A method for preparing high-uniform TC11 titanium alloy small-size bars

Abstract

The present invention relates to the field of titanium alloy forging technology and specifically discloses a method for preparing highly uniform TC11 titanium alloy bars (Ø70-100 mm). The method comprises the steps of blanking forging, homogenization forging, transfer blank forming forging, and radial forging. The method can produce highly uniform TC11 titanium alloy bars (Ø70-100 mm), achieving an ultrasonic flaw detection noise level of Ø0.8-12 dB and significantly superior structural uniformity to similar products.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloy material processing, and in particular to a method for preparing a small-size (Φ70-100mm) high-uniform TC11 titanium alloy bar. Background Art

[0002] Titanium alloys have been used in aviation, aerospace, shipbuilding, chemical industry, petroleum and other fields due to their low density, high specific strength, good corrosion resistance, low elastic modulus, low thermal conductivity, and high yield strength ratio. In the aviation field, titanium alloys are one of the main structural materials of contemporary advanced aircraft, mainly used in aircraft landing gear components, fuselage skins, frames, beams, heat shields and shells. The large-scale adoption of advanced titanium alloy materials is one of the significant signs of the advancement of new generation aircraft and engines, which can greatly improve the weight reduction effect and safety and reliability of structures. TC11 titanium alloy is an α+β type titanium alloy with excellent high-temperature performance and can be used in aircraft engine disks, blades and structural parts. With the rapid development of high-performance aircraft engines and gas turbines, higher requirements have been placed on titanium alloy materials.

[0003] Numerous studies have been conducted in China on factors affecting ultrasonic flaw detection of titanium alloys. The results consistently indicate that ultrasonic flaw detection noise in titanium alloy bars is related to microstructural uniformity, such as the presence of large, elongated α phase, insufficient fragmentation of α lamellar structures, and the formation of microtexture. In current industrial production, large-scale TC11 titanium alloy ingots undergoing three VAR refining processes often exhibit microstructural heterogeneity despite achieving macroscopic compositional uniformity. For example, aluminum enrichment directly or indirectly causes differences in the nucleation and precipitation of α phase. This is due to microscopic compositional heterogeneity. This variation in alloying elements within small localized regions leads to differences in the size and rate of α phase precipitation. During subsequent repeated heating, precipitates in areas rich in α-stabilizing elements become coarser, while those in areas depleted of α-stabilizing elements become finer, thus affecting microstructural homogeneity. Furthermore, TC11 titanium alloy billets are prone to cracking, incomplete forging, and uneven deformation during free forging, resulting in insufficient fragmentation of β grains and α phase clusters, leading to microstructural heterogeneity. During the precision forging process of small-sized bars, the rapid temperature dissipation causes a large temperature difference between the inner and outer surfaces. The uneven temperature and strain field from the surface to the core of the billet can also cause differences in structure, forming adiabatic shear bands and cracking during the rapid forging process. For TC11 titanium alloy Φ70-100mm bars for aircraft engine or gas turbine rotor blades, in order to meet the standard's requirements for ultrasonic flaw detection of rotor blades of Φ0.8-12dB for bars under Φ36mm, and to ensure the absence of single-signal signals (the wave height of a single clutter wave does not exceed twice the wave height of weed-like clutter), a more uniform and finer structure is required. Therefore, the invention of a TC11 titanium alloy Φ70-100mm bar capable of producing a highly uniform structure is crucial to improving the service life of engine blades and developing advanced aircraft engines and gas turbines. Summary of the Invention

[0004] In response to the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing small-sized (Φ70-100mm) highly uniform TC11 titanium alloy bars. The ultrasonic flaw detection noise level of the prepared bars can reach above Φ0.8-12dB, which can be used for rotor blades of aircraft engines and gas turbines and is suitable for industrial production.

