High-strength titanium alloy cold-rolled seamless pipe and method for manufacturing the same

Abstract

The application discloses a high-strength titanium alloy cold-rolled seamless pipe and a preparation method thereof, and belongs to the technical field of titanium alloy seamless pipe processing. The high-strength titanium alloy cold-rolled seamless pipe comprises the following components: Al 4.0-5.0%, V 3.5-4.5%, Mo 1.5-2.5%, the first pass cold rolling deformation amount is controlled to be 30-45%, the second pass rolling deformation amount is 40-50%, the rolling deformation amount of the remaining passes is 30-45%, and after the first pass cold rolling, the pipe is heated to 980-1000 DEG C at a heating rate of 10-20 DEG C / min, water cooling is carried out after discharging, then the pipe is heated to 910-920 DEG C at a heating rate of 5-10 DEG C / min, and intermediate heat treatment is carried out. Through optimization of the chemical components, intermediate heat treatment and cold rolling process, the surface crack problem easily formed in the cold rolling process is solved, the qualified rate of finished products is improved, and batch production of the TC4 titanium alloy cold-rolled seamless pipe is realized.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy seamless tube processing technology, specifically relating to a high-strength titanium alloy cold-rolled seamless tube and its preparation method. Background Technology

[0002] TC4 (Ti-6Al-4V) is a typical (α+β) dual-phase titanium alloy. Its strength is close to that of high-strength steel, but its density (about 4.5 g / cm³) is only about 57% of that of steel. It is very suitable for lightweight design. It has good corrosion resistance in oxidizing media and neutral and weak chloride media, and can resist stress corrosion. It also has good fatigue performance and crack propagation resistance.

[0003] The article "Research on the Preparation Process and Texture Evolution Law of Cold-Rolled Seamless TC4 Titanium Alloy Tubes" reported by Yan Mengqi et al. disclosed that Φ88mm×9mm TC4 rough tubes were prepared by skew rolling piercing method. The chemical composition was: Al (6.29%), V (4.11%), Fe (0.03%), C (0.002%), O (0.16%), N (0.003%), H (0.003%), Ti (balance). After four passes, the tubes were rolled to Φ41mm×2.5mm. The intermediate and finished heat treatments were carried out in a vacuum heat treatment furnace. The heating process was: 750~850℃ and holding for 1 hour. The deformation of each cold rolling pass was 40.9%, 35.6%, 37.1%, and 29.5%, respectively, and the Q values ​​were 2.44, 0.86, 1.5, and 0.77, respectively. This method mainly controls the Fe and O content in the chemical composition of TC4 titanium alloy, and specifies the cold rolling process and intermediate annealing process. The focus is on studying the influence of Q value design on texture. This invention aims to improve the cold rolling plasticity of TC4 titanium alloy seamless tubes. The composition has been adjusted, and a water cooling + annealing heat treatment process for the tube blank has been added. At the same time, the deformation process has been redesigned.

[0004] CN108098269A discloses a method for processing and preparing high-strength, high-precision Ti6Al4V titanium alloy tubes. This method emphasizes the control range of Fe (0.15%–0.25%) and O (0.15%–0.18%) elements, and involves solution heating and aging treatment of the skew-rolled tube: solution heating temperature 800–950℃, holding time 60–120 min, water cooling after removal from the furnace; aging heating temperature 500–600℃, holding time 240–360 min, air cooling after removal from the furnace; and then machining to obtain the finished tube. This invention adjusts the chemical composition and redesigns the heat treatment process for pierced rough tubes, resulting in significantly different composition and heat treatment processes compared to this method. Furthermore, this invention ultimately uses cold-rolled tubes as the finished product.

[0005] CN114433654A discloses a short-process, low-cost method for preparing TC4 seamless pipes. The chemical composition is 6.0%≤Al≤6.75%, 4.0%≤V≤4.5%, C≤0.08%, N≤0.05%, H≤0.015%, 0.13%≤O≤0.20%, 0.15%≤Fe≤0.30%, with the balance being Ti. The method involves two vacuum arc melting processes to prepare φ400~φ700mm ingots, which are then forged into φ70~φ120mm billets. These billets are then rolled into φ70~φ120×(10~30)mm rough pipes by two-roll skew rolling and hot-rolled into φ30(±0.3)~φ80(±0.3)×(5-15)(±0.3)mm finished pipes. This invention adjusts the chemical composition and redesigns the cold rolling and heat treatment process for pierced rough tubes, making the composition and cold rolling and heat treatment process significantly different from the present invention.

