The Experts below are selected from a list of 1500 Experts worldwide ranked by ideXlab platform
Seok Su Sohn - One of the best experts on this subject based on the ideXlab platform.
-
Interpretation of dynamic tensile behavior by austenite stability in ferrite-austenite duplex lightweight steels
Scientific Reports, 2017Co-Authors: Jaeyeong Park, Min Cheol Jo, Hyeok Jae Jeong, Seok Su Sohn, Jai-hyun KwakAbstract:Phenomena occurring in duplex lightweight steels under dynamic loading are hardly investigated, although its understanding is essentially needed in applications of automotive steels. In this study, quasi-static and dynamic tensile properties of duplex lightweight steels were investigated by focusing on how TRIP and TWIP mechanisms were varied under the quasi-static and dynamic loading conditions. As the annealing temperature increased, the grain size and volume fraction of austenite increased, thereby gradually decreasing austenite stability. The Strain-Hardening rate curves displayed a multiple-stage Strain-Hardening behavior, which was closely related with deformation mechanisms. Under the dynamic loading, the temperature rise due to adiabatic heating raised the austenite stability, which resulted in the reduction in the TRIP amount. Though the 950 °C-annealed specimen having the lowest austenite stability showed the very low ductility and strength under the quasi-static loading, it exhibited the tensile elongation up to 54% as well as High Strain-Hardening rate and tensile strength (1038 MPa) due to appropriate austenite stability under dynamic loading. Since dynamic properties of the present duplex lightweight steels show the excellent strength-ductility combination as well as continuously High Strain Hardening, they can be sufficiently applied to automotive steel sheets demanded for stronger vehicle bodies and safety enhancement.
-
achievement of High yield strength and Strain Hardening rate by forming fine ferrite and dislocation substructures in duplex lightweight steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017Co-Authors: Hyejin Song, Seok Su SohnAbstract:Abstract Lightweight steels containing a considerable content of Al show High specific strength and ductility, but there are some drawbacks such as low yield strength and stringer-type bands formed along the rolling direction. Here we design new duplex lightweight steel in order to complement the drawbacks, and achieve ultra-High yield strength (865 MPa), good ductility (41%). Submicron ferrite mainly affects High yield-to-tensile ratio, and High Strain Hardening is attributed to Lomer-Cottrell lock and planar slip, and cell structure by further deformation in austenite. These results are expected to provide a desirable possibility for applications to reinforcement components requiring High yield-to-tensile ratio.
-
dramatic improvement of Strain Hardening and ductility to 95 in Highly deformable High strength duplex lightweight steels
Scientific Reports, 2017Co-Authors: Seok Su Sohn, Hyejin Song, Jai-hyun KwakAbstract:Ferrite + austenite duplex lightweight steels have been actively developed by adding low-density Al for overcoming a limitation of stiffness deterioration by a traditional approach to obtain a weight reduction. Multiple-stage deformation mechanism in lightweight steels, i.e., simultaneous formation of deformation-induced martensite and deformation twin and additional plasticity by twinning, has been nominated as an attractive strategy, but shows a steady flow behavior with early plastic instability. Here, we present a newly designed Fe-0.3C-9Mn-5Al steel in order to obtain an optimal level of stability of austenite and a resultant outstanding combination of tensile strength and ductility, e.g., 874 MPa and 72%, together with sufficiently High Strain Hardening. These enhanced properties are attributed to the decreased austenite stability by controlling the austenite size and alloying partitioning due to variation in austenite fraction inside duplex microstructures. The present work gives a promise for structural applications requiring both reduced specific weight and remarkable deformability.
F Prima - One of the best experts on this subject based on the ideXlab platform.
-
a β titanium alloy with extra High Strain Hardening rate design and mechanical properties
Scripta Materialia, 2016Co-Authors: Cedrik Brozek, F Sun, Philippe Vermaut, Y Millet, A Lenain, David Embury, Patrice Jacques, F PrimaAbstract:In this paper, a new β-metastable titanium alloy, based on the Ti–Cr–Sn system, displaying both an extremely High work Hardening rate and a uniform deformation larger than 0.35, was designed and successfully tested. The compositional design was guided through a stability mapping approach based on the “d-electron design method” and using an unexploited region of the Bo/Md map. Detailed analysis of deformation mechanisms shows combined transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) effects, resulting in a complex network of microstructural features and giving rise to marked kinematic Hardening.
-
a new titanium alloy with a combination of High strength High Strain Hardening and improved ductility
Scripta Materialia, 2015Co-Authors: Jing Zhang, Cedrik Brozek, Philippe Vermaut, Patrice Jacques, Matthieu Marteleur, E F Rauch, M Veron, F PrimaAbstract:A ternary β-metastable titanium Ti–9Mo–6W (wt.%) was designed. A very High work Hardening rate close to 2100 MPa and a uniform deformation larger than 35% were recorded, thanks to combined transformation-induced plasticity and twinning-induced plasticity effects. In this paper, detailed microstructural analysis was performed to understand the deformation process. Various mechanisms, {3 3 2}〈1 1 3〉 mechanical twinning, stress-induced ω phase and stress-induced α″ martensite were identified after mechanical testing, resulting in a complex network of deformed microstructures with very special synergetic features.
