A method for preparing a beta state TC17 titanium alloy bar

Abstract

The present application belongs to the technical field of titanium alloy material processing, and particularly relates to a preparation method of beta-state TC17 titanium alloy bar. The TC17 titanium alloy ingot is subjected to open-die forging, and after high-temperature heating and holding, is subjected to first three-dimensional elongation forging. Then, after high-temperature heating and holding, upsetting and diagonal elongation forging are performed, and meanwhile, the relative radial direction of the blank to the ingot is changed. After high-temperature heating and holding, second three-dimensional elongation forging is performed. Then, after low-temperature heating and holding below the phase transition point, upsetting and elongation forging are performed. After heating in a furnace and heating to medium temperature above the phase transition point, upsetting forging is performed. After air cooling to room temperature, elongation forging is performed at low temperature below the phase transition point. After heating in a furnace and heating to medium temperature above the phase transition point, elongation forging is performed. After cooling, beta-state TC17 titanium alloy bar with a diameter of Φ250mm-Φ350mm is obtained. The process has a short production flow and a high yield, and can relatively quickly obtain beta-state TC17 bar with fine and uniform beta grain structure.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy material processing technology, specifically relating to a method for preparing β-state TC17 titanium alloy rods. Background Technology

[0002] TC17 titanium alloy, with a nominal composition of Ti-5Al-2Sn-2Zr-4Cr-4Mo, is a near-β type titanium alloy with high strength, high toughness and high hardenability. It maintains significant strength advantages from room temperature to 400℃, and has excellent high-temperature creep resistance and endurance performance. It is widely used in key parts such as aero-engine fans and compressor discs.

[0003] Currently, the production process for TC17 alloy parts is generally as follows: 1) Three-stage VAR melting to prepare ingots; 2) Using a high-speed forging mill, multiple forging processes are performed to prepare bars with a two-phase region (α+β) forged structure. The structure of the bars is equiaxed, and its characteristics are described in [reference needed]. Figure 1 3) After the bar stock passes inspection, it is sawn into sections, heated to a two-phase temperature below the phase transformation point, and then formed into a billet by a fast forging machine. After that, it is heated to a temperature above the phase transformation point and then β-forged to form a forging. 4) After the forging passes inspection, it is machined into usable parts.

[0004] Currently, the general method for melting titanium alloy ingots is vacuum arc melting technology. TC17 contains up to 4% Cr, which is very easy to segregate. In order to improve the homogeneity of the ingot composition, the macrostructure of the ingot is basically parallel to the ingot axis and consists of coarse columnar crystals through melting process design.

[0005] For β-forged forgings, the β grain size is a key factor affecting their performance. Coarse β grains lead to performance deterioration such as fatigue in forgings, rendering them unusable. Therefore, one of the key aspects of bar stock preparation is to obtain fine and uniform β grains through forging design.

[0006] To refine the large grains in cast ingots, the existing method involves first undergoing multiple high-temperature heating followed by upsetting and drawing (hereinafter referred to as "upsetting and drawing") forging to initially break down the large grains in the cast state. Then, multiple low-temperature upsetting and drawing forgings combined with medium-temperature upsetting and drawing forging are used to refine the β grains. Finally, multiple low-temperature upsetting and drawing processes are used to prepare the bar stock, thereby further refining the β grains and obtaining a two-phase (α+β) forged microstructure. This production process is lengthy, requiring 12–16 heating and forging cycles. The numerous heating cycles and post-forging crack polishing treatments result in a low yield of the bar stock. The prepared bars possess an equiaxed microstructure and exhibit excellent tensile properties during inspection, but their fracture toughness and creep resistance are poor. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing β-state TC17 titanium alloy bars. A forging process is designed based on the microstructure characteristics of the ingot. This process has a short production flow and a high yield, and can obtain β-state TC17 bars with fine and uniform β-grain microstructure relatively quickly. At the same time, in response to the performance shortcomings of α+β forged bars with equiaxed microstructure, β-state bars obtain better fracture toughness and creep resistance.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing β-state TC17 titanium alloy rods, comprising the following steps:

[0009] Step 1: After heating and holding the TC17 titanium alloy ingot at high temperature, forge it into a billet with dimensions a×b×c.

