Ultrahigh-strength drill rod pipe body, ultrahigh-strength drill rod and preparation method of ultrahigh-strength drill rod pipe body

Abstract

The invention discloses an ultrahigh-strength drill rod pipe body, an ultrahigh-strength drill rod and a preparation method of the ultrahigh-strength drill rod pipe body. Relates to the technical field of petroleum drill rods. The ultrahigh-strength drill rod pipe body comprises the following chemical components: 0.23%-0.29% of C, 0.20%-0.35% of Si, 0.62%-0.83% of Mn, less than or equal to 0.012% of P, less than or equal to 0.003% of S, 0.95%-1.05% of Cr, 0.40%-0.53% of Ni, 0.60%-0.72% of Mo, 0.06%-0.11% of V, 0.030%-0.045% of Ti, 0.003%-0.009% of Re, 0.010%-0.020% of Al, 0.009%-0.018% of Ca and the balance of Fe and inevitable impurities, and the contents of P, S, O, H and N are controlled. The drill rod pipe body has ultrahigh strength and good low-temperature toughness.

Description

Technical Field

[0001] This invention relates to the field of oil drill pipe technology, and in particular to an ultra-high strength drill pipe body, an ultra-high strength drill pipe, and a method for preparing the same. Background Technology

[0002] With the continuous development of oil and gas resource exploration and development, deep wells (4500-6000m), ultra-deep wells (6000-9000m), and extra-deep wells (9000-12000m) are becoming increasingly common, and drilling of 10,000-meter extra-deep wells has also begun. Breakthrough progress has been made in drilling technology for these ultra-deep and extra-deep wells. The basic requirements for drill pipes in ultra-deep and extra-deep well exploration and development are high strength and fatigue life to withstand high tensile, compressive, bending, and torsional combined loads and complex alternating loads, as well as high toughness and low-temperature toughness to ensure safe use of the drill pipe during operation (downhole temperatures can reach 250℃, and surface temperatures can reach -40℃). The highest strength level for drill pipes in existing ISO and API standards is 135ksi, while oil and gas exploration and development under complex conditions such as ultra-deep and extra-deep wells require drill pipes with a yield strength of 150ksi or higher. In reality, early fracture accidents frequently occur during the drilling of ultra-deep and extra-deep wells, severely impacting normal drilling and oil and gas development. There is an urgent need to develop ultra-high-strength drill pipes and their manufacturing technologies to meet current and future exploration and development needs for ultra-deep and extra-deep oil and gas reservoirs. However, higher material strength requires higher toughness to ensure safe use, and the relationship between strength and toughness is often inversely proportional, making the design and manufacture of ultra-high-strength drill pipes extremely difficult.

[0003] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide an ultra-high strength drill pipe body, an ultra-high strength drill pipe and its preparation method, aiming to provide an ultra-high strength drill pipe body and drill pipe with a steel grade of 150ksi and above and good low temperature toughness to meet the demand for ultra-high strength drill pipe in the development of oil and gas fields under harsh conditions such as ultra-deep and ultra-deep low temperature.

[0005] The technical solution of the present invention is as follows: In a first aspect, embodiments of the present invention provide an ultra-high strength drill pipe body, wherein, by mass percentage, the ultra-high strength drill pipe body comprises the following chemical components: C 0.23%~0.29%, Si 0.20%~0.35%, Mn 0.62%~0.83%, P≤0.012%, S≤0.003%, Cr0.95%~1.05%, Ni 0.40%~0.53%, Mo 0.60%~0.72%, V 0.06%~0.11%, Ti 0.030%~0.045%, Re 0.003%~0.009%, Al 0.010%~0.020%, Ca 0.009%~0.018%, O≤0.002%, H≤0.00015%, N≤0.005%, N+H+O≤0.007%, balance Fe and unavoidable impurities.

[0006] Optionally, the ultra-high strength drill pipe body comprises the following chemical components by weight percentage: C 0.23%~0.26%, Si 0.20%~0.25%, Mn 0.62%~0.69%, P≤0.012%, S≤0.002%, Cr0.95%~1.00%, Ni 0.40%~0.45%, Mo 0.60%~0.65%, V 0.06%~0.09%, Ti 0.030%~0.035%, Re 0.003%~0.008%, Al 0.010%~0.015%, Ca 0.009%~0.014%, O≤0.002%, H≤0.00015%, N≤0.0045%, balance Fe and unavoidable impurities.

[0007] Optionally, the ultra-high strength drill pipe body comprises the following chemical components by weight percentage: C 0.25%~0.28%, Si 0.26%~0.31%, Mn 0.70%~0.76%, P≤0.011%, S≤0.0018%, Cr 0.98%~1.03%, Ni 0.46%~0.51%, Mo 0.66%~0.71%, V 0.08%~0.11%, Ti 0.036%~0.041%, Re 0.005%~0.007%, Al 0.014%~0.016%, Ca 0.013%~0.016%, O≤0.0018%, H≤0.00014%, N≤0.0039%, balance Fe and unavoidable impurities.

[0008] Optionally, the ultra-high strength drill pipe body comprises the following chemical components by weight percentage: C 0.27%~0.29%, Si 0.29%~0.35%, Mn 0.77%~0.83%, P≤0.010%, S≤0.0019%, Cr 0.99%~1.05%, Ni 0.47%~0.53%, Mo 0.67%~0.72%, V 0.08%~0.10%, Ti 0.042%~0.045%, Re 0.006%~0.009%, Al 0.015%~0.020%, Ca 0.015%~0.018%, O≤0.0017%, H≤0.00013%, N≤0.0037%, balance Fe and unavoidable impurities.

[0009] A second aspect of the present invention provides a method for preparing the ultra-high strength drill pipe body as described above, comprising the following steps: After batching, smelting, and continuous casting according to the chemical composition of the ultra-high strength drill pipe body, a continuously cast billet is obtained. After hot piercing, controlled rolling and cooling, and residual heat treatment of the continuously cast bar billet, a tube billet is obtained; After thickening the tube ends, performing heat treatment on the entire tube body, hot straightening, and stress-relieving tempering on the tube blank, the ultra-high strength drill pipe body is obtained.

[0010] Optionally, the steps of obtaining a tube blank by hot piercing, controlled rolling and cooling, and residual heat treatment of the continuously cast bar billet specifically include: The continuously cast billet is heated to 1190–1210℃ in an annular heating furnace and held for 90–120 min. Hot piercing is then performed at 1150–1200℃, followed by hot continuous rolling at 900–1170℃. The rolling ratio is controlled to be ≥5, and the final rolling temperature is controlled to be 900℃. After controlled rolling and sizing, the billet is water-cooled at a rate controlled to be ≥25℃ / s. Finally, the billet is tempered at 680–710℃ for 60–90 min and then water-cooled.

