Forming method of fine grain TC4 titanium alloy disc without obvious anisotropy

Abstract

The invention relates to the technical field of material forming, in particular to a forming method of a fine-grain TC4 titanium alloy disc without obvious anisotropy, which comprises the following steps: selecting a TC4 titanium alloy rod-shaped blank; the blank is subjected to heat preservation at the temperature of 1010-1050 DEG C for 50-120 min, and after heat preservation is finished, the blank is water-cooled to the room temperature; the blank is heated to 700 DEG C to 970 DEG C, and heat preservation is conducted for 60 min to 120 min; the heated blank is transferred to an ACDR forging machine, a lower die is started, the lower die rotates, an upper die begins to press downwards, and forging is completed until the rolling reduction meets the design requirement; according to the method, beta treatment is carried out once before forging, and then the titanium alloy disc part obtained through the ACDR forming superposition annealing or solid solution aging process is obviously refined in structure, the performance anisotropy is obviously improved, and the strength plasticity also reaches the high level.

Description

Technical Field

[0001] This invention relates to the field of material forming technology, specifically to a method for forming fine-grained TC4 titanium alloy discs without significant anisotropy. Background Technology

[0002] TC4 titanium alloy is an α+β titanium alloy. Different microstructures can be obtained through specific processing and heat treatment methods, such as equiaxed microstructure and bimodal microstructure, each with varying properties. The equiaxed microstructure is characterized by a proportion of equiaxed α grains greater than 50%. This microstructure exhibits good plasticity but lower strength. The bimodal microstructure contains a certain amount of equiaxed α grains (30%-50%), and this microstructure offers the best overall mechanical properties, combining high strength and plasticity.

[0003] The problem with traditional forging processes is that the resulting titanium alloy discs have insufficient microstructure refinement, with the α phase size generally exceeding 10 μm. This leads to lower strength in discs produced by traditional forging processes, typically not exceeding 1000 MPa; poor plasticity, with elongation generally not exceeding 15%. Furthermore, the α phase structure of titanium alloys is a close-packed hexagonal structure with few slip systems, making it prone to texture formation during deformation and resulting in significant anisotropy in properties. The radial and chordal yield strength differences in traditional TC4 titanium alloy discs can reach 50-100 MPa, and the tensile strength differences exceed 20 MPa.

[0004] Axial closed rolling process (ACDR process) is a type of oscillating rolling process. Compared with traditional processes, in addition to axial compression and radial tension, the workpiece deformation also includes tangential torsional deformation, which can effectively increase the amount of deformation. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for forming fine-grained TC4 titanium alloy discs without significant anisotropy. This method involves a pre-forging β treatment followed by ACDR forming and subsequent annealing or solution aging, resulting in a significantly refined microstructure, improved anisotropy, and high strength and plasticity.

[0006] This invention discloses a method for forming fine-grained TC4 titanium alloy disks without significant anisotropy, comprising the following steps: S1: Select TC4 titanium alloy rod-shaped billet; S2: Hold the billet from S1 at 1010-1050℃ for 50-120 minutes, and then cool it to room temperature with water after the holding period. S3: Heat the billet from S2 to 700-970℃ and hold for 60-120 minutes; S4: Transfer the heated billet from S3 to the ACDR forging machine and fix the billet in the lower die groove to prevent the billet from shifting during subsequent forging. S5: Start the lower die, the lower die rotates, the upper die begins to press down, the pressing rate is 4-12mm / s, the upper die tilt angle is 3-12°, until the pressing amount reaches the design requirements, then the forging is completed; S6: After the forging process is completed, a fine-grained TC4 titanium alloy disc is obtained. The fine-grained TC4 titanium alloy disc is then air-cooled to room temperature. S7: Annealing or solution aging treatment is performed on fine-grained TC4 titanium alloy discs. Annealing treatment: Annealing temperature 700-950℃, holding time 1-4h, air cooling to room temperature after holding; Solution aging treatment: Solution temperature 940-970℃, holding time 1-2h, water cooling after holding, aging temperature 550-750℃, holding time 1-4h, air cooling to room temperature after holding.

[0007] Preferably, in S1, the TC4 titanium alloy rod-shaped blank is processed into a blank with a positioning platform diameter of 60-80mm and a height of 10-20mm, and a deformation section diameter of 120mm and a height of 150mm.

[0008] Preferably, the rotational speed of the lower mold in S5 is 30-70 rpm.

[0009] Preferably, the transfer process in S4 does not exceed 15 seconds.

[0010] The present invention uses a β treatment before forging, followed by ACDR forming and superimposed annealing or solution aging process to significantly refine the microstructure of titanium alloy discs, significantly improve the anisotropy of properties, and achieve a high level of strength and plasticity.

