Preparation method of high-strength low-cost TC20 small-specification bar

Abstract

The invention discloses a preparation method of a high-strength low-cost TC20 small-specification bar, which comprises the following steps of: 1, cutting off a dead head and an ingot bottom of a TC20 titanium alloy round cast ingot, heating and preserving heat above a beta phase transformation point, and then upsetting and drawing out to obtain a cuboid blank; secondly, the cuboid-shaped blank is heated to the temperature below the beta phase transformation point, heat preservation is conducted, then multi-pass rolling forming is conducted, and a bar with black skin is obtained; thirdly, the bar with the black skin is subjected to heat treatment, and then waste heat straightening and air cooling are adopted; and fourthly, the TC20 small-specification bar is obtained through lathe machining. The TC20 small-specification bar with good structure uniformity and high strength is prepared by adopting a beta-phase region one-fire cogging forging and two-phase region one-fire rolling process and utilizing a crystalline recrystallization and crystalline spheroidization mechanism generated by low-temperature large deformation, the preparation heating number is reduced, the cost is low, the method is suitable for industrial production, the prepared bar is high in reliability and stability, and the production cost is low. The method is suitable for the fields of biomedical treatment and aerospace.

Description

Technical Field

[0001] This invention belongs to the field of titanium and titanium alloy rod preparation technology, specifically relating to a method for preparing high-strength, low-cost TC20 small-diameter rods. Background Technology

[0002] TC20 (Ti-6Al-7Nb) titanium alloy bars possess high specific strength, good corrosion resistance, and excellent biocompatibility, making them promising for applications in various fields. Compared to V, TC20 uses non-toxic Nb, significantly improving its safety and making it particularly suitable for biomaterials, such as orthopedic implants like bone screws and plates. In recent years, with the increasing accessibility and affordability of medical care, there has been a growing demand for lower-cost biomedical titanium alloys. Currently, the common methods for preparing TC20 titanium alloy bars include melting, forging, and rolling. Forging often employs multi-stage forging at and below the phase transformation point to prepare the billet, followed by rolling. However, multi-stage forging increases production costs and extends the production cycle, reducing profitability for enterprises. Furthermore, more forging stages increase energy consumption, leading to a lower final yield and higher costs. Therefore, there is an urgent need for a method to prepare high-strength, low-cost TC20 small-diameter bars. This method is of great significance for reducing production costs, increasing product yield, achieving excellent product performance, reducing costs and increasing efficiency, and promoting the development of medical titanium alloys in my country. Summary of the Invention

[0003] The technical problem to be solved by this invention is to provide a method for preparing high-strength, low-cost TC20 small-diameter bars, addressing the shortcomings of the prior art. This invention first uses forging above the β-phase transformation point to obtain a cuboid billet, and then directly uses large-deformation single-pass rolling above the β-phase transformation point to obtain the bar. By controlling key process parameters such as rolling deformation and rolling temperature, the α-lamellae structure is completely broken up and spheroidized, improving the uniformity of the structure. Simultaneously, the process is optimized to reduce the number of passes, significantly reducing production costs and achieving the preparation of high-strength, low-cost TC20 small-diameter bars, solving the problems of long production cycles and high costs associated with existing preparation processes.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for preparing high-strength, low-cost TC20 small-diameter bars, characterized in that the method includes the following steps: Step 1, billet forging: After removing the riser and bottom of the TC20 titanium alloy round ingot, heat and hold it above the β phase transformation point, then upsetting and drawing it to obtain a cuboid billet; the cuboid billet has a side length of 150mm~170mm and a length of 1000mm~1500mm. Step 2, One-pass rolling below the phase transformation point: The rectangular billet obtained in Step 1 is heated to below the β phase transformation point and held at that temperature, and then rolled in multiple passes to obtain a bar with black skin; the diameter of the bar with black skin is Ф12mm~Ф22mm. Step 3, Annealing treatment: The black-skinned bar obtained in Step 2 is heat-treated, then straightened using residual heat and air-cooled; Step 4, Machining: The air-cooled bar with black skin from Step 3 is machined on a lathe to obtain TC20 small-diameter bar; the diameter of the TC20 small-diameter bar is Ф10mm~Ф20mm, the tensile strength is 1010MPa~1110MPa, the yield strength is 910MPa~980MPa, and the elongation is 11%~17%.

[0005] This invention first involves heating and holding a TC20 titanium alloy circular ingot above its β-phase transformation point, followed by upsetting and drawing to obtain a cuboid billet. By controlling the size and shape of the forged product, the cuboid billet, the cooling rate is controlled to ensure that the resulting α-lamellae are small, facilitating subsequent crushing. Then, a single-fire rolling process with a large deformation at the β-phase transformation point is performed to fully crush the α-lamellae and obtain a large distortion energy in the internal deformed structure of the resulting bar. Combined with a suitable heat treatment regime, this distortion energy is released, allowing for crystal recrystallization and spheroidization processes, thereby improving the uniformity of the microstructure and obtaining high-strength TC20 small-diameter bars. Furthermore, the deformation process in this invention only includes single-fire forging in the β-phase region and single-fire rolling in the two-phase region, effectively reducing the number of rolling passes, optimizing the process, and achieving cost reduction.

