Springs are used within their elastic range and should return to their original position after unloading. Minimal plastic deformation is desirable; therefore, the steel wire should possess high elastic limit, yield strength, and tensile strength. A higher yield strength ratio means the elastic limit is closer to the tensile strength, thus improving strength utilization and resulting in a stronger spring.
Springs absorb impact energy through elastic deformation, so spring steel wire doesn't necessarily need high plasticity, but it must at least have enough plasticity to withstand spring forming and sufficient toughness to withstand impact energy.
Springs typically operate under alternating stress for extended periods, therefore requiring a high fatigue limit and good creep and relaxation resistance.
Springs used in specific environments have additional requirements for the steel wire. For example, springs used in corrosive media must have good corrosion resistance. Springs used in precision instruments should have long-term stability and sensitivity, a low temperature coefficient, a high quality factor, minimal aftereffects, and a constant elastic modulus. Springs operating at high temperatures must maintain sufficient elastic limit and good creep resistance even at high temperatures.
In addition, the forming and heat treatment processes of spring steel wire should also be considered. Cold-drawn spring steel wire and oil-quenched and tempered spring steel wire are supplied in their original state and directly wound into springs. After forming, the springs undergo stress relief treatment and are used directly. The tensile strength of cold-drawn spring steel wire is slightly higher than that of oil-quenched and tempered steel wire. Large-diameter cold-drawn steel wire has too much elasticity, making spring winding difficult. Therefore, the diameter of cold-drawn spring steel wire used is generally less than 8.0 mm, and the diameter of oil-quenched and tempered steel wire used is generally less than 13.0 mm. In practice, springs with a diameter of 13.0 mm often use lightly drawn spring steel wire, which is cold-drawn, wound, and then quenched and tempered before use. Steel wires with a diameter of 15.0 mm or more are mostly made using a heated winding process.
