Phase field simulation of martensitic-transformation-induced plasticity in steel

The influence of martensitic-transformation-induced plastic deformation in steel is studied using phase field simulations. A phase field framework that incorporates elastic as well as plastic effects is used. A high-carbon steel is considered as an example to illustrate the coupling of martensitic transformations and plasticity. In this work, all 24 transformation variants associated with the Kurdjumov-Sachs orientational relationship are considered to realistically describe the martensitic transformation in steel. Temperature-induced as well as stress-induced transformations are studied. The role of plasticity is investigated by performing simulations with and without the plastic flow. It is found that transformation plasticity plays a dual role: (1) in the case of temperature-induced transformations it helps in the initial nucleation of the martensite by stabilizing the initial embryo, and (2) once the martensite starts to grow, transformation-induced plasticity resists the further growth and results in stabilization of retained austenite. In contrast, the simulations in the absence of transformation-induced plasticity show that the entire system transforms into martensite. For stress-induced transformations, it is found that transformation induces plastic deformations, even though the applied (macroscopic) stress is lower than the yield stress. Although the dominant contribution to the stress-induced strain arises due to the formation of favored martensite variants, transformation-induced plasticity generates significant additional deformation that can influence the mechanical properties and the resulting martensite domain pattern.