[0005] The raw material used in this application is TC11 titanium alloy φ680mm specification ingot, and its manufacturing method includes several steps such as blank forging, homogenization forging, transfer blank forming forging, and radial forging.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing a highly uniform TC11 titanium alloy Φ70-100mm bar, which is achieved by the following steps:

[0007] (1) Open forging

[0008] The TC11 ingot is first heated at 1150-1200℃, then subjected to 1-2 rounds of upsetting and drawing forging on a 45MN high-speed forging machine, and finally forged into a square billet, which is then air-cooled.

[0009] (2) Homogenization forging

[0010] The process is completed in 6-8 steps: ① first, the billet treated in step (1) is heated at 30-70°C below the β-transform temperature, and then subjected to 1 fire of upsetting and drawing forging to forge a 400-600mm square billet with an upsetting deformation of 30-50%. After forging, air cooling is adopted; ② the billet after forging is then heated at 1150-1200°C for a long time, and after heating, it is forged into a 400-600mm square billet, and slow cooling is adopted after forging; ③ then, it is heated at 30-70°C below the β-transform temperature, and then upsetting or drawing forging is performed to a square billet, and air cooling is adopted after forging; ④ then, the forged billet is heated at 10-80°C above the β-transform temperature, and after being taken out of the furnace, it is drawn and forged into a square billet, and slow cooling is adopted after forging; the above steps ③ and ④ are repeated 2-3 times to finally forge a 250-400mm square billet;

[0011] (3) Transfer billet forming forging

[0012] The blank treated in step (2) is heated to 30-70°C below the β-transus temperature and kept warm, and then the blank is forged into a Φ200mm round bar in 2-3 stages with a total deformation greater than 50%, and air-cooled after forging;

[0013] (4) Radial forging

[0014] The blank treated in step (3) is heated at 40-70°C below the β-transus temperature and kept warm, and then radially forged into a Φ70-100mm round bar in 1-2 passes on an SKK17 precision forging machine, with a total forging deformation greater than 50%; and air-cooled after forging.

[0015] Furthermore, in step (1), the blank forging specifically adopts two upsetting and two drawing, the upsetting and drawing method adopts reversing upsetting and drawing, the upsetting deformation amount of a single fire is 30-40%, and air cooling is performed after forging is completed.

[0016] Furthermore, in step (ii) ①, the upsetting forging specifically adopts two upsetting and two drawing, the upsetting method adopts reversing upsetting, the upsetting deformation is 30-40%, and air cooling is performed after forging is completed.

[0017] Furthermore, the specific heating time of the medium-long heating in step (ii) ② is 1200-1500 min. After the insulation is completed, the steel is taken out of the furnace and subjected to one upsetting and one drawing. The upsetting deformation is 10-15%. After the forging is completed, the steel is cooled at a cooling rate of 3-5°C / min.

[0018] Furthermore, after forging in step (ii), step ④ is cooled at a cooling rate of 3-5°C / min; and the heating time in steps ③ and ④ is calculated according to the minimum cross-sectional size of the billet × heating coefficient δ (min / mm), and the heating coefficient δ is generally 0.4-0.8.

[0019] Furthermore, step (2) of step ④ is repeatedly performed, wherein the heating temperature during the first 1-2 executions is 50-80°C above the β-transus temperature, and the heating temperature during the last execution is 10-30°C above the β-transus temperature.

[0020] Furthermore, in step (iv), the forging frequency is 600 times / min, and the pulling speed is 4.5-5 m / min.

[0021] In order to achieve an ultrasonic flaw detection noise level of Φ0.8-12dB for TC11 titanium alloy bars with a specification of Φ70~100mm, the present invention combines the processes of recrystallization and high-temperature homogenization, and uses grain boundaries as fast channels for element diffusion to improve the uniformity of micro-region composition. Uniform and fine β grains are obtained through a single-phase zone heating method with step-by-step cooling. The uniformity of phase precipitation is improved by controlling the cooling rate of the single-phase zone. The finished product forging utilizes the characteristics of fast forging of the SKK17 precision forging machine to fully crush the structure. The above steps are all indispensable key links of the present invention, and the steps are closely related.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention can produce a highly uniform TC11 titanium alloy bar with a diameter of 70 to 100 mm. The ultrasonic flaw detection noise level of the bar can reach 0.8 to 12 dB, and the structural uniformity is significantly better than that of similar products.

