Petroleum drill collar and preparation method thereof

Abstract

The invention provides a petroleum drill collar and a preparation method thereof, and the petroleum drill collar comprises the following components in percentage by mass: 0.43%-0.48% of C, 0.17%-0.37% of Si, 0.90%-1.05% of Mn, less than or equal to 0.015% of P, less than or equal to 0.005% of S, 0.90%-1.05% of Cr, 0.40%-0.55% of Mo, 0.03%-0.08% of V, 0.02%-0.05% of Zr, 0.015%-0.025% of Al, 0.015%-0.025% of Ca, less than or equal to 0.007% of O + H + N, and the balance of Fe and inevitable impurities. The petroleum drill collar has high strength, good plasticity and toughness, fatigue performance and wear resistance, and can meet the requirements of oil and gas development of ultra-deep wells and extra-deep wells for the high-strength petroleum drill collar.

Description

Technical Field

[0001] This invention belongs to the field of special steel and oil drill collars, and relates to a high-strength oil drill collar and its preparation method. 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. Drill collars used in oil and gas drilling are typically classified into only one steel grade in relevant standards and actual production. The required yield strength is no less than 110 ksi (outer diameter 79.4-171.4mm) or 100 ksi (outer diameter 177.8-279.4mm), and the tensile strength is no less than 140 ksi (outer diameter 79.4-171.4mm) or 135 ksi (outer diameter 177.8-279.4mm). While this generally meets the requirements for some deep and ultra-deep wells, it is insufficient for some ultra-deep and extra-deep wells with stringent service conditions. This leads to frequent early fracture accidents, severely impacting normal drilling and oil and gas development in ultra-deep and extra-deep wells.

[0003] Chinese patent application CN 116479325 A discloses a 130ksi high-strength drill collar steel for ultra-deep wells and its manufacturing method. Although it has high strength, its toughness is low (≥54J at room temperature, ≥47J at -20℃), which is difficult to meet the needs of safe drilling in ultra-deep wells. The technical solution uses a medium-carbon low-alloy V-Nb microalloyed steel with high Mn content, extremely low Ca content, and low Ca / S ratio. The composition design is not reasonable, which is an important reason for its low plasticity and toughness. Summary of the Invention

[0004] To overcome the problem that existing drill collar steel designs cannot meet the requirements of some ultra-deep and extra-deep wells with stringent service conditions, this invention provides an oil drill collar and its manufacturing method. The oil drill collar not only has high strength, but also good plasticity, toughness and fatigue life.

[0005] This invention is achieved through the following technical solution:

[0006] This invention provides a high-strength oil drill collar, the composition of which, by mass percentage, comprises: C: 0.43%–0.48%, Si: 0.17%–0.37%, Mn: 0.90%–1.05%, P≤0.015%, S≤0.005%, Cr: 0.90%–1.05%, Mo: 0.40%–0.55%, V: 0.03%–0.08%, Zr: 0.02%–0.05%, Al: 0.015%–0.025%, Ca: 0.015%–0.025%, O+H+N≤0.007%, with the balance being Fe and unavoidable impurities.

[0007] Preferably, the oil drill collar has a room temperature yield strength of 935–949 MPa, a tensile strength of 1100–1116 MPa, and an elongation of 18%; a longitudinal Charpy impact toughness of 98–109 J at -20℃, a transverse Charpy impact toughness of 79–90 J, and a hardness of 300–350 HB.

[0008] Preferably, the surface hardness of the internal threaded joint of the oil drill collar is 51-56 HRC.

[0009] This invention provides a method for preparing the high-strength oil drill collar, comprising:

[0010] Step 1: Steelmaking in an electric furnace or oxygen-blown converter, followed by ladle refining and vacuum degassing, and then feeding Si-Ca wire to control the deformation of inclusions in the steel to obtain molten steel; the composition of the molten steel is controlled to be consistent with that of the oil drill collar.

[0011] Step 2: Continuously cast the molten steel into a rod-shaped continuous casting billet;

[0012] Step 3: Roughly machine the bar-shaped continuous casting billet and machine the inner hole to obtain the tube blank;

[0013] Step 4: Heat treat the tube blank;

[0014] Step 5: Perform finishing and threading on the heat-treated tube blank;

[0015] Step 6: Perform roll forming reinforcement on the root of the thread;

[0016] Step 7: Perform surface quenching and tempering treatment on the outer surface of the internal threaded joint of the tube blank.

[0017] Preferably, for oil drill collars with an outer diameter greater than 171.4 mm, step 3 includes:

[0018] The bar-shaped continuous casting billet is forged, the outer diameter of the forged bar-shaped continuous casting billet is machined, and then deep hole drilling is performed.

[0019] Furthermore, the bar-shaped continuous casting billet is forged, specifically: the bar-shaped continuous casting billet is heated to 1170℃~1220℃ and held for 90~120min, rough forged at 1080℃~1190℃, and fine forged at 900℃~1050℃, with the forging ratio controlled to be greater than or equal to 3, and then air-cooled after forging.

[0020] Preferably, for oil drill collars with an outer diameter of no more than 171.4 mm, step 3 includes: hot piercing and hot rolling of the bar-shaped continuous casting billet.

[0021] Furthermore, the bar-shaped continuous casting billet is subjected to hot piercing and hot rolling, specifically: the bar-shaped continuous casting billet is heated to 1170℃~1220℃ for 90~120min; then hot piercing is performed at 1150℃~1190℃, hot rolling is performed at 900℃~1150℃, and then cooling is performed.

