Void initiation and microstructural changes during wire drawing of pearlitic steels

Microstructural changes and void initiation in fully pearlitic steels during cold wire drawing were investigated by performing tensile tests and microstructural examination with scanning electron microscopy. In this investigation, the primary focus was on cementite lamellae aligned transversely to the drawing axis in pearlite colonies. Unlike the cementite lamellae aligned along the drawing axis that are deformed uniformly and thinned to a fibrous shape, those aligned transversely to the drawing axis are severely bent, curled and even fractured with increasing drawing strain. At high strain, a formation of globular cementite particles that are attributed to the densification of cementite was observed in colonies of lamellae aligned transversely to the drawing axis. In addition, it was found that voids were initiated in the vicinity of relatively large globular cementite particles due to the concentration of enhanced stress. The mechanisms of a formation of globular cementite particles and a void formation are discussed in conjunction with the deformation behavior of cementite lamellae during the drawing.