HYDROGEN EFFECTS ON THE DUCTILE TO BRITTLE TRANSITION BEHAVIOR OF 21-6-9-STAINLESS-STEEL

Charpy V-notched impact test studies on 21-6-9 austenitic stainless st eel at 293 and 77 K demonstrated that hydrogen charging promoted the f ormation of larger microvoids at 293 K, promoted the formation of face ts at 77 K, and reduced the energy absorbed by the material at both te mperatures. These observations suggest that the role of hydrogen in th e impact behaviour of this material is to enhance whatever crack-growt h mechanism is operating at a given temperature. Further, the observat ion that embrittlement exists even at liquid nitrogen temperatures ind icates that little or no localized rearrangement of hydrogen during th e test is required or that relatively high strain-rate effects on hydr ogen embrittlement need not be necessarily attributed to enhanced tran sport of hydrogen atmospheres by mobile dislocations. The data present ed in this paper are consistent with a model in which the mechanism of hydrogen embrittlement is affected by the extent of plastic deformati on.