Finite element simulation on strain-induced martensitic transformation effects in TRIP steel sheet forming

In this paper, Tomita and Iwanmoto (TI) model is improved to simulate the forming process of TRIP steel sheet with four phases (ferrite, bainite, retained austenite and martensite). Anisotropic yield function is used to replace Mises yield function in TI model. A mixture hardening law with four phases is used to substitute for the mixture hardening law with two phases, and is verified by experiment data. The results of experiment and simulation are compared by the retained austenite volume fraction. The comparisons under uniaxial stretching, plane-strain stretching and balance biaxial stretching conditions approve that the constitutive equation is feasible. Can deep drawing is simulated with the new constitutive equation, and transformation of retained austenitic is agreed with experiment results. The effect of plastic strain and stress states on the retained austenite transformation is analyzed. Thickness distribution of the sheet forming process of TRIP steel shows that the new model is more suitable than the TI model.