Micrographs - hydrogen-induced fatigue failure of 304 stainless steel

The effect of 104 mass ppm of hydrogen on the evolved microstructures associated with accelerated fatigue failure in type 304 austenitic stainless steel is reported. The fracture surface morphology changed from ductile striations to mixed mode that appeared “quasi-cleavage-like” and “flat.” Detailed microstructural characterization determined these fractures were along the austenite-martensite interfaces. The morphology and orientation of the strain-induced martensite were impacted by the presence of hydrogen. Hydrogen constrained the formation of 𝛼’-martensite into linear, planar bands in the grain nearest the fracture surface, and 𝜀-martensite was formed between the 𝛼′-martensite bands. The dislocation structure generated by the cyclic loading and the restriction of the martensitic transformation to specific forms by hydrogen is explained through the hydrogen-enhanced localized plasticity mechanism and accounts for the change in fracture mode.