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With the development of industrial technology, the demands of improving steelservice life to save resources increased. The steel wear is the main form of materialconsumption, and the background and purpose of this title is to improve the surfacewear performance of steel、prolong the service life and saving cost. Using the plasmaspray welding technology to spray different alloy welding layer on the surface of Q345steel, the alloy powder is based on Ni60A, adding different proportion of Ni coated WCpowder.Through the ways of optical microscopy, scanning electron microscopy,spectroscopy, XRD diffraction analysis etc, the microstructure and composition ofsamples are researched. And the hardness and wear-resistance of the coating areanalyzed, in using to study the different levels of Ni-WC addition on the mechanicalproperties of the coating. Then, the method of orthogonal optimization of plasma sprayprocess parameters were optimized, select the most outstanding performance of theoptimal process parameters, analysis the form of defects in the spray welding layer.In the part of alloy coating microstructure research, with the addition of Ni-WCpower, the irregular WC particles in the coating increased, WC particles are surroundedby Ni-based phase. The mixed power of Ni60A and Ni-WC containing Cr, B, C, W andother elements. WC, W3C, Cr7C3, Cr23C6, Cr3C2, CrB, and other hard phase will beproduced in the alloy coating. These hard phase can significantly improve the spraycoating hardness and wear resistance.The results of the coating performance analysis show that: Compared with thesubstrate, the hardness and wear resistance of the plasma spray welding coating areimproved significantly. With the addition of Ni-WC, the hardness of the coatingincreases generally, the highest hardness is Ni+45%WC coating（901.49HV）. The wearanalysis shows that wear resistance increase significantly because of the WC particles.But the excessive amounts of WC content also lead to increase brittleness of spraywelding coating.The change of spray welding current and feed rate will affect the appearance of thespray welding layer forming. Microstructure and properties of spray welding layer willalso change. Using orthogonal optimization methods, select the transferred arc weldingcurrent, welding speed and powder feed rate as three-factors orthogonal optimization ofplasma spray welding parameters. The results show that: the powder feed rateoptimization for plasma spray welding coating greatest impact the hardness index. Theoptimal parameters are given as below: transferred arc welding current60A, welding speed50mm/min, powder feed rate24g/min. Finally, using the optimization results,success spray the wear coating in the surface of42CrMo oil drill pipe.Through the analysis of the defects in plasma spray welding coating, find themainly form of defects are pores, non-fusion and oxide inclusions. Making a researchabout the causes of defects and propose improvement measures.
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