Ultra-large-diameter thick-wall seamless steel pipe and manufacturing method thereof
By employing electroslag ingot heating, piercing, rolling mill, and push-forming hot deformation processes, combined with medium-frequency heating push technology, the problems of equipment limitations and high costs in the production of ultra-large diameter thick-walled seamless steel pipes have been solved, enabling the production of high-quality steel pipes and meeting market demands.
Patent Information
- Application Number
- CN202610010732.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-06
- Publication Date
- 2026-03-03
AI Technical Summary
Existing technologies are insufficient for the efficient production of ultra-large diameter thick-walled seamless steel pipes, especially D6AE steel pipes, due to equipment limitations, high production costs, difficulties in dimensional control, and internal surface quality issues.
The process of electroslag ingot heating, piercing, rolling and pushing hot deformation is adopted, combined with medium frequency heating pushing technology, to control the heating temperature and speed, ensure uniform heating of steel ingots, avoid defects, and achieve high-quality production of ultra-large diameter thick-walled seamless steel pipes.
This technology enables high-quality production of ultra-large diameter, thick-walled seamless steel pipes, reduces production costs, meets market demands, improves economic efficiency, and ensures that the inner surface of the steel pipes is free from defects such as cracks, folds, and scabs.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of steel hot deformation technology, specifically relating to an ultra-large diameter thick-walled seamless steel pipe and its manufacturing method. Background Technology
[0002] D6AE is a low-alloy ultra-high-strength steel. Its high strength and good toughness ensure the safety and performance of aircraft under complex flight conditions. With industrial development, the application range of D6AE ultra-high-strength, high-toughness seamless steel pipes is expanding, leading to increased demand, especially for ultra-large diameter, thick-walled pipes. For seamless steel pipes with an outer diameter of 630mm or more and a wall thickness of 25mm or more, equipment limitations prevent direct rolling; a hot rolling + pipe expansion process is required. Furthermore, D6AE steel contains elements such as Ni alloys, resulting in high viscosity and a tendency for metal to adhere to the mandrel. This is particularly problematic when high dimensional accuracy of the inner diameter is required, necessitating high inner surface quality. Hot expansion pipe production results in poor dimensional tolerance control, and the pre-formed flared end of the pipe, due to equipment limitations, incurs significant production costs due to the removal of this flared end.
[0003] CN114178465A discloses a method for manufacturing ultra-large diameter thick-walled seamless steel pipes, including: before forging, further processing the billet through billet preparation and extrusion processes; heating the billet and then forging to expand the hole, using two passes of mandrel shaping during the forging and expanding process; and heat treatment after forging and expanding to prepare ultra-large diameter thick-walled seamless steel pipes. This method utilizes a combined billet preparation-extrusion-forging forming technology to produce ultra-large diameter thick-walled seamless steel pipes with an outer diameter greater than 900 mm and a wall thickness greater than 50 mm, using low-alloy steel such as 15CrMoG, P12, and P22, nickel-containing alloys such as WB36, and high-alloy steel such as P91 and P92. Although this method can produce ultra-large diameter thick-walled seamless steel pipes, the hollow electroslag ingots used before piercing have higher production costs than ordinary electroslag ingots. Furthermore, the forging and expanding process requires two passes of mandrel shaping for local shaping, making the process complex and not conducive to ensuring the overall microstructure and properties of the steel pipe. Summary of the Invention
[0004] The technical problem to be solved by this invention is to provide a hot-rolled billet feeding + push-forming hot deformation process for seamless steel pipes, thereby solving the production problem of D6AE ultra-large diameter thick-walled seamless steel pipes for ultra-high strength alloy structures.