[0011] Optionally, the steps of thickening the tube ends, performing heat treatment on the entire tube body, hot straightening, and stress-relieving tempering on the tube blank to obtain the ultra-high strength drill pipe body specifically include: The tube end of the tube blank is heated to 1050-1150°C, and upsetting is performed 1-3 times using the inner and outer diameter molds and the temperature gradient of the tube end to obtain a tube blank with thickened tube end. The tube blank with thickened ends is heated to 870-890℃ under a protective atmosphere and held for 40-60 minutes. It is then quenched by water spraying inside and outside the tube, with a cooling rate of ≥25℃ / s. Then, it is tempered at 540-590℃ for 90-120 minutes and water-cooled after tempering. Next, it is heated to 520-570℃ for hot straightening, and then stress-reduced tempered at 500-550℃ for 90-120 minutes and air-cooled after tempering to obtain the ultra-high strength drill pipe body.

[0012] A third aspect of the present invention provides an ultra-high strength drill pipe, wherein the ultra-high strength drill pipe includes a drill pipe body and a drill pipe joint connected to the drill pipe body by friction welding, and the drill pipe body is the ultra-high strength drill pipe body of the present invention as described above or an ultra-high strength drill pipe body prepared by the preparation method of the present invention as described above.

[0013] A fourth aspect of the present invention provides a method for preparing the ultra-high strength drill pipe as described above, comprising the following steps: The ultra-high strength drill rod is obtained by friction welding and heat treatment of the drill pipe body and drill pipe joint.

[0014] Optionally, the method for preparing the ultra-high strength drill pipe specifically includes the following steps: The inertial friction welding method is adopted, and the rotation speed, back pressure and upsetting pressure are controlled to weld the drill pipe body and the drill pipe joint together. At the moment after friction welding and upsetting, the temperature is 930-980℃. A mixture of water and compressed air is sprayed on the inner and outer surfaces of the weld area for quenching, and then the medium frequency induction heating is carried out to 670-700℃ for 5 minutes for tempering. Next, the weld area is heated to 870-890°C using medium-frequency induction heating. A mixture of water and compressed air is sprayed onto the inner and outer surfaces of the weld area for quenching. Then, the area is tempered by medium-frequency induction heating to 650-680°C and held for 5 minutes to obtain the ultra-high strength drill rod.

[0015] Beneficial effects: The ultra-high strength drill pipe body provided by this invention has comprehensive properties such as high strength, good plasticity, and low-temperature toughness. The specified minimum yield strength reaches steel grades of 150ksi, 155ksi, 160ksi, 165ksi, 170ksi, and 175ksi, respectively. The room temperature yield strength is 1135-1281MPa, the tensile strength is 1220-1377MPa, the elongation is 17%-22%, and the longitudinal Charpy V-notch impact toughness at -40℃ is 103-157J. It can meet the requirements of high-strength and high-low temperature toughness drill pipes for deep and ultra-deep low-temperature and complex oil and gas field development, and has good safety reliability and service life. Detailed Implementation

[0016] This invention provides an ultra-high strength drill pipe body, an ultra-high strength drill pipe, and a method for preparing the same. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0018] This invention provides an ultra-high strength drill pipe body, wherein, by mass percentage, the ultra-high strength drill pipe body comprises the following chemical components: C 0.23%~0.29%, Si 0.20%~0.35%, Mn 0.62%~0.83%, P≤0.012%, S≤0.003%, Cr0.95%~1.05%, Ni 0.40%~0.53%, Mo 0.60%~0.72%, V 0.06%~0.11%, Ti 0.030%~0.045%, Re 0.003%~0.009%, Al 0.010%~0.020%, Ca 0.009%~0.018%, O≤0.002%, H≤0.00015%, N≤0.005%, N+H+O≤0.007%, balance Fe and unavoidable impurities.

[0019] Re is a rare earth element, and in some specific embodiments, Re can be Ce (cerium).

[0020] In terms of composition design, this invention aims to meet multiple requirements for drill pipe bodies, including high strength, good plasticity, low-temperature toughness, and processing performance. It uses medium-low carbon (C), alloyed with Mn, Cr, Ni, and Mo, and micro-alloyed with V and Ti. Rare earth (Re) elements are added, and harmful elements such as P, S, O, H, and N are controlled. Al and Si fully deoxidized killed steel is used, and the molten steel is treated with Ca. Through the individual effects of C and alloying elements, especially their synergistic effects, the performance of the drill pipe body is improved. Specifically, the hardenability of the steel is improved through the synergistic effect of C-Cr-Mo-Ni-Mn; purification is achieved through the control of P, S, O, H, and N; grain refinement is achieved through the synergistic effect of V-Ti-Al; inclusions are modified through the synergistic effect of Ca-Re; and the performance of the weld heat-affected zone is improved through the synergistic effect of V-Ti-Al. This lays the foundation for the drill pipe to achieve comprehensive performance such as high strength, good plasticity, and low-temperature toughness. Ultimately, the specified minimum yield strength of the drill pipe body reaches steel grades of 150ksi, 155ksi, 160ksi, 165ksi, 170ksi, and 175ksi, respectively, with a room temperature yield strength of 1135–1281 MPa, a tensile strength of 1220–1377 MPa, an elongation of 17%–22%, and a longitudinal Charpy V-notch impact toughness of 103–157 J at -40℃. This meets the requirements for high-strength, high-low temperature toughness drill pipes in deep and ultra-deep cryogenic and complex oil and gas field development, and also possesses good safety, reliability, and service life.

[0021] The roles and content ranges of each element are as follows: C (carbon): It is the most important strengthening element. Too low a content is not conducive to improving hardenability and strength, while too high a content is detrimental to ductility and toughness. Taking all factors into consideration, it is advisable to control it within the range of 0.23% to 0.29%.

[0022] Silicon (Si) is the main deoxidizing element. Too low a content will affect the deoxidation effect, while too high a content will cause a decrease in plasticity and toughness. Taking all factors into consideration, it is advisable to control it within the range of 0.20% to 0.35%.

[0023] Manganese (Mn) is mainly used to improve the hardenability of steel, thereby increasing its strength. However, it has a strong tendency to segregate and needs to be properly controlled. Considering all factors, it is advisable to control it within the range of 0.62% to 0.83%.

[0024] Cr (chromium): Primarily used to improve the hardenability of steel, thereby increasing its strength and tempering stability. It also enhances the steel's corrosion resistance; however, excessive content increases costs. Considering all factors, it is advisable to control it within the range of 0.95% to 1.05%.

