Petroleum drill rod joint with high toughness and sulfur resistance and preparation method

Abstract

The invention discloses a petroleum drill rod joint with high toughness and sulfur resistance. The drill rod joint comprises the following components: C, Si, Mn, P, S, Cr, Mo, Ni, Cu, V, Ti, Re, Al, Ca and N, Mo / P is controlled to be greater than or equal to 25, Al / N is controlled to be greater than or equal to 3, (Ca + Re) / S is controlled to be greater than or equal to 4, and the balance of Fe and other inevitable impurities. The preparation method of the petroleum drill rod joint comprises the processes of smelting, continuous casting, punching, hot continuous rolling, die forging, two times of quenching and tempering heat treatment and the like, threads are machined into a sulfur-resistant drill rod joint product, the room-temperature yield strength of the sulfur-resistant drill rod joint product is 758-862 MPa, the tensile strength of the sulfur-resistant drill rod joint product is 862-1000 MPa, and the ductility of the sulfur-resistant drill rod joint product is larger than or equal to 15%; -20 DEG C longitudinal Charpy impact toughness is greater than or equal to 100J, and transverse Charpy impact toughness is greater than or equal to 90J; cracks or fractures are not generated in a 720-hour test under 85% SMYS loading, and the requirement for safe use of the sulfur-resistant drill rod in acid deep oil and gas field development can be met.

Description

Technical Field

[0001] The invention belongs to the technical field of oil drill pipe joints, relates to an oil drill pipe joint with high toughness and sulfur resistance, and also relates to a preparation method of the oil drill pipe joint. Background Art

[0002] Acidic oil and gas account for a large proportion of my country's oil and gas resources, mainly distributed in oil and gas fields such as Southwest, Tarim, Daqing, Changqing, Dagang, and North China. In a hydrogen sulfide environment, steel materials are prone to sulfide stress corrosion damage under the synergistic effect of corrosive media and working stress, which often leads to serious consequences. The higher the material strength, the greater the probability of sulfide stress corrosion damage. With the development of deep wells, ultra-deep wells, and highly acidic oil and gas fields, not only are higher requirements placed on the strength and toughness of drill pipes, but also on the resistance to hydrogen sulfide corrosion, especially hydrogen sulfide stress corrosion resistance. However, the strength and toughness of the material and the resistance to sulfide stress corrosion often show a phenomenon of one growing while the other shrinks, which makes the design and manufacture of high-strength sulfur-resistant drill pipes very difficult.

[0003] At present, the drill pipe joints produced by major drill pipe manufacturers at home and abroad can pass the NACE TM 0177A method A solution 65% SMYS (specified minimum yield strength) loading 720h test without cracking or breaking. With the development of deep acidic oil and gas, the stress of sulfur-resistant drill pipes has increased, and the drill pipe joint materials are required to be free of cracks or breaks in the 85% SMYS loading 720h test to meet the requirements of safe use of sulfur-resistant drill pipes in the development of deep acidic oil and gas fields. In view of the above situation, the present invention proposes a steel grade design and preparation method for a drill pipe joint with high toughness and resistance to hydrogen sulfide corrosion. Summary of the invention

[0004] The object of the present invention is to provide a petroleum drill pipe joint with high toughness and sulfur resistance.

[0005] The present invention also aims to provide a method for preparing a petroleum drill pipe joint with high toughness and sulfur resistance, thereby solving the problem that the strength and toughness of the drill pipe joint materials prepared during the development of existing highly acidic oil and gas fields cannot meet the requirements for sulfide stress corrosion resistance.

[0006] In terms of steel grade composition design, the technical solution adopted by the present invention is that the chemical composition of the oil drill pipe joint with high toughness and sulfur resistance includes the following components by mass percentage: C: 0.33% ~ 0.38%, Si: 0.17% ~ 0.37%, Mn: 0.52% ~ 0.68%, P ≤ 0.015%, S ≤ 0.003%, Cr: 0.95% ~ 1.05%, Mo: 0.42% ~ 0.58%, Ni: 0.90 ~ 1.00%, Cu: 0 .15~0.25%, V: 0.025%~0.045%, Ti: 0.015%~0.025%, Re: 0.006%~0.012%, Al: 0.009%~0.015%, Ca: 0.006%~0.012%, O≤0.002%, H≤0.00015%, N≤0.003%, control Mo / P≥25, control Al / N≥3, control (Ca+Re) / S≥4, the balance is Fe and other inevitable impurities.