[0006] CN114700387A discloses a method for preparing high-strength titanium alloy cold-rolled tubes. The method involves precision forging or extruding a titanium alloy ingot in the β-phase region, wherein the room temperature tensile strength of the titanium alloy constituting the ingot is ≥700 MPa, resulting in a billet. The billet is then skew-rolled and pierced in the β-phase region and water-cooled online to obtain tube blank 1. Tube blank 1 is then extruded or hot-rolled in the two-phase region to obtain tube blank 2. Tube blank 2 is then cold-rolled, surface-treated, and heat-treated to obtain the high-strength titanium alloy tube. While this invention also involves quenching of the tube blank and secondary heat treatment after quenching, based on the composition adjustments in this invention, the quenching timing, quenching temperature, and secondary heat treatment temperature and time are specifically optimized.

[0007] Because TC4 alloy has high deformation resistance and a significant tendency for work hardening, direct cold rolling easily leads to cracking and uneven deformation. A combination of multi-pass cold rolling and intermediate vacuum annealing is typically required to improve its plasticity, but the effect is not significant. Therefore, mass production of TC4 titanium alloy cold-rolled seamless tubes has not yet been achieved in the industry. Summary of the Invention

[0008] The purpose of this invention is to provide a high-strength titanium alloy cold-rolled seamless tube and its preparation method. Based on the chemical composition of TC4 titanium alloy, this invention designs a new composition system and intermediate heat treatment process, which can prepare titanium alloy cold-rolled seamless tubes with an outer diameter of Φ40~Φ50mm, a wall thickness of 2~3mm, and a length of ≥3m. It can solve the problem of surface cracks that are easily formed during cold rolling, and significantly improve the surface crack problem.

[0009] To achieve the above objectives, the present invention first provides a method for preparing high-strength titanium alloy cold-rolled seamless tubes, which includes the following steps: A. The chemical composition of the titanium alloy cold-rolled seamless tube, in mass percentage, is: Al 4.0%~5.0%, V 3.5%~4.5%, Mo 1.5%~2.5%, Fe≤0.05%, O≤0.05%, C≤0.02%, N≤0.01%, H≤0.0008%, with the remainder being Ti and unavoidable impurities; B. After the components in step A are batched and the electrodes are pressed, they are smelted to obtain Φ400mm~Φ600mm billets, then forged into 150~170mm×150~170mm square billets, and then hot-rolled into Φ87~Φ90mm round bars. C. After peeling the round bar from step B into a clean bar, cut it into 1000mm~1500mm long bar blanks; D. After the surface defects of the long bar billet in step C are repaired by grinding, it is kept at 860~880℃ and then rolled and pierced by skew rolling after being taken out of the furnace. E. Obtain the rough tube dimensions by skew rolling and piercing: outer diameter Φ88~Φ90mm, wall thickness 8~10mm, and air cool to room temperature after hot rolling and straightening. F. After the skew-rolled rough tube is flattened, the first cold rolling is carried out, with the deformation controlled at 30%~45% and the cold rolling Q value controlled at 1~2. G. After the first cold rolling, an intermediate heat treatment is performed. The temperature is raised to 980-1000℃ at a heating rate of 10-20℃ / min and held. The temperature is then removed from the furnace and water-cooled. The temperature is then raised to 910-920℃ at a heating rate of 5-10℃ / min and held. The temperature is then removed from the furnace and air-cooled. H. After intermediate heat treatment, the intermediate tube blank is surface treated and then rolled in the second pass. The deformation in the second pass is controlled at 40%~50% and the Q value is controlled at 0.5~2.5. Annealing is performed after the second pass rolling. I. After the intermediate tube blank is annealed by the second rolling pass, it is surface treated and then rolled for the third rolling pass. The deformation amount of the third rolling pass is controlled at 30%~45% and the Q value is controlled at 2~5.5. Annealing is performed after the third rolling pass. J. After the intermediate tube blank is annealed by the third rolling pass, it is surface treated and then rolled into a fourth rolling pass. The deformation amount of the fourth rolling pass is controlled at 30%~45% and the Q value is controlled at 2~5.5. Annealing is performed after the fourth rolling pass. K. After pickling, the finished product of cold-rolled seamless titanium alloy tube is obtained.

