Preparation method of large-size high-uniformity TC17 titanium alloy fine-grain rod material

Abstract

The application relates to a preparation method of large-specification high-uniformity TC17 titanium alloy fine-grain rod material, which comprises the following steps: S1, blooming forging: TC17 titanium alloy ingot is heated to above a phase transition point, multi-fire forging is carried out by adopting a combined upsetting and drawing deformation mode of stepwise temperature reduction and three-dimensional reversing, the blooming forging blank is obtained after air cooling of each fire forging; S2, intermediate blank forging: the blooming forging blank is heated, multi-fire upsetting and drawing forging is carried out by adopting an alternating circulation mode of below the phase transition point and above the phase transition point, water cooling is adopted for cooling after forging above the phase transition point, and the intermediate forging blank is obtained; S3, finished product forging: the intermediate forging blank is heated to below the phase transition point for multi-fire upsetting and drawing forming, air cooling is carried out after forging, and the TC17 titanium alloy fine-grain rod material is obtained. The technical problem that the organization uniformity of the large-specification TC17 titanium alloy rod material is difficult to control in the prior art is solved.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy preparation technology, specifically to a method for preparing large-size, highly uniform TC17 titanium alloy fine-grained rods. Background Technology

[0002] TC17 (Ti17) titanium alloy has a nominal composition of Ti-5Al-4Mo-4Cr-2Sn-2Zr. It was developed by GE in the early 1970s and has high strength, high toughness, high hardenability, excellent fatigue performance and good weldability. It is widely used in components such as discs, shafts and blades of fans and compressors in military and commercial aero engines.

[0003] With the pursuit of lightweight, large-scale, integrated, and higher thrust in aerospace engines, high-bypass turbofan engines have gradually become the mainstream. This has led to the integration and significant increase in size of core components (such as fan disks, compressor disks, and high-pressure compressor rotors). For example, the fan diameter has increased from 1.5 mm in the early days to more than 3 meters today. Traditional multi-stage compressors use split blade assembly, and the high-pressure compressor rotor is composed of multiple sections, requiring multiple welding and heat treatments. In order to effectively reduce the splicing of parts, reduce the weight of connecting parts, avoid welding weaknesses, and improve the integrity of the structure, modern engines tend to use integral blade disk designs, which require larger titanium alloy bars as forging blanks.

[0004] TC17 titanium alloy has a high content of β-stabilizing elements and a low phase transformation point, resulting in high deformation resistance in the two-phase region. This makes it difficult to forge the billet through, leading to insufficient deformation in the contact area between the billet and the anvil during forging. This creates a deformation "dead zone," causing uneven deformation and making it difficult to control the microstructure uniformity. Furthermore, as the bar size increases to ≥500mm, the heat storage during forging is higher, while the heat dissipation capacity is reduced. Energy accumulates in the core of the billet during deformation, resulting in a rapid rise in core temperature. This further reduces the deformation resistance in the core, making it more prone to plastic deformation and rapid strain accumulation, leading to excessive core deformation. In addition, a larger billet volume results in a larger contact area between the billet and the anvil during forging, creating a larger forging deformation "dead zone," making it even more difficult to forge through and causing regional uneven deformation, ultimately affecting the microstructure uniformity of the final bar. In addition, TC17 titanium alloy integral bladed disk forgings must adopt β forging to ensure high fracture toughness and creep resistance. The size and uniformity of the β recrystallized grains in the bar directly determine the microstructure of the forging. Insufficient or uneven deformation in the β single-phase region can easily lead to coarse β grains after β recrystallization treatment of the finished bar. Excessive deformation in the two-phase region can cause strong texture in the core of the billet. After β heat treatment, abnormal growth of the core grains due to recrystallization occurs, making it difficult to refine and homogenize the microstructure.

[0005] In view of this, there is an urgent need to develop a preparation process for large-size, highly uniform, fine-grained rods. Based on the processing characteristics of high-strength titanium alloys, the inventors hereby propose a method for preparing large-size, highly uniform, fine-grained TC17 titanium alloy rods. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a method for preparing large-size, highly uniform TC17 titanium alloy fine-grained bars. In the billet forging process, a stepped cooling and three-dimensional reversal upsetting deformation method is adopted. In the intermediate billet forging, the deformation amount above and below the phase transformation point is scientifically distributed. After forging above the phase transformation point, water cooling is used for cooling. In the finished product forging, multiple upsetting and drawing are performed to improve the uniformity of core and surface deformation and axial deformation of the billet. This solves the technical problem of difficulty in controlling the uniformity of the microstructure of large-size TC17 titanium alloy bars in the prior art.

[0007] To address the aforementioned technical problems, the present invention provides a method for preparing large-size, highly uniform TC17 titanium alloy fine-grained rods, comprising the following steps: S1. Forging: The TC17 titanium alloy ingot is heated to above the phase transformation point and then forged in multiple stages using a combination of stepped cooling and three-dimensional reversal upsetting deformation. After each stage of forging, it is air-cooled to obtain the forged blank. S2. Intermediate billet forging: The forged billet is heated and subjected to multiple upsetting and drawing forgings in an alternating cycle between below and above the phase transformation point. After forging above the phase transformation point, it is cooled by water cooling to obtain the intermediate billet. S3. Finished product forging: The intermediate forging billet is heated to below the phase transformation point and then subjected to multiple upsetting and drawing processes. After forging, it is air-cooled to obtain TC17 titanium alloy fine-grained bar stock.

