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Process and Application of Pressure Sintering of Cemented Carbide

Process and Application of Pressure Sintering of Cemented Carbide

Cemented carbide is made by powder metallurgy with one or several refractory carbides (tungsten carbide, titanium carbide, etc.) as the main component and metal powder (cobalt, nickel, etc.) as binder. Because of its superior properties, such as high strength, hardness, excellent wear resistance and oxidation resistance, it has been widely used in mechanical processing, petroleum mining, die forming and structural wear-resistant parts and other fields. Sintering is the most important process in cemented carbide production. Even though the compacts are the same, different sintering processes have different effects on the properties of sintered products.

For a long time, many kinds of sintering methods have been gradually formed by scientific researchers in various countries in actual production. The more traditional sintering methods include vacuum sintering, gas pressure sintering, hot isostatic pressing sintering, hot pressing sintering and so on. Since the advent of nano-cemented carbides in the 1980s, new sintering methods have gradually formed, such as microwave sintering, field-assisted sintering (such as spark plasma sintering, plasma activated sintering), two-stage sintering and selective laser sintering.

Sintering process (Pressure sintering)

Pressure sintering is a process of simultaneous hot isostatic pressing and sintering of workpieces under a pressure lower than conventional hot isostatic pressing (about 6MPa). Since Degussa designed and manufactured the first type of hot isostatic pressing furnace in 1984, this process has been gradually adopted by many cemented carbide manufacturers in the world. It combines the removing agent, sintering and hot isostatic pressing of the product in the same equipment. The workpiece is loaded into a hot isostatic pressing furnace. After dewaxing with low pressure carrier gas (such as hydrogen) at lower temperature, vacuum sintering is carried out at 1350-1450 C for a period of time, then hot isostatic pressing is carried out in the same furnace, and argon gas is used as the raw material. Pressure medium, pressure is about 6 MPa, then heat preservation for a certain time, and then cooling.

This process has many advantages: as sintering-hot isostatic pressing process is directly pressurized and pressurized at vacuum sintering temperature, it is conducive to improving the fluidity of liquid metals, eliminating voids, and avoiding structural defects such as "coarse grains" which are easy to occur after conventional hot isostatic pressing treatment; compared with vacuum sintering, carbon balance is easy to control and can be calibrated. The problem of carbon shortage or excess carbon in positive compacted products can reduce the internal voids of alloys and improve the strength and hardness of alloys to a certain extent. The process in the same furnace saves a lot of equipment investment, and its processing cost is twice as low as that of reheating isostatic pressing after vacuum sintering, which can greatly increase the service life of products. Life.

Application of Cemented Carbide

1 Tool materials

Cemented carbide can be used as cutting tool material in the largest number. It can be used to make turning tools, milling cutters, planers, drills and so on. Tungsten-cobalt cemented carbides are suitable for short chip processing of ferrous and non-ferrous metals and processing of non-metallic materials, such as cast iron, cast brass, bakelite, etc. Tungsten-titanium-cobalt cemented carbides are suitable for long chip processing of ferrous metals such as steel. Among the similar alloys, the more cobalt content is suitable for rough processing, and the less cobalt content is suitable for finish processing. The processing life of general cemented carbides is much longer than that of other cemented carbides for stainless steel and other difficult-to-machine materials.

2 Mold materials

Cemented carbide is mainly used for cold drawing dies, cold punching dies, cold extrusion dies, cold pier dies and other cold working dies.

3 Measuring tools and wear-resistant parts

Cemented carbide is used for wearable surface mosaic and parts of measuring tools, precision bearing of grinder, guide plate and guide rod of centerless grinder, top of lathe and other wear-resistant parts.

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