Passivity and resistance to localised corrosion of duplex stainless steels after ageing in solution containing chloride ions: local study using SIMS, high-resolution Auger and microcapillary techniques

摘要

The influence of long-term ageing in NaCI on the passivity and electrochemical behaviour of UNS S32304 was studied. The passive film thickness, the Cr/Fe ratio and the chloride content were significantly increased after ageing. The chloride distribution depends on residual stresses, the sample microstructure and surface preparation. Local electrochemical measurements revealed that pitting potentials are between 250 and 550 mV vs. SCE after electropolishing. The higher the chloride content, the lower the local pitting potential. It was also shown that the presence of chloride was balanced by the enrichment in chromium after ageing. Then no pitting potential could be measured.