High-strength steel pipe for scooter and manufacturing method of high-strength steel pipe

Abstract

The invention discloses a high-strength steel pipe for a scooter, which contains Fe, inevitable impurities and the following chemical elements in percentage by mass: 0.25-0.35% of C; si: 0.05 to 0.35%; 0.7% to 1.2% of Mn; 0.1% to 0.6% of Mo; 0.015 to 0.060% of Al; 0.5% to 1.2% of Cr; 0.03 to 0.1 percent of V; 0.02% to 0.01% of Nb; 0.001% to 0.006% of La; mo + 10V + 10Nb is greater than or equal to 1.3% and less than or equal to 2.1%. The invention further discloses a manufacturing method of the high-strength steel pipe for the scooter. The manufacturing method comprises the steps that a pipe blank is manufactured; the pipe blank is heated and then evenly heated, and the pipe blank is naturally cooled after being subjected to diameter reduction and wall thickness reduction; pickling, phosphating and saponifying after intermediate annealing heat treatment; performing cold machining to a finished product size; and induction quenching and tempering.

Description

Technical Field

[0001] The present invention relates to a steel pipe and a manufacturing method thereof, and in particular to a high-strength steel pipe and a manufacturing method thereof. Background Art

[0002] As a tool for extreme sports, extreme sports scooters can not only be used to exercise the body, but also promote physical and mental pleasure. They are a new product form of skateboarding after traditional skateboards. The speed of scooters can reach 20 kilometers per hour, which is deeply loved by modern young people.

[0003] Usually, extreme sports scooters include a horizontal handlebar and a vertical handlebar, a pulley mounted on the front fork head, and a skateboard connected to the front fork head. When athletes use scooters for sports, the parts of the skateboard that are subject to the greatest force are the horizontal bar and the connection between the horizontal handlebar and the vertical handlebar. When athletes fall from a high altitude, the horizontal handlebar often breaks due to insufficient strength, and the connection parts also break.

[0004] The patent with publication number CN 215883948 U and publication date September 24, 2021, and named "A front fork head for an extreme sports scooter" relates to a front fork head for an extreme sports scooter, and in particular to the technical field of accessories for an extreme sports scooter, including a front fork body and a moving block, the moving block is provided with a connecting rod, one end of the connecting rod is connected to the moving block, and the end of the connecting rod away from the moving block is detachably provided with a direction joystick, mainly introducing the design and assembly mode of the pipe fittings of the extreme sports scooter.

[0005] The above patent documents mainly involve the design and assembly mode of the pipe parts of extreme sports scooters, and do not provide a solution to the breakage of the handlebars caused by insufficient strength of the handlebars. Summary of the invention

[0006] One of the purposes of the present invention is to provide a high-strength steel pipe for a scooter, which can achieve high strength, high impact resistance and high impact fatigue resistance through reasonable chemical element composition design and reasonable manufacturing process, and the material has good welding performance, and the welding position does not break under impact service conditions.

[0007] In order to achieve the above object, the present invention provides a high-strength steel pipe for a scooter, which contains Fe and other inevitable impurities, and further contains the following chemical elements in the following mass percentages:

[0008] C: 0.25~0.35%; Si: 0.05~0.35%; Mn: 0.7~1.2%; Mo: 0.1~0.6%; Al: 0.015~0.060%; Cr: 0.5~1.2%; V: 0.03~0.1%; Nb: 0.02~0.1%; La: 0.001~0.006%; the mass percentage of each chemical element also satisfies: 1.3%≤Mo+10V+10Nb≤2.1%.

[0009] Furthermore, the present invention provides a high-strength steel pipe for a scooter, wherein the mass percentages of the chemical elements are as follows: C: 0.25-0.35%; Si: 0.05-0.35%; Mn: 0.7-1.2%; Mo: 0.1-0.6%; Al: 0.015-0.060%; Cr: 0.5-1.2%; V: 0.03-0.1%; Nb: 0.02-0.1%; La: 0.001-0.006%; the remainder is Fe and unavoidable impurities; and the mass percentages of the chemical elements also satisfy: 1.3%≤Mo+10V+10Nb≤2.1%.

