Study On Repairing Process Of U75V Railsurface By Laser Cladding Additive

With the rapid growth of high-speed railway construction and operation mileage in recent years,the damage of high-speed rail is also increasing.Aiming at the typical damage phenomena of rail,such as corrugation,collapse and mark after long-term use,laser cladding technology is used to repair the damaged surface.According to the different damage forms and repair requirements of the rail,the U75 V rail for high-speed rail is used as the matrix material.Firstly,the comprehensive mechanical properties and microstructure of the matrix are systematically analyzed.Combined with the forming and manufacturing process of the base metal including heat treatment process,18 kinds of powder materials made by Beijing Longyuan automatic forming system Co.,Ltd.are used for comprehensive test and analysis and AFS-T6 metal powder with similar performance to the base material is selected as the final cladding repair powder material.base on this basis,combined with the characteristics of substrate forming process and laser cladding technology with high energy / low heat effect,through the optimization of the process parameters in the process of laser cladding,including laser power,scanning speed,powder feeding speed,lap rate,etc.determined the influence of different process parameters on the cladding process and cladding quality.According to the requirements of hardness,wear resistance,tension,fatigue and other properties in the repair area,the relationship between microstructure,surface hardness and mechanical properties of substrate,cladding layer,bonding interface layer and other different areas before / after heat treatment was studied by means of comprehensive material detection and analysis,combined with the heat treatment process in the repair forming area,and the optimized cladding repair process and heat treatment process parameters were obtained.The results show that laser power 900 W,scanning speed 600 mm / min,powder feeding speed 7.58g/min,lap ratio 58.8%,and z-axis lifting amount0.6mm are the best processing parameters of laser cladding repair of U75 V rail.By comparing the microstructure and properties of laser cladding repair area and rail before and after heat treatment,the microstructure and properties of cladding under different conditions are obtained.The results show that the microstructure of single-layer single pass laser cladding zone is mainly composed of columnar crystal and a small amount of equiaxed crystal.The multi-layer and multi pass laser cladding zone is mainly composed of equiaxed crystal and the heat affected zone is mainly acicular martensite.After tempering at 500 ?,the martensite is transformed into tempered sorbite,the average hardness of the cladding zone is reduced from 480 HV to 345 HV,the average hardness of the heat affected zone is reduced from 630 HV to 395 HV,the wear resistance is95% of the base metal and the tensile strength is 834.64 MPa,which meets the national TB/T3276-2011 high speed railway U75 V rail repair standard.In addition,preheat treatment is beneficial to reduce the cracks in laser cladding process,and the preheat temperature is better at 200?.