A rolling method of large-size TA15 titanium alloy super-thick plate

Abstract

The application discloses a rolling method of a large-size TA15 titanium alloy super-thick plate, and the method comprises the following steps: firstly, sequentially performing twice beta single-phase zone forging, twice alpha+beta two-phase zone forging and forming forging on a TA15 titanium alloy ingot to obtain a TA15 titanium alloy slab; secondly, performing ladder heating on the TA15 titanium alloy slab; thirdly, obtaining a TA15 titanium alloy rolling slab through one-time rolling; fourthly, performing finish heat treatment after turning over, and air cooling after reciprocating straightening; and fifthly, performing shape correction treatment to obtain a finished TA15 titanium alloy super-thick plate. The original beta grains are fully broken through the five-time forging, ladder heating and one-time rolling in sequence, the rolling slab with consistent structure and performance is obtained, the grain growth is inhibited, the strengthening phase is precipitated through the rapid water cooling treatment, the heat treatment and the shape correction treatment, the TA15 titanium alloy super-thick plate with small grain size, small anisotropy and excellent performance is obtained, and the TA15 titanium alloy super-thick plate is suitable for large structural parts in the fields of aviation and spaceflight.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy sheet preparation technology, specifically relating to a rolling method for large-size TA15 titanium alloy ultra-thick plates. Background Technology

[0002] The nominal composition of TA15 titanium alloy is Ti-6.5Al-2Zr-1Mo-1V. Because TA15 titanium alloy has moderate room temperature strength and high temperature strength, good thermal stability and weldability, TA15 finished products, including thick plates, forgings, bars, and profiles, are widely used in aircraft, engine parts, structural parts and other fields below 500℃.

[0003] With the rapid development of the aerospace industry, the demand for large-size forgings is increasing. However, large titanium alloy forgings currently face the following problems: First, due to equipment limitations, forgings are typically small in length and width, and large forgings require welding, increasing the risk of failure. Second, forging is a discontinuous process; if free forging occurs, the degree of deformation inside and outside the billet can easily become uneven, resulting in inhomogeneous microstructure and properties. Furthermore, forging requires a large machining allowance for surface finishing, has a long production cycle, and a low yield, making mass production impossible. Therefore, as the aerospace industry demands lower raw material costs, rolled thick plates offer advantages. On the one hand, they can be processed into larger sizes with higher production efficiency; on the other hand, they have a higher yield and lower production costs. Thus, the advantages of using rolled ultra-thick plates instead of forgings are becoming increasingly apparent. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a rolling method for large-size TA15 titanium alloy ultra-thick plates, addressing the shortcomings of the prior art. This method first involves five-pass forging to fully break down the original β grains and achieve a uniform microstructure. After stepped heating, a three-pass single-pass rolling process is performed. By reversing the rolling direction and controlling the deformation, the slab is fully deformed with consistent microstructure and properties. Rapid water cooling is then used to suppress excessive grain growth. Finally, heat treatment and shaping promote the precipitation of strengthening phases, resulting in TA15 titanium alloy ultra-thick plates with fine grain size, low anisotropy, and excellent properties. This method offers high production efficiency and low cost, solving the problems of limited forging size, uneven microstructure and properties, long production cycles, and high costs associated with existing forgings.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a rolling method for large-size TA15 titanium alloy ultra-thick plates, characterized in that the method includes the following steps:

[0006] Step 1: The TA15 titanium alloy ingot is subjected to two β single-phase forgings, two α+β two-phase forgings, and forming forging in sequence to obtain TA15 titanium alloy slabs with a thickness of 300mm~360mm, a width of 900mm~1250mm, and a length of 1500mm~2200mm; the TA15 titanium alloy slabs meet the A1 grade technical requirements in GB / T 5193-2020 "Ultrasonic Testing Methods for Titanium and Titanium Alloy Processed Products", and the original β grains of the slab are fully broken and the microstructure is uniform;

[0007] Step 2: Coat the upper, lower and side surfaces of the TA15 titanium alloy slab obtained in Step 1 with an anti-oxidation coating. Then, heat it using a stepped heating method. The first step is held at 600℃. After holding, the temperature is raised to the second step at 800℃ and held. After holding, the temperature is raised to the third step at 920℃~940℃ and held.

[0008] Step 3: The heated TA15 titanium alloy slab from Step 2 is rolled in one pass to obtain a TA15 titanium alloy rolled billet.

