature, which produces fine-grained martensitic microstructure with high density of dislocations and large M 23 C 6 carbides but no lath structure. The welded joints were fractured in fine-grained HAZ at low stresses, indicating Type IV fracture, which resulted in shorter Creep life than those of base metal. Reducing the width of HAZ by means of EB welding is effective for the extension of Creep life but the brittle Type IV fracture appears at low-stress and long-time conditions. The addition of about 100 ppm boron combined with minimized nitrogen of 10–20 ppm suppresses the formation of fine-grained region in HAZ and hence suppresses the Type IV fracture.
Hideaki Kushima - One of the best experts on this subject based on the ideXlab platform.
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effect of precipitation behavior on Creep Strength of 15 cr ferritic steels at high temperature between 923 and 1023k
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: M Shibuya, Kota Sawada, Hideaki Kushima, Yoshiaki Toda, Kazuhiro KimuraAbstract:Abstract The effect of precipitation Strengthening on the high-temperature Creep Strength of heat-resistant 15Cr steels with dual phases of ferrite and martensite was investigated. The Creep rupture lifetime of the 15Cr steel at temperatures up to 1023 K was 10 times longer than that of conventional 9Cr steel (ASME Grade T92) with a tempered martensitic microstructure. The Creep rupture Strength of the 15Cr steel after 10,000 h at 973 and 1023 K was approximately two times higher than that of the T92 steel. The precipitates identified in the Creep ruptured 15Cr steels were intermetallic compounds (Laves phase and χ-phase) and carbide (Cr23C6). In the 15Cr steels Creep ruptured at high temperatures of 973 K and above, the Laves phase was precipitated in both ferritic and martensitic grains, and Cr23C6 carbide was precipitated at the grain boundaries. The 15Cr steel exhibited longer Creep rupture lifetime than 9Cr steel with a tempered martensitic microstructure Strengthened by carbides and carbonitrides, due to the precipitation of Laves phase and Cr23C6.
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the formation and dissolution of residual δ ferrite in asme grade 91 steel plates
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: Satoru Kobayashi, Kota Sawada, Hideaki Kushima, Toru Hara, Kazuhiro KimuraAbstract:Abstract This paper investigated the relationship between Creep Strength and the existence of residual δ ferrite in the initial microstructure in three heats of Grade 91 steel plates and examined the origin, the transformation process and the dissolution of the δ ferrite in the steel plates. The Creep Strength of the steel specimens was lower when the δ ferrite was present in the initial microstructure. The δ ferrite showed a disk shape and a bumpy interface, and had MX carbonitride particle arrays inside and coarse M 23 C 6 carbide particles on the bumpy interface. Chromium and molybdenum were found to segregate in/around the δ ferrite disk. The residual δ ferrite dissolved completely after an additional normalizing heat treatment at 1050 °C for 30 min. The results obtained strongly indicate that the presence of δ ferrite is due to insufficient normalizing heat treatment time to remove segregation during solidification. The δ ferrite was also found to grow through a diffusional transformation during cooling from the normalizing heat treatment.
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influence of chemical composition and heat treatment on long term Creep Strength of grade 91 steel
Procedia Engineering, 2013Co-Authors: Kazuhiro Kimura, Kota Sawada, Hideaki Kushima, Yoshiaki TodaAbstract:Abstract Long-term Creep Strength of ASTM/ASME Grade 91 steels was investigated. Two heats of Grade 91 steels indicated lower Creep rupture Strength than the other four heats from short-term to long-term, and presence of delta ferrite phase was observed. In the short-term, no difference in Creep rupture Strength was observed among four heats of Grade 91 steels, however, the large heat-to-heat variation of Creep rupture Strength was observed in the long-term at 600 °C. The higher nickel containing heat indicates lower Creep rupture Strength in the long-term at 600 °C, although nickel concentration was 0.28mass% in maximum. Homogeneously recovered subgrain structure was observed on the specimens Creep ruptured after about 80,000 h at 600 °C for both high nickel low Strength heat and low nickel high Strength one. Only a small number of fine MX carbonitride particles with a large number of coarse Z-phase were observed on the Creep ruptured specimen of high nickel low Strength heat, in contrast to low nickel high Strength heat in which many MX particles were still observed and Z- phase formation was not pronounced. The difference in stability of fine MX carbonitride particles during Creep exposure at the elevated temperatures is a cause of heat-to-heat variation of long-term Creep Strength of the steels. Decrease in phase transformation temperature of Ac1 with increase in nickel content may reduce stability of the precipitates at the elevated temperatures. Nickel content should be reduced in order to suppress a large drop in long-term Creep Strength of Grade 91 steel.