[0005] This invention provides a method for manufacturing ultra-large diameter thick-walled seamless steel pipes, which includes the following steps: A. Heating of electroslag ingots: After boring the center of the electroslag ingot (the composition of the electroslag ingot is the same as that of the D6AE seamless steel pipe), place it in the annular heating furnace. When loading the furnace, control the furnace bottom temperature to ≤700℃ and load the ingot at a rate of 8~12 minutes per piece (the total loading amount is determined according to the capacity of the annular heating furnace and common knowledge in this field). After loading is completed, heat the annular heating furnace. The heating temperature is controlled according to Table 1 below. During this period, rotate the furnace bottom at a rate of 8~12 minutes / 4.0°~5.0°. Table 1 Heating Temperature Regulation for Circular Furnace B. Electroslag ingot piercing: After the second stage of soaking heat is completed, the steel ingot is moved from the annular heating furnace to the piercing machine for piercing. The parameters of the piercing machine are controlled according to Table 2 below. Table 2 Parameters of the punching machine C. Rolling: The pierced tube is moved to the rolling mill for rolling. The rolling mill parameters and dimensions are controlled according to Table 3 below. Table 3 Rolling Mill Parameters and Dimensional Control D. Finished product pushing and expanding: After cleaning the inner surface of the rolled tube blank, apply graphite lubricant to the inner surface, and then perform one-stage medium frequency heating pushing or two-stage medium frequency heating pushing. The pushing parameters for one-stage or two-stage medium frequency heating pushing are controlled according to Table 4 below. Table 4. Pushing parameters This yields ultra-large diameter, thick-walled, seamless steel pipes.
[0006] In the manufacturing method of the aforementioned ultra-large diameter thick-walled seamless steel pipe, the seamless steel pipe is a D6AE seamless steel pipe, and its chemical composition by weight percentage is: C 0.42%~0.48%, Mn 0.60%~0.90%, Si 0.17%~0.35%, Cr 0.90%~1.20%, Mo 0.90%~1.10%, V 0.05%~0.15%, Ni 0.40%~0.70%, with the balance being Fe and unavoidable impurities.
[0007] In the manufacturing method of the above-mentioned ultra-large diameter thick-walled seamless steel pipe, unavoidable impurities include P and S, with P ≤ 0.015% and S ≤ 0.015% by weight percentage.
[0008] In the manufacturing method of the aforementioned ultra-large diameter thick-walled seamless steel pipe, step A involves boring a Φ180mm hole in the center of an electroslag ingot with a diameter of Φ600mm / 4~5.2t. For large-diameter thick-walled pipe products, this invention selects an electroslag ingot with a maximum size of Φ600mm, which is then processed into different specifications using a piercing mill and a rolling mill.
[0009] In step A of this invention, without affecting the risk of the steel ingot cracking or breaking due to excessive heating temperature, the higher the furnace bottom temperature, the more time the steel ingot will be saved in the preheating time in the ring furnace. Therefore, this invention controls the furnace bottom temperature to be ≤700℃ when loading the furnace.
[0010] In step A of this invention, the furnace bottom is rotated to ensure that the electroslag ingots are heated evenly in the ring furnace. Therefore, the furnace bottom needs to be rotated throughout the heating process until all steel ingots are taken out of the ring furnace.
[0011] In step A of this invention, the heating temperature system of the annular furnace is controlled by the size of the natural gas flame emitted by the burners on the furnace wall. The heating section is for heating the steel ingot from a low temperature to a high temperature, requiring the burner flame to be turned up high. The soaking section is for maintaining the temperature of the entire steel ingot after it has been heated to a certain temperature.
[0012] In the manufacturing method of the above-mentioned ultra-large diameter thick-walled seamless steel pipe, in step D, the outer diameter * wall thickness of the obtained ultra-large diameter thick-walled seamless steel pipe is Φ630~790mm×25~35mm.
[0013] In the manufacturing method of the above-mentioned ultra-large diameter thick-walled seamless steel pipe, in step D, when preparing ultra-large diameter thick-walled seamless steel pipe with an outer diameter ≤ Φ650mm, a single-stage medium-frequency heating push is used; when preparing ultra-large diameter thick-walled seamless steel pipe with an outer diameter > Φ650mm, a two-stage medium-frequency heating push is used.
[0014] In the manufacturing method of the aforementioned ultra-large diameter thick-walled seamless steel pipe, in step D, during the first stage of medium-frequency heating and pushing, the diameter of the pusher sizing section rod is controlled to be Φ520mm~Φ600mm; during the second stage of medium-frequency heating and pushing, the diameter of the pusher sizing section rod during the first stage of pushing is controlled to be Φ520mm~Φ600mm, and the diameter of the pusher sizing section rod during the second stage of pushing is controlled to be Φ600mm~Φ720mm.
