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Research progress of mold materials and mold heat treatment

    4 Cemented carbide and steel bonded cemented carbide

    Cemented carbide is a type of composite material manufactured by powder metallurgy. Cemented carbide has high hardness, good wear resistance, high elastic modulus and high working temperature. Used to make some molds, the service life of the mold can be increased several times or more than tens of times. However, cemented carbide is brittle, has poor bending strength and toughness, and cannot be machined. Cemented carbide is used as a mold material, mainly used for wire drawing dies, cold extrusion and cold punching dies that are not subject to impact. At present, my country can produce various grades of cemented carbide, which can basically meet the needs of the domestic market.

    In order to meet the needs of manufacturing micro-drills for drilling holes in integrated circuit boards, dot matrix printing needles for computers, precision tools and dies, etc., in recent years, various countries have developed some microcrystals (WC grains less than 1 micron) and ultrafine crystals. Granular cemented carbide (WC grains less than 0.6 microns), in traditional cemented carbide, the WC grain size is 1.3 to 1.5 microns. Ultra-fine grained cemented carbide has made up for many shortcomings of conventional cemented carbide, expanded its application range, and achieved good results in the manufacture of wear-resistant and impact-resistant tooling. Some research institutes and cemented carbide factories in my country have developed a variety of grades of microcrystalline cemented carbide and ultra-fine grained cemented carbide [16, 17]. The development of high-performance ultra-fine grained cemented carbide is still a hot spot in cemented carbide research.

    Steel-bonded cemented carbide is a composite material formed by carbide as the hard phase and steel as the bonding phase. Steel-bonded cemented carbide has good wear resistance, its strength and toughness are generally higher than that of cemented carbide, and has some process properties such as heat treatment, machinability, forgeability and weldability. Die is the main application field of steel bonded cemented carbide. my country began to develop this material in the 1960s, and has developed a variety of grades of steel-bonded cemented carbide, which is used as the steel-bonded cemented carbide for molds. The hard phase mainly uses TiC and WC, and the steel matrix mainly uses low alloy chromium. Molybdenum steel, medium-high alloy tool steel or high-speed steel, such as GT35, R5, D1, T1 of TiC series and TLMW50, GW50, GJW50 of WC series. Steel-bonded cemented carbide has been used to make cold heading dies, extrusion dies, drawing dies, punching dies, drawing dies, hot heading dies, etc. [11, 18].

    The development of powder metallurgy technology and the application of hot isostatic pressing led to the production and use of segregation-free powder high-speed steel in the 1970s. Its main characteristics are toughness, grindability, isotropy, and heat treatment processability. High-speed steel, and has a relatively high service life. In the future, this technology will be used to produce high-carbon, high-vanadium and high-wear-resistant cold die steels that cannot be produced by conventional processes. This type of steel has better machinability and grinding performance, and has better toughness. Some cemented carbides are similar. Many grades of powder metallurgy high wear-resistant cold die steel have been produced abroad, and there is still little research in China [11].