An 890MPa grade hydraulic cylinder tube and its manufacturing method

Abstract

This invention provides an 890MPa grade hydraulic cylinder tube, containing Fe and unavoidable impurities, and further containing the following chemical elements in the following mass percentages: C: 0.14-0.20%; Si: 0.15-0.55%; Mn: 0.5-1.5%; Cr: 0.5-1.5%; Mo: 0.25-0.65%; W: 0.3-0.8%; V: 0.05-0.1%; Nb: 0.02-0.06%; Al: 0.01-0.05%; Ca: 0.0005-0.005%. Accordingly, this invention also discloses a method for manufacturing the aforementioned 890MPa grade hydraulic cylinder tube. Through a rational design of the chemical element composition and a specific process, this invention enables the hydraulic cylinder tube to achieve higher strength, lower residual stress and yield strength ratio, and good weldability.

Description

Technical Field

[0001] This invention relates to a type of steel and a method for manufacturing the same, and more particularly to a hydraulic cylinder tube and a method for manufacturing the same. Background Technology

[0002] Currently, the requirements for lightweight construction machinery are becoming increasingly stringent, which places higher and higher demands on the strength of cylinder tubes. However, as the strength increases, the carbon equivalent of the tubes also increases, leading to a decrease in welding machine performance. At the same time, the increased strength also results in increased residual stress in the cylinder tubes, causing dimensional changes in the tubes after machining and resulting in oil leakage from the cylinders.

[0003] The publication number is CN116162849A, the publication date is May 26, 2023, and the title is "A Cylinder Tube and Its Manufacturing Method". The weight percentage of its components is: C 0.16~0.3%, Si 0.15~0.5%, Mn 1.2~1.8%, P≤0.01%, S≤0.001%, Nb 0.02~0.04%, Mo 0.1~0.2%. When the wall thickness of the cylinder tube is ≥20mm, Ti and B are added, with Ti 0.015~0.03% and B 0.0015~0.0035%. The remainder is Fe and other unavoidable impurities. This invention patent employs different graded cooling processes after the steel pipe is tensioned and quenched. By increasing the stiffness and straightness of the steel pipe, the distribution of phase transformation and thermal stress across the entire wall thickness of the cylinder tube is controlled, as well as the distribution of ferrite in the microstructure of the cylinder tube. This results in a cylinder tube with high strength and low residual stress, with a yield strength ≥600MPa, tensile strength ≥730MPa, and residual stress ≤50MPa.

[0004] However, the aforementioned patent documents still cannot meet the requirements for higher strength. Summary of the Invention

[0005] One of the objectives of this invention is to provide an 890MPa grade hydraulic cylinder tube, which achieves higher strength, lower residual stress and yield strength ratio, and good weldability through reasonable chemical element composition and process design.

[0006] To achieve the above objectives, the present invention provides an 890MPa grade hydraulic cylinder tube, which contains Fe and unavoidable impurities, and also contains the following chemical elements in the following mass percentages:

[0007] C: 0.14-0.20%; Si: 0.15-0.55%; Mn: 0.5-1.5%; Cr: 0.5-1.5%; Mo: 0.25-0.65%; W : 0.3-0.8%; V: 0.05-0.1%; Nb: 0.02-0.06%; Al: 0.01-0.05%; Ca: 0.0005-0.005%.

[0008] Accordingly, the present invention also provides an 890MPa grade hydraulic cylinder tube, the mass percentage content of each element of which is as follows:

[0009] C: 0.14-0.20%; Si: 0.15-0.55%; Mn: 0.5-1.5%; Cr: 0.5-1.5%; Mo: 0.25-0.65%; W: 0.3-0.8%; V: 0.05-0.1%; Nb: 0.02-0.06%; Al: 0.01-0.05%; Ca: 0.0005-0.005%; balance Fe and other unavoidable impurities.

[0010] The design principles of each chemical element in the 890MPa grade hydraulic cylinder tube described in this invention are as follows:

[0011] C: In the 890MPa grade hydraulic cylinder tube described in this invention, carbon (C) is a fundamental element ensuring strength and hardenability. Simultaneously, the C content affects the carbon equivalent and weldability. If the C content in the steel is below 0.14%, the hardenability is poor and the strength does not meet requirements. Conversely, if the C content exceeds 0.2%, the excessively high C content leads to poor weldability and reduced ductility and toughness. Therefore, this invention controls the mass percentage of C between 0.14% and 0.2%.

