Method for preparing fine-grain TC32 titanium alloy rod material with high impact toughness

Abstract

The application provides a preparation method of TC32 titanium alloy fine-grain rod material with high impact toughness, and relates to the technical field of metal material hot working, and comprises the following steps: step one, selecting a TC32 titanium alloy ingot; step two, high-temperature beta zone cogging forging; step three, alpha+beta two-phase zone intermediate forging; step four, multi-pass radial forging; and step five, double annealing heat treatment. The application provides the preparation method of the TC32 titanium alloy fine-grain rod material with high impact toughness, and through the whole-process collaborative control of "high-temperature beta zone cogging, two-phase zone forging, multi-pass radial forging, furnace heat supplement, and controlled slow cooling double annealing", primary alpha phase fine-grain (2-5 microns) and secondary alpha phase homogenization are realized; while the tensile strength is ensured to be not lower than 950 MPa, the impact toughness is stably improved to be higher than 90 J / cm2, and the highest impact toughness is 110 J / cm2, which is greatly improved compared to the prior art with the impact toughness of 80 J / cm2; the method takes into account high strength and excellent impact resistance, and has uniform structure and controllable process.

Description

Technical Field

[0001] This invention relates to the field of hot working technology of metal materials, and in particular to a method for preparing fine-grained TC32 titanium alloy rods with high impact toughness. Background Technology

[0002] TC32 titanium alloy is a medium-to-high strength, high-toughness α+β type titanium alloy independently developed by the Beijing Institute of Aeronautical Materials, China Aero Engine Corporation. Its nominal composition is Ti-5Al-3Mo-3Cr-1Zr-0.1Si, and it possesses significant advantages such as excellent impact performance, high fracture toughness, and low cost. This alloy has a wide hot working window, excellent strength-toughness matching, and significantly superior overall performance compared to TC4 and TA15 titanium alloys. Furthermore, its low overall processing cost makes it considered the most suitable material for developing into my country's next-generation backbone structural titanium alloy. TC32 titanium alloy has already found important applications in aircraft structural components, landing gear forgings, and other fields, where increasingly stringent requirements for impact resistance are being placed.

[0003] The mechanical properties of α+β type titanium alloys are closely related to their microstructure characteristics. By adjusting the hot working process parameters, the type and parameters of the microstructure can be controlled to a certain extent, thereby achieving the optimal match of strength, plasticity, toughness, fatigue, and other properties. Common microstructure types of TC32 titanium alloys include equiaxed structure, bimodal structure, basketweave structure, and Widmanstätten structure, etc., and different microstructure types have significantly different effects on impact toughness. Studies have shown that during β heat treatment, from furnace cooling to water cooling, as the cooling rate increases, the size of the α bundle, the lamellar α phase in the bundle, the grain boundary α phase, and the size of the residual β phase all show a significant decreasing trend, and the room temperature impact toughness also decreases significantly with the increase of the cooling rate.

[0004] Currently, there have been some studies on the preparation methods of TC32 titanium alloy bars. For example, the existing technology CN119332188A discloses a processing method that significantly improves the impact toughness of TC32 titanium alloy bars. Through hot deformation at 845℃~890℃ and double annealing treatment, the volume fraction of the primary α phase is maintained at 15%~35%, and the impact toughness can stably reach above 80J / cm². In addition, some literature reports a method for synergistic optimization of the microstructure of TC32 titanium alloy by multi-pass radial forging and annealing treatment, achieving a breakthrough in impact toughness from 88.13J / cm² to 116.88J / cm² under radial forging conditions at 860℃.

