MODELING OF ISOTHERMAL AUSTENITE TO FERRITE TRANSFORMATION IN A Fe-C ALLOY BY PHASE-FIELD METHOD

Austenite-to-ferrite transformation in modern steels is a key metallurgical phenomenon as it can be exploited to produce microstructures that are closely associated with significant improvement of their properties. Both experimental and theoretical studies of this transformation have received much attention. In particular, in recent years, considerable efforts have been directed to the development of numerical models for adequate quantitative descriptions of the nucleation and growth of ferrite grains as well as the overall transformation kinetics. In this work, a modified multi-phase field model has been developed to simulate the isothermal gamma-alpha transformation in a Fe C alloy. This model takes both the effect of a finite interface mobility and a finite diffusivity into account, which hence enables a clear description of the mixed-mode nature of the transformation. In contrast to the diffusion controlled phase transformation model, the carbon concentration in front of the moving gamma-alpha interface is found to be non-equilibrium under this circumstance. In order to study the microstructural behavior and kinetics over the entire temperature range of the phase transformation, three different isothermal transformation processes have been