Titanium alloy small-size fine-grain rod preparation method and tc11 titanium alloy fine-grain rod

Abstract

The application provides a titanium alloy small-size fine-grain rod preparation method, which comprises the following steps of high-temperature homogenization treatment, low-temperature large-deformation rolling and annealing treatment of titanium alloy rod blanks with equiaxed structure and a diameter of less than 350 mm in sequence. The application also provides a TC11 fine-grain rod obtained by the method, which has fine and uniform equiaxed structure, and the size of primary alpha phase is 3-7 microns. The application eliminates the problem of large difference between the horizontal and vertical structures of titanium alloy rods in the traditional process, and finally obtains fine and uniform equiaxed structure titanium alloy material. The tensile strength at room temperature, the yield strength at room temperature, the tensile strength at 500 DEG C, the thermal stability strength at 500 DEG C x 100 h of the TC11 fine-grain rod prepared by the application are slightly improved compared with those of the traditional process, the elongation at 500 DEG C is improved by 31%, and the reduction of area is improved by 8.7%.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy material processing technology. Background Technology

[0002] Titanium alloys are widely used in aero-engine components such as blades, discs, drums, and casings due to their excellent comprehensive properties. With the continuous development of aerospace technology, higher requirements are being placed on the strength, plasticity, and fatigue performance of the raw materials used to manufacture aero-engine blades. Relevant research at home and abroad has shown that fine-grain strengthening can effectively refine the microstructure of titanium alloys (such as TC11), thereby improving the strength, plasticity, and fatigue performance of the blades.

[0003] Traditional titanium alloy bars, taking the commonly used TC11 bar as an example, are often processed using a "forging + radial forging / rolling" method. Due to the unique characteristic of unidirectional deformation in the radial forging / rolling process, such as... Figure 1 As shown, there are significant differences in the transverse and longitudinal microstructures of small-sized TC11 titanium alloy bars produced domestically and internationally. The transverse microstructure is equiaxed, while the longitudinal microstructure is an elongated strip α, with a relatively large initial α size (approximately 15–30 μm).

[0004] It can be seen that the difference in transverse and longitudinal microstructure between existing conventional diameter forged / rolled titanium alloy bars is large and difficult to eliminate through heat treatment. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing small-sized fine-grained titanium alloy bars with fine and uniform equiaxed structures by first obtaining fine lamellar α-structure through high-temperature homogenization treatment; then eliminating the difference in transverse and longitudinal structure of the billet through low-temperature large deformation rolling; and finally further homogenizing the fine-grained structure through heat treatment to completely eliminate the difference in transverse and longitudinal structure of the billet.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for preparing small-sized fine-grained titanium alloy rods, comprising the following steps:

[0007] Step 1: High-temperature homogenization treatment:

[0008] At a temperature of 10°C to 40°C above the β transformation temperature, a titanium alloy billet with an equiaxed structure and a diameter of less than 350 mm is subjected to a high-temperature homogenization heat treatment for 60 min to 280 min. After the treatment, it is cooled to room temperature by water to obtain a titanium alloy billet with a fine lamellar α structure.

[0009] Step 2: Low-temperature large deformation rolling:

[0010] Under heating conditions of 50°C to 200°C below the β transformation temperature, titanium alloy rods with fine lamellar α-structure are subjected to 2 to 4 large deformation rolling passes, each pass consisting of 5 to 15 passes, at a rolling speed of 1.0 to 3 m / s, with a pass elongation coefficient of 1.1 to 1.8, and a final rolling temperature of not less than 650°C. After rolling, the rods are air-cooled to room temperature. This process is used to allow the lamellar α-structure to fully recover and recrystallize, resulting in fine-grained titanium alloy rods with eliminated transverse and longitudinal microstructure differences.

