A method for producing a titanium alloy forging having a thickness greater than 200 mm by homogenizing and fine-graining

Abstract

The present application relates to titanium alloy forging technical field, especially to a kind of preparation method of homogeneous fine grain of titanium alloy forge piece with thickness greater than 200mm, which uses titanium alloy ingot as raw material, and carries out five stages of forging in turn: the first stage is carried out in beta phase region with upsetting and drawing forging ratio of 1.25~1.3;The second stage is carried out in (alpha + beta) phase region with upsetting and drawing forging ratio of 1.1~1.25;The third stage is carried out in beta phase region with drawing forging ratio of 1.3, and then water cooling;The fourth stage is carried out in (alpha + beta) phase region with drawing forging ratio of 1.3;The fifth stage is carried out in (alpha + beta) phase region with drawing forging ratio of 1.3~1.4, and finally formed.The present application realizes the short process preparation of very thick forge piece by the crystal control strategy of beta phase region small deformation + water cooling, combined with dynamic phase transition point temperature control and asymmetric anvil type deformation, obtains the uniform and fine structure from core to surface, the grain size difference is not more than 1 level, the mechanical property consistency is good, significantly reduces the production cost, and is suitable for the manufacture of large bearing structure in aviation and other fields.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy forging technology, and in particular to a method for preparing homogeneous fine grains of titanium alloy forgings with a thickness greater than 200 mm. Background Technology

[0002] Titanium alloys, due to their excellent specific strength, corrosion resistance, and high-temperature performance, have been widely used in high-end fields such as aerospace, shipbuilding, and nuclear energy equipment, and are an irreplaceable key material for manufacturing large load-bearing structural components. With the development of large-scale and high-performance aerospace equipment in my country, the demand for ultra-thick titanium alloy forgings with a thickness greater than 200 mm is becoming increasingly urgent, while higher requirements are also being placed on the uniformity of the microstructure and the stability of the performance of the forgings.

[0003] However, the existing manufacturing processes for large-size titanium alloy forgings with a thickness greater than 200mm have the following technical bottlenecks: First, the process is lengthy and inefficient. The traditional method for preparing Ti-6Al-4V titanium alloy forgings involves a two-step process: "ingot casting → billet forging → forging bar → peeling and flaw detection → forging." This method is not only lengthy, but also requires multiple peeling, flaw detection, and incoming / outgoing physical and chemical inspections due to the significant interfacial relationship between the forging bar and the forging. This results in low production efficiency, significant material waste, and high manufacturing costs.

[0004] Second, uneven microstructure and performance fluctuations. For ultra-thick forgings with a thickness greater than 200 mm, the internal stress and strain states of the forging vary greatly under traditional forging methods. The surface area deforms sufficiently, resulting in well-refined grains; however, the core area often suffers from insufficient deformation due to the difficulty in penetration, leading to the retention of coarse cast microstructure or abnormal grain growth. This uneven deformation directly manifests as significant differences in high-magnification microstructure dimensions from the surface to the core of the forging. The presence of coarse-grained and mixed-grained regions may become performance bottlenecks or crack initiation sources, leading to premature failure of the forging.

[0005] Third, the process involves numerous forging passes, resulting in high costs. To address the issue of coarse core microstructure, traditional processes often employ repeated upsetting and drawing forging with multiple forging passes and large deformations. While this helps refine the grains to some extent, for ultra-large forgings with a thickness greater than 200mm, this method is extremely inefficient, energy-intensive, and costly, and it still cannot guarantee sufficient deformation and a uniform microstructure in the core.

[0006] Therefore, how to achieve short-process, fewer firing cycles, and homogeneous fine-grained preparation of titanium alloy forgings with a thickness greater than 200 mm has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing homogeneous fine grains of titanium alloy forgings with a thickness greater than 200 mm, so as to solve the problems of lengthy process, numerous heating steps, coarse core structure, poor microstructure uniformity, and large performance fluctuations in existing production processes.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for preparing homogeneous fine-grained titanium alloy forgings with a thickness greater than 200 mm. The method uses titanium alloy ingots as raw materials and adopts a five-stage step-forging path. By combining the different heating regime, deformation parameters and cooling methods of each stage, the method achieves a controllable evolution from the as-cast structure to a fine-grained homogeneous structure. Finally, it directly forges a homogeneous fine-grained forging with a thickness greater than 200 mm, thereby eliminating the intermediate forging bar stage in the traditional process and achieving the purpose of short-process preparation.

