Anomalous corrosion resistance behavior of Mo-containing SS in alkaline media: The role of microstructure

Electrochemical and microscopy techniques were used to investigate the role of the microstructure in the corrosion behavior of Mo-containing stainless steel grades in alkaline chloride rich media. It is shown that under certain conditions, Mo containing grades can be even less corrosion resistant than Mo free ones. This anomalous behavior is straightforwardly related to the austenite phase. On the other hand, results show that Mo confirms its clearly beneficial effect in ferritic and duplex steels. Current transient analysis indicated that the protection mechanism in those cases appears to be related to an inhibited pit initiation rather than faster repassivation kinetics.