Process for improving extremely low temperature performance of titanium alloy

Abstract

The invention relates to a process for improving the extremely low temperature performance of a titanium alloy, which comprises the following operations: forging a titanium alloy cast ingot obtained by casting to prepare a titanium alloy bar with a uniform equiaxed beta grain structure; the operation S is executed repeatedly and circularly until the titanium alloy bar is rolled to the preset size, and the target titanium alloy material is obtained; and the operation S comprises the steps that the titanium alloy bar is connected with pulse current to be heated to the preset temperature, the titanium alloy bar is rolled by keeping the connection of the pulse current, and after rolling is finished, the pulse current is disconnected, and the titanium alloy bar is air-cooled. According to the scheme provided by the invention, the titanium alloy bar with the superfine fiber crystal heterostructure is prepared through continuous groove rolling assisted by pulse current, and the superfine fiber crystal heterostructure can inhibit crack initiation and propagation in a low-temperature environment, so that the low-temperature toughness of the titanium alloy is improved, brittleness is prevented, and the service life of the titanium alloy is prolonged. And the safety and the service life of the fastener prepared from the titanium alloy are improved.

Description

Technical Field

[0001] The invention relates to the field of titanium alloy production, and in particular to a process for improving the extremely low temperature performance of titanium alloy. Background Art

[0002] Titanium alloy is the preferred material for manufacturing fasteners in aerospace. These fasteners are used in complex environments. For example, in the future, when a space station is built on the surface of the moon, the temperature at night can reach -200℃~-150℃, while the temperature on the surface of the moon facing the sun can rise to 150℃. Faced with such an extreme temperature environment, high requirements are placed on the mechanical properties of titanium alloy fasteners. At present, the blanks prepared by conventional processes for manufacturing fasteners are generally uniform equiaxed (the grain shape is approximately circular or regular polygonal) dual-state (alpha phase + beta phase) titanium alloy bars. This kind of titanium alloy bar has excellent comprehensive mechanical properties at room temperature. However, at extremely low temperatures, the toughness drops sharply, showing sensitive brittleness. This feature greatly limits the widespread application of fasteners made of titanium alloy in extreme aerospace environments. Therefore, it is necessary to solve this problem. Summary of the invention

[0003] The purpose of the present invention is to provide a process for improving the extremely low temperature performance of titanium alloy, which can effectively improve the low temperature performance of titanium alloy.

[0004] The present invention is specifically implemented according to the technical solutions described below.

[0005] A process for improving the ultra-low temperature performance of titanium alloy, characterized by comprising the following operations.

[0006] S10: Forging the titanium alloy ingot obtained by casting to obtain a titanium alloy bar with a uniform equiaxed beta grain structure.

[0007] S20: Repeat the operation S until the titanium alloy bar is rolled to a preset size to obtain the target titanium alloy material.

[0008] Operation S is: connecting a pulse current to heat the titanium alloy bar to a preset temperature, keeping the pulse current connected to roll the titanium alloy bar, and after the rolling process is completed, disconnecting the pulse current and air cooling the titanium alloy bar.

[0009] A further solution is: before performing the next operation S each time, the titanium alloy bar is rotated 90°.

[0010] The number of times that operation S is repeatedly performed in step S20 is 8 times.

[0011] In step S20 , as the number of times the operation S is performed increases, the magnitude of the pulse current turned on in the operation S gradually decreases.

[0012] The pulse current turned on in operation S is a sharp pulse current with a frequency of 0.1 and a duty cycle of 0.1.

[0013] In operation S, the titanium alloy bar is heated to the deformation temperature by a pulse current (specifically, ), and preheat the upper and lower rolls to 300℃ at the same time.

[0014] During the rolling process in operation S, the gap size between the upper and lower rolls was 1.0 mm, the roll speed was 1.2 rad / sec, and graphite lubrication was used.

[0015] In operation S, the titanium alloy bar is air-cooled for 30 seconds, and the temperature drop is not higher than 100° C. Preferably, the bar is air-cooled to room temperature.

[0016] When operation S is performed for the first time in step S20, the pulse current connected is 700A, when operation S is performed for the second time, the pulse current connected is 650A, when operation S is performed for the third time, the pulse current connected is 615A, when operation S is performed for the fourth time, the pulse current connected is 580A, when operation S is performed for the fifth time, the pulse current connected is 550A, when operation S is performed for the sixth time, the pulse current connected is 530A, when operation S is performed for the seventh time, the pulse current connected is 500A, and when operation S is performed for the eighth time, the pulse current connected is 480A.