[0009] Specifically, the method comprises the following five forging stages performed sequentially: The first stage: β-phase forging; the billet is heated in the β-phase region and then upsetting and drawing deformation with a forging ratio of 1.25~1.3 to break up the as-cast structure and initially improve the plasticity of the billet.

[0010] The second stage: (α+β) zone transition forging; a third forging is carried out, in which the intermediate billet is heated in the (α+β) two-phase zone and upsetting deformation with a forging ratio of 1.1~1.25 is performed to introduce the α phase and create conditions for subsequent β zone recrystallization.

[0011] The third stage: β-zone controlled crystal forging; a fourth forging is carried out, in which the intermediate billet is heated in the β-phase region and elongated by a forging ratio of 1.3. After deformation, the billet is water-cooled to control the recrystallization size of the β grains and obtain a uniform and fine β grain structure.

[0012] Fourth stage: one fine forging in the (α+β) zone; the fifth to seventh forgings are carried out, in which the intermediate billet is heated in the (α+β) two-phase zone and elongated by a forging ratio of 1.3. By utilizing the fine β grains obtained in the previous stage, a uniform α+β two-phase structure can be obtained by simple elongation.

[0013] Fifth stage: Secondary precision forging in the (α+β) zone; the intermediate billet is heated in the (α+β) two-phase zone for the eighth forging and subsequent forgings, and then elongated by a forging ratio of 1.3~1.4, finally forming a homogeneous fine-grained forging with a thickness greater than 200mm.

[0014] Furthermore, to achieve more precise organizational control, this invention introduces a dynamic phase transition point control strategy at key nodes: Before water cooling after the third stage (fourth firing) elongation deformation, the billet is cut into samples and its phase transformation point T is measured. β1 The heating temperature in the (α+β) two-phase region during the fourth stage (fifth to seventh firings) is based on the phase transition point T. β1 Confirmed, specifically T β1 -40℃. Heating at this temperature ensures that the forging process is always in the optimal (α+β) two-phase region, avoiding overheating or underheating caused by phase transformation point drift.

[0015] After the fourth stage (seventh firing) of elongation deformation, the head and tail are removed, and the billet is cut into samples to determine its phase transformation point T. β2 The heating temperature in the (α+β) two-phase region during the fifth stage (eighth firing and subsequent firings) is based on the phase transition point T. β2 Confirmed, specifically T β2 -40℃. Meanwhile, the heating and holding time for the eighth heating cycle is calculated as 0.7 × the thickness of the billet before deformation; the holding time for subsequent hot parts to be returned to the furnace is 90 minutes.

[0016] Furthermore, to enhance the core deformation and penetration capability, this invention employs an asymmetric anvil shape combined with a specific feed rate in the critical firing stage: During the third stage (fourth firing) of elongation deformation, an asymmetric elongation anvil is used, with an upper anvil width of 600 mm and a lower anvil width of 1800 mm. The elongation feed is controlled at 300-400 mm. This anvil shape, narrower at the top and wider at the bottom, can produce a stronger core penetration effect, making it easier for deformation to be transmitted to the core of the forging. Combined with small deformation in the β zone and water cooling, this achieves sufficient refinement of the core structure.

[0017] During the fifth stage (the eighth heat and thereafter) of elongation deformation, the elongation feed rate is controlled at 200~300mm. The feed rate is further reduced in this stage, which is beneficial to achieve uniform deformation of the entire cross section and improve the uniformity of the microstructure of the finished forging.

[0018] Furthermore, the present invention optimizes and limits the heating regime for each key heating cycle: The heating regime in the β phase region during the first stage (first and second heating cycles) is as follows: first, heat to 1065℃ and hold, then raise the temperature to 1150℃ and hold. This stepped heating helps to homogenize the temperature inside and outside the ingot and avoids excessive thermal stress.

