Resistance of Hydrogen Embrittlement on Hot-Sheared Surface during Die-Quench Process

This study investigated resistance of hydrogen embrittlement on a hot-sheared surface of die-quenched steel sheets. The specimens were sheared at 750 °C and 650 °C after austenitization, and then quenched by water cooling. Additionally, the specimens were cathodically hydrogenized for 48 hours to accelerate cracking by hydrogen embrittlement. This sequence resulted in the residual tensile stress of over 1 GPa on the sheared surface and hydrogen concentration of about 1.5 ppm. Despite these severe conditions, cracking by hydrogen embrittlement was not observed. The state of micro-structure 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.