3D ATOM-PROBE CHARACTERIZATION OF STRESS AND COLD-WORK IN STRESS CORROSION CRACKING OF 304 STAINLESS STEEL

Abstract

Cold-worked 304 stainless steels (SS) are known to be susceptible to stress corrosion cracking (SCC). This study employs atom-probe tomography (APT) for local chemical analysis of the oxides formed. Autoclave experiments on a set of samples with/without cold-work prior to oxidation, and with/without stress applied during oxidation, were carried out under simulated pressurised water reactor (PWR) primary conditions. APT and analytical transmission electron microscopy (ATEM) were combined to investigate chemical and structural implications of surface and grain boundary oxidation in 304 SS. Focussed ion beam (FIB) milling was used to prepare specimens containing the same grain boundary for every analysis technique. Grain boundary and deformation band oxidation were observed in all but the unstressed and non-cold worked sample. Cavities were found ahead of the Cr-rich oxide in some of the samples. APT data suggests the presence of hydrogen in Nickel-rich regions.