Kinetic analysis on the long term stability of the effect obtained by various residual stress improvement methods. Evaluation for long term stability of residual stress improving treatment on Ni base alloy (report 2)

Stress corrosion cracking (SCC) is one of serious aging degradation problems for the Alloy 600 components of pressurized water reactors (PWRs). In order to prevent SCC, various methods such as water jet peening (WJP), laser peening (LP), surface polishing have been used to introduce compressive stresses at the surfaces of the PWR components. However, it has been reported that such compressive residual stress introduced by these methods might be relaxed during the practical operation, because of high temperature environment. In this study, the hardness reduction behavior of the Alloy 600 processed by LP, Buff and WJP in the thermal aging process has been investigated to estimate the stability of the residual stress improving effect by each method, based on the fact that there is a correlation between the compressive residual stress relaxation and the decrease of hardness. The behavior of the residual stress relaxation in the processed materials in the high temperature environment has been discussed with kinetic analysis. (author)