Stages and Fracture Mechanisms of Lamellar Pearlite of 100-m-Long Differentially Hardened Rails Under Long-Term Operation Conditions

Abstract

Using the methods of transmission electron microscopy, the carbide phase evolution in surface layers of the differentially quenched rails is studied after the passed tonnage of 691.8 million tons at the depth up to 10 mm along the central axis and fillet of rail head. The action of two mutual supplement mechanisms of steel carbide phase transformation in surface layers at rail operation is established: (1) cutting mechanism of cementite particles with the following departure in the volume of ferrite grains or plates (in pearlite structure); (2) cutting mechanism and following dissolution of cementite particles, transfer of carbon atoms on dislocations (in Cottrell atmospheres and dislocation cores), transfer of carbon atoms by moving dislocations into ferrite grains volume (or plates) with the following repeated formation of nanosized cementite particles. The first mechanism is accompanied by the change in linear sizes and morphology of carbide particles. Cementite element composition change is not essential. Carbide structure change can take place during the second mechanism.

Strain Stress Model of the Rail with Crack in its Head and Estimation of its Operational Lifetime

“…The value of stresses in areas of concentration can exceed the yield strength, so the rail can be broken down soon [5,6]. Residual stresses appear within the processes of production, welding and installation [7][8][9]. The total sum of residual, thermal and load stresses effect on the crack development [10,11].…”