[0010] The high-strength steel pipe for scooters of the present invention adopts the addition of Cr and Mo elements to improve the strength of the steel pipe during the composition design, and refines the grains by adding V and Nb elements. At the same time, by controlling the synergistic relationship of the three elements Mo, V and Nb, the comprehensive strength and toughness of the steel can reach the optimal ratio, and the purity of the steel is ensured by adding the rare earth element La, and the impact toughness of the steel is improved. At the same time, under the premise of ensuring strength and impact toughness, the coordinated addition of alloy elements is controlled to ensure that the welding position of the steel pipe does not break under impact service conditions.

[0011] Specifically, the design principles of the chemical elements in the high-strength steel tube for scooters of the present invention are:

[0012] C: In the high-strength steel pipe for scooters described in the present invention, the C element is one of the main elements for improving the strength of steel, and is mainly used to solve the strength of the high-strength steel pipe for scooters. It can effectively improve the strength of steel through the formation of carbides, and the cost of addition is low. The purpose of higher finished product strength can be achieved on the basis of adding less alloying elements. It should be noted that when the content of the C element is too high, the C equivalent will be significantly increased, affecting the welding performance. At the same time, when the content of the C element is too low, the strength of the steel will be affected. Therefore, in order to maximize the role of the C element, in the high-strength steel pipe for scooters described in the present invention, the mass percentage of the C element is controlled between 0.25 and 0.35%.

[0013] Si: In the high-strength steel pipe for scooters described in the present invention, the Si element is added as a reducing agent and deoxidizer during the steelmaking process. The Si element does not form carbides in the steel, and its solid solubility in the steel is relatively large, which can better strengthen the ferrite in the steel to improve the strength of the steel. Therefore, the present invention appropriately increases the Si content to improve the strength of the steel in the quenched state. It should be noted that when the content of the Si element is lower than 0.05%, the strength of the steel will be insufficient; at the same time, when the content of the Si element exceeds 0.35%, the toughness of the steel pipe will be reduced. Therefore, in the high-strength steel pipe for scooters described in the present invention, the mass percentage of the Si element is controlled between 0.05 and 0.35%. Furthermore, the mass percentage of the Si element can be controlled between 0.1 and 0.3%.

[0014] Mn: In the high-strength steel pipe for scooters described in the present invention, the Mn element is an important alloying element and a weak carbide forming element. The Mn element mainly improves the strength of steel by solid solution strengthening. At the same time, the addition of the Mn element can effectively increase the hardenability of steel, which is an important guarantee for ensuring that the finished steel pipe has high strength. Therefore, in the present invention, when the Mn element content reaches 0.7%, the strength of the steel will be significantly improved. It should be noted that when the Mn element content is too high, the plasticity and impact toughness of the steel will decrease significantly, and at the same time, it will have a greater impact on the welding performance, and will also have a certain impact on the rotational fatigue performance of the finished steel pipe. Therefore, in the high-strength steel pipe for scooters described in the present invention, the mass percentage of the Mn element is controlled between 0.7 and 1.2%.

[0015] Mo: In the high-strength steel pipe for scooters described in the present invention, the Mo element has the effect of solid solution strengthening and improving the hardenability of steel. Since this type of steel needs to achieve high tensile strength and toughness after quenching, when the content of the Mo element reaches 0.1%, it will have significant solid solution strengthening and hardenability improvement effects; it should be noted that when the content of the Mo element exceeds a certain range, it will affect the toughness and welding performance of the steel pipe. At the same time, cost factors must also be considered. Therefore, in the high-strength steel pipe for scooters described in the present invention, the mass percentage of the Mo element is controlled between 0.1 and 0.6%.

[0016] Al: In the high-strength steel pipe for scooters described in the present invention, the Al element has a deoxidizing effect, and the Al element helps to improve the toughness and processability of the steel. When the Al element content reaches more than 0.015%, the effect of improving the toughness and processability of the steel is more significant. However, it should be noted that when the Al element content exceeds 0.060%, the sulfide inclusions in the steel increase, which will have a greater impact on the toughness fatigue performance of the steel pipe. Therefore, in order to exert the best effect of the Al element, in the high-strength steel pipe for scooters described in the present invention, the mass percentage of the Al element is controlled between 0.015 and 0.060%.

[0017] Cr: In the high-strength steel pipe for scooters described in the present invention, the Cr element is an element that forms medium-strong carbides. Part of the Cr element in the steel is replaced by iron to form alloy cementite to improve the stability of the steel, and the other part is dissolved in the ferrite to play a solid solution strengthening role, thereby improving the strength and hardness of the ferrite. At the same time, the Cr element is also the main element for improving the hardenability of steel. When the Cr content reaches 0.5%, the effect of improving the strength and hardenability of steel is more significant, but it should be noted that when the Cr content exceeds 1.2%, the toughness of the steel pipe matrix and the weld will be greatly affected. Therefore, in the high-strength steel pipe for scooters described in the present invention, the mass percentage of the Cr element is controlled between 0.5 and 1.2%.

