Evolution of the Fine Structure and Properties of Rail Metal during Long-Term Operation

Autor: V. E. Panin, Yu. A. Rubannikova, A. A. Yuriev, Viktor E. Gromov, V. E. Kormyshev, Yu. F. Ivanov, Sergey V. Panin
Rok vydání: 2021
Předmět:
Zdroj: Physical Mesomechanics. 24:202-210
ISSN: 1990-5424
1029-9599
Popis: TEM and X-ray diffraction studies were carried out to examine changes in the structure, phase composition, and defect substructure in the head of a differentially hardened rail after 691.8 and 1411 million gross tons (MGT) of traffic. The rail material was examined along the central axis of the head and along the gauge corner radius at distances of 0, 2, and 10 mm from the tread surface. The redistribution of carbon atoms was quantitatively analyzed. It was shown that long-term operation of rails is accompanied by two simultaneous processes related to the evolution/degradation of the structure and phase composition of lamellar pearlite colonies, namely, cutting and cold dissolution of cementite lamellae. The first process involves the cutting of carbide particles and the subsequent dragging of their fragments, which causes changes only in their linear dimensions and morphology. The second process is the fracture of cementite lamellae in pearlite colonies due to the migration of carbon atoms from the cementite lattice to dislocations, which creates favorable conditions for a structural-phase transformation in the rail metal. The reason of this is the low average binding energy of carbon atoms with dislocations (~0.6 eV) and with iron atoms in the cementite lattice (~0.4 eV). Cementite nanoparticles were revealed in the ferrite matrix; their appearance was accompanied by dislocation glide and deformation-induced decomposition of carbon solid solution in α-iron. The curves of the change in the total yield strength versus the distance to the tread surface along different directions in the rail head were plotted. The carbon content in the structural elements of rail steel was estimated. It was found that carbon in the initial state is mainly contained in cementite particles, while in rails subjected to traffic loading it is located, along with cementite particles, at crystal structure defects (dislocations, grain boundaries, subgrains). In the surface layer of steel, carbon is also present in the crystal lattice of α-iron. The results on the redistribution of carbon atoms are interpreted using the concept of interstitial bifurcation structural states in lattice curvature zones.
Databáze: OpenAIRE
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