[0019] The second stage (third heating) is heated at 960℃ in the (α+β) two-phase region, and the holding time is 600min.

[0020] The heating temperature in the β phase region during the third stage (fourth heating cycle) is 1065℃, and the holding time is 240min.

[0021] Furthermore, the present invention specifies the cooling process for different stages: After the first stage (first and second forging), the billet is cooled in air for 30-60 minutes before being reheated in the furnace. After the second stage (third firing) forging, the billet is cooled in air for no less than 180 minutes before being reheated in the furnace; After the third stage (fourth firing) of forging, the billet is water-cooled; In the fourth and fifth stages, except for the seventh firing followed by air cooling, the billets are reheated in the furnace after deformation in the remaining firing stages.

[0022] The method of this invention is particularly applicable to Ti-6Al-4V titanium alloy, whose ingot chemical composition is controlled by weight percentage as follows: Al: 6.4%~6.7%, V: 4.0%~4.4%, Fe: 0.16%~0.25%, O: 0.168%~0.20%, C: 0.020%~0.035%, N: 0.005%~0.015%.

[0023] The titanium alloy forgings with a thickness greater than 200 mm prepared by the above technical solution have uniform equiaxed or bimorphic microstructures in the core, 1 / 4 thickness and near-surface positions, and the grain size difference at different positions does not exceed level 1, thus achieving true homogeneous fine grain preparation.

[0024] Compared with the prior art, the present invention has the following beneficial effects: (1) Using titanium alloy ingots as raw materials, the final forging is formed in one step through a five-stage forging path, which completely eliminates the intermediate forging bar step in the traditional two-step method of "ingot → forging bar → forging". It also saves the processes of forging bar peeling, flaw detection, and physical and chemical inspection upon arrival and departure from the factory. This not only saves a large amount of titanium alloy material (reducing peeling loss), but also significantly shortens the production cycle, reduces production and manufacturing costs, and achieves high-efficiency short-process preparation.

[0025] (2) Through the process path of “β-zone billet opening → (α+β)-zone transition → β-zone controlled crystallization water cooling → (α+β)-zone precision forging”, especially the controlled crystallization strategy of rapid water cooling after small deformation in the β-zone during the fourth forging, the growth of β grains was successfully suppressed, and a uniform and fine β grain structure was obtained. Based on this, the subsequent (α+β) zone only requires simple small forging ratio drawing to obtain a uniform α+β dual-phase structure, which completely solves the problem of coarse core structure and significant difference between surface and core structure in extremely thick forgings under traditional processes. The forgings prepared by this invention have a uniform equiaxed or dual-phase structure from near the surface to the core, with a grain size difference of no more than 1 level, and minimal fluctuation in mechanical properties at different locations, demonstrating excellent structural uniformity and performance stability.

[0026] (3) Real-time measurement of the phase transformation point T of the billet at key nodes. β and with "T" β -40℃ is used as the temperature reference for subsequent (α+β) zone heating. This dynamic control strategy fully considers the evolution of composition and structure of large ingots after multiple forgings, ensuring that the heating temperature is always in the optimal (α+β) zone, avoiding structural abnormalities caused by phase transformation point drift. It has strong process adaptability and is particularly suitable for long-process forging with large specifications and multiple heating cycles.

[0027] (4) In the β-zone controlled crystal forging stage, an asymmetric elongated anvil (upper anvil 600mm / lower anvil 1800mm) with a narrow upper anvil and a wide lower anvil was used, along with a feed rate of 300~400mm, which significantly enhanced the core penetration ability of the deformation, allowing the core area, which was originally difficult to deform, to obtain sufficient strain, laying a solid foundation for subsequent microstructure refinement. In the finished product forging stage, the feed rate was further reduced to 200~300mm, achieving uniform deformation of the entire cross section and ensuring the consistency of the microstructure of the finished forging. Attached Figure Description

[0028] Figure 1 The images show the high-magnification microstructure (100× and 500×) at different locations on the head of the forging prepared in Example 1 of this invention, where: (a) near the surface (100×); (b) near the surface (500×); (c) one-quarter thickness location (100×); (d) one-quarter thickness location (500×); (e) core location (100×); and (f) core location (500×).

