Resistance of Hydrogen Embrittlement on Hot-sheared Surface during Die-quench Process

Abstract

This study investigated the resistance of hydrogen embrittlement on a hot-sheared and quenched surface of 22MnB5 steel sheets. The specimens were sheared at 750°C and 650°C after austenitization, and then quenched by water cooling. Additionally, these specimens were cathodically hydrogenized for 48 h to accelerate cracking by hydrogen embrittlement. This sequence resulted in a residual tensile stress of over 1 GPa on the hot-sheared surface and a diffusible hydrogen density of about 1.5 ppm. Despite these severe conditions, cracking by hydrogen embrittlement did not arise. The state of the microstructure in the vicinity of the sheared surface might cause this high resistance against cracking. Indeed, sub-micron grained ferrite or deformed uncertain soft and hard phases, which might be more ductile than martensite, were observed around the sheared surface.