Spring wires are in the category of carbon steels, whose carbon percentage varies depending on the type and design of the spring. The amount of carbon in steels is the main factor in determining the strength and hardness of steel, but it is not the only factor, but the increase of other elements in steel as well as the type of steel production process can be effective in the quality of steel. The most widely used steel in spring production, which has a reasonable price, is 75CK.