Martensite formation during heating from cryogenic temperatures-A phase-field study

A 3D elastoplastic phase-field model is used to study the effect of isochronal heating on martensitic transformation in stainless steel quenched to cryogenic temperature. The results show that the slower the heating, the larger is the martensite volume fraction developed on heating. The simulated microstructures show that the transformation is driven by autocatalysis during the early stages and by coarsening of existing martensite units during later stages of the transformation. The internal stresses are mainly relaxed by autocatalysis during the initial stages of the transformation, whereas they are relaxed by plastic deformation during the later stages of the transformation. The temperature for attaining a certain martensite fraction increases with increasing heating rate, which is consistent with a thermally activated transformation. Kissinger-like analysis of the simulated transformation curves provides an activation energy of 11.9 kJ/mol.