Degradation of rail-steel structure and properties of the surface layer

• Published in: Steel in translation 2016-08, Vol.46 (8), p.567-570
• Main Authors: Ivanov, Yu. F., Morozov, K. V., Peregudov, O. A., Gromov, V. E.
• Format: Article
• Language: English
• Subjects: Carbon; Cementite; Chemistry and Materials Science; Dislocations; Dynamic recrystallization; Electrostatic precipitation; Entrainment; Ferrite; Fragmentation; Grains; Materials Science; Microhardness; Microscopy; Optical microscopy; Optical properties; Pearlite; Plates; Plates (structural members); Rail steels; Rails; Steel; Surface layers; Tonnage; Transmission electron diffraction; Tribology; Wear rate; Wear resistance
• ISSN: 0967-0912; 1935-0988
• DOI: 10.3103/S0967091216080088

The change in the structure–phase states and defect substructure of the rail surface after prolonged operation (passed tonnage of 500 and 1000 million t) is studied by optical microscopy, by scanning and transmission electron diffraction microscopy, and by measurement of the microhardness and tribological characteristics. It is found that the wear rate increases by a factor of 3.0 and 3.4 after passed tonnage of 500 and 1000 million t, respectively, while the frictional coefficient is reduced by a factor of 1.4 and 1.1, respectively. After 500 million t, the cementite plates break down completely, and rounded cementite particles (10–50 nm) are formed. After 1000 million t, the initial stage of dynamic recrystallization is noted. Possible explanations of the observations are discussed. Two competing processes may occur in rail operation: (1) fragmentation of the cementite particles, with their subsequent entrainment in the ferrite grains or plates (in the pearlite structure); (2) fragmentation and subsequent solution of the cementite particles, with transfer of the carbon particles to dislocations (Cottrell atmospheres) and transportation of carbon atoms by dislocations within the ferrite grains (or plates), culminating in the formation of cementite nanoparticles.