High-strength cold-drawn welded pipe for anti-roll bar and manufacturing method of high-strength cold-drawn welded pipe

Abstract

The invention discloses a high-strength cold-drawn welded pipe for an anti-roll bar, which contains Fe and inevitable impurities, and further contains the following chemical elements in percentage by mass: 0.36 to 0.42 percent of C, 0.15 to 0.30 percent of Si, 1.2 to 1.4 percent of Mn, 0.0015 to 0.0035 percent of B, 0.02 to 0.060 percent of Al, 0.1 to 0.3 percent of Cr, 0.02 to 0.05 percent of Ti and the balance of Fe. The high-strength cold-drawn welded pipe for the anti-roll bar does not contain Ca, Mg and rare earth elements. The invention also discloses a manufacturing method of the cold-drawn welded pipe, which comprises the following steps: smelting, casting and rolling to obtain a plate coil; the plate coil obtained after longitudinal shearing and splitting is formed and welded, and a welded pipe is obtained; welded pipe heat treatment; cold machining of the welded pipe; and finished product heat treatment.

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] The anti-roll bar of a passenger car is also called a stabilizer bar. It is an auxiliary elastic element in the automobile suspension system. Its function is to prevent the body from excessive lateral tilt when turning, prevent the car from lateral tipping, and improve ride comfort. At present, the anti-roll bar is generally produced with hollow steel pipes.

[0003] The anti-roll bar is actually a transverse torsion bar spring, which can be regarded as a special elastic element in terms of function. When the body only moves vertically, the deformation of the suspension on both sides is the same, and the anti-roll bar does not work; when the body rolls, the suspension on both sides jumps inconsistently, the outer suspension will press against the anti-roll bar, the anti-roll bar will twist, and the elastic force of the bar body will prevent the wheel from lifting, thus preventing the vehicle from tilting.

[0004] As the vehicle industry has discovered, new energy vehicles are driven by battery output power, and their three-electric system will increase the weight of the vehicle. Compared with fuel vehicles of the same model, the weight increase caused by the three-electric system of new energy vehicles will cause the weight of the vehicle to increase by about 200-300kg. In other words, the weight of a new energy vehicle when unloaded is almost equivalent to the weight of a traditional vehicle when fully loaded. Therefore, the anti-roll bar of a new energy vehicle has higher requirements on the strength of the material than the anti-roll bar of a fuel vehicle.

[0005] Therefore, based on current usage requirements, the anti-roll bar needs to use higher strength materials while ensuring its torsional fatigue resistance. The product's dimensional accuracy, internal and external surface quality, and decarburization of the internal and external surfaces all need to be controlled. Summary of the invention

[0006] One of the purposes of the present invention is to provide a high-strength cold-drawn welded tube for an anti-roll bar, which has good strength and plasticity and high torsional fatigue resistance under a large stress level, and can meet the use of the anti-roll bar under high stress conditions.

[0007] In order to achieve the above object, the present invention provides a high-strength cold-drawn welded tube for an anti-roll bar, which contains Fe and inevitable impurities, and further contains the following chemical elements in the following mass percentages:

[0008] C: 0.36-0.42%, Si: 0.15-0.30%, Mn: 1.2-1.4%, B: 0.0015-0.0035%, Al: 0.02-0.060%, Cr: 0.1-0.3%, Ti: 0.02-0.05%;

[0009] The high-strength cold-drawn welded pipe for the anti-roll bar does not contain Ca, Mg and rare earth elements.

[0010] Furthermore, the present invention provides a high-strength cold-drawn welded tube for an anti-roll bar, wherein the mass percentage of each chemical element is:

[0011] C: 0.36-0.42%, Si: 0.15-0.30%, Mn: 1.2-1.4%, B: 0.0015-0.0035%, Al: 0.02-0.060%, Cr: 0.1-0.3%, Ti: 0.02-0.05%; the balance is Fe and inevitable impurities.