[0017] Step S10 includes the following operations: S11: Smelting high-purity grade 0 titanium sponge with uniform particle size three times in a vacuum consumable arc furnace to obtain a cylindrical titanium alloy ingot.

[0018] S12: The titanium alloy ingot is heated with the furnace to And keep warm T 1 After the heat preservation is completed, the titanium alloy ingot is quickly transferred to the press, and the upper and lower molds are flame-heated to 300°C. The titanium alloy ingot is upset to 40% of the original height, and the pressing rate is controlled to be 5-10 mm / s. Then, it is turned 90° and stretched to the original height of the titanium alloy ingot, and air-cooled to room temperature. The titanium alloy ingot is heated to 40% of the original height with the furnace again. And keep warm T 2 Minutes, after the insulation is over, the titanium alloy ingot is quickly transferred to the press, and the upper and lower molds are flame heated to 300°C, the titanium alloy ingot is upset to 40% of the original height, the pressing rate is controlled to be 5-10 mm / s, then turned 90° and stretched to the original height of the titanium alloy ingot, and air-cooled to room temperature.

[0019] S13: The titanium alloy ingot is heated with the furnace to , and keep warm T 3After the heat preservation is completed, the titanium alloy ingot is quickly transferred to the press, and the upper and lower molds are flame-heated to 300°C. The titanium alloy ingot is upset to 50% of the original height, and the pressing rate is controlled to be 5-10 mm / s. Then, it is turned 90° and stretched to twice the original height of the titanium alloy ingot, and air-cooled to room temperature. The titanium alloy bar is heated to 400°C with the furnace again. , and keep warm T 4 Minutes, after the insulation is over, the titanium alloy ingot is quickly transferred to the press, and the upper and lower molds are flame heated to 300 ° C, the titanium alloy ingot is upset to 50% of the original height, the pressing rate is controlled to 5-10 mm / s, and then turned 90° to draw a titanium alloy bar with a diameter of 40 mm, and air-cooled to room temperature.

[0020] S14: performing solid solution treatment on the titanium alloy bar, keeping the bar heat-resistant for 50 minutes after the solid solution treatment, and then taking the bar heat-resistant out of the furnace and air cooling it to room temperature after the end of the heat-resistant period. It is the approximate temperature of alpha→beta transformation in titanium alloy.

[0021] T 1 =k 1 D 1 , T 2 =k 1 D 2 , k 1 =0.8, D 1 , D 2 They are the current diameters of titanium alloy ingots respectively.

[0022] T 3 =k 2 D 3 , T 4 =k 2 D 3 , k 2 =0.6, D 3 , D 4 They are the current diameters of titanium alloy bars respectively.

[0023] In the above-mentioned scheme provided by the present invention, the pulse current has a local Joule heating effect, and in the continuous hole rolling process, the material is simultaneously subjected to the effects of bidirectional extrusion + axial stretching, so that the hard phase alpha grains can be broken, and the soft phase beta can be elongated to present fiberization, and under the action of the local Joule heat of the pulse current, the grains are more easily broken and elongated to present fiberization, thereby preparing a titanium alloy rod with an ultrafine fibrous crystal heterogeneous structure. This ultrafine fibrous crystal heterogeneous structure can inhibit the initiation and propagation of cracks in a low-temperature environment, thereby improving the low-temperature toughness of the titanium alloy, preventing the occurrence of brittleness, and improving the safety and service life of fasteners prepared from the titanium alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the principle of the present invention.

[0025] Figure 2 It is a schematic diagram of the process of the present invention.

[0026] Figure 3 This is the microstructure diagram of the material prepared in Example 1.

[0027] Figure 4 This is a diagram of the low-temperature mechanical properties of the material prepared in Example 1.

[0028] Figure 5 This is the microstructure diagram of the material prepared in Example 2.

[0029] Figure 6 This is a diagram of the low-temperature mechanical properties of the material prepared in Example 2.

[0030] Figure 7 This is the microstructure diagram of the material prepared in Example 3.

