Size dependence of delamination of high-carbon steel wire

In order to find out major causes to produce the wire-size dependence of de lamination, comparative experiments were performed with high-carbon steel w ires. A large-size wire and a small-size wire were patented, drawn, and blu ed under almost the same conditions and the resultant wires were compared q uantitatively. Consequently, the experiments showed that even when the wire -making processes were controlled equivalently between the two different si zes, 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 obse rved size dependence was not substantially associated with applied shear st ress in torsion, while the yield shear stress had a significant effect on d elamination occurrence. Close observation with SEM showed that significantl y large microvoids form in the large-size delaminated wires, but not in the small-size non-delaminated wires. Microvoids were found to be nucleated pr eferentially at the interface between a fragmented cementite particle and r elatively thick ferrite. The difference in the stress intensity factor betw een the different size wires seems to be one of the major causes bringing a bout the size dependence. Another finding that the as-patented large-size w ire had a larger volume of proeutectoid ferrite than the as-patented small- size wire suggests the strong likelihood of proeutectoid ferrite being asso ciated with void formation.