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S Van Der Zwaag - One of the best experts on this subject based on the ideXlab platform.
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three dimensional phase field modelling of the austenite to ferrite transformation
Acta Materialia, 2006Co-Authors: Matthias Militzer, M G Mecozzi, Jilt Sietsma, S Van Der ZwaagAbstract:The phase field method has been used to simulate the austenite-to-ferrite phase transformation in steel, for the first time in three-dimensional (3D) space. The effect of the exact morphology of the initial 3D austenitic microstructure is shown to be small, but the nucleus density and the temperature range in which nucleation takes place, both derived from experimental observations, are of primary importance for the kinetics. When 3D simulations are compared to two-dimensional (2D) simulations, it becomes evident that 2D simulations predict faster transformation rates. In the often-used practice of considering the Interface Mobility as an adjustable model parameter, systematically too low values will be obtained if 2D simulations are compared with experiments. Moreover, unrealistic features can be observed in the simulated 2D microstructures, whereas the 3D microstructures show a realistic representation of the actual microstructure. The overall conclusion is therefore that phase field modelling is distinctly more powerful when applied in 3D space.
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analysis of γ α transformation in a nb micro alloyed c mn steel by phase field modelling
Acta Materialia, 2006Co-Authors: M G Mecozzi, S Van Der ZwaagAbstract:Abstract The phase field model is used to simulate the γ → α transformation in a Nb micro-alloyed C–Mn steel during cooling from different austenitisation temperatures. The initial austenitic microstructure and the nucleation conditions, derived by metallographic tests, are set as input data of the model. The Interface Mobility is taken as representative for the effect of NbC on the phase transformation. It is used as a fitting parameter to optimise the agreement between the experimental ferrite fraction curve, obtained by dilatometry, and the simulated ferrite fraction curve. A decrease of the γ/α Interface Mobility is found when the austenitisation temperature decreases from 1373 to 1173 K as a consequence of the presence of NbC precipitates during austenitisation. The presence of NbC has a distinct effect on the nature of the phase transformation with respect to the Interface-controlled or diffusion-controlled mode.
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the influence of nitrogen on the austenite ferrite Interface Mobility in fe 1at si
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2002Co-Authors: T.a. Kop, S Van Der ZwaagAbstract:Abstract The relation between the nitrogen content and the Mobility of the austenite/ferrite Interface during the austenite to ferrite transformation have been investigated. Samples of an Fe–1at.%Si alloy were given various internal nitriding treatments, leading to nitrogen concentrations between 20 and 3000 appm. Dilatometric measurements during cooling indicate a clear shift in the transformation curves. The transformation is shifted to lower temperatures and is slowed down at higher nitrogen contents. The transformation kinetics were modelled using an Interface Mobility model in combination with a tetrakaidecahedron as a representation of the austenite grain. For nitrogen concentrations smaller than 500 appm there is a good agreement between experimental and modelled fraction curves, using an exponential relation for the nitrogen dependence of the pre-exponential Mobility factor, M 0 . For higher nitrogen levels, M 0 decreases less rapidly. Moreover, only the first stage of the ferrite formation is accurately modelled. Towards the end of the transformation the discrepancy between experimental and modelled fraction curves increases. This suggests that for the determination of the driving force in the case of nitrogen concentrations larger than 500 appm long range diffusion of nitrogen should be taken into account.
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a study on the austenite to ferrite phase transformation in binary substitutional iron alloys
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2000Co-Authors: J J Wits, T.a. Kop, Y Van Leeuwen, J Seitsma, S Van Der ZwaagAbstract:Abstract The massive transformation from austenite to ferrite (γ→α) in binary substitutional Fe–X alloys, where X represents successively about 1 or 2 at.% of Co, Cu, Mn, Cr or Al, is experimentally investigated by means of dilatometry. The resulting transformation curves have been modelled by an Interface-controlled growth model, taking the characteristics of the austenitic microstructure into account. The assumption of an Arrhenian temperature dependence of the Interface Mobility, defined as the ratio between the Interface velocity and the driving force, is found to give a consistent picture of the observations with an activation energy for atoms crossing the Interface of 140 kJ mol−1. The spurious presence of interstitial nitrogen is shown to have a significant effect on the Mobility, as large as a factor 8 at concentration levels on the order of 10−4.
