Wheelset is one of the main elements of the railway wagon, which must ensure high reliability and safety of train traffic. Sharpness of the ridge roll, potholes, sliders and thin-skinned ridge in excess of permissible values can be one of the factors of derailment of rolling stock from the rail gauge. Over the last 7 years the Latvian railroad has increased its axle load from 21 tons to 25 tons, which could not but affect the increase in defects of wheel pairs of freight wagons. According to the statistics gathered on wheel set defects in the Latvian Railway from 2016 to 2022 indicates that this problem is acute, therefore a decision was taken to remove defective wheelsets from the operation of freight cars in international traffic and to conduct a detailed study of the causes of emergence and development of wheel set defects. In this article, for the study was taken a wheel set with a defect, a pothole on the surface of the wheel rolling. The hardness of the metal according to the Brinell scale using a modern device "Tinius O Olsen" Fikrmware Version 1.07, FH - 31 Series: at the edge of the wheel rolling surface and in the middle of the sample according to ISO 6508. The chemical composition of the cut out wheel fragment was examined in detail with the help of an optical-emission analyzer "PMI-Master PRO". The results were analyzed and compared with the normative and technical documentation of the manufacturer. At the final stage of the study the microstructure and metal structure of the defective fragment of the wheelset using a microscope Carl Zeiss Axiovert 40 MAT were determined, the main conclusions about the steel quality of the wheelset were made and the economic costs for the repair of wheelsets were given.