Investigation of Stress Corrosion Cracking Initiation in Machined 304 Austenitic Stainless Steel in Magnesium Chloride Environment

The effect of the machining-induced residual stresses and microstructural changes on the stress corrosion cracking (SCC) initiation in 304 austenitic stainless steel was investigated. The residual stress was measured with an x-ray diffractometer, and the microstructural changes were characterized by the electron backscatter diffraction. Through a load-free testing in the boiling magnesium chloride solution, the subsurface zone of high SCC sensitivity was identified by detecting the depth of the micro-cracks. The development of the SCC micro-crack was related to the machining-induced residual stresses and microstructural changes. The results showed that the SCC micro-crack was prone to propagate in the subsurface where the residual stress was larger than 200 MPa, along with high-density grain boundary. Additionally, the SCC micro-crack initiation was observed to develop along the machining-induced slip bands.