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Kouichi Maruyama - One of the best experts on this subject based on the ideXlab platform.
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causes of heat to heat variation of creep Strength in grade 91 steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017Co-Authors: Kouichi Maruyama, J. Nakamura, Nobuaki Sekido, Kyosuke YoshimiAbstract:Abstract Heat-to-heat variation of creep Strength is significant in grade 91 (Gr.91) steel, but the causes of the variation have not been well understood yet. In the present paper, creep Rupture data of 14 heats of Gr.91 steel were analyzed paying attention to their chemical compositions and microstructures. The longest creep Rupture lives analyzed are 2 × 105 h at 500 and 550 °C and 105 h at 600 °C. The causes of the heat-to-heat variation are different, depending on creep test conditions. At low temperature and high stress (creep Rupture life of 104 h at 500 and 550 °C), creep Rupture Strength increases with increase of hardness after tempering. This suggests Strengthening by a fine subgrain microstructure developed during normalizing and subsequent tempering. At higher temperature and intermediate time range (104 h at 600 °C), creep Rupture Strength depends on Cr concentration of the heats in addition to the hardness. This finding suggests an important contribution of recovery process of the subgrain microstructures to creep Strength of the steel. In long-term creep (2×105 h at 550 °C and 105 h at 600 °C) creep Rupture Strength primarily increases with increasing grain size of the heats. This suggests that grain boundary sliding is an important deformation mode at low strain rate because of fine grain size usual with Gr.91 steel. Specifications on Ni concentration and N%/Al% ratio are newly introduced in the type II version of Gr.91 steel. They are not effective to eliminate a heat with low creep Strength.
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Assessment of Long-Term Creep Rupture Strength of T91 Steel by Multiregion Rupture Data Analysis
Journal of Pressure Vessel Technology, 2016Co-Authors: Kouichi Maruyama, J. Nakamura, Kyosuke YoshimiAbstract:Creep Rupture Strength of creep Strength enhanced ferritic steels is often overestimated, and its evaluated value has been reduced repeatedly. In this paper, the cause of the overestimation is discussed, and the creep Rupture Strength of T91 steel is assessed with its updated creep Rupture data. Effects of residual Ni concentration on the creep Rupture Strength and necessity of F factor in T91 steel are also discussed. Decrease in activation energy Q for Rupture life in long-term creep is the cause of the overestimation, since conventional time–temperature parameter (TTP) methods cannot deal with the change in Q. Due to the decrease in Q, long-term creep Rupture Strength evaluated decreases as longer-term data points are added or shorter-term data points are discarded in the conventional TTP analysis. The long-term region with small values of activation energy and stress exponent is named region L2 in this paper. Region L2 appears in all the heats of T91 steel and plate products of Gr.91 steel. Since service conditions of the T91 steel are usually in region L2, the creep Rupture Strength under the service conditions should be evaluated from the Rupture data in region L2 only. The 5 × 105 hrs Rupture Strength at 550 °C decreases from 129 MPa (evaluated from the whole data of T91 steel) to 79 MPa (evaluated from the data in region L2 only) with increasing cut-off time for data selection. The 105 hrs Rupture Strength at 600 °C also decreases from 87 MPa (whole data) to 70 MPa (region L2 only) despite sufficient number of long-term data points at 600 °C. Careful consideration on the data selection is necessary in evaluation of creep Rupture Strength of the T91 steel. A multiregion Rupture data analysis (MRA) is helpful to select data points belonging to region L2.
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prediction of breakdown transition of creep Strength in advanced high cr ferritic steels by hardness measurement of aged structures at high temperature
Key Engineering Materials, 2007Co-Authors: Hassan Ghassemi Armaki, Kouichi Maruyama, Mitsuru Yoshizawa, Masaaki IgarashiAbstract:Recent researches have shown the premature breakdown of creep Rupture Strength in long term creep region of advanced high Cr ferritic steels. As safe operation of power plants becomes a serious problem we should be able to detect and predict the breakdown transition of creep Rupture Strength. Some methods for detecting the breakdown transition have been presented till now like the measurement of reduction of area after creep Rupture and particle size of laves phase. However it will be more economic if we make use of non-destructive tests, for example, hardness testing. In this paper 3 types of ferritic steels with different Cr concentration have been studied. The results suggest that the hardness of aged structures is constant independently of exposure time in short term region, whereas the hardness breaks down in long term region. The boundary of breakdown in hardness coincides with that of breakdown in creep Rupture Strength.