[0015] In the manufacturing method of the above-mentioned ultra-large diameter thick-walled seamless steel pipe, in step D, during the two-stage medium-frequency heating and pushing process, the steel pipe with specifications of Φ508mm×30~45mm is pushed into a steel pipe with specifications of Φ540~660mm×28~43mm in one push, and then pushed into a steel pipe with specifications of Φ650~790mm (excluding Φ650mm)×25~35mm in a second push.
[0016] During the steel pipe pushing process of this invention, the steel pipe is subjected to axial and radial compressive stress as well as tangential tensile stress. Therefore, the surface quality requirements for the rolled steel pipe are relatively high. Thus, the surface of the rolled steel pipe must not have defects such as cracks, folds, scars, delamination, or pitting. If any of the above defects are present, they must be removed before pushing.
[0017] In this invention, the heating temperature and pushing speed of the tube expander are key technologies: (1) During heating, the tube blank must be located in the middle of the coil to ensure that the steel billet is heated evenly. If the heating temperature is not well controlled, it will not only affect the smooth progress of the pushing process and cause the product size to be unqualified, but also make it difficult to ensure that the performance indicators of the steel pipe meet the normalizing performance requirements; (2) If the pushing speed is too fast, the tube expander temperature will drop, which will lead to low-temperature tube expander tearing, unstable steel pipe performance, or even unqualified performance; if the pushing speed is too slow, the pushing temperature will rise, resulting in defects such as bulging and steel piling, and will also reduce the service life of the tool.
[0018] The present invention also provides an ultra-large diameter thick-walled seamless steel pipe, which is prepared by the above-described manufacturing method.
[0019] The ultra-high strength alloy structure ultra-large diameter thick-walled seamless steel pipe prepared by this invention has no defects such as cracks, folds, scars, delamination, or pits on the inner surface of the steel pipe. Its dimensions meet the following requirements: inner diameter tolerance D ± 0.5%, wall thickness tolerance S ± 8%, and curvature 1~3 mm / m.
[0020] The beneficial effects of this invention are: This invention employs a process of rolling billets using a periodic tube rolling mill and then pushing them into finished products. This process is relatively simple, and the surface quality and dimensional tolerances of the steel pipes are well controlled. It successfully produces ultra-large diameter, thick-walled D6AE seamless steel pipes, reducing production costs, meeting market demands, and improving the economic benefits of the product. Detailed Implementation
[0021] The present invention will be further described in detail below through embodiments, but the scope of protection of the present invention is not limited to the embodiments described herein.
[0022] Table 5 Product Technical Requirements Example 1 This embodiment provides a method for preparing ultra-large diameter thick-walled seamless steel pipes. Taking a seamless steel pipe with a specification of Φ790×35mm as an example, the heat treatment process is as follows: (1) Heating control of the ring furnace After boring a Φ600mm / 5.2t electroslag ingot with a center hole of Φ180mm, it is placed in an annular heating furnace for heating. Feeding begins when the furnace bottom temperature reaches 700℃, with each ingot being loaded every 10 minutes. After loading, the furnace bottom is rotated at a rate of 4.5° every 10 minutes. Annular furnace heating temperature control: 700℃ for non-feeding section, 1000℃ for preheating section I, 1130℃ for preheating section II, 1245℃ for heating section I, and 1270℃ for heating section II and soaking section (soaking section includes soaking sections I and II).
[0023] (2) Control of perforation technology of perforation machine Because this steel has high deformation resistance, it is prone to ring cracking. Therefore, it is necessary to adjust the appropriate piercing mill parameters. The piercing mill adjustment parameters are: mandrel 430mm, rolling angle +1°, mandrel extension 170mm, roll gap 552mm, rotation speed 100rpm, guide torque 618mm, graphite powder + graphite emulsion lubrication, and capillary outer diameter after piercing 640~645mm.
[0024] (3) Rolling technology control of rolling mill To level the gap between the left and right rolls, a trial roll test is required before final rolling. Mill parameters and dimensional control: roll pass ΦDk521, roll diameter 1000mm, outer diameter D±0.75%, mandrel Φ426mm, wall thickness deviation 41.6~46.6mm, wall thickness range ≤4.2mm, speed 180rpm, feed rate 18mm. The rolled steel pipe dimensions are Φ508×41mm.
