Abstract: Microstructure, mechanical properties, FLC and cold bending property of the dual phase (DP) steels with strength of 780-1180 MPa were tested by means of optical microscope, tension and compression machine, universal forming machine and three point bending machine. The results show that with the increase of yield strength of the DP steels, martensite content is increased, grain size is refined, elongation, n and r values are decreased, plane strain forming limits are declined from 22.7% to 12.6%, the tensile limits are reduced from 15.8% to 8.6%, and minimum bending radius is increased from 1.13 to 2.86. With the increase of yield strength of the 980 MPa DP steels, microstructure homogeneity is increased, bulging deformation limit is enhanced from 22.8% to 34.5%, and minimum bending radius is decreased from 2.50 to 1.82. The Bauschinger effect constant of the CR420/780DP, CR700/980DP and CR820/1180DP steels is 0.82, 0.78 and 0.79, respectively. Instantaneous hardening rate of initial plastic deformation stage in compression process of the CR420/780DP and CR820/1180DP steels is higher than that of the reverse tension and unixial tension processes.

Key words: DP steel, formability, FLC(Forming limit curve), three point bending, tension and compression test