Titanium alloy sheet and titanium alloy coil, and method for manufacturing titanium alloy sheet and method for manufacturing titanium alloy coil

Abstract

The titanium alloy sheet contains prescribed chemical components, an area ratio of α phase is 80% or more, an area ratio of α phase having a circular equivalent diameter of 1 μm or more is more than 53%, in a (0001) pole figure based on a sheet thickness direction, an angle formed by a direction of a peak indicating a degree of aggregation calculated by texture analysis using a spherical harmonics method of an electron backscattering diffraction method at a spread coefficient of 16 and a Gaussian half-height width of 5° and the sheet thickness direction is 65° or less, and an average sheet thickness is 2.5 mm or less.

Description

Technical Field

[0001] This disclosure relates to a titanium alloy plate and a titanium alloy coil, as well as a method for manufacturing the titanium alloy plate and the titanium alloy coil. Background Technology

[0002] Titanium is a lightweight, high-strength, and highly corrosion-resistant material, making it suitable for the aircraft industry from the perspectives of weight reduction and improved fuel efficiency. Therefore, the development of titanium alloys that meet the specific properties required for various structural components of aircraft is gaining momentum.

[0003] For example, Patent Document 1 discloses an α+β type titanium alloy wire containing 1.4% or more and less than 2.1% Fe, 4.4% or more and less than 5.5% Al, the balance being titanium and impurities.

[0004] Patent document 2 discloses an α+β type titanium alloy rod containing 0.5% or more and less than 1.4% Fe, 4.4% or more and less than 5.5% Al, the balance being titanium and impurities.

[0005] Patent document 3 discloses a method for manufacturing a Ti-6Al-4V alloy thin plate based on lamination rolling. The method involves covering one or more plate-shaped core materials with spacer materials and cover materials to form a lamination plate, and rolling the lamination plate to reduce the thickness of the core material. The method is characterized in that the thickness of the cover material is set such that the ratio of the core material to the lamination plate is at least 0.25 with respect to the initial plate thickness of each material.

[0006] Patent document 4 discloses a method for manufacturing a Ti-6Al-4V alloy thin plate based on stacked rolling. The method involves covering one or more plate-shaped core materials with spacer materials and covering materials to form a composite material, and rolling the composite material to reduce the thickness of the core material to form a thin plate. The method is characterized in that, for rolling where the reduction ratio of the plate thickness before and after the reduction of the composite material is 3 or more, the rolling rate of each pass is set to 15% or more.

[0007] Patent document 5 discloses a method for manufacturing a titanium alloy sheet, characterized in that a hot-rolled annealed sheet of titanium alloy is cold-rolled in the same direction as the hot rolling direction with a total rolling ratio of 67% or more, and then annealed at a temperature between 650 and 900°C. The titanium alloy contains, by weight %: Al: 2.5-3.5%, V: 2.0-3.0%, balance Ti and common impurities.

[0008] Patent document 6 discloses a method for manufacturing α+β type titanium alloy thin sheet, characterized in that, in the manufacturing process of α+β type titanium alloy cold-rolled sheet, an intermediate annealing is performed after cold rolling under the following conditions: annealing temperature: above and below the β phase transformation point (-25°C); annealing time: 0.5 to 4 hours; cooling rate after heating and holding: 0.5 to 5°C / second; and cooling temperature range at the above cooling rate: up to below 300°C.

[0009] Patent document 7 discloses an α+β type titanium alloy sheet, characterized in that the α+β type titanium alloy sheet contains: at least one fully solid-solution type β stabilizing element in the amount of 2.0 to 4.5% by mass of Mo equivalent, at least one eutectoid type β stabilizing element in the amount of 0.3 to 2.0% by mass of Fe equivalent, at least one type α stabilizing element in the amount of more than 3.0% by mass and less than 5.5% by mass of Al equivalent, with the balance being Ti and unavoidable impurities, wherein the average particle size of the α phase is less than 5.0 μm and the maximum particle size of the α phase is less than 10.0 μm, the average aspect ratio of the α phase is less than 2.0 and the maximum aspect ratio of the α phase is less than 5.0.

