Evaluation of initiation behavior of stress corrosion cracking for type 316L stainless steel in high temperature water. Behavior of crack initiation and effects of distribution of plastic strain on crack initiation

It is known that the initiation of stress corrosion cracking (SCC) in components such as the reactor core shroud and primary loop re-circulation piping made of L-grade stainless steel is affected by the properties of surface work hardened layer. Therefore, it is important to clarify the effect of the hardened layer on SCC initiation behavior. In this study, creviced bent beam (CBB) test using specimens made of Type 316L stainless steel with controlled distribution of surface work hardened layer was conducted in a simulated BWR environment in order to evaluate the effect of the controlled layer on SCC initiation behavior. The results obtained are as follows; (1) Micro intergranular SCC of low carbon stainless steel was initiated in 50 hours. (2) In this SCC test, it was found that only micro cracks whose depths were smaller than 50 μm were observed until 250 hours and cracks whose depths were larger than 50 μm were observed after 500 hours. (3) SCC was initiated preferentially on the region with high plastic strain gradient in the specimen with controlled distribution of work hardened layer. (author)