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Abstract Surface machining is often assumed to be detrimental to stress corrosion cracking (SCC) in nuclear power plant components because of localized deformation, high associated hardness, roughness and tensile residual stresses. However, in the present work, SCC initiation studies for a warm-forged Type 304L stainless steel in high-temperature water showed that the ~1–2 μm thick ultrafine-grained layer introduced by machining improved SCC initiation resistance. Removing the macroscopic machining ridges via grinding decreased the residual tensile stress but led to more extensive cracking. This paradigm shift demonstrates the dominant effect of the microstructure on the oxidation over the mechanical driving force for SCC. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

The effect of machining on stress corrosion crack initiation of annealed Type 316L stainless steel was investigated through accelerated testing in high-temperature hydrogenated water. It was observed that stress corrosion cracks only initiated on machined surfaces with machining marks perpendicular to the loading direction and a porous inner oxide layer was identified as an important factor contributing to crack initiation. Furthermore, most cracks stopped within the machining-induced near-surface ultrafine-grained layer and the machining-induced residual stresses did not appear to have a significant effect on crack initiation. A correlation between crack initiation and the surface/near-surface features is identified and discussed. [ABSTRACT FROM AUTHOR]

Abstract Warm-forged Type 304L stainless steel specimens have been tested in high temperature hydrogenated water under slow strain rate tensile test conditions to investigate the effect of machining on stress corrosion crack initiation. Roughness, residual stress and cross-section microstructures of the as-machined surfaces were characterized prior to the tests, and both plan-view and cross-section examinations were performed post-test. The results indicated that machining produced a deformation layer characterized by an ultrafine-grained outer layer and a highly deformed inner layer. The ultrafine-grained layer promoted a more uniform oxidation and enhanced SCC initiation resistance of the material compared to the highly polished deformation-free surfaces, which initiated significantly more intergranular cracks. The mechanisms for SCC initiation in the material have been discussed. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]