Method for improving mechanical properties of titanium alloy sheet and product

Abstract

The application discloses a method for improving mechanical properties of titanium alloy plate and a product, and belongs to the field of titanium alloy forging technology, and comprises the following steps: heating a titanium alloy ingot, adopting upsetting and drawing breakdown, then adopting a length-drawing mode to perform single-phase rapid small deformation forging, using air cooling after each length-drawing forging, finally performing unidirectional rolling and annealing treatment to obtain the titanium alloy plate. The application obtains specific organization through the beta-phase rapid small deformation forging and air cooling in the whole process, and improves the fracture toughness and mechanical properties of the Ti80 plate. The normal mechanical properties of the plate meet the requirements, and the transverse and rolling direction properties are obviously better than those of the plate prepared by a traditional process. Moreover, the preparation method is simple, and is convenient for popularization and application.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy forging technology, and particularly relates to a method and product for improving the mechanical properties of titanium alloy plates. Background Technology

[0002] Ti80 titanium alloy (Ti-6Al-3Nb-2Zr-1Mo) is a near-alpha type titanium alloy with high strength, toughness, high pressure resistance, and corrosion resistance. This alloy is suitable for many fields, including deep-sea equipment, shipbuilding, marine engineering, military protection, and aerospace, and is particularly suitable for critical structural components in extreme environments. Ti80 titanium alloy performs exceptionally well in marine protection scenarios, resisting seawater corrosion and withstanding high hydrostatic pressure, while also possessing excellent comprehensive mechanical properties to meet long-term service requirements under complex conditions. Compared to traditional materials, Ti80 significantly improves safety and reliability while reducing structural weight.

[0003] Currently, more stringent requirements have been placed on the fracture toughness and impact resistance of Ti80 titanium alloy materials. Especially under extreme load conditions, instantaneous impact may cause severe plastic deformation or even fracture failure of the material, directly affecting the structural integrity and safety performance of equipment, posing a major challenge to engineering applications.

[0004] In existing technologies, Ti80 titanium alloy plates produced in actual production often exhibit significant differences in fracture toughness, impact resistance, and other mechanical properties between different manufacturers of the same model. Ti80 plates prepared using traditional materials research approaches show good isotropy and excellent mechanical properties, but their fracture toughness and impact resistance are significantly lacking.

[0005] Therefore, how to provide a method for preparing Ti80 titanium alloy plates that can significantly improve the fracture toughness and impact resistance of the plates while ensuring excellent mechanical properties and meeting standards is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a method and product for improving the mechanical properties of titanium alloy sheets.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for improving the mechanical properties of titanium alloy sheets includes the following steps:

[0009] The titanium alloy ingot is heated and then uptaken to form a blank. It is then forged by drawing in a single phase region with rapid small deformation. After each drawing and forging, it is cooled by air cooling. Finally, it is rolled in one direction and annealed to obtain titanium alloy sheet.

[0010] Beneficial effects: This invention uses a rapid, small-deformation elongation forging method in the β-phase region to flatten the β grains and simultaneously cause the crystal orientation distribution of the material to exhibit a directional arrangement, resulting in a layered microstructure (a microstructure with significant directional morphology and crystal orientation). The titanium alloy sheet prepared through the above steps has a thickness-to-single-layer thickness ratio between 1200:5 and 1200:10, which can effectively improve the fracture toughness of the material. Compared with traditional preparation methods, the titanium alloy sheet provided by this invention can better resist the severe plastic deformation or even fracture failure caused by instantaneously applied impact loads when subjected to impact loads, significantly enhancing the survivability and impact resistance of the products used.

[0011] Furthermore, this invention employs air cooling throughout the entire process to cool the material, avoiding the problems of rapid cooling leading to martensite formation and reduced material plasticity, and slow cooling resulting in coarse lamellar structures and poor mechanical properties. Air cooling results in a finer lamellar structure in the material after forging in the single-phase region, and a denser, uniformly distributed distribution of equielic α-grains in the material after forging in the two-phase region, thus improving the material's mechanical properties.

