Abstract
The formation process of Widmanstätten 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 Widmanstätten 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 Widmanstätten ferrite plate is in good agreement with the experimentally observed one. The simulation results of the growth of a single Widmanstätten ferrite plate suggest that the lengthening rate of the Widmanstätten 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 Widmanstätten ferrite from a grain boundary allotriomorph ferrite are performed. The results clarify that the growth of Widmanstätten 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 Widmanstätten ferrite plates due to the morphological instability. The distribution of Widmanstätten ferrite plates depends on the initial interface shape of the grain boundary allotriomorph ferrite.
