Repassivation Behavior and Stress Corrosion Cracking Susceptibility of Stainelss Steels Containing Silicon

Austenitic stainless steels (SS) core internals components in nuclear light water reactors are susceptible to irradiation assisted stress corrosion cracking (IASCC). One of the effects of irradiation is the hardening of the SS and a change in the dislocation distribution in the alloy. Irradiation also alters the local chemistry of these austenitic alloys, for example in the vicinity of grain boundaries. The segregation or depletion phenomena at near grain boundaries may enhance the susceptibility of these alloys to stress corrosion cracking (SCC). It is also apparent that the segregation to the grain boundaries of elements such as carbon (C), sulfur (S), phosphorus (P), oxygen (O), nitrogen (N) and silicon (Si) are important factors on the resistance of SS to IASCC. However, the role of the segregation of these minor alloying elements on EAC-IASCC is still poorly understood.  The objective of the present work was to perform laboratory tests in order to better understand the role of Si on microstructure, electrochemical behavior and susceptibility to SCC. Experimental results are presented for two main types of especially prepared stainless steels: (1) Type 304L SS + 1-5% added Si and (2) 12% Cr Steel + 5% added Si. The latter chemistry was developed at Tohoku University to simulate the chemical composition of a typically irradiated austenitic SS.