The essential of a spring is that is has the quality to react to loading by elastic deformation. Therefore, materials with high elasticity are necessary. As in each case a small design is desired, spring materials should have the hightensile strength and a high elastic limit.

In addition to high strain in the elastic region, there must also be sufficient plasticity. This allows the manufacture of cold formed springs which will not break through the greatest unforeseen overloading.

Moreover, a high fatigue limit is required which is however not a characteristic value of the material as, for example, the tensile strength. For a high fatigue strength, a high degree of purity, a homogenous structure and a smooth carbon-free surface are pre-supposed.

These requirements are fulfilled very well by steel, therefore most springs are made of steel. Apart from this there will be the requirement in some cases for corrosion resistance, heat resistance or anti-magnetic properties where special materials will be required.

An important property of spring material is Young’s Modulus (E). From this material constant is derived a linear relationship between load and deflection. The ‘E’ of steel is practically not affected by heat treatment, but it is temperature dependent and this must be taken into consideration at higher working temperatures.