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M. Enomoto - One of the best experts on this subject based on the ideXlab platform.
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Growth Kinetics of Proeutectoid Ferrite in Fe-0.1C-1.5Mn-1Si Quaternary and Fe-0.1C-1.5Mn-1Si-0.2Al Quinary Alloys
Metallurgical and Materials Transactions A, 2012Co-Authors: G. H. Zhang, M. Enomoto, R. Wei, D. W. SuhAbstract:The growth kinetics of Proeutectoid Ferrite in the early stages of transformation were studied in Fe-0.1C-1.5Mn-1Si (mass pct) quaternary and Fe-0.1C-1.5Mn-1Si-0.2Al quinary alloys. The observed kinetic transition temperatures from partitioned slow growth to unpartitioned fast growth of Ferrite in both alloys are in good agreement with predictions using a local equilibrium model for multicomponent systems. The measured parabolic growth rate constants were smaller than those calculated assuming paraequilibrium in the unpartitioned growth region, but the difference between the measured and the calculated growth rate constants gradually diminished with a decreasing reaction temperature. The dissipation of driving force, derived from the diffusion of the substitutional solute within the transformation interface, possibly constitutes a major part of the discrepancy between the measured and the calculated growth kinetics.
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Influence of magnetic field on isothermal pearlite transformation in Fe-C-Ni hypoeutectoid alloy
Materials Science and Technology, 2010Co-Authors: G. H. Zhang, M. EnomotoAbstract:AbstractThe influence of an external magnetic field of 8 T on isothermal pearlite transformation was studied in an Fe–0·4 mass%C–2 mass%Ni hypoeutectoid alloy, in which both Proeutectoid Ferrite and pearlite transformations were accelerated by the field. Whereas the pearlite volume fraction increased with decreasing reaction temperature, the magnetic field increased the proportion of pearlite relative to Proeutectoid Ferrite only at low undercoolings. The interlamellar spacing of pearlite was reduced 5–15% by the magnetic field, which may have led to a substantial increase in growth rate of pearlite nodules. Whereas the pearlite carbon content fell near the paraequilibrium γ/(γ+cem) phase boundary, other features, e.g. interlamellar spacing, seem to be in accord with the condition of non-partition local equilibrium at the pearlite/austenite boundary as reported in Fe–C base hypoeutectoid alloys.
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Simulation of Nucleation of Proeutectoid Ferrite at Austenite Grain Boundaries during Continuous Cooling
Metallurgical and Materials Transactions A, 2008Co-Authors: M. Enomoto, J.b. YangAbstract:The nucleation kinetics of Proeutectoid Ferrite during continuous cooling in three Fe-C-Mn-Si steels, measured in-situ by three-dimensional X-ray diffraction microscope, are compared with numerical simulation that takes into account differences in the activation energy of nucleation among grain boundary faces, edges, and corners. The essential feature of Ferrite nucleation in the 0.21 pct C steel, i.e. , nucleation occurred just below Ae_3 and ceased at a small undercooling, is reproduced taking into account the site consumption, primarily at grain corners and overlap of solute diffusion fields in the grain boundary region or the matrix and assuming a very small or almost null activation energy of nucleation. In the 0.35 and 0.45 pct C steels, small activation energy, as reported by Offerman et al. , was not unequivocally obtained because Ferrite nucleation occurred at considerably large undercoolings, even below the paraequilibrium Ae_3 in these steels. The increasing rate of the observed particle number with decreasing temperature is considerably smaller than calculation.
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Influence of magnetic field on the kinetics of Proeutectoid Ferrite transformation in iron alloys
Metallurgical and Materials Transactions A, 2001Co-Authors: M. Enomoto, Y. Tazuke, M. ShimotomaiAbstract:The kinetics of Proeutectoid Ferrite transformation in Fe-C base alloys in a strong magnetic field (7.5 T) were studied. The transformation kinetics were accelerated at temperatures not only below but also significantly above the Curie temperature. The free energy and equilibrium Ferrite/austenite phase boundaries in applied magnetic fields were calculated using the reported experimental magnetic susceptibility and Weiss molecular field theory. The persistence of magnetic field effects above the Curie temperature can be attributed to the rapidly diminishing difference in relative stability between Ferrite and austenite toward the Ae _3 temperature of iron.
