Development of the structure of differentially hardened 100 m rails during their long operation

Using methods of modern physical materials science, structural-phase states and mechanical properties of the rolling surface have been analyzed at distance of 0 to 22 mm along the central axis and along the fillet of differentially hardened 100 m rails of DT 350 category manufactured by JSC “EVRAZ – United West Siberian Metallurgical Plant” after their long-term operation (passed gross tonnage of 1.411 million tons) on experimental test ring. In terms of chemical composition, metal of the rails meets TU 0921-276-01124323 – 2012 requirements for E76KhF steel. Impact strength and hardness on head surface and along cross-section meet TU specifications. Microstructure of rails metal is represented by finely dispersed plate perlite of 1.5 points with inclusions of excessive ferrite along the grain boundaries (1.5 points by GOST 8233 scale No. 7). Interlamellar distance in the rail head varies between 0.10 and 0.15 microns. Long-term operation of rails is accompanied by development of gradient structure, manifested in regular change in hardness, microhardness, impact strength along cross-section of the rail head. Microhardness at 2 mm depth from the rolling surface is 1481 – 1486 MPa. At 10 mm depth microhardness decreases to 1210 – 1385 MPa, which is caused by an increase in interlamellar distance and decrease in the level of strain hardening of metal during long-term operation of rails. It has been suggested that this may be due to an increase in interlamellar distance and a decrease in level of strain hardening during long-term operation.