[0008] Furthermore, in S1, the multi-fire forging is a 3-fire forging; The first heating is carried out at 200°C to 280°C above the phase transition point, and held for 500 to 650 minutes. The second heating is carried out at 150°C to 200°C above the phase transition point, and held for 400 to 550 minutes. The third heating is carried out at 100°C to 150°C above the phase transition point, and held for 400 to 550 minutes. The final forging temperature for each heat treatment shall not be lower than 750℃.

[0009] Furthermore, in S1, the upsetting ratio is controlled at 1.3 to 1.9, and the elongation deformation is controlled at 25% to 50%.

[0010] Furthermore, in S2, the multi-fire upsetting and drawing forging is a 4-fire forging; The first heating is carried out at 30°C to 70°C below the phase transformation point, and after holding at that temperature, upsetting and drawing are performed, followed by air cooling. The second heating is carried out to 30°C to 100°C above the phase transformation point, and after holding at that temperature, upsetting and drawing are performed, followed by water cooling. The third heating is carried out to 30°C to 70°C below the phase transformation point, and after holding at that temperature, upsetting and drawing forging are performed, followed by air cooling. The fourth heating is carried out to 30°C to 100°C above the phase transformation point, and after holding at that temperature, it is upsetting and drawing forging, followed by water cooling. The final forging temperature for each heat treatment shall not be lower than 650℃.

[0011] Furthermore, in S2, the holding time for the first firing is 400 min to 550 min, the holding time for the second firing is 300 min to 450 min, the holding time for the third firing is 400 min to 550 min, and the holding time for the fourth firing is 300 min to 450 min.

[0012] Furthermore, in S2, each forging process adopts a combination of multi-dimensional reversal and flattening deformation method, with the upsetting ratio controlled at 1.4 to 1.9 and the elongation deformation controlled at 30% to 50%.

[0013] Furthermore, in S3, the multi-fire upsetting and drawing process is a 4-5 fire forging process, with the heating temperature being 30°C to 70°C below the phase transformation point.

[0014] Furthermore, in S3, the upsetting and drawing process adopts a deformation method that alternates between flat and multi-dimensional reversal, the upsetting-to-forging ratio is controlled at 1.3 to 1.8, and the drawing deformation is controlled at 25% to 45%.

[0015] Furthermore, in S3, the elongation forming process adopts a deformation method that combines alternating transverse axes, alternating facets, diagonal drawing, and octagonal drawing.

[0016] Furthermore, in S3, the final forging temperature is not lower than 650℃.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The preparation method provided by this invention adopts a stepped cooling + three-dimensional reversal upsetting deformation method in the billet forging process, which can eliminate the deformation dead zone, fully break up the coarse cast structure, and refine the grains.

[0018] The intermediate billet forging employs a low-high cycle combined upsetting and drawing forging process. Through the scientific allocation of deformation above and below the phase transformation point, the deformation and phase transformation effects are utilized to achieve recrystallization and refinement of the billet microstructure. Furthermore, water cooling is used after forging above the phase transformation point, which rapidly freezes the deformed β grains, preventing static recrystallization and rapid growth during slow cooling, thus preserving a relatively fine β grain morphology. During rapid cooling, the phase cannot transform into a balanced close-packed hexagonal α phase through atomic diffusion; instead, a diffusionless hexagonal martensite α' is formed. This hexagonal martensite α' is abundantly generated in lath or needle-like forms within the original β grains. Although these laths are very small, their orientation differences are small, belonging to the same variant. Therefore, the effective grain size is the hexagonal martensite α' size, much smaller than the original β grains, achieving significant microstructure refinement.

[0019] During the forging process, the upsetting and drawing process adopts a flat square + multi-dimensional alternating deformation method, which effectively reduces the dead zone of insufficient deformation and improves the uniformity of billet deformation and forging penetration. The drawing and forming process adopts a transverse axial alternating + facet alternating + diagonal drawing + octagonal deformation method, thereby improving the uniformity of core and surface deformation and axial deformation of the billet, and obtaining large-size bars with uniform and fine structure of Φ500mm to Φ600mm. Attached Figure Description

[0020] Figure 1 This is a flowchart of the preparation method of the present invention.

[0021] Figure 2 This is a schematic diagram of the multi-dimensional reversing forging process in this invention.

[0022] Figure 3 This is a low-magnification microstructure of the forged head of a Φ600mm bar prepared in Example 1 of this invention.

[0023] Figure 4 This is a low-magnification microstructure of the tail section of a Φ600mm bar prepared in Example 1 of this invention.

[0024] Figure 5 These are high-magnification microstructure images of the edge, R / 2, and core of the Φ600mm bar prepared in Example 1 of this invention.

[0025] Figure 6 These are high-magnification microstructure images of the edge, R / 2, and core of the Φ600mm bar prepared in Example 1 of this invention under forging conditions.

[0026] Figure 7 This is a low-magnification image of the β-crystal hollow-burning head of a Φ600mm bar prepared in Example 1 of this invention.

[0027] Figure 8This is a low-magnification image of the tail β-crystal hollow burn-out of a Φ600mm bar prepared in Example 1 of this invention.

[0028] Figure 9 This is a low-magnification microstructure of the forged head of a Φ500mm bar prepared in Example 2 of this invention.