[0022] Preferably, in step 4, the tube blank is heat-treated by quenching and tempering; wherein, the quenching heating temperature is 840℃~860℃, the holding time is 60~90min, and the cooling medium is PAG quenching liquid; the tempering temperature is 600℃~620℃, and the tempering time is 90~120min; after tempering, water cooling is performed.

[0023] Preferably, in step 7, the outer surface of the internal threaded joint of the tube blank is subjected to surface quenching and tempering treatment, specifically: the quenching heating temperature is 870~900℃, the tempering temperature is 200~220℃, and the tempering time is 90~120min.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] This invention relates to a high-strength oil drill collar containing a low Mn content, taking into account the different effects of Mn on hardenability and segregation. A higher Ca content and a higher Ca / S ratio allow Ca to improve the properties and morphology of inclusions; controlling the Ca / S ratio to ≥3 ensures controlled deformation of inclusions, thereby improving the steel's ductility and toughness. Simultaneously, V is added to the steel, forming VC and VN with C and N, which inhibit austenite grain growth and refine the grain structure, thus improving strength and ductility. Zr is added to the steel, forming ZrC and ZrN with C and N, refining the grain structure and improving strength and toughness. The use of V-Zr composite microalloying achieves better strengthening and toughening effects than single microalloying elements V or Zr. Furthermore, the combination of Mn, Cr, Mo, and Al enables the oil drill collar to achieve a comprehensive performance of high strength and high ductility and toughness. Among them, Mn, Cr, and Mo can improve the hardenability of steel, thereby increasing its strength; Al forms oxides with oxygen, playing a deoxidizing role, and Al also forms nitrides with nitrogen, partially eliminating N, while simultaneously refining grains and improving strength and toughness. Furthermore, this invention limits the content of harmful elements P, S, O, H, and N to avoid these harmful elements affecting the toughness and plasticity of the steel. In summary, this invention, by adding a low content of Mn, a high content of Ca, and controlling a high Ca / S ratio, employs V-Zr composite microalloying, and incorporates Cr, Mo, and Al alloying elements while controlling the content of harmful elements, achieves a room temperature yield strength greater than 862 MPa (125 ksi), a tensile strength greater than 1034 MPa (150 ksi), and an elongation ≥15% for its oil drill collar; a longitudinal Charpy impact toughness ≥90 J and a transverse Charpy impact toughness ≥70 J at -20℃. It combines high strength, good ductility and toughness, fatigue performance, and wear resistance, meeting the requirements for high-strength oil drill collars in ultra-deep and extra-deep well oil and gas development.

[0026] The high-strength oil drill collar preparation method of this invention includes smelting, continuous casting, rough machining and internal hole machining, heat treatment, thread machining and roll forming to form the drill collar product. During the steelmaking process, feeding Si-Ca wire controls the deformation of inclusions in the steel, controlling the Ca / S ratio to ≥3, which improves the steel's ductility and toughness. Surface quenching and tempering treatment increases the hardness of the outer surface of the drill collar's internal thread joint, which is beneficial for improving the drill collar's wear resistance and extending its service life. The oil drill collar obtained through the preparation process of this invention has excellent comprehensive performance, with a room temperature yield strength greater than 862 MPa (125 ksi), a tensile strength greater than 1034 MPa (150 ksi), and an elongation ≥15%; a longitudinal Charpy impact toughness ≥90 J and a transverse Charpy impact toughness ≥70 J at -20℃. The drill collar body has a hardness of 300-350HB, and the outer surface hardness of the internal threaded joint is ≥50HRC, which can meet the requirements of high-strength oil drill collars for ultra-deep and extra-deep well oil and gas development. Detailed Implementation

[0027] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0028] It should be noted that the process equipment or apparatus not specifically mentioned in the following embodiments are all conventional equipment or apparatus in the art.

[0029] It should be noted that the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or apparatuses. Furthermore, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not intended to limit the order of the method steps or define the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0030] In terms of composition design, this invention employs a medium carbon content, adding Mn, Cr, and Mo for alloying, and using V-Zr composite microalloying to control harmful elements such as P, S, O, H, and N in the steel. It also utilizes Al and Si for complete deoxidation and performs Ca treatment on the molten steel. The key features of this invention are the use of a lower Mn content, a higher Ca content, and a higher Ca / S ratio, combined with Zr-V composite microalloying and optimized design of other alloying elements, to achieve excellent comprehensive performance of high strength and high ductility and toughness in oil drill collars.

[0031] The functions and content ranges of the main elements are as follows:

[0032] Carbon (C) is a strengthening element in steel. Too low a carbon content is detrimental to improving the hardenability and strength of the steel; too high a carbon content is detrimental to the ductility and toughness of the steel. Considering all factors, it is advisable to control the carbon content within the range of 0.43% to 0.48%.

[0033] Si is a common element in steel. Considering all factors, it is advisable to control its content within the range of 0.17% to 0.37%.

[0034] Mn: Primarily used to improve the hardenability of steel, thereby increasing its strength; however, excessively high content can increase the tendency for segregation. Considering all factors, it is advisable to control it within the range of 0.90% to 1.05%.

[0035] Cr: Primarily used to improve the hardenability of steel, thereby increasing its strength; however, excessive content can increase costs. Considering all factors, it is advisable to control the content within the range of 0.90% to 1.05%.

[0036] Mo is mainly used to improve the hardenability of steel to increase its strength and tempering stability, but excessive content will increase costs. Considering all factors, it is advisable to control it within the range of 0.40% to 0.55%.

[0037] V: When added to steel, it forms VC and VN with C and N in the steel, which can inhibit the growth of austenite grains and refine the grains, thereby improving strength and toughness. Taking all factors into consideration, it is advisable to control it within the range of 0.03% to 0.08%.