[0006] The above-mentioned method for preparing high-strength, low-cost TC20 small-diameter bars is characterized in that the diameter of the TC20 titanium alloy circular ingot in step one is 600mm~800mm and the single weight is 2000kg~3000kg.

[0007] The above-mentioned method for preparing high-strength, low-cost TC20 small-diameter bars is characterized in that the heating and heat preservation temperature in step one is 1150℃~1200℃, and the time is 8h~15h.

[0008] The above-mentioned method for preparing high-strength, low-cost TC20 small-diameter bars is characterized in that, in step two, the temperature is heated to 70°C~100°C below the β phase transformation point and held for 6h~10h, and the total deformation of the multi-pass rolling process is 85%~93%.

[0009] The above-mentioned method for preparing high-strength, low-cost TC20 small-diameter bars is characterized in that the heat treatment temperature in step three is 700℃~750℃, and the holding time is 60min~180min.

[0010] Compared with the prior art, the present invention has the following advantages: 1. The present invention employs low-temperature rolling below the β phase transformation point after billet forging, which enables more primary lamellar α phases to participate in deformation, resulting in a finer microstructure and effectively improving the mechanical properties of TC20 small-diameter bars.

[0011] 2. This invention adopts the method of increasing the deformation amount of the first rolling process, so that the α-lamellae are fully broken, which improves the distortion energy inside the substructure and provides sufficient driving force for the nucleation, growth and spheroidization of the α-phase structure during the subsequent annealing heat treatment process. This achieves the purpose of further refining the structure and improving the uniformity of the structure, realizing the uniform distribution of the structure of the bar and improving the strength of TC20 small-diameter bars.

[0012] 3. The annealing heat treatment temperature range used in this invention can ensure the full spheroidization and recrystallization of the bar structure, while ensuring a large number of primary α phases, so that the mechanical properties of TC20 small-diameter bars reach a high level.

[0013] 4. Compared with traditional preparation methods, this invention only uses one forging above the β phase transformation point and one rolling below the β phase transformation point, for a total of two deformation processes, which greatly reduces the number of forging and rolling processes, lowers production costs, and produces TC20 small-diameter bars with uniform and fine microstructure, excellent performance and strong applicability, and has good prospects for production applications.

[0014] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0015] Figure 1 This is a high-magnification microstructure image of the cross-section of a small-diameter TC20 bar prepared in Example 1 of the present invention.

[0016] Figure 2 This is a high-magnification microstructure image of the cross-section of the TC20 small-diameter bar prepared in Example 2 of the present invention.

[0017] Figure 3 This is a high-magnification microstructure image of the cross-section of the TC20 small-diameter bar prepared in Example 3 of the present invention.

[0018] Figure 4 This is a high-magnification microstructure image of the cross-section of the TC20 small-diameter bar prepared in Example 4 of the present invention.

[0019] Figure 5 This is a high-magnification microstructure image of the cross-section of the TC20 small-diameter bar prepared in Example 5 of the present invention.

[0020] Figure 6 This is a high-magnification microstructure image of the cross-section of the TC20 small-diameter bar prepared in Example 6 of the present invention. Detailed Implementation

[0021] Example 1 This embodiment includes the following steps: Step 1: Forging: After removing the riser and bottom of the TC20 titanium alloy round ingot with a diameter of 600mm and a single weight of 2000kg, heat it at 1150℃ above the β phase transformation point and hold it for 8 hours. Then, it is upsetting and drawing to obtain a rectangular billet with a side length of 150mm and a length of 1000mm. Step 2, One-fire rolling below the phase transformation point: The rectangular billet obtained in Step 1 is heated to 70°C below the β phase transformation point and held for 6 hours. Then, it is rolled in multiple passes with a total deformation of 92%. After the rolling is completed, it is air-cooled to obtain a bar with a diameter of Ф12mm and black skin. Step 3, Annealing treatment: The black bar obtained in Step 2 is subjected to heat treatment at 700℃ for 60 minutes, followed by residual heat straightening and air cooling; Step 4, Machining: The air-cooled bar with black skin from Step 3 is machined on a lathe to obtain a small-diameter TC20 bar with a diameter of Ф10mm.

[0022] Figure 1 This is a high-magnification microstructure image of the cross-section of the TC20 small-diameter bar prepared in this embodiment. Figure 1 It can be seen that the primary α phase in this small-diameter TC20 bar is fine, and the overall microstructure is relatively uniform.