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kinetics of γ α phase transformation in fe mn alloys containing low manganese
Materials Science and Technology, 1998Co-Authors: G P Krielaart, S Van Der ZwaagAbstract:AbstractThe kinetics of the γ → α phase transformation in Fe-Mn alloys with low Mn contents was studied using differential scanning calorimetry. Analysis of the measured heat capacity yielded both the austenite fractions as a function of temperature as well as the enthalpy difference between ferrite and austenite which decreases with increases in both the temperature and the Mn concentration. The transformation was modelled using an Interface controlled growth model. It was assumed that the Interface velocity is proportional to the chemical potential difference of the Fe lattice. The Interface Mobility has a simple exponential temperature dependence. Taking into account the austenite grain size distribution, the activation energy and the pre-exponential factor for the Interface Mobility were estimated from the heat effects at 140 kJ mol−1 and 58 mm mol J−1 S−1 respectively.
Matthias Militzer - One of the best experts on this subject based on the ideXlab platform.
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mixed mode model for ferrite to austenite phase transformation in dual phase steel
Computational Materials Science, 2018Co-Authors: Melanie Ollat, Matthias Militzer, V Massardier, Damien Fabregue, Eric Buscarlet, Fanny Keovilay, Michel PerezAbstract:Abstract A mixed-mode model is proposed to predict the austenite formation during intercritical annealing of a low-carbon steel with ferrite-cementite microstructure. The transformation kinetics is decribed by carbon diffusion in combination with an Interface Mobility, representative of complex phenomena slowing down the transformation rate (solute drag, slow diffusivity of other alloying elements, cementite dissolution). The model approach is formulated to be relevant for complex chemistries typical of industrial steels. Model predictions have been successfully benchmarked with experimental data including heating and holding stages at various heating rates and holding temperatures.
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phase field modeling of the simultaneous formation of bainite and ferrite in trip steel
Acta Materialia, 2018Co-Authors: Morteza Toloui, Matthias MilitzerAbstract:Abstract In transformation-induced plasticity (TRIP) steels, Si and/or Al delay cementite precipitation during bainite transformation leading to a transformation product that is usually referred to as carbide-free bainite. The present work proposes an approach to calibrate the parameters of a multi-phase field model to simulate the austenite decomposition into ferrite and bainite in a TRIP steel. Ferrite nuclei are introduced at austenite grain boundaries and suitable interfacial mobilities are selected to reproduce experimental ferrite formation kinetics. Bainite nucleation occurs for a sufficiently high undercooling at available Interface sites (i.e. austenite grain boundaries, austenite-ferrite Interfaces) and/or within austenite grains. For simplicity, the formation of carbide-free bainite is considered and a suitable anisotropy approach is proposed for the austenite-bainite Interface Mobility. The proposed model is benchmarked and validated with experimental continuous cooling transformation data.
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the effect of solute nb on the austenite to ferrite transformation
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2015Co-Authors: Tao Jia, Matthias MilitzerAbstract:Niobium is a widely used micro-alloying element in steels that can retard the austenite-to-ferrite transformation primarily by solute drag when Nb remains in solution. It is critical to develop quantitative models to predict the effect of Nb on the transformation kinetics. In the present work, dedicated continuous cooling transformation (CCT) studies were performed for a low-carbon steel microalloyed with 0.047 wt pct Nb starting from fully recrystallized austenite states with the same grain size but different amounts of Nb in solution. The austenite-to-ferrite transformation kinetics is described from a fundamental perspective by assuming a mixed-mode reaction including solute drag of Nb. Using the solute drag model of Fazeli and Militzer, the intrinsic Interface Mobility, trans-Interface diffusivity of Nb, and its binding energy to the Interface have been determined from the CCT data. The interfacial parameters are critically analyzed and compared with independent measurements of diffusion and grain boundary segregation.
