A forging method of a small-size rod of a Ti2AlNb alloy

Abstract

The application discloses a forging method for small-size Ti2AlNb alloy rods, and belongs to the technical field of metallurgy.The forging method comprises the following steps: determining the total deformation of finish forging, the diameter and length of a rough rod blank, setting a forging frequency according to the total deformation, carrying out dirt removal and sand blasting treatment on the surface of the blank, preheating the cleaned blank in a heating furnace, finish forging the blank in multiple stages and multiple passes by using a finish forging machine, straightening the rod after the forging, and machining the rod to obtain a finished rod after air cooling to room temperature.The forging method controls the pass tempering time by constructing a regulation and control model between the deformation and the forging frequency, optimizes the surface treatment and preheating steps before forging, and makes the microstructure of the small-size Ti2AlNb alloy rod after finish forging uniformly distributed and excellent in room temperature strength and plasticity.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology of titanium-based intermetallic compounds, and in particular to a forging method for small-sized Ti2AlNb alloy bars. Background Technology

[0002] Ti2AlNb-based alloys, derived from titanium alloys and the Ti-Al alloy system, are novel intermetallic compounds developed in the 1990s. They possess characteristics such as low thermal expansion coefficient, non-magnetic properties, and high flame retardancy, allowing for long-term service in the 650–750℃ temperature range, and show broad application prospects in high-temperature components such as aero-engines. Compared to traditional duplex titanium alloys, Ti2AlNb-based alloys exhibit superior high-temperature strength and creep resistance; compared to Ti-Al-based alloys, they demonstrate better formability and fracture toughness. However, as intermetallic compounds, Ti2AlNb-based alloys are lightweight and difficult-to-deform materials. While possessing excellent high-temperature performance, they also exhibit intrinsic brittleness. Since these critical components require extremely high material uniformity and flaw detection capabilities, the large deformation resistance and inherent brittleness are bottlenecks restricting their development and application.

[0003] Ti2AlNb alloy ingots are typically prepared using a vacuum arc remelting furnace. After annealing, the ingots are forged into bars using a free forging press. Free forging offers high throughput and low cost, but the resulting bars have coarse grains and poor plastic deformation capabilities, requiring precision forging for subsequent machining. Existing free forging technology can refine alloy grains, but it suffers from drawbacks such as complex processes and poor microstructure uniformity. In particular, the low specific heat capacity of Ti2AlNb alloys makes them prone to localized temperature rises during hot working, leading to abnormal growth of the B2 matrix grains. This results in macroscopically unstable flaw detection levels and anisotropic mechanical properties, directly impacting the service life and reliability of components. The choice of forging process depends on the size, shape, batch size, and technical requirements. For large-sized forgings (e.g., diameters over 300mm), free forging is the preferred process to ensure formability and mechanical properties. For small-sized bar forgings with a large length-to-diameter ratio (commonly with a diameter below 250mm), precision forging technology is widely used due to its excellent dimensional control and production efficiency. Furthermore, the axial force generated by the hammer-anvil entry angle during precision forging facilitates axial extension of the workpiece, making it particularly suitable for slender shafts, rods, and bars. However, in actual precision forging, it is difficult to precisely control the balance between deformation, pass intervals, and reheating times. Fewer passes with large deformation can lead to localized overheating and longitudinal cracks; more passes with smaller deformation require multiple reheating cycles, which is inefficient and causes grain growth with each heating cycle, resulting in performance degradation. Therefore, how to control these parameters to obtain forged bars with high dimensional accuracy and uniform microstructure has become a pressing problem to be solved in precision forging. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the defects of the existing technology and provide a forging method for small-sized Ti2AlNb alloy bars. By constructing a control model between deformation amount and forging frequency, controlling the tempering time of each pass, and optimizing the surface treatment and preheating steps before forging, the microstructure of the small-sized Ti2AlNb alloy bars obtained after precision forging is uniformly distributed and has excellent room temperature strength and plasticity.

