Effects of Cr2N on the pitting corrosion of high nitrogen stainless steels

Effects of nitrogen (N) content on the precipitation behavior of Cr₂N with its relevant influences on the resistance to localized corrosion of high nitrogen stainless steels (HNSs) were examined using an electrochemical microcell. HNS of Fe-18Cr-20Mn-3Mo-1.07N was highly resistant to pitting corrosion. With aging the alloy at 900 °C, Cr₂N precipitated initially along grain boundaries, then within grain, and eventually formed a lamellar structure, accompanied with a drastic decrease in the resistance to pitting corrosion. It was found from the electrochemical microcell tests that the lamellar Cr₂N was the most susceptible site for pitting corrosion when compared with any other heterogeneity such as a (Mn, Cr)-oxide or a Cr₂N precipitated along the grain boundaries.