Effect of intergranular carbides on the cracking behavior of cold worked alloy 690 in subcritical and supercritical water

Abstract

The effect of intergranular (IG) carbides on the cracking behavior of cold worked Alloy 690 was studied in both subcritical and supercritical water (SCW) environments. The crack growth rate (CGR) was lower when IG carbides were removed by prior solution annealed (SA) treatment, indicating a detrimental effect of IG carbides. The presence of IG carbides enhances the local strain accumulation at the grain boundary due to the lattice mismatch, thus promotes the crack tip strain rate and increases the CGR. The detrimental effect of IG carbides is more significant in subcritical water than in SCW, which can be attributed to the different controlling parameters of cracking between these two environments. The widely recognized beneficial effect of IG carbides on stress corrosion cracking in Alloy 600 is detrimental in cold worked Alloy 690, which might be related to the different degrees of grain boundary oxidation that contributed to IG cracking.