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Levente Vitos - One of the best experts on this subject based on the ideXlab platform.
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stacking fault energies in Austenitic Stainless Steels
Acta Materialia, 2016Co-Authors: Jun Lu, Levente Vitos, Lars Hultman, Erik Holmstrom, Karin H Antonsson, Mikael Grehk, Wei Li, Ardeshir GolpayeganiAbstract:Abstract We measure the stacking fault energy of a set of 20 at% Cr-Austenitic Stainless Steels by means of transmission electron microscopy using the weak beam dark field imaging technique and the isolated dislocations method. The measurements are analyzed together with first principles calculations. The results show that experiment and theory agree very well for the investigated concentration range of Mn (0–8%) and Ni (11–30%). The calculations show that simultaneous relaxation of atomic and spin degrees of freedom is important in order to find the global energy minimum for these materials. Our results clearly show the great potential of the weak beam dark field technique to obtain accurate measurements of the stacking fault energy of Austenitic Steels and that the reliable predictability of first principles calculations can be used to design new Steels with optimized mechanical properties.
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stacking fault energies of mn co and nb alloyed Austenitic Stainless Steels
Acta Materialia, 2011Co-Authors: Song Lu, Levente Vitos, Börje Johansson, Qingmiao HuAbstract:The alloying effects of Mn, Co and Nb on the stacking fault energy (SFE) of Austenitic Stainless Steels, Fe–Cr–Ni with various Ni contents, are investigated via quantum–mechanical first-principles calculations. In the composition range (cCr = 20%, 8 6 cNi 6 20%, 0 6 cMn, cCo, cNb 6 8%, balance Fe) studied here, it is found that Mn always decreases the SFE at 0 K but increases it at room temperature in high-Ni (cNi J 16%) alloys. The SFE always decreases with increasing Co content. Niobium increases the SFE significantly in low-Ni alloys; however, this effect is strongly diminished in high-Ni alloys. The SFE-enhancing effect of Ni usually observed in Fe–Cr–Ni alloys is inverted to an SFE-decreasing effect by Nb for cNb J 3%. The revealed nonlinear composition dependencies are explained in terms of the peculiar magnetic contributions to the total SFE. 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Stacking fault energy and magnetism in Austenitic Stainless Steels
Physica Scripta, 2008Co-Authors: Levente Vitos, J. O. Nilsson, Pavel A. Korzhavyi, B JohanssonAbstract:The stacking fault energies are used to illustrate the footprint of magnetism on the mechanical properties of Fe–Cr–Ni alloys forming the basis of Austenitic Stainless Steels. We find that the usual chemical effects of alloying additions are accompanied by major magnetic effects, which stabilize the most common industrial alloy Steels at normal service temperatures. We suggest that part of the uncertainties associated with the experimental data on the stacking fault energies are due to the strong concentration and temperature dependence originating from the persisting local magnetic moments.
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alloying effects on the stacking fault energy in Austenitic Stainless Steels from first principles theory
Acta Materialia, 2006Co-Authors: Levente Vitos, Börje Johansson, Janolof NilssonAbstract:The stacking fault energy (SFE) of Austenitic Stainless Steels has been determined using a quantum mechanical first-principles approach. We identify the electronic, magnetic and volume effects responsible for the compositional dependence of the SFE. We find that both the alloying element and the composition of the host material are important for understanding the alloying effects. Our results show that no simple and universally valid composition equations exist for the SFE.
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Alloying effects on the stacking fault energy in Austenitic Stainless Steels from first-principles theory
Acta Materialia, 2006Co-Authors: Levente Vitos, J. O. Nilsson, B JohanssonAbstract:The stacking fault energy (SFE) of Austenitic Stainless Steels has been determined using a quantum mechanical first-principles approach. We identify the electronic, magnetic and volume effects responsible for the compositional dependence of the SFE. We find that both the alloying element and the composition of the host material are important for understanding the alloying effects. Our results show that no simple and universally valid composition equations exist for the SFE. © 2006 Acta Materialia Inc.
Börje Johansson - One of the best experts on this subject based on the ideXlab platform.
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stacking fault energies of mn co and nb alloyed Austenitic Stainless Steels
Acta Materialia, 2011Co-Authors: Song Lu, Levente Vitos, Börje Johansson, Qingmiao HuAbstract:The alloying effects of Mn, Co and Nb on the stacking fault energy (SFE) of Austenitic Stainless Steels, Fe–Cr–Ni with various Ni contents, are investigated via quantum–mechanical first-principles calculations. In the composition range (cCr = 20%, 8 6 cNi 6 20%, 0 6 cMn, cCo, cNb 6 8%, balance Fe) studied here, it is found that Mn always decreases the SFE at 0 K but increases it at room temperature in high-Ni (cNi J 16%) alloys. The SFE always decreases with increasing Co content. Niobium increases the SFE significantly in low-Ni alloys; however, this effect is strongly diminished in high-Ni alloys. The SFE-enhancing effect of Ni usually observed in Fe–Cr–Ni alloys is inverted to an SFE-decreasing effect by Nb for cNb J 3%. The revealed nonlinear composition dependencies are explained in terms of the peculiar magnetic contributions to the total SFE. 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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alloying effects on the stacking fault energy in Austenitic Stainless Steels from first principles theory
Acta Materialia, 2006Co-Authors: Levente Vitos, Börje Johansson, Janolof NilssonAbstract:The stacking fault energy (SFE) of Austenitic Stainless Steels has been determined using a quantum mechanical first-principles approach. We identify the electronic, magnetic and volume effects responsible for the compositional dependence of the SFE. We find that both the alloying element and the composition of the host material are important for understanding the alloying effects. Our results show that no simple and universally valid composition equations exist for the SFE.