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Creep rupture ductility of Creep Strength enhanced ferritic steels
Journal of Pressure Vessel Technology-transactions of The Asme, 2012Co-Authors: Kazuhiro Kimura, Kota Sawada, Hideaki KushimaAbstract:Creep rupture Strength and ductility of Creep Strength enhanced ferritic steels of Grades 23, 91, 92, and 122 was investigated with particular emphasis on remarkable drop in the long-term. Large difference in Creep rupture Strength and ductility was observed on three heats of Grade 23 steels. Remarkable drop of Creep rupture Strength in the long-term of T91 was comparable to those of Grades 92 and 122. Remarkable drop in Creep rupture ductility in a stress regime below 50% of 0.2% offset yield stress was observed on Grade T23 steel, however, that of Grade P23 steel did not indicate any degradation of Creep rupture ductility. Higher Creep rupture ductility of Grade P23 steel was considered to be caused by its lower Creep Strength than that of T23 steels. Creep rupture ductility of Grades 92 and 122 steels indicated rapid and drastic decrease with decrease in stress at 50% of 0.2% offset yield stress. Stress dependence of Creep rupture ductility of Grades 92 and 122 steels was well described by a ratio of stress to 0.2% offset yield stress, regardless of temperature. On the other hand, large drop in Creep rupture ductility of Grade 91 steel was observed only in the very low-stress regime at 650 °C. Alloying elements including impurities and changes in precipitates may influence on Creep rupture ductility, however, remarkable drop in ductility of the steels cannot be explained by chemical composition and precipitates. High ductility in the high-stress regime above 50% of 0.2% offset yield stress should be provided by easy plastic deformation, and it has been concluded that a remarkable drop in ductility in the low-stress regime is derived from a concentration of Creep deformation into a tiny recovered region formed at the vicinity of grain boundary.
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Creep Strength of high chromium steel with ferrite matrix
International Journal of Pressure Vessels and Piping, 2010Co-Authors: Kazuhiro Kimura, Hideaki Kushima, Yoshiaki Toda, Kota SawadaAbstract:Abstract Long-term Creep Strength of material in the low-stress regime below elastic limit is difficult to predict by an extrapolation of short-term Creep Strength in the high-stress regime above elastic limit. Long-term Creep Strength of fully annealed ferrite-pearlite microstructure of low alloy Cr–Mo steel is higher than that of martensite and bainite microstructures. It is explained by lower dislocation density of fully annealed microstructure. According to the above concept, Creep Strength of high chromium steel with ferrite matrix is investigated. Creep rupture life of 15Cr–Mo–W–Co steel with ferrite matrix which is longer than that of ASME Grade 92 steel is obtained at 650 °C by controlling the chemical composition and heat treatment condition.
Kota Sawada - One of the best experts on this subject based on the ideXlab platform.
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effect of precipitation behavior on Creep Strength of 15 cr ferritic steels at high temperature between 923 and 1023k
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: M Shibuya, Kota Sawada, Hideaki Kushima, Yoshiaki Toda, Kazuhiro KimuraAbstract:Abstract The effect of precipitation Strengthening on the high-temperature Creep Strength of heat-resistant 15Cr steels with dual phases of ferrite and martensite was investigated. The Creep rupture lifetime of the 15Cr steel at temperatures up to 1023 K was 10 times longer than that of conventional 9Cr steel (ASME Grade T92) with a tempered martensitic microstructure. The Creep rupture Strength of the 15Cr steel after 10,000 h at 973 and 1023 K was approximately two times higher than that of the T92 steel. The precipitates identified in the Creep ruptured 15Cr steels were intermetallic compounds (Laves phase and χ-phase) and carbide (Cr23C6). In the 15Cr steels Creep ruptured at high temperatures of 973 K and above, the Laves phase was precipitated in both ferritic and martensitic grains, and Cr23C6 carbide was precipitated at the grain boundaries. The 15Cr steel exhibited longer Creep rupture lifetime than 9Cr steel with a tempered martensitic microstructure Strengthened by carbides and carbonitrides, due to the precipitation of Laves phase and Cr23C6.