[0009] The single-pass rolling process consists of three passes. Specifically, the heated TA15 titanium alloy slab is first subjected to a first pass (reversal rolling), with a pass deformation rate of 5%–10%, 2–3 passes, and a rolling speed of 3–4 m / s, resulting in a first-pass slab with a thickness of 250–304 mm, a width of 1500–2200 mm, and a length of 1080–1480 mm. Then, the first-pass slab is subjected to intermediate online reheating at 920–940 °C, followed by two more passes of reversal rolling. In the second pass (reversal rolling), the pass deformation rate is 8%–15%, 3–4 passes, and a rolling speed of 2 m / s. The rolling speed is ~3m / s to obtain a second-pass billet with a thickness of 140mm~225mm, a width of 1080mm~1480mm, and a length of 2450mm~2850mm. The second-pass billet is then subjected to intermediate online reheating at 920℃~940℃, and the third-pass rolling process, i.e., reversing the second-pass rolling process, is carried out. The pass deformation rate of the third-pass rolling process is 10%~16%, the number of passes is 2, the rolling speed is 3m / s~4m / s, and the rolling direction is the same as that of the second-pass rolling process, to obtain a third-pass billet. Then, it is quickly water-cooled to obtain a TA15 titanium alloy billet with a thickness of 100mm~180mm, a width of 1080mm~1480mm, and a length of 3200mm~3300mm.

[0010] Step 4: The TA15 titanium alloy billet obtained in Step 3 is flipped using a flipping machine and subjected to finished product heat treatment. Then, it is quickly passed through a straightening machine for 2-4 passes of reciprocating straightening, followed by air cooling to room temperature to obtain the heat-treated TA15 titanium alloy billet.

[0011] Step 5: The heat-treated TA15 titanium alloy billet obtained in Step 4 is shaped to obtain a finished TA15 titanium alloy ultra-thick plate with a thickness of 100mm~180mm, a width of 1080mm~1480mm, and a length of 3200mm~3300mm. The flatness of the TA15 titanium alloy ultra-thick plate is less than 4mm / m, and the distance between each corner platform is not greater than 5mm.

[0012] This invention first involves forging a TA15 titanium alloy ingot five times to obtain a TA15 titanium alloy slab. Then, an anti-oxidation coating is applied to the surface of the TA15 titanium alloy slab. Subsequently, the slab undergoes a series of processes, including stepped heating, first-stroke forward rolling, intermediate online reheating, second-stroke reversing rolling, intermediate online reheating, third-stroke reversing rolling, hot material water cooling, finished product heat treatment, air cooling, and shaping treatment, ultimately yielding an ultra-thick TA15 titanium alloy plate. In this preparation process, firstly, two β-phase forging processes are performed to fully break down the β grains using a unidirectional large deformation method. Then, two α+β two-phase forging processes are performed to fully refine the microstructure using a multi-directional upsetting and drawing deformation method, breaking down the original β grains, grain boundaries (α), and intragranular α bundle regions. This process, followed by forming and forging, yields a TA15 titanium alloy slab with fully broken original β grains, a uniform microstructure, and fine grain size. Next, an anti-oxidation coating (typically about 1.5 mm thick) is applied to the surface of the TA15 titanium alloy slab to enhance its heat retention and anti-oxidation effects. A three-stage stepped heating treatment is then employed. This effectively reduces the temperature difference between the slab's core and surface, and shortens the holding time of the final step, effectively preventing excessive grain growth and the formation of a thick oxide layer due to prolonged high-temperature heating. Finally, a three-pass, one-fire rolling process with reversing direction ensures that the slab undergoes sufficient and uniform deformation in both the transverse and longitudinal directions. Combined with a rolling method that uses large deformation and controls the amount of deformation, the deformation penetrates deep into the slab's core, ensuring the slab's microstructure and properties. To ensure consistency, the TA15 titanium alloy billet was prepared by controlling the reheating after the second rolling pass and controlling the deformation amount (20%~30%) of the last rolling pass. This ensured sufficient element diffusion and homogenization of the plate composition and microstructure, resulting in a TA15 titanium alloy billet with low anisotropy. Simultaneously, the billet temperature before water cooling was effectively maintained. Next, rapid water cooling allowed dislocations and stored energy formed during rolling deformation to be retained as nucleation points for recrystallization, refining the microstructure and suppressing excessive grain growth, thus reducing performance differences during billet cooling. Subsequently, the TA15 titanium alloy billet was flipped to reduce the temperature difference between the upper and lower surfaces caused by water cooling, and heat treatment of the finished product reduced internal stress and stabilized the microstructure. Finally, a shaping process eliminated internal stress and improved plate flatness. Furthermore, the precipitation of dispersed Ti3Al phases in the plate acted as a reinforcing phase, effectively improving the mechanical properties of the plate. Ultimately, a TA15 titanium alloy ultra-thick plate with fine grain size, low anisotropy, and excellent performance was produced.

