Thermo-mechanical finite element analysis incorporating the temperature dependent stress-strain response of low alloy steel for practical application to the hot stamped part

The isothermal stress-strain responses of a low alloy steel sheet (0.2C-0.1Si-1.4Mn-0.5Cr-0.01Mo-0.002B steel, 1.2t) at elevated temperature, which simulates the material response in the hot stamping process, were measured by the Gleeble3500 thermo-mechanical simulator. The measured stress-strain responses fitted to the Swift equations discretized within the deformation temperature were used for the practical finite element simulation of the hot stamping process, in which the complicated effects of the volumetric mismatch between phases and phase transformation inducing plasticity were effectively ignored due to the significant constraints by the press stamping. The material parameters for the thermo-mechanical FE simulations were determined by considering the effects of plastic work and phase transformation on the temperature history. A mini-sized b-pillar reinforcing part was used as the simulation model. In spite of the simplified approach adopted in this paper, the finite element procedure could provide important information on the temperature distribution, martensitic phase distribution (or final product hardness), and the effect of process parameters such as punch force on the performance of the final hot stamped product.