A forging method to improve the macrostructure uniformity of large-scale TC2 titanium alloy bars

Abstract

The present invention relates to the field of titanium alloy processing technology and specifically discloses a forging method for improving the uniformity of the macrostructure of large-sized TC2 titanium alloy bars. The method is achieved through cogging forging, two cycles of dynamic β-recrystallization forging in the α+β phase region, two-phase region upsetting and drawing forging, and two-phase region stretching forging. TC2 titanium alloy bars with a diameter of 300 to 400 mm prepared using this method have a fine and uniform macrostructure that meets the 1-5 level of the macro- and macro-magnification rating diagram of the product standard. Ring forgings die-forged using this bar also have significantly improved microstructure, meeting standard requirements.

Description

Technical Field

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

[0002] Titanium alloys are widely used in aviation, aerospace, naval equipment, weapons, petrochemicals, and other fields due to their high specific strength, high toughness, excellent corrosion and heat resistance, and non-magnetic properties. With the continuous upgrading of various equipment, titanium alloy forgings have gradually evolved from small forgings spliced ​​together to large forgings formed as a whole. The increasingly harsh service environment has also placed higher requirements on the size specifications and microstructure uniformity of titanium alloy bars.

[0003] In the free forging of titanium alloys, the workable 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 and anvil is restricted due to friction, forming a deformation dead zone. As a result, the bar naturally has organizational differences such as forging dead zones and streamline zones. Especially in the end area in contact with the hammer and anvil during upsetting, the combined effect of the deformation dead zone and the rapid temperature drop at the free end leads to insufficient deformation of the bar end, which in turn leads to a large difference in organizational uniformity between the end and the middle of the bar. In addition, free forging often requires a combination of repeated upsetting and drawing, which makes the organizational structure of the end of the final forged bar billet show obvious unevenness compared to 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 problems of free forging of titanium alloys mentioned above. Because the composition of TC2 is simple, with only Ti, Al, and Mn as the main elements, TC2 grains are very easy to grow compared to titanium alloys with more elements such as TC11 and TA15. Moreover, because the structure of TC2 is mostly α-phase, combined with the above factors, TC2 is easy to form large blocks of α-phase regions 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, so as to improve the deformation uniformity of the large-sized forging blanks 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-sized TC2 titanium alloy bars, characterized by being achieved through the following steps:

[0007] Step 1: Forging

[0008] Using a 4-5 stage heating curve, the titanium alloy ingot is heated to 1050-1150℃ with a heating coefficient of 0.3-0.9, and is upset and stretched horizontally to a square using a flat anvil;

[0009] Step 2: First α+β phase region remelting dynamic β recrystallization forging

[0010] 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 forging. After forging, the hot material is returned to the furnace for dynamic β recrystallization treatment; wherein the billet is returned to the furnace by holding the temperature 10° C. below the phase transition point for a period of time 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 forging, i.e., upsetting along the radial direction of the ingot and elongating perpendicular to the radial direction of the ingot, at which time the metal at the original end is distributed on the circumference of the billet;

[0011] Step 3: Secondary α+β phase region remelting dynamic β recrystallization forging

[0012] The blank obtained in step 2 is heated to 10-100° C. below the phase transition point, 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 holding it at 10° C. below the phase transition point for a period of time and then rapidly heated to 50-100° C. above the phase transition point, 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;

[0013] Step 4: Two-phase zone upsetting forging

[0014] The billet 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, 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 fire is controlled between 20% and 45%, and remelting or air cooling is adopted after each fire forging;

[0015] Step 5: Two-phase zone drawing forging

[0016] The billet 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 subjected to two-phase zone drawing forging. During the drawing process, the square forging is changed to octagonal forging, thereby changing the large difference in metal flow resistance caused by the different contact areas between the edges and surfaces of the billet and the hammer anvil during the drawing process, improving the uniformity of deformation, and controlling the amount of drawing deformation per fire to be between 10% and 40%. After each fire forging, the billet is returned to the furnace or air-cooled, and then rolled and drawn to obtain the final required large-size titanium alloy bar.

