AISI JIS mark mark chemical composition C Si Mn C Si Mn P S Cr Cu Copper chrome V vanadium SUP3 0.75-0.90 0.15-0.35 0.30-0.60 ≦ 0.035 ≦ 0.035 ≦ 0.030 - mechanical properties of commonly used grade spring steel heat treatment system mechanical properties ≥ quenching temperature / ℃ quenching medium quenching temperature / ℃ yield point / MPa Tensile strength / MPa Elongation δ (%) Reduction (%) δ5 δ10 CK85 820 Oil 4809801127630 spring steel should have excellent overall properties, such as mechanical properties (especially elastic limit, ultimate strength, yield ratio), reduced ballistic performance (ie, decreased resistance to elastic properties, also known as the sag resistance), fatigue properties, hardenability, physical and chemical properties (heat , low temperature resistance, anti-oxidation, corrosion, etc.). To meet these performance requirements, the spring steel has excellent metallurgical quality (high purity and homogeneity), good surface quality (strict control of surface defects and decarburization), the exact shape and size