The influences of microstructure and nitrogen alloying on pitting corrosion of type 316L and 20 wt.% Mn-substituted type 316L stainless steels

Abstract

The effects of nitrogen alloying on pitting corrosion of type 316LN and 20 wt.% Mn-substituted type 316LN stainless steels were investigated by potentiodynamic polarization tests in Cl− ion-bearing neutral and acidic solutions. Pitting resistance was markedly improved through the nitrogen alloying in both types of alloys, compared with the nitrogen-free alloys. It was confirmed that the added nitrogen was solid-solutioned in the austenitic phase without forming any nitrides under 20 min heat treatment at 1150°C. From the in situ observation on the initiation and growth of pits, pitting was found to occur consistently at the sites of inclusions. The pitting corrosion behaviors in both types of alloys were discussed with respect to the role of sulfides as initiators of pitting corrosion, and the changes of repassivation properties due to the nitrogen alloying in the alloys.