Study On Strengthening Technoloay Of Laser Cladding Ni-based WC Cladding On The Surface Of Valve Steel

Engine intake and exhaust valves are the key components of the engine combustion chamber.The intake and exhaust valves are opened or closed according to a certain rule,so that the combustion chamber of the engine can discharge combustion exhaust gas and obtain fresh air in time.At the same time,it also seals the combustion chamber.It has an important impact on engine performance,fuel consumption and reliability.However,the engine valve will bear a greater load when it is working,resulting in the valve rod end face and rod often being worn,resulting in a decrease in engine power output and an increase in fuel consumption.Therefore,the research on the strengthening process of engine valve materials has important practical engineering significance.40Cr10Si2Mo steel is a kind of valve steel,which is often used to make engine valves.The main task of this paper is to use laser cladding technology,selects nickel-coated tungsten carbide powder with a tungsten carbide content of 35%as the cladding material,and prepares a Ni-based WC cladding layer on the surface of the valve steel to improve the wear resistance of the valve steel or repair worn valves.First,design the orthogonal experiment of laser cladding process parameters,and determine the process parameters of laser cladding by comparing the amount of wear.Secondly,preheat the surface of the substrate to different temperatures before cladding,and obtain the best preheating temperature of the substrate by observing and analyzing the surface morphology,phase,structure and performance of the Ni-based WC cladding layer at different preheating temperatures.Next,by adding 0.5%,1%,and 1.5%rare earth Y₂O₃powder to the nickel-coated tungsten carbide powder,the influence of Y₂O₃content on the morphology,phase,structure and performance of the Ni-based WC cladding layer was analyzed.The optimal addition amount of Y₂O₃was obtained.In order to prevent the cladding layer from being excessively oxidized,the above tests were all carried out under the protection of direct blowing of nitrogen.Finally,the direct nitrogen blowing protection was changed to vacuum environmental protection,and the influence of vacuum environmental protection on the morphology,phase,structure and performance of Ni-based WC cladding layer and Ni-based WC/Y₂O₃cladding layer was explored.The test results show that the best process parameters for laser cladding nickel-coated tungsten carbide powder on the surface of valve steel are:laser power1200W,scanning speed 4mm/s,and overlap rate 40%.The wear resistance of the cladding layer obtained under the optimal process parameters is significantly higher than that of 40Cr10Si2Mo steel that has undergone traditional heat treatment,but there are crack defects on the surface of the cladding layer obtained under the optimal process.By preheating the substrate before coating,macroscopic cracks on the surface of the coating layer can be eliminated,and the number of coarse hard phases in the coating layer can be reduced.The preheating matrix will increase the dilution rate of the cladding layer and make the microstructure of the cladding layer grow obviously.Although the performance of the cladding layer has been improved,the best performance of the Ni base WC cladding layer has not been brought into play.The addition of rare earth Y₂O₃can purify the molten pool,refine the grains,reduce the dilution rate,and significantly improve the hardness and wear resistance of the cladding layer.However,excessive addition of Y₂O₃will produce a large amount of refractory impurities,which will affect the structure and performance of the cladding layer;when the content of rare earth Y₂O₃is 1%,the structure and performance of the cladding layer are the most excellent.After testing and analysis,the average hardness of the Ni-based WC cladding layer with 1%Y₂O₃added is 1054HV,and the wear mechanism is abrasive wear,which is 26.7%higher than the wear resistance of the Ni-based WC cladding layer without rare earth addition.Vacuum environment protection does not significantly improve the structure and performance of the Ni-based WC cladding layer with 1%Y₂O₃.However,vacuum environmental protection can significantly improve the structure of the Ni-based WC cladding layer,and enhance the hardness and wear resistance of the Ni-based WC cladding layer.After testing,the average hardness of the Ni-based WC cladding layer obtained under vacuum environment protection is 1020HV,and the wear mechanism is abrasive wear,which is22.4%higher than the wear resistance of the cladding layer under the protection of nitrogen gas.Therefore,the laser cladding technology can prepare a cladding layer with excellent wear resistance and few defects on the surface of the valve material.