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phase field modelling of microstructure evolution in the haz of x80 linepipe steel
2012 9th International Pipeline Conference, 2012Co-Authors: Morteza Toloui, Matthias MilitzerAbstract:The heat affected zone (HAZ) during welding experiences a very steep temperature gradient which results in significant microstructure gradients. Thus, model approaches on the length scale of the microstructure, i.e. the so-called mesoscale, are useful to accurately simulate microstructure evolution in the HAZ. In this study, a phase field model (PFM) is employed to simulate austenite grain growth and austenite decomposition in the HAZ of an X80 linepipe steel microalloyed with Nb and Ti. The interfacial mobilities and nucleation conditions are obtained by benchmarking the PFM with experimental data from austenite grain growth and continuous cooling transformation tests. An effective grain boundary Mobility is introduced for austenite grain growth to implicitly account for dissolution of NbC. Subsequently, austenite decomposition into polygonal ferrite and bainite is considered. For this purpose the PFM is coupled with a carbon diffusion model. Ferrite nuclei are introduced at austenite grain boundaries and suitable interfacial mobilities are selected to reproduce experimental ferrite formation kinetics. Bainite nucleation occurs for a sufficiently high undercooling at available Interface sites (i.e. austenite grain boundaries and/or austenite-ferrite Interfaces). For simplicity, the formation of carbide-free bainite is considered and a suitable anisotropy approach is proposed for the austenite-bainite Interface Mobility. The model is then used to predict austenite grain growth and phase transformation in the HAZ.Copyright © 2012 by ASME
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modelling phase transformation kinetics in fe mn alloys
Isij International, 2012Co-Authors: Tao Jia, Matthias MilitzerAbstract:A unified model is proposed for the austenite-to-ferrite transformation kinetics in binary Fe–Mn alloys that accounts for solute drag of Mn. To aid the model development, continuous cooling transformation (CCT) tests were conducted for an interstitial-free steel that can be considered as Fe–0.1%Mn alloy. The experimental transformation data are supplemented with literature data for Fe–1%Mn and Fe–2%Mn alloys to establish a CCT database for Fe–Mn alloys. The austenite-to-ferrite transformation kinetics is described from a fundamental perspective by assuming an Interface-controlled reaction and including solute drag of Mn. Using the solute drag model of Fazeli and Militzer, intrinsic Interface Mobility, trans-Interface diffusivity of Mn and its binding energy have been determined from the CCT data. The interfacial parameters are critically analyzed and compared with independent measurements of diffusion and grain boundary segregation.
Hao Chen - One of the best experts on this subject based on the ideXlab platform.
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a comparative study on intrinsic Mobility of incoherent and semicoherent Interfaces during the austenite to ferrite transformation
Scripta Materialia, 2020Co-Authors: Hao Chen, Haokai Dong, Yongjie Zhang, Goro Miyamoto, Zhigang Yang, Tadashi FuruharaAbstract:Abstract A straightforward approach to experimentally determine intrinsic Interface Mobility as well as extrinsic energy dissipation is proposed based on the measurements of total energy dissipation and Interface velocity. These parameters have been comparatively studied for incoherent allotriomorphic ferrite (AF) and semicoherent Widmanstatten ferrite (WF) in an Fe-C alloy. It reveals that extrinsic energy dissipation for AF is negligibly small whereas that for WF is about 20J/mol, which should correspond to the dissipation by associated transformation strain. Furthermore, the intrinsic Mobility of the semicoherent WF/austenite Interface is found to be much smaller than the incoherent AF/austenite Interface counterpart.
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carbon enrichment during ferrite transformation in fe si c alloys
Acta Materialia, 2018Co-Authors: Z G Yang, Chao Zhang, Hao ChenAbstract:Abstract The microstructure evolution, transformation kinetics and especially the C enrichment during isothermal ferrite transformation at 800, 750, 700 °C for Fe-(1.5, 3.0) mass%Si-0.4mass%C alloys were investigated in the present study. Both transformation kinetics and C enrichment in austenite (γ) at grain boundary ferrite (GBF)/γ Interfaces suggest that negligible partitioning local equilibrium (NPLE) mode operates during non-partitioned ferrite growth under the conditions investigated. Deviations of C enrichment in γ at Widmanstatten ferrite (WF)/γ Interfaces from NPLE limit at early stages were observed. These deviations are deduced to be resulted from intrinsic Interface Mobility rather than solute drag effect. In addition, Mobility of WF/γ Interfaces is found to be lower than that for incoherent GBF/γ Interfaces reported in literature.