[0013] The above-mentioned rolling method for large-size TA15 titanium alloy ultra-thick plates is characterized in that, in step one, the forging temperature of the two β single-phase region forgings is 1050℃~1150℃, the forging ratio is 7.0~10.0, the initial forging temperature is not lower than 1000℃, the final forging temperature is not lower than 850℃, and the plates are air-cooled to room temperature after forging; the forging temperature of the two α+β two-phase region forgings is 920℃~960℃, the forging ratio is 4.0~7.0, the initial forging temperature is not lower than 850℃, the final forging temperature is not lower than 700℃, and the plates are air-cooled to room temperature after forging; the forging temperature of the forming forging is 920℃~940℃, the initial forging temperature is not lower than 850℃, the final forging temperature is not lower than 700℃, and the plates are air-cooled to room temperature after forging.

[0014] The above-mentioned rolling method for large-size TA15 titanium alloy ultra-thick plates is characterized in that the specific process of heating by step-by-step heating in step two is as follows: the first step is held at 600℃ for 1.5h~2h, after which the temperature is increased with the furnace at 4℃ / min to the second step at 800℃ and held for 2h~2.5h, after which the temperature is increased with the furnace at 3℃ / min to the third step at 920℃~940℃ and held for 3h~4h.

[0015] The above-mentioned rolling method for large-size TA15 titanium alloy ultra-thick plates is characterized in that, in step three, the initial rolling temperature of the first rolling stroke is not lower than 900℃, the final rolling temperature is not lower than 780℃, the total deformation rate is 16%, and the billet in the first rolling stroke is reheated in the furnace online for 1.5h~2h; the total deformation rate of the reversing rolling of the two rolling strokes is 40%~60%, and the initial rolling temperature of the second rolling stroke is not lower than 900℃, the final rolling temperature is not lower than 820℃, and the billet in the second rolling stroke is reheated in the furnace online for 1h~1.5h; the initial rolling temperature of the third rolling stroke is not lower than 900℃, the final rolling temperature is not lower than 850℃, and the total deformation rate is 20%~30%; the temperature of the billet in the third rolling stroke before water cooling treatment is not lower than 850℃, the temperature after water cooling treatment is not higher than 250℃, and the water cooling time does not exceed 4min.

[0016] The above-mentioned rolling method for large-size TA15 titanium alloy ultra-thick plates is characterized in that the temperature of the finished product heat treatment in step four is 750℃~800℃, the holding time is 1.5h~2.5h, and the temperature of the TA15 titanium alloy billet after reciprocating straightening before air cooling is not lower than 720℃.

[0017] The above-mentioned rolling method for large-size TA15 titanium alloy ultra-thick plates is characterized in that the temperature of the shaping treatment in step five is 520℃~550℃, the holding time is 5h~7h, and the shaping treatment is followed by air cooling to room temperature.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. This invention utilizes a five-stage forging process, including two β single-phase forgings, two α+β two-phase forgings, and a forming forging, to fully break down the original β grains, grain boundaries α, and intragranular α bundle regions and refine the microstructure, thereby obtaining a TA15 titanium alloy slab with a uniform microstructure and fine grain size, which provides a guarantee for subsequent rolling and other processes.

[0020] 2. The present invention adopts a three-stage stepped heating method, which effectively reduces the temperature difference between the core and surface of the slab, and avoids excessive growth of slab grain size and formation of a thick oxide layer on the surface caused by prolonged high-temperature heating.

[0021] 3. This invention employs a single-pass rolling process with three rolling passes. By reversing the rolling direction and controlling the amount of deformation, the slab is fully deformed, ensuring the consistency of the microstructure and properties of the TA15 titanium alloy slab. Combined with rapid water cooling, the deformed dislocations are retained, energy is stored, and they act as nucleation points to recrystallize and refine the microstructure, thus suppressing excessive grain growth.

[0022] 4. This invention combines finished product heat treatment with shaping treatment to fully eliminate internal stress in the sheet material and improve its flatness. At the same time, it promotes the precipitation of reinforcing phases to exert a pinning effect, effectively improving the mechanical properties of the sheet material.

