A method for preparing TA12A small-size rod with high organizational uniformity and toughness matching

Abstract

The application discloses a TA12A small-size rod preparation method with high organizational uniformity and excellent matching of toughness, breaks the technical prejudice that TA12A single process needs multiple cold material heating, and realizes excellent matching of organizational uniformity and toughness through gradient deformation and precise hot material re-melting temperature compensation technology without increasing equipment investment.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy technology, specifically to a method for preparing small-diameter TA12A bars with high microstructure uniformity and a good balance of strength and toughness. Background Technology

[0002] TA12A is a near-alpha type high-temperature titanium alloy with a long-term service temperature of up to 550℃. Due to its excellent high-temperature strength, creep resistance, and thermal stability, it is widely used in key hot-end components such as compressor disks and blades in aero-engines. However, the high content of TA12A titanium alloy elements and the low content of β-stabilizing elements result in a narrow hot working process window, high deformation resistance, and susceptibility to cracking. This poses a significant bottleneck to the low-cost industrial production of existing small-diameter bars (Φ20-Φ50mm).

[0003] Low-cost processing routes for general-purpose titanium alloys (TC4, TA15, etc.) (such as CN111519067B, CN122012989A, CN114769477B) are not suitable for TA12A. Composition optimization routes cannot adjust the composition due to strict restrictions in GJB2744A; although short-process casting and forging routes can reduce the number of heat treatments, the cracking rate is as high as 40% or more when used for TA12A, and the common problem of "multiple cold material heating in a single process" has not been overcome. The overall cost reduction is only 15-20%, which cannot meet the cost reduction requirements for mass production.

[0004] The problem of multiple reheatings of cold materials within a single process directly leads to three fatal shortcomings in existing low-cost routes: 1. High energy consumption and costs: The energy consumption for heating cold materials in a single process accounts for more than 70% of the total processing energy consumption. The total number of cold material heating times in the whole process reaches more than 10 times, and the energy consumption cost per piece accounts for more than 40%, which has become the core factor restricting further cost reduction. 2. Extremely low production efficiency: The multiple heating and cooling processes of cold materials extend the production cycle of a single process by several times, and the entire production cycle can last for several weeks. The equipment turnover rate is low, which cannot meet the delivery requirements of large-volume orders. 3. Large fluctuations in product quality: The huge thermal stress generated by repeated heating and cooling can easily lead to microcracks inside the billet, and repeated heating will cause coarse grains and severe oxidation and burning. The product performance fluctuation range exceeds 15%, which makes it difficult to meet the performance consistency requirements of the aerospace field.

[0005] Existing technologies have attempted to improve the above problems by optimizing heating methods and adjusting deformation parameters, but all of these require multiple cold material heating cycles within a single process. Therefore, developing a low-cost, high-performance method for preparing small-diameter TA12A bars that requires only one cold material heating cycle within a single process has become a pressing technical challenge in this field. Summary of the Invention

[0006] To address the shortcomings of the existing technology, the purpose of this invention is to provide a method for preparing small-diameter TA12A bars with high microstructure uniformity and a good balance of strength and toughness. This method breaks the technical prejudice that "TA12A requires multiple cold material heatings in a single process." Through the synergistic innovation of gradient deformation and precise hot material reheating technology, it eliminates the need for additional cold material heatings in a single process without increasing equipment investment, while achieving a good balance between microstructure uniformity and toughness.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing small-diameter TA12A bars with high microstructure uniformity and a good balance of strength and toughness, characterized by comprising the following steps: Step 1) High-speed forging machine forging billet preparation The ingot is forged into a billet using a high-speed forging machine, and the billet is forged into an octagonal or hexagonal cross section. After forging, it is air-cooled to room temperature and then ground. Step 2) Intermediate forging of billets using a large precision forging machine The cold forging material completed in step 1) is heated to 30℃-40℃ below the β phase transformation temperature and held at that temperature. The forging process is carried out by multi-pass continuous precision forging using a large precision forging machine. The hot material is returned to the furnace for reheating during the forging process. After forging, the material is air-cooled to room temperature and then ground. Step 3) Intermediate forging of billets using a small precision forging machine The cold forging material completed in step 2) is heated to 35℃-45℃ below the β phase transformation temperature and held at that temperature. The forging process is carried out by multiple passes of continuous precision forging using a small precision forging machine. The hot material is returned to the furnace for reheating during the forging process. After forging, the material is air-cooled to room temperature and then ground. Step 4) Rolling of finished product on the rolling mill The cold forging material completed in step 3) is heated to 40℃-50℃ below the β phase transformation temperature and held at that temperature. It is then subjected to multiple passes of continuous hot rolling without secondary heating of the cold material in between. The rolled material is then air-cooled to room temperature. Step 5) Heat treatment The rolled bar obtained in step 4) is subjected to double annealing.

