High-strength oil casing pipe and method for manufacturing the same

Abstract

The present invention discloses a high-strength oil casing pipe containing Fe and inevitable impurity elements, and further containing the following chemical elements in the following mass percentage contents: C: 0.06 - 0.15%; Si: 0.3 - 0.5%; Mn: 1.5 - 2.2%; rare earths (La, Ce): 0.002 - 0.006%; Ti ≤ 0.05%; Al: 0.01 - 0.03%; 0 < N ≤ 0.008%. Correspondingly, the present invention further discloses a manufacturing method of the above high-strength oil casing pipe, including the following steps: (1) smelting and casting; (2) drilling; (3) rolling; (4) sizing; (5) online quenching: controlling the temperature of the casing pipe body before cooling to 780°C or higher, water-cooling the outer surface of the casing pipe at a cooling rate of 40 - 100°C / S, and controlling the final cooling temperature to 100°C or lower; (6) tempering: controlling the tempering temperature to 500 - 620°C and controlling the holding time to 40 - 70 min; (7) hot stress relief.

Description

Technical Field

[0001] The present invention relates to a steel pipe and a method for manufacturing the same, and particularly to an oil casing pipe and a method for manufacturing the same.

Background Art

[0002] In recent years, seamless steel pipes have been widely used in fields such as oil, gas, and energy, playing a very important role. They are called the "blood vessels of the industry" and are an indispensable and important steel type.

[0003] In the prior art, as steel grades of seamless pipes for oil wells and gas wells, model numbers such as N80-Q and P110 according to API standards are generally used. According to the research of the present inventors, all of these casing pipes are manufactured by adopting a hot rolling + quenching and tempering heat treatment process in the manufacturing process. After hot rolling, it is necessary to cool to room temperature and then reheated in a quenching heating furnace to perform quenching heat treatment. Such a process not only causes waste of waste heat after rolling the steel pipe (usually, the temperature of the rolled steel pipe is above 900 °C), but also adds one pass of the heat treatment process to increase the cost, and its resource and energy consumption are high, bringing many limitations to the development of high-quality pipe materials and efficient production.

[0004] Therefore, in order to reduce energy consumption and increase the strength of steel materials, existing sheet materials are often manufactured by a controlled rolling and controlled cooling process. However, due to the special annular cross-section characteristics of seamless steel pipes, their internal stress state becomes more complex compared with sheet materials. In a controlled cooling process such as online quenching that utilizes waste heat, cracks are likely to occur in the steel pipe, and it should be noted that since the rolling temperature is high, the crystal grain size of the steel pipe becomes large, which is disadvantageous for improving toughness.

[0005] For example, in a Chinese patent document with publication number CN103774063A, publication date May 7, 2014, and title "Large-diameter oil casing pipe and its TMCP manufacturing method", a low-carbon equivalent micro-alloy steel pipe and its online normalizing process are disclosed, which have stable mechanical properties and good collapse resistance performance. The technical solution adopts a TMCP manufacturing method with simple processes and high production efficiency. However, in this patent, since a medium-carbon CrMo steel material similar to the material of conventional oil well pipes is used, the risk of cracking still exists during online quenching.

[0006] Also, for example, in a Chinese patent document with publication number CN103757561A, publication date April 30, 2014, and title "Large-diameter thick-walled seamless steel pipe for offshore use and its TMCP manufacturing method", a large-diameter thick-walled seamless steel pipe for offshore use and its TMCP manufacturing method are disclosed, which have stable mechanical properties and good low-temperature impact performance. However, due to its relatively high alloy content, the risk of cracking exists during online quenching.

[0007] Therefore, the present invention hopes to develop a novel high-strength oil casing pipe and its manufacturing method in order to solve such problems existing in the prior art.

Summary of the Invention

Problems to be Solved by the Invention

[0008] One object of the present invention is to provide a high-strength oil casing pipe. By adopting reasonable component matching and process design, the high-strength oil casing pipe has both high strength and high toughness, with a yield strength of 552 - 965 MPa, a tensile strength of ≥689 MPa, an elongation rate of ≥20%, and a 0°C transverse Charpy impact energy of ≥80 J, and can meet the usage requirements of oil and gas fields for the performance of high-strength casing pipes.

