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Fujio Abe - One of the best experts on this subject based on the ideXlab platform.
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Creep Strain Behavior in Transient Region and Minimum Creep Rate of Tempered Martensitic 9%Cr Steel
2020Co-Authors: Fujio AbeAbstract:Abstract. The effect of fine precipitates, excess dislocations and sub-boundary hardening on Creep strain behavior in the transient region has been investigated for tempered martensitic 9%Cr steel at 600 and 650 o C. The fine precipitates that form during tempering or during Creep decrease the Creep Rate in the transient region, while excess dislocations produced by cold rolling promote the recovery of dislocations during Creep, resulting in higher Creep Rates. The sub-boundary hardening is enhanced by fine precipitates along lath and block boundaries, which retards the onset of acceleration Creep. The movement and annihilation process of dislocations in the transient region is controlled by not only the movement of dislocations in the matrix but also the absorption of dislocations at boundaries. The minimum Creep Rate is basically determined by the time to minimum Creep Rate
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Creep behavior deformation mechanisms and Creep life of mod 9cr 1mo steel
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2015Co-Authors: Fujio AbeAbstract:The Creep behavior, deformation mechanisms, and the correlation between Creep deformation parameters and Creep life have been investigated for Mod.9Cr-1Mo steel (Gr.91, 9Cr-1Mo-VNb) by analyzing Creep strain data at 723 K to 998 K (450 °C to 725 °C), 40 to 450 MPa, and t r = 11.4 to 68,755 hours in NIMS Creep Data Sheet. The time to rupture t r is reasonably correlated with the minimum Creep Rate $$ {\dot{\varepsilon }}_{ \hbox{min} } $$ and the acceleration of Creep Rate by strain in the acceleration region dln $$ {\dot{\varepsilon }} $$ /d e, as t r = 1.5/[ $$ {\dot{\varepsilon }}_{ \hbox{min} } $$ (dln $$ {\dot{\varepsilon }} $$ /d e)], where $$ {\dot{\varepsilon }}_{ \hbox{min} } $$ and dln $$ {\dot{\varepsilon }} $$ /d e reflect the Creep behavior in the transient and acceleration regions, respectively. The $$ {\dot{\varepsilon }}_{ \hbox{min} } $$ is inversely proportional to the time to minimum Creep Rate t m, while it is proportional to the strain to minimum Creep Rate e m, as $$ {\dot{\varepsilon }}_{ \hbox{min} } $$ = 0.54 (e m/t m). The e m decreases with decreasing stress, suggesting that the Creep deformation in the transient region becomes localized in the vicinity of prior austenite grain boundaries with decreasing stress. The duration of acceleration region is proportional to the duration of transient region, while the dln $$ {\dot{\varepsilon }} $$ /d e is inversely proportional to the e m. The t r is also correlated with the t m, as t r = g t m, where g is a constant. The present Creep life equations reasonably predict the degradation in Creep rupture strength at long times. The downward deviation takes place in the t r vs $$ {\dot{\varepsilon }}_{ \hbox{min} } $$ curves (Monkman–Grant plot). At the same $$ {\dot{\varepsilon }}_{ \hbox{min} } $$ , both the e m and t m change upon the condition of t m ∝ e m. The decrease in e m with decreasing stress, corresponding to decreasing $$ {\dot{\varepsilon }}_{ \hbox{min} } $$ , causes a decrease in t m, indicating the downward deviation of the t r vs $$ {\dot{\varepsilon }}_{ \hbox{min} } $$ curves.
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stress to produce a minimum Creep Rate of 10 5 h and stress to cause rupture at 105h for ferritic and austenitic steels and superalloys
International Journal of Pressure Vessels and Piping, 2008Co-Authors: Fujio AbeAbstract:Abstract Long-term Creep and rupture data of NIMS Creep Data Sheets show that the time to rupture at a minimum Creep Rate of 10 −5 %/h is longer than 10 5 h for most ferritic steels, while it is shorter than 10 5 h for most austenitic steels, Ni base and Co base superalloys. This is correlated with the larger total elongation in ferritic steels than in austenitic steels and in Ni base and Co base superalloys at a minimum Creep Rate of 10 −5 %/h. However, 67% of the average stress to cause rupture at the end of 10 5 h is lower than the stress to produce a minimum Creep Rate of 10 −5 %/h for all the materials examined. This indicates that the ASME allowable stress in a high-temperature Creep region is determined by Creep rupture data but not by Creep strain data. The Creep and Creep Rate curves are compared between 2.25Cr–1Mo steel and 18Cr–8Ni austenitic steel at approximately the same minimum Creep Rate. 18Cr–8Ni austenitic steel reaches a minimum Creep Rate in shorter time and spends shorter time in the acceleration Creep before Creep rupture than 2.25Cr–1Mo steel at low stress and long time conditions. This is correlated with different microstructure evolution during Creep.