[0024] (2) The TC11 titanium alloy rod produced by the present invention has no large blocky α phase and unbroken α phase clusters, which weakens the structural inhomogeneity problem caused by micro-region composition inhomogeneity and effectively improves the single-display problem of TC11 titanium alloy rod;

[0025] (3) According to the problem characteristics of the product, step (ii) of the present invention can effectively regulate the diffusion, recrystallization and phase transformation process of alloy elements by regulating the temperature and holding time of high-temperature heating, controlling the deformation amount and cooling rate of the single-phase zone, and obtaining uniform and fine β grains, effectively improving the difference in phase size between the grain boundary and the internal phase of the grain, significantly reducing the formation of large blocky α phase and lamellar α phase, and further improving the structural uniformity of the bar. The main contribution of this step is that the billet after the open forging accumulates a certain amount of deformation energy after forging in the two-phase zone, and then in the long-term high-temperature homogenization process of 1150~1200℃, the originally coarse and uneven β grains are further refined and homogenized. At the same time, in the long-term heating process of 1100~1500min, the large number of β grain boundaries increased by recrystallization become fast channels for element diffusion, which can further make the composition more uniform. Furthermore, in step (ii), the stepwise reduction of the heating temperature in the single-phase zone is conducive to the further refinement of the β grains, thereby obtaining a uniform and fine single-phase zone structure. By controlling the forging deformation and cooling rate in the single-phase region, the lamellar α phase precipitation process is brought close to equilibrium, reducing the structural differences caused by uneven deformation and temperature. Ultimately, uniform β grains and lamellar α phase are obtained.

[0026] (4) In the present invention, the SKK17 precision forging machine is used to forge the finished product in step (iv), and the characteristics of rapid forging are utilized to increase the residual stress inside the material, so that the long strip α phase is fully broken, thereby improving the uniformity of the finished bar. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a low-magnification microstructure diagram of the TC11 titanium alloy Φ70 mm bar prepared in Example 1 of the present invention;

[0028] Figure 2 This is a high-magnification microstructure diagram of the TC11 titanium alloy Φ70 mm bar prepared in Example 1 of the present invention;

[0029] Figure 3 This is the ultrasonic flaw detection clutter curve of the TC11 titanium alloy Φ70mm bar in Example 1 of the present invention;

[0030] Figure 4 This is a macroscopic microstructure diagram of a 70 mm TC11 titanium alloy bar prepared in a comparative example of the present invention;

[0031] Figure 5 This is a high-magnification microstructure diagram of a 70 mm TC11 titanium alloy bar prepared in a comparative example of the present invention;

[0032] Figure 6 This is the ultrasonic flaw detection noise curve of TC11 titanium alloy Φ70mm bar in the comparative example of the present invention. Implementation Method

[0033] The present invention will now be further described with reference to the accompanying drawings and specific embodiments. The following are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any identical or similar solutions that do not depart from the concept of the present invention should fall within the scope of protection of the present invention. Hereinafter, "□" refers to the side length of a square blank, "Φ" refers to the diameter of a blank with a circular cross-section, and "L" refers to the length of the material.

[0034] Example 1: TC11 titanium alloy Φ70mm bar produced by the present invention

[0035] (TC11 titanium alloy Φ680mm ingot is selected, and the ingot β transformation temperature is 1000℃.)

[0036] Step 1: Heat the TC11 ingot to 1150℃ and keep it at this temperature for 480min. After heating, take it out of the furnace and forge it.

[0037] Step 2: The ingot treated in Step 1 is forged using a 45MN high-speed forging machine. The forging method involves forging the Φ680 mm ingot through a single heat, two upsetting, and two drawing cycles to a square billet of 600 mm in diameter. The upsetting deformation is 30-40%, and the final forging temperature is no less than 850°C. The two-upsetting and two-drawing cycles utilize a reversing upsetting and drawing process.

