Alloy design employing high Cr concentrations for Mo-free stainless steels with enhanced corrosion resistance

•Mo was strategically replaced with Cr in stainless steels.•The feasibility of developing Mo-free, high-Cr stainless steels was investigated.•Pitting corrosion resistance was superior for Fe-25Cr compared to Fe-20Cr-2Mo.•The enhancement of corrosion resistance by Cr addition was investigated. In this study, we demonstrate the strategic replacement of Mo with excess Cr in Fe-Cr alloys and report their corrosion resistances. To better understand pitting corrosion, the electrochemical properties of the passive films observed on different alloys (Fe-20Cr-2Mo and Fe-25Cr) were compared. Mo-free Fe-25Cr offered comparable or better pitting corrosion resistance than Fe-20Cr-2Mo during film breakdown, repassivation, and pit propagation stages. We investigated the reason for enhanced stability against pitting corrosion as a result of Mo exclusion in such alloys. Mo accelerated co-dissolution of Fe and Mo itself, consequently enriching Cr on the surface and ultimately promoting onset of passivity.