The main steps of the cemented carbide sintering process include:
- Forming agent removal and pre-sintering stage: At this stage, the following changes occur in the sintered body: the forming agent is removed. As the temperature increases in the early stage of sintering, the forming agent gradually decomposes or vaporizes, and the sintered body is eliminated. At the same time, , the molding agent adds more or less carbon to the sintered body, and the amount of carbonization will change with the type and quantity of the molding agent and the sintering process. The oxides on the powder surface are reduced. At the sintering temperature, hydrogen can reduce the oxides of cobalt and tungsten. If the molding agent is removed in vacuum and sintering, the carbon-oxygen reaction is not strong. The contact stress between powder particles is gradually eliminated, the bonded metal powder begins to recover and recrystallize, surface diffusion begins to occur, and the strength of the compact increases.
- Plasticizer removal stage: The plasticizer removal stage starts from room temperature and heats up to about 200°C. The gas adsorbed on the surface of the powder particles in the compact breaks away from the surface of the particles under the action of heat and continuously escapes from the compact. . Maintaining a high degree of vacuum is conducive to the release and escape of gas. Generally, the vaporization temperature of plasticizers is below 550°C.
- Pre-sintering stage: The pre-sintering stage refers to pre-sintering before high-temperature sintering, so that the combined oxygen and carbon in the powder particles undergo a reduction reaction to generate carbon monoxide gas and leave the compact. If this gas cannot be eliminated when the liquid phase appears, They will remain in the alloy as closed pores, which are difficult to eliminate even with pressure sintering.
- High-temperature sintering stage: The high-temperature sintering stage is the key stage for the densification of the cemented carbide compact, and the sintering temperature and sintering time are important process parameters for the compact to achieve densification, form a uniform structure, and obtain the required performance.
- Cooling phase: The cooling rate should be controlled.
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