Study On N80 Tubing Ion Nitriding And Its Nitriding Layer Performance

Corrosion and wear are the primary reasons causing the performance failures of oil tubes, and how to improve the performances of oil tubes catchs more attention. Plasma nitriding as a surface treatment technology is widely used in recent years, and it can obtain good diffusion layers that have good corrosion and wear resistance. However, when the plasma nitriding is applied to the large diameter and length ratio tubes, due to the existacne of electric field shielding, fail to nitride the inner wall of oil tubes. In this paper, using self-developed and applied separate anode plasma nitriding equipment to nitride the large diameter and length ratio N80 oil tubes to improve the corrosion and wear resistance.Discuss the niriding process of N80 tubing,the influence of nitriding layer of 4 factors that are nitriding temperature,niriding preasure,soaking time and voltage are analyzed by orthogonal experiment,and find out the optimal process parameters.Discuss the sphere of influence of independent anode and analyze its reason.The performance of N80 nitriding layer is finally examined by metallographic experiment、microhardness test、tensile test、friction and wear test and corrosion test.The Orthogonal test consequences show that on the microstructure and properties of nitriding layer of the influence of the primary and secondary order(from the main to time) was followed by nitriding temperature, holding time, voltage and air pressure,the best nitriding prosess that nitriding temperature at 530℃,nitriding preasure at 160 Pa,soaking time about 8h and voltage at 700 V is finded by the orthogonal experiment method, The surface hardness of N80 oil tubes can reach 800HV0.2 after ion nitriding. The thickness of the nitrided layer is 0.57 mm.The friction resistance can be increased by five times. The erosion resistance can be increased by four times.However,the toughness of the oil tubes gets worse after nitriding,and the elongation is half of the untreated oil tubes, the consequensce of tensile test shows that the fracture mechanism of nitrided oil tubes is brittle fracture.Friction and wear test of wear forms are mainly abrasive wear and adhesive wear.The investigation of sphere of influence of the independent anode shows that the sphere of influence of the independent anode is at a distance from 5 to 30 cm to the anode.