[0029] Figure 2 The images show the high-magnification microstructure (100× and 500×) at different locations on the tail of the forging prepared in Example 1 of this invention, where: (a) near the surface (100×); (b) near the surface (500×); (c) one-quarter thickness (100×); (d) one-quarter thickness (500×); (e) core (100×); and (f) core (500×).

[0030] Figure 3 The images show the high-magnification microstructure (100× and 500×) at different locations on the head of the forging prepared in Example 2 of this invention, where: (a) near the surface (100×); (b) near the surface (500×); (c) one-quarter thickness location (100×); (d) one-quarter thickness location (500×); (e) core location (100×); and (f) core location (500×).

[0031] Figure 4The images show the high-magnification microstructure (100× and 500×) at different locations on the tail of the forging prepared in Example 2 of the present invention, wherein: (a) near the surface (100×); (b) near the surface (500×); (c) one-quarter thickness (100×); (d) one-quarter thickness (500×); (e) core (100×); and (f) core (500×). Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0033] Example 1: This embodiment provides a method for preparing a Ti-6Al-4V titanium alloy forging with an outer contour dimension of 1230mm (length) × 340mm (width) × 240mm (thickness). The specific steps are as follows: Step 1: Ingot preparation; Ti-6Al-4V titanium alloy ingots with a diameter of 810 mm and a length of 1850 mm were prepared using a three-stage vacuum arc remelting (VAR) process. Chemical composition analysis was performed on slices from both ends of the ingot, and the results are shown in Table 1, conforming to the composition range required in this embodiment.

[0034] Step 2: First firing, β zone forging; The ingot was heated in a stepped manner in the β phase region: first, it was heated to 1065℃ and held for 480 min; then, it was heated to 1150℃ and held for 180 min.

[0035] The heated ingot was axially upset on an 80MN high-speed forging mill, with the length upset from 1850mm to 1480mm (forging ratio 1.25). Then, axial drawing and rounding were performed, lengthening the ingot to 720mm × 720mm, and then rounding it to a diameter of 810mm (forging ratio 1.3). A second axial upsetting was then performed, again lengthening the ingot from 1850mm to 1420mm (forging ratio 1.3); this was followed by a second axial drawing and rounding, lengthening the ingot to 740mm × 740mm, and then rounding it to a diameter of 840mm. The final ingot size was 840mm × 1720mm (forging ratio 1.25). After deformation, the ingot was air-cooled for 60 minutes and then reheated in the furnace.

[0036] Step 3: Second firing, β-zone forging; The intermediate billet was heated in the β phase region at a temperature of 1065℃ and held for 180 min.

[0037] The heated billet was axially upset on an 80MN high-speed forging mill, with the length upset from 1720mm to 1325mm (forging ratio 1.3). Then, it was axially drawn and rounded to 740mm × 740mm, and then rounded to a diameter of 840mm, resulting in a final billet size of 840mm × 1720mm (forging ratio 1.3). After deformation, the billet was air-cooled for 240 minutes and then reheated in the furnace.

[0038] Step 4: Third firing, transition forging in the (α+β) zone; The intermediate billet was heated in the (α+β) two-phase region at a temperature of 960℃ and a holding time of 600min.

[0039] The heated billet is axially upset on an 80MN high-speed forging mill, with the length upset from 1720mm to 1375mm (forging ratio 1.25); then axially drawn into a flattened shape, lengthening the billet to 700mm×900mm×1510mm (forging ratio 1.1). The drawing feed is controlled at 300~400mm. After deformation, the billet is returned to the furnace for reheating.

[0040] Step 5: Fourth firing, β-zone controlled crystal forging; The intermediate billet was heated in the β phase region at a temperature of 1065℃ and held for 240 min.

