Forging method for improving macrostructure uniformity of TC2 titanium alloy large-specification bar

Abstract

The invention relates to the technical field of titanium alloy machining, and particularly discloses a forging method for improving the macrostructure uniformity of a TC2 titanium alloy large-specification bar, which is realized through cogging forging, twice alpha + beta phase region remelting dynamic beta recrystallization forging, two-phase region upsetting and drawing forging and two-phase region drawing forging. The TC2 titanium alloy bar with the specification of phi 300-phi 400 mm prepared through the method is fine and uniform in macrostructure and meets the 1-5 grade of a macroscopic rating chart in the product standard, and the structure of a ring forge piece subjected to die forging through the bar is greatly improved and meets the standard requirement.

Description

Technical Field

[0001] The invention relates to the technical field of titanium alloy forging, and in particular to a forging method for improving the macrostructure uniformity of a large-size TC2 titanium alloy bar. Background Art

[0002] Titanium alloys are widely used in aviation, aerospace, marine equipment, weapons, petrochemicals and other fields due to their high specific strength, high toughness, excellent corrosion resistance and heat resistance, and non-magnetic properties. With the continuous upgrading of various equipment, titanium alloy forgings have gradually developed from the splicing method of small forgings to the integral forming of large forgings. The service environment is becoming more and more harsh, which has put forward higher requirements for the size specifications and uniformity of titanium alloy bars.

[0003] In the free forging of titanium alloys, the processable temperature range in the (α+β) two-phase region is small, and as the forging temperature decreases, the deformation resistance increases rapidly, the metal flow is not constrained by the die, and the local flow in contact with the hammer anvil is restricted due to friction, forming a deformation dead zone, which makes the bar naturally have differences in organization such as forging dead zone and streamline zone, especially in the end area in contact with the hammer anvil during upsetting of the billet. The superposition of the deformation dead zone and the excessive temperature drop at the free end leads to insufficient deformation of the end of the bar, which in turn leads to a large difference in the uniformity of the organization between the end and the middle of the bar. In addition, free forging often requires repeated upsetting and drawing, so that the organization of the end of the final forged bar billet shows obvious unevenness compared with the middle of the bar, and the larger the forging billet specification, the greater the unevenness.

[0004] TC2 titanium alloy is a near-α-type titanium alloy with a strength grade of 700MPa and good plasticity and thermal strength. It is suitable for manufacturing aircraft engine parts. Although TC2 titanium alloy has good hot formability, it also has the above-mentioned problem of free forging of titanium alloy. Because the composition of TC2 is simple, the main elements are only Ti, Al, and Mn. Compared with titanium alloys with more elements such as TC11 and TA15, TC2 grains are very easy to grow. And because the structure of TC2 is mostly α phase, combined with the previous factors, TC2 is easy to form large blocks of α phase areas with consistent directions, which appear as coarse grains at low magnification (such as Figure 1 As shown in Figure 2, this has become a difficult problem to solve in TC2 free forging. Summary of the invention

[0005] In view of the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a forging method for improving the uniformity of the macrostructure of large-sized TC2 titanium alloy bars, thereby improving the deformation uniformity of the large-sized forging billets during the upsetting and drawing process, thereby improving the problem of low-magnification coarse grains in the bars.