[0008] Furthermore, the forging process in step 1) above is specifically as follows: First stage: Heat the Φ680mm ingot cold material to 130℃-170℃ above the β phase transformation temperature and hold it at that temperature. Then, perform billet forging to form an octagonal billet with a side distance of 440-460mm and a total deformation of ≥60%. After forging, air cool and grind. Second stage: Heat the cold forging material obtained in the first stage to 20℃-50℃ below the β phase transformation temperature and hold it for medium temperature deformation to forge an octagonal billet with a side distance of 330-350mm and a total deformation of ≥40%. The billet is then returned to the furnace after forging. The third stage: The forged billet completed in the second stage is returned to the furnace and held at 50℃-80℃ above the β phase transformation temperature for high-temperature shaping to obtain an octagonal or hexagonal billet with a side-to-side distance of 325-345mm; the holding time is strictly controlled, and the holding time = minimum billet size × 0.3 + (30-60) min.

[0009] Furthermore, in step 2) above, the deformation amount of each pass in the large precision forging is controlled at 10%-15%, and the total deformation amount is controlled at 75%-85%. The hot material is returned to the furnace for reheating under the following conditions: when the billet temperature drops to 70°C below the β phase transformation temperature, it is immediately returned to the furnace for heating to 20°C-50°C below the β phase transformation temperature. After holding at this temperature for 30-60 minutes, it is taken out of the furnace for further forging. There is no secondary heating of cold material in this process. The final forging temperature is not lower than 70°C below the β phase transformation temperature.

[0010] Furthermore, in step 3) above, the deformation amount of each pass in small precision forging is controlled at 8%-12%, and the total deformation amount is controlled at 70%-80%. The conditions for hot material to be returned to the furnace for reheating are as follows: when the billet temperature drops to 80°C below the β phase transformation temperature, it is immediately returned to the furnace for heating to 30°C-50°C below the β phase transformation temperature. After holding at this temperature for 20-40 minutes, it is taken out of the furnace for further forging. There is no secondary heating of cold material in this process. The final forging temperature is not lower than 80°C below the β phase transformation temperature.

[0011] Furthermore, in step 4) above, the deformation amount per rolling pass is controlled at 15%-25%, the total deformation amount is controlled at ≥80%, the rolling speed is controlled at 0.5m / s-1.5m / s, there is no intermediate cold material heating, and the final rolling temperature is not lower than 90℃ below the β phase transformation temperature.

[0012] Furthermore, in step 1), the heating and holding time of the cold material in the fast forging mill is the minimum size of the billet × (0.5-0.8) min, and in steps 2) and 3), the heating and holding time of the precision forging mill and the rolling mill in step 4) is the minimum size of the billet × 0.5 + (30-70) min.

[0013] Furthermore, in steps 1) to 4) above, a high-temperature coating is applied before the cold material is loaded into the furnace; at the same time, after the second stage of step 1) and steps 2) to 4) reach the holding time, the material is taken out of the furnace, wrapped with lattice asbestos, and then put back into the furnace for holding for 30-60 minutes before processing.

[0014] Furthermore, the double annealing process described in step 5 is as follows: First annealing: Heat to 970-1000℃, hold for 1-2 hours, then air cool; Second annealing: Heat to 590-610℃, hold for 1-3 hours, then air cool.

