Microstructure and properties of 780 MPa grade cold rolled dual-phase steel

Cold rolled dual-phase steels of 780 MPa grade were trial-produced in laboratory.The chemical composition design,rolling technology and continuous annealing process of the cold rolled dual-phase steels were introduced.The effect of over-ageing temperature on the mechanical properties and microstructure was studied.The microstructure after continuous annealing was analyzed using SEM and transmission electron microscopy.The results indicate that the dual-phase steels which have good mechanical properties can be obtained by annealing at 820 ℃,over-ageing at 320 ℃.After heat treatment,the yield strength is 408 MPa,the tensile strength is 812 MPa and the elongation reaches 23.1%.