Planetary lead screw steel pipe for oil and gas drilling and production environment and manufacturing method of planetary lead screw steel pipe

Abstract

The invention relates to a hollow planetary lead screw steel pipe for an oil gas drilling and production environment. The hollow planetary lead screw steel pipe comprises the following chemical components in percentage by mass: 0.25-0.50% of C, 1.50-2.00% of Si, 1.20-1.60% of Mn, 0.80-1.20% of Cr, less than or equal to 0.002% of S, less than or equal to 0.025% of P, 0.02-0.06% of Nb, 0.50-1.30% of W, less than or equal to 0.05% of Al, 0.002-0.006% of Ca, less than or equal to 0.003% of Ti, less than or equal to 0.0010% of O, less than or equal to 0.04% of As, less than or equal to 0.03% of Sn, less than or equal to 0.005% of Sb, less than or equal to 0.002% of Pb and the balance of Fe and The requirements for the high-temperature tensile property at 350 DEG C and the low-temperature impact property at-20 DEG C in the delivery state of the steel pipe are as follows: the yield strength is greater than or equal to 1350 MPa, the tensile strength is greater than or equal to 1580 MPa, the ductility is greater than or equal to 5%, and the Charpy impact energy AKU2 at-20 DEG C is greater than And a JIS G 0561 method is adopted to test the end hardenability, and the J9mm hardness is required to be larger than or equal to 58 HRC.

Description

Technical Field

[0001] The invention belongs to the technical field of special steel smelting, and in particular relates to a planetary screw steel pipe used in an oil and gas drilling environment and a manufacturing method thereof. Background Art

[0002] With the development of the oil and gas extraction industry, the traditional "kowtow machine" is being replaced by a planetary screw. Since the service environment is often accompanied by a high temperature of 200-350°C, the material itself is required to be high temperature resistant. Secondly, oil and gas extraction also requires downhole parts to meet the ability to resist hydrogen sulfide corrosion. This requires the steel of the present invention to have higher toughness, wear resistance, hydrogen sulfide corrosion resistance and resistance to heat treatment deformation.

[0003] Traditional lead screws use high-carbon chromium bearing steels such as GCr15 and GCr15SiMn. Such materials have insufficient resistance to temper softening in high-temperature environments, and the heat treatment deformation of high-carbon bearing steel is difficult to control, especially when making hollow thin-walled parts such as planetary lead screw nuts. This is the main factor that leads to the failure of the final planetary lead screw grinding accuracy to meet the standards. In terms of hydrogen sulfide corrosion resistance, high-carbon chromium bearing steel has a very high tendency to hydrogen embrittlement and cannot be used in the oil and gas extraction industry. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a planetary screw steel tube for oil and gas drilling and production environments and a manufacturing method thereof in response to the above-mentioned prior art, so that the processed planetary screw can maintain ultra-high hardness, strength, wear resistance and hydrogen sulfide corrosion resistance on the surface under high temperature service conditions, and has good dimensional stability during processing and use, thereby ensuring the precision and life of the final screw during service.

[0005] The non-metallic inclusion requirements for the steel of the present invention are shown in Table 1 below: Table 1

[0006] The mechanical properties of the invention are tested in the delivery state, and the requirements for high temperature tensile properties at 350°C and impact properties at -20°C are shown in Table 2 below: Table 2 Mechanical properties Yield Strength tensile strength Elongation <![CDATA[Impact energy AKU2 at -20°C]]> Require ≥1350MPa ≥1580MPa ≥5% ≥27J The JIS G 0561 method is used to test the end hardenability, requiring the J9mm hardness to be ≥58HRC.