[0031] Figure 8 This is a diagram of the low-temperature mechanical properties of the material prepared in Example 3. DETAILED DESCRIPTION

[0032] In order to make the purpose and advantages of the present invention more clearly understood, the present invention is specifically described below in conjunction with embodiments. It should be understood that the following text is only used to describe one or several specific embodiments of the present invention, and does not strictly limit the scope of protection of the specific claims of the present invention.

[0033] As used herein, the terms "parallel," "perpendicular," and the like are not limited to their strict geometric definitions, but include tolerances for reasonable and inconsistent machining or human errors.

[0034] The present invention provides a process for improving the ultra-low temperature performance of titanium alloy, such as Figure 1 , 2 As shown, the specific operations include the following.

[0035] High-purity grade 0 titanium sponge with uniform particle size is melted three times in a vacuum consumable arc furnace to obtain a titanium alloy cylindrical ingot with a diameter of 200 mm.

[0036] The titanium alloy ingot is cast Two-time upsetting deformation is carried out within a certain range to mechanically break up the coarse as-cast grains so as to achieve sufficient crushing of the as-cast structure and elimination of as-cast defects. Represents the near temperature of alpha→beta transformation in titanium alloy. Specifically, the ingot is first heated to Keep warm 1 Minutes, T 1 =k1 D 1 , k 1 is the insulation coefficient, the value is 0.8, D 1 is the current diameter of the titanium alloy ingot, in millimeters. After the insulation is completed, the titanium alloy ingot is quickly transferred (within 1 minute) to the press, and the upper and lower molds are flame-heated to 300°C to reduce the heat exchange of the titanium alloy ingot. The titanium alloy ingot is upset to 40% of the original height, and the pressing rate is controlled in the range of 5-10mm / s, then turned 90° and stretched to the original ingot height, and air-cooled to room temperature. The titanium alloy ingot is heated again with the furnace to Keep warm 2 Minutes, T 2 =k 1 D 2 , D 2 is the current diameter of the titanium alloy ingot, in millimeters. After the insulation is completed, the ingot is quickly transferred (within 1 minute) to the press, and the upper and lower molds are flame-heated to 300°C to reduce the heat exchange of the titanium alloy ingot. The titanium alloy ingot is upset to 40% of the original height, and the pressing rate is controlled in the range of 5-10mm / s. Then, it is turned 90° and stretched to the original ingot height, and air-cooled to room temperature.

[0037] The titanium alloy forged cylindrical rod obtained above is heated to , two times of upsetting and drawing deformation were carried out, and finally a rod with a diameter of 40 mm was obtained, and an alpha+beta dual-state structure of equiaxed structure was obtained. Specifically, the titanium alloy rod was first heated to , and keep warm T 3 Minutes, T 3 =k 2 D 3 , k 2 is the insulation coefficient, the value is 0.6, D 3 is the current diameter of the titanium alloy ingot, in millimeters. After the insulation is completed, the ingot is quickly transferred (within 1 minute) to the press, and the upper and lower molds are flame-heated to 300°C to reduce the heat exchange of the titanium alloy ingot. The titanium alloy ingot is upset to 50% of the original height, and the pressing rate is controlled in the range of 5-10mm / s, then turned 90° and stretched to twice the original ingot height, and air-cooled to room temperature. The titanium alloy bar is heated again with the furnace to , and keep warm T 4 Minutes, T 4 =k 2 D 4 , D 4is the current diameter of the titanium alloy ingot, in millimeters. After the insulation is completed, the ingot is quickly transferred (within 1 minute) to the press, and the upper and lower molds are flame-heated to 300°C to reduce the heat exchange of the titanium alloy ingot. The titanium alloy ingot is upset to 50% of the original height, and the pressing rate is controlled in the range of 5 to 10 mm / s. Then, it is turned 90° and stretched to a rod with a diameter of 40 mm, and then air-cooled to room temperature.

[0038] The above-mentioned 40 mm diameter titanium alloy bar The purpose of the solution treatment is to fully dissolve the alloy elements and obtain a uniform equiaxed beta grain structure.

