Study on the Corrosion Behavior of Low-Carbon 9Cr-ODS Steel in Oxygen-Saturated Lead–Bismuth Eutectic for 1000 Hours

A novel low-carbon 9Cr-ODS steel was exposed to corrosion in lead–bismuth eutectic saturated with oxygen at 500 °C for 1000 h, leading to the formation of three distinct layers of oxide film. From the outermost to the innermost layer, these included a Fe₃O₄ layer infiltrated with Pb, a FeCr₂O₄ layer, and an inner oxide zone. The inner oxide zone was primarily composed of an unoxidized matrix and Cr₂O₃. The formation of the inner oxide zone was primarily attributed to the preferential oxidation of Cr following the infiltration of insufficient O content. Two distinct morphologies of the inner oxide zone were identified: one is porous, while the other is non-porous. The porous morphology is characterized by low Fe content and Pb infiltration. The loss of Fe is the main factor contributing to the development of the porous inner oxide zone and the infiltration of Pb, while the short-range diffusion of Cr promotes the growth of Cr₂O₃, resulting in a needle-like morphology.