[0007] The technical solution adopted by the present invention to solve the above problems is: a planetary screw steel pipe for oil and gas drilling and production environment, the chemical composition of the steel pipe is C: 0.25-0.50%, Si: 1.50-2.00%, Mn: 1.20-1.60%, Cr: 0.80-1.20%, S: ≤0.002%, P≤0.025%, Nb: 0.02-0.06%, W: 0.50-1.30%, Al≤0.05%, Ca: 0.002-0.006%, Ti≤0.003%, O≤0.0010%, As≤0.04%, Sn≤0.03%, Sb≤0.005%, Pb≤0.002%, and the balance is Fe and unavoidable impurities.

[0008] The chemical composition design basis of the planetary screw steel of the present invention is as follows: 1) Determination of C content C is an element necessary to ensure wear resistance. Carbon in steel increases hardness and strength by increasing martensite transformation ability, thereby improving wear resistance. However, a C content exceeding 0.50% will increase the pipe penetration and heat treatment crack sensitivity of the pipe. The present invention controls its content to 0.25-0.50%.

[0009] 2) Determination of Si content Si is a deoxidizer in the steelmaking process and improves the hardness, strength, elastic limit and yield strength ratio of steel in the form of solid solution strengthening. It reduces the diffusion rate of C in ferrite, making it difficult for carbides precipitated during tempering to aggregate, and improves the steel's resistance to tempering softening. In addition, Si reduces the oxidation effect during frictional heating and increases the cold deformation hardening rate of steel, thereby improving the wear resistance of the material. However, too high Si content will reduce the toughness of steel. The present invention controls the Si content to 1.50-2.00%.

[0010] 3) Determination of Mn content Mn, as a deoxidizing element in the steelmaking process, is an effective element for strengthening steel. It plays a role in solid solution strengthening to compensate for the strength loss caused by the reduction of C content in steel. In addition, Mn can improve the hardenability of steel and improve the hot working performance of steel. Mn can eliminate the influence of S (sulfur): Mn can form high melting point MnS with S in steel smelting, thereby weakening and eliminating the adverse effects of S. A Mn content as high as 1.60% will significantly reduce the toughness of steel. The Mn content of the present invention is controlled at 1.20-1.60%.

[0011] 4) Determination of Cr content Cr is a carbide-forming element that can improve the hardenability, wear resistance and corrosion resistance of steel. Part of the Cr in the steel replaces iron to form alloy cementite, which improves the tempering stability of the steel; part of it dissolves into the ferrite to produce solid solution strengthening, which improves the strength and hardness of the ferrite. However, if the Cr content is too high, it will combine with the carbon in the steel to easily form large carbides, which will reduce the contact fatigue life of the steel. Based on the above analysis, the range of the Cr content in the present invention is determined to be 0.80-1.20%.

[0012] 5) Determination of Al content Al is a deoxidizer in the smelting process. In addition to reducing the dissolved oxygen in the molten steel, Al and N form dispersed and fine aluminum nitride inclusions to refine the grains. However, when the Al content exceeds 0.05%, the fluidity of the molten steel decreases significantly, increasing the difficulty of casting. The range of the Al content in the present invention is determined to be ≤0.05%.

[0013] 6) Determination of Nb content Nb is a strong ferrite-forming element and a strong carbonitride-forming element. It is easy to form metal compounds when heated for a long time. In addition to its own solid solution strengthening, NbC and Nb (CN) precipitate material points during hot working to organize grain boundary movement and refine grains. In order to control costs and achieve the expected effect, the range of Nb content in the present invention is determined to be Nb: 0.02-0.06%.

[0014] 7) Determination of W content The tungsten element W improves the tempering resistance of steel. The carbide is very hard, thus improving the wear resistance of steel and giving it a certain degree of hot hardness, while improving the creep resistance of steel at high temperatures. During quenching and heating, carbides such as (FeW6)C are difficult to dissolve, which plays a role in refining grains. In the tempering process, within the range of 500-600°C, tungsten carbide W2C is mainly precipitated and dispersed in the martensite matrix, which has a secondary hardening function. However, due to the high melting point of W, the stress concentration caused by "tungsten inclusion" is reduced as much as possible on the basis of ensuring high temperature strength. Combined with the smelting cost control, the range of W content in the present invention is determined to be 0.50-1.30%.