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An Overview of the Cyclic Partial Austenite-Ferrite Transformation Concept and Its Potential
Metallurgical and Materials Transactions A, 2016Co-Authors: Hao Chen, Sybrand Van Der ZwaagAbstract:Over the past decades, the mechanism of Interface migration during the austenite-ferrite transformation in steels has attracted significant attention from physical metallurgists. There are two challenging research questions in this field: (i) What is the effect of (substitutional) alloying elements on migrating Interfaces? and (ii) How to accurately determine the value of Interface Mobility?. Recently, a cyclic partial phase transformation approach has been proposed to study Interface migration, and new insights into the above two questions have been provided. An overview of the cyclic partial phase transformation concept is given, and pathways for future research are suggested.
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a general mixed mode model for the austenite to ferrite transformation kinetics in fe c m alloys
Acta Materialia, 2014Co-Authors: Hao Chen, Sybrand Van Der ZwaagAbstract:Abstract Using the Gibbs energy balance (GEB) concept, a concise GEB model assuming a planar Interface is proposed to study the austenite-to-ferrite transformation kinetics in Fe–C–M alloys (where M is a substitutional alloying element). Compared with the binary mixed-mode model, the newly developed GEB model is a more general mixed-mode model, and can physically describe the mixed-mode kinetics during the austenite-to-ferrite transformation in binary, ternary and even higher alloy systems. The GEB model can also predict kinetic transitions during the austenite-to-ferrite transformation, and the classical paraequilibrium and Local equilibrium are found to be its two specific cases. Furthermore, the GEB model provides a physical understanding of the effect of solute drag on the effective Interface Mobility. Experiments in Fe–C–Mn and Fe–C–Ni alloys indicate that the transformation stasis phenomenon can also occur during the austenite-to-ferrite transformation. The degree of incomplete transformation increases with increasing Mn or Ni concentration, while Mn has a stronger effect on the degree of incomplete transformation than Ni does due to its higher partitioning coefficient. The GEB model describes well the austenite-to-ferrite transformation stasis phenomenon.
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application of the cyclic phase transformation concept for determining the effective austenite ferrite Interface Mobility
Computational Materials Science, 2014Co-Authors: Ernst Gamsjager, Hao Chen, Sybrand Van Der ZwaagAbstract:Abstract A series of cyclic partial austenite–ferrite phase transformation computer simulation experiments have been performed to elucidate the rate controlling dissipative processes during austenite-to-ferrite and the ferrite-to-austenite transformation in lean C–Mn steels. The transformation kinetics is analyzed by comparing the results of two complementary sharp Interface models – one is based on the assumption of local equilibrium at the migrating Interface − in the other model diffusion in the Interface and the interfacial reaction is implemented by an effective Interface Mobility but substitutional diffusion in the bulk phases is neglected. Values for effective Interface mobilities have been obtained for both the austenite-to-ferrite transformation and vice versa. By means of effective mobilities which depend only on initial composition and temperature, the transformation kinetics has been studied for other heat treatments than used to determine the effective interfacial Mobility values. Although substitutional diffusion in the bulk is not taken into account, for the low Mn alloys it is possible to obtain similar trends by the effective Mobility model as provided by the local equilibrium model. At modest to high Interface velocities long range diffusion of the substitutional alloying elements can be ignored but then the effects of local diffusion processes near the Interface need to be taken into account via an effective Interface Mobility. The effective Mobility for the austenite-to-ferrite transformation differs from the effective Mobility during the ferrite-to-austenite transformation in a rather essential manner.
Sybrand Van Der Zwaag - One of the best experts on this subject based on the ideXlab platform.
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An Overview of the Cyclic Partial Austenite-Ferrite Transformation Concept and Its Potential
Metallurgical and Materials Transactions A, 2016Co-Authors: Hao Chen, Sybrand Van Der ZwaagAbstract:Over the past decades, the mechanism of Interface migration during the austenite-ferrite transformation in steels has attracted significant attention from physical metallurgists. There are two challenging research questions in this field: (i) What is the effect of (substitutional) alloying elements on migrating Interfaces? and (ii) How to accurately determine the value of Interface Mobility?. Recently, a cyclic partial phase transformation approach has been proposed to study Interface migration, and new insights into the above two questions have been provided. An overview of the cyclic partial phase transformation concept is given, and pathways for future research are suggested.
