Method for short process preparation of high strength titanium alloy seamless pipe

Abstract

The application belongs to the technical field of titanium alloy preparation, and discloses a short-process method for preparing high-strength titanium alloy seamless pipes, the room-temperature tensile strength of the high-strength titanium alloy seamless pipe is greater than 1000 MPa, and the method comprises the following steps: forging a titanium alloy casting blank into a rod; performing heat treatment on the rod, which comprises the following steps: performing annealing treatment on the rod under the condition of applying a first pressure, wherein the first pressure is 6-10 Gpa, and the annealing temperature is 130-200 DEG C lower than the beta phase transition temperature of the titanium alloy; and performing a through hole on the heat-treated rod to obtain a high-strength titanium alloy seamless pipe. According to the application, multi-pass rolling, annealing treatment during rolling and surface treatment are not needed to obtain high-strength titanium alloy pipes, so that the process flow can be shortened and the yield can be improved.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy preparation technology, and specifically to a short-process method for preparing high-strength seamless titanium alloy tubes. Background Technology

[0002] Titanium alloys possess high strength and excellent machinability, making them widely used in aerospace, medical, and chemical industries. However, with the continuous development of these fields, increasingly stringent requirements are being placed on the performance of titanium alloy tubes. Typically, seamless titanium alloy tubes are manufactured by preparing tube blanks from forged bars through methods such as skew rolling and hot extrusion, followed by hot rolling, cold rolling, and machining processes to create seamless tubes. Each rolling pass requires annealing and surface grinding, resulting in a long process flow, significant processing losses, and low yield.

[0003] For example, patent CN101825200A discloses a method for preparing TC4 hot-rolled titanium alloy tubes, which can achieve a tensile strength of 895-1300 MPa. In this patent, the tube blank is heated online and rolled in 1-10 passes. During the rolling of the titanium alloy tube, a colloidal lubricant is added to the inner and outer surfaces of the tube blank or semi-finished tube before rolling. After each rolling pass, oxidation annealing or vacuum annealing must be performed. Before the last one or two rolling passes, alkaline washing and pickling or pickling followed by water washing are required to remove all oxide scale and defects before rolling. This method requires multiple rolling passes, annealing after each rolling pass, and removal of oxide scale before the last one or two rolling passes, making the process relatively complex.

[0004] For example, patent CN116921491A discloses a method for preparing high-strength titanium alloy tubing. In this patent, the tubular billet undergoes multiple intermediate rolling passes (2-6 passes), followed by annealing after each intermediate rolling pass to obtain intermediate tubing. The intermediate tubing is then subjected to multiple finished product rolling passes (2-4 passes) to obtain the finished tubing. This method also requires multiple rolling passes, followed by annealing after each pass, making the process lengthy.

[0005] Therefore, existing technologies still need improvement. Summary of the Invention

[0006] The main objective of this invention is to provide a short-process method for preparing high-strength titanium alloy seamless tubes, in order to solve the problems of long process and low yield in existing methods for preparing high-strength titanium alloy tubes.

[0007] According to one aspect of the present invention, a method for short-process preparation of high-strength titanium alloy seamless tubes is provided, wherein the room temperature tensile strength of the high-strength titanium alloy seamless tubes is greater than 1000 MPa, the method comprising:

[0008] Titanium alloy billets are forged into bars;

[0009] The bar is subjected to heat treatment, including: annealing the bar under a first pressure, wherein the first pressure is 6 to 10 GPa and the annealing temperature is 130 to 200°C below the β phase transformation temperature of the titanium alloy.

[0010] By drilling through holes in heat-treated bars, high-strength seamless titanium alloy tubes are obtained.

[0011] According to one embodiment of the present invention, the method does not require rolling.

[0012] According to one embodiment of the present invention, the heat treatment further includes: holding the annealed bar under pressure and rapidly cooling it to room temperature at a cooling rate of 120-150°C / min.

[0013] According to one embodiment of the present invention, the heat treatment further includes: aging the rapidly cooled bar under a second pressure, wherein the second pressure is 5 to 8 GPa and the aging temperature is 400 to 500°C.