[0038] Zr: When added to steel, it reacts with C and N to form ZrC and ZrN, refining the grains and thus improving strength and toughness. However, excessive content can increase the brittleness of the steel and lead to higher costs. Considering all factors, it is advisable to control the content within the range of 0.02% to 0.05%.

[0039] Using V-Zr composite microalloying can achieve better strengthening and toughening effects than using single microalloying elements V or Zr.

[0040] Al is an important deoxidizer. It forms oxides with oxygen, thus deoxidizing; it forms nitrides with nitrogen, which can partially eliminate nitrogen; and it also refines grains and improves strength and toughness. Considering all factors, it is advisable to control its concentration within the range of 0.015% to 0.025%.

[0041] Ca can improve the properties and morphology of inclusions, thereby enhancing the ductility and toughness of steel. To ensure the effectiveness of inclusion-controlled deformation, the Ca / S ratio should be controlled to be ≥3. Considering all factors, it is advisable to control it within the range of 0.015% to 0.025%.

[0042] P: A harmful element that primarily affects the ductility and toughness of steel. Considering all factors, P should ideally be controlled to ≤0.015%.

[0043] S: A harmful element that primarily affects the ductility and toughness of steel. Considering all factors, S should ideally be controlled to ≤0.005%.

[0044] O: A harmful element that mainly affects the ductility and toughness of steel.

[0045] H: A harmful element that mainly affects the ductility and toughness of steel.

[0046] N: A harmful element that mainly affects the plasticity and toughness of steel.

[0047] Taking all factors into account, it is advisable to control O+H+N ≤ 0.007%.

[0048] In summary, the high-strength oil drill collar of the present invention comprises, by mass percentage: C: 0.43%–0.48%, Si: 0.17%–0.37%, Mn: 0.90%–1.05%, P≤0.015%, S≤0.005%, Cr: 0.90%–1.05%, Mo: 0.40%–0.55%, V: 0.03%–0.08%, Zr: 0.02%–0.05%, Al: 0.015%–0.025%, Ca: 0.015%–0.025%, O+H+N≤0.007%, with the balance being Fe and unavoidable impurities.

[0049] In terms of the manufacturing process of oil drill collars, this invention mainly achieves a reasonable match between the strength, toughness, fatigue performance and wear resistance of drill collars through processes such as steelmaking (including ladle refining and vacuum degassing), continuous casting, forging, hot continuous rolling, deep hole drilling, heat treatment, thread processing and roll forming, and surface heat treatment.

[0050] The manufacturing process of the high-strength oil drill collar of the present invention includes:

[0051] Step 1, steelmaking: Batching, steelmaking in an electric furnace or oxygen-blown converter, refining outside the furnace and vacuum degassing, feeding Si-Ca wire to control the deformation of inclusions in the steel to obtain molten steel; controlling the composition of the molten steel to be consistent with the composition of the oil drill collar.

[0052] Step 2, continuous casting: The molten steel is cast into a bar-shaped continuous casting billet. Electromagnetic stirring and light reduction technology are used during the continuous casting process to control segregation in the bar-shaped continuous casting billet.

[0053] Step 3, rough machining and inner hole machining: Rough machining and inner hole machining are performed on the bar-shaped continuous casting billet to obtain the tube blank.

[0054] Step 4, Heat Treatment: The tube blank undergoes heat treatment using a combination of induction heating quenching and high-temperature tempering. The quenching temperature is controlled at 840℃~860℃, with a holding time of 60~90min. PAG quenching fluid is used as the cooling medium, and its temperature is controlled to be less than or equal to 40℃ to ensure that the quenched tube contains almost all the martensite. Tempering is performed using induction heating at 600℃~620℃ for 90~120min to obtain fine and uniform tempered sorbite. Water cooling is applied after tempering to prevent potential temper brittleness. Non-destructive testing is then performed.

[0055] Step 5, finishing and threading: According to standards and user requirements, the heat-treated tube blank is finished, and API standard threads or special threads are machined. Magnetic particle testing is then performed on the threads.

[0056] Step 6, Thread machining and roll forming reinforcement: Machining the tube blank with a root fillet radius ≥ 0.965mm according to the drill collar thread standard, and rolling the root of the thread to enhance the fatigue strength of the thread.

[0057] Step 7: Perform high-frequency surface quenching followed by low-temperature tempering on the outer surface of the internal threaded joint of the tube blank. The quenching temperature is 870–900℃, the tempering temperature is 200–220℃, and the tempering time is 90–120 min. This ensures that the hardened layer depth of the internal thread is ≥2.5 mm and the hardness of the outer surface of the internal threaded joint is ≥50 HRC, resulting in a high-strength oil drill collar. The surface quenching and tempering treatment improves the hardness of the outer surface of the drill collar's internal threaded joint, which is beneficial for improving the wear resistance of the drill collar and extending its service life.

[0058] In this invention, step 3 is divided into two cases depending on the outer diameter of the oil drill collar to be manufactured:

[0059] For oil drill collars with an outer diameter greater than 171.4 mm, step 3 includes:

[0060] Forging: Heat the bar-shaped continuous casting billet to 1170℃~1220℃ and hold for 90~120min. Rough forging is performed at 1080℃~1190℃, and finish forging is performed at 900℃~1050℃. The forging ratio is controlled to be ≥3. After forging, air cooling is performed. Controlling the forging ratio is beneficial to breaking up dendritic segregation in the casting structure and effectively controlling anisotropy.

[0061] Machining and deep hole drilling: The outer diameter of the forged bar-shaped continuous casting billet is machined, and then deep hole drilling is performed, leaving a machining allowance of 1-3 mm.

