On the Mechanism of Stress Corrosion Cracking in Austenitic Stainless Steels

Abstract

Stress corrosion behaviours of austenitic stainless steels containing various contents of nitrogen and of Inconel were investigated using thin-foil and bulk specimens.The mode of micro-attack in thin-foil specimens of nitrogen-rich stainless steel in a 3% NaCl aqueous solution (pH 1.6) at room temperature and of Inconel in a boiling 42% MgCl2 aqueous solution was almost the same as that for nitrogen-rich stainless steel in a boiling 42% MgCl2 aqueous solution. Stress corrosion behaviours of bulk specimens observed by the replica technique indicated that at the initial stage of corrosion no difference was recognized in the nucleation of micro-attack in all the cases, but with increase in exposure time there appeared a remarkable difference in the corrosion behaviours depending on the relative difficulty of the cracking conditions. In a nitrogen-rich stainless steel aged at 200°C after deformation, the segregation and precipitation were recognized in both the transmission electron microscope observations and the constant strain rate stress-strain relations.From these results, it seems that the segregation of solute atoms is particularly necessary for the propagation of stress corrosion cracking in austenitic stainless steels, and that the nucleation and propagation of cracking have different mechanisms.