Degradation mechanism of oxide film on SIMP steel in LBE at temperatures above 550 °C

The corrosion behavior of SIMP steel in liquid lead-bismuth eutectic was investigated to elucidate the degradation mechanism of Fe-based protective oxide film in LBE when the temperature exceeds the critical threshold of 550 °C. Results show that a three-layer oxide film structure is formed on the surface of SIMP steel, consisting of an outer oxidation layer of Fe 3 O 4 , an inner oxidation layer of Fe-Cr spinel, and an internal oxidation zone. At 550 °C, SIMP steel forms a stable oxide layer and exhibits excellent resistance to LBE corrosion. However, at 600 °C, the increased diffusion coefficients of elements and their higher solubility in LBE accelerate elemental depletion, leading to the dissolution of the outer oxidation layer. The formation of a Cr 2 O 3 band protects the matrix but also impedes elements diffusion from matrix to the oxides, promoting the formation of nanoscale voids and pores in the inner oxidation layer, resulting the failure of oxide film to resist lead-bismuth eutectic corrosion at 600 °C. The failure of the inner oxidation layer further accelerates the corrosion of the matrix.