Microstructural evolution and mechanical property of ultrafine-grained pearlitic steel by cold rolling: The influence of cementite morphology

Microstructural evolution of a pearlitic steel during cold rolling, which was heat treated by four different routes to obtain different volume fractions of granular cementite (GC) and lamellar cementite (LC) including full GC, GC-dominated, LC-dominated and full LC samples, was investigated. It was found that ferrite grains and pearlitic colonies were elongated along rolling direction and LC particles become curled and bent shaped during cold rolling. Ultrafine ferrite grains were obtained by heavy cold rolling (HCR). At the early stage of cold rolling, GC greatly enhanced the generation and multiplication of dislocations. Sub-grain boundaries and high angle grain boundaries were gradually evolved from dense dislocation walls in ferrite. The decomposition of carbide occurred during HCR process, owing to the interaction of high-density dislocations with carbon atoms. The maximum yield strength and ultimate tensile strength were obtained in full LC sample by HCR.