[0029] Figure 10 This is a low-magnification microstructure of the forged head of a Φ500mm bar prepared in Example 2 of this invention.

[0030] Figure 11 These are high-magnification microstructure images of the edge, R / 2, and core of the Φ500mm bar prepared in Example 2 of this invention.

[0031] Figure 12 These are high-magnification microstructure images of the edge, R / 2, and core of the Φ500mm bar prepared in Example 2 of this invention under forging conditions.

[0032] Figure 13 This is a low-magnification image of the β-crystal hollow-burning head of a Φ500mm specification bar prepared in Example 2 of the present invention.

[0033] Figure 14 This is a low-magnification image of the tail β-crystal hollow-burning of a Φ500mm bar prepared in Example 2 of the present invention. Detailed Implementation

[0034] like Figure 1 As shown, the present invention provides a method for preparing large-size, highly uniform TC17 titanium alloy fine-grained rods, comprising the following steps: S1. Forging of blanks: The TC17 titanium alloy ingot is heated above the phase transformation point, and then subjected to multiple forging processes using a combination of stepped cooling and three-dimensional reversal. After each forging process, the ingot is air-cooled to obtain a rough forging billet.

[0035] In this embodiment, the multi-fire forging is a three-fire forging.

[0036] Specifically, select qualified ingots, first heat the ingots to 200℃~280℃ above the phase transformation point, hold for 500min~650min for the first forging, and then air-cool for repair. Next, heat to 150℃~250℃ above the phase transformation point, hold for 400min~550min for the second forging, and then air-cool for repair. Finally, heat to 120℃~200℃ above the phase transformation point, hold for 400min~550min for the third forging, and then air-cool the billet. The final forging temperature for each stage should not be lower than 750℃.

[0037] In actual forging, the following methods are used: Figure 2The forging process combines flat and square shapes using an upsetting and drawing deformation method. The upsetting-to-roughing ratio is controlled at 1.3 to 1.9, and the drawing deformation is controlled at 25% to 50%. Combined with a stepped cooling forging method, the deformation dead zone is eliminated, the coarse as-cast structure is fully broken up, the grains are refined, and an intermediate billet is obtained.

[0038] S2. Intermediate billet forging: The forged billet is heated and subjected to multiple upsetting and drawing forgings in an alternating cycle between the phase transformation point and the phase transformation point. After forging above the phase transformation point, it is cooled by water cooling to obtain the intermediate billet.

[0039] Specifically, in this embodiment, the multi-fire upsetting and drawing forging is a four-fire forging. The intermediate billet obtained in S1 is first heated and held at a certain temperature, and then subjected to four-fire forging.

[0040] The first heating process involves heating the material to 30°C–70°C below the phase transformation point, holding it at that temperature for 400–550 minutes, followed by upsetting and forging, and then air cooling.

[0041] Then heat to 30℃~100℃ above the phase transformation point, hold for 300min~450min, and then perform a second upsetting and drawing forging, followed by water cooling.

[0042] The cold material is heated to 30°C to 70°C below the phase transformation point in the third heating process, held for 400 to 550 minutes, and then upsetting and drawing are performed. After forging, the material is air-cooled.

[0043] Then heat to 30℃~100℃ above the phase transformation point, hold for 300min~450min, and then perform the fourth forging. After forging, water cool.

[0044] The final forging temperature of each of the above forging processes is not lower than 650℃, and the final intermediate forging billet is obtained.

[0045] Preferably, in this embodiment, the upsetting deformation method of S2 adopts the following... Figure 2 The multi-dimensional reversal + flat deformation method shown has an upsetting ratio controlled at 1.4 to 1.9 and an elongation deformation amount controlled at 30% to 50%.

[0046] By employing a combination of low and high cycle upsetting and drawing forging, and through the scientific distribution of deformation above and below the phase transformation point, the effects of deformation and phase transformation are brought into play, thereby achieving recrystallization and refinement of the billet structure.

[0047] In addition, after forging above the phase transformation point, water cooling is used to quickly freeze the deformed β grains, preventing them from undergoing static recrystallization and rapid growth during slow cooling, thus preserving a relatively fine β grain morphology.

[0048] Furthermore, during rapid cooling, it cannot transform into a balanced close-packed hexagonal α phase through atomic diffusion. Instead, a diffusionless hexagonal martensite α' is formed. This hexagonal martensite α' is generated in large quantities in the form of laths or needles within the original β grains. Although these laths are very small, their orientation differences are small, and they belong to the same variant. Therefore, the effective grain size is the size of the hexagonal martensite α', which is much smaller than the original β grains, and significant microstructure refinement can be achieved.

[0049] S3. Finished product forging: The intermediate forging billet is heated to below the phase transformation point and then subjected to multiple upsetting and drawing processes. After forging, it is air-cooled to obtain TC17 titanium alloy fine-grained bar stock.

[0050] Specifically, the intermediate forging billet in S2 is heated to 30℃~70℃ below the phase transformation point, and then upsetting and drawing is performed 4~5 times. The final forging temperature is not lower than 650℃, and the billet is air-cooled after forging. This yields a 500mm~600mm high-uniformity TC17 titanium alloy fine-grained bar.

