Study of Tailored Hot Stamping Process on Advanced High-Strength Steels

Abstract

Ultra-high-strength steels (UHSS) combined with tailor-stamping technologies are increasingly being adopted in automotive body production due to crashworthiness improvements and part weight reduction, which meet safety and energy saving demands. Recently, USIBOR®2000 (37MnB5) steel has been added to the family of UHSS. This new material allows higher performance with respect to its predecessor USIBOR®1500 (22MnB5). In this work, the two steels are compared for the manufacturing of an automotive B-Pillar by press-hardening with a tailored tool tempering approach. A Finite Element (FE) model has been developed for the numerical simulation of thermomechanical cycles of the press-hardening process. The FE-simulations have been performed with the aim of obtaining soft zones in the part, by varying the quenching time and the temperature of heated tools. The effects of these parameters on the mechanical properties of the part have been experimentally evaluated thanks to hardness and tensile tests performed on specimens subjected to the numerical thermo-mechanical cycles using the Geeble-3180 physical simulator. The results show that for both UHSS, an increase in quenching time leads to a decrease in hardness up to a threshold value, which is lower for the USIBOR®1500. Moreover, higher mechanical resistance and lower elongation at break values are derived for the USIBOR®2000 steel than for USIBOR®1500 steel.