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Fujio Abe - One of the best experts on this subject based on the ideXlab platform.

  • Creep Strain Behavior in Transient Region and Minimum Creep Rate of Tempered Martensitic 9%Cr Steel
    2020
    Co-Authors: Fujio Abe
    Abstract:

    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

  • Behavior of Boron in 9Cr Heat Resistant Steel during Heat Treatment and Creep Deformation
    2016
    Co-Authors: Fujio Abe
    Abstract:

    Abstract. The effect of boron on microstructure evolution and Creep deformation behavior has been investigated for a tempered martensitic 9Cr-3W-3Co-0.2V-0.05Nb steel at 650 o C. Creep tests were carried out at 650 o C for up to about 6 x 10 4 h. The addition of boron retards the onset of acceleration Creep at low stress and long time conditions, which results in lower Minimum Creep Rate and longer time to rupture. The addition of boron also retards the Ostwald ripening of M23C6 carbides near prior austenite grain boundaries (PAGBs) during Creep. The retardation of the onset of acceleration Creep results from the retardation of the recovery of martensitic microstructure near PAGBs by pinning effects due to fine M23C6 carbides. The main effect due to boron is considered to occupy vacancies near growing M23C6 carbides, which makes it difficult to accommodate local volume change around the growing carbides. This reduces the Rate of Ostwald ripening of M23C6 carbides

  • Creep behavior deformation mechanisms and Creep life of mod 9cr 1mo steel
    Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2015
    Co-Authors: Fujio Abe
    Abstract:

    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.

  • effect of boron on microstructure and Creep strength ofadvanced ferritic power plant steels
    Procedia Engineering, 2011
    Co-Authors: Fujio Abe
    Abstract:

    Abstract The boundary and sub-boundary hardening is shown to be the most important strengthening mechanism in Creep of 9Cr steel. The soluble boron reduces the coarsening Rate of M23C6 carbides along boundaries near prior austenite grain boundaries during Creep, enhancing the boundary and sub-boundary hardening for up to long times. The enhancement of boundary and sub-boundary hardening retards the onset of acceleration Creep, which decreases the Minimum Creep Rate and improves the Creep life.Excess addition of boron and nitrogen promotes the formation of boron nitrides during normalizing heat treatment, which significantly reduces soluble boron and nitrogen concentrations and offsets the benefit due to boron and nitrogen.

  • 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, 2008
    Co-Authors: Fujio Abe
    Abstract:

    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.

Jie Yuan - One of the best experts on this subject based on the ideXlab platform.

  • tensile and compressive Creep behavior of extruded mg 10gd 3y 0 5zr wt alloy
    Materials Characterization, 2015
    Co-Authors: Huiying Wang, D D Yin, C J Boehlert, Qingzhao Wang, Jie Yuan
    Abstract:

    Abstract The tensile and compressive Creep behavior of an extruded Mg–10Gd–3Y–0.5Zr (wt.%) alloy was investigated at temperatures ranging from 200 °C to 300 °C and under stresses ranging from 30 MPa to 120 MPa. There existed an asymmetry in the tensile and compressive Creep properties. The Minimum Creep Rate of the alloy was slightly greater in tension than in compression. The measured values of the transient strain and initial Creep Rate in compression were greater than those in tension. The Creep stress exponent was approximately 2.5 at low temperatures (T

  • tensile Creep behavior and microstructure evolution of extruded mg 10gd 3y 0 5zr wt alloy
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013
    Co-Authors: Huan Wang, Qudong Wang, D D Yin, Jie Yuan
    Abstract:

    Abstract The tensile Creep behavior and microstructure evolution of the extruded Mg–10Gd–3Y–0.5Zr (wt%, GW103) alloy were investigated at temperatures from 523 K to 573 K and stresses from 30 MPa to 120 MPa. The peak-aged extruded GW103 alloy exhibited a Minimum Creep Rate ranging from 3.49×10−8 s−1 to 2.43×10−6 s−1, and the aging treatment exerted limited effect on its Creep performance. The measured stress exponent and activation energy of the peak-aged extruded alloy were 2.9±0.5 and 182.5±1.3 kJ/mol, respectively. Increasing precipitates formed during Creep, which contributed to improving its Creep-resistance. Precipitate free zones (PFZs) were observed in the tertiary stage near the boundaries which were perpendicular to the loading direction, and the formation of specially directional PFZs was demonstRated mainly stress-induced. Fractographic analysis revealed that intergranular ductile fracture was the main fracture mode after Creep rupture. The low values of stress exponent and the formation of specially directional PFZs in the extruded alloy indicated that diffusion Creep acted as a predominant mechanism.

Tresa M Pollock - One of the best experts on this subject based on the ideXlab platform.

  • Creep resistance of bulk copper niobium composites an inverse effect of multilayer length scale
    Acta Materialia, 2019
    Co-Authors: Jaclyn T Avallone, Thomas Nizolek, Benjamin B Bales, Tresa M Pollock
    Abstract:

    Abstract Metallic multilayer systems show promising performance in extreme environments, with high stability of bi-metal interfaces down to nanometer length scales. The Creep behavior of bulk, accumulative roll bonded (ARB) Copper–Niobium (Cu–Nb) composites has been studied at 400 °C as a function of layer thickness, ranging from 2 μ m to 65 n m . Similar to single phase metallic systems, three regimes are observed during Creep: transient, steady-state and tertiary. The mechanism controlling Minimum Creep Rate for all conditions tested has a strong dependence on stress, consistent with dislocation-dominated Creep. Unlike the conventional effect of grain size on Creep resistance, this study reveals that decreasing length scale increases Creep resistance.