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the formation and dissolution of residual δ ferrite in asme grade 91 steel plates
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: Satoru Kobayashi, Kota Sawada, Hideaki Kushima, Toru Hara, Kazuhiro KimuraAbstract:Abstract This paper investigated the relationship between Creep Strength and the existence of residual δ ferrite in the initial microstructure in three heats of Grade 91 steel plates and examined the origin, the transformation process and the dissolution of the δ ferrite in the steel plates. The Creep Strength of the steel specimens was lower when the δ ferrite was present in the initial microstructure. The δ ferrite showed a disk shape and a bumpy interface, and had MX carbonitride particle arrays inside and coarse M 23 C 6 carbide particles on the bumpy interface. Chromium and molybdenum were found to segregate in/around the δ ferrite disk. The residual δ ferrite dissolved completely after an additional normalizing heat treatment at 1050 °C for 30 min. The results obtained strongly indicate that the presence of δ ferrite is due to insufficient normalizing heat treatment time to remove segregation during solidification. The δ ferrite was also found to grow through a diffusional transformation during cooling from the normalizing heat treatment.
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influence of chemical composition and heat treatment on long term Creep Strength of grade 91 steel
Procedia Engineering, 2013Co-Authors: Kazuhiro Kimura, Kota Sawada, Hideaki Kushima, Yoshiaki TodaAbstract:Abstract Long-term Creep Strength of ASTM/ASME Grade 91 steels was investigated. Two heats of Grade 91 steels indicated lower Creep rupture Strength than the other four heats from short-term to long-term, and presence of delta ferrite phase was observed. In the short-term, no difference in Creep rupture Strength was observed among four heats of Grade 91 steels, however, the large heat-to-heat variation of Creep rupture Strength was observed in the long-term at 600 °C. The higher nickel containing heat indicates lower Creep rupture Strength in the long-term at 600 °C, although nickel concentration was 0.28mass% in maximum. Homogeneously recovered subgrain structure was observed on the specimens Creep ruptured after about 80,000 h at 600 °C for both high nickel low Strength heat and low nickel high Strength one. Only a small number of fine MX carbonitride particles with a large number of coarse Z-phase were observed on the Creep ruptured specimen of high nickel low Strength heat, in contrast to low nickel high Strength heat in which many MX particles were still observed and Z- phase formation was not pronounced. The difference in stability of fine MX carbonitride particles during Creep exposure at the elevated temperatures is a cause of heat-to-heat variation of long-term Creep Strength of the steels. Decrease in phase transformation temperature of Ac1 with increase in nickel content may reduce stability of the precipitates at the elevated temperatures. Nickel content should be reduced in order to suppress a large drop in long-term Creep Strength of Grade 91 steel.
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Creep rupture ductility of Creep Strength enhanced ferritic steels
Journal of Pressure Vessel Technology-transactions of The Asme, 2012Co-Authors: Kazuhiro Kimura, Kota Sawada, Hideaki KushimaAbstract:Creep rupture Strength and ductility of Creep Strength enhanced ferritic steels of Grades 23, 91, 92, and 122 was investigated with particular emphasis on remarkable drop in the long-term. Large difference in Creep rupture Strength and ductility was observed on three heats of Grade 23 steels. Remarkable drop of Creep rupture Strength in the long-term of T91 was comparable to those of Grades 92 and 122. Remarkable drop in Creep rupture ductility in a stress regime below 50% of 0.2% offset yield stress was observed on Grade T23 steel, however, that of Grade P23 steel did not indicate any degradation of Creep rupture ductility. Higher Creep rupture ductility of Grade P23 steel was considered to be caused by its lower Creep Strength than that of T23 steels. Creep rupture ductility of Grades 92 and 122 steels indicated rapid and drastic decrease with decrease in stress at 50% of 0.2% offset yield stress. Stress dependence of Creep rupture ductility of Grades 92 and 122 steels was well described by a ratio of stress to 0.2% offset yield stress, regardless of temperature. On the other hand, large drop in Creep rupture ductility of Grade 91 steel was observed only in the very low-stress regime at 650 °C. Alloying elements including impurities and changes in precipitates may influence on Creep rupture ductility, however, remarkable drop in ductility of the steels cannot be explained by chemical composition and precipitates. High ductility in the high-stress regime above 50% of 0.2% offset yield stress should be provided by easy plastic deformation, and it has been concluded that a remarkable drop in ductility in the low-stress regime is derived from a concentration of Creep deformation into a tiny recovered region formed at the vicinity of grain boundary.
