Study On Hot Deformation Behavior And Processing Map Of Drill Pipe Joint Steel Containing Niobium And Vanadium

With the development of ultra deep well technology,the performance requirements for drill pipe joints are constantly improving.At present,the highest strength drill pipe in the American Petroleum Institute（API）series uses S135 grade drill pipe joints,which are still powerless in the face of some ultra deep wells.Therefore,the research and application of new high-strength and high toughness drill pipe joint materials is of great significance for China’s oil and natural gas fields.Based on the above background,this article develops a new type of drill pipe joint steel by adding microalloy elements such as niobium and vanadium on the basis of S135 grade drill pipe joint steel.Niobium and vanadium can inhibit the recrystallization of austenite and prevent grain growth in the process of hot working,and improve the strength and toughness of the material.The drill pipe joint needs to undergo hot working processes such as rolling and forging in the production process,so the optimal hot working window can be determined by studying its hot deformation behavior.This article uses a Gleeble-3500 thermal simulation testing machine to conduct single pass compression tests on niobium vanadium bearing drill pipe joint steel at a deformation temperature of 950～1250℃,strain rate of 0.01～10 s^-1,and strain range of 0.7.The rheological curve and microstructure at high temperature were analyzed,and the Arrhenius type constitutive equation based on peak stress was established.The hot deformation activation energies of R1 and R2 test steels were 337.367 k J/mol and339.448 k J/mol,respectively.Considering the influence of strain,a constitutive model based on strain was also constructed,and the rheological stress of the test steel in the compression test range was predicted.Compare the predicted stress with the experimental stress,with a correlation coefficient of 0.9302 for R1 test steel and 0.98423 for R2 test steel.Based on the dynamic material model and Prasad flow instability criterion,the hot working diagrams of two test steels were drawn.According to the hot working diagram,the optimal hot working windows of R1 test steel at 0.7 strain are 1030～1250℃,0.01～0.026 s^-1,1159～1238℃,0.026～0.068 s^-1,and the optimal hot working windows of R2 test steel at0.7 strain are 1055～1250℃,0.05～0.12 s^-1,1130～1250℃,0.12～2.79 s^-1.