Effect Of Laser Selective Quenching On Wear Performance Of U71Mn Rails

Wheel-rail wear has always been a key technical problem in railway transportation.It is closely related to a series of important issues such as improving axle load and speed in railway transportation.Laser quenching technology plays an important role in improving the surface hardness and wear resistance of materials.It has been used in surface strengthening of rails.However,the distribution of mechanical properties from the surface to the internal matrix of the quenched zone is not clear,and the mechanism of wear resistance improvement in quenching layer is not clear yet.Due to the small size of the quenching spot,it is impossible to carry out the macro tensile test to obtain the basic mechanical performance parameters.The indentation test of the quenching layer material is required by nanoindentation testing technology,and the material model parameters describing the monotonic tensile behavior and cyclic behavior are obtained through reverse analysis.Then a three-dimensional finite element model of laser selective quenching rail is established to analyze the effect of quenching spot on the wear performance of U71 Mn rail.The research results have important guiding significance for improving rail service life and reducing railway operation cost.The main contents of this work are summarized as below:1)The metallographic structure of laser selective quenching U71 Mn rail base material and quenching spot material were analyzed respectively,and the effect of laser selective quenching on the microstructures of the material was obtained.The basic mechanical properties of the base material and quenching spot material were obtained by monotonic tensile test.The difference of elastic modulus and hardness before and after quenching was obtained by nanoindentation test.2)Reverse analysis of load-depth curve was carried out to determine the material parameters of quenching spot material based on power-hardening constitutive model.Based on this,the parameters of Chaboche model of quenching spot material are determined.3)Based on the secondary development of ABAQUS/Python,the finite element model of laser selective quenching rail was established.The difference of contact stress,equivalent stress and equivalent plastic strain between rail base metal and quenching spot under cyclic loading is analyzed by applying normal and tangential loads with user-defined subroutine.4)Based on the periodic wear element theory,the wear rates of quenching spot and base metal were calculated respectively.The results show that laser quenching can delay the accumulation of plastic strain and improve the wear performance of rail surface under high contact stress.The wear mechanism of rail base metal surface is mainly plastic rheology and contact fatigue spalling,while the wear mechanism of quenching spot surface changes to slight fatigue spalling.