A 2-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 purpos e, the diffusion equations are solved within each phase (alpha and gam ma) 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 t ransition to an alpha/gamma interface state before becoming gamma. Thi s procedure allows us to handle the displacement of the interface whil e respecting the flux condition at the interface. The model has been a pplied to the austenitization of a hypoeutectoid plain carbon steel du ring heating. Simulated microstructures showing the dissolution of fer rite particles in the austenite matrix are presented at different stag es of the phase transformation. Specifically, the influence of the mic rostructure scale and of the heating rate on the transformation kineti cs 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.