High Speed Railway Whell Tread Damage Mechanism And Gradient Coating By Laser Cladding Security Research

With the rapid development of Chinese high-speed railway, train wheels under the high load operation of the long-term problems of wheel wear and damage, increased the railway operation cost, influence the train comfort and smoothness, endangering the train running safety. Railway departments have to spend a huge sum of money each year on the wheel/rail for repair or replacement. High speed train wheels security countermeasures study, therefore,not only can improve the comfort and stability of the train operation, increase the train running safety, also can greatly reduce the railway operating costs.This paper designed a kind of self fluxed iron base alloy powder as the cladding material,the use of LDM2500-60 type semiconductor solid-state laser, through orthogonal experiment,optimization of cladding process parameters, the high-speed train wheel material specimen surface gradient of laser cladding coating experiment was carried out. Using optical microscope(OM), scanning electron microscope(SEM), X-ray diffraction(XRD), rockwell hardness tester, micro hardness tester, friction and wear testing machine, such as testing equipment, systematic analysis of the laser cladding process before and after the wheel material(ER8), rail material(U75V) the organization composition and structure, friction coefficient and wear volume and the friction and wear morphology, and so on and so forth.The main conclusions are as follows:1 、 The optimum technological parameters for: laser power 1.8 KW, scanning speed,feeding rate of 300 mm/min, 20 g/min, overlapping rate was 40%. Under the technological parameters of cladding layer surface morphology, single-channel cladding layer thickness in1.5 mm or so, the cladding layer dilution rate is about 13%, the cladding layer porosity, crack,and metallurgical bonding to the substrate. Under the optimal laser process parameters,comparison of different alloy powder single-channel cladding layer and matrix combined with the topography, bonding strength, surface hardness of cladding layer, determine the choice of powder number F-2 as the first layer of the gradient coating, F-3 as a gradient coating layer 2,F-4 F as the gradient coating on the third floor.2、Gradient coating each lap zone in the presence of larger particles of cellular crystal,lower lap zone on the combination of zone and heat affected zone thickness is bigger. By EDS spectrometer found in the gradient coating due to the layers of different alloy powder, the upper cladding layer of Cr, Ni elements such as the lower part of cladding layer, the gradient coating particles in the overlapping area of Cr, Ni and Mn in cellular crystal element content is significantly reduced, matrix of Cr, Ni, Mn element content increased significantly. ByXRD diffraction analysis found that the gradient coating by a large number of gamma- Fe solid solution, Fe3 C, Cr7C3 and Mn7C3 carbide, boride and intermetallic alloys, etc.3 、Microhardness distribution of the gradient coating a single-channel cladding layer microhardness distribution improved substantially, and the microhardness of the gradient coating gently reduce continuously from the surface to the substrate, does not appear as single channel of cladding layer step down. This is due to the cladding substrate and the cladding layer in the process of diffusion of elements, due to the overlap regions exist at the same time,the lap zone by laser remelting, organizes relatively bulky, results in lower hardness and reduce the hardness difference between the cladding layer. Microhardness gradient cladding layer in about 450 HV, the untreated sample wheel increases by about 50%. Round than the cladding of the friction pair of cladding reduced the friction coefficient of friction pair, always wear rate by 58.56%, the rail wear rate reduced by 31.41%, vice anti-wear performance improvement is about 5.5 times that of the wheel, anti-wear performance is greatly improved.Not cladding wheel friction pair of sample surface with a large number of corrosion pit more exfoliate, stripping phenomenon is more serious, and the grinding of the surface of the rail sample have many corrosion pits, accompanied by a small amount of furrows and flake exploitation, not cladding of the friction pair of rail wear mechanism is adhesive wear and abrasive wear. Wheel cladding friction pair of wheel/rail grinding crack mainly for a small amount of sample surface furrow, damage is slight, the wear morphology of grinding rails were investigated with also have certain to improve, the main wear mechanism is abrasive wear.