Dierk Raabe - One of the best experts on this subject based on the ideXlab platform.
-
shape preserving machining produces gradient nanolaminate medium entropy alloys with High Strain Hardening capability
Acta Materialia, 2019Co-Authors: Xiahan Sang, Jonathan D Poplawsky, Stefanie Bruschi, Jun Qu, Dierk RaabeAbstract:Abstract A High density of grain boundaries can potentially increase structural materials' strength, but at the expense of losing the materials' Strain Hardening ability at High flow stress levels. However, endowing materials with grain size gradients and a High density of internal interfaces can simultaneously increase the strength and Strain Hardening ability. This applies particularly for through-thickness gradients of nanoscale interface structures. Here we apply a machining method that produces metals with nanoscale interface gradients. Conventional bulk plastic deformation such as rolling, a process applied annually to about 2 billion tons of material, aims to reduce the metal thickness. We have modified this process by introducing severe Strain path changes, realized by leading the sheet through a U-turn while preserving its shape, an approach known as ‘hard turning’. We applied this process at both room temperature and 77 K to a NiCrCo medium entropy alloy. Micropillar compression was conducted to evaluate the mechanical response. After hard turning at room temperature, the surface microstructure obtained a ∼50% increase in yield stress (0.9 GPa) over the original state with homogeneous grain size (0.4 GPa), but the initial Strain Hardening rate did not show significant improvement. However, after hard turning at 77 k, the gradient nanolaminate structure tripled in yield stress and more than doubled its initial Strain Hardening rate. The improvements were achieved by introducing a specific microstructure that consists of gradient nanolaminates in the form of nanospaced twins and martensite in the face center cubic (fcc) phase. This microstructure was formed only at cryogenic temperature. It was found after turning at room temperature that only nanospaced twins were present in the fcc phase inside nanolaminates that had formed at the surface. The origin of the enhanced Strain Hardening mechanism was studied. Joint density functional theory (DFT) and axial next nearest neighbor Ising (ANNNI) models were used to explain the temperature-dependent phase formation of the NiCrCo nanolaminate at the surface of the hard-turned material.
-
Strain Hardening by dynamic slip band refinement in a High mn lightweight steel
Acta Materialia, 2016Co-Authors: Emanuel David Welsch, Dirk Ponge, S Hafez M Haghighat, Stefanie Sandlobes, Pyuckpa Choi, Michael Herbig, Stefan Zaefferer, Dierk RaabeAbstract:Abstract The Strain Hardening mechanism of a High-Mn lightweight steel (Fe-30.4Mn-8Al-1.2C (wt%)) is investigated by electron channeling contrast imaging (ECCI) and transmission electron microscopy (TEM). The alloy is characterized by a constant High Strain Hardening rate accompanied by High strength and High ductility (ultimate tensile strength: 900 MPa, elongation to fracture: 68%). Deformation microstructures at different Strain levels are studied in order to reveal and quantify the governing structural parameters at micro- and nanometer scales. As the material deforms mainly by planar dislocation slip causing the formation of slip bands, we quantitatively study the evolution of the slip band spacing during Straining. The flow stress is calculated from the slip band spacing on the basis of the passing stress. The good agreement between the calculated values and the tensile test data shows dynamic slip band refinement as the main Strain Hardening mechanism, enabling the excellent mechanical properties. This novel Strain Hardening mechanism is based on the passing stress acting between co-planar slip bands in contrast to earlier attempts to explain the Strain Hardening in High-Mn lightweight steels that are based on grain subdivision by microbands. We discuss in detail the formation of the finely distributed slip bands and the gradual reduction of the spacing between them, leading to constantly High Strain Hardening. TEM investigations of the precipitation state in the as-quenched state show finely dispersed atomically ordered clusters (size
Jai-hyun Kwak - One of the best experts on this subject based on the ideXlab platform.
-
Interpretation of dynamic tensile behavior by austenite stability in ferrite-austenite duplex lightweight steels
Scientific Reports, 2017Co-Authors: Jaeyeong Park, Min Cheol Jo, Hyeok Jae Jeong, Seok Su Sohn, Jai-hyun KwakAbstract:Phenomena occurring in duplex lightweight steels under dynamic loading are hardly investigated, although its understanding is essentially needed in applications of automotive steels. In this study, quasi-static and dynamic tensile properties of duplex lightweight steels were investigated by focusing on how TRIP and TWIP mechanisms were varied under the quasi-static and dynamic loading conditions. As the annealing temperature increased, the grain size and volume fraction of austenite increased, thereby gradually decreasing austenite stability. The Strain-Hardening rate curves displayed a multiple-stage Strain-Hardening behavior, which was closely related with deformation mechanisms. Under the dynamic loading, the temperature rise due to adiabatic heating raised the austenite stability, which resulted in the reduction in the TRIP amount. Though the 950 °C-annealed specimen having the lowest austenite stability showed the very low ductility and strength under the quasi-static loading, it exhibited the tensile elongation up to 54% as well as High Strain-Hardening rate and tensile strength (1038 MPa) due to appropriate austenite stability under dynamic loading. Since dynamic properties of the present duplex lightweight steels show the excellent strength-ductility combination as well as continuously High Strain Hardening, they can be sufficiently applied to automotive steel sheets demanded for stronger vehicle bodies and safety enhancement.