[0011] Furthermore, it also includes step three, annealing:

[0012] The titanium alloy fine-grained rods are subjected to single or double annealing below the β transformation temperature. The first annealing temperature is 30°C to 300°C below the β transformation temperature, and the holding time is 0.5h to 9h. After annealing, the rods are air-cooled to room temperature. In double annealing, the second annealing temperature is not lower than 500°C, and the holding time is 0.5h to 9h. After annealing, the rods are air-cooled to room temperature. This process is used to further homogenize the fine-grained structure and is intended to address the issue of insufficient driving force and incomplete recrystallization in a small number of titanium alloy fine-grained rods with a fine and uniform equiaxed structure.

[0013] Furthermore, the method for preparing the titanium alloy billet with equiaxed structure includes the following steps:

[0014] Step 1) High-temperature blanking:

[0015] Titanium alloy ingots prepared by traditional processes are subjected to high-temperature large deformation forging in 2 to 4 passes at a forging heating temperature of 20°C to 250°C above the β transformation temperature. The forging heating temperature is decreased with each pass, and the ingots are air-cooled to room temperature after forging. This process is used to fully break up the as-cast grains and improve the plasticity of the casting structure.

[0016] Step 2), Low-temperature forging:

[0017] Under the forging temperature conditions of 20℃ to 80℃ below the β transformation temperature, the forging is carried out alternately 2 to 4 times, followed by air cooling to room temperature; this is used to complete the spheroidization process of the primary α phase and obtain a uniform equiaxed structure.

[0018] Step 3) Low-temperature molding:

[0019] Under the forming and forging temperature conditions of 20℃ to 80℃ below the β transformation temperature, the billet is sequentially drawn and rounded, and then air-cooled to room temperature to obtain a billet with a diameter of less than 350mm. This is to avoid insufficient cooling of the core of the material due to excessive billet size, which would affect the uniformity of the microstructure.

[0020] Furthermore, in step 1), the deformation amount in a single forging during high-temperature billet forging is 20% to 80%, the total deformation amount is 80% to 95%, and the final forging temperature is not lower than 750°C.

[0021] Furthermore, in step 2), the deformation amount of a single forging at low temperature is 20% to 80%, the total deformation amount is controlled at 80% to 95%, and the final forging temperature is not lower than 750°C.

[0022] Furthermore, in step 3), the deformation amount of a single forging is 20% to 80%, the total deformation is controlled at 70% to 90%, and the final forging temperature is not lower than 750°C.

[0023] Furthermore, during the high-temperature homogenization heat treatment described in step one, the furnace temperature uniformity is controlled to be ±5℃, and the temperature is increased along with the furnace.

[0024] Furthermore, step two specifically involves subjecting a titanium alloy billet with a fine lamellar α structure to 1-3 passes of large deformation rolling under the heating temperature conditions, controlling the dynamic recrystallization during rolling and the static recrystallization during heating to achieve a length-to-short axis ratio of 15-30 for the lamellar α structure; then, under the parameter control of the rolling heating temperature and rolling deformation, a final pass of rolling is performed to directly achieve the recovery recrystallization of the elongated lamellar α structure, resulting in a fine-grained titanium alloy billet with eliminated transverse and longitudinal microstructure differences.

[0025] Furthermore, the titanium alloy billet is a TC11 or TA11 or TC4 or TC6 or TC8 or TC8-1 or TC8M or TC8M-1 or TA15 billet.

[0026] The present invention also provides a titanium alloy fine-grained rod obtained by the method described above, wherein the titanium alloy is TC11, and the obtained is a TC11 titanium alloy fine-grained rod. The transverse and longitudinal microstructure of the TC11 titanium alloy fine-grained rod is an equiaxed structure processed in the (α+β) region. The equiaxed structure is fine and uniform, and the size of the primary α phase is 3-7 μm.

[0027] The beneficial effects of this invention are as follows: Compared with the traditional "forging + radial forging / rolling" process for small-sized TC11 bars, this invention, for bar blanks with traditional equiaxed structures, eliminates the problem of large differences in transverse and longitudinal structures in the traditional process of TC11 small-sized bars through the process of "high-temperature homogenization treatment" + "low-temperature large deformation rolling" + "annealing treatment"; the size of the primary α phase is reduced from 15μm~30μm to 3μm~7μm, resulting in a fine and uniform equiaxed structure.