[0012] The high-strength cold-drawn welded pipe for anti-roll bars of the present invention does not contain Ca, Mg or rare earth metals. It optimizes the chemical composition, takes C and Mn as the main strengthening elements, and adds B and Cr in combination to ensure the hardenability of the product, so that the finished welded pipe can meet the high strength requirements after the heat treatment process of quenching and tempering in the use process, thereby avoiding the reduction of steel plasticity caused by excessive addition of alloy elements and the easy generation of cold bending cracks during the subsequent cold bending of the welded pipe. At the same time, the present invention can improve the strength and plasticity of steel by adding Ti elements, ensure the cold bending forming performance of the welded pipe and the anti-torsion fatigue performance of the welded pipe; by controlling the P, S, and O elements in the steel, the toughness of the steel is improved, and the final anti-torsion fatigue performance of the welded pipe is ensured.

[0013] Specifically, the design principles of the chemical elements in the high-strength cold-drawn welded tube for anti-roll bars of the present invention are:

[0014] C: C is one of the main elements for improving the strength of steel. It is mainly used to solve the strength of hollow anti-roll bars. It can effectively improve the strength of steel through the formation of carbides, and the cost of addition is low. In order to achieve the purpose of achieving higher finished product strength on the basis of less addition of alloy elements, the lower limit of the C content is set to 0.36%; at the same time, when the C content is too high, there will be a problem of quenching cracks in the weld. Therefore, in order to maximize the role of C, in the high-strength cold-drawn welded tube for anti-roll bars described in the present invention, the C content can be controlled between 0.36-0.42%. In some further embodiments, the C content can be controlled between 0.38-0.42%.

[0015] Si: Si element is added as a reducing agent and deoxidizer during the steelmaking process. It does not form carbides in steel, and its solid solubility in steel is relatively large, which can strengthen the ferrite in the steel to improve the strength of the steel. In the high-strength cold-drawn welded tube for the anti-roll bar described in the present invention, the Si content can be appropriately increased to improve the strength of the steel in the quenched state; however, when the Si content is too high at the same time, the toughness of the steel tube will be reduced. Therefore, in the high-strength cold-drawn welded tube for the anti-roll bar described in the present invention, the Si content can be controlled between 0.15% and 0.30%. In some further embodiments, the Si content can be controlled between 0.20% and 0.30%.

[0016] Mn: Mn is an important alloying element and a weak carbide-forming element. Mn can improve the strength of steel by solid solution strengthening. At the same time, the addition of Mn can effectively increase the hardenability of steel, thereby ensuring that the finished steel pipe has high strength. However, when the Mn content is too high, the plasticity and impact toughness of the steel decrease significantly, which has an adverse effect on the torsional fatigue resistance of the finished steel pipe. Therefore, in the high-strength cold-drawn welded tube for anti-roll bar described in the present invention, the Mn content can be controlled between 1.2-1.4%.

[0017] B: The B element in steel has a significant effect of improving the hardenability of steel. The addition of the B element can significantly increase the hardenability and strength, but once the B element content is too high, it will affect the toughness of the steel pipe. Based on this, in the high-strength cold-drawn welded pipe for the anti-roll bar of the present invention, the B element content can be controlled between 0.0015-0.0035%.

[0018] Al: Al has a deoxidizing effect in steel and helps to improve the plasticity, toughness and processability of steel. The Al content can be appropriately increased in the high-strength cold-drawn welded tube for anti-roll bars of the present invention, which has a more significant effect on improving the plasticity, toughness and processability of steel. However, when the Al content exceeds 0.06%, the sulfide inclusions in the steel increase, which has a greater impact on the torsional fatigue resistance of the steel tube. Therefore, in the high-strength cold-drawn welded tube for anti-roll bars of the present invention, the Al content can be controlled between 0.02-0.06%.

[0019] Cr: Cr is a medium-strong carbide-forming element. Part of the Cr in the steel is replaced by iron to form alloy cementite to improve its stability; the other part of the Cr is dissolved in the ferrite to play a solid solution strengthening role, improving the strength and hardness of the ferrite. At the same time, Cr is also the main element to improve the hardenability of steel. However, when the Cr content is too high, the plasticity and toughness of the steel tube matrix and the weld will be greatly affected. Therefore, in the high-strength cold-drawn welded tube for anti-roll bars described in the present invention, the Cr content can be controlled between 0.1-0.3%.

[0020] Ti: Ti is a strong nitride-forming element, and forms TiN compounds with N in steel, thereby inhibiting the precipitation of brittle BN produced by adding B in steel, and improving the toughness and plasticity of steel. After considering the cost of addition, the content of Ti in the high-strength cold-drawn welded tube for anti-roll bars of the present invention can be controlled between 0.02% and 0.05%.