[0005] However, existing technologies have the following problems: First, for critical load-bearing components in aerospace, the impact toughness level of 80 J / cm² is still insufficient to meet the safety margin requirements under some harsh service conditions, especially the requirement to further improve impact toughness while maintaining a high strength level (tensile strength not less than 950 MPa). The reported high impact toughness processes still need to be optimized in terms of strength maintenance and process controllability. Second, most existing radial forging processes use a single temperature range for deformation, lacking systematic optimization of the temperature windows in the billet opening stage and radial forging stage, resulting in limited grain refinement and insufficient microstructure uniformity. Third, there is a lack of systematic matching and optimization of the process parameters for the entire process of multi-fire billet opening, multi-pass radial forging, and double annealing, which fails to fully leverage the combined effect of fine grain strengthening and multi-phase synergistic toughening. Summary of the Invention

[0006] Based on the technical problems existing in the background art, the present invention proposes a method for preparing fine-grained TC32 titanium alloy rods with high impact toughness.

[0007] This invention proposes a method for preparing fine-grained TC32 titanium alloy rods with high impact toughness, comprising the following steps: Step 1: Select TC32 titanium alloy ingot, the nominal composition of which is Ti-5Al-3Mo-3Cr-1Zr-0.1Si, and determine the β phase transformation temperature Tβ of the TC32 titanium alloy ingot. Step 2, High-Temperature β-Zone Forging: The TC32 titanium alloy ingot is heated to a temperature range of (Tβ+150℃) to (Tβ+200℃), and held for a time equal to the ingot cross-sectional diameter × 1.0 min / mm to 1.5 min / mm. Then, a first upsetting and drawing forging is performed, with an upsetting deformation of 30% to 45% and a drawing ratio of 2.5 to 3.5. The ingot is then air-cooled to room temperature. Next, the resulting billet is heated to a temperature range of (Tβ+30℃) to (Tβ+80℃), and held for a time equal to the billet cross-sectional diameter × 0.8 min / mm to 1.2 min / mm. Then, a second upsetting and drawing forging is performed, with an upsetting deformation of 25% to 40% and a drawing ratio of 2.0 to 3.0. The billet is then air-cooled to room temperature. Step 3, intermediate forging in the α+β two-phase region: Heat the billet obtained in Step 2 to a temperature range of (Tβ-60℃) to (Tβ-30℃), hold it for a time of 0.8 min / mm to 1.2 min / mm (diameter of billet cross section), and perform 1 to 2 upsetting and drawing forgings. The upsetting deformation per upsetting is 25% to 35%, and the drawing forging ratio is 1.8 to 2.5. Air cool to room temperature. Step 4, multi-pass radial forging: The billet obtained in Step 3 is heated to a temperature range of (Tβ-120℃) to (Tβ-80℃), and the holding time is 1.0 min / mm to 1.5 min / mm of the billet cross-section diameter. Then, multi-pass radial forging is performed on a radial forging machine. The number of passes in the multi-pass radial forging is 4 to 8, the diameter reduction in each pass is 5% to 12%, and the cumulative total deformation is 40% to 65%. Before each forging pass, the billet is reheated in the furnace at a temperature of (Tβ-120℃) to (Tβ-80℃) and the holding time in the furnace is 8 min to 15 min. Step 5, double annealing heat treatment: The bar obtained in Step 4 is subjected to the first annealing, heated to (Tβ-70℃) to (Tβ-40℃), held for 2h to 4h, and then slowly cooled in the furnace to 500℃ to 550℃ at a cooling rate of 0.5℃ / min to 3℃ / min, and then air-cooled to room temperature; then the bar is subjected to the second annealing, heated to 520℃ to 580℃, held for 4h to 8h, and then air-cooled to room temperature.

[0008] Preferably, in step two, the upsetting deformation of the first upsetting and drawing forging is 35% to 45%, and the drawing-to-forging ratio is 2.8 to 3.5.

[0009] Preferably, in step two, the upsetting deformation of the second upsetting and drawing forging is 25% to 35%, and the drawing-to-forging ratio is 2.0 to 2.8.

[0010] Preferably, in step three, two upsetting and drawing forging processes are performed.

[0011] Preferably, in step four, the number of passes in the multi-pass radial forging is 5 to 7, and the diameter reduction per pass is 6% to 10%.

