There are several aspects to improving the service life of a spring:
(1) Austempering of springs
For springs with small diameters or sufficient hardenability, austempering can be used, which not only reduces the variation of the core, but also improves the toughness. It is better to temper again after austempering to increase the elastic limit, and the tempering temperature is the same as the austempering temperature.
(2) deformation heat treatment
The deformation heat treatment combines both the deformation strengthening of the steel and the heat treatment strengthening to further improve the strength and toughness of the steel. The deformation heat treatment has high temperature, medium temperature and low temperature. The high temperature deformation heat treatment is quenched immediately after deformation in a stable austenite state, and may also be combined with forging or hot rolling, that is, quenching immediately after thermoforming. The automobile leaf spring made of 60Si2Mn steel is quickly tempered by high temperature deformation heat treatment (930 ° C + thermal variable 18%, oil quenching), and its strength and fatigue life are greatly improved by rapid tempering at 650 ° C × 3.25 min.
(3) Relaxation treatment of the spring
The spring works under the action of external force for a long time. Due to the stress relaxation, a small amount of permanent (plastic) deformation will occur, especially the spring working at high temperature, the stress relaxation phenomenon is more serious at high temperature, and the precision of the spring is lowered, which is generally precise. Springs are not allowed. Therefore, such springs should be relaxed after quenching and tempering. Heat treatment process: preload the spring so that the amount of deformation exceeds the amount of deformation that may occur when the spring is working. Then, it is heated at a temperature higher than the working temperature of 20 ° C for 8 to 24 hours.
(4) Shot peening
Shot peening is one of the most widely used methods to improve the surface quality of springs. Springs require a high surface quality. Surface defects such as scratches, folds, oxidative decarburization, etc. tend to be places where stress is concentrated during spring operation and sources of fatigue fracture. If the surface of the spring is sprayed at a high speed with a small steel shot, the shot peening treatment not only improves the surface quality of the spring, but also improves the surface strength and makes the surface under compressive stress, thereby improving the fatigue strength and service life of the spring.
(5) Low temperature carbonitriding
For the coil spring, the combination of tempering and low-temperature carbonitriding (soft nitriding) can significantly improve the fatigue life and corrosion resistance of the spring.
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Tags: spring soft nitriding automotive leaf spring thermoforming compressive stress
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