[0039] The titanium alloy bar is subjected to a pulse current assisted pass rolling process, and bars of different diameters are obtained according to the rolling passes. Before rolling begins, the titanium alloy bar is heated to a preset deformation temperature by a pulse current, and the continuous pass rolling equipment is started. The bar is gradually brought into the rolling hole under the action of friction to achieve rolling deformation. In the rolling process, the titanium alloy bar is always supplied with a pulse current to ensure that the bar is deformed isothermally. After each rolling pass, the bar is rotated 90° axially, and the pulse current is turned off at the same time, so that the bar is air-cooled and fine alpha phase grains are precipitated. Then the next rolling deformation is carried out, and the pulse current is supplied again, and so on until the deformation is completed. By selecting appropriate pulse current density, rolling passes, rolling rate and lubrication conditions, the preparation of ultrafine fibrous crystal heterogeneous structure of titanium alloy bars can be achieved to improve the low-temperature mechanical properties of titanium alloy bars. Through the electroplastic effect and local Joule heating effect of pulse current assisted deformation, the electroplastic effect can effectively reduce the phase transition temperature of the material, and the local Joule heating effect can cause uneven deformation at the grain scale, further promoting the fragmentation of the alpha phase and the fiberization of the beta phase.

[0040] The pulse current assisted continuous groove rolling method provided by the present invention has the following advantages: by means of the electroplastic effect, the deformation temperature is lower than At 150-200℃, the material is subjected to complex stress states, and is subjected to radial stress and axial tensile stress at the same time. Moreover, after the orthogonal decomposition of radial stress, the effects of "double pressure" and "shear" can be generated. Under the action of "double pressure", the hard and brittle alpha phase is prone to mechanical crushing. In particular, the "targeting" effect causes the temperature of the alpha grain boundary region to be higher than the temperature inside the grain, making the deformation inside the grain and the grain boundary more uneven. In addition, the "shearing and cutting" effect will accelerate the crushing of the alpha phase. After crushing, the alpha will be further refined and equiaxed through continuous dynamic recrystallization as the cumulative deformation increases. The soft phase beta structure is elongated and fiberized under the "raw pulling and hard pulling" of the axial tensile stress. At the same time, the "targeting" effect causes the temperature of the phase boundary region to rise and promotes grain rotation and atomic diffusion, which will further accelerate fiberization. The prepared titanium alloy bar with ultrafine fiber crystal heterogeneous structure has excellent ultra-low temperature performance and has broad application prospects.

[0041] The present invention is described in detail below with reference to specific embodiments.

[0042] Example 1. Preparation of Ti55531 ultrafine fiber crystal heterogeneous structure rod The chemical composition of Ti55531 titanium alloy is (mass fraction): aluminum 5.3%, molybdenum 5.2%, vanadium 5.2%, chromium 2.65%, zirconium 1.02%, and the rest is titanium. The phase transition temperature T of Ti55531 β =850℃. The initial diameter of the bar blank is 40 mm. The bar blank is first processed according to operations S11 to S14, and then the bar blank is processed by pulse current assisted groove rolling process according to operation S20. The specific operation steps are as follows: S11: high-purity grade 0 titanium sponge with uniform particle size is melted three times in a vacuum consumable arc furnace to obtain a Ti55531 ingot with an initial diameter of 150 mm and a height of 200 mm; S12: The Ti55531 ingot is heated to 1050°C with the furnace and kept warm for 120 minutes. After the end of the insulation, it is upset to 40% of the original height, with a pressing rate of 5-10 mm / s, turned 90° and pulled to the original 200 mm; the titanium alloy ingot is heated to 1000°C with the furnace again and kept warm for 120 minutes, and the upsetting and pulling are repeated to the original 200 mm; before upsetting, the upper and lower dies are preheated to 300°C; S13: The Ti55531 ingot is heated to 820°C in the furnace and kept warm for 90 minutes. After the end of the insulation, it is upset to 50% of the original height, with a pressing rate of 5-10 mm / s, turned 90° and pulled to a height of 400 mm and a diameter of 106 mm; the titanium alloy ingot is heated to 800°C in the furnace again and kept warm for 64 minutes, and the upsetting is repeated to a diameter of 40 mm and a height of 2815 mm; before upsetting, the upper and lower dies are preheated to 300°C; S14: The Ti55531 bar with a diameter of 40 mm is subjected to solution treatment at 950°C for 50 minutes, and then taken out of the furnace and air-cooled to room temperature after the end of the insulation; S20: The Ti55531 bar with a diameter of 40 mm was moved to the groove rolling equipment, and the power was turned on for 8 passes of rolling. The current value and equipment parameters of each pass are shown in Table 1.

