What Are The Effective Methods To Extend The Service Life of Stainless Steel Springs?

In daily life, springs can be seen everywhere. So how can we extend the service life of springs? The following are specific methods. 

(1)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 dimensional changes but also enhances strength and toughness. It is advisable to perform a second tempering process after isothermal quenching, which can increase the elastic limit. The tempering temperature should be the same as the isothermal quenching temperature. 

(2) Deformation heat treatment 

Deformation heat treatment combines the deformation strengthening of steel with the heat treatment strengthening to further enhance the strength and toughness of the steel. Deformation heat treatment can be classified as high-temperature, medium-temperature, and low-temperature. 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. For example, automotive leaf springs made of 60Si2Mn steel, after high-temperature deformation heat treatment (930℃ + thermal variable 18%, oil quenching), and followed by a high-temperature rapid tempering at 650℃ for 3.25 minutes, their strength and fatigue life have been significantly improved. 

(3) After quenching and tempering, the spring should undergo relaxation treatment. 

When a spring operates under external force for a long time, due to stress relaxation, it will undergo a small amount of permanent (plastic) deformation. Especially for springs operating at high temperatures, the stress relaxation phenomenon becomes more severe at high temperatures, which reduces the accuracy of the spring. This is not allowed for most precision springs. Therefore, such springs should undergo relaxation treatment after quenching and tempering. Heat treatment process: Apply an initial loading force to the spring to make its deformation exceed the deformation that the spring may undergo during operation. Then, heat it at a temperature 20℃ higher than the operating temperature for 8 to 24 hours. 

(4) Shot peening treatment 

The spring requires a high surface quality. Surface defects such as scratches, folds, oxidation and decarburization often become the areas where stress concentration occurs and the sources of fatigue fracture during the spring's operation. Shot peening treatment is currently one of the most widely used methods for improving the surface quality of springs. If the spring surface is subjected to high-speed shot peening with fine steel balls, not only will the surface quality of the spring be improved, but the surface strength will also be enhanced, making the surface remain in a compressive stress state. As a result, the fatigue strength and service life of the spring will be increased. 

(5) Low-temperature carbon and nitrogen co-permeation 

For the coil springs, the 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.