Torsional ductility of high carbon steel wire

The product quality and process control factors which determine the degree of torsional ductility in finished 0.5-0.8%C pearlitic steel wire have been defined. The observed torsional deformation phenomena and their interrelationship with the drawn structure are described. Although the operative mechanisms are not yet fully understood or quantified, it has been possible to provide guidelines for the enhancement of performance. These have been validated by successful collaborative production trials involving British Steel and a leading UK rod roller and wire drawer. As well as recommending specific composition limits for manganese, phosphorus, sulphur, and nitrogen, importance has been attached to the control of cleanness and other aspects of product quality particularly in the surface region, where torsional deformation is concentrated. The design of the wire drawing process is extremely critical, and should avoid microstructural damage, strain aging embrittlement, and creation of large tensile residual stresses which facilitate the localisation of torsional deformation. The extent to which the torsion testing variables can affect the measured value of ductility has also been considered.