[0012] Preferably, in step four, the reheating time is 10 min to 15 min.

[0013] Preferably, in step five, the cooling rate of the first annealing is 1.0℃ / min to 2.5℃ / min.

[0014] Preferably, in step five, the holding time of the first annealing is related to the cumulative total deformation in step four. When the cumulative total deformation is 40% to 50%, the holding time of the first annealing is 2.0h to 2.5h; when the cumulative total deformation is 50% to 65%, the holding time of the first annealing is 3.0h to 4.0h.

[0015] Preferably, in steps two, three, and four, the forging die is preheated to 200°C to 350°C before each forging.

[0016] Preferably, the TC32 titanium alloy fine-grained rod obtained by the preparation method has a primary α phase grain size of 2μm to 5μm and a primary α phase volume fraction of 20% to 35% in its microstructure. The secondary α phase in the β-transformed matrix is ​​distributed in the form of fine lamellar and short rod-like morphologies, with a lamellar spacing of 0.3 μm to 1.0 μm; and its room temperature tensile strength is not less than 950 MPa, and its room temperature U-notch impact toughness αKU is not less than 90 J / cm². The room temperature tensile strength is determined according to GB / T228.1, and the room temperature U-notch impact toughness is determined according to GB / T229.

[0017] The present invention proposes a method for preparing high-impact toughness TC32 titanium alloy fine-grained bars, which has the following beneficial effects: Through a fully coordinated process design of "high-temperature β-zone forging → α+β two-phase zone intermediate forging → multi-pass radial forging → controlled cooling double annealing," a complete process chain from ingot to finished bar is established. The temperature windows, deformation parameters, and heat treatment regimes of each process are systematically matched. Under the premise that the tensile strength is not less than 950 MPa, the room-temperature U-notch impact toughness of TC32 titanium alloy bars is stably increased to over 90 J / cm², with a maximum of 110 J / cm². Compared with the existing technology's impact toughness level of 80 J / cm², the present invention improves the impact toughness by approximately 12.5% ​​or more. Furthermore, compared with the higher impact toughness reported in some literature, the present invention has advantages in terms of microstructure uniformity, process repeatability, and comprehensive balance of strength, plasticity, and toughness.

[0018] In step two, a two-stage β-zone forging process with a combination of high and low temperatures is adopted. The first stage is upsetting and drawing with a large deformation at a relatively high temperature (Tβ+150℃~200℃) to fully utilize the high plasticity of the β phase region and completely break the as-cast structure. The second stage is deformed at a temperature close to the β phase transformation point (Tβ+30℃~80℃) to control the recrystallization and growth of β grains. The synergistic effect of the two stages enables the forged billet to obtain a uniform and fine β transformation structure, which provides a good foundation for subsequent refinement.

[0019] In step four, the multi-pass radial forging process employs a cumulative deformation method with 4 to 8 passes and small diameter reductions, and precisely controls the deformation temperature through reheating in the furnace between each pass. Compared with the existing technology that uses single-pass small deformation combined with cumulative large deformation, this invention ensures the consistency of deformation temperature and the uniformity of the deformed microstructure through multi-pass reheating in the furnace, thereby achieving uniform grain refinement of the bar from the surface to the core, and avoiding the problem of uneven microstructure caused by insufficient core deformation.

[0020] In the double annealing process in step five, the first annealing adopts a controlled slow cooling rate of 0.5℃ / min to 3℃ / min. By precisely controlling the cooling rate, the precipitation size and distribution morphology of the secondary α phase are optimized. This avoids the decrease in impact toughness caused by excessive cooling, while also avoiding the coarsening of the microstructure and loss of strength caused by excessive furnace cooling, thus achieving the optimal balance between strength and toughness. Attached Figure Description

[0021] Figure 1 This is a flowchart of a method for preparing fine-grained TC32 titanium alloy rods with high impact toughness, as proposed in this invention. Detailed Implementation

