Pre-oxidation And Post-oxidation Technology Research Of N80 Tubing Based On Pulse Plasma Nitriding

N80 steel is the main material of oilfield.There are problems like dissolved oxygen and produced liquid,the wear failure friction with sucker rod and the Reminders seepage problem.Ion nitriding technology has long been a common method of solving N80 steel corrosion and wear problem.we explore the new ion nitriding on the basis of preoxidation and post-oxidation process.And the nitriding layer were characterized by a series of observation and analysis such as microstructure analysis,micro hardness analysis,nitriding depth,XRD,SEM,corrosion resistance and wear resistance analysis.While doing the ion nitriding experiments with preoxidation process,the orthogonal experimental studies show that the factors of affecting the properties of the nitrided layer are pre-oxidation temperature,the ratio of hydrogen gas,flow and pre-oxidation time.The best pre-oxidation process parameters are 400 ?,10 min,200ml and hydroxide gas flow ratio of 6: 1.Pre-oxidation promotes nitriding and improves the comprehensive performance of the nitriding layer.Through phase analysis and mechanism analysis,we can get that a small amount of Fe3O4 and Fe2O3 oxide film become the diffusion path of the nitrogen atom and after the oxide film is reduced to be clean surface,nitrogen atoms increases to achieve infiltration catalytic effect.After the ion nitriding tests on the basis of post-oxidation,according to the economic factors and use requirements the best parameters for post-oxidation process is at 350 ?,insulation 30 min,hydrogen ratio of 6: 1 obtained by the orthogonal experimental studies.After the post-oxidation process,the comprehensive performence of the nitrided layer improves.The nitrided layer is composed of Fe3O4 phase,?'-Fe4 N phase,?-Fe2-3N phase and ?-phase.Fe3O4 phase surface has a low coefficient of friction and high chemical stability,and therefore wear and corrosion resistance of the sample were improved in varying degrees.While the oxide film forms,the nitrogen atoms spread inside in order to improve the thickness and hardness of the nitrided layer.