Requirements for grain size of cemented carbide

Cemented carbide for different purposes uses WC (tungsten carbide) with different grain sizes. Carbide cutting tools: For example, cutting machine blades, V-CUT knives and other fine-grained alloys use ultra-fine, sub-fine, fine-grained WC, rough-cut alloys use medium-grained WC, gravity cutting and heavy-duty cutting alloys use medium and coarse Granular WC as raw material; mining tools: high rock hardness, large impact load, use coarse grain WC, small rock impact and small impact load, use medium grain WC as raw material; wear-resistant parts: when emphasizing its wear resistance, compression resistance and surface finish When using ultra-fine, sub-fine, fine, and medium-grained WC as raw materials, impact-resistant tools mainly use medium- and coarse-grained WC raw materials.

The theoretical carbon content of WC is 6.128% (atomic 50%). When the carbon content of WC is greater than the theoretical carbon content, free carbon (WC+C) appears in WC. The presence of free carbon makes the surrounding WC grains grow up during sintering, resulting in uneven cemented carbide grains. Tungsten carbide generally requires high combined carbon (≥6.07%), free carbon (≤0.05%), and the total carbon depends on the production process and application range of cemented carbide.

Under normal circumstances, the total carbon of WC for vacuum sintering in paraffin wax process is mainly determined by the combined oxygen content in the compact before sintering. One part of oxygen needs to be added by 0.75 parts of carbon, that is, total carbon of WC=6.13%+oxygen content%×0.75 (assuming that the sintering furnace is a neutral atmosphere, in fact, most vacuum furnaces are carburizing atmospheres at present, and the total carbon of WC used is less than Calculated).

At present, the total carbon content of WC in my country is roughly divided into three types: the total carbon of WC for vacuum sintering in paraffin process is about 6.18±0.03% (free carbon will increase). The total carbon content of WC for hydrogen sintering in paraffin process is 6.13±0.03%. WC total carbon for hydrogen sintering in rubber process=5.90±0.03%. The above processes are sometimes carried out alternately, so the determination of the total carbon of WC depends on the specific situation.

Some small adjustments can be made for the WC total carbon used in alloys with different application ranges, different Co (cobalt) contents, and different grain sizes. Low-cobalt alloys can use tungsten carbide with high total carbon, and high-cobalt alloys can use tungsten carbide with low total carbon. In short, the specific use requirements of cemented carbide have different requirements for the particle size of tungsten carbide.