The spring should return to its original position after unloading. The smaller the plastic deformation, the better. Therefore, the steel wire should have high elastic limit, yield strength and tensile strength. The higher the yield ratio is, the closer the elastic limit is to the tensile strength, so the higher the strength utilization ratio is, the stronger the spring elasticity is.
The spring absorbs the impact energy by elastic deformation, so the spring steel wire does not have to have high plasticity, but at least it must have the plasticity that can bear the spring forming and enough toughness to bear the impact energy.
Spring usually works under alternating stress for a long time, so it should have high fatigue limit and good creep and relaxation resistance.