The ternary-based Fe-24Mn-3Cr alloy has superior mechanical properties based on an attractive combination of high strength and ductility, with long-term environmental stability in highly corrosive environments compared to conventional ferritic steel alloys. This study reports that the environmental instability caused by the rapid electrochemical corrosion kinetics on the surface of conventional high Mn-bearing ferrous alloys could be overcome by a combination of high Mn–low Cr-balanced Fe and their synergistic interactions. In contrast to Cr-free Mn-bearing alloys, the high Mn–low Cr-bearing alloy showed comparatively lower corrosion kinetic parameters, without a continuously increasing trend, and higher polarization resistance according to electrochemical polarization and impedance spectroscopy measurements. Moreover, the rate of degradation caused by erosion–corrosion synergistic interaction under erosion–corrosion dynamic flow conditions was the lowest in the high Mn–low Cr-bearing alloy. These surface-inhibiting characteristics of the alloy were attributed primarily to the formation of a bilayer scale structure consisting of inner α-Fe2−xCrxO3/outer FexMn3−xO4 on the surface.

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The corrosion behaviour of electrochemically induced surface annealed (EISA) 304L stainless steel was analysed using a range of electrochemical methods, such as polarisation, impedance and Mott-Schottky techniques. Secondary ion mass spectroscopy was used to examine the elemental distribution around the surface of an EISA-treated specimen. The results showed that the EISA treatment increases the resistance to pitting corrosion due to surface densification caused by the absorption of NO and/or N 2 , which had been reduced under cathodic polarisation during the EISA process. Owing to the limited annealing depth, however, the prolonged corrosion process (i.e. Fe dissolution) can lead to the dissolution of NO and/or N 2 species, which had been absorbed on the outer surface, and only smaller portions remained with an uneven distribution at the surface. This can make the EISA-treated steel more vulnerable to corrosion.