Structure and properties of differentially hardened 100-m rails after long-term operation

Abstract

Using methods of modern materials science the analysis of structural phase states of defect substructure and mechanical properties of tread surface at different distance (from 0 to 22 mm) along central axis and fillet of differentially hardened 100 meter rails of DT 350 category manufactured at JSC “Evraz-Integrated West-Siberian” metallurgical combine after long term operation (passed tonnage 1411 mln. t. brutto) at experimental test ring has been performed. Microstructure of rails’ metal is presented by fine-dispersed lamellar pearlite (grain confidence index 2) with inclusions of excess ferrite along grain boundaries estimated by 2 numbers of scale No. 7 of State Standard 8233. The value of interplate distance in rail head varies within 0.10-0.15 μm. Long term operation of rails is accompanied by the formation of gradient structure being expressed in regular change in hardness, microhardness, impact strength, destruction degree of cementite plates, scalar dislocation density throughout cross-section of rails head. The failure mechanisms of lamellar pearlite structure have been discussed. It has been shown that microhardness at 2 mm depth from tread surface amounts to 1481-1486 MPa. At depth up to 10 mm the microhardness values decrease up to 1210-1385 MPa that is caused by increase in interplate distance and decrease in level of cold strain hardening of metal in long-term operation of rails.