[0014] According to one embodiment of the present invention, the heat treatment further includes: holding the aged bar under pressure and air cooling it to room temperature.

[0015] According to one embodiment of the present invention, a six-sided press is used to apply a first pressure and a second pressure to the bar.

[0016] According to one embodiment of the present invention, the annealing time is 30 to 50 minutes; and / or the aging time is 4 to 6 hours.

[0017] According to one embodiment of the present invention, the titanium alloy billet is forged in at least four heats; and / or the bar is surface treated before annealing; and / or the tube obtained after through-hole is machined.

[0018] According to one embodiment of the present invention, the titanium alloy is an α+β type dual-phase titanium alloy, including TC4, TC9 or TC11 titanium alloys.

[0019] According to one embodiment of the present invention, the bar is placed in an inert atmosphere during the heat treatment.

[0020] In the technical solution of this invention, by subjecting the bar to high-pressure annealing, the dislocation density inside the alloy can be increased, while the diffusion of alloying elements is suppressed, thereby increasing the nucleation rate and suppressing grain growth, achieving grain refinement, and improving the strength of the bar. It can then be further processed into a seamless tube without the need for multi-pass rolling and annealing and surface treatment during rolling, thereby shortening the process flow and increasing the yield. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A flowchart illustrating a short-process method for preparing high-strength titanium alloy seamless tubes according to an embodiment of the present invention is shown. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0024] It should be noted that all uses of "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two entities or parameters with the same name but different names. It is clear that "first" and "second" are only for the convenience of expression and should not be construed as limiting the embodiments of the present invention. Subsequent embodiments will not explain this in detail.

[0025] As mentioned in the background section above, the inventors of this application recognize that traditional production methods for seamless titanium alloy tubes involve skew rolling piercing, extrusion, and rolling processes. For tubes with high service performance requirements, multiple cold rolling or warm rolling passes are often required to improve the overall performance of the product. Therefore, the preparation of seamless titanium alloy tubes generally involves a long production process, numerous annealing steps, and the removal of surface defects or oxide scale in each rolling pass, ultimately resulting in high production costs and low yield. To solve this technical problem, this application proposes one or more embodiments as described below.

[0026] Figure 1 A flowchart illustrating a short-process method for preparing high-strength titanium alloy seamless tubes according to an embodiment of the present invention is shown. In this embodiment, the room temperature tensile strength of the high-strength titanium alloy seamless tube is greater than 1000 MPa. (Reference) Figure 1 In some embodiments, the method includes the following steps:

[0027] Titanium alloy billets are forged into bars;

[0028] The bar stock is subjected to heat treatment, including: annealing the bar stock under a first pressure, wherein the first pressure is 6 to 10 GPa (for example, it can be 6 GPa, 7 GPa, 8 GPa, 9 GPa, 10 GPa, or any other value between any two adjacent values), and the annealing temperature is the β-phase transformation temperature T of the titanium alloy. βThe annealing temperature is 130–200°C. In some embodiments, the annealing time is 30–50 minutes to ensure the annealing effect.

[0029] By drilling through holes in annealed bars, high-strength seamless titanium alloy tubes are obtained.

[0030] The inventors of this application recognized that applying pressure to an alloy during heat treatment generates internal stress, increasing its density. Simultaneously, lattice distortion introduces numerous dislocations, leading to work hardening, increased strength and hardness, and the increased dislocation density provides more sites for phase deformation nuclei, promoting new phase nucleation and refining grain size. Furthermore, high-pressure heat treatment can suppress alloy element diffusion, hinder grain growth, refine grain size, effectively reduce stress concentration, and improve the alloy's mechanical properties. The inventors further realized that high-strength titanium alloy bars can be obtained through high-pressure heat treatment, and then perforated to ultimately obtain high-strength titanium alloy tubes. This replaces the multi-pass rolling process and multiple annealing and surface treatments such as oxide scale or defect removal required in existing technologies for producing high-strength titanium alloy tubes, achieving a short-process production of seamless high-strength titanium alloy tubes.