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prediction of ttt diagram of Proeutectoid Ferrite reaction in iron alloys from diffusion growth theory
Isij International, 1992Co-Authors: M. EnomotoAbstract:A computer model is developed to simulate the time-temperature-transformation (TTT-)diagram for the Proeutectoid Ferrite transformation in Fe-C and Fe-C-X alloys, where X is a substitutional alloying element, from the diffusion growth theory which assumes para- and/or local equilibrium of solute atoms at advancing phase interfaces. The incubation time of Ferrite allotriomorph nucleus calculated from the nucleation theory is assumed to be the initiation time of transformation. The influence of the enrichment (or depletion) of solute atoms in the untransformed austenite matrix on subsequent transformation is incorporated by using the quasi-stationary approximation to calculate the diffusion field in the matrix. Both the planar growth and the growth of spherical interfaces (toward the center of sphere) are considered. The model reproduces the basic features of Proeutectoid Ferrite transformation in iron alloys during isothermal holding and can be used to predict approximately and quickly the TTT-diagram for the transformation when the alloy composition and the austenite grain size are given.
Guo-dong Wang - One of the best experts on this subject based on the ideXlab platform.
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Super long-range diffusion of carbon during Proeutectoid Ferrite transformation
Journal of Central South University, 2019Co-Authors: Suo-quan Zhang, Jian-hua Ding, Sihai Jiao, Guo-dong WangAbstract:In order to explore the possible diffusion distance of carbon during Proeutectoid Ferrite transformation, a slow cooling test of low carbon steel was carried out under vacuum of the thermal simulator. The microstructure and thermal expansion curve were discussed and the carbon concentration inside the sample was measured. The Ferrite layer of about 450 µm thickness was obtained without pearlite on the surface of the sample in the microstructure. The thermal expansion curve shows that the Ferrite layer without pearlite is formed during the local phase transformation, which is followed by the global transformation. The carbon concentration in the core of the sample (0.061%) is significantly higher than that of the bulk material (0.054%). All results show that carbon has long-range diffusion from the outer layer to the inner layer of the sample. The transformation is predominantly interface-controlled mode during local transformation, and the interface migration rate is about 2.25 µm/s.
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control of carbon content in steel by introducing Proeutectoid Ferrite transformation into hot rolled q p process
Journal of Materials Engineering and Performance, 2018Co-Authors: Jian Kang, Guo Yuan, Guo-dong WangAbstract:A processing strategy involving primary and secondary carbon partitioning is proposed for the hot-rolled quenching and partitioning process through the introduction of Proeutectoid Ferrite transformation after rolling. The microstructures of the steels were characterized using scanning electron microscopy, transmission electron microscopy, electron probe microanalysis, and x-ray diffraction, and the mechanical properties were evaluated using a universal tensile machine. The blocky retained austenite that distributed along the Ferrite grain boundaries was promoted based on the coupling action of the primary and secondary carbon partitioning, which enhanced the transformation-induced plasticity effect during deformation despite the high carbon concentration. A Ferrite formation temperature range of ~ 760 to 800 °C was proposed. In addition, from the perspective of industrialization, the observed ‘plateau trends’ for the retained austenite fraction and product of strength and elongation suggest the availability of a wide processing window of 215-362 °C for controlling the coiling temperature.