[0041] The heated billet was axially drawn on an 80MN high-speed forging mill using an asymmetric drawing anvil (upper anvil width 600mm, lower anvil width 1800mm). The drawing feed was controlled at 300-400mm, drawing the billet to 700mm×700mm×1940mm (forging ratio 1.3). After deformation, the billet was immediately water-cooled. After water cooling, a sample was cut to determine the phase transformation point of the current billet, denoted as T. β1 ; Actual measured T β1 It is 1005℃.

[0042] Step 6: From the fifth to the seventh firing, perform a final forging in the (α+β) zone; Fifth heating: The intermediate billet is heated in the (α+β) two-phase region at a temperature of T. β1 Heating to -40℃ (up to 965℃), holding time calculated as 0.7 × undeformed billet thickness, billet thickness 700mm, holding time 490min. The heated billet is axially elongated on an 80MN high-speed forging mill, with elongation feed controlled at 300~400mm, elongating the billet to 610mm×610mm×2538mm (forging ratio 1.3). After deformation, the hot billet is returned to the furnace.

[0043] Sixth heating cycle: The hot intermediate billet is returned to the furnace and heated in the (α+β) two-phase region at 965℃ for 90 minutes. The heated billet is then axially drawn on an 80MN high-speed forging mill, with the drawing feed controlled at 300~400mm, resulting in a billet length of 530mm×530mm×3385mm (forging ratio 1.3). After deformation, the hot billet is returned to the furnace.

[0044] Seventh heating cycle: The intermediate billet is returned to the furnace and heated in the (α+β) two-phase region at 965℃ for 90 minutes. The heated billet is then axially drawn on an 80MN high-speed forging mill, with the drawing feed controlled at 300~400mm, resulting in a billet length of 460mm×460mm×4490mm (forging ratio 1.3). After deformation, the billet is air-cooled.

[0045] Step 7: Phase transition point determination and material feeding; The beginning and end of the billet are removed, and low-magnification inspection confirms that the beginning and end have been completely removed. A sample is taken to determine the phase transformation point of the current billet, denoted as T. β2 Actual T β2 The temperature is 1005℃. Cut the forging to the required weight, and cut the blank to a size of 460mm×460mm×475mm. Then reheat it in the furnace.

[0046] Step 8: Secondary fine forging in the (α+β) zone from the eighth to the tenth firing; Eighth heating cycle: The billet after cutting is heated in the (α+β) two-phase region at a temperature of T. β2 Heating to -40℃ (up to 965℃), holding time is calculated as 0.7 times the original billet thickness. For a billet thickness of 460mm, the holding time is 322 minutes (approximately 320 minutes). The heated billet is then axially elongated on an 80MN high-speed forging mill, with the elongation feed controlled at 200~300mm, elongating the billet to 390mm×390mm×660mm (forging ratio 1.3~1.4). After deformation, the hot billet is returned to the furnace.

[0047] Ninth heating cycle: The intermediate billet is returned to the furnace and heated in the (α+β) two-phase region at 965℃ for 60 minutes. The heated billet is then axially drawn on an 80MN high-speed forging mill, with the drawing feed controlled at 200~300mm, to a length of 310mm×350mm×925mm (forging ratio 1.3~1.4). After deformation, the billet is air-cooled.

[0048] Tenth heating cycle: The intermediate billet is returned to the furnace and heated in the (α+β) two-phase region at 965℃ for 60 minutes. The heated billet is then axially drawn on an 80MN high-speed forging mill, with the drawing feed controlled at 200-300mm, resulting in a billet length of 240mm × 340mm × 1230mm (forging ratio 1.3-1.4), ultimately forming a 240mm thick forging. After deformation, the billet is air-cooled.

[0049] Step 9: Heat Treatment The forging is heated to 730℃, held for 3 hours, and then subjected to ordinary annealing to obtain the final forging.

[0050] Example 2: This embodiment provides a method for preparing a Ti-6Al-4V titanium alloy forging with an outer contour dimension of 2715mm (length) × 650mm (width) × 235mm (thickness); wherein steps 1 to 7 are exactly the same as in embodiment 1, until the billet size is 460mm × 460mm × 4490mm after the seventh forging.

