Research On Rolling Contact Fatigue Characteristics Of Subway Wheel Local Damage Repair Based On Laser Cladding

The wear and fatigue damage of wheel tread during the operation of rail trains are currently the focus of research on train wheel rail systems.The peeling of wheel tread materials and the initiation of internal cracks are the two main forms of damage to train wheels,which can cause serious safety hazards to train operation and are difficult to effectively prevent.Therefore,it is currently the focus of research on train wheel damage.This article combines laser cladding local repair technology and adopts the method of double wheel rolling friction test to simulate the fatigue damage during the actual operation of subway,and conducts a study on the rolling contact fatigue characteristics of subway wheels.Laser cladding technology,as a new type of surface repair technology,has a critical impact on the performance of the cladding coating due to its cladding materials and process parameters.The paper conducts laser cladding repair treatment on local damage areas of train wheel materials,and conducts 1.6×10⁶cycle rolling friction tests on wheel specimens on a rolling testing machine.The surface morphology,microstructure,surface hardness,roughness,and crack damage morphology of Fe based alloy,Co based alloy,and 316L stainless steel alloy coatings are compared,and the damage mechanism is revealed.By changing the laser power of Fe based alloy coating laser cladding,Fe based cladding coatings were prepared at the local damage location of the wheel material with laser power of 2600W,2900W,and3200W,respectively.The surface morphology,microstructure,surface hardness,roughness,and crack damage morphology of the repaired coatings were compared and analyzed,and their damage mechanism was revealed.The aim of this study is to provide theoretical guidance for the repair of local damage to subway wheels,in order to improve the surface performance of wheels and the reliability of train operation during actual subway operation.The main conclusions of the paper research are as follows:（1）Comparing the laser cladding samples of Fe based,Co based,and 316L stainless steel alloy with three different powder materials under the same process parameters,the surface damage of Co based samples is the smallest,and the surface roughness of the coating is the smallest（1.06μm）The average friction coefficient is the lowest（0.074）,and the wear rate is the lowest（0.08μg/m）,the microstructure is the smallest and most compact,mainly in the form of dendrites and eutectic,and there is a certain amount of equiaxed grains.The average hardness of the coating surface is located between the other two samples（525HV）,and no obvious cracks are found on the coating surface and profile position;The average surface hardness of the Fe based sample coating is the highest（630HV）,and the surface roughness of the coating is the highest（2.81μm）The average friction coefficient is the highest（0.262）,and the wear rate is the highest（0.19μg/m）,the microstructure of the coating is similar to that of the Co based sample,with several small microcracks at the top of the coating profile;The surface damage of 316L stainless steel sample is the most severe,with the average hardness of the coating surface being the smallest（350HV）and the surface roughness of the coating being 1.97μm)The average friction coefficient（0.123）is located between the other two samples,and a slender crack extending from the surface to the inside of the coating is found at the coating profile position.（2）Compared with the phase composition of the coating prepared by three powder materials,the Fe based alloy coating is mainly composed of（Fe,Ni）solid solution and Cr₇C₃phase,and the Co based alloy coating is mainly composed ofγ-Composed of Co phase and Cr₂₃C₆phase,the 316L stainless steel alloy coating mainly consists ofα-Fe phase sumγ-Fe composition.Comparing the elemental composition and content of the three coatings,the Cr atom percentage at the dendrite position of the Co based cladding coating is as high as 34.42%,while the C atom percentage accounts for 26.30%.Therefore,the coating area contains a large amount of hard phases Cr₇C₃and Cr₂₃C₆,effectively improving the wear resistance of the Co based coating.The eutectic position of the Co based cladding coating contains 2.8%Ni element,which is used to refine grains and improve the impact toughness of the material.In addition,The Co based alloy coating also includes a high-performance W element,which can combine with C element to form carbides,effectively improving the strength,hardness,and wear resistance of the coating.The average content of Mn element in Fe based cladding coating and 316L stainless steel cladding coating is0.21%and 3.95%respectively.The solid solution formed by Mn and Fe can improve the hardness and strength of ferrite and austenite at the coating location,but too high Mn element will affect the ductility of the material,so the 316L stainless steel sample has relatively high crack sensitivity.（3）Comparing the Fe based alloy repair coating wheel samples under three different laser powers,the average microhardness of the coating surface of the samples was 620.6HV,538.6HV,and 421.8HV at laser powers of 2600W,2900W,and3200W,and the surface roughness was 2.81,respectivelyμm.2.93μm and 3.26μm.The average friction coefficients are 0.262,0.295,0.353,and the wear rates are 0.19,μg/m,0.2μg/m,0.35μg/m,as the laser power increases from 2600W to 3200W,the rolling contact surface wear of the sample becomes increasingly severe,and the microstructure grains become coarser.