The heat treatment of tungsten plate mainly includes three stages: heating, insulation, and cooling. The specific steps are as follows:

Heating: Place the tungsten plate into a heating furnace and raise the temperature to the desired range through electric heating, gas heating, and other methods. During the heating process, it is important to control the temperature and heating speed to avoid overheating or localized overheating.
Insulation: After the heating stage is completed, the tungsten plate needs to be kept within a constant temperature range to complete the necessary phase transition and alloy element diffusion process. The insulation time needs to be determined according to specific requirements, and generally requires maintaining temperature stability for a certain period of time.
Cooling: After the heating and insulation stages are completed, the tungsten plate needs to be cooled. According to specific requirements, natural cooling, air blowing cooling, or water quenching cooling can be selected. During the cooling process, attention should be paid to controlling the cooling rate to avoid defects such as cracks or deformations.

Appearance inspection: The surface of tungsten plate is inspected by visual or optical instruments to check for defects such as cracks, pores, inclusions, etc.

Dimensional inspection: Use measuring tools to measure the dimensions of tungsten plates, including thickness, width, length, etc., to ensure that the dimensions meet the requirements.
Performance testing: Conduct mechanical performance tests on tungsten plates, such as hardness, tensile strength, yield strength, etc., to ensure that their mechanical properties meet the requirements.
Composition detection: By using chemical analysis or spectral analysis methods, the content of various elements in tungsten plates is detected to ensure that the composition meets the requirements.
Production process control: Strictly control the melting, rolling, annealing and other production processes of tungsten plates to ensure stable quality of the produced tungsten plates.
Quality Management System: Establish a comprehensive quality management system to comprehensively monitor all aspects of tungsten plate production, processing, inspection, etc., ensuring that product quality meets requirements.
Through the above methods, comprehensive quality inspection and control can be carried out on tungsten plates to ensure that their quality and performance meet the requirements, and to improve the reliability and stability of the products.

Reasons for the formation of oxide layer
High temperature exposure: Although tungsten has strong antioxidant properties at room temperature, it reacts with oxygen in the air at high temperatures (usually>400 ℃) to form tungsten oxide (such as WO3), forming a visible oxide layer.
Lack of protective atmosphere: If the tungsten plate is exposed to an oxygen-containing environment (such as air) during heating or use, rather than vacuum or inert gas protection, oxidation reactions are more likely to occur.
Insufficient surface passivation: Without effective passivation treatment (such as forming a dense oxide film), the surface is more prone to sustained oxidation.

 
Reasons for the formation of black spots

Localized uneven oxidation: In specific areas (such as stress concentration points and near impurities), the oxidation reaction rate accelerates, generating dark tungsten oxide (such as WO ₂) with black spots.Impurity contamination: During processing or storage, the surface of tungsten plates is contaminated with sulfur, carbon, or other metal ions, which react to form black compounds in high temperature or humid environments.Mechanical wear or friction: During storage, transportation, or assembly, surface friction may cause local changes in metal structure or increased oxidation, resulting in the formation of dark spots.Welding or heat treatment residue: If tungsten plates are used for high-temperature applications such as electrodes, local overheating may cause surface carbonization or oxide deposition, forming black spots.