Abstract：High speed turnout is the key of track structure for the high speed railway. Its structure and state have a great influence on the operation safety and quality of trains. The manufacture of turnout switch rail involves many steps, including forging, heat treatment, machining and so on. The switch rail is a key component influencing the ride comfort and safety of turnouts. Therefore, the analysis of damaged morphology and structure of switch rail has guiding significance to deal with the similar damage problems in the future. According to the ultrasonic detection, serious internal damage existed on the head of one switch rail. The check analysis was mainly conducted from both macro and micro aspects. Through macro morphology observation, the scanning electron microscope (SEM), energy spectrum composition analysis and metallographic microscope were employed for the microscopic observation and analysis of damaged structure. Clear grain boundary and a large number of fine voids could be observed in the defected area. The edge of voids was smooth with metal melting characteristics. Moreover, there were some dendritic crystals on the fracture surface. These dendritic crystals were formed by melting and resolidification. The contents of S and Mn were very high in stripped precipitates on the dendritic crystal. The inclusion was mainly composed of MnS. In addition, the cracks along the overburnt grains also existed in the defected area. The grains of metallographic structure in the defected area were coarse and uneven. The grain size of coarse grain structure was grade 4.5, and the grain size of the fine grain structure was grade 7.5. The results above showed that in the manufacturing process of switch rail, the improper temperature control caused the overheating and partial overburning on the head in the deformation area of the rail. Finally, a serious damage was formed.
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