[0015] Compared with the prior art, the present invention has the following main advantages: 1. This invention breaks through existing technological biases and achieves significant cost reduction. Specifically, it is the first to adopt the "precise control of deformation per pass + hot material reheating at critical temperature" technology, specifically targeting the narrow process window characteristics of TA12A. This technology enables only 1-2 cold material heating cycles in each single process throughout the entire process. The total number of cold material heating cycles is reduced from more than 10 in the traditional process to 5-6, a reduction of nearly 50%. At the same time, the energy consumption for hot material reheating is only 1 / 4-1 / 3 of that for cold material heating, reducing the total processing energy consumption by about 50%. The production cycle is significantly shortened, and the direct processing cost per piece is reduced by more than 20%. The cost reduction effect is significantly better than the average reduction of 15-20% for general titanium alloys. 2. This invention eliminates thermal stress, significantly improving yield. Specifically, it avoids the enormous thermal stress generated by repeated heating and cooling of the billet within a single process. Combined with strict control of the deformation per pass and the final forging (rolling) temperature, it effectively suppresses the generation of surface cracks and internal micro-cracks. Compared with traditional processes, it eliminates the need for frequent shutdowns to repair cracks, reduces grinding losses from over 15% to below 7%, increases product yield by nearly 8%, and significantly improves material utilization. 3. This invention features gradient high cumulative deformation, resulting in high microstructure uniformity. Specifically, it achieves uniform and refined microstructure throughout the entire process from casting to finished product through a gradient high cumulative deformation design of "rapid forging and crushing of the as-cast microstructure + large precision forging 75-85% + small precision forging 70-80% + rolling ≥80%". The grain size difference between the edge and core of the finished bar is ≤0.5 grade, with no obvious elongated microstructure or micro-region segregation. The performance fluctuation range is controlled within 5%, which is far superior to the 10-15% fluctuation level of general titanium alloy routes, meeting the stringent requirements of aerospace for material performance consistency. 4. This invention exhibits excellent strength and toughness matching, resulting in superior overall performance. High cumulative deformation promotes full dynamic recrystallization, yielding a uniform and fine equiaxed α-phase structure with a small amount of β-phase, enabling the bar to achieve a perfect combination of high strength and high toughness at room temperature, high temperature, and under thermally stable conditions. Specific performance indicators are: room temperature tensile strength ≥980MPa, elongation ≥17%; 550℃ high-temperature tensile strength ≥650MPa, elongation ≥26%; tensile strength after 550℃ / 100h heat exposure ≥980MPa, elongation ≥14%. The overall mechanical properties are comparable to those of traditional processes, with a slight improvement in plasticity, all far exceeding the requirements of the GJB2744A standard. 5. This invention has strong process compatibility and can be promoted without modification. The equipment used in this invention are all general-purpose high-speed forging machines, precision forging machines, and rolling mills in the field of titanium alloy processing, which do not require modification of existing production lines; the process parameter window is wide (the allowable fluctuation range of temperature and deformation at each stage is ±10%), the operation has good reproducibility, and the skill requirements for operators are low. It can be directly promoted and applied in existing titanium alloy processing enterprises and is suitable for large-scale, stable production. Attached Figure Description

[0016] Figure 1 The images show the microstructures of TA12A small-diameter bars of different sizes obtained by conventional processes in Comparative Example 1 and Examples 1, 2, and 3 of this invention. Specifically: (a) is a microstructure image of the edge portion of the head cross-section of the Φ28mm bar in Comparative Example 1; (b) is a microstructure image of the core portion of the head cross-section of the Φ28mm bar in Comparative Example 1; (c) is a microstructure image of the edge portion of the head cross-section of the Φ20mm bar in Example 1; (d) is a microstructure image of the core portion of the head cross-section of the Φ20mm bar in Example 1; (e) is a microstructure image of the edge portion of the head cross-section of the Φ35mm bar in Example 2; (f) is a microstructure image of the core portion of the head cross-section of the Φ35mm bar in Example 2; (g) is a microstructure image of the edge portion of the head cross-section of the Φ50mm bar in Example 3; and (h) is a microstructure image of the core portion of the head cross-section of the Φ50mm bar in Example 3. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to specific embodiments. The following are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Based on the embodiments of the present invention, any identical or similar substitutions in the art that do not depart from the concept of the present invention should fall within the scope of protection of the present invention.

[0018] Material: Φ680mm TA12A titanium alloy ingot, measured β phase transformation temperature T β =1000℃.

