Effect of machining on stress corrosion crack initiation in warm-forged type 304L stainless steel in high temperature water

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.