A two-dimensional diffusion model for the prediction of phase transformations: Application to austenitization and homogenization of hypoeutectoid Fe-C steels

A two-dimensional (2D) model has been developed for the prediction of diffusive phase transformations (e.g. alpha to gamma). For that purpose, the diffusion equations are solved within each phase (alpha and gamma) using an explicit finite volume technique formulated for a regular hexagonal grid. The discrete alpha/gamma interface is represented by special volume elements alpha/gamma. An a volume element undergoes a transition to an alpha/gamma interface state before becoming gamma. This procedure allows us to handle the displacement of the interface while respecting the flux condition at the interface. The model has been applied to the austenitization of a hypoeutectoid plain carbon steel during heating. Simulated microstructures showing the dissolution of ferrite particles in the austenite matrix are presented at different stages of the phase transformation. Specifically, the influence of the microstructure scale and of the heating rate on the transformation kinetics has been investigated. Reverse TTT-diagrams calculated with this 2D model are compared with experimental results from the literature and with the predictions of a simpler one-dimensional (1D) front-tracking calculation. Finally, it is shown that interface instabilities leading to the formation of dendrites can also be reproduced by such a model. Copyright (C) 1997 Acta Metallurgica Inc.