[0010] In the above preparation method, step B involves smelting in a VAR furnace 2 to 4 times.

[0011] In the above preparation method, step B involves forging in 5 to 7 passes.

[0012] In the above preparation method, in step C, the optical rod has a specification of Φ85~Φ87mm.

[0013] In the above preparation method, in step D, the heat preservation time is 40~60 min.

[0014] In the preparation method described above, step D involves first heating in an induction furnace at a temperature of 830-850°C, and then transferring the material to a box-type resistance furnace at a temperature of 860-880°C for heat preservation.

[0015] In the above preparation method, in step F, the first cold rolling pass uses a two-roll mill.

[0016] In the above preparation method, in step G, the holding time at 980~1000℃ is 30~40min.

[0017] In the above preparation method, in step G, the holding time at 910~920℃ is 40~60min.

[0018] In the above preparation method, step H, the surface treatment is an external scraping and internal boring surface treatment.

[0019] In the above preparation method, in step H, the material feeding length is 2~2.5m.

[0020] In the above preparation method, in step H, the second rolling pass uses a two-roll mill.

[0021] In the above preparation method, in step H, the annealing temperature is 800~850℃.

[0022] In the above preparation method, in step H, the annealing and holding time is 1.5~2h.

[0023] In the above preparation method, step I, the surface treatment is an external scraping and internal boring surface treatment.

[0024] In the above preparation method, in step I, the material feeding length is 2~2.5m.

[0025] In the above preparation method, in step I, the third rolling pass is performed using a two-roll mill.

[0026] In the above preparation method, in step I, the annealing temperature is 800~850℃.

[0027] In the above preparation method, in step I, the annealing and holding time is 1.5~2h.

[0028] In the above preparation method, step J, the surface treatment is an external scraping and internal boring surface treatment.

[0029] In the above preparation method, in step J, the material feeding length is 2~2.5m.

[0030] In the above preparation method, in step J, the fourth rolling pass is performed using a three-roll mill.

[0031] In the above preparation method, in step J, the annealing temperature is ≥600℃.

[0032] In the above preparation method, in step J, the annealing and holding time is 1~2h.

[0033] The present invention also provides a high-strength titanium alloy cold-rolled seamless tube, which is prepared by the above-mentioned preparation method and has an outer diameter of Φ40~Φ50mm, a wall thickness of 2~3mm, and a length of ≥3m.

[0034] The beneficial effects of this invention are: This invention optimizes the chemical composition of traditional TC4 by reducing Al content, adding Mo, and reducing impurity element content, thereby increasing the β phase content of the body-centered cubic structure and rationally distributing the β and α phase ratios to enhance cold deformation plasticity. Combined with a new intermediate heat treatment and cold rolling process, equiaxed grains are generated, solving the surface cracking problem of high-strength titanium alloy seamless tubes. This invention has a significant role in addressing industry technical challenges such as easy cracking and rolling difficulties in difficult-to-deform titanium alloy seamless tubes, improving the finished product qualification rate. Furthermore, the technology can be industrially applied, demonstrating good economic benefits and promotional value. Attached Figure Description

[0035] Figure 1 This is a microstructure diagram of the finished tube from Embodiment 1 of the present invention.

[0036] Figure 2 This is a microstructure diagram of the finished tube from Embodiment 2 of the present invention. Detailed Implementation

[0037] Specifically, a method for preparing a high-strength titanium alloy cold-rolled seamless tube includes the following steps: (1) The chemical composition of the titanium alloy cold-rolled seamless tube, in terms of mass percentage, is: Al 4.0%~5.0%, V 3.5%~4.5%, Mo 1.5%~2.5%, Fe≤0.05%, O≤0.05%, C≤0.02%, N≤0.01%, H≤0.0008%, with the remainder being Ti and unavoidable impurities; This invention optimizes the chemical composition of traditional TC4 titanium alloy. By reducing the Al content, the close-packed hexagonal α phase in the alloy is reduced, increasing cold deformation plasticity. Adding Mo increases the content of the body-centered cubic β phase, which, due to its superior plasticity compared to the α phase, also contributes to improved cold deformation plasticity. However, the β phase content cannot be arbitrarily increased; the ratio of β to α phases (total content 100%) must be controlled within a reasonable range. Experiments have shown that this invention, by reducing the Al content (strictly controlling Al to 4.0%~5.0%) and adding an additional 1.5%~2.5% Mo to traditional TC4, appropriately increases the β phase content. This allows for the successful fabrication of high-strength titanium alloy cold-rolled seamless tubes through subsequent special heat treatment and a specific cold rolling process.

