STRESS-CORROSION CHARACTERISTICS OF COPPER-CONTAINING 18CR-8NI STAINLESS-STEEL IN SULFURIC-ACID-SOLUTION

Stress corrosion cracking (SCC) tests on 18Cr-8Ni stainless steel (SS) with Cu addition were carried out in H2SO4 solutions (with no additions) under constant loads, where SCC occurred. The SCC susceptibilities, attack morphology, and average, uniform dissolution rates, r(d), were examined as functions of environmental variables (applied potentials, current densities, H2SO4 concentrations, and test temperatures) and stress levels. Analyses of the corrosion product surface layer and measurements of both corroding electrode impedance and polarization curves were also made. SCC occurred at and near corrosion potentials where r(d) (controlled by the above variables) was below about 2.5 nm/s. The Cu addition acted as an anodic and cathodic inhibitor and the surface layer contained metallic Cu or was metallic Cu itself. Preferential crack paths were along (111) plane, deformation bands, and twin boundaries. Some discussion about SCC conditions and a role of Cu in SCC was made.