[0018] V: In the high-strength steel pipe for scooters described in the present invention, the V element has a strong affinity with carbon and nitrogen, and can therefore form corresponding stable compounds with carbon and nitrogen. The V element mainly exists in the form of carbides in steel, and its main function is to refine the structure and grains of the steel, and to form dispersed VC and VN particles with the C and N elements. At the same time, VC and VN particles can improve the strength and toughness of the steel, but it should be noted that adding too much V element will form a larger lamellar structure, which will have a greater impact on the impact toughness of the steel. Therefore, in order to better exert its beneficial effects, in the high-strength steel pipe for scooters described in the present invention, the mass percentage of the V element is controlled between 0.03 and 0.1%.

[0019] Nb: In the high-strength steel tube for scooters described in the present invention, Nb is added to the steel as a microalloying element, but the Nb does not change the structure of iron, but combines with carbon, nitrogen and sulfur in the steel to change the microstructure of the steel. The strengthening effect of Nb on steel is mainly fine grain strengthening and dispersion strengthening. Nb can not only generate stable carbides and carbonitrides with carbon and nitrogen in steel, but also disperse the carbides and form steel with fine grains. In addition, Nb can also achieve dispersed distribution of precipitates by inducing precipitation and controlling the cooling rate, and adjust the toughness level of steel in a wide range. Therefore, when the content of Nb reaches 0.02%, it has a significant effect on improving the strength of steel, the toughness of steel, high temperature oxidation resistance and corrosion resistance; at the same time, it can also reduce the brittle transition temperature of steel, so that it can obtain good welding performance and forming performance. However, it should be noted that when the content of Nb reaches 0.1%, the above effect has reached saturation and the cost is relatively high. Therefore, taking into account the requirements of the present invention and the cost control problem, in the high-strength steel pipe for a scooter of the present invention, the mass percentage of the Nb element is controlled between 0.02 and 0.1%.

[0020] La: In the high-strength steel pipe for scooters described in the present invention, La element has a strong deoxidizing effect. Adding an appropriate amount of La element to the steel can not only significantly reduce the harmful impurity elements in the steel, but also significantly improve the purity of the steel. At the same time, the impact toughness and welding performance of the steel can also be significantly improved. It should be noted that when the content of La element is too high, the strength of the steel will be reduced. Therefore, considering the needs and cost factors of the present invention, in the high-strength steel pipe for scooters described in the present invention, the mass percentage of La element is controlled between 0.001 and 0.006%.

[0021] Furthermore, among the inevitable impurities in the high-strength steel pipe for a scooter of the present invention, S≤0.006%, P≤0.015%, and O≤0.003%.

[0022] The inevitable impurities in the present invention are mainly S, P and O elements. If conditions permit, it is hoped that their contents are as low as possible. Among them, the increase in S content will have a great impact on the content of sulfides in the steel grade, so it is hoped that the S mass percentage is controlled below 0.006% and the P mass percentage is controlled below 0.015%. At the same time, the O content in the steel has a great impact on the oxide inclusions in the steel, so it is hoped that the O mass percentage is controlled below 0.003%.

[0023] Furthermore, the microstructure of the high-strength steel pipe for scooters of the present invention is a columnar bainite structure and dispersed granular carbides, and there is no decarburized structure on the inner and outer surfaces of the high-strength steel pipe for scooters.

[0024] Furthermore, the particle size of the granular carbide of the high-strength steel pipe for a scooter according to the present invention is not greater than 50 μm, and the granular carbide includes VC and NbC.

[0025] Furthermore, the wall thickness of the high-strength steel pipe for the scooter of the present invention is 0.8-4.5 mm.

[0026] Furthermore, the outer diameter of the high-strength steel pipe for the scooter of the present invention is 15 to 50 mm.

[0027] Furthermore, the performance of the high-strength steel pipe for scooters described in the present invention meets the following requirements: yield strength ≥ 1300MPa, tensile strength ≥ 1600MPa, -60°C impact absorption energy ≥ 40J, elongation ≥ 20%, lateral deformation force > 1200kg without fracture, and up and down bending fatigue times > 100,000 times.