[0038] Meanwhile, in titanium alloy cold-rolled seamless tubes, Fe, O, C, N, and H can be considered impurity elements. Since the present invention requires subsequent cold rolling processes, it is necessary to strictly control the content of impurity elements. Therefore, the present invention further reduces these impurity elements, improves plasticity to a certain extent, and is more conducive to cold rolling.

[0039] (2) After the above ingredients are batched and the electrodes are pressed, the billet is smelted in 2 to 4 VAR furnaces (the theoretical weight of a single VAR ingot is 3 tons) to obtain a Φ400mm~Φ600mm billet. Then it is forged into a 150~170mm×150~170mm square billet after 5 to 7 heats, and then hot rolled into a Φ87~Φ90mm round bar. In this invention, the ingredient preparation, electrode pressing, and smelting processes are conventional methods in the field, and can be implemented by those skilled in the art using existing technologies. Therefore, they will not be described in detail here.

[0040] (3) After the above-mentioned round bars are peeled by a peeling machine into Φ85~Φ87mm smooth bars, they are cut into 1000mm~1500mm long bar blanks; (4) After the surface defects of the above long billet are repaired and ground, it is first heated in an induction furnace at a temperature of 830~850℃, and then transferred to a box-type resistance furnace at 860~880℃. After the last billet enters the furnace, it is kept at the temperature for 40~60 minutes, and then it is taken out of the furnace and rolled and pierced. In step (4), the box-type resistance furnace is used directly for heating and heat preservation, resulting in low heating efficiency. Under the box-type resistance furnace heating system alone, it may take several hours to heat a batch of products, while skew rolling piercing can generally be completed in just a few minutes. This leads to a serious mismatch between the heating system and the rolling system. Therefore, in step (4) of this invention, the product is first heated in an induction furnace at a temperature of 830~850℃, and then transferred to a box-type resistance furnace at 860~880℃. After the last billet is put into the furnace, it is held at a temperature of 40~60 minutes, which significantly improves the heating efficiency.

[0041] (5) The rough tube obtained by skew rolling and piercing is: outer diameter Φ88~Φ90mm, wall thickness 8~10mm, and then air-cooled to room temperature after hot rolling and straightening; (6) After the above-mentioned skew-rolled rough tube is flattened, the first pass of cold rolling is carried out in a two-roll mill, with the deformation controlled at 30%~45% and the cold rolling Q value controlled at 1~2; This invention optimizes the chemical composition of traditional TC4 titanium alloy, thereby significantly improving the material's plasticity and cold deformation capability. Therefore, in the first cold rolling pass, this invention can significantly increase the deformation amount. In existing processes for producing seamless titanium alloy tubes, rolling is generally performed at a relatively low deformation amount (≤25%) to ensure product performance.

[0042] (7) After the first cold rolling, intermediate heat treatment is carried out. The temperature is heated to 980-1000℃ at a heating rate of 10-20℃ / min and held for 30-40min. The furnace is then cooled with water. Then the temperature is heated to 910-920℃ at a heating rate of 5-10℃ / min and held for 40-60min. The furnace is then cooled with air. Ti is a metallic element with a strong tendency to work harden, which results in TC4 alloy having high deformation resistance and a pronounced work hardening tendency. During rolling, the product will form highly directional grains. TC4 is also a high-strength duplex titanium alloy, with a much higher content of alloying elements than pure titanium, leading to even greater deformation resistance, a more pronounced work hardening tendency, and a very strong directional texture, severely affecting subsequent cold rolling plasticity. This invention improves the texture orientation through a "heating-water cooling-reheating" method, forming larger equiaxed grains. Water cooling fixes the grains, followed by reheating to induce an α-phase + β-phase transformation. This microstructure is more favorable for subsequent cold rolling.

