Enhanced corrosion resistance by surface cold working of a high-Si Fe-Cr-Ni austenitic stainless steel exposed to flowing oxygen-controlled lead-bismuth eutectic

High-Si austenitic stainless steels (ASSs) exhibit good corrosion resistance in oxygen-controlled liquid lead-bismuth eutectic (LBE) at service temperatures due to the formation of SiO 2 . However, limited Si content and slow Si diffusion in austenite matrix hinder the formation of a continuous protective SiO 2 layer, allowing LBE penetration and dissolution corrosion during prolonged exposure. Here, cold working was used to modify the near-surface microstructure of a high-Si Fe-Cr-Ni ASS and thereby alter the local elemental distribution and diffusion during LBE corrosion. Corrosion tests were performed in flowing (~1 m/s) LBE containing ~1×10 -6 wt.% oxygen at 500 ℃ for 1500 h. Cold working produced a defect-rich nanostructured surface and, after exposure, a pronounced surface-decomposed region containing M 6 C carbides, finely dispersed G-phase, and nanocrystalline α-ferrite. The improved corrosion behavior is associated with combined effects of the cold-working-induced near-surface microstructural modifications. The α-ferrite matrix, together with the high densities of grain boundaries and dislocations, is expected to facilitate Cr, Mn, and Si transport, while Cr/Si-rich M 6 C and Si/Mn-rich G-phase could provide additional local elemental sources for oxide formation. These synergistic effects favor the formation of continuous protective SiO 2 and (Mn, Cr)-rich oxide layers, with a thickness of ~144 nm, compared to the untreated austenite surface, which formed a ~7.51 μm-thick duplex-structured oxide layer. Finely dispersed G-phase may additionally contribute to retaining the nanocrystalline decomposed structure by retarding recovery, recrystallization, and grain coarsening. These results demonstrate that cold-working-induced near-surface microstructural modification provides a promising approach for improving the LBE corrosion resistance of high-Si Fe-Cr-Ni ASSs.