[0006] To achieve the above object, one of the technical solutions adopted by the present invention is: a forging method for improving the macrostructure uniformity of large-size TC2 titanium alloy bars, characterized in that it is achieved through the following steps: Step 1: Forging Using a 4-5 stage heating curve, the titanium alloy ingot is heated to 1050-1150°C, with a heating coefficient of 0.3-0.9, and is upset and stretched horizontally to a square using a flat anvil; Step 2: First α+β phase region remelting dynamic β recrystallization forging The blank obtained in step 1 is heated to 10-100°C below the phase transition point temperature, with a heating coefficient of 0.4-0.8, and subjected to square upsetting and drawing forging. After forging, the hot material is returned to the furnace for dynamic β recrystallization treatment; wherein the blank is returned to the furnace by keeping the temperature below the phase transition point temperature for a period of time at 10°C, and then rapidly heated to 50-100°C above the phase transition point temperature, with a heating coefficient of 0.2-0.7, and subjected to square reversing upsetting and drawing forging, that is, upsetting along the radial direction of the ingot, and elongating along the direction perpendicular to the radial direction of the ingot, at which time the metal at the original end is distributed on the circumference of the blank; Step 3: Secondary α+β phase region remelting dynamic β recrystallization forging The blank obtained in step 2 is heated to 10-100°C below the phase transition point temperature, with a heating coefficient of 0.4-0.8, and subjected to square upsetting forging. After forging, the hot material is returned to the furnace for dynamic β recrystallization treatment; wherein the blank is returned to the furnace by rapidly heating to 50-100°C above the phase transition point temperature after being kept at 10°C below the phase transition point for a period of time, with a heating coefficient of 0.2-0.7, and subjected to square upsetting forging, at which time the metal at the original end is still distributed on the circumference of the blank; Step 4: Two-phase zone upsetting and forging The blank obtained in step 3 is heated to 10-100°C below the phase transition point temperature, with a heating coefficient of 0.4-0.8, and subjected to two-phase zone upsetting forging. During the upsetting of the penultimate fire, a reversing upsetting is performed, that is, upsetting is performed along the radial direction of the relatively vertical ingot, and elongation is performed along the radial direction of the ingot to achieve end return; the upsetting deformation of each fire is controlled between 20% and 45%, and remelting or air cooling is adopted after each fire forging; Step 5: Two-phase zone drawing forging The blank obtained in step 4 is heated to 10-100°C below the phase transition point temperature, with a heating coefficient of 0.4-0.8, and two-phase zone drawing forging is performed. During the drawing process, the four-sided forging is changed to an octagonal forging, so as to change the large difference in metal flow resistance caused by the different contact areas between the edges and surfaces of the blank and the hammer anvil during the drawing process, improve the uniformity of deformation, control the amount of drawing deformation in each fire within a range of 10%-40%, return to the furnace or air cool after each fire forging, and then obtain the required large-size titanium alloy bars through rolling and drawing.

[0007] Further, in the above step 1, the blank forging is 2 times, and the specific process is as follows: the first heating is to charge the furnace from 800°C, keep it for a period of time, and fully heat it at 30°C below the phase change point temperature, then heat it to the phase change point temperature and keep it for a period of time, then quickly heat it to 1100-1150°C, keep it for 90-120min, then take it out of the furnace for 2 upsettings and 2 drawing, each upsetting and drawing deformation is controlled to 35%-45%, and air cooling is performed after forging; the second heating is also charged from 800°C, keep it for a period of time, and fully heat it at 30°C below the phase change point temperature, then heat it to the phase change point temperature and keep it for a period of time, then quickly heat it to 1050-1100°C, keep it for 90-120min, then take it out of the furnace for 2 upsettings and 2 drawing, each upsetting and drawing deformation is controlled to 35%-45%, and water cooling is performed within 2 hours after forging, and the cooling rate is ≥400°C / hour.

[0008] Further, the specific process of the above step 2 is as follows: The first heating is to 10-100℃ below the phase transition point for 2 upsetting and 2 drawing. The deformation of each upsetting and drawing is controlled to be 30%-40%. After forging, the hot material is returned to the furnace. The second fire adopts a two-stage heating method. The billet is returned to the furnace and kept at 10℃ below the phase transition point for a period of time, then quickly heated to 50-100℃ above the phase transition point. After keeping the temperature for 60-150min, it is subjected to a reversing upsetting and drawing forging process of 1 upsetting and 1 drawing, that is, upsetting along the radial direction of the ingot and then drawing vertically in the radial direction of the ingot, wherein the upsetting and drawing deformation is controlled to be 20%-30%; the cross section after forging is square, so that the original section metal of the billet is distributed on the circumference of the billet; after forging, it is cooled to 20-50℃ within 2 hours by water cooling, and the cooling rate is ≥400℃ / hour. Rapid cooling increases the grain nucleation rate and hinders grain growth.

[0009] Further, the specific process of the above step 3 is as follows: The first fire is heated to 10-100℃ below the phase transition point, and then two upsetting and two drawing are performed. The deformation of each upsetting and drawing is controlled between 30% and 40%. At this time, the metal at the original end is still distributed on the peripheral surface of the billet, and it is returned to the furnace after forging; The second fire adopts a two-stage heating method. The billet is returned to the furnace and kept at 10℃ below the phase transition point for a period of time, then quickly heated to 50-100℃ above the phase transition point. After keeping for 60-150min, it is upset and drawn. The deformation of upsetting and drawing is controlled between 20%-30%. The cross section after forging is square. At this time, the metal at the original end is still distributed on the periphery of the billet. The original organization state of the middle of the ingot is optimized through this recrystallization process. After forging, water cool to 20-50℃ within 2 hours, and the cooling rate is ≥400℃ / hour. Rapid cooling increases the grain nucleation rate and hinders grain growth.