[0010] Step 2: After heating and holding the above billet at high temperature, perform the first three-dimensional elongation forging.

[0011] Step 3: After the billet forged in Step 2 is heated and held at high temperature, it is upsetting and diagonally drawn into a billet with dimensions of a×b×c. At the same time, the radial orientation of the billet relative to the ingot is changed. After being returned to the furnace and heated and held at high temperature, it is subjected to a second three-dimensional drawing forging.

[0012] Step 4: After the billet forged in Step 3 is heated and held at a low temperature below the phase transformation point, it is subjected to two upsetting and drawing forging processes. Then, it is heated in the furnace to a medium temperature above the phase transformation point and held for upsetting forging. After air cooling to room temperature, the forged billet is cylindrical.

[0013] Step 5: After the billet forged in Step 4 is heated and held at a low temperature below the phase transformation point, it is then drawn and forged multiple times. After that, it is heated in the furnace to a medium temperature above the phase transformation point and held for a forming fire to obtain a bar billet. Finally, it is cooled and processed to obtain TC17 titanium alloy bar.

[0014] Preferably, the temperature of the high-temperature heating and heat preservation is T = T β +(130℃~355℃), the temperature of the medium-temperature heating and heat preservation is T=T β +(20℃~35℃), the temperature of the low-temperature heating and heat preservation is T=T β -(35℃~55℃), Tβ is the β phase transformation temperature of the alloy, generally 895℃±5℃. When the billet is cold, the heating and holding time t≥0.4D, where D is the minimum side dimension of the billet in mm and t is in min. When the billet is hot, the reheating and holding time t≥30min.

[0015] Preferably, the blank has dimensions of a×b×c, wherein a, b, and c satisfy b≥1.2a and c≥1.2b.

[0016] Preferably, the elongation deformation amount in both the first and second three-dimensional elongation forging is 30% to 60%. Preferably, in step 4, of the two upsetting forging processes, the last elongation deformation amount is ≥50%, and the deformation amount in the upsetting forging is ≥30%.

[0017] Preferably, in step 5, the elongation forging performed after low-temperature heating and heat preservation has a deformation amount of 35% to 55% per elongation forging.

[0018] Preferably, the final microstructure of the bar in step 5 can be controlled according to the forging deformation amount of the forming fire. When the target microstructure is Widmanstätten microstructure, the deformation amount is controlled to be ≤20%, and when the target microstructure is basket weir microstructure, the deformation amount is controlled to be 40% to 70%.

[0019] Preferably, the diameter of the TC17 titanium alloy bar obtained in step 5 is Φ250mm~Φ350mm.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] (1) Compared with traditional α+β state bars, the preparation method of β state TC17 titanium alloy bars of the present invention has the characteristics of short process and high yield. The number of heating forging times is reduced from 12-16 times to 8-9 times, and the yield is increased from 73%-77% to 80%-85%. At the same time, the process of the present invention is simple and highly operable. It mainly uses drawing forging, which improves the problem of uneven deformation caused by multiple upsetting and drawing forging in the traditional process. The uniformity of the structure of the bars prepared by the present invention is significantly improved. The ultrasonic water immersion test noise level of bars with diameter Φ250mm-Φ350mm is reduced by 5dB-8dB compared with traditional α+β forged bars.

[0022] (2) Compared with traditional α+β state bars with equiaxed structure, β state bars with Widmanstätten structure have better fracture performance and creep resistance, but poor tensile plasticity. However, they can still meet the requirements of the corresponding industry standards. β state bars with basket structure have performance between the two and have better overall performance.

