1. A (whole) hardness method. 65mn, 60si2mn and other steels are quenched or isothermal quenching to obtain an overall hardness of 50-55 hrc. This heat treatment method is simple, the performance of the elastic part is ideal, but the hardness of the head is low, easy to wear, and the service life is not high.
2. Two-stage hardness method. 9Sicr, GCR15 and other steels are achieved by integral quenching and local tempering methods to obtain a head hardness of 60~63 HRC and a neck and tail hardness of 50-55 HRC. This heat treatment method often has early brittle fracture due to insufficient elasticity of the neck and tail.
It can also be achieved by integral heating and segmented cooling quenching, such as TIOA spring chuck, heated to 810 °C in a salt bath furnace (or flowing particle furnace), after heating, first quench the head with local water for about 5s, and then cool all human oil, so that the neck and tail meet the hardness requirements, and the hardness of the head after treatment is 50-55 hrc, and the neck and tail hardness are 40-45 hrc.
3. Three-stage hardness method. CCR15, 9SICR and other steels are installed in the fixture for overall heating. After heat preservation, put the chuck and neck into the 260-280 °C nitrate isothermal tank, the clamp tail is air-cooled, and when it is cold to black, it also enters the nitrate isothermal temperature, and then 380-400 °C as a whole with the same fire, at this time the neck hardness is 50-55 hrc, and the clamp tail hardness is 30-35 hrc. Since the hardness of the chuck has not been reached, 2/3 of the central head is locally heated and quenched in a neutral salt bath at 860 °C± 10 °C to achieve a hardness of 60-63 hrc, and then the spring chuck is tempered as a whole in a 200-220 °C bath to meet the final requirements, and this heat treatment method is complicated.