[0043] Table 1 Pulse current assisted pass rolling process parameters of Example 1 The titanium alloy material prepared above was tested and the microstructure was observed using a field emission scanning electron microscope (model: JSM 7200F). The results are as follows: Figure 3 . Figure 3 The microstructure of the obtained material is shown in Figure 1. The black one is the matrix beta structure, and the white ultrafine grains are elongated along the rolling direction to become fiber structures. The low-temperature tensile testing machine (model: MTSE45.305) and the low-temperature pendulum impact testing machine (model: JB-S500) were used to test the low-temperature tensile strength, elongation and impact toughness. Figure 4 Low temperature mechanical properties of the obtained material. Figure 3 It shows that the microstructure of the prepared material consists of ultrafine alpha grains and elongated fibrous beta phases. Due to this special heterogeneous structure, the low-temperature mechanical properties of this microstructure rod are significantly better than those of conventional equiaxed structures.

[0044] Example 2: Preparation of Ti6554 ultrafine fiber crystal heterogeneous structure rod The chemical composition of Ti6554 titanium alloy is (mass fraction): chromium 5.7%, molybdenum 4.7%, vanadium 4.8%, aluminum 3.9%, iron 0.08%, silicon 0.028%, carbon 0.025%, and the rest is titanium. The phase transition temperature T of Ti6554 β =820℃. The initial diameter of the bar blank is 40 mm. The bar blank is first processed according to operations S11 to S14, and then the bar blank is processed by pulse current assisted groove rolling process according to operation S20. The specific operation steps are as follows: S11: high-purity grade 0 titanium sponge with uniform particle size is melted three times in a vacuum consumable arc furnace to obtain a Ti6554 ingot with an initial diameter of 150 mm and a height of 200 mm; S12: The Ti6554 ingot is heated to 1050°C with the furnace and kept warm for 120 minutes. After the end of the insulation, it is upset to 40% of the original height, with a pressing rate of 5-10 mm / s, turned 90° and pulled to the original 200 mm; the titanium alloy ingot is heated to 970°C with the furnace again and kept warm for 120 minutes, and the upsetting and pulling are repeated to the original 200 mm; before upsetting, the upper and lower dies are preheated to 300°C; S13: The Ti6554 ingot is heated to 790°C in the furnace and kept warm for 90 minutes. After the end of the warming, it is upset to 50% of the original height, with a pressing rate of 5-10 mm / s, turned 90° and pulled to a height of 400 mm and a diameter of 106 mm; the titanium alloy ingot is heated to 770°C in the furnace again and kept warm for 64 minutes, and the upsetting is repeated to a diameter of 40 mm and a height of 2815 mm; before upsetting, the upper and lower dies are preheated to 300°C; S14: The Ti6554 bar with a diameter of 40 mm is subjected to solution treatment at 920°C for 50 minutes, and then taken out of the furnace and air-cooled to room temperature after the end of the insulation; S20: The Ti6554 bar with a diameter of 40 mm was moved to the groove rolling equipment, and the power was turned on for 8 passes of rolling. The current value and equipment parameters of each pass are shown in Table 2.

[0045] Ti6554 ultrafine fiber crystal heterogeneous structure rods were obtained.

[0046] Table 2 Pulse current assisted pass rolling process parameters of Example 2 The titanium alloy material prepared above was tested and the microstructure was observed using a field emission scanning electron microscope (model: JSM 7200F). The results are as follows: Figure 5 shown. Figure 5 The microstructure of the obtained material is shown in Figure 1. The black one is the matrix beta structure, and the white ultrafine grains are elongated along the rolling direction to become fiber structures. The low-temperature tensile testing machine (model: MTSE45.305) and the low-temperature pendulum impact testing machine (model: JB-S500) were used to test the low-temperature tensile strength, elongation and impact toughness. Figure 6 Low temperature mechanical properties of the obtained material. Figure 6 It shows that the microstructure of the prepared material consists of ultrafine alpha grains and elongated fibrous beta phases. Due to this special heterogeneous structure, the low-temperature mechanical properties of this microstructure rod are significantly better than those of conventional equiaxed structures.