[0051] The same method is used in the upsetting process. Figure 2 The deformation pattern shown is a combination of flattened and multi-dimensional alternating deformation. Specifically, the upsetting ratio of S3 is controlled at 1.3 to 1.8, and the elongation deformation is controlled at 25% to 45%. This effectively reduces the dead zone of insufficient deformation and improves the uniformity of billet deformation and forging penetration.

[0052] Meanwhile, in S3, the drawing and forming process employs alternating transverse and axial deformation methods, as well as alternating facets, and a combination of diagonal and octagonal drawing. This improves the consistency of core and surface deformation, and the consistency of axial deformation in the billet, resulting in large-diameter bars with uniform and fine microstructure, ranging from Φ500mm to Φ600mm. Specific Implementation Example 1 like Figure 1 As shown, the present invention provides a method for preparing large-size, highly uniform TC17 titanium alloy fine-grained rods, comprising the following steps: S1. Forging of blanks: The TC17 titanium alloy ingot is heated above the phase transformation point, and then subjected to multiple forging processes using a combination of stepped cooling and three-dimensional reversal. After each forging process, the ingot is air-cooled to obtain a rough forging billet.

[0054] In this embodiment, the multi-fire forging is a three-fire forging.

[0055] Specifically, select a qualified ingot, heat the ingot to 200°C above the phase transformation point, hold it for 500 minutes, and then perform the first forging. After forging, air cool and repair the defects.

[0056] Then heat to 150°C above the phase transformation point, hold for 400 minutes, and perform a second forging. After forging, air cool for repair.

[0057] Then heat to 120°C above the phase transformation point, hold for 400 minutes, and perform a third forging. After forging, air cool the billet. The final forging temperature of each section is not lower than 750°C.

[0058] In actual forging, the following methods are adopted: Figure 2 The forging process combines flat and square shapes using an upsetting and drawing deformation method. The upsetting ratio is controlled at 1.3, and the drawing deformation is controlled at 25%. Combined with a stepped cooling forging method, the deformation dead zone is eliminated, the coarse as-cast structure is fully broken up, the grains are refined, and an intermediate billet is obtained.

[0059] S2. Intermediate billet forging: The forged billet is heated and subjected to multiple upsetting and drawing forgings in an alternating cycle between the phase transformation point and the phase transformation point. After forging above the phase transformation point, it is cooled by water cooling to obtain the intermediate billet.

[0060] Specifically, in this embodiment, the multi-fire upsetting and drawing forging is a four-fire forging process. The intermediate billet obtained in S1 is first heated and held at a certain temperature, and then subjected to four fire forging processes.

[0061] The first heating process involves heating the material to 30°C below the phase transformation point, holding it at that temperature for 400 minutes, and then performing upsetting and drawing forging. The material is then air-cooled after forging.

[0062] Then heat to 30°C above the phase transformation point, hold for 300 minutes, and then perform a second upsetting and drawing forging, followed by water cooling.

[0063] The cold material is heated to 30°C below the phase transformation point in the third heating process, held at that temperature for 400 minutes, and then upset and drawn. After forging, it is air-cooled.

[0064] Then heat to 30°C above the phase transformation point, hold for 300 minutes, and then perform the fourth forging. After forging, water cool.

[0065] The final forging temperature of each of the above forging processes is not lower than 650℃, and the final intermediate forging billet is obtained.

[0066] In this embodiment, the upsetting deformation method of S2 adopts the following... Figure 2 The multi-dimensional reversal + flat deformation method shown has an upsetting ratio controlled at 1.4 and an elongation deformation amount controlled at 30%.

[0067] S3. Finished product forging: The intermediate forging billet is heated to below the phase transformation point and then subjected to multiple upsetting and drawing processes. After forging, it is air-cooled to obtain TC17 titanium alloy fine-grained bar stock.

[0068] Specifically, the intermediate forging billet in S2 is heated to 30°C below the phase transformation point, and then subjected to four upsetting and drawing processes. The final forging temperature is not lower than 650°C, and the billet is air-cooled after forging. This yields a fine-grained TC17 titanium alloy bar with high uniformity, ranging from Φ500mm to Φ600mm.

[0069] The same method is used in the upsetting process. Figure 2 The deformation pattern shown is a combination of flattened and multi-dimensional alternating deformation. Specifically, the upsetting ratio of S3 is controlled at 1.3, and the elongation deformation is controlled at 25%. This effectively reduces the dead zone of insufficient deformation and improves the uniformity of billet deformation and forging penetration.

[0070] Meanwhile, in S3, the drawing and forming process employs alternating transverse and axial deformation methods, as well as alternating facets, and a combination of diagonal and octagonal drawing. This improves the consistency of core and surface deformation, and the consistency of axial deformation in the billet, resulting in large-diameter bars with uniform and fine microstructure, ranging from Φ500mm to Φ600mm. Specific Implementation Example 2 like Figure 1 As shown, the present invention provides a method for preparing large-size, highly uniform TC17 titanium alloy fine-grained rods, comprising the following steps: S1. Forging of blanks: The TC17 titanium alloy ingot is heated above the phase transformation point, and then subjected to multiple forging processes using a combination of stepped cooling and three-dimensional reversal. After each forging process, the ingot is air-cooled to obtain a rough forging billet.

[0072] In this embodiment, the multi-fire forging is a three-fire forging.

