Stress corrosion and hydrogen embrittlement of two precipitation hardening stainless steels

Abstract

Straining of smooth tensile specimens of two precipitation hardening stainless steels over a wide range of controlled potentials in natural sea water has revealed regimes of low ductility above about — 200 mV(SCE) and below — 600 mV(SCE). The apparent loss inductility in the anodic region was attributable to dissolution and was found to be associated with pitting and crevice corrosion effects that were exacerbated when straining was conducted in acidified sea water. The embrittlement observed at more cathodic potentials, which gave rise to transgranular or intergranular failure depending upon the material and its heat treatment, is believed to be due to hydrogen that is evolved at such potentials. The occurrence of embrittlement by hydrogen in these materials, to produce similar modes of failure, was confirmed by testing smooth specimens ajtercathodic charging and both smooth and precracked specimens in gaseous hydrogen. Cracking of precracked specimens in gaseous hydrogen is complicated by the presence of δ ferrite stringers in the microstructure, which can give rise to delamination perpendicular to the principal plane of fracture if the stresses ahead of the crack are not reduced significantly by hydrogen embrittlement.