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.

Research highlights
► In this study we show the anomalous corrosion resistance behavior of Mo-containing austenitic SS in alkaline conditions.
► Conversely, in the same electrolytes, Mo has a strong beneficial effect on the corrosion resistance of ferritic and duplex stainless steels.
► Mo role is more likely to be ascribed to some prior-to-the-attack metallurgical effects rather than to post-attack interfacial kinetic processes, like those related to Mo cations interactions with electrolyte anions.