Whether the spring is in use or in production, it is necessary to consider its service life. If the service life of the spring produced by the manufacturer is very short, it means that the quality of the spring is very poor, so the spring manufacturer is in production. In the process, we must think about this point, which is also an explanation to the customer. Usually in the process of use, we will also shorten the service life of the spring due to the inappropriate use method. Next, we will introduce some methods to improve the service life of the spring.
1. Deformation heat treatment
Deformation heat treatment combines the deformation strengthening and heat treatment strengthening of steel, which can greatly 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 quenched immediately after deformation in a stable austenitic state, and can also be combined with forging or hot rolling, ie quenching immediately after hot forming. The automotive leaf spring made of 60Si2Mn steel is rapidly tempered by high temperature deformation heat treatment (930°C + heat change of 18%, oil quenching), and its strength and fatigue life can be greatly improved by rapid tempering at 650°C × 3.25 min .
2, isothermal quenching
For springs with small diameter or sufficient hardenability, isothermal quenching can be used, which can not only reduce the change of dead center, but also further improve the strength and toughness of the spring. After isothermal quenching, it is best to re-temper to increase the elastic limit, and the tempering temperature is the same as the isothermal quenching temperature.
3. 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.
4. Deal with the relaxation of the spring
When the spring works under the action of external force for a long time, due to stress relaxation, slight permanent (plastic) deformation will occur, especially for springs working at high temperature, the stress relaxation phenomenon is more serious at high temperature, and the accuracy of the spring is reduced, which is usually precise. Springs are not allowed. Therefore, such springs should be relaxed after quenching and tempering. Heat treatment process: Preload the spring so that the deformation exceeds the deformation that may occur when the spring is working. It is then heated at a working temperature above 20°C for 8 to 24 hours.
5. Shot peening
The way to improve the surface quality of the spring is shot peening, which is one of the most commonly used methods. Springs demand high surface quality requirements. Surface defects such as scratches, creases, oxidative decarburization, etc. are often the central source of stress concentrations and fatigue fractures during spring operation. If small steel shot is used to radiate the surface of the spring at high speed, this shot peening treatment can 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, which effectively improves the fatigue strength and service life of the spring. .
