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The article focuses on the results from recent experimental of severe plastic deformation (SPD) of low carbon steel AISI 1010 and medium carbon steel AISI 1045 performed at increased temperatures. The grain refinement of ferrite respectively ferrite-pearlite structure is monitored and described. While LC steel was deformed by ECAP die with a channel angle phi = 90 doa and by strain epsilonef = 3. The ECAP severe deformation of MC steel was conducted with die channel angle of 120° and epsilonef = 2.6 - 4) and TECAP - 400 °C. The high straining in LC steel resulted in extensively elongated ferrite grains with dense dislocation network, and randomly recovered and polygonized structure was observed although. The small period of work hardening appeared at tensile deformation. On the other side, the warm ECAP deformation of MC steel in dependence of increased effective strain resulted in more progressive recovery process in deformed structure. In interior of the elongated ferrite grains the subgrain structure with dislocation network prevailed. As straining increases dynamic polygonization and recrystallization became active to form mixture of polygonized subgrain and submicrocrystalline grain structure. The straining and moderate ECAP temperature caused the cementite lamellae fragmentation and spheroidzation as number of passes increased. The tensile behaviour of the both steels was characterized by strength increase however the absence of strain hardening was found at low carbon steel. The favourable effect of ferrite-pearlite structure modification due straining was reason for extended work hardening period observed at MC steel.