Deformation heat treatment

Deformation heat treatment combines the deformation strengthening of steel with the heat treatment strengthening, further enhancing the strength and toughness of the steel. Deformation heat treatment can be classified into high-temperature, medium-temperature and low-temperature types.

High-temperature deformation heat treatment involves generating deformation in a stable austenite state and then immediately quenching, or it can be combined with forging or hot rolling, that is, quenching immediately after hot forming.

2. Isothermal quenching of the spring

For springs with smaller diameters or those with sufficient hardenability, isothermal quenching can be adopted. This method not only reduces deformation but also enhances strength and toughness. After isothermal quenching, it is advisable to perform a second tempering process, which can increase the elastic limit. The tempering temperature should be the same as the isothermal quenching temperature.

3. Shot peening treatment

Shot peening is currently one of the most widely used methods for improving the surface quality of springs. Springs are required to have a high surface quality. Surface defects such as scratches, folds, oxidation and decarburization often become the areas where stress concentrates and the sources of fatigue fractures during the operation of the springs. If the surface of the spring is subjected to high-speed shot peening with fine steel balls, not only can the surface quality of the spring be improved, but also the surface strength can be enhanced, making the surface remain in a compressive stress state. Thus, the fatigue strength and service life of the spring can be increased.

4. Relaxation treatment of the spring

When a spring works under external force for a long time, due to stress relaxation, it will undergo a small amount of permanent (plastic) deformation. Especially for springs working at high temperatures, the stress relaxation phenomenon is more severe at high temperatures, which reduces the precision of the spring. This is unacceptable for most precision springs. Therefore, such springs should undergo relaxation treatment after quenching and tempering.

5. Heat treatment process

Pre-load the spring to make its deformation exceed the deformation that the spring may undergo during normal operation. Then heat it at a temperature 20℃ higher than the working temperature for 8 to 24 hours.

6. Low-temperature carbon and nitrogen co-permeation

For the coil springs, a combined process of tempering and low-temperature carbon-nitrogen co-plating (soft nitriding) is adopted, which can significantly enhance the fatigue life and corrosion resistance of the springs.