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effect of fine precipitation and subsequent coarsening of fe2w laves phase on the Creep deformation behavior of tempered martensitic 9cr w steels
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2005Co-Authors: Fujio AbeAbstract:The effect of fine precipitation and subsequent coarsening of Fe2W Laves phase on the Creep deformation behavior was investigated for simple 9Cr-W steels containing 0, 1, 2, and 4 wt pct W. After tempering, the specimens were subjected to Creep tests at 823, 873, and 923 K for up to 15,000 hours. The precipitation of Fe2W Laves phase takes place during Creep at boundaries from the supersatuRated solid solution of the high-W steels, the 9Cr-2W and 9Cr-4W steels, but not in the low-W steels, the 9Cr-0W and 9Cr-1W steels. The fine precipitation of Fe2W Laves phase decreases the Creep Rate in the primary or transient Creep region, while the subsequent large coarsening of Fe2W Laves phase reduces the precipitation strengthening and promotes the acceleration of Creep Rate in the tertiary or acceleration Creep region after reaching a minimum Creep Rate. The change in shape of Creep Rate curves with stress and temperature is explained by taking fine precipitation and subsequent coarsening of Fe2W Laves phase into account.
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contribution of coarsening of mx carbonitrides to Creep strength degradation in high chromium ferritic steel
Materials Science and Technology, 2003Co-Authors: Kota Sawada, K Kubo, Fujio AbeAbstract:AbstractThe coarsening process of MX carbonitrides during Creep and its effect on Creep behaviour have been investigated for P92 steel (9Cr-0.5Mo-1.8W-VNb). At 1023 K after long term aging, Creep rupture strength and tertiary stage Creep Rate rapidly decrease and increase, respectively. The stress exponent n of minimum Creep Rate decreases with increasing temperature, and the value of n at 1023 K was evaluated to be 5.7. MX carbonitrides coarsen during Creep and the coarsening process corresponds to the early stage of Ostwald ripening. Creep deformation acceleRates the coarsening of the MX carbonitrides. At 1023 K, the coherent strain between the MX carbonitrides and matrix reduces to a negligibly small value at times longer than 550 h, leading to a decrease in the resistance to dislocation motion. This contributes to the rapid increase of Creep Rate in the tertiary stage and the abrupt decrease of Creep rupture strength in the long term.
Henricus J M Bouwmeester - One of the best experts on this subject based on the ideXlab platform.
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influence of thermal history on the cubic to hexagonal phase transformation and Creep behaviour of ba0 5sr0 5co0 8fe0 2o3 ceramics
Journal of Membrane Science, 2011Co-Authors: Bogdan Rutkowski, Jurgen Malzbender, R W Steinbrech, Tilmann Beck, Henricus J M BouwmeesterAbstract:Abstract The influence of the partial cubic-to-hexagonal phase transformation of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) on the Creep behaviour of this perovskite-type oxygen transport membrane was investigated. Isothermal compressive Creep tests were carried out in air in the temperature range 750–950 °C. Arrhenius plots of the Creep Rate revealed a significant hysteresis effect. During heating, the Creep Rate changed slightly up to about 850 °C and increased substantially above this temperature. Upon cooling from 950 °C it decreased in a nearly linear manner to temperature. Microstructural investigations support the conclusion that the hysteresis is linked with the growth and transformation kinetics of the hexagonal polymorph at the boundaries of cubic grains of BSCF.
