The Experts below are selected from a list of 18291 Experts worldwide ranked by ideXlab platform
Sybrand Van Der Zwaag - One of the best experts on this subject based on the ideXlab platform.
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In situ high-temperature EBSD and 3D phase field studies of the Austenite-Ferrite Transformation in a medium Mn steel
Microscopy and microanalysis : the official journal of Microscopy Society of America Microbeam Analysis Society Microscopical Society of Canada, 2019Co-Authors: Hussein Farahani, Gerrit S Zijlstra, Vaclav Ocelik, M.g. Mecozzi, Jeff Th. M. De Hosson, Sybrand Van Der ZwaagAbstract:In this research, in situ high-temperature electron backscattered diffraction (EBSD) mapping is applied to record and analyze the migration of the α/3 interfaces during cyclic Austenite-Ferrite phase Transformations in a medium manganese steel. The experimental study is supplemented with related 3D phase field (PF) simulations to better understand the 2D EBSD observations in the context of the 3D Transformation events taking place below the surface. The in situ EBSD observations and PF simulations show an overall Transformation behavior qualitatively similar to that measured in dilatometry. The behavior and kinetics of individual Austenite-Ferrite interfaces during the Transformation is found to have a wide scatter around the average interface behavior deduced on the basis of the dilatometric measurements. The trajectories of selected characteristic interfaces are analyzed in detail and yield insight into the effect of local conditions in the vicinity of interfaces on their motion, as well as the misguiding effects of 2D observations of processes taking place in 3D.
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Analysis of ferrite growth retardation induced by local Mn enrichment in austenite created by prior interface passages
Acta Materialia, 2013Co-Authors: Hao Chen, Sybrand Van Der ZwaagAbstract:Abstract A series of new cyclic phase Transformation dilatometric experiments has been designed to investigate systematically and in detail the newly discovered “growth retardation stage” during the final austenite–ferrite Transformation, and to provide further evidence for the existence of residual Mn spikes in austenite created during prior cyclic phase Transformations. The magnitude of growth retardation increases with increasing Mn concentration, and is absent in the binary Fe–C alloy. New experiments also prove that growth retardation does not occur at a particular temperature but when the moving austenite–ferrite interface hits the residual Mn spike. The magnitude of growth retardation is proportional to the number of prior temperature cycles in the cyclic phase Transformations, and there is no growth retardation in experiments with only one temperature cycle. The fact that the growth retardation can be observed by dilatometry implies that the interface moved back and forth in a retraceable manner. The classical local equilibrium model can still qualitatively predict the newly observed features of growth retardation, while the paraequilibrium model does not work.
Pedro P. Gómez - One of the best experts on this subject based on the ideXlab platform.
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recrystallisation driving forces against pinning forces in hot rolling of ti microalloyed steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2006Co-Authors: Maria Isabel Vega, Alberto Quispe, Sebastián F. Medina, Manuel Gomez, Pedro P. GómezAbstract:In this work the pinning forces exerted by TiN particles in the austenitic phase in four Ti-microalloyed steels have been determined and compared with the driving forces for recrystallisation determined in each rolling pass. The thermomechanical simulation has been carried out in the laboratory by means of torsion tests in a sequence of 20 passes with the final passes in a mixed austenitic/ferritic phase. The driving forces were found to be approximately two orders of magnitude higher than the pinning forces, which explains why the austenite in these steels barely experiences hardening during rolling and why the accumulated stress prior to the austenite → ferrite Transformation is insufficient to refine the ferritic grain.
E. J. Mittemeijer - One of the best experts on this subject based on the ideXlab platform.
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austenite ferrite Transformation kinetics under uniaxial compressive stress in fe 2 96 at ni alloy
Acta Materialia, 2009Co-Authors: Ferdinand Sommer, E. J. MittemeijerAbstract:Abstract The effect of an applied constant uniaxial compressive stress on the kinetics of the austenite (γ) → ferrite (α) massive Transformation in the substitutional Fe–2.96 at.% Ni alloy upon isochronal cooling has been studied by differential dilatometry. All imposed stress levels are below the yield stress of austenite and ferrite in the temperature range of the Transformation. An increase in compressive stress results in a small but significant increase of the onset temperature of the γ → α Transformation and a decrease of the overall Transformation time. A phase Transformation model, involving site saturation, interface-controlled growth and incorporation of an appropriate impingement correction, has been employed to extract the interface-migration velocity of the γ/α interface. The interface-migration velocity for the γ → α Transformation is approximately constant at fixed uniaxial compressive stress and increases with increasing applied uniaxial compressive stress. Furthermore, the value obtained for the energy corresponding with the elastic and plastic deformation associated with the accommodation of the γ/α volume misfit depends on the transformed fraction and decreases significantly as the applied uniaxial compressive stress increases. An understanding of the observed effects is obtained, recognizing the constraints imposed on the phase Transformation due to the applied stress.
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the austenite ferrite Transformation of ultralow carbon fe c alloy transition from diffusion to interface controlled growth
Acta Materialia, 2006Co-Authors: F Sommer, E. J. MittemeijerAbstract:Abstract The kinetics of the isochronal austenite (γ) → ferrite (α) Transformation of ultralow-carbon Fe–C alloy were investigated for cooling rates in the range 5–20 K min −1 by high-resolution dilatometry and differential thermal analysis. The starting temperature of the Transformation decreases with increasing cooling rate. The Transformation kinetics, as characterized by the formation rate of product (ferrite) phase, varies greatly with cooling rate. At a small cooling rate of 5 K min −1 the Transformation rate curve has a multiple-peaked nature. Upon increasing the cooling rate from 5 to 20 K min −1 , the first Transformation rate maxima vanish gradually, and finally so-called normal Transformation behavior, characterized by the (remaining) one maximum in the Transformation rate curve, is observed. On the basis of microstructural analysis and thermodynamic and kinetic reasoning, it is shown that the first Transformation rate maxima pertain to diffusion-controlled ferrite growth, whereas the later single, main Transformation rate maximum is due to interface-controlled, massive Transformation.
Riki Okamoto - One of the best experts on this subject based on the ideXlab platform.
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interphase precipitation in niobium microalloyed steels
Acta Materialia, 2010Co-Authors: Riki Okamoto, Annika Borgenstam, John AgrenAbstract:The interphase precipitation in niobium steel has been investigated. In the present work, the austenite/ferrite Transformation speed should be fast due to hot deformations, and interphase precipita ...
Maria Isabel Vega - One of the best experts on this subject based on the ideXlab platform.
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recrystallisation driving forces against pinning forces in hot rolling of ti microalloyed steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2006Co-Authors: Maria Isabel Vega, Alberto Quispe, Sebastián F. Medina, Manuel Gomez, Pedro P. GómezAbstract:In this work the pinning forces exerted by TiN particles in the austenitic phase in four Ti-microalloyed steels have been determined and compared with the driving forces for recrystallisation determined in each rolling pass. The thermomechanical simulation has been carried out in the laboratory by means of torsion tests in a sequence of 20 passes with the final passes in a mixed austenitic/ferritic phase. The driving forces were found to be approximately two orders of magnitude higher than the pinning forces, which explains why the austenite in these steels barely experiences hardening during rolling and why the accumulated stress prior to the austenite → ferrite Transformation is insufficient to refine the ferritic grain.
