Temperature-time effects on metals based on the relaxation model of plasticity have been evaluated. The plastic deformation of 7xxx and 2xxx aluminium alloys and EUROFER97 steel in a strain rate range from 0.001 to 4200 s−1 and a temperature range from −100 to 700 °C was analysed to determine the structural and temporal characteristics of the material, independent of loading history. Expressions of the static yield stress and the characteristic time as a function of temperature are formulated based on the “temperature multiplier” of the Johnson-Cook model (Johnson and Cook, 1985), which is obtained for the case of static loading and zero plastic strain. It is shown that the expanded relaxation model of plasticity is effectively capable to predict material responses of metals in wide ranges of strain rates and temperatures with a constant characteristic relaxation time. Based on theoretical stress-strain dependence, calculated by the relaxation model of plasticity, estimations of the ductile-brittle transition temperature of 2519A aluminium alloy at strain rates of the order 103 s−1 are given.