[0012] Preferably, the titanium alloy is Ti80, wherein the metallic elements include the following components by mass fraction: Al 5.5%~6.5%, Nb 2.5%~3.5%, Zr 1.5%~2.5%, Mo 0.5%~1.5%, with the balance being Ti and unavoidable impurities.

[0013] More preferably, the titanium alloy is obtained by mixing Ti, Al, Nb, Zr and Mo powders in a mass ratio of 88:6:3:2:1.

[0014] More preferably, the thickness of the titanium alloy ingot is 800~850mm.

[0015] Preferably, the titanium alloy ingot is prepared by four vacuum arc remelting processes, wherein the specific parameters for the four vacuum arc remelting processes are as follows:

[0016] The current for the first vacuum self-consumable melting is 4kA~8kA, the vacuum degree is ≤5Pa, and the melting voltage is 25V~35V;

[0017] The current for the second vacuum self-consumption melting is 8kA~12kA, the vacuum degree is ≤1Pa, and the melting voltage is 25V~35V;

[0018] The current for the third vacuum self-consumption melting is 12kA~16kA, the vacuum degree is ≤0.8Pa, and the melting voltage is 25V~35V;

[0019] The current for the fourth vacuum self-consumption melting is 16kA~25kA, the vacuum degree is ≤0.6Pa, and the melting voltage is 25V~35V.

[0020] Beneficial effects: Four vacuum self-consuming arc melting processes improve the density and uniformity of the ingot structure, reduce the content of inclusions, eliminate defects, and improve the purity and toughness of the material.

[0021] Preferably, the upsetting and drawing temperature is 150-220°C above the phase transformation point of the titanium alloy, the final forging temperature is ≥980°C, and the total deformation is 50% of the thickness of the titanium alloy ingot.

[0022] More preferably, the upsetting and drawing temperature is 1200℃ and the time is 8-10h.

[0023] More preferably, the thickness of the titanium alloy sheet after upsetting and drawing is 400~425mm.

[0024] More preferably, the upsetting and drawing of the billet is followed by air cooling.

[0025] Beneficial effects: Under the above conditions, the billet-opening process can eliminate defects such as pores in the billet, while promoting the refinement and homogenization of the microstructure. Furthermore, rapid cooling easily generates martensitic microstructure, reducing material plasticity, while slow cooling easily forms coarse lamellar microstructure, affecting the material's mechanical properties. Therefore, this invention employs air cooling after upsetting and drawing to obtain a fine lamellar microstructure.

[0026] Preferably, the temperature for rapid small deformation forging in the single-phase region is 100-180°C above the phase transformation point of the titanium alloy, and the final forging temperature is ≥980°C.

[0027] More preferably, the temperature for the single-phase region rapid small deformation forging is 1120℃, and the time is 4-6h.

[0028] Preferably, the single-phase region rapid small deformation forging is performed twice, and the single reduction amount does not exceed 25%, the single feed time does not exceed 5s, and the total deformation does not exceed 25% of the plate thickness obtained in the previous step.

[0029] More preferably, the single feed amount is 210~230mm, and the feed rate is required to be about 3s / time.

[0030] More preferably, in the single-phase region rapid small deformation forging, the thickness of the titanium alloy plate obtained after the first drawing is 300~320mm, and the thickness of the titanium alloy plate obtained after the second drawing is 225~240mm.

[0031] Beneficial effects: The elongation forging method in this invention can suppress the recrystallization process of the material, promote the flattening of β grains, and obtain a layered structure. Furthermore, the air cooling method after forging can also obtain a finer layered lamellar structure.

[0032] Preferably, the number of unidirectional rolling cycles is 2-6, and the total deformation in a single rolling cycle is 40-45% of the thickness before deformation.

[0033] Beneficial effects: The present invention employs a texture-controlled forging method, which flattens the β grains. The flattened β structure is transformed into a layered α structure according to the Burgers orientation relationship.

[0034] Preferably, the bite rate of the unidirectional rolling is 0.8~1.2m / s, and the feed rate is 3~4m / s.

[0035] More preferably, the temperature of the unidirectional rolling is 20~50°C below the phase transformation point, and the end temperature of each rolling pass is ≥850°C.

[0036] More preferably, the thickness of the slab after the first unidirectional rolling is 120~140mm; the thickness of the plate after the second unidirectional rolling is 60~80mm; the thickness of the plate after the third unidirectional rolling is 30~45mm; the thickness of the plate after the fourth unidirectional rolling is 15~25mm; the thickness of the plate after the fifth unidirectional rolling is 8~15mm; and the thickness of the plate after the sixth unidirectional rolling is 4~8mm.

[0037] More preferably, air cooling is used after each rolling, and the plate needs to be cut after every two rolling passes to avoid the plate being too long and failing to be rolled unidirectionally at the appropriate temperature in time.

[0038] Beneficial effects: By applying a certain amount of deformation within a suitable temperature range, this invention can significantly improve the number and uniformity of nuclei while promoting α-grain spheroidization. Furthermore, air cooling is used after rolling to control the growth rate of α-grains, promote microstructure uniformity, and ensure the mechanical properties of the sheet.

[0039] Preferably, the annealing treatment is performed at a temperature of 850-900℃ for 2-6 hours.

[0040] More preferably, the plate is heated for 4 to 6 hours for plate that has been rolled twice, for 3 to 4 hours for plate that has been rolled three to four times, and for 2 to 3 hours for plate that has been rolled five to six times.

[0041] Beneficial effects: Different sheet thicknesses require different times to reach the desired core temperature, thus necessitating varying heating durations. Excessive heating time is equivalent to aging treatment, leading to precipitates within the sheet structure and decreased toughness. Higher rolling rates tend to result in higher dislocation densities in the sheet; annealing helps eliminate residual stress and reduce dislocation density.

[0042] A titanium alloy sheet prepared by the method described above, wherein the ratio of the thickness of the titanium alloy sheet to the thickness of a single layer of the layered structure is between 1200:5 and 1200:10.

[0043] Beneficial effects: At this ratio, the layered structure can "disperse" the transmission of stress in the impact direction, thus creating a certain degree of resistance to stress transmission.

[0044] Compared with the prior art, the present invention has the following advantages and technical effects:

[0045] This invention utilizes rapid, small-deformation elongation forging in the β-phase region to flatten the β-grains and align their orientation, resulting in a layered microstructure. The ratio of plate thickness to the thickness of a single layer in the layered microstructure is approximately 1200:5 to 1200:10, which improves fracture toughness and enhances product durability and impact resistance. Simultaneously, this invention employs air cooling throughout the process, avoiding the formation of martensite during rapid cooling and coarse lamellar structures during slow cooling. This results in a finer lamellar structure after forging in the single-phase region and a dense, uniformly distributed, equielic α-grain structure after forging in the two-phase region, thus improving mechanical properties. Furthermore, while the normal mechanical properties of the Ti80 plate prepared by this invention are weaker than those in the transverse and rolling directions, they still meet industry requirements. Moreover, the mechanical properties in the transverse and rolling directions are significantly higher than those of plates prepared using traditional processes, exhibiting excellent impact resistance and making it suitable for applications in marine vessel protection. In addition, the method provided by this invention is simple and easy to promote and apply. Attached Figure Description

[0046] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0047] Figure 1 The image shown is a scanning electron microscope (SEM) image of the Ti80 substrate obtained in Example 1.

[0048] Figure 2 The image shown is an EBSD image of the Ti80 substrate obtained in Example 1.

[0049] Figure 3 This is a scanning electron microscope (SEM) image of the Ti80 substrate obtained in Example 2;

[0050] Figure 4 The image shown is an EBSD image of the Ti80 substrate obtained in Example 2.

[0051] Figure 5 The image shows a scanning electron microscope (SEM) image of the Ti80 substrate obtained in Comparative Example 1.

[0052] Figure 6 The image shown is an EBSD image of the Ti80 substrate obtained in Comparative Example 1.

[0053] Figure 7 The image shows a scanning electron microscope (SEM) image of the Ti80 substrate obtained in Comparative Example 2.

