Mechanisms of hardening of heavy-loaded rails made of hypereutectoid steel during long-term operation

Using transmission electron microscopy methods, the structural-phase states and defective substructure were studied at distances of 0; 2 and 10 mm from the surface along the central axis and rounding radius of rails head fillet. Differentially hardened long rails of the DT400IK category made of hypereutectoid steel have been studied after operation on the Trans-Baikal Railway (passed tonnage equal to 234.7 million tons gross). It has been established that steel strength characteristics are determined by certain physical mechanisms. A qualitative assessment of the contributions from crystal lattice friction, solidsolution strengthening, strengthening of the pearlite component, incoherent cementite particles, grain boundaries and subboundaries, dislocation substructure and internal stress fields was carried out, and their hierarchy was established. A quantitative assessment of the additive yield strength of steel in different directions was carried out depending on the distance from the rolling surface. It is shown that the main mechanisms of strengthening are strengthening by incoherent particles, long-range stress fields and substructural strengthening. The additive yield strength on the fillet surface is significantly greater than on the rolling surface of the head along the central axis.