The Influence Of Laser Hardening On Contact Fatigue Of Hypoeutectoid Steel

During the running of the high-speed train, the profile of wheel and rail surface matching is extremely important. Inappropriate surface matching can lead to vibration and noise, which will affect the stability, comfort and even the safety of the train running. Under the condition of appropriate surface matching, flange wear and tread fatigue is the main problem of wheel/rail contact. As sliding wear is the major wear form between wheel flange and rail side, flange wear is more serious than that of tread. In order to match the profile of wheel and rail, a small amount of flange turning will be accompanied by a large number of tread turning which results in the enormous waste. As the heating and cooling speed of laser phase transformation hardening is very fast, the generated martensite has higher hardness than conventional quenching because of fine grain size, high dislocation density, while the original toughness of the material will still be remained. A large number of studies have showed that laser transformation hardening can significantly improve the wear resistance of wheel/rail material, while the impact on the wheel/rail rolling contact fatigue has not been studied.In this thesis, the influence of parameters of laser hardening on microstructure, hardness, residual stress and content of retained austenite within hardened layer are discussed in order to design suitable laser hardening processing. The wear experiment and rolling contact fatigue experiment were conducted to explore the effect of laser hardening processing on wear resistance and rolling contact fatigue resistance of hypoeutectoid steel. The mechanism of rolling contact fatigue of the hypoeutectoid steel was explored by measuring the residual stress and the content of retained austenite, the microhardness, and the microstructure analysis by microscope. The temperature field of the laser hardening processing was simulated by finite element method. The hardness value of the laser hardening layer was simulated through combination between the temperature field and phase field, providing the theoretical basis for laser hardening treatment of the high speed train wheel.