Research On High Speed Rail Strengthening Based On Laser Cladding

Lanzhou Xinjiang high iron is one of the important transportation hub in Silk Road Economic Belt,which across plains,Gobi,desert,sand and other different areas.This complex environment on the high-speed rail along the line brings great challenges.When high speed rail is moving,the rail is not only undergoing conventional impact such as lash,wear and tear,fatigue,but also withstand the region's special climate.The large temperature difference between day and night makes the rail surface crack,and the repeated erosion of the rain makes the surface of the rail produce corrosion pits,which aggravates the aging of the rail.Wind erosion is another facing problem between Lanzhou rail and Xinjiang line.Wind erosion will not only washout the head and base of rail,and the scour hole is filled with tiny sand,which aggravated the abrasive wear of rail.Therefore,the high speed rail should be made research to strengthen the high speed rail by laser cladding technology.The purpose of this study is to increase the wear resistance,corrosion resistance and erosion resistance in the harsh environment,which will be helpful to improve the stability and safety of high-speed rail operation,and the study has certain practical significance for the protection of the Silk Road transportation.In this paper,fiber laser has been used as the experimental instrument to strengthen the rail.First of all,An process test was made on the rail surface,and analyzed its internal structure and microhardness.secondly,cladding Ni/WC alloy on the specimens of laser,optimizing process parameters,and observing its inner structure with OM,SEM,EDS.finally,The abrasion and erosion between cladding layer and the substrate were carried out by using the abrasion machine and the wind erosion equipment.Through the above experiments,the following conclusions are drawn:1,Laser remelting parameters: laser power1300 W,4mm/s scanning speed and defocusing amount is 8mm,The rail is melting best,its hardness is 1013 HV,reaches the maximum value.Measurement shows that the microhardness of the melting zone is 3.6 times of the substrate.In this condition,When laser power is more than 1100 W,rail specimens appear melting zone.2,Through the orthogonal experiment,the optimum process parameters of rail laser cladding are: laser power 1500 W,speed 6mm/s,powder feeding rate 1r/min,defocus 0mm,the range of factors that affect the appearance of the cladding layer is:The influence of the width: powder feeding speed> moving speed>defocus>laser powerEffect of height: powder feeding speed>moving speed=laser powerThe influence of the crack: powder feeding rate>the laser power>moving speed >defocus3.The cladding layer with the thickness of 1mm was coated on the surface of the rail with the overlap ratio of 50%,and its surface was smooth,without cracks,bubbles,impurities and other defects.Under the microscope,it is found that there is a bright band between the cladding layer and the substrate,the dilution rate is 14.8%,and the dialysis element appears in the phase change zone.The cladding layer are divided into four regions,respectively,the cladding layer,substrate melting zone,transition zone and matrix.The main crystal in the cladding layer is the dendrite crystal.Closer the matrix is,the bigger the crystal,and two dendrites appear in the above.In the cladding layer,there are some incompletely melted WC particles which refined grain.The strength of the cladding layer is increased.4.The wear of the specimen and the erosion of sand blown show that the wear amount of the substrate is 5-10 times of the cladding layer,and the scour hole of the cladding layer is obviously smaller than the substrate.