Means for Solving the Problems

[0009] To achieve the above object, the present invention contains Fe and inevitable impurity elements, and further contains the following chemical elements in the following mass percentage contents: C: 0.06 to 0.15%; Si: 0.3 to 0.5%; Mn: 1.5 to 2.2%; La + Ce: 0.002 to 0.006%; Ti ≤ 0.05%; Al: 0.01 to 0.03%; 0 < N ≤ 0.008% and provides a high-strength oil casing pipe.

[0010] Furthermore, in the high-strength oil casing pipe according to the present invention, the mass percentage of each chemical element is C: 0.06 to 0.15%; Si: 0.3 to 0.5%; Mn: 1.5 to 2.2%; La + Ce: 0.002 to 0.006%; Ti ≤ 0.05%; Al: 0.01 to 0.03%; 0 < N ≤ 0.008%; the balance is Fe and inevitable impurities; preferably, La + Ce: 0.002 to 0.005%.

[0011] In the high-strength oil casing pipe according to the present invention, the design principle of each chemical element is as follows.

[0012] C: In the high-strength oil casing pipe according to the present invention, C is a carbide-forming element and can improve the strength of the steel. When the content of the C element in the steel is less than 0.06%, the hardenability of the steel material is reduced and the toughness of the steel is reduced. However, when the content of the C element in the steel exceeds 0.15%, the segregation of the steel is significantly worsened and hot cracking is likely to occur. Therefore, considering the influence of the C element content on the steel material performance, in order to meet the requirement of high strength of the oil casing pipe, in the high-strength oil casing pipe according to the present invention, the mass percentage content of the C element is controlled to be 0.06 - 0.15%.

[0013] Of course, in some preferred embodiments, in order to obtain better implementation effects, preferably, the mass percentage content of the C element may be controlled to be 0.08 - 0.14%.

[0014] Si: In the high-strength oil casing pipe according to the present invention, the Si element can dissolve in ferrite and can improve the yield strength of the steel material. Moreover, Si is also a ferrite-forming element and contributes to the improvement of the toughness of the steel material. When the content of the Si element is less than 0.3%, the oil casing pipe is likely to be oxidized, so the content of the Si element in the steel should not be too high. At the same time, it should be noted that too high a content of the Si element will deteriorate the workability and toughness of the steel material, so the addition amount of the Si element in the steel should not be too low. Therefore, in order to exert the beneficial effects of the Si element, it is necessary to strictly control the content of the Si element in the steel. In the high-strength oil casing pipe according to the present invention, the mass percentage content of the Si element is controlled to be 0.3 - 0.5%.

[0015] Of course, in some preferred embodiments, in order to obtain better implementation effects, preferably, the mass percentage content of the Si element may be controlled to be 0.3 - 0.45%.

[0016] Mn: In the high-strength oil casing pipe according to the present invention, Mn is an austenite-forming element and can improve the hardenability of steel. In the steel material system designed according to the present invention, when the content of the Mn element is less than 1.5%, the hardenability of the steel material significantly decreases, resulting in a reduction in the proportion of martensite in the steel and a decrease in the toughness of the steel. However, when the Mn content in the steel exceeds 2.2%, component segregation is likely to occur and hot cracking is likely to occur. Therefore, considering the influence of the Mn element content on the steel material performance, in the high-strength oil casing pipe according to the present invention, the mass percentage content of the Mn element is controlled to be 1.5% - 2.2%.

[0017] Of course, in some preferred embodiments, in order to obtain better implementation effects, preferably, the mass percentage content of the Mn element may be controlled to be 1.6 - 2.0%.

[0018] Rare earths (La, Ce): In the high-strength oil casing pipe according to the present invention, both Ce and La are rare earth elements. By adding a rare earth mixture in a certain proportion to the steel, the inclusions in the steel can be modified and refined. The formed rare earth modified product is REAlO3, thereby removing large inclusions, reducing the oxygen content, and improving the toughness index of the steel material. At the same time, the refined inclusions can also promote the formation of recrystallization as nucleation particles for dynamic recrystallization during rolling, thereby refining the austenite grain size and suppressing direct hot cracking after rolling. According to the research of the inventors, when the amount of Ce + La in the steel is >0.006%, coarse inclusions are likely to form, thereby reducing the toughness of the material. However, when the Ce + La content in the steel is <0.002%, the effect of refining crystal particles and modified inclusions becomes insignificant and hot cracking is likely to occur. Therefore, in order to exert the beneficial effects of La and Ce rare earth elements, in the high-strength oil casing pipe according to the present invention, the "rare earths (La, Ce)", which is the total content of La and Ce elements, is controlled to be 0.002 - 0.006%.

