The oxide film formed on Fe–15Cr–9Ni–2.5Si austenitic stainless steel exposed to oxygen-saturated static lead-bismuth eutectic (LBE) at 550 °C for 1–50 h has been investigated by multiscale characterization methods such as scanning electron microscope (SEM) and transmission electron microscopy (TEM). The results reveal that the oxide film formed at the early stage of corrosion has a multi-layer structure. The thickness of the oxide film increases linearly and the stratification of the oxide film becomes more pronounced with the extension of time. The outer oxide film is composed of magnetite and plumboferrite, and the loose porous plumboferrite promotes LBE penetration resulting in reduced protection of the outer oxide film. The inner oxide film is composed of an extremely thin (Cr, Si)-rich oxide film, a Ni-depleted spinel layer and a dual-phase network structure composed of (Fe, Ni) phase and spinel. The high Si content leads to the preferential formation of a thin (Cr, Si)-rich oxide film at the interface and the formation of Si-rich spinel inner oxide film, which suppress the dissolution and diffusion of elements and improve the oxidation resistance of the inner oxide film. The early corrosion mechanism of austenitic stainless steel in liquid LBE is discussed. • A multi-layer oxide film is formed on Fe–15Cr–9Ni–2.5Si austenitic stainless steel exposed to oxygen-saturated liquid LBE at 550 °C at the early stage of corrosion. The thickness of the oxide film increases linearly and the stratification of the oxide film becomes more pronounced with the extension of time. • The outer oxide film formed later than the inner oxide film. The outer oxide film is composed of equiaxed magnetite and columnar plumboferrite, and the loose porous plumboferrite leads to LBE penetration, which will reduce the protection of outer oxide film. • The inner oxide film is composed of an extremely thin (Cr, Si)-rich oxide film, Ni-depleted spinel layer and a dual-phase network structure composed of (Fe, Ni) phase and spinel. The high Si content leads to the preferential formation of a thin (Cr, Si)-rich oxide film at the interface and the formation of Si-rich spinel inner oxide film, which suppress the dissolution and diffusion of elements and improve the oxidation resistance of the inner oxide film.
Geng et al. (Sun,) studied this question.