[0028] The room temperature tensile strength, room temperature yield strength, 500℃ tensile strength, and 500℃×100h thermal stability strength of the TC11 small-sized fine-grained rods prepared by the present invention are slightly improved compared with those of the traditional process. The elongation at 500℃ is increased by 31%, and the reduction of area is increased by 8.7%. Attached Figure Description

[0029] Figure 1 Microstructure of traditional TC11 titanium alloy bar after double annealing;

[0030] Figure 2 Flowchart of the TC11 titanium alloy fine-grained rod preparation process;

[0031] Figure 3 Schematic diagram of sampling at the head, middle, and tail of the titanium alloy rod;

[0032] Figure 4 : Microstructure of a 2TC11 titanium alloy rod after standard double annealing treatment, as a specific example of the present invention;

[0033] Figure 5 : Microstructure of a 3TC11 titanium alloy rod after standard double annealing treatment, as a specific example of the present invention;

[0034] Figure 6 Specific example of the present invention: Grain morphology and size of 2TC11 titanium alloy rod. Detailed Implementation

[0035] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0036] To achieve the above objectives, the present invention provides the following specific embodiments:

[0037] Example 1: A method for preparing small-sized fine-grained titanium alloy rods, comprising the following steps:

[0038] Step 1: High-temperature homogenization treatment:

[0039] At a temperature of 10°C to 40°C above the β transformation temperature, a titanium alloy billet with an equiaxed structure and a diameter of less than 350 mm is subjected to a high-temperature homogenization heat treatment for 60 min to 280 min. After the treatment, it is cooled to room temperature by water to obtain a titanium alloy billet with a fine lamellar α structure.

[0040] During the high-temperature homogenization heat treatment, the furnace temperature uniformity is controlled at ±5℃, and the temperature is increased along with the furnace.

[0041] Step 2: Low-temperature large deformation rolling:

[0042] Under heating conditions of 50°C to 200°C below the β transformation temperature, titanium alloy rods with fine lamellar α-structure are subjected to 2 to 4 large deformation rolling passes, each pass consisting of 5 to 15 passes, at a rolling speed of 1.0 to 3 m / s, with a pass elongation coefficient of 1.1 to 1.8, and a final rolling temperature of not less than 650°C. After rolling, the rods are air-cooled to room temperature. This process is used to allow the lamellar α-structure to fully recover and recrystallize, resulting in fine-grained titanium alloy rods with eliminated transverse and longitudinal microstructure differences.

[0043] Step 3, Annealing:

[0044] Titanium alloy fine-grained rods are subjected to single or double annealing below the β transformation temperature. The first annealing temperature for single or double annealing is 30℃ to 300℃ below the β transformation temperature, and the holding time is 0.5h to 9h. After annealing, the rods are air-cooled to room temperature. For double annealing, the second annealing temperature is not lower than 500℃, and the holding time is 0.5h to 9h. After annealing, the rods are air-cooled to room temperature. This process is used to further homogenize the fine-grained structure and is intended to address small quantities of titanium alloy fine-grained rods with fine, uniform equiaxed structures due to insufficient driving force or incomplete recrystallization.

[0045] The titanium alloy billet is TC11 or TA11 or TC4 or TC6 or TC8 or TC8-1 or TC8M or TC8M-1 or TA15 billet.

[0046] Example 2: Same as Example 1, except that it also includes a method for preparing a titanium alloy billet with an equiaxed structure, specifically:

[0047] Step 1) High-temperature blanking:

[0048] Titanium alloy ingots prepared by traditional processes are subjected to high-temperature large deformation forging in 2 to 4 passes at a forging heating temperature of 20°C to 250°C above the β transformation temperature. The forging heating temperature is decreased with each pass, and the ingots are air-cooled to room temperature after forging. This process is used to fully break up the as-cast grains and improve the plasticity of the casting structure.

[0049] In the high-temperature forging process, the deformation per forging pass is 20% to 80%, the total deformation is 80% to 95%, and the final forging temperature is not lower than 750°C.