[0019] Of course, in some preferred embodiments, in order to obtain better implementation effects, preferably, the contents of rare earth elements La and Ce may be controlled to be 0.0025-0.004%.

[0020] Ti: In the high-strength oil casing pipe according to the present invention, Ti is a strong carbonitride-forming element, which can significantly refine the austenite crystal grains in the steel and compensate for the strength reduction caused by the reduction of carbon content. When the content of Ti element in the steel exceeds 0.05%, coarse TiN is likely to form, leading to a decrease in the toughness of the material. Therefore, in the high-strength oil casing pipe according to the present invention, it is necessary to control the mass percentage content of Ti element to Ti≤0.05%.

[0021] Of course, in some preferred embodiments, in order to obtain better implementation effects, preferably, the mass percentage content of Ti element may be controlled to Ti≤0.03%.

[0022] Al: In the high-strength oil casing pipe according to the present invention, Al is a good deoxidation and nitrogen-fixing element, which can effectively refine crystal grains. Therefore, in the present invention, the mass percentage content of Al element is controlled to be 0.01-0.03% to exert the beneficial effects of Al element.

[0023] Of course, in some preferred embodiments, in order to obtain better implementation effects, preferably, the mass percentage content of Al element may be controlled to be 0.01-0.025%.

[0024] N: In the high-strength oil casing pipe according to the present invention, N can form Ti and TiN, which can refine austenite crystal grains, thereby suppressing direct cracking after rolling. Therefore, in the present invention, the mass percentage content of N element is controlled to 0<N≤0.008%.

[0025] Furthermore, in the high-strength oil casing pipe according to the present invention, among inevitable impurities, P≤0.015% and S≤0.008%.

[0026] Furthermore, in the high-strength oil casing pipe according to the present invention, among inevitable impurities, P ≤ 0.013% and S ≤ 0.0025%.

[0027] In the high-strength oil casing pipe according to the present invention, both the P element and the S element are impurity elements in the steel pipe. When the technical conditions permit, in order to obtain a pipe material with better performance and quality, the content of impurity elements in the high-strength oil casing pipe should be reduced as much as possible.

[0028] Therefore, in the present invention, it is necessary to strictly control the contents of P and S elements in the steel, and control them as P ≤ 0.015% and S ≤ 0.008%. Of course, in some preferred embodiments, in order to obtain better implementation effects, the contents of P and S elements may be further controlled as P ≤ 0.013% and S ≤ 0.0025%.

[0029] Furthermore, in the high-strength oil casing pipe according to the present invention, the mass percentage content of each chemical element further satisfies at least one of the following: C: 0.08 - 0.14%; Si: 0.3 - 0.45%; Mn: 1.6 - 2.0%; La + Ce: 0.0025 - 0.004%; Ti ≤ 0.03%; Al: 0.01 - 0.025%.

[0030] Furthermore, in the high-strength oil casing pipe according to the present invention, its microstructure is tempered sorbite.

[0031] Furthermore, in the high-strength oil casing pipe according to the present invention, the crystal grain size level of its structure exceeds level 8.5.

[0032] Furthermore, in the high-strength oil casing pipe according to the present invention, its yield strength is ≧552 MPa, its tensile strength is ≧689 MPa, its elongation rate is ≧20%, and its 0°C transverse Charpy impact energy is ≧80 J.

[0033] Furthermore, in the high-strength oil casing pipe according to the present invention, its yield strength is ≧630 MPa, its tensile strength is ≧720 MPa, its elongation rate is ≧20%, and its 0°C transverse Charpy impact energy is ≧80 J.

[0034] Furthermore, in the high-strength oil casing pipe according to the present invention, its yield strength is 552 - 965 MPa, its tensile strength is ≧689 MPa, its elongation rate is ≧20%, and its 0°C transverse Charpy impact energy is ≧80 J.