[0062] For oil drill collars with an outer diameter not exceeding 171.4 mm, step 3 includes:

[0063] Piercing and hot rolling: The continuously cast bar billet is heated in an annular heating furnace at a temperature of 1170℃~1220℃ for 90~120min. It is then hot-pierced at 1150℃~1190℃ and hot-rolled at 900℃~1150℃. After cooling, it is made into a thick-walled tube and sawn to a suitable length.

[0064] Example 1

[0065] The high-strength oil drill collar described in this embodiment comprises, by mass percentage: C: 0.45%, Si: 0.25%, Mn: 0.99%, P: 0.011%, S: 0.003%, Cr: 1.05%, Mo: 0.44%, V: 0.04%, Zr: 0.04%, Al: 0.025%, Ca: 0.015%, O+H+N ≤ 0.007%, with the balance being Fe and unavoidable impurities. Its outer diameter is 171.4 mm.

[0066] The manufacturing process of the high-strength oil drill collar described in this embodiment is as follows:

[0067] ① Steelmaking: Using sponge iron and high-quality scrap steel as raw materials, steel is produced in an electric furnace. After ladle refining and vacuum degassing, Si-Ca wire is fed to control the deformation of inclusions in the steel to obtain molten steel. The ratio of sponge iron to high-quality scrap steel is controlled to ensure that the composition of the molten steel is consistent with that of the oil drill collar.

[0068] ② Continuous casting: 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.

[0069] ③ Piercing and hot rolling: The continuously cast bar billet is heated in an annular heating furnace at a temperature of 1190±15℃ for 120 minutes. It is then hot-pierced at 1150℃~1190℃ and hot-rolled at 900℃~1150℃. After cooling, it is made into a thick-walled tube and sawn to a suitable length.

[0070] ④ Heat treatment: The heat treatment process of induction hardening followed by high-temperature tempering is adopted. The quenching temperature is 850±10℃, the holding time is 60min, and then quenching is performed. The quenching cooling medium is PAG quenching liquid, and the temperature of the quenching liquid is controlled not to exceed 40℃. The tempering temperature is 610±10℃, and the tempering time is 90min. Non-destructive testing is then performed.

[0071] ⑤ Finishing and threading: The drill collar is finished according to standards and user requirements, and the threads are machined and tested with magnetic particles.

[0072] ⑥ Thread machining and roll forming reinforcement: Machining digital threads with a root fillet radius ≥ 0.965mm according to drill collar thread standards, and performing roll forming reinforcement on the thread root.

[0073] ⑦ The outer surface of the drill collar internal threaded joint is subjected to high-frequency surface quenching and low-temperature tempering. The quenching temperature is 885±15℃, the tempering temperature is 210±10℃, and the tempering time is 90min.

[0074] Example 2

[0075] The high-strength oil drill collar described in this embodiment comprises, by mass percentage: C: 0.43%, Si: 0.37%, Mn: 1.05%, P: 0.010%, S: 0.002%, Cr: 1.01%, Mo: 0.55%, V: 0.05%, Zr: 0.03%, Al: 0.017%, Ca: 0.019%, O+H+N≤0.007%, with the balance being Fe and unavoidable impurities. Its outer diameter is 158.8 mm.

[0076] The manufacturing process of the high-strength oil drill collar described in this embodiment is as follows:

[0077] ① Steelmaking: Using blast furnace hot metal and high-quality scrap steel as raw materials, steelmaking is carried out in an oxygen-blown converter. After ladle refining and vacuum degassing, Si-Ca wire is fed to control the deformation of inclusions in the steel to obtain molten steel. The ratio of blast furnace hot metal and high-quality scrap steel is controlled so that the composition of the molten steel is consistent with that of the oil drill collar.

[0078] ② Continuous casting: 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.

[0079] ③ Piercing and hot rolling: The continuously cast bar billet is heated in an annular heating furnace at a temperature of 1190±15℃ for 120 minutes. It is then hot-pierced at 1150℃~1190℃ and hot-rolled at 900℃~1150℃. After cooling, it is made into a thick-walled tube and sawn to a suitable length.

[0080] ④ Heat treatment: The heat treatment process of induction hardening followed by high-temperature tempering is adopted. The quenching temperature is 850±10℃, the holding time is 60min, and then quenching is performed. The quenching cooling medium is PAG quenching liquid, and the temperature of the quenching liquid is controlled not to exceed 40℃. The tempering temperature is 610±10℃, and the tempering time is 90min. Non-destructive testing is then performed.

[0081] ⑤ Finishing and threading: The drill collar is finished according to standards and user requirements, and the threads are machined and tested with magnetic particles.

[0082] ⑥ Thread machining and roll forming reinforcement: Machining digital threads with a root fillet radius ≥ 0.965mm according to drill collar thread standards, and performing roll forming reinforcement on the thread root.

[0083] ⑦ The outer surface of the drill collar internal threaded joint is subjected to high-frequency surface quenching and low-temperature tempering. The quenching temperature is 885±15℃, the tempering temperature is 210±10℃, and the tempering time is 90min.

[0084] Example 3

[0085] The high-strength oil drill collar described in this embodiment, by mass percentage, comprises: C: 0.48%, Si: 0.29%, Mn: 0.90%, P: 0.012%, S: 0.003%, Cr: 0.96%, Mo: 0.40%, V: 0.08%, Zr: 0.02%, Al: 0.018%, Ca: 0.017%, O+H+N≤0.007%, with the balance being Fe and unavoidable impurities. Its outer diameter is 165.1 mm.