[0038] Step 3: The blank obtained in step 2 is kept at 965°C for 480 minutes, and after heating is completed, it is taken out of the furnace for forging.

[0039] Step 4: The billet after step 3 is forged in a 45MN fast forging machine with 1 fire, 2 upsetting and 2 drawing to a square of 600 mm. The upsetting deformation is 30-40%. The 2 upsetting and 2 drawing adopts the forging method of reversing upsetting and drawing, and air cooling is performed after forging.

[0040] Step 5: Heat the blank obtained in step 4 to 1150°C and keep it at this temperature for 1200 minutes. After heating, remove it from the furnace and forge it.

[0041] Step 6: The billet completed in step 5 is subjected to one upsetting and one drawing forging in a 45MN fast forging machine to a square billet □ 600 mm, with an upsetting deformation of 10-15%, and a final forging temperature of not less than 850°C. After forging, it is cooled to 650°C at a rate of 3-5°C / min and then air-cooled.

[0042] Step 7: After completing step 6, the billet is kept at 970°C for a period of time. The holding time is calculated according to the minimum cross-sectional size of the billet × the heating coefficient δ (min / mm). The heating coefficient δ is 0.6-0.8.

[0043] Step 8: The billet after step 7 is subjected to one upsetting and one drawing forging in a 45MN fast forging machine to a square billet of 600mm in diameter, with an upsetting deformation of 30-40%. After forging, it is taken out of the furnace and air-cooled, and the final forging temperature is not less than 800℃.

[0044] Step 9: Keep the blank obtained in step 8 at 1050°C for a period of time. The holding time is calculated based on the minimum cross-sectional size of the blank × the heating coefficient δ (min / mm). The heating coefficient δ is generally 0.6-0.8.

[0045] Step 10: The billet obtained in step 9 is forged into a 600mm square billet using a 45MN fast forging machine. The final forging temperature is not less than 800°C. After forging, it is cooled to 650°C at a rate of 3-5°C / min and then air-cooled.

[0046] Step 11: The blank completed in step 10 is kept at 965°C for a period of time. The holding time is calculated according to the minimum cross-sectional size of the blank × heating coefficient δ (min / mm), and the heating coefficient δ is 0.6-0.8.

[0047] Step 12: The billet obtained in step 11 is stretched and forged into a square billet with a size of 600 mm on a 45MN fast forging machine. The final forging temperature is not less than 800°C, and air cooling is performed after forging is completed.

[0048] Step 13: The blank completed in step 12 is kept at 1030°C for a period of time. The holding time is calculated according to the minimum cross-sectional size of the blank × heating coefficient δ (min / mm). The heating coefficient δ is generally 0.6-0.8.

[0049] Step 14: The billet after step 13 is forged into a 500mm square billet by upsetting and drawing on a 45MN fast forging machine. The final forging temperature is not less than 800°C. After forging, it is cooled to 650°C at a rate of 3-5°C / min and then air-cooled.

[0050] Step 15: After completing step 14, the blank is kept at 950°C for a period of time. The holding time is calculated according to the minimum cross-sectional size of the blank × heating coefficient δ (min / mm). The heating coefficient δ is generally 0.6-0.8.

[0051] Step 16: The billet after step 15 is taken out of the furnace and forged in a 45MN fast forging machine for drawing and forging, and finally forged into a square billet of 250-400mm in diameter, and air-cooled after forging.

[0052] Step 17: After completing step 16, the blank is kept at 950°C for a period of time. The holding time is calculated according to the minimum cross-sectional size of the blank × heating coefficient δ (min / mm). The heating coefficient δ is generally 1.0-2.0.

[0053] Step 18: After completing step 17, the billet is taken out of the furnace and forged in a 45MN fast forging machine for drawing and forging, and finally forged into a Φ200mm bar, and air-cooled after forging.

[0054] Step 19: After completing step 18, the billet is kept at 945°C in a continuous heating walking furnace for 150 minutes, and then forged after being taken out of the furnace.

