The quality of the spring after heat treatment is mainly determined by the life of the spring. From the perspective of performance, it is necessary to adjust the balance between the elastic parameters and the toughness parameters. The performance is closely related to the hardenability of the spring steel. At present, the spring manufacturing methods can be divided into three categories according to the different steel materials and process routes. The first is to use cold-rolled steel strips and cold-drawn steel wires, cold-rolled forming, quenched and tempered or low-temperature tempered. The second is to use hot-rolled non-annealed steel, hot-formed, quenched and tempered. This method is generally used in the manufacture of leaf springs and large coil springs. The third is to use hot-rolled annealed steel, cold-rolled forming, stress-relief shaping, and then heated quenching and tempering heat treatment. Generally, the steel wire diameter is 6-12mm for medium-sized coil springs. The heat treatment of spring steel can be divided into the heat treatment of cold-drawn steel wire and the heat treatment of hot-rolled spring steel.