Investigation of the progressive hot die stamping of a complex boron steel part using numerical simulations and Gleeble tests

Abstract

During hot progressive stamping processes, quenchable steels undergo complex thermomechanical forming cycles which include transfer operations, local cooling and heating steps, and various successive contact conditions with the tools. In order to define appropriate process parameters, it is therefore necessary to define the limits of the thermomechanical cycles to which the steels can be subjected. Using the commercial FE software PAM-STAMP 2GTM, a fully coupled thermomechanical-metallurgical numerical model for the progressive hot stamping process was applied to a complex automotive part called a heel board. These simulations were performed in order to define the successive heating/forming/quenching steps required to form this part. The numerical model was then validated by simulating the thermomechanical cycles undergone at critical points on this part on a Gleeble machine using a specially designed sample and monitoring the cooling rate during the quenching steps. The Vickers hardness distribution and the microstructural evolution of the samples were analyzed by testing whether the part was completely in the martensitic state at the end of the multi-step operations. The heating/forming/quenching steps applied to the phase transformation kinetics showed that the mechanical and geometrical characteristics required for the forming of the heel board were achieved.