Warm deformation enhances strength and inhibits hydrogen induced fatigue crack growth in metastable 304 and 316 austenitic stainless steels

The effect of deforming temperature on fatigue crack growth rate (FCGR) was investigated for cold/warm deformed 304 and 316 stainless steels under 5.0 MPa hydrogen and argon gas atmospheres. The slope of the FCGR vs ΔK curve in both steels declined with increasing deforming temperature, especially in type 304 steel. Strain-induced α′ martensite was prone to flat-facetted, step-like and quasi-cleavage fracture. Warm deformation (400 °C) can inhibit the formation of α′ martensite around crack tip and cause cellular dislocation structures, which led to multi-directional crack pathway and lower FCGR. The microstructure was adjusted by warm deformation, and then hydrogen embrittlement resistance was improved on the basis of high-strength in metastable austenitic stainless steels.