Modelling of heat conduction and phase transformations during sliding of railway wheels

When a railway wheel is locked and skids along the rail, the wheel material close to the contact surface experiences high mechanical and thermal loads. The friction heat generated causes the temperature to rapidly rise up to roughly 800–1000 °C, which is high enough to cause phase transformations in the wheel steel. In this paper, a finite element (FE) model is presented that enables computation of temperature variations and resulting phase transformations in the steel. The results are compared to the outcome of full-scale experiments on wheel sliding and good agreement is achieved. It was found that cooling rates are similar in depth within the transformed regions which lead to evenness in formed phases. Further, cooling rates are much higher in the periphery of the damaged volume due to the increased degree of divergence of the heat flow. This is also a reason why smaller contact surfaces between wheel and rail give higher cooling rates. The results give increased understanding on what happens during a wheel slide and enables prediction of how alternative materials would stand the thermal loads.