Progress and future of high-speed cutting tool materials (4)

Ceramic knives have high hardness and wear resistance, hardness of 93 ~ 95HRA, good wear resistance, suitable for processing high hardness materials of 50 ~ 65HRC, such as chilled cast iron and hardened steel. High temperature performance, cutting at 1200 ° C. It has good anti-blocking property. Al2O3 has low affinity with metal. Its mutual reaction ability with various metals is lower than that of many carbides, nitrides and borides. It is not easy to bond with metals and has good chemical stability. The dissolution rate of Al2O3 in iron is about 1/5 of that of WC, and the diffusion wear is small. The oxidation resistance of Al2O3 is particularly good. Even if the blade is in a hot state, it can be used continuously for a long time, and is suitable for high-speed cutting. Ceramic tools also have a lower coefficient of friction than cemented carbide. The main disadvantages of Al2O3 based ceramic tools are low strength and fracture toughness, high brittleness, poor thermal conductivity and low thermal shock resistance. However, for decades, a lot of fruitful research work has been done on improving the mechanical properties of ceramic tools, such as hot pressing and hot isostatic pressing processes, adding various toughening and reinforcing phases, such as adding metal carbides to Al2O3. Nitride, boride and pure metals and whiskers, such as Al2O3 + TiC, Al2O3 + ZrO2, Al2O3 + SiCw (whiskers), Al2O3 + TiN, Al2O3 + TiCN, etc., some add a small amount of Mo in these composite ceramic tools Metals such as Ni and rare earth elements improve the performance of ceramic tools. Alumina-based ceramic tools can cut steel, cast iron and alloys at high speed, and Al2O3+SiCw is suitable for processing nickel-based alloys.

Compared with Al2O3 based ceramics, silicon nitride (Si3N4) based ceramics have the most remarkable characteristics of high strength and fracture toughness, low thermal expansion coefficient and low elastic modulus, so they have high thermal shock resistance. Si3N4 based ceramic tools are suitable for processing cast iron. Both continuous and interrupted cutting are superior to Al2O3 based ceramic tools. They can also be used for finishing and semi-finishing of high hardness materials such as chilled cast iron and high hardness rolls. However, because its chemical affinity with iron is significantly higher than that of Al2O3-based ceramics, the low melting point compound formed by chemical reaction will cause the blade to break in a short time. Therefore, the Si3N4-based ceramic tool is much worse than the Al2O3 base. The Si3N4 based ceramic tool also incorporates various toughening and reinforcing phases into the Si3N4 to form a variety of ceramic tools.

The Si3N4-Al2O3 (Sialon) ceramic tool is a new type of ceramic tool. It is developed on the basis of Si3N4 by replacing the nitrogen in Si3N4 with oxygen and replacing the silicon with aluminum. It is developed by Si-Al. -ON A general term for a variety of compound groups of various compositions. Sialon ceramic cutters have high strength and fracture toughness, good chemical stability, oxidation resistance and high temperature creep resistance. They have high thermal conductivity and small thermal expansion coefficient, so they have high thermal shock resistance. Due to its high creep strength, it is not subjected to repeated high stress and heat at the tip of the tool, and there is no obvious increase in damage due to plastic deformation. It is excellent for high speed roughing cast iron and nickel based alloy. Tool material. Whisker toughened ceramic knives are superior in difficult-to-machine materials such as fine cars and semi-finished nickel-based alloys. Sialon ceramic tools are more adaptable for roughing and milling, but their dissolution wear rate is much higher than that of Al2O3 based ceramic tools, making them unsuitable for machining steel.

Choosing the right type of ceramic tool can cut the cast iron at a high speed of 500-1000 m/min, cut the steel piece at a speed of 300-800 m/min, and cut the high-hard material (50-65HRC) at a speed of 100-200 m/min. The heat resistant alloy is cut at a speed of ~300 m/min.

TiC(N) based hard alloy

The main components of TiC (N)-based cemented carbide are TiC (titanium carbide), TiN (titanium nitride) and TiCN (titanium carbonitride), which are highly wear-resistant TiC+Ni or Mo, high toughness. TiC+WC +TaC+Co and tough TiN are the main components, and TiC(N) based on high strength and toughness TiC+NbC is used as the base alloy. Compared with WC hard alloy, hardness, strength, toughness, plastic deformation resistance and chipping resistance are significantly improved, mainly high temperature strength, high temperature hardness, thermal conductivity, oxidation resistance and thermal shock resistance. Steel has a low affinity, a low coefficient of friction, and is resistant to crater wear and adhesion. It has now evolved into an independent series of tool materials. TiC(N)-based cemented carbide with high nitrogen content and uniform fine hard structure developed in recent years, suitable for cutting general steel and high speed at 200-400m/min due to good wear resistance and chipping resistance. Alloy steel can also be used for the finishing of cast iron.

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