[0023] The mechanical properties of the TC20 small-diameter bars prepared in this embodiment are as follows: tensile strength 1035MPa, yield strength 927MPa, elongation 14.5%, and reduction of area 38%.

[0024] Example 2 This embodiment includes the following steps: Step 1: Forging: After removing the riser and bottom of the TC20 titanium alloy round ingot with a diameter of 600mm and a single weight of 2000kg, heat it at 1150℃ above the β phase transformation point and hold it for 8 hours. Then, it is upsetting and drawing to obtain a rectangular billet with a side length of 150mm and a length of 1000mm. Step 2, One-fire rolling below the phase transformation point: The rectangular billet obtained in Step 1 is heated to 70°C below the β phase transformation point and held for 6 hours. Then, it is rolled in multiple passes with a total deformation of 85%. After the rolling is completed, it is air-cooled to obtain a bar with a diameter of Ф22mm and black skin. Step 3, Annealing treatment: The black bar obtained in Step 2 is subjected to heat treatment at 700℃ for 60 minutes, followed by residual heat straightening and air cooling; Step 4, Machining: The air-cooled bar with black skin from Step 3 is machined on a lathe to obtain a small-diameter TC20 bar with a diameter of Ф20mm.

[0025] Figure 2 This is a high-magnification microstructure image of the cross-section of the TC20 small-diameter bar prepared in this embodiment. Figure 2 It can be seen that the overall microstructure distribution in this small-diameter TC20 bar is relatively uniform.

[0026] The mechanical properties of the TC20 small-diameter bars prepared in this embodiment are as follows: tensile strength 1013 MPa, yield strength 915 MPa, elongation 16.5%, and reduction of area 44%.

[0027] Example 3 This embodiment includes the following steps: Step 1: Forging: After removing the riser and bottom of the TC20 titanium alloy round ingot with a diameter of 800mm and a single weight of 3000kg, heat it at 1200℃ above the β phase transformation point and hold it for 15h. Then, it is upsetting and drawn to obtain a rectangular billet with a side length of 170mm and a length of 1500mm. Step 2, One-pass rolling below the phase transformation point: The rectangular billet obtained in Step 1 is heated to 100°C below the β phase transformation point and held for 10 hours. Then, it is rolled in multiple passes with a total deformation of 93%. After the rolling is completed, it is air-cooled to obtain a bar with a diameter of Ф12mm and black skin. Step 3, Annealing treatment: The black bar obtained in Step 2 is subjected to heat treatment at 750℃ for 180 minutes, then straightened with residual heat and air cooled. Step 4, Machining: The air-cooled bar with black skin from Step 3 is machined on a lathe to obtain a small-diameter TC20 bar with a diameter of Ф10mm.

[0028] Figure 3 This is a high-magnification microstructure image of the cross-section of the TC20 small-diameter bar prepared in this embodiment. Figure 3 It can be seen that the overall microstructure distribution in this small-diameter TC20 bar is relatively uniform.

[0029] The mechanical properties of the TC20 small-diameter bars prepared in this embodiment are as follows: tensile strength 1103 MPa, yield strength 975 MPa, elongation 11.5%, and reduction of area 37%.

[0030] Example 4 This embodiment includes the following steps: Step 1: Forging: After removing the riser and bottom of the TC20 titanium alloy round ingot with a diameter of 800mm and a single weight of 3000kg, heat it at 1200℃ above the β phase transformation point and hold it for 15h. Then, it is upsetting and drawn to obtain a rectangular billet with a side length of 170mm and a length of 1500mm. Step 2, One-fire rolling below the phase transformation point: The rectangular billet obtained in Step 1 is heated to 100°C below the β phase transformation point and held for 10 hours. Then, it is rolled in multiple passes with a total deformation of 87%. After the rolling is completed, it is air-cooled to obtain a bar with a diameter of Ф22mm and black skin. Step 3, Annealing treatment: The black bar obtained in Step 2 is subjected to heat treatment at 750℃ for 180 minutes, then straightened with residual heat and air cooled. Step 4, Machining: The air-cooled bar with black skin from Step 3 is machined on a lathe to obtain a small-diameter TC20 bar with a diameter of Ф20mm.

[0031] Figure 4 This is a high-magnification microstructure image of the cross-section of the TC20 small-diameter bar prepared in this embodiment. Figure 4 It can be seen that the overall microstructure distribution in this small-diameter TC20 bar is relatively uniform.

[0032] The mechanical properties of the TC20 small-diameter bars prepared in this embodiment are as follows: tensile strength 1078 MPa, yield strength 951 MPa, elongation 13.5%, and reduction of area 40%.

