THEORETICAL STUDY OF THE MECHANISM OF FORMING DEFECTS ON THE ROLLING SURFACE OF WHEEL PAIRS OF THE ROLLING STOCK

The study objective: To determine the physical and operational mechanisms of forming defects on the rolling surface of wheel pairs of the rolling stock, as well as to find the influence of thermal and mechanical factors that occur during braking on the formation of these defects. The task to which the paper is devoted: Theoretical study of the mechanism and causes of defects on the rolling surface of wheel pairs. Research methods: Statistic analysis of braking equipment failures according to JSC Russian Railways; theoretical analysis of thermal and mechanical processes during braking in the shoe-wheel-rail system, including phase transformations in the surface layers of steel wheels. The novelty of the work: The role of martensite transformations is found out in the surface layers of the wheel, which occur during rapid cycles of heating and cooling, as a key mechanism for forming microcracks and defects. Research results: Theoretical substantiation of the defect formation mechanism is developed, including phase and diffusion processes in the contact zone of the wheel and the shoe. Conclusions: Based on an assessment of the conditions of antiskid braking and the reliability of braking equipment, it is found out that defects in the rolling surface of wheel pairs such as slid flat and shelled tread do not always occur during train braking; jam of the wheel pair may occur as a result of intermolecular diffusion bonds after stopping the train with shoe heating, which leads to the wheel pair skidding after the train starts moving; during intensive braking, a phase transformation occurs in the subsurface layers of the wheel steel with the formation of austenite, thus the metal softened due to thermal action can partially adhere and deposit back onto the rolling surface, forming a weld-on deposit.