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.