Preparation method of titanium alloy small-specification fine-grain rod and TC11 titanium alloy fine-grain rod

Abstract

The invention provides a preparation method of a titanium alloy small-size fine-grain bar. The preparation method comprises the steps of high-temperature homogenization treatment, low-temperature large-deformation rolling and annealing treatment which are sequentially carried out on a titanium alloy bar blank with an equiaxed structure, wherein the diameter of the titanium alloy bar blank is smaller than 350 mm. The invention also provides the TC11 fine-grain rod obtained by the method, the equiaxed structure of the TC11 fine-grain rod is fine and uniform, and the size of a primary alpha phase is 3-7 microns. According to the method, the problem of large difference between transverse and longitudinal structures of a titanium alloy rod in a traditional process is solved, and the fine and uniform equiaxed structure titanium alloy material is finally obtained. The room-temperature tensile strength, the room-temperature yield strength, the tensile strength at the temperature of 500 DEG C and the thermal stability strength at the temperature of 500 DEG C * 100 h of the TC11 fine-grain bar prepared through the method are slightly improved compared with those of a traditional process, the elongation at the temperature of 500 DEG C is improved by 31%, and the percentage reduction of area is improved by 8.7%.

Description

Technical Field

[0001] The invention relates to the technical field of titanium alloy material processing. Background Art

[0002] Titanium alloys are widely used in aero-engine blades, disks, drums, casings and other parts due to their excellent comprehensive properties. With the continuous development of aviation technology, higher requirements are placed on the strength, plasticity and fatigue properties of raw material bars used to manufacture aero-engine blades. Relevant studies at home and abroad have shown that through fine grain strengthening, the microstructure of titanium alloys (such as TC11) can be effectively refined, and the strength, plasticity and fatigue properties of blades can be improved.

[0003] Traditional titanium alloy rods, such as the commonly used TC11 rod, are often processed by the "forging + radial forging / rolling" method. Due to the special characteristics of the radial forging / rolling process with unidirectional deformation, such as Figure 1 As shown in the figure, there are obvious differences in the transverse and longitudinal structures of the small-size TC11 titanium alloy bars currently produced at home and abroad. The transverse structure is equiaxed, and the longitudinal structure is elongated strips α. The primary α size is large (about 15 to 30 μm).

[0004] It can be seen that the existing ordinary radial forging / rolling titanium alloy bars have large differences in transverse and longitudinal structures, which are difficult to eliminate by heat treatment. Summary of the invention

[0005] The object of the present invention is to avoid the shortcomings of the prior art and provide a method for preparing a titanium alloy small-sized fine-grained rod with a fine and uniform equiaxed structure, which first obtains a fine lamellar α structure through high-temperature homogenization treatment; then eliminates the transverse and longitudinal structure differences of the rod blank through a low-temperature large deformation rolling method; and finally further homogenizes the fine-grained structure through heat treatment, completely eliminating the transverse and longitudinal structure differences of the rod blank, and obtaining a TC11 titanium alloy fine-grained rod obtained by the method.

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

[0007] Step 1: High temperature homogenization treatment:

[0008] Under the temperature condition of 10°C to 40°C above the β transformation temperature, a titanium alloy rod blank with an equiaxed structure and a diameter of less than 350 mm is subjected to a high temperature homogenization heat treatment for 60min to 280min, and then water-cooled to room temperature to obtain a titanium alloy rod with a fine lamellar α structure;

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

[0010] Under the heating temperature condition of 50°C to 200°C below the β transformation temperature, a titanium alloy rod with a fine lamellar α structure is subjected to 2 to 4 rounds of large deformation rolling, with 5 to 15 rolling passes per round, a rolling speed of 1.0 to 3 m / s, a pass elongation coefficient of 1.1 to 1.8, a final rolling temperature of not less than 650°C, and air cooling to room temperature after rolling; the method is used to allow the lamellar α structure to fully recover and recrystallize, thereby obtaining a titanium alloy fine-grained rod with the difference between the transverse and longitudinal structures eliminated.

