Preparation method of low-cost TC4 titanium alloy fine grain bar for fastener

Abstract

The invention discloses a preparation method of a low-cost TC4 titanium alloy fine-grain bar for a fastener. The preparation method comprises the following steps: S1, preparing a cast ingot: taking a TC4 titanium alloy cast ingot with the diameter phi of 700mm-800mm; s2, cast ingot forging, specifically, the cast ingot is heated to 1100-1200 DEG C, cogging forging is conducted after heat preservation, and the cast ingot is continuously returned to a furnace and drawn out to form a round billet with the diameter phi ranging from 170 mm to 190 mm; s3, rolling for the first time: heating the round billet obtained in the step S2 to 900-930 DEG C, preserving heat, and then rolling to obtain a rod billet with the diameter of 95mm-105mm; s4, rolling for the second time: heating the round billet obtained in the step S3 to 880-920 DEG C, preserving heat, and then rolling to obtain a rolled bar with the diameter of 10-25mm; s5, heat treatment is conducted, specifically, a heat treatment furnace is adopted for conducting heat treatment on the rolled bar at the temperature of 730-800 DEG C, and heat preservation is conducted for 60-90 min; s6, straightening is conducted, specifically, the bar subjected to heat treatment in the S5 is heated and then straightened; and S7, finishing is conducted, specifically, the bar obtained in S6 is peeled and polished, and the finished TC4 titanium alloy fine-grain bar with the diameter phi ranging from 10 mm to 25 mm is prepared. According to the invention, excellent fatigue performance of the fastener is ensured, and the fastener has good thread rolling formability.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy processing technology, and specifically relates to a method for preparing low-cost TC4 titanium alloy fine-grained rods for fasteners. Background Technology

[0002] Titanium alloy fasteners are characterized by low density, high specific strength, good corrosion resistance, non-magnetic properties, and low coefficient of thermal expansion and modulus of elasticity. They are widely used in aviation, aerospace, and high-end automobiles, where lightweighting is crucial, directly improving carrying efficiency and reducing energy consumption. The United States pioneered the use of TC4 (Ti-6Al-4V) bolts in the B-52 bomber, achieving significant weight reduction. Developed countries in Europe and America have extensively adopted TC4 (Ti-6Al-4V) fasteners in various military and civilian aircraft (such as the C-5A and Boeing 747) to replace traditional 30CrMnSiA steel, achieving a weight reduction of approximately 30%. TC4 (Ti-6Al-4V) has become the mainstream material for aerospace fasteners, accounting for over 95% of titanium alloy fasteners.

[0003] In the domestic and international aerospace fields, TC4 fasteners in sizes M4, M5, M6, and M8 account for a large proportion, and the corresponding titanium alloy raw materials are wire rods with a diameter of less than 10mm. Currently, various research institutes in China have carried out a large number of key research projects on fasteners in this size range and are gradually achieving domestic production. There is less research on TC4 raw materials for large-size bolts such as M16, M18, and M20. The microstructure and properties of the TC4 titanium alloy rods used in these bolts still have certain gaps compared with imported ones, mainly manifested in coarser grains and lower performance after heat treatment strengthening. This can lead to problems such as upsetting, thread rolling cracking, and lower fatigue strength of parts during fastener manufacturing.

[0004] In China, TC4 titanium alloy bars are mostly produced using tandem rolling mills. Due to equipment limitations, the rolling deformation is relatively small, requiring multiple forging processes to produce rolled billets with fine and uniform microstructure. This results in a long overall processing cycle and high production costs, and the finished products still lag behind imported ones in terms of microstructure and properties. Therefore, researching a low-cost manufacturing process for fine-grained straight TC4 titanium alloy bars for fasteners is of significant engineering importance. Summary of the Invention

