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2 Powdered high-speed steel quenched metallographic grade 10 to 11:
3 tempering temperature is generally 550 ~ 560 °C, tempered 4 times. 3 Conclusion High-speed steel tool hardness is the main indicator of the tool life, high hardness, wear resistance, but poor toughness. Excessive hardness is liable to cause chipping during use, resulting in permanent failure of the tool: moderate hardness, good toughness, wear inevitably during use, but can be worn to restore the tool to its original function. When the hardness of the material being cut is high, the hardness of the tool is taken as an upper limit, and vice versa. The hardness of 63-64HRC tools, although reaching the national standard, but in actual use, the life will not be very high. To sum up, how to position the high-speed steel tool, how to match the hardness and toughness, may be an eternal subject for the research of tool workers and heat treatment workers.
Hardness is the ability of the material to resist local plastic deformation of the surface layer. So far, only the hardness of this parameter can directly reflect the mechanical and technological properties of the surface layer and the surface wear layer. Now on the high-speed steel tool hardness and heat treatment issues, talk about superficial view. Table 1 High-speed steel tool hardness recommended tool name recommended hardness (HRC) overheating HSS HSS-E, SPM straight shank twist drill ≤ Ø4mm 63.5 ~ 66 64 ~ 66 not allowed> Ø4mm 64 ~ 66 65 ~ 67 ≤ 2 dense Large blade cutters 62 to 65 64 to 66 Do not overheat turning tools 4 to 16 mm 64 to 66 66 to 67 ≤ 2 >16 mm 65 to 67 66 to 68 ≤ 4 Gear hob 64 to 66 65 to 67.5 ≤ 2 Medium tooth saw Chip cutter screw groove cutter thickness ≤1mm 62.5～65 64～65.5 Do not overheat thickness >1mm 63.5～66 65～67 ≤1 End mill ≤Ø6mm 63.5～66 65～66.5 ≤1 >Ø6mm 64.5～66.5 65～67 ≤2 Three-blade cutter thickness ≤8mm 64～66 65～67 ≤1 Thickness>8mm 64～66.5 65～67 ≤2 Taps for the grinding machine M3～8 62～65 64～66 Do not overheat M>8 63～66 65 ~ 67 Not allowed to overheat bumps Semi-circular milling cutters 64 to 66 65 to 67.5 ≤ 1 Angle cutters 63.5 to 66 64 to 67 ≤ 1 Broaching tools 63.5 to 66 64 to 67 Do not overheat push cutters 64 to 66 65 to 67.5 ≤ 1 Slotting cutters 64～66 65～67 ≤1 Planing cutter 64～66 65～67 ≤2 å‰ Blade 62～64 63～65 Do not overheat Bevel gear milling cutter 64～66 65～67 Do not overheat 1 Common high speed steel cutter hardness recommendation The hardness of quenched and tempered high-speed steel (HSS) can reach 63 ~ 67HRC, high-performance high-speed steel (HSS-E), powder high-speed steel (SPM) up to 66 ~ 70HRC. For a tool under certain cutting conditions, there must be a proper hardness value. Table 1 is the recommended value of the hardness of some HSS tools. As can be seen from Table 1, for the general tool, if the use of HSS hardness control in the better 65 ~ 66HRC, while the M42 like HSS-E hardness can reach 69 ~ 70HRC, but in fact the hardness of such tools is the most The best range is 66 to 67 HRC. 2 Relationship between hardness and toughness of the tool Hardness and toughness are the most prominent contradictions on the tool pair. The tool material is developed from carbon tool steel, alloy tool steel, high speed steel, hard alloy to the current ceramic, cubic nitridation Boron and other superhard materials, the hardness of the tool is getting higher and higher, the toughness is getting worse. In a sense, it is much harder to seek the high toughness of tools than high hardness. In the high-speed steel cutting tool products, only the hardness is specified. With HSS-made tools, except for drills and center drills with lower hardness (HRCP63) requirements, the rest of the products are all 63-66HRC, and no toughness is required. Decades of practice have proved that excessive hardness makes the life of the tool drop. At the beginning of the 1960s, the National Conference of Engineers of the Tool Industry had decided that high-speed steel tool hardness exceeding 66.5HRC would not be shipped. Due to the fact that ultra-hard high-speed steel and powder high-speed steel had not been applied at the time, such regulations would have guiding significance for the development of the tool industry. In the 1970s, Japanese scholars proposed the idea of ​​controlling the hardness to 65 to 66 HRC for general tools. According to the results of the tool evaluation conducted throughout the country, it can be seen that the hardness of high-speed steel cutters with first-class products and superior products is more than 65HRC, which means that low-hardness cannot be high in life. The lower limit of the hardness prescribed by the state, the author believes that only the minimum level of qualified products, even if the quality standards can not reach, there is no place in the market competition. It should be specifically pointed out here that, with the same specifications of tools, often due to different materials and different heat treatment process, although the hardness is the same, but the tool life is not the same, and even a large gap, is the same material with the same number of materials Specifications cutters, also appear above. Hardness is only a surface phenomenon. Metallographic structure is the essential thing. Photometric hardness does not look good on metallurgy. High hardness is not a long life, high tool life, but also with the raw material carbide deflection, quenching grain size, carbide dissolution, tempering conditions, overheating levels and many other factors. Through what kind of heat treatment process to achieve the hardness value of the process requirements, has always been the concern of the heat treatment experts, of which the quenching heating temperature is the most important, a little negligence, there will be quality problems. The quenching temperature of common high-speed steels is shown in Table 2. Table 2 Commonly used high-speed steel quenching temperature grade W18Cr4V W6Mo5Cr4V2 W9Mo3Cr4V W2Mo9Cr4V W7Mo4Cr4V W4Mo3Cr4V W6Mo5Cr4V2Al Recommended quenching temperature (°C) 1260~1290 1210~1230 1220~1240 1180~1200 1210~1240 1160~1185 1200~1215 Brand W2Mo9Cr4VCo8 W6Mo5Cr4V2Co5 APM23 HAP50 S390PM CPM M4 Recommended quenching temperature (°C) 1160~1190 1190~1215 1170~1190 1180~1220 1190~1230 1170~1190 1. In addition to the large-size drill, turning tool and hob quenching metallurgical austenite grain size of 9 to 9.5 In addition, the rest of the hardened quenching tools should be controlled in the range of 10 to 10.5: