A method for producing ultra-large diameter duplex stainless steel radial forging tube blanks

Abstract

This invention discloses a method for producing ultra-large diameter duplex stainless steel radial forged tube blanks, comprising: selecting an 8.4t square billet as the billet material, heating the square billet at a temperature of 1250±10℃ for a soaking time of 2.0~8.0h, and then upsetting it into a round billet with a diameter of φ900~1000mm after exiting the furnace; radially forging the round billet into a tube blank with a diameter of φ500~600mm, wherein during the radial forging process, the heating temperature is 1250±10℃ for a heating time of 2.0~4.0h, the initial forging temperature is 1050~1150℃, and the radial forging adopts a three-stage forging process, with the forging deformation rates of the first to third stages being 5~8%, 10~15%, and 20~30%, respectively; and directly annealing the tube blank in a furnace at a temperature of 1050±20℃ for a time of 6~12h, and immediately water cooling it in a water tank after exiting the furnace. This invention marks the first successful production and qualified delivery of ultra-large diameter forged tube blanks of S32205 series duplex stainless steel with a diameter of φ500~600mm. The specifications, surface and various properties of the finished ultra-large diameter forged tube blanks of duplex stainless steel meet the high requirements of marine mining platforms for materials, providing a solution for the preparation and production of ultra-large diameter forged tube blanks of duplex stainless steel.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel manufacturing technology, and in particular relates to a method for producing ultra-large diameter duplex stainless steel radial forging tube blanks. Background Technology

[0002] Duplex stainless steel exhibits a coexistence of austenite and ferrite in its room-temperature microstructure, with a duplex ratio approaching 1:1. This type of steel boasts high strength, with its yield strength typically twice that of austenitic stainless steel, and possesses excellent resistance to chloride ions (Cl). - With its outstanding advantages such as pitting resistance, stress corrosion resistance, and weldability, it is widely used in petrochemical, salt production, hydraulic engineering, shipbuilding, and civil applications.

[0003] With the increasing scale and complexity of international engineering projects, more and more projects require larger-specification products to meet design requirements. Offshore mining platforms are one such example, and ultra-large diameter duplex stainless steel radial forging billets (φ500~600mm) are a common raw material used for piercing to produce seamless tubes. However, the domestically produced S32205 series duplex stainless steel radial forging billets currently have a limited diameter due to insufficient radial forging compression ratio, which cannot meet customer demand. Summary of the Invention

[0004] To address the technical problems existing in the prior art, the present invention provides a method for producing ultra-large diameter duplex stainless steel radial forging tube blanks, wherein the diameter of the duplex stainless steel radial forging tube blank is φ500~600mm, and the method for producing ultra-large diameter duplex stainless steel radial forging tube blanks includes the following steps:

[0005] S1. Billet making: Select 8.4t square billet as billet material. Control the heating temperature of the square billet to 1250±10℃ and control the heating time to 2.0~8.0h. After taking it out of the furnace, roll the square billet into a round billet with a diameter of φ900~1000mm.

[0006] S2. Radial forging: A round billet with a diameter of 900-1000mm is radially forged into a tube billet with a diameter of 500-600mm. During the radial forging process, the heating temperature is controlled at 1250±10℃, the heating time is controlled at 2.0-4.0h, and the initial forging temperature is controlled at 1050-1150℃. The radial forging adopts a three-stage forging process. The forging deformation rate of the first stage is controlled at 5-8%, the forging deformation rate of the second stage is controlled at 10-15%, and the forging deformation rate of the third stage is controlled at 20-30%. The final forging temperature of each stage is controlled at ≥900℃. After each stage of radial forging is completed, the tube is heated and held in the furnace.

[0007] S3. Annealing: The tube blank obtained after forging is directly put into the furnace for annealing. The annealing temperature is controlled at 1050±20℃ and the annealing time is controlled at 6~12h. After being taken out of the furnace, it is immediately put into a water tank for water cooling.

[0008] Furthermore, in the above-mentioned production method of ultra-large diameter duplex stainless steel radial forging tube blank, the duplex stainless steel is S32205 series duplex stainless steel, and its chemical composition by weight percentage is: C≤0.030%, Si≤1.00%, Mn≤2.00%, P≤0.035%, S≤0.020%, Cr 21.0~23.0%, Ni 4.5~6.5%, Mo 2.5~3.5%, N0.08%~0.22%, with the remainder being Fe and unavoidable impurities.

