1. Yield strength The yield strength of materials is related to fatigue to a certain extent. Generally speaking, the higher the yield strength of the material, the higher the fatigue strength. Therefore, in order to improve the fatigue strength of the finger spring, please try to increase the yield strength of the finger spring material. Materials having high strength or yield strength to tensile strength. For the same material, fine grain structure has higher yield strength than coarse grain structure.

2. Surface stress mainly occurs on the surface of the spring material, so the surface quality of the spring has a great impact on the fatigue strength. Cracks, defects and scratches in the rolling, stretching and rolling process of spring materials are usually the causes of spring fatigue fracture. The smaller the surface roughness is, the smaller the stress concentration is and the higher the fatigue strength is. Influence of material surface roughness on fatigue. Fatigue decreases with the increase of surface roughness. When the roughness is the same, different kinds of steel and rolling methods will reduce the fatigue to different degrees. For example, a cold coil spring decelerates less than a hot coil spring. Because the steel coil spring and its heat treatment heating, the surface of the spring material will become rough and decarbonized due to oxidation, thus reducing the fatigue strength of the spring. Grind, press, sand blast and roll the surface of the material. Both can improve the fatigue strength of the spring.

3. Size effect The larger the size of the material, the greater the possibility of defects in various cold and hot processing processes, and the greater the possibility of surface defects, resulting in the decline of fatigue performance. Therefore, the influence of size effect should be considered when calculating the fatigue strength of spring.

4. Metallurgical shortcomings refer to non-metallic inclusions, bubbles, element segregation and so on in materials. The inclusion on the surface is the source of stress concentration, which may lead to premature fatigue cracks at the interface between the inclusion and the matrix. Vacuum melting, vacuum casting and other measures can greatly improve the quality of steel.