[0028] Correspondingly, another object of the present invention is to provide a method for manufacturing a high-strength steel pipe for a scooter. The high-strength steel pipe for a scooter manufactured by the manufacturing method has high strength, high impact resistance and high impact fatigue resistance, and the material has good welding performance, and the welding position does not break under impact service conditions and other excellent properties, and can be effectively used in extreme sports.

[0029] In order to achieve the above object, the present invention proposes a method for manufacturing the above-mentioned high-strength steel pipe for a scooter, which comprises the steps of:

[0030] (1) Producing a tube blank;

[0031] (2) After heating the tube billet, the tube billet is heated evenly, and the tube billet is reduced in diameter and wall thickness, and then cooled naturally;

[0032] (3) After intermediate annealing heat treatment, pickling, phosphating and saponification;

[0033] (4) Cold working to finished size;

[0034] (5) Induction quenching + tempering: The quenching temperature is controlled at 880-920°C and the holding time is 15-30 minutes; the tempering temperature is controlled at 200-550°C and the holding time is 30-75 minutes.

[0035] In the manufacturing method described in the present invention, the quenching and tempering process is adopted to ensure the strength and toughness of the steel pipe, while ensuring that there is no decarburized structure on the surface of the steel pipe. The straightness of the steel pipe can also be ensured by adjusting the torque of the clamping roller during the quenching process after induction coil heating.

[0036] Furthermore, in the method for manufacturing the high-strength steel pipe for a scooter of the present invention, in step (1), the tube blank is heated to 1200° C. to 1250° C. and is heat-treated for 15 to 35 minutes.

[0037] In this embodiment, the tube blank is heated to 1200°C to 1250°C and is heated for 15 to 35 minutes because the tube blank has the best thermoplasticity in this temperature range, ensuring that the steel tube does not produce defects such as folding during the hot perforation forming process, while ensuring the production efficiency of the steel tube.

[0038] Furthermore, in the method for manufacturing the high-strength steel pipe for a scooter of the present invention, in step (4), cold working is performed by cold drawing or cold rolling.

[0039] Furthermore, in the method for manufacturing the high-strength steel pipe for a scooter of the present invention, in step (4), the elongation coefficient of each cold working pass is ≤1.5.

[0040] In this embodiment, the elongation coefficient of each cold working pass is controlled to be ≤1.5 in order to ensure the production efficiency of the steel pipe while avoiding defects such as cracking of the steel pipe after cold working.

[0041] Furthermore, in the manufacturing method of the high-strength steel pipe for a scooter described in the present invention, in step (5), the frequency of the quenching induction coil is 5000-8000 Hz, and the passing speed of the steel pipe is 2-10 m / min to ensure that the entire steel pipe is fully hardened after quenching.

[0042] The high-strength steel pipe for scooters and the manufacturing method thereof of the present invention have the following advantages and beneficial effects:

[0043] From the perspective of component design, the present invention improves the strength of the high-strength steel pipe for scooters by controlling the addition of Cr and Mo elements, and refines the grains by adding V and Nb elements. By controlling the synergistic relationship of the three elements Mo, V and Nb, the comprehensive strength and toughness of the steel can reach an optimal ratio. At the same time, the purity of the steel is ensured by adding the rare earth element La, and the impact toughness of the steel is improved.

[0044] Accordingly, from the perspective of manufacturing process, the present invention adopts specific quenching and tempering processes in combination with the component design of the present invention to obtain the microstructure morphology that the present invention aims to obtain, and ultimately achieves a good match between strength and toughness.

[0045] In some embodiments, the high-strength steel pipe for scooters described in the present invention has a yield strength ≥1300MPa, a tensile strength ≥1600MPa, an impact absorption energy at -60°C ≥40J, an elongation ≥20%, a lateral deformation force >1200kg without fracture, and an up and down bending fatigue number >100,000 times.

[0046] The high-strength steel pipe for scooters and the manufacturing method thereof of the present invention can be effectively applied to extreme sports scooters, and have good promotion prospects and application value. DETAILED DESCRIPTION

[0047] The high-strength steel tube for a scooter and the method for manufacturing the same according to the present invention will be further explained and illustrated below in conjunction with specific embodiments. However, such explanation and illustration do not constitute an undue limitation on the technical solution of the present invention.

