Thermal stability of mechanical properties of a high strength cold-drawn pearlitic steel wire

Cold-drawn nano-pearlitic steel wires with a true strain of 3 were annealed at different temperatures. The thermal stability of the mechanical properties of the annealed wires were investigated. It is found that the thermal stability of the mechanical properties of the wires can maintain at 523 K. Based on the experimental results and the theoretical models, the microscale mechanism controlling the thermal stability was analyzed. The results show that the thermal stability is controlled by the evolution of the vacancy clusters concentration and the dislocation density in the ferrite and the interaction between carbon atoms and dislocations. When annealing temperature is higher than 523 K, the overall effects of the annihilation of vacancy clusters and the decrease of dislocation density in ferrite, and the disappearance of pinning effect of carbon on the dislocations lead to the rapid degradation of the mechanical properties of the wires.