Optimization of Multi-Pass Cold Drawing and Annealing for High-Purity Vanadium Wires

Multi-pass cold drawing and subsequent annealing are critical processing steps determining the microstructure and mechanical performance of vanadium wires, as they directly influence the performance of the final product. This study systematically investigated the microstructural evolution and mechanical property changes of high-purity vanadium wire during multi-pass cold drawing and annealing, which was prepared by combining powder metallurgy and electron beam melting, with the aim of establishing an optimal processing window for nuclear-grade applications. The results indicated that cold drawing progressively transformed the equiaxed grains into a fibrous microstructure, accompanied by pronounced work hardening dominated by dislocation accumulation. At a strain of 0.71, the tensile strength increased to 467 MPa, while elongation decreased to 2.3%, with dislocation strengthening contributing to over 50% of the strength increment. Annealing processed through three distinct stages: recovery (600–700 °C), recrystallization (800–900 °C), and rapid grain growth (1000 °C). Complete recrystallization eliminated the cold-worked substructure, resulting in the loss of work hardening and a tensile strength below the nuclear-grade requirement. The optimal processing route involved high-strain cold drawing followed by recovery annealing at 600–700 °C, resulting in wires with a tensile strength greater than 430 MPa and elongation exceeding 14%, thereby fully meeting the specifications for self-powered neutron detectors. This work provides practical guidance for the industrial production of vanadium wires for self-powered neutron detector.