Corrosion Behavior of High-Mn Austenitic Fe–Mn–Al–Cr–C Steels in NaCl and NaOH Solutions

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The corrosion behavior of austenitic Fe-Mn-Al-Cr-C twinning-induced plasticity (TWIP) and microband-induced plasticity (MBIP) steels with different alloying elements ranging from 22.6-30 wt.% Mn, 5.2-8.5 wt.% Al, 3.1-5.1 wt.% Cr, to 0.68-1.0 wt.% C was studied in 3.5 wt.% NaCl (pH 7) and 10 wt.% NaOH (pH 14) solutions. The results obtained using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques, alongside optical microscopy analysis, revealed pitting as the dominant corrosion mechanism in high-Mn TWIP steels. An X-ray diffraction analysis of the surface revealed that the main corrosion products were hematite (Fe₂O₃), braunite (Mn₂O₃), and hausmannite (Mn₃O₄), and binary oxide spinels were also identified, such as galaxite (MnAl₂O₄) and jacobsite (MnFe₂O₄). This is due to the higher dissolution rate of Fe and Mn, which present a more active redox potential. In addition, a protective Al₂O₃ passive film was also revealed, showing enhanced corrosion protection. The highest corrosion susceptibility in both electrolytes was exhibited by the MBIP steel (30 wt.% Mn). Pitting corrosion was observed in both chloride and alkaline solutions.