Effect Of Cold Drawing And Heat Treatment On The Microstructure And Mechanical Properties Of 30CrMo Steel Sucker Rod

At present,mechanical oil recovery is common in the process of oil production,and the proportion of sucker rod pumping reaches 90%.The beam pumping unit is used as oil production equipment in Liaohe oil field,and the sucker rod plays the rol e of connecting the pumping unit with the oil pump to realize gas-lift oil production.With increasing workloads,the demand of the sucker rods is increasing,and failure accidents of the sucker rods in service are increasing gradually.In order to reduce the cost of replacing the sucker rods in enterprises,the rods are used again after being repaired;and this is an effective means to reduce the cost.In this thesis,a series of continuous treatment processes of annealing-cold drawing-quenching and tempering for sucker rods 30 CrMo are studied.Firstly,the changes of microstructures and mechanical properties at different heating temperature and holding time are analyzed to achieve an appropriate annealing heat treatment process.Secondly,cold drawing is performed twice to analyze its influence on the microstructures of the annealed sucker rods.Finally,quenched-tempered heat treatment is performed on the cold-drawn sucker rods.The changes of physical and chemical properties and microstructures of the repaired sucker rods 30 CrMo are analyzed by means of SEM,X-ray diffraction,XRD,EBSD,universal testing machines,or the like,so as to verify the service performance of the repaired sucker rods 30 CrMo.The results show that steel sucker rods 30 CrMo are heated at 860? and held at this temperature for 60 minutes in the annealing process.The annealed sucker rods have yield strength of 390 MPa,tensile strength of 653 MPa and elongation of 28.88%.It can be seen that the tensile strength and yield strength of the sucker rods are obviously reduced and the elongation is obviously increased.The microstructures are uniform ferrite and pearlite,and the materials have low strength and good plasticity,thus being suitable to be subsequently drawn.The internal micr ostructures of the cold-drawn steel sucker rods 30 CrMo are obviously elongated and deformed in the cold-drawn direction,so that deformed ferrite+pearlite structures can be obtained,the formation of a large number of dislocation lines can be viewed,and a large number of dimple structures are formed at the tensile fracture surface.The drawn sucker rods are quenched at 880? and held at this temperature for 30 minutes and are tempered at 620? and held at this temperature for 60 minutes in the quenching and tempering process.The quenched and tempered steel sucker rods 30 CrMo have yield strength of 1032 MPa,tensile strength of 1058 MPa and elongation of 11.2%.The mechanical properties are significantly enhanced,the microstructures are tempered sorbite and a small amount of ferrite,and a large number of dimple structures can be viewed in the fracture area,which meets the requirements of the SY/T 5029-2013 standard.The yield strength and tensile strength of old steel sucker rods 30 CrMo can be significantly improved by means of the annealing-cold drawing-quenching and tempering.The properties of the old steel sucker rods 30 CrMo are enhanced by means of fatigue defects generated by repair in use,which meets the use requirements of new steel sucker rods 30 CrMo.