[0007] The present invention is also characterized in that:

[0008] The room temperature yield strength of the oil drill pipe joint is 758-862MPa, the tensile strength is 862-1000MPa, and the elongation is ≥15%; the longitudinal Charpy impact toughness at -20℃ is ≥100J, and the transverse Charpy impact toughness is ≥90J.

[0009] In terms of composition design, the present invention intends to use medium C, add Cr, Ni, Mo, Cu, control Mn, V, Ti micro-alloying, add Re element, control harmful elements such as P, S, O, H, N in steel, use Al and Si for full deoxidation, and perform Ca treatment on the molten steel. The functions and content ranges of the main elements are as follows:

[0010] C: It is a strengthening element in steel. Too low carbon content is not conducive to improving the hardenability of steel and the strength of steel; too high carbon content is not conducive to the toughness and corrosion resistance of steel. It is advisable to control it within the range of 0.33% to 0.38%.

[0011] Si: It is a common element in steel and should be controlled within the range of 0.17% to 0.37%.

[0012] Mn: It is mainly used to improve the hardenability of steel, thereby improving the strength of steel, but it has a greater tendency to segregate and is easy to form MnS inclusions with S, which is unfavorable to the toughness and corrosion resistance of steel, so it must be strictly controlled. It is best to control it within the range of 0.52% to 0.68%.

[0013] Cr: Mainly used to improve the hardenability of steel, thereby improving the strength, tempering stability and corrosion resistance of steel. It is best to control it within the range of 0.95% to 1.05%.

[0014] Mo: Mainly used to improve the hardenability of steel, thereby improving the strength, tempering stability and corrosion resistance of steel. It is best to control it within the range of 0.42% to 0.58%.

[0015] Ni: Mainly used to improve the hardenability of steel, thereby improving the strength, toughness and corrosion resistance of steel, and at the same time improve the hot brittleness that may be caused by the addition of Cu. It is best to control it within the range of 0.90-1.00%.

[0016] Cu: Mainly used to improve the corrosion resistance of steel, and can also improve the hardenability and strength of steel, but too high a content will also cause Cu brittleness. It is best to control it within the range of 0.15-0.25%.

[0017] V: added to steel to form VC and VN with C and N in steel, which has the effect of hindering the growth of austenite grains, refining grains, and improving strength and toughness. It is best to control it within the range of 0.025% to 0.045%.

[0018] Ti: Ti is added to steel to form TiC and TiN with C and N in the steel, which has the effect of hindering the growth of austenite grains and refining grains, thereby improving strength and toughness. Ti20 formed during welding can prevent overheating of the welding area. It is best to control it within the range of 0.015% to 0.025%.

[0019] Re: It has multiple functions of purifying molten steel, refining grains, modifying inclusions, and alloying. It is best to control it within the range of 0.006% to 0.012%.

[0020] Ca: It can improve the properties and morphology of inclusions, thereby improving the toughness and corrosion resistance of steel. It is best to control it within the range of 0.006% to 0.012%.

[0021] Al: It is an important deoxidizer. It forms oxides with oxygen to deoxidize, and forms nitrides with nitrogen to eliminate the adverse effects of N. It also refines grains and improves strength and toughness. It is best to control it within the range of 0.009% to 0.015%.

[0022] P: Harmful element, mainly affecting the plasticity and toughness of steel. It is advisable to control P ≤ 0.015%.

[0023] S: Harmful element, mainly affecting the plasticity, toughness and corrosion resistance of steel. It is advisable to control S ≤ 0.003%.

[0024] O: Harmful element, mainly affects the plasticity, toughness and corrosion resistance of steel. It is advisable to control O≤0.002%.

[0025] H: Harmful element, mainly affects the plasticity and toughness of steel. It is advisable to control H≤0.00015%.

[0026] N: Harmful element, mainly affects the plasticity and toughness of steel. It is advisable to control N ≤ 0.003%.

[0027] At the same time, Mo / P ≥ 25 is controlled to control the adverse effects of P segregation on corrosion resistance and toughness; Al / N ≥ 3 is controlled to eliminate the adverse effects of N on toughness; (Ca+Re) / S ≥ 4 is controlled to control the effect of inclusion modification treatment and improve the toughness and corrosion resistance of steel.