[0015] 8) Determination of Ca content Ca can form point-like sulfides with S, changing the morphology of long strip-like sulfides, thereby obtaining very good hydrogen sulfide resistance, and the optimal calcium-sulfur ratio is 2-2.5. However, too much Ca content will increase the number and size of point-like oxides in the steel. At the same time, due to the high hardness and poor plasticity of the point-like oxides, they will not deform when the steel is deformed, and it is easy to form gaps at the interface, which will deteriorate the performance of the steel. The range of Ca content in the present invention is determined to be 0.002-0.006%.

[0016] 9) Determination of Ti content Ti harms steel in the form of titanium nitride and titanium carbonitride inclusions. Such inclusions are hard and angular, which seriously affect the fatigue life of the material. Especially when the purity is significantly improved and the number of other oxide inclusions is small, the harm of titanium-containing inclusions is particularly prominent. At the same time, combined with smelting cost control, the range of Ti content in the present invention is determined to be ≤0.003%.

[0017] 10) Determination of O content The oxygen content represents the total amount of oxide inclusions. Oxide brittle inclusions limit the service life of the finished product. A large number of tests have shown that reducing the oxygen content is significantly beneficial to improving the purity of steel, especially reducing the content of oxide brittle inclusions in steel grades. At the same time, combined with smelting cost control, the range of oxygen content in the present invention is determined to be ≤0.0010%.

[0018] 11) Determination of P and S content P in steel can cause serious segregation during solidification. P dissolves in ferrite to cause grain distortion and coarsening, and increase cold brittleness. At the same time, it is combined with smelting cost control. The range of P content in the present invention is determined to be ≤0.025%. S makes steel hot brittle, reduces the ductility and toughness of steel, and the S element of hydrogen sulfide corrosion-resistant steel needs to be strictly controlled, combined with smelting cost control. The range of S content in the present invention is determined to be ≤0.002%.

[0019] 12) Determination of As, Sn, Sb and Pb content As, Sn, Sb, Pb and other trace elements are all low melting point non-ferrous metals. The presence of them in steel materials causes soft spots on the surface of parts and uneven hardness. Therefore, they are regarded as harmful elements in steel and combined with smelting cost control. The content range of these elements in the present invention is determined as As≤0.04%, Sn≤0.03%, Sb≤0.005%, and Pb≤0.002%.

[0020] The manufacturing process of the above-mentioned planetary screw steel is KR pretreatment - electric furnace or converter - refining outside the furnace - VD or RH vacuum degassing - continuous casting - continuous rolling - shearing or sawing - slow cooling - spheroidizing annealing - finishing - punching and warehousing.

[0021] The manufacturing method mainly comprises the following steps: 1) Use high-quality molten iron, scrap steel and raw and auxiliary materials to reduce the content of harmful elements in molten steel, and complete deep desulfurization through KR pretreatment. Strengthen the deoxidation in the refining process to ensure the amount of residual aluminum in the steel. Use the good dynamic conditions in the molten steel to carry out centralized advance deoxidation and VD or RH vacuum degassing treatment to fully float non-metallic inclusions and control the gas content at a low level. After vacuum degassing, perform long-term soft argon blowing to ensure that the inclusions fully float. At the same time, anti-oxidation protection should be carried out throughout the continuous casting process to reduce the number of inclusions in the steel. In addition, high-quality refractory materials are used to reduce the control technology of foreign inclusions on molten steel pollution and strengthen the control of the production process.

[0022] 2) The continuous casting process adopts electromagnetic stirring and light pressure reduction technology, and adopts low superheat casting to effectively improve and reduce the composition segregation of the continuous casting billet. In particular, after adding advanced equipment such as electromagnetic stirring and light pressure reduction at the end of solidification, the density of the solidification structure of the billet is improved, the looseness and shrinkage holes in the center of the billet are effectively controlled, and the spacing between the secondary dendrite arms is significantly improved. The central equiaxed crystal rate is significantly improved, and the grains are refined, thereby significantly improving the quality of the billet and reducing the composition segregation.

