Microstructures and fracture features of cold-rolled low carbon steel sheet after annealing and mechanical stress concurrently loaded

The microstructure and fracture feature of a cold-rolled low carbon steel sheet after annealing under a stress were investigated by using the optical microscope (OM), scanning-electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that a commixed grain structure was formed when concurrently stressed and annealed at 650 °C, and that both the tensile strength and hardness of the steel are still higher while the elongation is increased markedly. The dimple like fracture feature with delamination cracks was observed after tensile deformation. These superior mechanical properties were derived from the commixed grain structure composing of cold-rolled lamellar grains, fine equiaxed grains, and sub-grains as well as ultrafine carbide precipitates.