Phase-Field Simulation of Austenite to Ferrite Transformation and Widmanstätten Ferrite Formation in Fe-C Alloy

Abstract

The formation process of Widmanstatten ferrite plates during the isothermal austenite to ferrite transformation in Fe-C alloy is simulated by the phase-field method. The effects of the anisotropy of interfacial properties on the growth kinetics of Widmanstatten ferrite plates are investigated by the regularized gradient energy coefficient method, which enables us to introduce a wide range of interface anisotropy. It is found that by employing this method, a very sharp tip of the plate can be simulated and the morphology of Widmanstatten ferrite plate is in good agreement with the experimentally observed one. The simulation results of the growth of a single Widmanstatten ferrite plate suggest that the lengthening rate of the Widmanstatten ferrite plate increases with increasing strength of anisotropy, which causes the increase of interfacial energy at the tip. Furthermore, the simulations of the morphological changes of Widmanstatten ferrite from a grain boundary allotriomorph ferrite are performed. The results clarify that the growth of Widmanstatten ferrite plates from allotriomorph ferrite requires high anisotropy of interfacial energy. It is also proved that, in the early stage of the growth, the plate tips directly formed at the convex part of allotriomorph ferrite can preferentially develop into Widmanstatten ferrite plates due to the morphological instability. The distribution of Widmanstatten ferrite plates depends on the initial interface shape of the grain boundary allotriomorph ferrite.