The Experts below are selected from a list of 4611 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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grain boundary segregation engineering and Austenite reversion turn embrittlement into toughness example of a 9 wt medium mn steel
Acta Materialia, 2015Co-Authors: Margarita Kuzmina, Dirk Ponge, Dierk RaabeAbstract:Abstract We study grain boundary embrittlement in a quenched and tempered Fe–Mn high-purity model martensite alloy using Charpy impact tests and grain boundary characterization by atom probe tomography. We observe that solute Mn directly embrittles martensite grain boundaries while reversion of martensite to Austenite at high-angle grain boundaries cleans the interfaces from solute Mn by partitioning the Mn into the newly Formed Austenite, hence restoring impact toughness. Microalloying with B improves the impact toughness in the quenched state and delays temper embrittlement at 450 °C. Tempering at 600 °C for 1 min significantly improves the impact toughness and further tempering at lower temperature does not cause the embrittlement to return. At higher temperatures, regular Austenite nucleation and growth takes place, whereas at lower temperature, Mn directly promotes its growth.
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on the effect of manganese on grain size stability and hardenability in ultrafine grained ferrite martensite dual phase steels
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2012Co-Authors: Marion Calcagnotto, Dirk Ponge, Dierk RaabeAbstract:Two plain carbon steels with varying manganese content (0.87 wt pct and 1.63 wt pct) were refined to approximately 1 μm by large strain warm deformation and subsequently subjected to intercritical annealing to produce an ultrafine grained ferrite/martensite dual-phase steel. The influence of the Mn content on microstructure evolution is studied by scanning electron microscopy (SEM). The Mn distribution in ferrite and martensite is analyzed by high-resolution electron backscatter diffraction (EBSD) combined with energy dispersive X-ray spectroscopy (EDX). The experimental findings are supported by the calculated phase diagrams, equilibrium phase compositions, and the estimated diffusion distances using Thermo-Calc (Thermo-Calc Software, McMurray, PA) and Dictra (Thermo-Calc Software). Mn substantially enhances the grain size stability during intercritical annealing and the ability of Austenite to undergo martensitic phase transformation. The first observation is explained in terms of the alteration of the phase transformation temperatures and the grain boundary mobility, while the second is a result of the Mn enrichment in cementite during large strain warm deformation, which is inherited by the newly Formed Austenite and increases its hardenability. The latter is the main reason why the ultrafine-grained material exhibits a hardenability that is comparable with the hardenability of the coarse-grained reference material.
Youngkook Lee - One of the best experts on this subject based on the ideXlab platform.
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reverse transformation mechanism of martensite to Austenite in a metastable austenitic alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2009Co-Authors: Seok Jae Lee, Yongmin Park, Youngkook LeeAbstract:The reverse transformation of martensite to Austenite in a metastable austenitic alloy was investigated during continuous heating followed by isothermal holding. The diffusionless reverse transformation occurred irrespective of heating rate during continuous heating, resulting in lath-shaped Austenite with high dislocation density. During isothermal holding, the equiaxed grains are nucleated and grow due to the diffusive reverse transformation. With further holding time, the diffusionlessly Formed Austenite laths were recovered to be subgrains. These results are summarized by the reverse transformation–temperature–time diagram.
Jerren Yang - One of the best experts on this subject based on the ideXlab platform.
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microstructural characterization of simulated heat affected zone in a nitrogen containing 2205 duplex stainless steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2002Co-Authors: T H Chen, Jerren YangAbstract:Abstract In order to investigate the microstructural evolution in a nitrogen-bearing 2205 duplex stainless steels (DSS) during welding, a simulated weld thermal cycle with 5 kJ cm−1 heat input followed by exposure at 700 °C for different time intervals was perFormed. The microstructure of high-temperature heat affected zone (HTHAZ) developed with the thermal experience was characterized via optical metallography and transmission electron microscopy (TEM). The duplex structure with equivalent phase components was drastically destroyed by the rapid thermal cycle. In the simulated HTHAZ structure, three different morphologies of newly Formed Austenite were observed in the coarse-grained δ-ferrite matrix; i.e. allotriomorphic Austenite, Widmanstaten autenite and intragranularly nucleated autenite. During the exposure at 700 °C, the intragranularly nucleated Austenite got coarse and the Widmanstaten Austenite grew progressively. TEM revealed that several variants of rod-like Cr2N were precipitated selectively at intragranular and intergranular sites. From the analyses of diffraction patterns of TEM, Kurdjumov–Sachs orientation relationship was found to describe the interface between intragranularly nucleated autenite and δ-ferrite, while Pitch–Schrader orientation relationship to describe the disposition between hexagonal Cr2N precipitates and δ-ferrite matrix.