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Elastic property maps of Austenitic Stainless Steels.
Physical Review Letters, 2002Co-Authors: Levente Vitos, Pavel A. Korzhavyi, Börje JohanssonAbstract:The most recent advances in theory and methodology are directed towards obtaining a quantitative description of the electronic structure and physical properties of alloy Steels. Specifically, we employ ab initio alloy theories to map the elastic properties of Austenitic Stainless Steels as a function of chemical composition. The so generated data can be used in the search for new steel grades, and, as an example, we predict two basic compositions with outstanding properties among the Austenitic Stainless Steels.
Michihiko Nagumo - One of the best experts on this subject based on the ideXlab platform.
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hydrogen embrittlement of Austenitic Stainless Steels revealed by deformation microstructures and strain induced creation of vacancies
Acta Materialia, 2014Co-Authors: Masaharu Hatano, Masaki Fujinami, H. Fujii, K Arai, Michihiko NagumoAbstract:Abstract Hydrogen embrittlement of Austenitic Stainless Steels has been examined with respect to deformation microstructures and lattice defects created during plastic deformation. Two types of Austenitic Stainless Steels, SUS 304 and SUS 316L, uniformly hydrogen-precharged to 30 mass ppm in a high-pressure hydrogen environment, are subjected to tensile straining at room temperature. A substantial reduction of tensile ductility appears in hydrogen-charged SUS 304 and the onset of fracture is likely due to plastic instability. Fractographic features show involvement of plasticity throughout the crack path, implying the degradation of the Austenitic phase. Electron backscatter diffraction analyses revealed prominent strain localization enhanced by hydrogen in SUS 304. Deformation microstructures of hydrogen-charged SUS 304 were characterized by the formation of high densities of fine stacking faults and e-martensite, while tangled dislocations prevailed in SUS 316L. Positron lifetime measurements have revealed for the first time hydrogen-enhanced creation of strain-induced vacancies rather than dislocations in the Austenitic phase and more clustering of vacancies in SUS 304 than in SUS 316L. Embrittlement and its mechanism are ascribed to the decrease in stacking fault energies resulting in strain localization and hydrogen-enhanced creation of strain-induced vacancies, leading to premature fracture in a similar way to that proposed for ferritic Steels.
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Hydrogen embrittlement of Austenitic Stainless Steels revealed by deformation microstructures and strain-induced creation of vacancies
Acta Materialia, 2014Co-Authors: Masaharu Hatano, Masaki Fujinami, H. Fujii, K Arai, Michihiko NagumoAbstract:Hydrogen embrittlement of Austenitic Stainless Steels has been examined with respect to deformation microstructures and lattice defects created during plastic deformation. Two types of Austenitic Stainless Steels, SUS 304 and SUS 316L, uniformly hydrogen-precharged to 30 mass ppm in a high-pressure hydrogen environment, are subjected to tensile straining at room temperature. A substantial reduction of tensile ductility appears in hydrogen-charged SUS 304 and the onset of fracture is likely due to plastic instability. Fractographic features show involvement of plasticity throughout the crack path, implying the degradation of the Austenitic phase. Electron backscatter diffraction analyses revealed prominent strain localization enhanced by hydrogen in SUS 304. Deformation microstructures of hydrogen-charged SUS 304 were characterized by the formation of high densities of fine stacking faults and ε-martensite, while tangled dislocations prevailed in SUS 316L. Positron lifetime measurements have revealed for the first time hydrogen-enhanced creation of strain-induced vacancies rather than dislocations in the Austenitic phase and more clustering of vacancies in SUS 304 than in SUS 316L. Embrittlement and its mechanism are ascribed to the decrease in stacking fault energies resulting in strain localization and hydrogen-enhanced creation of strain-induced vacancies, leading to premature fracture in a similar way to that proposed for ferritic Steels. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Masaharu Hatano - One of the best experts on this subject based on the ideXlab platform.