[0011] Furthermore, the method further comprises step three, annealing treatment:

[0012] The titanium alloy fine crystal rod is subjected to a single annealing or a double annealing treatment below the β transformation temperature. The first annealing heating temperature of the single annealing or the double annealing is 30°C to 300°C below the β transformation temperature, and the heating temperature is kept for 0.5h to 9h, and the rod is air-cooled to room temperature after annealing. The second annealing temperature of the double annealing is not less than 500°C, and the heating time is 0.5h to 9h, and the rod is air-cooled to room temperature after annealing. The method is used to further homogenize the fine crystal structure, so as to obtain a titanium alloy fine crystal rod with a fine and uniform equiaxed structure for a small amount of titanium alloys that are not sufficiently recrystallized due to insufficient driving force.

[0013] Furthermore, the method for preparing the titanium alloy bar blank having an equiaxed structure comprises the following steps:

[0014] Step 1), high temperature blanking:

[0015] The titanium alloy ingot prepared by the conventional process is subjected to 2 to 4 rounds of high-temperature large-deformation forging at a forging heating temperature of 20°C to 250°C above the β-transformation temperature, wherein the forging heating temperature is reduced with each round, and air-cooled to room temperature after forging, so as to fully break the as-cast grains and improve the plasticity of the casting structure;

[0016] Step 2), low temperature forging:

[0017] Under the forging temperature condition of 20°C to 80°C below the β transformation temperature, 2 to 4 times of upsetting and drawing are alternately performed, and air cooling is performed to room temperature after forging 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 forging temperature condition of 20°C to 80°C below the β transformation temperature, drawing and rounding are carried out in sequence, and air cooling is carried out to room temperature after forging to obtain a rod blank with a diameter of less than 350 mm, so as to avoid insufficient cooling of the core of the material due to excessive billet size, which affects the uniformity of the structure.

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

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

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

[0023] Furthermore, during the high temperature homogenization heat treatment described in step 1, the furnace temperature uniformity is controlled to be ±5°C and the temperature is increased along with the furnace.

[0024] Furthermore, the step 2 specifically comprises performing 1 to 3 rounds of large deformation rolling on the titanium alloy bar billet having fine lamellar α structure under the heating temperature conditions, and controlling the dynamic recrystallization during rolling and the static recrystallization during heating, so that the major-minor axis ratio of the lamellar α structure reaches 15 to 30; then, performing the last round of rolling under the control of the rolling heating temperature and rolling deformation parameters, directly realizing the recovery recrystallization of the elongated lamellar α structure, and obtaining a titanium alloy fine-grained rod with the horizontal and vertical structure differences eliminated.

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

[0026] The present invention also provides a titanium alloy fine crystal rod obtained by the method, wherein the titanium alloy is TC11, and the obtained is a TC11 titanium alloy fine crystal rod, the transverse and longitudinal microstructures of the TC11 titanium alloy fine crystal rod are equiaxed structures processed in the (α+β) zone, the equiaxed structures are fine and uniform, and the size of the primary α phase is 3 to 7 μm.

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

[0028] The room temperature tensile strength, room temperature yield strength, 500°C tensile strength and 500°C×100h thermal stability strength of the TC11 small-size fine-grained rod prepared by the present invention are slightly improved compared with the traditional process, the elongation at 500°C is increased by 31%, and the cross-sectional shrinkage is increased by 8.7%. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 : Microstructure of conventional TC11 titanium alloy rod after double annealing;

[0030] Figure 2 :TC11 titanium alloy fine crystal rod preparation process flow chart;

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

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

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

[0034] Figure 6 : Grain morphology and size of TC11 titanium alloy rod in specific example 2 of the present invention. DETAILED DESCRIPTION

[0035] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0036] In order to achieve the above object, the present invention provides the following specific implementation methods:

[0037] Embodiment 1: A method for preparing a small-sized fine-grained titanium alloy rod comprises the following steps:

[0038] Step 1: High temperature homogenization treatment:

[0039] Under the temperature condition of 10°C to 40°C above the β transformation temperature, a titanium alloy rod blank with an equiaxed structure and a diameter of less than 350 mm is subjected to a high temperature homogenization heat treatment for 60min to 280min, and then water-cooled to room temperature to obtain a titanium alloy rod with a fine lamellar α structure;

[0040] During high temperature homogenization heat treatment, the furnace temperature uniformity is controlled to be ±5°C and the temperature rises with the furnace.

