1. Isothermal quenching of springs
For springs with small diameter or sufficient hardenability, isothermal quenching can be used, which can not only reduce the change of heart, but also improve the strength and toughness. After isothermal quenching, it is best to perform another tempering, which can increase the elastic limit, and the tempering temperature is the same as the isothermal quenching temperature.
2. Deformation heat treatment
Deformation heat treatment is a combination of 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 and low temperature. High temperature deformation heat treatment is to quench immediately after deformation in a stable austenite state, and it can also be combined with forging or hot rolling, that is, quenching immediately after hot forming. The automobile leaf spring made of 60Si2Mn steel is subjected to high temperature deformation heat treatment (930 ° C + thermal variable 18%, oil quenching), and then adopts high temperature rapid tempering at 650 ° C × 3.25min, and its strength and fatigue life are greatly improved.
3. Spring relaxation treatment
The spring works under the action of external force for a long time. Due to stress relaxation, a small amount of permanent (plastic) deformation will occur. Especially for springs working at high temperature, the stress relaxation phenomenon is more serious at high temperature, which reduces the accuracy of the spring. Springs are not allowed. Therefore, such springs should be relaxed after quenching and tempering. Heat treatment process: preload the spring so that its deformation exceeds the deformation that may occur when the spring is working. Then heat at 20°C higher than the working temperature for 8~24h.
4. Shot peening
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, folds, and oxidative decarburization tend to become stress concentrations and fatigue fracture sources during spring operation. If the surface of the spring is blasted with small steel shot at high speed and shot peened, it will not only improve the surface quality of the spring, but also improve the surface strength, so that the surface is in a state of compressive stress, thereby improving the fatigue strength and service life of the spring.
5. Low temperature carbonitriding
For coil springs, the combination of tempering and low-temperature carbonitriding (soft nitriding) can significantly improve the fatigue life and corrosion resistance of the spring.
