Metastable beta titanium alloy thin strip and preparation method thereof

Abstract

The present invention discloses a metastable β-titanium alloy thin strip and a preparation method thereof. The method comprises: 1. subjecting a β-titanium alloy ingot to four-pass forging to obtain a forged slab; 2. subjecting the forged slab to three-pass hot rolling to obtain a hot-rolled plate; 3. annealing the hot-rolled plate; 4. subjecting the annealed hot-rolled plate to multiple-pass strip tension cold rolling to obtain a cold-rolled strip; and 5. solution annealing the cold-rolled strip to obtain the metastable β-titanium alloy thin strip. By adjusting the forging process, temperature, and deformation, optimizing the hot-rolling temperature, cold-rolling deformation, and solution treatment regime, the present invention effectively suppresses the precipitation of the ω brittle phase, improves cold forming and cold working capabilities, and produces a metastable β-titanium alloy thin strip with uniform thickness, good surface quality, stable performance, and excellent plasticity, meeting the application needs of various fields.

Description

Technical Field

[0001] The invention belongs to the technical field of nonferrous metal material processing, and particularly relates to a metastable beta titanium alloy thin strip and a preparation method thereof. Background Art

[0002] β-titanium alloy has the characteristics of high specific strength, excellent forming properties and corrosion resistance, and has good development prospects. TB5 (Ti-15V-3Cr-3Sn-3Al) is a metastable β-type titanium alloy with broad application prospects in the aerospace industry. The main advantages of this alloy are excellent casting performance and cold formability, high specific strength, and disadvantages are low elastic modulus, large rebound during cold deformation, and strong anisotropy. In the actual production process of TB5 alloy plates, due to improper hot working and heat treatment processes, the room temperature processing plasticity of the alloy deteriorates, making cold working difficult and product performance difficult to meet the requirements. In the plate rolling link, in order to ensure the consistency of the cold forming performance of the plate, the plate needs to have stable mechanical properties, good plate shape and plate difference. Especially when preparing thin plates or strips, how to control the cold rolling process and heat treatment process urgently needs in-depth research. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to address the shortcomings of the above-mentioned prior art and provide a method for preparing metastable β-titanium alloy thin strip. This method sequentially subjects a β-titanium alloy ingot to four-pass forging, three-pass hot rolling, and multiple-pass cold rolling with tension, followed by solution treatment. By adjusting the forging process, temperature, and deformation, and optimizing the hot rolling temperature, cold rolling deformation, and solution treatment regime, the precipitation of the ω brittle phase is effectively suppressed, and cold forming and cold working capabilities are improved. The result is a metastable β-titanium alloy thin strip with uniform thickness, good surface quality, stable performance, and excellent plasticity. This method solves the technical problems of cold-rolled cracking of titanium alloy thin strip and the difficulty in producing high-plasticity thin strip.

[0004] To solve the above technical problems, the present invention adopts a technical solution: a method for preparing a metastable β titanium alloy thin strip, characterized in that the method comprises the following steps:

[0005] Step 1: Slab forging: Remove the riser and oxide scale from the β-titanium alloy ingot obtained by three vacuum arc melting processes and use it as a billet, then perform four-stage forging to obtain a forged slab.

[0006] Step 2, hot rolling of the plate: the forged slab obtained in step 1 is subjected to three-pass hot rolling to obtain a hot-rolled plate; the temperature of the three-pass hot rolling is all above the phase transformation point temperature of the β titanium alloy, and the holding time is t=h×b, where h is the thickness of the corresponding processed slab, in mm, and b is the time coefficient, b is 0.8 min / mm to 1.5 min / mm, and the thickness of the hot-rolled plate is 2.5 mm to 3.0 mm;

[0007] Step 3, plate annealing: annealing the hot-rolled plate obtained in step 2; the annealing temperature is 20°C to 40°C above the phase transition point of the β titanium alloy, and the holding time is 30min to 40min;

[0008] Step 4: Cold rolling the strip: The hot-rolled sheet annealed in Step 3 is subjected to multi-pass tension cold rolling, followed by leveling and trimming to obtain a cold-rolled strip; the total deformation of each pass in the multi-pass tension cold rolling is 33% to 50%, and the cold-rolled billet is cleaned, degreased, and annealed after each pass; the thickness of the strip is 0.15 mm to 0.8 mm;

[0009] Step 5: Strip heat treatment: The cold-rolled strip obtained in step 4 is heat-treated by online solution annealing to obtain a metastable β titanium alloy thin strip.