[0023] (3) In view of the characteristics of columnar crystals in ingots, the columnar grains with a cross-sectional size of 10mm to 20mm and a length of ≥50mm are fully flattened along their axial direction and pulled out in multiple radial directions by three-dimensional elongation + diagonal elongation + three-dimensional elongation forging after high temperature heating, thereby significantly improving the "crushing" efficiency and quickly and uniformly refining their size to 2mm to 3mm; then, through large deformation (≥50%) elongation forging at low temperature, firstly, the minimum edge size of the billet is reduced, thereby shortening the holding time of subsequent medium temperature heating and minimizing grain growth; secondly, the original β grains are fully elongated, accumulating a large amount of distortion energy, thereby further refining the grain size of the billet to 1mm to 2mm through phase transformation recrystallization in the subsequent medium temperature heating process. The above process of low temperature elongation forging and furnace return to medium temperature forging is repeated to obtain β-state rods, and the grain size is further refined to below 0.5mm. Attached Figure Description

[0024] Figure 1 The equiaxed structure of TC17 alloy bars.

[0025] Figure 2 Widmanstätten structure of TC17 alloy bars.

[0026] Figure 3 The mesh structure of TC17 alloy bars.

[0027] Figure 4 Figure 1 shows the three-dimensional orientation of TC17 alloy ingots and billets. Figure 1a represents the three-dimensional orientation of the ingot, and Figure 1b represents the three-dimensional orientation of the billet before three-dimensional elongation. The billet is a cuboid with dimensions a×b×c.

[0028] Figure 5 The high-magnification longitudinal microstructure of the 350mm TC17 alloy bar from Example 1 is shown in Figure a (50x magnification) and Figure b (200x magnification).

[0029] Figure 6 The longitudinal high-magnification microstructure of the 300mm TC17 alloy bar in Example 2 is shown in Figure a (50x magnification) and Figure b (200x magnification).

[0030] Figure 7 The longitudinal high-magnification microstructure of the 250mm TC17 alloy bar in Example 3; wherein, Figure a is the microstructure magnified 50 times and Figure b is the microstructure magnified 200 times.

[0031] Figure 8 The longitudinal high-magnification microstructure of the 250mm TC17 alloy bar in Example 4; wherein, Figure a is the microstructure magnified 50 times and Figure b is the microstructure magnified 200 times. Detailed Implementation

[0032] A method for preparing β-state TC17 titanium alloy rods includes the following steps:

[0033] Step 1: After heating and holding the TC17 titanium alloy ingot at high temperature, forge it into a billet with dimensions of a×b×c (b≥1.2a, c≥1.2b);

[0034] Step 2: After heating and holding the above billet at high temperature, perform the first three-dimensional elongation forging.

[0035] Step 3: After forging in Step 2, the billet is heated and held at high temperature, then upset and diagonally drawn to form a billet with dimensions a×b×c, while changing the radial orientation of the billet relative to the ingot. It is then returned to the furnace for a second three-dimensional drawing forging after high-temperature heating and holding, thereby obtaining a billet with relatively fine and uniform β grains. The deformation amount for each of the three-dimensional drawing processes is 30%–60%, while the deformation amount for other upsetting and drawing processes is 35%–45%. The high-temperature heating and holding temperature is T = T β +(130℃~355℃);

[0036] Step 4: After the billet forged in Step 3 is heated and held at a low temperature below the phase transformation point, it is subjected to two upsetting and drawing forging processes. The deformation amount of the last drawing forging is ≥50%. Then, it is heated in the furnace to a medium temperature above the phase transformation point and held at that temperature before upsetting forging with a deformation amount ≥30%. During the upsetting process, the surface of the billet is regularized in a timely manner, and then air-cooled to room temperature. The forged billet is a cylinder.

