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An SCC Initiation Model: Effects of Cold-Work in Austenitic Stainless Steels in Light Water Reactor Environment
並列摘要
The growing recognition of cold-work as an accelerant in stress corrosion cracking (SCC) is well justified because of its common or persistent impact as a key factor in both the initiation and crack growth regimes. This recognition is also a result of the presence of cold-work often noted in the initial failures of several service components. The presence of cold-work limited to surface layer has been often attributed to the relatively early intiation of SCC. A component with bulk or volumetric cold-work condition resulting from mechanical or weld-related fabrication is also subject to a relatively higher growth rate due to SCC. In addition to the accelearating effects on SCC the cold-work increases the material strength and the sequence of fabrication can significantly affect the residual stress often related to the material strength as well. Therefore, the impact of cold-work on the SCC degradation and useful remaining life of such components needs to be assessed with some technical basis and a quantitative framework that account for the various influences of the cold-work. The above aspects are reviewed in this paper focusing on the non-precipitation-hardening stainless steels subject to the reactor water environments. Also, the related field observations and their significance in assessing the cold-work impact are discussed. It is shown that the residual stress including the strain-path and stress state, as well as the material condition seem to dominate the operating influence of cold-work on SCC. These factors are explicitly related to the SCC susceptibility in a quantitative framework discussed in this paper. The basis for inter-relation between the cold-work effects and SCC is presented in relation to the model parameters. Additional factors pertinent to the austenitic steels include their susceptibility to sensitization and phase transformation, particularly interacting with the presence and sequence of cold-work. Observations from the surveyed literature on these aspects are also discussed in relation to the proposed model.