Effect of Heat Treatment on Corrosion and Stress Corrosion Cracking of S32205 Duplex Stainless Steel in Caustic Solution

Duplex stainless steels (DSSs) have generally performed very well in caustic environments. However, some corrosion and stress corrosion cracking (SCC) of DSSs have been reported in different pulp mill environments employing caustic solutions. Studies have shown that the corrosion and SCC susceptibility of DSSs depend on the alloy composition and microstructure of the steel. In this study, the effect of a sulfide-containing caustic environment (pulping liquor) and material properties (DSS alloy composition and microstructure) on the corrosion and SCC of DSSs was evaluated. During metal fabrication processes, localized areas of DSSs may be exposed to different temperatures and cooling rates, which may lead to changes in the microstructure in these regions. This change in microstructure, in turn, may affect the general and localized corrosion or SCC susceptibility of the affected area as compared to the rest of the metal. Hence, the effect of different annealing and aging temperatures as well as cooling rates on the microstructure and corrosion behavior of S32205 DSSs in caustic environment was evaluated. The results showed that changes in the microstructure of S32205 DSSs due to selected heat treatments did not have a significant effect on the general corrosion susceptibility of the steel in caustic environment, but its SCC susceptibility varied with changes in microstructures.