How to improve the service life of spring?
The measures to improve the quality of spring are as follows:
(1) Isothermal quenching can be used for springs with small diameter or enough hardenability. It can not only reduce the change of center, but also improve the strength and toughness. It is better to tempering again after austempering to increase the elastic limit. The tempering temperature is the same as that of Austempering.
(2) Thermomechanical treatment is a combination of deformation strengthening and heat treatment strengthening of steel to further improve the strength and toughness of steel. Thermomechanical treatment can be divided into high temperature, medium temperature and low temperature. High temperature thermomechanical treatment is to quench immediately after deformation in stable austenite state. It can also be combined with forging or hot rolling, that is, quenching immediately after hot forming. After high temperature thermomechanical treatment (930 ℃ + thermal variable 18%, oil quenching), the strength and fatigue life of automobile leaf spring made of 60Si2Mn steel are greatly improved by high temperature rapid tempering at 650 ℃× 3.25min.
(3) Spring relaxation treatment spring works under external force for a long time. Due to stress relaxation, a small amount of permanent (plastic) deformation will be produced. Especially for the spring working at high temperature, the stress relaxation phenomenon is more serious under high temperature, which reduces the accuracy of spring, which is not allowed for general precision spring spring. Therefore, this kind of spring should be relaxed after quenching and tempering. Heat treatment process: pre load the spring to make its deformation exceed the deformation that may occur when the spring works. Then, it is heated at 20 ℃ higher than the working temperature for 8 ~ 24h.
(4) Shot peening is one of the most widely used methods to improve spring surface quality. Spring requires high surface quality. Surface defects such as scratch, fold, oxidation and decarburization often become the place of stress concentration and fatigue fracture source. If the surface of spring is shot peened with small steel shot at high speed, the surface quality and strength of spring can be improved, and the surface will be in the state of compressive stress, so as to improve the fatigue strength and service life of spring.
(5) The combination of tempering and low temperature carbonitriding (soft nitriding) can significantly improve the fatigue life and corrosion resistance of coil spring.