[0023] 5. This invention can prepare TA15 titanium alloy ultra-thick plates by combining one-time rolling with subsequent water cooling, heat treatment and shaping treatment. Its performance can reach the same level as that of forged plates, while the size of the plates that can be processed is much larger than that of forged plates. At the same time, the rolling process of ultra-thick plates has the characteristics of high production efficiency and yield, and lower production cost, which meets the needs of mass production, stable production and actual use.

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0025] Figure 1 Metallographic image (200×) of the TA15 titanium alloy ultra-thick plate prepared in Example 1 of this invention.

[0026] Figure 2 Metallographic image (200×) of the TA15 titanium alloy ultra-thick plate prepared in Example 2 of this invention.

[0027] Figure 3 Metallographic image (200×) of the TA15 titanium alloy ultra-thick plate prepared in Example 3 of this invention. Detailed Implementation

[0028] Example 1

[0029] This embodiment includes the following steps:

[0030] Step 1: The TA15 titanium alloy ingot is subjected to two β single-phase forgings, two α+β two-phase forgings, and a forming forging. The forging temperatures for the two β single-phase forgings are 1150℃ and 1100℃, with forging ratios of 10.0 and 7.0, respectively. The initial forging temperatures are 1100℃ and 1050℃, and the final forging temperatures are 945℃ and 905℃, respectively. After forging, the ingot is air-cooled to room temperature. The forging temperatures for the two α+β two-phase forgings are 960℃ and 940℃, respectively. The forging temperatures were 7.0 and 4.0, with initial forging temperatures of 910℃ and 890℃, and final forging temperatures of 780℃ and 740℃, respectively. After forging, the plates were air-cooled to room temperature. For forming forging, the forging temperature was 940℃, the initial forging temperature was 870℃, and the final forging temperature was 720℃. After forging, the plates were air-cooled to room temperature to obtain TA15 titanium alloy slabs with a thickness of 300mm, a width of 900mm, and a length of 1500mm. The TA15 titanium alloy slabs met the A1 grade technical requirements in GB / T 5193-2020 "Ultrasonic Testing Methods for Titanium and Titanium Alloy Processed Products". The original β grains of the slabs were fully broken and the microstructure was uniform.

[0031] Step 2: Coat the upper, lower and side surfaces of the TA15 titanium alloy slab obtained in Step 1 with a 1.5mm thick anti-oxidation coating. Then, heat it using a stepped heating method. The first step is held at 600℃ for 1.5 hours. After the holding time, the temperature is increased with the furnace at 4℃ / min to the second step at 800℃ and held for 2 hours. After the holding time, the temperature is increased with the furnace at 3℃ / min to the third step at 920℃ and held for 4 hours.

[0032] Step 3: The heated TA15 titanium alloy slab from Step 2 is subjected to a single-pass rolling process, which consists of three rolling strokes. Specifically, the heated TA15 titanium alloy slab is first subjected to the first rolling stroke (reversal rolling), with a pass deformation rate of 8.8% and 9.4%, two passes, a rolling speed of 4 m / s, an initial rolling temperature of 910℃, a final rolling temperature of 840℃, and a total deformation rate of 16.7%, resulting in a first-pass slab with a thickness of 250 mm, a width of 1500 mm, and a length of 1080 mm. Then, the first-pass slab is subjected to intermediate online reheating at 920℃ for 2 hours, followed by two more reversal rolling strokes with a total deformation rate of 60%. In the second rolling stroke (reversal rolling), the pass deformation rates are 12.0%, 13.6%, 14.7%, and 13.6%, with four passes. The rolling speed was 3 m / s, the initial rolling temperature was 908℃, and the final rolling temperature was 835℃, resulting in a second-pass billet with a thickness of 140 mm, a width of 1080 mm, and a length of 2450 mm. The second-pass billet was then subjected to an intermediate online reheating process at 920℃ for 1.5 h, followed by a third-pass rolling process, which involved reversing the direction of the second pass. The deformation rates of the passes in the third-pass were 15.4% and 15.6%, with two passes, a rolling speed of 4 m / s, and a total deformation rate of 28.5%. The rolling direction was the same as that of the second pass. The initial rolling temperature was 910℃, and the final rolling temperature was 880℃, resulting in a third-pass billet. This billet was then rapidly water-cooled. The initial temperature was 885℃, and the final temperature was 230℃, with a water-cooling time of 3 min, resulting in a TA15 titanium alloy billet with a thickness of 100 mm, a width of 1080 mm, and a length of 3200 mm.