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microstructure and partitioning behavior characteristics in low carbon steels treated by hot rolling direct quenching and dynamical partitioning processes
Materials Characterization, 2016Co-Authors: Guo Yuan, Jian Kang, Dong Chen, Guo-dong WangAbstract:Abstract In this work, a new process and composition design are proposed for “quenching and partitioning” or Q&P treatment. Three low carbon steels were treated by hot-rolling direct quenching and dynamical partitioning processes (DQ&P). The effects of Proeutectoid Ferrite and carbon concentration on microstructure evolution and mechanical properties were investigated. The present work obtained DQ&P prototype steels with good mechanical properties and established a new notion on compositions for Q&P processing. Microstructures were characterized by means of electro probe microanalyzer (EPMA), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and X-ray diffraction (XRD), especially the morphology and size of retained austenite. Mechanical properties were measured by uniaxial tensile tests. The results indicated that introducing Proeutectoid Ferrite can increase the volume fraction of retained austenite and thus improve mechanical properties. TEM observation showed that retained austenite included the film-like inter-lath austenite and blocky austenite located in martensite/Ferrite interfaces or surrounded by Ferrites. It was interesting that when the carbon concentration is as low as ~ 0.078%, the film-like inter-lath untransformed austenite cannot be stabilized to room temperature and almost all of them transformed into twin martensite. The blocky retained austenite strengthened the interfaces and transformed into twin martensite during the tensile deformation process. The PSEs of specimens all exceeded 20 GPa.%.
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microstructure and texture of strip cast grain oriented silicon steel after symmetrical and asymmetrical hot rolling
Steel Research International, 2014Co-Authors: Hong-yu Song, Hai-tao Liu, Dian-qiao Geng, Zhenyu Liu, Devesh R K Misra, Guo-dong WangAbstract:A grain-oriented silicon steel as-cast strip was produced by twin-roll strip casting. Then the as-cast strip was symmetrically and asymmetrically hot rolled, respectively. The microstructure and texture evolution was investigated by a combination of optical microscopy, X-ray diffraction, and electron backscattered diffraction methods. The microstructure of the as-cast strip consisted of Ferrite matrix and martensite, and the texture was characterized by pronounced {001} 〈0vw〉 fiber texture in the outer layers and nearly random texture in the inner layers. After symmetric hot rolling, the microstructure was composed of deformed Ferrite grains, Proeutectoid Ferrite grains and pearlite. The texture was characterized by pronounced {001} 〈0vw〉 fiber texture in the outer layers and mild γ-fiber texture in the inner layers. By contrast, when asymmetric hot rolling was applied, considerably dispersive Proeutectoid Ferrite and pearlite and relatively strong Goss texture were observed, together with strong {001} 〈0vw〉 fiber texture in the outer layers.
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microstructure evolution and mechanical properties of a hot rolled directly quenched and partitioned steel containing Proeutectoid Ferrite
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: Xiao Dong Tan, Xiao Long Yang, Fei Peng, Guo-dong WangAbstract:Abstract A low carbon V microalloyed steel was treated by hot-rolling direct quenching and partitioning (HDQ&P) processes. The microstructures were characterized by polygonal Proeutectoid Ferrite and lath martensite accompanying with both blocky and film-like retained austenite. This kind of HDQ&P steel possesses a lower yield ratio and similar tensile strength and elongation when compared with the existing HDQ&P steel without Ferrite. Partitioning processes with different time were designed to optimize the characteristics of the retained austenite and to control its stability. The microstructure–properties relationship, the stability of the retained austenite, and the transformation-induced plasticity (TRIP) behavior were investigated by comparing the microstructures and mechanical properties of the HDQ&P sheets with those of the TRIP sheets. The results show that the introduction of Proeutectoid Ferrite can ensure the low yield strengths of the materials and simultaneously intensify the inhomogeneous distributions of carbon and silicon in the untransformed austenite. The particular element distributions result in a considerable amount of large blocky retained austenite locating on the Ferrite/martensite boundaries or in some regions surrounded by Ferrite. The high tensile strength of the HDQ&P steel can be attributed to the major martensitic structure, the V-bearing precipitates in Ferrite and the TRIP effect of the retained austenite. The outstanding combination of strength, yield ratio and ductility, which synthesizes the advantages of dual-phase (DP) steel, TRIP steel and Q&P steel, indicates that the HDQ&P steel has a great potential for practical application.
Masato Enomoto - One of the best experts on this subject based on the ideXlab platform.