[0012] Si: In the 890MPa grade hydraulic cylinder tube described in this invention, Si acts as an important deoxidizer in the steel. Si can dissolve in ferrite to improve the yield strength of the steel. However, it is important to note that the Si content in the steel should not be too high. When the Si content exceeds 0.55%, the processing performance and toughness of the steel deteriorate; conversely, if the Si content is too low, below 0.15%, the steel becomes more susceptible to oxidation. Therefore, this invention controls the mass percentage of Si between 0.15% and 0.55%.

[0013] Mn: In the 890MPa grade hydraulic cylinder tube described in this invention, Mn acts as a deoxidizing and desulfurizing agent, significantly affecting the hardenability and toughness of the steel. A higher Mn content (above 0.5%) produces better results, but excessive Mn can lead to excessively high hardenability, reducing the toughness of the weld heat-affected zone and causing center segregation during continuous casting, thus deteriorating the impact toughness of the base material. Therefore, this invention controls the mass percentage of Mn between 0.5% and 1.5%.

[0014] Cr: In the 890MPa grade hydraulic cylinder tube described in this invention, Cr can increase the strength and hardenability of the steel, and the effect of Cr combined with Mo is even better. However, it should be noted that if the Cr content in the steel is too high, it will significantly increase the carbon equivalent, leading to increased sensitivity to welding cracking and reduced toughness of the weld heat-affected zone. Therefore, this invention controls the mass percentage of Cr between 0.5% and 1.5%.

[0015] Mo: In the 890MPa grade hydraulic cylinder tube described in this invention, Mo is one of the main additive elements. It can improve the hardenability of steel. The combined effect of Mo and Cr further enhances the hardenability. In addition, Mo also has good precipitation strengthening and solid solution strengthening effects. Mo has good interaction with microalloying elements, which can effectively refine the precipitates, increase the stability and volume fraction of the precipitates, and improve the strength and toughness of the weld heat-affected zone. However, it should be noted that Mo is expensive. Adding too much Mo to the steel will not only lead to an excessively high carbon equivalent, but also increase the cost of the alloy. Therefore, this invention controls the mass percentage of Mo between 0.25% and 0.65%.

[0016] W: W is used as the main additive element in this steel grade. It can effectively improve the strength in the form of solid solution strengthening without increasing the carbon equivalent. It has no significant impact on the weldability and has a good effect on maintaining the strength after welding. In this invention, the W content is required to be in the range of 0.3-0.8%.

[0017] V: In the 890MPa grade hydraulic cylinder tube described in this invention, element V can refine the grains in the steel, and the carbides it participates in forming can significantly improve the strength of the steel. However, when the amount of V added to the steel reaches a certain level, its strengthening effect is not obvious, and V is a relatively expensive alloying element, so it should not be added in excess. Therefore, in this invention, the mass percentage of V is controlled between 0.05% and 0.1%.

[0018] Nb: The main function of Nb is to refine phase transformation and grain size through the precipitation of carbides. In this invention, the addition of a small amount of Nb not only refines the microstructure and improves the strength-toughness ratio, but also has a good effect on improving post-weld softening.

[0019] Al: In the 890MPa grade hydraulic cylinder tube described in this invention, Al is a good deoxidizing element. However, adding too much Al to the steel can easily cause alumina inclusions. It is necessary to maximize the proportion of acid-soluble aluminum to total aluminum and then feed an appropriate amount of Al wire after vacuum degassing. Therefore, this invention controls the mass percentage of Al element between 0.01% and 0.05%.

[0020] Ca: In the 890MPa grade hydraulic cylinder tube described in this invention, Ca can purify molten steel, promote MnS spheroidization, and improve the impact toughness of the material. However, it should be noted that the Ca content in the steel should not be too high. When the Ca content in the steel is too high, it is easy to form coarse non-metallic inclusions, which will affect the performance of the steel. Therefore, this invention controls the mass percentage of Ca between 0.0005% and 0.005%.

[0021] Furthermore, it should be noted that the 890MPa grade hydraulic cylinder tube described in this invention contains some unavoidable impurity elements, mainly sulfur (S) and phosphorus (P). Where technical conditions permit, the content of these impurity elements should be reduced as much as possible to obtain hydraulic cylinder tubes with better performance and higher quality.