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

[0042] Under the heating temperature condition of 50°C to 200°C below the β transformation temperature, a titanium alloy rod with a fine lamellar α structure is subjected to 2 to 4 rounds of large deformation rolling, with 5 to 15 rolling passes per round, a rolling speed of 1.0 to 3 m / s, a pass elongation coefficient of 1.1 to 1.8, a final rolling temperature of not less than 650°C, and air cooling to room temperature after rolling; the method is used to allow the lamellar α structure to fully recover and recrystallize, thereby obtaining a titanium alloy fine-grained rod with the difference between the transverse and longitudinal structures eliminated.

[0043] Step 3: Annealing:

[0044] The titanium alloy fine crystal rod is subjected to a single annealing or double annealing treatment below the β transformation temperature. The first annealing heating temperature of the single annealing or double annealing is 30°C to 300°C below the β transformation temperature, and the temperature is kept for 0.5h to 9h. After annealing, it is air-cooled to room temperature; in the case of double annealing, the second annealing temperature is not less than 500°C, the temperature is kept for 0.5h to 9h, and the temperature is air-cooled to room temperature after annealing; it is used to further homogenize the fine crystal structure, and to obtain a titanium alloy fine crystal rod with a fine and uniform equiaxed structure for a small amount of titanium alloy fine crystal rods due to insufficient driving force and insufficient recrystallization;

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

[0046] Example 2: The same as Example 1, except that it also includes a method for preparing a titanium alloy bar blank having an equiaxed structure, specifically:

[0047] Step 1), high temperature blanking:

[0048] The titanium alloy ingot prepared by the conventional process is subjected to 2 to 4 rounds of high-temperature large-deformation forging at a forging heating temperature of 20°C to 250°C above the β-transformation temperature, wherein the forging heating temperature is reduced with each round, and air-cooled to room temperature after forging, so as to fully break the as-cast grains and improve the plasticity of the casting structure;

[0049] The deformation amount of a single fire in the high-temperature forging is 20% to 80%, the total deformation amount is 80% to 95%, and the final forging temperature is not less than 750°C.

[0050] Step 2), low temperature forging:

[0051] Under the forging temperature condition of 20°C to 80°C below the β transformation temperature, 2 to 4 times of upsetting and drawing are alternately performed, and air cooling is performed to room temperature after forging to complete the spheroidization process of the primary α phase and obtain a uniform equiaxed structure;

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

[0053] Step 3), low temperature molding:

[0054] Under the forming forging temperature condition of 20°C to 80°C below the β transformation temperature, drawing and rounding are performed in sequence, and air cooling is performed to room temperature after forging to obtain a rod blank with a diameter of less than 350 mm, so as to avoid insufficient cooling of the core of the material due to excessive billet size, which affects the uniformity of the structure;

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

[0056] Embodiment 3: Same as Embodiment 1, except that step 2 is specifically:

[0057] Under the heating temperature conditions, the titanium alloy bar billet with fine lamellar α structure is subjected to 1 to 3 rounds of large deformation rolling, and the dynamic recrystallization during rolling and the static recrystallization during heating are controlled so that the major-minor axis ratio of the lamellar α structure reaches 15 to 30; then, the last round of rolling is carried out under the control of the rolling heating temperature and rolling deformation parameters to directly realize the recovery recrystallization of the elongated lamellar α structure, so as to obtain a titanium alloy fine-grained rod with the difference between the transverse and longitudinal structures eliminated.

