Tungsten wire usually needs to undergo the following heat treatments during processing:
- Annealing heat treatment
Purpose: To eliminate the residual stress and deformation of the tungsten wire during processing and restore its original performance.
Steps: It includes three processes: heating, insulation and cooling. The heating temperature is generally controlled at about 100°C below the melting point of the tungsten wire, and the duration depends on the specifications of the tungsten wire. The holding time is determined according to the diameter, length and thickness of the tungsten wire to ensure that the tungsten wire can be fully annealed.
- Homogenization heat treatment
Purpose: Due to uneven composition or processing deformation of the tungsten wire, its internal structure may be uneven. The purpose of homogenization heat treatment is to make the internal composition of the tungsten wire reach a uniform state.
Steps: Similar to annealing heat treatment, it also includes three processes: heating, insulation and cooling. The heating temperature is also controlled at about 100°C below the melting point of the tungsten wire, but the insulation time is generally longer than the annealing heat treatment time to ensure that the internal structure of the tungsten wire can reach a uniform state as much as possible.
- Stress release annealing
Purpose: Further eliminate the residual stress and deformation of the tungsten wire and improve its bending life.
Steps: It also includes three processes: heating, insulation and cooling. However, the heating temperature and insulation time will be adjusted according to the material and deformation degree of the tungsten wire to achieve the best stress release effect.
- Recrystallization annealing (for specific stages)
Purpose: In the blanking stage of tungsten wire, recrystallization annealing is often used to reduce or eliminate the inhomogeneity of the structure.
Conditions: The temperature and time need to be strictly controlled, such as recrystallization annealing at 1750℃ and 60min. However, it should be noted that this method cannot be used when approaching the finished product or annealing the finished product, otherwise it may lead to an increase in the ductility-brittle transition temperature.
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