[0010] Further, the specific process of the upsetting forging in step 4 is as follows: It is completed by four fires. After each fire, it is subjected to 1 upsetting and 1 drawing, and then it is returned to the furnace for 1 upsetting and 1 drawing. The deformation of each upsetting and drawing is controlled between 20% and 45%. It is air-cooled after each fire forging. In the first upsetting and drawing of the third fire, it is subjected to reversing upsetting and drawing, that is, upsetting along the radial direction of the vertical ingot, and drawing along the radial direction of the ingot to achieve the end return, and then it is returned to the furnace for 1 upsetting and 1 drawing. Then it is subjected to 1 fire upsetting and drawing to improve the original state of the organization at the end of the ingot, which is located on the peripheral surface of the billet after reversing, which is conducive to disrupting the directionality of the grains and avoiding the formation of low-magnification coarse grains.

[0011] Further, the specific process of the upsetting forging in step 5 is as follows: It is carried out in 2-3 fires, and each fire is heated to 10-50℃ below the phase transformation point temperature. After keeping warm for a period of time, two-phase zone drawing forging is carried out. Except for the rounding drawing in the last fire, the reduction amount in each fire is ≥100mm and the feed amount is ≥400mm. The drawing deformation amount in each fire is controlled at 10%-40%. After each fire forging, it is returned to the furnace or air-cooled. The drawing directions of adjacent fires are opposite. For example, the current fire is drawn from the head end to the bottom end, and the next fire is drawn from the bottom end to the head end, so as to avoid the drawing as much as possible to cause the grain growth direction to tend to be consistent.

[0012] The forging method is mainly used to prepare TC2 bars with a diameter of φ300-400 mm, and is used to improve the macrostructure uniformity of the finished TC2 titanium alloy bars. Of course, it can also be used to prepare other grades of titanium alloys, such as TC1, TC4 and other titanium alloy bars for aircraft engines.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention uses a 4-5-stage heating curve to perform billet forging, which reduces the heating time in the single-phase zone (the conventional heating curve should be 3 stages or less, and the 4-5-stage method, for example, the holding time at 1100°C-1150°C in the first fire of billet forging is only 90-120 minutes, while the 3-stage method requires at least 240 minutes of holding at 1100°C-1150°C), reduces the grain growth time at high temperature, and the rapid cooling after forging can accelerate the grain nucleation and hinder the growth of billet grains; 2. The present invention can effectively reduce the deformation difference between the end and the middle of the bar during free forging by performing two α+β phase region remelting dynamic β recrystallization forgings and fire-interval reversing forgings (referring to upsetting along the radial direction of the ingot and stretching along the radial direction perpendicular to the ingot during recrystallization in steps 2 and 3, and upsetting along the radial direction perpendicular to the ingot and stretching along the radial direction of the ingot in step 4). In addition, the fire-interval reversing disrupts the directionality of the grains, avoids the formation of low-magnification coarse grains, and effectively improves the uniformity of the low-magnification structure of the bar; 3. The present invention uses four-way rotation, large reduction and feed amount, and head-bottom alternating stretching forging during the two-phase zone stretching forging in step 5, which can improve the problem of grain growth direction tending to be consistent due to metal flow restriction during stretching, and improve the uniformity of the rod structure.