[0010] The above-mentioned method for preparing a metastable β titanium alloy thin strip is characterized in that the first and second fire forging processes of the four-fire forging in step 1 are two upsetting and two drawing, the third fire forging process is reversing three upsetting and three drawing, and the deformation from the first to the third fire forging is 40% to 50%, and the fourth fire forging process is side drawing.

[0011] Typically, the final forging temperature of the four-step forging in the present invention is greater than 850°C.

[0012] The above-mentioned method for preparing a metastable β titanium alloy thin strip is characterized in that the first hot rolling temperature in the three hot rolling in step 2 is 80°C to 120°C above the phase transformation point temperature of the β titanium alloy, the holding time is 1 to 1.5 times the thickness of the corresponding processed slab, the unit is min, and the rolling deformation is 75% to 80%.

[0013] The above-mentioned method for preparing a metastable β titanium alloy thin strip is characterized in that the second hot rolling in the three-pass hot rolling in step 2 is reversing rolling, the temperature is 80°C to 120°C above the phase transformation point temperature of the β titanium alloy, the holding time is 0.8 to 1.2 times the thickness of the corresponding processed slab, the unit is min, and the rolling deformation is 65% to 80%.

[0014] The above-mentioned method for preparing a metastable β titanium alloy thin strip is characterized in that the third hot rolling temperature in the three-pass hot rolling in step 2 is 50°C to 100°C above the phase transformation point temperature of the β titanium alloy, the holding time is 0.8 to 1.2 times the thickness of the corresponding processed slab, the unit is min, and the rolling deformation is 57% to 68%.

[0015] Preferably, the rolling deformation of each pass of the three-pass hot rolling in the present invention is 10% to 20%.

[0016] The above-mentioned method for preparing a metastable β titanium alloy thin strip is characterized in that the total deformation of the first rolling pass and the second rolling pass in the multi-rolling pass tension cold rolling in step four is 40% to 50%, and after each rolling pass, the cold-rolled billet is cleaned and degreased, stress-relief annealing is performed, and the cracked edges and head of the strip are removed. Thereafter, the total deformation of each rolling pass is 33% to 43%, and after each rolling pass, the cold-rolled billet is cleaned and degreased, stress-relief annealing is performed, and the cracked edges and head of the strip are removed.

[0017] The above-mentioned method for preparing a metastable β titanium alloy thin strip is characterized in that the rolling deformation of each pass in the first and second rolling passes of the multi-pass strip tension cold rolling in step four is 10% to 15%, and the rolling deformation of each pass in the third and fourth rolling passes is 5% to 10%.

[0018] The above-mentioned method for preparing a metastable β titanium alloy thin strip is characterized in that the temperature of the online solution annealing in step 5 is 25°C to 40°C above the phase transformation point temperature of the β titanium alloy, the holding time is 10min to 30min, and then high-purity argon gas quenching is used for cooling.

[0019] At the same time, the present invention also discloses a metastable β titanium alloy thin strip prepared by the above method, characterized in that it is composed of the following components in percentage by mass: Al 3.02% to 3.34%, Cr 3.10% to 3.17%, Sn 2.99% to 3.16%, V 14.98% to 15.06%, Fe≤0.25%, C≤0.05%, N≤0.05%, H≤0.015%, O≤0.15%, and the balance is Ti. The β titanium alloy has a phase transformation point of 780°C to 790°C, and the metastable β titanium alloy thin strip has a tensile strength of 704MPa to 740MPa, a yield strength of 696MPa to 736MPa, and an elongation of 26.5% to 32.5% after solution annealing. The strip has uniform thickness, good surface quality, and stable performance.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1. The present invention adopts four-fire forging to make the as-cast structure of the β-titanium alloy ingot undergo repeated deformation to achieve the purpose of grain refinement, and at the same time adjust the deformation temperature and overall deformation amount during the forging process to realize the overall regulation of the deformation capacity of the forged slab; compared with the one- to two-fire unidirectional drawing forging process in the prior art, the three-upsetting + one-drawing preparation process of the present invention can fully crush the as-cast structure of the ingot, and the obtained forged slab has a more uniform structure and finer grains, which is conducive to the improvement of the processing performance of the subsequent forged plate, thereby improving the stability of the performance of the product β-titanium alloy thin strip.