[0054] Figure 8 The image shows the EBSD image of the Ti80 substrate obtained in Comparative Example 2.

[0055] Figure 9 The image shows a scanning electron microscope (SEM) image of the Ti80 substrate obtained in Comparative Example 3.

[0056] Figure 10 The image shown is an EBSD image of the Ti80 substrate obtained in Comparative Example 3. Detailed Implementation

[0057] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0058] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0059] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels;

[0060] In this embodiment of the invention, the raw materials for the Ti80 ingot are weighed only according to the ratio of Ti:Al:Nb:Zr:Mo = 88:6:3:2:1. In practice, it is difficult to perfectly achieve this ratio for doping. The actual mass fraction of the raw materials fluctuates within the following range: Al 5.5%~6.5%, Nb 2.5%~3.5%, Zr 1.5%~2.5%, Mo 0.5%~1.5%, with the balance being Ti and unavoidable impurities.

[0061] Unless otherwise specified, room temperature or normal temperature in the embodiments of the present invention refers to 25±3℃.

[0062] Example 1

[0063] A method for preparing a 60mm thick Ti80 substrate includes the following steps:

[0064] (1) Material feeding and electric arc melting

[0065] Ti, Al, Nb, Zr, and Mo powders were weighed in a ratio of 88:6:3:2:1 and mixed evenly. The uniform Ti-6Al-3Nb-2Zr-1Mo powder was fabricated into an electrode block by four vacuum arc remelting (VAR) processes. Four VAR processes were then performed to ensure the uniformity of the Ti80 ingot structure, resulting in a Ti-6Al-3Nb-2Zr-1Mo ingot (Ti80 ingot) with a thickness of 800 mm.

[0066] In the four vacuum arc remelting (VAR) processes, the current for the first VAR process was 4 kA, with a vacuum level of less than or equal to 5 Pa; the current for the second VAR process was 8 kA, with a vacuum level of less than or equal to 1 Pa; the current for the third VAR process was 12 kA, with a vacuum level of less than or equal to 0.8 Pa; and the current for the fourth VAR process was 16 kA, with a vacuum level of less than or equal to 0.6 Pa. The melting voltage was 25 V during all four VAR processes.

[0067] (2) Blanking

[0068] The Ti80 ingot obtained in step (1) was placed in an electric heating furnace. After the furnace temperature stabilized at 1200℃, it was heated for 8 hours. Then, the ingot was forged in one firing by upsetting. During this process, the final forging temperature was greater than or equal to 980℃, and the total deformation was 50% of the ingot thickness. After forging, the ingot was cooled by air cooling, and the material was trimmed and the surface was ground to finally obtain a Ti80 slab with a thickness of 400mm in one firing state.

[0069] (3) Single-phase zone one fire

[0070] The Ti80 slab obtained in step (2) is placed in an electric heating furnace. After the furnace temperature stabilizes at 1150℃, it is heated for 6 hours. Then, the Ti80 slab is rapidly forged with small deformation by drawing. During this process, the final forging temperature should be greater than or equal to 980℃, the single feed amount is 280mm, the feed rate is required to draw 3s / time, and the total deformation of the single-phase zone forging is 25% of the thickness of the Ti80 slab in the first-fire forging. After forging, it is cooled by air cooling, and the material is trimmed and the surface is ground to obtain a Ti80 slab with a thickness of 300mm in the first-fire forging state.

[0071] (4) Single-phase zone two-fire

[0072] The Ti80 slab obtained in step (3) is placed in an electric heating furnace. After the furnace temperature stabilizes at 1120℃, it is heated for 4 hours. The slab is then rapidly forged with small deformation by drawing. During this process, the final forging temperature is greater than or equal to 980℃, the single feed is 210mm, and the feed rate is required to draw about 3s / time. The total deformation of the single-phase region forging is 25% of the thickness of the Ti80 slab. After forging, it is cooled by air cooling, and the material is trimmed and the surface is ground. Finally, a Ti80 slab with a thickness of 225mm is obtained.