[0073] Specifically, select qualified ingots, first heat the ingots to 280°C above the phase transformation point, hold for 650 minutes, and perform the first forging. After forging, air cool and repair any defects. Then heat to 250°C above the phase transformation point, hold for 550 minutes, and perform the second forging. After forging, air cool and repair any defects. Then heat to 200°C above the phase transformation point, hold for 550 minutes, and perform the third forging. After forging, air cool the billet. The final forging temperature for each stage should not be lower than 750°C.

[0074] In actual forging, the following methods are used: Figure 2 The forging process combines flat and square shapes using an upsetting and drawing deformation method. The upsetting ratio is controlled at 1.9, and the drawing deformation is controlled at 50%. Combined with a stepped cooling forging method, the deformation dead zone is eliminated, the coarse as-cast structure is fully broken up, the grains are refined, and an intermediate billet is obtained.

[0075] S2. Intermediate billet forging: The forged billet is heated and subjected to multiple upsetting and drawing forgings in an alternating cycle between the phase transformation point and the phase transformation point. After forging above the phase transformation point, it is cooled by water cooling to obtain the intermediate billet.

[0076] Specifically, in this embodiment, the multi-fire upsetting and drawing forging is a four-fire forging process. The intermediate billet obtained in S1 is first heated and held at a certain temperature, and then subjected to four fire forging processes.

[0077] The first heating process involves heating the material to 70°C below the phase transformation point, holding it at that temperature for 550 minutes, and then performing upsetting and drawing forging. The material is then air-cooled after forging.

[0078] Then heat to 100°C above the phase transformation point, hold for 450 minutes, and then perform a second upsetting and drawing forging, followed by water cooling.

[0079] The cold material is heated to 70°C below the phase transformation point in the third heating process, held at that temperature for 550 minutes, and then upset and drawn, followed by air cooling.

[0080] Then heat to 100°C above the phase transformation point, hold for 450 minutes, and then perform the fourth forging. After forging, water cool.

[0081] The final forging temperature of each of the above forging processes is not lower than 650℃, and the final intermediate forging billet is obtained.

[0082] In this embodiment, the upsetting deformation method of S2 adopts the following... Figure 2 The multi-dimensional reversal + flattened deformation method shown has an upsetting ratio controlled at 1.9 and an elongation deformation amount controlled at 50%.

[0083] S3. Finished product forging: The intermediate forging billet is heated to below the phase transformation point and then subjected to multiple upsetting and drawing processes. After forging, it is air-cooled to obtain TC17 titanium alloy fine-grained bar stock.

[0084] Specifically, the intermediate forging billet in S2 is heated to 70°C below the phase transformation point, and then subjected to five upsetting and drawing processes. The final forging temperature is not lower than 650°C, followed by air cooling. This yields a fine-grained TC17 titanium alloy bar with a diameter of Φ500mm to Φ600mm and high uniformity.

[0085] The same method is used in the upsetting process. Figure 2 The deformation pattern shown is a combination of flat and multi-dimensional alternating deformation. Specifically, the upsetting ratio of S3 is controlled at 1.8, and the elongation deformation is controlled at 45%.

[0086] Meanwhile, in S3, the drawing and forming process employs alternating transverse and axial deformation methods, as well as alternating facets, and a combination of diagonal and octagonal drawing. This improves the consistency of core and surface deformation, and the consistency of axial deformation in the billet, resulting in large-diameter bars with uniform and fine microstructure, ranging from Φ500mm to Φ600mm. Specific Implementation Example 3 like Figure 1 As shown, the present invention provides a method for preparing large-size, highly uniform TC17 titanium alloy fine-grained rods, comprising the following steps: S1. Forging of blanks: The TC17 titanium alloy ingot is heated above the phase transformation point, and then subjected to multiple forging processes using a combination of stepped cooling and three-dimensional reversal. After each forging process, the ingot is air-cooled to obtain a rough forging billet.

[0088] In this embodiment, the multi-fire forging is a three-fire forging.

[0089] Specifically, select a qualified ingot, heat it to 250°C above the phase transformation point, and hold it at that temperature for 600 minutes. Perform the first forging, followed by air cooling for repair.

[0090] Then heat to 200°C above the phase transformation point, hold for 500 minutes, and perform a second forging. After forging, air cool for repair.

[0091] Then heat to 160°C above the phase transformation point, hold for 480 minutes, and perform the third forging. After forging, air cool the billet.

[0092] Furthermore, the final forging temperature of each stage is not lower than 750℃.

[0093] In actual forging, the following methods are used: Figure 2 The forging process combines flat and square shapes using an upsetting and drawing deformation method. The upsetting ratio is controlled at 1.6, and the drawing deformation is controlled at 35%. Combined with a stepped cooling forging method, the deformation dead zone is eliminated, the coarse as-cast structure is fully broken up, the grains are refined, and an intermediate billet is obtained.

[0094] S2. Intermediate billet forging: The forged billet is heated and subjected to multiple upsetting and drawing forgings in an alternating cycle between the phase transformation point and the phase transformation point. After forging above the phase transformation point, it is cooled by water cooling to obtain the intermediate billet.

[0095] Specifically, in this embodiment, the multi-fire upsetting and drawing forging is a four-fire forging. The intermediate billet obtained in S1 is first heated and held at a certain temperature, and then subjected to four-fire forging.

[0096] The first heating process involves heating the material to 50°C below the phase transformation point, holding it at that temperature for 500 minutes, and then performing upsetting and drawing forging. The material is then air-cooled after forging.

