In today's market, the drill pipe with three edges is usually made of cemented carbide because the wear of epoxy glass cloth composite copper foil is especially fast for cutting tools. The so-called hard bit diamond is made of tungsten carbide powder and pressed with cobalt powder as binder. It is usually composed of 94% tungsten carbide and 6% cobalt.
Because of its high hardness, very wearable and a certain intensity, it is suitable for high speed cutting. But the toughness is poor and very brittle. In order to improve the properties of the cemented carbide, the chemical vapor deposition of a layer of 5~7 microns of titanium carbide (TIC) or titanium nitride (TIN) on the carbonized matrix has been adopted to make it more hard. Some ion implantation techniques have been used to inject titanium, nitrogen, and carbon into a certain depth of the matrix, which not only improves the hardness and strength, but can also be moved inside when the bit is regrinding.
There is also a physical method to produce a diamond film on the top of the bit, which greatly improves the hardness and wear resistance of the drill bit. The hardness and strength of cemented carbide are related not only to the ratio of tungsten carbide to cobalt, but also to the particles of powder. The average size of tungsten carbide phase grain is below 1 microns. The drill bit not only has high hardness, but also has high compressive and flexural strength.
In order to save cost, many drill stem bits use the welding handle structure. The original drill bit is hard alloy as a whole. Now the rear drill stem is made of stainless steel, and the cost is greatly reduced, but the dynamic concentricity of different material is less than the whole carbide bit, especially in the small diameter.