[0010] Patent document 8 discloses an α+β type titanium alloy plate with excellent cold rolling properties and cold working performance. The α+β type titanium alloy plate is characterized by being an α+β type hot-rolled titanium alloy plate. (a) The normal direction (thickness direction) of the hot-rolled plate is set as ND, the hot rolling direction is set as RD, the width direction of the hot-rolled plate is set as TD, the normal direction of the (0001) plane of the α phase is set as the c-axis orientation, the angle between the c-axis orientation and ND is set as θ, and the plane containing the c-axis orientation and ND is connected to the plane containing N... The angle between the surfaces of D and TD is Φ. (b1) The strongest intensity of the relative intensity of X-ray (0002) reflection caused by grains with θ greater than 0 degrees and less than 30 degrees and Φ falling within the entire circumference (-180 degrees to 180 degrees) is XND. (b2) The strongest intensity of the relative intensity of X-ray (0002) reflection caused by grains with θ greater than 80 degrees and less than 100 degrees and Φ falling within ±10 degrees is XTD. (c) XTD / XND is 5.0 or greater.

[0011] Patent document 9 discloses a high-strength α+β type titanium alloy plate with excellent cold-working properties in coils (strips). The plate is characterized by containing, by mass%, Fe: 0.8–1.5%, Al: 4.8–5.5%, and N: less than 0.030%, and containing O and N such that, when the O content (mass%) is set to [O] and the N content (mass%) is set to [N], Q(%) = 0.14–0.38 as defined by Q(%) = [O] + 2.77·[N]. The balance contains Ti and unavoidable impurities. (a) The normal direction of the hot-rolled plate is set to ND, the hot-rolling direction is set to RD, and the width of the hot-rolled plate is... The direction is set as TD, the normal direction of the (0001) plane of the α phase is set as the c-axis azimuth, the angle between the c-axis azimuth and ND is set as θ, the angle between the plane containing the c-axis azimuth and the ND direction and the plane containing ND and TD is set as φ, (b1) the strongest intensity of the relative intensity of X-ray (0002) reflection caused by grains with θ above 0 degrees and below 30 degrees and φ falling within the full circumference (-180 degrees to 180 degrees) is set as XND, (b2) the strongest intensity of the relative intensity of X-ray (0002) reflection caused by grains with θ above 80 degrees and below 100 degrees and φ falling within ±10 degrees is set as XTD, (c) XTD / XND is 4.0 or above.

[0012] Patent document 10 discloses a method for manufacturing α+β type titanium alloy thin sheet, characterized in that after cold rolling of α+β type titanium alloy thin sheet manufactured by rolling or forging with a reduction rate of more than 20%, it is annealed at a temperature of more than 700°C and below the β phase transformation point, thereby obtaining a sheet with fine equiaxed α structure.

[0013] Non-patent document 1 discloses an α+β titanium alloy sheet that exhibits anisotropy in strength in the rolling direction and in the direction perpendicular to the rolling direction.

[0014] Non-patent document 2 discloses an α+β titanium alloy sheet that is hot-rolled at a temperature higher than the β phase transformation point to reduce the anisotropy of strength in the rolling direction and in the direction perpendicular to the rolling direction.

[0015] Existing technical documents

[0016] Patent documents

[0017] Patent Document 1: Japanese Patent Application Publication No. 7-62474

[0018] Patent Document 2: Japanese Patent Application Publication No. 7-70676

[0019] Patent Document 3: Japanese Patent Application Publication No. 2001-300603

[0020] Patent Document 4: Japanese Patent Application Publication No. 2001-300604

[0021] Patent Document 5: Japanese Patent Application Publication No. 61-147864

[0022] Patent Document 6: Japanese Patent Application Publication No. 1-127653

[0023] Patent Document 7: Japanese Patent Application Publication No. 2013-227618

[0024] Patent Document 8: International Publication No. 2012 / 115242

[0025] Patent Document 9: International Publication No. 2012 / 115243

[0026] Patent Document 10: Japanese Patent Application Publication No. 62-33750

[0027] Non-patent literature

[0028] Non-patent literature 1: KOBE STEEL ENGINEERING REPORTS / Vol.59, No.1 (2009), pp.81-84

[0029] Non-patent literature 2: KOBE STEEL ENGINEERING REPORTS / Vol.60, No.2 (2010), pp.50-54 Summary of the Invention

[0030] The problem the invention aims to solve

[0031] Furthermore, titanium used in aircraft structural components requiring higher strength contains a significant amount of Al. However, due to the high deformation resistance during hot or cold rolling, the allowable load of the rolling mill is sometimes exceeded when manufacturing thin sheets. Therefore, it is difficult to manufacture high-strength titanium alloy sheets using conventional hot or cold rolling methods.

[0032] This disclosure was made in view of the above-mentioned problems, and the purpose of this disclosure is to provide a high-strength titanium alloy plate and titanium alloy coil, as well as a method for manufacturing the titanium alloy plate and the titanium alloy coil.