[0009] The method for producing ultra-large diameter duplex stainless steel radial forging tube blanks of the present invention has at least the following beneficial effects:

[0010] The production method of ultra-large diameter duplex stainless steel radial forging tube blanks of the present invention controls the billet heating temperature to 1250±10℃ and the billet soaking time to 2.0~8.0h, the radial forging heating temperature to 1250±10℃ and the radial forging heating time to 2.0~4.0h, the forging deformation rate of the three-stage radial forging to 5~8%, 10~15%, and 20~30% respectively, and the annealing temperature to 1050±20℃ and the annealing time to 6~12h. For the first time in China, the successful production and qualified delivery of ultra-large diameter S32205 series duplex stainless steel radial forging tube blanks with a diameter of φ500~600mm have been achieved. The specifications, surface and various properties of the finished ultra-large diameter duplex stainless steel radial forging tube blanks meet the high requirements of marine mining platforms, providing a solution for the preparation and production of ultra-large diameter duplex stainless steel radial forging tube blanks. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings:

[0012] Figure 1 A photograph of an ultra-large diameter S32205 series duplex stainless steel radial forging tube blank with a diameter of φ570mm, produced using the ultra-large diameter duplex stainless steel radial forging tube blank production method of Embodiment 1 of the present invention.

[0013] Figure 2 Metallographic images of an ultra-large diameter S32205 series duplex stainless steel radial forging tube blank with a diameter of φ570mm, produced using the ultra-large diameter duplex stainless steel radial forging tube blank production method of Example 1 of the present invention. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0015] The method for producing ultra-large diameter duplex stainless steel radial forging billets of this invention targets S32205 series duplex stainless steel, whose chemical composition by weight percentage is: C≤0.030%, Si≤1.00%, Mn≤2.00%, P≤0.035%, S≤0.020%, Cr21.0~23.0%, Ni4.5~6.5%, Mo2.5~3.5%, N0.08%~0.22%, with the remainder being Fe and unavoidable impurities. This method for producing ultra-large diameter duplex stainless steel radial forging billets achieves successful production and qualified delivery of S32205 series duplex stainless steel ultra-large diameter radial forging billets with a diameter of φ500~600mm by strictly controlling the billet specifications, billet opening temperature and heating time, three-stage radial forging process parameters, and annealing process parameters, thus meeting the high material requirements of offshore mining platforms.

[0016] Specifically, the production method of the ultra-large diameter duplex stainless steel radial forging tube blank of the present invention includes the following steps:

[0017] S1. For billet preparation, select an 8.4t square billet as the billet material. The billet heating temperature is controlled at 1250±10℃, and the heating time is controlled at 2.0~8.0h. After exiting the furnace, immediately press the square billet into a round billet with a diameter of φ900~1000mm.

[0018] S2. Radial forging: The round billet with a diameter of 900-1000mm is radially forged into a tube billet with a diameter of 500-600mm. During the radial forging process, the heating temperature is controlled at 1250±10℃, the heating time is controlled at 2.0-4.0h, and the initial forging temperature is controlled at 1050-1150℃. The radial forging adopts a three-stage forging process. The forging deformation rate of the first stage is controlled at 5-8%, the forging deformation rate of the second stage is controlled at 10-15%, and the forging deformation rate of the third stage is controlled at 20-30%. The final forging temperature of each stage is controlled at ≥900℃. After each stage of radial forging is completed, the tube is immediately placed in the furnace for heating and heat preservation.

[0019] S3. Annealing: The tube blank obtained after forging is directly put into the furnace for annealing. The annealing temperature is controlled at 1050±20℃ and the annealing time is controlled at 6~12h. After being taken out of the furnace, it is immediately put into a water tank for water cooling.

