The Study On Recrystallization Behavior Of RE Drill Collar Steel During Hot Deformation

4145H drill collar steel is one of the most important petroleum drill, it not onlybear by tensile stress and compressive stress,but also worked by friction and bendingforce, and with the environment of drill collar exploratory drilling is going form bad toworse,it will also affected by corrosion from the mud or something else. So, theperformance of drill collar is becoming more and more strictly. It required that the drillcollar need to keep high strength, hardness and good plasticity, tenacity. Rare earthworked in steel can refine the crystalline structure, uniform organization, influence therecrystallization behavior of steel, thus to influence the mechanical properties of steel.This study analyzes4145H, by adding trace rare earths to study the effect of rare earthon the recrystallization behavior, it has a great practical and theoretical significance tomake full use of local resources and develop new type of drill collar steel.In this paper, adding6ppm and16ppm rare earth (Lanthanum cerium alloy) into4145H steel respectively, using Zeiss metallographic microscope and electronmicroscope to observe original forging stock structure and inclusion in4145H steel.Through this operation we can study the influence of rare earth addition for drill collarsteel organization and inclusion’s morphology、distribution、size and so on. By usingGleeble-1500D thermal simulator to perform single and double time compressionexperiment at4145H steel to study what kinds of influence will be made by the contentof rare earth and different deformation process parameters (the deformationtemperature:850℃,950℃,1050℃,1150℃; the deformation rate:0.01s-1,0.1s-1,1s-1)for4145H steel dynamic recrystallization behavior and static recrystallization behavior.use thermal chemical etching techniques reveal theprior-austenite grain boundaries of4145H; and use software of IPP measure the average size of defferent temperature andstrain rate of grain of4145H. Stress strain curve was studied to calculate the staticsoftening rate by double pass compression test.The static softening rate of steel withtwo different content of rare earth would be found by softening rules. The results show that there are obvious banded structure(Ferrite+Pearlite). Afterhigh temperature diffusion annealing，Observed microstructure we can found the16ppm RE of4145H can apparent restrain Eutectoid ferrite separating out，theinclusions are more smalland round, MnS change into REO and Oxysulfide of RE.REwhose content is16ppm in2#steel, can inhibit the dynamic recrystallization. When thecritical strain value is increased, RE aslo can delay the dynamic recrystallization.Thethermal simulated samples were etched to get the the original austenite grain boundaryby chemical etching method.The average size of the same temperature austenite grainsin the different strain rate was analyzed through the IPP software.It is showed that theaverage size of austenite grain in the0.1s-1strain rate is minimal,the size is5.52μm.Theinhibition period was prolonged with the increase amount of the static softeningincreased with temperature and the increasase of RE content.