[0097] Then heat to 75°C above the phase transformation point, hold for 400 minutes, and then perform a second upsetting and drawing forging, followed by water cooling.

[0098] The cold material is heated to 50°C below the phase transformation point in the third heating process, held at that temperature for 500 minutes, and then upset and drawn. After forging, it is air-cooled.

[0099] Then heat to 75°C above the phase transformation point, hold for 400 minutes, and then perform the fourth forging. After forging, water cool.

[0100] The final forging temperature of each of the above forging processes is not lower than 650℃, and the final intermediate forging billet is obtained.

[0101] In this embodiment, the upsetting deformation method of S2 adopts the following... Figure 2 The multi-dimensional reversal + flat deformation method shown has an upsetting ratio controlled at 1.7 and an elongation deformation amount controlled at 40%.

[0102] S3. Finished product forging: The intermediate forging billet is heated to below the phase transformation point and then subjected to multiple upsetting and drawing processes. After forging, it is air-cooled to obtain TC17 titanium alloy fine-grained bar stock.

[0103] Specifically, the intermediate forging billet in S2 is heated to 50°C below the phase transformation point, and then subjected to four upsetting and drawing processes. The final forging temperature is not lower than 650°C, and the billet is air-cooled after forging. This yields a fine-grained TC17 titanium alloy bar with high uniformity, ranging from Φ500mm to Φ600mm.

[0104] The same method is used in the upsetting process. Figure 2 The deformation pattern shown is a combination of flattened and multi-dimensional alternating deformation. Specifically, the upsetting ratio of S3 is controlled at 1.6, and the elongation deformation is controlled at 35%. This effectively reduces the dead zone of insufficient deformation and improves the uniformity of billet deformation and forging penetration.

[0105] Meanwhile, in S3, the drawing and forming process employs alternating transverse and axial deformation methods, as well as alternating facets, and a combination of diagonal and octagonal drawing. This improves the consistency of core and surface deformation, and the consistency of axial deformation in the billet, resulting in large-diameter bars with uniform and fine microstructure, ranging from Φ500mm to Φ600mm.

[0106] To further verify the effectiveness of the preparation method of this invention, TC17 titanium alloy with a phase transformation point of 895±10℃ was selected for the following specific implementation: Option 1: This option provides a method for preparing a Φ600mm high-uniformity TC17 titanium alloy fine-grained rod, specifically implemented according to the following steps: S1, Forging in rough blanks The qualified ingot is first heated to 1170℃ and held for 600 minutes before being taken out of the furnace for the first upsetting and drawing deformation. The forging ratio is controlled at 1.6 during upsetting and the deformation amount is controlled at 35% during drawing. After forging, it is air cooled.

[0107] Then, after heating to 1080℃ and holding for 500 minutes, a second upsetting and drawing process is carried out. During upsetting, the forging ratio is controlled at 1.6, and during drawing, the deformation is controlled at 35%. After forging, the material is air-cooled.

[0108] Then, after heating to 1050℃ and holding for 500 minutes, the third upsetting and drawing process is carried out. During upsetting, the forging ratio is controlled at 1.6, and during drawing, the deformation is controlled at 35%. After forging, the defects are removed by air cooling.

[0109] All final forging temperatures were controlled above 750℃. The billet size after the third forging was □690mm. □ indicates square billet.

[0110] S2, intermediate billet forging The intermediate billet forging is completed in four stages.

[0111] Specifically, the heating temperature for the first heat treatment is 850℃~860℃, and after holding at that temperature for 500 minutes, the material is upset and drawn, and then air-cooled after forging.

[0112] Then heat to 980℃~990℃, hold for 400 minutes, and then perform a second upsetting and drawing, followed by water cooling.

[0113] Then heat to 850℃~860℃, hold for 450 minutes, and then perform the third upsetting and drawing, followed by air cooling.

[0114] Then heat to 960℃~970℃, hold for 350 minutes, and then perform the fourth upsetting and drawing, followed by water cooling.

[0115] The final forging temperature of the above-mentioned heat treatment is controlled above 650℃, the upsetting ratio is controlled between 1.5 and 1.8, the elongation deformation is controlled between 35% and 45%, and the specification after the fourth heat treatment is □650mm.

[0116] S3, Finished product forging: The forging process is completed in five stages, with a heating temperature of 850℃~860℃. The first three stages employ a flattened forging with alternating upsetting and drawing processes, with the upsetting ratio controlled at 1.5~1.7 and the drawing deformation controlled at 30%~45%. The final forging temperature is not lower than 600℃, followed by air cooling. The final forging specification after the second stage is a flattened square of 600×700mm.

[0117] The fourth and fifth heating cycles are at a temperature of 840℃ to 850℃. The deformation process involves alternating horizontal and axial deformation, alternating facet deformation, diagonal drawing, and octagonal drawing. The elongation deformation is controlled between 25% and 45%. Air cooling is used for cooling. The forged size is Φ610mm, and the final machined bar is Φ600mm.

[0118] Results analysis: Figure 3 , Figure 4 The images show the head and tail sections of a Φ600mm bar prepared by forging using the process of this invention, as described in Example 1. The images show that the low-magnification structures are free of delamination, cracks, pores, segregation, metallic and non-metallic inclusions, and other visible metallurgical defects. The structures are uniform and exhibit a blurred crystalline appearance. The low-magnification rating is Level 4, conforming to Appendix A of Technical Standard-2211-2021.

