Gibbs Energy Minimisation Model For The Austenite-Ferrite Phase Transformation In Fe-C-X-Y Alloys

A new model has been developed to predict austenite <-> ferrite transformation kinetics in steels. For each alloying element, the concentration profile is computed solving a unique diffusion equation (including the 2 phases and the interface). The interface is described assuming linear variation of chemical potentials, saving thus computational time. Interface motion is driven by the minimisation of Gibbs energy. The model naturally reproduces the transition between thermodynamic equilibria (Para equilibrium, Local equilibrium with negligible partitioning, Local equilibrium) during heating. The validity of the model for reverse transformation has been validated on ternary and quaternary systems Fe-C-(Mn-Si-Mo) on decarburisation experiments.