[0023] 3) The smelting raw materials are sequentially smelted in an electric furnace or converter, LF refined, RH or VD vacuum degassed and continuously cast, and the continuous casting square billets with specifications of 390×510mm and above that are consistent with the chemical composition of the finished steel products are continuously cast; the continuous casting billets should be slowly cooled in the pit to prevent the continuous casting billets from cracking, and the slow cooling time should be not less than 72 hours. Then the continuous casting billets are electroslag remelted again to make φ600mm electroslag ingots, and slowly cooled for 72 hours. Then they are sent to a heating furnace with a neutral or weak oxidizing atmosphere for heating and billeting into intermediate billets of 200×200mm-300×300mm, with a heating temperature of 1020-1270℃ and a heating time of more than 5 hours. The rolling temperature during billet rolling is 1000℃-1250℃, the final rolling temperature is ≥850℃, the billet rolling compression ratio is greater than 5, the intermediate billet should be slowly cooled in the pit, the pit temperature is ≥500℃, and the slow cooling time is not less than 72 hours.

[0024] 4) Then send the intermediate billet to the heating furnace and roll it into the target steel pipe. The specific rolling process is: the temperature of the preheating section is controlled at 500-800℃, the temperature of the heating section is controlled at 1050-1250℃, and the temperature of the soaking section is controlled at 1050-1250℃. In order to ensure that the billet is fully and evenly heated, the total heating time is more than 8 hours. The rolling start temperature is controlled at 1000℃-1200℃, the final rolling temperature is controlled at more than 850℃, and the stack cooling is performed after the rolling is completed.

[0025] In order to ensure that the steel pipe only needs to be turned and then the roller surface laser quenched to meet the service hardness when manufacturing the planetary screw, and the organization is stable to ensure the dimensional accuracy while meeting the strength required for service, the steel pipe production innovatively adopts the online normalizing + sub-temperature quenching + secondary tempering process: When hot-rolling steel pipes, water is passed online after final rolling to ensure that the temperature range of the upper cooling bed is 600~750℃, so that the hot-rolled stack cooling structure is a mixed state of bainite + martensite, providing distortion energy for subsequent spheroidizing annealing. By heating at 820±10℃ for 7 hours, it is ensured that in the two-phase region of ferrite and austenite, part of the cementite is dissolved in austenite, and the matrix retains cementite particles for subsequent nucleation to achieve dynamic equilibrium. Then salt bath quenching, 880±10℃ for 3 hours to obtain a dual-phase structure of martensite-ferrite. Then successively 710±10℃ for 3.5 hours of tempering water cooling + 610±10℃ for 5 hours of tempering air cooling, to obtain uniform point-shaped cementite (generally 0.1~0.5μm) while giving full play to the tempering strengthening function of tungsten element. The tensile strength of the final delivery state can reach more than 1580MPa.

[0026] Compared with the prior art, the advantages of the present invention are: 1) Different from the traditional GCr15 bearing steel, the chemical composition has been optimized, which significantly improves the steel's hardenability, yield strength, tensile strength, hydrogen sulfide corrosion resistance and high temperature softening resistance, and has a low crack tendency. It meets the machining strength requirements of hollow materials.

[0027] 2) Better than the coarse spherical cementite (generally 1~3μm) of the traditional GCr15 bearing steel, the cementite of the steel of the present invention is in a uniform and finer spheroidized state (generally 0.1~0.5μm) when it is delivered, with a spheroidization rate of more than 95%, and the rest of the structure is ferrite. The structure distortion energy is small, the heat treatment deformation during the processing of the screw product is small, the dimensional accuracy is high, and it can meet the precision use requirements of the planetary screw.

