Why Do Tungsten Carbide Products Shrink After Sintering?

Tungsten carbide is one of the most popular tool materials in the modern industry. In the factory, we always apply powder metallurgy to manufacture tungsten carbide products. In sintering, you may find that the tungsten carbide products shrunk. So what happened to tungsten carbide products, and why did tungsten carbide products shrink after sintering? In this article, we are going to explore the reason.

Manufacturing of tungsten carbide products

1. Choosing and purchasing the 100% raw material, tungsten carbide;

2. Mixing tungsten carbide powder with cobalt powder;

3. Milling the mixed powder in the ball mixing machine with some liquid such as water and ethanol;

4. Spray drying the wet powder;

5. Compacting powder into different shapes and sizes according to customers’ requirements. The suitable pressing methods are decided by the types and sizes of tungsten carbide products;

6. Sintering in the sintering furnace;

7. Final quality checking.

Stages of sintering tungsten carbide products

1. Removal of the molding agent and pre-burning stage;

In this stage, the worker should control the temperature to increase gradually. As the temperature increases gradually, the moisture, gas, and residual solvent in the compacted tungsten carbide will evaporate, so this stage is to remove the molding agent and other residual substances and pre-burn. This stage happens below 800℃

2. Solid-phase sintering stage; 

As the temperature increases and surpass 800℃, it turns to the second stage. This stage happens before a liquid can exist in this system. In this stage, the plastic flow increases, and the sintered body shrinks significantly. Tungsten carbide shrinking can be observed seriously, especially above 1150℃.

Cr. Sandvik

3. Liquid-phase sintering stage;

During the third stage, the temperature will increase to the sintering temperature, the highest temperature during sintering. The shrinkage is completed quickly when the liquid phase appears on the tungsten carbide and the porosity of tungsten carbide decreases.

4. Cooling stage.

The cemented carbide after sintering can be removed from the sintering furnace and cooled to room temperature. Some factories will use the waste heat in the sintering furnace for new thermal utilization. At this point, as the temperature drops, the final microstructure of the alloy is formed.

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