This kind of steel mainly contains silicon, manganese and chromium alloy elements. It is specially used to manufacture spiral spring, torsion spring and other spring shapes. It is widely used in transportation tools such as aircraft, railway vehicles, automobiles and tractors and other industrial products. Spring is mainly used under the condition of impact, vibration or long-term uniform periodic alternating stress. Therefore, high elastic limit, high fatigue strength, high impact toughness and plasticity are required. It is also required to have high conductivity when used in the manufacture of electrical instruments and precision instruments. High temperature and corrosion resistance. This kind of steel is usually made into flat bar, wire rod and steel wire for the user, and then made into flat spring, spiral spring and other kinds of spring and used after heat treatment. Therefore, the requirements for surface properties and decarburization performance of steel are more strict than that of No. 1 steel.