Multi-phase-field simulation of cyclic phase transformation in Fe-C-Mn and Fe-C-Mn-Si alloys

Abstract The stagnant and inverse transformation stages during cyclic phase transformation in the two-phase region “ferrite + austenite” (intercritical region) of Fe-C-Mn and Fe-C-Mn-Si alloys were investigated using the non-equilibrium multi-phase-field (NEMPF) model, i.e. an MPF model with finite interface dissipation. We showed that if we used large interfacial permeability parameters that characterize the partitioning rate of solute atoms in the ferrite/austenite interface, the NEMPF model predicted the same transformation behavior as that simulated using the MPF model based on the assumption of the parallel tangent law. The simulation demonstrated that the inverse transformation stage, in which ferrite-to-austenite transformation proceeds despite decreasing temperature, could be naturally described by the NEMPF model coupled with the CALPHAD-based thermodynamic database. This study also elucidated a switching of the polarities of Mn and Si spike formed at the ferrite/austenite interface governed the driving force of the austenite-to-ferrite transformation and caused the stagnant stage where the phase transformation was suppressed. Furthermore, the impact of the amount of Mn and Si atoms on the stagnant stage length was examined using the NEMPF model. The simulations revealed that increasing the concentration of Mn and Si extended the stagnant stage, with a more pronounced effect with Mn rather than Si atoms.