[0022] Furthermore, in the 890MPa grade hydraulic cylinder tube of the present invention, the mass percentage content of each chemical element further satisfies at least one of the following:

[0023] Si: 0.15-0.35%;

[0024] Mn: 1.1-1.5%;

[0025] Cr: 0.5-1%.

[0026] Furthermore, in the 890MPa grade hydraulic cylinder tube described in this invention, its carbon equivalent is ≤0.7.

[0027] Furthermore, in the 890MPa grade hydraulic cylinder tube described in this invention, its carbon equivalent is 0.45-0.65.

[0028] In this invention, carbon equivalent = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu)15, where each chemical element is replaced with the value before the percentage sign of its corresponding mass percentage content.

[0029] Furthermore, in the 890MPa grade hydraulic cylinder tube of the present invention, the outer wall and central structure is tempered sorbite structure + less than 10% bainite, and the inner wall structure is tempered sorbite structure + bainite and ferrite with a total volume content of less than 20%.

[0030] This invention, through the proportioning of components and processes, obtains an outer wall and central structure consisting of tempered sorbite with a small amount of bainite, and an inner wall structure consisting of tempered sorbite with a small amount of bainite and a small amount of ferrite. This is because when only the outer wall is cooled, the inner wall temperature drops below Ar3, precipitating some ferrite. At this time, after water is sprayed onto the inner wall, the remaining austenite is transformed into martensite and bainite. The tempering process transforms the structure into tempered sorbite with a small amount of bainite and ferrite.

[0031] Furthermore, in the 890MPa grade hydraulic cylinder tube described in this invention, its performance meets the following requirements: yield strength ≥ 890MPa, tensile strength 960-1100MPa, yield-to-tensile ratio ≤ 0.93, and impact toughness KV8 ≥ 45J at -40℃.

[0032] Furthermore, in the 890MPa grade hydraulic cylinder tube described in this invention, the residual stress is -100MPa to 48MPa.

[0033] Accordingly, another object of the present invention is to provide a method for manufacturing an 890MPa grade hydraulic cylinder tube.

[0034] To achieve the above objectives, this invention proposes a method for manufacturing an 890MPa grade hydraulic cylinder tube, comprising the following steps:

[0035] Smelting and continuous casting to obtain tube blanks;

[0036] Heating, piercing, rolling, sizing;

[0037] Online controlled cooling: The initial cooling temperature is ≥800℃, and cooling is carried out by external wall water spraying. The average cooling rate is controlled at 20-40℃ / s, and the final cooling temperature is 600℃-680℃; then the air is cooled to room temperature.

[0038] Quenching: Control the heating temperature to 820-880℃, and hold it at that temperature for 20-40 minutes. After quenching, use water cooling. During cooling, rotate the steel pipe and spray water onto the outer wall of the steel pipe. After cooling for 35-40 seconds, start spraying water onto the inner wall of the steel pipe.

[0039] Tempering.

[0040] This invention employs a low-carbon steel grade containing W, Cr, Mo, and microalloying, controlling the carbon equivalent of the steel to ≤0.7, thus ensuring excellent weldability. Simultaneously, it is coupled with the aforementioned online controlled cooling process, utilizing the residual heat after tube rolling for rapid cooling to refine the rolled microstructure, thereby further refining the microstructure after tempering heat treatment and ensuring a good balance of strength and toughness. Furthermore, during the tempering heat treatment process, a process of cooling the outer wall first and then delaying the inner wall with water spray cooling is adopted. Seamless tubes produced through this process exhibit characteristics such as easy welding, low yield strength ratio, and low residual stress.

[0041] To further refine the rolled microstructure and utilize its genetic characteristics to refine the final quenching and tempering heat treatment microstructure, a rapid cooling technology after sizing is employed, effectively utilizing the residual heat from the rolling process. The thermal deformation during sizing results in numerous dislocations in the tube body. Rapid cooling to a certain temperature effectively preserves these dislocations, which can serve as nucleation sites for phase transformation and precipitates. Furthermore, rapid cooling increases the undercooling degree of phase transformation, thereby increasing the driving force for phase transformation. Both factors contribute to a significant refinement of the rolled microstructure. Based on this, the present invention employs online controlled cooling: an initial cooling temperature ≥800℃, using external wall water spraying for cooling, controlling the average cooling rate at 20-40℃ / s, and a final cooling temperature of 600℃-680℃; followed by air cooling to room temperature, and then subsequent quenching and tempering heat treatment. In this invention, the online controlled cooling step involves water spraying on the outer wall to form a hardened layer, which increases the deformation resistance of the outer wall and ensures that the tube body is less prone to bending deformation during subsequent cooling, thus ensuring the straightness of the tube body. At the same time, it reduces the residual stress level of the entire tube. Since the surface is a hardened layer, compressive stress is generated, which increases the tube body's tolerance to surface defects.