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Creep Strength of high chromium steel with ferrite matrix
International Journal of Pressure Vessels and Piping, 2010Co-Authors: Kazuhiro Kimura, Hideaki Kushima, Yoshiaki Toda, Kota SawadaAbstract:Abstract Long-term Creep Strength of material in the low-stress regime below elastic limit is difficult to predict by an extrapolation of short-term Creep Strength in the high-stress regime above elastic limit. Long-term Creep Strength of fully annealed ferrite-pearlite microstructure of low alloy Cr–Mo steel is higher than that of martensite and bainite microstructures. It is explained by lower dislocation density of fully annealed microstructure. According to the above concept, Creep Strength of high chromium steel with ferrite matrix is investigated. Creep rupture life of 15Cr–Mo–W–Co steel with ferrite matrix which is longer than that of ASME Grade 92 steel is obtained at 650 °C by controlling the chemical composition and heat treatment condition.
K. Laha - One of the best experts on this subject based on the ideXlab platform.
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materials development for fast reactor applications
Nuclear Engineering and Design, 2013Co-Authors: T. Jayakumar, K. Laha, M.d. Mathew, R SandhyaAbstract:Abstract Materials play a crucial role in the economic competitiveness of electricity produced from fast reactors. It is necessary to increase the fuel burn-up and design life in order to realize this objective. The burnup is largely limited by the void swelling and Creep resistance of the fuel cladding and wrapping materials. India's 500 MWe Prototype Fast Breeder Reactor (PFBR) is in advanced stage of construction. The major structural materials chosen for PFBR with MOX fuel are D9 austenitic stainless steel as fuel clad and wrapper material, 316LN austenitic stainless steel for reactor components and piping and modified 9Cr-1Mo steel for steam generator. In order to improve the burnup, titanium, phosphorous and silicon contents in alloy D9 have been optimized for decreased void swelling and increased Creep Strength and this has led to the development of a modified version of alloy D9 as IFAC-1. Ferritic steels are inherently resistant to void swelling. The disadvantage is their poor Creep Strength. Creep resistance of 9Cr-ferritic steel has been improved with the dispersion of nano-size yttria to develop oxide dispersion Strengthened (ODS) steel clad tube with long-term Creep Strength, comparable to alloy D9 so as to achieve higher fuel burnup. Improved versions of 316LN stainless steel with nitrogen content of about 0.14 wt% having higher Creep Strength to increase the life of fast reactors and modified 9Cr-1Mo steel with reduced nitrogen content and controlled addition of boron to improve type IV cracking resistance for steam generator application are other developments being perused towards improving the economic competitiveness of fast reactor technology.
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development of india specific rafm steel through optimization of tungsten and tantalum contents for better combination of impact tensile low cycle fatigue and Creep properties
Journal of Nuclear Materials, 2013Co-Authors: K. Laha, Abha Moitra, Raghu Sandhya, T. Jayakumar, S Saroja, M.d. Mathew, Rajendra E KumarAbstract:Abstract Effects of tungsten and tantalum contents on impact, tensile, low cycle fatigue and Creep properties of Reduced Activation Ferritic–Martensitic (RAFM) steel were studied to develop India-specific RAFM steel. Four heats of the steel have been melted with tungsten and tantalum contents in the ranges 1–2 wt.% and 0.06–0.14 wt.% respectively. Increase in tungsten content increased the ductile-to-brittle transition temperature (DBTT), low cycle fatigue and Creep Strength of the steel, whereas the tensile Strength was not changed significantly. Increase in tantalum content increased the DBTT and low cycle fatigue Strength of the steel whereas the tensile and Creep Strength decreased. Detailed TEM investigations revealed enhanced microstructural stability of the steel against Creep exposure on tungsten addition. The RAFM steel having 1.4 wt.% tungsten with 0.06 wt.% tantalum was found to possess optimum combination of impact, tensile, low cycle fatigue and Creep properties and is considered for Indian-specific RAFM steel.