[0025] Ni (Ni): Primarily used to improve the hardenability of steel, thereby increasing its strength and low-temperature toughness. It also improves the corrosion resistance of steel. Its synergistic effect with Cr and Mo yields even better results, but excessively high content increases costs. Considering all factors, it is advisable to control its content within the range of 0.40% to 0.53%.

[0026] Mo (Mo): Primarily used to improve the hardenability of steel, thereby increasing its strength and tempering stability; Mo can suppress temper brittleness; synergistically with microalloying elements such as V, it can form carbides such as Mo2C, enhancing precipitation strengthening; Mo can inhibit austenite grain growth, refine the microstructure, and improve the high-temperature strength of steel; it can also improve the corrosion resistance of steel, but excessive content will increase costs. Considering all factors, it is advisable to control it within the range of 0.60% to 0.72%.

[0027] Vanadium (V): In steel, V primarily enhances overall performance through precipitation strengthening, grain refinement and toughening, and hardenability regulation. V combines with carbon and nitrogen to form fine VC, VN, or V(C,N) nanoprecipitates. These particles can precipitate in both austenite and ferrite, effectively hindering dislocation movement and increasing steel strength. During high-temperature tempering, V carbonitrides inhibit softening and improve tempering stability. V inhibits austenite grain growth, especially in the weld heat-affected zone (HAZ), where V carbonitrides pin grain boundaries, reducing coarse-grained regions and refining the final microstructure, thus improving the strength and toughness of the HAZ. V not only improves strength by refining grains but also significantly improves low-temperature impact toughness. V also enhances hardenability; when synergistically combined with elements such as Mn and Cr, V can further optimize hardenability. V carbides exhibit high-temperature stability, effectively resisting softening in the high-temperature environment of deep wells. The synergistic effect of V with microalloying elements such as Ti can further unleash its potential. However, excessive V may increase brittleness and cost due to the formation of coarse carbonitrides. Considering all factors, it is advisable to control it within the range of 0.06% to 0.11%.

[0028] Titanium (Ti): In steel, Ti enhances overall performance primarily through precipitation strengthening, grain refinement and toughening, and microstructure regulation. Ti combines with C and N to form fine TiC, TiN, or composite carbonitrides (such as Ti4C2S2). These nanoscale precipitates effectively hinder dislocation movement, significantly improving steel strength. TiN preferentially precipitates in the high-temperature austenite region, inhibiting grain growth and refining the original austenite grains, thereby improving the steel's strength and toughness. The fine-grained structure also improves the steel's low-temperature impact toughness and fatigue resistance. The addition of Ti can form a dense passivation film (such as TiO2), enhancing the steel's corrosion resistance in corrosive environments containing H2S and CO2. Ti combines with N to form high-melting-point TiN particles (stable to approximately 1400℃), which pin austenite grain boundaries during the high-temperature thermal cycling of welding, effectively preventing grain coarsening. The refined austenite grains transform into an even finer microstructure upon cooling, thereby improving the strength and toughness of the heat-affected zone. TiN particles can act as nucleation sites for phase transformation, promoting the formation of phase transformation structures and significantly improving the low-temperature impact toughness of the heat-affected zone. However, excessive Ti may lead to the precipitation of coarse TiN phases, causing brittleness and increasing costs. Considering all factors, it is advisable to control the content within the range of 0.030% to 0.045%.

[0029] Re (rare earth elements) has the following functions: Purifying molten steel and improving the morphology of inclusions: Specifically, Re can combine with impurities such as S and O to form high-melting-point compounds such as Re2O3 and Re2S3, reducing harmful inclusions (such as MnS) and improving the purity of steel.

[0030] Changing the morphology of sulfides (from elongated to spherical) improves the transverse impact toughness of steel.

[0031] Refines grain size and improves strength and toughness. Specifically, Re can inhibit austenite grain growth, refine the microstructure, and improve the strength and toughness of steel.

[0032] To improve corrosion resistance, specifically, Re can form a dense oxide film on the steel surface, thereby improving corrosion resistance.

[0033] However, excessively high Re content may lead to the aggregation of inclusions and increase costs. Taking all factors into consideration, it is advisable to control it within the range of 0.003% to 0.009%.

[0034] Ca (calcium) has the following functions: Inclusion modification improves toughness. Specifically, Ca can combine with S and O in steel to form CaS, CaO or composite calcium aluminate (CaO·Al2O3), which transforms brittle MnS inclusions into spherical or spindle-shaped structures, reduces anisotropy, and improves transverse impact toughness.

[0035] To improve corrosion resistance, specifically, Ca treatment can optimize the oxide film structure on the steel surface, improve corrosion resistance in corrosive environments containing H2S, CO2, etc., and reduce pitting corrosion and stress corrosion cracking (SCC).

[0036] Improving continuous casting processability: Specifically, Ca can prevent Al2O3 from forming nodules at the continuous casting nozzle, thus improving the surface quality of the continuously cast billet. However, excessive addition may lead to liquid calcium aluminate inclusions, affecting purity. Considering all factors, it is advisable to control the content within the range of 0.009% to 0.018%.

[0037] Al (aluminum) has the following functions: Deoxidation and purification of molten steel: Specifically, Al is a strong deoxidizer, preferentially combining with O in molten steel to form Al2O3, reducing oxide inclusions in the steel and improving the purity of the steel.

[0038] Refining grains improves strength and toughness. Specifically, Al combines with N to form AlN, which pins austenite grain boundaries during hot rolling or welding, inhibits grain growth, and refines the final microstructure (ferrite / bainite). Grain refinement can simultaneously improve the strength and toughness of steel and lower the ductile-brittle transition temperature.

[0039] Improving weldability: Specifically, an appropriate amount of Al can reduce grain coarsening in the heat-affected zone of the weld and improve weld toughness.

[0040] However, excessive Al content can lead to the formation of excessive Al2O3 hard inclusions, affecting the fatigue properties of the steel. Furthermore, the formation of coarse AlN may promote embrittlement in the weld heat-affected zone. Considering all factors, the Al content should be controlled within the range of 0.010% to 0.020%.

[0041] P (phosphorus): A harmful element that mainly affects the ductility, toughness, and corrosion resistance of steel. It is advisable to control P to ≤0.012%.

[0042] Sulfur (S): A harmful element that mainly affects the ductility, toughness, and corrosion resistance of steel. It is advisable to control S to ≤0.003%.

[0043] O (O): A harmful element that mainly affects the ductility, toughness, and corrosion resistance of steel. O should be controlled to ≤0.002%. H (hydrogen): A harmful element that mainly affects the ductility, toughness, and corrosion resistance of steel. H should be controlled to ≤0.00015%.

