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Physical Nature of Rail Surface Hardening during Long-Term Operation

Physical Nature of Rail Surface Hardening during Long-Term Operation A comparative quantitative analysis of the physical mechanisms of hardening of rail surface layers after extremely long-term operation is performed. The method is based on the previously established regularities in the formation of structural-phase states and mechanical properties of differentially hardened long-length rails produced by JSC EVRAZ ZSMK at a depth of up to 10 mm in the rail head along the central axis and fillet after the passed tonnage of 1411 million tons. The calculations consider the volume fractions and characteristics of particular substructure types. The increase in the microhardness and hardness of the surface layers of the rails exposed to extremely operation on the experimental ring of the Russian Railways is multifactorial and determined by the superposition of a number of physical mechanisms. The contributions conditioned by the friction of the matrix lattice, intraphase boundaries, dislocation substructure, presence of carbide particles, internal stress fields, solid hardening, and pearlitic component of the steel structure are estimated. The strength of the rail metal depends on the distance to the surface: it increases on approaching the top of the head and does not depend on the analysis direction (along the central axis of the head or along the fillet symmetry axis). The most significant physical mechanisms are established, which ensure high strength properties of the metal of the rail head exposed to extremely long-term operation. In the subsurface layer of the rail head at a depth of 2–10 mm, the most significant physical mechanism is dislocation conditioned by the interaction of moving and stationary dislocations (forest dislocations). In the surface layer of the rail head, the most significant physical mechanism is substructural conditioned by the interaction of dislocations with small-angle boundaries of fragments and subgrains of nanometer polygons. A comparison with the quantitative values of the rail hardening mechanisms after the passed tonnage of 691.8 million tons is performed. It is shown that an increase in the passed tonnage in the range of 691.8–1411 million tons significantly increases the steel strength by 50 or 100%. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Steel in Translation Springer Journals

Physical Nature of Rail Surface Hardening during Long-Term Operation

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References (32)

Publisher
Springer Journals
Copyright
Copyright © Allerton Press, Inc. 2021. ISSN 0967-0912, Steel in Translation, 2021, Vol. 51, No. 12, pp. 859–865. © Allerton Press, Inc., 2021. Russian Text © The Author(s), 2021, published in Izvestiya Vysshikh Uchebnykh Zavedenii, Chernaya Metallurgiya, 2021, No. 12, pp. 886–894.
ISSN
0967-0912
eISSN
1935-0988
DOI
10.3103/s0967091221120147
Publisher site
See Article on Publisher Site

Abstract

A comparative quantitative analysis of the physical mechanisms of hardening of rail surface layers after extremely long-term operation is performed. The method is based on the previously established regularities in the formation of structural-phase states and mechanical properties of differentially hardened long-length rails produced by JSC EVRAZ ZSMK at a depth of up to 10 mm in the rail head along the central axis and fillet after the passed tonnage of 1411 million tons. The calculations consider the volume fractions and characteristics of particular substructure types. The increase in the microhardness and hardness of the surface layers of the rails exposed to extremely operation on the experimental ring of the Russian Railways is multifactorial and determined by the superposition of a number of physical mechanisms. The contributions conditioned by the friction of the matrix lattice, intraphase boundaries, dislocation substructure, presence of carbide particles, internal stress fields, solid hardening, and pearlitic component of the steel structure are estimated. The strength of the rail metal depends on the distance to the surface: it increases on approaching the top of the head and does not depend on the analysis direction (along the central axis of the head or along the fillet symmetry axis). The most significant physical mechanisms are established, which ensure high strength properties of the metal of the rail head exposed to extremely long-term operation. In the subsurface layer of the rail head at a depth of 2–10 mm, the most significant physical mechanism is dislocation conditioned by the interaction of moving and stationary dislocations (forest dislocations). In the surface layer of the rail head, the most significant physical mechanism is substructural conditioned by the interaction of dislocations with small-angle boundaries of fragments and subgrains of nanometer polygons. A comparison with the quantitative values of the rail hardening mechanisms after the passed tonnage of 691.8 million tons is performed. It is shown that an increase in the passed tonnage in the range of 691.8–1411 million tons significantly increases the steel strength by 50 or 100%.

Journal

Steel in TranslationSpringer Journals

Published: Dec 1, 2021

Keywords: rails; surface layers; hardening mechanisms; long-term operation; structure; phase composition; rolling surface; fillet

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