A micromechanical model based on a new self-consistent formulation has been applied to describe the elastic-viscoplastic behaviour of steels at high strain rates. A good agreement between experimental and calculated data is found concerning the behaviour of a ferritic single-phase IF steel in uniaxial tests in a large range of strain rates. Because of the introduction of relevant physical parameters in the modelling, a good description of the difference observed between the Dual-phase steel and the single-phase steel is obtained.