Corrosion behavior of nitrogen containing nickel-free manganese stainless steel

Abstract

The corrosion behavior of nitrogen containing nickel free manganese stainless steel in acidic and acidchloride medium was investigated by electrochemical polarisation and noise techniques. The alloy was subjected to different heat treatments, which resulted in its microstructure as step, dual and ditch according to ASTM A 262 practice A test. Electrochemical polarisation experiments were carried out in acidic (0.5M H2S0, 1M, 4M, 6M HNO,) and acid-chloride (0.5M H2S0,+ 0.5M NaCI) environment.The results of the investigation revealed that the specimens with step and dual structures showed stable passive region and similar corrosion behaviour in 0.5M sulphuric acid medium as well as in nitric acid medium up to a concentration of 4M, above which the dual microstructure showed deterioration in its corrosion behaviour. The ditch microstructure showed deterioration in sulphuric acid and at all concentrations of nitric acid. In acidic chloride medium, the dual microstructure exhibited lower pitting potentials compared to the specimens with step microstructure while the specimen with ditch microstructure dissolved continuously after open circuit potential. Electrochemical noise investigations carried out at open circuit potentials for the dual microstructure indicated poor corrosion resistance in sulphuric acid medium. In nitric acid medium, the alloy exhibited highest corrosion resistance in 0.5M HNO,, which decreased with increase in concentration.The corrosion resistance was found to be in close proximity in 4, 6 and 8M acid. The results of the investigation are detailed in this paper.