Kinetics of Cr2N Precipitation and Its Effect on Pitting Corrosion of Nickel-Free High-Nitrogen Austenitic Stainless Steel

In the present work, hot-rolled nickel-free high-nitrogen austenitic stainless steels (HNSS) were solution annealed and aged at 700, 800 and 900 °C for 14 h. Precipitation behavior of Cr2N at the grain boundaries (GB) of HNSS was studied using TC-PRISMA simulation and TEM analysis. Pitting corrosion behavior of HNSS at solution annealed and aged conditions were studied using cyclic polarization and electrochemical impedance spectroscopy (EIS) analysis. TC-PRISMA simulation results showed that equal volume fraction of chromium nitride (Cr2N) precipitates was observed in GBs of austenite in all three aging conditions. However, large size precipitates were observed in samples aged at 900 °C compared to samples aged at 700 and 800 °C. TEM investigations showed the presence of discrete needle like Cr2N precipitates at the GBs and coarse lamellar austenite in regions adjoining the GBs in samples aged at 700 °C aging temperature. Disk-type Cr2N precipitates were observed in GBs of austenite in 900 °C aging temperature. Besides, sample aged at 900 °C exhibited relatively higher repassivation behavior compared to solution annealed and samples aged at 700 and 800 °C.