Heat Treatment Of 37CrMnMo Oil Drill Pipe And Joint Performance Of Friction Welding

In this thesis, 37 CrMnMo oil drill pipe joints were quenched and tempered with different heat treatment temperature to determine the optimum heat treatment scheme,and the drill pipe body and joint were welded with inertial friction welding. By metallographic test, mechanical properties experiments, discuss the influence of quenching temperature and tempering temperature on 37 CrMnMo joint microstructure and mechanical properties. Analyze the correlation between different welding parameters and joint quality, study metal plastic flow properties of welding joint, joint fracture mechanism, the element diffusion mechanism on weld-seam and heat affected zone.37CrMnMo joint were quenched in 860℃-890℃ and tempered at 560℃. Hardness tests results show that the hardness gradually increase with the quenching temperature rising. When quenched at 870℃ and tempered at 560℃, the joint impact absorbed energy is 117.68 J, average hardness is 28.38 HRC. Quenched in four selected temperature range and tempered at 560℃, as the quenching temperature rises step by step, the tensile strength shows no significant change, while the yield strength decreased after increasing, peaking at 870℃.As quenching temperature continues to increase, the value of the yield strength decreases.When quenched at 860℃, observe presence of undissolved ferrite. When the temperature reaches 890℃, because austenite grains have a tendency to grow up and then large crystal martensite grains appear after quenching,resulting in the presence of large crystal sorbite after tempering and reducd the impact absorbing energy.Quenched at 870℃,37 CrMnMo steel is water-cooled, microstructure is mainly lath martensite with others like acicular martensite. When tempered at 500℃-640℃, tensile strength and yield strength increased first then decreased. The sample impact absorbing energy rises rapidly and decreases at 600℃. By microscopic observation, the microstructure is tempered sorbite. With the tempering temperature rising, the uneven distribution of carbide morphology flaky gradually evolve into a granular dispersed,enhancing the impact toughness. When tempered at 640℃, granular carbide coarsening cause impact toughness decrease. From the fracture morphology, while having dimples in560℃ and 640℃ tempering treatment, but dimples in fracture is far less in number and less densely distributed than 600℃. To ensure the safety of 37 CrMnMo steel engineering applications, it can get better strength and toughness tempered at 600℃.During inertia friction welding, with other parameters unchanged,when the rotation speed increases friction intensified, the weld metal plastic flow aggravate, under the action of axial pressure along the radial direction of the joint there will be a steady flowout, burrs morphology is getting bigger, also increased loss of axial specimens.Weld joint can be divided into four areas for plastic deformation zone(Zpl), part of the plastic deformation zone(Zpd), undeformation zone(Zud) and base metal(BM). By torsion and forging force, the metal at the interface moved in flat circular and in axial extended directions move in spirals, resulting in horizontal, vertical and curved metal flow. Welded joints form a solid combination after friction welding and post weld heat treatment. There is "100μm" width of occlusion on weld interface, concave-shaped embedded in other organizations. Element diffuse at the interface, Si elements moved from drill pipe to the drill pipe joint side and disperse about "30μm". Zpl microstructure is tempered sorbite after post weld heat treatment, and in end of undeformation zone on both sides there is soft ferrite, resulting in lower hardness on both sides. On tube side in the end of undeformation zone appear blocky ferrite and coarse grains, which are more than drill pipe joint, resulting in prone break.