MECHANISM OF BRITTLE-FRACTURE IN A DUCTILE 316 ALLOY DURING STRESS-CORROSION

The ductile f.c.c. 316 alloy is shown to exhibit brittle transgranular (and intergranular) stress corrosion cracking in a 153°C MgCl2 solution at free corrosion potential. Tests on smooth and pre-cracked specimens are performed to identify the mechanisms of fracture. Transgranular cracking is related to both a discontinuous microcleavage mainly on {100} planes and a microshearing on {111} planes. A new physical modelization is proposed to explain the brittle transgranular cracking. It is based on the influence of the localized anodic dissolution on the enhancement of the plasticity at the crack tip. The formation of dislocation pile-ups and the conditions of restricted slip induce a brittle microcracking. The crack propagation is then limited and arrested by the strong effect of relaxation in the ductile 316 alloy. Such a model is discussed as a function of the main factors governing the transgranular stress corrosion cracking sensitivity of ductile f.c.c. single-phase materials. © 1990.