12th International Conference on Zinc & Zinc Alloy Coated Steel Sheet - GALVATECH 2021

22MnB5 press hardening steel is widely applied for automobile parts due to its reduced spring back effect after forming. In press hardening process, 22MnB5 steels are deformed by the press at high temperature and simultaneously quenched to obtain fully martensitic microstructure after the austenitization process. However, during the press hardening of Zn-coated 22MnB5 steels, the presence of liquid Zn generates microcracks on the steel surface, which is related to Zn-assisted liquid metal embrittlement (LME). The present work has investigated the effect of Si addition on Zn-assisted LME in 22MnB5 steels. 22MnB5 steels with 0.25 wt.% Si and 1 wt.% Si were prepared for comparison. Both of 22MnB5 steels were heated to 900 °C to be austenitized. After the austenitization, the specimens were air-quenched to 700 °C and isothermally deformed to 40 % engineering strain. All the process was conducted by Gleeble 3500. The heating speed and the holding time at 900 °C were controlled to investigate the LME sensitivity depending on the various austenitization conditions. The Zn-assisted LME was severer with faster heating speed and shorter holding time, and the Si-added 22MnB5 steel exhibited higher LME sensitivity. The deformed specimens were cut cross-sectionally to analyse the microstructures of steel/Zn coating interface and the steel matrix. The Fe-Zn alloying reaction at the steel/Zn coating interface was strongly related to the Zn-assisted LME of 22MnB5 steel.