[0005] The purpose of this invention is to provide a low-cost method for preparing fine-grained TC4 titanium alloy bars for fasteners. This invention, through a shorter production process, produces fine-grained straight bars with transverse and longitudinal microstructures that meet the A1 and AA1 levels of the ETTC2 "Microstructure Standard for Titanium Alloy Bars". This ensures excellent fatigue performance of fastener products and also provides good thread rolling formability.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing low-cost TC4 titanium alloy fine-grained rods for fasteners includes the following steps: S1, Ingot preparation: Take TC4 titanium alloy ingots with a diameter of Φ700mm~Φ800mm. The chemical composition of the ingots includes Al: 6.20%~6.65%; V: 4.0%~4.4%; Fe: 0.1%~0.2%; C: 0.01%~0.04%; N: ≤0.03%; O: 0.14~0.18%; H≤0.008%, with the balance being Ti. S2, Ingot forging: The TC4 titanium alloy ingot obtained in S1 is heated to 1100℃~1200℃, held at the temperature, and then forged into a round billet with a diameter of Φ170mm~Φ190mm. S3, First rolling: The round billet obtained in S2 is placed in a heating furnace and heated to 900℃~930℃ and held for a period of time, and then rolled into a bar billet with a diameter of Φ95mm~Φ105mm; S4, Second rolling: The round billet obtained in S3 is placed in a heating furnace and heated to 880℃~920℃ and held for a period of time, and then rolled into a rolled bar with a diameter of Φ10mm~Φ25mm. S5, heat treatment: The rolled bars were heat-treated in a heat treatment furnace at 730℃~800℃ and held for 60min~90min. S6, Straightening: The bars that have undergone S5 heat treatment are then heated and straightened. S7, Finished: The bar obtained from S6 was peeled and polished to prepare TC4 titanium alloy fine-grained bar products with a diameter of Φ10mm~Φ25mm.

[0007] Preferably, in step S1, the process of preparing the ingot is as follows: sponge titanium, aluminum briquettes, aluminum-vanadium master alloy, aluminum-iron master alloy, and titanium dioxide are mixed and pressed into electrodes, vacuum plasma welded, and then subjected to three vacuum arc melting processes to obtain a TC4 titanium alloy ingot with a diameter of Φ700mm~Φ800mm.

[0008] Preferably, in step S2, the ingot forging process involves two hot material reheating processes, with the reheating temperature being 1000℃~1100℃.

[0009] Preferably, in step S3, the rolling process uses a two-roll reversible rolling mill, and the rolling process involves 10 passes, with a cumulative deformation of 65% to 75%.

[0010] Preferably, in step S4, the continuous rolling process involves 18 to 22 passes, with a cumulative deformation of 95% to 99%. The final rolling speed is controlled at 1.0 m / s to 4.0 m / s, and the final rolling temperature is controlled at 800°C to 850°C.

[0011] Preferably, in step S6, the bar straightening heating temperature is 650℃~700℃, the holding time is 30min~60min, the straightening is performed using a roller straightener, and the straightness of the bar after straightening is ≤0.5mm / m.

[0012] Preferably, in step S7, the surface roughness Ra after polishing is ≤1.2μm.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. In terms of composition design, controlling Al: 6.20%~6.65%; V: 4.0%~4.4%; Fe: 0.1%~0.2%; C: 0.01%~0.04%; N: ≤0.03%; O: 0.14%~0.18%; H≤0.008% can effectively improve the solid solution aged strength of the finished bar stock, thus compensating for the poor hardenability of large-size TC4 titanium alloy, while also exhibiting good plasticity.

[0014] 2. The present invention adopts a processing method of continuous direct drawing in one furnace above the phase change point and rolling in two furnaces below the phase change point, which has the advantages of shorter process and lower cost compared with the traditional multi-fire billet upsetting and drawing.

[0015] 3. The last rolling of this invention uses 24 continuous rolling stands, with a total rolling deformation of more than 95%. The rolling process is temperature and rolling controlled throughout. The large deformation and reasonable deformation temperature range can achieve sufficient refinement of the microstructure, while the microstructure of the beginning and end of the batch is well consistent.

[0016] 4. This invention produces TC4 titanium alloy fine-grained straight bars with diameters of Φ10mm~Φ25mm for aerospace fasteners at a relatively low cost. Both the transverse and longitudinal dimensions of these bars meet the A1 and AA1 levels of the ETTC2 "Standard for Microstructure of Titanium Alloy Bars". After solution treatment and aging heat treatment, the tensile strength is consistently greater than 1150MPa, the elongation is consistently greater than 10%, and the shear strength is consistently greater than 700MPa. This fully meets the requirements for the preparation and processing of large-size bolts and the service requirements for aerospace fasteners. Attached Figure Description

[0017] Figure 1 This is a flowchart of the method of the present invention.