[0028] 3) Traditional GCr15 bearing steel has poor tempering resistance. Long-term high temperature environment will reduce the strength of the steel and cause deformation and loss of precision. The planetary screw steel of the present invention has yield strength (≥1350MPa) and tensile strength (≥1580MPa) under 350°C environment. At the same time, in order to cope with the low temperature environment often encountered by high-altitude equipment, the present invention has low-temperature toughness far exceeding that of bearing steel (Charpy impact energy AKU2≥27J at -20°C). BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is an organizational diagram of the delivery status of Example 1 of the present invention.

[0030] Figure 2 This is an organizational diagram of the delivery status of Example 2 of the present invention.

[0031] Figure 3 This is an organizational diagram of the delivery status of Example 3 of the present invention. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is described in more detail in conjunction with the preferred embodiments of the present invention. However, these embodiments are only descriptions of the preferred implementation methods of the present invention and cannot impose any limitation on the scope of the present invention.

[0033] Examples 1-3 respectively exemplify the chemical composition and manufacturing method of the steel for planetary screws of the present invention, and compare them with GCr15 bearing steel commonly used in the market.

[0034] The chemical composition (wt%) of each example is shown in Tables 3 and 4. Table 3 Example C Si Mn P S Cr W Nb Al The present invention 1 0.37 1.65 1.41 0.013 0.001 1.05 0.98 0.031 0.022 The present invention 2 0.38 1.67 1.43 0.013 0.001 1.02 0.95 0.026 0.021 The present invention 3 0.38 1.68 1.42 0.013 0.001 1.03 0.93 0.025 0.021 GCr15 4 0.99 0.25 0.32 0.020 0.015 1.48 -- 0.05 0.020 Table 4 Example As Sn Sb Pb Ca Ti O The present invention 1 0.0031 0.012 0.0013 0.001 0.0022 0.0012 0.00056 The present invention 2 0.0034 0.011 0.0012 0.001 0.0026 0.0011 0.00051 The present invention 3 0.0026 0.012 0.0011 0.001 0.0029 0.0012 0.00049 GCr15 4 0.0051 0.021 0.0023 0.001 0.0001 0.0023 0.00071 The inclusions of the steel materials in each example are shown in Table 5. Table 5 Example A Fine inclusions A Coarse inclusions B Fine inclusions B Coarse inclusions C Fine inclusions C Coarse inclusions D Fine inclusions D Coarse inclusions Ds inclusion The present invention 1 0-0.5 0-0.5 0-1.0 0 0 0 0-0.5 0-0.5 0-0.5 The present invention 2 0-0.5 0-0.5 0-1.0 0 0 0 0-0.5 0-0.5 0-0.5 The present invention 3 0-0.5 0-0.5 0-0.5 0-0.5 0 0 0-0.5 0-0.5 0-0.5 GCr15 4 0-0.5 0-0.5 0-0.5 0-0.5 0 0 0-1.0 0-1.0 1.0-1.5 The mechanical properties (delivery status) of each embodiment are compared. The tensile properties at 350°C and the impact properties at -20°C are shown in Table 6. Table 6 Example Yield strength Rel (MPa) Tensile strength Rm (MPa) <![CDATA[Elongation A5 (%)]]> <![CDATA[Charpy impact energy AKU2 at -20°C]]> Hardness HRC The present invention 1 1399 1616 10.0 54 47.9 The present invention 2 1411 1633 10.0 59 48.0 The present invention 3 1391 1621 10.0 70 48.2 GCr15 4 938 1089 13.0 13 35.8 The end hardenability data of the steel materials in each embodiment are shown in Table 7 Table 7 Example J9mm(HRC) The present invention 1 58.92 The present invention 2 59.11 The present invention 3 58.12 GCr15 4 43.33 The microstructure of the steel materials in each embodiment is shown in Figure 1-3 Different from the coarse spherical cementite of the traditional GCr15 bearing steel, the cementite of the steel in the delivery state of the present invention exists in a uniform and finer (generally 0.1~0.5μm) spheroidized state, with a spheroidization rate of more than 95%, and the rest of the structure is ferrite. The structure distortion energy is small, the heat treatment deformation during the processing of the screw product is small, the dimensional accuracy is high, and it can meet the precision use requirements of the planetary screw.