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

[0059] Step 1: High temperature blanking:

[0060] The TC11 titanium alloy ingot is subjected to 2-3 rounds of high temperature large deformation forging at a forging heating temperature of 30°C to 150°C above the β transformation temperature, with a single-round deformation of 30% to 80%, a total deformation of 85% to 95%, a final forging temperature of not less than 850°C, and air cooling to room temperature after forging;

[0061] Step 2: Low temperature forging:

[0062] The TC11 titanium alloy ingot after high-temperature blanking is subjected to 3-4 fire upsetting and drawing alternately at a forging temperature of 30°C to 60°C below the β transformation temperature, with a deformation amount of 30% to 80% in a single fire, and a total deformation amount controlled at 85% to 95%, a final forging temperature of not less than 850°C, and air cooling to room temperature after forging;

[0063] Step 3: Low temperature molding:

[0064] The TC11 titanium alloy ingot after low temperature forging is sequentially stretched and rounded under the forming forging temperature condition of 30°C to 60°C below the β transformation temperature, the deformation amount of a single fire is 20% to 80%, the total deformation amount is 70% to 90%, the final forging temperature is not less than 850°C, and air-cooled to room temperature after forging;

[0065] Step 4: High temperature homogenization treatment:

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

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

[0068] Under the heating temperature condition of 50°C to 110°C below the β transformation temperature, 2 to 3 rounds of large deformation rolling are carried out, with 5 to 15 passes in each round, a rolling speed of 1.0 to 2.5 m / s, a pass elongation coefficient of 1.1 to 1.5, a final rolling temperature of not less than 650°C, and air cooling to room temperature after rolling to obtain a TC11 titanium alloy fine grain rod.

[0069] Step 6: Annealing treatment:

[0070] The obtained TC11 titanium alloy fine crystal rod is first kept at a temperature of 950℃±10℃ for 1h, and then air-cooled to room temperature; then kept at a temperature of 530℃±10℃ for 6h, and then air-cooled to room temperature, to obtain a TC11 titanium alloy fine crystal rod with a fine and uniform equiaxed structure.

[0071] Example 5: The present invention also provides a titanium alloy fine crystal rod obtained by the method, wherein the titanium alloy is TC11, and the obtained is a TC11 titanium alloy fine crystal rod. The transverse and longitudinal microstructures of the TC11 titanium alloy fine crystal rod are equiaxed structures processed in the (α+β) zone, the equiaxed structures are fine and uniform, and the size of the primary α phase is 3 to 7 μm.

[0072] In order to further illustrate the technical scheme and technical effects of the present invention, the following specific examples are provided:

[0073] Specific example 1: A TC11 titanium alloy fine crystal rod preparation process flow Figure 2 As shown, the following steps are included:

[0074] (1) Ingot preparation:

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

[0076] Table 1

[0077]

[0078] (2) High temperature blanking:

[0079] The ingot is subjected to high-temperature large deformation forging for 2 to 3 times at 30°C to 150°C above the β transformation temperature. The forging heating temperature is reduced with each fire. The deformation amount of a single fire is 30% to 80%, the total deformation amount is 85% to 95%, the final forging temperature is not less than 850°C, and the ingot is air-cooled to room temperature after forging to fully break up the cast grains and improve the plasticity of the casting structure.

[0080] (3) Low temperature forging:

[0081] Perform 3-4 times of upsetting and drawing alternately at 30℃~60℃ below the β transformation temperature to complete the spheroidization process of the primary α phase and obtain a uniform equiaxed structure. During low-temperature forging, the deformation of each fire is controlled to be 30-80%, the total deformation is controlled to be 85%-95%, the final forging temperature is not less than 850℃, and air cooling is performed to room temperature after forging.

[0082] (4) Low temperature molding:

[0083] The drawing and rounding are carried out in sequence at 30℃~60℃ below the β transformation temperature, the deformation amount of single fire is 20%~80%, the total deformation amount is controlled at 70%~90%, the final forging temperature is not less than 850℃, and the titanium alloy rod blank with equiaxed structure is obtained after forging.

[0084] (5) High temperature homogenization treatment:

[0085] The titanium alloy billet with equiaxed structure is subjected to high-temperature homogenization heat treatment at 10℃~40℃ above the β transformation temperature, and the furnace temperature uniformity is controlled to be ±5℃. As the furnace temperature rises, water cooling is adopted after heat treatment to obtain fine lamellar α structure, which is well prepared for the subsequent rolling fine grain.

