Size Dependence of Delamination of High-carbon Steel Wire

Abstract

In order to find out major causes to produce the wire-size dependence of delamination, comparative experiments were performed with high-carbon steel wires. A large-size wire and a small-size wire were patented, drawn, and blued under almost the same conditions and the resultant wires were compared quantitatively. Consequently, the experiments showed that even when the wire-making processes were controlled equivalently between the two different sizes, the delamination of the large-size wire tended to be less reduced than the small-size wire. An analysis with torsion tests revealed that the observed size dependence was not substantially associated with applied shear stress in torsion, while the yield shear stress had a significant effect on delamination occurrence. Close observation with SEM showed that significantly large microvoids form in the large-size delaminated wires, but not in the small-size non-delaminated wires. Microvoids were found to be nucleated preferentially at the interface between a fragmented cementite particle and relatively thick ferrite. The difference in the stress intensity factor between the different size wires seems to be one of the major causes bringing about the size dependence. Another finding that the aspatented large-size wire had a larger volume of proeutectoid ferrite than the as-patented small-size wire suggests the strong likelihood of proeutectoid ferrite being associated with void formation.