[0022] Reference Figure 1 This invention proposes a method for preparing fine-grained TC32 titanium alloy rods with high impact toughness, comprising the following steps: Step 1: Ingot preparation and β phase transformation point determination TC32 titanium alloy ingots with a nominal composition of Ti-5Al-3Mo-3Cr-1Zr-0.1Si were selected. The β-phase transformation temperature Tβ of the ingot was determined by metallographic method. The β-phase transformation temperature of TC32 titanium alloy is usually in the range of 905℃~915℃. The ingot specifications were selected according to the target bar specifications, with ingots with a diameter of Φ300mm~Φ780mm being preferred.

[0023] Step 2: High-temperature β-zone billet forging The TC32 titanium alloy ingot from step one is heated to a temperature range of 150℃ to 200℃ above the β phase transformation point, i.e., (Tβ+150℃) to (Tβ+200℃). The holding time is 1.0 min / mm to 1.5 min / mm of the ingot cross-section diameter. Then, the first upsetting and drawing forging is carried out, with an upsetting deformation of 30% to 45% and a drawing forging ratio of 2.5 to 3.5. After forging, the ingot is air-cooled to room temperature.

[0024] Then, a second forging is performed: the billet is heated to a temperature range of 30℃ to 80℃ above the β phase transformation point, i.e., (Tβ+30℃) to (Tβ+80℃), and the holding time is 0.8 min / mm to 1.2 min / mm of the billet cross-section diameter. Then, a second upsetting and drawing forging is performed, with an upsetting deformation of 25% to 40% and a drawing forging ratio of 2.0 to 3.0. After forging, the billet is air-cooled to room temperature.

[0025] After two rounds of β-zone forging, the original coarse grains in the as-cast state are fully broken down, resulting in a relatively uniform β-recrystallization structure, which lays the microstructure foundation for subsequent fine-graining deformation.

[0026] Step 3: Intermediate forging in the α+β two-phase region The billet obtained in step two is heated to a temperature range of 30℃ to 60℃ below the β phase transformation point, i.e. (Tβ-60℃) to (Tβ-30℃). The holding time is 0.8 min / mm to 1.2 min / mm of the billet cross-section diameter. The billet is then subjected to 1 to 2 upsetting and drawing forging cycles, with an upsetting deformation of 25% to 35% per cycle and a drawing forging ratio of 1.8 to 2.5. After forging, the billet is air-cooled to room temperature.

[0027] This step involves forging at the upper temperature of the two-phase region, utilizing the dynamic recrystallization mechanism under conditions of coexistence of α and β phases to further refine the grains and improve the uniformity of the microstructure.

[0028] Step 4: Multi-pass radial forging The billet obtained in step three is heated to a temperature range of 80℃ to 120℃ below the β phase transformation point, i.e., (Tβ-120℃) to (Tβ-80℃), and the holding time is 1.0 min / mm to 1.5 min / mm of the billet cross-section diameter. Then, the heated billet is subjected to multi-pass radial forging on a radial forging machine. The number of passes in the multi-pass radial forging is 4 to 8, the diameter reduction in each pass is 5% to 12%, and the cumulative total deformation is 40% to 65%.

[0029] In the multi-pass radial forging process, the billet is reheated in the furnace before each forging pass. The reheating temperature is the same as the heating temperature, i.e. (Tβ-120℃) to (Tβ-80℃), and the reheating time is 8min to 15min. This ensures that the billet is in the optimal deformation temperature range during each deformation pass, and avoids increased deformation resistance and uneven microstructure caused by temperature drop.

[0030] Multi-pass radial forging uses a high-frequency, small-deformation-amount cumulative deformation method to form a uniform strain distribution in all parts of the billet cross section, effectively avoiding the deformation dead zone and core-edge microstructure differences caused by single-pass large deformation, and achieving uniform and fine graining of the entire bar microstructure.

