Si segregation and relevant effect on the corrosion propagation in F/M steel exposed to liquid lead-bismuth eutectic

Clarification of the relationship between oxygen diffusion and microstructural evolution in liquid lead-bismuth eutectic (LBE) is of great importance for understanding and consequently tailoring the oxidation process. In the present study, a Si-modified ferritic martensitic steel was exposed to oxygen-saturated LBE at 500°C at various times and the interface between the internal oxidation zone and matrix was investigated. Microstructural characterisation reveals that grain boundaries and martensitic lath boundaries provide a fast pathway for oxygen diffusion, resulting in the high amount of oxidation products, as well as cracks. The internal stress caused by the formation of oxidation products along grain boundary results in the proliferation of dislocations, which subsequently play as the new diffusion channel for oxygen. The chemical analysis demonstrates that Si preferably concentrates along the dislocations in a form of Si-rich oxide, suggesting the oxidation of Si is prior to the Cr-rich oxide.