[0044] Nitrogen (N): A harmful element that primarily affects the ductility, toughness, and corrosion resistance of steel. It is advisable to control N to ≤0.005%.

[0045] At the same time, N+H+O ≤ 0.007%.

[0046] Meanwhile, Mo / P ≥ 50 (i.e., the ratio of Mo mass percentage to P mass percentage is greater than or equal to 50) is controlled to mitigate the adverse effects of P segregation on toughness; Al / N ≥ 2 is controlled to eliminate the adverse effects of N on toughness and strain aging properties; Ca / S ≥ 3 and (Ca+Re) / S ≥ 4 are controlled to control the effect of inclusion shape modification treatment and improve the ductility, toughness and corrosion resistance of steel.

[0047] In some embodiments, the ultra-high strength drill pipe body comprises the following chemical components by weight percentage: C 0.23%~0.26%, Si 0.20%~0.25%, Mn 0.62%~0.69%, P≤0.012%, S≤0.002%, Cr0.95%~1.00%, Ni 0.40%~0.45%, Mo 0.60%~0.65%, V 0.06%~0.09%, Ti 0.030%~0.035%, Re 0.003%~0.008%, Al 0.010%~0.015%, Ca 0.009%~0.014%, O≤0.002%, H≤0.00015%, N≤0.0045%, balance Fe and unavoidable impurities.

[0048] In this embodiment, the minimum yield strength level of the ultra-high strength drill pipe body can reach 150-155 ksi, the room temperature yield strength is 1135-1163 MPa, the tensile strength is 1220-1251 MPa, the elongation is 21%-22%, and the longitudinal Charpy V-notch impact toughness at -40℃ is 142-157 J.

[0049] In some embodiments, the ultra-high strength drill pipe comprises the following chemical components by weight percentage: C 0.23%~0.25%, Si 0.20%~0.22%, Mn 0.62%~0.65%, P≤0.012%, S≤0.002%, Cr0.95%~0.97%, Ni 0.40%~0.42%, Mo 0.60%~0.62%, V 0.06%~0.08%, Ti 0.030%~0.032%, Re 0.003%~0.005%, Al 0.010%~0.012%, Ca 0.009%~0.011%, O≤0.002%, H≤0.00015%, N≤0.0045%, with the balance being Fe and other unavoidable impurities.

[0050] In this embodiment, the minimum yield strength level of the ultra-high strength drill pipe body can reach 150 ksi, the room temperature yield strength is 1135-1141 MPa, the tensile strength is 1220-1227 MPa, the elongation is 22%, and the longitudinal Charpy V-notch impact toughness of the pipe body at -40℃ is 152-157 J.

[0051] In some embodiments, the ultra-high strength drill pipe comprises the following chemical components by weight percentage: C 0.24%~0.26%, Si 0.23%~0.25%, Mn 0.66%~0.69%, P≤0.011%, S≤0.0019%, Cr 0.98%~1.00%, Ni 0.43%~0.45%, Mo 0.63%~0.65%, V 0.07%~0.09%, Ti 0.033%~0.035%, Re 0.006%~0.008%, Al 0.013%~0.015%, Ca 0.012%~0.014%, O≤0.0019%, H≤0.00014%, N≤0.0042%, with the balance being Fe and other unavoidable impurities.

[0052] In this embodiment, the minimum specified yield strength level of the ultra-high strength drill pipe body can reach 155 ksi, the room temperature yield strength is 1157-1163 MPa, the tensile strength is 1244-1251 MPa, the elongation is 21%, and the longitudinal Charpy V-notch impact toughness of the pipe body at -40℃ is 142-145 J.

[0053] In some embodiments, the ultra-high strength drill pipe body comprises the following chemical components by weight percentage: C 0.25%~0.28%, Si 0.26%~0.31%, Mn 0.70%~0.76%, P≤0.011%, S≤0.0018%, Cr 0.98%~1.03%, Ni 0.46%~0.51%, Mo 0.66%~0.71%, V 0.08%~0.11%, Ti 0.036%~0.041%, Re 0.005%~0.007%, Al 0.014%~0.016%, Ca 0.013%~0.016%, O≤0.0018%, H≤0.00014%, N≤0.0039%, balance Fe and unavoidable impurities.

[0054] In this embodiment, the minimum yield strength level of the ultra-high strength drill pipe body can reach 160-165 ksi, the room temperature yield strength is 1185-1223 MPa, the tensile strength is 1274-1315 MPa, the elongation is 19%-20%, and the longitudinal Charpy V-notch impact toughness at -40℃ is 122-134 J.

[0055] In some embodiments, the ultra-high strength drill pipe comprises the following chemical components by weight percentage: C 0.25%~0.27%, Si 0.26%~0.28%, Mn 0.70%~0.72%, P≤0.011%, S≤0.0018%, Cr 1.01%~1.03%, Ni 0.46%~0.48%, Mo 0.66%~0.68%, V 0.08%~0.10%, Ti 0.036%~0.038%, Re 0.005%~0.007%, Al 0.014%~0.016%, Ca 0.013%~0.015%, O≤0.0018%, H≤0.00014%, N≤0.0039%, with the balance being Fe and other unavoidable impurities.

[0056] In this embodiment, the minimum specified yield strength level of the drill pipe can reach 160 ksi, the room temperature yield strength is 1185-1190 MPa, the tensile strength is 1274-1280 MPa, the elongation is 20%, and the longitudinal Charpy V-notch impact toughness of the pipe body at -40℃ is 131-134 J.

[0057] In some embodiments, the ultra-high strength drill pipe body comprises the following chemical components by weight percentage: C 0.26%~0.28%, Si 0.29%~0.31%, Mn 0.73%~0.76%, P≤0.011%, S≤0.0017%, Cr 0.98%~1.01%, Ni 0.49%~0.51%, Mo 0.69%~0.71%, V 0.09%~0.11%, Ti 0.039%~0.041%, Re 0.005%~0.007%, Al 0.014%~0.016%, Ca 0.014%~0.016%, O≤0.0018%, H≤0.00013%, N≤0.0038%, with the balance being Fe and other unavoidable impurities.

[0058] In this embodiment, the minimum specified yield strength level of the ultra-high strength drill pipe body can reach 165 ksi, the room temperature yield strength is 1218-1223 MPa, the tensile strength is 1310-1315 MPa, the elongation is 19%, and the longitudinal Charpy V-notch impact toughness of the pipe body at -40℃ is 122-125 J.