[0055] Step 20: The billet from Step 19 is forged to finished specifications through two rounds of radial drawing on an SKK17 finishing forging machine. The forging frequency is 600 strokes / min, the drawing rate is 4.5-5 m / min, and the final forging temperature is no less than 800°C. Air cooling is used after forging. The first round of radial drawing is to Φ130 mm, and the second round is to Φ70 mm.

[0056] Figure 1 This is a macroscopic photograph of the Φ70 mm TC11 titanium alloy prepared by the forging process of Example 1. It can be seen that the macroscopic structure has no obvious metallurgical defects and is uniform. Figure 2 The high-magnification microstructure photos at different positions of the bar show that the high-magnification microstructure is very uniform, the microstructure is a typical dual-state microstructure, the original β grain boundaries are fully broken, the primary α phase content is greater than 40%, and the microstructure consistency is good. Figure 3 This is the noise curve of the flaw detection of the finished product of Example 1. The noise of the bar is less than 20% of the relative wave height, and the noise meets the Φ0.8-12dB requirement. Table 1 shows the mechanical properties of the corresponding forging blank at different positions. The comprehensive performance of the bar is excellent, and the performance difference at different positions is small:

[0057] .

[0058] Comparative example: TC11 titanium alloy Φ70mm bar produced by conventional process

[0059] (TC11 titanium alloy Φ680mm ingot is selected, and the ingot β transformation temperature is 1000℃.)

[0060] Step 1: Heat the TC11 ingot to 1150℃ and keep it at this temperature for 480min. After heating, take it out of the furnace and forge it.

[0061] Step 2: The ingot processed in step 1 is forged using a 45MN high-speed forging machine. The forging method is to forge the Φ680mm ingot through one heat, two upsetting, and two drawing forging to a square of 600mm. The upsetting deformation is 30-45%, the final forging temperature is not less than 850℃, and air cooling is performed after forging.

[0062] Step 3: The blank obtained in step 2 is kept at 1080°C for 480 minutes, and then taken out of the furnace for forging after heating is completed.

[0063] Step 4: After completing step 3, the billet is subjected to 1 fire, 2 upsetting, and 2 drawing forging in a 45MN fast forging machine to a square of 600 mm. The upsetting deformation is 30-40%, the final forging temperature is not lower than 850°C, and air cooling is performed after forging.

[0064] Step 5: Heat the blank obtained in step 4 to 1050°C and keep it at this temperature for 480 minutes. After heating, remove it from the furnace and forge it.

[0065] Step 6: The blank completed in step 5 is subjected to 2 upsetting and 2 drawing forging in a 45MN fast forging machine to a square of 600 mm, with an upsetting deformation of 30-45%. The final forging temperature is not less than 800°C, and air cooling is performed after forging is completed.

[0066] Step 7: After finishing the 4th and 5th heats, keep the blank after step 6 at 970℃ for a period of time, the holding time is 480min;

[0067] Step 8: After step 7, the billet is drawn and forged into a Φ200mm bar in a 45MN fast forging machine for 4 to 5 times. The drawing deformation of each time is 20 to 40%. The final forging temperature is not less than 650℃, and air cooling is performed after forging.

[0068] Step 9: After completing step 8, the billet is kept at 960°C in a continuous heating walking furnace for 150 minutes, and then forged after being taken out of the furnace.

[0069] Step 10: The billet from Step 9 is forged to the finished product specifications through two rounds of radial drawing on an SKK17 finishing forging machine. The forging frequency is 350 strokes / min, the final forging temperature is not less than 800°C, and air cooling is used after forging. The first round of radial drawing is to Φ100mm, and the second round is to Φ70mm.

[0070] Figure 4 This is the macrostructure of the comparative example. The macrostructure has no metallurgical defects and is uniform. Figure 5 This is the high-magnification structure of the rod in the comparative example. The high-magnification structure is relatively uniform, and there are local large blocky α phases and short rod-shaped α phases. Figure 6 The ultrasonic flaw detection noise curve of the comparative example is shown in the figure. It can be seen from the figure that the bar has a relatively obvious single-display signal. Table 2 shows the mechanical properties of the TC11Φ70mm bar produced in the comparative example:

[0071] .

