The effects of annealing on microstructure and tensile properties of cold drawn steel wire

Abstract

Annealing is a process that could improve the tensile properties of material while eliminating internal residual stress created during cold drawing process. This study aimed to investigate the effect of annealing temperature and soaking time on cold-drawn steel wire in terms of microstructural changes and mechanical properties. The effects of annealing temperature and soaking time were investigated using tensile test, X-ray diffractometer (XRD) and field emission scanning electron microscope (FESEM). The tensile strength decreased from 2030.48 MPa (untreated) to 1984.81, 1988.04 and 1978.15 MPa when annealed at 425 ºC for 0.5, 5, 10 minutes of soaking times, respectively. As the annealing temperature increased to 475 ºC, the tensile strength further decreased to 1855.90, 1864.35 and 1774.39 MPa, for the same soaking times respectively. Obviously, prolonged soaking time at higher annealing temperature will only reduce the tensile strength up until 2.5%. The reduction of tensile strength for the annealed samples was attributed to the age softening due to the break-up of the lamellar cementite structure and the recovery of lamellar ferrite. This accompany with stress reduction which has been evidenced by analysing XRD peak patterns. The XRD peak shows that increasing in annealing temperature and soaking time resulted in the decrease of full width at half maximum (FWHM) values, indicating the reduction in the residual stress. Overall, this study demonstrated that controlled annealing at 425 ºC and the soaking time as low as 0.5 minute is sufficient to effectively reduce the residual stress caused by cold drawing process, while maintaining materials strength.