The Effect of Nitrogen on the Localized Corrosion Resistance of Duplex Stainless Steel Simulated Weldments

Abstract

The effect of nitrogen, which is one of the most important elements in duplex stainless steels (SSs), was investigated for resistance to pitting corrosion and stress corrosion cracking (SCC) in various environments. The increase in nitrogen content increases the resistance of the base metal, which results from the improvement in the resistance of the γ-phase, which has lower chromium and molybdenum contents compared to α-phase. Nitrogen is an important element in sustaining the corrosion resistance of the heat affected zone (HAZ), which is heated to 1350 C or higher, because nitrogen promotes the formation of γ-phase during the cooling process after welding and avoids the precipitation of chromium carbides or nitrides at grain boundaries. When the nitrogen content is less than 0.08% in 22%Cr, 5.5%Ni, and 3%Mo base composition, the HAZ has little -γ-phase to lead to the high susceptibility to intergranular corrosion and intergranular stress corrosion cracking (IGSCC) occurs even in a pure CO₂-Cl⁻ environment containing no H₂S. Nitrogen has little effect on the precipitation behavior of the other phase in the base metal during aging heat treatment of around 700 C.