[0005] The technical problem described in this invention is solved by the following technical solution:

[0006] A forging method for small-sized Ti2AlNb alloy bars, the forging method comprising the following steps:

[0007] Step 1): Determine the total deformation amount of precision forging, estimate the required diameter and length of the rough bar billet based on the total deformation amount, and set the forging frequency according to the total deformation amount;

[0008] The relationship between total deformation and forging frequency is as follows: 50-60% total deformation requires 3-5 forging passes, 60-70% total deformation requires 4-6 forging passes, and 70-80% total deformation requires 5-7 forging passes.

[0009] Step 2): Clean and sandblast the surface of the billet. After sandblasting, purge the surface of the billet with nitrogen and take a small sample from the billet to determine the β phase transition point.

[0010] Step 3): Place the cleaned billet into the heating furnace for preheating;

[0011] Step 4): After the billet is fully preheated, the furnace temperature is raised to 20℃~40℃ below the β phase transformation point for holding. After holding, the billet is taken out of the furnace and quickly transferred to the precision forging machine for forging.

[0012] Step 5): Use a precision forging machine for multiple passes, with a hammer striking frequency of 200-450 times / min and a deformation amount of 5%-35% per pass. After each pass of forging, air cool for 3-5 minutes, then return to the heating furnace for heating. The furnace temperature is maintained at 20℃-40℃ below the β phase transformation point for heat preservation. After heat preservation, the billet is removed from the furnace and returned to the precision forging machine for the next pass of forging.

[0013] Step 6): After forging, the bar is straightened, air-cooled to room temperature, and then machined to obtain the finished bar.

[0014] The forging method for small-sized Ti2AlNb alloy bars described above, wherein step 5) involves a multi-pass precision forging process.

[0015] The first forging pass has a frequency of 400 forgings per minute and a deformation rate of 8-13.5%.

[0016] The second forging pass has a frequency of 320-350 forgings per minute and a deformation rate of 15-20%.

[0017] The intermediate forging frequency is 290-300 times / min, and the deformation amount is 18-35%.

[0018] The final forging pass has a forging frequency of 420 times / min and a deformation amount of 5.5%~9%.

[0019] The forging method for the above-mentioned Ti2AlNb alloy small-sized bars includes step 1) forging 5 times with a total deformation of 55-65%, forging 6 times with a total deformation of 65-75%, and forging 7 times with a total deformation of 75-80%.

[0020] The forging method for small-sized Ti2AlNb alloy bars described above, wherein the decontamination and sandblasting process in step 2) is as follows: the surface contaminants of the rough forging billet are wiped off with anhydrous ethanol, the surface is purged with nitrogen or compressed air, and then the cleaned billet surface is sandblasted with white corundum as the abrasive, the sandblasting pressure is 0.4 to 0.6 MPa, the spray angle is 70° to 85°, and the spray distance is 150 to 300 mm.

[0021] In the forging method of the above-mentioned Ti2AlNb alloy small-sized bars, the holding time of the billet in the heating furnace in step 4) is 1.0×D~1.0×D+30min, and the holding time of the billet in the heating furnace after each pass in step 5) is (0.2~0.3)×D min; D is the diameter of the billet.

[0022] The forging method for small-sized Ti2AlNb alloy bars described above, wherein the preheating treatment in step 3) is as follows: the heating furnace slowly and uniformly heats the billet to 550℃~650℃, holds it at that temperature for 1~2 hours, and the heating furnace continues to heat the billet to 800℃~850℃, holds it at that temperature for 1~2 hours; the heating rate during the heating process in steps 3) and 4) is ≤10℃ / min.

[0023] In the forging method of the above-mentioned small-sized Ti2AlNb alloy bars, the transfer time from the billet exiting the furnace to the precision forging machine in step 5) is less than 60s.

