Ł. Wojciechowski

Influence of operation on tram wheels and rails surface layer condition

Trams have become a constant in the landscape of many European metropolises in recent decades. The aim of presented research was to evaluate material changes in the surface layer of Siemens Combino, Konstal 105Na, Moderus Beta and Duewag GT tram wheels and rails as a consequence of wheel and rail exploitation in Poznan agglomeration. Microscopic study and hardness measurement were performed. The surface layer of tram wheel was highly deformed, particularly on the top of the wheel flange and under the rolling surface. In the tram wheel so-called overhangs on the top of the wheel flange and on the outer part of the rolling surface were found. Plastic deformation caused an increase of hardness in comparison to the core material. Hardness increase in case of the top of the wheel flange (even 60%) was bigger than in case of the rolling surface (up to 30%). It was also found that the longer approximate total mileage of the wheel was, the higher hardness increase of the surface layer was. ‘White layer’ as a result of presence of higher temperature during exploitation caused by friction was observed. Hard (even 2.5-times harder than the core material) and brittle layer can cause cracks. In case of Moderus Beta and Konstal 105Na wheels in the part from their frontal side decarbonization was noticed. It was stated that decarbonization is also present in the new wheel. It means that it is a defect of PST type wheel production. An area with so low hardness (below 100 HV0.1) could cause faster deformation and wear of whole wheel. A deformation in the surface layer were also revealed in rails. It was observed even in the coating area generated by welding — slip lines in austenite and martensite phase presence. Some recommendations for better wheel exploitation for Poznan Public Transport Company were also determined.