[0033] Solution for solving the problem

[0034] The inventors have discovered that titanium alloy sheets, by containing a specified amount of Al and having a texture in which the peaks of grain aggregation in the (0001) pole figure based on the thickness direction exist within a specified angle relative to the width direction of the final rolled material, exhibit high strength and excellent processability. Furthermore, a method for manufacturing titanium alloy sheets by cold rolling that simultaneously achieves such chemical composition and texture has been discovered, thus completing this disclosure.

[0035] Based on the above understanding, the main contents of this disclosure are as follows.

[0036] (1) One aspect of this disclosure relates to a titanium alloy plate containing, by mass percent: Al: greater than 4.0% and less than 6.6%, Fe: greater than 0% and less than 2.3%, V: greater than 0% and less than 4.5%, Si: greater than 0% and less than 0.60%, C: greater than 0% and less than 0.080%, N: greater than 0% and less than 0.050%, O: greater than 0% and less than 0.40%, Ni: greater than 0% and less than 0.15%, Cr: greater than 0% and less than 0.25%, and Mn: greater than 0% and less than 0%. Less than 0.25%, with the balance being Ti and impurities. The area ratio of the α phase in the titanium alloy plate is greater than 80%, and the area ratio of the α phase with a circular equivalent diameter of 1 μm or more is greater than 53%. In the (0001) pole figure based on the plate thickness direction, the angle between the direction of the peak representing the aggregation degree calculated by texture analysis using the spherical harmonic function method for the inverse pole figure of electron backscatter diffraction with an expansion coefficient of 16 and a Gaussian half-width of 5° and the plate thickness direction is less than 65°. The average plate thickness of the titanium alloy plate is less than 2.5 mm.

[0037] (2) The titanium alloy plate described in (1) above has a microstructure consisting of an equiaxed structure with an aspect ratio of 3.0 or less and a banded structure with an aspect ratio greater than 3.0 and extending in the length direction. The average grain diameter of the equiaxed structure is 0.1 μm or more and 20.0 μm or less, and the area ratio of the banded structure relative to the area of ​​the microstructure can be 10.0% or less.

[0038] (3) The titanium alloy plate described in (1) or (2) above contains, by mass %, either Fe: 0.5% or more and 2.3% or less, or V: 2.5% or more and 4.5% or less.

[0039] (4) The titanium alloy plate of any one of (1) to (3) above contains, by mass percent, one or more of one of the following: Ni: less than 0.15%, Cr: less than 0.25% and Mn: less than 0.25% in place of a portion of the Fe or V.

[0040] (5) The titanium alloy plate of any one of (1) to (4) above, wherein the smaller of the 0.2% yield strength in the length direction at 25°C or the 0.2% yield strength in the width direction at 25°C may be 700 MPa or more and 1200 MPa or less.

[0041] (6) The titanium alloy plate according to any one of (1) to (5) above, wherein, in the (0001) pole figure based on the plate thickness direction, the angle between the direction of the peak representing the degree of aggregation calculated by texture analysis using the spherical harmonic function method for the inverse pole figure of electron backscatter diffraction with an expansion coefficient of 16 and a Gaussian half-width of 5° and the width direction is 10° or less, and the ratio of the 0.2% yield strength in the width direction to the 0.2% yield strength in the length direction can be 1.05 or more and 1.18 or less.

[0042] (7) The titanium alloy plate according to any one of (1) to (5) above, wherein, in the (0001) pole figure based on the plate thickness direction, the angle between the direction of the peak representing the degree of aggregation calculated by texture analysis using the spherical harmonic function method for the inverse pole figure of electron backscatter diffraction with an expansion coefficient of 16 and a Gaussian half-width of 5° and the plate thickness direction is 35° or less, and the ratio of the 0.2% yield strength in the width direction to the 0.2% yield strength in the length direction can be 0.85 or more and 1.10 or less.

[0043] (8) The titanium alloy plate of any one of (1) to (7) above, wherein the dimensional accuracy of the plate thickness is less than 5.0% relative to the average plate thickness.

[0044] (9) Another aspect of this disclosure relates to a titanium alloy coil containing, by weight percent: Al: greater than 4.0% and less than 6.6%, Fe: greater than 0% and less than 2.3%, V: greater than 0% and less than 4.5%, Si: greater than 0% and less than 0.60%, C: greater than 0% and less than 0.080%, N: greater than 0% and less than 0.050%, O: greater than 0% and less than 0.40%, Ni: greater than 0% and less than 0.15%, Cr: greater than 0% and less than 0.25%, and Mn: greater than 0% and less than 0%. Less than 0.25%, with the balance being Ti and impurities. The area ratio of the α phase of the titanium alloy coil is greater than 80%, and the area ratio of the α phase with a circular equivalent diameter of 1 μm or more is greater than 53%. In the (0001) pole figure based on the plate thickness direction, the angle between the direction of the peak representing the degree of aggregation and the plate thickness direction is less than 65°, calculated by texture analysis using the spherical harmonic function method of electron backscatter diffraction with an expansion coefficient of 16 and a Gaussian half-width of 5°. The average plate thickness of the titanium alloy coil is less than 2.5 mm.

