Quantitatively evaluating the contribution of intergranular carbides, Cr-depleted zone, and grain boundary to intergranular stress corrosion cracking of Alloy 600 in a simulated boiling water reactors environment with high oxygen concentrations

The microstructure and stress corrosion cracking (SCC) behavior of Alloy 600 exposed to various sensitization parameters and subsequent cold work under simulated boiling water reactor (BWR) condition with high oxygen concentrations were systematically studied. The results show that a hardening layer of around 100 µm caused by grinding is still visible on the surface after 100 h of sensitization at 600 °C without cold work, while it is less pronounced at higher temperatures and/or cold work conditions. Larger and more dispersed intergranular (IG) carbides, and wider Cr-depleted zones (CrDZ) with less variation in Cr content correspond to higher sensitization temperatures and longer time, which improves the IGSCC resistance. The crack length is positively correlated with changes in Cr content in CrDZ, while a Cr content of around 5 wt.% is the critical value for mitigating IG crack growth. The crack propagation path and growth rate are influenced by the fraction of Σ3n coincident site lattice (CSL) boundaries and the feature of IG carbides and related CrDZ. Meanwhile, a new parameter named the Negative factor was proposed for the first time, which considers the three main influencing factors. Its correlation with IGSCC was also treated.