[0028] In terms of preparation process, the technical solution adopted by the present invention is a method for preparing a petroleum drill pipe joint with high toughness and sulfur resistance, which includes the following steps: steelmaking, continuous casting, perforating and hot rolling, die forging, rough machining and heat treatment, fine machining and thread machining, and welding a wear-resistant belt on the outer diameter part of the joint.

[0029] The present invention is also characterized in that:

[0030] The preparation method of the oil drill pipe joint with high toughness and sulfur resistance, the specific operation steps are as follows:

[0031] Step 1: Steelmaking: batching, steelmaking in an electric furnace or oxygen-blown converter, adding rare earth (Re) wire, refining outside the furnace and vacuum degassing to obtain molten steel, and feeding Si-Ca wire to denature inclusions in the molten steel;

[0032] Step 2: Continuous casting: Cast the molten steel treated in step 1 into a rod-shaped continuous casting billet, and use electromagnetic stirring and soft pressure reduction technology to control segregation in the continuous casting billet during the continuous casting process;

[0033] Step 3: Piercing and hot rolling: The continuous casting billet is heated in a ring heating furnace at a temperature of 1150°C to 1250°C for 90 to 120 minutes, hot-pierced at 1080°C to 1180°C, hot-rolled at 950°C to 1150°C, and then cooled to form a thick-walled tube, which is sawn to a suitable length;

[0034] Step 4: Die forging: heat the thick-walled tubular raw material to 1150°C-1200°C, keep it warm for 60-90 minutes, perform rough forging at 970°C-1170°C, perform fine forging at 850°C-950°C, control the forging ratio to be ≥3, and air cool after forging to obtain the drill pipe joint blank;

[0035] Step 5: Rough machining and heat treatment: Rough machining is performed on the forged drill pipe joint blank according to the size requirements specified in national standards, leaving a machining allowance of 1 to 3 mm, and then heat treatment is performed, followed by non-destructive testing.

[0036] Step 6: Finishing and threading: According to standards and user requirements, the drill pipe joints are finished, API standard threads or special threads are processed, and magnetic particle inspection is performed on the threads.

[0037] The chemical composition of the molten steel in step 2 includes the following components by mass percentage: C: 0.33% ~ 0.38%, Si: 0.17% ~ 0.37%, Mn: 0.52% ~ 0.68%, P≤0.015%, S≤0.003%, Cr: 0.95% ~ 1.05%, Mo: 0.42% ~ 0.58%, Ni: 0.90 ~ 1.00%, Cu: 0.15 ~ 0.25%, V: 0.025% ~ 0.045%, Ti: 0.015%~0.025%, Re: 0.006%~0.012%, Al: 0.009%~0.015%, Ca: 0.006%~0.012%, O≤0.002%, H≤0.00015%, N≤0.003%, control Mo / P≥25, control Al / N≥3, control (Ca+Re) / S≥4, the balance is Fe and other unavoidable impurities.

[0038] Step 5 adopts a tempering heat treatment of heating in a protective atmosphere furnace, quenching twice + high temperature tempering. Through multiple recrystallizations, the grains and structure are refined, and the residual stress is effectively eliminated, thereby obtaining the desired performance.

[0039] The details of the 2nd quenching and tempering heat treatment are as follows:

[0040] The first quenching and tempering heat treatment: use a higher quenching heating temperature to fully dissolve the alloy elements into the high-temperature austenite and make the austenite fully homogenized, and use a higher tempering temperature to fully decompose the quenched martensite to avoid the inheritance of quenched structure and grains. The quenching heating temperature is controlled at 880℃~900℃, the holding time is 40~60 minutes, the quenching cooling medium is PAG quenching liquid, the quenching liquid temperature is controlled at 20℃~40℃, and the time from the quenching heating temperature to the quenching cooling medium is ≤5s, ensuring that all martensitic structures are basically obtained after quenching; the tempering temperature is controlled at 690℃~710℃, and the tempering time is 90~120 minutes to obtain fine and uniform tempered troostite with a grain size of 8~9. After tempering, water cooling is used to avoid possible temper brittleness;

[0041] Second quenching and tempering heat treatment: Use a lower quenching heating temperature to prevent the austenite grains from growing excessively, so that a finer metallographic structure can be obtained after quenching and cooling. The quenching heating temperature is controlled at 820℃~840℃, the holding time is 40~60 minutes, the quenching cooling medium is PAG quenching liquid, the quenching liquid temperature is controlled at 20℃~40℃, and the time from the quenching heating temperature to the quenching cooling medium is ≤5s, ensuring that all martensitic structures are basically obtained after quenching; the tempering temperature is controlled at 640℃~660℃, and the tempering time is 90~120 minutes to obtain fine and uniform tempered troostite, with a grain size of 9~10, and water cooling after tempering to avoid possible temper brittleness.

