1: Removal of forming agent and pre-sintering stage, at this stage the sintered body undergoes the following changes:
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 intensify, 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 steel have some changes with different cooling conditions. This feature can be used to heat tungsten steel to improve its physical and mechanical properties.
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