Spheroidized and ultra-fine structure formed by cold-rolling and annealing of eutectoid pearlite steel

The effect of cold roiling followed by annealing on the ultra-refinement of microstructure and the mechanical properties of eutectoid steel was investigated. The experimental results showed that the combination of cold roiling to 90% and annealing within the temperature range of 600-700℃ leads a duplex microstructure consisting of sub-micron ferritic grains and dispersive cementite particles. The distribution of cementite particle size displayed bimodal. In comparison with traditional spheroidizing treatment, the spheroidization time was significantly shortened and the microstructure markedly refined. This could be attributed to the formation of high-density dislocations and vacancies during cold deformation, which provided a high diffusion path of carbon atoms. The formation of dispersive distribution of fine cementite particles could be explained by the mechanism of dissolution-re-precipitation. It is also indicated that the present combined treatment of cold rolling and annealing results in pronounced increases in yield strength and ultimate strength, a slight decrease in tensile plasticity, and a relatively high yield ratio.