New insight of the enhanced oxidation resistance of T91 steel in 450 °C liquid lead-bismuth eutectic by adding Al and Si element

Abstract

The study investigated the oxidation behavior of T91 steel modified with Al (T91-Al) and Si (T91-Si) in lead-bismuth eutectic (LBE) at 450 °C under oxygen-saturated conditions (10−7–10−8 wt.%) and oxygen-controlled conditions (3.2 × 10−4 wt.%). Advanced characterization techniques were employed to understand the thermodynamic and kinetic mechanisms of enhanced oxidation properties of the modified T91 steel. The results indicate that the oxidation resistance of the materials follows this order: T91 < T91-Al < T91-Si. Noteworthy, the oxidation resistance of T91-Si material exhibited minimal correlation with dissolved oxygen. Under oxygen-controlled conditions, the oxide film of T91 and T91-Al was attacked and broken by LBE, with the former eventually peeling off. In contrast, both materials showed significant oxide film thickening, except T91-Si under oxygen-saturated conditions. The addition of Al improved the quality of the inner oxide film on T91-Al by generating Al2O3, thereby slowing down the diffusion of Fe from the matrix and enhancing oxidation resistance. Conversely, Si actively participated in the oxidation process of T91-Si, slowing down the diffusion of Fe, and facilitating the diffusion of Cr, thereby strengthening the oxide film protection. Consequently, the oxide thickness of T91-Si material was only 24 % of T91 and 35 % of T91-Al under saturated oxygen conditions.