A superhard material synthesized by a method similar to the diamond manufacturing method—cubic boron nitride (CBN) is second only to diamond in terms of hardness and thermal conductivity, and has excellent thermal stability, even when heated to 10000C in the atmosphere. Oxidation occurs. CBN has extremely stable chemical properties for ferrous metals and can be widely used in the processing of steel products.

⑴    Types of cubic boron nitride tools

Cubic boron nitride (CBN) is a substance that does not exist in nature. There are single crystals and polycrystals, namely CBN single crystal and polycrystalline cubic boron nitride (PCBN). CBN is one of the allotropes of boron nitride (BN), and its structure is similar to diamond.

PCBN (Polycrystalline Cubic Boron Nitride) is a polycrystalline material made by sintering fine CBN materials through bonding phases (TiC, TiN, Al, Ti, etc.) under high temperature and high pressure. It is currently the second only to artificially synthesized hardness Diamond tool materials, which are collectively referred to as superhard tool materials with diamond. PCBN is mainly used to make knives or other tools. PCBN cutting tools can be divided into integral PCBN blades and PCBN composite blades sintered with cemented carbide. The PCBN composite blade is made by sintering a layer of 0.5～1.0mm thick PCBN on a cemented carbide with better strength and toughness. Its performance has both better toughness and higher hardness and wear resistance. Solved the problems of low bending strength and welding difficulties of CBN blades.

⑵    The main performance and characteristics of cubic boron nitride

Although the hardness of cubic boron nitride is slightly inferior to diamond, it is much higher than other high hardness materials. The outstanding advantage of CBN is that the thermal stability is much higher than that of diamond, which can reach above 1200℃ (diamond is 700～800℃). Another outstanding advantage is that it is chemically inert and does not react with iron at 1200～1300℃. reaction. The main performance characteristics of cubic boron nitride are as follows.

①  High hardness and wear resistance: The crystal structure of CBN is similar to that of diamond, and the hardness and strength are similar to that of diamond. PCBN is particularly suitable for processing high-hardness materials that can only be ground before, and can obtain better surface quality of the workpiece.

②  High thermal stability: The heat resistance of CBN can reach 1400～1500℃, which is almost 1 times higher than the heat resistance of diamond (700～800℃). PCBN tools can cut high-temperature alloys and hardened steel at a speed 3 to 5 times higher than that of cemented carbide tools.

③  Excellent chemical stability: it does not have a chemical effect when it reaches 1200-1300℃ with iron-based materials, and will not wear as sharply as diamond. At this time, it can still maintain the hardness of cemented carbide; PCBN tools are suitable for cutting hardened steel Parts and chilled cast iron can be widely used in high-speed cutting of cast iron.

④  It has good thermal conductivity: Although the thermal conductivity of CBN is not as good as diamond, the thermal conductivity of PCBN is second only to diamond in various tool materials, and is much higher than that of high-speed steel and cemented carbide.

⑤  Has a low coefficient of friction: a low coefficient of friction can lead to a reduction in cutting force during cutting, lower cutting temperature, and improved surface quality.

⑶    Cubic boron nitride tool application

Cubic boron nitride is suitable for finishing various hard-cutting materials such as hardened steel, hard cast iron, high-temperature alloys, hard alloys, and surface spraying materials. The machining accuracy can reach IT5 (hole is IT6), and the surface roughness value can be as small as Ra1.25～0.20μm. Cubic boron nitride tool materials have poor toughness and bending strength. Therefore, cubic boron nitride turning tools are not suitable for rough machining at low speeds and large impact loads; at the same time, they are not suitable for cutting materials with high plasticity (such as aluminum alloys, copper alloys, nickel-based alloys, steel with high plasticity, etc.), because of cutting these In the case of metal, serious built-up edge will be produced and the machined surface will be deteriorated.