Preparation of hard alloy

The production of hard alloy involves mixing tungsten carbide and cobalt in a certain proportion, pressing them into various shapes, and then semi sintering them. This sintering process is usually carried out in a vacuum furnace. Place it in a vacuum furnace to complete sintering, at a temperature of approximately 1300 to 1500 degrees Celsius.
Hard alloy sintering molding is the process of pressing powder into billets, heating them in a sintering furnace to a certain temperature (sintering temperature), holding them for a certain time (insulation time), and then cooling them down to obtain the required performance of hard alloy materials.
The sintering process of hard alloys can be divided into four basic stages:
1: During the removal of the forming agent and pre firing stage, the sintered body undergoes the following changes:
The removal of the forming agent, as the temperature increases in the early stage of sintering, the forming agent gradually decomposes or vaporizes, excluding the sintered body. At the same time, the forming agent adds more or less carbon to the sintered body, and the amount of carbon increase will change with the type, quantity, and sintering process of the forming agent.
The surface oxides of the powder are reduced, and at sintering temperature, hydrogen can reduce the oxides of cobalt and tungsten. If the forming agent is removed in vacuum and sintered, the carbon oxygen reaction is not yet strong. The contact stress between powder particles gradually dissipates, the bonded metal powder begins to recover and recrystallize, surface diffusion begins to occur, and the compressive strength of the block increases.
2: Solid phase sintering stage (800 ℃ - eutectic temperature)
At the temperature before the appearance of the liquid phase, in addition to continuing the process that occurred in the previous stage, solid phase reactions and diffusion intensify, plastic flow increases, and the sintered body exhibits significant shrinkage.
3: Liquid phase sintering stage (eutectic temperature - sintering temperature)
After the liquid phase appears in the sintered body, shrinkage is quickly completed, followed by crystallization transformation, forming the basic structure and structure of the alloy.
4: Cooling stage (sintering temperature - room temperature)
At this stage, the microstructure and phase composition of the alloy undergo certain changes with different cooling conditions, which can be utilized to heat treat the hard alloy to improve its physical and mechanical properties.