Microstructure and mechanical properties of low carbon steel wires with serial and reverse-direction cold drawing

Low carbon steel wires were prepared by two processes, serial drawing (SD) and reverse-direction drawing (RD). Effects of the two processes on microstructure and mechanical properties in steel wires were investigated by field emission-scanning electron microscopy, electron backscatter diffraction (EBSD), X-ray diffraction and transmission electron microscopy (TEM). Residual compressive stress and more low-angle grain boundaries were introduced into the steel wire by the RD. As a result, the RD wires exhibited a greater tensile strength when drawing strain epsilon < 1.18. The SD encouraged grain refinement and texture formation in the wire. The SD wires exhibited a smaller average width of the elongated ferrite grain and a higher intensity of < 110 > fiber texture at all drawing strains. Therefore, the SD wires showed a bit greater tensile strength and 20% greater torsion performance than the RD wires at epsilon = 2.51. TEM and EBSD analysis indicated that dislocation tangle was formed easily in RD wires, and it transformed into twist boundary. This twist boundary impeded the grain refinement in the RD wires, and there were still non-fibrous grains in the RD wires even after heavy drawing.