The quantitative estimation of strengthening mechanisms of rails’ surface layer is carried out on the basis of regularities and formation mechanisms of structure-phase states revealed by the methods of modern physical materials science. It is performed at different depths of the rail head along the central axis and fillet of differentially quenched 100-meter rails after the extremely long-term operation (gross passed tonnage of 1411 mln tons). A long-term operation of rails is accompanied by the formation of structural constituent gradient consisting of a regular change in the relative content of lamellar pearlite, fractured pearlite, the structure of ferrite-carbide mixture, scalar, and excess dislocation density along the cross-section of the rail head. As the distance to the rail fillet surface decreases, the relative content of metal volume with lamellar pearlite decreases. However, the relative content of metal volume with the presence of the fractured pearlite structure and ferrite-carbide mixture increases. The contributions caused by the matrix lattice friction, intraphase boundaries, dislocation substructure, presence of carbide particles, internal stress fields, solid-solution strengthening, pearlite component of steel structure are estimated. It is shown that the main mechanism of strengthening in the surface layer is due to the interaction of moving dislocations with low-angle boundaries of nanometer dimensional fragments and subgrains. The main dislocation strengthening mechanism in a near-surface layer at a depth of 2-10 mm is due to the interaction of moving dislocations with immobile ones.

Detection of physical mechanisms of formation and evolution of structure-phase states and dislocation substructures in steels is one of the important problems of condensed-state physics and modern material science because it forms the basis of development and formation of effective methods for increasing the service characteristics of articles. Experimental investigations of structures and phase states being formed in a cross-section of articles as a result of thermomechanical treatment are very significant for understanding the physical nature of transformations as they make it possible to change structure and mechanical characteristics purposefully. Thermomechanical treatment of low carbon steel 09G2S (0.09 wt.% C, 2 wt.% Mn, 1 wt.% Si) is done by rolling of H- beam DP 155 and forced water cooling in the process of rolling on rolling mill 450 open joint-stock company "Evraz- Western Siberian metallurgical combine" By methods of physical material science the investigations of structure-phase states, defect substructure mechanical and tribological properties of H-beam surface from steel 09G2S being formed as a result of thermomechanical hardening in the process of rolling on rolling mill. The qualitative correspondence of change in microhardness and scalar dislocation density along the cross-section of H-beam has been established. The processes were analyzed and the analysis of mechanisms contributing to the formation of nano-dimensional cementite phase in the conditions of thermomechanical treatment of low-alloy steel was done. It was shown that the cementite particles were formed: in dispersion of cementite plates of pearlite colonies by its cutting with moving dislocations; in dissolution of cementite plates of pearlite colonies and its repeated precipitation on dislocations, boundaries of subgrains and grains; the decomposition of solid solution of carbon in alpha-iron occurring in the conditions of " self-tempering" of martensite loads to formation of particles precipitated in the volume of martensite crystals on dislocations and at boundaries of martensite crystals. in diffusion gamma ->alpha transformation in the conditions of high degree of deformation and high temperatures of treatment a dispersion of lamellar pearlite structure is observed. It is established that the phenomenon of increase in hardness of steel surface layer is a multi-factor, morphologically multi-component one and is determined by the nature of gamma ->alpha transformation.

Results of investigations of the structure-phase state and dislocation substructure formation during thermomechanical hardening of Fe–0.09C–2Mn–1Si steel in different regimes are presented. Methods of transmission electron microscopy reveal the formation of gradient states characterized by regular changes of the structure, phase composition, types, and parameters of the dislocation substructures over the structure cross section.

Analysis of structure-phase states and mechanical properties of I-beam profile DP155, subjected to accelerate cooling with different regimes in hot rolling mill 450 line, are carried out by the methods of modern material science.