Performance requirements and composition characteristics of spring steel

(1) General characteristics of spring steel
Spring is an important part of all kinds of machinery and instruments. It mainly uses the energy stored in elastic deformation to ease the vibration and impact of machinery. It also uses the stored energy of elastic deformation to work. Because the spring is usually used under dynamic load, the spring steel must have high elastic limit a, high strength B, high bending strength (s / b), high fatigue strength R (especially notch fatigue strength), sufficient plasticity, toughness and good surface quality. At the same time, it is also required to have good hardenability and low decarburization sensitivity in cold and hot state It is easy to process and form.

 

(2) Chemical composition characteristics of spring steel
In order to obtain the required properties of spring, the carbon content of spring steel is higher than that of quenched and tempered steel, and the carbon spring steel is usually in the range of 0.6% ~ 0.75% C. Because of the poor hardenability of carbon spring steel (such as 65, 75 steel, etc.), when its cross-section size exceeds 12mm, it can not be hardened in oil. If it is quenched with water, it is easy to produce cracks. Therefore, the spring with large section size and heavy load is made of alloy spring steel.

The carbon content of alloy spring steel is generally between 0.46% and 0.70%. The alloy elements in alloy spring steel often include Si, Mn, Cr, V, etc. their main functions are to improve the hardenability and tempering stability of the steel, strengthen ferrite and refine grain size, so as to effectively improve the mechanical properties of spring steel, increase the elastic limit and yield ratio. Si and Mn mainly improve hardenability and yield ratio, and the effect is most prominent than Si. However, it promotes surface decarburization during heat treatment, while Mn makes steel easy to overheat. Therefore, important spring steel must be added with Cr, V, W and other elements, such as Si CR spring steel surface is not easy to decarburize; CR-V spring steel is not easy to overheat, fine grain, not easy to grow and coarsen, good impact resistance and high temperature strength, among which CR and V are also conducive to improve the high temperature strength of spring steel.