New insights into oxidation mechanism and kinetics of 9Cr–1Mo ferritic-martensitic steel in oxygen-saturated liquid lead-bismuth eutectic

The evolution of oxide scales on a 9Cr–1Mo ferritic-martensitic steel (T91) in oxygen-saturated liquid LBE at 500 °C was investigated. While taken out at around 500 °C, the T91 steel, after corrosion, shows clean surface with little LBE adhesion due to the poor wettability induced by surface oxides, due to the formation of an oxide layer. The results reveal the evolution of surface oxides from irregular strip shapes to regular crystalline grains, and stack-packed equiaxed crystals in the outer magnetite layer. Thermally-induced cracks were captured in the oxide scale on T91 steel after 1,000h exposure to LBE. A new oxidation mechanism is proposed, with consideration of the formation of the outer layer by metal dissolution/oxide precipitation, and a thin film of chromium oxide at the inner/outer layers interface. The dependency of temperature and oxygen concentration on the oxidation kinetics of T91 steel in LBE at the present condition is discussed.