The forging method of superconducting tantalum bar is characterized by the following steps: (1) Taking superconducting tantalum ingots as raw materials, preheating them at 150-180℃ and holding for 20-40 minutes, then removing the heated tantalum ingots, uniformly coating the surface with an anti-oxidation coating of 2-3 mm thickness, and then air-drying; then heating at 450-500℃ and holding for 210-240 minutes before removing; (2) First radial upsetting and first radial elongation; (3) Second radial upsetting and second radial elongation; (4) Third radial upsetting, stopping forging, air-cooling for 5-10 minutes, and then third radial elongation. The method of this invention, through forging tantalum ingots for superconducting products and combining it with a suitable hot forging heating process, obtains a microstructure with grain size and cross-sectional microstructure uniformity that meets the requirements of the initial microstructure preparation.
Tantalum rods for superconducting applications are key and crucial components in the production of multi-core superconducting composite wires, primarily serving as the inner support liner in extruded composite components. The deformation uniformity of the tantalum core support liner in multi-core superconducting wires is critical to the final product. This depends on the grain size range of the tantalum core support liner and the fluctuation range of the average grain size across the rod's cross-section. The finer and more uniform the grains, the more regular the deformation of the tantalum core support liner, resulting in a more perfectly circular cross-section after machining into small-diameter superconducting wires.
Current technologies mainly employ hot forging, which results in low throughput per pass and low overall throughput. The forged billets obtained through this forging process have low degrees of fragmentation in their as-cast state, and internal defects are not thoroughly eliminated. This leads to irregular deformation of the tantalum core support liner during subsequent superconducting wire processing, causing clumps to encroach on the superconducting wire's structure, affecting superconducting performance and causing quality problems such as wire breakage—unacceptable in the production of high-cost superconducting wires.
The forged billet for the tantalum support lining of the superconducting wire core is produced by forging a tantalum ingot for superconducting products, combined with a suitable hot forging heating process, to obtain a microstructure with grain size and cross-sectional microstructure uniformity that meets the requirements of the initial microstructure preparation. This invention's method, through radial machining of the ingot with a large machining rate, fully breaks down the columnar crystal regions in the center and core, increasing the degree of metal flow in the columnar crystal regions of the ingot's center towards the circumference. Uniform force under surface contact on the outer circumference of the ingot further promotes the flow of the columnar crystal structure towards the transverse core and radial ends, thus significantly improving the inhomogeneity of the as-cast microstructure. Repeating this forging cycle eliminates the presence of dendrites, crystal bands, non-equiaxed crystals, and coarse grains in the as-cast tantalum ingot. Furthermore, it simultaneously refines the grain size of the material and prepares the microstructure for subsequent processing, ensuring that the overall average grain size fluctuation range of the transverse cross-section is within ±5μm, and that the tantalum support lining the superconducting wire core does not undergo irregular deformation and has a perfectly circular transverse cross-section. The outer diameter of the conventional tantalum bar is φ55.5mm, φ47.5mm, φ60.8mm, φ70mm. It is subjected to three radial upsettings and hot forgings using a 3-ton electro-hydraulic drop hammer. It is also subjected to three radial drawings and hot forgings using a 3-ton electro-hydraulic drop hammer.