[0037] Step 5: After forging the billet in Step 4, heat it to a low temperature below the phase transformation point and hold it therefore, then perform 2-3 drawing forgings, with a deformation amount of 35%-55% each time. Then, reheat it in the furnace to a medium temperature above the phase transformation point and hold it therefore, performing a forming forging to obtain a bar billet. This billet is then cooled and machined into bars, obtaining TC17 titanium alloy bars with diameters ranging from Φ250mm to Φ350mm. The final microstructure of the bars can be controlled according to the forging deformation amount in the forming forging. When the target microstructure is Widmanstätten microstructure, the deformation amount should be controlled to ≤20%. See [link to microstructure description] for the obtained microstructure characteristics. Figure 2 When the target microstructure is a basket weave, the deformation is controlled at 40%–70%, and the obtained microstructure characteristics are described in [reference needed]. Figure 3 The temperature for the above-mentioned medium-temperature heating and heat preservation is T = T β +(20℃~35℃), the temperature for low-temperature heating and heat preservation is T=T β -(35℃~55℃), T β The β-phase transformation temperature of the alloy is typically 895℃±5℃. When the billet is cold, the heating and holding time t≥0.4D, where D is the minimum side dimension of the billet in mm and t is in min. When the billet is hot, the reheating and holding time t≥30 min. Preferably, in this embodiment, the β-phase transformation temperature is 895℃.

[0038] Three-dimensional elongation forging, such as Figure 4 As shown, the initial shape of the billet is a cuboid. The X and Y directions correspond to a pair of perpendicular radial directions of the ingot, and the Z direction corresponds to the axial direction of the ingot. The billet is subjected to a drawing forging with a deformation of 30% to 60% in sequence along the X, Y and Z directions. This forging method is for the TC17 alloy ingot, which has a microstructure of long columnar crystals that are approximately parallel to the axial direction Z. Through the drawing forging in the X and Y directions, the columnar crystals are repeatedly flattened and broken along the axial direction, thereby achieving the effect of rapidly refining the β grains.

[0039] In actual operation, three-dimensional drawing forging does not require identification of the axial and radial directions of the billet. Each drawing operation only requires drawing the shortest side (side length a) of the billet to the longest side (side length c), the second shortest side (side length b) to the shortest side (side length a), and the longest side (side length c) to the second shortest side (side length b). After one three-dimensional drawing operation, the billet returns to its initial dimensions. It has the advantages of simple operation and avoidance of errors caused by memorizing the billet direction. Among them, a, b, and c satisfy b≥1.2a and c≥1.2b.

[0040] In step 3, the diagonal elongation involves forging the billet along its diagonal into a new billet, thereby changing the radial direction of the initial state of the billet before the second three-dimensional elongation. This causes a 45° orientational deviation between the initial radial (X and Y directions) state of the billet before the first three-dimensional elongation, denoted as X′ and Y′. After elongation forging in the X′, Y′, X, and Y directions, the coarse cast columnar crystal structure is flattened along its axial direction and elongated in all directions, thus being fully "broken up". This improves the refinement efficiency of the large cast grains, shortens the production cycle, and improves the uniformity of the TC17 titanium alloy structure.

[0041] In step 4, the low-temperature forging process involves elongation forging with a deformation of ≥50%, which serves two main purposes: first, to reduce the minimum edge size of the billet, thereby shortening the holding time during subsequent medium-temperature heating and minimizing grain growth; and second, to fully elongate the β grains while accumulating a large amount of distortion energy, which then leads to extensive nucleation and recrystallization within the elongated β grains during subsequent medium-temperature heating, refining the coarse β grains.

[0042] The following preferred embodiments further illustrate the technical solution of the present invention.

[0043] Example 1

[0044] The TC17 alloy ingot has a diameter of 720mm and a β-phase transformation temperature of 895℃. The ingot is processed through the following steps to obtain a 350mm diameter bar with a target Widmanstätten microstructure:

[0045] Step 1: After the ingot is held at 1250℃ for ≥10h, it is forged twice by upsetting and drawing to form a billet with dimensions of X600×Y730×Z1100. X and Y correspond to a pair of perpendicular radial directions of the ingot, and Z corresponds to the axial direction of the ingot.

[0046] Step 2: After holding at 1080℃ for 300 minutes, complete one three-dimensional elongation forging.

[0047] Step 3: After holding at 1030℃ for 300 minutes, a first upsetting and diagonal drawing are completed. At the end, the billet size is X′600×Y′730×Z1100, where X′ and Y′ correspond to the other pair of perpendicular radial directions of the ingot, and Z still corresponds to the axial direction of the ingot. After returning to the furnace and holding for 60 minutes, a second three-dimensional drawing and forging is completed, thereby obtaining a relatively fine and uniform β-grain billet. The deformation amount of each three-dimensional drawing is 45%, and the deformation amount of other upsetting and drawing is 35% to 45%.