[0018] Figure 2 The image shows the microstructure of a 11.8 mm TC4 titanium alloy bar prepared in Example 1 of this invention, where a represents the transverse direction and b represents the longitudinal direction.

[0019] Figure 3 The image shows the microstructure of a 16.2 mm TC4 titanium alloy bar prepared in Example 2 of this invention, where a represents the transverse direction and b represents the longitudinal direction.

[0020] Figure 4 The image shows the microstructure of a 20.5mm TC4 titanium alloy bar prepared in Example 3 of this invention, where a represents the transverse direction and b represents the longitudinal direction. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0022] like Figure 1 As shown, a method for preparing low-cost TC4 titanium alloy fine-grained rods for fasteners includes the following steps: S1, Ingot preparation: Sponge titanium, aluminum briquettes, aluminum-vanadium master alloy, aluminum-iron master alloy, and titanium dioxide were used as raw materials. The chemical composition was calculated according to the following mass ratio: Al: 6.20%~6.65%; V: 4.0%~4.4%; Fe: 0.1%~0.2%; C: 0.01%~0.04%; N: ≤0.03%; O: 0.14%~0.18%; H≤0.008%, with the balance being Ti. The mixture was pressed into electrodes, vacuum plasma welded, and then subjected to three vacuum arc melting processes to obtain TC4 titanium alloy cylindrical ingots with a diameter of Φ700mm~Φ800mm. The ingots were then peeled and the risers were removed.

[0023] In terms of composition design, controlling Al: 6.20%~6.65%; V: 4.0%~4.4%; Fe: 0.1%~0.2%; C: 0.01%~0.04%; N: ≤0.03%; O: 0.14%~0.18%; H≤0.008% can effectively improve the solid solution aged strength of the finished bar stock, thus compensating for the poor hardenability of large-size TC4 titanium alloy, while also exhibiting good plasticity.

[0024] S2, Ingot forging: The ingot obtained from S1 is heated to 1100℃~1200℃ in an industrial box furnace. After holding at the temperature, it is forged using a high-speed forging machine. Then, it undergoes two hot material reheating cycles at 1000℃~1100℃ and is continuously drawn into a round billet of Φ170mm~Φ190mm. Surface defects are then repaired by grinding.

[0025] S3, First rolling: The round billet obtained in S2 is placed in a heating furnace and heated to 900℃~930℃ and held at that temperature. Then, it is rolled into a bar billet of Φ95mm~Φ105mm through 10 passes using a 650 two-roll reversible rolling mill, with a cumulative deformation of 65%~75%. After straightening using residual heat, surface defects are repaired by grinding.

[0026] S4, Second rolling: The round billet obtained in S3 is placed in a heating furnace and heated to 880℃~920℃ and held at that temperature. Then, it is rolled into Φ10mm~Φ25mm bars through 18~22 passes using a 24-stand continuous rolling mill, with a cumulative deformation of 95%~99%. The final rolling speed is controlled at 1.0m / s~4.0m / s, and the final rolling temperature is controlled at 800℃~850℃. Temperature and rolling are controlled throughout the entire rolling process.

[0027] The processing method of continuous direct drawing in one furnace above the phase transformation point and rolling in two furnaces below the phase transformation point has the advantages of shorter process and lower cost compared with the traditional multi-fire billet upsetting and drawing.

[0028] The final rolling process uses 24 continuous rolling stands, with a total deformation of more than 95%. The rolling process is temperature and rolling controlled throughout. The large deformation and reasonable deformation temperature range can achieve sufficient microstructure refinement, while the microstructure of the beginning and end of the batch is well consistent.

[0029] S5, heat treatment: The rolled bars are heat-treated in a heat treatment furnace at 730℃~800℃ and held for 60min~90min.

[0030] S6, Straightening: After S5 heat treatment, the bars are heated at 650℃~700℃ and held for 30min~60min. Then, they are straightened using a roller straightener. The straightness of the bars after straightening is ≤0.5mm / m.

[0031] S7, Finished: The bar obtained from S6 was peeled using a peeling machine and polished using a round tube polishing machine to achieve a surface roughness Ra≤1.2μm and ensure that the dimensional tolerances were within the tolerance range. Finally, TC4 titanium alloy fine-grained straight bars with diameters of Φ10mm~Φ25mm were produced.