[0020] The mechanism of the production method of ultra-large diameter duplex stainless steel radial forging tube blank of the present invention is as follows:

[0021] Billet specifications, billet temperature, and heating time control: Since the final product requires ultra-large diameter duplex stainless steel radial forging billets with a diameter of φ500~600mm, large-size square billets must be used to ensure a certain compression ratio. Due to the large size of the square billets, two points must be considered during billet heating: heating temperature and heating time. If the temperature is too low, the temperature drop will be rapid during subsequent radial forging, increasing the forging force and making the surface billet prone to defects such as cracks; if the temperature is too high or the heating time is too long, the billet grains will easily grow and coarse, leading to billet cracking during radial forging. Therefore, in the production method of ultra-large diameter duplex stainless steel radial forging billets of this invention, the billet heating temperature is controlled at 1250±10℃, and the soaking time is controlled at 2.0~8.0h.

[0022] Three-stage radial forging process parameter control: Due to the large billet size, the temperature drop between the edge and the core during forging is different, leading to uneven temperature and a high risk of forging cracks. Furthermore, as forging progresses, the forging pressure increases, and the equipment capacity is insufficient to forge to the final size in one step. Therefore, in the production method of ultra-large diameter duplex stainless steel radial forged billets of this invention, considering both process temperature drop and forging pressure levels, a three-stage radial forging process is adopted. During radial forging, the heating temperature is controlled at 1250±10℃, the heating time is controlled at 2.0~4.0h, the initial forging temperature is controlled at 1050~1150℃, the forging deformation rate of the first stage radial forging is controlled at 5~8%, the forging deformation rate of the second stage radial forging is controlled at 10~15%, and the forging deformation rate of the third stage radial forging is controlled at 20~30%. The final forging temperature of each stage is controlled at ≥900℃. After each stage of radial forging is completed, the billet is immediately placed in a furnace for heating and holding to ensure the smooth progress of the next forging step.

[0023] Annealing process parameter control: The microstructure of the tube blank obtained after forging is in the rolled state. Annealing is necessary for the microstructure to recover and recrystallize. High annealing temperatures will lead to an imbalance in the duplex phase ratio, while low annealing temperatures may result in harmful precipitates in the core microstructure. Short annealing times result in incomplete core microstructure recovery and recrystallization, while long annealing times lead to a decrease in the performance of the final product. Therefore, in the production method of the ultra-large diameter duplex stainless steel radial forging tube blank of this invention, the annealing temperature is controlled at 1050±20℃, and the annealing time is controlled at 6~12h. Furthermore, due to the large size of the tube blank, if it is not water-cooled in time, the slow temperature drop in the core will easily lead to the formation of harmful precipitates. Therefore, in the production method of the ultra-large diameter duplex stainless steel radial forging tube blank of this invention, the tube blank must be immediately placed in a water tank for water cooling after annealing.

[0024] The following specific embodiments further illustrate the production method of the ultra-large diameter duplex stainless steel radial forging tube blank of the present invention.

[0025] Example 1

[0026] The method for producing ultra-large diameter duplex stainless steel radial forging tube blanks according to Embodiment 1 of the present invention is used to produce ultra-large diameter S32205 series duplex stainless steel radial forging tube blanks with a diameter of φ570mm, and includes the following steps:

[0027] S11. For billet preparation, select an 8.4t square billet as the billet material. The billet heating temperature is controlled at 1250±10℃ and the heating time is controlled at 6.0h. After exiting the furnace, immediately press the square billet into a φ1000mm round billet.

[0028] S12. Radial forging: A φ1000mm round billet is radially forged into a φ570mm tube billet. During the radial forging process, the heating temperature is controlled at 1250±10℃, the heating time is controlled at 4.0h, and the initial forging temperature is controlled at 1150℃. The radial forging adopts a three-stage forging process. The forging deformation rate of the first stage is controlled at 7%, the forging deformation rate of the second stage is controlled at 15%, and the forging deformation rate of the third stage is controlled at 28%. The final forging temperature of each stage is controlled at 900℃. After each stage of radial forging is completed, the billet is immediately placed in the furnace for heating and heat preservation.

[0029] S13. Annealing: The tube blank obtained after forging is directly put into the furnace for annealing. The annealing temperature is controlled at 1050℃ and the annealing time is controlled at 6h. After being taken out of the furnace, it is immediately put into a water tank for water cooling.