[0033] Example 5 This embodiment includes the following steps: Step 1: Forging: After removing the riser and bottom of the TC20 titanium alloy round ingot with a diameter of 700mm and a single weight of 2500kg, heat it at 1170℃ above the β phase transformation point and hold it for 12h. Then, it is upsetting and drawing to obtain a rectangular billet with a side length of 160mm and a length of 1250mm. Step 2, One-fire rolling below the phase transformation point: The rectangular billet obtained in Step 1 is heated to 85°C below the β phase transformation point and held for 8 hours. Then, it is rolled in multiple passes with a total deformation of 92.5%. After the rolling is completed, it is air-cooled to obtain a bar with a diameter of Ф12mm and black skin. Step 3, Annealing treatment: The black bar obtained in Step 2 is subjected to heat treatment at 730℃ for 120 minutes, then straightened with residual heat and air cooled. Step 4, Machining: The air-cooled bar with black skin from Step 3 is machined on a lathe to obtain a small-diameter TC20 bar with a diameter of Ф10mm.

[0034] Figure 5This is a high-magnification microstructure image of the cross-section of the TC20 small-diameter bar prepared in this embodiment. Figure 5 It can be seen that the overall microstructure distribution in this small-diameter TC20 bar is relatively uniform.

[0035] According to the test results, the mechanical properties of the TC20 small-diameter bar prepared in this embodiment are as follows: tensile strength 1093MPa, yield strength 963MPa, elongation 12%, and reduction of area 38%.

[0036] Example 6 This embodiment includes the following steps: Step 1: Forging: After removing the riser and bottom of the TC20 titanium alloy round ingot with a diameter of 700mm and a single weight of 2500kg, heat it at 1170℃ above the β phase transformation point and hold it for 12h. Then, it is upsetting and drawing to obtain a rectangular billet with a side length of 160mm and a length of 1250mm. Step 2, One-fire rolling below the phase transformation point: The rectangular billet obtained in Step 1 is heated to 85°C below the β phase transformation point and held for 8 hours. Then, it is rolled in multiple passes with a total deformation of 86.2%. After the rolling is completed, it is air-cooled to obtain a bar with a diameter of Ф22mm and black skin. Step 3, Annealing treatment: The black bar obtained in Step 2 is subjected to heat treatment at 730℃ for 120 minutes, then straightened with residual heat and air cooled. Step 4, Machining: The air-cooled bar with black skin from Step 3 is machined on a lathe to obtain a small-diameter TC20 bar with a diameter of Ф20mm.

[0037] Figure 6 This is a high-magnification microstructure image of the cross-section of the TC20 small-diameter bar prepared in this embodiment. Figure 6 It can be seen that the overall microstructure distribution in this small-diameter TC20 bar is relatively uniform.

[0038] The mechanical properties of the TC20 small-diameter bars prepared in this embodiment are as follows: tensile strength 1058 MPa, yield strength 937 MPa, elongation 13%, and reduction of area 39%.

[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing high-strength, low-cost TC20 small-diameter bars, characterized in that, The method includes the following steps: Step 1, billet forging: After removing the riser and bottom of the TC20 titanium alloy round ingot, heat and hold it above the β phase transformation point, then upsetting and drawing it to obtain a cuboid billet; the cuboid billet has a side length of 150mm~170mm and a length of 1000mm~1500mm. Step 2, One-pass rolling below the phase transformation point: The rectangular billet obtained in Step 1 is heated to below the β phase transformation point and held at that temperature, and then rolled in multiple passes to obtain a bar with black skin; the diameter of the bar with black skin is Ф12mm~Ф22mm. Step 3, Annealing treatment: The black-skinned bar obtained in Step 2 is heat-treated, then straightened using residual heat and air-cooled; Step 4, Machining: The air-cooled bar with black skin from Step 3 is machined on a lathe to obtain TC20 small-diameter bar; the diameter of the TC20 small-diameter bar is Ф10mm~Ф20mm, the tensile strength is 1010MPa~1110MPa, the yield strength is 910MPa~980MPa, and the elongation is 11%~17%.

2. The method for preparing high-strength, low-cost TC20 small-diameter bars according to claim 1, characterized in that, The diameter of the TC20 titanium alloy round ingot mentioned in step one is 600mm~800mm, and the weight of a single ingot is 2000kg~3000kg.

3. The method for preparing high-strength, low-cost TC20 small-diameter bars according to claim 1, characterized in that, The heating and heat preservation temperature in step one is 1150℃~1200℃, and the time is 8h~15h.

4. The method for preparing high-strength, low-cost TC20 small-diameter bars according to claim 1, characterized in that, In step two, the temperature is raised to 70°C to 100°C below the β phase transformation point and held for 6 to 10 hours. The total deformation of the multi-pass rolling process is 85% to 93%.

5. The method for preparing high-strength, low-cost TC20 small-diameter bars according to claim 1, characterized in that, The heat treatment temperature in step three is 700℃~750℃, and the holding time is 60min~180min.

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