Delamination of Pearlitic Steel Wires: The Defining Role of Prior-Drawing Microstructure

Abstract

This article reports the occasional (< 10 pct of the actual production) delamination of pearlitic wires subjected to a drawing strain of ~ 2.5. The original wire rods which exhibited post-drawing delamination had noticeably lower axial alignment of the pearlite: 22 ± 5 pct vs 34 ± 4 pct in the nondelaminated wires. Although all wires had similar through-thickness texture and stress gradients, delaminated wires had stronger gradients in composition and higher hardness across the ferrite–cementite interface. Carbide dissolution and formation of supersaturated ferrite were clearly correlated with delamination, which could be effectively mitigated by controlled laboratory annealing at 673 K. Direct observations on samples subjected to simple shear revealed significant differences in shear localizations. These were controlled by pearlite morphology and interlamellar spacing. Prior-drawing microstructure of coarse misaligned pearlite thus emerged as a critical factor in the wire drawing-induced delamination of the pearlitic wires.