Study On The Processing, Microstructure And Properties Of Surface Layer Of Plasma RE Nitrided N80 Steel

N80 oil tubes are widely used in oil fields. Due to the corrosion of dissolved oxygen in the production and rod eccentric wear problem, tubing life are affected, in order to improve their life, the project adopts the ion nitriding process to improve the wear resistance and corrosion resistance, to study the ion nitriding process and the role of rare earth played in ion nitriding process. Metallurgic microstructure observation, micro-vickers hardness test, electrochemical corrosion, friction-wear test and X-ray analysis, SEM analysis are applied in the nitriding samples respectively, founded that adding rare earth ion nitriding can effectively improve the nitriding speed, increase the permeability layer thickness, enhance the resistance and corrosion resistance of permeability layer.Analysis of ion nitriding process, indicate that the main process parameters affecting the overall perfomances of nitrided layer is the ratio of N2 and H2, followed by nitriding temperature and keeping time. Under the condition of this test, The nitrided layer has the best overall performances, when the parameter is that the nitriding temperature 540℃, keeping time 8 or 10 hours and the ratio of N2 and H2 is 2:3.In order to further improve the microstructures and properties of materials, add rare earth in the process of ion nitriding, in the condition of constant hydrogen nitrogen ratio and temperature, permeability layer thickness increase with the increase of nitriding time, When the temperature is 540℃,N2 and H2 proportion is 2:3,nitriding time is 6h、8h、10h、12h,the nitriding layer improve 11.7%、28.95%、27.38%、25.58% respectively, The infiltration of the rare earth is best when the nitriding time is 8h,at this time the thickness of the nitriding layer is 0.49 mm, and the surface hardness can be 920HV0.3 which improves 26.84% compared to normal plasma nitriding. The friction coefficient of ion nitriding 8h with rare earth is 0.34, and in this condition the corrosion current density decrease, wear resistance and corrosion resistance are improved significantly, rare earth has obvious seepage effect. Plasma nitriding after adding the rare earth doesn’t change the phase structure at the XRD surface.The phase structure of nitriding layer areα,γ’-Fe4 N and ε-Fe2-3N,and the γ’-Fe4 N presents the preferential growth orientation at the plane of 200. Considering the overall performance and cost factors of the material, 540℃,N2 and H2 proportion is 2:3 and the nitriding 8h are the optimal parameters of the plasma nitriding under the addition of rare earth on the steel N80. The addition of the rare earth improves nitriding speed as well as the wear and corrosion resistance of the material.