[0035] Furthermore, in the high-strength oil casing pipe according to the present invention, its yield strength is 630 - 965 MPa, its tensile strength is 720 - 1040 MPa, its elongation rate is 21 - 26%, and its 0°C transverse Charpy impact energy is 89 - 150 J.

[0036] Correspondingly, another object of the present invention is to provide a manufacturing method of the above high-strength oil casing pipe. The manufacturing method utilizes the waste heat of the steel pipe after hot rolling for quenching, realizes production of on-line quenching + tempering heat treatment, thereby reducing the manufacturing cost, and at the same time, can efficiently manufacture the high-strength oil casing pipe according to the present invention, having good application prospects.

[0037] In order to achieve the above object, the manufacturing method of the above high-strength oil casing pipe provided by the present invention includes the following steps: (1) Smelting and casting; (2) Piercing; (3) Rolling; (4) Sizing; (5) Online quenching: Control the temperature of the casing pipe body before cooling to 780 °C or higher, water-cool the outer surface of the casing pipe at a cooling rate of 40 - 100 °C / S, and control the final cooling temperature to 100 °C or lower; (6) Tempering: Control the tempering temperature to 500 - 620 °C and control the holding time to 40 - 70 min; (7) Hot straightening.

[0038] In the prior art, a general high-strength casing pipe is usually manufactured by the process of offline quenching + tempering heat treatment. After hot rolling, it needs to be cooled to room temperature and then reheated in a quenching heating furnace to perform quenching heat treatment. Such a processing process for seamless steel pipes not only causes waste of waste heat after rolling the steel pipes, but also adds one more heat treatment process, increasing the cost. Its resource consumption is high, bringing many limitations to the development of high-quality pipe materials and efficient production.

[0039] Different from the prior art, in the manufacturing method of the high-strength oil casing pipe according to the present invention, the inventors utilize the waste heat of the steel pipe after hot rolling to perform quenching, remove the offline quenching process, and realize the production of online quenching + tempering heat treatment. Thereby, the production efficiency can be significantly improved, the manufacturing cost can be reduced, the energy consumption can be reduced, and green manufacturing can be realized.

[0040] However, if the casing pipe is quenched directly after hot rolling, high energy is stored in the distortion of crystal grains. Therefore, cracks are likely to occur in the casing pipe during the quenching process. At the same time, due to the high rolling temperature of the casing pipe, the crystal grain size of the rolled casing pipe becomes large, generally at level 5 - 7, and it should be noted that burn cracks are likely to occur. Therefore, in such a process adopted in the present invention, in order to prevent cracks and stress concentration in the pipe body and ensure safe manufacturing and stable quality, it is necessary to optimize the design of the alloy type and content. For this reason, when the present inventors design the chemical composition, La and Ce rare earth elements are added to the steel to modify and refine the inclusions in the steel, remove large inclusions, reduce the oxygen content, improve the toughness index. At the same time, the refined inclusions promote the formation of recrystallization as nucleation particles for dynamic recrystallization during rolling, thereby refining the austenite crystal grains, obtaining a structure with a crystal grain size of level 8.5 or more, and suppressing direct burn cracks after rolling.

[0041] In addition, a small amount of Ti may be added to the high-strength oil casing pipe designed according to the present invention. The formation of TiN compounds can refine the austenite crystal grains and suppress direct burn cracks after rolling.

[0042] Furthermore, in the manufacturing method according to the present invention, in the steelmaking process of step (1), rare earth alloys are added in the VD (Vacuum Degassing) or LF (Ladle Furnace refining) process, and in the casting process, the superheat degree of the molten steel is controlled to be 40°C or less, and the drawing speed of continuous casting is controlled to be 1.6 - 2.4 m / min, preferably 1.8 - 2.4 m / min. Preferably, the superheat degree of the molten steel is 15 - 40°C.

[0043] Furthermore, in the manufacturing method according to the present invention, in step (2), the round billet is soaked in a furnace at 1200 - 1290°C, and the perforated temperature is 1120 - 1240°C.

[0044] Furthermore, in the manufacturing method according to the present invention, in step (3), the finish rolling temperature is controlled to be 920 to 1000 °C.