[0047] Example 3: Preparation of TC18 ultrafine fiber crystal heterogeneous structure rod The chemical composition of TC18 titanium alloy is (% mass fraction): aluminum 5.5%, molybdenum 4.7%, vanadium 4.6%, chromium 1.0%, iron 1.0%, nitrogen 0.05%, hydrogen 0.015%, oxygen 0.02%, and the rest is titanium. The phase transition temperature of TC18 is T β =860℃. The initial diameter of the bar stock is 40mm. The bar stock is first processed according to operations S11 to S14, and then the bar stock is subjected to pulse current assisted pass rolling process according to operation S20. The specific operation steps are as follows: S11: high-purity grade 0 titanium sponge with uniform particle size is melted three times in a vacuum consumable arc furnace to obtain a TC18 ingot with an initial diameter of 150 mm and a height of 200 mm; S12: The TC18 ingot is heated to 1060°C with the furnace and kept warm for 120 minutes. After the end of the insulation, it is upset to 40% of the original height, with a pressing rate of 5-10 mm / s, turned 90° and pulled to the original 200 mm; the titanium alloy ingot is heated to 1010°C with the furnace again and kept warm for 120 minutes, and the upsetting and pulling are repeated to the original 200 mm; before upsetting, the upper and lower dies are preheated to 300°C; S13: The TC18 ingot is heated to 830°C in the furnace and kept warm for 90 minutes. After the end of the warming, it is upset to 50% of the original height, with a pressing rate of 5-10 mm / s, turned 90° and pulled to a height of 400 mm and a diameter of 106 mm; the titanium alloy ingot is heated to 810°C in the furnace again and kept warm for 64 minutes, and the upsetting is repeated to a diameter of 40 mm and a height of 2815 mm; before upsetting, the upper and lower dies are preheated to 300°C; S14: The TC18 bar with a diameter of 40 mm is subjected to solution treatment at 960°C for 50 minutes, and then taken out of the furnace and air-cooled to room temperature after the end of the insulation; S20: The TC18 bar with a diameter of 40 mm is moved to the groove rolling equipment, and the power is turned on to perform 8 passes of rolling. The current value and equipment parameters of each pass are shown in Table 3.

[0048] Table 3 Pulse current assisted pass rolling process parameters of Example 3 The titanium alloy material prepared above was tested and the microstructure was observed using a field emission scanning electron microscope (model: JSM 7200F). The results are as follows: Figure 7 shown. Figure 7 The microstructure of the obtained material is shown in Figure 1. The black one is the matrix beta structure, and the white ultrafine grains are elongated along the rolling direction to become fiber structures. The low-temperature tensile testing machine (model: MTSE45.305) and the low-temperature pendulum impact testing machine (model: JB-S500) were used to test the low-temperature tensile strength, elongation and impact toughness. Figure 8 Low temperature mechanical properties of the obtained material. Figure 7 It shows that the microstructure of the prepared material consists of ultrafine alpha grains and elongated fibrous beta phases. Due to this special heterogeneous structure, the low-temperature mechanical properties of this microstructure rod are significantly better than those of conventional equiaxed structures.

[0049] The above is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications should also be considered as the protection scope of the present invention. The structures, devices and operating methods not specifically described and explained in the present invention shall be implemented according to the conventional means in the art unless otherwise specified and limited.

Claims

1. A process for improving the ultra-low temperature performance of titanium alloy, characterized in that: The following operations are included: S10: forging the titanium alloy ingot obtained by casting to obtain a titanium alloy bar with a uniform equiaxed beta grain structure; S20: Repeat the operation S until the titanium alloy bar is rolled to a preset size to obtain a target titanium alloy material; Operation S is: connecting a pulse current to heat the titanium alloy bar to a preset temperature, keeping the pulse current connected to roll the titanium alloy bar, and after the rolling process is completed, disconnecting the pulse current and air cooling the titanium alloy bar.

2. The process for improving the ultra-low temperature performance of titanium alloy according to claim 1, characterized in that: Before performing the next operation S each time, the titanium alloy bar is rotated 90°.

3. The process for improving the ultra-low temperature performance of titanium alloy according to claim 2, characterized in that: The number of times that operation S is repeatedly performed in step S20 is 8 times.