[0050] Step 2), Low-temperature forging:

[0051] Under the forging temperature conditions of 20℃ to 80℃ below the β transformation temperature, the forging is carried out alternately 2 to 4 times, followed by air cooling to room temperature; this is used to complete the spheroidization process of the primary α phase and obtain a uniform equiaxed structure.

[0052] The deformation amount of a single forging at low temperature is 20% to 80%, the total deformation is controlled at 80% to 95%, and the final forging temperature is not lower than 750°C.

[0053] Step 3) Low-temperature molding:

[0054] Under the forming and forging temperature conditions of 20℃ to 80℃ below the β transformation temperature, the billet is drawn and rounded in sequence, and then air-cooled to room temperature after forging to obtain a billet with a diameter of less than 350mm. This is to avoid insufficient cooling of the core of the material due to excessive billet size, which would affect the uniformity of the microstructure.

[0055] The deformation amount of a single forging is 20% to 80%, the total deformation is controlled at 70% to 90%, and the final forging temperature is not lower than 750°C.

[0056] Example 3: Same as Example 1, except that step two is as follows:

[0057] Under the heating temperature conditions, titanium alloy billets with fine lamellar α-structure are subjected to 1 to 3 large deformation rolling passes, and the dynamic recrystallization during the rolling process and the static recrystallization during the heating process are controlled to make the length-to-short axis ratio of the lamellar α-structure reach 15 to 30. Then, under the parameter control of the rolling heating temperature and rolling deformation, a final rolling pass is performed to directly achieve the recovery recrystallization of the elongated lamellar α-structure, resulting in a fine-grained titanium alloy billet with eliminated transverse and longitudinal microstructure differences.

[0058] Example 4: Same as Example 1, except that the titanium alloy billet is a TC11 billet. The preparation method of the TC11 small-diameter fine-grained rod is as follows:

[0059] Step 1: High-temperature blanking:

[0060] The TC11 titanium alloy ingot is subjected to 2 to 3 high-temperature large deformation forging at a forging heating temperature of 30℃ to 150℃ above the β transformation temperature. The deformation amount of a single forging is 30% to 80%, the total deformation amount is 85% to 95%, the final forging temperature is not lower than 850℃, and the forging is air-cooled to room temperature.

[0061] Step 2, Low-Temperature Forging:

[0062] After high-temperature forging, the TC11 titanium alloy ingot is subjected to 3 to 4 alternating upsetting and drawing processes at a reforging temperature of 30°C to 60°C below the β transformation temperature. The deformation amount per process is 30% to 80%, the total deformation amount is controlled at 85% to 95%, the final forging temperature is not lower than 850°C, and the ingot is air-cooled to room temperature after forging.

[0063] Step 3: Low-temperature molding:

[0064] The TC11 titanium alloy ingot after low-temperature forging is drawn and rounded sequentially under a forming forging temperature of 30℃~60℃ below the β transformation temperature. The deformation amount per forging is 20%~80%, the total deformation amount is 70%~90%, the final forging temperature is not lower than 850℃, and it is air-cooled to room temperature after forging.

[0065] Step 4: High-temperature homogenization treatment:

[0066] After low-temperature forming, the TC11 titanium alloy ingot is subjected to high-temperature homogenization heat treatment at a temperature of 10℃ to 40℃ above the β transformation temperature. The furnace temperature uniformity is controlled to be ±5℃. The furnace temperature is increased, and the ingot is water-cooled after heat treatment to obtain a TC11 titanium alloy rod with fine lamellar α structure.

[0067] Step 5: Low-temperature large deformation rolling:

[0068] Under heating conditions of 50℃ to 110℃ below the β transformation temperature, large deformation rolling is performed in 2 to 3 passes, with 5 to 15 passes per pass, a rolling speed of 1.0 to 2.5 m / s, a pass elongation coefficient of 1.1 to 1.5, and a final rolling temperature of not less than 650℃. After rolling, the material is air-cooled to room temperature to obtain TC11 titanium alloy fine-grained rods.

