Cemented titanium-tung-sten carbide (cemented titanium-tung-sten carbide) is a multiphase cemented carbide composed of WC%26mdash;TiC, WC and cobalt bonding metal or only WC%26mdash;TiC solid solution and cobalt. The cobalt content of the alloy is 4%-10%, TiC5%-30%, and the balance is WC. It is mainly used for cutting steel.
Cemented titanium-tung-sten carbide (cemented titanium-tung-sten carbide) cemented titanium-tung-sten carbide has high resistance to crater wear and is suitable for tools for long cutting materials. Crescent wear is prone to occur when cutting steel with tungsten-cobalt carbide tools, which is mainly caused by the diffusion reaction between the tool and the chips at the cutting temperature. In order to overcome the crater wear during steel processing, in the early 1920s, a cemented carbide containing TiC and a cemented carbide containing TaC were developed, and later a cemented carbide containing both titanium carbide and tantalum carbide was developed. In this type of alloy, the content of TiC and TaC depends on the severity of the crescent crater wear. TiC can reach 35% and TaC can reach 7%.
Tungsten-titanium-tantalum-cobalt cemented carbide (ie WC%26mdash; TiC%26mdash; TaC%26mdash; Co alloy) has developed into an important material for cutting steel. In Western Europe, the original WC-TiC%26mdash; Co cutting steel grade alloy is almost cancelled. In the United States and Japan, the cutting steel grade alloy is mainly WC%26mdash; TiC%26mdash; TaC%26mdash; Co alloy, but in Eastern Europe , Especially in the former Soviet Union, the cutting steel grade alloy is still dominated by WC%26mdash; TiC%26mdash; Co alloy. WC%26mdash; TiC%26mdash; Co and WC-TiC%26mdash; TaC%26mdash; The proportion of Co cutting grade alloys in cemented carbide varies depending on the situation of each country. , In China, WC%26mdash; TiC%26mdash; Co alloy production is second only to tungsten-cobalt cemented carbide. Use the code YT to represent WC%26mdash; TiC%26mdash; Co alloy, and the code YW to represent WC%26mdash; TiC%26mdash; TaC%26mdash; Co alloy, which is also called general alloy. Table 1 and Table 2 list the grades, compositions and properties of China’s tungsten-titanium-cobalt cemented carbide and tungsten-titanium-tantalum-cobalt cemented carbide.
WC-TiC%26mdash; Co alloy and WC%26mdash; TiC%26mdash; Tac%26mdash; The characteristic of the Co alloy production process is that the solid solution of various carbides, namely compound carbides, must be prepared first. The compound carbide can be carbonized with a mixture of tungsten powder, TiO2, Ta2O5 and carbon black, heated to 2000C in a vacuum induction furnace, and can produce TiC%26mdash;TaC or WC%26mdash;TiC solid solution. The use of vacuum in the final stage of carbonization can ensure sufficient carbon content. Another method is to heat a mixture of several carbides in a high vacuum to 2000-2500C for carbonization. This treatment can reduce the oxygen and nitrogen content in the mixture. Another method to produce WC%26mdash;TiC solid solution is the so-called %26ldquo;solvent method%26rdquo;, first dissolve various single carbides in liquid nickel, and when cooled, the solid solution carbides are then precipitated out in crystalline form. . The other processes are the same as the tungsten-cobalt cemented carbide production process.
Compared with tungsten-cobalt cemented carbide, the flexural strength of tungsten-titanium-cobalt cemented carbide with the same cobalt content is lower, and decreases with the increase of TiC content. Similar to tungsten-cobalt cemented carbide, when the carbon content is inappropriate, graphite or %26eta; 1 phase will also appear in the alloy. After adding TiC, the allowable carbon content of the alloy fluctuates wider than that of tungsten-cobalt cemented carbide. (Ti, w) C solid solution composition and grain size have a great influence on the structure and properties of the alloy. Using unsaturated solid solution (such as TiC:WC=50:50) at the sintering temperature, the alloy has higher hardness and cutting life, and the bending strength is reduced. Using saturated solid solution (such as TiC: WC=28.75: 71.25), the alloy has higher bending strength, lower hardness and lower cutting life. The hardness of the alloy increases as the grain size of the carbide phase (including the WC phase and (Ti, W)C solid solution phase) decreases. For three-phase alloys, due to the small content of (Ti, W)C phase, the increase of WC grains can increase the bending strength of the alloy, while the increase of (Ti, W)C phase grains in two-phase alloys will reduce the alloy的flexural strength.