The phase composition, mechanical properties, and microstructure of binary Fe-C alloys with various carbon concentrations (0.25, 0.45, 0.6, 1.3, 1.5, and 1.7 wt.%) were studied by transmission electron microscopy, X-ray diffraction analysis, and microhardness measurements. The investigations were carried out for three states of the material, namely for as-cast, annealed (725 degrees C) and deformed by high-pressure torsion (HPT) samples. The grain size after HPT is in the nanometer range. Only Fe3C (cementite) and alpha-Fe remain in the alloys after HPT. The residual austenite disappears and phase composition closely approaches the equilibrium corresponding to the temperature and pressure of HPT. Analysis of the microhardness behavior revealed that hardening of the deformed alloys takes place due to the grain refinement and dispersoid mechanism.