[0021] Furthermore, among the inevitable impurities in the high-strength cold-drawn welded tube for the anti-roll bar of the present invention, S≤0.005%, P≤0.02%, and O≤0.003%.

[0022] The inevitable impurities in the technical solution of the present invention are mainly S, P and O elements, especially the increase of S content will have a great influence on the sulfide content in the steel, therefore, in some embodiments, S is controlled to be below 0.005%, and P is controlled to be below 0.02%. At the same time, the O content in the steel has a great influence on the oxide inclusions in the steel, therefore, in some embodiments, the O content is controlled to be below 0.003%.

[0023] Furthermore, the microstructure of the high-strength cold-drawn welded tube for the anti-roll bar of the present invention is ferrite+pearlite+dispersed carbide.

[0024] By selecting ferrite plus pearlite structure and dispersed carbide structure as the microstructure of high-strength cold-drawn welded tube for anti-roll bar, the strong plasticity of the product can be guaranteed, providing a basic guarantee for the high torsional fatigue resistance of the product.

[0025] Furthermore, the high-strength cold-drawn welded tube for the anti-roll bar of the present invention has no decarburized structure on the inner and outer surfaces, and the weld metal streamline rise angle is 30-70°.

[0026] The inner and outer surfaces of the high-strength cold-drawn welded tube for the anti-roll bar described in the present invention are in a bright state, and there is no decarburized structure on the inner and outer surfaces, which can ensure that there are no weak and easily fractured links on the surface during the torsional fatigue process, and the metal flow direction in the microstructure of the weld part is clear; by controlling the rise angle of the weld metal streamline, it can be ensured that the weld part does not become a fracture source during the torsional fatigue process, so that the product as a whole has high torsional fatigue resistance.

[0027] Furthermore, the wall thickness of the high-strength cold-drawn welded pipe for the anti-roll bar of the present invention is 2.0 to 7.0 mm.

[0028] Furthermore, the diameter of the high-strength cold-drawn welded pipe for the anti-roll bar of the present invention is 16 to 42.7 mm.

[0029] Furthermore, the performance of the high-strength cold-drawn welded pipe for the anti-roll bar described in the present invention meets the following requirements: quenched tensile strength ≥1900MPa, quenched yield strength ≥1500MPa, quenched elongation ≥8%, full decarburization depth of inner and outer surfaces is 0, single-side depth of partial decarburization layer is not more than 0.05mm, and torsional fatigue number is more than 300,000 times (under the conditions of 550MPa stress and 14.31° short stroke).

[0030] Correspondingly, another object of the present invention is to provide a method for manufacturing a high-strength cold-drawn welded pipe for an anti-roll bar, which controls the finished heat treatment process of the welded pipe to ensure that there is no decarburized structure in the structure of the finished steel pipe and that the inner and outer surfaces of the steel pipe are in a bright state.

[0031] In order to achieve the above object, the present invention proposes a method for manufacturing the above-mentioned high-strength cold-drawn welded tube for anti-roll bar, which comprises the steps of:

[0032] Smelting, casting and rolling to produce coils;

[0033] The plate coils after longitudinal shearing and stripping are formed and welded to obtain welded pipes;

[0034] Heat treatment of welded pipes;

[0035] Cold processing of welded pipes;

[0036] Finished product heat treatment: Finished product heat treatment is carried out in a reducing atmosphere furnace, and the finished product heat treatment temperature is 800-900℃.

[0037] Furthermore, in the step of preparing the coil of the method for manufacturing the high-strength cold-drawn welded tube for the anti-roll bar of the present invention, the coiling temperature of the coil is controlled to be 570-650°C.

[0038] In this embodiment, the present invention further ensures the formability of the coil by controlling the coiling temperature of the coil, while ensuring the final strength of the product.

[0039] Furthermore, in the welded pipe heat treatment (i.e., intermediate heat treatment) step of the method for manufacturing the high-strength cold-drawn welded pipe for anti-roll bar of the present invention, the heat treatment temperature is 700-800°C.

[0040] In this embodiment, the heat treatment temperature can be controlled to eliminate the internal stress of the weld structure of the welded pipe, ensuring that the hardness and strength of the weld and the heat-affected zone are consistent with those of the parent material.