[0031] Therefore, this application proposes the solution described above. In the technical solution of this invention, by subjecting the bar to high-pressure annealing, the dislocation density inside the alloy can be increased, while the diffusion of alloying elements is suppressed, thereby increasing the nucleation rate and suppressing grain growth, achieving grain refinement, and improving the strength of the bar, which is then further processed into a seamless tube. This can completely replace the original long-process seamless tube manufacturing process, eliminating the need for multiple rolling passes and annealing and surface treatment during rolling, thus shortening the process and increasing the yield. Considering that the pressure used in high-pressure annealing is as high as 6-10 GPa, this invention anneals the bar and then forms it into a tube through a hole to avoid the tube being damaged due to high-pressure annealing.

[0032] refer to Figure 1In some embodiments, the heat treatment further includes: holding the annealed bar under pressure (i.e., maintaining it at a first pressure) and rapidly cooling it to room temperature at a cooling rate of 120–150 °C / min. Rapid cooling helps suppress grain growth during high-temperature cooling, controls grain size, and further refines the grains to improve the strength of the bar. Rapid cooling can be achieved by spraying water mist or compressed gas onto the bar, and the cooling rate can be controlled within a suitable range by adjusting the pressure, flow rate, and / or spray direction, nozzle size, distance between the nozzle and the bar, and number of nozzles. The cooling rate can be, for example, 120 °C / min, 130 °C / min, 140 °C / min, 150 °C / min, or any other value between any two adjacent values.

[0033] refer to Figure 1 In some embodiments, the heat treatment further includes aging the rapidly cooled bar under a second pressure of 5–8 GPa and an aging temperature of 400–500 °C. High-pressure aging ensures the precipitation of a finer, more uniform second-phase structure, resulting in dispersion strengthening and improved alloy strength. The second pressure can be 5 GPa, 6 GPa, 7 GPa, 8 GPa, or any other value between any two adjacent values. The aging temperature can be 400 °C, 410 °C, 420 °C, 430 °C, 440 °C, 450 °C, 460 °C, 470 °C, 480 °C, 490 °C, 500 °C, or any other value between any two adjacent values. In some embodiments, the aging time is 4–6 hours to ensure a good aging effect.

[0034] refer to Figure 1 In some embodiments, the heat treatment further includes: holding the aged bar under pressure (i.e., maintaining it at a second pressure) and air-cooling it to room temperature, after which the pressure can be released.

[0035] In some embodiments, a six-sided press is used to apply a first pressure and a second pressure to the bar stock. The six-sided press is equipped with six independently controllable working pistons, arranged in pairs opposite each other, applying pressure to the sample from the X, Y, and Z directions respectively. By placing the bar stock in the six-sided press and applying uniform pressure from multiple directions, the performance of the bar stock is ensured to be uniformly improved in multiple directions.

[0036] In some embodiments, the titanium alloy billet is forged at least four times to achieve the desired forging effect, and the forging method may be free forging.

[0037] In some embodiments, before annealing, the forged bar stock undergoes surface treatment, including but not limited to: removing oxide scale from the bar stock surface, sanding it smooth, and cleaning it to ensure a clean surface. Surface treatment prevents oxide scale from affecting subsequent heat treatment processes and ensures a clean bar stock surface so that the bar stock can be well-fitted with pressure application equipment (e.g., a six-sided press).

[0038] In some embodiments, the pipe obtained after the through hole is machined, including simple surface machining processes such as grinding and polishing.

[0039] In some embodiments, during heat treatment (including the annealing, rapid cooling, aging and / or air cooling described above), a high-purity inert gas (e.g., argon) can be blown into the equipment to place the bar in an inert atmosphere, preventing oxygen from seeping into the surface of the titanium alloy and causing a decrease in toughness and plasticity.

[0040] In embodiments of the present invention, the titanium alloy may be an α+β type dual-phase titanium alloy, including TC4, TC9 or TC11 titanium alloys.