[0042] This invention employs water cooling after quenching. During cooling, the steel pipe rotates, and external water spray is used to cool the outer wall of the pipe. After 35-40 seconds of cooling, internal water spray is activated to ensure that areas where external cooling was ineffective receive sufficient cooling through internal spray. Because the external water spray cools the entire length of the steel pipe simultaneously, and the rotating cooling process ensures good uniformity, it increases the pipe's rigidity. This superior cooling uniformity also guarantees good straightness, preventing significant residual stress caused by subsequent bending and straightening deformation. Compared to simultaneous external spray cooling and internal axial flow cooling, this method achieves even better straightness.

[0043] In addition, the residual stress of the steel pipe is closely related to the phase transformation and thermal stress during the cooling process. Through this cooling method, a gradient distribution of phase transformation and thermal stress is obtained in the wall thickness direction. After water cooling, the outer wall generates compressive stress due to thermal expansion and contraction, and the phase transformation stress is tensile stress. The sum of the two is in the range of 0-200MPa. At the center of the wall thickness, the thermal stress is tensile stress, and the phase transformation stress is compressive stress. The sum of the two is negative. The thermal stress and phase transformation stress of the inner wall are both positive. The inner wall has a certain risk of cracking. Therefore, tempering treatment should be carried out as soon as possible after cooling.

[0044] Furthermore, in the quenching step of the manufacturing method described in this invention, the flow rate density of water spray cooling on the outer wall of the steel pipe is 3000-3500 m³ / s. 3 / (h*mm 2 ), where "h" represents hours.

[0045] Furthermore, in the tempering step of the manufacturing method described in this invention, the tempering temperature is controlled at 500-600℃ and the holding time is 20-30min.

[0046] The residual stress in the tube wall thickness direction is reduced after tempering, but the gradient distribution trend does not change. The residual stress level of the overall tube after tempering is -100MPa to 48MPa.

[0047] The 890MPa grade hydraulic cylinder tube and its manufacturing method described in this invention have the following advantages and beneficial effects:

[0048] This invention employs a low-carbon microalloyed steel grade containing W, Cr, and Mo, controlling the carbon equivalent of the steel to ≤0.7, thus ensuring excellent weldability. Simultaneously, it incorporates an online controlled cooling process, utilizing residual heat from tube rolling for rapid cooling to refine the rolled microstructure, further refining the microstructure after tempering and heat treatment, ensuring a good balance of strength and toughness. Furthermore, the tempering process employs a method of cooling the outer wall first, followed by delayed water-spray cooling of the inner wall. Seamless tubes produced using this process exhibit characteristics such as easy welding, low yield strength ratio, and low residual stress.

[0049] In some embodiments, the 890MPa grade hydraulic cylinder tube of the present invention has the following properties: yield strength ≥ 890MPa, tensile strength 960-1100MPa, yield-to-tensile ratio ≤ 0.93, impact toughness KV8 ≥ 45J at -40℃, and residual stress -100MPa to 48MPa. Detailed Implementation

[0050] The 890MPa grade hydraulic cylinder tube and its manufacturing method described in this invention will be further explained and described below with reference to specific embodiments. However, this explanation and description do not constitute an improper limitation on the technical solution of this invention.

[0051] Examples 1-8 and Comparative Examples 1-8

[0052] The 890MPa grade hydraulic cylinder tubes in Examples 1-8 were prepared using the following steps:

[0053] (1) Smelting and continuous casting are carried out according to conventional processes to obtain tube blanks;

[0054] (2) The tube blank is heated, pierced, rolled and sized according to conventional processes to obtain the tube body;

[0055] (3) Utilize the residual heat of the rolled tube and control the cooling online after sizing: the initial cooling temperature is ≥800℃, and the external wall is sprayed with water for cooling, controlling the average cooling rate to be 20-40℃ / s, and the final cooling temperature to be 600℃-680℃; then air cooling to room temperature.

