Electrochemical corrosion behaviour of a novel submicron-grained austenitic stainless steel in an acidic NaCl solution

Novel microstructures consisting of various fractions of tempered martensite, retained austenite and submicron-grained austenite were processed in an AISI 301LN type austenitic stainless steel by reversion annealing of severely cold-rolled strips. Corrosion resistance of the special microstructures was investigated and compared with that of the conventional cold-rolled or annealed grades. Potentiodynamic anodic polarization study showed that the corrosion resistance in an acidic chloride solution (1 M NaCl + 0.1 M HCl, pH 1) is impaired by heavy cold working, but upon annealing it gets improved, faster in the 75% than in the 45% cold-rolled steel. The presence of martensite seems to be the factor reducing the general corrosion resistance. However, the submicron-grained structure exhibits better pitting corrosion resistance than the coarse-grained one in the acidic chloride solution and also in immersion in the ferric chloride solution, where pit initiation takes place preferably at grain boundaries.