Reinhold Ebner - One of the best experts on this subject based on the ideXlab platform.
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in situ analysis of the effect of high heating rates and initial microstructure on the formation and homogeneity of Austenite
Journal of Materials Science, 2019Co-Authors: Annika Eggbauer, Andreas Stark, Marina Lukas, Gerald Ressel, Petri Prevedel, Francisca Mendezmartin, Jozef Keckes, Reinhold EbnerAbstract:Decreasing processing time of a quench and temper heat treatment is of high interest for industry due to the possibility of cost reduction. One option to reduce processing time is to shorten the austenitizing cycle by applying high heating rates and minimum holding times. However, due to the high heating rates, the analysis of their influences on the formation kinetics of Austenite and its crystallographic parameters is challenging. Thus, this work concentrates on the in situ analysis of the austenitization process by means of high-energy X-ray diffraction to study a range of heating rates applied to ferritic–pearlitic and soft annealed initial microstructures. The transformation kinetics from ferrite/pearlite and soft annealed state to Austenite, the cementite dissolution behavior and the homogeneity of the freshly Formed Austenite were analyzed. The results indicate three distinct steps of Austenite formation independent of initial microstructure and heating rate: (1) nucleation of carbon-rich Austenite at cementite–ferrite interfaces, (2) growth of Austenite phase fraction accompanied by a reduction of the carbon content, until reaching the mean carbon content of the steel, followed by growth of the Austenite grain size, (3) regarding Austenite homogeneity, the combination of austenitization temperature and initial microstructure are the main influencing factors.
Dirk Ponge - One of the best experts on this subject based on the ideXlab platform.
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grain boundary segregation engineering and Austenite reversion turn embrittlement into toughness example of a 9 wt medium mn steel
Acta Materialia, 2015Co-Authors: Margarita Kuzmina, Dirk Ponge, Dierk RaabeAbstract:Abstract We study grain boundary embrittlement in a quenched and tempered Fe–Mn high-purity model martensite alloy using Charpy impact tests and grain boundary characterization by atom probe tomography. We observe that solute Mn directly embrittles martensite grain boundaries while reversion of martensite to Austenite at high-angle grain boundaries cleans the interfaces from solute Mn by partitioning the Mn into the newly Formed Austenite, hence restoring impact toughness. Microalloying with B improves the impact toughness in the quenched state and delays temper embrittlement at 450 °C. Tempering at 600 °C for 1 min significantly improves the impact toughness and further tempering at lower temperature does not cause the embrittlement to return. At higher temperatures, regular Austenite nucleation and growth takes place, whereas at lower temperature, Mn directly promotes its growth.
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on the effect of manganese on grain size stability and hardenability in ultrafine grained ferrite martensite dual phase steels
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2012Co-Authors: Marion Calcagnotto, Dirk Ponge, Dierk RaabeAbstract:Two plain carbon steels with varying manganese content (0.87 wt pct and 1.63 wt pct) were refined to approximately 1 μm by large strain warm deformation and subsequently subjected to intercritical annealing to produce an ultrafine grained ferrite/martensite dual-phase steel. The influence of the Mn content on microstructure evolution is studied by scanning electron microscopy (SEM). The Mn distribution in ferrite and martensite is analyzed by high-resolution electron backscatter diffraction (EBSD) combined with energy dispersive X-ray spectroscopy (EDX). The experimental findings are supported by the calculated phase diagrams, equilibrium phase compositions, and the estimated diffusion distances using Thermo-Calc (Thermo-Calc Software, McMurray, PA) and Dictra (Thermo-Calc Software). Mn substantially enhances the grain size stability during intercritical annealing and the ability of Austenite to undergo martensitic phase transformation. The first observation is explained in terms of the alteration of the phase transformation temperatures and the grain boundary mobility, while the second is a result of the Mn enrichment in cementite during large strain warm deformation, which is inherited by the newly Formed Austenite and increases its hardenability. The latter is the main reason why the ultrafine-grained material exhibits a hardenability that is comparable with the hardenability of the coarse-grained reference material.