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

[0087] Firstly, the lamellar α structure is further elongated by low temperature large deformation, and the dynamic recrystallization during rolling and the static recrystallization during heating are controlled. The heating temperature is controlled at 50℃~110℃ below the β transformation temperature for 1~2 rounds of rolling deformation, so that the aspect ratio of the lamellar α structure reaches 15~30;

[0088] Then, the heating temperature is controlled to be 50°C to 110°C below the β transformation temperature for the last large deformation rolling, with 5 to 15 rolling passes, a rolling speed of 1.0 to 2.5 m / s, a pass elongation coefficient of 1.1 to 1.5, a final rolling temperature of not less than 650°C, and air cooling to room temperature after rolling to directly achieve the recovery recrystallization of the elongated lamellar α structure, thereby obtaining a titanium alloy fine-grained rod with the horizontal and vertical structure differences eliminated.

[0089] (7) Double annealing treatment:

[0090] First, keep the temperature at 950℃±10℃ for 1h, then air cool to room temperature; then keep the temperature at 530℃±10℃ for 6h, then air cool to room temperature. It is used to further homogenize the fine grain structure, completely eliminate the difference between the horizontal and vertical structures of the titanium alloy rod, and obtain a fine and uniform equiaxed structure.

[0091] (8) Physical and chemical testing:

[0092] Samples were cut from the head, middle and tail of the finished titanium alloy rod for microstructure testing. Figure 3 shown.

[0093] Specific example 2: TC11 titanium alloy is used this time.

[0094] (1) Ingot preparation:

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

[0096] (2) High temperature blanking:

[0097] The ingot is subjected to three rounds of high temperature large deformation forging at 140°C, 80°C and 40°C above the β transformation temperature in sequence. The deformation of each round is 70% to 80%, the total deformation is 93%, the final forging temperature is not less than 850°C, and it is air-cooled to room temperature after forging.

[0098] (3) Low temperature forging:

[0099] Four times of upsetting and drawing are performed alternately at 40°C below the β transformation temperature. The deformation of a single fire is 60% to 80%, the total deformation is controlled at 92%, the final forging temperature is not lower than 850°C, and the steel is air-cooled to room temperature after forging.

[0100] (4) Low temperature molding:

[0101] The steel is stretched and tumbled in sequence at 40℃ below the β transformation temperature. The deformation amounts of each fire are 75% and 23% respectively, and the total deformation amount is 85%. The final forging temperature is not less than 850℃, and the steel is air-cooled to room temperature after forging.

[0102] (5) High temperature homogenization treatment:

[0103] Carry out high temperature homogenization heat treatment at 20℃ above the β transformation temperature, control the furnace temperature uniformity to ±5℃, heat up with the furnace, and water cool after heat treatment.

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

[0105] Two heats of large deformation rolling are carried out below the β transformation temperature:

[0106] The first rolling was carried out at 90°C below the β transformation temperature, with 12 rolling passes, a rolling speed of 2.5 m / s, a pass elongation coefficient of 1.15, a final rolling temperature of 831°C, and air cooling to room temperature after rolling.

[0107] The second rolling was 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 coefficient of 1.15, a final rolling temperature of 667°C, and air cooling to room temperature after rolling.

[0108] (7) Double annealing treatment:

[0109] The first annealing treatment was carried out at 950°C for 1 h and then air-cooled to room temperature.

[0110] The second annealing treatment was carried out at 530°C for 6 h and then air-cooled to room temperature.

[0111] (8) Physical and chemical testing:

[0112] Samples were cut from the head, middle and tail of the finished TC11 titanium alloy rod for microstructure testing. Figure 4 As shown in the figure, the transverse and longitudinal microstructures of the finished titanium alloy rod are equiaxed structures processed in the (α+β) zone. The equiaxed structures are fine and uniform, and there are no elongated strips α in the longitudinal direction. The grain size of the longitudinal sample was detected using the electron backscatter diffraction technique (EBSD). The grain size and distribution are shown in Figure 6 As shown, the average grain size of the primary α phase is about 5μm.

[0113] Specific example 3: TC11 titanium alloy is used this time.

