Tungsten processing
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.
According to the size of the deformation of the opened tungsten rod, the temperature of further forging is generally selected in the range of 1100~1400℃. Generally, air hammer, rotary forging machine or other forging methods are used for forging hammer. Tungsten bars with a diameter of 3~60mm can be obtained by forging. Generally, recrystallization is not allowed in forging. More than 80% of the finished bar needs to be forged to ensure the uniformity of the deformation of the bar, and stress relief treatment is carried out at 1150℃.
The tungsten wire with a diameter of less than 3mm needs to be stretched and deformed in single pass or multiple pass on the drawing die. Generally, the heating and stress relief method is used, and graphite milk is the lubricant.
In addition to tungsten wire, tungsten plate, tungsten strip is the most commonly used tungsten material. Due to the great deformation resistance of tungsten, the deformation temperature is generally 1000~1400℃, so the rolling mill is generally required to have a large enough rolling force, roll not only requires high temperature resistance, but also must meet a certain high temperature strength. Therefore, rolling relatively wide tungsten plate is very difficult.
After the blank of tungsten plate reprocessing, with the increase of processing amount, need to constantly reduce the processing temperature, when the total processing amount is more than 90%, can choose 200~600℃ for processing, processing deformation of about 10%. The total deformation is about 80%, which needs stress relief annealing treatment.
There are two ways to produce tungsten strips. When the strips are wide, they are usually rolled and then sheared for foil. When the width of the tungsten strip is small, it becomes difficult to cut. Direct rolling of strip by tungsten wire has become a feasible method. Although tungsten wire has undergone great deformation before rolling, but it is still a brittle material, it is impossible to carry out rolling at normal temperature, so the wire rolling strip is still selected by heating method, heating is generally direct electric heating and indirect resistance furnace or gas heating. After reaching a certain amount of deformation, the tungsten strip needs appropriate stress relief and electrolytic polishing.
