Structure-phase states and properties of rail tread surface at long-term operation

Using the methods of modern physical material science the investigations of structure-phase states and properties at different depth from tread surface of differentially quenched rails at extremely long-term operation (passed tonnage 1411 mln t) are carried out. The hardness decrease from 37.1 to 35.8 HRC at the depth 2 and 10 mm and microhardness from 1481 to 1210 MPa, respectively is revealed. The established multiple transformation of tread surface structure concludes in: fracture of lamellar pearlite structure and subgrain structure formation of submicronsizes (100-150 nm); precipitation of carbide phase nanoparticles (30-55 nm)along the boundaries and in the volume ofsubgrains; growth of microdistorsions and α-Fe crystal lattice parameter; growth of scalar and excess dislocation density. The suggestions about the possible reasons of observable regularities are made.