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high temperature compressive Creep behaviour of the perovskite type oxide ba0 5sr0 5co0 8fe0 2o3 δ
Solid State Ionics, 2009Co-Authors: Hilde Lea Lein, Tor Grande, S Yakovlev, Henricus J M BouwmeesterAbstract:Compressive Creep tests have been performed on perovskite-type Ba0.5Sr0.5Co0.8Fe0.2O3 − δ ceramics. The activation energy, stress exponent and inverse grain size exponent of the steady-state Creep Rates are evaluated at p(O2) = 0.21 ∙ 105 Pa and 0.01 ∙ 105 Pa in the stress, temperature and grain size ranges 5–20 MPa, 1078–1208 K and 2.5–17.4 µm, respectively. The results indicate that the Creep Rate of Ba0.5Sr0.5Co0.8Fe0.2O3 − δ is controlled by diffusion of cations via both the oxide lattice (bulk diffusion) and along grain boundaries. The Creep Rate of Ba0.5Sr0.5Co0.8Fe0.2O3 − δ increases profoundly by more than one order of magnitude at 1153–1178 K, which is tentatively linked with the onset of the hexagonal-to-cubic phase transition in this compound.
M.d. Mathew - One of the best experts on this subject based on the ideXlab platform.
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Creep properties of grade 91 steel steam generator tube at 923k
Procedia Engineering, 2013Co-Authors: D Rao P Palaparti, Isaac E Samuel, M.d. MathewAbstract:Abstract Creep-rupture properties of T91 steam generator (SG) tube steel have been examined at 923 K in normalised and tempered condition in the stress range 55-150 MPa. At all stress conditions, the Creep deformation was characterised by a decrease in Creep Rate in the transient Creep followed by a minimum Creep Rate in secondary Creep and a rapid increase in Creep Rate in tertiary Creep stage. A systematic decrease in Creep Rate with decreasing stress was observed in transient, secondary and tertiary Creep. Stress dependence of minimum Creep Rate and rupture life obeyed power law Creep. Both minimum Creep Rate and rupture life exhibited deviations in terms of lower respective stress exponent values at low stresses than those obtained at high stresses. A decrease in Creep ductility was observed with increase in rupture life. The fracture mode remained transgranular at all test conditions. Creep-rupture strength of SG tube steel has been found to be comparable to those reported in literature as well as specified in French Nuclear Design Code, RCC-MR for the steel.
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Creep deformation and rupture behaviour of p92 steel at 923 k
Procedia Engineering, 2013Co-Authors: Isaac E Samuel, D Rao P Palaparti, B K Choudhary, M.d. MathewAbstract:Abstract Creep deformation and rupture behaviour of P92 steel has been examined at 923 K for stresses ranging from 75 to 150 MPa. The steel exhibited well defined primary, secondary characterized by minimum Creep Rate and prolonged tertiary Creep stages. The stress dependence of minimum Creep Rate obeyed Norton's power law and exhibited distinct stress regimes characterised by sepaRate values of stress exponents in low and high stress regimes. Similarly, the stress dependence of rupture life also obeyed power law and displayed two stress regimes with sepaRate stress exponent values. The steel displayed decrease in Creep ductility with increase in rupture life in the low stress regime and followed generalised Monkman-Grant relation interrelating minimum Creep Rate and rupture life. Modified Monkman-Grant relation has been found to be valid for the steel. Fractographic examination indicated dominance of transgranular fracture on the fracture surfaces of tested specimens.
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Creep deformation and rupture behaviour of 9cr 1w 0 2v 0 06ta reduced activation ferritic martensitic steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2012Co-Authors: J Vanaja, K Laha, R Mythili, K S Chandravathi, S Saroja, M.d. MathewAbstract:Abstract This paper presents the Creep deformation and rupture behaviour of indigenously produced 9Cr–1W–0.2V–0.06Ta Reduced Activation Ferritic–Martensitic (RAFM) steel for fusion reactor application. Creep studies were carried out at 773, 823 and 873 K over a stress range of 100–300 MPa. The Creep deformation of the steel was found to proceed with relatively shorter primary regime followed by an extended tertiary regime with virtually no secondary regime. The variation of minimum Creep Rate of the material with applied stress followed a power law relation, έ m = Aσ n , with stress exponent value ‘ n ’ decreasing with increase in temperature. The product of minimum Creep Rate and Creep rupture life was found to obey the modified Monkman–Grant relation. The time to onset of tertiary stage of deformation was directly proportional to rupture life. TEM studies revealed relatively large changes in martensitic sub-structure and coarsening of precipitates in the steel on Creep exposure as compared to thermal exposure. Microstructural degradation was considered as the prime cause of extended tertiary stage of Creep deformation, which was also reflected in the damage tolerance factor λ with a value more than 2.5. In view of the microstructural instability of the material on Creep exposure, the variation of minimum Creep Rate with stress and temperature did not obey Dorn's equation modified by invoking Lagneborg and Bergman's concepts of back stress.