[0048] Step 4: After holding the alloy at 860℃ for 450 minutes, it undergoes two upsetting and drawing forging processes. The last drawing deformation is 65%, and the size of the forged billet is X500×Y550×Z1730. Then, it is heated back to 920℃ and held for 240 minutes to complete the upsetting process, with a deformation of 55%. During the upsetting process, the surface of the billet is regularized in a timely manner. The forged billet is a cylinder with a diameter of Φ890mm.

[0049] Step 5: The alloy is held at 850℃ for 480 min to complete a 50% elongation deformation. It is then reheated to 850℃ for 30 min to complete a 36% elongation deformation. This is followed by another 30 min at 850℃ to complete a 35% elongation deformation. Finally, it is reheated to 915℃ for 160 min to complete a 20% elongation forging, resulting in a Φ360mm diameter bar blank. This blank is then machined into a Φ350mm diameter bar, with a bar yield of 85%. The microstructure is β-Widmanstätten structure with an average β grain size of 0.4mm. For its longitudinal high-magnification microstructure, please refer to [reference needed]. Figure 5 The mechanical properties and ultrasonic flaw detection test results are shown in Table 1.

[0050] Example 2

[0051] The TC17 alloy ingot has a diameter of 720mm and a β-phase transformation temperature of 895℃. The ingot is processed into 300mm diameter bars through the following steps:

[0052] Step 1: After the ingot is held at 1250℃ for ≥10h, it is forged twice by upsetting and drawing to form a billet with dimensions of X600×Y730×Z1100. X and Y correspond to a pair of perpendicular radial directions of the ingot, and Z corresponds to the axial direction of the ingot.

[0053] Step 2: After holding at 1080℃ for 300 minutes, complete one three-dimensional elongation forging.

[0054] Step 3: After holding at 1025℃ for 300 minutes, complete one upsetting and diagonal drawing. The final billet dimensions are X′600×Y′730×Z1100. X′ and Y′ correspond to the other pair of perpendicular radial directions of the ingot. The relationship with X and Y is shown in [reference needed]. Figure 4 Z still corresponds to the ingot axis. After being held in the furnace for 60 minutes, the second three-dimensional elongation forging is completed. The deformation amount of each elongation in the above three-dimensional elongation is 45%, and the deformation amount of other upsetting and elongation is 35% to 45%.

[0055] Step 4: After holding the alloy at 860℃ for 450 minutes, it undergoes two upsetting and drawing forging processes. The last drawing deformation is 65%, and the size of the forged billet is X500×Y550×Z1730. Then, it is heated back to 930℃ and held for 240 minutes before being taken out of the furnace for upsetting forging. The deformation is 42%. During the upsetting process, the surface of the billet is regularized in a timely manner. The forged billet is a cylinder with a diameter of Φ740mm.

[0056] Step 5: The alloy is held at 850℃ for 420 minutes to complete a 55% elongation deformation. It is then reheated to 850℃ for 30 minutes to complete a 35% elongation deformation. Finally, it is reheated to 915℃ for 190 minutes to complete a 40% elongation forging, resulting in a Φ310mm diameter bar blank. After cooling, it is machined into a Φ300mm diameter bar, with a bar yield of 84%. Its microstructure is a β-basket structure with fully elongated β grains and an aspect ratio ≥2.0. For its longitudinal high-magnification microstructure, please refer to [reference needed]. Figure 6 The mechanical properties and ultrasonic flaw detection test results are shown in Table 1.

[0057] Example 3

[0058] The TC17 alloy ingot has a diameter of Φ720mm and a β-phase transformation temperature of 895℃. The ingot is processed into a Φ250mm bar through the following steps:

[0059] Step 1: After the ingot is held at 1250℃ for ≥10h, it is forged twice by upsetting and drawing to form a billet with dimensions of X540×Y660×Z1350. X and Y correspond to a pair of perpendicular radial directions of the ingot, and Z corresponds to the axial direction of the ingot.