[0114] (1) Ingot preparation:

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

[0116] (2) High temperature blanking:

[0117] The ingot is subjected to three rounds of high temperature large deformation forging at 140°C, 75°C and 30°C above the β transformation temperature in sequence. The deformation of each round is 70% to 80%, the total deformation is 93%, the final forging temperature is not less than 850°C, and it is air-cooled to room temperature after forging.

[0118] (3) Low temperature forging:

[0119] The steel is subjected to three alternate upsetting and drawing processes at 30°C below the β transformation temperature. The deformation of each fire is 60% to 80%, the total deformation is controlled at 91.4%, the final forging temperature is not less than 850°C, and the steel is air-cooled to room temperature after forging.

[0120] (4) Low temperature molding:

[0121] The steel is stretched and tumbled in sequence at 40℃ below the β transformation temperature. The deformation amounts of each fire are 75% and 23% respectively, and the total deformation amount is 85%. The final forging temperature is not less than 850℃, and the steel is air-cooled to room temperature after forging.

[0122] (5) High temperature homogenization treatment:

[0123] High temperature homogenization heat treatment is carried out at 15℃ above the β transformation temperature, and the furnace temperature uniformity is controlled to be ±5℃. The temperature rises with the furnace and water-cooling is performed after heat treatment.

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

[0125] Two heats of large deformation rolling are carried out below the β transformation temperature:

[0126] The first rolling was carried out at 90°C below the β transformation temperature, with 12 rolling passes, a rolling speed of 2.5 m / s, a pass elongation coefficient of 1.15, a final rolling temperature of 831°C, and air cooling to room temperature after rolling.

[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, a final rolling temperature of 667°C, and air cooling to room temperature after rolling.

[0128] (7) Double annealing treatment:

[0129] The first annealing treatment was carried out at 950°C for 1 h and then air-cooled to room temperature.

[0130] The second annealing treatment was carried out at 530°C for 6 h and then air-cooled to room temperature.

[0131] (8) Physical and chemical testing:

[0132] Samples were cut from the head, middle and tail of the finished TC11 titanium alloy rod for microstructure testing. Figure 5As shown in the figure, the transverse and longitudinal microstructures of the finished titanium alloy rod are equiaxed structures processed in the (α+β) zone. The equiaxed structure is fine and uniform, and there is no elongated strip α in the longitudinal direction.

[0133] The mechanical properties of the TC11 titanium alloy rod after the specific treatment of the present invention are shown in Table 2.

[0134] Table 2

[0135]

[0136] The room temperature tensile strength, room temperature yield strength, 500°C tensile strength and 500°C×100h thermal stability strength of the TC11 titanium alloy fine-grained rod prepared by the present invention are slightly improved compared with the traditional process, the 500°C elongation is increased by 31%, and the cross-sectional shrinkage 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a small-sized fine-grained titanium alloy rod, characterized in that: The following steps are involved: Step 1: High temperature homogenization treatment: Under the temperature condition of 10°C to 40°C above the β transformation temperature, a titanium alloy rod blank with an equiaxed structure and a diameter of less than 350 mm is subjected to a high temperature homogenization heat treatment for 60min to 280min, and then water-cooled to room temperature to obtain a titanium alloy rod with a fine lamellar α structure; Step 2: Low temperature large deformation rolling: Under the heating temperature condition of 50°C to 200°C below the β transformation temperature, the titanium alloy rod with fine lamellar α structure is subjected to 2 to 4 rounds of large deformation rolling, with 5 to 15 rolling passes per round, a rolling speed of 1.0 to 3 m / s, a pass elongation coefficient of 1.1 to 1.8, a final rolling temperature of not less than 650°C, and air cooling to room temperature after rolling, so as to allow the lamellar α structure to fully recover and recrystallize, thereby obtaining a titanium alloy fine-grained rod with the difference between the transverse and longitudinal structures eliminated.

