Pitting Corrosion Resistance of Mn-Alloyed Austenitic Stainless Steels

The aim of the study was to examine the role of composition, inclusions, and precipitates on the pitting corrosion resistance of Mn-alloyed austenitic stainless steels. The pitting corrosion measurements were conducted in three electrolytes: sea water (3.56wt% NaCl), sulfuric acid (0.5M H2SO4), and sulfuric acid+salt (0.5M H2SO4+0.4M NaCl) solutions. In the tests, it was observed that manganese sulfides act as corrosion pit initiators. As the Cr content was decreased and Ni partially replaced by Mn, the pitting corrosion resistance was reduced in seawater and H2SO4+NaCl solutions. On the other hand, the amount of inclusions was not found to have a clear correlation to the potential at which the corrosion pits initiate. In the sulfuric acid solution, no pitting was observed and all the materials exhibited similar behavior in the passive range. However, in the transpassive range the dissolution rate of AISI 304 steel was greatest, whereas more Mn and less Ni and Cr containing steels exhibited a secondary passivation behavior.