[0051] Step 8: Phase transition point determination and material feeding; Cut off the head and tail of the billet and measure the phase transformation point T. β2 Actual T β2 The temperature is 1005℃. Cut the forging to the required weight, and cut the blank to a size of 460mm×460mm×1960mm. Then reheat it in the furnace.

[0052] Step 9: Eighth firing, secondary precision forging in the (α+β) zone; Eighth heating cycle: The billet after cutting is heated in the (α+β) two-phase region at a temperature of T. β2 The temperature was -40℃ (i.e., 965℃), and the holding time was calculated as 0.7 times the original billet thickness. The billet thickness was 460mm, and the holding time was 322 minutes (approximately 320 minutes). The heated billet was then axially drawn on an 80MN high-speed forging mill, with the drawing feed controlled at 200~300mm, directly drawing the billet to 235mm×650mm×2715mm (forging ratio 1.3~1.4), ultimately forming a forging with a thickness of 235mm. After deformation, the billet was air-cooled.

[0053] Step 10: Heat treatment; The forging is heated to 730℃, held for 3 hours, and then subjected to ordinary annealing to obtain the final forging.

[0054] Chemical composition analysis, room temperature tensile property testing, and high-magnification microstructure observation were performed on the Ti-6Al-4V titanium alloy forgings prepared in Examples 1 and 2.

[0055] 1. Chemical Composition Analysis: The chemical composition of the ingots from Examples 1 and 2 was analyzed, and the results are shown in Table 1. It can be seen that the composition of the ingots from both ends is uniform and within the range required by this invention.

[0056] Table 1. Chemical composition of ingots in Examples 1 and 2 (Wt.%)

[0057] 2. Room temperature tensile properties: Forgings prepared in Examples 1 and 2 were sampled at different locations (1 / 2 thickness longitudinal direction, 1 / 2 thickness high direction, 1 / 2 thickness transverse direction, 1 / 4 thickness transverse direction) for room temperature tensile tests. The results are shown in Table 2.

[0058] Table 2. Room temperature tensile properties of Examples 1 and 2

[0059] As can be seen from the data in Table 2, the forgings prepared by the method of this invention exhibit excellent consistency and stability in room temperature tensile properties, regardless of the direction (longitudinal, transverse, and top) or thickness position (1 / 2 thickness, 1 / 4 thickness). The yield strength is consistently between 860 and 895 MPa, the tensile strength between 920 and 965 MPa, the elongation between 17% and 22%, and the reduction of area between 25% and 41%. All performance indicators meet the stringent requirements for aerospace titanium alloy forgings.

[0060] 3. High-magnification microstructure observation: Samples were taken from the near-surface of the head and tail, at 1 / 4 thickness, and at the core of the forgings prepared in Examples 1 and 2, respectively, for high-magnification microstructure observation (100× and 500×). The results are as follows: Figures 1 to 4 As shown.

[0061] from Figures 1 to 4 It is clearly visible that, from near the surface to the core, both the head and tail of the forging exhibit a uniform equiaxed or bimodal microstructure, with no obvious coarse grains, mixed grains, or residual cast microstructure. The grain size difference between different locations is extremely small; statistical measurements show that the grain size difference at each location does not exceed level 1, indicating that the method of this invention achieves truly homogeneous fine-grained preparation. 500× high-magnification images show that the α and β phases are uniformly distributed, the lamellar structure is fully broken, and the microstructure details are excellent.

[0062] This invention provides a method for preparing homogeneous fine-grained titanium alloy forgings with a thickness greater than 200 mm. The process flow is clear, and the parameters are precisely controlled. It can be directly implemented on existing forging equipment such as an 80MN high-speed forging machine without additional investment or modification. The forgings prepared by this method have uniform microstructure and stable properties, and can be widely used in the manufacture of large load-bearing structural components in high-end fields such as aerospace, shipbuilding, and nuclear energy equipment. It has broad industrial application prospects and promotional value.

[0063] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing homogeneous fine-grained titanium alloy forgings with a thickness greater than 200 mm, characterized in that, This includes forging using titanium alloy ingots as raw materials, and performing the following stages sequentially: The first stage involves the first and second forging processes, in which the billet is heated in the β phase region and subjected to upsetting deformation with a forging ratio of 1.25 to 1.

