How to Choose CNC Cutting Tools for Hardened Steel?
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How to Choose CNC Cutting Tools for Hardened Steel?
For the hardened workpieces and parts of various difficult-to-machine materials encountered in turning production, selecting suitable cutting tool materials, cutting quantities, tool geometric angles and operating methods can achieve good comprehensive economic effects.
Hardened steel parts of different materials have completely different requirements for tool performance under the same hardness, which can be divided into the following three categories:
①High-alloy steel: refers to tool steel and die steel (mainly various high-speed steels) with a total amount of alloy elements exceeding 10%.
②Alloy steel: refers to tool steel and die steel with an alloy element content of 2-9%, such as 9SiCr, CrWMn and high-strength alloy structural steel.
③Carbon steel: Including various carbon tool steels and carburizing steels such as T8, T10, 15 steel or 20 steel carburizing steel.
For carbon steel, the microstructure after quenching is tempered martensite and a small amount of carbides. The hardness is HV800～1000, which is harder than WC and TiC in cemented carbide and A12D3 in ceramic tools. It is much lower. In addition, it has lower thermal hardness than martensite without alloying elements, and generally does not exceed 200℃. As the content of alloying elements in steel increases, the carbide content of steel after quenching and tempering also increases, and the types of carbides become quite complicated. Taking high-speed steel as an example, the content of carbides in the microstructure after quenching and tempering can reach 10-15% (volume ratio) and contains MC, M2C, M6 and M3, 2C and other types of carbides, of which VC High hardness (HV2800), much higher than the hardness of the hardpoint phase in general tool materials. In addition, due to the existence of a large number of alloying elements, the thermal hardness of martensite containing multiple alloying elements can be increased to about 600℃. The machinability of hardened steel with the same macroscopic hardness is not the same, and the difference is very big. Before turning the hardened steel, analyze which type it belongs to, master its characteristics, and select the appropriate tool material, cutting amount and tool geometry angle can smoothly complete the turning of hardened steel parts.
If the tungsten carbide turning inserts are used for turning hardened steel, the general cutting speed is below 18m/min, and the surface roughness of the workpiece can reach Ra1.6～0.80μm.
The CBN tool can process all kinds of hardened steel and sprayed parts, the cutting speed can reach 100m/min, and the surface roughness can reach Ra0.80～0.20μm. The processing effect is worse than that of cemented carbide (but the strength is not as good as that of cemented carbide, the depth is smaller, and the price is more expensive than that of cemented carbide. In addition, the cutter head is easily damaged if used improperly).
The above various tools have their own characteristics in turning hardened parts, and should be selected according to specific conditions such as turning different materials and different hardnesses. As a CNC cutting tools manufacturer, if you have any inquiries about tungsten carbide milling inserts and turning inserts, just feel free to contact us.
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