Influence of work-hardening on the dynamic stress-strain curves of 4340 steel

The experimentally determined one-dimensional strain dynamic stress-strain curve of Rc54 hardness 4340 steel is shown to be in agreement with the uniaxial strain curve calculated from quasi-static properties. Strain-rate independent elastic-plastic theory including workhardening was employed in the calculation. The agreement between theory and experiment shows that the stress-strain curve of fully hardened 4340 obtained at low strain rate, which indicates appreciable work-hardening, can be used to predict dynamic behavior. In contrast, the experimental data for RC15and Rc32-4340 steel showed strain-rate sensitivity. When these data are analyzed by the same procedure used for the fully hardened steel, a different stress-strain path is obtained for each peak stress level investigated. The results suggest that the observed large increase in flow stress with increase in strain rate is not limited to stress levels around the yield point but persists as long as the strain rate is high.