Ultra-high-strength steel structures are exposed to corrosive environments in service, and there is a risk of hydrogen assisted cracking(HAC) due to stress corrosion cracking and hydrogen embrittlement. In this paper, the HAC threshold stress intensit...
Ultra-high-strength steel structures are exposed to corrosive environments in service, and there is a risk of hydrogen assisted cracking(HAC) due to stress corrosion cracking and hydrogen embrittlement. In this paper, the HAC threshold stress intensity factor (KIHAC) and fatigue life of ultra-high-strength steel were evaluated by applying stress in a corrosive environment to prevent structures fracture. On the surface of the crack, grain boundaries were embrittled by corrosion, and the grains were clearly observed, and cracks in the surface direction propagated slightly, but cracks in the depth direction did not. Therefore, the HAC threshold stress intensity factor of the depth was determined as 1.96MPa·m<SUP>0.5</SUP>. The static fatigue limit of ultra-high strength steel (SKD11:HV670) was determined as 400MPa.