[0073] (5) Rolling in one fire

[0074] The two-fire forged Ti80 slab obtained in step (4) is placed in an electric heating furnace. After the furnace temperature stabilizes at 950℃, it is heated for 4 hours. Then, the slab is rolled unidirectionally. The end temperature of each unidirectional rolling is greater than 850℃, the bite rate is 0.8m / s, and the feed rate is 3m / s. After the first rolling is completed, it is cooled by air cooling. The material is trimmed and the surface is ground to obtain a Ti80 slab with a thickness of 120mm after one unidirectional rolling.

[0075] (6) Rolling Second Fire

[0076] Repeat step (5), after the second rolling is completed, use air cooling, and trim and grind the material to obtain a Ti80 slab with a thickness of 60mm after the second rolling in one direction.

[0077] (7) Annealing

[0078] The Ti80 slab, rolled unidirectionally in two passes, was placed in a heating furnace and annealed at 850°C for 4 hours. After annealing, it was air-cooled to obtain the Ti80 sheet. The ratio of the thickness of the obtained titanium alloy sheet to the thickness of a single layer of the layered structure was 1200:10.

[0079] Example 2

[0080] A method for preparing a 7mm thick Ti80 substrate includes the following steps:

[0081] (1) Material feeding and electric arc melting

[0082] Ti, Al, Nb, Zr, and Mo powders were weighed in a ratio of 88:6:3:2:1 and mixed evenly. The uniform Ti-6Al-3Nb-2Zr-1Mo powder was fabricated into an electrode block by four vacuum arc remelting (VAR) processes. Four VAR processes were then performed to ensure the uniformity of the Ti80 ingot structure, resulting in a Ti-6Al-3Nb-2Zr-1Mo ingot (Ti80 ingot) with a thickness of 850 mm.

[0083] In the four vacuum arc remelting (VAR) processes, the current for the first VAR process was 8 kA, with a vacuum level of ≤5 Pa; the current for the second VAR process was 12 kA, with a vacuum level of ≤1 Pa; the current for the third VAR process was 16 kA, with a vacuum level of ≤0.8 Pa; and the current for the fourth VAR process was 25 kA, with a vacuum level of ≤0.6 Pa. The melting voltage was 25 V during all four VAR processes.

[0084] (2) Blanking

[0085] The Ti80 ingot obtained in step (1) was placed in an electric heating furnace. After the furnace temperature stabilized at 1200℃, it was heated for 10 hours. Then, the ingot was forged in one firing by upsetting. During this process, the final forging temperature was greater than or equal to 980℃, and the total deformation was 50% of the ingot thickness. After forging, the ingot was cooled by air cooling, and the material was trimmed and the surface was ground. Finally, a Ti80 slab with a thickness of 425mm was obtained in the one-fired forging state.

[0086] (3) Single-phase zone one fire

[0087] The Ti80 slab obtained in step (2) is placed in an electric heating furnace. After the furnace temperature stabilizes at 1150℃, it is heated for 8 hours. Then, the Ti80 slab is rapidly forged with small deformation by drawing. During this process, the final forging temperature should be greater than or equal to 980℃, the single feed amount is 300mm, the feed rate is required to draw 3s / time, and the total deformation of the single-phase zone forging is 25% of the thickness of the Ti80 slab in the first-fire forging. After forging, it is cooled by air cooling, and the material is trimmed and the surface is ground to obtain a Ti80 slab with a thickness of 319mm in the first-fire forging state.

[0088] (4) Single-phase zone two-fire

[0089] The Ti80 slab obtained in step (3) was placed in an electric heating furnace. After the furnace temperature stabilized at 1120℃, it was heated for 6 hours. The slab was then rapidly forged with small deformation by drawing. During this process, the final forging temperature was greater than or equal to 980℃, the single feed amount was 210mm, and the feed rate required to draw about 3s / time. The total deformation of the single-phase region forging was 25% of the thickness of the Ti80 slab. After forging, it was cooled by air cooling, and the material was trimmed and the surface was ground. Finally, a Ti80 slab with a thickness of 239mm was obtained.