[0059] In some embodiments, the ultra-high strength drill pipe body comprises the following chemical components by weight percentage: C 0.27%~0.29%, Si 0.29%~0.35%, Mn 0.77%~0.83%, P≤0.010%, S≤0.0019%, Cr 0.99%~1.05%, Ni 0.47%~0.53%, Mo 0.67%~0.72%, V 0.08%~0.10%, Ti 0.042%~0.045%, Re 0.006%~0.009%, Al 0.015%~0.020%, Ca 0.015%~0.018%, O≤0.0017%, H≤0.00013%, N≤0.0037%, balance Fe and unavoidable impurities.

[0060] In this embodiment, the minimum yield strength level of the ultra-high strength drill pipe body can reach 170-175 ksi, the room temperature yield strength is 1240-1281 MPa, the tensile strength is 1333-1377 MPa, the elongation is 17%-18%, and the longitudinal Charpy V-notch impact toughness at -40℃ is 103-114 J.

[0061] In some embodiments, the ultra-high strength drill pipe body comprises the following chemical components by weight percentage: C 0.27%~0.29%, Si 0.32%~0.34%, Mn 0.77%~0.79%, P≤0.010%, S≤0.0019%, Cr 0.99%~1.02%, Ni 0.47%~0.49%, Mo 0.69%~0.72%, V 0.08%~0.10%, Ti 0.042%~0.044%, Re 0.006%~0.008%, Al 0.015%~0.017%, Ca 0.015%~0.017%, O≤0.0017%, H≤0.00013%, N≤0.0037%, with the balance being Fe and other unavoidable impurities.

[0062] In this embodiment, the minimum yield strength level of the ultra-high strength drill pipe body can reach 170 ksi, the room temperature yield strength is 1240-1245 MPa, the tensile strength is 1333-1339 MPa, the elongation is 18%, and the longitudinal Charpy V-notch impact toughness of the pipe body at -40℃ is 111-114 J.

[0063] In some embodiments, the ultra-high strength drill pipe body comprises the following chemical components by weight percentage: C 0.27%~0.29%, Si 0.29%~0.35%, Mn 0.80%~0.83%, P≤0.010%, S≤0.0018%, Cr 1.03%~1.05%, Ni 0.51%~0.53%, Mo 0.67%~0.71%, V 0.08%~0.10%, Ti 0.043%~0.045%, Re 0.007%~0.009%, Al 0.018%~0.020%, Ca 0.016%~0.018%, O≤0.0017%, H≤0.00012%, N≤0.0037%, with the balance being Fe and other unavoidable impurities.

[0064] In this embodiment, the minimum specified yield strength level of the ultra-high strength drill pipe body can reach 175 ksi, the room temperature yield strength is 1273-1281 MPa, the tensile strength is 1369-1377 MPa, the elongation is 17%, and the longitudinal Charpy V-notch impact toughness of the pipe body at -40℃ is 103-106 J.

[0065] This invention develops a matching preparation process for the aforementioned proportions of chemical composition. This process primarily involves steelmaking (including ladle refining and vacuum degassing), continuous casting (electromagnetic stirring and light reduction), hot rolling in the austenitic region, controlled rolling and cooling, residual heat treatment during rolling, pipe end thickening, full-body tempering heat treatment, hot straightening, and stress-relief tempering. These processes enable the material to obtain a fine and uniform tempered sorbite microstructure, achieving a reasonable balance of high strength, plasticity, and low-temperature toughness. Specifically, this invention also provides a method for preparing an ultra-high strength drill pipe body, comprising the following steps: S1. Based on the chemical composition of the ultra-high strength drill pipe, the raw materials are batched, smelted, and continuously cast to obtain a continuously cast billet. S2. After hot piercing, controlled rolling and cooling, and residual heat treatment of the continuously cast bar billet, a tube billet is obtained. S3. After thickening the tube ends, performing heat treatment on the entire tube body, hot straightening, and stress-relieving tempering on the tube blank, the drill pipe body is obtained.

[0066] The ultra-high strength drill pipe body prepared by the preparation method provided by this invention is a drill pipe body for the development of deep and complex oil and gas fields. It has high strength and excellent comprehensive properties such as plasticity and low temperature toughness. The specified minimum yield strength of the ultra-high strength drill pipe body reaches steel grades of 150ksi, 155ksi, 160ksi, 165ksi, 170ksi and 175ksi respectively. The room temperature yield strength is 1135-1281MPa, the tensile strength is 1220-1377MPa, the elongation is 17-22%, and the longitudinal Charpy V-notch impact toughness of the pipe body at -40℃ is 103-157J.

[0067] In step S1, in some embodiments, the step of obtaining a continuously cast billet after batching, smelting, and continuous casting according to the chemical composition of the ultra-high strength drill pipe specifically includes: The process involves batching materials according to the chemical composition of the ultra-high strength drill rod, followed by oxygen-blown converter steelmaking, feeding rare earth wire (feeding Si-Ca wire to control the shape modification of inclusions in the steel), ladle refining, and vacuum degassing to obtain molten steel. The molten steel is cast into a rod-shaped continuous casting billet (electromagnetic stirring and light reduction technology are used in the continuous casting process to control segregation in the continuous casting billet).

[0068] The steps in this embodiment can improve purity and uniformity, reduce segregation, and control the modification of inclusions.

[0069] In step S2, in some embodiments, the step of obtaining a tube blank after hot piercing, controlled rolling and cooling, and residual heat treatment of the continuously cast bar billet specifically includes: The continuously cast billet is heated to 1190–1210℃ in an annular heating furnace and held for 90–120 min. Hot piercing is then performed at 1150–1200℃, followed by hot continuous rolling at 900–1170℃. The rolling ratio is controlled to be ≥5, and the final rolling temperature is controlled to be 900℃. After controlled rolling and sizing, the billet is water-cooled at a rate controlled to be ≥25℃ / s. Finally, the billet is tempered at 680–710℃ for 60–90 min and then water-cooled.

[0070] In this embodiment, controlling the rolling ratio to be ≥5 and the final rolling temperature to be 900℃ is to obtain a finer and more uniform microstructure; controlling the cooling rate to be ≥25℃ / s is to obtain a fully martensitic quenched structure so that a fine and uniform tempered sorbite structure can be obtained after tempering; water cooling after tempering is used to avoid possible temper brittleness. Utilizing the residual heat from rolling for heat treatment can reduce one repeated heating and save energy.