  • Creep resistance of bulk copper niobium composites an inverse effect of multilayer length scale
    Social Science Research Network, 2019
    Co-Authors: Jaclyn T Avallone, Thomas Nizolek, Benjamin B Bales, Tresa M Pollock
    Abstract:

    Metallic multilayer systems show promising performance in extreme environments, with high stability of bi-metal interfaces down to nanometer length scales. The Creep behavior of bulk, accumulative roll bonded (ARB) Copper-Niobium (Cu-Nb) composites has been studied at 400°C as a function of layer thickness, ranging from 2 microns to 65 nanometers. Similar to single phase metallic systems, three regimes are observed during Creep: transient, steady-state and tertiary. The mechanism controlling Minimum Creep Rate for all conditions tested has a strong dependence on stress, consistent with dislocation-dominated Creep. Unlike the conventional effect of grain size on Creep resistance, this study reveals that decreasing length scale increases Creep resistance.

  • The Dependence of Creep Behavior on Elemental Partitioning in Mg-5Al-3Ca-xSn Alloys
    Metallurgical and Materials Transactions A, 2012
    Co-Authors: Jessica R. Terbush, Olivia H. Chen, J. Wayne Jones, Tresa M Pollock
    Abstract:

    Cast Mg-5Al-3Ca- x Sn alloys have been examined to investigate the effect of Sn additions on elemental partitioning during solidification, microstructure development, and compressive Creep behavior at 453 K (180 °C). Alloys containing 0.25 to 3.0 wt pct Sn were cast with a permanent mold technique. The addition of 0.75 to 1.0 wt pct Sn had a beneficial effect on Ca partitioning to the α -Mg phase. Additions beyond 1 wt pct Sn resulted in the formation of an orthorhombic Mg-Ca-Sn phase, with decreased Ca partitioning to the α -Mg. A lower Minimum Creep Rate was observed for the Mg-5Al-3Ca- x Sn alloy with increased Ca partitioning. Consistent with this finding, analyses that consider the influence of solute and precipitation strengthening on Creep in Mg-5Al-3Ca- x Sn alloys suggest that Ca in the α -Mg contributes to a greater degree than Al in solution to the Creep resistance at 453 K (180 °C).

M.d. Mathew - One of the best experts on this subject based on the ideXlab platform.

  • Creep properties of grade 91 steel steam generator tube at 923k
    Procedia Engineering, 2013
    Co-Authors: D Rao P Palaparti, Isaac E Samuel, M.d. Mathew
    Abstract:

    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.

  • Creep deformation and rupture behaviour of p92 steel at 923 k
    Procedia Engineering, 2013
    Co-Authors: Isaac E Samuel, D Rao P Palaparti, B K Choudhary, M.d. Mathew
    Abstract:

    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.

  • 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, 2012
    Co-Authors: J Vanaja, K Laha, R Mythili, K S Chandravathi, S Saroja, M.d. Mathew
    Abstract:

    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.

  • tensile and Creep properties of reduced activation ferritic martensitic steel for fusion energy application
    Journal of Nuclear Materials, 2011
    Co-Authors: M.d. Mathew, J Vanaja, K Laha, K S Chandravathi, Varaprasad G Reddy, Bhanu Sankara K Rao
    Abstract:

    Abstract Tensile and Creep properties of a reduced activation ferritic–martensitic (RAFM) steel for Indian Test Blanket Module (TBM) to be tested in ITER have been evaluated. The tensile strength was found to decrease with temperature; the Rate of decrease being slower in the intermediate temperature range of 450–650 K. Tensile ductility of the steel decreased with increase in temperature up to 650 K, followed by a rapid increase beyond 650 K. Creep studies have been carried out at 773, 823 and 873 K over a stress range of 100–300 MPa. The variation of Minimum Creep Rate with applied stress followed a power law, e ´ m  = Aσn. The ‘n’ value decreased with increase in temperature. The Creep rupture life was found to relate inversely with Minimum Creep Rate through the Monkman–Grant relation, tr ·  e ´ m  = constant. The tensile and Creep properties of the steel were comparable with those of Eurofer 97.

Zhuangqi Hu - One of the best experts on this subject based on the ideXlab platform.

  • effect of mo concentration on Creep properties of a single crystal nickel base superalloy
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2010
    Co-Authors: Jinguo Li, Zhuangqi Hu
    Abstract:

    The effect of Mo concentration on Creep properties of a single crystal nickel-base superalloy has been studied at 1010 degrees C and 800 degrees C by using three kinds of alloys with 1%, 2% and 4% of Mo (wt.). The Creep properties of alloys were measured and microstructure evolution was analyzed. The results showed that after heat treatment, all the three alloys were composed of gamma and gamma' phase without TCP phase precipitation. The increase of Mo concentration from 1 wt.% to 2 wt.% pronouncedly enhanced the Creep properties. Compared with 1 wt.% Mo content, 2 wt.% Mo addition can geneRate denser gamma/gamma' interfacial dislocation networks during high temperature Creep test, thus lower Minimum Creep Rate. At medium temperature Creep condition, Mo addition enhanced Creep properties by decreasing the stacking fault energy. When the Mo content reached to 4%, the over-saturation of Mo content in gamma phase led to the formation of p. phase precipitation which degraded the Creep properties at both high and medium temperature Creep conditions. (C) 2010 Elsevier B.V. All rights reserved.