[0024] This invention addresses the characteristics of Ti2AlNb-based alloys, including a narrow hot working window, high deformation resistance, poor plasticity and toughness, and high crack sensitivity. It employs a multi-pass precision forging process and innovatively constructs a control model between deformation amount and forging frequency. This optimizes the distribution of forging passes and deformation amount, using appropriate deformation to promote sufficient recrystallization of the B2 phase grains, breaking up coarse grains and refining them, reducing the risk of localized overheating and cracking. Simultaneously, it avoids grain growth caused by excessive forging passes requiring multiple heating cycles. Short-time reheating between passes eliminates work hardening, effectively refines the B2 grains, reduces deformation resistance during hot working, and improves the formability of the material. The resulting small-sized Ti2AlNb alloy bars exhibit a uniform microstructure distribution from edge to core, primarily composed of equiaxed α2 phase, lath O phase, and a B2 matrix. The B2 parent phase grains are fully broken up, and the equiaxed α2 phase is diffusely distributed without continuous grain boundary α2 phase brittle weak zones. The surface quality is excellent, and the full-path ultrasonic flaw detection performance is outstanding. It can stably identify Φ1.2mm flat-bottom hole defects along the diameter direction, and the clutter level is controlled below -12dB. At the same time, the bars prepared by this process have excellent room temperature strength and plasticity.

[0025] The radial precision forging machine of the present invention adopts a four-hammer synchronous forging system, which significantly improves the uniformity of plastic deformation during bar forging. Furthermore, the production process is simple, the time cycle is short, and it is suitable for large-scale industrial applications. Attached Figure Description

[0026] Figure 1 This is a process flow diagram of the present invention based on the control between deformation amount and forging frequency;

[0027] Figure 2 This is a schematic diagram illustrating the control relationship between deformation amount and forging frequency in this invention;

[0028] Figure 3 These are high-magnification images of the edge, 1 / 2R, and core of the Φ60mm rod prepared in Example 1 of this invention;

[0029] Figure 4 These are high-magnification images of the edge, 1 / 2R, and core of the Φ120mm rod prepared in Example 2 of this invention;

[0030] Figure 5 This is a metallographic photograph of the Φ60mm bar prepared according to the comparative example of this invention. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the embodiments and corresponding drawings. Those skilled in the art can make appropriate adjustments without departing from the spirit of the invention. The following embodiments can illustrate the present invention in more detail, but do not limit the present invention in any way.

[0032] The specific preparation process of Ti2AlNb alloy rods is as follows:

[0033] Step 1): Based on the dimensions of the custom alloy bar, determine the total deformation amount according to the alloy material and forging requirements. Ensure that the Ti2AlNb alloy structure is fully broken, the grains are refined, the internal pores are closed, and the chemical composition is uniform. At the same time, avoid excessive deformation that may lead to cracking and abnormal grain growth. Based on this, the range of the total deformation amount for precision forging of Ti2AlNb alloy is set to 50-80% (this deformation amount does not include loss). Estimate the required diameter and length of the rough bar billet based on the total deformation amount. Then, set the forging frequency reasonably according to the total deformation amount. For example, if the forging frequency is 50-60% of the total deformation amount, 3-5 forging passes are required; if the total deformation amount is 60-70%, 4-6 forging passes are required; and if the total deformation amount is 70-80%, 5-7 forging passes are required.

[0034] Step 2): Wipe away oil, dust, and other loose contaminants from the surface of the rough forging billet with anhydrous ethanol, and then blow the surface with nitrogen or compressed air. Next, sandblast the cleaned billet surface. The sandblasting should be continuous and uniform, avoiding prolonged local contact. Use white corundum as the abrasive, with a grit size of F36–F60, a sandblasting pressure of 0.4–0.6 MPa, a spray angle of 70°–85°, and a spray distance of 150–300 mm. After sandblasting, thoroughly blow the billet surface with dry, oil-free, clean compressed air or nitrogen. Take a small sample from the billet to determine the β-phase transition point.

[0035] The dual pretreatment of anhydrous ethanol and surface sandblasting can thoroughly remove high-temperature oxide scale, oxygen-rich layer and contaminants, while avoiding the introduction of secondary pollution or surface damage, thus ensuring high-quality forging in the future.

[0036] Step 3): Preheating treatment: Place the dried billet into a heating furnace for low-temperature preheating treatment. As the temperature inside the heating furnace gradually rises, heat the billet to 550℃~650℃ and hold for 1~2 hours. Continue to heat the billet at a uniform rate to 800℃~850℃ and hold for 1~2 hours.

