Some aspects of pitting corrosion susceptibility of As‐welded and thermally aged nitrogen‐alloyed 316SS weld metal

Abstract

Type 316N (0.07% N) stainless-steel welds prepared by shielded metal arc welding were evaluated for their pitting corrosion susceptibility in an acidified chloride environment and a neutral chloride environment in as-welded and thermally aged conditions at 823 and 923 K for 4, 10, 24, and 100 h. After 100 h thermal aging at 823 K, 46% of δ ferrite was transformed into carbide and 81% δ ferrite was transformed into carbide and sigma phases at 923 K for 100 h. On thermal aging at 823 K (0-10 h) and 923 K (10-100 h), the changes in the degree of alloy depletion (DOA) and pitting potential were marginal due to the presence of nitrogen. Thermally aged samples at 823 K beyond 24 h showed a significant decrease in pitting potential in acidic and neutral chloride media, whereas at 923 K, the pitting potential decreased significantly up to 10 h. The results of DOA and passive current density from the double-loop electrochemical potentiokinetic reactivation (DLEPR) test and the electrochemical reactivation test (ERT) correlated well with the observed secondary phases.The role of alloy depletion in terms of the parameters DLEPR, ERT, microstructure, and nitrogen alloying on pitting corrosion is discussed.