Quasi-adiabatic effects during the high strain rate deformation of dispersed-phase systems with strain-induced martensitic transformation

High strength low alloy TRIP-aided steels are being developed by the steel industry because of their promising high strain rate performance, which makes these steels ideally suited for safety-related structural automotive applications. This is due to a high strain rate "composite effect", i.e. the complex synergy of the high strain rate behavior of the ferrite, bainite and meta-stable austenite within the TRIP-aided steel microstructure. Of particular importance is the strain rate dependence of the strain-induced martensitic transformation of the austenite phase. The present contribution focuses oil the effect of the strain rate oil the mechanical behavior of the low alloy high strength TRIP steels, at static (similar to10(-3) s(-1)) and high (650-1500 s(-1)) strain rate. High strain rate tensile tests were carried out in tension using the Split Hopkinson bar technique. In addition, a detailed micro-structural analysis of the plastically deformed microstructure as a function of the strain rate was carried out by means of XRD, TEM and SEM. A deformation model, which takes into account the strain rate and temperature-dependent physical properties of each phase, is proposed to explain the particularly favorable high strain rate behavior of the low alloy TRIP-aided steels.