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[References: 16 tit.]

The paper presents transmission electron microscopic investigations of the structure and X-ray diffraction analysis of the phase composition of tempered martensite steel of 0.06Mo-1V-1Nb-Fe type deformed via the Equal Channel Angular Extrusion (ECAE) technique. As it turns, the ECAE has an effect on the morphology and phase composition of the alloy. Its faulted structure, dislocation density, internal stresses, and the size of coherent scattering areas are investigated in this paper. A special attention is paid to misorientations between grains. It is shown that in its original state (before ECAE), the steel structure represents tempered lath martensite and grains of [alpha]-phase. Carbide particles of М[2]С type are present inside these grains and at their boundaries. ECAE deformation results in a complete fragmentation of lath martensite and grinding of [alpha]-phase grains. A partial fracture and dissolution of carbide particles occurs. Carbon releases from carbides and localizes on defects of the crystal lattice. ECAE deformation increases misorientations in lath martensite (up to 25-30 degrees) and nucleation of micrograins in former grains of [alpha]-phase.