Antipin Y. Technology of flash-butt welding of railway rails of converter production

The dissertation is devoted to the development of an effective technology of flash-butt welding of heat-strengthened railway rails of converter production. Operational indicators of welded joints of railway rails are an important component of the durability of railways and are regulated by current domestic and international standards. The non-separable joining of the rails during the manufacture and laying in the track of long-dimension rail plates is mainly performed by flash-butt welding. The world's leading manufacturers of railway rails are constantly improving rail steels in order to increase hardness, resistance to brittle fracture, and wear resistance, particularly in the rail head. The transition to the oxygen-converter method of smelting rail steels significantly affected the weldability of railway rails. On the railways of Ukraine, heat-strengthened rails manufactured by converters of the hardness class 350HV30 of steel grades K76F, R350HT are mainly used. Indicators of strength and wear resistance of the rails are provided due to the regulated distribution of hardness along the cross-section of the rail. Ensuring compliance of welded joints of railway rails with the requirements of the national standard DSTU EN 14587-2:2015 (EN 14587-2:2009, IDT), harmonized with the relevant European regulatory document, necessitates taking into account the energy parameters of the FBW process, which determine thermal cycles during flashing and temperature distribution in the heat affected zone (HAZ) of rails welded joints. Until now, no reliable algorithm has been developed to ensure the compliance of welded rail joints with regulatory requirements when changing the technological parameters of FBW and external factors (rail manufacturer, steel grade, condition of the rail welding machine, diesel generator parameters, quality of rail end preparation, etc.). Therefore, in practice, the FBW technology is optimized experimentally for the available batch of railway rails and the conditions of work, in particular, the specific rail welding machine and diesel generator. The relevance of the dissertation topic was the need for a scientific justification for the development of an effective technology of FBW railway rails of converter production of hardness class 350HV30, which will ensure compliance of welded rail joints with the requirements of current regulatory documents. The purpose of the work is to develop an effective technology of flash-butt welding of railway rails of converter production, which ensures compliance of welded rail joints with the requirements of standards in force. In order to achieve the purpose of the work, a computational and experimental study of the thermal cycles of FBW and temperature distribution in the joint zone was carried out, an assessment of their influence on the structure and mechanical properties of welded joints of railway rails was carried out, on this basis, the ranges of changes in the main technological parameters of FBW of railway rails of strength class 350HV30 were determined , which ensure compliance of welded joints with the requirements of current regulatory documents. The paper examines the process of forming welded joints of rails at FBW, implemented on stationary and mobile rail welding machines K1000 and K922-1 developed by the E.O. Paton Electric Welding Institute of the National Academy of Sciences of Ukraine. Mathematical models and corresponding means of computer simulation of the kinetics of temperature fields at the FBW of railway rails have been developed. The numerical solution of the non-stationary heat conduction equation was used along with a set of necessary laboratory measurements of the influence of welding technological parameters on temperature cycles in the welded rails. This made it possible to take into account the multiphysical processes of rail end flashing, to determine the characteristic thermal efficiency of the FBW process, and to confirm the proper accuracy of calculations at the level of 8%.