[0022] 2. The present invention adopts a three-pass hot rolling process. By optimizing the hot rolling temperature and deformation amount, and controlling the second pass hot rolling to be reversing rolling, it not only improves the uniformity of the structure of the hot-rolled plate, but also effectively crushes and refines the grains, making the microstructure of the hot-rolled plate more uniform, which is beneficial to reducing the difference in performance of the hot-rolled plate in different directions, making the mechanical properties of the hot-rolled plate in various directions closer, and improving the overall quality and reliability of the hot-rolled plate. At the same time, it avoids excessive accumulation of stress in a single direction, reduces the residual stress inside the plate, reduces the risk of deformation and cracking of the plate during subsequent processing or use, and improves the subsequent cold processing performance of the hot-rolled plate, thereby obtaining a hot-rolled plate with better deformation structure and comprehensive performance.

[0023] 3. The present invention adopts high-purity argon gas quenching cooling after solution annealing, strictly controls the cooling rate, and effectively avoids the α phase precipitation and grain growth of the β titanium alloy thin strip during the slow cooling process, thereby completely retaining the β phase fine grain structure, which is beneficial to improving the strength and plasticity matching of the β titanium alloy thin strip.

[0024] 4. The present invention optimizes the hot rolling temperature and controls the strip tension, multi-rolling cold rolling deformation and solution annealing system to effectively suppress the precipitation of the ω brittle phase, thereby improving the cold working and cold forming capabilities and achieving the regulation of the dimensional accuracy, microstructure and mechanical properties of the metastable β titanium alloy thin strip.

[0025] 5. The preparation method of the present invention is simple, has strong process applicability, is not limited by production equipment, is easy to operate and implement, saves costs, can realize batch production, and has broad application prospects.

[0026] 6. The metastable β titanium alloy thin strip prepared by the present invention has a tensile strength of 704MPa to 740MPa, a yield strength of 696MPa to 736MPa, and an elongation of 26.5% to 32.5% in the solid solution state. It has uniform thickness, good surface quality, stable performance, excellent plasticity, good plate shape, and small performance anisotropy difference. It meets the technical requirements of GB / T 3621-2007 "Titanium and Titanium Alloy Plates", meets the application needs of different fields, and is conducive to the industrial promotion and application of high-strength and high-plasticity TB5 titanium alloy thin strip.

[0027] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the microstructure diagram of the metastable β titanium alloy thin strip prepared in Example 2 of the present invention.

[0029] Figure 2 This is the microstructure diagram of the metastable β titanium alloy thin strip prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0030] Example 1

[0031] This embodiment includes the following steps:

[0032] Step 1, slab forging: A β-titanium alloy ingot obtained by three vacuum arc melting processes is selected, the ingot comprising the following components by weight: Al 3.34%, Cr 3.11%, Sn 2.99%, V14.98%, Fe 0.19%, C 0.008%, N 0.01%, H 0.009%, O 0.04%, and the balance being Ti, and the β-titanium alloy has a phase transition point of 780°C;

[0033] The β-titanium alloy ingot was surface treated to remove the riser and oxide scale, and then used as a billet. The billet with a diameter × height of Φ235mm × 435mm was placed in a heating furnace and heated at 800℃ for 90 minutes, then heated to 1050℃ and kept at this temperature for 360 minutes, and then subjected to open forging, i.e., first-fire forging. The forging process was two upsetting and two drawing, with an upsetting ratio greater than 1.8. After forging, the product was ground to remove surface defects, resulting in a first-fire forging billet with a side length × length of □230mm × 470mm.

[0034] The first-fire forging billet is sequentially subjected to the second and third-fire forging processes, wherein the second-fire forging process is two upsetting and two drawing processes, and the third-fire forging process is three upsetting and three drawing processes with a reversing direction. After forging, the product is ground to remove surface defects, and a three-fire forging billet with a side length of 230 mm × a length of 470 mm is obtained.