[0025] (4) Push-type technology control Because the finished seamless steel pipe is large in size (Φ790×35mm), it requires a two-stage pushing process.
[0026] a. Cleaning and lubrication of the inner surface of the steel pipe After cleaning the iron oxide scale and defects on the inner surface of the rolled steel pipe billet (Φ508×41mm), a compressed air blower is used to blow air to keep the inner surface of the steel pipe clean, and a layer of evenly distributed graphite lubricant is applied to the inner surface of the steel pipe. b. First push One end of a cleaned steel pipe is placed in a 950mm inner diameter medium-frequency induction coil for heating. When the steel pipe temperature reaches 800℃, a pusher with a diameter of Φ529mm is used to push the pipe with a pushing voltage of 680V, a pushing force of 117 tons, and a pushing speed of 35mm / min. The steel pipe with a specification of Φ508×41mm is pushed into a steel pipe with a specification of Φ610×40.5mm. c. Second push After the first pushing process, a 60% graphite lubricant was evenly applied to the inner surface of the steel pipe (Φ610×40.5mm). The steel pipe was then placed again in a 950mm inner diameter medium-frequency induction coil for heating at 800℃. A pusher with a sizing section rod diameter of Φ718mm was then used to push the pipe from Φ610×40.5mm to Φ790×35mm using a pushing voltage of 700V, a pushing force of 117 tons, and a pushing speed of 50mm / min.
[0027] Example 2 This embodiment provides a method for preparing ultra-large diameter, thick-walled seamless steel pipes. Taking a seamless steel pipe with a specification of Φ640×26mm as an example, the heat treatment process is as follows: (1) Heating control of the ring furnace After boring a Φ600mm / 4t electroslag ingot into a Φ180mm center hole, place it in an annular heating furnace for heating. Feeding begins when the furnace bottom temperature reaches 700℃, with each ingot being loaded every 10 minutes. After loading, rotate the furnace bottom at a rate of 4.5° every 10 minutes. Annular furnace heating temperature control: 700℃ for the non-heating section, 1000℃ for preheating section I, 1130℃ for preheating section II, 1245℃ for heating section I, and 1270℃ for heating section II and the soaking section (which includes soaking sections I and II).
[0028] (2) Control of perforation technology of perforation machine This steel has high deformation resistance and is prone to ring cracking. Therefore, it is necessary to adjust the appropriate piercing mill parameters. The piercing mill adjustment parameters are: mandrel 450mm, rolling angle +0.8°, mandrel extension 170mm, roll gap 550mm, rotation speed 100rpm, guide torque 611mm, graphite powder + graphite emulsion lubrication, and the hot outer diameter of the pore after piercing is 630~635mm.
[0029] (3) Rolling technology control of rolling mill To level the left and right roll gaps, a trial roll test is required before final rolling. Mill parameters and dimensional control: roll pass ΦDk521, roll diameter 1000mm, outer diameter D±0.75%, mandrel Φ450mm, rotation speed 185rpm, feed rate 18mm. During rolling, the steel pipe wall thickness deviation is controlled within 30.1~33.9mm, with a wall thickness range ≤3.2mm. The rolled steel pipe dimensions are Φ508×32mm.
[0030] (4) Finished product Φ640×26mm push-forming technology control a. Cleaning and lubrication of the inner surface of the steel pipe After cleaning the iron oxide scale and defects on the inner surface of the rolled steel pipe billet (Φ508×32mm), a compressed air blower is used to blow air to keep the inner surface of the steel pipe clean, and a layer of evenly distributed graphite lubricant is applied to the inner surface of the steel pipe. b. Control of the pushing process technology One end of a cleaned steel pipe is placed in a 740mm inner diameter medium-frequency induction coil for heating. When the steel pipe reaches 800℃, a pusher with a diameter of Φ585mm is used to push the pipe. The pushing voltage is 550V, the pushing force is 41 tons, and the pushing speed is 40mm / min. The steel pipe with a specification of Φ508×32mm is pushed into a steel pipe with a specification of Φ640×26mm.
[0031] The dimensional properties of the products obtained according to Examples 1 and 2 after conventional heat treatment are shown in Table 6.
