Physical nature of rails strengthening in extremely long-term operation

On the basis of regularities of structural-phase states formation of differentially quenched 100-meter rails revealed by the methods of modern physical material science at different depth in rail head along central axis and fillet after extremely long-term operation the quantitative estimation of strengthening mechanisms of rails surface layer is carried out. The contributions caused by the matrix lattice friction, intraphase boundaries, dislocation substructure, presence of carbide particles, internal stress fields, solid-solution strengthening of pearlite component of steel structure are estimated. It is shown that the main mechanism of strengthening in the surface layer is mechanism due to the interaction of moving dislocations with low-angle boundaries of nanometer-sized fragments and subgrains. The dislocation strengthening mechanism due to interaction of moving dislocations with immobile ones is the main mechanism in a near-surface layer at a depth of 2–10 mm.