Selective dissolution of retained austenite in nanostructured bainitic steels

Nanostructured bainitic steels, containing bainitic ferrite laths and retained austenite films, formed at two different isothermal temperatures were compared  for corrosion behavior in chloride-containing solution using electrochemical techniques. The potentiodynamic polarization results suggest that nanostructured bainite formed at 200 °C exhibits marginally higher corrosion resistance compared with that at 350 °C. Post-corrosion analysis of the galvanostatically polarized samples revealed localized corrosion for both the steels, but the degree of attack was higher in the 350 °C steel than in the 200 °C steel. The localized corrosion attack was due to selective dissolution of the retained austenite phase. The higher volume fraction and larger size of retained austenite in the 350 °C steel as compared to that of the 200 °C steel contributed to the pronounced corrosion attack in the 350 °C steel.