3. The second stage involves a third forging process, in which the intermediate billet is heated in the (α+β) two-phase region and subjected to upsetting deformation with a forging ratio of 1.1 to 1.

25. The third stage: the fourth forging is carried out, the intermediate billet is heated in the β phase region and drawn out with a forging ratio of 1.3, and the billet is water-cooled after deformation; The fourth stage involves the fifth to seventh forging processes, in which the intermediate billet is heated in the (α+β) two-phase region and subjected to elongation deformation with a forging ratio of 1.

3. Fifth stage: Forging is carried out for the eighth time and thereafter. The intermediate billet is heated in the (α+β) two-phase region and elongated by a forging ratio of 1.3~1.4, and finally formed into a forging with a thickness greater than 200mm.

2. The method for preparing homogeneous fine grains of titanium alloy forgings with a thickness greater than 200 mm according to claim 1, characterized in that, Before water cooling after the fourth drawing deformation, the process also includes cutting the billet into samples and determining its phase transformation point T. β1 The steps; the heating temperature in the (α+β) two-phase region during the fifth to seventh firings is based on the phase transition point T. β1 Confirmed, specifically T β1 -40℃.

3. The method for preparing homogeneous fine-grained titanium alloy forgings with a thickness greater than 200 mm according to claim 2, characterized in that, After the seventh forging, the process also includes removing the head and tail of the billet and measuring the phase transformation point T of the billet. β2 The steps; the heating temperature in the (α+β) two-phase region after the eighth heating cycle is based on the phase transition point T. β2 Confirmed, specifically T β2 -40℃.

4. The method for preparing homogeneous fine grains of titanium alloy forgings with a thickness greater than 200 mm according to claim 1, characterized in that, In the fifth stage, the heating and holding time for the eighth heat is calculated as 0.7 × the thickness of the billet before deformation; the holding time for subsequent hot parts to be returned to the furnace is 90 minutes.

5. The method for preparing homogeneous fine grains of titanium alloy forgings with a thickness greater than 200 mm according to claim 1, characterized in that, When the fourth drawing forging is performed, an asymmetric drawing anvil is used, with an upper anvil width of 600mm and a lower anvil width of 1800mm, and the drawing feed is controlled at 300~400mm; when the eighth drawing forging and subsequent drawing forging are performed, the drawing feed is controlled at 200~300mm.

6. The method for preparing homogeneous fine grains of titanium alloy forgings with a thickness greater than 200 mm according to claim 1, characterized in that, The heating regime in the β phase region for the first and second firings is as follows: first heat to 1065℃ and hold, then heat to 1150℃ and hold.

7. The method for preparing homogeneous fine grains of titanium alloy forgings with a thickness greater than 200 mm according to claim 1, characterized in that, The third heating in the (α+β) two-phase region was at a temperature of 960℃, and the holding time was 600 min.

8. The method for preparing homogeneous fine grains of titanium alloy forgings with a thickness greater than 200 mm according to claim 1, characterized in that, The third heating process in the (α+β) two-phase region is heated at 960℃ and held for 600 min; the fourth heating process in the β phase region is heated at 1065℃ and held for 240 min.

9. The method for preparing homogeneous fine grains of titanium alloy forgings with a thickness greater than 200 mm according to claim 1, characterized in that, After the first stage (first and second forging), the billet is cooled in air for 30-60 minutes before being reheated in the furnace; after the second stage (third forging), the billet is cooled in air for at least 180 minutes before being reheated in the furnace.

10. A method for preparing homogeneous fine-grained titanium alloy forgings with a thickness greater than 200 mm according to any one of claims 1-9, characterized in that, The titanium alloy is a Ti-6Al-4V titanium alloy, and its ingot chemical composition by weight percentage is: Al: 6.4%~6.7%, V: 4.0%~4.4%, Fe: 0.16%~0.25%, O: 0.168%~0.20%, C: 0.020%~0.035%，N：0.005%~0.015%。

Images