[0042] The oil drill pipe joint prepared by the method of the present invention does not produce cracks or breaks in the 720h test of loading 65% SMYS and 85% SMYS in A solution according to NACE TM 0177A method, and can meet the requirements for safe use of sulfur-resistant drill pipes in the development of deep acidic oil and gas fields.

[0043] The beneficial effects of the present invention are:

[0044] The sulfur-resistant drill pipe joint material of the present invention has excellent comprehensive properties after being properly prepared, with room temperature yield strength of 758-862MPa, tensile strength of 862-1000MPa, elongation ≥15%, longitudinal Charpy impact toughness ≥100J at -20°C, and transverse Charpy impact toughness ≥90J. According to the NACE TM 0177A method A solution loading 65% SMYS and 85% SMYS 720h test, no cracks or fractures are generated, and the requirements for safe use of sulfur-resistant drill pipes in the development of acidic deep oil and gas fields can be met. DETAILED DESCRIPTION

[0045] The embodiments of the present invention are described in detail below.

[0046] Example 1

[0047] The invention discloses a petroleum drill pipe joint with high toughness and sulfur resistance. The chemical composition of the drill pipe joint includes the following components by mass percentage: C: 0.33% to 0.38%, Si: 0.17% to 0.37%, Mn: 0.52% to 0.68%, P≤0.015%, S≤0.003%, Cr: 0.95% to 1.05%, Mo: 0.42% to 0.58%, Ni: 0.90% to 1.00%, Cu: 0.15% to 0.25%, V: 0.025%~0.045%, Ti: 0.015%~0.025%, Re: 0.006%~0.012%, Al: 0.009%~0.015%, Ca: 0.006%~0.012%, O≤0.002%, H≤0.00015%, N≤0.003%, control Mo / P≥25, control Al / N≥3, control (Ca+Re) / S≥4, the balance is Fe and other inevitable impurities.

[0048] Example 2

[0049] The preparation method of the oil drill pipe joint with high toughness and sulfur resistance, the specific operation steps are as follows:

[0050] Step 1: Steelmaking: batching, steelmaking in an electric furnace or oxygen-blown converter, refining outside the furnace and vacuum degassing to obtain molten steel, and feeding Si-Ca wire to denature inclusions in the molten steel;

[0051] Step 2: Continuous casting: Cast the molten steel treated in step 1 into a rod-shaped continuous casting billet, and use electromagnetic stirring and soft pressure reduction technology to control segregation in the continuous casting billet during the continuous casting process;

[0052] Step 3: Piercing and hot rolling: The continuous casting billet is heated in a ring heating furnace at a temperature of 1150°C to 1250°C for 90 to 120 minutes, hot-pierced at 1080°C to 1180°C, hot-rolled at 950°C to 1150°C, and then cooled to form a thick-walled tube, which is sawn to a suitable length;

[0053] Step 4: Die forging: heat the thick-walled tubular raw material to 1150°C-1200°C, keep it warm for 60-90 minutes, perform rough forging at 970°C-1170°C, perform fine forging at 850°C-950°C, control the forging ratio to be ≥3, and air cool after forging to obtain the drill pipe joint blank;

[0054] Step 5: Rough machining and heat treatment: Rough machining is performed on the forged drill pipe joint blank according to the size requirements specified in national standards, leaving a machining allowance of 1 to 3 mm, and then heat treatment is performed, followed by non-destructive testing.

[0055] Step 6: Finishing and threading: According to standards and user requirements, the drill pipe joints are finished, API standard threads or special threads are processed, and magnetic particle inspection is performed on the threads.

[0056] The chemical composition of the molten steel in step 2 includes the following components by mass percentage: C: 0.33%-0.38%, Si: 0.17%-0.37%, Mn: 0.52%-0.68%, P≤0.015%, S≤0.003%, Cr: 0.95%-1.05%, Mo: 0.42%-0.58%, Ni: 0.90-1.00%, Cu: 0.15-0.25%, V: 0.0 25%~0.045%, Ti: 0.015%~0.025%, Re: 0.006%~0.012%, Al: 0.009%~0.015%, Ca: 0.006%~0.012%, H≤0.00015%, N≤0.003%, control Mo / P≥25, control Al / N≥3, control (Ca+Re) / S≥4, the balance is Fe and other inevitable impurities.