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hydrogen embrittlement of Austenitic Stainless Steels revealed by deformation microstructures and strain induced creation of vacancies
Acta Materialia, 2014Co-Authors: Masaharu Hatano, Masaki Fujinami, H. Fujii, K Arai, Michihiko NagumoAbstract:Abstract Hydrogen embrittlement of Austenitic Stainless Steels has been examined with respect to deformation microstructures and lattice defects created during plastic deformation. Two types of Austenitic Stainless Steels, SUS 304 and SUS 316L, uniformly hydrogen-precharged to 30 mass ppm in a high-pressure hydrogen environment, are subjected to tensile straining at room temperature. A substantial reduction of tensile ductility appears in hydrogen-charged SUS 304 and the onset of fracture is likely due to plastic instability. Fractographic features show involvement of plasticity throughout the crack path, implying the degradation of the Austenitic phase. Electron backscatter diffraction analyses revealed prominent strain localization enhanced by hydrogen in SUS 304. Deformation microstructures of hydrogen-charged SUS 304 were characterized by the formation of high densities of fine stacking faults and e-martensite, while tangled dislocations prevailed in SUS 316L. Positron lifetime measurements have revealed for the first time hydrogen-enhanced creation of strain-induced vacancies rather than dislocations in the Austenitic phase and more clustering of vacancies in SUS 304 than in SUS 316L. Embrittlement and its mechanism are ascribed to the decrease in stacking fault energies resulting in strain localization and hydrogen-enhanced creation of strain-induced vacancies, leading to premature fracture in a similar way to that proposed for ferritic Steels.
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Hydrogen embrittlement of Austenitic Stainless Steels revealed by deformation microstructures and strain-induced creation of vacancies
Acta Materialia, 2014Co-Authors: Masaharu Hatano, Masaki Fujinami, H. Fujii, K Arai, Michihiko NagumoAbstract:Hydrogen embrittlement of Austenitic Stainless Steels has been examined with respect to deformation microstructures and lattice defects created during plastic deformation. Two types of Austenitic Stainless Steels, SUS 304 and SUS 316L, uniformly hydrogen-precharged to 30 mass ppm in a high-pressure hydrogen environment, are subjected to tensile straining at room temperature. A substantial reduction of tensile ductility appears in hydrogen-charged SUS 304 and the onset of fracture is likely due to plastic instability. Fractographic features show involvement of plasticity throughout the crack path, implying the degradation of the Austenitic phase. Electron backscatter diffraction analyses revealed prominent strain localization enhanced by hydrogen in SUS 304. Deformation microstructures of hydrogen-charged SUS 304 were characterized by the formation of high densities of fine stacking faults and ε-martensite, while tangled dislocations prevailed in SUS 316L. Positron lifetime measurements have revealed for the first time hydrogen-enhanced creation of strain-induced vacancies rather than dislocations in the Austenitic phase and more clustering of vacancies in SUS 304 than in SUS 316L. Embrittlement and its mechanism are ascribed to the decrease in stacking fault energies resulting in strain localization and hydrogen-enhanced creation of strain-induced vacancies, leading to premature fracture in a similar way to that proposed for ferritic Steels. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Yukitaka Murakami - One of the best experts on this subject based on the ideXlab platform.
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hydrogen transport in solution treated and pre strained Austenitic Stainless Steels and its role in hydrogen enhanced fatigue crack growth
International Journal of Hydrogen Energy, 2009Co-Authors: Yukitaka Murakami, Saburo Matsuoka, Yoji Mine, Chihiro Narazaki, K MurakamiAbstract:Abstract Hydrogen solubility and diffusion in Type 304, 316L and 310S Austenitic Stainless Steels exposed to high-pressure hydrogen gas has been investigated. The effects of absorbed hydrogen and strain-induced martensite on fatigue crack growth behaviour of the former two Steels have also been measured. In the pressure range 10–84 MPa, the hydrogen permeation of the Stainless Steels could be successfully quantified using Sieverts' law modified by using hydrogen fugacity and Fick's law. For the Austenitic Stainless Steels, hydrogen diffusivity was enhanced with an increase in strain-induced martensite. The introduction of dislocation and other lattice defects by pre-straining increased the hydrogen concentration of the austenite, without affecting diffusivity. It has been shown that the coupled effect of strain-induced martensite and exposure to hydrogen increased the growth rate of fatigue cracks.
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Hydrogen embrittlement mechanism in fatigue of Austenitic Stainless Steels
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 2008Co-Authors: Yukitaka Murakami, Toshihiko Kanezaki, Yoji Mine, Saburo MatsuokaAbstract:The basic mechanism of the hydrogen embrittlement (HE) of Stainless Steels under fatigue loading is revealed as microscopic ductile fracture, resulting from hydrogen concentration at crack tips leading to hydrogen-enhanced slip. Fatigue crack growth rates in the presence of hydrogen are strongly frequency dependent. Nondiffusible hydrogen, at a level of 2 to approximately 3 wppm, is contained in ordinarily heat-treated Austenitic Stainless Steels, but, over the last 40 years, it has been ignored as the cause of HE. However, it has been made clear in this study that, with decreasing loading frequency down to the level of 0.0015 Hz, the nondiffusible hydrogen definitely increases fatigue crack growth rates. If the nondiffusible hydrogen at O-sites of the lattice is reduced to the level of 0.4 wppm by a special heat treatment, then the damaging influence of the loading frequency disappears and fatigue crack growth rates are significantly decreased.