-
dramatic improvement of Strain Hardening and ductility to 95 in Highly deformable High strength duplex lightweight steels
Scientific Reports, 2017Co-Authors: Seok Su Sohn, Hyejin Song, Jai-hyun KwakAbstract:Ferrite + austenite duplex lightweight steels have been actively developed by adding low-density Al for overcoming a limitation of stiffness deterioration by a traditional approach to obtain a weight reduction. Multiple-stage deformation mechanism in lightweight steels, i.e., simultaneous formation of deformation-induced martensite and deformation twin and additional plasticity by twinning, has been nominated as an attractive strategy, but shows a steady flow behavior with early plastic instability. Here, we present a newly designed Fe-0.3C-9Mn-5Al steel in order to obtain an optimal level of stability of austenite and a resultant outstanding combination of tensile strength and ductility, e.g., 874 MPa and 72%, together with sufficiently High Strain Hardening. These enhanced properties are attributed to the decreased austenite stability by controlling the austenite size and alloying partitioning due to variation in austenite fraction inside duplex microstructures. The present work gives a promise for structural applications requiring both reduced specific weight and remarkable deformability.
Hyejin Song - One of the best experts on this subject based on the ideXlab platform.
-
Effects of Strain rate on room- and cryogenic-temperature compressive properties in metastable V10Cr10Fe45Co35 High-entropy alloy
Scientific Reports, 2019Co-Authors: Hyejin Song, Min Cheol Jo, Yong Hee JoAbstract:Quasi-static and dynamic compressive properties of an FCC-based metastable HEA (composition; V10Cr10Fe45Co35 (at.%)) showing both Transformation Induced Plasticity (TRIP) and TWinning Induced Plasticity (TWIP) were investigated at room and cryogenic temperatures. During the quasi-static and dynamic compression at room temperature, the FCC to BCC TRIP occurred inside FCC grains, and resulted in very High Strain-Hardening rate and consequently maximum compressive strength over 1.6 GPa. The dynamic compressive strength was Higher by 240 MPa than the quasi-static strength because of Strain-rate-Hardening effect, and kept increasing with a High Strain-Hardening rate as the twinning became activated. The cryogenic-temperature strength was Higher than the room-temperature strength as the FCC to BCC TRIP amount increased by the decrease in stability of FCC phase with decreasing temperature. Under dynamic loading at cryogenic temperature, twins were not formed because the increase in SFE due to adiabatic heating might not be enough to reach the TWIP regime. However, the dynamically compressed specimen showed the Higher strength than the quasi-statically compressed specimen as the Strain-rate-Hardening effect was added with the TRIP.
-
achievement of High yield strength and Strain Hardening rate by forming fine ferrite and dislocation substructures in duplex lightweight steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017Co-Authors: Hyejin Song, Seok Su SohnAbstract:Abstract Lightweight steels containing a considerable content of Al show High specific strength and ductility, but there are some drawbacks such as low yield strength and stringer-type bands formed along the rolling direction. Here we design new duplex lightweight steel in order to complement the drawbacks, and achieve ultra-High yield strength (865 MPa), good ductility (41%). Submicron ferrite mainly affects High yield-to-tensile ratio, and High Strain Hardening is attributed to Lomer-Cottrell lock and planar slip, and cell structure by further deformation in austenite. These results are expected to provide a desirable possibility for applications to reinforcement components requiring High yield-to-tensile ratio.
-
dramatic improvement of Strain Hardening and ductility to 95 in Highly deformable High strength duplex lightweight steels
Scientific Reports, 2017Co-Authors: Seok Su Sohn, Hyejin Song, Jai-hyun KwakAbstract:Ferrite + austenite duplex lightweight steels have been actively developed by adding low-density Al for overcoming a limitation of stiffness deterioration by a traditional approach to obtain a weight reduction. Multiple-stage deformation mechanism in lightweight steels, i.e., simultaneous formation of deformation-induced martensite and deformation twin and additional plasticity by twinning, has been nominated as an attractive strategy, but shows a steady flow behavior with early plastic instability. Here, we present a newly designed Fe-0.3C-9Mn-5Al steel in order to obtain an optimal level of stability of austenite and a resultant outstanding combination of tensile strength and ductility, e.g., 874 MPa and 72%, together with sufficiently High Strain Hardening. These enhanced properties are attributed to the decreased austenite stability by controlling the austenite size and alloying partitioning due to variation in austenite fraction inside duplex microstructures. The present work gives a promise for structural applications requiring both reduced specific weight and remarkable deformability.