Study On The Thermal Damage Of Cast Steel Wheel For Tread Braking

With the continuous development of the railway system, railway wagons in our country toward the direction of high speed and heavy load. However, the problem of braking is more and more prominent. For heavy haul freight cars in our country is still the tread braking, so the thermal load generated by the friction of the tread braking process will cause the thermal damage of the wheel. Therefore, thermal damage has become an urgent problem to be solved in the process of heavy haul freight transportation.This paper mainly studies the phenomenon of thermal fatigue damage of the emergency braking process of heavy haul freight cars with cast steel wheels. The main work includes the following aspects:first, introduces several main forms of wheel damage, mainly focuses on the formation mechanism of thermal crack; then,3D model is imported into ANSYS from Solidworks, determine the boundary condition, calculation of heat flux and convective heat transfer coefficient, setting load step, then simulation of temperature field and stress field during emergency braking; finally, make plan of thermal fatigue test for steel material, analysis the test results, and the crack fracture morphology was observed by scanning electron microscope.The simulation and experimental results show that:(1) In the process of emergency braking, the highest temperature of the wheel is always on the tread of the wheel; however, for the maximum thermal stress, the braking process occurs on the tread surface, and the end of the brake will move to the hub. (2) The farther away from the center of the tread, or the depth of the radial depth from the surface, the smaller the maximum temperature and the thermal stress are achieved and the time delay. (3) From the variation curve of the crack length with the cyclic number, the crack length at the upper cycle temperature of 650℃ is longer than the upper cycle temperature of 450℃. The lower of upper limit temperature, the thermal fatigue resistance properties will be better, difficult to produce crack. (4) It was found that there was an inclusion on the fracture, which was most likely to exist as a crack source. And the presence of blowhole decreases the strength of the material.According to the results of the research, the temperature generated in the braking process is the key factor to influence the thermal fatigue damage. The lower the maximum temperature gradient is formed in the brake, the maximum thermal stress will be lower, the more difficult to produce crack and cause damage, and favorable to the wheels. So in the process of applying cast steel wheel for braking, we should to improve the environment or use of new shoe material and so on, as far as possible to reduce the heat acting on the wheel.