[0035] The manufacturing process of the planetary screw steel in each embodiment is electric furnace or converter - refining outside the furnace - VD or RH vacuum degassing - continuous casting - electroslag remelting - electroslag ingot squaring into intermediate billet - intermediate billet hot rolling into material - heat treatment - finishing - punching and warehousing.

[0036] During the specific smelting, high-quality molten iron, scrap steel and raw and auxiliary materials, high-quality deoxidizers and refractory materials are selected. In the production process of electric furnace / converter, the steel tapping end point C of the three embodiments is controlled at 0.05-0.35%, the end point P is required to be ≤0.025%, and the continuous casting superheat is controlled within 15-35°C.

[0037] Table 8

[0038] The intermediate billet is sent to the heating furnace and rolled into the target steel pipe. The specific rolling process is: the preheating section temperature is set at 500-800℃, the heating section temperature is controlled at 1050-1250℃, and the soaking section temperature is controlled at 1050-1250℃. To ensure that the billet is fully and evenly heated, the total heating time is 2 hours or more. The rolling start temperature is controlled at 1000-1200℃, and the final rolling temperature is controlled at above 850℃. When hot-rolling steel pipes, water is passed online after final rolling to ensure that the temperature range of the upper cooling bed is 600~750℃. After rolling, the stack cooling is completed to make the hot-rolled stack cooling structure a mixed state of bainite + martensite. The finished steel pipes that have been rolled and normalized online are subjected to sub-temperature quenching + secondary tempering treatment. They are heated at 825±10℃ for 7 hours to ensure that part of the cementite is dissolved in the austenite in the two-phase region of ferrite and austenite, and the matrix retains cementite particles for subsequent nucleation to achieve dynamic equilibrium. Then, they are quenched in a salt bath and quenched at 880±10℃ for 3 hours to obtain a dual-phase structure of martensite-ferrite. Then, they are tempered and water-cooled at 680±10℃ for 3.5 hours and tempered and air-cooled at 580±10℃ for 5 hours. After tempering, they are straightened and inspected to obtain the target steel pipe products, which are finally punched and put into storage.

[0039] It can be seen from Tables 3, 4, 5, 6, and 7 that the planetary screw steel pipe for oil and gas drilling environment in the above embodiments of the present invention has significantly better control levels of harmful elements such as oxygen, titanium, and non-metallic inclusions than the traditional GCr15 bearing steel. Especially in terms of mechanical properties under high temperature environment, the yield strength, tensile strength, low temperature impact, hydrogen sulfide corrosion resistance, and high temperature softening resistance of the present invention are significantly better than the traditional GCr15 bearing steel, the yield strength is increased by nearly 500MPa, the tensile strength is increased by 500MPa, the low temperature impact performance is increased by nearly 60J, and the hardness is increased by nearly 15HRC. The hardenability is also significantly better than the traditional GCr15 bearing steel.

[0040] Although the preferred embodiments of the present invention are described in detail above, it should be clearly understood that various modifications and variations are possible for those skilled in the art. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A planetary screw steel tube for oil and gas drilling and production environment, characterized in that: The chemical composition of the steel pipe is calculated by mass percentage as follows: C: 0.25-0.50%, Si: 1.50-2.00%, Mn: 1.20-1.60%, Cr: 0.80-1.20%, S: ≤0.002%, P≤0.025%, Nb: 0.02-0.06%, W: 0.50-1.30%, Al≤0.05%, Ca: 0.002-0.006%, Ti≤0.003%, O≤0.0010%, As≤0.04%, Sn≤0.03%, Sb≤0.005%, Pb≤0.002%, and the balance is Fe and unavoidable impurities.

