Four Basic Stages of the Tungsten Carbide Sintering Process

Tungsten carbide, also known as cemented carbide, has the characteristics of high hardness, high strength, good wear resistance and toughness, excellent heat resistance, and corrosion resistance. And it is often used to make drilling tools, mining tools, cutting tools, wear-resistant parts, metal dies, precision bearings, nozzles, etc. 

Sintering is the main process for making tungsten carbide products. There are four basic stages of the tungsten carbide sintering process.

1. Pre-sintering stage (Removal of forming agent and pre-sintering stage)

Removal of the forming agent: With the increase of the initial temperature of sintering, the forming agent gradually decomposes or vaporizes, thereby eliminating from the sintered base. At the same time, the forming agent will increase carbon to the sintered base more or less, and the amount of carbon increase will vary with the type and quantity of the forming agent and the sintering process.

The oxides on the surface of the powder are reduced: at the sintering temperature, hydrogen can reduce the oxides of cobalt and tungsten. If the forming agent is removed in a vacuum and sintered, the carbon-oxygen reaction will not be very strong. As the contact stress between powder particles is gradually eliminated, the bonding metal powder will begin to recover and recrystallize, the surface will begin to diffuse, and the compact strength will increase accordingly.

At this stage, the temperature is less than 800℃

2. Solid-phase sintering stage (800℃——eutectic temperature)

800~1350C° tungsten carbide powder grain size grow big and combine with cobalt powder to become eutectic.

At the temperature before the appearance of the liquid phase, 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)

At 1400~1480C° the binder powder will melt into a liquid. When the liquid phase appears in the sintered base, the shrinkage is completed quickly, followed by crystallographic transformation to form 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 has changed with different cooling conditions. This feature can be used to heat-trench tungsten carbide to improve its physical and mechanical properties.

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