In this work, material models are developed to describe the thermoplastic material behavior of a dual-phase steel DP600 on a microscopic and a macroscopic length scale. Since the material exhibits a polycrystalline microstructure on a microscopic length scale with the phases martensite and ferrite, a continuum mechanical material model for both phases is developed. While the martensitic phase is treated purely thermoelastic, the processes related to the dislocation structure in the ferritic phase are analysed and considered to describe the thermoplastic behavior. Numerical methods are provided and utilized to compare the prediction of the material model for the ferritic phase with experimental results of tensile tests on iron single crystals. The ideas developed on a microscopic length scale are propagated to the macroscopic length scale and the corresponding thermoplastic material behavior is described mathematically. The subsequent comparison of the model prediction with experimental results shows good agreement.