[0048] Examples A1-A10 and Comparative Examples B1-B5

[0049] The high-strength steel pipes for scooters of Examples A1-A10 and Comparative Examples B1-B5 are all prepared by the following steps:

[0050] (1) Smelting and forming a tube blank, the mass percentage of chemical elements of the tube blank is shown in Table 1;

[0051] (2) The tube blank is heated to 1200°C to 1250°C in an annular heating furnace and heated for 15 to 35 minutes; then, a vertical conical hot piercing machine is used for hot piercing, and the tube blank is reduced in diameter and wall thickness by a three-roll tension reducing mill and then cooled naturally;

[0052] (3) After intermediate annealing heat treatment, pickling, phosphating and saponification;

[0053] (4) Cold working to the finished product size by cold drawing or cold rolling. In some embodiments, the elongation coefficient of each cold working pass is controlled to be ≤1.5, and the wall thickness of the finished steel pipe after cold working is 0.8-4.5 mm and the outer diameter is 15-50 mm;

[0054] (5) Induction quenching + tempering heat treatment: the quenching temperature is controlled to be 880-920°C, the holding time is 15-30 min, the tempering temperature is controlled to be 200-550°C, and the holding time is 30-75 min. In some embodiments, the frequency of the quenching induction coil is controlled to be 5000-8000 Hz, and the passing speed of the steel pipe is 2-10 m / min.

[0055] It should be noted that the high-strength steel pipes for scooters of Examples A1-A10 of the present invention are all prepared by the above steps, and their chemical compositions and related process parameters meet the control requirements of the design specifications of the present invention. The steel pipes for scooters of Comparative Examples B1-B5 are also prepared by the above process flow, but the chemical compositions and / or related process parameters of the steel pipes for scooters of Comparative Examples B1-B5 do not meet the design requirements of the present invention.

[0056] Table 1 lists the mass percentages of the chemical elements in Examples A1-A10 of the present invention and Comparative Examples B1-B5.

[0057] Table 1. (wt.%, the balance is Fe and other inevitable impurities except P, S and O)

[0058]

[0059]

[0060] Table 2 lists the process parameters of each step in Examples A1 to A10 and Comparative Examples B1 to B5.

[0061] Table 2.

[0062]

[0063]

[0064] The high-strength steel pipes for scooters of Examples A1-A10 and the comparative steel pipes of Comparative Examples B1-B5 were sampled respectively, and their microstructures were observed under an optical microscope after being etched with an etchant. The test results are listed in Table 3.

[0065] Table 3.

[0066]

[0067] It can be seen from Table 3 that some comparative examples have strip-shaped bainite structures, and some comparative examples have precipitates larger in size than those in the embodiments, or are not VC and NbC precipitates, which all affect the properties of the steel.

[0068] In addition, the high-strength steel pipes for scooters of Examples A1-A10 and the comparative steel pipes of Comparative Examples B1-B5 were sampled and their properties were tested, and the results are listed in Table 3.

[0069] in:

[0070] (1) Tensile strength, yield strength and elongation are measured according to the method specified in GB / T 228.

[0071] (2) The -60℃ impact energy absorption is measured by converting the full-wall notched sample to the national standard half-size sample in GB / T 229.

[0072] (3) The transverse deformation force is measured according to the load borne by the whole pipe. If the transverse deformation force is greater than 600 kg without breaking, it is considered qualified, otherwise it is considered unqualified.

[0073] (4) The bending fatigue times are measured by the whole pipe test, with a load of >200Kg in the middle of the horizontal position of the steel pipe. If the upper and lower bending fatigue times are >100,000 times, it is considered qualified, otherwise it is considered unqualified.

[0074] Table 4 lists the comprehensive mechanical property parameters of the steel pipes in Examples A1-A10 and Comparative Examples B1-B5.

[0075] Table 4.

[0076]

[0077] It can be seen from Table 1, Table 2, Table 3 and Table 4 that since the steel pipes in Examples A1-A10 adopt the chemical element mass percentage ratio of the present invention and are processed and produced according to the manufacturing method provided by the present invention, they have excellent mechanical properties. The tensile strength of Examples A1-A10 is ≥1730MPa, the yield strength is ≥1320MPa, the elongation is ≥20%, the impact absorption energy at -60℃ is ≥45J, the lateral deformation force is >1200kg without breaking, and the number of upper and lower bending fatigue times is >100,000 times.