[0090] (5) Rolling in one fire

[0091] The two-fire forged Ti80 slab obtained in step (4) is placed in an electric heating furnace. After the furnace temperature stabilizes at 950℃, it is heated for 6 hours. Then, the slab is rolled unidirectionally. The end temperature of each unidirectional rolling is greater than 850℃, the bite rate is 0.8m / s, and the feed rate is 3m / s. After the first rolling is completed, it is cooled by air cooling. The material is trimmed and the surface is ground to obtain a Ti80 slab with a thickness of 135mm after one unidirectional rolling.

[0092] (6) Rolling Second Fire

[0093] Repeat step (5), after the second rolling is completed, use air cooling, and trim and grind the material to obtain a Ti80 slab with a thickness of 75mm after the second rolling in one direction.

[0094] (7) Rolling three times

[0095] Repeat step (6), after the three-fire rolling is completed, use air cooling, and trim and grind the material to obtain a Ti80 slab with a thickness of 40mm after three-fire unidirectional rolling.

[0096] (8) Rolling four times

[0097] Repeat step (7), after the fourth rolling is completed, use air cooling, and trim and grind the material to obtain a Ti80 slab with a thickness of 20mm after four unidirectional rolling.

[0098] (9) Rolling five fires

[0099] Repeat step (8), after the five-fire rolling is completed, use air cooling, and trim and grind the material to obtain a Ti80 slab with a thickness of 12mm after five-fire unidirectional rolling.

[0100] (10) Rolling six fires

[0101] Repeat step (9), after the sixth rolling is completed, use air cooling, and trim and grind the material to obtain a Ti80 slab with a thickness of 7mm after six unidirectional rolling.

[0102] (11) Annealing

[0103] The Ti80 slab, rolled unidirectionally in six passes, was placed in a heating furnace and annealed at 900℃ for 3 hours. After annealing, it was air-cooled to obtain the Ti80 sheet. The ratio of the thickness of the obtained titanium alloy sheet to the thickness of a single layer of the layered structure was 1200:5.

[0104] Comparative Example 1

[0105] Unlike Example 1, steps (3) and (4) do not include rapid small-deformation forging of the slab using a drawing method; instead, they are ordinary forging processes. The remaining steps are the same as in Example 1. Specifically, the following steps are included:

[0106] Steps (1) and (2) are the same as in Example 1;

[0107] (3) Single-phase zone one fire

[0108] The Ti80 slab obtained in step (2) was placed in an electric heating furnace. After the furnace temperature stabilized at 1150℃, it was heated for 6 hours. Then, the Ti80 slab was subjected to large deformation forging by drawing. The total deformation of the single-phase region forging was 45% of the thickness of the Ti80 slab in the first-fire forging. During this process, the final forging temperature was greater than or equal to 980℃. After forging, it was cooled by air cooling. The material was trimmed and the surface was ground to obtain a Ti80 slab with a thickness of 225mm in the first-fire forging state.

[0109] (4) Single-phase zone two-fire

[0110] The Ti80 slab obtained in step (3) was placed in an electric heating furnace. After the furnace temperature stabilized at 1120℃, it was heated for 4 hours. The slab was then subjected to large deformation forging by drawing. The total deformation of the single-phase region forging was 45% of the thickness of the Ti80 slab in the first-fire forging. During this process, the final forging temperature was greater than or equal to 980℃. After forging, the slab was cooled by air cooling and the material was trimmed and the surface was ground. Finally, a Ti80 slab with a thickness of 160mm was obtained.

[0111] (5) Rolling in one fire

[0112] The two-fire forged Ti80 slab obtained in step (4) is placed in an electric heating furnace. After the furnace temperature stabilizes at 950℃, it is heated for 6 hours. Then, the slab is rolled unidirectionally. The end temperature of each unidirectional rolling is greater than 850℃, the bite rate is 0.8m / s, and the feed rate is 3m / s. After the first rolling is completed, it is cooled by air cooling. The material is trimmed and the surface is ground to obtain a Ti80 slab with a thickness of 100mm after one unidirectional rolling.