[0056] (4) Quenching: Control the heating temperature to 820-880℃, and hold at that temperature for 20-40 minutes. After quenching, use water cooling. During cooling, rotate the steel pipe and spray water onto the outer wall of the pipe. After 35-40 seconds of cooling, start spraying water onto the inner wall of the pipe until the pipe body is cooled to below 100℃. In some embodiments, the flow rate density of water spraying onto the outer wall of the pipe is 3000-3500 m³ / s. 3 / (h*mm 2 The water pressure can be 0.5 MPa.

[0057] (5) Tempering: Control the tempering temperature to 500-600℃ and the holding time to 20-30min.

[0058] It should be noted that the chemical element composition and related process design of the 890MPa grade hydraulic cylinder tubes in Examples 1-8 of this invention all meet the design specifications of this invention. While the steps and processes of Comparative Examples 1-8 are roughly the same as those of this invention, their chemical element content or specific process parameters do not conform to these specifications.

[0059] Table 1 lists the mass percentage of each chemical element for the 890MPa-grade cylinder tubes of Examples 1-8 and the comparative oil casings of Comparative Examples 1-8.

[0060] Table 1. (wt%, balance is Fe and other unavoidable impurities)

[0061] C Si Mn Cr Mo W V Nb Al Ca carbon equivalent Example 1 0.14 0.16 1.5 0.5 0.3 0.3 0.06 0.025 0.01 0.0005 0.56 Example 2 0.15 0.25 1 0.6 0.25 0.35 0.07 0.035 0.025 0.002 0.50 Example 3 0.19 0.35 0.6 1.5 0.28 0.4 0.05 0.02 0.035 0.0015 0.66 Example 4 0.2 0.55 0.5 1.1 0.3 0.8 0.1 0.06 0.03 0.003 0.58 Example 5 0.17 0.45 0.7 1.1 0.6 0.55 0.1 0.045 0.025 0.005 0.65 Example 6 0.16 0.3 0.8 1.2 0.65 0.6 0.09 0.045 0.045 0.003 0.68 Example 7 0.15 0.28 0.9 1.3 0.4 0.7 0.08 0.048 0.025 0.0009 0.66 Example 8 0.16 0.32 1 1.4 0.5 0.55 0.07 0.035 0.05 0.001 0.72 Comparative Example 1 0.23 0.25 0.6 0.8 0.5 0.5 0.075 0.025 0.03 0.002 0.61 Comparative Example 2 0.12 0.24 0.9 0.9 0.55 0.6 0.085 0.03 0.02 0.001 0.58 Comparative Example 3 0.21 0.31 1.5 1.5 0.65 0.75 0.1 0.04 0.035 0.0015 0.91 Comparative Example 4 0.16 0.27 0.9 0.9 0.4 0.6 0.095 0.06 0.025 0.0025 0.59 Comparative Example 5 0.17 0.3 0.6 0.6 0.5 0.45 0.095 0.04 0.025 0.002 0.51 Comparative Example 6 0.18 0.35 0.7 0.8 0.35 0.52 0.09 0.05 0.025 0.002 0.54 Comparative Example 7 0.19 0.32 1 0.8 0.5 0.43 0.08 0.025 0.03 0.0015 0.63 Comparative Example 8 0.16 0.23 1.1 0.8 0.55 0.7 0.07 0.02 0.04 0.002 0.63

[0062] Note: Carbon equivalent = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu)15. Since this case does not contain Cu and Ni elements, the values ​​of these two elements are substituted into 0 for calculation.

[0063] Table 2 lists the specific process parameters of the 890MPa grade hydraulic cylinder tubes of Examples 1-8 and the comparative oil casing tubes of Comparative Examples 1-8 in the online controlled cooling and tempering treatment steps.

[0064] Table 2.

[0065]

[0066] Note: The three columns of data for online controlled cooling in Comparative Example 4 are marked with " / ", indicating that online controlled cooling was not used in this comparative example; the internal spray opening delay time for Comparative Example 8 is marked with " / ", indicating that the internal spray was not turned on in this comparative example.

[0067] Samples were taken from the 890MPa grade hydraulic cylinder tubes of Examples 1-8 and the control tubes of Comparative Examples 1-8, and tested. The test results are listed in Table 3. The relevant test procedures are as follows:

[0068] (1) Microstructure observation: The cross-section of the tube was taken for microstructure observation. The sample was polished and etched with 4% nitric acid + alcohol. The microstructure was observed using a metallographic microscope.

