Very High Cycle Fatigue Behaviors and Surface Crack Growth Mechanism of Hydrogen-Embrittled AISI 304 Stainless Steels

The influence of hydrogen embrittlement on the fatigue behaviors of AISI 304 stainless steel is investigated. The fatigue endurance limits of the untreated and hydrogen-embrittled materials were almost the same at 400 MPa, and hydrogen embrittlement had little influence even though the sample contained about 8.1 times more hydrogen. Thus, the sensitivity of hydrogen gas in this material is very low. A surface crack initiation, growth, coalescence, and micro ridge model is proposed in this study. Slip line formation ⇒ microcrack formation ⇒ increases in the crack width, and blunting of the crack tip as it grows ⇒ formation of many slip lines because of deformation in the shear direction ⇒ growth of the crack in the shear direction, forming micro ridges, coalescence with adjacent cracks ⇒ continuous initiation, growth, coalescence, and ridge formation of surface cracks and specimen breakage.