Prediction of the Volume Fraction of Retained Austenite in Sheet Metal Forming for Trip Steels

The dependence of the transformation rate on the multiaxial stress state corresponding to different loading paths is investigated. To achieve different loading paths, single shear uniaxial tension, plane strain and equi-biaxial stretching tests have been carried out for BTR380 steel. On Based of the experimental results, the influence of the stress state on stability of retained austenite is analyzed and an equation of transformation kinetics is developed to predict stress triaxiality-dependence strain-induced transformation. In sheet metal forming, the material undergoes complicated deformation. The prediction of the volume fraction of retained austenite during forming process is essential to estimate the contribution of the TRIP effect to improving formability. To this aim, the volume fraction of retained austenite in the part’s different regions has been calculated using the proposed transformation kinetics equation introduced into finite element method. The calculated results were successfully compared with the experimental data measured in deep drawing experiments.