Study on effect of heat treatment on sensitization and stress corrosion cracking initiation of cold-worked and heat affected zone of 316L stainless steels

Abstract

The residual stress and cold work is common in most dissimilar weld components because of surface grinding and welding shrinkage and, these are significant contributing factors to stress corrosion cracking susceptibility. Because the post weld heat treatment is known as effective methods for reduction of residual stress and relaxation of degree of cold work, it is most effective way to alleviate primary stress corrosion cracking. On the other hand, the application of post weld heat treatment is limited to weld and low alloy steel region due to sensitization of stainless steels. Although the stainless steels containing low carbon is hardly sensitized, the applicability of post weld heat treatment has been not intimately evaluated. This work has confirmed that trend and shown the considerable benefit and limitation for reducing the susceptibility of primary stress corrosion cracking initiation. The stainless steels were not sensitized despite of post weld heat treatment at 600oC for 1.5 and 5 hours. The residual stress and microhardness of alloy 52/152 weld and 316L heat affected zone were markedly decreased after post weld heat treatment. Also, it was confirmed that the resistance of primary water stress corrosion cracking is improved by post weld heat treatment. And, it did not accelerate the intergranular stress corrosion cracking of 316L heat affected zone. Therefore, post weld heat treatment could be one of the effective mitigation methods applicable to nuclear power plants. However, in this study, the post weld heat treatment is not optimized because the heat treatment condition and test data are limited. The most effective post weld heat treatment procedure for reduction of residual stress in dissimilar weld metal is needed. For this reason, the sensitization behaviors of stainless steels have been investigated through accelerated heat treatment condition. The sensitization behaviors were different from ferrite morphologies of stainless steels. The stainl...