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Strengthening Mechanisms of Creep Resistant Tempered Martensitic Steel
ISIJ Iternational, 2001Co-Authors: Kouichi Maruyama, Kota Sawada, Jun-ichi KoikeAbstract:The creep deformation resistance and Rupture life of high Cr ferritic steel with a tempered martensitic lath structure are critically reviewed on the basis of experimental data. Special attention is directed to the following three subjects: creep mechanism of the ferritic steel, its alloy design for further Strengthening, and loss of its creep Rupture Strength after long-term use. The high Cr ferritic steel is characterized by its fine subgrain structure with a high density of free dislocations within the subgrains. The dislocation substructure is the most densely distributed obstacle to dislocation motion in the steel. Its recovery controls creep rate and Rupture life at elevated temperatures. Improvement of creep Strength of the steel requires a fine subgrain structure with a high density of free dislocations. A sufficient number of pinning particles (MX particles in subgrain interior and M 23 C 6 particles on sub-boundaries) are necessary to cancel a large driving force for recovery due to the high dislocation density. Coarsening and agglomeration of the pinning particles have to be delayed by an appropriate alloy design of the steel. Creep Rupture Strength of the high Cr ferritic steel decreases quickly after long-term use. A significant improvement of creep Rupture Strength can be achieved if we can prevent the loss of Rupture Strength. In the steel tempered at high temperature, enhanced recovery of the subgrain structure along grain boundaries is the cause of the premature failure and the consequent loss of Rupture Strength. However, the scenario is not always applicable. Further studies are needed to solve this important problem of high Cr ferritic steel. MX particles are necessary to retain a fine subgrain structure and to achieve the excellent creep Strength of the. high Cr ferritic steel. Strengthening mechanism of the MX particles is another important problem left unsolved.
Evan Khaleghi - One of the best experts on this subject based on the ideXlab platform.
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graphene induced Strengthening in spark plasma sintered tantalum carbide nanotube composite
Scripta Materialia, 2013Co-Authors: Debrupa Lahiri, Evan Khaleghi, Eugene A. Olevsky, Srinivasa R. Bakshi, Arvind AgarwalAbstract:Transverse Rupture Strength of spark plasma sintered tantalum carbide (TaC) composites reinforced with long and short carbon nanotubes (CNTs) is reported. The Rupture Strength depends on the transformation behavior of the CNTs during spark plasma sintering, which is dependent on their length. The TaC composite with short nanotubes shows the highest specific Rupture Strength. Shorter CNTs transform into multi-layered graphene sheets between TaC grains, whereas long ones retain the tubular structure. Two-dimensionsal graphene platelets offer higher resistance to pull-out, resulting in delayed fracture and higher Strength.
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spark plasma sintering of tantalum carbide
Scripta Materialia, 2010Co-Authors: Evan Khaleghi, M A Meyers, Eugene A. OlevskyAbstract:A tantalum carbide powder was consolidated by spark plasma sintering. The specimens were processed under various temperature and pressure conditions and characterized in terms of relative density, grain size, Rupture Strength and hardness. The results are compared to hot pressing conducted under similar settings. It is shown that high densification is accompanied by substantial grain growth. Carbon nanotubes were added to mitigate grain growth; however, while increasing specimens’ Rupture Strength and final density, they had little effect on grain growth.
Kazuhiro Kimura - One of the best experts on this subject based on the ideXlab platform.