[0113] (6) Rolling Second Fire

[0114] Repeat step (5), after the second rolling is completed, use air cooling, and trim and grind the material to obtain a Ti80 slab with a thickness of 60mm after the second rolling in one direction.

[0115] Steps (5)-(6) are similar to those in Example 1, and a Ti80 slab with a thickness of 60 mm is finally obtained. The resulting titanium alloy slab has a uniform microstructure.

[0116] It should be noted that, due to the large deformation forging, the thickness of the plate in Comparative Example 1 cannot be exactly the same as that in Example 1. Therefore, the thickness of the plate rolled in the subsequent process will also be reduced accordingly. However, the overall processing technology is the same as that in Example 1, that is, the deformation amount, deformation rate and deformation temperature of the plate in a single rolling are the same.

[0117] Comparative Example 2

[0118] Unlike Example 1, in steps (3) and (4), air cooling is used after rapid small deformation forging; the remaining steps are the same as in Example 1. Specifically, the steps include:

[0119] (3) Single-phase zone one fire

[0120] The Ti80 slab obtained in step (2) is placed in an electric heating furnace. After the furnace temperature stabilizes at 1150℃, it is heated for 6 hours. Then, the Ti80 slab is rapidly forged with small deformation by drawing. During this process, the final forging temperature should be greater than or equal to 980℃, the single feed amount is 280mm, the feed rate is required to draw 3s / time, and the total deformation of the single-phase zone forging is 25% of the thickness of the Ti80 slab in the first-fire forging. After forging, it is cooled by air cooling, and the material is trimmed and the surface is ground to obtain a Ti80 slab with a thickness of 300mm in the first-fire forging state.

[0121] (4) Single-phase zone two-fire

[0122] The Ti80 slab obtained in step (3) is placed in an electric heating furnace. After the furnace temperature stabilizes at 1120℃, it is heated for 4 hours. The slab is then rapidly forged with small deformation by drawing. During this process, the final forging temperature is greater than or equal to 980℃, the single feed is 210mm, and the feed rate is required to draw about 3s / time. The total deformation of the single-phase region forging is 25% of the thickness of the Ti80 slab. After forging, it is cooled by air cooling, and the material is trimmed and the surface is ground. Finally, a Ti80 slab with a thickness of 225mm is obtained.

[0123] Steps (5)-(7) are the same as in Example 1, and a Ti80 slab with a thickness of 60 mm is finally obtained. The microstructure of the obtained titanium alloy sheet shows local layered characteristics, but most areas are still uniform in microstructure.

[0124] Comparative Example 3

[0125] Unlike Example 1, the bite rate of the rolling process in steps (5) and (6) is 0.5 m / s, the feed rate is 2 m / s, and the annealing heating time in step (7) is 1.5 h. The remaining steps are the same as in Example 1. Specifically, it includes the following steps:

[0126] Steps (1)-(4) are the same as in Example 1;

[0127] (5) Rolling in one fire

[0128] The Ti80 slab obtained in step (4) was placed in an electric heating furnace. After the furnace temperature stabilized at 950℃, it was heated for 4 hours. Then, the slab was rolled unidirectionally. The temperature at the end of each unidirectional rolling was greater than 850℃, the bite rate was 0.5m / s, and the feed rate was 2m / s. After the first rolling was completed, it was cooled by air cooling. The material was trimmed and the surface was ground to obtain a Ti80 slab with a thickness of 120mm after one unidirectional rolling.

[0129] (6) Rolling Second Fire

[0130] Repeat step (5), after the second rolling is completed, use air cooling, and trim and grind the material to obtain a Ti80 slab with a thickness of 60mm after the second rolling in one direction.

[0131] (7) Annealing

[0132] The Ti80 slab, which has been rolled in two unidirectional directions, is placed in a heating furnace and annealed at 850°C for 1.5 hours. After annealing, it is cooled by air to obtain Ti80 sheet.

