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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.

In order to understand the composition of the Nb-Mo bcc phase suitable to introduce B2-NiAl phase for the improvement of oxidation resistance as an Al reservoir layer for maintaining Al2O3 surface layer, a NiAl-Nb-Mo section of the quaternary Al-Nb-Ni-Mo phase diagram is studied. It is found that the ternary τ2 phase appears in wide composition range of alloys, both the hardness and cracking tendency decreases with increasing the Mo concentration of the alloys.

This study investigated resistance of hydrogen embrittlement on a hot-sheared surface of die-quenched steel sheets. The specimens were sheared at 750 ºC and 650 ºC 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, submicron grained ferrite or deformed uncertain soft and hard phases, which might be more ductile than martensite, were observed around the sheared surface.

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