[0014] After actual verification, the TC2 titanium alloy bars with specifications of Φ300-Φ400mm prepared by this method have fine and uniform low-magnification structure, which meets the 1-5 levels of the low-magnification rating diagram in the product standard. The structure of the ring forgings forged with this bar is also greatly improved, meeting the standard requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a low-magnification structure of TC2 titanium alloy produced by free forging in the prior art and its EBSD test result diagram; Figure 2 It is the low- and medium-magnification tissue rating diagram of the product standard; Figure 3 This is a transverse low-magnification microstructure diagram of the end of a rod with a specification of Φ400mm prepared in Example 1 of the present invention; Figure 4 This is a transverse macrostructure diagram of the middle part of a rod with a size of Φ400 mm prepared in Example 1 of the present invention; Figure 5 This is the EBSD test result diagram of the rod with a specification of Φ400mm prepared in Example 1 of the present invention; Figure 6 This is a low-magnification microstructure diagram of the inner ring surface of a ring forging made of a rod with a specification of Φ400 mm prepared in Example 1 of the present invention; Figure 7 This is a low-magnification microstructure diagram of the inner ring surface of a ring forging made of a Φ400mm bar that is not prepared using the process of the present invention; Figure 8 This is a transverse low-magnification microstructure diagram of the end of a rod with a specification of Φ350mm prepared in Example 2 of the present invention; Fig. 9 This is a transverse macrostructure diagram of the middle part of a rod with a specification of Φ350mm prepared in Example 2 of the present invention; Fig.10 This is the EBSD test result diagram of the rod with a specification of Φ350mm prepared in Example 2 of the present invention; Fig.11 This is a low-magnification microstructure diagram of the inner ring surface of a ring forging made of a Φ350 mm bar prepared in Example 2 of the present invention. Fig.12 This is a low-magnification microstructure diagram of the inner ring surface of a ring forging made from a Φ350mm bar that is not prepared using the process of the present invention. DETAILED DESCRIPTION

[0016] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. The following are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any identical or similar schemes that do not depart from the concept of the present invention should fall within the scope of protection of the present invention. In the following, "□" refers to the height of a square blank with a cross section, "◇" refers to the height of an octagonal blank with a cross section, and "Φ" refers to the diameter of a circular blank with a cross section.

[0017] Example 1 (Preparation of TC2 titanium alloy rod with a specification of Φ400 mm) In this embodiment, the raw material is a TC2 Φ680mm ingot, the ingot phase transition temperature is 950°C, and the finished product is a Φ400mm large-size bar. The specific forging process is as follows: ① Open forging: Heat the titanium alloy ingot to 800℃, keep it warm for 90min, heat it to 920℃, keep it warm for 90min, heat it to 950℃, keep it warm for 120min, quickly heat it to 1100℃, and keep it warm for 90min. After the heat preservation is completed, take it out of the furnace, and forge the ingot into a □600mm square billet by 2 upsets and 2 draws, and air cool it after forging; then heat the square billet to 800℃, keep it warm for 90min, heat it to 920℃, keep it warm for 90min, heat it to 950℃, keep it warm for 120min, quickly heat it to 1050℃, and keep it warm for 90min. After the heat preservation is completed, change the direction of the billet to 2 upsets and 2 draws to forge it into a □600mm square billet, and water cool it after forging; ② First α+β phase region remelting dynamic β recrystallization forging: the billet obtained after billeting is heated to 920℃, the insulation coefficient (i.e. heating coefficient) is 0.7, and after the insulation is completed, 2 upsets and 2 draws are performed to forge to □600mm square billet, and after forging, it is loaded into a heating furnace with a furnace temperature of 940℃, and the temperature is kept for 220min, and then the temperature is quickly raised to 1030℃, and the temperature is kept for 120min. After the insulation is completed, 1 upset and 1 draw reversing upset forging is performed, that is, after upsetting along the radial direction of the ingot, it is drawn along the radial direction perpendicular to the ingot, so that the original end face metal of the billet is distributed on the circumference of the billet, and it is forged to □600mm square billet, and water-cooled after forging; ③ Dynamic β-recrystallization forging in secondary α+β phase region: heat the billet obtained after step ② to 920℃, with a heat preservation coefficient of 0.7. After the heat preservation, perform 2 upsets and 2 draws to forge to □600mm square billet. After forging, load it into a heating furnace with a furnace temperature of 940℃ and keep it for 220min. Then quickly heat it to 1010℃ and keep it for 120min. After the heat preservation, perform 1 upset and 1 draw. At this time, the metal at the original end is still distributed on the circumference of the billet. Forge to □600mm square billet, water-cooled after forging; ④ Two-phase zone upsetting and drawing forging: The billet is subjected to two-phase zone upsetting and drawing forging, which is carried out in 4 fires. The heating temperature of each fire is 930℃, 900℃, 930℃, and 900℃ respectively. After each heat preservation, the billet is upset and drawn once, and then returned to the original temperature and upset and drawn once again. In the first upsetting and drawing of the third fire heating forging, the reversing upsetting and drawing is carried out, that is, the upsetting is carried out along the radial direction of the relatively vertical ingot, and the drawing is carried out along the radial direction of the ingot to achieve the end return. Finally, it is forged into a square billet of □540mm.

