Abstract: Quasi static tensile experiments are done by CMT4105, and dynamic tensile experiments are done by Hopkinson tester. At room temperature, strain rate of the quasi static tensile experiments of DP1200 cold rolled steel are 1×10^-4 s^-1, 1×10^-3 s^-1, 1×10^-2 s^-1; strain rate of dynamic tensile experiments are 500 s^-1, 1 000 s^-1, 2 250 s^-1. And fracture morphology analysis is done. The results reveals that with the increase of the strain rate on the conditions of quasi static tensile experiments and dynamic tensile experiments of the DP1200 cold rolled steel, the tensile strength increases from 1 205 MPa to 1 515 MPa, the yield strength increases from 723 MPa to 998 MPa and the yield strength ratio increases from 6.0 to 6.6, while the elongation decreases from 9.0% to 7.7%. Fracture morphology is toughening nest under quasi static tensile and dynamic tensile conditions. When the strain rates are 1×10^-4 s^-1,1×10^-3 s^-1,1×10^-2 s^-1,500 s^-1,1 000 s^-1,2 250 s^-1,the average sizes of fracture toughness are 7.5 μm, 7.2 μm, 6.9 μm, 4.3 μm, 3.5 μm and 2.6 μm. Fracture morphology changes little with the different strain rates under quasi static tensile condition, while the increasing strain rates make the toughening nest deeper under dynamic tensile conditions.

Key words: deformation microscopic mechanism, dual phase steel, fracture morphology, high strain rate, lath martensite