[0057] Step 5 adopts a tempering heat treatment of heating in a protective atmosphere furnace, quenching twice + high temperature tempering. Through multiple recrystallizations, the grains and structure are refined, and the residual stress is effectively eliminated, thereby obtaining the desired performance.

[0058] The details of the 2nd quenching and tempering heat treatment are as follows:

[0059] The first quenching and tempering heat treatment: use a higher quenching heating temperature to allow the alloy elements to fully dissolve into the high-temperature austenite and fully homogenize the austenite, and use a higher tempering temperature to fully decompose the quenched martensite to avoid the inheritance of quenched structure and grains. The quenching heating temperature is controlled at 890℃±10℃, the holding time is 40 to 60 minutes, the quenching cooling medium is PAG quenching liquid, the quenching liquid temperature is controlled at 20℃~40℃, and the time from the quenching heating temperature to the quenching cooling medium is ≤5s, ensuring that all martensitic structures are basically obtained after quenching; the tempering temperature is controlled at 700℃±10℃, and the tempering time is 90 to 120 minutes to obtain fine and uniform tempered troostite with a grain size of 8 to 9. After tempering, water cooling is used to avoid possible temper brittleness;

[0060] Second quenching and tempering heat treatment: Use a lower quenching heating temperature to prevent the austenite grains from growing excessively, so that a finer metallographic structure can be obtained after quenching and cooling. The quenching heating temperature is controlled at 830℃±10℃, the holding time is 40 to 60 minutes, the quenching cooling medium is PAG quenching liquid, the quenching liquid temperature is controlled at 20℃~40℃, and the time from the quenching heating temperature to the quenching cooling medium is ≤5s, ensuring that all martensitic structures are basically obtained after quenching; the tempering temperature is controlled at 650℃±10℃, and the tempering time is 90 to 120 minutes to obtain fine and uniform tempered troostite, with a grain size of 9 to 10, and water cooling after tempering to avoid possible temper brittleness.

[0061] Example 3

[0062] The chemical composition of the sulfur-resistant petroleum drill pipe joint material provided by the embodiment of the present invention is shown in Table 1, wherein O≤0.002%, H≤0.00015%, N≤0.003% not listed, and the balance is Fe and unavoidable impurities.

[0063] Table 1 Chemical composition of sulfur-resistant oil drill pipe joints of Examples 3-1 to 3-6

[0064] Number C Si Mn P S Cr Mo Ni Cu V Ti R Ca Al 3-1 0.35 0.33 0.60 0.011 0.002 0.95 0.50 0.95 0.20 0.035 0.025 0.009 0.012 0.009 3-2 0.36 0.20 0.63 0.010 0.003 0.97 0.45 0.97 0.17 0.030 0.023 0.010 0.007 0.011 3-3 0.38 0.28 0.52 0.012 0.002 0.99 0.42 0.96 0.15 0.025 0.020 0.006 0.006 0.013 3-4 0.37 0.24 0.55 0.010 0.003 1.01 0.48 0.98 0.19 0.038 0.015 0.011 0.010 0.012 3-5 0.34 0.17 0.58 0.011 0.002 1.03 0.53 0.99 0.23 0.040 0.018 0.008 0.008 0.010 3-6 0.33 0.37 0.68 0.012 0.003 1.05 0.58 1.00 0.25 0.045 0.020 0.012 0.009 0.015

[0065] The embodiment of the present invention also provides a method for preparing a sulfur-resistant petroleum drill pipe joint, comprising the following steps:

[0066] ① Steelmaking: batching, electric furnace steelmaking (Examples 3-1, 3-3, 3-5; using sponge iron and high-quality scrap steel as raw materials) or oxygen-blown converter steelmaking (Examples 3-2, 3-4, 3-6; using blast furnace iron and high-quality scrap steel as raw materials), after refining outside the furnace and vacuum degassing, the above chemical composition is obtained, and Si-Ca wire is fed to modify the inclusions in the steel.