[0031] Step 5: Double annealing heat treatment The bar material obtained in step four is subjected to a double annealing heat treatment. The specific process is as follows: First annealing: Heat the bar to a temperature range of 40℃ to 70℃ below the β phase transformation point, i.e. (Tβ-70℃) to (Tβ-40℃), hold for 2h to 4h, and then slowly cool it in the furnace to 500℃ to 550℃ at a controlled cooling rate of 0.5℃ / min to 3℃ / min. Then remove it from the furnace and air cool it to room temperature.

[0032] Second annealing: Heat the bar to 520℃~580℃, hold for 4h~8h, and then air cool to room temperature.

[0033] The first annealing employs a controlled, slow cooling method. On the one hand, this allows the distortion energy stored in the forging deformation structure to be fully released, achieving static recrystallization. On the other hand, by precisely controlling the cooling rate, it promotes the precipitation of the secondary α phase in an appropriate size and morphology, forming a microstructure that is conducive to improving impact toughness. The second annealing further stabilizes the structure, eliminates residual stress, and enables the alloy to achieve the best balance between strength and toughness.

[0034] Through the above steps, TC32 titanium alloy fine-grained rods with the following microstructure characteristics are finally obtained: the primary α phase grain size is 2μm to 5μm, and the volume fraction of the primary α phase is 20% to 35%; the secondary α phase in the β-transformed matrix is ​​distributed in the form of fine lamellar layers and short rods, with a lamellar spacing of 0.3μm to 1.0μm; the room temperature tensile strength of the TC32 titanium alloy fine-grained rods is not less than 950MPa, and the room temperature U-notch impact toughness αKU is not less than 90J / cm².

[0035] Example 1 A 500mm TC32 titanium alloy ingot was selected, and its β-phase transformation temperature Tβ was determined to be 910℃ by metallographic method.

[0036] Step Two (High-Temperature β-Zone Forging): Heat the ingot to 1070℃ (Tβ+160℃), hold for 500×1.2=600min, and then perform the first upsetting and drawing forging: upsetting deformation 38%, drawing forging ratio 3.0, and air cool to room temperature. Then heat the billet to 960℃ (Tβ+50℃), hold for 400min, and perform the second upsetting and drawing forging: upsetting deformation 30%, drawing forging ratio 2.5, and air cool to room temperature.

[0037] Step 3 (Intermediate forging in the α+β two-phase region): Heat the billet to 865℃ (Tβ-45℃), hold for 360 minutes, and perform a single upsetting and drawing forging: upsetting deformation of 30%, drawing forging ratio of 2.0, and air cool to room temperature.

[0038] Step 4 (Multi-pass radial forging): Heat the billet to 810℃ (Tβ-100℃), hold for 400 min, and perform 6 passes of radial forging on a radial forging machine. The diameter reduction in each pass is 10%, 9%, 8%, 8%, 7%, and 6%, respectively, with a cumulative total deformation of approximately 48%. Before each forging pass, the billet is reheated to 810℃ in the furnace and held for 12 min.

[0039] Step 5 (Double Annealing Heat Treatment): First Annealing: Heat to 855℃ (Tβ-55℃), hold for 2.5h, then slowly cool in the furnace to 520℃ at a cooling rate of 1.5℃ / min, and air cool to room temperature; Second Annealing: Heat to 550℃, hold for 6h, and air cool to room temperature.

[0040] Testing revealed that the microstructure of the obtained TC32 titanium alloy fine-grained rods showed that the primary α-phase grain size ranged from 2.5 μm to 4.5 μm, with a volume fraction of approximately 28%. In the β-transformation matrix, the secondary α-phase was distributed in fine lamellar and short rod-like morphologies, with a lamellar spacing of 0.4 μm to 0.8 μm. Room temperature tensile properties were: tensile strength 986 MPa, yield strength 892 MPa, and elongation after fracture 12.5%. The room temperature U-notch impact toughness αKU = 97 J / cm².

[0041] Example 2 A 350mm TC32 titanium alloy ingot was selected, and its β-phase transformation temperature Tβ was determined to be 908℃ by metallographic method.