[0011] The annealed α-phase grains of this invention have an average equivalent circle diameter of 2.5 μm and an average size of 5 μm for primary α-phase grains in the solution-aged state, which is significantly finer than traditional forgings; the strength and plasticity are significantly improved, with tensile strength exceeding 1010 MPa and elongation exceeding 16%; the anisotropy of the properties is significantly improved, with the difference in radial and chordal tensile strength not exceeding 10 MPa and the difference in yield strength not exceeding 20 MPa. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the tissue in Embodiment 1 of the present invention.

[0013] Figure 2 This is a schematic diagram of the tissue in Embodiment 2 of the present invention. Detailed Implementation

[0014] This invention discloses a method for forming fine-grained TC4 titanium alloy disks without significant anisotropy, comprising the following steps: S1: Select TC4 titanium alloy rod-shaped billet; S2: Hold the billet from S1 at 1010-1050℃ for 50-120 minutes, and then cool it to room temperature with water after the holding period. S3: Heat the billet from S2 to 700-970℃ and hold for 60-120 minutes; S4: Transfer the heated billet from S3 to the ACDR forging machine and fix the billet in the lower die groove to prevent the billet from shifting during subsequent forging. S5: Start the lower die, the lower die rotates, the upper die begins to press down, the pressing rate is 4-12mm / s, the upper die tilt angle is 3-12°, until the pressing amount reaches the design requirements, then the forging is completed; S6: After the forging process is completed, a fine-grained TC4 titanium alloy disc is obtained. The fine-grained TC4 titanium alloy disc is then air-cooled to room temperature. S7: Annealing or solution aging treatment is performed on fine-grained TC4 titanium alloy discs. Annealing treatment: Annealing temperature 700-950℃, holding time 1-4h, air cooling to room temperature after holding; Solution aging treatment: Solution temperature 940-970℃, holding time 1-2h, water cooling after holding, aging temperature 550-750℃, holding time 1-4h, air cooling to room temperature after holding.

[0015] In one embodiment, in S1, a TC4 titanium alloy rod-shaped blank is processed into a blank with a positioning platform diameter of 60-80mm and a height of 10-20mm, and a deformation section diameter of 120mm and a height of 150mm.

[0016] In S5, the rotational speed of the lower die is 30-70 rpm.

[0017] The transfer process in S4 does not exceed 15 seconds.

[0018] Example 1 This invention discloses a method for forming fine-grained TC4 titanium alloy disks without significant anisotropy, comprising the following steps: S1: Select TC4 titanium alloy rod blank. There is a titanium rod with a diameter of 120mm*170mm. Process it into a deformed section with a diameter of 120mm*150mm and a positioning platform with a diameter of 80mm*20mm as blanks and number them A. S2: Heat the billet in S1 to 1020℃ and hold for 80 minutes, then cool it to room temperature with water; S3: Heat the billet from S2 to 900℃ and hold for 120 minutes until thoroughly heated; S4: Transfer the heated billet from S3 to the ACDR forging machine and fix the billet in the lower die groove to prevent the billet from shifting during subsequent forging. The transfer process shall not exceed 15 seconds. S5: Start the lower die, the lower die rotates at a speed of 40 rpm, the upper die begins to press down at a rate of 10 mm / s, the upper die tilt angle is 6°, the deformation is 80%, that is, the pressing amount is 120 mm, the forging size is Φ268 mm * 30 mm, then the forging is completed; S6: After the forging process is completed, a fine-grained TC4 titanium alloy disc is obtained. The fine-grained TC4 titanium alloy disc is then air-cooled to room temperature. Forging sampling: Take out microstructure samples, room temperature tensile test samples and high temperature tensile test samples from fine-grained TC4 titanium alloy disc A. For each test sample, take two radial samples and two chordal samples, and ensure that the gauge length is located between 1 / 2R-edge of the fine-grained TC4 titanium alloy disc. S7: Sample heat treatment: The microstructure and performance samples taken from the fine-grained TC4 titanium alloy disc A were annealed at 750℃ for 2 hours.

[0019] Tissue observation and performance testing: The tissue samples after heat treatment are observed, and the performance samples are tested.

