INVESTIGATION OF THE PROBLEMS OF EXISTING METHODS OF ELECTRIC CONTACT WELDING OF RAILS AND LOCAL HEAT TREATMENT OF WELDED JOINTS

Abstract

The article presents a statistical analysis of the operational cycle of welded joints of domestic and imported rails on all Russian Railways (JSC Russian Railways), which indicate insufficient reliability of welded joints. Statistical data on defective rails en route of JSC Russian Railways are presented as of 01.01.2022, 01.01.2023 and 01.01.2024. During contact welding of rails, parts of the welded rails are in two states: at the weld site, the metal is heated to a temperature exceeding the melting point of 1520 °C, where the metal melts and the metal is ejected from the weld, and in a plastic state in the HAZ. The ends of the rails are heated to temperatures below the solidus (for steel up to 1100–1200 °C), and under the action of a compressive force, they are plastically deformed by a certain amount (subsidence) and welded. The amount of upsetting, the compressive force, and the heating temperature of the rails have a decisive effect on the formation of the welded joint and are the main factors in the process of contact welding. Insufficient fatigue strength of welded joints has become increasingly evident when welding rails using the pulsed flashing method in steels alloyed with chromium and silicon. The high cooling rate of the HAZ leads to the formation of martensite areas that act as stress concentrators and subsequently to the possible formation of defects in welded joints, i.e. to the development of fatigue cracks in the foot, neck and head of the rail with subsequent brittle fracture. If the hardening technology is violated, the metal of the head of the welded joint spalls, and the softening of the metal during welding leads to the crushing of the metal of the head of the welded joint. Welded joints in rail strings must not have internal and external defects of a certain type that exceed the standard dimensions. As the speed of movement increases, the requirements for the straightness of the rails and welded joints increase.