[0071] In step S3, in some embodiments, the steps of thickening the tube ends, performing heat treatment on the entire tube body, hot straightening, and stress-relieving tempering on the tube blank to obtain the ultra-high strength drill pipe body specifically include: The tube end of the tube blank is heated to 1050-1150°C, and upsetting is performed 1-3 times using the inner and outer diameter molds and the temperature gradient of the tube end to obtain a tube blank with thickened tube end. The tube blank with thickened ends is heated to 870-890℃ under a protective atmosphere and held for 40-60 minutes. It is then quenched by water spraying inside and outside the tube, with a cooling rate of ≥25℃ / s. Then, it is tempered at 540-590℃ for 90-120 minutes and water-cooled after tempering. Next, it is heated to 520-570℃ for hot straightening, and then stress-reduced tempered at 500-550℃ for 90-120 minutes and air-cooled after tempering to obtain the ultra-high strength drill pipe body.

[0072] In this embodiment, heating under a protective atmosphere is used to prevent decarburization. The quenching followed by high-temperature tempering heat treatment process eliminates non-martensitic structures formed during pipe end thickening. Recrystallization refines the grains and microstructure of the pipe end and body. Internal and external water-spray quenching with a cooling rate ≥25℃ / s ensures that almost all martensite is obtained after quenching, and fine, uniform tempered sorbite is obtained after tempering. Water cooling after tempering avoids potential temper brittleness. Hot straightening reduces work hardening and residual stress during the straightening process. Stress-relief tempering effectively eliminates or reduces residual stress generated during hot straightening. Reduction of residual stress significantly improves the fatigue life of the drill pipe body. This embodiment also provides an ultra-high strength drill pipe, comprising a drill pipe body and a drill pipe joint connected to the drill pipe body by friction welding. The drill pipe body is the ultra-high strength drill pipe body described above or an ultra-high strength drill pipe body prepared using the preparation method described above.

[0073] The ultra-high strength drill pipe provided by this invention possesses comprehensive properties such as high strength, good plasticity, and low-temperature toughness. It specifies minimum yield strengths of 150ksi, 155ksi, 160ksi, 165ksi, 170ksi, and 175ksi steel grades. The room temperature yield strength of the drill pipe body is 1135–1281 MPa, the tensile strength is 1220–1377 MPa, the elongation is 17%–22%, and the longitudinal Charpy V-notch impact toughness at -40℃ is 103–157 J. The weld bearing capacity is greater than that of the pipe body; the transverse Charpy V-notch impact toughness of the drill pipe weld at -40℃ is 61–89 J. It can meet the requirements for high-strength, high-low-temperature toughness drill pipes in deep and ultra-deep cryogenic and complex oil and gas field development, and also has good safety, reliability, and service life.

[0074] In some implementations, the inner surface of the drill pipe may be coated to improve its corrosion resistance and corrosion fatigue resistance.

[0075] This invention also provides a method for preparing the ultra-high strength drill pipe as described above, comprising the following steps: The ultra-high strength drill rod is obtained by friction welding and heat treatment of the drill pipe body and drill pipe joint.

[0076] The preparation method of the drill pipe body is the same as that of the ultra-high strength drill pipe body described above.

[0077] In some embodiments, the method for preparing the ultra-high strength drill pipe specifically includes the following steps: The inertial friction welding method is used to control the rotation speed, back pressure and upsetting pressure to weld the drill pipe body and drill pipe joint together. At the moment after friction welding and upsetting, the temperature is 930-980℃. A mixture of water and compressed air is sprayed on the inner and outer surfaces of the weld area for quenching. Then, the surface is heated to 670-700℃ by medium frequency induction heating for 5 minutes for tempering (after which the flash and burrs inside and outside the weld area are processed). Next, the weld area is heated to 870-890°C using medium-frequency induction heating. A mixture of water and compressed air is sprayed onto the inner and outer surfaces of the weld area for quenching. Then, the area is tempered by medium-frequency induction heating to 650-680°C and held for 5 minutes to obtain the ultra-high strength drill rod.

[0078] In this embodiment, utilizing the residual heat from friction welding for weld heat treatment organically combines phase transformation strengthening and deformation strengthening, significantly improving the overall performance of the weld. Utilizing the residual heat from friction welding for heat treatment also saves energy. Medium-frequency induction heating and high-temperature tempering are beneficial for removing burrs and flash from both inside and outside the weld zone.

[0079] The present invention will be further described below through specific embodiments.

[0080] Example 1 This embodiment provides 18 types of ultra-high strength drill pipes and their preparation methods. The ultra-high strength drill pipe includes a drill pipe body and a drill pipe joint connected to the drill pipe body by friction welding.

[0081] The chemical compositions of the 18 types of drill pipe tubing are shown in Tables 1-1, 1-2, and 1-3 (the chemical compositions of drill pipe tubing types 1 to 6 are shown in Table 1-1, types 7 to 12 are shown in Table 1-2, and types 13 to 18 are shown in Table 1-3). Some process parameters are shown in Table 2. In Tables 1-1, 1-2, 1-3, and 2, number 1 corresponds to the first type of drill pipe tubing, number 2 corresponds to the second type, and number 3 corresponds to the third type. Specifically, number 1 in Table 1-1 corresponds to the chemical composition of the first type of drill pipe tubing, and number 1 in Table 2 corresponds to some process parameters of the first type of drill pipe tubing. The remaining numbers follow the same pattern.

[0082] The method for preparing ultra-high strength drill pipe includes the following steps: ① Steelmaking: According to the chemical composition of different drill pipe bodies in Table 1, the raw materials are batched, and steelmaking is carried out in an oxygen-blown converter. Rare earth (Re) wire is fed, and after ladle refining and vacuum degassing, Si-Ca wire is fed to control the shape modification of inclusions in the steel to obtain molten steel (containing the chemical composition in Table 1).

[0083] ② Continuous casting: The molten steel is poured into a rod-shaped continuous casting billet. Electromagnetic stirring and light reduction technology are used in the continuous casting process to control segregation in the continuous casting billet.

[0084] ③ Piercing, controlled rolling and cooling and residual heat treatment: The continuously cast billet is heated in an annular heating furnace at a temperature of 1200℃ for 120 minutes. Hot piercing is performed at 1200℃. Controlled rolling and cooling process is adopted, and hot continuous rolling is performed at a temperature of 900-1170℃ (initial rolling temperature of 1170℃ and final rolling temperature of 900℃). The rolling ratio is controlled at 5. After rolling and sizing, it is water cooled at a controlled cooling rate of 25℃ / s. Then it is tempered at 700℃ for 90 minutes and water cooled after tempering.

[0085] ④ Pipe end thickening: Heat the pipe end to 1100℃, and use the inner and outer diameter molds and the pipe end temperature gradient to perform three upsetting forgings to obtain the inner and outer thickening dimensions and shape of the pipe end, forming the drill pipe body.

