Simulations of pro-eutectoid ferrite formation using a mixed control growth model

Abstract

A simple numerical model is proposed to describe the formation of pro-eutectoid ferrite during the decomposition of austenite. The growth kinetics are analysed using a recently developed mixed control growth model. This model describes the movement of an interface in terms of an interaction between carbon volume diffusion and the intrinsic mobility of the α/γ-interface. Nucleation phenomena are treated using classical nucleation kinetics modified for compatibility with the mixed control growth model. A simple geometry is assumed for the ferrite nuclei. Isothermal transformation (IT) diagrams, as well as continuous cooling transformation (CCT) diagrams, are constructed from this model. The model yields C-shaped curves for pro-eutectoid ferrite formation during both isothermal and continuous cooling conditions. At deeper undercoolings, the transformation kinetics are determined primarily by the intrinsic interface mobility. An overlap between pro-eutectoid ferrite formation and pearlite formation is predicted. The fraction of pro-eutectoid ferrite is predicted to decrease with increasing undercooling or cooling rate. The effects of various model parameters on the transformation kinetics are investigated and discussed.