Structure, Phase Composition, and Dislocation Substructure Gradients in Rails during Ultralong Operation

Modern physical metallurgy methods are used to study the structure, phase composition, dislocation substructure, and carbon redistribution in differentially quenched 100-m rails after extremely long operation (passed gross tonnage 1770 mln t since 2013). The laws of changing the main parameters, namely, the relative content of various morphological varieties of a structure, the scalar and excess dislocation densities, the volume fraction of cementite, and the redistribution of carbon atoms, are revealed in the cross section of the rail head along the central axis of symmetry and the radius of rounding of the fillet at distances of 0, 2, and 10 mm from the surface. The decrease in the volume fraction of the carbide phase in the surface layer of the head is assumed to be associated with decarbonization and the motion of carbon atoms to defects in the steel structure. The transformations along the central axis are found to proceed much more slowly as compared to the change relative to the fillet radius.