1 Features and application range 55Si2Mn spring steel elastic silicon and manganese increase the strength and yield ratio, improve hardenability, temper resistance and resistance to relaxation stability, thermal sensitivity is small, but decarbonization tend to be larger, in particular, is higher silicon and carbon content, carbon is easy to graphite, steel brittle. 55Si2Mn spring steel used for cars, tractors and locomotives damping leaf springs and coil springs, cylinder valve springs, thermal springs can also be used below 250 ℃ use. 2 Chemical composition Carbon C: 0.52 ~ 0.60 Si Si: 1.50 ~ 2.00 Manganese Mn: 0.60 ~ 0.90 Sulfur S: ≤0.035 phosphorus P: ≤0.035 chromium Cr: ≤0.35 Ni-Ni: ≤0.35 copper Cu: ≤0.25 3 anti-mechanical properties tensile strength σb (MPa): ≥1274 (130) yield strength σs (MPa): ≥1176 (120) Elongation δ10 (%): ≥6 section shrinkage ψ (%): ≥30 Hardness: hot, ≤ 302HB; Cold Drawn + heat treatment, ≤321HB 4 Heat treatment and microstructure Heat Treatment Specification: quenching 870 ℃ ± 20 ℃, oil cooling; tempering 480 ℃ ± 50 ℃ (when special needs, ± 30 ℃). Microstructure: Tempered troostite. Alloy carbon steel major strengthening element, the impact of spring steel often than any other alloying elements. According to requirements, spring steel material should be in high-carbon steel. The world today spring steel, widely used in the vast majority of the carbon content of 0.45% - 0.65%. To overcome after spring steel strength increased toughness and ductility reduce the problem, but also reduce the carbon content of the trend. China low-carbon martensitic spring steel-depth studies, such as 28mnsib, 35mnsib, with its carbon content of about 0.30%. Practice shows that these may be in the spring steel lath martensite tempering of use, there is sufficient strength and excellent mechanical properties, especially excellent ductility, toughness. Japanese research and development of several high-strength spring steel, such as uhs1900, vhs2000, nd120s, nd250s etc., carbon content of about 0.40 percent. The main role of alloying elements in steel spring is to improve the mechanical properties, improved process performance and giving some special properties (such as temperature, corrosion), etc. Many spring steel with silicon as the main alloying element, which is the largest bomb minus Resistance of alloying elements, mainly due to the silicon with a strong solid solution strengthening effect; at the same time, can inhibit crystal silicon cementite during tempering of nucleation and growth, tempering carbide precipitation when changing the number, size and shape, to improve stability of steel tempering. At present, the domestic steel grades in wsi 1.8% to 2.2%, which is the highest existing standards silicon spring steel. But silicon content is too high, will promote decarbonization of steel and graphite tendency in the process of rolling and heat treatment, and the smelting and easy form inclusions difficult, therefore, the use of high silicon content spring steel still cautious. Because chromium can significantly improve the steel hardenability, prevents si-cr ball annealing graphitization tendency to reduce carbon layer is therefore commonly used spring steel alloying elements, chromium as the main strengthening element of spring steel 50crv more extensive use. Manganese is most effective to improve hardenability alloying elements, which dissolved in the ferrite solid solubility of the action. Studies have shown that, wmn must be greater than 0.5%, so when hardened spring steel core section representing an entirely into martensite, but wmn exceeds 1.5%, toughness decreased significantly, which should be given priority in selection of spring steel. Mo can improve the steel hardenability, prevent temper brittleness, improve fatigue performance, few existing standards plus molybdenum spring steel, is generally added in an amount of 0.4% or less. Vanadium is a strong carbide forming elements, the solid state of the dispersed precipitated mc type carbide has a strong precipitation strengthening effect. Added 0.11% v in 35crmnb steel, can significantly improve the steel hardenability, also found that vanadium can reduce the sensitivity of decarburization 35simnb steel and vanadium that this reduces carbon steel effective solution to prevent grain growth and prevent grain boundary diffusion and oxidation resistance related increase