[0033] Step 4: The TA15 titanium alloy billet obtained in Step 3 is flipped using a flipping machine and subjected to heat treatment at 750℃ for 2.5 hours. Then, it is quickly passed through a straightener for three passes of reciprocating straightening, followed by air cooling to room temperature. The temperature before air cooling is 725℃, resulting in a heat-treated TA15 titanium alloy billet with a thickness of 100mm, a width of 1080mm, and a length of 3200mm.

[0034] Step 5: The heat-treated TA15 titanium alloy billet obtained in Step 4 is subjected to a shaping process at a temperature of 520℃ for 7 hours, followed by air cooling to room temperature to obtain a finished TA15 titanium alloy ultra-thick plate with a thickness of 100mm, a width of 1080mm, and a length of 3200mm. The flatness of the TA15 titanium alloy ultra-thick plate is 3.5mm / m, and the distance between each corner platform is 4mm.

[0035] Figure 1Metallographic image (200×) of the TA15 titanium alloy ultra-thick plate prepared in this embodiment. Figure 1 It can be seen that the TA15 titanium alloy ultra-thick plate has a uniform structure processed through the α+β two-phase region. The original β grains are fully broken, and there are no continuous and straight grain boundary α phases. Moreover, the microstructure morphology at different locations is basically consistent, which meets the microstructure requirements of TA15 titanium alloy plates in GJB 2505A-2018 "Specification for Titanium and Titanium Alloy Plates and Strips for Aviation".

[0036] Example 2

[0037] This embodiment includes the following steps:

[0038] Step 1: The TA15 titanium alloy ingot is subjected to two β single-phase forgings, two α+β two-phase forgings, and a forming forging. The forging temperatures for the two β single-phase forgings are 1120℃ and 1070℃, with forging ratios of 9.5 and 7.8, respectively. The initial forging temperatures are 1090℃ and 1040℃, and the final forging temperatures are 950℃ and 910℃, respectively. After forging, the ingot is air-cooled to room temperature. The forging temperatures for the two α+β two-phase forgings are 960℃ and 940℃, respectively. The forging ratios were 5.8 and 5.2, the initial forging temperatures were 925℃ and 900℃, and the final forging temperatures were 785℃ and 720℃, respectively. After forging, the plates were air-cooled to room temperature. The forging temperature for forming the plate was 920℃, the initial forging temperature was 880℃, and the final forging temperature was 730℃. After forging, the plates were air-cooled to room temperature to obtain TA15 titanium alloy slabs with a thickness of 340mm, a width of 1070mm, and a length of 1850mm. The TA15 titanium alloy slabs met the A1 grade technical requirements in GB / T 5193-2020 "Ultrasonic Testing Methods for Titanium and Titanium Alloy Processed Products". The original β grains of the slabs were fully broken and the microstructure was uniform.

[0039] Step 2: Coat the upper, lower and side surfaces of the TA15 titanium alloy slab obtained in Step 1 with a 1.5mm thick anti-oxidation coating. Then, heat it using a stepped heating method. The first step is held at 600℃ for 2 hours. After holding, the temperature is increased at 4℃ / min to the second step at 800℃ and held for 2 hours. After holding, the temperature is increased at 3℃ / min to the third step at 930℃ and held for 4 hours.

[0040] Step 3: The heated TA15 titanium alloy slab from Step 2 is subjected to a single-pass rolling process, which consists of three passes. Specifically, the heated TA15 titanium alloy slab is first subjected to the first pass, i.e., a forward rolling process. The pass deformation rates for the forward rolling are 5.3%, 6.3%, and 6.2%, with 3 passes, a rolling speed of 4 m / s, an initial rolling temperature of 910℃, and a final rolling temperature of 835℃. The total deformation rate is 16.4%, resulting in a first-pass slab with a thickness of 284 mm, a width of 1850 mm, and a length of 1280 mm. Then, the first-pass slab is subjected to intermediate online reheating at 930℃ for 2 hours, followed by two more forward rolling processes. The total deformation rate is 50.7%. Specifically, the second pass, i.e., the forward rolling process, has pass deformation rates of 9.2%, 10.1%, 11.2%, and 9.7%, with 4 passes. The rolling speed was 3 m / s, the initial rolling temperature was 915℃, and the final rolling temperature was 865℃, resulting in a second-pass billet with a thickness of 186 mm, a width of 1280 mm, and a length of 2700 mm. The second-pass billet was then subjected to an intermediate online reheating process at 930℃ for 1.5 h, followed by a third-pass rolling process, i.e., reversing the second-pass rolling. The deformation rates of the passes in the third-pass rolling process were 14.0% and 12.5%, with 2 passes, a rolling speed of 4 m / s, and a total deformation rate of 24.7%. The rolling direction was the same as that of the second-pass rolling process. The initial rolling temperature was 919℃, and the final rolling temperature was 897℃, resulting in a third-pass billet. This billet was then rapidly water-cooled. The initial temperature was 900℃, and the final temperature was 225℃, with a water-cooling time of 3.5 min, resulting in a TA15 titanium alloy billet with a thickness of 140 mm, a width of 1280 mm, and a length of 3300 mm.