[0032] Table 6. Dimensional properties of the product after heat treatment
Claims
1. A method for manufacturing ultra-large diameter thick-walled seamless steel pipes, characterized in that: Includes the following steps: A. Heating of electroslag ingots: After boring the center hole of the electroslag ingot, place it in the annular heating furnace. When loading the furnace, control the furnace bottom temperature to ≤700℃. Load the ingots at a rate of 8~12 minutes per ingot. After loading, heat the annular heating furnace. The heating temperature is controlled according to the table below. During this period, rotate the furnace bottom at a rate of 8~12 minutes / 4.0°~5.0°. Heating temperature regime of annular furnace B. Electroslag ingot piercing: After the second stage of soaking heat is completed, the steel ingot is moved from the annular heating furnace to the piercing machine for piercing. The parameters of the piercing machine are controlled according to the following table. Perforation machine parameters C. Rolling: The pierced tube is moved to the rolling mill for rolling. The rolling mill parameters and dimensions are controlled according to the following table. Rolling mill parameters and dimensional control D. Finished product pushing and expanding: After cleaning the inner surface of the rolled tube blank, apply graphite lubricant to the inner surface, and then perform one-stage medium frequency heating pushing or two-stage medium frequency heating pushing. The pushing parameters for one-stage or two-stage medium frequency heating pushing are controlled according to the table below. Push parameters This yields ultra-large diameter, thick-walled, seamless steel pipes.
2. The method for manufacturing ultra-large diameter thick-walled seamless steel pipe according to claim 1, characterized in that: The seamless steel pipe is a D6AE seamless steel pipe, and its chemical composition by weight percentage is: C 0.42%~0.48%, Mn 0.60%~0.90%, Si 0.17%~0.35%, Cr 0.90%~1.20%, Mo 0.90%~1.10%, V 0.05%~0.15%, Ni 0.40%~0.70%, with the balance being Fe and unavoidable impurities.
3. The method for manufacturing ultra-large diameter thick-walled seamless steel pipe according to claim 2, characterized in that: Unavoidable impurities include P and S, with P ≤ 0.015% and S ≤ 0.015% by weight.
4. The method for manufacturing ultra-large diameter thick-walled seamless steel pipe according to claim 1, characterized in that: In step A, the center hole of the Φ600mm / 4~5.2t electroslag ingot is bored to Φ180mm.
5. The method for manufacturing ultra-large diameter thick-walled seamless steel pipe according to claim 1, characterized in that: In step D, the outer diameter * wall thickness of the obtained ultra-large diameter thick-walled seamless steel pipe is Φ630~790mm×25~35mm.
6. The method for manufacturing ultra-large diameter thick-walled seamless steel pipe according to claim 5, characterized in that: In step D, when preparing ultra-large diameter thick-walled seamless steel pipes with an outer diameter ≤ Φ650mm, a single-stage medium-frequency heating push is used; when preparing ultra-large diameter thick-walled seamless steel pipes with an outer diameter > Φ650mm, a two-stage medium-frequency heating push is used.
7. The method for manufacturing ultra-large diameter thick-walled seamless steel pipe according to claim 6, characterized in that: In step D, during the first stage of medium-frequency heating and pushing, the diameter of the pusher sizing section rod is controlled to be Φ520mm~Φ600mm; during the second stage of medium-frequency heating and pushing, the diameter of the pusher sizing section rod during the first stage of pushing is controlled to be Φ520mm~Φ600mm, and the diameter of the pusher sizing section rod during the second stage of pushing is controlled to be Φ600mm~Φ720mm.
8. The method for manufacturing ultra-large diameter thick-walled seamless steel pipe according to claim 6, characterized in that: In step D, during the two-stage medium-frequency heating and pushing process, the steel pipe with specifications of Φ508mm×30~45mm is pushed into a steel pipe with specifications of Φ540~660mm×28~43mm in one push, and then pushed into a steel pipe with specifications of Φ650~790mm×25~35mm in a second push.
9. The ultra-large diameter thick-walled seamless steel pipe prepared by the manufacturing method according to any one of claims 1 to 8.
10. The ultra-large diameter thick-walled seamless steel pipe according to claim 9, characterized in that: Its dimensions meet the following requirements: inner diameter tolerance D ± 0.5%, wall thickness tolerance S ± 8%, and curvature 1~3 mm / m.