Lead-cooled fast reactors (LFRs) have garnered significant attention due to their inherent advantages in meeting clean energy demands. Lead-bismuth eutectic (LBE), as a coolant, can lead to severe degradation due to LBE corrosion. T91 steel, a representative ferritic/martensitic steel, exhibits remarkable corrosion resistance in LBE. However, under oxygen-saturated conditions, T91 steel undergoes oxidation and dissolution, resulting in the degradation of the outer magnetite layer. Researchers at Tianjin University have explored modifying T91 steel by adding elements like Al and Si to enhance its oxidation resistance.
Methods
Prof. Gang Chen et al. at Tianjin University investigated the oxidation behavior of T91 steel modified with Al (T91-Al) and Si (T91-Si) in LBE at 450 °C. The study examined the materials under both 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 responsible for the enhanced oxidation properties of the modified T91 steel.
Fig. 1. (a) Experimental setup used for the exposure of static LBE; (b) real diagram of the experimental device; (c) photo of the oxygen sensor.
Highlights
The oxidation resistance of the materials follows this order: T91 < T91-Al < T91-Si.
Notably, the oxidation resistance of T91-Si exhibited minimal correlation with dissolved oxygen.
Under oxygen-controlled conditions, the oxide films of T91 and T91-Al were attacked and broken by LBE, with the former eventually peeling off. In contrast, both materials showed significant oxide film thickening, except for 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.
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.
The oxide thickness of T91-Si material was only 24% of T91 and 35% of T91-Al under saturated oxygen conditions.
Fig. 3. The TEM cross-section morphology, EDS results, and HRTEM image of T91 material after exposing to 450 °C LBE for 500 h with the oxygen-saturated condition; (a) cross-section morphology and EDS mapping results, (b) line scanning results marked in (a), (c–e) HRTEM images of points marked in (a), and corresponding (f–h) SAED images.
Editor: Dr. Jun-Jing He
