HYDROGEN-INDUCED STRAIN LOCALIZATION AND FAILURE OF AUSTENITIC STAINLESS-STEELS AT HIGH HYDROGEN CONCENTRATIONS

Mechanical behavior and fractography of hydrogen-austenitic stainless steel solid solutions were studied to determine the microstructural origins of hydrogen-assisted fracture. AISI 310S and 304 stainless steels containing hydrogen in homogeneous solid solution in concentrations up to approximately 15 at. % resulted in an increase in flow stress by more than a factor two. The loss in ductility increased with increasing hydrogen content and was accompanied by an increasing frequency of "brittle" secondary cracks. The 304 alloy was embrittled at lower concentrations than was the 310S. In the polycrystalline austenitic stainless steels "brittle" cracking was predominantly intergranular, although there was evidence of shear crack formation along operating slip planes. Intensely localized shear along active slip planes was found on both fracture surface and on polished side surfaces of specimens containing solute hydrogen. Shear localization in the hydrogen-austenitic stainless steel solid solutions appeared to result from the limitation of the number of active slip systems by increasing the local stress to operate dislocation sources. In this study there was no evidence that hydrogen lowered the strength of internal interfaces, rather fracture was found to result from an extreme localization of slip into narrow slip bands and increased difficulty in slip transfer across interfaces.