Study On Microstructure And Properties Of Heavy-haul Wheel Steel CL70 Under Rolling Friction

With the rapid development of railway transportation in China has brought many conveniences to the society,the requirements for the performance of wheels and rails are also increasing.Especially in the heavy-haul transportation,with the increase of the axle weight of the train,the friction and wear performance of the heavy-haul wheels has been widely concerned.Therefore,it is of great significance to study the wear properties of wheel steel and the internal evolution of the wheel during wheel operation.High carbon pearlitic steel CL70 has been widely used in the material selection of heavy-haul wheel steel due to its high strength and high wear resistance.However,cracks tend to spread along the pearlite layer during train operation,with serious consequences.Therefore,this paper starts from the relationship between the carbide morphology inside the material and its wear performance.Spherical pearlitic structure was obtained by spheroidizing annealing of heavy-haul wheel steel CL70.The steel CL70 whose original microstructure was lamellar pearlite or spherical pearlite,was subjected to dry friction pure rolling test on the rolling friction and wear tester with rail steel U75V under the same parameters.The wear loss was measured by the mass loss;the digital microscope and the scanning electron microscope with the function of electron backscattered diffraction were used to observe and analyze the running surface topography of the sample after wear and the surface layer microstructure of the material;and the micro-hardness tester was used to measure the hardness changes of the rolling surfaces of the two kinds of microstructures.The results show that the wear performance of the lamellar pearlitic structure is much better than the spheroidal pearlitic structure.This is embodied in the fact that the lamellar pearlitic structure has less mass loss,a lower and smoother wear rate and coefficient of friction,a lower surface roughness,and a higher surface hardness and a more pronounced degree of surface hardening.During a total of 3.0×105r wear,there was no large angle crack and "white layer" phenomenon,and only the wheel samples showed a multilateral appearance.The wear mechanism and strengthening mechanism of the two are different,the lamellar pearlitic structure is mainly fatigue wear,and through plastic deformation and grain refinement to fiber structure to nanocrystal,dislocations accumulate and achieve good strengthening effect.Spherical pearlitic structure is mainly adhesive wear,only ferrite and a small amount of cementite deformation and fragmentation,the increase in hardness is mainly due to the accumulation of dislocations around the cementite particles,the hardening effect is poor.