Hydrogen-enhanced oxidation of ferrite phase in stainless steel cladding and the contribution to stress corrosion cracking in deaerated high temperature water

Abstract

• Oxidation and SCC of 308L SS cladding with or without hydrogen are studied. • Phase boundary (PB) has lower oxidation resistance than austenite and δ-ferrite. • Hydrogen-induced PB oxidation and preferential grain boundary oxidation. • Charged hydrogen decreases the oxidation resistance of δ-ferrite and austenite. • Charged hydrogen increases the SCC susceptibility of 308L SS cladding. Oxide film properties and stress corrosion cracking (SCC) behaviour are investigated in the 308L stainless steel cladding layer with and without being H-charged in a deaerated high temperature water. Phase boundary (PB) has lower oxidation resistance than austenite and δ-ferrite matrix. A compact and high Cr content-bearing inner oxide layer improves the oxidation resistance of the δ-ferrite phase without H charging. H-induced PB penetration oxidation and grain boundary (GB) preferential oxidation are observed in H-charged specimen due to the PB and GB act as H trapping sites. Charged H decreases the oxidation resistance of δ-ferrite and austenite. δ-Ferrite acts as a path for H diffusing and H flux facilitates mass transport, resulting in the poor oxidation resistance of δ-ferrite. The mechanism underlying the effect of H on the oxidation behaviours of δ-ferrite and austenitic phases, as well as SCC performance, are discussed.