Mechanical properties and application range of various high-speed steels
High-speed steel (HSS) is a high-alloy tool steel incorporating alloying elements such as tungsten, molybdenum, chromium, and vanadium. It exhibits high hardness, wear resistance, and heat resistance, maintaining excellent cutting performance even at temperatures of 500-600°C. Therefore, it is widely used in the manufacture of various cutting tools, such as drills, milling cutters, taps, and gear cutters. Depending on its composition and performance, HSS can be categorized as general-purpose, high-performance, and powder metallurgy HSS. Each type of HSS has its own unique mechanical properties and application range. Choosing the right HSS type is crucial for ensuring tool performance and machining quality.
General-purpose high-speed steel (HSS) is the most widely used type of HSS. Typical grades include W18Cr4V (18-4-1 type) and W6Mo5Cr4V2 (6-5-4-2 type). These steels exhibit excellent overall mechanical properties and are suitable for cutting general metal materials. W18Cr4V HSS has a high tungsten content (18%), resulting in high hardness (62-65 HRC) and wear resistance. It can withstand heat up to 600°C, but its toughness is relatively low. This makes it suitable for manufacturing cutting tools that require high cutting speeds and work with harder materials, such as milling cutters and gear hobs. It is primarily used for machining carbon steel, alloy steel, and cast iron. W6Mo5Cr4V2 HSS uses molybdenum instead of tungsten, resulting in lower cost and better toughness and thermoplasticity than W18Cr4V. While its hardness (63-66 HRC) and wear resistance are slightly lower, its cutting performance is similar. This makes it suitable for manufacturing complex tools such as drills, taps, and broaches, and is particularly well-suited for machining difficult-to-machine materials such as stainless steel and heat-resistant steel. The bending strength of general high-speed steel is generally 3000-4000MPa, and the impact toughness is 10-20J/cm². It is suitable for medium and low speed cutting (cutting speed generally does not exceed 50m/min) and is widely used in ordinary machine tools and mass production.
High-performance high-speed steel (HSS) is a general-purpose high-speed steel with the addition of alloying elements such as cobalt, aluminum, and vanadium to enhance its hardness, wear resistance, and heat resistance. It is suitable for machining difficult-to-machine materials such as high-strength steel, high-temperature alloys, and titanium alloys. Typical grades include W12Cr4V5Co5 (5% cobalt high-speed steel) and W6Mo5Cr4V2Al (aluminum high-speed steel). W12Cr4V5Co5 HSS, due to its high cobalt content (5%), significantly improves its heat resistance, reaching temperatures up to 650°C. Its hardness reaches 65-68 HRC, and it exhibits excellent wear resistance and high-temperature hardness. Its flexural strength ranges from 2800-3500 MPa and its impact toughness from 8-15 J/cm². It is suitable for manufacturing cutting tools such as milling cutters, turning tools, and drills for machining high-temperature alloys and high-strength steels. Cutting speeds can be increased by 20%-30% compared to general-purpose HSS. W6Mo5Cr4V2Al high-speed steel, by adding aluminum (approximately 1%), improves its hardness (66-69 HRC) and wear resistance. It also has a heat resistance of up to 630°C and is less expensive than cobalt high-speed steel. Its bending strength is 2500-3200 MPa, and its impact toughness is 6-12 J/cm². It is suitable for manufacturing taps, broaches, gear tools, and is particularly well-suited for machining materials such as stainless steel and high-strength cast iron. High-performance high-speed steel offers higher cutting efficiency and tool life than general-purpose high-speed steel, but its toughness is lower, making it suitable for continuous cutting and finishing.
Powder metallurgy high-speed steel (PHS) is produced using a powder metallurgy process. Molten HSS is atomized into a powder, then pressed and sintered. This overcomes the uneven performance issues associated with ingot segregation in traditional HSS, resulting in higher hardness, wear resistance, toughness, and uniformity, making it suitable for manufacturing high-precision, long-life cutting tools. Typical grades of PHS include ASP-60 and S390. PHS can achieve hardnesses of 68-70 HRC, flexural strengths of 4000-5000 MPa, impact toughness of 20-30 J/cm², and heat resistance of 650-700°C. Its wear resistance is two to three times that of conventional HSS. Its uniform microstructure and lack of coarse carbides enable the manufacture of large, complex-shaped cutting tools, such as precision gear hobs, broaches, and end mills. It is suitable for machining difficult-to-machine materials such as high-strength steel, high-temperature alloys, and titanium alloys, and excels in high-speed cutting and precision machining. The cutting speed of powder metallurgy high-speed steel can be increased by more than 50% compared with general high-speed steel, and the tool life can be extended by 2-5 times, but the cost is relatively high. It is mainly used in the demanding fields of aerospace, precision machinery, etc.
Coated high-speed steel (HSS) is a high-speed steel tool coated with one or more layers of wear-resistant coating (such as TiN, TiCN, TiAlN, etc.) to improve its wear resistance, heat resistance, and lubricity, thereby expanding its application range. Coated HSS tools can achieve a surface hardness of 2000-3000 HV, reduce the coefficient of friction to 0.2-0.4, and lower cutting temperatures by 50-100°C. Tool life is increased by 2-10 times compared to uncoated HSS, while cutting speeds are increased by 30%-50%. TiN-coated HSS tools offer high wear and oxidation resistance, making them suitable for machining materials such as carbon steel, alloy steel, and cast iron. TiCN-coated tools offer even better wear resistance than TiN and are suitable for machining stainless steel and high-strength steel. TiAlN-coated tools have a heat resistance of up to 800°C, making them suitable for high-speed cutting and machining high-temperature alloys. Coated high-speed steel tools are suitable for various high-speed steel substrates, such as general-purpose high-speed steel, high-performance high-speed steel, etc. They can be used to manufacture drills, milling cutters, taps, gear cutters, etc. They are especially widely used in CNC machine tools and automated production lines, and can significantly improve processing efficiency and surface quality.
When selecting high-speed steel (HSS), factors such as the material being machined, cutting conditions, tool type, and precision requirements must be considered. When machining materials like ordinary carbon steel and cast iron at low cutting speeds, general-purpose HSS offers a cost-effective alternative. When machining difficult-to-machine materials like high-strength steel and high-temperature alloys, or when higher cutting speeds are required, high-performance HSS or powder metallurgy HSS should be selected. For high-volume production and high-speed cutting, coated HSS is an ideal choice, effectively improving tool life and efficiency. The tool manufacturing process must also be considered. Complex-shaped tools (such as taps and broaches) generally use high-toughness HSS (such as W6Mo5Cr4V2), while simpler tools (such as turning tools and milling cutters) can use more wear-resistant HSS (such as W18Cr4V or high-performance HSS). By choosing the right HSS type, you can maximize its performance advantages, reduce production costs, and improve machining quality.