[0069] Step Six: Annealing Treatment

[0070] The obtained TC11 titanium alloy fine-grained rod was first held at 950℃±10℃ for 1 hour, and then air-cooled to room temperature; then held at 530℃±10℃ for 6 hours, and then air-cooled to room temperature, thus obtaining a TC11 titanium alloy fine-grained rod with a fine and uniform equiaxed structure.

[0071] Example 5: The present invention also provides a titanium alloy fine-grained rod obtained by the method described above. The titanium alloy is TC11, and the obtained is a TC11 titanium alloy fine-grained rod. The transverse and longitudinal microstructure of the TC11 titanium alloy fine-grained rod is an equiaxed structure processed in the (α+β) region. The equiaxed structure is fine and uniform, and the size of the primary α phase is 3-7 μm.

[0072] To further illustrate the technical solution and technical effects of the present invention, the following specific examples are provided:

[0073] Specific Example 1: A process flow for preparing TC11 titanium alloy fine-grained rods is as follows: Figure 2 As shown, it includes the following steps:

[0074] (1) Ingot preparation:

[0075] Check that the composition of the ingot meets the requirements of the TC11 titanium alloy composition table, as shown in Table 1. The surface of the ingot is machined to remove surface porosity, contaminants and oxides. The ingot riser and ingot bottom should be completely removed and the end face rounded.

[0076] Table 1

[0077]

[0078] (2) High-temperature billet preparation:

[0079] The ingot is subjected to high-temperature large deformation forging in 2 to 3 passes at 30°C to 150°C above the β transformation temperature. The forging heating temperature is reduced with each pass. The deformation amount per pass is 30% to 80%, and the total deformation amount is 85% to 95%. The final forging temperature is not lower than 850°C. After forging, the ingot is air-cooled to room temperature to fully break up the as-cast grains and improve the plasticity of the casting structure.

[0080] (3) Low-temperature forging:

[0081] Upsetting and drawing are performed alternately at temperatures between 30°C and 60°C below the β transformation temperature for 3 to 4 passes to complete the spheroidization process of the primary α phase and obtain a uniform equiaxed structure. During low-temperature forging, the deformation per pass is controlled at 30% to 80%, the total deformation is controlled at 85% to 95%, the final forging temperature is not lower than 850°C, and the forging is air-cooled to room temperature after forging.

[0082] (4) Low temperature molding:

[0083] The titanium alloy billet is drawn and rounded sequentially at temperatures 30℃ to 60℃ below the β transformation temperature. The deformation amount per forging is 20% to 80%, and the total deformation amount is controlled at 70% to 90%. The final forging temperature is not lower than 850℃. After forging, it is air-cooled to room temperature to obtain a titanium alloy billet with an equiaxed structure.

[0084] (5) High-temperature homogenization treatment:

[0085] Titanium alloy billets with equiaxed structure are subjected to high-temperature homogenization heat treatment at 10℃~40℃ above the β transformation temperature, with furnace temperature uniformity controlled within ±5℃. The temperature is increased with the furnace, and water cooling is used after heat treatment to obtain fine lamellar α structure, which prepares the microstructure for subsequent rolling of fine grains.

[0086] (6) Low-temperature large deformation rolling:

[0087] First, the lamellar α structure is further elongated by low-temperature large deformation, and the dynamic recrystallization during the rolling process and the static recrystallization during the heating process are controlled. The heating temperature is controlled at 50℃~110℃ below the β transformation temperature for 1~2 rolling deformations, so that the length-to-short axis ratio of the lamellar α structure reaches 15~30.

[0088] Next, the heating temperature is controlled at 50℃~110℃ below the β transformation temperature for a final large deformation rolling, with 5~15 rolling passes, rolling speed of 1.0~2.5m / s, pass elongation coefficient of 1.1~1.5, and final rolling temperature not lower than 650℃. After rolling, the material is air-cooled to room temperature, which directly achieves the recovery recrystallization of the elongated lamellar α structure, resulting in a titanium alloy fine-grained rod that eliminates the difference between transverse and longitudinal structures.

