Study On Process Of Isothermal Quenching And Plasma Nitriding Of S135 Drill And Its Performance

S135 drill pipe is widely used in oil drilling process,not only effected by the variety of alternating stress,but also by wear and corrosion in drilling fluids.In order to improve the drill overall strength and toughness,while improving the wear and corrosion properties of the surface of the drill pipe,we use composite technology of isothermal quenching and plasma nitriding on drill pipe.We study the effect of isothermal quenching temperature and time on the drill pipe microstructure and properties,discuss the synergistic effect of different heat treatment methods and plasma nitriding,and do orthogonal experiment of isothermal quenching and plasma nitriding process to determine the optimum parameters to obtain excellent overall performance of the drill pipe,through the analysis of microstructure,wear resistance and corrosion resistance and mechanical property test.The study on S135 drill isothermal quenching showed that: when isothermal quenching for 30 min,with the isothermal quenching temperature,due to the different rate of isothermal transformation,the size of bainite and martensite in drill pipe increases,and XRD analysis show that the content of retained austenite increases,the yield strength of the drill pipe is gradually reduced,and the impact toughness is first increased and then decreased.At 320℃ isothermal quenching,with the extension of austempering time,isothermal transforms more fully,the size of bainite and martensite in drill pipe increases,the yield strength of the drill is gradually decreased,while the impact toughness gradually rise high.By comparing the synergistic effect of isothermal quenching with plasma nitriding and the synergistic effect of quenching and tempering with plasma nitriding,found that S135 drill pipe after isothermal quenching and plasma nitriding than after quenched and tempered and plasma nitriding can get thicker nitrided layer and the bright layer,the surface contains more ε-phase and,and the yield strength of drill pipe after isothermal quenching and plasma nitriding is 10% higher than drill pipe after quenched and tempered and plasma nitriding,and the impact toughness is also 33% higher.Through the orthogonal test analysis of isothermal quenching and plasma nitriding process,the factors that affect the overall performance of drill pipe from the primary to the secondary is isothermal quenching time,nitriding time,the furnace pressure and nitriding temperature.under the experimental conditions,the optimum process parameters are that isothermal quenching time at 320℃ is 30 min,nitriding temperature is 550℃,nitriding time is 8h and nitriding furnace pressure is 180 Pa.The hardness of Nitrided layer after isothermal quenching plasma nitriding from surface to inside decreases,and it decreases rapidly within 0.1mm from surface.Compared to the sample after isothermal quenching,the wear resistance and corrosion resistance of the sample after isothermal quenching and nitriding plasma has been greatly improved,and the yield strength is slightly reduced,but the impact toughness increased.