2. The planetary screw steel tube for oil and gas drilling environment according to claim 1, characterized in that: The steel pipe has the following requirements for high temperature tensile properties at 350°C and low temperature impact properties at -20°C in the delivery state: yield strength ≥1350MPa, tensile strength ≥1580MPa, elongation ≥5%, -20°C Charpy impact energy AKU2 ≥27J, and the end hardenability is tested by JIS G 0561 method, requiring J9mm hardness ≥58HRC.

3. The planetary screw steel tube for oil and gas drilling environment according to claim 1, characterized in that: In the delivery state of the steel pipe, cementite exists in a spheroidized state of 0.1-0.5 μm, with a spheroidization rate of more than 95%, and the remaining structure is ferrite.

4. A method for manufacturing a planetary screw steel tube for oil and gas drilling and production environment as claimed in claim 1, characterized in that: The method comprises the following steps: 1) The smelting raw materials are sequentially subjected to electric furnace or converter smelting, LF refining, RH or VD vacuum degassing and continuous casting to continuously cast continuous casting square billets with specifications of 390×510mm and above that are consistent with the chemical composition of the finished steel products; 2) The continuous casting billet is slowly cooled in the pit for no less than 72 hours, and then the continuous casting billet is electroslag remelted again to make a φ600mm electroslag ingot, which is slowly cooled for 72 hours; 3) After being sent to a heating furnace in a neutral or weakly oxidizing atmosphere for heating, the intermediate billet is cut into 200×200mm-300×300mm intermediate billets, and the intermediate billets are slowly cooled in a pit, the pit temperature is ≥500℃, and the slow cooling time is not less than 72 hours; 4) The intermediate billet is sent to the heating furnace and rolled into the target steel pipe. The temperature of the preheating section is controlled at 500-800℃, the temperature of the heating section is controlled at 1050-1250℃, and the temperature of the soaking section is controlled at 1050-1250℃. In order to ensure that the billet is fully and evenly heated, the total heating time is more than 8 hours, the rolling start temperature is controlled at 1000℃-1200℃, the final rolling temperature is controlled at more than 850℃, and the stack cooling is performed after the rolling is completed; 5) Adopting online normalizing + sub-temperature quenching + secondary tempering process, the cementite in the delivery state is in a uniform and finer spheroidized state, the spheroidization rate is more than 95%, and the rest of the organization is ferrite steel pipe; 6) After tempering, the steel pipe is straightened and inspected to obtain the target steel pipe product.

5. The method for manufacturing a planetary screw steel tube for oil and gas drilling and production environment according to claim 4, characterized in that: During the production process of electric furnace / converter, the steel tapping end point C is controlled at 0.05-0.35%, the end point P is required to be ≤0.025%, and the continuous casting superheat is controlled within 15-35℃.

6. The method for manufacturing a planetary screw steel tube for oil and gas drilling and production environment according to claim 4, characterized in that: In step 3), the heating temperature is 1020-1270°C, the heating time is greater than 5 hours, the opening temperature during slab rolling is 1000°C-1250°C, the final rolling temperature is ≥850°C, and the slab rolling compression ratio is greater than 5.

7. The method for manufacturing a planetary screw steel tube for oil and gas drilling and production environment according to claim 4, characterized in that: Step 5) During hot rolling of the steel pipe, water is passed online after final rolling to ensure that the temperature range of the upper cooling bed is 600-750°C, so that the hot rolled state stack cooling structure is a mixed state of bainite + martensite.

8. The method for manufacturing a planetary screw steel tube for oil and gas drilling and production environment according to claim 4, characterized in that: In step 5), the online normalizing + sub-temperature quenching + secondary tempering process is as follows: the steel pipe is heated at 820±10℃ for 7 hours; then salt bath quenching, 880±10℃ for 3 hours to obtain a dual-phase structure of martensite-ferrite; then successively tempered by water cooling at 710±10℃ for 3.5 hours, and tempered by air cooling at 610±10℃ for 5 hours to obtain uniform point-like cementite.

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