[0019] Comparative Example 1 (Preparation of Φ28mm TA12A small-diameter bars using traditional processes) Step 1: High-speed forging machine forging of billets ("high-low-high" forging process) After uniformly coating the ingots with a high-temperature anti-oxidation coating, they are loaded into the furnace, and the cold material is heated to 1150℃ (T). β +150℃), hold for 480 min; the first stage is large deformation forging at 1150℃, the Φ680mm ingot is forged into an octagonal billet with a side-to-side distance of 620mm through two upsetting and two drawing, the upsetting deformation is 40% each time, breaking up the large columnar crystals in the cast state, after forging air cooling to room temperature and surface grinding; the second stage is after uniformly applying a high-temperature anti-oxidation coating and loading into the furnace, the cold material is heated to 975℃ (Tβ -25℃), after holding at this temperature for 300 minutes, immediately remove from the furnace, wrap with asbestos, and return to the furnace for holding at this temperature for 60 minutes before starting medium-temperature deformation. The octagonal billet with a side-to-side distance of 620mm is then forged into an octagonal billet with a side-to-side distance of 620mm through a single upsetting and drawing process. The upsetting deformation is 35%, refining the grains and improving the uniformity of the microstructure. After forging, it is returned to the furnace. The third stage involves reheating in the furnace to 1055℃ (T β (+55℃), hold for 210 minutes, draw and forge the billet into a square billet with a side length of 480mm, air cool to room temperature after forging, and then perform surface grinding. Step 2: Intermediate forging to produce precision forging billets The forged billet completed in step 1 is subjected to five heats of cold material heating and drawing to form a billet with a diameter of Φ200mm. The furnace temperature for each heat is 970℃ (T). β In a heating furnace at -30℃, the holding time is the minimum size of the billet × (0.5-0.8) min. After reaching the holding time, the billet is removed from the furnace, covered with asbestos, and held in the furnace for 60 min before forging. The elongation deformation of the five forging passes is 36%, 32%, 28%, 27%, and 24%, respectively. After each forging pass, the billet is air-cooled and the cracks are cleaned. Step 3: Finished product forging on a precision forging machine The forged billet completed in step 2 is subjected to four cold-material heating and drawing forging processes to obtain a billet with a diameter of Φ28mm. The furnace temperature for each cold-material loading process is 970℃ (T). β In a heating furnace at -30℃, the holding time is 0.5 + (30-70) min for the minimum size of the billet. The elongation deformation amounts for the four forging passes are 66%, 64%, 61%, and 47%, respectively. After each forging pass, the billet is air-cooled and the cracks are cleaned. Step 4: Double annealing The first annealing process involves heating to 980℃, holding for 1 hour, and then air cooling. The second annealing process involves heating to 600℃, holding for 2 hours, and then air cooling.