[0017] Further, in the above step 1, the blank forging is performed for 2 fires, and the specific process is as follows: the first fire heating is to charge the furnace from 800°C, keep it warm for a period of time, and then fully heat through at 30°C below the phase transition point temperature, then heat it to the phase transition point temperature and keep it warm for a period of time, then quickly heat it to 1100-1150°C, keep it warm for 90-120min, then take it out of the furnace for 2 upsetting and 2 drawing, each upsetting and drawing deformation is controlled to 35%-45%, and air cooling is performed after forging; the second fire heating is also to charge the furnace from 800°C, keep it warm for a period of time, and fully heat through at 30°C below the phase transition point temperature, then heat it to the phase transition point temperature and keep it warm for a period of time, then quickly heat it to 1050-1100°C, keep it warm for 90-120min, then take it out of the furnace for 2 upsetting and 2 drawing, each upsetting and drawing deformation is controlled to 35%-45%, and water cooling is performed to 20-50°C within 2 hours after forging, and the cooling rate is ≥400°C / hour.

[0018] Furthermore, the specific process of the above step 2 is as follows:

[0019] The first heat 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 to be 30%-40%. After forging, the hot material is returned to the furnace;

[0020] The second heat uses a two-stage heating method. The billet is returned to the furnace and held at 10°C below the phase transition point for a period of time. After that, it is rapidly heated to 50-100°C above the phase transition point. After holding for 60-150 minutes, it undergoes a reverse upsetting and drawing process, which involves upsetting along the ingot's radial direction and then drawing perpendicular to the ingot's radial direction. The upsetting and drawing deformations are controlled at 20%-30%. The cross-section after forging is square, so that the original section of the billet is distributed around the billet's circumference. After forging, it is water-cooled to 20-50°C within 2 hours, with a cooling rate of ≥400°C / hour. This rapid cooling increases the grain nucleation rate and hinders grain growth.

[0021] Furthermore, the specific process of the above step 3 is as follows:

[0022] The first heat 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;

[0023] The second heat uses a two-stage heating method. The billet is returned to the furnace and held at 10°C below the phase transition point for a period of time. After that, it is rapidly heated to 50-100°C above the phase transition point. After holding for 60-150 minutes, it is subjected to one upsetting and one drawing. The deformation of upsetting and drawing is controlled between 20% and 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. This recrystallization process optimizes the microstructure of the original ingot center. After forging, it is cooled to 20-50°C in water within 2 hours, with a cooling rate of ≥400°C / hour. Rapid cooling increases the grain nucleation rate and hinders grain growth.

[0024] Furthermore, the specific process of the upsetting forging in step 4 is as follows:

[0025] The process is completed in four fires. After each fire, the steel is subjected to one upsetting and one drawing, followed by remelting and another upsetting and drawing. The deformation of each upsetting and drawing is controlled between 20% and 45%. Air cooling is performed after each fire. During the first upsetting and drawing in the third fire, a reversing upsetting is performed, i.e., upsetting is performed along the radial direction perpendicular to the ingot, and drawing is performed along the radial direction of the ingot to achieve end return. The steel is then returned to the furnace for one upsetting and one drawing. Finally, another upsetting is performed in one fire to improve the microstructure of the ingot end, which is located on the billet surface after reversing direction. This helps disrupt the directionality of the grains and avoid the formation of low-magnification coarse grains.

[0026] Furthermore, the specific process of the upsetting forging in step 5 is as follows:

[0027] 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 of each fire in the remaining fires is ≥100mm and the feed amount is ≥400mm. The drawing deformation of 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, if the current fire is drawing from the head end to the bottom end, the next fire is drawing from the bottom end to the head end, so as to avoid the drawing causing the grain growth direction to tend to be consistent.

[0028] The forging method is primarily used to produce TC2 bars with diameters of 300-400 mm, improving the macroscopic uniformity of the finished TC2 titanium alloy bars. It can also be used to produce other grades of titanium alloys, such as TC1 and TC4 for aircraft engines.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The present invention adopts a 4-5 stage heating curve for blank forging, which reduces the single-phase heating time (the conventional heating curve should be 3 stages or less. If a 4-5 stage heating curve is used, the holding time at 1100℃-1150℃ in the first heat of blanking is only 90-120 minutes, while a 3-stage heating curve requires at least 240 minutes of holding time at 1100℃-1150℃). This reduces the grain growth time at high temperature. Combined with the rapid cooling method after forging, it can accelerate grain nucleation and hinder the growth of billet grains.

[0031] 2. The present invention uses two α+β phase region remelting dynamic β recrystallization forgings and fire-interval reversing forging (referring to the radial upsetting along the ingot and the radial elongation perpendicular to the ingot during recrystallization in steps 2 and 3, and the radial upsetting perpendicular to the ingot and the radial elongation in step 4). This can effectively reduce the deformation difference between the end and middle parts of the bar during the free forging process. In addition, the fire-interval reversing forging disrupts the directionality of the grains, avoids the formation of low-magnification coarse grains, and effectively improves the uniformity of the low-magnification microstructure of the bar.