[0089] (7) Double annealing treatment:

[0090] First, it is held at 950℃±10℃ for 1 hour, then air-cooled to room temperature; then it is held at 530℃±10℃ for 6 hours, then air-cooled to room temperature. This is used to further homogenize the fine-grained structure, completely eliminate the differences in transverse and longitudinal structure of the titanium alloy rod, and obtain a fine, uniform equiaxed structure.

[0091] (8) Physicochemical testing:

[0092] Samples were cut from the head, middle, and tail of the finished titanium alloy rod for microstructural analysis. A sampling diagram is shown below. Figure 3 As shown.

[0093] Specific example 2: TC11 titanium alloy was used in this case.

[0094] (1) Ingot preparation:

[0095] Check that the composition of the ingot meets the requirements of Table 1. The surface of the ingot is machined to remove surface porosity, contaminants and oxides. The riser and bottom of the ingot should be completely removed and the end face rounded.

[0096] (2) High-temperature billet preparation:

[0097] The ingot is subjected to three high-temperature large deformation forgings at 140℃, 80℃ and 40℃ above the β transformation temperature, with a single forging deformation of 70% to 80% and a total deformation of 93%. The final forging temperature is not lower than 850℃, and the ingot is air-cooled to room temperature after forging.

[0098] (3) Low-temperature forging:

[0099] Four alternating upsetting and drawing processes are carried out at 40°C below the β transformation temperature, with a single upsetting deformation of 60% to 80% and a total deformation controlled at 92%. The final forging temperature is not lower than 850°C, and the forging is then air-cooled to room temperature.

[0100] (4) Low temperature molding:

[0101] The forging process involves drawing and rounding at 40°C below the β transformation temperature, with single-pass deformation of 75% and 23% respectively, and a total deformation of 85%. The final forging temperature is not lower than 850°C, and the forging is then air-cooled to room temperature.

[0102] (5) High-temperature homogenization treatment:

[0103] High-temperature homogenization heat treatment was carried out at 20°C above the β-transformation temperature, with furnace temperature uniformity controlled within ±5°C. The furnace temperature was increased, and the furnace was water-cooled after heat treatment.

[0104] (6) Low-temperature large deformation rolling:

[0105] Two-stage large deformation rolling processes are performed below the β transformation temperature:

[0106] The first rolling pass is 90°C below the β transformation temperature, with 12 rolling passes, a rolling speed of 2.5 m / s, a pass elongation factor of 1.15, and a final rolling temperature of 831°C. After rolling, the material is air-cooled to room temperature.

[0107] The second rolling process is carried out at 100°C below the β transformation temperature, with 8 rolling passes, a rolling speed of 2.5 m / s, a pass elongation factor of 1.15, and a final rolling temperature of 667°C. After rolling, the material is air-cooled to room temperature.

[0108] (7) Double annealing treatment:

[0109] The first annealing process was carried out at 950℃ for 1 hour, followed by air cooling to room temperature.

[0110] The second annealing process was carried out at 530℃ for 6 hours, followed by air cooling to room temperature.

[0111] (8) Physicochemical testing:

[0112] Samples were cut from the head, middle, and tail sections of the finished TC11 titanium alloy rod for microstructural analysis. The microstructure is shown below. Figure 4 As shown in the figure, the transverse and longitudinal microstructure of the finished titanium alloy rod is an equiaxed structure processed in the (α+β) region. The equiaxed structure is fine and uniform, with no elongated α strips in the longitudinal direction. Backscattered electron diffraction (EBSD) was used to detect the grain size of the longitudinal sample, and the grain size and distribution are shown below. Figure 6 As shown in the figure, the average grain size of the primary α phase is about 5 μm.

[0113] Specific example 3: TC11 titanium alloy was used in this case.

[0114] (1) Ingot preparation:

[0115] Check that the composition of the ingot meets the requirements of Table 1. The surface of the ingot is machined to remove surface porosity, contaminants and oxides. The riser and bottom of the ingot should be completely removed and the end face rounded.

[0116] (2) High-temperature billet preparation:

[0117] The ingot is subjected to three high-temperature large deformation forgings at 140℃, 75℃ and 30℃ above the β transformation temperature, with a single forging deformation of 70% to 80% and a total deformation of 93%. The final forging temperature is not lower than 850℃, and the ingot is air-cooled to room temperature after forging.