[0037] Two preheating treatments, one at low temperature and the other at medium temperature, can eliminate residual stress that may result from machining or sandblasting, allowing the billet to reach a safe intermediate temperature uniformly throughout.

[0038] Step 4): After sufficient preheating, raise the furnace temperature to 20℃~40℃ below the β phase transformation point and hold for 1.0×D~1.0×D+30 (min), where D is the billet diameter (mm); after exiting the furnace, quickly transfer it to a precision forging machine for forging;

[0039] Among them, the heating rate during the preheating treatment and step 4) heating process in the heating furnace is ≤10℃ / min. The temperature is slowly and gradually increased through three gradients: low temperature, medium temperature and high temperature, so that the entire billet is heated evenly and reaches temperature equilibrium.

[0040] Step 5): Use the four-hammer radial forging system of the GFM SX25 precision forging machine. The forging process adopts a multi-stage approach, and the hammer striking frequency is controlled at 200~450 times / min (i.e., forging frequency). The deformation degree of each pass is controlled within the range of 5%~35%. After each forging pass is completed, it needs to be air-cooled for 3~5 minutes before returning to the heating furnace for reheating. The furnace temperature is maintained at 20℃~40℃ below the β phase transformation point. The holding time is (0.2~0.3)×D (where D is the diameter of the billet after the previous pass deformation). After holding, the billet is taken out of the furnace for forging. The transfer time of the billet from the heating furnace to the precision forging machine does not exceed 60s.

[0041] according to Figure 1 , Figure 2 The forging frequency diagram shows the reasonable setting of the forging process. The forging frequency of the first pass is 400 times / min with a deformation of 8~13.5%; the forging frequency of the second pass is 320~350 times / min with a deformation of 15~20%; the forging frequency of the intermediate passes is 290~300 times / min with a deformation of 18~35%; and the forging frequency of the final pass is 420 times / min with a deformation of 5.5~9%.

[0042] The first forging pass uses a smaller deformation amount. Since forging is a process of gradually transferring deformation force from the outside to the inside, if the deformation amount in the first pass is too large, the huge deformation energy will be mainly consumed in the surface layer of the billet, leading to severe deformation and heating of the surface layer, while the core may not be fully forged. Therefore, a smaller deformation amount in the first pass allows the deformation force to be transferred to the core more gently and deeply, which is conducive to breaking the original cast structure or coarse grains in the core, laying a good foundation for subsequent passes. As the deformation amount gradually increases in the second and intermediate passes, the forging deformation force is transferred to the core, making the internal structure more uniform. The final forging pass uses a smaller deformation amount to precisely control the final size, geometry, surface quality, and internal structure of the product.

[0043] Step 6): After forging, the bar is straightened using a multi-roller precision straightener to control the curvature to ≤5mm / m. After air cooling to room temperature, it is machined to obtain the finished bar.

[0044] The working process of the present invention will be further illustrated by the following examples:

[0045] Example 1

[0046] Custom-made Ti2AlNb alloy rods with a diameter of Φ60mm are required. The composition of the alloy rod blank is: Ti-21.91Al-24.08Nb-0.51Mo. The alloy's T...β The phase transformation point is 1055℃. The precision forging process for the bar stock is as follows:

[0047] Step 1): Based on the diameter of the custom bar and the forging requirements, the total deformation is determined to be approximately 70%. Therefore, a blank bar with specifications of Φ130mm×2000mm is selected, and the forging frequency is set to six passes.

[0048] Step 2): First, use anhydrous ethanol to wipe off oil, dust and other loose contaminants from the surface of the billet. Let it stand for a while in a well-ventilated environment. Then, use dry, clean, high-purity nitrogen to gently blow the surface of the billet from all directions. After drying, the surface is sandblasted. The billet is sprayed evenly and continuously to avoid local dwell time. The abrasive type is white corundum, the abrasive particle size is F46, the sandblasting pressure is 0.4MPa, the spraying angle is 85° and the spraying distance is 200mm. After sandblasting, use dry, clean, high-purity nitrogen to thoroughly blow the surface of the billet.