[0086] ⑤ Full-body heat treatment, hot straightening, and stress-relief tempering: A protective atmosphere furnace is used for heating (to prevent decarburization). The quenching temperature is controlled at 880℃, with a holding time of 60 minutes. Water is sprayed internally and externally for quenching, with a cooling rate of 25℃ / s to ensure that almost all martensite is obtained after quenching. Then, tempering is performed at a temperature controlled at 540–590℃ (the tempering temperature is adjusted according to different steel grades of high-strength drill pipe bodies, see Table 2 for details), with a tempering time of 120 minutes. The microstructure is fine and uniform tempered sorbite with a grain size of 9–10. After tempering, the drill pipe body is water-cooled. The drill pipe body is then heated to 520–570℃ for hot straightening, followed by stress-relief tempering at 500–550℃ for 120 minutes, and then air-cooled to obtain the drill pipe body (the hot straightening temperature and stress-relief tempering temperature are adjusted according to different steel grades of the drill pipe body, see Table 2 for details).

[0087] ⑥ Friction welding and heat treatment of drill pipe body and drill pipe joint: Select a suitable drill pipe joint and use inertial friction welding method, reasonably control the rotation speed, back pressure and upsetting pressure to firmly weld the drill pipe body and drill pipe joint together. Immediately after friction welding upsetting (950℃), spray a mixture of water and compressed air onto the inner and outer surfaces of the weld area for quenching, then induction heat to 690℃ for 5 minutes for tempering. The weld microstructure is tempered sorbite, and the heat-affected zone is a mixture of tempered sorbite, pearlite and ferrite. Then, remove burrs and flash from the inner and outer surfaces of the weld area.

[0088] ⑦ Secondary heat treatment of the welded area: The weld area is heated to 880°C using medium-frequency induction heating. A mixture of water and compressed air is sprayed onto the inner and outer surfaces of the weld area for quenching. Then, the area is tempered to 670°C for 5 minutes using medium-frequency induction heating.

[0089] In other words, among the above 18 types of ultra-high strength drill pipes, only the process parameters for tempering, hot straightening, and stress-relief tempering in the whole-pipe heat treatment process are different; the other steps are the same.

[0090] Table 1-1 Chemical Composition of Drill Pipe Types 1 to 6

[0091] Table 1-2 Chemical Composition of Drill Pipe Types 7 to 12

[0092] Table 1-3 Chemical Composition of Drill Pipe Types 13 to 18

[0093] In Tables 1-1, 1-2, and 1-3, the balance is Fe and unavoidable impurities. Additionally, taking 150ksi in parentheses after number 1 as an example, it indicates that the first type of drill pipe corresponding to number 1 is a 150ksi grade drill pipe; the rest follow the same principle.

[0094] Table 2. Some process parameters

[0095] Mechanical properties tests were conducted on the ultra-high strength drill pipes prepared above, specifically room temperature yield strength, tensile strength, elongation, longitudinal Charpy V-notch impact toughness of the pipe body at -40℃, and transverse Charpy V-notch impact toughness of the drill pipe weld at -40℃. The results are shown in Table 3 (in Table 3, number 1 corresponds to the mechanical properties of the first type of ultra-high strength drill pipe mentioned above, number 2 corresponds to the mechanical properties of the second type of ultra-high strength drill pipe mentioned above, and so on for the remaining numbers).

[0096] Table 3. Test results of mechanical properties of 18 types of ultra-high strength drill pipes

[0097] Note: 150ksi and 155ksi grade drill pipes have an outer diameter of 5 7 / 8 in (149.22 mm) and a wall thickness of 9.17 mm; 160ksi and 165ksi grade drill pipes have an outer diameter of 5 7 / 8 in (149.22 mm) and a wall thickness of 11.50 mm; 170ksi and 175ksi grade drill pipes have an outer diameter of 5 7 / 8 in (149.22 mm) and a wall thickness of 13.26 mm.

[0098] The test results above show that the ultra-high strength drill pipe of this invention has excellent comprehensive performance. The specified minimum yield strengths reach 150 kSi, 155 kSi, 160 kSi, 165 kSi, 170 kSi, and 175 kSi, respectively. The mechanical properties of the pipe body are: room temperature yield strength of 1135–1281 MPa, tensile strength of 1220–1377 MPa, elongation of 17–22%, and longitudinal Charpy V-notch impact toughness of 103–157 J at -40℃. The weld bearing capacity is greater than that of the pipe body; the transverse Charpy V-notch impact toughness of the drill pipe weld at -40℃ is 61–89 J. A reasonable balance of high strength, plasticity, and low-temperature toughness is achieved. Specifically: 150ksi grade drill pipe (Types 1-3 ultra-high strength drill pipe): room temperature yield strength is 1135-1141MPa, tensile strength is 1220-1227MPa, elongation is 22%, longitudinal Charpy V-notch impact toughness of the pipe body at -40℃ is 152-157J; the weld bearing capacity is greater than that of the pipe body; the transverse Charpy V-notch impact toughness of the drill pipe weld at -40℃ is 86-89J.

[0099] 155ksi grade drill pipe (types 4-6 of ultra-high strength drill pipe): room temperature yield strength is 1157-1163MPa, tensile strength is 1244-1251MPa, elongation is 21%, longitudinal Charpy V-notch impact toughness of the pipe body at -40℃ is 142-145J; the weld bearing capacity is greater than that of the pipe body; the transverse Charpy V-notch impact toughness of the drill pipe weld at -40℃ is 82-85J.

[0100] 160ksi grade drill pipe (types 7-9 of ultra-high strength drill pipe): room temperature yield strength of 1185-1190MPa, tensile strength of 1274-1280MPa, elongation of 20%, longitudinal Charpy V-notch impact toughness of the pipe body at -40℃ of 131-134J; weld bearing capacity is greater than that of the pipe body; transverse Charpy V-notch impact toughness of the drill pipe weld at -40℃ of 77-80J.

[0101] 165ksi grade drill pipe (types 10-12 ultra-high strength drill pipe): room temperature yield strength is 1218-1223MPa, tensile strength is 1310-1315MPa, elongation is 19%, longitudinal Charpy V-notch impact toughness of the pipe body at -40℃ is 122-125J; the weld bearing capacity is greater than that of the pipe body; the transverse Charpy V-notch impact toughness of the drill pipe weld at -40℃ is 71-75J.

[0102] 170ksi grade drill pipe (types 13-15 of ultra-high strength drill pipe): room temperature yield strength of 1240-1245MPa, tensile strength of 1333-1339MPa, elongation of 18%, longitudinal Charpy V-notch impact toughness of the pipe body at -40℃ of 111-114J; weld bearing capacity is greater than that of the pipe body; transverse Charpy V-notch impact toughness of the drill pipe weld at -40℃ of 66-68J.

