The Effect Of Cryogenic Treatment On The Corrosion Resistance Of 42CrMo

Drill pipe joints are key parts in oil and gas production.As the oil and gas industry gradually develops into open seas and deep wells,the downhole environment is getting worse and worse,and there are higher requirements for the material performance of drill pipe joints.Therefore,exploring the manufacturing process of drill pipe joints is of great value for improving oil and gas production efficiency and economic benefits.42CrMo alloy steel is a commonly used processing material for drill pipe joints,and the cryogenic treatment process has been proved to improve the overall performance of the material.Therefore,this article conducts electrochemical corrosion test and stress corrosion test on 42 Cr Mo alloy steel.To improve the corrosion resistance of 42 Cr Mo alloy steel,with the help of microscopic observation,phase analysis and other methods,in-depth study of the effect of cryogenic treatment on the corrosion resistance of 42 Cr Mo.The main research contents and conclusions of the thesis are as follows:(1)The cryogenic temperature was selected as the test variable for the cryogenic treatment test of 42 Cr Mo alloy steel.The microstructure of 42 Cr Mo alloy steel before and after the cryogenic treatment was observed and analyzed by scanning electron microscope,and it was found that the cryogenic treatment could promote the precipitation and precipitation of carbides in the grain interstices and defects,and the microstructure showed homogenization and densification.(2)Electrochemical corrosion tests were carried out on samples of each process group to study the effect of cryogenic treatment on the electrochemical corrosion performance of 42 Cr Mo alloy steel.After cryogenic treatment,the electrochemical impedance spectroscopy modulus of the process group increased,and the comparison of the polarization curves showed that the self-corrosion potential all moved to the positive direction,and the self-corrosion current density decreased.Among the three test groups,the self-corrosion current density of the-120? process group is the smallest,and the self-corrosion current density of the-160? process group is the largest.Observation of the sample by scanning electron microscope found that the surface corrosion morphology was significantly improved,indicating that the cryogenic treatment increased the electrochemical corrosion performance of 42 Cr Mo alloy steel.(3)The stress corrosion test was carried out on the samples of each process group to study the effect of cryogenic treatment on the stress corrosion performance of 42 Cr Mo alloy steel.It is found that the stress corrosion sensitivity indexes F(?)and F(A)of the process group after cryogenic treatment are better than those without cryogenic treatment.Among the three test groups,the corrosion sensitivity index of the-120? process group was the smallest,with a value of F(A)=34.22%;the corrosion sensitivity index of the-160? process group was the largest,with a value of F(A)=39.41%.Using scanning electron microscope to observe the fracture of the sample,it is found that the fracture mode of-120? and-190? process group is quasi-cleavage fracture,and the fracture mode of-160? process group is intergranular fracture,which is a typical cleavage fracture.(4)Through the finite element simulation analysis of the stress corrosion of42 Cr Mo alloy steel,the results show that after the tensile strain reaches the initial yield limit,as the cryogenic temperature decreases,the corrosion potential and the corrosion medium current density show a trend of first increasing and then decreasing.Cold temperature-120? has the smallest corrosion rate,and-160?has the largest corrosion rate.The finite element simulation results are consistent with the test results,indicating that the finite element simulation model has reference value for stress corrosion.