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Discussion on the Alloying Element Partition and Growth Kinetics of Proeutectoid Ferrite in Fe-C-Mn-X Alloys
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2011Co-Authors: Masato EnomotoAbstract:Experimental data on alloying element partition and growth kinetics of Proeutectoid Ferrite in quaternary Fe-C-Mn-Si, Ni, and Co alloys were reanalyzed using an approximate method, which permits a quick evaluation of alloy partitioning to be made. The method yielded results in good agreement with DICTRA and is applicable to Fe-C base multicomponent alloys. Differences of the predicted local condition at the α/γ boundary from those previously presented in the alloys are noted.
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alloying element partition and growth kinetics of Proeutectoid Ferrite in hot deformed fe 0 1c 3mn 1 5si austenite
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2011Co-Authors: K Kanno, Masato EnomotoAbstract:Alloying element partition and growth kinetics of Proeutectoid Ferrite in deformed austenite were studied in an Fe-0.1C-3Mn-1.5Si alloy. Very small Ferrite particles, less than several microns in size, were formed within the austenite matrix, presumably at twin boundaries as well as at austenite grain boundaries. Scanning transmission electron microscopy–energy-dispersive X-ray (STEM-EDX) analysis revealed that Mn was depleted and Si was enriched in the particles formed at temperatures higher than 943 K (670 °C). These were compared with the calculation of local equilibrium in quaternary alloys, in which the difference in diffusivity between two substitutional alloying elements was assumed to be small compared to the difference from the carbon diffusivity in austenite. Although the growth kinetics were considerably faster than calculated under volume diffusion control, a fine dispersion of Ferrite particles was readily obtained in the partition regime due to sluggish growth engendered by diffusion of Mn and Si.
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influence of solute drag on the growth of Proeutectoid Ferrite in fe c mn alloy
Acta Materialia, 1999Co-Authors: Masato EnomotoAbstract:The diffusion-controlled growth of Proeutectoid Ferrite (α) from austenite (γ) in an Fe–C–Mn alloy was simulated incorporating the possible drag effect of Mn on the migration of α:γ interphase boundaries. The magnitude of drag force or the dissipation of free energy by drag was evaluated by means of Cahn and Purdy–Brechet models. The growth rate of Ferrite was calculated from the flux balance equation for carbon taking into account the fact that the carbon concentration at the boundary in austenite varied with time. Whereas the time exponent of growth deviated from one-half at each moment, the overall time dependence was dictated by carbon volume diffusion in austenite. The reported differences of experimental growth rates from those calculated assuming paraequilibrium were reduced considerably by incorporating the drag of Mn, although simulation results may largely depend on the shape and depth of solute interaction potential with α:γ boundaries and Mn diffusivity within the boundary, etc.
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grain boundary nucleation of Proeutectoid Ferrite in an fe c ni alloy
Isij International, 1999Co-Authors: Masato Enomoto, Y KobayashiAbstract:The nucleation kinetics of Proeutectoid Ferrite at austenite grain boundaries were studied in an Fe-C-Ni alloy by observing Ferrite particles on fracture facets along prior austenite grain boundaries. Whereas a large scatter in the Ferrite particle numbers was observed among grain boundary facets, the average particle number appeared to increase with isothermal holding time. The particle number measured on the polished surface of specimens applying Schwartz-Saltykov analysis also increased with holding time. Diffusion-controlled growth of a Ferrite nucleus was simulated incorporating Gibbs-Thomson capillary effect to indicate that the time for a nucleus to grow to a detectable size was insignificantly small. These results seem to show that Ferrite nucleation occurred in a sizable time range and continuous nucleation, rather than site saturation (instantaneous nucleation), may account better for Ferrite nucleation kinetics at temperatures of measurement. The difference in Ferrite particle numbers between the two methods of measurement is discussed in terms of the possible omission of small particles and non-sphericity of Ferrite particles etc.