[0018] ⑤ Two-phase zone drawing forging: The billet is subjected to two-phase zone drawing forging for 2 times, and the heating temperature of each fire is 920℃. After the first fire is finished, the billet is drawn from four sides to eight sides and drawn to ◇430mm. The second fire is rounding drawing and finally forged to a finished product Φ400mm bar. The drawing directions are opposite between the two fires.

[0019] Low-magnification specimens were cut from the end and middle of the Φ400 mm TC2 titanium alloy rod prepared in this embodiment, and the microstructure photos after corrosion are as follows: Figure 3 , 4 As shown, the rating is organized by low and medium times of product standards Figure 2 Rated as level 2 and level 2, used to evaluate the uniformity of the structure of the end and middle of the rod. The EBSD test results are as follows Figure 5 As shown in the figure, its directionality is significantly weakened compared with the original rod. At the same time, the Φ400mmTC2 titanium alloy rod forged by the existing process without the present invention is compared with the Φ400mmTC2 titanium alloy rod of this embodiment. The local low magnification of the ring forging under the same die forging process is shown in the figure. Figure 6 , 7 As shown, the rating is organized by low and medium times of product standards Figure 2 Rated as 5 and 8, used to prove the uniformity of the rod structure.

[0020] Example 2 (Preparation of TC2 titanium alloy bar with a specification of Φ350 mm)

[0021] In this embodiment, the raw material is a TC2 Φ680mm ingot, the ingot phase transition temperature is 950°C, and the finished product is a Φ350mm large-size bar. The specific forging process is as follows: ① Heat the titanium alloy ingot to 800℃, keep it warm for 90min, raise the temperature to 920℃, keep it warm for 90min, raise the temperature to 950℃, keep it warm for 120min, quickly raise the temperature to 1100℃, and keep it warm for 90min. After the insulation, forge the ingot into a □600mm square billet by 2 upsets and 2 draws, and air cool it after forging; then heat the square billet to 800℃, keep it warm for 90min, raise the temperature to 920℃, keep it warm for 90min, raise the temperature to 950℃, keep it warm for 120min, quickly raise the temperature to 1050℃, keep it warm for 90min, and after the insulation, change the direction of the billet to 2 upsets and 2 draws to forge it into a □600mm square billet, and water cool it after forging; ② First α+β phase region remelting dynamic β recrystallization forging: the billet obtained after blanking is heated to 920℃, the insulation coefficient is 0.75, and after the insulation is completed, 2 upsetting and 2 drawing are performed to forge to □590mm square billet, and after forging, it is loaded into a heating furnace with a furnace temperature of 940℃, and the temperature is kept for 220min, and then the temperature is quickly raised to 1040℃, and the temperature is kept for 120min. After the insulation is completed, 1 upsetting and 1 drawing are performed, that is, after upsetting along the radial direction of the ingot, it is stretched along the radial direction perpendicular to the ingot, so that the original end face metal of the billet is distributed on the circumference of the billet, and it is forged to □590mm square billet, and water-cooled after forging; ③ Dynamic β-recrystallization forging in secondary α+β phase region: heat the billet obtained after step ② to 920℃, with a heat preservation coefficient of 0.7. After the heat preservation, perform 2 upsets and 2 draws to forge to □590mm square billet. After forging, load it into a heating furnace with a furnace temperature of 940℃ and keep it for 220min. Then quickly heat it to 1020℃ and keep it for 120min. After the heat preservation, perform 1 upset and 1 draw. At this time, the metal at the original end is still distributed on the circumference of the billet. Forge to □590mm square billet, water-cooled after forging; ④ Two-phase zone forging: The billet is subjected to two-phase zone upsetting and drawing forging for 4 times, and the heating temperatures for the 4 times are 940℃, 910℃, 940℃, and 910℃ respectively. After each heat preservation, the billet is upset and drawn once, and then returned to the original temperature for upsetting and drawing once again. During the first upsetting and drawing of the second 940℃ heating forging, the upsetting and drawing is reversed, that is, the billet is upset along the radial direction of the relatively vertical ingot, and the billet is drawn along the radial direction of the ingot to achieve end return, and finally forged into a □540mm square billet; ⑤ Two-phase zone drawing forging: The billet is subjected to three rounds of two-phase zone drawing forging, with the heating temperature of each fire being 920℃. After the first fire is finished, the billet is drawn from four sides to eight sides to ◇410mm. After the second fire is finished, it is drawn to ◇380mm. The third fire is rounding and drawing, and finally it is forged into a finished product Φ350mm bar. The drawing directions between the first and second fires are opposite.

