Properties of high speed steel tool materials II
Properties of high speed steel tool materials
2. Strength, toughness and heat resistance
The strength and toughness of high speed steel are the highest among existing tool materials. Therefore, high-speed steel tools can withstand large impact loads, which is one of the main reasons why high-speed steel is still widely used. The strength and toughness of high speed steel are related to grain size, carbide distribution, residual stress and austenite quantity. With the increase of grain growth and carbide distribution in steel, the strength and toughness of steel also decrease. Increasing the content of carbon, vanadium and cobalt in high-speed steel will reduce the strength and toughness of steel. When the drilling content is very high, its toughness will even be reduced to close to the toughness index of cemented carbide, so it can not withstand large impact.
The thermal stability of universal high-speed steel is 550~600°C, and superhard high-speed steel can reach 650~700°C. Although the thermal stability of high-speed steel is not as good as carbide, it is much higher than alloy tool steel and carbon tool steel, which is the main reason why the cutting performance of high-speed steel tools is higher than the latter two, its cutting speed and tool life are much higher, and the cutting speed of hob made of superhard high-speed steel can be as high as 100m/min or more.
When the content of C, V and Co in high-speed steel increases, the high temperature hardness of steel can be improved, and the effect of adding C is the most significant. Many high-performance high-speed steel components produced abroad are added to the drill, the main purpose is to improve its high temperature hardness. The hardness of high-carbon drilling superhard high-speed steel W2Mo9Cr4VCo8 when the temperature is not very high has reached the hardness range of WC-Co carbide containing more cobalt.
3. Process performance
The forging performance, heat treatment performance and cutting performance of high-speed steel are better, and it is easy to make a variety of complex shapes of tools than carbide, which is the main reason why high-speed steel still dominates in tool materials, especially in complex tools. Grinding performance is one of the most important process performance that determines tool quality. In tool manufacturing, the cost of grinding is very high, sometimes accounting for 50%-60% of the total cost of tools, while the cost of materials and heat treatment only accounts for 10% to 20%. In this case, the quality of grinding processing performance often becomes the main basis for whether workers are willing to use a certain grade of high-speed steel. Although the high vanadium high speed steel tool has good wear resistance and significantly improved tool life, its use scope is greatly limited due to its poor grinding performance.
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