Tungsten carbide sintering molding is to press the powder into a blank, then heat it into a sintering furnace to a certain temperature (sintering temperature), keep it for a certain time (holding time), and then cool it down to obtain the tungsten carbide material with the required performance.
The four basic stages of tungsten carbide sintering process:
1. In the stage of removing the forming agent and calcining, the sintered body undergoes the following changes at this stage:
Removal of the forming agent, as the temperature rises in the initial stage of sintering, the forming agent gradually decomposes or vaporizes to remove the sintered body. At the same time, the forming agent more or less carbonizes the sintered body, and the amount of carbon increase will follow the forming agent. The type, quantity, and sintering process vary.
The oxides on the powder surface are reduced. At the sintering temperature, hydrogen can reduce the oxides of cobalt and tungsten. If the forming agent is removed in vacuum and sintering, the carbon-oxygen reaction is not strong. The contact stress between the powder particles is gradually eliminated, the bonding metal powder begins to recover and recrystallize, surface diffusion begins to occur, and the strength of the compact increases.
2, solid phase sintering stage (800℃——eutectic temperature)
At the temperature before the liquid phase appears, in addition to continuing the process that occurred in the previous stage, the solid phase reaction and diffusion are intensified, the plastic flow is enhanced, and the sintered body shrinks significantly.
3, liquid phase sintering stage (eutectic temperature-sintering temperature)
When the sintered body appears in the liquid phase, the shrinkage is quickly completed, and then crystalline transformation occurs, forming the basic structure and structure of the alloy.
4, cooling stage (sintering temperature-room temperature)
At this stage, the structure and phase composition of tungsten carbide have some changes with different cooling conditions. This feature can be used to heat tungsten carbide to improve its physical and mechanical properties.
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