[0022] Low-magnification specimens were cut from the end and middle of the Φ350 mm TC2 titanium alloy rod prepared in this embodiment. The microstructure photos after corrosion are as follows: Figure 8-9 As shown, the rating is organized by low and medium times of product standards Figure 2 The EBSD test results are as follows: Fig.10 As shown in the figure, the directionality is significantly weakened compared with the original rod. At the same time, the Φ350mmTC2 titanium alloy rod forged without the existing process of the present invention is compared with the Φ350mmTC2 titanium alloy rod of this embodiment. The local low magnification of the ring forging under the same die forging process is shown in the figure. Fig.11 , 12 As shown, the rating is organized by low and medium times of product standards Figure 2 Rated as 4 and 8, used to prove the uniformity of the rod structure.

Claims

1. A forging method for improving the macrostructure uniformity of large-size TC2 titanium alloy bars, characterized in that: This is accomplished by: Step 1: Forging Using a 4-5 stage heating curve, the titanium alloy ingot is heated to 1050-1150°C, with a heating coefficient of 0.3-0.9, and is upset and stretched horizontally to a square using a flat anvil; Step 2: First α+β phase region remelting dynamic β recrystallization forging The billet obtained in step 1 is heated to 10-100° C. below the phase transition point temperature, with a heating coefficient of 0.4-0.8, and subjected to square upsetting and drawing forging. After forging, the hot material is returned to the furnace for dynamic β recrystallization treatment; the billet is returned to the furnace by rapidly heating to 50-100° C. above the phase transition point temperature after being kept at 10° C. below the phase transition point for a period of time, with a heating coefficient of 0.2-0.7, and subjected to square reversing upsetting and drawing forging, that is, upsetting along the radial direction relative to the ingot, and elongating along the radial direction perpendicular to the ingot, at which time the metal at the original end is distributed on the circumference of the billet; Step 3: Secondary α+β phase region remelting dynamic β recrystallization forging The blank obtained in step 2 is heated to 10-100°C below the phase transition point temperature, with a heating coefficient of 0.4-0.8, and square upsetting forging is performed. After forging, the hot material is returned to the furnace for dynamic β recrystallization treatment; the blank is returned to the furnace by rapidly heating to 50-100°C above the phase transition point temperature after being kept at 10°C below the phase transition point for a period of time, with a heating coefficient of 0.2-0.7, and square upsetting forging is performed, at which time the metal at the original end is still distributed on the circumference of the blank; Step 4: Two-phase zone upsetting and forging The blank obtained in step 3 is heated to 10-100°C below the phase transition point temperature, with a heating coefficient of 0.4-0.8, and subjected to two-phase zone upsetting forging. During the penultimate upsetting, a reversing upsetting is performed, i.e., upsetting is performed along the radial direction of the relatively vertical ingot, and elongation is performed along the radial direction of the ingot to achieve end return; the upsetting deformation of each upsetting is controlled between 20% and 45%, and remelting or air cooling is performed after each forging; Step 5: Two-phase zone drawing forging The blank obtained in step 4 is heated to 10-100°C below the phase transition point temperature, with a heating coefficient of 0.4-0.8, and two-phase zone drawing forging is performed. During the drawing process, the four-sided forging is converted into an octagonal forging. The amount of drawing deformation in each fire is controlled between 10% and 40%. After each fire forging, the blank is returned to the furnace or air-cooled, and finally the required large-size titanium alloy bar is obtained by rolling and drawing.