[0035] The three-fire forging billet is subjected to the fourth-fire forging process, and the fourth-fire forging process is drawing. After forging, the product is ground to remove surface defects to obtain a four-fire forging billet, i.e., a forging slab, with a thickness × width × length of δ90 mm × 250 mm × 1100 mm;

[0036] Step 2, hot rolling of the plate: the forged slab obtained in step 1 is heated to 860°C and kept at this temperature for 135 minutes, and then quickly subjected to the first hot rolling after being taken out of the furnace, with the total rolling deformation being 78% and the single-pass rolling deformation not exceeding 20%. After cooling, the slab is ground to obtain a first hot-rolled slab with a thickness of 20 mm;

[0037] The first-heat slab is heated to 860°C and kept at this temperature for 24 minutes. After being taken out of the furnace, it is quickly hot-rolled in the second heat to obtain a second-heat slab with a thickness of 7 mm.

[0038] The second hot rolled slab was heated to 830℃ and kept at this temperature for 8 minutes, and then immediately hot rolled for the third time after being taken out of the furnace to obtain a hot rolled plate with a thickness of 3 mm.

[0039] Step 3: Plate annealing: The hot-rolled plate obtained in step 2 is placed in a roller-hearth heating furnace for annealing; the annealing temperature is 800°C, the holding time is 40 minutes, and the plate is air-cooled after being taken out of the furnace. Sanding is used to remove surface defects such as cracks, indentations, and scale on the plate;

[0040] Step 4, cold rolling of the strip: the heads of both ends of the hot-rolled plate after annealing and defect removal in step 3 are cut off, and the strips are welded at both ends to perform three-pass strip tension cold rolling, wherein the total deformation of the first rolling pass is 50%, and a first cold-rolled billet with a thickness of δ1.5 mm is obtained. The first cold-rolled billet is intermediate annealed at an intermediate annealing condition of 820°C / 30 min. The total deformation of the second rolling pass is 40%, and a second cold-rolled billet with a thickness of δ0.9 mm is obtained. The second cold-rolled billet is intermediate annealed at an intermediate annealing condition of 820°C / 20 min. The rolling deformation of each pass from the first to the second rolling pass is 10% to 15%. The total deformation of the third rolling pass is 33%, and the rolling deformation of each pass is 5% to 10%, and a third cold-rolled billet with a thickness of δ0.6 mm is obtained. After each rolling pass, the cold-rolled billet is cleaned, degreased, and stress-relief annealed, and cracked edges and heads of the strip are leveled and removed to obtain a cold-rolled strip with a thickness of 0.6 mm;

[0041] Step 5: Strip heat treatment: The cold-rolled strip obtained in step 4 is heat treated by online solution annealing at a temperature of 820° C. for 30 min, and then cooled by gas quenching with high-purity argon to obtain a metastable β titanium alloy thin strip.

[0042] According to testing, the thickness tolerance of the metastable β titanium alloy thin strip prepared in this embodiment is less than ±0.05 mm.

[0043] Example 2

[0044] This embodiment includes the following steps:

[0045] Step 1, slab forging: A β-titanium alloy ingot obtained by three vacuum arc melting processes is selected, the ingot consisting of the following components by weight: Al 3.28%, Cr 3.17%, Sn 3.16%, V15.06%, Fe 0.15%, C 0.009%, N 0.01%, H 0.009%, O 0.03%, and the balance is Ti, and the phase transition point of the β-titanium alloy is 780°C;

[0046] The β-titanium alloy ingot was surface treated to remove the riser and oxide scale, and then used as a billet. The billet with a diameter × height of Φ330mm × 500mm was placed in a heating furnace and heated at 800℃ for 90 minutes, then heated to 1150℃ and kept at this temperature for 180 minutes, and then subjected to open forging, i.e., first-fire forging. The forging process was two upsetting and two drawing, with an upsetting ratio greater than 1.8. After forging, the product was ground to remove surface defects, obtaining a first-fire forging billet with a side length × length of □300mm × 470mm.

[0047] The first-fire forging billet is sequentially subjected to the second and third-fire forging processes, wherein the second-fire forging process is two upsetting and two drawing processes, and the third-fire forging process is three upsetting and three drawing processes with a reversing direction. After forging, the product is ground to remove surface defects, and a three-fire forging billet with a side length of 300 mm × 470 mm is obtained.

