Effect of Mn on the Growth Behavior of Pre-oxidized Film on the Heat-resistant Steel Surface

The phase composition of the pre-oxidized film on an alloy surface usually has a great influence on its corrosion resistance. In this work, the surface oxide film growth behavior in low-oxygen atmosphere at 720 °C of two 12Cr heat-resistant steels with different Mn content was studied, and their corrosion resistance in liquid lead–bismuth eutectic (LBE) with saturated oxygen at 600 °C was tested. The results indicated that the pre-oxidized film of 1.6Mn steel is mainly composed of large-size Mn–Cr spinel and Fe–Cr spinel, while that of improved 0Mn steel is mainly composed of continuous and dense Cr₂O₃ and Fe–Cr spinel. This is because Mn has a high diffusion rate in Cr₂O₃, so it can pass through the Cr₂O₃ layer and combine with O to form Mn-rich oxides, and then the Mn-rich oxides react with Cr₂O₃ to form Mn–Cr spinel. However, due to the high solubility of Mn in LBE, the Mn-rich pre-oxidized film of 1.6Mn steel will dissolve and fail quickly, so its long-term corrosion resistance in LBE is lower than that of 0Mn steel.