[0041] Furthermore, in the cold working step of the welded pipe in the method for manufacturing the high-strength cold-drawn welded pipe for the anti-roll bar of the present invention, the elongation coefficient of the cold working is 1.5 to 2.5.

[0042] In this embodiment, by controlling the elongation coefficient of cold working, it is further ensured that the product has the best cold formability while maximizing the deformation in each pass, thereby improving manufacturing efficiency, reducing costs, and avoiding the defect of cracking of the steel pipe after cold working.

[0043] Furthermore, in the method for manufacturing the high-strength cold-drawn welded tube for anti-roll bar described in the present invention, the reducing atmosphere furnace contains reducing gases CO and H2, wherein the volume percentage of CO is 5-8%, and the volume percentage of H2 is 8-12%.

[0044] In some embodiments, the finished product heat treatment can be carried out in a reducing atmosphere furnace with a controlled atmosphere. The heat treatment atmosphere in the reducing atmosphere furnace contains reducing gases CO and H2. CO can prevent decarburization of the inner and outer surfaces during the heating process; H2 can ensure that the surface of the steel pipe is bright and can also prevent decarburization of the inner and outer surfaces during the heating process.

[0045] The high-strength cold-drawn welded tube for anti-roll bar and the manufacturing method thereof of the present invention have the following advantages and beneficial effects:

[0046] The present invention improves the hardenability of steel by controlling the composite addition of Mn, Ti, and a small amount of Cr and B elements from the perspective of component design, thereby achieving the purpose of high strength plasticity and high torsional fatigue resistance, and no precious metal elements are added, so the product raw material cost is relatively low.

[0047] The high-strength cold-drawn welded tube for anti-roll bars of the present invention uses C and Mn as main strengthening elements to improve the hardenability of the steel tube, ensuring that the steel tube has high strength after quenching and tempering when used by downstream users. At the same time, the plasticity of the steel is improved by adding Ti elements.

[0048] The present invention optimizes and controls the manufacturing process so that the steel pipe has high strength and high plasticity in the quenched state, thereby obtaining high torsional fatigue resistance. During manufacturing, the finished steel pipe is heat treated at 800-900°C in a reducing protective atmosphere so that there is no decarburized structure in the steel pipe structure, and the inner and outer surfaces of the steel pipe are bright, so that the product as a whole has high torsional fatigue resistance. The steel pipe can be used to produce hollow anti-roll bars used under high stress level conditions and can reduce the weight of the hollow anti-roll bars.

[0049] In some embodiments, the performance of the high-strength cold-drawn welded pipe for anti-roll bar described in the present invention meets the following requirements: quenched tensile strength ≥1900MPa, quenched yield strength ≥1500MPa, quenched elongation ≥8%, full decarburization depth of inner and outer surfaces is 0, partial decarburization layer depth is not more than 0.05mm on one side, and under the conditions of 550MPa stress and 14.31° short stroke, the number of torsional fatigue times is greater than 300,000 times. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 The microstructure of the weld fusion area of ​​Example 5 of the high-strength cold-drawn welded tube for anti-roll bars according to the present invention is shown.

[0051] Figure 2 The microstructure of the weld surface and decarburization of Example 5 of the high-strength cold-drawn welded tube for anti-roll bars of the present invention is shown. DETAILED DESCRIPTION

[0052] The high-strength cold-drawn welded tube for anti-roll bar and the manufacturing method thereof according to the present invention will be further explained and illustrated below in conjunction with the drawings of the specific embodiment description. However, such explanation and illustration do not constitute an improper limitation to the technical solution of the present invention.

[0053] Examples 1-10 and Comparative Examples 1-5

[0054] The high-strength cold-drawn welded tubes for anti-roll bars of Examples 1-10 and Comparative Examples 1-5 are prepared by the following steps:

[0055] (1) Smelting, casting and rolling to obtain a coil, wherein the mass percentage of chemical elements in the coil is shown in Table 1, and the coiling temperature of the coil is controlled to be 570-650°C.

[0056] In some specific embodiments, the yield strength of the coil can be controlled to be 450-550 MPa and the tensile strength to be 550-750 MPa to ensure the formability of the coil and the ultimate strength of the high-strength cold-drawn welded pipe.

