Effect of thermal aging on oxide film of stainless steel weld overlay cladding exposed to high temperature water

Characteristics of the oxide film formed on stainless steel weld overlay cladding aged at 400 °C for different times in high temperature water were studied. The results showed that thermal aging showed no obvious effect on the volume fraction of ferrite phase but resulted in high corrosion susceptibility of the aged ferrite phase mainly. The oxide film formed on the unaged cladding material consisted of 100-nm-thick inner oxide layer (FeCr2O4 and Cr2O3) and Fe-rich outer oxide particles (Fe3O4) with a size of <500 nm. By comparison, 300-nm-thick Fe-Cr inner oxide layer (FeCr2O4, Cr2O3 and Fe3O4) and outer oxide particles (Fe3O4 and FeCr2O4) with a size of <700 nm formed on the aged ferrite phase. Spinodal decomposition was considered as the main factor to promote the corrosion of the aged ferrite phase, and existence of carbides along phase boundary facilitated corrosion of the cladding material in high temperature water.