[0041] Step 4: The TA15 titanium alloy billet obtained in Step 3 is flipped using a flipping machine and subjected to heat treatment at 780℃ for 2 hours. Then, it is quickly passed through a straightening machine for three passes of reciprocating straightening, followed by air cooling to room temperature at 750℃. This yields a heat-treated TA15 titanium alloy billet with a thickness of 140mm, a width of 1280mm, and a length of 3300mm.

[0042] Step 5: The heat-treated TA15 titanium alloy billet obtained in Step 4 is subjected to a shaping process at a temperature of 530℃ for 6 hours, followed by air cooling to room temperature to obtain a finished TA15 titanium alloy ultra-thick plate with a thickness of 140mm, a width of 1280mm, and a length of 3300mm. The flatness of the TA15 titanium alloy ultra-thick plate is 3mm / m, and the distance between each corner platform is 5mm.

[0043] Figure 2Metallographic image (200×) of the TA15 titanium alloy ultra-thick plate prepared in this embodiment. Figure 2 It can be seen that the TA15 titanium alloy ultra-thick plate has a uniform structure processed through the α+β two-phase region. The original β grains are fully broken, and there are no continuous and straight grain boundary α phases. Moreover, the microstructure morphology at different locations is basically consistent, which meets the microstructure requirements of TA15 titanium alloy plates in GJB 2505A-2018 "Specification for Titanium and Titanium Alloy Plates and Strips for Aviation".

[0044] Example 3

[0045] This embodiment includes the following steps:

[0046] Step 1: The TA15 titanium alloy ingot is subjected to two β single-phase forgings, two α+β two-phase forgings, and a forming forging. The forging temperatures for the two β single-phase forgings are 1150℃ and 1070℃, with forging ratios of 8.8 and 8.2, respectively. The initial forging temperatures are 1085℃ and 1020℃, and the final forging temperatures are 955℃ and 910℃, respectively. After forging, the ingot is air-cooled to room temperature. The forging temperatures for the two α+β two-phase forgings are 960℃ and 940℃, respectively. The forging ratios were 6.5 and 5.5, the initial forging temperatures were 915℃ and 905℃, and the final forging temperatures were 765℃ and 715℃, respectively. After forging, the plates were air-cooled to room temperature. The forging temperature for forming forging was 920℃, the initial forging temperature was 885℃, and the final forging temperature was 735℃. After forging, the plates were air-cooled to room temperature to obtain TA15 titanium alloy slabs with a thickness of 360mm, a width of 1250mm, and a length of 2200mm. The TA15 titanium alloy slabs met the A1 grade technical requirements in GB / T 5193-2020 "Ultrasonic Testing Methods for Titanium and Titanium Alloy Processed Products". The original β grains of the slabs were fully broken and the microstructure was uniform.

[0047] Step 2: Coat the upper, lower, and side surfaces of the TA15 titanium alloy slab obtained in Step 1 with a 1.5mm thick anti-oxidation coating. Then, heat it using a stepped heating method. The first step is held at 600℃ for 2 hours. After holding, the temperature is increased at 4℃ / min to the second step at 800℃ and held for 2.5 hours. After holding, the temperature is increased at 3℃ / min to the third step at 940℃ and held for 3 hours.