[0057] (2) The coil is pickled, uncoiled, and longitudinally sheared, and then the longitudinally sheared coil is formed and welded to produce a welded pipe.

[0058] Among them, in some more specific implementations, high-frequency resistance welding can be used to weld the welded pipe, and after welding, burrs on the inner and outer surfaces are removed, and online eddy current flaw detection is performed on the welded pipe.

[0059] (3) Heat treatment of welded pipe (and intermediate heat treatment): The welded pipe is heat treated in a reducing atmosphere furnace with controlled atmosphere. The temperature of the welded pipe heat treatment is controlled at 700-800°C to eliminate the internal stress of the weld structure of the welded pipe and ensure that the hardness and strength of the weld and heat-affected zone are consistent with those of the parent material.

[0060] (4) Cold processing of welded pipes: cold drawing or cold rolling is used to cold process the pipes to the finished product size and the elongation coefficient of the cold processing is controlled to be 1.5-2.5.

[0061] In some specific embodiments, the finished size of the cold-processed steel pipe can be controlled to have a wall thickness of 2.0-7.0 mm and an outer diameter of 16-42.7 mm.

[0062] (5) Finished product heat treatment: Heat treatment is carried out in a heat treatment furnace containing a reducing atmosphere of CO and H2, the heat treatment temperature is 800-900°C, the holding time is 50-70min, and the volume percentages of CO and H2 are CO: 5-8% and H2: 8-12% respectively.

[0063] It should be noted that the high-strength cold-drawn welded pipes for anti-roll bars of Examples 1-10 of the present invention are all manufactured by the above steps, and their chemical compositions and related process parameters meet the control requirements of the design specification of the present invention. The welded pipes of Comparative Examples 1-5 are also manufactured by the above process flow, but the chemical compositions of the welded pipes of Comparative Examples 1-5 do not meet the design requirements of the present invention.

[0064] Table 1 lists the mass percentages of the chemical elements in Examples 1-10 and Comparative Examples 1-5 of the present invention.

[0065] Table 1. (wt.%, the balance is Fe and other inevitable impurities except P, S and O)

[0066]

[0067]

[0068] Table 2 lists the process parameters of each step in Examples 1-10 and Comparative Examples 1-5.

[0069] Table 2.

[0070]

[0071] The high-strength cold-drawn welded pipes of Examples 1-10 and the comparative steel pipes of Comparative Examples 1-5 were sampled respectively, and the microstructures were observed using GB / T 13299, and the test results are listed in Table 3. Based on the observation of the microstructure, the microstructures of the embodiments of the present invention are all in the form of a banded ferrite + pearlite structure matrix with fine carbide particles dispersedly distributed.

[0072] Table 3.

[0073]

[0074]

[0075] also, Figure 1 A microstructure photograph of the fusion zone of the weld of Example 5 of the present invention is also shown.

[0076] from Figure 1 It can be seen that the metal flow direction of Example 1 is clear, and the weld metal streamline rise angle is between 30-70°, which ensures the high plasticity and torsional fatigue resistance of the weld structure.

[0077] Figure 2 The microstructure photograph of the weld surface area and decarburization of Example 5 is shown.

[0078] from Figure 2 It can be seen that the microstructure of Example 1 is: fine carbide particles are dispersed in a banded ferrite pearlite matrix, which ensures the strength and plasticity of the matrix, thereby ensuring that the steel pipe has good torsional fatigue resistance.

[0079] In addition, the high-strength cold-drawn welded pipes of Examples 1-10 and the comparative steel pipes of Comparative Examples 1-5 were sampled again, and their various properties were tested, and the results are listed in Table 4. Among them:

[0080] (1) Tensile strength, yield strength and elongation are measured according to GB / T 2975 method after quenching and tempering heat treatment of cold drawn welded pipe.

[0081] (2) The depth of the outer surface decarburization layer, the depth of the inner surface decarburization layer and the single side length of the partial decarburization layer depth are measured according to the GB / T224 method.

[0082] (3) Torsional fatigue resistance: Under the conditions of 550 MPa stress and 14.31° short stroke, if the number of torsional fatigue tests is greater than 300,000 times, it is considered qualified; otherwise, it is considered unqualified.

[0083] Table 4.

