Analysis of γ→α transformation in Fe-C-Mn ternary alloy by phase-field simulation coupled with CALPHAD database

We investigate the isothermal austenite-to-ferrite (γ→α) transformation behaviors in a Fe-C-Mn ternary alloy simulated by the phase-field (PF) models based on the Kim-Kim-Suzuki (KKS) model and the linearized phase diagram by comparing with that predicted by the analytical model of diffusional phase transformations: the Coates model. The growth rates of the α phase during the transformation calculated by one- and two-dimensional PF simulations coupled with the CALPHAD (CALculation of PHAse Diagram) database are compared with that obtained from the Coates model. The results show that the kinetics of the γ→α transformation in the Fe-0.55C-3.12Mn [at%] alloy simulated by both PF models are close to the paraequilibrium (PE) mode. The results also indicate that the growth behavior of the α phase transits from interface-controlled to diffusion-controlled growth as the mobility of the austenite/ferrite (γ/α) interface increases. Furthermore, we clarify that the growth rate of the α phase calculated by the PF model based on the KKS model is found to be in good agreement with that calculated by the Coates model under the specific condition where the γ→α transformation proceeds without Mn diffusion, i.e., the PE mode, and the mobility of the γ/α interface is high.