Gradients of Structure, Phase Composition, and Dislocation Substructure of Rails under the Ultra Long-Term Operation

In this paper, the structure, phase composition, dislocation substructure, and carbon redistribution in differentially quenched 100-meter rails after the ultra long-term operation (passed gross tonnage since 2013 — 1770 mln. tons) are studied using modern materials science and engineering approaches. The regularities of main parameters variations, such as changes in a relative variety of different morphological structures, scalar and excessive dislocation density, volume fractions of cementite, and redistribution of carbon atoms, are identified at the rail head cross section along the central axis and fillet rounding radius at the distances of 0, 2, 10 mm from the surface. It is suggested that the decrease of volume fraction of carbide phase in head surface layer can be related to the decarburization and appearance of carbon atoms at the steel structure defects. It is noted that transformations along the central axis proceed slower in relation to changes of the rounding radius of the fillet.