[0133] Technical effects:

[0134] 1. Performance Characterization

[0135] The SEM and EBSD images of the Ti80 slabs obtained in Examples 1-2 and Comparative Examples 1-3 are as follows: Figure 1-10 As shown, the Ti80 plate obtained in the embodiments of the present invention exhibits obvious layered banded structure characteristics. The ratio of the plate thickness to the single-layer thickness of the layered structure is between 1200:5 and 1200:10. The plate obtained by large deformation in the β single-phase region has a uniform structure. The plate obtained by air cooling in each process step shows the characteristics of local layered banded structure, but most areas still have a uniform structure. The plate obtained by not increasing the rolling rate in the two-phase region (i.e., the bite rate is 0.5m / s and the feed rate is 2m / s) has sufficient dynamic recovery, larger grains, and smaller residual stress, so the annealing time is reduced accordingly.

[0136] 2. Mechanical properties

[0137] The mechanical properties of the Ti80 slabs obtained in Examples 1-2 and Comparative Examples 1-3 in the normal (ND), transverse (TD), and rolling direction (RD) directions were tested according to GB / T228.1-2021 standard. Impact toughness was also tested using a drop hammer test, specifically an NI300C instrumented Charpy impact testing machine (this equipment can simultaneously acquire load-displacement curves, facilitating energy distribution calculation). The results are shown in Table 1.

[0138] Table 1

[0139]

[0140] As shown in Table 1, compared to the transverse (TD) and rolling direction (RD), the Ti80 slab obtained in the embodiments of the present invention has weaker mechanical properties in the normal (ND) direction, but it meets the industry's requirements for the mechanical properties of materials. Moreover, the mechanical properties in the transverse and rolling directions are significantly higher than those of Ti80 plates prepared by traditional processes. At the same time, the Ti80 slab obtained in the embodiments of the present invention exhibits excellent impact toughness in the directions required by actual working conditions.

[0141] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for improving the mechanical properties of titanium alloy sheets, characterized in that, Includes the following steps: The titanium alloy ingot is heated and then uptaken to form a blank. Then, it is forged by drawing and stretching in a single-phase region with rapid small deformation. After each drawing and forging, it is cooled by air cooling. Finally, it is rolled and annealed to obtain titanium alloy sheet. The upsetting and drawing temperature is 150-220℃ above the phase transformation point of the titanium alloy, the final forging temperature is ≥980℃, and the total deformation is 50% of the thickness of the titanium alloy ingot. The temperature for rapid small deformation forging in the single-phase region is 100-180℃ above the phase transformation point of titanium alloy, and the final forging temperature is ≥980℃. The single-phase region rapid small deformation forging is performed twice, with each reduction not exceeding 25%, each feed time not exceeding 5 seconds, and the total deformation not exceeding 25% of the plate thickness obtained in the previous step. The number of unidirectional rolling processes is 2-6, and the total deformation in a single rolling process is 40-45% of the thickness before deformation. The bite rate of the unidirectional rolling is 0.8~1.2m / s, and the feed rate is 3~4m / s; The titanium alloy is Ti80.

2. The method for improving the mechanical properties of titanium alloy plates according to claim 1, characterized in that, The titanium alloy ingot was prepared by four vacuum consumable arc melting processes, the specific parameters of which are as follows: The current for the first vacuum self-consumable melting is 4kA~8kA, the vacuum degree is ≤5Pa, and the melting voltage is 25V~35V; The current for the second vacuum self-consumption melting is 8kA~12kA, the vacuum degree is ≤1Pa, and the melting voltage is 25V~35V; The current for the third vacuum self-consumption melting is 12kA~16kA, the vacuum degree is ≤0.8Pa, and the melting voltage is 25V~35V; The current for the fourth vacuum self-consumption melting is 16kA~25kA, the vacuum degree is ≤0.6Pa, and the melting voltage is 25V~35V.

3. The method for improving the mechanical properties of titanium alloy plates according to claim 1, characterized in that, The annealing process is carried out at a temperature of 850-900℃ for 2-6 hours.

4. The titanium alloy sheet prepared by the method according to any one of claims 1-3, characterized in that, The ratio of the thickness of the titanium alloy sheet to the thickness of a single layer of the layered structure is between 1200:5 and 1200:10.

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