[0032] 3. The present invention uses four-way rotation, large reduction and feed, 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 bar structure.

[0033] 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 ring forgings forged with this bar also have greatly improved structure, meeting the standard requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a diagram showing the macrostructure of TC2 titanium alloy produced by free forging in the prior art and its EBSD test results;

[0035] Figure 2 This is the product standard low- and medium-magnification tissue rating diagram;

[0036] Figure 3 This is a transverse macroscopic microstructure diagram of the end of a Φ400mm rod prepared in Example 1 of the present invention;

[0037] Figure 4 This is a transverse macroscopic microstructure diagram of the middle portion of a Φ400mm rod prepared in Example 1 of the present invention;

[0038] Figure 5 This is the EBSD test result of the Φ400mm bar prepared in Example 1 of the present invention;

[0039] Figure 6This is a macroscopic microstructure of the inner ring surface of a ring forging made from a Φ400mm bar according to Example 1 of the present invention;

[0040] Figure 7 This is a low-magnification microstructure diagram of the inner ring surface of a ring forging made from a Φ400mm bar that is not prepared using the process of the present invention;

[0041] Figure 8 This is a transverse macroscopic microstructure diagram of the end of a Φ350mm rod prepared in Example 2 of the present invention;

[0042] Figure 9 This is a horizontal macrostructure diagram of the middle part of a Φ350mm rod prepared in Example 2 of the present invention;

[0043] Figure 10 This is the EBSD test result of the Φ350mm bar prepared in Example 2 of the present invention;

[0044] Figure 11 This is a low-magnification microstructure of the inner ring surface of a ring forging made of a Φ350mm bar prepared in Example 2 of the present invention.

[0045] Figure 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

[0046] The present invention will now be further described with reference to 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 solutions 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 billet with a square cross section, "◇" refers to the height of a billet with an octagonal cross section, and "Φ" refers to the diameter of a billet with a circular cross section.

[0047] Example 1 (Preparation of TC2 titanium alloy bar with a specification of Φ400 mm)

[0048] In this embodiment, the raw material is a TC2 Φ680mm ingot with a phase transition temperature of 950°C. The finished product is a Φ400mm large-size bar. The specific forging process is as follows:

[0049] ① Open forging: Heat the titanium alloy ingot to 800℃, hold the temperature for 90min, then heat it to 920℃, hold the temperature for 90min, then heat it to 950℃, hold the temperature for 120min, then quickly heat it to 1100℃, and hold the temperature for 90min. After the heat holding period, remove the ingot from the furnace and perform two upsets and two draws to forge a 600mm square billet, which is then air-cooled. Then heat the billet to 800℃, hold the temperature for 90min, then heat it to 920℃, hold the temperature for 90min, then heat it to 950℃, hold the temperature for 120min, then quickly heat it to 1050℃, hold the temperature for 90min. After the heat holding period, reverse the direction and perform two upsets and two draws to forge a 600mm square billet, which is then water-cooled.

[0050] ② First α+β phase region remelting dynamic β recrystallization forging: The billet obtained after blanking is heated to 920℃, with a holding coefficient (i.e., heating coefficient) of 0.7. After the holding period, it is subjected to 2 upsetting and 2 drawing to forge to a □600mm square billet. After forging, it is loaded into a heating furnace with a furnace temperature of 940℃ and held for 220min. Then, the temperature is rapidly raised to 1030℃ and held for 120min. After the holding period, a reversing upsetting and drawing forging with 1 upsetting and 1 drawing is performed, i.e., upsetting along the radial direction of the ingot is followed by drawing 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. The billet is forged to a □600mm square billet and water-cooled after forging.

[0051] ③ Secondary α+β phase region remelting dynamic β recrystallization forging: The billet obtained after step ② is heated to 920℃ with a holding coefficient of 0.7. After the holding period, it is subjected to two upsets and two draws to forge into a 600mm square billet. After forging, it is loaded into a heating furnace with a furnace temperature of 940℃ and held for 220min. Then, the temperature is rapidly raised to 1010℃ and held for 120min. After the holding period, it is subjected to one upset and one draw. At this time, the metal at the original end is still distributed on the circumference of the billet. It is forged into a 600mm square billet and water-cooled after forging.