[0118] (3) Low-temperature forging:

[0119] Three alternating upsetting and drawing processes are carried out at 30°C below the β transformation temperature, with a single upsetting deformation of 60% to 80% and a total deformation controlled at 91.4%. The final forging temperature is not lower than 850°C, and the forging is then air-cooled to room temperature.

[0120] (4) Low temperature molding:

[0121] The forging process involves drawing and rounding at 40°C below the β transformation temperature, with single-pass deformation of 75% and 23% respectively, and a total deformation of 85%. The final forging temperature is not lower than 850°C, and the forging is then air-cooled to room temperature.

[0122] (5) High-temperature homogenization treatment:

[0123] High-temperature homogenization heat treatment was carried out at 15°C above the β-transformation temperature, with furnace temperature uniformity controlled within ±5°C. The furnace temperature was increased, and the furnace was water-cooled after heat treatment.

[0124] (6) Low-temperature large deformation rolling:

[0125] Two-stage large deformation rolling processes are performed below the β transformation temperature:

[0126] The first rolling pass is 90°C below the β transformation temperature, with 12 rolling passes, a rolling speed of 2.5 m / s, a pass elongation factor of 1.15, and a final rolling temperature of 831°C. After rolling, the material is air-cooled to room temperature.

[0127] The second rolling process was carried out at 95°C below the β transformation temperature, with 8 rolling passes, a rolling speed of 2.5 m / s, a pass elongation coefficient of 1.15, and a final rolling temperature of 667°C. After rolling, the material was air-cooled to room temperature.

[0128] (7) Double annealing treatment:

[0129] The first annealing process was carried out at 950℃ for 1 hour, followed by air cooling to room temperature.

[0130] The second annealing process was carried out at 530℃ for 6 hours, followed by air cooling to room temperature.

[0131] (8) Physicochemical testing:

[0132] Samples were cut from the head, middle, and tail sections of the finished TC11 titanium alloy rod for microstructural analysis. The microstructure is shown below. Figure 5As shown in the figure, the transverse and longitudinal microstructure of the finished titanium alloy bar is an equiaxed structure processed in the (α+β) region. The equiaxed structure is fine and uniform, with no elongated strips α in the longitudinal direction.

[0133] Table 2 shows a comparison of the mechanical properties of the TC11 titanium alloy rods after the specific treatment according to the present invention.

[0134] Table 2

[0135]

[0136] The TC11 titanium alloy fine-grained rods prepared by the present invention have slightly improved room temperature tensile strength, room temperature yield strength, 500℃ tensile strength, and 500℃×100h thermal stability strength compared with traditional processes. The elongation at 500℃ is increased by 31%, and the reduction of area is increased by 8.7%.

[0137] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing small-sized fine-grained titanium alloy rods, characterized in that, Includes the following steps: Step 1: High-temperature homogenization treatment: At a temperature of 10℃ to 40℃ above the β transformation temperature, titanium alloy billets with an equiaxed structure and a diameter of less than 350mm are subjected to high-temperature homogenization heat treatment for 60min to 280min. After completion, they are water-cooled to room temperature to obtain titanium alloy billets with fine lamellar α structure. Step 2: Low-temperature large deformation rolling: Under heating conditions of 50°C to 200°C below the β transformation temperature, titanium alloy rods with fine lamellar α-structure are subjected to 2 to 4 large deformation rolling passes, each pass consisting of 5 to 15 passes, with a rolling speed of 1.0 to 3 m / s, a pass elongation coefficient of 1.1 to 1.8, and a final rolling temperature of not less than 650°C. After rolling, the rods are air-cooled to room temperature to allow the lamellar α-structure to fully recover and recrystallize, thereby obtaining a fine-grained titanium alloy rod that eliminates the differences in transverse and longitudinal structures. Step 3, Annealing: The titanium alloy fine-grained rods are subjected to single or double annealing below the β transformation temperature. The first annealing temperature is 30°C to 300°C below the β transformation temperature, and the holding time is 0.5h to 9h. After annealing, the rods are air-cooled to room temperature. In double annealing, the second annealing temperature is not lower than 500°C, and the holding time is 0.5h to 9h. After annealing, the rods are air-cooled to room temperature. This process is used to further homogenize the fine-grained structure and is intended to address the issue of insufficient driving force and incomplete recrystallization in a small number of titanium alloy fine-grained rods with a fine and uniform equiaxed structure.

