Effect of drawing speed on microstructure distribution and drawability in twinning-induced plasticity steel during wire drawing

The effect of drawing speed on temperature rise and microstructure distribution in twinning-induced plasticity (TWIP) steel during wire drawing has been investigated to improve drawability for wire rod applications. Although wire drawing process is performed at room temperature, heat is generated due to the plastic deformation and friction at the wire–die interface. The steel wires subjected to the low drawing speed (LD) of 0.5 m/min and the high drawing speed (HD) of 5.0 m/min were analyzed using the numerical simulation and electron backscatter diffraction techniques. Interestingly, the specimens subjected to the HD had a higher drawability by about 18% compared to the LD, which is totally different from the general behavior of plain carbon pearlitic steels. The LD wire had uniform temperature distribution along the radial direction during wire drawing. In contrast, the HD wire had a temperature gradient along the radial direction due to the higher frictional effect at surface: the minimum temperature of 58 °C at center area and the maximum temperature of 143 °C at surface area. The higher stacking fault energy of HD wire at the surface area due to the high temperature rise retarded twinning rate, resulting in the prevention of fast exhaustion in ductility in comparison with the LD wires since the earlier depletion of twins at surface area is known as the main reason for the fracture of TWIP steel during wire drawing. Consequently, HD process delayed the fracture strain of wire and increased the uniformity of microstructure and mechanical properties along the radial direction.