[0052] ④ Two-phase zone upsetting and drawing forging: The billet is subjected to two-phase zone upsetting and drawing forging in four heats, with heating temperatures of 930°C, 900°C, 930°C, and 900°C, respectively. After each holding period, the billet undergoes upsetting and drawing, then returns to the original temperature and undergoes upsetting and drawing again. During the first upsetting and drawing of the third heating and forging heat, a reverse upsetting is performed, i.e., upsetting is performed in a radial direction perpendicular to the ingot, and drawing is performed in the radial direction of the ingot to achieve end retraction. Finally, the billet is forged to a 540mm square billet.

[0053] ⑤ Two-phase zone drawing forging: The billet is subjected to two-phase zone drawing forging for 2 times, with the heating temperature of each fire being 920℃. After the first fire is completed, 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 of Φ400mm bar. The drawing directions are opposite between the two fires.

[0054] The low-magnification specimens were cut from the end and middle of the Φ400mm TC2 titanium alloy rod prepared in this embodiment, and the microstructure photos after corrosion are as follows: Figure 3 、 4 As shown, the product standard is organized in low and medium times the rating 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 FIG, its directionality is significantly weakened compared with the original rod. At the same time, the Φ400mmTC2 titanium alloy rod forged without the existing process of the present invention is compared with the Φ400mmTC2 titanium alloy rod of this embodiment. The local magnification of the ring forgings under the same die forging process is as follows: Figure 6 、 7 As shown, the product standard is organized in low and medium times the rating Figure 2 Rated as 5 and 8, it is used to prove the uniformity of the rod structure.

[0055] Example 2 (Preparation of TC2 titanium alloy bar with a specification of Φ350mm)

[0056] In this embodiment, the raw material is TC2 Φ680mm ingot, the ingot phase transition temperature is 950°C, and the finished product is Φ350mm large-size bar. The specific forging process is as follows:

[0057] ① Heat the titanium alloy ingot to 800℃, hold the temperature for 90 minutes, then heat it to 920℃, hold the temperature for 90 minutes, heat it to 950℃, hold the temperature for 120 minutes, quickly heat it to 1100℃, and hold the temperature for 90 minutes. After the heat preservation, the ingot is forged into a 600mm square billet by two upsets and two draws, and then air-cooled after forging. Then heat the billet to 800℃, hold the temperature for 90 minutes, heat it to 920℃, hold the temperature for 90 minutes, heat it to 950℃, hold the temperature for 120 minutes, quickly heat it to 1050℃, hold the temperature for 90 minutes, and then reverse the direction of the billet and perform two upsets and two draws to form a 600mm square billet, and then water-cooled after forging.

[0058] ② First α+β phase region remelting dynamic β recrystallization forging: The billet obtained after blanking is heated to 920℃ with a holding coefficient of 0.75. After the holding period, it is subjected to two upsetting and two drawing operations to forge a □590mm square billet. After forging, it is loaded into a heating furnace with a furnace temperature of 940℃ and held for 220min. Then, the temperature is rapidly raised to 1040℃ and held for 120min. After the holding period, a reverse upsetting and drawing operation of one upsetting and one drawing is performed, i.e., upsetting along the radial direction of the ingot is followed by drawing 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. The billet is forged to a □590mm square billet and water-cooled after forging.

[0059] ③ Secondary α+β phase region remelting dynamic β recrystallization forging: The billet obtained after step ② is heated to 920℃ with a holding coefficient of 0.7. After the holding period, it is subjected to two upsets and two draws to forge a □590mm square billet. After forging, it is loaded into a heating furnace with a furnace temperature of 940℃ and held for 220min. Then, the temperature is rapidly raised to 1020℃ and held for 120min. After the holding period, it is subjected to one upset and one draw. At this time, the metal at the original end is still distributed on the circumference of the billet. It is forged to a □590mm square billet and water-cooled after forging.

[0060] ④ Two-phase zone forging: The billet is subjected to four rounds of two-phase zone upsetting and drawing forging. The heating temperatures for the four rounds are 940℃, 910℃, 940℃, and 910℃, respectively. After each holding period, the billet is upset and drawn once, then returned to the original temperature and upset and drawn again. During the second 940℃ heating forging, the first upsetting and drawing is reversed, i.e., upsetting is performed along the radial direction relative to the vertical ingot, and drawing is performed along the radial direction of the ingot to achieve end return. Finally, the billet is forged into a 540mm square billet.

[0061] 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 completed, the billet is drawn from four sides to eight sides to ◇410mm. After the second fire is completed, it is drawn to ◇380mm. The third fire is rounding drawing, and finally forged into a finished product Φ350mm bar. The drawing directions between the first and second fires are opposite.