[0069] (2) Tensile test: The tensile properties at room temperature are tested according to GB / T 228.1-2000 standard.

[0070] (3) Impact test: The impact energy test at -40℃ was conducted in accordance with GB / T 229-2007 "Metallic Materials Charpy Pendulum Impact Test Method".

[0071] (4) Welding performance testing: Welding evaluation shall be carried out in accordance with NB / T-47014-2011 Welding process qualification for pressure equipment.

[0072] (5) Residual stress test: The measurement shall be carried out in accordance with the ISO / TR 10400 standard.

[0073] Table 3 lists the test results of the 890MPa grade hydraulic cylinder tubes of Examples 1-8 and Comparative Examples 1-8.

[0074] Table 3.

[0075]

[0076] As can be seen from Table 3, the 890MPa grade hydraulic cylinder tubes of Examples 1-8 of the present invention have a yield strength of ≥900MPa, a tensile strength of ≥1025MPa, an impact energy of ≥70J at -40℃, a yield strength ratio of ≤0.91, a residual stress of -30MPa to 40MPa, and good weldability.

[0077] Comparative Examples 1-3 failed to meet the design requirements of this invention due to their chemical element composition not conforming to the requirements of this invention; Comparative Example 4 did not undergo online controlled cooling; and the quenching of Comparative Examples 5-8 did not meet the requirements of this invention. Consequently, none of them could achieve a balance of high strength, low yield strength ratio, good low-temperature toughness, and excellent weldability.

[0078] It should be noted that the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0079] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. An 890MPa grade hydraulic cylinder tube, characterized in that, Its elemental mass percentage content is as follows: C: 0.14-0.20%; Si: 0.15-0.55%; Mn: 0.5-1.5%; Cr: 0.5-1.5%; Mo: 0.25-0.65％；W：0.3-0.8％； V：0.05-0.1％； Nb: 0.02-0.06%; Al: 0.01-0.05%; Ca: 0.0005-0.005%; balance is Fe and other unavoidable impurities; The outer wall and central structure of the 890MPa grade hydraulic cylinder tube is tempered sorbite with a volume content of less than 10% bainite; the inner wall structure is tempered sorbite with a small amount of bainite and a small amount of ferrite, wherein the total volume content of bainite and ferrite in the inner wall structure is less than 20%. The performance of the 890MPa grade hydraulic cylinder tube meets the following requirements: yield strength ≥ 890MPa, tensile strength 960-1100MPa, yield-to-tensile ratio ≤ 0.93, impact toughness KV8 ≥ 45J at -40℃, and residual stress -100MPa-48MPa.

2. The 890MPa grade hydraulic cylinder tube as described in claim 1, characterized in that, Its mass percentage content of each chemical element further satisfies at least one of the following: Si: 0.15-0.35%; Mn: 1.1-1.5%; Cr：0.5-1％。 3. The 890MPa grade hydraulic cylinder tube as described in claim 1, characterized in that, Its carbon equivalent is ≤0.

7.

4. The 890MPa grade hydraulic cylinder tube as described in claim 3, characterized in that, Its carbon equivalent is 0.45-0.

65.

5. The method for manufacturing an 890MPa grade hydraulic cylinder tube as described in any one of claims 1-4, characterized in that, It includes the following steps: Smelting and continuous casting to obtain tube blanks; Heating, piercing, rolling, sizing; Online controlled cooling: The initial cooling temperature is ≥800℃, and cooling is carried out by external wall water spraying. The average cooling rate is controlled at 20-40℃ / s, and the final cooling temperature is 600℃-680℃; then the air is cooled to room temperature. Quenching: Control the heating temperature to 820-880℃, and hold it at that temperature for 20-40 minutes. After quenching, use water cooling. During cooling, rotate the steel pipe and spray water onto the outer wall of the steel pipe. After cooling for 35-40 seconds, start spraying water onto the inner wall of the steel pipe. (5) Tempering.

6. The manufacturing method as described in claim 5, characterized in that, During the quenching process, the flow rate density of water spray cooling applied to the outer wall of the steel pipe is 3000-3500 m³ / s. 3 / (h*mm 2 ).

7. The manufacturing method as described in claim 5, characterized in that, During the tempering process, the tempering temperature is controlled at 500-600℃, and the holding time is 20-30 minutes.

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