Stress-Corrosion Cracking in Austenitic Stainless Steel under Constant Strain Rate and Constant Polarization

The mechanism of stress-corrosion cracking of an austenitic stainless steel in 42% MgCl2 aqueous aerated and deaerated solutions was investigated under constant strain rates and constant polarization. From measurements of the stress-strain curves and the observation of corrosion behaviours at slip steps produced during stress-corrosion, it was found that the susceptibility of stress-corrosion cracking depended largely on the dissolved oxygen and the oxidizer in a corrosive medium and on the polarization of specimens, and also that the mechanism of stress-corrosion cracking differed depending on the strain rates. The presence of surface films on the austenitic stainless steel which failed in air (electropolished surface) and in a 42% MgCl2 aqueous solutions was confirmed by a reflection electron diffraction technique, and the surface films were found to consist of varying mixtures of Fe–Cr–Ni spinel type oxides, α- or γ-FeOOH and or α-Fe2O3.The combined action of the repassivation of fresh slip steps produced in the alloy-corrosive system and the stress to proceed the corrosion at particular slip steps play an important role in stress-corrosion cracking.