Nature of the structural degradation of rail surfaces during operation

Resumo

Patterns in the transformation of the structural and phase states and the defect substructure of rail surface layers up to 10 mm thick during long-term operation (gross transit tonnages of 500 and 1000 mln t) are found via optical, scanning, and transmission electron microscopy. According to the nature of the fracture and the degree of defectiveness, three layers can be distinguished: a surface layer, a transition layer, and the base metal. It is shown that the operation of steel rails is accompanied by full fractures in surface layers up to 15 μm thick with lamellar pearlite grains and the formation of ferrite–carbide mixtures with nanosized particles. The deformation of steel increases the densities of scalar and excess dislocations, the curvature–torsion values of the crystal lattice, and the amplitudes of internal stress fields. Structural elements that can act as stress concentrators are identified.