INFLUENCE OF BRAKING ON THE MICROSTRUCTURE AND MECHANICAL BEHAVIOR OF RAILROAD WHEEL STEELS

摘要

We study the changes in the microstructure, micromechanism of fracture, and characteristics of cyclic crack resistance of high-strength (KP-T-type) and medium-strength (KP-2-type) railroad wheel steels under the conditions simulating the process of braking in a wheel-rail couple. It is shown that, in the contact zone, their initial pearlitic structure is transformed into martensite and the initial compressive residual stresses of the second kind are replaced by tensile stresses, and the higher the carbon content of steel and its cooling rate, the more intense are these changes. The analyzed processes lead to the realization of low-energy cleavage intergranular mechanism of fracture of steels under cyclic loads and to a significant (almost twofold) decrease in their cyclic fracture toughness ΔK_(fc).