2. The method for preparing a small-sized fine-grained titanium alloy rod according to claim 1, characterized in that: Also includes step three, annealing treatment: The titanium alloy fine crystal rod is subjected to a single annealing or a double annealing treatment below the β transformation temperature. The first annealing heating temperature of the single annealing or the double annealing is 30°C to 300°C below the β transformation temperature, and the heating temperature is kept for 0.5h to 9h, and the rod is air-cooled to room temperature after annealing. The second annealing temperature of the double annealing is not less than 500°C, and the heating time is 0.5h to 9h, and the rod is air-cooled to room temperature after annealing. The method is used to further homogenize the fine crystal structure, so as to obtain a titanium alloy fine crystal rod with a fine and uniform equiaxed structure for a small amount of titanium alloys that are not sufficiently recrystallized due to insufficient driving force.

3. The method for preparing a small-sized fine-grained titanium alloy rod according to claim 1, characterized in that: The method for preparing the titanium alloy bar blank with equiaxed structure comprises the following steps: Step 1), high temperature blanking: The titanium alloy ingot prepared by the conventional process is subjected to 2 to 4 rounds of high-temperature large-deformation forging at a forging heating temperature of 20°C to 250°C above the β-transformation temperature, wherein the forging heating temperature is reduced with each round, and air-cooled to room temperature after forging, so as to fully break the as-cast grains and improve the plasticity of the casting structure; Step 2), low temperature forging: Under the forging temperature condition of 20°C to 80°C below the β transformation temperature, 2 to 4 times of upsetting and drawing are alternately performed, and air cooling is performed to room temperature after forging to complete the spheroidization process of the primary α phase and obtain a uniform equiaxed structure; Step 3), low temperature molding: Under the forming forging temperature condition of 20°C to 80°C below the β transformation temperature, drawing and rounding are carried out in sequence, and air cooling is carried out to room temperature after forging to obtain a rod blank with a diameter of less than 350 mm, so as to avoid insufficient cooling of the core of the material due to excessive billet size, which affects the uniformity of the structure.

4. The method for preparing a small-sized fine-grained titanium alloy rod according to claim 3, characterized in that: In the high temperature forging of the blank in step 1), the deformation amount of a single fire is 20% to 80%, the total deformation amount is 80% to 95%, and the final forging temperature is not less than 750°C.

5. The method for preparing a small-sized fine-grained titanium alloy rod according to claim 3, characterized in that: The deformation of a single fire in the low temperature forging in step 2) is 20% to 80%, the total deformation is controlled at 80% to 95%, and the final forging temperature is not less than 750°C.

6. The method for preparing a small-sized fine-grained titanium alloy rod according to claim 3, characterized in that: The deformation of the single fire in the forming forging in step 3) is 20% to 80%, the total deformation is controlled at 70% to 90%, and the final forging temperature is not less than 750°C.

7. The method for preparing a small-sized fine-grained titanium alloy rod according to claim 1, characterized in that: During the high temperature homogenization heat treatment described in step 1, the furnace temperature uniformity is controlled to be ±5°C and the temperature rises with the furnace.

8. The method for preparing a small-sized fine-grained titanium alloy rod according to claim 1, characterized in that: The step 2 specifically comprises: performing 1 to 3 rounds of large deformation rolling on the titanium alloy bar billet with fine lamellar α structure under the heating temperature conditions, and controlling the dynamic recrystallization during rolling and the static recrystallization during heating, so that the major-minor axis ratio of the lamellar α structure reaches 15 to 30; then, performing the last round of rolling under the control of the rolling heating temperature and rolling deformation parameters, directly realizing the recovery recrystallization of the elongated lamellar α structure, and obtaining a titanium alloy fine-grained bar with the horizontal and vertical structure differences eliminated.

9. The method for preparing a small-sized fine-grained titanium alloy rod according to any one of claims 1 to 8, characterized in that: The titanium alloy bar blank is TC11 or TA11 or TC4 or TC6 or TC8 or TC8-1 or TC8M or TC8M-1 or TA15 bar blank.

10. A titanium alloy fine crystal rod obtained by the method according to claim 9, characterized in that: The titanium alloy is TC11, and the obtained titanium alloy fine crystal rod is TC11. The transverse and longitudinal microstructures of the titanium alloy fine crystal rod are equiaxed structures processed in the (α+β) zone. The equiaxed structures are fine and uniform, and the size of the primary α phase is 3-7 μm.

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