For large and medium-sized springs with high load accuracy and stress, cold-drawn or cold-drawn polished steel should be selected. Hot rolled steel can be used for springs with lower load accuracy and stress.Leaf springs are generally made of flat steel of 55Si2Mn, 60Si2MnA, 55SiMnVB, 55SiMnMoV, 60CrMn and 60CrMnB grades.
The material cross section of helical spring should be preferred to circular cross section. Square and rectangular cross-section materials have strong bearing capacity, good impact resistance and miniaturization of springs, but they have few sources of materials. And the price is high, except for special needs, generally try not to use this material. In recent years, round steel wire rolling flat instead of trapezoidal steel wire has been developed, and good results have been achieved.
Spring materials working at high temperatures require good thermal stability, relaxation or creep resistance, oxidation resistance and corrosion resistance of certain media.
The selection of hardness (i.e. strength) of spring made of spring steel should depend on the load-bearing property and stress magnitude of spring. However, the hardness has a great relationship with plane strain fracture toughness.