[0020] Example 2 This invention discloses a method for forming fine-grained TC4 titanium alloy disks without significant anisotropy, comprising the following steps: S1: Select TC4 titanium alloy rod blank. There is a titanium rod with a diameter of 120mm*170mm. Process it into a deformed section with a diameter of 120mm*150mm and a positioning platform with a diameter of 80mm*20mm as blank and number it B. S2: Heat the billet in S1 to 1020℃ and hold for 80 minutes, then cool it to room temperature with water; S3: Heat the billet from S2 to 900℃ and hold for 120 minutes until thoroughly heated; S4: Transfer the heated billet from S3 to the ACDR forging machine and fix the billet in the lower die groove to prevent the billet from shifting during subsequent forging. The transfer process shall not exceed 15 seconds. S5: Start the lower die, the lower die rotates at a speed of 40 rpm, the upper die begins to press down at a rate of 10 mm / s, the upper die tilt angle is 6°, the deformation is 80%, that is, the pressing amount is 120 mm, the forging size is Φ268 mm * 30 mm, then the forging is completed; S6: After the forging process is completed, a fine-grained TC4 titanium alloy disc is obtained. The fine-grained TC4 titanium alloy disc is then air-cooled to room temperature. Forging sampling: Take out microstructure samples, room temperature tensile test samples and high temperature tensile test samples from fine-grained TC4 titanium alloy disc B. For each test sample, take two radial samples and two chordal samples, and ensure that the gauge length is located between 1 / 2R-edge of the fine-grained TC4 titanium alloy disc. S7: Sample heat treatment: The microstructure and property samples taken from the fine-grained TC4 titanium alloy disc B were subjected to solution aging treatment. The solution aging treatment regime was 960℃*1h / WQ+750℃*2h / AC.

[0021] Tissue observation and performance testing: The tissue samples after heat treatment are observed, and the performance samples are tested.

[0022] Example Results The organizational results of Example 1 are as follows Figure 1 As shown, the tissue results of Example 2 are as follows: Figure 2 As shown. In Example 1, the microstructure is dominated by equiaxed α phase with an average grain size of 1.54 μm; in Example 2, the microstructure is dominated by equiaxed primary α phase with fine lamellar β-transformation, and the average size of the primary α phase is 5.22 μm. The microstructure is significantly finer than that of conventional forging.

[0023] Table 1 Performance data for Example 1 and Example 2 The performance data of each embodiment of the present invention are shown in the table above. The overall mechanical properties are excellent and significantly improved compared with traditional processes. The radial and chordal properties are similar and the anisotropy of the properties is not obvious.

[0024] Using existing technology as a comparative example, this illustrates how the solution of the present invention solves the problems of the prior art: Li Xue and others from Shenyang University of Technology obtained TC4 titanium alloy discs with room temperature tensile strength generally not exceeding 950MPa and a maximum of 970MPa using traditional forging technology combined with annealing at 780℃ / 2h, and the elongation was only between 10% and 12%.

[0025] Ding Rongrong et al. from Chongqing University obtained Ti6242 titanium alloy discs with a tangential room temperature tensile strength exceeding 1030 MPa using traditional forging technology combined with 994℃×4h water cooling + 595℃×10h air cooling. However, the radial and axial room temperature tensile strengths were less than 930 MPa, indicating severe anisotropy.

Claims

1. A method for forming fine-grained TC4 titanium alloy disks without significant anisotropy, characterized in that, Includes the following steps: S1: Select TC4 titanium alloy rod-shaped billet; S2: Hold the billet from S1 at 1010-1050℃ for 50-120 minutes, and then cool it to room temperature with water after the holding period. S3: Heat the billet from S2 to 700-970℃ and hold for 60-120 minutes; S4: Transfer the heated billet from S3 to the ACDR forging machine and fix the billet in the lower die groove to prevent the billet from shifting during subsequent forging. S5: Start the lower die, the lower die rotates, the upper die begins to press down, the pressing rate is 4-12mm / s, the upper die tilt angle is 3-12°, until the pressing amount reaches the design requirements, then the forging is completed; S6: After the forging process is completed, a fine-grained TC4 titanium alloy disc is obtained. The fine-grained TC4 titanium alloy disc is then air-cooled to room temperature. S7: Annealing or solution aging treatment is performed on fine-grained TC4 titanium alloy discs. Annealing treatment: Annealing temperature 700-950℃, holding time 1-4h, air cooling to room temperature after holding; Solution aging treatment: Solution temperature 940-970℃, holding time 1-2h, water cooling after holding, aging temperature 550-750℃, holding time 1-4h, air cooling to room temperature after holding.

2. The method for forming fine-grained TC4 titanium alloy disks without significant anisotropy as described in claim 1, characterized in that, In S1, TC4 titanium alloy rod blanks are processed into blanks with a positioning table diameter of 60-80mm and a height of 10-20mm, and a deformation section diameter of 120mm and a height of 150mm.

3. The method for forming fine-grained TC4 titanium alloy disks without significant anisotropy as described in claim 1, characterized in that, In S5, the rotational speed of the lower die is 30-70 rpm.

4. The method for forming fine-grained TC4 titanium alloy disks without significant anisotropy as described in claim 1, characterized in that, The transfer process in S4 does not exceed 15 seconds.

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