Study of thermal forming limit of medium-Mn steel based on finite element analysis and experiments

摘要

The medium-Mn steel, which is an outstanding representative of third-generation advanced automotive steel, is newly developed. Thus, studies on the thermal forming of this steel have just been initiated. This study was performed primarily on the thermal formability of medium-Mn steel. The uniaxial tensile simulation model was established in LSDYNA based on various material property experiments, and the ductile fracture critical values were obtained by simulated and experimental force-deformation curves. Results show that the medium-Mn steel is an isotropic material, and the strain rate has no significant effect on its flow stress at elevated temperature. The predicted thermal forming limit diagram (TFLD) was achieved from the numerical simulation results and was verified by the TFLD experiments based on the Nakazima test. Results show that the formability of medium-Mn steel increases rapidly at the beginning and then decreases gradually as the temperature increase. The theoretical optimal temperature for the formability was approximately 400 A degrees C, and the recommended initial forming temperature is approximately 450 A degrees C in actual industrial application of the thermal forming medium-Mn steel by considering the influence of contact heat transfer and heat radiation.