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