LKAB has tried new iron ore wagons for the 30 tonnes axle load. They got problems with cracking and material removal from the rim of the wheels during the tests. Martensite, which is more prone to cracking than other microstructures, was found at these locations. The initial material microstructure is supposed to contain no martensite. The purpose of this investigation is to find whether the thermal cycle due to braking, possibly with assistance of the mechanical load, can cause martensite formation