Oxidation behavior of T91 steel in flowing oxygen-containing lead-bismuth eutectic at 500 °C

T91 is considered as a possible structural material for lead‐bismuth eutectic (LBE) cooled reactors. However, one of the main issues is the compatibility of T91 with LBE. In this work, the corrosion tests of T91 were performed in flowing (1 m/s) oxygen‐controlled LBE (1–3 × 10−6 wt% O) at 500 °C for up to 5000 h. The results show that a three‐layer oxide scale forms at the interface of T91 and LBE, consisting of Fe3O4 (magnetite), Fe‐Cr spinel and an internal oxidation zone (IOZ). The growth kinetics of the oxide scale follows a parabolic dependence (Δx2=kpt). The rate constants (kp) of Fe3O4, Fe‐Cr spinel, and IOZ are 0.052, 0.040, and 0.0057 μm2/h, respectively. In addition, the growth model of the oxide scale is established under consideration of the exfoliation process. This model clarifies the growth direction of each oxide layer and the transformation of Fe‐Cr spinel to magnetite. The growth model of oxide scale is established in combination with the exfoliation process: (a) magnetite that grows outwards, while Fe‐Cr spinel grows inwards. Besides, the solid‐state transformation of spinel to magnetite occurs at the magnetite/Fe‐Cr spinel interface; (b) magnetite firstly flakes off at the local regions. Subsequently, Fe‐Cr spinel and IOZ flake off. The exfoliation region becomes larger with time and can be oxidized in situ again.