[0084]

[0085]

[0086] It can be seen from Table 1, Table 2, Table 3 and Table 4 that since the high-strength cold-drawn welded pipes in Examples 1-10 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 quenched tensile strength of Examples 1-10 is greater than or equal to 1900MPa, the quenched yield strength is greater than 1500MPa, the quenched elongation is greater than 8%, the full decarburization depth of the inner and outer surfaces is 0, and the single-side depth of the partial decarburization layer is not greater than 0.05mm. Under the conditions of 550MPa stress and 14.31° short stroke, the torsional fatigue number is greater than 300,000 times, so the torsional fatigue resistance is qualified.

[0087] Different from the embodiment, the mass percentage of chemical elements in each steel pipe in comparative examples 1-5 does not conform to the range defined by the present invention, so its comprehensive mechanical properties are obviously inferior to those of the high-strength cold-drawn welded pipe of embodiments 1-10.

[0088] 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.

[0089] 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.

[0090] 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 cold-drawn welded tube for an anti-roll bar, containing Fe and unavoidable impurities, characterized in that: It also contains the following chemical elements in the following mass percentages: C: 0.36-0.42%, Si: 0.15-0.30%, Mn: 1.2-1.4%, B: 0.0015-0.0035%, Al: 0.02-0.060%, Cr: 0.1-0.3%, Ti: 0.02-0.05%; The high-strength cold-drawn welded pipe for the anti-roll bar does not contain Ca, Mg and rare earth elements.

2. The high-strength cold-drawn welded tube for anti-roll bar according to claim 1, characterized in that: The mass percentage of each chemical element is: C: 0.36-0.42%, Si: 0.15-0.30%, Mn: 1.2-1.4%, B: 0.0015-0.0035%, Al: 0.02-0.060%, Cr: 0.1-0.3%, Ti: 0.02-0.05%; the balance is Fe and inevitable impurities.

3. The high-strength cold-drawn welded tube for anti-roll bar according to claim 1 or 2, characterized in that: Among the inevitable impurities, S≤0.005%, P≤0.02%, and O≤0.003%.

4. The high-strength cold-drawn welded tube for anti-roll bar according to claim 1 or 2, characterized in that: Its microstructure is ferrite + pearlite + dispersed carbides.

5. The high-strength cold-drawn welded tube for anti-roll bar according to claim 1 or 2, characterized in that: There is no decarburized structure on the inner and outer surfaces, and the weld metal flow line angle is 30 to 70°.

6. The high-strength cold-drawn welded tube for anti-roll bar according to claim 1 or 2, characterized in that: Its wall thickness is 2.0~7.0mm.

7. The high-strength cold-drawn welded tube for anti-roll bar according to claim 1 or 2, characterized in that: Its outer diameter is 16~42.7mm.

8. The high-strength cold-drawn welded tube for anti-roll bar according to claim 1 or 2, characterized in that: Its performance meets the following requirements: quenched tensile strength ≥1900MPa, quenched yield strength ≥1500MPa, quenched elongation ≥8%, full decarburization depth of inner and outer surfaces is 0, single-side depth of partial decarburization layer is not more than 0.05mm, and torsional fatigue times are greater than 300,000 times.

9. The method for manufacturing a high-strength cold-drawn welded tube for an anti-roll bar according to any one of claims 1 to 8, characterized in that: Includes steps: Smelting, casting and rolling to produce coils; The plate coils after longitudinal shearing and stripping are formed and welded to obtain welded pipes; Heat treatment of welded pipes; Cold processing of welded pipes; Finished product heat treatment: Finished product heat treatment is carried out in a reducing atmosphere furnace, and the finished product heat treatment temperature is 800-900℃.

10. The manufacturing method according to claim 9, characterized in that: In the step of preparing the coil, the coiling temperature of the coil is controlled to be 570-650°C.

11. The manufacturing method according to claim 9, characterized in that: In the heat treatment step of the welded pipe, the heat treatment temperature is 700-800°C.

12. The manufacturing method according to claim 9, characterized in that: In the cold working step of the welded pipe, the elongation coefficient of cold working is 1.5 to 2.

5.

13. The manufacturing method according to claim 9, characterized in that: The reducing atmosphere furnace contains reducing gases CO and H2, wherein the volume percentage of CO is 5-8%, and the volume percentage of H2 is 8-12%.

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