effect factors of the spring fatigue strength

Surface state of maximum stress occurs in the surface layer of spring material, so the quality of the surface of the spring has much effect on the fatigue strength.Spring material caused in the process of rolling, drawing, and rolling defects such as cracks, defects and scars are often the cause of spring fatigue fracture.
The smaller the materials on the surface roughness, the smaller the stress concentration and fatigue strength is also higher.The influence of surface roughness on the fatigue limit.With the increase of surface roughness, fatigue limit.In the case of the same roughness, different steel grade and different extent of the coiling method of the fatigue limit is different also, such as cold heat coil spring small extent of the coil spring.When heated, because steel hot coil spring and its heat treatment due to oxidation make the spring material surface roughness and decarburization phenomenon, thus reduced the fatigue strength of the spring.