[0086] The manufacturing process of the high-strength oil drill collar described in this embodiment is as follows:

[0087] ① Steelmaking: Using sponge iron and high-quality scrap steel as raw materials, steel is produced in an electric furnace. After ladle refining and vacuum degassing, Si-Ca wire is fed to control the deformation of inclusions in the steel to obtain molten steel. The ratio of sponge iron to high-quality scrap steel is controlled so that the composition of the molten steel is consistent with that of the oil drill collar.

[0088] ② Continuous casting: 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.

[0089] ③ Piercing and hot rolling: The continuously cast bar billet is heated in an annular heating furnace at a temperature of 1190±15℃ for 120 minutes. It is then hot-pierced at 1150℃~1190℃ and hot-rolled at 900℃~1150℃. After cooling, it is made into a thick-walled tube and sawn to a suitable length.

[0090] ④ Heat treatment: The heat treatment process of induction hardening followed by high-temperature tempering is adopted. The quenching temperature is 850±10℃, the holding time is 60min, and then quenching is performed. The quenching cooling medium is PAG quenching liquid, and the temperature of the quenching liquid is controlled not to exceed 40℃. The tempering temperature is 610±10℃, and the tempering time is 90min. Non-destructive testing is then performed.

[0091] ⑤ Finishing and threading: The drill collar is finished according to standards and user requirements, and the threads are machined and tested with magnetic particles.

[0092] ⑥ Thread machining and roll forming reinforcement: Machining digital threads with a root fillet radius ≥ 0.965mm according to drill collar thread standards, and performing roll forming reinforcement on the thread root.

[0093] ⑦ The outer surface of the drill collar internal threaded joint is subjected to high-frequency surface quenching and low-temperature tempering. The quenching temperature is 885±15℃, the tempering temperature is 210±10℃, and the tempering time is 90min.

[0094] Example 4

[0095] The high-strength oil drill collar described in this embodiment comprises, by mass percentage: C: 0.44%, Si: 0.17%, Mn: 0.96%, P: 0.011%, S: 0.003%, Cr: 1.02%, Mo: 0.48%, V: 0.07%, Zr: 0.03%, Al: 0.015%, Ca: 0.023%, O+H+N≤0.007%, with the balance being Fe and unavoidable impurities. Its outer diameter is 177.8 mm.

[0096] The manufacturing process of the high-strength oil drill collar described in this embodiment is as follows:

[0097] ① Steelmaking: Using blast furnace hot metal and high-quality scrap steel as raw materials, steelmaking is carried out in an oxygen-blown converter. After ladle refining and vacuum degassing, Si-Ca wire is fed to control the deformation of inclusions in the steel to obtain molten steel. The ratio of blast furnace hot metal and high-quality scrap steel is controlled so that the composition of the molten steel is consistent with that of the oil drill collar.

[0098] ② Continuous casting: 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.

[0099] ③ Forging: Heat the bar-shaped continuous casting billet to 1190±15℃ and hold for 120min. Rough forging is performed at 1080℃~1190℃, and fine forging is performed at 900℃~1050℃. The forging ratio is controlled to be ≥3. After forging, air cool.

[0100] ④ Machining and deep hole drilling: The outer diameter of the forged bar-shaped continuous casting billet is machined, and then deep hole drilling is performed, leaving a machining allowance of 2mm.

[0101] ⑤ Heat treatment: The heat treatment process of induction hardening followed by high-temperature tempering is adopted. The quenching temperature is 850±10℃, the holding time is 90min, and then quenching is performed. The quenching cooling medium is PAG quenching liquid, and the temperature of the quenching liquid is controlled not to exceed 40℃. The tempering temperature is 610±10℃, and the tempering time is 120min. Non-destructive testing is then performed.

[0102] ⑥ Finishing and threading: According to standards and user requirements, the drill collar is finished and the threads are machined. Magnetic particle testing is then performed on the threads.

[0103] ⑦ Thread machining and roll forming reinforcement: Machining digital threads with a root fillet radius ≥ 0.965mm according to drill collar thread standards, and roll forming reinforcement of the thread root.

[0104] ⑧ The outer surface of the drill collar internal threaded joint is subjected to high-frequency surface quenching and low-temperature tempering. The quenching temperature is 885±15℃, the tempering temperature is 210±10℃, and the tempering time is 120min.

[0105] Example 5

[0106] The high-strength oil drill collar described in this embodiment comprises, by mass percentage: C: 0.46%, Si: 0.27%, Mn: 1.03%, P: 0.010%, S: 0.002%, Cr: 0.93%, Mo: 0.51%, V: 0.03%, Zr: 0.05%, Al: 0.022%, Ca: 0.025%, O+H+N≤0.007%, with the balance being Fe and unavoidable impurities. Its outer diameter is 203.2 mm.

[0107] The manufacturing process of the high-strength oil drill collar described in this embodiment is as follows:

[0108] ① Steelmaking: Using sponge iron and high-quality scrap steel as raw materials, steel is produced in an electric furnace. After ladle refining and vacuum degassing, Si-Ca wire is fed to control the deformation of inclusions in the steel to obtain molten steel. The ratio of sponge iron to high-quality scrap steel is controlled so that the composition of the molten steel is consistent with that of the oil drill collar.

[0109] ② Continuous casting: 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.

[0110] ③ Forging: Heat the bar-shaped continuous casting billet to 1190±15℃ and hold for 120min. Rough forging is performed at 1080℃~1190℃, and fine forging is performed at 900℃~1050℃. The forging ratio is controlled to be ≥3. After forging, air cool.

[0111] ④ Machining and deep hole drilling: The outer diameter of the forged bar-shaped continuous casting billet is machined, and then deep hole drilling is performed, leaving a machining allowance of 2mm.