[0042] Step 2 (High-Temperature β-Zone Forging): Heat the ingot to 1080℃ (Tβ+172℃), hold for 350×1.0=350min, and then perform the first upsetting and drawing forging: upsetting deformation 42%, drawing forging ratio 3.2, and air cool to room temperature; then heat the billet to 955℃ (Tβ+47℃), hold for 260min, and perform the second upsetting and drawing forging: upsetting deformation 35%, drawing forging ratio 2.8, and air cool to room temperature.

[0043] Step 3 (Intermediate forging in the α+β two-phase region): Heat the billet to 860℃ (Tβ-48℃), hold for 240 min, and perform a single upsetting and drawing forging: upsetting deformation 32%, drawing forging ratio 2.2, and air cool to room temperature.

[0044] Step 4 (Multi-pass radial forging): Heat the billet to 800℃ (Tβ-108℃), hold for 280 min, and perform 5 passes of radial forging on a radial forging machine. The diameter reduction in each pass is 10%, 9%, 8%, 8%, and 7%, respectively, with a cumulative total deformation of approximately 42%. Before each forging pass, the billet is reheated to 800℃ in the furnace and held for 10 min.

[0045] Step 5 (Double Annealing Heat Treatment): First Annealing: Heat to 850℃ (Tβ-58℃), hold for 2.0h, then slowly cool in the furnace to 530℃ at a cooling rate of 1.0℃ / min, and air cool to room temperature; Second Annealing: Heat to 540℃, hold for 5h, and air cool to room temperature.

[0046] Testing revealed that the microstructure of the obtained TC32 titanium alloy fine-grained rods showed that the primary α-phase grain size was 3.0 μm to 5.0 μm, with a volume fraction of approximately 25%. The secondary α-phase in the β-transformed matrix was distributed in the form of fine lamellar layers and short rods, with a lamellar spacing of 0.3 μm to 0.9 μm. The room temperature tensile properties were: tensile strength 965 MPa, yield strength 876 MPa, and elongation after fracture 13.8%. The room temperature U-notch impact toughness αKU = 103 J / cm².

[0047] Example 3 A 650mm TC32 titanium alloy ingot was selected, and its β-phase transformation temperature Tβ was determined to be 912℃ by metallographic method.

[0048] Step 2 (High-Temperature β-Zone Forging): Heat the ingot to 1065℃ (Tβ+153℃), hold for 650×1.3=845min, and then perform the first upsetting and drawing forging: upsetting deformation 35%, drawing forging ratio 2.8, and air cool to room temperature; then heat the billet to 965℃ (Tβ+53℃), hold for 500min, and perform the second upsetting and drawing forging: upsetting deformation 28%, drawing forging ratio 2.3, and air cool to room temperature.

[0049] Step 3 (Intermediate forging in the α+β two-phase region): Heat the billet to 860℃ (Tβ-52℃) and perform two-stage upsetting and drawing forging: the first stage has an upsetting deformation of 28% and a drawing forging ratio of 1.9, the second stage has an upsetting deformation of 25% and a drawing forging ratio of 1.8, each stage is held for 380 minutes and then air-cooled to room temperature.

[0050] Step 4 (Multi-pass radial forging): Heat the billet to 815℃ (Tβ-97℃), hold for 520 min, and perform 8 passes of radial forging on a radial forging machine. The diameter reduction in each pass is 8%, 8%, 7%, 7%, 6%, 6%, 6%, and 5%, respectively. The cumulative total deformation is approximately 53%. Before each forging pass, the billet is reheated to 815℃ in the furnace and held for 15 min.

[0051] Step 5 (Double Annealing Heat Treatment): First Annealing: Heat to 858℃ (Tβ-54℃), hold for 3.5h, then slowly cool in the furnace to 510℃ at a cooling rate of 2.5℃ / min, and air cool to room temperature. Second Annealing: Heat to 560℃, hold for 7h, and air cool to room temperature.

