Research of defects during manufacturing R65 rails from K76F steel by modern methods of non-destructive testing

Non-destructive testing of rails is one of the most important stages of production because it allows the most objective determination of whether rails manufactured according to a certain technological process meet the necessary requirements. The ability to withstand constant shock loads is one of the important parameters that characterize the durability of rails, especially at negative temperatures. This characteristic depends on many factors, including the size and nature of the distribution of non-metallic inclusions, grain size, the presence of strengthening particles, the uniformity of their distribution and much more. Non-destructive methods of examination are carried out by continuous control over the entire cross-section of each rail directly during their production to prevent contact-fatigue cracks and other defects during their operation, which can provoke disturbances in railway transport operation. The tasks of improving the process of detecting defects by nondestructive testing methods remain relevant because of the many factors affecting them or even a complex of factors. This paper presents the results of evaluation of internal metallurgical defects detected by nondestructive ultrasonic flaw detection during production of rails R65 made of steel K76F. Electron-microscopic examination of chemical composition, structure, size, shape, character of distribution of the detected defects has been carried out. They represent complex aluminosilicates, sulfides, bordered by titanium and vanadium carbides, and also scale rolled during rolling. Defects were found mainly in the rail neck. These are non-metallic inclusions formed in the steel during melting, deoxidizing, casting and rolling. The crystallization conditions of the continuously cast billet promote the formation of nonmetallic inclusions mainly in its center, from which the rail neck is formed during subsequent rolling.