Effect Of Rare Earth Ce On Recrystallization Behaviour In Hot Rolling And Microstructure And Properties Of4145H Drill Collar Steel

4145H steel has high hardenability and good mechanical properties, it is the most widely used steel in the production of drill collars. With the increase of the drilling depth and deterioration of drilling environment, higher requirements have been raised on the mechanical properties of drill collar steel. By using rare earth to improve steel’s microstructure, grain refinement, recrystallization behavior and other characteristics, study on the impacts of rare earth Ce on4145H drill collar steel was carried out, which is of great importance in enhancing the mechanical properties of drill collar steel.In this paper, three kinds of4145H drill collar steels (1#steel,2#steel and3#steel) with different contents of rare earth Ce (0ppm,120ppm and200ppm) were taken as study subjects. Gleeble-1500D thermal simulation testing machine was used to simulate the rolling process and obtain the true stress-strain curves derived from single-pass compression and double-pass compression, the recrystallization behavior was studied; many analytical and experimental machines and equipment such as metallurgical microscope, scanning electron microscopy, energy spectrometer, hardness tester and impact testing machine, were used for the analysis of microstructure and determination of impact properties, the obtained results were shown as below:According to the true stress-strain curves derived from single-pass compression test, when the rate of deformation was0.1s-1and deformation temperature was1050℃, the critical strain of dynamic recrystallization of1#steel,2#steel and3#steel were0.36,0.37and0.30respectively. The true stress-strain curves derived from double-pass compression test were used to calculate the static recrystallization volume fraction of the three experimental steels, it was drawn that the austenite recrystallization region of1#steel was above1050℃, partial recrystallization region was between980℃and1050℃, non-recrystallization region was below980℃; the austenite recrystallization region of2#steel was above1050℃, partial recrystallization region was between900℃and1050℃, non-recrystallization region was below900℃; the austenite recrystallization region of3#steel was above980℃, partial recrystallization region was between900℃and980℃, non-recrystallization region was below 900℃. Meanwhile, through two-pass compression test, the impacts of different deformation rates, deformation temperatures, deformation degrees, gap time and initial austenite grain sizes on the static recrystallization volume fraction were analyzed, Static recrystallization models of three kinds of experimental steels were established. In addition, through annealing experiment, the process that can meet the organizational performance requirements was obtained: the heating temperature of865℃, preserved heat for2.5hours, then lower the temperature to650℃at the speed of45℃/h and preserved heat for2hours, then cooled furnace. The results of the annealing experiment indicated that the crystalline grain and pearlite interlamellar spacing became more obvious with the increase of rare earth content. The results of room-temperature impact test showed that the room-temperature impact properties of4145H drill collar steel constantly increased with the increase of rare earth content, when the rare earth Ce content was200ppm, the steel had the best impact properties. Compared with the impact power experimental steel that contains no rare earth, its impact power increased from85.38J to98.06J, representing an increase of14.9%.The paper provides a basis for the optimization of4145H drill collar steel’s production engineering, and lays a theoretical foundation for the research on the adding of rare earth Ce into4145H drill collar steel.