Manufacturing of Medium Carbon Steel Wires with Improved Spheroidization by Non-circular Drawing Sequence

Abstract

A non-circular drawing sequence was investigated for manufacturing medium carbon steel wires with improved spheroidization of cementite for better cold workability compared to those produced by the conventional wire drawing. The wire drawing and non-circular drawing processes with 20% area reduction per each pass were numerically and experimentally applied up to the fourth pass (total area reduction of 59%). The drawn wire by the non-circular drawing sequence shows higher average effective strain value than the one of the wire drawing in the numerical result. To investigate the effect of prior cold working on spheroidization of the drawn wire, spheroidization annealing was conducted at subcritical temperature of 705oC for 2h for both processes. According to the present investigation, the wires subject to subcritical annealing following the non-circular drawing sequence showed the reduced ultimate tensile strength and micro-hardness, and the enhanced reduction of area compared to those for the wire drawing. From upsetting test results, cold workability was also improved for the annealed specimen processed by the non-circular drawing sequence compared to the one produced by the wire drawing. Scanning electron microscopy (SEM) was employed to investigate microstructure changes during spheroidization annealing. Owing to the SEM results, the spheroidization of the annealed specimens processed by the non-circular drawing sequence was improved than the one produced by the wire drawing. It is demonstrated that the non-circular drawing sequence could manufacture the wires with improved spheroidization of cementite and cold workability compared to the wire drawing in the present work.