Research On High-energy Beam Oil Tube Inner Surface Modification For Improving Wear And Corrosion Properties

In suck-rod pumping unit,tubing works in the harsh environment with the high stress wear and accompanied by the certain degree of corrosion over a long-term,resulting in the service life shortened and a serious cost of tubing.Facing to this situation,in this paper,the laser beam and plasma beam of new surface modification techniques are utilized to produce protective coatings on the surface of tubing and improve the wear and corrosion resistance and prolong the service life of tubing.The laser surface hardening,laser surface alloying with nitrogen and carbon and laser cladding with WC were respectively employed to produce modified layers on the surface of N80 steel.Microstructure of the modified layers was analyzed,and the microhardness distribution and corrosion resistance properties were also tested.The experiment results showed that microstructure of the above types of the modified layer was small uniform.Compared the modified layers with N80 steel,the hardness was pronounced greatly,and there were gradient change characteristics in the microstructure and microhardness,the thinner the modified layer,the higher the hardness.And the modified layers had excellent corrosion resistance,in which laser carburizing layer had the best corrosion resistance.The wear resistance and corrosion resistance Cr₃Si/γ-Fe composite coatings were fabricated on surface of N80 steel by plasma cladding using the Fe-42.4Cr-7.6Si(wt.%) and Fe-25.4Cr-4.6Si(wt.%) mixed alloy powders as the precursor materials respectively. Microstructure of the composite coatings was characterized,and the micro-hardness, tribological properties and electrochemical corrosion properties were also tested.The results showed that the wear resistant plasma clad Cr₃Si/γ-Fe metal silicide reinforced composite coatings with high hardness and tiny uniformly distributed,and the microstructure was totally metallurgic ally bonded to the substrate;the coating had the microstructure that irregular blocky primary phases Cr₃Si metal silicide are uniformly distributed in the solid solution matrixγ-Fe which contained lots of Cr and Si elements; the coating performed excellent wear resistance under dry sliding wear test conditions at room temperature,and the fiction coefficient was low and steady,at the same time,the coating had excellent electrochemical corrosion resistance.The volume fraction of the primary Cr₃Si dendrites had a remarkable influence on hardness,wear and corrosion resistance of the laser clad intermetallic coatings.The Cr₃Si volume fraction in the coatings of the higher,the higher the hardness and the better the wear and corrosion resistant.According to optimum parameters and the powders ratio,wear resistant and corrosion resistant Cr₃Si/γ-Fe composite coatings were fabricated on the diameter of 2.5 inches oil tube inner by plasma transferred arc cladding machine tool.The plasma cladding coatings with the roughness usually metallurgical bonded to the substrate.It is expected to be effective in improving wear resistance and corrosion resistant of the tubing.