Recrystallization Behavior and Mechanical Property of a Medium-Si 12%Cr Reduced Activation Ferritic/Martensitic Steel Cladding Tube During the Manufacture

The present work investigates the microstructural evolution and mechanical properties in a novel medium-Si 12%Cr reduced activation ferritic/martensitic steel cladding tube (Fe–11.8Cr–0.2C–1.4W–0.17Ta–0.2V–0.55Si–0.5Mn, wt%) during multi-pass cold rolling and annealing. The initial hot-extruded tube exhibited a full martensitic matrix with the prior austenite grain size of ~ 32 μm. After annealing, Cr₂₃C₆ and TaC particles were precipitated, which are basically unchanged (152–183 nm and 84–113 nm, respectively) during the manufacturing process. Meanwhile, with the cold-rolling strain (ε) increasing and subsequent annealing, the martensitic lath gradually diminishes, and the recrystallization volume fraction (f_r) is increased. Based on the static recrystallization kinetics model, a clear relationship between f_r and ε is established, in which the newly proposed kinetic equation demonstrates a strong correlation with the experimental results. Furthermore, the yield strength (σ_YS = 362 MPa) of the final annealed state was much lower than that (σ_YS = 482 MPa) of the initial annealed state, which can be attributed to the recrystallization from the martensitic matrix to ferritic matrix. Various strengthening mechanisms are further discussed, and the calculated strengths are in good agreement with the experimental results. This work provides a guidance for the optimization of cold-rolling and annealing treatments in the manufacture of cladding tube.