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Proceedings of CREEP8 Eighth International Conference on Creep and Fatigue at Elevated Temperatures PVP2007-26406 REGION SPLITTING ANALYSIS ON CREEP Strength ENHANCED FERRITIC STEELS
2020Co-Authors: Kazuhiro Kimura, Kota Sawada, Hideaki Kushima, Yoshiaki TodaAbstract:ABSTRACT Overestimation of long-term creep Strength of creep Strength enhanced ferritic steels is caused by inflection of a relation between stress and time to Rupture. Creep Rupture Strength of those steels has been re-evaluated by a region splitting analysis and allowable tensile stress of some steels regulated in METI (Ministry of Economy, Trade and Industry) Thermal Power Standard Code in Japan has been reduced. A region splitting analysis method evaluates creep Rupture Strength in the short-and the long-term individually, which is separated by 50% of 0.2% offset yield stress. Inflection of stress vs. time to Rupture curve is attributable to longer creep Rupture life with a stabilized microstructure of creep Strength enhanced ferritic steels, since tensile Strength property, which determines short-term creep Rupture Strength, remains the same level. Accuracy of creep Rupture Strength evaluation is improved by region splitting analysis. Delta ferrite produces concentration gap due to difference in equilibrium composition of austenite and ferrite at the normalizing temperature. It increases driving force for diffusion and promotes recovery of tempered martensite adjacent to delta-ferrite. Concentration gap may be produced also in heat affected zone (HAZ), especially in fine grain HAZ similar to that in dual phase steel, and it has possibilities to promote recovery and, therefore, to decrease creep Strength
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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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long term creep Strength and Strength reduction factor for welded joints of asme grades 91 92 and 122 type steels
International Journal of Microstructure and Materials Properties, 2011Co-Authors: Kazuhiro Kimura, Masaaki Tabuchi, Yukio Takahashi, Kazuo Yoshida, Koichi YagiAbstract:Creep Rupture data of base metal and welded joints of several creep Strength enhanced ferritic (CSEF) steels was collected and long-term creep Strength of those steels was evaluated by the SHC committee in Japan. The previous allowable tensile stress of those steels regulated in METI Thermal Power Standard Code was reviewed and weld Strength reduction factor was investigated. The master creep life equations for not only base metal, but also welded joints were developed. According to the evaluated creep Rupture Strength, allowable tensile stress of ASME Grade 122 type steels was revised in December 2005 and those of ASME Grade 91 and 92 type steels was revised in August 2007. The creep Strength reduction factor obtained from 100,000 hours creep Rupture Strength of welded joints and base metal was given as a function of temperature.
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microstructural stability and long term creep Strength of grade 91 steel
Energy Materials, 2009Co-Authors: Kazuhiro Kimura, Kota Sawada, Hideaki Kushima, Yoshiaki TodaAbstract:Abstract Long term creep Strength of ASTM grade 91 steels was investigated in conjunction with microstructural stability during creep exposure. 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. Good correspondence between long term creep Rupture Strength and nickel content was observed, and the long term creep Strength of grade 91 steel decreased with an increase in nickel content, although the nickel concentration was 0·28 mass-% in maximum. 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. Although the influence of nickel on the precipitation sequence during creep exposure is not yet clearly understood, the nickel content should be reduced in order to suppress a large drop in long term creep Strength of grade 91 ...
Kyosuke Yoshimi - One of the best experts on this subject based on the ideXlab platform.
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causes of heat to heat variation of creep Strength in grade 91 steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017Co-Authors: Kouichi Maruyama, J. Nakamura, Nobuaki Sekido, Kyosuke YoshimiAbstract:Abstract Heat-to-heat variation of creep Strength is significant in grade 91 (Gr.91) steel, but the causes of the variation have not been well understood yet. In the present paper, creep Rupture data of 14 heats of Gr.91 steel were analyzed paying attention to their chemical compositions and microstructures. The longest creep Rupture lives analyzed are 2 × 105 h at 500 and 550 °C and 105 h at 600 °C. The causes of the heat-to-heat variation are different, depending on creep test conditions. At low temperature and high stress (creep Rupture life of 104 h at 500 and 550 °C), creep Rupture Strength increases with increase of hardness after tempering. This suggests Strengthening by a fine subgrain microstructure developed during normalizing and subsequent tempering. At higher temperature and intermediate time range (104 h at 600 °C), creep Rupture Strength depends on Cr concentration of the heats in addition to the hardness. This finding suggests an important contribution of recovery process of the subgrain microstructures to creep Strength of the steel. In long-term creep (2×105 h at 550 °C and 105 h at 600 °C) creep Rupture Strength primarily increases with increasing grain size of the heats. This suggests that grain boundary sliding is an important deformation mode at low strain rate because of fine grain size usual with Gr.91 steel. Specifications on Ni concentration and N%/Al% ratio are newly introduced in the type II version of Gr.91 steel. They are not effective to eliminate a heat with low creep Strength.
