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

Using the methods of transmission electron microscopy, the carbide phase evolution in surface layers of the differentiallyquenched rails is studied after the passed tonnage of 691.8 million tons at the depth up to 10 mm along the central axis andfillet of rail head. The action of two mutual supplement mechanisms of steel carbide phase transformation in surface layersat rail operation is established： （1） cutting mechanism of cementite particles with the following departure in the volume offerrite 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 bymoving dislocations into ferrite grains volume （or plates） with the following repeated formation of nanosized cementiteparticles. The first mechanism is accompanied by the change in linear sizes and morphology of carbide particles. Cementiteelement composition change is not essential. Carbide structure change can take place during the second mechanism.