[0078] Different from the embodiment, the mass percentage of chemical elements in each steel pipe in the comparative examples B1-B5 does not conform to the range defined by the present invention, and thus its comprehensive mechanical properties are significantly inferior to those of the high-strength steel pipe for scooters of the embodiments A1-A10.

[0079] It should be noted that the prior art in the protection scope of the present invention is not limited to the embodiments given in the present application documents. All prior art that does not contradict the scheme of the present invention, including but not limited to prior patent documents, prior public publications, prior public uses, etc., can be included in the protection scope of the present invention.

[0080] In addition, the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0081] It should also be noted that the above examples are only specific embodiments of the present invention, and the present invention is obviously not limited to the above examples, and there are many similar variations. All variations directly derived or associated from the contents disclosed by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A high-strength steel pipe for a scooter, containing Fe and inevitable impurities, characterized in that: It also contains the following chemical elements in the following mass percentages: C: 0.25~0.35%; Si: 0.05~0.35%; Mn: 0.7~1.2%; Mo: 0.1~0.6%; Al：0.015～0.060％； Cr：0.5～1.2％； V：0.03～0.1％； Nb: 0.02~0.1%; La: 0.001~0.006%; The mass percentage of each chemical element also satisfies: 1.3%≤Mo+10V+10Nb≤2.1%.

2. The high-strength steel pipe for scooters according to claim 1, characterized in that: The mass percentage of each chemical element is: C: 0.25~0.35%; Si: 0.05~0.35%; Mn: 0.7~1.2%; Mo: 0.1~0.6%; Al：0.015～0.060％； Cr：0.5～1.2％； V：0.03～0.1％； Nb ：0.02～0.1％； La: 0.001-0.006%; the balance is Fe and unavoidable impurities; The mass percentage of each chemical element also satisfies 1.3%≤Mo+10V+10Nb≤2.1%.

3. The high-strength steel pipe for scooters according to claim 1 or 2, characterized in that: The mass percentage of Si element further satisfies: Si: 0.1-0.3%.

4. The high-strength steel pipe for scooters according to claim 1 or 2, characterized in that: Among the inevitable impurities, S≤0.006%, P≤0.015%, and O≤0.003%.

5. The high-strength steel pipe for scooters according to claim 1 or 2, characterized in that: The microstructure thereof comprises columnar bainite structure and dispersed granular carbides, and the inner and outer surfaces of the high-strength steel pipe for scooters are free of decarburized structure.

6. The high-strength steel pipe for a scooter according to claim 5, characterized in that: The particle size of the granular carbide is not greater than 50 μm, and the granular carbide includes VC and NbC.

7. The high-strength steel pipe for scooters according to claim 1 or 2, characterized in that: Its wall thickness is 0.8~4.5mm.

8. The high-strength steel pipe for scooters according to claim 1 or 2, characterized in that: Its outer diameter is 15 to 50 mm.

9. The high-strength steel pipe for a scooter according to claim 1 or 2, characterized in that: Its performance meets the following requirements: yield strength ≥ 1300MPa, tensile strength ≥ 1600MPa, -60℃ impact absorption energy ≥ 40J, elongation ≥ 20%, lateral deformation force > 1200kg without fracture, and up and down bending fatigue times > 100,000 times.

10. A method for manufacturing a high-strength steel pipe for a scooter according to any one of claims 1 to 9, characterized in that: Includes steps: (1) Producing a tube blank; (2) After heating the tube billet, the tube billet is heated evenly, and the tube billet is reduced in diameter and wall thickness, and then cooled naturally; (3) After intermediate annealing heat treatment, pickling, phosphating and saponification; (4) Cold processing to the finished steel pipe size; (5) Induction quenching + tempering: The quenching temperature is controlled at 880-920°C and the holding time is 15-30 minutes; the tempering temperature is controlled at 200-550°C and the holding time is 30-75 minutes.

11. The manufacturing method according to claim 10, characterized in that: In step (1), the tube blank is heated to 1200°C to 1250°C, and the soaking time is 15-35 minutes.

12. The manufacturing method according to claim 10, characterized in that: In step (4), cold working is performed by cold drawing or cold rolling.

13. The manufacturing method according to claim 10, characterized in that: In step (4), the elongation coefficient of each cold working pass is ≤1.

5.

14. The manufacturing method according to claim 10, characterized in that: In the induction quenching step of step (5), the frequency of the quenching induction coil is controlled to be 5000-8000 Hz, and the passing speed of the steel pipe is 2-10 m / min.

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