Claims

1. A method for preparing a high-uniform TC11 titanium alloy Φ70-100mm bar, characterized in that: This is achieved by following these steps: Step 1) Open forging: first heat the TC11 ingot at 1150-1200℃, then perform 1-2 rounds of upsetting forging on a 45MN fast forging machine, and finally forge the ingot into a square billet, and air cool it after forging; Step 2) Homogenization forging: 6-8 fires: ① First, heat the billet treated in step 1) at 30-70℃ below the β transformation temperature, and then perform 1 fire of upsetting forging to forge it into a 400-600mm square billet with an upsetting deformation of 30-50%. After forging, air cooling is adopted; ② Then heat the billet after forging at 1150-1200℃ for a long time. The specific heating time for long-term heating is 1200-1 500min, after heating is completed, forge into a 400-600mm square billet, and adopt slow cooling after forging; ③ then heat at 30-70℃ below the β-transform temperature, and then upsetting or stretching forging into a square billet, and adopt air cooling after forging; ④ then heat the forged billet at 10-80℃ above the β-transform temperature, and stretch forge into a square billet after taking it out of the furnace, and adopt slow cooling after forging; the above steps ③ and ④ are repeated 2-3 times, and finally forging into a 250-400mm square billet; Step 3) Transfer the billet to forging: Heat the billet treated in step 2) to 30-70°C below the β-transus temperature and keep it warm. Then, forge the billet into a Φ200mm round bar in 2-3 steps, with a total deformation greater than 50%. After forging, air cool the billet. Step 4) Radial forging: The billet treated in step 3) is heated at 40-70°C below the β-transus temperature and kept warm, and then forged radially into a Φ70-100mm round bar in 1-2 passes on an SKK17 precision forging machine, with a total forging deformation greater than 50%; air cooling is performed after forging is completed.

2. The method for preparing a high-uniform TC11 titanium alloy Φ70-100 mm bar according to claim 1, characterized in that: In step 1), the blank forging specifically adopts two upsetting and two drawing, the upsetting and drawing method adopts reversing upsetting and drawing, the upsetting deformation amount of a single fire is 30-45%, and air cooling is performed after forging is completed.

3. The method for preparing a high-uniform TC11 titanium alloy Φ70-100 mm bar according to claim 1, characterized in that: In step 2) ①, the upsetting forging specifically adopts two upsetting and two drawing, the upsetting method adopts reversing upsetting, the upsetting deformation is 30-40%, and air cooling is performed after forging is completed.

4. The method for preparing a high-uniform TC11 titanium alloy Φ70-100 mm bar according to claim 1, 2 or 3, characterized in that: After the heating in step 2) is completed, the steel is taken out of the furnace and subjected to 1 upsetting and 1 drawing. The upsetting deformation is 10-15%. After the forging is completed, the steel is cooled at a cooling rate of 3-5°C / min.

5. The method for preparing a high-uniform TC11 titanium alloy Φ70-100 mm bar according to claim 4, characterized in that: After forging in step 2), the forging is completed in step 4, and the cooling is carried out at a cooling rate of 3-5°C / min; and the heating time in steps 3 and 4 is calculated according to the minimum cross-sectional size of the billet × heating coefficient δ (min / mm), and the heating coefficient δ is generally 0.4-0.

8.

6. The method for preparing a high-uniform TC11 titanium alloy Φ70-100 mm bar according to claim 5, characterized in that: Step ④ of step 2) is repeatedly performed, wherein the heating temperature during the first 1-2 executions is 50-80°C above the β-transus temperature, and the heating temperature during the last execution is 10-30°C above the β-transus temperature.

7. The method for preparing a high-uniform TC11 titanium alloy Φ70-100 mm bar according to claim 1, characterized in that: In step 4), the forging frequency is 600 times / min and the pulling speed is 4.5-5m / min.

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