[0119] Figure 5 , Figure 6 The forged microstructures of the head, tail, edge, R / 2, and core of the corresponding bars show that the microstructure is a typical equiaxed structure after processing in a two-phase region. The high-magnification microstructures at different locations are consistent and all meet the standard requirements.

[0120] Figure 7 , Figure 8The grain size of the β recrystallization at the head and tail of the corresponding bar was checked by air burning (30℃ above the phase transformation point). It can be seen that the grain size is small and uniform, which meets the M-11.0 grade of GB / T6394 and satisfies the requirements of the standard.

[0121] As shown in Table 1 below, the mechanical properties of the Φ600mm bar prepared by Scheme 1 of the present invention meet all the standard requirements.

[0122] Table 1. Mechanical properties of Φ600mm bars prepared according to Scheme 1 of the present invention.

[0123] Option 2: This option provides a method for preparing a Φ500mm high-uniformity TC17 titanium alloy fine-grained rod, specifically implemented according to the following steps: S1, Forging in rough blanks The qualified ingots are first heated to 1170℃ and held for 550 minutes before being taken out of the furnace for the first upsetting and drawing deformation. During upsetting, the forging ratio is controlled at 1.5, and the deformation during drawing is controlled at 30%. After forging, the ingots are air-cooled. Then, the ingots are heated to 1050℃ and held for 450 minutes before the second upsetting and drawing deformation. During upsetting, the forging ratio is controlled at 1.6, and the deformation during drawing is controlled at 35%. After forging, the ingots are air-cooled. Then, the ingots are heated to 1020℃ and held for 450 minutes before the third upsetting and drawing deformation. During upsetting, the forging ratio is controlled at 1.6, and the deformation during drawing is controlled at 35%. The final forging temperature is controlled above 750℃. After forging, the ingots are air-cooled and cleaned. The billet size after the third forging is □600mm (where □ is square).

[0124] S2, intermediate billet forging The intermediate billet forging is completed in four stages.

[0125] Specifically, the heating temperature for the first heat treatment is 840℃~850℃, and after holding at that temperature for 450 minutes, upsetting and drawing are performed, followed by air cooling.

[0126] Then heat to 960℃~970℃, hold for 300 minutes, and then perform a second upsetting and drawing, followed by water cooling.

[0127] Then heat to 830℃~840℃, hold for 450 minutes, and then perform the third upsetting and drawing, followed by air cooling.

[0128] Then heat to 950℃~960℃, hold for 300 minutes, and then perform the fourth upsetting and drawing, followed by water cooling.

[0129] The final forging temperature of the above-mentioned heat treatment is controlled above 650℃, the upsetting ratio is controlled between 1.5 and 1.8, the elongation deformation is controlled between 35% and 45%, and the specification after the fourth heat treatment is □550mm.

[0130] S3, Finished product forging: The forging process is completed in four stages, with a heating temperature of 840℃~850℃. The first and second stages employ a flattened forging with alternating upsetting and drawing processes, with the upsetting ratio controlled at 1.5~1.7 and the drawing deformation controlled at 30%~45%. The final forging temperature is not lower than 600℃, followed by air cooling. The finished product after the second stage forging is a flattened square with dimensions of 500×550mm.

[0131] The third and fourth heating cycles are conducted at a temperature of 830℃ to 840℃. The deformation process involves alternating facets, diagonal drawing, and octagonal deformation. The elongation deformation is controlled between 25% and 45%. Air cooling is used for the process. The final forging size is Φ510mm, which is then machined into a Φ500mm bar.

[0132] Results analysis: Figure 9 , Figure 10 The low-magnification microstructure of the Φ500mm bar prepared by forging using the process of this invention in Scheme 2 shows that the low-magnification microstructure is free of delamination, cracks, pores, segregation, metallic and non-metallic inclusions and other metallurgical defects visible to the naked eye. The microstructure is uniform and exhibits a blurred crystal structure. Figure 11 , Figure 12 The forged microstructures of the head, tail, R / 2, and core of the corresponding bars show that the microstructure is a typical equiaxed structure after processing in a two-phase region. The high-magnification microstructures at different locations are consistent and meet the standard requirements. Figure 13 , Figure 14 The grain size of the β recrystallization at the head and tail of the corresponding bar was checked by air burning (30℃ above the phase transformation point). It can be seen that the grain size is small and uniform, which meets the M-11.0 grade of GB / T6394 and satisfies the requirements of the standard.

[0133] As shown in Table 2 below, the mechanical properties of the Φ500mm bar prepared by Scheme 2 of the present invention meet all the standard requirements.

[0134] Table 2 Mechanical properties of Φ500mm bars prepared according to Scheme 2 of the present invention

[0135] In summary, the preparation method of the present invention adopts a stepped cooling + three-dimensional reversal upsetting deformation method in the billet forging process, which can eliminate the deformation dead zone, fully break up the coarse cast structure, and refine the grains.