[0103] 175ksi grade drill pipe (types 16-18 of ultra-high strength drill pipe): room temperature yield strength of 1273-1281MPa, tensile strength of 1369-1377MPa, elongation of 17%, longitudinal Charpy V-notch impact toughness of the pipe body at -40℃ of 103-106J; weld bearing capacity is greater than that of the pipe body; transverse Charpy V-notch impact toughness of the drill pipe weld at -40℃ of 61-63J.

[0104] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A high-strength drill pipe body, characterized in that, The ultra-high strength drill pipe body comprises the following chemical components by weight percentage: C 0.23%~0.29%, Si 0.20%~0.35%, Mn 0.62%~0.83%, P≤0.012%, S≤0.003%, Cr0.95%~1.05%, Ni 0.40%~0.53%, Mo 0.60%~0.72%, V 0.06%~0.11%, Ti 0.030%~0.045%, Re 0.003%~0.009%, Al 0.010%~0.020%, Ca 0.009%~0.018%, O≤0.002%, H≤0.00015%, N≤0.005%, N+H+O≤0.007%, balance Fe and unavoidable impurities.

2. The ultra-high strength drill pipe body according to claim 1, characterized in that, The ultra-high strength drill pipe body comprises the following chemical components by weight percentage: C 0.23%~0.26%, Si 0.20%~0.25%, Mn 0.62%~0.69%, P≤0.012%, S≤0.002%, Cr0.95%~1.00%, Ni 0.40%~0.45%, Mo 0.60%~0.65%, V 0.06%~0.09%, Ti 0.030%~0.035%, Re 0.003%~0.008%, Al 0.010%~0.015%, Ca 0.009%~0.014%, O≤0.002%, H≤0.00015%, N≤0.0045%, balance Fe and unavoidable impurities.

3. The ultra-high strength drill pipe body according to claim 1, characterized in that, The ultra-high strength drill pipe body comprises the following chemical components by weight percentage: C 0.25%~0.28%, Si 0.26%~0.31%, Mn 0.70%~0.76%, P≤0.011%, S≤0.0018%, Cr0.98%~1.03%, Ni 0.46%~0.51%, Mo 0.66%~0.71%, V 0.08%~0.11%, Ti 0.036%~0.041%, Re 0.005%~0.007%, Al 0.014%~0.016%, Ca 0.013%~0.016%, O≤0.0018%, H≤0.00014%, N≤0.0039%, balance Fe and unavoidable impurities.

4. The ultra-high strength drill pipe body according to claim 1, characterized in that, The ultra-high strength drill pipe body comprises the following chemical components by weight percentage: C 0.27%~0.29%, Si 0.29%~0.35%, Mn 0.77%~0.83%, P≤0.010%, S≤0.0019%, Cr0.99%~1.05%, Ni 0.47%~0.53%, Mo 0.67%~0.72%, V 0.08%~0.10%, Ti 0.042%~0.045%, Re 0.006%~0.009%, Al 0.015%~0.020%, Ca 0.015%~0.018%, O≤0.0017%, H≤0.00013%, N≤0.0037%, balance Fe and unavoidable impurities.

5. A method for preparing an ultra-high strength drill pipe body according to any one of claims 1-4, characterized in that, Includes the following steps: After batching, smelting, and continuous casting according to the chemical composition of the ultra-high strength drill pipe body, a continuously cast billet is obtained. After hot piercing, controlled rolling and cooling, and residual heat treatment of the continuously cast bar billet, a tube billet is obtained; After thickening the tube ends, performing heat treatment on the entire tube body, hot straightening, and stress-relieving tempering on the tube blank, the ultra-high strength drill pipe body is obtained.

6. The preparation method according to claim 5, characterized in that, The steps for obtaining a tube blank after hot piercing, controlled rolling and cooling, and residual heat treatment of the continuously cast bar billet specifically include: The continuously cast billet is heated to 1190–1210℃ in an annular heating furnace and held for 90–120 min. Hot piercing is then performed at 1150–1200℃, followed by hot continuous rolling at 900–1170℃. The rolling ratio is controlled to be ≥5, and the final rolling temperature is controlled to be 900℃. After controlled rolling and sizing, the billet is water-cooled at a rate controlled to be ≥25℃ / s. Finally, the billet is tempered at 680–710℃ for 60–90 min and then water-cooled.

7. The preparation method according to claim 5, characterized in that, The specific steps for obtaining the ultra-high strength drill pipe body after thickening the pipe ends, performing heat treatment on the entire pipe body, hot straightening, and stress-relieving tempering on the pipe blank include: The tube end of the tube blank is heated to 1050-1150°C, and upsetting is performed 1-3 times using the inner and outer diameter molds and the temperature gradient of the tube end to obtain a tube blank with thickened tube end. The tube blank with thickened ends is heated to 870-890℃ under a protective atmosphere and held for 40-60 minutes. It is then quenched by water spraying inside and outside the tube, with a cooling rate of ≥25℃ / s. Then, it is tempered at 540-590℃ for 90-120 minutes and water-cooled after tempering. Next, it is heated to 520-570℃ for hot straightening, and then stress-reduced tempered at 500-550℃ for 90-120 minutes and air-cooled after tempering to obtain the ultra-high strength drill pipe body.

8. A high-strength drill pipe, characterized in that, The ultra-high strength drill pipe includes a drill pipe body and a drill pipe joint connected to the drill pipe body by friction welding. The drill pipe body is the ultra-high strength drill pipe body according to any one of claims 1-4 or the ultra-high strength drill pipe body prepared by the preparation method according to any one of claims 5-7.

9. A method for preparing the ultra-high strength drill pipe according to claim 8, characterized in that, Includes the following steps: The ultra-high strength drill rod is obtained by friction welding and heat treatment of the drill pipe body and drill pipe joint.

10. The preparation method according to claim 9, characterized in that, The method for preparing the ultra-high strength drill pipe specifically includes the following steps: The inertial friction welding method is adopted, and the rotation speed, back pressure and upsetting pressure are controlled to weld the drill pipe body and the drill pipe joint together. At the moment after friction welding and upsetting, the temperature is 930-980℃. A mixture of water and compressed air is sprayed on the inner and outer surfaces of the weld area for quenching, and then the medium frequency induction heating is carried out to 670-700℃ for 5 minutes for tempering. Next, the weld area is heated to 870-890°C using medium-frequency induction heating. A mixture of water and compressed air is sprayed onto the inner and outer surfaces of the weld area for quenching. Then, the area is tempered by medium-frequency induction heating to 650-680°C and held for 5 minutes to obtain the ultra-high strength drill rod.

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