Corrosion Behaviour of Chrome-Manganese Austenitic Stainless Steels and AISI 304 Stainless Steel in Chloride Environment

Electrochemical behaviour of chrome-manganese austenitic stainless steels (Cr-Mn ASS) and AISI 304 stainless steel (SS) is evaluated in various chloride (Cl-) concentrations (Cl- free to 20,000 ppm) to simulate rural, industrial and marine environment. Potentiodynamic polarization and electrochemical impedance spectroscopy has clearly shown that with increase in Cl- concentration, the corrosion rate of both Cr-Mn ASS and AISI 304 SS increases and polarization resistance decreases. Comparatively, Cr-Mn ASS is more affected by Cl- concentration than AISI 304 SS. This is attributed to relatively low Cr content and lack of Ni. The findings have been explained with the help of point defect model. However, in less aggressive environment of up to 100 ppm Cl- concentration, Cr-Mn ASS may be a candidate material as a cheaper substitute of AISI 304 SS. Ways of improving corrosion resistance of Cr-Mn ASS by alloying with various elements have also been discussed. It is argued that a dedicated effort is needed to improve corrosion resistance of Ni-free or low-Ni Cr-Mn ASS.