[0112] ⑤ Heat treatment: The heat treatment process of induction hardening followed by high-temperature tempering is adopted. The quenching temperature is 850±10℃, the holding time is 90min, and then quenching is performed. The quenching cooling medium is PAG quenching liquid, and the temperature of the quenching liquid is controlled not to exceed 40℃. The tempering temperature is 610±10℃, and the tempering time is 120min. Non-destructive testing is then performed.

[0113] ⑥ Finishing and threading: According to standards and user requirements, the drill collar is finished and the threads are machined. Magnetic particle testing is then performed on the threads.

[0114] ⑦ Thread machining and roll forming reinforcement: Machin the root fillet radius of the thread according to the drill collar thread standard.

[0115] Numerical threads with a diameter of ≥0.965mm, and the root of the thread is rolled to strengthen it.

[0116] ⑧ The outer surface of the drill collar internal threaded joint is subjected to high-frequency surface quenching and low-temperature tempering. The quenching temperature is 885±15℃, the tempering temperature is 210±10℃, and the tempering time is 120min.

[0117] Example 6

[0118] The high-strength oil drill collar described in this embodiment comprises, by mass percentage: C: 0.47%, Si: 0.28%, Mn: 1.01%, P: 0.012%, S: 0.003%, Cr: 0.90%, Mo: 0.49%, V: 0.06%, Zr: 0.03%, Al: 0.021%, Ca: 0.02%, O+H+N≤0.007%, with the balance being Fe and unavoidable impurities. Its outer diameter is 228.6 mm.

[0119] The manufacturing process of the high-strength oil drill collar described in this embodiment is as follows:

[0120] ① Steelmaking: Using sponge iron and high-quality scrap steel as raw materials, steel is produced in an electric furnace. After ladle refining and vacuum degassing, Si-Ca wire is fed to control the deformation of inclusions in the steel to obtain molten steel. The ratio of sponge iron to high-quality scrap steel is controlled so that the composition of the molten steel is consistent with that of the oil drill collar.

[0121] ② Continuous casting: 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.

[0122] ③ Forging: Heat the bar-shaped continuous casting billet to 1190±15℃ and hold for 120min. Rough forging is performed at 1080℃~1190℃, and fine forging is performed at 900℃~1050℃. The forging ratio is controlled to be ≥3. After forging, air cool.

[0123] ④ Machining and deep hole drilling: The outer diameter of the forged bar-shaped continuous casting billet is machined, and then deep hole drilling is performed, leaving a machining allowance of 2mm.

[0124] ⑤ Heat treatment: The heat treatment process of induction hardening followed by high-temperature tempering is adopted. The quenching temperature is 850±10℃, the holding time is 90min, and then quenching is performed. The quenching cooling medium is PAG quenching liquid, and the temperature of the quenching liquid is controlled not to exceed 40℃. The tempering temperature is 610±10℃, and the tempering time is 120min. Non-destructive testing is then performed.

[0125] ⑥ Finishing and threading: According to standards and user requirements, the drill collar is finished and the threads are machined. Magnetic particle testing is then performed on the threads.

[0126] ⑦ Thread machining and roll forming reinforcement: Machining digital threads with a root fillet radius ≥ 0.965mm according to drill collar thread standards, and roll forming reinforcement of the thread root.

[0127] ⑧ The outer surface of the drill collar internal threaded joint is subjected to high-frequency surface quenching and low-temperature tempering. The quenching temperature is 885±15℃, the tempering temperature is 210±10℃, and the tempering time is 120min.

[0128] Comparative Example 1: Without Ca

[0129] The oil drill collar described in this comparative example, by mass percentage, comprises: C: 0.45%, Si: 0.25%, Mn: 0.99%, P: 0.011%, S: 0.003%, Cr: 1.05%, Mo: 0.44%, V: 0.04%, Zr: 0.04%, Al: 0.025%, O+H+N ≤ 0.007%, with the balance being Fe and unavoidable impurities. Its outer diameter is 171.4 mm.

[0130] The manufacturing process of the high-strength oil drill collar described in this comparative example is as follows:

[0131] ① Steelmaking: Using sponge iron and high-quality scrap steel as raw materials, steel is produced in an electric furnace, followed by ladle refining and vacuum degassing to obtain molten steel. The ratio of sponge iron to high-quality scrap steel is controlled to ensure that the composition of the molten steel is consistent with that of the oil drill collar.

[0132] ② Continuous casting: 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.

[0133] ③ Piercing and hot rolling: The continuously cast bar billet is heated in an annular heating furnace at a temperature of 1190±15℃ for 120 minutes. It is then hot-pierced at 1150℃~1190℃ and hot-rolled at 900℃~1150℃. After cooling, it is made into a thick-walled tube and sawn to a suitable length.

[0134] ④ Heat treatment: The heat treatment process of induction hardening followed by high-temperature tempering is adopted. The quenching temperature is 850±10℃, the holding time is 60min, and then quenching is performed. The quenching cooling medium is PAG quenching liquid, and the temperature of the quenching liquid is controlled not to exceed 40℃. The tempering temperature is 610±10℃, and the tempering time is 90min. Non-destructive testing is then performed.

[0135] ⑤ Finishing and threading: The drill collar is finished according to standards and user requirements, and the threads are machined and tested with magnetic particles.

[0136] ⑥ Thread machining and roll forming reinforcement: Machining digital threads with a root fillet radius ≥ 0.965mm according to drill collar thread standards, and performing roll forming reinforcement on the thread root.

[0137] ⑦ The outer surface of the drill collar internal threaded joint is subjected to high-frequency surface quenching and low-temperature tempering. The quenching temperature is 885±15℃, the tempering temperature is 210±10℃, and the tempering time is 90min.

