The Experts below are selected from a list of 24 Experts worldwide ranked by ideXlab platform
Dierk Raabe - One of the best experts on this subject based on the ideXlab platform.
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formation of eta carbide in ferrous martensite by room temperature aging
Acta Materialia, 2018Co-Authors: Michael Herbig, Christian Liebscher, Lutz Morsdorf, Ross K W Marceau, Gerhard Dehm, Dierk RaabeAbstract:Abstract For several decades, the formation of carbon(C)-rich domains upon room temperature aging of supersaturated martensite has been a matter of debate. C-rich tweed-like patterns are observed to form after short aging times at room temperature and coarsen upon further aging. Here, we present a systematic atomic-scale investigation of carbide formation in Fe-15Ni-1C (wt.%) martensite after two to three years of isothermal room temperature aging by a combination of atom probe tomography and transmission electron microscopy. Owing to the sub-zero martensite start temperature of −25 °C, a fully austenitic microstructure is maintained at room temperature and the martensitic phase transformation is initiated during quenching in liquid nitrogen. In this way, any diffusion and redistribution of C in martensite is suppressed until heating up the specimen and holding it at room temperature. The microstructural changes that accompany the rearrangement of C atoms have been systematically investigated under controlled isothermal conditions. Our results show that after prolonged room temperature aging nanometer-sized, plate-shaped η-Fe2C carbides form with a macroscopic martensite habit plane close to {521}. The orientation relationship between the η-Fe2C carbides and the parent martensite grain (α′) follows [001]α’//[001]η, ( 1 ¯ 10 ) α’//(020)η. The observation of η-Fe2C–carbide formation at room temperature is particularly interesting, as transition carbides have so far only been reported to form above 100 °C. After three years of room temperature aging a depletion of Fe is observed in the η carbide while Ni remains distributed homogenously. This implies that the Substitutional Element Fe can diffuse several nanometers in martensite at room temperature within three years.
Takashi Ishikawa - One of the best experts on this subject based on the ideXlab platform.
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calculation for grain growth rate of carbon steels by solute drag model considering segregation effect of each Substitutional Element
Materials Science and Technology, 2011Co-Authors: Yasuhiro Yogo, Kouji Tanaka, Hideaki Ikehata, Noritoshi Iwata, Koukichi Nakanishi, Takashi IshikawaAbstract:Based on the solute drag model, a practical model incorporating the segregation effect is proposed to calculate grain growth rates in carbon steels. The segregation effect is modelled using two factors: the difference in atomic diameter between a solvent and a Substitutional Element, and the solubility of a Substitutional Element. By including the segregation energy, the proposed model enables the simulated retardation of grain growth by the addition of microalloying Elements. The calculated grain growth rate by the proposed model shows reasonable correspondence between grain growth rates for experimental and calculated results. The temperature dependence of the grain growth rate is also well simulated.
Yasuya Ohmori - One of the best experts on this subject based on the ideXlab platform.
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pearlite to austenite transformation in an fe 2 6cr 1c alloy
Acta Materialia, 1999Co-Authors: D V Shtansky, Kiyomichi Nakai, Yasuya OhmoriAbstract:Abstract The mechanism of austenite formation, the kinetics of cementite lamellae dissolution and the crystallography of the austenitization from pearlite have been studied in an Fe–2.6 wt% Cr–0.96 wt% C alloy. Austenite grains nucleate after rather long incubation time both at pearlite colony boundaries and at the ferrite/cementite interfaces within a pearlite. Characteristic morphologies of transformation products were observed at various stages of transformation. Particular attention was paid to the structural evolution close to the α / γ interfaces. No indications of the diffusion ahead of the α / γ interface were found. The kinetics of austenite growth is controlled initially by carbon diffusion but in later stages by chromium diffusion. The results are discussed by assuming local equilibrium at the moving interfaces with the software and database ThermoCalc. The method involves the driving force determination for the diffusion of carbon and Substitutional Element during austenitization. The orientation relationships between ferrite, martensite and cementite were also determined. The possible austenite orientations were evaluated assuming the α / θ , α / γ and γ / θ orientation relationships so far obtained.
Michael Herbig - One of the best experts on this subject based on the ideXlab platform.
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formation of eta carbide in ferrous martensite by room temperature aging
Acta Materialia, 2018Co-Authors: Michael Herbig, Christian Liebscher, Lutz Morsdorf, Ross K W Marceau, Gerhard Dehm, Dierk RaabeAbstract:Abstract For several decades, the formation of carbon(C)-rich domains upon room temperature aging of supersaturated martensite has been a matter of debate. C-rich tweed-like patterns are observed to form after short aging times at room temperature and coarsen upon further aging. Here, we present a systematic atomic-scale investigation of carbide formation in Fe-15Ni-1C (wt.%) martensite after two to three years of isothermal room temperature aging by a combination of atom probe tomography and transmission electron microscopy. Owing to the sub-zero martensite start temperature of −25 °C, a fully austenitic microstructure is maintained at room temperature and the martensitic phase transformation is initiated during quenching in liquid nitrogen. In this way, any diffusion and redistribution of C in martensite is suppressed until heating up the specimen and holding it at room temperature. The microstructural changes that accompany the rearrangement of C atoms have been systematically investigated under controlled isothermal conditions. Our results show that after prolonged room temperature aging nanometer-sized, plate-shaped η-Fe2C carbides form with a macroscopic martensite habit plane close to {521}. The orientation relationship between the η-Fe2C carbides and the parent martensite grain (α′) follows [001]α’//[001]η, ( 1 ¯ 10 ) α’//(020)η. The observation of η-Fe2C–carbide formation at room temperature is particularly interesting, as transition carbides have so far only been reported to form above 100 °C. After three years of room temperature aging a depletion of Fe is observed in the η carbide while Ni remains distributed homogenously. This implies that the Substitutional Element Fe can diffuse several nanometers in martensite at room temperature within three years.
W Y Yang - One of the best experts on this subject based on the ideXlab platform.
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effect of the alloying Element chromium on the room temperature ductility of fe3al intermetallics
Intermetallics, 2001Co-Authors: Y.d. Huang, W Y YangAbstract:Abstract The effect of the alloying Element chromium on the room temperature ductility of Fe 3 Al intermetallics has been investigated by considering its effect on (1) intrinsic ductility related to the microstructure, etc.; (2) extrinsic ductility related to the surface state. Based on the dissociation energy, the effect of atom interactions on the room temperature ductility is discussed after considering the site occupation of the Substitutional Element Cr at sublattice sites in DO 3 type stoichiometric Fe 3 Al intermetallics. The deduced results are in good agreement with those obtained from tensile tests of the samples with different structure and surface states in air and vacuum, and the observation of slip traces and APB trails left by imperfect dislocation slipping.
