A mechanistic study on dealloying-induced stress corrosion cracking of Alloy 800 in boiling caustic solutions

Alloy 800 (Fe-30Ni-20Cr) is used in steam generators of some nuclear power plants. In-service performance has been excellent, but stress corrosion cracking (SCC) can occur in certain off-chemistry environments. In this study, the SCC mechanism for Alloy 800 in boiling caustic solution is investigated. After exposure, a Ni-rich porous surface film is formed with a large density of cracks. Complementary electron microscopy techniques are applied to study the SCC mechanism at the nanoscale from chemical and mechanical perspectives. Results suggest SCC initiation occurs by transmission of a micro-crack from the Ni-rich layer into the substrate material via a cleavage mechanism.