In machining, taps are the most common type of cutting tool used to machine internal thread fasteners, consisting of a cutting portion and a shank. In addition to a variety of stress in the cutting process is also subject to strong friction. Therefore, the tap is required to have high strength, hardness, abrasion resistance and less distortion after the heat treatment. According to the above requirements, the materials used in the manufacture of taps are generally selected from T12A, T10A carbon tool steels, CrWMn steels, 9CrSi and W18Cr4V high speed steels, and W6Mo5Cr4V2 steels.
During the heat treatment process of the tap, as people often ignore some of the details, resulting in distortion of the heat treatment of the tap, and even scraping and scrapping, resulting in a higher scrap rate, resulting in greater economic losses. For this purpose, the following issues should be noted in production:
1. The quality of the material used to make the tap must be checked before machining. The microstructure of the material should be spheroidized and the carbides should be fine and well distributed. If the microstructure of the material is flaky pearlite and the size of the carbide is too large, the degree of unevenness is too high or there are carbides in the mesh, the plasticity of the tap is reduced, the cracking tendency of the quenching distortion increases, and the brittleness of the blade tip is increased. The chipping reduces the service life of the tap.
2. To reduce the tendency of distortion cracking during quenching before the tap is quenched, especially for taps with high precision, the machining stress generated in the previous process should be eliminated.
3. Prior to quenching, taps should be preheated to reduce the temperature difference, reduce the thermal stress, and reduce the distortion tendency of the tap. Especially for W18Cr4V high-speed steel, due to the high quenching heating temperature, if the hot tap is placed in a high-temperature salt bath with a temperature of up to 1280°C, it will be heated directly. This will cause great thermal stress and increase the heating speed. Distortion tends to crack. Therefore, the tap should be preheated before quenching and heating to reduce the temperature difference and reduce the thermal stress.
4. When the tap is heat-treated, only the blade and shank can be quenched, and the intermediate transition is not quenched. This will make the transition part tough enough to facilitate future corrections. Quenching heating temperature should try to choose a lower temperature to prevent coarse grains, reducing the strength, plasticity and toughness of the tap. Especially for small diameter taps, it is preferred to reduce some of the hardness, and it must also maintain its toughness. Absolutely avoid high temperature quenching. At the same time, the quenching and heating time should not be too long, otherwise the high heating temperature and holding time will lead to the coarse crystal grains of the tap, decarburization, overheating and even overheating, affecting its performance and service life, and even scrapping.
5. Taps after quenching should be tempered immediately to prevent prolonged placement. The tempering temperature should be determined according to the tap hardness requirements, and also need to pay attention to the following two points: 1 timely adjustment of the tempering temperature according to the quenching condition; 2 avoid the first temper brittle zone of steel, such as the tempering temperature of CrWMn steel It is 250°C to 300°C. The tempering holding time should be as long as possible. The hardness of carbon steel and alloy steel cone after heat treatment is preferably 61-63HRC, and high-speed steel is 63-66HRC.
Practice has proved that “details determine success or failureâ€. If attention is paid to the above details in the production process of taps, the heat treatment defects and distortion and cracking of the taps will be greatly reduced, the qualification rate and service life of the taps will be improved, and the production cost will be reduced to increase the economic benefits.
During the heat treatment process of the tap, as people often ignore some of the details, resulting in distortion of the heat treatment of the tap, and even scraping and scrapping, resulting in a higher scrap rate, resulting in greater economic losses. For this purpose, the following issues should be noted in production:
1. The quality of the material used to make the tap must be checked before machining. The microstructure of the material should be spheroidized and the carbides should be fine and well distributed. If the microstructure of the material is flaky pearlite and the size of the carbide is too large, the degree of unevenness is too high or there are carbides in the mesh, the plasticity of the tap is reduced, the cracking tendency of the quenching distortion increases, and the brittleness of the blade tip is increased. The chipping reduces the service life of the tap.
2. To reduce the tendency of distortion cracking during quenching before the tap is quenched, especially for taps with high precision, the machining stress generated in the previous process should be eliminated.
3. Prior to quenching, taps should be preheated to reduce the temperature difference, reduce the thermal stress, and reduce the distortion tendency of the tap. Especially for W18Cr4V high-speed steel, due to the high quenching heating temperature, if the hot tap is placed in a high-temperature salt bath with a temperature of up to 1280°C, it will be heated directly. This will cause great thermal stress and increase the heating speed. Distortion tends to crack. Therefore, the tap should be preheated before quenching and heating to reduce the temperature difference and reduce the thermal stress.
4. When the tap is heat-treated, only the blade and shank can be quenched, and the intermediate transition is not quenched. This will make the transition part tough enough to facilitate future corrections. Quenching heating temperature should try to choose a lower temperature to prevent coarse grains, reducing the strength, plasticity and toughness of the tap. Especially for small diameter taps, it is preferred to reduce some of the hardness, and it must also maintain its toughness. Absolutely avoid high temperature quenching. At the same time, the quenching and heating time should not be too long, otherwise the high heating temperature and holding time will lead to the coarse crystal grains of the tap, decarburization, overheating and even overheating, affecting its performance and service life, and even scrapping.
5. Taps after quenching should be tempered immediately to prevent prolonged placement. The tempering temperature should be determined according to the tap hardness requirements, and also need to pay attention to the following two points: 1 timely adjustment of the tempering temperature according to the quenching condition; 2 avoid the first temper brittle zone of steel, such as the tempering temperature of CrWMn steel It is 250°C to 300°C. The tempering holding time should be as long as possible. The hardness of carbon steel and alloy steel cone after heat treatment is preferably 61-63HRC, and high-speed steel is 63-66HRC.
Practice has proved that “details determine success or failureâ€. If attention is paid to the above details in the production process of taps, the heat treatment defects and distortion and cracking of the taps will be greatly reduced, the qualification rate and service life of the taps will be improved, and the production cost will be reduced to increase the economic benefits.
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