[0138] Comparative Example 2: Ca content is too low

[0139] The oil drill collar described in this comparative example, by mass percentage, comprises: C: 0.45%, Si: 0.25%, Mn: 0.99%, P: 0.011%, S: 0.003%, Cr: 1.05%, Mo: 0.44%, V: 0.04%, Zr: 0.04%, Al: 0.025%, Ca: 0.0015%, O+H+N ≤ 0.007%, with the balance being Fe and unavoidable impurities. Its outer diameter is 171.4 mm.

[0140] The manufacturing process of the high-strength oil drill collar described in this comparative example is as follows:

[0141] ① Steelmaking: Using sponge iron and high-quality scrap steel as raw materials, steel is produced in an electric furnace, refined outside the ladle, and degassed under vacuum. Si-Ca wire is then fed to obtain molten steel. The ratio of sponge iron to high-quality scrap steel is controlled so that the composition of the molten steel is consistent with that of the oil drill collar.

[0142] ② Continuous casting: 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.

[0143] ③ Piercing and hot rolling: The continuously cast bar billet is heated in an annular heating furnace at a temperature of 1190±15℃ for 120 minutes. It is then hot-pierced at 1150℃~1190℃ and hot-rolled at 900℃~1150℃. After cooling, it is made into a thick-walled tube and sawn to a suitable length.

[0144] ④ Heat treatment: The heat treatment process of induction hardening followed by high-temperature tempering is adopted. The quenching temperature is 850±10℃, the holding time is 60min, and then quenching is performed. The quenching cooling medium is PAG quenching liquid, and the temperature of the quenching liquid is controlled not to exceed 40℃. The tempering temperature is 610±10℃, and the tempering time is 90min. Non-destructive testing is then performed.

[0145] ⑤ Finishing and threading: The drill collar is finished according to standards and user requirements, and the threads are machined and tested with magnetic particles.

[0146] ⑥ Thread machining and roll forming reinforcement: Machining digital threads with a root fillet radius ≥ 0.965mm according to drill collar thread standards, and performing roll forming reinforcement on the thread root.

[0147] ⑦ The outer surface of the drill collar internal threaded joint is subjected to high-frequency surface quenching and low-temperature tempering. The quenching temperature is 885±15℃, the tempering temperature is 210±10℃, and the tempering time is 90min.

[0148] Comparative Example 3: No Zr added

[0149] The high-strength oil drill collar described in this embodiment, by mass percentage, comprises: C: 0.45%, Si: 0.25%, Mn: 0.99%, P: 0.011%, S: 0.003%, Cr: 1.05%, Mo: 0.44%, V: 0.04%, Al: 0.025%, Ca: 0.015%, O+H+N ≤ 0.007%, with the balance being Fe and unavoidable impurities. Its outer diameter is 171.4 mm.

[0150] The manufacturing process of the high-strength oil drill collar described in this embodiment is as follows:

[0151] ① Steelmaking: Using sponge iron and high-quality scrap steel as raw materials, steel is produced in an electric furnace. After ladle refining and vacuum degassing, Si-Ca wire is fed to control the deformation of inclusions in the steel to obtain molten steel. The ratio of sponge iron to high-quality scrap steel is controlled so that the composition of the molten steel is consistent with that of the oil drill collar.

[0152] ② Continuous casting: 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.

[0153] ③ Piercing and hot rolling: The continuously cast bar billet is heated in an annular heating furnace at a temperature of 1190±15℃ for 120 minutes. It is then hot-pierced at 1150℃~1190℃ and hot-rolled at 900℃~1150℃. After cooling, it is made into a thick-walled tube and sawn to a suitable length.

[0154] ④ Heat treatment: The heat treatment process of induction hardening followed by high-temperature tempering is adopted. The quenching temperature is 850±10℃, the holding time is 60min, and then quenching is performed. The quenching cooling medium is PAG quenching liquid, and the temperature of the quenching liquid is controlled not to exceed 40℃. The tempering temperature is 610±10℃, and the tempering time is 90min. Non-destructive testing is then performed.

[0155] ⑤ Finishing and threading: The drill collar is finished according to standards and user requirements, and the threads are machined and tested with magnetic particles.

[0156] ⑥ Thread machining and roll forming reinforcement: Machining digital threads with a root fillet radius ≥ 0.965mm according to drill collar thread standards, and performing roll forming reinforcement on the thread root.

[0157] ⑦ The outer surface of the drill collar internal threaded joint is subjected to high-frequency surface quenching and low-temperature tempering. The quenching temperature is 885±15℃, the tempering temperature is 210±10℃, and the tempering time is 90min.

[0158] The chemical composition of the high-strength oil drill collar material provided in the various embodiments and comparative examples of the present invention is shown in Table 1, wherein O+H+N not listed are ≤0.007%, and the balance is Fe and unavoidable impurities.

[0159] Table 1. Chemical composition of high-strength oil drill collars in each embodiment and comparative example.

[0160]

[0161] The performance of the high-strength oil drill collars provided in the various embodiments and comparative examples of the present invention is shown in Table 2.

[0162] Table 2. Heat treatment processes and performance of high-strength oil drill collars in each embodiment and comparative example.

[0163]

[0164] As shown in Table 2, the oil drill collars prepared in the various embodiments of the present invention have a room temperature yield strength of 935–949 MPa, a tensile strength of 1100–1116 MPa, and an elongation of 18%; a longitudinal Charpy impact toughness of 98–109 J and a transverse Charpy impact toughness of 79–90 J at -20℃; a drill collar body hardness of 300–350 HB; and an outer surface hardness of 51–56 HRC for the internal threaded joint. Therefore, the oil drill collars prepared in the various embodiments of the present invention have a room temperature yield strength greater than 862 MPa (125 ksi), a tensile strength greater than 1034 MPa (150 ksi), an elongation ≥15%, a longitudinal Charpy impact toughness ≥90 J at -20℃, a transverse Charpy impact toughness ≥70 J, and an outer surface hardness ≥50 HRC for the internal threaded joint. Thus, the oil drill collars of the present invention, while possessing high strength, also exhibit good plasticity, toughness, fatigue performance, and wear resistance, meeting the requirements for high-strength oil drill collars in ultra-deep and extra-deep well oil and gas development.