2. A forging method for improving the macrostructure uniformity of large-size TC2 titanium alloy bars according to claim 1, characterized in that: In the above step 1, the blank forging is 2 times, and the specific process is as follows: the first heating is to charge the furnace from 800°C, keep it for a period of time, and fully heat it at 30°C below the phase change point temperature, then heat it to the phase change point temperature and keep it for a period of time, then quickly heat it to 1100-1150°C, keep it for 90-120min, then take it out of the furnace for 2 upsettings and 2 drawing, each upsetting and drawing deformation is controlled to 35%-45%, and air cooling is performed after forging; the second heating is also to charge the furnace from 800°C, keep it for a period of time, and fully heat it at 30°C below the phase change point temperature, then heat it to the phase change point temperature and keep it for a period of time, then quickly heat it to 1050-1100°C, keep it for 90-120min, then take it out of the furnace for 2 upsettings and 2 drawing, each upsetting and drawing deformation is controlled to 35%-45%, and water cooling is performed after forging.

3. A forging method for improving the macrostructure uniformity of large-size TC2 titanium alloy bars according to claim 2, characterized in that: The post-forging water cooling in step 1 is cooled to 20-50°C within 2 hours, and the cooling rate is ≥400°C / hour.

4. A forging method for improving the macrostructure uniformity of large-size TC2 titanium alloy bars according to claim 1, characterized in that: The specific process of step 2 above is as follows: The first heating is to 10-100℃ below the phase transition point for 2 upsetting and 2 drawing. The deformation of each upsetting and drawing is controlled to be 30%-40%. After forging, the hot material is returned to the furnace. The second fire adopts a two-stage heating method. The billet is returned to the furnace and kept at 10℃ below the phase change point for a period of time, then quickly heated to 50-100℃ above the phase change point. After keeping for 60-150 minutes, it is subjected to a reversing upsetting and drawing forging process of 1 upsetting and 1 drawing, that is, after upsetting along the radial direction of the ingot, it is drawn vertically in the radial direction of the ingot, and the upsetting and drawing deformation is controlled to be 20%-30%; the cross-section after forging is square, so that the original section metal of the billet is distributed on the circumference of the billet; and it is water-cooled after forging.

5. A forging method for improving the macrostructure uniformity of large-size TC2 titanium alloy bars according to claim 4, characterized in that: The post-forging water cooling in step 2 is cooled to 20-50°C within 2 hours, and the cooling rate is ≥400°C / hour.

6. A forging method for improving the macrostructure uniformity of large-size TC2 titanium alloy bars according to claim 1, characterized in that: The specific process of step 3 above is as follows: The first fire is heated to 10-100℃ below the phase transition point, and then two upsetting and two drawing are performed. The deformation of each upsetting and drawing is controlled between 30% and 40%. At this time, the metal at the original end is still distributed on the peripheral surface of the billet, and it is returned to the furnace after forging; The second fire adopts a two-stage heating method. The billet is returned to the furnace and kept at 10℃ below the phase transformation point for a period of time. Then it is quickly heated to 50-100℃ above the phase transformation point. After keeping it for 60-150 minutes, it is upset and drawn. The deformation of upsetting and drawing is controlled between 20%-30%. The cross-section after forging is square. At this time, the metal at the original end is still distributed on the circumference of the billet. It is water-cooled after forging.

7. A forging method for improving the macrostructure uniformity of large-size TC2 titanium alloy bars according to claim 6, characterized in that: The post-forging water cooling in step 3 is cooled to 20-50°C within 2 hours, and the cooling rate is ≥400°C / hour.

8. A forging method for improving the macrostructure uniformity of large-size TC2 titanium alloy bars according to claim 1, characterized in that: The specific process of step 4 above is as follows: It is completed in four firings. After each firing, the steel is returned to the furnace for another upsetting and drawing, and the deformation of each upsetting and drawing is controlled between 20% and 45%. Air cooling is performed after each forging. During the first upsetting and drawing in the third firing, reversing upsetting and drawing is performed, i.e., upsetting is performed along the radial direction of the vertical ingot, and drawing is performed along the radial direction of the ingot to achieve end return.

9. A forging method for improving the macrostructure uniformity of large-size TC2 titanium alloy bars according to claim 1, characterized in that: The specific process of upsetting and forging in step 5 above is as follows: It is carried out in 2-3 fires, and each fire is heated to 10-50℃ below the phase change point temperature. After keeping warm for a period of time, two-phase zone drawing forging is carried out. Except for the rounding and drawing in the last fire, the reduction amount of each fire in the remaining fires is ≥100mm and the feed amount is ≥400mm. The drawing deformation amount of each fire is controlled at 10%-40%. After each forging, it is returned to the furnace or air-cooled. The drawing direction between two adjacent fires is opposite.

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