1. Isothermal quenching of the spring
For springs with small diameters or sufficient hardenability, isothermal quenching can be used, which not only reduces centering, but also improves toughness. After isothermal quenching, Z is better to temper again, which can improve the elastic limit, and the tempering temperature is the same as the isothermal quenching temperature.
2. Deformation heat treatment
Deformation heat treatment is to combine the deformation strengthening and heat treatment strengthening of steel to further improve the strength and toughness of steel. Deformation heat treatment is divided into high temperature, medium temperature and low temperature. High-temperature deformation heat treatment is quenched immediately after deformation in a stable austenite state, and can also be combined with forging or hot rolling, that is, quenching immediately after hot forming. The automotive leaf spring made of 60Si2Mn steel, after high temperature deformation heat treatment (930 °C + thermal variable 18%, oil quenching), adopts 650 °C×3.25min high temperature rapid tempering, its strength and fatigue life are greatly improved.
3. Relaxation treatment of spring
The spring works under the action of external force for a long time, due to stress relaxation, a trace amount of permanent (plastic) deformation will occur, especially the spring working at high temperature, the stress relaxation phenomenon at high temperature is more serious, so that the accuracy of the spring is reduced, which is not allowed for general precision springs. Therefore, such springs should be relaxed after quenching and tempering. Heat treatment process: the spring is preloaded to make its deformation exceed the amount of deformation that may be generated when the spring is working. Then heat under the condition of 20 °C higher than the working temperature, keep warm for 8~24h.
4. Shot peening treatment
Shot peening is one of the most widely used methods to improve the surface quality of springs. Springs require high surface quality, and surface defects such as scratches, folding, oxidation and decarburization often become places where stress is concentrated and fatigue fracture sources when springs are working. If the surface of the spring is sprayed with a fine steel shot at high speed and shot peening is carried out, it not only improves the surface quality of the spring, improves the surface strength, and makes the surface in a state of compressive stress, thereby improving the fatigue strength and service life of the spring.
5. Low temperature carbonitriding
For coiled springs, the combination of tempering and low-temperature carbonitriding (soft nitriding) can significantly improve the fatigue life and corrosion resistance of the spring.