[0043] (8) After the intermediate tube blanks undergoing intermediate heat treatment are surface treated by external scraping and internal boring, they are cut into blanks for subsequent rolling passes. The blank length for each subsequent rolling pass is 2~2.5m. (9) In the subsequent cold rolling process, only the last pass of the finished product is rolled using a three-roll mill, and the rest are rolled using a two-roll mill. The deformation amount of the second pass is controlled at 40%~50% and the Q value is controlled at 0.5~2.5. The deformation amount of the remaining passes is controlled at 30%~45% and the Q value is controlled at 2~5.5. Except for the last pass, after each of the remaining passes, the annealing temperature is 800~850℃ and the holding time is 1.5~2h. Similarly, this invention optimizes the chemical composition based on the traditional TC4 titanium alloy, thereby significantly improving the material's plasticity and cold deformation capability. Therefore, in subsequent rolling passes (passes 2 to 4), this invention can also significantly increase the deformation amount, especially in the second pass where the deformation amount can be increased to 40% to 50%.

[0044] (10) After the last rolling, the finished seamless tube is annealed at ≥600℃ and held for 1~2h. After pickling, the finished titanium alloy cold-rolled seamless tube is obtained and subjected to mechanical property testing and surface quality testing.

[0045] In this invention, except for the final seamless tube annealing after rolling which requires vacuum annealing, the other annealing passes do not necessarily require vacuum annealing.

[0046] 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.

[0047] Example 1: This embodiment describes the production of Φ50×2mm cold-rolled seamless tubes using the chemical composition, cold rolling, and heat treatment processes designed in this invention.

[0048] Specifically as follows: (1) The chemical composition (wt%) of the ingot is: Al 4.8%, V 4.4%, Mo 2.5%, Fe 0.05%, O 0.03%, C 0.018%, N 0.01%, H 0.0007%, with the remainder being Ti and unavoidable impurities.

[0049] (2) After the above components are batched and pressed into electrodes, they are smelted in a 3-ton VAR furnace three times to obtain Φ600mm, then forged into 160mm square in 6 heats, and then hot rolled into Φ90mm round bar.

[0050] (3) The above-mentioned round bars are peeled by a peeling machine into Φ87mm smooth bars and then cut into 1500mm long bar blanks.

[0051] (4) After the surface defects of the billet are repaired, it is first heated in an induction furnace at a temperature of 850°C, and then transferred to an 880°C box-type resistance furnace. After the last billet enters the furnace, it is kept at a temperature of 60 minutes and then rolled and pierced.

[0052] (5) The rough tube obtained by skew rolling and piercing of the billet is: outer diameter Φ88.5mm and wall thickness 8.5mm. After hot rolling and straightening, it is air-cooled to room temperature.

[0053] (6) After the above-mentioned skew-rolled rough tube is flattened, the first cold rolling is carried out, and the rolled size is Φ72×6mm (deformation amount 41.7%, Q value 1.6).

[0054] (7) After the first pass of cold rolling in a two-roll mill, the rough tube is subjected to intermediate heat treatment. It is heated to 1000°C at a heating rate of 18°C / min and held for 40 minutes. It is then removed from the furnace and water-cooled. Then it is heated to 920°C at a heating rate of 6°C / min and held for 60 minutes before being removed from the furnace and air-cooled.

[0055] (8) After the above-mentioned intermediate tube blank has undergone surface treatment by external scraping and internal boring, the blank length is 2m.

[0056] (9) The second rolling pass has a rolled size of Φ60×4mm (deformation 43.4%, Q value 2), and the annealing temperature after rolling is 850℃ and the holding time is 2h.

[0057] (10) The intermediate tube blank after annealing is 2m long after surface treatment by external scraping and internal boring.

[0058] (11) The third rolling pass has a rolled size of Φ53×2.8mm (deformation 37.2%, Q value 2.57). The annealing temperature after rolling is 850℃ and the holding time is 2h.

[0059] (12) The intermediate tube blank after annealing is 2m long after surface treatment by external scraping and internal boring.

[0060] (13) The fourth rolling pass was performed using a three-roll mill. The rolled size was Φ50×2mm (deformation 31.7%, Q value 5.04). The annealing temperature after rolling was 650℃ and the holding time was 2h.

