Si and Mn increased elastic strength and yield strength ratio, improve hardenability, anti tempering stability and the relaxation resistant stability, thermal sensitivity is also small, but decarburization tends to be larger, especially when silicon and carbon content is high, carbon is easy to graphite, which making the steel brittle. Used in automobile, tractors and machine vibration of the plate spring and spiral spring, cylinder safety valve spring, also can be used as heat-resistant spring below 250 ℃.