[0032] This invention produces low-cost TC4 titanium alloy fine-grained straight bars with diameters ranging from 10mm to 25mm for aerospace fasteners at a relatively low cost. Both the transverse and longitudinal dimensions of these bars meet the A1 and AA1 levels of the ETTC2 "Standard for Microstructure of Titanium Alloy Bars". After solution aging heat treatment for strengthening, the tensile strength is consistently greater than 1150MPa, the elongation is consistently greater than 10%, and the shear strength is consistently greater than 700MPa. This fully meets the requirements for the preparation and processing of large-size bolts and the service requirements for aerospace fasteners.

[0033] The present invention will be further described in detail below with reference to specific embodiments.

[0034] Example 1 S1, Ingot preparation: Using sponge titanium, aluminum briquettes, aluminum-vanadium master alloy, aluminum-iron master alloy, and titanium dioxide as raw materials, and through three vacuum arc melting processes, a cylindrical TC4 titanium alloy ingot with a diameter of 720 mm was obtained. The ingot was then peeled and the risers were removed to prepare a 4-ton TC4 titanium alloy ingot with the following composition: Al: 6.65%; V: 4.21%; Fe: 0.16%; C: 0.011%; N: ≤0.03%; O: 0.167%; H ≤0.001%, with the balance being Ti.

[0035] S2, Ingot forging: The TC4 titanium alloy ingot obtained from S1 was heated to 1170℃ in an industrial box furnace and held for 400 minutes. Then it was forged in a high-speed forging machine. After two hot material reheating cycles, it was drawn into a round billet with a diameter of 180mm. After breaking, the surface defects were repaired by grinding.

[0036] S3, First rolling: The round billet obtained in S2 is placed in a heating furnace and heated to 900℃ and held for 120 minutes. Then, it is rolled into a Φ100mm bar billet through 10 passes using a 650 two-roll reversible rolling mill, with a cumulative deformation of 69%. After straightening using residual heat, the surface defects are repaired by grinding.

[0037] S4, Second rolling: The round billet obtained in S3 is placed in a heating furnace and heated to 920℃ and held for 60 minutes. Then, it is rolled into a Φ13.2mm rolled bar through 22 passes using a 24-stand continuous rolling mill, with a cumulative deformation of 98.2%. The final rolling speed is controlled at 3.0m / s~3.5m / s and the final rolling temperature is controlled at 800℃~850℃. After rolling, it is air-cooled on a cooling bed and then sawn into blanks.

[0038] S5, heat treatment: The rolled bars were heat-treated at 750℃ in a heat treatment furnace, held at that temperature for 90 minutes, and then air-cooled after being removed from the furnace.

[0039] S6, Straightening: The S5 heat-treated bars are placed in an industrial box furnace, heated to 690℃ and held for 60 minutes before being removed from the furnace and straightened using a roller straightener. The straightness of the bars after straightening is ≤0.5mm / m.

[0040] S7, Finished: The bar obtained from S6 was peeled using a peeling machine until it reached Φ11.8mm. It was then polished using a round tube polishing machine to achieve a surface roughness Ra≤1.2μm. The final size was controlled to be Φ11.8(0, -0.03)mm.

[0041] Example 2 S1, Ingot preparation: Using sponge titanium, aluminum briquettes, aluminum-vanadium master alloy, aluminum-iron master alloy, and titanium dioxide as raw materials, and through three vacuum arc melting processes, a cylindrical TC4 titanium alloy ingot with a diameter of 720 mm was obtained. The ingot was then peeled and the risers were removed to prepare a 4-ton TC4 titanium alloy ingot with the following composition: Al: 6.65%; V: 4.21%; Fe: 0.16%; C: 0.011%; N: ≤0.03%; O: 0.167%; H ≤0.001%, with the balance being Ti.

[0042] S2, Ingot forging: The ingot obtained from S1 is heated to 1170℃ in an industrial box furnace and held for 400 minutes. Then it is forged in a high-speed forging machine. After two hot material reheating cycles, it is drawn into a round billet with a diameter of 180mm. After cutting, the surface defects are repaired by grinding.

[0043] S3, First rolling: The round billet obtained in S2 is placed in a heating furnace and heated to 900℃ and held for 120 minutes. Then, it is rolled into a Φ100mm bar billet through 10 passes using a 650 two-roll reversible rolling mill, with a cumulative deformation of 69%. After straightening using residual heat, the surface defects are repaired by grinding.