[0041] The high-strength titanium alloy seamless tubes obtained by the above method have a room temperature yield strength greater than 950 MPa, a room temperature tensile strength greater than 1000 MPa, and a tensile strength greater than 700 MPa at a high temperature of 400℃, exhibiting excellent mechanical properties.

[0042] In summary, this invention employs a multi-stage heat treatment process of "high-pressure annealing + high-pressure aging," combined with rapid cooling, to refine the grain structure of the bar material and obtain a fine, dispersed second-phase structure during the aging process. This comprehensively improves the overall performance of the bar material, allowing for direct machining into seamless tubes. This process completely replaces the original long-process seamless tube manufacturing steps, resulting in high-performance titanium alloy seamless tubes. It reduces machining losses and costs in intermediate processes, and the overall production process is short, highly operable, and yields a high tube production rate.

[0043] This invention can achieve the following effects:

[0044] 1. After forging, the bar is directly subjected to "high-pressure annealing + high-pressure aging" heat treatment. The heat treatment process improves the mechanical properties of the bar, replacing the original long production process of "forging-skew rolling piercing / extrusion-multi-pass rolling". This improves the performance of the tube while shortening the seamless tube preparation process and reducing costs.

[0045] 2. High-pressure annealing heat treatment is performed in the two-phase region of the titanium alloy, instead of the conventional phase transformation temperature (T). β The high-temperature solution heat treatment above, combined with high pressure, further refines the grain size.

[0046] 3. By rapidly cooling the two-phase region, the refined microstructure of the titanium alloy after high-pressure annealing is preserved, thus inhibiting grain growth.

[0047] 4. High-pressure aging: Through pressure, fine and dispersed α-phase structures are precipitated during the aging process, further enhancing the strength of titanium alloys and replacing the performance enhancement introduced by cold / hot deformation of bars and tubes.

[0048] The following description is based on specific embodiments and comparative examples.

[0049] Example 1

[0050] Titanium alloy tubing is prepared using the following steps:

[0051] (1) After the TC4 titanium alloy ingot is opened, it is forged into a bar by four upsetting and drawing processes in the two-phase region.

[0052] (2) Remove the oxide scale from the surface of the TC4 titanium alloy bar in step (1), polish it with sandpaper, and clean the surface with ethanol.

[0053] (3) Place the TC4 bar from step (2) in a six-sided press, apply a pressure of 6 GPa, blow in high-purity argon, and gradually heat it to the annealing temperature of 850℃ for 30 minutes.

[0054] (4) High pressure rapid cooling treatment: The TC4 bar after high pressure annealing is held under pressure and rapidly cooled to room temperature. The bar cooling rate is 120℃ / min.

[0055] (5) Ultra-high pressure aging treatment and air cooling treatment: Place the bar in a six-sided top press, apply a pressure of 5GPa, blow in high-purity argon, heat up to 500℃, and keep it at that temperature for 4 hours; then keep it under pressure and air cool to room temperature, and then unload the pressure.

[0056] (6) The bar stock is drilled through and machined to form titanium alloy pipes, which are then stored in the warehouse.

[0057] Example 2

[0058] Titanium alloy tubing is prepared using the following steps:

[0059] (1) After the TC4 titanium alloy ingot is opened, it is forged into a bar by four upsetting and drawing processes in the two-phase region.

[0060] (2) Remove the oxide scale from the surface of the TC4 titanium alloy bar in step (1), polish it with sandpaper, and clean the surface with ethanol.

[0061] (3) Place the TC4 bar from step (2) in a six-sided press, apply a pressure of 10 GPa, blow in high-purity argon, and gradually heat it to the annealing temperature of 800℃ for 50 min.

[0062] (4) High pressure rapid cooling treatment: The TC4 bar after high pressure annealing is held under pressure and rapidly cooled to room temperature. The bar cooling rate is 150℃ / min.

