The carbon content of a steel wire is crucial for many of its properties. The higher the carbon content, the greater the tensile strength but the smaller the elongation to fracture. Wire with a very low carbon content is referred to as iron wire. Its tensile strength is low. Wire made of spring steel generally has a high carbon content of between 0.4 and 1.0%, resulting in high tensile strength values.
See Also
Adapted from “"We do it straight" — Wire Straightening”, p. 39 (ISBN 3-00-005897-4).