[0061] (14) After pickling, the finished titanium alloy cold-rolled seamless tube is obtained. The room temperature mechanical properties and surface quality of the finished product are shown in Table 1, and the microstructure is as follows: Figure 1 As shown.

[0062] Table 1 Mechanical properties and surface quality of finished titanium alloy seamless tubes from Example 1

[0063] Example 2 This embodiment describes the production of a Φ40×3mm cold-rolled seamless tube using the chemical composition, cold rolling, and heat treatment processes designed in this invention.

[0064] Specifically as follows: (1) The chemical composition (wt%) of the ingot is: Al 4.2%, V 3.8%, Mo 1.7%, Fe 0.05%, O 0.05%, C 0.016%, N 0.008%, H 0.0007%, with the remainder being Ti and unavoidable impurities.

[0065] (2) After the above components are batched and pressed into electrodes, they are smelted in a 3-ton VAR furnace three times to obtain Φ580mm, then forged into 160mm square in 6 heats, and then hot rolled into Φ87mm round bar.

[0066] (3) The above-mentioned round bars are peeled by a peeling machine into Φ85mm smooth bars and then cut into 1500mm long bar blanks.

[0067] (4) After the surface defects of the billet are repaired, it is first heated in an induction furnace at a temperature of 830°C, and then transferred to an 860°C box-type resistance furnace. After the last billet enters the furnace, it is kept at a temperature of 45 minutes and then rolled and pierced.

[0068] (5) The rough tube obtained by slant rolling and piercing of the billet is: outer diameter Φ88mm, wall thickness 10mm, and then air-cooled to room temperature after hot rolling and straightening.

[0069] (6) After the above-mentioned skew-rolled rough tube is flattened, the first cold rolling is carried out, and the rolled size is Φ75×8mm (deformation amount 31.3%, Q value 1.35).

[0070] (7) After the first cold rolling of the rough tube by the two-roll mill, it is subjected to intermediate heat treatment. It is heated to 980°C at a heating rate of 15°C / min and held for 30 minutes. It is then removed from the furnace and water-cooled. Then it is heated to 910°C at a heating rate of 8°C / min and held for 40 minutes before being removed from the furnace and air-cooled.

[0071] (8) After the above-mentioned intermediate tube blank has undergone surface treatment by external scraping and internal boring, the blank length is 2.5m.

[0072] (9) The second rolling pass has a rolled size of Φ52×6mm (deformation 48.5%, Q value 0.8), and the annealing temperature after rolling is 810℃ and the holding time is 1.5h.

[0073] (10) After the above-mentioned intermediate tube blanks are annealed and then subjected to surface treatment by external scraping and internal boring, the blank length is 2.5m.

[0074] (11) The third rolling pass has a rolled size of Φ45×4mm (deformation 40.5%, Q value 2.48), and the annealing temperature after rolling is 810℃ and the holding time is 1.5h.

[0075] (12) The intermediate tube blank after annealing is 2.5m long after surface treatment by external scraping and internal boring.

[0076] (13) The fourth rolling pass was performed using a three-roll mill. The rolled size was Φ40×3mm (deformation 32.3%, Q value 2.25). The annealing temperature after rolling was 610℃ and the holding time was 1.7h.

[0077] (14) After pickling, the finished titanium alloy cold-rolled seamless tube is obtained. The room temperature mechanical properties and surface quality of the finished product are shown in Table 2, and the microstructure is as follows: Figure 2 As shown.

[0078] Table 2 Mechanical properties and surface quality of finished titanium alloy seamless tubes from Example 2