[0062] The low-magnification specimens were cut from the end and middle of the Φ350mm TC2 titanium alloy rod prepared in this embodiment. The microstructure photos after corrosion are as follows: Figure 8-9 As shown, the product standard is organized in low and medium times the rating Figure 2 The EBSD test results are as follows: Figure 10 As shown in FIG, compared with the original rod, its directionality is significantly weakened. 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 FIG. Figure 11 、 12 As shown, the product standard is organized in low and medium times the rating Figure 2 Rated as 4 and 8, it is used to prove the uniformity of the rod structure.

Claims

1. A forging method for improving the macrostructure uniformity of large-scale TC2 titanium alloy bars, characterized in that: This is achieved by the following steps: Step 1: Forging Using a 4-5 stage heating curve, the titanium alloy ingot is heated to 1050-1150℃ with a heating coefficient of 0.3-0.9, and is upset using a flat anvil and stretched horizontally to a square. 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 forging. After forging, the hot material is returned to the furnace for dynamic β recrystallization treatment; the billet is returned to the furnace by holding it at 10° C. below the phase transition point for a period of time, 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 forging, that is, upsetting in the radial direction relative to the ingot and stretching in a 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 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 subjected to square upsetting forging. After forging, the hot material is returned to the furnace for dynamic β recrystallization treatment; the blank is returned to the furnace by holding it at 10° C. below the phase transition point for a period of time, 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 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 forging The billet 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 billet 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 subjected to two-phase zone drawing forging. During the drawing process, the square is converted to octagonal forging; the drawing deformation amount of each fire is controlled between 10%-40%, and after each fire forging, it 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-sized TC2 titanium alloy bars according to claim 1, characterized in that: In the above step 1, the blank forging is performed in two fires, and the specific process is as follows: the first fire heating is to charge the furnace from 800°C, keep it warm for a period of time, and then fully heat through at 30°C below the phase transition point temperature, then heat it to the phase transition point temperature and keep it warm for a period of time, then quickly heat it to 1100-1150°C, keep it warm 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 fire heating is also to charge the furnace from 800°C, keep it warm for a period of time, and then fully heat through at 30°C below the phase transition point temperature, then heat it to the phase transition point temperature and keep it warm for a period of time, then quickly heat it to 1050-1100°C, keep it warm 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-sized TC2 titanium alloy bars according to claim 2, characterized in that: After forging in step 1, the steel is cooled to 20-50°C in 2 hours with a cooling rate of ≥400°C / hour.

4. The forging method for improving the macrostructure uniformity of large-sized TC2 titanium alloy bars according to claim 1, characterized in that: The specific process of step 2 above is as follows: The first heat 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 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. After that, it is quickly heated to 50-100℃ above the phase transition point. After keeping it 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 perpendicular to the radial direction of the ingot. The deformation of upsetting and drawing is controlled at 20%-30%. The cross-section after forging is square, so that the original metal of the billet is distributed on the circumference of the billet. It is water-cooled after forging.

5. A forging method for improving the macrostructure uniformity of large-sized TC2 titanium alloy bars according to claim 4, characterized in that: After forging in step 2, the steel is cooled to 20-50°C in 2 hours with a cooling rate of ≥400°C / hour.

6. The forging method for improving the macrostructure uniformity of large-sized TC2 titanium alloy bars according to claim 1, characterized in that: The specific process of step 3 above is as follows: The first heat 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 it is quickly heated to 50-100℃ above the phase transition point. After keeping it for 60-150 minutes, it is upset and drawn once. 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 macrostructure uniformity of large-sized TC2 titanium alloy bars according to claim 6, characterized in that: After forging in step 3, the steel is cooled to 20-50°C in 2 hours with a cooling rate of ≥400°C / hour.

8. The forging method for improving the macrostructure uniformity of large-sized 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 the insulation of each firing, one upsetting and one drawing is carried out, and the steel is returned to the furnace and then upsetting and drawing is carried out again. The deformation of each upsetting and drawing is controlled between 20% and 45%, and air cooling is performed after each firing. During the first upsetting and drawing of the third firing, a reversing upsetting is performed, that is, 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. The forging method for improving the macrostructure uniformity of large-sized 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 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 of each fire in the remaining fires is ≥100mm and the feed amount is ≥400mm. The drawing deformation of each fire is controlled at 10%-40%. After each fire forging, it is returned to the furnace or air-cooled. The drawing direction between two adjacent fires is opposite.

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