[0045] Furthermore, in the manufacturing method according to the present invention, in step (4), the sizing temperature is controlled to be 840 to 910 °C. Preferably, after the completion of step (4) and before the temperature is lowered, step (5) is directly carried out using the waste heat of the pipe body.

[0046] Furthermore, in the manufacturing method according to the present invention, in step (7), the hot straightening temperature is controlled to be 400 to 520 °C.

[0047] Furthermore, in step (5), the temperature of the casing pipe body before cooling is controlled to be 780 °C to 910 °C, and the finish cooling temperature is controlled to be 30 to 90 °C.

[0048] Furthermore, in step (6), the tempering temperature is controlled to be 520 °C to 600 °C. The high-strength oil casing pipe and its manufacturing method according to the present invention have the following advantages and beneficial effects as compared with the prior art: In the present invention, the inventors utilize the waste heat of the steel pipe after hot rolling to perform quenching, eliminate the off-line quenching process, and realize the production of on-line quenching + tempering heat treatment. Thereby, the production efficiency can be significantly improved, the manufacturing cost can be reduced, the energy consumption can be reduced, and green manufacturing can be realized.

[0049] In the manufacturing method of the high-strength oil casing pipe according to the present invention, by adopting the TMCP technology, high strength and good toughness are brought to the steel material. The process and operation are simple, it is easy to realize large-scale production and manufacturing, and the economic advantages are also great. By adopting such a manufacturing process, the finally manufactured high-strength oil casing pipe of 80 - 110 ksi steel grade has very excellent mechanical properties. Its yield strength is 552 - 965 MPa, the tensile strength is ≥ 689 MPa, the elongation rate is ≥ 20%, and the 0°C transverse Charpy impact energy is ≥ 80 J, which can meet the usage requirements in oil and gas fields for the performance of high-strength casing pipes and has good application prospects.

Brief Description of the Drawings

[0050]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0051] Hereinafter, based on the drawings and specific examples, the high-strength casing pipe and its manufacturing method according to the present invention will be further interpreted and described, but such interpretation and description do not unduly limit the technical solution of the present invention.

[0052] Examples 1 - 6 and Comparative Examples 1 - 7 The high-strength casing pipes according to Examples 1 - 6 of the present invention and the comparative steel pipes according to Comparative Examples 1 - 7 were all prepared by the following steps: (1) Smelting and casting were carried out according to the mass percentage ratios of the chemical elements shown in Table 1: During the refining process, the mass percentage ratios of the respective chemical elements in the high-strength casing pipes according to Examples 1 to 6 and the comparative steel pipes according to Comparative Examples 1 to 7 were controlled as shown in Table 1, and rare earth alloys were added in the VD or LF process; after the refining was completed, continuous casting was performed on the pipe billets, and the superheat degree of the molten steel was controlled to be less than 40°C, and the drawing speed of the continuous casting was controlled to be 1.8 to 2.4 m / min.

[0053] (2) Piercing: The round billets obtained through continuous casting were soaked in an annular furnace at 1200 to 1290°C, and the piercing temperature was controlled to be 1120 to 1240°C.

[0054] (3) Rolling: The rolling end temperature was controlled to be 920 to 1000°C; (4) Sizing: The sizing temperature was controlled to be 840 to 910°C.

[0055] (5) Online quenching: The temperature of the casing pipe body before cooling was controlled to be 780°C or higher, the outer surface of the casing pipe was water-cooled at a cooling rate of 40 to 100°C / S, and the cooling end temperature was controlled to be 100°C or lower; (6) Tempering: The tempering temperature was controlled to be 500 to 620°C, and the heat preservation time was controlled to be 40 to 70 min.

[0056] (7) Hot stress relief: The hot stress relief temperature was controlled to be 400 to 520°C. It should be noted that the chemical element compositions of the high-strength casing pipes according to Examples 1 to 6 of the present invention and the designs of the related processes all met the requirements of the design specifications of the present invention. On the other hand, the comparative steel pipes according to Comparative Examples 1 to 7 were prepared by the above processes and steps, but their chemical element compositions and / or related process parameters included parameters that did not meet the design of the present invention.

