Abstract
A 3D model has been developed to predict the average ferrite grain size and grain size distribution for an austenite-to-ferrite phase transformation during continuous cooling of an Fe-C-Mn steel. Using a Voronoi construction to represent the austenite grains, the ferrite is assumed to nucleate at the grain corners and to grow as spheres. Classical nucleation theory is used to estimate the density of ferrite nuclei. By assuming a negligible partition of manganese, the moving ferrite–austenite interface is treated with a mixed-mode model in which the soft impingement of the carbon diffusion fields is considered. The ferrite volume fraction, the average ferrite grain size, and the ferrite grain size distribution are derived as a function of temperature. The results of the present model are compared with those of a published phase-field model simulating the ferritic microstructure evolution during linear cooling of an Fe-0.10C-0.49Mn (wt pct) steel. It turns out that the present model can adequately reproduce the phase-field modeling results as well as the experimental dilatometry data. The model presented here provides a versatile tool to analyze the evolution of the ferrite grain size distribution at low computational costs.
Highlights
FE-C-MN steels hold and retain an important position in high-quality construction and automotive steels, and their transformation behavior receives a lot of attention in academia and industry.[1,2,3,4,5,6] Their mechanical properties, which are controlled by their microstructure, can be tuned relatively by thermomechanical processing
The initial calculations of the transformation kinetics with the present model use exactly the same parameters for the simplified nucleation model as used in the Number density ρα (m-3)
A 3D model that couples classical nucleation theory and the interface moving under mixed-mode interface condition has been developed for ferrite formation in Fe-C-Mn steels during continuous cooling
Summary
FE-C-MN steels hold and retain an important position in high-quality construction and automotive steels, and their transformation behavior receives a lot of attention in academia and industry.[1,2,3,4,5,6] Their mechanical properties, which are controlled by their microstructure, can be tuned relatively by thermomechanical processing. Ferrite is the first transformation product that forms during cooling as a result of austenite decomposition. Understanding the decomposition of austenite (c) into ferrite (a) during cooling is of central importance for predicting the development of the microstructure during thermomechanical processes.
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