Phase field modeling of Widmanstätten ferrite formation in steel

Widmanstätten Ferrite (WF) formation is a complex transformation process, in which various physical variables are involved. In this work, we propose a phase field model of WF formation, which involves the interfacial anisotropy, misfit strain and multicomponent diffusion, for comprehending their coupled effects. The Fe-N-C system is adopted in numerical simulation and the realistic thermodynamic parameters are used. Attention is paid to growth speed and radius of the WF tip, which are dependent on the strength of anisotropic interfacial energy, eigenstrain, concentration and temperature. The simulation results reveal the individual effect of each of these variables and that none of the separate effect can be strong enough to achieve the large aspect ratio of Widmanstätten pattern. The morphology should be the result of their combined effect, which is not a simple linear super-position.