High purity niobium has a series of excellent properties such as high melting point, low steam pressure, good cold working performance, high chemical stability, strong resistance to liquid metal and acid corrosion, etc. It is mainly used in niobium sputtering targets, superconducting accelerators and superconducting resonators.
Traditional methods of high purity niobium ingot processing such as extrusion, rolling, the common forging, due to the thermal effect, the surface is often blue peeling, caused great difficulties to the subsequent cleaning, reduce the rate of material, at the same time due to restricted by extrusion, rolling equipment, molding limited size range, on the common press or hammer forging low efficiency, big hammer to print, the cost is high, often blue peeling, leading to the surface quality and yield decrease. This paper presents a forging method for high purity niobium bar to overcome the shortcomings in the existing technology, so as to solve the problems of surface quality, yield, production efficiency and tooling versatility.
The forging method of high purity niobium bar comprises turning the outer circumferential surface of niobium ingot. The turning size is allowed to take steps according to the surface quality, and the steps need to be inclined to wear transition; According to the set intermediate size, the niobium ingot is placed on the radial forging machine for forging, with the reduction of 20 ~ 30mm, the drawing speed ≤1.5m/min, single pass drawing, and reciprocating forging is prohibited. The water pipe spray cooling is started throughout the process, and the dynamic real-time temperature is measured. The process temperature and the final temperature are ≤330℃, otherwise the forging is stopped. When the final forging temperature of niobium ingot reaches 330℃, the forging is stopped immediately, and the billet is lifted away from the forging equipment. The billet is cooled in water for 15 ~ 20min, and the water depth is greater than or equal to 0.5m. The blank after water cooling is continued to be forged on the radial forging machine, the press amount is 5 ~ 10mm, the drawing speed is less than or equal to 1.2m/min, the single pass drawing, the reciprocating forging is prohibited, and the water pipe spraying is opened throughout the process to cool down. After forging and forming, straighten by the straightening machine while remaining temperature is remaining. After straightening, lay the air cold air drying material, and prohibit stacking.
Using this forging method, there is no blue skin on the surface, which improves the surface quality and the yield of finished products. The general hammer head is used on the radial forging machine, which does not need the input of tooling and reduces the manufacturing cost.