[0049] Step 3): After the billet is dried, it is placed in a heating furnace for low-temperature preheating treatment at a heating rate of 10℃ / min. The billet is heated to 500℃ and held for 1 hour. The heating rate is maintained for medium-temperature preheating, and the furnace temperature is raised to 800℃ and held for 1 hour.

[0050] Step 4): Raise the furnace temperature to 1020℃ at a heating rate of 10℃ / min and hold for 160min. After the billet is removed from the furnace, quickly transfer it to the forging area for the first forging.

[0051] Step 5): The first forging pass is performed using a GFM SX25 precision forging machine with a four-hammer system. The forging frequency is set to 400 forgings / min, the hammer impact speed to 12 m / s, and the axial feed rate to 3 m / min. The forging is completed to Φ121 mm with a deformation of 13.4% (the deformation is calculated as the cross-sectional area of ​​the previous pass minus the cross-sectional area after deformation / the cross-sectional area of ​​the previous pass). After the first forging pass, the forging is air-cooled for 3 minutes, then reheated in the furnace at 1020℃ for 25 minutes before proceeding to the second forging pass. The forging frequency is adjusted to 320 forgings / min, and the hammer impact speed and feed rate remain the same as above. The forging is completed to Φ109 mm with a deformation of 18.9%. After the second forging pass, the billet is air-cooled for 3 minutes, then reheated in the furnace at 1020℃ for 22 minutes before being removed for the third forging pass. The forging frequency is adjusted to 290 times / min, and the hammer impact speed and feed rate remain the same as before. The billet is forged to Φ94mm with a deformation of 25.7%. After the third forging pass, the billet is air-cooled for 3 minutes, then reheated in the furnace at 1020℃ for 20 minutes before being removed for the fourth forging pass. The forging frequency remains 290 times / min, and the hammer impact speed and feed rate remain the same as before. The billet is forged to Φ78mm with a deformation of 31.3%. After the fourth forging pass, the billet is air-cooled for 3 minutes, then reheated in the furnace at 1020℃ for 15 minutes before being removed for the fifth forging pass. The forging frequency remains 290 times / min, and the hammer impact speed and feed rate remain the same as before. The billet is forged to Φ70mm with a deformation of 19.5%. After the fifth forging, the billet was air-cooled for 3 minutes, then reheated in the furnace at 1020℃. After holding at that temperature for 14 minutes, it was taken out of the furnace for the sixth forging. The forging frequency was changed to 420 times / min, and the hammer impact speed and feed rate remained the same as above. The billet was forged to Φ68mm with a deformation of 5.7% and a total deformation of 72.6%.

[0052] Step 6): After the sixth final forging, the billet is straightened using a precision straightener at a speed of 2 m / min and a pressure of 120 kN, in three progressive straightening stages, until the final bar curvature is ≤5 mm / m. The straightened bar is then cooled to room temperature in still air, and after machining and peeling, a Φ60 mm finished bar is obtained.

[0053] like Figure 3 As shown in Table 1, the bar prepared in Example 1 has a uniform microstructure, mainly composed of equiaxed α2 phase, lath O phase and B2 phase matrix. The bar has excellent tensile properties, and water immersion ultrasonic testing along the diameter direction shows Φ0.8mm flat bottom holes with noise levels below -12dB.

[0054] Table 1. Room temperature tensile properties of Ti2AlNb-based alloy rods prepared in Example 1

[0055]

[0056] Example 2

[0057] Ti2AlNb alloy rods were selected, with the following composition: Ti-22.06Al-23.98Nb-0.49Mo. The alloy's T... β The phase transformation point is 1058℃. The precision forging process for the bar stock is as follows:

[0058] Step 1): An alloy bar with a diameter of 120mm needs to be forged. According to the forging requirements, the total deformation is determined to be about 60%. A blank bar with a diameter of 200mm × 2300mm is selected, and the forging frequency is set to five passes.