[0030] The finished product of the ultra-large diameter S32205 series duplex stainless steel radial forging tube blank with a diameter of φ570mm, produced using Example 1 of the present invention, is shown below. Figure 1 The metallographic structure of the ultra-large diameter S32205 duplex stainless steel radial forging tube blank with a diameter of φ570mm produced using Example 1 of the present invention is shown in [reference]. Figure 2 .

[0031] Example 2

[0032] The method for producing ultra-large diameter duplex stainless steel radial forging tube blanks according to Embodiment 2 of the present invention is used to produce ultra-large diameter S32205 series duplex stainless steel radial forging tube blanks with a diameter of φ555mm, and includes the following steps:

[0033] S21. For billet preparation, select an 8.4t square billet as the billet material. The billet heating temperature is controlled at 1250±10℃ and the heating time is controlled at 8.0h. After exiting the furnace, immediately press the square billet into a φ950mm round billet.

[0034] S22. Radial forging: A φ950mm round billet is radially forged into a φ555mm tube billet. During the radial forging process, the heating temperature is controlled at 1250±10℃, the heating time is controlled at 3.5h, and the initial forging temperature is controlled at 1130℃. The radial forging adopts a three-stage forging process. The forging deformation rate of the first stage is controlled at 8%, the forging deformation rate of the second stage is controlled at 13%, and the forging deformation rate of the third stage is controlled at 27%. The final forging temperature of each stage is controlled at 900℃. After each stage of radial forging is completed, the tube is immediately placed in the furnace for heating and heat preservation.

[0035] S23. Annealing: The tube blank obtained after forging is directly put into the furnace for annealing. The annealing temperature is controlled at 1040℃ and the annealing time is controlled at 6h. After being taken out of the furnace, it is immediately put into a water tank for water cooling.

[0036] In summary, the production method of ultra-large diameter duplex stainless steel radial forging billets of the present invention, by controlling the billet heating temperature to 1250±10℃ and the billet soaking time to 2.0~8.0h, the radial forging heating temperature to 1250±10℃ and the radial forging heating time to 2.0~4.0h, the forging deformation rate of the three-stage radial forging to 5~8%, 10~15%, and 20~30% respectively, and the annealing temperature to 1050±20℃ and the annealing time to 6~12h, has for the first time in China successfully produced and delivered qualified S32205 series duplex stainless steel ultra-large diameter radial forging billets with a diameter of φ500~600mm. The specifications, surface, and various properties of the finished duplex stainless steel ultra-large diameter radial forging billets all meet the high requirements of marine mining platforms for materials, providing a solution for the preparation and production of ultra-large diameter duplex stainless steel radial forging billets.

[0037] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for producing ultra-large diameter duplex stainless steel radial forging tube blanks, characterized in that, Includes the following steps: S1. Billet making: Select 8.4t square billet as billet material. Control the heating temperature of the square billet to 1250±10℃ and control the heating time to 2.0~8.0h. After taking it out of the furnace, roll the square billet into a round billet with a diameter of φ900~1000mm. S2. Radial forging: A round billet with a diameter of 900-1000mm is radially forged into a tube billet with a diameter of 500-600mm. During the radial forging process, the heating temperature is controlled at 1250±10℃, the heating time is controlled at 2.0-4.0h, and the initial forging temperature is controlled at 1050-1150℃. The radial forging adopts a three-stage forging process. The forging deformation rate of the first stage is controlled at 5-8%, the forging deformation rate of the second stage is controlled at 10-15%, and the forging deformation rate of the third stage is controlled at 20-30%. The final forging temperature of each stage is controlled at ≥900℃. After each stage of radial forging is completed, the tube is heated and held in the furnace. S3. Annealing: The tube blank obtained after forging is directly put into the furnace for annealing. The annealing temperature is controlled at 1050±20℃ and the annealing time is controlled at 6~12h. After being taken out of the furnace, it is immediately put into a water tank for water cooling.

2. The method for producing ultra-large diameter duplex stainless steel radial forging tube blanks according to claim 1, characterized in that, The duplex stainless steel is S32205 series duplex stainless steel, and its chemical composition by weight percentage is: C≤0.030%, Si≤1.00%, Mn≤2.00%, P≤0.035%, S≤0.020%, Cr 21.0~23.0%, Ni 4.5~6.5%, Mo 2.5~3.5%, N0.08%~0.22%, with the remainder being Fe and unavoidable impurities.

Images