In-situ characterization of the electrochemistry of grain and grain boundary of an X70 steel in a near-neutral pH solution

An in-situ scanning vibrating electrode technique (SVET) was used to characterize microscopically the local electrochemistry of grain and grain boundary in an X70 steel in a near-neutral pH solution. It was found that the grain was anodic relative to the grain boundary. Localized corrosion, such as pitting, preferentially occurs on the grain, rather than on the grain boundary. Once a stress corrosion crack initiates from the corrosion pit, there is a higher electrochemical driving force for the crack growth within a grain than that at grain boundary. Therefore, the stress corrosion cracking follows a transgranular mode.