[0060] Step 2: After holding at 1080℃ for 300 minutes, complete one three-dimensional elongation forging.

[0061] Step 3: After holding at 1030℃ for 300 minutes, complete one upsetting and diagonal drawing. The final billet dimensions are X′540×Y′660×Z1350. X′ and Y′ correspond to the other pair of perpendicular radial directions of the ingot. The relationship with X and Y is shown in [reference needed]. Figure 4 Z still corresponds to the ingot axis. After being held in the furnace for 60 minutes, the second three-dimensional elongation forging is completed. The deformation amount of each elongation in the above three-dimensional elongation is 60%, while the deformation amount of other upsetting and elongation is 35% to 45%.

[0062] Step 4: After holding the alloy at 860℃ for 450 minutes, it undergoes two upsetting and drawing forging processes. The last drawing deformation is 65%, and the size of the forged billet is X500×Y550×Z1730. Then, it is heated back to 920℃ and held for 240 minutes before being taken out of the furnace for upsetting forging. The deformation is 35%. During the upsetting process, the surface of the billet is regularized in a timely manner. The forged billet is a cylinder with a diameter of Φ715mm.

[0063] Step 5: The alloy is held at 840℃ for 390 min to complete a 55% elongation deformation. It is then reheated to 840℃ for 30 min to complete a 35% elongation deformation. Finally, it is reheated to 915℃ for 180 min to complete a 55% elongation forging, resulting in a Φ260mm diameter bar blank. After cooling, it is machined into a Φ250mm diameter bar. The bar yield is 82%. Its microstructure is a β-basket structure with fully elongated β grains and an aspect ratio ≥3.0. For its longitudinal high-magnification microstructure, see [reference needed]. Figure 7 The mechanical properties and ultrasonic flaw detection test results are shown in Table 1.

[0064] Example 4

[0065] The TC17 alloy ingot has a diameter of Φ720mm and a β-phase transformation temperature of 895℃. The ingot is processed into a Φ250mm bar through the following steps:

[0066] Step 1: After the ingot is held at 1250℃ for ≥10h, it is forged twice by upsetting and drawing to form a billet with dimensions of X650×Y795×Z930. X and Y correspond to a pair of perpendicular radial directions of the ingot, and Z corresponds to the axial direction of the ingot.

[0067] Step 2: After holding at 1080℃ for 300 minutes, complete one three-dimensional elongation forging.

[0068] Step 3: After holding at 1030℃ for 300 minutes, complete one upsetting and diagonal drawing. The final billet dimensions are X′650×Y′795×Z930. X′ and Y′ correspond to the other pair of perpendicular radial directions of the ingot. The relationship with X and Y is shown in [reference needed]. Figure 4Z still corresponds to the ingot axis. After being held in the furnace for 60 minutes, the second three-dimensional elongation forging is completed. The deformation amount of each elongation in the above three-dimensional elongation is 30%, and the deformation amount of other upsetting and elongation is 35% to 45%.

[0069] Step 4: After the alloy is held at 860℃ for 450 minutes, it undergoes two upsetting and drawing forging processes. The last drawing deformation is 65%, and the size of the forged billet is X500×Y550×Z1730. Then, it is heated back to 930℃ and held for 240 minutes before being taken out of the furnace for upsetting forging. The deformation is 50%. During the upsetting process, the surface of the billet is regularized in a timely manner. The forged billet is a cylinder with a diameter of Φ830.

[0070] Step 5: The alloy is held at 850℃ for 450 min to complete a 55% elongation deformation. It is then reheated to 850℃ for 30 min to complete a 35% elongation deformation. Finally, it is reheated to 920℃ for 220 min to complete a 70% elongation forging, resulting in a Φ260mm diameter bar blank. After cooling, it is machined into a Φ250mm diameter bar. The bar yield is 80%. Its microstructure is a β-basket structure with fully elongated β grains and an aspect ratio ≥4.0. Some β recrystallization exists. For its longitudinal high-magnification microstructure, please refer to [reference needed]. Figure 8 The mechanical properties and ultrasonic flaw detection test results are shown in Table 1.

