Investigations of influence of preliminary heat treatment on structure and properties of 20 and 45 carbon structural steels with ultra-fine grain structure after uni-channeled angular extrusion have been conducted. Forming of featured microstructure (mainly with ultra-fine grains 200-500 nm in size with large angular and non-equilibrium boundaries, with dispersed particles of carbide phase) is revealed. For 20 steel, rise of micro-hardness makes 43 % while for 45 steel — 18 %, depending on structure formed before uni-channeled angular extrusion. Substantiation of revealed differences of deformation strengthening in uni-channeled angular extrusion of structural carbon steels with different carbon content is proposed.