[0067] ②Continuous casting: The molten steel is cast into rod-shaped continuous casting billets. During the continuous casting process, electromagnetic stirring and light pressure reduction technology are used to control the segregation in the continuous casting billets.

[0068] ③Piercing and hot rolling: Heat the continuous casting billet in a ring-shaped heating furnace at a temperature of 1150°C to 1250°C for 90 to 120 minutes, hot pierce at 1080°C to 1180°C, hot roll at 950°C to 1150°C, and then air cool to make a thick-walled tube, which is sawn to a suitable length.

[0069] ④ Die forging: Heat the thick-walled tubular raw material to 1150℃~1200℃, keep warm for 60~90 minutes, rough forge at 970℃~1170℃, fine forge at 850℃~950℃, control the forging ratio ≥3, and air cool after forging.

[0070] ⑤ Rough machining and heat treatment: Rough machining is performed on the forged drill pipe joint blank according to the size requirements specified in national standards, leaving a machining allowance of 1 to 3 mm, and then heat treatment is performed, followed by non-destructive testing. The heat treatment process is heated in a protective atmosphere furnace (to prevent decarburization), quenched twice, and tempered at high temperature.

[0071] The first quenching and tempering heat treatment: quenching heating temperature 890℃±10℃, holding time 40~60 minutes, then quenching, quenching cooling medium is PAG quenching liquid, quenching liquid temperature is 20℃~40℃, time from quenching heating temperature to quenching cooling medium is ≤5s; tempering temperature 700℃±10℃, tempering time 90~120 minutes, water cooling after tempering. The metallographic structure is fine and uniform tempered troostite, grain size 8~9.

[0072] Second quenching and tempering heat treatment: quenching heating temperature 830℃±10℃, holding time 40~60 minutes, then quenching, quenching cooling medium is PAG quenching liquid, quenching liquid temperature is 20℃~40℃, time from quenching heating temperature to quenching cooling medium is ≤5s; tempering temperature 650℃±10℃, tempering time 90~120 minutes, water cooling after tempering. The metallographic structure is fine and uniform tempered troostite, grain size 9~10.

[0073] ⑥ Finishing and thread processing: According to standards and user requirements, the drill pipe joints are finished, API standard threads or special threads are processed, and magnetic particle inspection is performed on the threads.

[0074] The properties of the sulfur-resistant oil drill pipe joint prepared according to the above composition and process (see Table 2) are as follows: room temperature yield strength 811-846MPa, tensile strength greater than 936-972MPa, elongation 26-28%; -20℃ longitudinal Charpy impact toughness 131-148J, transverse Charpy impact toughness 113-128J. According to NACE TM 0177A method A solution loading 65% SMYS and 85% SMYS 720h test, no cracks or fractures are generated. It has the characteristics of high strength, high toughness, and resistance to sulfide stress corrosion, and can meet the requirements for the safe use of sulfur-resistant drill pipes in the development of deep acidic oil and gas fields.

[0075] Table 2 Heat treatment process and performance of sulfur-resistant oil drill pipe joints in the embodiment

[0076]

[0077]

[0078] Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. Oil drill pipe joint with high toughness and sulfur resistance, characterized in that: The chemical composition of the drill pipe joint includes the following components by mass percentage: C: 0.33% ~ 0.38%, Si: 0.17% ~ 0.37%, Mn: 0.52% ~ 0.68%, P ≤ 0.015%, S ≤ 0.003%, Cr: 0.95% ~ 1.05%, Mo: 0.42% ~ 0.58%, Ni: 0.90 ~ 1.00%, Cu: 0.15 ~ 0.25%, V: 0.025% ~ 0 .045%, Ti: 0.015%~0.025%, Re: 0.006%~0.012%, Al: 0.009%~0.015%, Ca: 0.006%~0.012%, O≤0.002%, H≤0.00015%, N≤0.003%, control Mo / P≥25, control Al / N≥3, control (Ca+Re) / S≥4, the balance is Fe and other unavoidable impurities.

2. The oil drill pipe joint with high toughness and sulfur resistance according to claim 1, characterized in that: The room temperature yield strength of the oil drill pipe joint is 758-862MPa, the tensile strength is 862-1000MPa, the elongation is ≥15%, the longitudinal Charpy impact toughness at -20°C is ≥100J, and the transverse Charpy impact toughness is ≥90J.

