The Role of Lattice Curvature in Structural Degradation of the Metal Surface Layer of a Rail under Long-term Operation

The evolution/degradation of the structure and phase composition of rail head material of 100-meter differentially quenched rails after extremely long-term operation is analyzed. It is shown that similar conditions of loading result in different structural transformations on the rail head surface. The formation of lattice curvature in crystal interstitial sites and initiation of highly mobile interstitial structural states there cause a dissolution of pearlite. It occurs at a depth of ≈10 mm. It is superimposed by the formation of a nanoscale substructure in the tread surface in a layer ≈2 mm thick. The nanoparticles of the carbide phase precipitate on the boundaries of the substructure. The failure of the rail metal will proceed, in the first place, in the surface layer where a critical level of the crystal lattice curvature is formed and the concentration of interstitial vacancies is maximum.