Claims

1. A method for preparing high-strength titanium alloy cold-rolled seamless tubes, characterized in that: Includes the following steps: A. The chemical composition of the titanium alloy cold-rolled seamless tube, in mass percentage, is as follows: Al 4.0%~5.0%, V 3.5%~4.5%, Mo 1.5%~2.5%, Fe≤0.05%, O≤0.05%, C≤0.02%, N≤0.01%, H≤0.0008%, with the remainder being Ti and unavoidable impurities; B. After the components in step A are batched and the electrodes are pressed, they are smelted to obtain Φ400mm~Φ600mm billets, then forged into 150~170mm×150~170mm square billets, and then hot-rolled into Φ87~Φ90mm round bars. C. After peeling the round bar from step B into a clean bar, cut it into 1000mm~1500mm long bar blanks; D. After the surface defects of the long bar billet in step C are repaired by grinding, it is first heated in an induction furnace at a temperature of 830~850℃, then transferred to a box-type resistance furnace at 860~880℃ for heat preservation, and then rolled and pierced after exiting the furnace. E. Obtain the rough tube dimensions by skew rolling and piercing: outer diameter Φ88~Φ90mm, wall thickness 8~10mm, and air cool to room temperature after hot rolling and straightening. F. After the skew-rolled rough tube is flattened, the first cold rolling is carried out, with the deformation controlled at 30%~45% and the cold rolling Q value controlled at 1~2. G. After the first cold rolling, an intermediate heat treatment is performed. The temperature is raised to 980-1000℃ at a heating rate of 10-20℃ / min and held. The temperature is then removed from the furnace and water-cooled. The temperature is then raised to 910-920℃ at a heating rate of 5-10℃ / min and held. The temperature is then removed from the furnace and air-cooled. H. After intermediate heat treatment, the intermediate tube blank is surface treated and then rolled in the second pass. The deformation in the second pass is controlled at 40%~50% and the Q value is controlled at 0.5~2.

5. After the second pass rolling, it is annealed at 800~850℃. I. After the intermediate tube blank is annealed by the second rolling pass, it is surface treated and then rolled for the third time. The deformation in the third pass is controlled at 30%~45% and the Q value is controlled at 2~5.

5. After the third rolling pass, it is annealed at 800~850℃. J. After the intermediate tube blank is annealed by the third rolling pass, it is surface treated and then rolled into a fourth rolling pass. The deformation amount of the fourth rolling pass is controlled at 30%~45% and the Q value is controlled at 2~5.

5. After the fourth rolling pass, it is annealed at ≥600℃. K. After pickling, the finished product of cold-rolled seamless titanium alloy tube is obtained.

2. The method for preparing high-strength titanium alloy cold-rolled seamless tube according to claim 1, characterized in that: At least one of the following must be met: In step B, the smelting process involves 2 to 4 VAR furnace smelting processes. In step B, the forging process involves 5 to 7 heats.

3. The method for preparing high-strength titanium alloy cold-rolled seamless tube according to claim 1, characterized in that: In step C, the specifications of the light rod are Φ85~Φ87mm.

4. The method for preparing high-strength titanium alloy cold-rolled seamless tube according to claim 1, characterized in that: In step D, the heat preservation time is 40~60 minutes.

5. The method for preparing high-strength titanium alloy cold-rolled seamless tube according to claim 1, characterized in that: In step F, the first cold rolling pass uses a two-roll mill.

6. The method for preparing high-strength titanium alloy cold-rolled seamless tube according to claim 1, characterized in that: At least one of the following must be met: In step G, the holding time at 980~1000℃ is 30~40 minutes; In step G, the holding time at 910~920℃ is 40~60 minutes.

7. The method for preparing high-strength titanium alloy cold-rolled seamless tube according to claim 1, characterized in that: At least one of the following must be met: In step H, the surface treatment is an external scraping and internal boring surface treatment; In step H, the material cutting length is 2~2.5m; In step H, the second rolling pass uses a two-roll mill; In step H, the annealing holding time is 1.5~2 hours.

8. The method for preparing high-strength titanium alloy cold-rolled seamless tube according to claim 1, characterized in that: At least one of the following must be met: In step I, the surface treatment is an external scraping and internal boring surface treatment; In step I, the cutting length is 2~2.5m; In step I, the third rolling pass uses a two-roll mill; In step I, the annealing and holding time is 1.5~2 hours.

9. The method for preparing high-strength titanium alloy cold-rolled seamless tube according to claim 1, characterized in that: At least one of the following must be met: In step J, the surface treatment is an external scraping and internal boring surface treatment; In step J, the material cutting length is 2~2.5m; In step J, the fourth rolling pass uses a three-roll mill; In step J, the annealing holding time is 1~2 hours.

10. A high-strength titanium alloy cold-rolled seamless tube prepared by the preparation method according to any one of claims 1 to 9, having an outer diameter of Φ40~Φ50mm and a wall thickness of 2~3mm.

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