[0048] The three-fire forging billet is subjected to a fourth-fire forging process, and the fourth-fire forging process is drawing. After forging, the product is ground to remove surface defects to obtain a four-fire forging billet, i.e., a forging slab, with a thickness × width × length of δ100 mm × 300 mm × 1400 mm;

[0049] Step 2, hot rolling of the plate: the forged slab obtained in step 1 is heated to 900°C and kept at this temperature for 120 minutes, and then quickly subjected to the first hot rolling after being taken out of the furnace, with the total rolling deformation being 80% and the single-pass rolling deformation not exceeding 20%. After cooling, the slab is polished to obtain a first hot-rolled slab with a thickness of 20 mm;

[0050] The first-heat slab was heated to 900℃ and kept at this temperature for 16 minutes. After being taken out of the furnace, it was quickly hot-rolled in the second heat to obtain a second-heat slab with a thickness of 7 mm.

[0051] The second hot rolled slab was heated to 880℃ and kept at this temperature for 6 minutes, and then immediately hot rolled for the third time after being taken out of the furnace to obtain a hot rolled plate with a thickness of 2.5 mm.

[0052] Step 3: Plate annealing: The hot-rolled plate obtained in step 2 is placed in a roller-hearth heating furnace for annealing; the annealing temperature is 820°C, the holding time is 30 minutes, and the plate is air-cooled after being taken out of the furnace. Sanding is used to remove surface defects such as cracks, indentations, and scale on the plate;

[0053] Step 4, strip cold rolling: the ends of the hot-rolled plate after annealing and defect removal in step 3 are cut off, and the strip is welded at both ends for four-pass strip tension cold rolling, wherein the total deformation of the first rolling pass is 44%, and a first cold-rolled billet with a thickness of δ1.4mm is obtained. The first cold-rolled billet is intermediate annealed at an intermediate annealing temperature of 810°C / 20min. The total deformation of the second rolling pass is 43%, and a second cold-rolled billet with a thickness of δ0.8mm is obtained. The deformation of each rolling pass from the first to the second rolling pass is 10% to 15%. The second cold-rolled billet is intermediate annealed. The intermediate annealing condition is 810°C / 20min, and the total deformation of the third rolling process is 38%, obtaining a third cold-rolled billet with a thickness of δ0.5mm. The third cold-rolled billet is intermediate annealed at 810°C / 20min, and the total deformation of the fourth rolling process is 40%, obtaining a fourth cold-rolled billet with a thickness of δ0.3mm. The rolling deformation of each pass from the third to the fourth rolling process is 5% to 10%. After each rolling process, the cold-rolled billet is cleaned, degreased, and subjected to stress relief annealing treatment. The cracked edges and heads of the strip are leveled and removed to obtain a cold-rolled strip with a thickness of 0.3mm.

[0054] Step 5: Strip heat treatment: The cold-rolled strip obtained in step 4 is heat treated by online solution annealing at a temperature of 820° C. for 10 min, and then cooled by gas quenching with high-purity argon to obtain a metastable β titanium alloy thin strip.

[0055] According to testing, the thickness tolerance of the metastable β titanium alloy thin strip prepared in this embodiment is less than ±0.05 mm.

[0056] Figure 1 This is the microstructure of the 0.3 mm metastable β titanium alloy thin strip prepared in this embodiment. Figure 1 It can be seen that the structure of the metastable β titanium alloy thin strip is a uniform and fine β phase structure.

[0057] Example 3

[0058] This embodiment includes the following steps:

[0059] Step 1, slab forging: A β-titanium alloy ingot obtained by three vacuum arc melting processes is selected, the ingot comprising the following components by weight: Al 3.02%, Cr 3.10%, Sn 3.08%, V15.01%, Fe 0.16%, C 0.009%, N 0.012%, H 0.008%, O 0.03%, and the balance being Ti, and the β-titanium alloy has a phase transition point of 785°C;

[0060] The β-titanium alloy ingot was surface treated to remove the riser and oxide scale, and then used as a billet. The billet with a diameter × height of Φ330mm × 500mm was placed in a heating furnace and heated at 800°C for 90 minutes, then heated to 1100°C and kept at this temperature for 270 minutes, and then subjected to open forging, i.e., first-fire forging. The forging process was two upsetting and two drawing, with an upsetting ratio greater than 1.8. After forging, the product was ground to remove surface defects, obtaining a first-fire forging billet with a side length × length of □300mm × 470mm.

