Cemented carbide is a general term for alloys prepared by powder metallurgy method by nine metal carbides of IVa, Va, VIa groups in the periodic table of elements and iron group metals such as Fe, Co, Ni, etc. The carbide phase gives the alloy high hardness and wear resistance, while the binder phase gives the alloy some strength and toughness.

According to the composition, cemented carbide can be divided into five categories: tungsten carbide based cemented carbide, titanium carbide based cemented carbide, coated cemented carbide, steel based cemented carbide and other cemented carbide.

Cemented carbide according to its scope of application can be divided into: hard alloy cutting tools, hard alloy mold, hard alloy mold and wear-resistant parts, as well as mine petroleum geology with hard alloy four categories.

Generally speaking, WC-Co hard alloy is widely used, which can be used for cutting tools of cast iron, non-ferrous metals and their alloys, metal drawing dies, stamping dies, measuring tools and wear-resistant parts for mining machinery and geological exploration. WC-Ti-Co alloys are mainly used for steel cutting; WC-TiC-(NbC)-Co alloys are mainly used for cutting high hardness material parts.

Although other types of cemented carbide in recent years has been considerable development, and in some special applications has achieved great success, but due to the WC-Co system (that is, YG) cemented carbide has a very excellent comprehensive mechanical properties, this kind of cemented carbide is currently the most widely used in industry, the largest amount of a class of cemented carbide.

1. Problems encountered in brazing of cemented carbide

The brazeability of the cemented carbide is poor. This is because the cemented carbide has a high carbon content, and the uncleaned surface often contains more free carbon, which hinders the wetting of the solder. In addition, the cemented carbide is easily oxidized to form an oxide film at the brazing temperature, which also affects the wetting of the solder. Therefore, the surface cleaning before brazing is very important to improve the wettability of the solder on the cemented carbide, and measures such as copper plating or nickel plating can be taken if necessary.

Another problem in the brazing of cemented carbides is the susceptibility of joints to cracking. This is because its linear expansion coefficient is only half of that of low carbon steel. When the cemented carbide is brazed with the matrix of this type of steel, a large thermal stress will be generated in the joint, which will cause the joint to crack. Therefore, when brazing cemented carbide with different materials, crack prevention measures should be taken.