[0020] Example 1 (Preparation of Φ20mm TA12A small-diameter rods according to the present invention) Step 1: Forging and billet preparation using a high-speed forging mill After uniformly coating the ingots with a high-temperature anti-oxidation coating, they are loaded into the furnace, and the cold material is heated to 1150℃ (T). β +150℃), hold for 480 min; the first stage is large deformation forging at 1150℃, forging the Φ680mm ingot into an octagonal billet with a side-to-side distance of 450mm, with a total deformation of 62%, breaking up the coarse columnar crystals in the cast state, and then air-cooling to room temperature and surface grinding; the second stage is to uniformly coat with a high-temperature anti-oxidation coating and then load it into the furnace, heating the cold material to 980℃ (T β-20℃), after holding at this temperature for 300 minutes, immediately remove from the furnace and wrap with lattice asbestos. Return to the furnace and hold for 60 minutes before starting the deformation process. Forge the octagonal billet with a side-to-side distance of 450mm into an octagonal billet with a side-to-side distance of 340mm, with a total deformation of 43%. This refines the grains and improves the uniformity of the microstructure. After forging, return to the furnace. The third stage involves returning to the pre-prepared 1080℃ (T) temperature. β In a heating furnace at +80℃, after holding at that temperature for 150 minutes, high-temperature shaping is performed to forge an octagonal billet with a side-to-side distance of 335mm. After forging, the billet is air-cooled to room temperature and then surface-ground. Step 2: Intermediate forging of billets using a large precision forging machine After uniformly coating the cold blank from step 1 with a high-temperature anti-oxidation coating, load it into the furnace and heat it to 970℃ (T). β -30℃), after holding at this temperature for 200 minutes, immediately remove from the furnace, wrap with lattice asbestos, return to the furnace for holding for 60 minutes, and then begin deformation processing; employ 12 consecutive forging passes, with a deformation amount of 12% per pass and a total deformation amount of 79%, forging into a transfer billet bar with a diameter of Φ140mm; during the forging process, when the billet temperature drops to 930℃ (T β When the temperature reaches -70℃, immediately reheat it to 975℃ (T). β -25℃), hold for 40 minutes and continue forging. There is no secondary heating of cold material in this process. After forging, air cool to room temperature and perform surface grinding. Step 3: Intermediate forging of billets using a small precision forging machine After uniformly coating the cold stock blanks from step 2 with a high-temperature anti-oxidation coating, load them into the furnace and heat them to 965℃ (T). β -35℃), after holding at this temperature for 110 minutes, immediately remove from the furnace, wrap with lattice asbestos, return to the furnace for holding for 60 minutes, and then begin deformation processing; employ 13 consecutive forging passes, with a deformation amount of 10% per pass, for a total deformation amount of 71%, forging into a rolled billet with a diameter of Φ75mm; during the forging process, when the billet temperature drops to 920℃ (T β When the temperature reaches -80℃, immediately reheat it to 965℃ (T). β -35℃), hold for 30 minutes and continue forging. There is no secondary heating of cold material in this process. After forging, air cool to room temperature and perform surface grinding. Step 4: Rolling of finished products on the rolling mill After uniformly coating the cold blank with a high-temperature anti-oxidation coating as completed in step 3, load it into the furnace and heat it to 960℃ (T). β -40℃), after holding at this temperature for 70 minutes, immediately remove from the furnace and wrap with lattice asbestos, then return to the furnace for holding at this temperature for 60 minutes before starting the deformation process; use 9 passes of continuous hot rolling, without secondary heating of cold material in the middle, with a deformation amount of 20% per pass, a total deformation amount of 93%, a rolling speed of 1.0m / s, and roll into finished bars with a diameter of Φ20mm, and air-cool to room temperature after final rolling; Step 5: Double annealing The first annealing process involves heating to 980℃, holding for 1 hour, and then air cooling. The second annealing process involves heating to 600℃, holding for 2 hours, and then air cooling.

