Effects of the annealing temperature and time on the microstructural evolution and corresponding the mechanical properties of cold-drawn steel wires

The effects of the annealing temperature and annealing time on the microstructural evolution and corresponding mechanical properties of cold-drawn high carbon steel wires were investigated. During the annealing of cold-drawn steel wires, the increment of the tensile strength at low temperatures found to be due to age hardening, while the decrease in the tensile strength at high temperatures was attributed to age softening, involving the spheroidization of lamellar cementite and recovery of lamellar ferrite. To investigate the mechanisms of strain ageing, a thermal analysis using DSC was performed. The mechanisms for the first and second stages were found to be the diffusion of carbon atoms to dislocations in the lamellar ferrite and the decomposition of lamellar cementite. The third peak of the DSC curves was controlled by the re-precipitation of cementite or by the spheroidization of lamellar cementite.