The material of the cutting portion of a tool is a key factor in determining tool performance, directly affecting its cutting efficiency, wear resistance, heat resistance, and service life, and thus, the workpiece’s machining quality and production efficiency. In machining, the cutting portion of a tool must withstand enormous cutting forces, high temperatures, and intense friction, placing extremely high demands on the material’s mechanical, physical, and chemical properties. Commonly used tool cutting materials include high-speed steel, cemented carbide, ceramics, cubic boron nitride (CBN), and diamond. Each material has unique performance characteristics and application ranges. Selecting the right tool material is key to achieving efficient, high-quality machining.
High-speed steel (HSS) is a high-alloy tool steel infused with alloying elements such as tungsten, molybdenum, chromium, and vanadium. It exhibits high strength, toughness, and wear resistance, as well as excellent sharpenability, making it the most widely used traditional tool material. Its room-temperature hardness can reach 62-66 HRC and remains high at temperatures between 500-600°C. Its permitted cutting speed is generally between 15-50 m/min, making it suitable for machining non-ferrous metals, mild steel, and medium-carbon steel. The advantages of HSS tools include excellent toughness and impact resistance, making them suitable for producing complex shapes such as drills, taps, and broaches. They are also easy to sharpen and can be repeatedly sharpened, resulting in a relatively low cost. However, their heat and wear resistance are inferior to those of superhard materials such as cemented carbide, making them less effective in high-speed cutting and machining high-strength materials. Consequently, HSS has been gradually replaced by cemented carbide tools, although they remain indispensable in certain specialized applications.
Cemented carbide is an alloy material made through a powder metallurgy process from refractory metal carbides (such as tungsten carbide and titanium carbide) and a binder (primarily cobalt). It exhibits extremely high hardness and wear resistance, reaching a room-temperature hardness of 89-93 HRA (equivalent to 74-82 HRC). Its heat resistance is significantly superior to that of high-speed steel, maintaining excellent cutting performance at temperatures of 800-1000°C and allowing cutting speeds of 3-10 times that of high-speed steel. Cemented carbide tools are suitable for machining various materials, including steel, cast iron, and non-ferrous metals, and excel at high-speed cutting and machining difficult-to-machine materials. Based on their composition and properties, cemented carbide can be categorized as tungsten-cobalt (YG), tungsten-cobalt-titanium (YT), and general-purpose (YW). YG cemented carbide offers superior toughness and is suitable for machining cast iron and non-ferrous metals; YT cemented carbide offers excellent wear resistance and heat resistance and is suitable for machining steel; and YW cemented carbide combines the advantages of both YG and YT cemented carbide types, making it suitable for machining a wide range of materials. The disadvantages of cemented carbide are greater brittleness, poor impact resistance, difficulty in sharpening and high cost.
Ceramic cutting tools are primarily composed of aluminum oxide ( Al₂O₃ ) or silicon nitride ( Si₃N₄ ), with small amounts of metallic or non-metallic additives. They possess exceptional hardness and wear resistance, reaching 90-95 HRA at room temperature and heat resistance of up to 1200-1400 °C. They also allow for higher cutting speeds than carbide, reaching 200-1000 m/min . Ceramic cutting tools are suitable for machining difficult-to-machine materials such as high-strength steel, hardened steel, and chilled cast iron. They exhibit exceptional performance at high cutting speeds, achieving high machining precision and surface quality. Ceramic cutting tools offer advantages such as excellent wear resistance, high heat resistance, and chemical stability, as well as low affinity with metals and resistance to tool sticking. However, they are brittle and have poor impact resistance, making them incapable of withstanding high cutting forces and shock loads. They are suitable for continuous cutting and finishing, but not for intermittent cutting and roughing. With the advancement of ceramic material technology, the toughness of toughened ceramic cutting tools has been significantly improved, and their application range is continuously expanding.
Cubic boron nitride (CBN) tools are an ultra-hard tool material with a hardness of 8000-9000 HV, second only to diamond. They offer exceptional wear and heat resistance, maintaining stable cutting performance at temperatures up to 1300°C. They also exhibit excellent chemical stability and low affinity with iron-group elements , making them less susceptible to chemical reactions. CBN tools are suitable for machining difficult-to-machine materials such as various hardened steels (hardness 50 HRC and above), high-speed steel, bearing steel, and chilled cast iron. They excel in finishing and semi-finishing operations, achieving exceptionally high precision and surface quality, with surface roughness Ra reaching 0.1-0.4μm. CBN tools typically operate at cutting speeds of 80-300 m/min, significantly higher than carbide and ceramic tools. However, they are brittle, have poor impact resistance, and are expensive. They are suitable for high-precision, high-efficiency machining applications but not for roughing or applications subject to impact loads.
Diamond tools, which come in both natural and synthetic varieties, are currently the hardest tool material, reaching hardnesses up to 10,000 HV. They offer exceptional wear resistance and cutting edge sharpness, enabling mirror-finish cutting with surface roughnesses as fine as 0.01-0.1 μm Ra. Diamond tools have excellent thermal conductivity, low affinity for non-ferrous metals, and are less susceptible to tool sticking. They are suitable for machining non-ferrous metals (such as aluminum, copper, and magnesium alloys), non-metallic materials (such as plastics, ceramics, and glass), and composite materials, achieving exceptional surface quality in finishing and superfinishing. However, diamond tools have poor heat resistance, carbonizing at temperatures between 700 and 800°C and reacting chemically with iron-group elements at high temperatures. Therefore, they cannot be used for machining steel or cast iron. Diamond tools are also brittle, have poor impact resistance, and are extremely expensive. They are primarily used in applications requiring high-precision, high-surface-quality machining.