[0021] Example 2 (Preparation of Φ35mm TA12A small-diameter rods according to the present invention) Step 1: Forging and billet preparation using a high-speed forging mill After uniformly coating the ingots with a high-temperature anti-oxidation coating, they are loaded into the furnace, and the cold material is heated to 1150℃ (T). β +150℃), hold for 480 min; the first stage is large deformation forging at 1150℃, forging the Φ680mm ingot into an octagonal billet with a side-to-side distance of 455mm, with a total deformation of 61%, breaking up the coarse columnar crystals in the cast state, and then air-cooling to room temperature and grinding the surface; the second stage is to uniformly coat with a high-temperature anti-oxidation coating and then load it into the furnace, heating the cold material to 980℃ (T β -20℃), after holding at this temperature for 300 minutes, immediately remove from the furnace and wrap with lattice asbestos. Return to the furnace and hold for 60 minutes before starting medium-temperature deformation. Forge the octagonal billet with a side-to-side distance of 455mm into an octagonal billet with a side-to-side distance of 345mm, with a total deformation of 43%. This refines the grains and improves the uniformity of the microstructure. After forging, return to the furnace. The third stage involves returning to the pre-prepared 1070℃ (T... β +70℃), hold for 150 minutes, perform high-temperature shaping, forge into an octagonal billet with a side-to-side distance of 340mm, air cool to room temperature after forging, and perform slight grinding; Step 2: Intermediate forging of billets using a large precision forging machine After uniformly coating the cold blank from step 1 with a high-temperature anti-oxidation coating, load it into the furnace and heat it to 970℃ (T). β -30℃), after holding at this temperature for 200 minutes, immediately remove from the furnace, wrap with lattice asbestos, return to the furnace for holding for 60 minutes, and then begin deformation processing; employ 14 consecutive forging passes, with each pass involving 11% deformation, for a total deformation of 80%, to forge a Φ175mm diameter transfer billet; during the forging process, when the billet temperature drops to 930℃ (T β When the temperature reaches -70℃, immediately reheat it to 970℃ (T). β -30℃), hold at this temperature for 45 minutes and then continue forging. There is no secondary heating of cold material in this process. After forging, air cool to room temperature. Step 3: Intermediate forging of billets using a small precision forging machine After uniformly coating the cold stock blanks from step 2 with a high-temperature anti-oxidation coating, load them into the furnace and heat them to 960℃ (T). β -40℃), after holding at this temperature for 120 minutes, immediately remove from the furnace, wrap with lattice asbestos, return to the furnace for holding at this temperature for 60 minutes, and then begin deformation processing; employ 15 consecutive forging passes, with a deformation amount of 9% per pass and a total deformation amount of 75%, forging into a rolled billet with a diameter of Φ100mm; during the forging process, when the billet temperature drops to 920℃ (T βWhen the temperature reaches -80℃, immediately reheat it to 960℃ (T). β -40℃), hold for 30 minutes and continue forging. There is no secondary heating of cold material in this process. After forging, air cool to room temperature. Step 4: Rolling of finished products on the rolling mill After uniformly coating the cold stock blanks completed in step 3 with a high-temperature anti-oxidation coating, load them into the furnace and heat them to 955℃ (T). β -45℃), after holding at the temperature for 90 minutes, immediately remove from the furnace and wrap with lattice asbestos, return to the furnace for holding at the temperature for 60 minutes before starting the deformation process; adopt 7-pass continuous hot rolling, without secondary cold material heating in the middle, the deformation amount of each pass is 18%, the total deformation amount is 84%, the rolling speed is 0.8m / s, and roll into finished bars with a diameter of Φ35mm, and air cool to room temperature after final rolling; Step 5: Double annealing The first annealing process involves heating to 980℃, holding for 1 hour, and then air cooling. The second annealing process involves heating to 600℃, holding for 2 hours, and then air cooling.

[0022] Example 3 (Preparation of Φ50mm TA12A small-diameter rods according to the present invention) Step 1: Forging and billet preparation using a high-speed forging mill After uniformly coating the ingots with a high-temperature anti-oxidation coating, they are loaded into the furnace, and the cold material is heated to 1150℃ (T). β +150℃), hold for 480 min; the first stage is large deformation forging at 1150℃, forging the Φ680mm ingot into an octagonal billet with a side-to-side distance of 445mm, with a total deformation of 64%, breaking up the coarse columnar crystals in the cast state, and then air-cooling to room temperature and grinding the surface; the second stage is to uniformly coat with a high-temperature anti-oxidation coating and then load it into the furnace, heating the cold material to 975℃ (T β -25℃), after holding at this temperature for 300 minutes, immediately remove from the furnace and wrap with lattice asbestos. Return to the furnace and hold for 60 minutes before starting medium-temperature deformation. Forge the octagonal billet with a side-to-side distance of 445mm into an octagonal billet with a side-to-side distance of 335mm, with a total deformation of 44%. This refines the grains and improves the uniformity of the microstructure. After forging, return to the furnace. The third stage involves reheating in the furnace to 1055℃ (T). β +55℃), hold for 150 minutes, perform high-temperature shaping, forge into an octagonal billet with a side distance of 330mm, air cool to room temperature after forging, and perform slight grinding; Step 2: Intermediate forging of billets using a large precision forging machine After uniformly coating the cold blank from step 1 with a high-temperature anti-oxidation coating, load it into the furnace and heat it to 965℃ (T). β-35℃), after holding at this temperature for 200 minutes, immediately remove from the furnace, wrap with lattice asbestos, return to the furnace for holding for 60 minutes, and then begin deformation processing; employ 11 consecutive forging passes, with a deformation amount of 13% per pass and a total deformation amount of 76%, forging into a transfer billet bar with a diameter of Φ240mm; during the forging process, when the billet temperature drops to 930℃ (T β When the temperature reaches -70℃, immediately reheat it to 965℃ (T). β -35℃), hold at this temperature for 50 minutes and continue forging. There is no secondary heating of cold material in this process. After forging, air cool to room temperature. Step 3: Intermediate forging of billets using a small precision forging machine After uniformly coating the cold stock blanks from step 2 with a high-temperature anti-oxidation coating, load them into the furnace and heat them to 955℃ (T). β -45℃), after holding at this temperature for 180 minutes, immediately remove from the furnace, wrap with lattice asbestos, return to the furnace for holding for 60 minutes, and then begin deformation processing; employ 12 consecutive forging passes, with each pass involving 11% deformation, for a total deformation of 72%, forging into a rolled billet with a diameter of Φ130mm; during the forging process, when the billet temperature drops to 920℃ (T β When the temperature reaches -80℃, immediately reheat it to 955℃ (T). β -45℃), hold for 35 minutes and continue forging. There is no secondary heating of cold material in this process. After forging, air cool to room temperature. Step 4: Rolling of finished products on the rolling mill After uniformly coating the cold stock blanks completed in step 3 with a high-temperature anti-oxidation coating, load them into the furnace and heat them to 950℃ (T). β -50℃), after holding at this temperature for 110 minutes, immediately remove from the furnace and wrap with lattice asbestos, then return to the furnace for holding at this temperature for 60 minutes before starting the deformation process; use 6 passes of continuous hot rolling, without secondary heating of cold material in the middle, with a deformation amount of 22% per pass, a total deformation amount of 85%, a rolling speed of 1.2m / s, and roll into finished bars with a diameter of Φ50mm, and air-cool to room temperature after final rolling; Step 5, Double annealing treatment: First annealing: heat to 980℃, hold for 1 hour, and air cool; Second annealing: heat to 600℃, hold for 2 hours, and air cool.

