Dynamic compression property of a low-carbon quenching and partitioning steel

The dynamic compression properties of a low carbon quenched and partitioned (Q&P) steel were investigated over the strain rate range of 500-2500 s−1 using split-Hopkinson pressure bar equipment. Traditional quenched and tempered (Q&T) steel with an identified composition was used for comparison. For both types of steel, the flow stress and yield strength gradually increased as the strain rate was increased from 500 to 2000 s−1, indicating that strain-rate hardening dominates the deformation behavior. At a higher strain rate (2500 s−1), the flow stress and yield strength begin to decrease, indicating that the thermal softening of the martensite matrix caused by adiabatic heating begins to exceed the effect of the strain-rate hardening. Based on the Johnson-Cook equation, which describes the deformation behavior as well as the parameters calculated by this equation, the Q&P specimens exhibited less pronounced strain-rate dependencies than the Q&T specimens. In addition, the impact shearing tests demonstrated that adiabatic shear failure is less likely to occur in Q&P specimens than in Q&T specimens. Analysis revealed that a considerable amount of retained austenite in the Q&P specimen was responsible for these differences, and in turn, its stability was affected by the strain rate. At a relatively low strain rate, stress/strain induced martensitic transformations easily occur. With higher strain rates, martensitic transformations are suppressed because adiabatic heating decreases the driving force of martensitic transformations.