[0052] Testing revealed that the microstructure of the obtained TC32 titanium alloy fine-grained rods showed that the primary α-phase grain size ranged from 2.0 μm to 4.0 μm, with a volume fraction of approximately 32%. In the β-transformed matrix, the secondary α-phase was distributed in fine lamellar and short rod-like morphologies, with a lamellar spacing of 0.3 μm to 0.7 μm. Room temperature tensile properties were: tensile strength 954 MPa, yield strength 861 MPa, and elongation after fracture 14.2%. The room temperature U-notch impact toughness αKU = 110 J / cm².

[0053] Comparative Example 1 (using existing technology CN119332188A scheme) Take the same batch of TC32 titanium alloy ingots as in Example 2 and process them according to the technical solution of CN119332188A: perform hot deformation and radial forging in the temperature range of 845℃~890℃, and then perform double annealing treatment.

[0054] The test results showed that the room temperature tensile strength of the obtained bar was 1015 MPa, but the room temperature U-notch impact toughness αKU was only 82 J / cm².

[0055] Performance Comparison Analysis As can be seen from the table above, the TC32 titanium alloy fine-grained rods prepared in the three embodiments of the present invention maintain a tensile strength of not less than 950 MPa, while the impact toughness αKU reaches more than 97 J / cm², and can reach up to 110 J / cm², which is significantly better than the 82 J / cm² obtained by Comparative Example 1 using the prior art; the present invention improves the impact toughness by about 18% to 34%.

[0056] The significant improvement in impact toughness is mainly attributed to the following three aspects: First, the two-pass β-zone forging in step two and the intermediate forging in step three refine the original β-grains and primary α-phase grains. The grain refinement strengthens the strength while effectively hindering crack propagation by increasing the grain boundary area, thus contributing to the toughening effect. Second, the multi-pass radial forging in step four, combined with reheating in each pass, achieves uniform refinement of the entire microstructure of the bar while ensuring the stability of the deformation temperature, avoiding large grain areas and stress concentration caused by insufficient local deformation. Third, the controlled slow cooling rate (0.5℃ / min~3℃ / min) of the first annealing in step five causes the secondary α-phase to precipitate uniformly in the β-transformed matrix in the form of fine lamellar layers and short rods, forming a composite effect of grain refinement and multi-phase synergistic toughening, which significantly improves the impact toughness without significantly sacrificing strength.

[0057] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing fine-grained TC32 titanium alloy rods with high impact toughness, characterized in that, Includes the following steps: Step 1: Select TC32 titanium alloy ingot, the nominal composition of which is Ti-5Al-3Mo-3Cr-1Zr-0.1Si, and determine the β phase transformation temperature Tβ of the TC32 titanium alloy ingot. Step 2, High-Temperature β-Zone Forging: The TC32 titanium alloy ingot is heated to a temperature range of (Tβ+150℃) to (Tβ+200℃), and held for a time equal to the ingot cross-sectional diameter × 1.0 min / mm to 1.5 min / mm. Then, a first upsetting and drawing forging is performed, with an upsetting deformation of 30% to 45% and a drawing ratio of 2.5 to 3.

5. The ingot is then air-cooled to room temperature. Next, the resulting billet is heated to a temperature range of (Tβ+30℃) to (Tβ+80℃), and held for a time equal to the billet cross-sectional diameter × 0.8 min / mm to 1.2 min / mm. Then, a second upsetting and drawing forging is performed, with an upsetting deformation of 25% to 40% and a drawing ratio of 2.0 to 3.

0. The billet is then air-cooled to room temperature. Step 3, intermediate forging in the α+β two-phase region: Heat the billet obtained in Step 2 to a temperature range of (Tβ-60℃) to (Tβ-30℃), hold it for a time of 0.8 min / mm to 1.2 min / mm (diameter of billet cross section), and perform 1 to 2 upsetting and drawing forgings. The upsetting deformation per upsetting is 25% to 35%, and the drawing forging ratio is 1.8 to 2.