[0136] The intermediate billet forging employs a low-high cycle combined upsetting and drawing forging process. Through the scientific allocation of deformation above and below the phase transformation point, the deformation and phase transformation effects are utilized to achieve recrystallization and refinement of the billet microstructure. Furthermore, water cooling is used after forging above the phase transformation point, which rapidly freezes the deformed β grains, preventing static recrystallization and rapid growth during slow cooling, thus preserving a relatively fine β grain morphology. During rapid cooling, the phase cannot transform into a balanced close-packed hexagonal α phase through atomic diffusion; instead, a diffusionless hexagonal martensite α' is formed. This hexagonal martensite α' is abundantly generated in lath or needle-like forms within the original β grains. Although these laths are very small, their orientation differences are small, belonging to the same variant. Therefore, the effective grain size is the hexagonal martensite α' size, much smaller than the original β grains, achieving significant microstructure refinement.

[0137] During the forging process, the upsetting and drawing process adopts a flat square + multi-dimensional alternating deformation method, which effectively reduces the dead zone of insufficient deformation and improves the uniformity of billet deformation and forging penetration. The drawing and forming process adopts a transverse axial alternating + facet alternating + diagonal drawing + octagonal deformation method, thereby improving the uniformity of core and surface deformation and axial deformation of the billet, and obtaining large-size bars with uniform and fine structure of Φ500mm to Φ600mm.

[0138] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

[0139] In the description of the embodiments of this application, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In addition, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0140] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

Claims

1. A method for preparing large-size, highly uniform TC17 titanium alloy fine-grained rods, characterized in that, Includes the following steps: S1. Forging: The TC17 titanium alloy ingot is heated to above the phase transformation point and then forged in multiple stages using a combination of stepped cooling and three-dimensional reversal upsetting deformation. After each stage of forging, it is air-cooled to obtain the forged blank. S2. Intermediate billet forging: The forged billet is heated and subjected to multiple upsetting and drawing forgings in an alternating cycle between below and above the phase transformation point. After forging above the phase transformation point, it is cooled by water cooling to obtain the intermediate billet. S3. Finished product forging: The intermediate forging billet is heated to below the phase transformation point and then subjected to multiple upsetting and drawing processes. After forging, it is air-cooled to obtain TC17 titanium alloy fine-grained bar stock.

2. The method for preparing large-size, highly uniform TC17 titanium alloy fine-grained rods according to claim 1, characterized in that, In S1, the multi-fire forging is a 3-fire forging; The first heating is carried out at 200°C to 280°C above the phase transition point, and held for 500 to 650 minutes. The second heating is carried out at 150°C to 200°C above the phase transition point, and held for 400 to 550 minutes. The third heating is carried out at 100°C to 150°C above the phase transition point, and held for 400 to 550 minutes. The final forging temperature for each heat treatment shall not be lower than 750℃.

3. The method for preparing large-size, highly uniform TC17 titanium alloy fine-grained rods according to claim 2, characterized in that, In S1, the upsetting ratio is controlled at 1.3 to 1.9, and the elongation deformation is controlled at 25% to 50%.

4. The method for preparing large-size, highly uniform TC17 titanium alloy fine-grained rods according to claim 1, characterized in that, In S2, the multi-fire upsetting and drawing forging is a 4-fire forging; The first heating is carried out at 30°C to 70°C below the phase transformation point, and after holding at that temperature, upsetting and drawing are performed, followed by air cooling. The second heating is carried out to 30°C to 100°C above the phase transformation point, and after holding at that temperature, upsetting and drawing are performed, followed by water cooling. The third heating is carried out to 30°C to 70°C below the phase transformation point, and after holding at that temperature, upsetting and drawing forging are performed, followed by air cooling. The fourth heating is carried out to 30°C to 100°C above the phase transformation point, and after holding at that temperature, it is upsetting and drawing forging, followed by water cooling. The final forging temperature for each heat treatment shall not be lower than 650℃.

5. The method for preparing large-size, highly uniform TC17 titanium alloy fine-grained rods according to claim 4, characterized in that, In S2, the holding time for the first heat treatment is 400 min to 550 min, the holding time for the second heat treatment is 300 min to 450 min, the holding time for the third heat treatment is 400 min to 550 min, and the holding time for the fourth heat treatment is 300 min to 450 min.

6. The method for preparing large-size, highly uniform TC17 titanium alloy fine-grained rods according to claim 4, characterized in that, In S2, each forging process adopts a combination of multi-dimensional reversal and flattening deformation method, with the upsetting ratio controlled at 1.4 to 1.9 and the elongation deformation controlled at 30% to 50%.

7. The method for preparing large-size, highly uniform TC17 titanium alloy fine-grained rods according to claim 1, characterized in that, In S3, the multi-fire upsetting and drawing process involves 4 to 5 fires of forging, with the heating temperature ranging from 30°C to 70°C below the phase transformation point.

8. The method for preparing large-size, highly uniform TC17 titanium alloy fine-grained rods according to claim 7, characterized in that, In S3, the upsetting and drawing process adopts a deformation method that alternates between flat and multi-dimensional reversal. The upsetting-to-forging ratio is controlled at 1.3 to 1.8, and the drawing deformation is controlled at 25% to 45%.

9. The method for preparing large-size, highly uniform TC17 titanium alloy fine-grained rods according to claim 7, characterized in that, In S3, the elongation forming process adopts a deformation method that combines alternating transverse axis, alternating facets, diagonal drawing, and octagonal drawing.

10. The method for preparing large-size, highly uniform TC17 titanium alloy fine-grained rods according to claim 1, characterized in that, In S3, the final forging temperature shall not be lower than 650℃.

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