[0048] Step 3: The heated TA15 titanium alloy slab from Step 2 is subjected to a single-pass rolling process, which consists of three passes. Specifically, the heated TA15 titanium alloy slab is first subjected to the first pass, i.e., a forward rolling process. The pass deformation rates for the forward rolling are 5%, 5.8%, and 5.6%, with 3 passes, a rolling speed of 3 m / s, an initial rolling temperature of 920℃, a final rolling temperature of 855℃, and a total deformation rate of 15.5%, resulting in a first-pass slab with a thickness of 304 mm, a width of 2200 mm, and a length of 1480 mm. Then, the first-pass slab is subjected to intermediate online reheating at 940℃ for 1.5 hours, followed by two more forward rolling passes. The total deformation rate is 40.7%, with the second pass (the forward rolling of the first pass) having pass deformation rates of 8.2%, 10.3%, and 10.0%, with 3 passes. The rolling speed was 2 m / s, the initial rolling temperature was 920℃, and the final rolling temperature was 870℃, resulting in a second-pass billet with a thickness of 225 mm, a width of 1480 mm, and a length of 2850 mm. The second-pass billet was then subjected to intermediate online reheating at 940℃ for 1 hour, followed by a third rolling pass, i.e., reversing the second-pass rolling. The deformation rates of the passes in the third rolling pass were 10.7% and 10.4%, with 2 passes, a rolling speed of 3 m / s, and a total deformation rate of 20%. The rolling direction was the same as that of the second rolling pass. The initial rolling temperature was 923℃, and the final rolling temperature was 906℃, resulting in a third-pass billet. This billet was then rapidly water-cooled. The initial temperature was 910℃, and the final temperature was 240℃, with a water-cooling time of 3.5 min, resulting in a TA15 titanium alloy billet with a thickness of 180 mm, a width of 1480 mm, and a length of 3250 mm.

[0049] Step 4: The TA15 titanium alloy billet obtained in Step 3 is flipped using a flipping machine and subjected to heat treatment at 800℃ for 1.5 hours. Then, it is quickly passed through a straightening machine for 4 passes of reciprocating straightening, followed by air cooling to room temperature. The temperature before air cooling was 780℃, resulting in a heat-treated TA15 titanium alloy billet with a thickness of 180mm, a width of 1480mm, and a length of 3250mm.

[0050] Step 5: The heat-treated TA15 titanium alloy billet obtained in Step 4 is subjected to a shaping process at a temperature of 550℃ for 5 hours, followed by air cooling to room temperature to obtain a finished TA15 titanium alloy ultra-thick plate with a thickness of 180mm, a width of 1480mm, and a length of 3300mm. The flatness of the TA15 titanium alloy ultra-thick plate is 3mm / m, and the distance between each corner platform is 3.5mm.

[0051] Figure 3Metallographic image (200×) of the TA15 titanium alloy ultra-thick plate prepared in this embodiment. Figure 3 It can be seen that the TA15 titanium alloy ultra-thick plate has a uniform structure processed through the α+β two-phase region. The original β grains are fully broken, and there are no continuous and straight grain boundary α phases. Moreover, the microstructure morphology at different locations is basically consistent, which meets the microstructure requirements of TA15 titanium alloy plates in GJB 2505A-2018 "Specification for Titanium and Titanium Alloy Plates and Strips for Aviation".

[0052] The properties of the TA15 titanium alloy ultra-thick plates prepared in Examples 1-3 of this invention are shown in Table 1 below.

[0053] Table 1

[0054]

[0055] As shown in Table 1, the transverse, longitudinal, and vertical properties of the TA15 titanium alloy ultra-thick plate prepared by the method of the present invention all meet the requirements of GJB2505A-2018 "Specification for Titanium and Titanium Alloy Plates and Strips for Aviation".