5. Air cool to room temperature. Step 4, multi-pass radial forging: The billet obtained in Step 3 is heated to a temperature range of (Tβ-120℃) to (Tβ-80℃), and the holding time is 1.0 min / mm to 1.5 min / mm of the billet cross-section diameter. Then, multi-pass radial forging is performed on a radial forging machine. The number of passes in the multi-pass radial forging is 4 to 8, the diameter reduction in each pass is 5% to 12%, and the cumulative total deformation is 40% to 65%. Before each forging pass, the billet is reheated in the furnace at a temperature of (Tβ-120℃) to (Tβ-80℃) and the holding time in the furnace is 8 min to 15 min. Step 5, double annealing heat treatment: The bar obtained in Step 4 is subjected to the first annealing, heated to (Tβ-70℃) to (Tβ-40℃), held for 2h to 4h, and then slowly cooled in the furnace to 500℃ to 550℃ at a cooling rate of 0.5℃ / min to 3℃ / min, and then air-cooled to room temperature; then the bar is subjected to the second annealing, heated to 520℃ to 580℃, held for 4h to 8h, and then air-cooled to room temperature.

2. The method for preparing high-impact toughness TC32 titanium alloy fine-grained rods according to claim 1, characterized in that, In step two, the upsetting deformation of the first upsetting and drawing forging is 35% to 45%, and the drawing forging ratio is 2.8 to 3.

5.

3. A method for preparing fine-grained TC32 titanium alloy rods with high impact toughness according to claim 1, characterized in that, In step two, the upsetting deformation in the second upsetting and drawing forging is 25% to 35%, and the drawing forging ratio is 2.0 to 2.

8.

4. A method for preparing a fine-grained TC32 titanium alloy rod with high impact toughness according to claim 1, characterized in that, In step three, two upsetting and drawing forging processes are performed.

5. A method for preparing a fine-grained TC32 titanium alloy rod with high impact toughness according to claim 1, characterized in that, In step four, the number of passes in the multi-pass radial forging is 5 to 7, and the diameter reduction per pass is 6% to 10%.

6. A method for preparing a fine-grained TC32 titanium alloy rod with high impact toughness according to claim 1, characterized in that, In step four, the heat preservation time during the reheating process is 10 to 15 minutes.

7. A method for preparing a fine-grained TC32 titanium alloy rod with high impact toughness according to claim 1, characterized in that, In step five, the cooling rate for the first annealing is 1.0℃ / min to 2.5℃ / min.

8. A method for preparing fine-grained TC32 titanium alloy rods with high impact toughness according to claim 1, characterized in that, In step five, the holding time of the first annealing is related to the cumulative total deformation in step four. When the cumulative total deformation is 40% to 50%, the holding time of the first annealing is 2.0h to 2.5h; when the cumulative total deformation is 50% to 65%, the holding time of the first annealing is 3.0h to 4.0h.

9. A method for preparing fine-grained TC32 titanium alloy rods with high impact toughness according to claim 1, characterized in that, In steps two, three, and four, the forging dies are preheated to 200℃~350℃ before each forging.

10. A method for preparing a fine-grained TC32 titanium alloy rod with high impact toughness according to any one of claims 1-9, characterized in that, The TC32 titanium alloy fine-grained rods obtained by the preparation method have a primary α phase grain size of 2μm to 5μm and a primary α phase volume fraction of 20% to 35% in their microstructure. In the β-transformed matrix, the secondary α phase is distributed in the form of fine lamellar and short rod-shaped morphologies, with interlamellar spacing of 0.3 μm to 1.0 μm; Furthermore, its room temperature tensile strength is not less than 950 MPa, and its room temperature U-notch impact toughness αKU is not less than 90 J / cm². The room temperature tensile strength is determined according to GB / T228.1, and the room temperature U-notch impact toughness is determined according to GB / T229.

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