Prediction of martensitic transformation and deformation behavior in the TRIP steel sheet forming

This paper presents a methodology for constitutive model construction of the multiphase steel coupling with TRIP (transformation-induced plasticity) effect and anisotropy characters. The TRIP effect is described by the evolution of phase transformation which is dependent on stress-state and temperature. The phase transformation kinetic model considering the dependence of the transformation rate on the multiaxial stress-state is established by means of simple-shear, uniaxial tension, plain strain and equibiaxial stretching tests at room temperature. It is shown that the stress triaxiality is decisive for the phase transformation rate. The higher the stress triaxiality, the faster the martensitic transformation, i.e. the more unstable the retained austenite is transformed. The proposed constitutive model is implemented into a commercial FE code to obtain a stress–strain curve of TRIP steel and predict the martensitic transformation at different regions of the rectangular deep drawing parts, which corresponds well with the experiment results. The variation of the elastic modulus with the martensitic transformation during stamping is also considered to improve the accuracy of springback simulation for TRIP steel. The results above present a foundation for the formability control technology.