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effects of vanadium and niobium on the nucleation kinetics of Proeutectoid Ferrite at austenite grain boundaries in fe c and fe c mn alloys
Materials Transactions Jim, 1994Co-Authors: Masato Enomoto, N Nojiri, Y SatoAbstract:Nucleation kinetics of Proeutectoid Ferrite allotriomorphs at austenite grain boundaries were measured in Fe-0.1 mass%C and Fe-0.1 mass%C-2 mass%Mn alloys with small amounts of V or Nb. Nb was one or two orders of magnitude more effective than V in reducing the nucleation kinetics of Ferrite compared at the same amount of addition. The segregation of alloying elements to austenite grain boundaries and the formation of atom clusters with carbon or fine coherent precipitates at Ferrite nucleation sites were considered as possible causes for the observed suppression of nucleation. However, quantitative agreement with theory or direct experimental evidence is yet to be obtained for these possibilities to be deemed operative in the present alloys
Zuo Liang - One of the best experts on this subject based on the ideXlab platform.
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effect of high magnetic field on eutectoid point in fe 0 76 c alloy
Transactions of Materials and Heat Treatment, 2009Co-Authors: Zuo LiangAbstract:The microstructure of Proeutectoid Ferrite and carbon content at eutectoid point of Fe-0.76%C alloy treated with different heat treatment process without and with applying magnetic field was examined.It is found that the amount of Proeutectoid Ferrite and the carbon content at eutectoid point increase obviously for the alloy under magnetic field heat treatment.Magnetic field decreases the driving force of nucleation of Proeutectoid Ferrite and shifts the eutectoid point to the side of high carbon content.
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effect of holding time on microstructure of Proeutectoid Ferrite in fe 0 76 c alloy in high magnetic field
Ironmaking & Steelmaking, 2008Co-Authors: Zuo LiangAbstract:The microstructure of Proeutectoid Ferrite transformed from austenite in Fe-0.76%C alloy after holding at 807 ℃ in magnetic field(12 T).It was found that the amount and grain number of Proeutectoid Ferrite in the steel treated in magnetic field were more than that treated without magnetic field.It is assumed that the magnetic field decreased the driving force of Proeutectoid Ferrite nucleation.The Proeutectoid Ferrite grains elongated along the magnetic field direction,and the angles between the major axis of Proeutectoid Ferrite and magnetic field direction decreased with the increase of holding time.It is because austenite grains in the sample grew with the holding time,and the distance between the nuclei of Proeutectoid Ferrite became larger,leading to increase of diffusion distance of Fe atom from austenite to Proeutectoid Ferrite.
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effect of magnetic field intensity on microstructure of Proeutectoid Ferrite in fe 0 76 c alloy
Acta Metallurgica Sinica, 2008Co-Authors: Zuo LiangAbstract:The microstructural features of Proeutectoid Ferrite during transformation from austen- ite to Ferrite in Fe-0.76%C alloy under different magnetic field intensities.It was found that the amount of Proeutectoid Ferrite transformed and the carbon content at eutectoid point increased considerably with the increase of magnetic field intensity.The most possible reason is that the magnetic field shifts the eutectoid point to the side of high carbon content and high temperature,which increases the starting-temperature of the transformation from austenite to Ferrite.The Proeutectoid Ferrite grains are elongated along the magnetic field direction,and the angle between the major axis of Proeutectoid Ferrite and magnetic field direction is decreased with the increase of magnetic field intensity,which can be explained as follows:the Proeutectoid Ferrite becomes the magnetic dipolar under high mag- netic field,and then the polarized austenite atoms are more easy to diffusion to Ferrite grain along the magnetic field direction.
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effect of austenizing temperature on the microstructure of Proeutectoid Ferrite in fe 0 76 c alloy under high magnetic field
Journal of materials and metallurgy, 2008Co-Authors: Zuo LiangAbstract:The present studies are to investigate the microstructure features of Proeutectoid Ferrite during transformation from austenite to Ferrite at different austenizing temperatures without and with applying the magnetic field(12T) on Fe-0.76%C alloy.It was found that the fraction and the number of Proeutectoid Ferrite grains with magnetic field heat treatment were more than those without magnetic field heat treatment.The possible reason is that the magnetic field increases the driving force of Proeutectoid Ferrite nuclei and shifts the eutectoid point to higher carbon and higher temperature sides.The Proeutectoid Ferrite grains elongated along the magnetic field direction,and the angle between the major axis of Proeutectoid Ferrite and magnetic field direction was increased with the increase of austenizing temperature.The possible reason is that the coarse austenite grains could weaken the diffusion rates of Fe atom to Proeutectoid Ferrite grains.
