Mechanical Properties and Fracture Behavior of DP1180 Duplex Steel at High Strain Rate

Quasi-static （strain rates of 0.001, 0.01 s⁻¹） and dynamic （strain rates of 0.1, 1, 10, 50, 100, 200, 500, 1 000 s⁻¹） tensile tests were conducted on DP1180duplex steel. The mechanical properties, fracture behavior, and microstructure evolution laws of the steel were studied. The results show that with the increase of strain rate, the tensile strength, yield strength, percentage elongation after fracture, and percentage uniform elongation of DP1180 duplex steel increased. At high strain rates （100−1000 s⁻¹）, the strain rate sensitivity of the yield strength was greater than that of the tensile strength. With the increase of strain rate, the micromorphology of the tensile sample surface changed from a fault-like shape to a tearing shape, and the number of transverse microcracks increased; but when the strain rate reached 1 000 s⁻¹, the transverse cracks almost disappeared, and a large number of micropore-type fracture patterns emerged. At different strain rates, the DP1180 dual-phase steel all exhibited micropore-aggregated ductile fracture. With the increase of strain rate, the number of large-sized dimple at the fracture surface increased, and deeper holes formed by martensite fragmentation appeared at the center of the dimple. After tension at high strain rates, the martensite laths were fine and the dislocation density was large. Dislocation strengthening and martensite deformation were the main reasons for the increase in the strength at high strain rates, and the activation of the plastic deformation ability of martensite through adiabatic temperature rise was the main reason for the increase in plasticity.