Effect of nitrogen content on microstructure, mechanical properties, and corrosion behaviour of coarse-grained heat-affected zone of nitrogen-containing austenitic stainless steel

Abstract

AbstractThe microstructures and properties of austenitic stainless steel with varying nitrogen content after welding thermal simulation were investigated. The results indicate that the nitrogen fraction has a considerable influence on the phase composition and properties. Low nitrogen fraction leads to formation of δ-ferrite. After a welding thermal cycle, the number of annealing twins of high nitrogen-containing steel decreases, M23C6 precipitates, and fine M23C6 are observed. For low nitrogen-containing steel, large-size M23C6 and elongated δ-ferrite are formed, which deteriorate the ductility. Meanwhile, equilibrium phase calculations also reveal the inhibiting effect of nitrogen on M23C6 and δ-ferrite. Furthermore, susceptibility to intergranular attack by 10 % oxalic acid solution was detected, and the synergistic effect of coherent twin boundaries, M23C6, and δ-ferrite leads to low resistance to corrosion for low nitrogen-containing steel.