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a general mixed mode model for the austenite to ferrite transformation kinetics in fe c m alloys
Acta Materialia, 2014Co-Authors: Hao Chen, Sybrand Van Der ZwaagAbstract:Abstract Using the Gibbs energy balance (GEB) concept, a concise GEB model assuming a planar Interface is proposed to study the austenite-to-ferrite transformation kinetics in Fe–C–M alloys (where M is a substitutional alloying element). Compared with the binary mixed-mode model, the newly developed GEB model is a more general mixed-mode model, and can physically describe the mixed-mode kinetics during the austenite-to-ferrite transformation in binary, ternary and even higher alloy systems. The GEB model can also predict kinetic transitions during the austenite-to-ferrite transformation, and the classical paraequilibrium and Local equilibrium are found to be its two specific cases. Furthermore, the GEB model provides a physical understanding of the effect of solute drag on the effective Interface Mobility. Experiments in Fe–C–Mn and Fe–C–Ni alloys indicate that the transformation stasis phenomenon can also occur during the austenite-to-ferrite transformation. The degree of incomplete transformation increases with increasing Mn or Ni concentration, while Mn has a stronger effect on the degree of incomplete transformation than Ni does due to its higher partitioning coefficient. The GEB model describes well the austenite-to-ferrite transformation stasis phenomenon.
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application of the cyclic phase transformation concept for determining the effective austenite ferrite Interface Mobility
Computational Materials Science, 2014Co-Authors: Ernst Gamsjager, Hao Chen, Sybrand Van Der ZwaagAbstract:Abstract A series of cyclic partial austenite–ferrite phase transformation computer simulation experiments have been performed to elucidate the rate controlling dissipative processes during austenite-to-ferrite and the ferrite-to-austenite transformation in lean C–Mn steels. The transformation kinetics is analyzed by comparing the results of two complementary sharp Interface models – one is based on the assumption of local equilibrium at the migrating Interface − in the other model diffusion in the Interface and the interfacial reaction is implemented by an effective Interface Mobility but substitutional diffusion in the bulk phases is neglected. Values for effective Interface mobilities have been obtained for both the austenite-to-ferrite transformation and vice versa. By means of effective mobilities which depend only on initial composition and temperature, the transformation kinetics has been studied for other heat treatments than used to determine the effective interfacial Mobility values. Although substitutional diffusion in the bulk is not taken into account, for the low Mn alloys it is possible to obtain similar trends by the effective Mobility model as provided by the local equilibrium model. At modest to high Interface velocities long range diffusion of the substitutional alloying elements can be ignored but then the effects of local diffusion processes near the Interface need to be taken into account via an effective Interface Mobility. The effective Mobility for the austenite-to-ferrite transformation differs from the effective Mobility during the ferrite-to-austenite transformation in a rather essential manner.
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application of the cyclic phase transformation concept for investigating growth kinetics of solid state partitioning phase transformations
Computational Materials Science, 2010Co-Authors: Hao Chen, Sybrand Van Der ZwaagAbstract:A heat treatment involving cyclic partial phase transformations has been analyzed to determining growth kinetics of the austenite to ferrite phase transformation and vice versa more accurately. The mixed-mode model and the diffusion-controlled phase transformation model, including the soft impingement effects at the later stage of phase transformation, are reformulated for the cyclic austenite to ferrite and ferrite to austenite transformation. A new growth mode parameter H is defined for the mixed-mode model. It shows that not all partitioning phase transformations starts as pure Interface-controlled growth but all of them shift gradually towards pure diffusion control when thermodynamic equilibrium is approached. The diffusion-controlled model predicts that the ferrite to austenite transformation should be faster than the austenite to ferrite, while the simulation of the mixed-mode model shows that the transformation rate ratio is a function of the ratio of Interface Mobility.
Jilt Sietsma - One of the best experts on this subject based on the ideXlab platform.