[0061] The first-fire forging billet is sequentially subjected to the second and third-fire forging processes, wherein the second-fire forging process is two upsetting and two drawing processes, and the third-fire forging process is three upsetting and three drawing processes with a reversing direction. After forging, the product is ground to remove surface defects, and a three-fire forging billet with a side length of 300 mm × 470 mm is obtained.

[0062] The three-fire forging billet is subjected to a fourth-fire forging process, and the fourth-fire forging process is drawing. After forging, the product is ground to remove surface defects to obtain a four-fire forging billet, i.e., a forging slab, with a thickness × width × length of δ100 mm × 300 mm × 1400 mm;

[0063] Step 2, hot rolling of the plate: the forged slab obtained in step 1 is heated to 865°C and kept at this temperature for 130 minutes, and then quickly subjected to the first hot rolling after being taken out of the furnace, with the total rolling deformation being 80% and the single-pass rolling deformation not exceeding 20%. After cooling, the slab is ground to obtain a first hot-rolled slab with a thickness of 20 mm;

[0064] The first-heat slab is heated to 865℃ and kept at this temperature for 20 minutes. After being taken out of the furnace, it is quickly hot-rolled in the second heat to obtain a second-heat slab with a thickness of 7 mm.

[0065] The second hot rolled slab was heated to 860℃ and kept at this temperature for 7 minutes. After being taken out of the furnace, it was quickly hot rolled for the third time to obtain a hot rolled plate with a thickness of 2.5 mm.

[0066] Step 3: Plate annealing: The hot-rolled plate obtained in step 2 is placed in a roller-hearth heating furnace for annealing; the annealing temperature is 820°C, the holding time is 30 minutes, and the plate is air-cooled after being taken out of the furnace. Sanding is used to remove surface defects such as cracks, indentations, and scale on the plate;

[0067] Step 4, strip cold rolling: the heads of both ends of the hot-rolled plate after annealing and defect removal in step 3 are cut off, and the strip tension cold rolling is carried out for five rolling passes with the lead strips welded at both ends, wherein the total deformation of the first rolling pass is 48%, and a first cold-rolled billet with a thickness of δ1.3 mm is obtained. The first cold-rolled billet is intermediate annealed at an intermediate annealing condition of 810°C / 20min. The total deformation of the second rolling pass is 46%, and a second cold-rolled billet with a thickness of δ0.7 mm is obtained. The rolling deformation of each pass from the first to the second rolling pass is 10% to 15%. The second cold-rolled billet is intermediate annealed at an intermediate annealing condition of 810°C / 20min. The total deformation of the third rolling pass is 43%, and a second cold-rolled billet with a thickness of δ0.7 mm is obtained. A third cold-rolled billet having a thickness of δ0.4 mm is subjected to intermediate annealing at an 810° C. / 20 min interval. The fourth rolling process has a total deformation of 38%, resulting in a fourth cold-rolled billet having a thickness of δ0.25 mm. The third cold-rolled billet has a thickness of δ0.4 mm and the deformation of each rolling process is 5% to 10%. The fourth cold-rolled billet is subjected to intermediate annealing at an 810° C. / 20 min interval. The fifth rolling process has a total deformation of 40%, resulting in a fifth cold-rolled billet having a thickness of δ0.15 mm. After each rolling process, the cold-rolled billet is cleaned and degreased, subjected to stress relief annealing, and the cracked edges and heads of the strip are leveled and removed, resulting in a cold-rolled strip having a thickness of 0.15 mm.

[0068] Step 5: Strip heat treatment: The cold-rolled strip obtained in step 4 is heat treated by online solution annealing at a temperature of 810° C. for 30 min, and then cooled by gas quenching with high-purity argon to obtain a metastable β titanium alloy thin strip.

[0069] According to testing, the thickness tolerance of the metastable β titanium alloy thin strip prepared in this embodiment is less than ±0.05 mm.