[0023] Table 1: Summary of Mechanical Properties of Comparative Example 1

[0024] Table 2: Summary of Mechanical Properties of Embodiments 1 to 3 of the Invention

[0025] The Φ28mm bars prepared in Comparative Example 1 and the Φ20mm, Φ35mm, and Φ50mm small-diameter TA12A bars prepared according to this invention exhibit various mechanical properties as shown in Tables 1 and 2. All meet the requirements of GJB2744A standard, with minimal difference in performance between the edge and core, achieving a perfect match between room temperature strength, high temperature strength, and thermal stability. The overall mechanical properties of Examples 1 to 3 are comparable to those of Comparative Example 1, with slightly improved plasticity, all far exceeding the requirements of GJB2744A standard, fully meeting the stringent requirements for hot-end components of aero-engines.

[0026] Meanwhile, metallographic observations were performed on bars of various specifications, such as... Figure 1 The results showed that Comparative Example 1 and Examples 1 to 3 all achieved uniform microstructure in the core and edges of the bars, consisting of fine equiaxed α phases with a small amount of β phase, without obvious elongated structures or coarse grains, exhibiting excellent microstructure uniformity. While significantly reducing the number of cold material reheating cycles, the material microstructure and properties were also excellent.

Claims

1. A method for preparing small-diameter TA12A bars with high microstructure uniformity and a good balance of strength and toughness, characterized in that, Includes the following steps: Step 1) High-speed forging machine forging billet preparation The ingot is forged into a billet using a high-speed forging machine, and the billet is forged into an octagonal or hexagonal cross section. After forging, it is air-cooled to room temperature and then ground. Step 2) Intermediate forging of billets using a large precision forging machine The cold forging material completed in step 1) is heated to 30℃-40℃ below the β phase transformation temperature and held at that temperature. The forging process is carried out by multi-pass continuous precision forging using a large precision forging machine. The hot material is returned to the furnace for reheating during the forging process. After forging, the material is air-cooled to room temperature and then ground. Step 3) Intermediate forging of billets using a small precision forging machine The cold forging material completed in step 2) is heated to 35℃-45℃ below the β phase transformation temperature and held at that temperature. The forging process is carried out by multiple passes of continuous precision forging using a small precision forging machine. The hot material is returned to the furnace for reheating during the forging process. After forging, the material is air-cooled to room temperature and then ground. Step 4) Rolling of finished product on the rolling mill The cold forging material completed in step 3) is heated to 40℃-50℃ below the β phase transformation temperature and held at that temperature. It is then subjected to multiple passes of continuous hot rolling without secondary heating of the cold material in between. The rolled material is then air-cooled to room temperature. Step 5) Heat treatment The rolled bar obtained in step 4) is subjected to double annealing.