[0044] S4, Second rolling: The round billet obtained in S3 is placed in a heating furnace and heated to 920℃ and held for 60 minutes. Then, it is rolled into a bar with a diameter of Φ17.7mm through 20 passes using a 24-stand continuous rolling mill. The cumulative deformation is 96.8%. The final rolling speed is controlled at 2.0m / s to 2.5m / s and the final rolling temperature is controlled at 800℃ to 850℃. After rolling, the bar is air-cooled on a cooling bed and then sawn into shape.

[0045] S5, heat treatment: The rolled bars were heat-treated at 750℃ in a heat treatment furnace, held at that temperature for 90 minutes, and then air-cooled after being removed from the furnace.

[0046] S6, Straightening: The S5 heat-treated bars are placed in an industrial box furnace, heated to 690℃ and held for 60 minutes before being removed from the furnace and straightened using a roller straightener. The straightness of the bars after straightening is ≤0.5mm / m.

[0047] S7, Refined The bar obtained from S6 was peeled using a peeling machine until it reached Φ16.2mm. It was then polished using a round tube polishing machine to achieve a surface roughness Ra≤1.2μm. The final size was controlled to be Φ16.2 (0, -0.03)mm.

[0048] Example 3 S1, Ingot preparation: Using sponge titanium, aluminum briquettes, aluminum-vanadium master alloy, aluminum-iron master alloy, and titanium dioxide as raw materials, and through three vacuum arc melting processes, a cylindrical TC4 titanium alloy ingot with a diameter of 720 mm was obtained. The ingot was then peeled and the risers were removed to prepare a 4-ton TC4 titanium alloy ingot with the following composition: Al: 6.65%; V: 4.21%; Fe: 0.16%; C: 0.011%; N: ≤0.03%; O: 0.167%; H ≤0.001%, with the balance being Ti.

[0049] S2, Ingot forging: The ingot obtained from S1 is heated to 1170℃ in an industrial box furnace and held for 400 minutes. Then it is forged in a high-speed forging machine. After two hot material reheating cycles, it is drawn into a round billet with a diameter of 180mm. After cutting, the surface defects are repaired by grinding.

[0050] S3, First rolling: The round billet obtained in S2 is placed in a heating furnace and heated to 900℃ and held for 120 minutes. Then, it is rolled into a Φ100mm bar billet through 10 passes using a 650 two-roll reversible rolling mill, with a cumulative deformation of 69%. After straightening using residual heat, the surface defects are repaired by grinding.

[0051] S4, Second rolling: The round billet obtained in S3 is placed in a heating furnace and heated to 920℃ and held for 60 minutes. Then, it is rolled into a Φ22.0mm rolled bar through 18 passes using a 24-stand continuous rolling mill, with a cumulative deformation of 95.2%. The final rolling speed is controlled at 1.2m / s~1.7m / s and the final rolling temperature is controlled at 800℃~850℃. After rolling, it is air-cooled on a cooling bed and then sawn into shape.

[0052] S5, heat treatment: The rolled bars were heat-treated at 750℃ in a heat treatment furnace, held at that temperature for 90 minutes, and then air-cooled after being removed from the furnace.

[0053] S6, Straightening: The S5 heat-treated bars are placed in an industrial box furnace, heated to 690℃ and held for 60 minutes before being removed from the furnace and straightened using a roller straightener. The straightness of the bars after straightening is ≤0.5mm / m.

[0054] S7, Finished: The bar obtained from S6 was peeled using a peeling machine until it reached Φ20.5mm. Then, it was polished using a round tube polishing machine to achieve a surface roughness Ra≤1.2μm. The final size was controlled to be Φ20.5 (0, -0.03)mm.

[0055] Figures 2 to 4 The figures show the transverse and longitudinal microstructures of TC4 titanium alloy straight bars with diameters of 11.8 mm, 16.2 mm, and 20.5 mm prepared in Examples 1 to 3 of this invention. As shown in the figures, the microstructure of the TC4 titanium alloy straight bars prepared in this embodiment is mainly composed of equiaxed α phases, with an average α phase size of 4~8 μm, and is rated as A1 in the transverse direction and AA1 in the longitudinal direction, respectively.