J Vanaja - One of the best experts on this subject based on the ideXlab platform.
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assessment of tungsten content on tertiary Creep deformation behavior of reduced activation ferritic martensitic steel
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2015Co-Authors: J VanajaAbstract: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, \( \varepsilon = \varepsilon_{\text{o}} + \dot{\varepsilon }_{\text{m}} t + \varepsilon_3{\exp }\left[ {p\left( {t - t_{\text{t}} } \right)} \right] \), considering minimum Creep Rate (\( \dot{\varepsilon }_{\text{m}} \)) 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 \( \dot{\varepsilon }_{\text{f}} \) 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.
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Creep deformation and rupture behaviour of 9cr 1w 0 2v 0 06ta reduced activation ferritic martensitic steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2012Co-Authors: J Vanaja, K Laha, R Mythili, K S Chandravathi, S Saroja, M.d. MathewAbstract:Abstract This paper presents the Creep deformation and rupture behaviour of indigenously produced 9Cr–1W–0.2V–0.06Ta Reduced Activation Ferritic–Martensitic (RAFM) steel for fusion reactor application. Creep studies were carried out at 773, 823 and 873 K over a stress range of 100–300 MPa. The Creep deformation of the steel was found to proceed with relatively shorter primary regime followed by an extended tertiary regime with virtually no secondary regime. The variation of minimum Creep Rate of the material with applied stress followed a power law relation, έ m = Aσ n , with stress exponent value ‘ n ’ decreasing with increase in temperature. The product of minimum Creep Rate and Creep rupture life was found to obey the modified Monkman–Grant relation. The time to onset of tertiary stage of deformation was directly proportional to rupture life. TEM studies revealed relatively large changes in martensitic sub-structure and coarsening of precipitates in the steel on Creep exposure as compared to thermal exposure. Microstructural degradation was considered as the prime cause of extended tertiary stage of Creep deformation, which was also reflected in the damage tolerance factor λ with a value more than 2.5. In view of the microstructural instability of the material on Creep exposure, the variation of minimum Creep Rate with stress and temperature did not obey Dorn's equation modified by invoking Lagneborg and Bergman's concepts of back stress.
Yu Sik Kong - One of the best experts on this subject based on the ideXlab platform.
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Statistical properties of Creep rupture data distribution for STS304 stainless steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Yu Sik KongAbstract:Abstract The aim of the work is the investigation of the statistical properties of short-term Creep rupture characteristic values in STS304 stainless steels. From short-term Creep rupture tests performed by constant stresses at three different elevated temperatures 600, 650 and 700 °C, the scatter characteristics of short-term Creep rupture data, and the probability distribution characteristics were examined for rupture time, total Creep Rate, steady state Creep Rate and initial strain. The influence of temperature on the statistical scatters (coefficient of variation) of rupture time, initial strain and total Creep Rate generally decreased with increasing Creep testing temperature. The influence of stress on the statistical scatter (coefficient of variation) of rupture time was smaller with increasing stresses. The probability distribution functions (PDFs) of short-term Creep rupture data were well followed 2-parameter Weibull distribution.
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On Statistical Properties of High Temperature Creep Rupture Data in STS304 Stainless Steels
Key Engineering Materials, 2006Co-Authors: Yu Sik Kong, Won Taek JungAbstract:This paper deals with the statistical properties of short time Creep rupture characteristic values (for example, Creep rupture time, steady state Creep Rate, total Creep Rate, initial strain, etc.) in STS304 stainless steels. From short time Creep rupture tests performed by constant stresses at three different elevated temperatures 600, 650 and 700, the scatter and probability distributions were investigated for rupture time, total Creep Rate, steady state Creep Rate, initial strain, and others. The effect of temperature on the statistical scatter of rupture time was the smallest at 700. The effect of stress on the statistical scatter of rupture time was smaller with increasing stresses. The probability distributions of short time Creep rupture data were well followed 2-parameter Weibull.