[0057] The mass percentages of the respective chemical elements in the high-strength casing pipes according to Examples 1 to 6 and the comparative steel pipes according to Comparative Examples 1 to 7 are shown in Table 1.

[0058]

Table 1

[0059] In the above manufacturing processes and steps of the high-strength casing pipes according to Examples 1 to 6 and the comparative steel pipes according to Comparative Examples 1 to 7, the specific process parameters adopted are shown in Tables 2-1 and 2-2.

[0060]

Table 2-1

[0061]

Table 2-2

[0062] In the above Examples and Comparative Examples, in Comparative Example 7, an offline heat treatment process was adopted without adopting a controlled cooling process, that is, tempering and heat preservation were carried out at 500°C for 60 minutes.

[0063] Samples were respectively taken from the manufactured finished high-strength casing pipes according to Examples 1 to 6 and the comparative steel pipes according to Comparative Examples 1 to 7, and the performances of the steel pipes according to each Example and Comparative Example were measured. The obtained measurement results are shown in Table 3.

[0064] The test means for the related performances were as follows: (1) Tensile test: Measured according to ASTM A370 standard, and the yield strength, tensile strength and elongation values at room temperature of the steel pipes according to each Example and Comparative Example were obtained.

[0065] (2) Impact test: Measured according to ASTM E23 standard, and the transverse impact toughness at 0°C of the steel pipes according to each Example and Comparative Example was obtained.

[0066] The measurement results of the performances of the high-strength casing pipes according to Examples 1 to 6 and the comparative steel pipes according to Comparative Examples 1 to 7 are shown in Table 3.

[0067]

Table 3

[0068] As is clear from Table 3, compared with the comparative steel pipes according to Comparative Examples 1 to 7, the high-strength casing pipes according to Examples 1 to 6 of the present invention have far superior comprehensive performance.

[0069] As can be seen from reading Table 3, the high-strength casing pipes according to Examples 1 to 6 obtained by the present invention all have excellent mechanical properties. Their yield strengths are in the range of 630 to 965 MPa, their tensile strengths are in the range of 720 to 1040 MPa, their elongation rates are in the range of 21 to 26%, and their 0°C transverse Charpy impact energies are in the range of 89 to 150 J. That is, the casing pipes according to Examples 1 to 6 all have the properties of high strength and high toughness.

[0070] On the other hand, in Comparative Examples 1 and 2, when designing the chemical composition, the content of the C element deviated from the range limited by the technical solution of the present invention. In Comparative Examples 3 and 4, the content of the Mn element deviated from the range limited by the technical solution of the present invention. In Comparative Examples 5 and 6, the content of rare earths (La, Ce) deviated from the range limited by the technical solution of the present invention. In Comparative Example 7, an offline heat treatment process was adopted without adopting a controlled cooling process (held at 900°C for 40 min and then water quenched, and held at 550°C for 60 min for tempering).

[0071] Due to such design, the comparative steel pipes manufactured in Comparative Examples 1 to 6 could not meet the requirements of high strength and high toughness for at least one mechanical property in this patent.

[0072] Figure 1 is a metallographic photograph of the high-strength casing pipe according to Example 4. As shown in Figure 1, in Example 4, the microstructure of the manufactured high-strength oil casing pipe is tempered sorbite, and its crystal grain size is level 8.5. Therefore, the added rare earths La and Ce can effectively refine the crystal grains and improve the toughness of the material.

[0073] Figure 2 is a metallographic photograph of the comparative steel pipe according to Comparative Example 5. As shown in Figure 2, for the comparative steel pipe manufactured in Comparative Example 5, since its crystal grain size is level 7 and the rare earth content is below the lower limit set in the present invention, there is no significant crystal grain refinement effect, and the toughness of the material decreases.

[0074] The above crystal grain size level was measured according to the GB / T 6394-2017 standard. In addition, the combination of each technical feature in the present application is not limited to the combination described in the claims of the present application or the combination described in the specific embodiments. As long as they do not conflict with each other, all the technical features described in the present application can be freely combined or joined in any form.

[0075] Furthermore, it should also be noted that the above-mentioned examples are only specific examples of the present invention. The present invention is not limited to the above examples, and it is obvious that any similar changes or modifications that can be directly derived from or easily conceived by those skilled in the art from the disclosure content of the present invention are included in the protection scope of the present invention.

