Phase-field theory based finite element analysis for ratchetting behavior of medium-manganese steel

A phase field model for martensitic transformation considering crystal plasticity was developed to investigate the microscopic mechanism of the transformation-induced plasticity in response to ratchetting of mediummanganese steel with a ferritic matrix containing retained austenite. This model introduced various inelastic deformation mechanisms, i.e., martensitic transformation, the austenite, ferrite and martensite plasticity caused by dislocation slip. Combining phase field model with finite element method, the ratchetting behavior of medium-manganese steel under asymmetric load was simulated by COMSOL software, and the martensitic transformation and its effect on ratchetting was discussed. The simulated results show that the ratchetting strains evolutions of the medium-manganese steel are well described by the developed phase field model. Ratchetting strain increases with increasing stress amplitude, mean stress and stress ratio. The martensite content increases with increasing stress amplitude and decreases with increasing mean stress and stress ratio.When the plastic strain exceeds a certain value, the plastic strain induced by martensitic transformation will increase the ratchetting strain of medium-manganese steel, which indicates that the critical importance of the martensitic transformation for the overall ratchetting behavior of medium-manganese steel. The plastic deformation of mediummanganese steel is mainly composed of dislocation slip of austenite and ferrite, where the former is the main part. Because of martensitic transformation, the non-uniformity of micro strain field in medium-manganese steel is aggravated, and the equivalent plastic strain increases.