[0070] Example 4

[0071] This embodiment includes the following steps:

[0072] Step 1, slab forging: A β-titanium alloy ingot obtained by three vacuum arc melting processes is selected, the ingot comprising the following components by weight: Al 3.30%, Cr 3.21%, Sn 3.02%, V14.96%, Fe 0.18%, C 0.009%, N 0.01%, H 0.008%, O 0.03%, and the balance being Ti, and the phase transition point of the β-titanium alloy is 790°C;

[0073] The β-titanium alloy ingot was surface treated to remove the riser and oxide scale, and then used as a billet. The billet with a diameter × height of Φ235mm × 435mm was placed in a heating furnace and heated at 800℃ for 90 minutes, then heated to 1100℃ and kept at this temperature for 180 minutes, and then subjected to open forging, i.e., first-fire forging. The forging process was two upsetting and two drawing, with an upsetting ratio greater than 1.8. After forging, the product was ground to remove surface defects, resulting in a first-fire forging billet with a side length × length of □230mm × 470mm.

[0074] The first-fire forging billet is sequentially subjected to the second and third-fire forging processes, wherein the second-fire forging process is two upsetting and two drawing processes, and the third-fire forging process is three upsetting and three drawing processes with a reversing direction. After forging, the product is ground to remove surface defects, and a three-fire forging billet with a side length of 230 mm × a length of 470 mm is obtained.

[0075] The three-fire forging billet is subjected to a fourth-fire forging process, and the fourth-fire forging process is stretching. After forging, the product is ground to remove surface defects to obtain a four-fire forging billet with a thickness × width × length of δ100 mm × 250 mm × 1000 mm, i.e., a forging slab;

[0076] Step 2, hot rolling of the plate: the forged slab obtained in step 1 is heated to 880°C and kept at this temperature for 100 minutes, and then quickly subjected to the first hot rolling after being taken out of the furnace, with the total rolling deformation being 75% and the single-pass rolling deformation not exceeding 20%. After cooling, the slab is polished to obtain a first hot-rolled slab with a thickness of 25 mm;

[0077] The first-heat slab is heated to 880℃ and kept at this temperature for 25 minutes. After being taken out of the furnace, it is quickly hot-rolled in the second heat to obtain a second-heat slab with a thickness of 8mm.

[0078] The second hot rolled slab was heated to 850℃ and kept at this temperature for 8 minutes. After being taken out of the furnace, it was quickly hot rolled for the third time to obtain a hot rolled plate with a thickness of 2.6 mm.

[0079] Step 3: Plate annealing: The hot-rolled plate obtained in step 2 is placed in a roller-hearth heating furnace for annealing; the annealing temperature is 815°C, the holding time is 40 minutes, and the plate is air-cooled after being taken out of the furnace. Sanding is used to remove surface defects such as cracks, indentations, and scale on the plate;

[0080] Step 4, cold rolling of the strip: the heads of both ends of the hot-rolled plate after annealing and defect removal in step 3 are cut off, and the strips are welded at both ends to perform multi-pass strip tension cold rolling, wherein the total deformation of the first rolling pass is 42%, and a first cold-rolled billet with a thickness of δ1.5 mm is obtained. The first cold-rolled billet is intermediate annealed at an intermediate annealing condition of 820°C / 30min. The total deformation of the second rolling pass is 47%, and a second cold-rolled billet with a thickness of δ0.8 mm is obtained. The rolling deformation of each pass from the first to the second rolling pass is 10% to 15%. After each rolling pass, the cold-rolled billet is cleaned, degreased, and stress-relief annealed, and cracked edges and heads of the strip are leveled and removed to obtain a cold-rolled strip with a thickness of 0.8 mm;

[0081] Step 5: Strip heat treatment: The cold-rolled strip obtained in step 4 is heat treated by online solution annealing at a temperature of 810° C. for 10 min, and then cooled by gas quenching with high-purity argon to obtain a metastable β titanium alloy thin strip.

[0082] According to testing, the thickness tolerance of the metastable β titanium alloy thin strip prepared in this embodiment is less than ±0.05 mm.

[0083] Figure 2 This is the microstructure of the 0.8 mm metastable β titanium alloy thin strip prepared in this embodiment. Figure 2 It can be seen that the structure of the metastable β titanium alloy thin strip is a uniform and fine β phase structure.

[0084] Tensile tests were performed on the metastable β titanium alloy thin strips prepared in Examples 1 to 4 of the present invention. The test results are shown in Table 1 below.

