Lead-cooled fast reactors exhibit strong inherent safety performance and good economic features, while material degradation due to corrosion and irradiation is still challenging. Oxide dispersion-strengthened steels are one of the promising candidates for fuel cladding materials. The effects of both irradiation and corrosion on ODS steel need to be further studied. In this work, MX-ODS steel was irradiated by Fe ions at 500 °C up to 46 dpa. Later, the as-received specimen and the irradiated specimen were used to conduct corrosion tests in oxygen-saturated Pb at 550 °C for 1 h. In the as-received specimen, discontinuous oxides penetrated by Pb and Pb in contact with steel matrix were observed, demonstrating unsatisfactory corrosion resistance of the material. However, in the irradiated specimen after corrosion experiment, a protective oxide layer formed and prevented Pb attack. The oxidation behavior differences between the two specimens can be attributed to the defects produced by irradiation and the structural discrepancy in oxides caused by the formation process. A possible mechanism of irradiation on the corrosion is discussed. In the as-received specimen, Fe atoms loss led to voids in the oxides, and lead penetrated the oxides through these voids. In the irradiated specimen, defects left by previous irradiation helped to form a more uniform oxide layer. The adhesive outer magnetite oxide and the Fe ions generated from where grain boundary oxidation developed retarded the presence of voids and made the oxide layer protective.

The effects of preheating temperature on the microstructural evolution and mechanical properties of low-activity martensitic steel welded joints were investigated, with emphasis on the relationship between preheating temperature, δ-ferrite content, and impact energy. Preheating temperature ranged from 150 °C to 300 °C. Optical microscopy and TEM were used for microstructural characterization, and tensile and impact tests were conducted to evaluate mechanical properties. The results showed that preheating temperature influenced the retained δ-ferrite content in the weld metal, whereas its effect on the heat-affected-zone microstructure was comparatively limited. The δ-ferrite fraction exhibited a non-monotonic dependence on preheating temperature, reaching a minimum of 2.76% in the filler weld pass at 250 °C. As the δ-ferrite fraction increased to approximately 13.27% at 150 °C, the average impact energy of the weld metal decreased from 47.37 J at 250 °C to 34.57 J at 150 °C. Impact fracture analysis revealed preferential crack propagation along δ ferrite/martensite interfaces and through δ-ferrite grains. An increase in the δ-ferrite fraction may promote the formation of interconnected ferrite networks, thereby facilitating crack propagation and reducing the impact toughness of the weld metal.