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

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 alpha/gamma-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. (C) 1998 Elsevier Science S.A. All rights reserved.