Effect of N and Nb Microalloying on Corrosion Resistance of 309S Stainless Steel for Canister-Stored Nuclear Waste

Stainless containers storing vitrified high-level nuclear waste are required to withstand Cl⁻ environment for at least 100 years. However, the corrosion properties of 309S stainless steel make it hard for this material to satisfy the above requirement. Here, to achieve this goal, stainless steel is microalloyed with N and Nb. The effect of the addition of N and Nb on the structure and corrosion resistance of stainless steel is discussed by comparing four kinds of stainless steel with different N and Nb contents, including 309S. The results indicate that adding both N and Nb is beneficial to the precipitation of Nb(C, N). Electrochemical and immersion tests show that after the addition of N and Nb, the breakdown potential is significantly increased, the impedance arc is increased, the number of pitting pits decreases, and the maximum width and depth of the pitting pits are reduced. The XPS results reveal that Nb₂O₅ and Nb(C, N) are formed in the passivation film; this makes the passivation film more stable. In addition, N may affect the formation of Cr₂O₃ and Nb₂O₅. Therefore, 309S stainless steel combined with N and Nb shows better corrosion resistance.