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Effect of Carbon Content on Morphology of Proeutectoid Ferrite Grains in Fe-C Alloy in High Magnetic Field
Journal of Northeastern University, 2008Co-Authors: Zuo LiangAbstract:The effect of carbon content on the morphology of Proeutectoid Ferrite grains in Fe-C alloys annealed in high magnetic field was investigated,especially in high-purity Fe-0.12C,Fe-0.36C,Fe-0.52C and Fe-0.76C alloys.The results showed that the grain size of the Proeutectoid Ferrite gradually decreases with increasing carbon content and the trend to elongating the grains in the magnetic field direction to form chain-like arrangement becomes weaker.This phenomenon is not only attributed to the different carbon contents of the Fe-C alloys,but also closely related to the formation process and evolution mechanism of the Proeutectoid Ferrite grains.Consequently,a magnetic dipole model is proposed applicable to the early stage of Proeutectoid Ferrite transformation in low carbon Fe-C alloys or in case the distance between Proeutectoid Ferrite nucleus is relatively long in the Fe-C alloys in which the carbon content approaches the eutectoid composition.
P. R. Howell - One of the best experts on this subject based on the ideXlab platform.
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The interaction between Proeutectoid Ferrite and austenite during the isothermal transformation of two low-carbon steels — a new model for the decomposition of austenite
Journal of Materials Science, 1993Co-Authors: J. W. Lee, S. W. Thompson, R. Varughese, P. R. HowellAbstract:Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) have been employed to examine the austenite to Proeutectoid Ferrite and Ferrite/carbide reactions in two low-carbon (0.04 wt%) steels. It is demonstrated that Proeutectoid Ferrite (both polygonal and Widmanstätten) can “partition” the prior austenite grains into several smaller units or pools. It is also shown that prior to the initiation of the pearlite reaction, Ferrite grain growth can occur. The pools of austenite exert a Zener-like drag force on the migrating Ferrite grain boundaries. However, the Ferrite boundaries can eventually break away and small pools of austenite become completely embedded in single Proeutectoid Ferrite grains. Subsequently, these small pools of austenite transform to discrete regions of cementite, together with epitaxial Ferrite. Conversely, certain small pools remain in contact with the Ferrite grain boundaries and it is considered that transformation of these latter pools will eventually lead to the formation of massive films of cementite at the Ferrite grain boundaries. Larger pools of austenite prevent Ferrite boundary breakaway, and these latter, austenitic regions eventually transform to pearlite.
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factors influencing Ferrite pearlite banding and origin of large pearlite nodules in a hypoeutectoid plate steel
Materials Science and Technology, 1992Co-Authors: S. W. Thompson, P. R. HowellAbstract:AbstractThe microstructure and distribution of alloying elements in a hot rolled, low alloy plate steel containing (wt-%) 0·15%C, 0·26%Si, l·49%Mn, and 0·03%Al were examined using light microscopy and electron probe microanalysis. Microstructural banding was caused by microchemical banding of manganese, where alternate bands of Proeutectoid Ferrite and pearlite were located in solute lean and solute rich regions, respectively. Bands were well defined for a cooling rate of 0·1 K s−1, but banding was much less intense after cooling at 1 K s−1. At a cooling rate of 0·1 K s−1 and for austenite grains smaller than the microchemical band spacing, austenite decomposition occurred via the formation of ‘slabs’ of Proeutectoid Ferrite in manganese lean regions resulting in the growth of Ferrite grains across austenite grain boundaries. Abnormally large austenite grains result in the formation of large, irregularly etching pearlite nodules which traversed several bands. In specimens cooled at 1 K s−1, Ferrite/pearli...
