Delamination of Pearlitic Steel Wires: The Defining Role of Prior-Drawing Microstructure
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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.
Supports from the Tata Steel and the DST (Department of Science and Technology, India) are acknowledged. The authors would also like to express their appreciation for the usage of the National Facility of Texture and OIM (at IIT Bombay), the Nano-Indention facility (a central facility of IIT Bombay), and the TEM laboratory (of SAIF, IIT Bombay). Support from the CoEST (Center of Excellence in Steel Technology) IIT Bombay is also acknowledged.
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