Effects of Nitrogen Addition on the Pitting Corrosion and Microstructure of High Mn stainless Steels

Effects of nitrogen addition on the pitting corrosion and microstructure of high manganese Fe-20Mn-17Cr-14Ni-2.2Mo stainless steels were examined in de-aerated 0.1 M KCl solutions at room temperature. The addition of nitrogen to the alloys increased the pitting potentials, and significantly reduced the peak current density and the number of occurrence of meta-stable pits, compared to that of nitrogen free alloy. It was confirmed that the added nitrogen was solid-solutioned in the austenitic phase without forming any nitrides under the heat treatment at 1150 .deg. C for 20min. From the in-situ observation of the initiation and growth of pits with an optical microscope, pitting was found to occur consistently at MnS inclusions. The pitting corrosion behavior in the alloys was discussed in the view of the role of MnS and the change of passivation properties due to nitrogen addition in the alloys