The Role of Lattice Curvature in Structural Degradation of the Metal Surface Layer of a Rail under Long-term Operation
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NICAL PHYSICS
The Role of Lattice Curvature in Structural Degradation of the Metal Surface Layer of a Rail under Long-term Operation Academician V. E. Panina, V. E. Gromovb,*, Yu. F. Ivanovc,
A. A. Yurievd, and V. E. Kormyshevb Received July 17, 2020; revised July 17, 2020; accepted July 20, 2020
Abstract—The evolution/degradation of the structure and phase composition of rail head material of 100meter 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. Keywords: differentially quenched rails, extremely long-term operation, evolution/degradation of phase composition and structure, crystal lattice curvature DOI: 10.1134/S1028335820100043
The problem of the behavior of rails during longterm operation and analysis of the reasons for their failure is of great interest [1]. Fundamental studies of the mechanisms of gradual degradation of the structure in a deformable material [2] will solve the practically significant problem of increasing the reliability of rails under conditions of a continuous increase in axis loads and travel speeds. One of the key ways to form high operational properties is to establish patterns of structural and phase transformations during long-term operation of rails within the framework of the concept of the curvature of the crystal lattice [2–4]. The emergence of contact pressures in the metal of the rail head causes significant irreversible changes even with a relatively small passed tonnage. They relate to the surface layers, where there is a significant change in the structure, abnormally high values of microhardness, the phenomenon of dissolution of
cementite, etc. These can all underlie the reasons for the failure of rails [5–9]. Previous studies [1, 8–11] have convincingly shown that the destruction of the rail metal is initiated precisely in the surface layer. The aim of this work is to analyze the mechanisms of degradation of the structure and phase composition of the rail head metal after extremely long-term operation. MATERIALS AND METHODS As the material for the study, we used 100-meter differentially hardened rails of the DT350 category, withdrawn from the track at the Experimental Ring of the Russian Railways in Shcherbinka after a passed tonnage of 1.411 billion gross tons. In terms of its chemical composition, the sample metal met the
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