[0085] Table 1

[0086] Serial number Tensile strength / MPa Yield strength / MPa Elongation / % Example 1 740 736 28 Example 2 710 699 30.5 Example 3 704 696 26.5 Example 4 733 726 32.5

[0087] From Table 1 and Examples 1 to 4, it can be seen that the metastable β titanium alloy thin strip prepared by the present invention has excellent plasticity, uniform thickness, good surface quality and stable performance.

[0088] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a metastable β titanium alloy thin strip, characterized in that: The metastable β titanium alloy thin strip is composed of the following components in percentage by mass: Al 3.02%-3.34%, Cr 3.10%-3.17%, Sn 2.99%-3.16%, V 14.98%-15.06%, Fe≤0.25%, C≤0.05%, N≤0.05%, H≤0.015%, O≤0.15%, and the balance is Ti. The β titanium alloy has a phase transition point of 780°C-790°C. The method comprises the following steps: Step 1: Slab forging: Remove the riser and oxide scale from the β-titanium alloy ingot obtained by three vacuum arc melting processes and use it as a billet, then perform four-stage forging to obtain a forged slab. Step 2, plate hot rolling: the forged slab obtained in step 1 is subjected to three-pass hot rolling to obtain a hot-rolled plate; the thickness of the hot-rolled plate is 2.5mm~3.0mm; the first hot rolling temperature of the three-pass hot rolling is 80℃~120℃ above the phase transition point temperature of the β titanium alloy, the holding time is 1~1.5 times the thickness of the corresponding processed slab, the unit is min, the rolling deformation is 75%~80%, the second hot rolling is reversing rolling, the temperature is β titanium alloy The temperature is 80-120°C above the phase transformation point, the holding time is 0.8-1.2 times the thickness of the corresponding slab to be processed, the unit is min, and the rolling deformation is 65%-80%. The third hot rolling temperature is 50-100°C above the phase transformation point temperature of β titanium alloy, the holding time is 0.8-1.2 times the thickness of the corresponding slab to be processed, the unit is min, and the rolling deformation is 57%-68%. The unit of the thickness of the corresponding slab to be processed in each hot rolling is mm. Step 3, plate annealing: annealing the hot-rolled plate obtained in step 2; the annealing temperature is 20°C to 40°C above the phase transition point of the β titanium alloy, and the holding time is 30min to 40min; Step 4, strip cold rolling: The hot-rolled plate annealed in step 3 is subjected to multi-pass tension cold rolling, followed by leveling and trimming to obtain a cold-rolled strip; the thickness of the cold-rolled strip is 0.15 mm to 0.8 mm; the total deformation of the first and second passes of the multi-pass tension cold rolling is 40% to 50%, and after each pass, the cold-rolled billet is cleaned, degreased, and subjected to stress relief annealing, and cracked edges and heads of the strip are removed. Thereafter, the total deformation of each pass is 33% to 43%, and after each pass, the cold-rolled billet is cleaned, degreased, and subjected to stress relief annealing, and cracked edges and heads of the strip are removed; Step 5, strip heat treatment: The cold-rolled strip obtained in step 4 is heat treated by online solution annealing. The online solution annealing temperature is 25°C to 40°C above the phase transition point of the β titanium alloy, and the holding time is 10min to 30min. Then, high-purity argon gas quenching is used to obtain a metastable β titanium alloy thin strip.

2. The method for preparing a metastable β titanium alloy thin strip according to claim 1, characterized in that: The first and second forging processes of the four-fire forging in step one are both two upsetting and two drawing, the third forging process is three upsetting and three drawing with reversing direction, and the fourth forging process is side drawing.

3. The method for preparing a metastable β titanium alloy thin strip according to claim 1, characterized in that: The rolling deformation of each pass in the first and second rolling passes of the multi-pass tension cold rolling in step 4 is 10% to 15%, and the rolling deformation of each pass in the third and fourth rolling passes is 5% to 10%.

4. A metastable β titanium alloy thin strip prepared by the method according to any one of claims 1 to 3, characterized in that: The metastable β titanium alloy thin strip after solution annealing has a tensile strength of 704MPa~740MPa, a yield strength of 696MPa~736MPa, and an elongation of 26.5%~32.5%. It also has uniform thickness, good surface quality, and stable performance.

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