[0056] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A rolling method for large-size TA15 titanium alloy ultra-thick plates, characterized in that, The method includes the following steps: Step 1: The TA15 titanium alloy ingot is subjected to two β single-phase forgings, two α+β two-phase forgings, and forming forging in sequence to obtain TA15 titanium alloy slabs with a thickness of 300mm~360mm, a width of 900mm~1250mm, and a length of 1500mm~2200mm; the TA15 titanium alloy slabs meet the A1 grade technical requirements in GB / T 5193-2020 "Ultrasonic Testing Methods for Titanium and Titanium Alloy Processed Products", and the original β grains of the slab are fully broken and the microstructure is uniform; Step 2: Coat the upper, lower and side surfaces of the TA15 titanium alloy slab obtained in Step 1 with an anti-oxidation coating. Then, heat it using a stepped heating method. The first step is held at 600℃. After holding, the temperature is raised to the second step at 800℃ and held. After holding, the temperature is raised to the third step at 920℃~940℃ and held. Step 3: The heated TA15 titanium alloy slab from Step 2 is rolled in one pass to obtain a TA15 titanium alloy rolled billet. The single-pass rolling process consists of three passes. Specifically, the heated TA15 titanium alloy slab is first subjected to a first pass (reversal rolling), with a pass deformation rate of 5%–10%, 2–3 passes, and a rolling speed of 3–4 m / s, resulting in a first-pass slab with a thickness of 250–304 mm, a width of 1500–2200 mm, and a length of 1080–1480 mm. Then, the first-pass slab is subjected to intermediate online reheating at 920–940 °C, followed by two more passes of reversal rolling. In the second pass (reversal rolling), the pass deformation rate is 8%–15%, 3–4 passes, and a rolling speed of 2 m / s. The rolling speed is ~3m / s to obtain a second-pass billet with a thickness of 140mm~225mm, a width of 1080mm~1480mm, and a length of 2450mm~2850mm. The second-pass billet is then subjected to intermediate online reheating at 920℃~940℃, and the third-pass rolling process, i.e., reversing the second-pass rolling process, is carried out. The pass deformation rate of the third-pass rolling process is 10%~16%, the number of passes is 2, the rolling speed is 3m / s~4m / s, and the rolling direction is the same as that of the second-pass rolling process, to obtain a third-pass billet. Then, it is quickly water-cooled to obtain a TA15 titanium alloy billet with a thickness of 100mm~180mm, a width of 1080mm~1480mm, and a length of 3200mm~3300mm. Step 4: The TA15 titanium alloy billet obtained in Step 3 is flipped using a flipping machine and subjected to finished product heat treatment. Then, it is quickly passed through a straightening machine for 2-4 passes of reciprocating straightening, followed by air cooling to room temperature to obtain the heat-treated TA15 titanium alloy billet. Step 5: The heat-treated TA15 titanium alloy billet obtained in Step 4 is shaped to obtain a finished TA15 titanium alloy ultra-thick plate with a thickness of 100mm~180mm, a width of 1080mm~1480mm, and a length of 3200mm~3300mm. The flatness of the TA15 titanium alloy ultra-thick plate is less than 4mm / m, and the distance between each corner platform is not greater than 5mm.

2. The rolling method for large-size TA15 titanium alloy ultra-thick plates according to claim 1, characterized in that, In step one, the forging temperature for the two β single-phase forgings is 1050℃~1150℃, the forging ratio is 7.0~10.0, the initial forging temperature is not lower than 1000℃, the final forging temperature is not lower than 850℃, and the forging is air-cooled to room temperature after forging; the forging temperature for the two α+β two-phase forgings is 920℃~960℃, the forging ratio is 4.0~7.0, the initial forging temperature is not lower than 850℃, the final forging temperature is not lower than 700℃, and the forging is air-cooled to room temperature after forging; the forging temperature for the forming forging is 920℃~940℃, the initial forging temperature is not lower than 850℃, the final forging temperature is not lower than 700℃, and the forging is air-cooled to room temperature after forging.

3. The rolling method for large-size TA15 titanium alloy ultra-thick plates according to claim 1, characterized in that, The specific process of heating using the stepped heating method described in step two is as follows: the first step is held at 600℃ for 1.5h~2h, after which the temperature is increased with the furnace at 4℃ / min to the second step at 800℃ and held for 2h~2.5h, after which the temperature is increased with the furnace at 3℃ / min to the third step at 920℃~940℃ and held for 3h~4h.

4. The rolling method for large-size TA15 titanium alloy ultra-thick plates according to claim 1, characterized in that, In step three, the initial rolling temperature of the first rolling pass is not lower than 900℃, the final rolling temperature is not lower than 780℃, and the total deformation rate is 16%. The billet in the first rolling pass is reheated in the furnace online for 1.5h to 2h. The total deformation rate of the reversing rolling of the two rolling passes is 40% to 60%, and the initial rolling temperature of the second rolling pass is not lower than 900℃, the final rolling temperature is not lower than 820℃, and the billet in the second rolling pass is reheated in the furnace online for 1h to 1.5h. The initial rolling temperature of the third rolling pass is not lower than 900℃, the final rolling temperature is not lower than 850℃, and the total deformation rate is 20% to 30%. The temperature of the billet in the third rolling pass before water cooling treatment is not lower than 850℃, the temperature after water cooling treatment is not higher than 250℃, and the water cooling time does not exceed 4min.

5. The rolling method for large-size TA15 titanium alloy ultra-thick plates according to claim 1, characterized in that, The temperature of the finished product heat treatment in step four is 750℃~800℃, and the holding time is 1.5h~2.5h. The temperature of the TA15 titanium alloy billet after reciprocating straightening before air cooling is not lower than 720℃.

6. The rolling method for large-size TA15 titanium alloy ultra-thick plates according to claim 1, characterized in that, The temperature for the shaping process described in step five is 520℃~550℃, the holding time is 5h~7h, and the temperature is cooled to room temperature by air after the shaping process.

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