Phase-field Simulation of Habit Plane Formation during Martensitic Transformation in Low-carbon Steels

The origin of the habit plane of the martensite phase (alpha') in low-carbon steels is elucidated by three-dimensional phase-field simulations. The cubic -> tetragonal martensitic transformation and the evolution of dislocations with Burgers vector a(alpha)'/2 < 111 >alpha', in the evolving alpha' phase are modeled simultaneously. By assuming a static defect in the undercooled parent phase (gamma), we simulate the heterogeneous nucleation in the martensitic transformation. The transformation progresses with the formation of the stress-accommodating cluster composed of the three tetragonal domains of the alpha' phase. With the growth of the alpha' phase, the habit plane of the martensitic cluster emerges near the (111)(gamma) plane, whereas it is not observed in the simulation in which the slip in the alpha' phase is not considered. We observed that the formation of the (111)(gamma) habit plane, which is characteristic of the lath martensite that contains a high dislocation density, is attributable to the slip in the alpha' phase during the martensitic transformation.