Fine-grained Tungsten Carbide

Carbides are used to produce cutters for cutting or forming objects such as end milling, knives and scissors. In this automatic cutting or automatic molding process, hard alloy tools need to be subjected to extremely harsh conditions.

However, a large number of fine-grained WC powders are particularly easy to carbonate at low temperatures or lower temperatures at 1300°C, therefore unstable. Tungsten carbide is easy to cause grain growth during heat treatment with cobalt. This means that the metallographic structure of WC phase in cobalt is adversely affected by the wide distribution of grain size. Therefore, in order to produce a WC powder with a grain of 1 μm or less, the W powder should also have 1 μm or below fine grain size. This fine grain size W powder is very expensive compared to the W powder of 1 μm or larger grain size.

The method of obtaining fine crystalline tungsten carbide consists of the following steps: preparing tungsten powder with an average grain of less than 1 μm, and mixing tungsten powder with carbon powder and chromium powder to form a mixture. The mixture was input into an atmosphere of hydrogen, vacuum or inert gas, such as nitrogen (N₂) and argon (Ar), and the fine particles of tungsten carbide were obtained by heating. The mixture was heated at a temperature of 3-100°C / min to 1200-1700°C and maintained for 200 minutes at that temperature. During the heat treatment process, the mixture is carbonized to form a composite carbide powder containing fine particles of tungsten carbide (WC).

The researchers found that the composite carbide powder was formed from fine cemented carbide grains with uniform average grain size. This shows that fine cemented carbide grain can be obtained without the use of fine WC powder. While WC powder has 1μm grain size when measured by FSSS method, it shows that fine grain tungsten carbide powder can be obtained by this simple method, and then the production cost of high quality hard alloy can be reduced. 

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