Powder metallurgy tungsten usually has a fine grain, its blank is generally selected by high temperature forging and rolling method, the temperature is generally controlled between 1500~1600℃. After the blank, the tungsten can be further rolled, forged or spun. The pressure machining is usually carried out below the recrystallization temperature, because the grain boundaries of the recrystallized tungsten are brittle, which limits the workability. Therefore, with the increase of the total processing amount of tungsten, the deformation temperature decreases correspondingly.
Tungsten plate rolling can be divided into hot rolling, warm rolling and cold rolling. Due to large deformation resistance of tungsten, common rollers cannot completely meet the requirements of rolling tungsten plates, while rollers made of special materials should be applied. In the rolling process, rollers need to be preheated, and the preheating temperature is 100~350℃ according to different rolling conditions. Blanks can be machined only when the relative density (the ratio of the actual density to theoretical density) is higher than 90%, and have good processibility at the density of 92~94%. The tungsten slab temperature is 1,350~1,500℃ in the hot rolling process; if the deformation process parameters are selected improperly, blanks will be layered. The starting temperature of warm rolling is 1,200℃; 8mm-thick hot rolled plates can reach the thickness of 0.5mm through warm rolling. Tungsten plates are high in deformation resistance, and the body of the roller can be bent and deformed in the rolling process, so the plates will form non-uniform thickness along the width direction, and may be cracked due to non-uniform deformation of all the parts in the roller exchange or rolling mill exchange process. The brittle-ductile transition temperature of 0.5mm-thick plates is room temperature or higher than room temperature; with brittleness, the sheets should be rolled into 0.2mm-thick sheets at the temperature of 200~500℃. In the later period of rolling, tungsten sheets are thin and long. To ensure uniform heating of plates, graphite or molybdenum disulphide are usually coated, which not only is beneficial for the heating of plates but also has a lubricating effect in the machining process.
Post time: Jan-15-2023