An original unified approach for the description of phase tranformations in steel during cooling : first application to binary Fe-C

Exploiting Landau's theory of phase transformations, defining an original order parameter and using the phenomenological transformation temperatures, it is reported that it is possible to describe in a global approach the conditions for the formation of each phase (ferrite, bainite, martensite) from austenite during cooling in steel. It allowed to propose a new rigorous classification of the different thermodynamic conditions controlling each phase tranformation. In a second step, the approach predicts naturally the effect of cooling rate on the bainite start temperature. Finally perspectives are assessed to extend the approach in order to take into account the effect of an external field such as applied stress.