[0071] Comparative Example 1

[0072] This comparative example uses a traditional α+β state Φ350mm bar forging process, differing from Example 1 in the following ways: 1) Three-dimensional drawing forging was not used; instead, multiple high-temperature heating followed by upsetting and forging was employed to break up the large grains in the cast state; 2) Low-temperature drawing forging combined with medium-temperature upsetting was not used; instead, multiple low-temperature upsetting and drawing forging processes were combined with medium-temperature upsetting and drawing forging to refine the β grains; 3) The forming temperature was below the phase transformation point, and the final finished bar was produced through multiple low-temperature upsetting and drawing forging processes; the bar yield was 75%, and its microstructure was equiaxed. The mechanical properties and ultrasonic flaw detection test data of the TC17 titanium alloy bar processed by this comparative example are shown in Table 1.

[0073] Comparative Example 2

[0074] This comparative example uses a traditional α+β state Φ300mm bar forging process, differing from Example 2 in the following ways: 1) Three-dimensional drawing forging was not used; instead, multiple high-temperature heating followed by upsetting and forging was employed to break up the large grains in the cast state; 2) Low-temperature drawing forging combined with medium-temperature upsetting was not used; instead, multiple low-temperature upsetting and drawing forging processes were combined with medium-temperature upsetting and drawing forging to refine the β grains; 3) The forming temperature was below the phase transformation point, and the final finished bar was produced through multiple low-temperature upsetting and drawing forging processes; the bar yield was 73%, and its microstructure was equiaxed. The mechanical properties and ultrasonic flaw detection test data of the TC17 titanium alloy bar processed by this comparative example are shown in Table 1.

[0075] Comparative Example 3

[0076] This comparative example uses a traditional α+β state Φ250mm bar forging process, differing from Example 3 in the following ways: 1) Three-dimensional drawing forging was not used; instead, multiple high-temperature heating followed by upsetting and drawing forging was employed to break up the large grains in the cast state; 2) Low-temperature drawing forging combined with medium-temperature upsetting was not used; instead, multiple low-temperature upsetting and drawing forging cycles combined with medium-temperature upsetting and drawing forging were used to refine the β grains; 3) The forming temperature was below the phase transformation point, and the final finished bar was produced through multiple low-temperature upsetting and drawing forging cycles; the bar yield was 77%, and its microstructure was equiaxed. The mechanical properties and ultrasonic flaw detection test data of the TC17 titanium alloy bar processed in this comparative example are shown in Table 1.

[0077] Comparative Example 4

[0078] This comparative example uses a traditional α+β state Φ250mm bar forging process, differing from Example 4 in the following ways: 1) Three-dimensional drawing forging was not used; instead, multiple high-temperature heating and upsetting forging were employed to break up the large grains in the cast state; 2) Low-temperature drawing forging combined with medium-temperature upsetting was not used; instead, multiple low-temperature upsetting and drawing forging processes combined with medium-temperature upsetting forging were used to refine the β grains; 3) The forming temperature was below the phase transformation point, and the final finished bar was produced through multiple low-temperature upsetting and drawing forging processes. Compared to Comparative Example 3, this involved one more upsetting and drawing forging process. The bar yield was 76%, and its microstructure was equiaxed. The mechanical properties and ultrasonic flaw detection test data of the TC17 titanium alloy bar processed by this comparative example are shown in Table 1.

[0079] For the organizational characteristics of Comparative Examples 1, 2, 3, and 4, please refer to [reference needed]. Figure 1 .

