Abstract: Continuous annealing process of a 1180 MPa grade complex phase steel was simulated by Gleeble-3500 thermal simulator, and the effect of cold rolling reduction ratio on microstructure evolution and mechanical properties of the complex phase steel was studied by means of scanning electron microscope and tensile testing machine. The results show that under the same heat treatment conditions, as the cold rolling reduction ratio increases, the proportion of martensite and bainite in the complex phase steel gradually decreases, the degree of ferrite recovery and recrystallization gradually increases, and the complex microstructure gradually weakens. The larger the cold rolling reduction ratio is, the stronger the carbon atom diffusion ability is in the subsequent heat treatment process, and the mechanical properties gradually deteriorate. With the cold rolling reduction ratio of 30%, the ferrite+martensite+bainite complex phase microstructure in the steel is the most complete, and the steel has the optimal strength and plasticity.

Key words: complex phase steel, continuous annealing, cold rolling reduction ratio, microstructure, properties