[0059] Step 2): First, wipe off loose contaminants such as oil and dust from the surface with anhydrous ethanol. Let it stand for a while in a well-ventilated environment. Then, gently blow dry, clean, high-purity nitrogen from all directions onto the surface of the billet. After drying, the surface is sandblasted. The billet is sprayed evenly and continuously to avoid prolonged local contact. White corundum is selected as the abrasive type, with an abrasive particle size of F46, a sandblasting pressure of 0.4MPa, a spray angle of 85°, and a spray distance of 200mm. After sandblasting, thoroughly blow dry, clean, high-purity nitrogen onto the surface of the billet.

[0060] Step 3): After the billet is dried, it is put into the furnace for low-temperature preheating treatment at a heating rate of 10℃ / min, and the billet is heated to 600℃ and held for 1.5h; then it is subjected to medium-temperature preheating treatment at a heating rate of 10℃ / min, and the billet is heated to 800℃ and held for 1.5h.

[0061] Step 4): Heating rate 10℃ / min, continue heating to 1030℃ and hold for 220 min. After the billet is removed from the furnace, it is quickly transferred to the forging area for forging;

[0062] Step 5): The first forging pass is performed using a GFM SX25 precision forging machine with a four-hammer system. The forging frequency is set to 400 strokes / min, the hammer impact speed to 12 m / s, and the axial feed rate to 3 m / min. The forging reaches Φ191 mm with a deformation of 8.8%. After the first forging pass, the billet is air-cooled for 4 minutes, then reheated in the furnace at 1030℃ for 55 minutes before being removed from the furnace for the second forging pass. The forging frequency is adjusted to 330 strokes / min, and the hammer impact speed and feed rate remain the same as above. The forging reaches Φ172 mm with a deformation of 19%. After the second forging pass, the billet is air-cooled for 4 minutes, then reheated in the furnace at 1030℃ for 50 minutes before being removed from the furnace for the third forging pass. The forging frequency is adjusted to 300 strokes / min, and the hammer impact speed and feed rate remain the same as above. The forging reaches Φ148 mm with a deformation of 26%. After the third forging pass, the billet was air-cooled for 4 minutes, then reheated in the furnace at 1030℃ for 43 minutes before being removed for the fourth forging pass. The forging frequency was adjusted to 290 forgings / min, with the hammer impact speed and feed rate remaining the same as before. The billet was forged to Φ134mm with a deformation of 18%. After the fourth forging pass, the billet was air-cooled for 4 minutes, then reheated in the furnace at 1030℃ for 40 minutes before being removed for the fifth forging pass. The forging frequency was adjusted to 420 forgings / min, with the hammer impact speed and feed rate remaining the same as before. The billet was forged to Φ128mm with a deformation of 9%, for a total deformation of 59.0%.

[0063] Step 6): After the fifth final forging, a precision straightener is used with a straightening speed of 2 m / min and a straightening pressure of 160 kN. The straightening is performed in three progressive steps until the final bar curvature is ≤5 mm / m. After straightening, the bar is cooled to room temperature in still air, and after machining and peeling, a Φ120 mm finished bar is obtained.

[0064] like Figure 4 As shown, the microstructure of the small-sized rod prepared in Example 2 is basically consistent with that in Example 1. The mechanical properties of the Ti2AlNb alloy rod prepared in this example are shown in Table 2. Water immersion ultrasonic testing along the diameter direction shows that the Φ0.8mm flat-bottom hole and the noise level are all below -6dB.

[0065] Table 2. Room temperature tensile properties of Ti2AlNb-based alloy rods prepared in Example 2

[0066]

[0067] Comparative example:

[0068] The comparative example used a Ti2AlNb alloy cold billet with dimensions of Φ130mm×2000mm and a composition of: Ti-21.94Al-23.93Nb-0.52Mo. The alloy's T... βThe phase transition point is 1053℃. Surface cleaning and preheating were performed according to Example 1, using the same model precision forging machine. The difference lies in the forging frequency; to maximize forging efficiency, two passes were used for precision forging, while other steps remained the same. The first pass forged to Φ95mm with a deformation of 47%, and the second pass forged to Φ68mm with a deformation of 49%. Only two forging passes were required to complete the process. After machining and peeling, a Φ60mm bar was obtained. This comparative example of bar preparation has a simple process and high forging efficiency, but the bar showed numerous edge defects, obvious microcracks, poor ultrasonic testing results, and a low yield. Metallographic images are shown below. Figure 5 The mechanical properties are unstable. See Table 3 for the mechanical properties.

