Effect of Carbon on the Microstructure and Mechanical Properties in Wire Rods Used for the Manufacture of Cold Heading Quality Steels

Wire rod is an intermediate product, used in the manufacture of cold head quality steel. The quality of the wire rod in the as-hot-rolled condition, was evaluated in a series of carbon steels with and without boron content and at two different wire rod thicknesses. While the effect of boron on hardenability in the hardened and tempered condition is well studied, the effect of boron on the quality in the ferrite–pearlite condition is not well analysed. Hence the present study established that the addition of boron improved strength and ductility in carbon steels compared to steels without boron. The increased strength was attributed to the increased pearlite content and fineness of interlamellar spacing, and the strength was compared with Gladman’s equation and a theoretical equation. The room-temperature flow curve evaluation showed a higher strain hardening exponent in boron-containing steel compared to the steel without it. The upset ratio, which measured the ability of the wire rod for the subsequent wire drawing operation, was found to decrease with carbon content for steels without boron, while it was found to marginally increase in boron-containing steels. The evaluations were substantiated with microstructures evaluated in different grades and thicknesses.