Spring Flat steel refers to steel which is specially used to make springs and elastic elements due to its elasticity under quenching and tempering. The elasticity of steel depends on its elastic deformation capacity, that is, within the specified range, the elastic deformation capacity makes it can bear certain load, and after the removal of the load not appear permanent deformation. Flat spring steel should have excellent comprehensive properties, such as mechanical properties (especially elastic limit, strength limit, yield ratio), anti-elastic-decline property (i.e. anti-elastic degradation property, also known as anti-relaxation property), fatigue property, hardenability, physical and chemical properties (heat resistance, low temperature resistance, anti-oxidation, anti-corrosion, etc.). In order to meet the above performance requirements, flat spring steel has excellent metallurgical quality (high purity and uniformity), good surface quality (strict control of surface defects and decarbonization), and accurate appearance and size.