There are many factors that harm the fatigue strength of spring

1. There is a certain correlation between the yield strength of the material and the fatigue limit. Generally speaking, the higher the yield strength of the material is, the higher the fatigue strength is. Therefore, in order to better improve the fatigue strength of the spring, we should try to improve the yield strength of the spring material, or choose materials with high yield strength and compressive strength ratio. For the same material, the fine crystal mechanism has higher yield strength than the large and small crystal mechanism.

2. The surface stress is generated on the surface of the spring material, so the surface mass of the spring has great harm to the fatigue strength. The cracks, defects and scars caused by spring materials in the whole process of cold rolling, drawing and production are usually the cause of spring fatigue and rupture.

The smaller the surface roughness is, the smaller the stress is and the higher the fatigue strength is. The damage of material surface roughness to fatigue limit. With the increase of surface roughness, the fatigue limit decreases. Under the condition of the same surface roughness, different steel brands and different production methods have different fatigue limit reduction levels. For example, the reduction level of cold rolled coil spring is smaller than that of hot coil spring.