The effect of strain rate and martensite volume fraction on tensile impact behavior of dual phase steels

In the present paper, tensile tests of dual phase steels (martensite volume fraction Vm are 30%, 40%, 48%, 56% and 60%) have been carried out by a self-designed tensile impact apparatus and Shimadzu-5000 testing apparatus. The complete stress strain curves of material in strain rate range fi om 0.001 l/s to 1300 l/s have been obtained. The experimental results show that 20Cr dual phase steels is strain rate sensitive material. At low strain rate, the yield stress (sigma(s)) slightly increases with the increasing of strain rate, however, at the high strain rate, the yield stress (sigma(r)) increases with the increasing of strain rate rapidly. At the same time, tensile mechanical properties of dual phase steels are also effected by martensite volume fraction (Vm). With the increasing of Vm, the yield stress and the ultimate strength increased, while the failure strain decreased. To characterize the combination of high strength and ductility of dual phase steels, the product of tensile strength and ductility (TS*EL) is inducted. At the same Vm, the TS*EL value increased with the strain rate. At the same strain rate, TS*EL value can not be regarded as linear with Vm. There exists a critical martensite volume fraction Vt, TS*EL value increased with Vm when Vm<Vt, and decreased with Vm when Vm>Vt.