[0056] Table 1 below shows the properties of the TC4 titanium alloy straight bars prepared in Examples 1 to 3 of the present invention after heat treatment strengthening. The TC4 bars prepared in the examples of the present invention were subjected to room temperature tensile tests according to GB / T228.1, the tensile testing method for metallic materials. After solution treatment and aging (solution treatment: 955℃ / 1h, water cooling; aging: 540℃ / 6h, air cooling), the results are shown in Table 1.

[0057] Table 1. Room Temperature Tensile Properties Test Table for TC4 Bars

[0058] After being strengthened by solution aging heat treatment, the prepared bars have a tensile strength that is consistently greater than 1150 MPa, an elongation that is consistently greater than 10%, and a shear strength that is consistently greater than 700 MPa, which can fully meet the requirements for the preparation and processing of large-size bolts and the service requirements for fasteners used in aerospace.

[0059] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention.

Claims

1. A method for preparing low-cost TC4 titanium alloy fine-grained rods for fasteners, characterized in that, Includes the following steps: S1, Ingot preparation: Take TC4 titanium alloy ingots with a diameter of Φ700mm~Φ800mm. The chemical composition of the ingots includes Al: 6.20%~6.65%. V：4.0%~4.4%； Fe: 0.1%~0.2%; C：0.01%~0.04%； N : ≤0.03%; O: 0.14~0.18%; H≤0.008%, balance is Ti; S2, Ingot forging: The TC4 titanium alloy ingot obtained in S1 is heated to 1100℃~1200℃, held at the temperature, and then forged into a round billet with a diameter of Φ170mm~Φ190mm. S3, First rolling: The round billet obtained in S2 is placed in a heating furnace and heated to 900℃~930℃ and held for a period of time, and then rolled into a bar billet with a diameter of Φ95mm~Φ105mm; S4, Second rolling: The round billet obtained in S3 is placed in a heating furnace and heated to 880℃~920℃ and held for a period of time, and then rolled into a rolled bar with a diameter of Φ10mm~Φ25mm. S5, heat treatment: The rolled bars were heat-treated in a heat treatment furnace at 730℃~800℃ and held for 60min~90min. S6, Straightening: The bars that have undergone S5 heat treatment are then heated and straightened. S7, Finished: The bar obtained from S6 was peeled and polished to prepare TC4 titanium alloy fine-grained bar products with a diameter of Φ10mm~Φ25mm.

2. The method for preparing low-cost TC4 titanium alloy fine-grained rods for fasteners according to claim 1, characterized in that, In S1, the process of preparing the ingot is as follows: sponge titanium, aluminum briquettes, aluminum-vanadium master alloy, aluminum-iron master alloy, and titanium dioxide are mixed and pressed into electrodes, vacuum plasma welded, and then subjected to three vacuum arc melting processes to obtain TC4 titanium alloy ingots with a diameter of Φ700mm~Φ800mm.

3. The method for preparing low-cost TC4 titanium alloy fine-grained rods for fasteners according to claim 1, characterized in that, In S2, the ingot forging process involves two hot material reheating processes, with the reheating temperature being 1000℃~1100℃.

4. The method for preparing low-cost TC4 titanium alloy fine-grained rods for fasteners according to claim 1, characterized in that, In S3, the rolling process uses a two-roll reversible rolling mill, and the rolling process involves 10 passes, with a cumulative deformation of 65% to 75%.

5. The method for preparing low-cost TC4 titanium alloy fine-grained rods for fasteners according to claim 1, characterized in that, In S4, rolling is carried out using a 24-stand continuous rolling mill, which undergoes 18 to 22 passes, with a cumulative deformation of 95% to 99%. The final rolling speed is controlled at 1.0 m / s to 4.0 m / s, and the final rolling temperature is controlled at 800℃ to 850℃.

6. The method for preparing low-cost TC4 titanium alloy fine-grained rods for fasteners according to claim 1, characterized in that, In S6, the bar straightening heating temperature is 650℃~700℃, the holding time is 30min~60min, the straightening is done by a roller straightener, and the straightness of the bar after straightening is ≤0.5mm / m.

7. The method for preparing low-cost TC4 titanium alloy fine-grained rods for fasteners according to claim 1, characterized in that, In S7, the surface roughness Ra after polishing is ≤1.2μm.

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