4. The process for improving the ultra-low temperature performance of titanium alloy according to claim 1, 2 or 3, characterized in that: In step S20 , as the number of times the operation S is performed increases, the magnitude of the pulse current turned on in the operation S gradually decreases.

5. The process for improving the ultra-low temperature performance of titanium alloy according to claim 4, characterized in that: The pulse current turned on in operation S is a sharp pulse current with a frequency of 0.1 and a duty cycle of 0.

1.

6. The process for improving the ultra-low temperature performance of titanium alloy according to claim 4, characterized in that: In operation S, the titanium alloy bar is connected to a pulse current and heated to the deformation temperature, and the upper and lower rolls are preheated to 300°C.

7. The process for improving the ultra-low temperature performance of titanium alloy according to claim 4, characterized in that: During the rolling process in operation S, the gap size between the upper and lower rolls was 1.0 mm, the roll speed was 1.2 rad / sec, and graphite lubrication was used.

8. The process for improving the ultra-low temperature performance of titanium alloy according to claim 4, characterized in that: In operation S, the air cooling time of the titanium alloy bar is 30 seconds, and the temperature drop is not higher than 100°C.

9. The process for improving the ultra-low temperature performance of titanium alloy according to claim 4, characterized in that: When operation S is performed for the first time in step S20, the pulse current connected is 700A, when operation S is performed for the second time, the pulse current connected is 650A, when operation S is performed for the third time, the pulse current connected is 615A, when operation S is performed for the fourth time, the pulse current connected is 580A, when operation S is performed for the fifth time, the pulse current connected is 550A, when operation S is performed for the sixth time, the pulse current connected is 530A, when operation S is performed for the seventh time, the pulse current connected is 500A, and when operation S is performed for the eighth time, the pulse current connected is 480A.

10. The process for improving the ultra-low temperature performance of titanium alloy according to claim 1, characterized in that: Step S10 includes the following operations: S11: melting high-purity grade 0 titanium sponge with uniform particle size three times in a vacuum consumable arc furnace to obtain a cylindrical titanium alloy ingot; S12: The titanium alloy ingot is heated with the furnace to And keep warm for T1 minute. After the end of the insulation, the titanium alloy ingot is quickly transferred to the press, and the upper and lower molds are flame-heated to 300℃, the titanium alloy ingot is upset to 40% of the original height, the pressing rate is controlled to be 5-10 mm / s, and then it is turned 90° and stretched to the original height of the titanium alloy ingot, and air-cooled to room temperature; the titanium alloy ingot is heated to 40% with the furnace again. And keep warm for T2 minutes. After the end of the heat preservation, the titanium alloy ingot is quickly transferred to the press, and the upper and lower molds are flame-heated to 300°C, the titanium alloy ingot is upset to 40% of the original height, the pressing rate is controlled to be 5-10 mm / s, and then turned 90° to stretch to the original height of the titanium alloy ingot, and air-cooled to room temperature; S13: The titanium alloy ingot is heated with the furnace to , and keep warm for T3 minutes. After the insulation is completed, the titanium alloy ingot is quickly transferred to the press, and the upper and lower molds are flame-heated to 300°C. The titanium alloy ingot is upset to 50% of the original height, and the pressing rate is controlled to be 5-10 mm / s. Then, it is turned 90° and stretched to twice the original height of the titanium alloy ingot, and air-cooled to room temperature; the titanium alloy bar is heated with the furnace again to , and keep warm for T4 minutes. After the end of the heat preservation, the titanium alloy ingot is quickly transferred to the press, and the upper and lower molds are flame-heated to 300°C, the titanium alloy ingot is upset to 50% of the original height, the pressing rate is controlled to be 5-10 mm / s, and then turned 90° to draw a titanium alloy bar with a diameter of 40 mm, and air-cooled to room temperature; S14: performing a solution treatment on the titanium alloy bar, keeping the bar heat-resistant for 50 minutes after the solution treatment, and then taking the bar heat-resistant out of the furnace and air-cooling it to room temperature after the end of the heat-resistant period; is the temperature near the alpha→beta transition in titanium alloy; T1=k1D1, T2=k1D2, k1=0.8, D1 and D2 are the current diameters of the titanium alloy ingot respectively; T3=k2D3, T4=k2D3, k2=0.6, D3 and D4 are the current diameters of the titanium alloy bar.

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