Coil wires are ranked as high carbon steels that have 6 to 9 percent carbon, so it is really appropriate for tension/extension, flat spring which is used in industrial operation. Spring due to its usage affected by different static and dynamic loading proper to loading must have suitable tensile and resistance thus it is necessary to produce in different degrees of tensile.

As we know carbon percentage determine main feature of steel (such as tensile and hardness). Not only carbon but also increasing other elements like manganese , reducing of harmful elements like phosphor and steel production process have effected on the quality of high carbon steel. As we saw before in structural steels (ST) section that how we can make steels with different qualities (1 to 3) by the same amount of carbon with different steel production process, each kind of these steels has particular final strength. This is true about high carbon steels, too. It means that in the melting process by decreasing Phosphorus and sulfur and increasing manganese whit the same amount of carbon, we can make different grades such as A, B, C and D high carbon steel, it is obvious high carbon wires with A grade are like ST-1, B grade is like ST-2 and etc. one of the qualitative parameters in steels specially high carbon steels is formability, It means the most qualitative steel is the most formability is. Or in other words in wire drawing industry, qualitative steels can be drawn more, and as it gets drawn and it doesn’t get cut or broke and conquer high strength steels. Nowadays according to EN10270-1 standards, high carbon (coil) steel’s grade are shown by these codes: SH, SM, SL, and DM.