Investigation of structure and mechanical properties aluminothermic welded joints of rails

Welded joints of rails are an integral part of continuous welded railway. However, they often do not have sufficient reliability during the operation. The paper presents the results of study of hardness and structure of aluminotermitic welded rail joints. It is found that the riding rail surface of welded joints has a reduced hardness compared to hardness of the rail metal, which can lead to the formation of soft sites with lower resistance to wear and crushing of the welded joints, particularly in the path curves. Hardness increases to 36-38 HRC on the boundary fusion line of the rail and welded metals. This is due to the harmful effects of overheating of the metal during welding process, which is confirmed by the results of microstructural analysis. Microstructural analysis also showed the differences in metal grain size in the welded zone and heat affected zone. The structure of welded metal zone is dendritic while the structure of heat affected zone is coarse-grained. Owing to the difference between structures of the welded joint zones, the probability of occurrence of brittle fracture on the boundary fusion line of the rail and welded metal is increased.