[0069] Table 3. Room temperature tensile properties of Ti2AlNb-based alloy rods prepared in the comparative example.

[0070]

Claims

1. A forging method for small-sized Ti2AlNb alloy bars, characterized in that, The forging method includes the following steps: Step 1): Determine the total deformation amount of precision forging, estimate the required diameter and length of the rough bar billet based on the total deformation amount, and set the forging frequency according to the total deformation amount; The relationship between total deformation and forging frequency is as follows: if the total deformation ε is 50% ≤ ε < 60%, 3 to 5 forging passes are required; if the total deformation is 60% ≤ ε < 70%, 4 to 6 forging passes are required; and if the total deformation is 70% ≤ ε ≤ 80%, 5 to 7 forging passes are required. Step 2): Clean and sandblast the surface of the billet. After sandblasting, purge the surface of the billet with nitrogen and take a small sample from the billet to determine the β phase transition point. Step 3): Place the cleaned billet into the heating furnace for preheating; Step 4): After the billet is fully preheated, the furnace temperature is raised to 20℃~40℃ below the β phase transformation point for holding. After holding, the billet is taken out of the furnace and quickly transferred to the precision forging machine for forging. Step 5): Use a precision forging machine for multiple passes, with a hammer striking frequency of 200-450 times / min and a deformation amount of 5%-35% per pass. After each pass of forging, air cool for 3-5 minutes, then return to the heating furnace for heating. The furnace temperature is maintained at 20℃-40℃ below the β phase transformation point for heat preservation. After heat preservation, the billet is removed from the furnace and returned to the precision forging machine for the next pass of forging. Step 6): After forging, the bar is straightened, air-cooled to room temperature, and then machined to obtain the finished bar. Step 5) is a multi-pass precision forging process. The first forging pass has a frequency of 400 forgings per minute and a deformation rate of 8-13.5%. The second forging pass has a frequency of 320-350 forgings per minute and a deformation rate of 15-20%. The intermediate forging frequency is 290-300 times / min, and the deformation amount is 18-35%. The final forging pass has a forging frequency of 420 times / min and a deformation amount of 5.5%~9%.

2. The forging method for small-sized Ti2AlNb alloy bars according to claim 1, characterized in that, In step 1), if the total deformation ε is 55% ≤ ε < 65%, forge 5 times; if the total deformation is 65% ≤ ε < 75%, forge 6 times; and if the total deformation is 75% ≤ ε ≤ 80%, forge 7 times.

3. The forging method for small-sized Ti2AlNb alloy bars according to claim 2, characterized in that, The process of cleaning and sandblasting in step 2) is as follows: wipe off the contaminants on the surface of the rough forging billet with anhydrous ethanol, blow the surface with nitrogen or compressed air, and then sandblast the cleaned billet surface. The abrasive is white corundum, the sandblasting pressure is 0.4 to 0.6 MPa, the spray angle is 70° to 85°, and the spray distance is 150 to 300 mm.

4. The forging method for small-sized Ti2AlNb alloy bars according to claim 3, characterized in that, In step 4), the holding time of the billet in the heating furnace is 1.0×D to 1.0×D+30 min. In step 5), the holding time of the billet in the heating furnace after each pass is (0.2~0.3)×D min; D is the diameter of the billet.

5. The forging method for small-sized Ti2AlNb alloy bars according to claim 4, characterized in that, The preheating process in step 3) is as follows: the heating furnace slowly and uniformly heats the billet to 550℃~650℃ and holds it for 1~2 hours. The heating furnace continues to heat the billet to 800℃~850℃ and holds it for 1~2 hours. The heating rate during the heating process in steps 3) and 4) is ≤10℃ / min.

6. The forging method for small-sized Ti2AlNb alloy bars according to claim 5, characterized in that, In step 5), the transfer time from the billet exiting the furnace to the precision forging machine for each pass is less than 60 seconds.

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