2. The method for preparing TA12A small-diameter bars with high microstructure uniformity and strength-toughness matching according to claim 1, characterized in that, The forging process in step 1) above is specifically as follows: First stage: Heat the Φ680mm ingot cold material to 130℃-170℃ above the β phase transformation temperature and hold it at that temperature. Then, perform billet forging to form an octagonal billet with a side distance of 440-460mm and a total deformation of ≥60%. After forging, air cool and grind. Second stage: Heat the cold forging material obtained in the first stage to 20℃-50℃ below the β phase transformation temperature and hold it for medium temperature deformation to forge an octagonal billet with a side distance of 330-350mm and a total deformation of ≥40%. The billet is then returned to the furnace after forging. The third stage: The forged billet completed in the second stage is returned to the furnace and held at 50℃-80℃ above the β phase transformation temperature for high-temperature shaping to obtain an octagonal or hexagonal billet with a side-to-side distance of 325-345mm; the holding time is strictly controlled, and the holding time = minimum billet size × 0.3 + (30-60) min.

3. The method for preparing TA12A small-diameter bars with high microstructure uniformity and strength-toughness matching according to claim 1 or 2, characterized in that, In step 2) above, the deformation amount of each pass in the large precision forging is controlled at 10%-15%, and the total deformation amount is controlled at 75%-85%. The hot material is returned to the furnace for reheating under the following conditions: when the billet temperature drops to 70°C below the β phase transformation temperature, it is immediately returned to the furnace for heating to 20°C-50°C below the β phase transformation temperature. After holding at this temperature for 30-60 minutes, it is taken out of the furnace for further forging. There is no secondary heating of cold material in this process. The final forging temperature is not lower than 70°C below the β phase transformation temperature.

4. The method for preparing TA12A small-diameter bars with high microstructure uniformity and strength-toughness matching according to claim 3, characterized in that, In step 3) above, the deformation amount of each pass of small precision forging is controlled at 8%-12%, and the total deformation amount is controlled at 70%-80%. The hot material is returned to the furnace for reheating under the following conditions: when the billet temperature drops to 80°C below the β phase transformation temperature, it is immediately returned to the furnace for heating to 30°C-50°C below the β phase transformation temperature. After holding at this temperature for 20-40 minutes, it is taken out of the furnace for further forging. There is no secondary heating of cold material in this process. The final forging temperature is not lower than 80°C below the β phase transformation temperature.

5. The method for preparing TA12A small-diameter bars with high microstructure uniformity and strength-toughness matching according to claim 4, characterized in that, In step 4) above, the deformation amount of each rolling pass is controlled at 15%-25%, the total deformation amount is controlled at ≥80%, the rolling speed is controlled at 0.5m / s-1.5m / s, there is no intermediate cold material heating, and the final rolling temperature is not lower than 90℃ below the β phase transformation temperature.

6. The method for preparing TA12A small-diameter bars with high microstructure uniformity and strength-toughness matching according to claim 5, characterized in that, In step 1) above, the heating and holding time of cold material in the fast forging mill is the minimum size of the billet × (0.5-0.8) min. In steps 2) and 3) the heating and holding time of the precision forging mill and the rolling mill in step 4) is the minimum size of the billet × 0.5 + (30-70) min.

7. The method for preparing TA12A small-diameter bars with high microstructure uniformity and strength-toughness matching according to claim 6, characterized in that, In steps 1) to 4) above, a high-temperature coating is applied before the cold material is loaded into the furnace; at the same time, after the second stage of step 1) and steps 2) to 4) reach the holding time, the material is taken out of the furnace, wrapped with lattice asbestos, and then kept in the furnace for 30-60 minutes before processing.

8. The method for preparing TA12A small-diameter bars with high microstructure uniformity and strength-toughness matching according to claim 1, characterized in that, The double annealing process described in step 5) is as follows: First annealing: Heat to 970-1000℃, hold for 1-2 hours, then air cool; Second annealing: Heat to 590-610℃, hold for 1-3 hours, then air cool.

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