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Assessment of Long-Term Creep Rupture Strength of T91 Steel by Multiregion Rupture Data Analysis
Journal of Pressure Vessel Technology, 2016Co-Authors: Kouichi Maruyama, J. Nakamura, Kyosuke YoshimiAbstract:Creep Rupture Strength of creep Strength enhanced ferritic steels is often overestimated, and its evaluated value has been reduced repeatedly. In this paper, the cause of the overestimation is discussed, and the creep Rupture Strength of T91 steel is assessed with its updated creep Rupture data. Effects of residual Ni concentration on the creep Rupture Strength and necessity of F factor in T91 steel are also discussed. Decrease in activation energy Q for Rupture life in long-term creep is the cause of the overestimation, since conventional time–temperature parameter (TTP) methods cannot deal with the change in Q. Due to the decrease in Q, long-term creep Rupture Strength evaluated decreases as longer-term data points are added or shorter-term data points are discarded in the conventional TTP analysis. The long-term region with small values of activation energy and stress exponent is named region L2 in this paper. Region L2 appears in all the heats of T91 steel and plate products of Gr.91 steel. Since service conditions of the T91 steel are usually in region L2, the creep Rupture Strength under the service conditions should be evaluated from the Rupture data in region L2 only. The 5 × 105 hrs Rupture Strength at 550 °C decreases from 129 MPa (evaluated from the whole data of T91 steel) to 79 MPa (evaluated from the data in region L2 only) with increasing cut-off time for data selection. The 105 hrs Rupture Strength at 600 °C also decreases from 87 MPa (whole data) to 70 MPa (region L2 only) despite sufficient number of long-term data points at 600 °C. Careful consideration on the data selection is necessary in evaluation of creep Rupture Strength of the T91 steel. A multiregion Rupture data analysis (MRA) is helpful to select data points belonging to region L2.
M.d. Mathew - One of the best experts on this subject based on the ideXlab platform.
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a comparison of creep Rupture Strength of ferritic austenitic dissimilar weld joints of different grades of cr mo ferritic steels
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2012Co-Authors: K Laha, K S Chandravathi, P Parameswaran, Sunil Goyal, M.d. MathewAbstract:Evaluations of creep Rupture properties of dissimilar weld joints of 2.25Cr-1Mo, 9Cr-1Mo, and 9Cr-1MoVNb steels with Alloy 800 at 823 K were carried out. The joints were fabricated by a fusion welding process employing an INCONEL 182 weld electrode. All the joints displayed lower creep Rupture Strength than their respective ferritic steel base metals, and the Strength reduction was greater in the 2.25Cr-1Mo steel joint and less in the 9Cr-1Mo steel joint. Failure location in the joints was found to shift from the ferritic steel base metal to the intercritical region of the heat-affected zone (HAZ) of the ferritic steel (type IV cracking) with the decrease in stress. At still lower stresses, the failure in the joints occurred at the ferritic/austenitic weld interface. The stress-life variation of the joints showed two-slope behavior and the slope change coincided with the occurrence of ferritic/austenitic weld interface cracking. Preferential creep cavitation in the soft intercritical HAZ induced type IV failure, whereas creep cavitation at the interfacial particles induced ferritic/austenitic weld interface cracking. Micromechanisms of the type IV failure and the ferritic/austenitic interface cracking in the dissimilar weld joint of the ferritic steels and relative cracking susceptibility of the joints are discussed based on microstructural investigation, mechanical testing, and finite element analysis (FEA) of the stress state across the joint.
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long term creep Rupture Strength prediction for modified 9cr 1mo ferritic steel and type 316l n austenitic stainless steel
Materials at High Temperatures, 2012Co-Authors: V.s. Srinivasan, B.k. Choudhary, M.d. Mathew, T. JayakumarAbstract:AbstractThe prediction of long-term creep-Rupture Strength values for mod. 9Cr –1Mo ferritic steel and 316L(N) austenitic stainless steel is made using several life prediction methodologies at 773, 823 and 873 K. Creep-Rupture Strength values have been predicted following the Larson –Miller parameter, the Orr – Sherby –Dorn parameter, artificial neural network, and Wilshire approaches for Rupture lives up to 60 years (5.2566105 h) using creep-Rupture data available in the literature. It has been demonstrated that the prediction of creep-Rupture Strength values using these approaches are comparable. Creep-Rupture Strength values have been also evaluated using linear extrapolation of average creepRupture Strength values given in French Nuclear Design Code RCC-MR for durations more than 36105 h. Predicted creep-Rupture Strength values using the literature data are found to be higher than those obtained from RCC-MR for both 9Cr –1Mo steel and 316L(N) SS. This suggested that the RCC-MR data are conservative an...
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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, 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.