Claims

1. Containing Fe and inevitable impurity elements, and further containing the following chemical elements in the following mass percentage contents: C: 0.06 - 0.15%; Si: 0.3 - 0.5%; Mn: 1.5 - 2.2%; La + Ce: 0.002 - 0.006%; Ti ≤ 0.05%; Al: 0.01 - 0.03%; 0 < N ≤ 0.008% A high-strength oil casing pipe containing these.

2. The mass percentage of each chemical element is: C: 0.06 - 0.15%; Si: 0.3 - 0.5%; Mn: 1.5 - 2.2%; La + Ce: 0.002 - 0.006%; Ti ≤ 0.05%; Al: 0.01 - 0.03%; 0 < N ≤ 0.008%; The balance is Fe and inevitable impurities; Preferably, La + Ce: 0.002 - 0.005% The high-strength oil casing pipe according to Claim 1, characterized by this.

3. Among the inevitable impurities, P ≤ 0.015%, S ≤ 0.008%, the high-strength oil casing pipe according to Claim 1 or 2, characterized by this.

4. Among the inevitable impurities, P ≤ 0.013%, S ≤ 0.0025%, the high-strength oil casing pipe according to Claim 3, characterized by this.

5. The mass percentage content of each of its chemical elements further satisfies at least one of the following, the high-strength oil casing pipe according to Claim 1 or 2, characterized by this: C: 0.08 - 0.14%; Si: 0.3 - 0.45%; Mn: 1.6 - 2.0%; La + Ce: 0.0025 - 0.004%; Ti ≤ 0.03%; Al: 0.01 - 0.025%.

6. Its microstructure is tempered sorbite, the high-strength oil casing pipe according to Claim 1 or 2, characterized by this.

7. The level of its crystal grain size exceeds level 8.5, the high-strength oil casing pipe according to Claim 6, characterized by this.

8. Its yield strength is ≥ 552 MPa, tensile strength is ≥ 689 MPa, elongation rate is ≥ 20%, and 0°C transverse Charpy impact energy is ≥ 80 J; preferably, its yield strength is 630 - 965 MPa, tensile strength is 720 - 1040 MPa, elongation rate is 21 - 26%, and 0°C transverse Charpy impact energy is 89 - 150 J, the high-strength oil casing pipe according to Claim 1 or 2, characterized by this.

9. The manufacturing method of the high-strength oil casing pipe according to any one of claims 1 to 8, characterized by including the following steps. (1) Smelting and casting; (2) Drilling; (3) Rolling; (4) Sizing; (5) Online quenching: Control the temperature of the casing pipe body before cooling to 780 °C or higher, water-cool the outer surface of the casing pipe at a cooling rate of 40 - 100 °C / S, and control the final cooling temperature to 100 °C or lower; (6) Tempering: Control the tempering temperature to 500 - 620 °C and the holding time to 40 - 70 min; (7) Hot stress relief.

10. In the refining process of step (1), a rare earth alloy is added in the VD or LF process. In the casting process, control the superheat degree of the molten steel to less than 40 °C, preferably 15 - 40 °C, and control the drawing speed of continuous casting to 1.6 - 2.4 m / min. The manufacturing method according to claim 9, characterized by this.

11. In step (2), the round billet is soaked in a furnace at 1200 - 1290 °C, and the drilling temperature is 1120 - 1240 °C. The manufacturing method according to claim 9, characterized by this.

12. In step (3), control the final rolling temperature to 920 - 1000 °C. The manufacturing method according to claim 9, characterized by this.

13. In step (4), control the sizing temperature to 840 - 910 °C; preferably, directly perform step (5) using the waste heat of the pipe body before lowering the temperature after the completion of step (4). The manufacturing method according to claim 9, characterized by this.

14. In step (7), control the hot stress relief temperature to 400 - 520 °C. The manufacturing method according to claim 9, characterized by this.

15. In step (5), control the temperature of the casing pipe body before cooling to 780 °C - 910 °C, and control the final cooling temperature to 30 - 90 °C; in step (6), control the tempering temperature to 520 °C - 600 °C. The manufacturing method according to claim 9, characterized by this.

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