2. The method for preparing small-sized fine-grained titanium alloy rods as described in claim 1, characterized in that, The method for preparing the titanium alloy billet with equiaxed structure includes the following steps: Step 1) High-temperature blanking: Titanium alloy ingots prepared by traditional processes are subjected to high-temperature large deformation forging in 2 to 4 passes at a forging heating temperature of 20°C to 250°C above the β transformation temperature. The forging heating temperature is decreased with each pass, and the ingots are air-cooled to room temperature after forging. This process is used to fully break up the as-cast grains and improve the plasticity of the casting structure. Step 2), Low-temperature forging: Under the forging temperature conditions of 20℃ to 80℃ below the β transformation temperature, the forging is carried out alternately 2 to 4 times, followed by air cooling to room temperature; this is used to complete the spheroidization process of the primary α phase and obtain a uniform equiaxed structure. Step 3), Low-temperature molding: Under the forming and forging temperature conditions of 20℃ to 80℃ below the β transformation temperature, the billet is sequentially drawn and rounded, and then air-cooled to room temperature to obtain a billet with a diameter of less than 350mm. This is to avoid insufficient cooling of the core of the material due to excessive billet size, which would affect the uniformity of the microstructure.

3. The method for preparing small-sized fine-grained titanium alloy rods as described in claim 2, characterized in that, In step 1), the deformation amount in a single forging process during high-temperature billet opening is 20% to 80%, the total deformation amount is 80% to 95%, and the final forging temperature is not lower than 750℃.

4. The method for preparing small-sized fine-grained titanium alloy rods as described in claim 2, characterized in that, In step 2), the deformation amount of a single forging at low temperature is 20% to 80%, the total deformation amount is controlled at 80% to 95%, and the final forging temperature is not lower than 750℃.

5. The method for preparing small-sized fine-grained titanium alloy rods as described in claim 2, characterized in that, In step 3), the deformation amount of a single forging is 20% to 80%, the total deformation is controlled at 70% to 90%, and the final forging temperature is not lower than 750℃.

6. The method for preparing small-sized fine-grained titanium alloy rods as described in claim 1, characterized in that, During the high-temperature homogenization heat treatment described in step one, the furnace temperature uniformity is controlled to be ±5℃, and the temperature is increased along with the furnace.

7. The method for preparing small-sized fine-grained titanium alloy rods as described in claim 1, characterized in that, Step two specifically involves performing 1 to 3 large deformation rolling processes on a titanium alloy billet with a fine lamellar α structure under the heating temperature conditions, and controlling the dynamic recrystallization during the rolling process and the static recrystallization during the heating process to achieve a major-minor axis ratio of 15 to 30 for the lamellar α structure. Then, under the parameter control of the rolling heating temperature and rolling deformation, a final rolling process is performed to directly achieve the recovery recrystallization of the elongated lamellar α structure, resulting in a fine-grained titanium alloy billet with eliminated transverse and longitudinal microstructure differences.

8. The method for preparing small-sized fine-grained titanium alloy rods according to any one of claims 1-7, characterized in that, The titanium alloy billet is TC11 or TA11 or TC4 or TC6 or TC8 or TC8-1 or TC8M or TC8M-1 or TA15 billet.

9. A fine-grained titanium alloy rod obtained by the method described in claim 8, characterized in that, The titanium alloy is TC11, and the obtained product is a TC11 titanium alloy fine-grained rod. The transverse and longitudinal microstructure of the TC11 titanium alloy fine-grained rod is an equiaxed structure processed in the (α+β) region. The equiaxed structure is fine and uniform, and the size of the primary α phase is 3~7μm.

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