STRENGTH, TRIBOLOGICAL PROPERTIES AND STRUCTURAL-PHASE STATES OF RAIL STEELS

10.25712/ASTU.1811-1416.2023.02.004

Abstract

For two rail steels with a carbon content (wt. %) of 0.73 % and 0.91 %, from which rails of the general purpose category DT 350 and DT 400 IK – increased wear resistance and contact endurance GOST R51685-2013 and TU 24.10.75111-208-05757676 2017 RZhD are made an analysis of mechanical, tribological properties, dislocation substructure and phase composition is performed. It is shown that under uniaxial compression the conditional yield strength is ~ 1100 MPa, strength (2160-2220) MPa for hypereutectoid steel and ~ 1000 MPa and (1750-1830) MPa for hypoeutectoid steel, respectively. It has been established that special-purpose rails of category DT 400 IK have higher values of microhardness (by 1.2 times), wear resistance (by 3.7 times), friction coefficient (by 1.5 times), scalar dislocation density (by 1.3 times). The physical reasons for the observed different quantitative parameters for the two steels are discussed. The structure of DT 350 rails is represented by lamellar perlite (0.75 volume fraction), grains of ferrite-carbide mixture (0.23 volume fraction) and structure-free ferrite. The structure of rails of category DT 400 IK consists of pearlite (0.98) and carbide phase (0.02); the main phases are a solid solution based on α-Fe and iron carbide Fe₂C. The revealed increase in the crystal lattice parameter of α-Fe 0.28736 nm, exceeding the tabular value, may be due to the presence of up to 0.0167 wt. % C in the crystal lattice.