[0080] Table 1 Mechanical properties and ultrasonic flaw detection data of TC17 titanium alloy bars (after appropriate heat treatment)

[0081]

[0082]

[0083] As shown in Table 1, compared with the equiaxed structure of the bars prepared by the traditional process, the bars prepared in Example 1 have lower room temperature tensile plasticity (corresponding to lower values ​​of indicators A and Z in Table 1) and higher fracture toughness (corresponding to indicator K in Table 1). ⅠC It has a high value and high creep resistance (corresponding to the index ε in Table 1). p (lower value); Compared with the microstructure of Example 1, the microstructure of Example 2 has better room temperature tensile plasticity, higher fracture toughness and slightly lower creep resistance, but is significantly better than the equiaxed microstructure and has better comprehensive performance; Compared with the microstructure of Example 2, the β grains of Example 3 are further elongated, and the corresponding performance is comparable; Compared with the microstructures of Example 2 and Example 3, Example 4 has some recrystallized β grains and shorter needle-like α phase, and the corresponding performance is comparable.

[0084] In summary, compared with the equiaxed microstructure of the bars prepared by the traditional processes in Comparative Examples 1, 2, 3, and 4, the TC17 titanium alloy bars prepared by the forging method provided in this embodiment of the invention have a yield rate increased from 73%–77% to 80%–85%, while maintaining comparable strength. The fracture toughness, creep resistance, and flaw detection level are significantly higher than those of the traditional α+β forged bars, and the microstructure uniformity of the bars is significantly improved. The ultrasonic water immersion flaw detection clutter level of the Φ250mm–Φ350mm diameter bars is reduced by 5dB–8dB compared to the traditional α+β forged bars.

[0085] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing β-state TC17 titanium alloy rods, characterized in that, Includes the following steps: Step 1: After heating and holding the TC17 titanium alloy ingot at high temperature, forge it into a billet with dimensions a×b×c. Step 2: After heating and holding the above billet at high temperature, perform the first three-dimensional elongation forging. Step 3: After the billet forged in Step 2 is heated and held at high temperature, it is upsetting and diagonally drawn into a billet with dimensions of a×b×c. At the same time, the radial orientation of the billet relative to the ingot is changed. After being returned to the furnace and heated and held at high temperature, it is subjected to a second three-dimensional drawing forging. Step 4: After heating and holding the billet forged in Step 3 at a low temperature below the phase transformation point, perform two upsetting and drawing forgings. The last drawing deformation is ≥50%. Then, heat it in the furnace to a medium temperature above the phase transformation point and hold it for upsetting forging with a deformation of ≥30%. Air cool it to room temperature. The forged billet is a cylinder. Step 5: After the billet forged in Step 4 is heated and held at a low temperature below the phase transformation point, it is subjected to multiple elongation forgings, with a deformation amount of 35%~55% each time. Then, it is heated in the furnace to a medium temperature above the phase transformation point and held for forming forgings to obtain bar billets. After cooling and processing, TC17 titanium alloy bars are obtained. The temperature of the high-temperature heating and heat preservation is T=T β +(130℃~355℃), the temperature of the medium-temperature heating and heat preservation is T=T β +(20℃~35℃), the temperature of the low-temperature heating and insulation is T=T β -(35℃~55℃), T β The β phase transformation temperature of the alloy is 895℃±5℃. When the billet is cold, the heating and holding time t≥0.4D, where D is the minimum side dimension of the billet in mm and t is in min. When the billet is hot, the reheating and holding time t≥30min. The first and second three-dimensional elongation forging processes each involved an elongation deformation of 30% to 60%.

2. The method for preparing β-state TC17 titanium alloy rods according to claim 1, characterized in that, The blank has dimensions of a×b×c, where a, b, and c satisfy b≥1.2a and c≥1.2b.

3. The method for preparing β-state TC17 titanium alloy rods according to claim 1, characterized in that, In step 5, the final microstructure of the bar is controlled according to the forging deformation amount of the forming fire. When the target microstructure is Widmanstätten microstructure, the deformation amount is controlled to be ≤20%. When the target microstructure is basketweave microstructure, the deformation amount is controlled to be 40%~70%.

4. The method for preparing β-state TC17 titanium alloy rods according to claim 1, characterized in that, Step 5 yields TC17 titanium alloy rods with diameters ranging from Φ250mm to Φ350mm.

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