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quantitative comparison of the phase transformation kinetics in a sharp Interface and a phase field model
Computational Materials Science, 2011Co-Authors: M G Mecozzi, Janin Eiken, Markus Apel, Jilt SietsmaAbstract:Abstract A sharp-Interface model, which provides an accurate description of diffusional phase-transformation kinetics [C. Bos, J. Sietsma, Scripta Mater. 57 (2007) 1085–1088], is used to evaluate the transformation kinetics as calculated by a diffuse-Interface multi-phase-field model, in particular the effect of the Interface thickness will be investigated. This is done for the isothermal austenite-to-ferrite transformation in a C–Mn steel, using the simple geometry of a single ferrite grain growing in the bulk of the austenite matrix. For the sake of computation time, this analysis is limited to one- and two-dimensional space, although it can be extended to three-dimensional space straightforwardly. Small deviations of the numerical phase-field profile from the analytical stationary solution, used to match the phase-field equation to the equation for the sharp-Interface kinetics, results in a lower effective Interface Mobility compared to the input value. This deviation, more pronounced in the early stage of transformation, can be minimised by reducing the grid size, while keeping the number of Interface grid points constant. During stationary growth, a good agreement was found between phase-field and sharp-Interface solution, although a small deviation of about 7% still remains if six grid points are chosen for the Interface width. This deviation could not be reduced further by a better grid resolution, but can be overcome by a higher number of grid points within the diffuse Interface.
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a microstructure model for recrystallisation and phase transformation during the dual phase steel annealing cycle
Computational Materials Science, 2010Co-Authors: C Bos, M G Mecozzi, Jilt SietsmaAbstract:Abstract A three-dimensional cellular automata model is developed for the description of the relevant metallurgical mechanisms occurring in the annealing stage of dual-phase steels: ferrite recrystallisation, pearlite-to-austenite and ferrite-to-austenite transformation on heating and austenite-to-ferrite transformation on cooling. Based on the local grain-boundary and Interface velocity, the latter controlled by both Interface Mobility and carbon diffusivity, the model is able to simulate the microstructure development throughout the annealing stage. The model also provides information on the carbon gradient in austenite at the end of the cycle, which is relevant for the prediction of martensite formation during the subsequent quenching. The simulated structure thus provides a realistic representation of many microstructural aspects.
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influence of Interface Mobility on the evolution of austenite martensite grain assemblies during annealing
Acta Materialia, 2009Co-Authors: M J Santofimia, John G Speer, A J Clarke, L Zhao, Jilt SietsmaAbstract:The quenching and partitioning (Q&P) process is a new heat treatment for the creation of advanced high-strength steels. This treatment consists of an initial partial or full austenitization, followed by a quench to form a controlled amount of martensite and an annealing step to partition carbon atoms from the martensite to the austenite. In this work, the microstructural evolution during annealing of martensite-austenite grain assemblies has been analyzed by means of a modeling approach that considers the influence of martensite-austenite Interface migration on the kinetics of carbon partitioning. Carbide precipitation is precluded in the model, and three different assumptions about Interface Mobility are considered, ranging from a completely immobile Interface to the relatively high Mobility of an incoherent ferrite-austenite Interface. Simulations indicate that different Interface mobilities lead to profound differences in the evolution of microstructure that is predicted during annealing.
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three dimensional phase field modelling of the austenite to ferrite transformation
Acta Materialia, 2006Co-Authors: Matthias Militzer, M G Mecozzi, Jilt Sietsma, S Van Der ZwaagAbstract:The phase field method has been used to simulate the austenite-to-ferrite phase transformation in steel, for the first time in three-dimensional (3D) space. The effect of the exact morphology of the initial 3D austenitic microstructure is shown to be small, but the nucleus density and the temperature range in which nucleation takes place, both derived from experimental observations, are of primary importance for the kinetics. When 3D simulations are compared to two-dimensional (2D) simulations, it becomes evident that 2D simulations predict faster transformation rates. In the often-used practice of considering the Interface Mobility as an adjustable model parameter, systematically too low values will be obtained if 2D simulations are compared with experiments. Moreover, unrealistic features can be observed in the simulated 2D microstructures, whereas the 3D microstructures show a realistic representation of the actual microstructure. The overall conclusion is therefore that phase field modelling is distinctly more powerful when applied in 3D space.