Tailoring the Hardness in Multi-stage Press Hardening of 22MnB5 Sheet Material in a Progressive Die

Multi-stage press hardening enables a stepwise control of the thermo-mechanical history during press hardening, thereby facilitating a flexible hardness tailoring. Further degrees of freedom arise from utilizing rapid austenitization by induction heating within the first process stage. To assess the potential of rapid austenitization and a subsequent multi-stage thermo-mechanical history for tailoring the hardness, near-process characterizations are carried out with 22MnB5 steel. By a variation of the austenitizing temperature and dwell time, when cooling at a rate of 30 K/s, a hardness between 310 and 448 HV was set. By inducing a strain of 0.1 after rapid austenitization, the hardness was reduced by 15% due to an accelerated ferrite and bainite transformation. However, it was observed that a second, subsequent induced strain can potentially increase the hardness by work hardening. Using the example of multi-stage press hardening with rapid austenitization implemented in a progressive die, the hardness of 22MnB5 sheet material is tailored. A hardness between 350 and 445 HV was set by varying the austenitization parameters and the strain induced with a controllable blank holder.