[0063] (5) Ultra-high pressure aging treatment and air cooling treatment: Place the bar in a six-sided top press, apply 8GPa pressure, blow in high-purity argon, heat up to 400℃, and keep it at that temperature for 6 hours; then keep it under pressure and air cool to room temperature, and then unload the pressure.

[0064] (6) The bar stock is drilled through and machined to form titanium alloy pipes, which are then stored in the warehouse.

[0065] Comparative Example 1

[0066] Titanium alloy tubing is prepared using the following steps:

[0067] (1) After the TC4 titanium alloy ingot is opened, it is forged into a bar by four upsetting and drawing processes in the two-phase region.

[0068] (2) The TC4 titanium alloy bar in step (1) is prepared into the required tube blank by oblique rolling and piercing.

[0069] (3) Heat the TC4 tube blank from step (2) to 950°C and perform hot rolling.

[0070] (4) Perform multiple cold rolling passes on the TC4 tube blank from step (2).

[0071] (5) Straighten, machine, and pickle the pipes to form titanium alloy pipes and put them into storage.

[0072] The room temperature and high temperature properties of the titanium alloy tubing obtained in Examples 1-2 and Comparative Document 1 were tested, and the results are shown in Table 1.

[0073] Table 1 Tensile properties of TC4 titanium alloy tubing in Examples 1-2 and Comparative Example 1

[0074]

[0075] As shown in Table 1, the yield strength R of the titanium alloy tubing obtained in Examples 1-2 is... p0.2 The tensile strength is 955–972 MPa, and the tensile strength R is... m The tensile strength R is 1013–1038 MPa, the elongation after fracture A is 13%–15%, and the tensile strength R at 400℃ is [missing information]. m The yield strength is 708–714 MPa. In comparison, the yield strength R of the titanium alloy tubing obtained in Comparative Example 1 is... p0.2 The tensile strength is 843 MPa, and the tensile strength R is... m The tensile strength R at 400℃ is 944 MPa, the elongation after fracture A is 12%, and the tensile strength R is 12%. mThe strength is 655 MPa. The mechanical properties of the titanium alloy tubing achievable in Examples 1-2 are superior to those in Comparative Example 1. Furthermore, Examples 1-2 do not require multi-pass rolling or annealing and surface treatment during rolling, thus shortening the process.

[0076] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of the different aspects of the invention as described above exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for preparing high-strength seamless titanium alloy tubes using a short-process method, characterized in that, The high-strength titanium alloy seamless tube has a room temperature tensile strength greater than 1000 MPa, and the method includes: Titanium alloy billets are forged into bars; The heat treatment of the bar includes: annealing the bar under a first pressure, wherein the first pressure is 6 to 10 GPa and the annealing temperature is 130 to 200°C below the β phase transformation temperature of the titanium alloy. The heat-treated bar is perforated to obtain the high-strength titanium alloy seamless tube.

2. The method according to claim 1, characterized in that, The method does not require rolling.

3. The method according to claim 1, characterized in that, The heat treatment further includes: holding the annealed bar under pressure and rapidly cooling it to room temperature at a cooling rate of 120-150°C / min.

4. The method according to claim 3, characterized in that, The heat treatment further includes aging the rapidly cooled bar under a second pressure, wherein the second pressure is 5-8 GPa and the aging temperature is 400-500°C.

5. The method according to claim 4, characterized in that, The heat treatment also includes: holding the aged bar under pressure and air-cooling it to room temperature.

6. The method according to claim 4, characterized in that, The first pressure and the second pressure are applied to the bar using a six-sided top press.

7. The method according to claim 4, characterized in that, Annealing time is 30–50 min; and / or aging time is 4–6 h.

8. The method according to claim 1, characterized in that, The titanium alloy billet is forged in at least four heat treatments; and / or the bar is surface treated before the annealing process is performed; and / or the tube obtained after the through hole is machined.

9. The method according to claim 1, characterized in that, The titanium alloy is an α+β type dual-phase titanium alloy, including TC4, TC9 or TC11 titanium alloys.

10. The method according to claim 1, characterized in that, During the heat treatment, the bar is placed in an inert atmosphere.

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