[0165] Compared with Example 1, Comparative Example 1 was different in that the step of feeding Si-Ca wire to modify the inclusions in the steel was not performed. As can be seen from Table 2, the plasticity and toughness of the oil drill collar of Comparative Example 1 were significantly lower than those of the oil drill collar of Example 1. Moreover, the longitudinal and transverse toughness of Comparative Example 1 differed greatly, indicating that the introduction of an appropriate amount of Ca can significantly improve the plasticity, toughness and uniformity of the steel.

[0166] Compared with Example 1, Comparative Example 2 differs in that the Ca content is too low. As can be seen from Table 2, the plasticity and toughness of the oil drill collar in Comparative Example 2 are significantly lower than those in Example 1, and the longitudinal and transverse toughness of Comparative Example 2 are significantly different. This indicates that the low Ca content will lead to poor steel plasticity, toughness and uniformity.

[0167] Compared with Example 1, Comparative Example 3 did not add Zr. As can be seen from Table 2, the strength and toughness of the oil drill collar in Comparative Example 3 are significantly lower than those in Example 1, indicating that V-Zr composite microalloying can achieve better strengthening and toughening effects than single microalloying element V.

[0168] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. An oilfield drill collar, characterized by, The composition of the petroleum drill collar includes, in percentage by mass, C: 0.43% to 0.48%, Si: 0.17% to 0.37%, Mn: 0.90% to 1.05%, P≤0.015%, S≤0.005%, Cr: 0.90% to 1.05%, Mo: 0.40% to 0.55%, V: 0.03% to 0.08%, Zr: 0.02% to 0.05%, Al: 0.015% to 0.025%, Ca: 0.015% to 0.025%, O+H+N≤0.007%, and the balance of Fe and inevitable impurities.

2. The petroleum drill collar of claim 1, wherein, The petroleum drill collar has a room temperature yield strength of 935 to 949 MPa, a tensile strength of 1100 to 1116 MPa, an elongation of 18%, a longitudinal Charpy impact toughness at -20℃ of 98 to 109 J, a transverse Charpy impact toughness of 79 to 90 J, and a hardness of 300 to 350 HB.

3. The petroleum drill collar of claim 1, wherein, The outer surface hardness of the internal thread joint of the petroleum drill collar is 51 to 56 HRC.

4. The method of producing a petroleum drill collar according to any one of claims 1 to 3, characterized by, The method comprises the following steps: Step 1, electric furnace or oxygen converter steelmaking, external refining and vacuum degassing, feeding Si-Ca wire to control the deformation of inclusions in the steel, and obtaining a molten steel; the composition of the molten steel is consistent with the composition of the petroleum drill collar in claim 1; Step 2, continuously casting the molten steel into a rod-shaped continuous casting billet; Step 3, rough machining and hole machining of the rod-shaped continuous casting billet to obtain a pipe blank; Step 4, heat treatment of the pipe blank; Step 5, finish machining and thread machining of the pipe blank after heat treatment; Step 6, thread root rolling strengthening; Step 7, surface quenching and tempering treatment of the outer surface of the internal thread joint of the pipe blank.

5. The method of claim 4, wherein the petroleum drill collar is prepared by the steps of: For the petroleum drill collar with an outer diameter greater than 171.4 mm, step 3 comprises: forging the rod-shaped continuous casting billet, and then performing external circle machining and deep hole drilling on the forged rod-shaped continuous casting billet.

6. The method of claim 5, wherein the petroleum drill collar is prepared by the steps of: The rod-shaped continuous casting billet is forged by heating the rod-shaped continuous casting billet to 1170℃ to 1220℃, maintaining for 90 to 120 min, rough forging at 1080℃ to 1190℃, and finish forging at 900℃ to 1050℃, and the forging ratio is greater than or equal to 3, and the forged billet is air cooled.

7. The method of claim 4, wherein the petroleum drill collar is prepared by a process comprising the steps of: For the petroleum drill collar with an outer diameter not greater than 171.4 mm, step 3 comprises: ​ 8. The method of claim 7, wherein the petroleum drill collar is prepared by a process comprising: hot piercing and hot rolling of the rod-shaped continuous casting billet. ​ 9. The method of claim 4, wherein the petroleum drill collar is prepared by a process comprising: The rod-shaped continuous casting billet is hot pierced and hot rolled by heating the rod-shaped continuous casting billet to 1170℃ to 1220℃ for 90 to 120 min, then hot piercing at 1150℃ to 1190℃, hot rolling at 900℃ to 1150℃, and then cooling. In step 4, the pipe blank is heat treated by using a quenching and tempering heat treatment process; the heating temperature of quenching is 840℃ to 860℃, the holding time is 60 to 90 min, the cooling medium is PAG quenching liquid, the tempering temperature is 600℃ to 620℃, the tempering time is 90 to 120 min, and the pipe blank is water cooled after tempering. ​ 10. The method of claim 4, wherein the petroleum drill collar is prepared by a process comprising: In step 7, the outer surface of the pipe blank internal thread joint is subjected to surface quenching and tempering treatment, specifically: quenching heating temperature is 870-900℃, tempering temperature is 200-220℃, and tempering time is 90-120min. ​

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