Study of wear resistance of railway rails welded joint

Abstract

Welding joints of rails are a weak point of a jointless railway line, which stipulates actuality of studies on increasing their operational resistance. Microstructures of welded joints made by existing at present welding technology and by a new one were compared. Existing (base) technology comprises further thermal treatment of the welded joint, while the new technology comprises welding followed by a short-time electric current impact during the rail joint cooling. To study the microstructures of welded joints, samples were cut out the welded seam zone and heat affected zone, as well as out of the base metal. The study was carried out in the depth of 5 mm from the surface, after thin section etching by 4% solution of nitric acid in alcohol. In the macro-structure of the metal of welded joint, made by the base technology, an uneven heat affected zone was detected. The zone had the following dimensions: 51 mm – in the head, from 45 mm to 62 mm – in the neck and 64 mm – in the bottom (by each of the seal side). In the longitudinal mac- ro-template of sample Б (the new welding method), the heat affected zone was even and along the whole joint had the width of 22 mm (in each of the joint side). It was shown, that the new welding method of railway rails enables to decrease the extension of zone with sorbitic and granular pearlite at various stage of coagulation. A short-time impact of electric current during rail joint cooling ensures obtaining a zone with a decreased hardness of 15 mm extension and decrease of welded seam metal hardness relatively the lower border of base metal hardness by less than 15%. Application an additional local thermal treatment by a separate induction heating during base technology results in forming zones of 30 mm extension in the area of welded joint, which wear resistance is 4.5 times lower comparing with wear resistance of the rail base metal. At the new welding method application, the extension of the abovementioned zone does not exceed 10 mm and wear resistance was decreased by less than 2 times.