Phase-field simulation of abnormal grain growth during carburization in Nb-added steel

Abstract

Abnormal grain growth of austenite phase often takes place during carburization of steels, originating from carbon concentration dependence of pinning pressure of fine precipitates, the size of which is typically a few orders of magnitude smaller than the austenite grain size. In this study, the phase-field model for simulating the abnormal grain growth during carburization in steels is developed based on a mean field approximation in which the curvature-driven growth with the pinning pressure due to fine particles is reproduced by explicitly introducing the pinning pressure into the time evolution equations of order parameters. This model is applied to simulations of the austenite grain growth during carburization in Nb-added steels. Simulations are carried out to understand the occurrence of abnormal grain growth at different carburization temperatures for different steel compositions. In addition, an effect of non-uniform distribution of fine particles, which often appears as a consequence of microsegregation, on abnormal grain growth is investigated.