High-strain-rate behavior of low-alloy multiphase aluminum- and silicon-based transformation-induced plasticity steels

High-strength, low-alloy transformation-induced plasticity (TRIP) steels are advanced multiphase steel grades that combine high-strength levels with an excellent ductility, making them ideally suited for application in crash-relevant parts of automotive car bodies. The enhanced plastic hardening and deformability are due to a complex interaction between the microstructural phases and to the transformation of metastable austenite to martensite during plastic deformation. During high-strain-rate loading, not only the material but also the transformation will be influenced by adiabatic heating. The impact-dynamic properties of CMnAl- and CMnSi-TRIP steels were determined in the range of 500 to 2000 s^-1 using a split Hopkinson tensile bar (SHTB) setup. Bake-hardening treatments were applied to study the effect of strain aging. The experiments show that strain-rate hardening is superior to thermal softening: yield stresses, deformation, and energy dissipation increase with the strain rate. Phenomenological material models were investigated to describe the strain-rate and temperature-dependent behavior of TRIP steels. Both the Johnson-Cook model and an extended version of the Ludwig model were found to give good agreement with the experimental data.