3. A method for preparing a petroleum drill pipe joint with high toughness and sulfur resistance, characterized in that: The method comprises the following steps: steelmaking, continuous casting, perforating and hot rolling, die forging, rough machining and heat treatment, fine machining and thread machining, and welding a wear-resistant belt on the outer diameter part of the joint.

4. The method for preparing a petroleum drill pipe joint with high toughness and sulfur resistance according to claim 3, characterized in that: The specific steps are as follows: Step 1: Steelmaking: batching, steelmaking in an electric furnace or oxygen-blown converter, refining outside the furnace and vacuum degassing to obtain molten steel, and feeding Si-Ca wire to denature inclusions in the molten steel; Step 2: Continuous casting: Cast the molten steel treated in step 1 into a rod-shaped continuous casting billet, and use electromagnetic stirring and soft pressure reduction technology to control segregation in the continuous casting billet during the continuous casting process; Step 3: Piercing and hot rolling: The continuous casting billet is heated in a ring heating furnace at a temperature of 1150°C to 1250°C for 90 to 120 minutes, hot-pierced at 1080°C to 1180°C, hot-rolled at 950°C to 1150°C, and then cooled to form a thick-walled tube; Step 4: Die forging: heat the thick-walled tubular raw material to 1150°C-1200°C, keep it warm for 60-90 minutes, perform rough forging at 970°C-1170°C, perform fine forging at 850°C-950°C, control the forging ratio to be ≥3, and air cool after forging to obtain the drill pipe joint blank; Step 5: Rough machining and heat treatment: Rough machining is performed on the forged drill pipe joint blank, leaving a machining allowance of 1 to 3 mm, followed by heat treatment and non-destructive testing; Step 6: Finishing and threading: Finish the drill pipe joint after rough machining and heat treatment in step 5, process the threads at the same time, and perform magnetic particle inspection on the threads.

5. The method for preparing a petroleum drill pipe joint with high toughness and sulfur resistance according to claim 4, characterized in that: The chemical composition of the molten steel in step 2 includes the following components by mass percentage: C: 0.33% ~ 0.38%, Si: 0.17% ~ 0.37%, Mn: 0.52% ~ 0.68%, P ≤ 0.015%, S ≤ 0.003%, Cr: 0.95% ~ 1.05%, Mo: 0.42% ~ 0.58%, Ni: 0.90 ~ 1.00%, Cu: 0.15 ~ 0.25%, V: 0.025% ~ 0.045%, Ti: 0.015%~0.025%, Re: 0.006%~0.012%, Al: 0.009%~0.015%, Ca: 0.006%~0.012%, O≤0.002%, H≤0.00015%, N≤0.003%, control Mo / P≥25, control Al / N≥3, control (Ca+Re) / S≥4, the balance is Fe and other unavoidable impurities.

6. The method for preparing a petroleum drill pipe joint with high toughness and sulfur resistance according to claim 4, characterized in that: Step 5 adopts a tempering heat treatment of heating in a protective atmosphere furnace, quenching twice + high temperature tempering. Through multiple recrystallizations, the grains and structure are refined, and the residual stress is effectively eliminated, thereby obtaining the desired performance.

7. The method for preparing a petroleum drill pipe joint with high toughness and sulfur resistance according to claim 4, characterized in that: The details of the 2nd quenching and tempering heat treatment are as follows: The first quenching and tempering heat treatment: the quenching heating temperature is controlled at 880℃~900℃, the holding time is 40~60 minutes, the quenching cooling medium is PAG quenching liquid, the quenching liquid temperature is controlled at 20℃~40℃, and the time from the quenching heating temperature to the quenching cooling medium is ≤5s, ensuring that all martensitic structures are basically obtained after quenching; the tempering temperature is controlled at 690℃~710℃, the tempering time is 90~120 minutes, in order to obtain fine and uniform tempered troostite, the grain size is 8~9, and water cooling is performed after tempering; The second quenching and tempering heat treatment: the quenching heating temperature is controlled at 820℃~840℃, the holding time is 40~60 minutes, the quenching cooling medium is PAG quenching liquid, the quenching liquid temperature is controlled at 20℃~40℃, and the time from the quenching heating temperature to the quenching cooling medium is ≤5s, ensuring that all martensitic structures are basically obtained after quenching; the tempering temperature is controlled at 640℃~660℃, the tempering time is 90~120 minutes, in order to obtain fine and uniform tempered troostite, the grain size is 9~10, and water cooling is performed after tempering.

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