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development of india specific rafm steel through optimization of tungsten and tantalum contents for better combination of impact tensile low cycle fatigue and Creep properties
Journal of Nuclear Materials, 2013Co-Authors: K. Laha, Abha Moitra, Raghu Sandhya, T. Jayakumar, S Saroja, M.d. Mathew, Rajendra E KumarAbstract:Abstract Effects of tungsten and tantalum contents on impact, tensile, low cycle fatigue and Creep properties of Reduced Activation Ferritic–Martensitic (RAFM) steel were studied to develop India-specific RAFM steel. Four heats of the steel have been melted with tungsten and tantalum contents in the ranges 1–2 wt.% and 0.06–0.14 wt.% respectively. Increase in tungsten content increased the ductile-to-brittle transition temperature (DBTT), low cycle fatigue and Creep Strength of the steel, whereas the tensile Strength was not changed significantly. Increase in tantalum content increased the DBTT and low cycle fatigue Strength of the steel whereas the tensile and Creep Strength decreased. Detailed TEM investigations revealed enhanced microstructural stability of the steel against Creep exposure on tungsten addition. The RAFM steel having 1.4 wt.% tungsten with 0.06 wt.% tantalum was found to possess optimum combination of impact, tensile, low cycle fatigue and Creep properties and is considered for Indian-specific RAFM steel.
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improving Creep Strength of 316l stainless steel by alloying with nitrogen
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2012Co-Authors: M.d. Mathew, K. Laha, V GanesanAbstract:Abstract The influence of nitrogen on the Creep behaviour of 316L(N) SS has been studied at nitrogen levels of 0.07, 0.11, 0.14 and 0.22 wt.%. Creep tests were carried out at 923 K at stress levels of 140, 175, 200 and 225 MPa with rupture life up to 16,000 h. Creep rupture Strength was found to increase substantially with increase in nitrogen content; rupture life increased almost 10 times by increasing nitrogen content from 0.07 wt.% to 0.22 wt.%. Steady state Creep rate decreased significantly with increasing nitrogen content. The extent of internal Creep damage and surface Creep damage decreased remarkably with increasing nitrogen content, resulting in increased Creep rupture Strength. Solid solution Strengthening, increase in Young's modulus, decrease in stacking fault energy and matrix precipitation of carbonitrides have contributed to the increase in Creep Strength with increasing nitrogen content.
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Improved Creep Strength and Creep ductility of type 347 austenitic stainless steel through the self-healing effect of boron for Creep cavitation
Metallurgical and Materials Transactions A, 2005Co-Authors: K. Laha, J. Kyono, T. Sasaki, S. Kishimoto, N. ShinyaAbstract:Composition of type 347 austenitic stainless steel was modified with the addition of boron and cerium. An improvement of Creep Strength coupled with Creep ductility of the steel was observed with boron and cerium additions. The observation of enhanced precipitation of carbonitrides in boron-containing steel over that of boron-free steel may in part contribute to the increase in Creep Strength. Both grain boundary sliding and nucleation and growth of intergranular Creep cavities were found to be suppressed in steel-containing boron. This results in an increase in Creep Strength and Creep ductility. Auger electron spectroscopic analysis of the chemistry of Creep cavity surfaces (exposed by breaking the Creep-exposed steel specimen at liquid nitrogen temperature under impact loading) revealed the segregation of elemental boron on the Creep cavity surface. Boron segregation, on the Creep cavity surface in the absence of sulfur contamination, suppressed the cavity growth and provided the steel with a self-healing effect for Creep cavitation. Cerium additions enabled boron to segregate on the cavity surface by effectively removing the traces of free sulfur in the matrix by the formation of ceriumoxysulfide (Ce_2O_2S).