[0045] (10) Another aspect of this disclosure relates to a method for manufacturing a titanium alloy plate, which is a method for manufacturing a titanium alloy plate according to any one of (1) to (8) above, comprising the following steps: a cold rolling step, wherein the titanium billet is subjected to one or more cold rolling passes in the length direction, wherein the titanium billet contains, by mass %: Al: greater than 4.0% and less than 6.6%, Fe: more than 0% and less than 2.3%, V: more than 0% and less than 4.5%, Si: more than 0% and less than 0.60%, C: more than 0% and less than 4.5%, Si: more than 0% and less than 0.60%, and C: more than 0% and less than 4.60%. The composition is less than 0.080%, N: 0% or more and less than 0.050%, O: 0% or more and less than 0.40%, Ni: 0% or more and less than 0.15%, Cr: 0% or more and less than 0.25%, and Mn: 0% or more and less than 0.25%, with the balance being Ti and impurities; and a final annealing process, in which the titanium billet after the last cold rolling pass is annealed, wherein the average rolling rate of each cold rolling pass in the cold rolling process is greater than 30%, and the total rolling rate is greater than 60%.

[0046] (11) The method for manufacturing the titanium alloy plate described in (10) above, wherein, when performing multiple cold rolling passes, an intermediate annealing process for annealing the titanium billet is included between the multiple cold rolling passes, and the annealing conditions for the intermediate annealing process and the final annealing process are as follows: the annealing temperature is 600°C or higher and (T β The annealing temperature is below -50℃, and the annealing temperature T (℃) and the holding time t (seconds) at the annealing temperature satisfy the following formula (1).

[0047] 22000≤(T+273.15)×(Log 10 (t)+20)≤27000…Equation (1)

[0048] In the formula, T β The β phase transition point (°C).

[0049] (12) Another aspect of this disclosure relates to a method for manufacturing a titanium alloy plate, which is the method for manufacturing a titanium alloy plate according to any one of (1) to (8) above, comprising the following steps: a cold cross-rolling step, wherein cold rolling passes are performed in the length and width directions of a titanium billet, wherein the titanium billet contains, by mass %: Al: greater than 4.0% and less than 6.6%, Fe: more than 0% and less than 2.3%, V: more than 0% and less than 4.5%, Si: more than 0% and less than 0.60%, C: more than 0% and less than 0.080%, N: 0%. The content of the titanium billet after the cold cross-rolling process is as follows: ≥0.050% and ≤0.050%, O: ≥0% and ≤0.40%, Ni: ≥0% and ≤0.15%, Cr: ≥0% and ≤0.25%, and Mn: ≥0% and ≤0.25%, with the balance being Ti and impurities; and a final annealing process, wherein the titanium billet after the cold cross-rolling process is annealed, wherein the total rolling rate in the cold cross-rolling process is ≥60%, and the ratio of the rolling rate in the length direction to the rolling rate in the width direction, i.e., the cross-rolling ratio, is ≥0.05 and ≤20.00.

[0050] (13) In the manufacturing method of the titanium alloy plate described in (12) above, when the cold rolling process or the cold cross-rolling process performs multiple cold rolling passes, an intermediate annealing process for annealing the titanium billet is included between the multiple cold rolling passes. The annealing conditions for the intermediate annealing process and the final annealing process are as follows: the annealing temperature is above 600°C and (T β The annealing temperature is below -50℃, and the annealing temperature T (℃) and the holding time t (seconds) at the annealing temperature satisfy the following formula (1).

[0051] 22000≤(T+273.15)×(Log 10 (t)+20)≤27000…Equation (1)

[0052] In the formula, T β The β phase transition point (°C).

[0053] (14) Another aspect of this disclosure relates to a method for manufacturing titanium alloy coils, which is the method for manufacturing titanium alloy coils described in (9) above, comprising the following steps: a cold rolling step, wherein the titanium billet is subjected to one or more cold rolling passes along its length, wherein the titanium billet contains, by mass %: Al: greater than 4.0% and less than 6.6%, Fe: greater than 0% and less than 2.3%, V: greater than 0% and less than 4.5%, Si: greater than 0% and less than 0.60%, and C: greater than 0% and less than 0%. The composition is as follows: 0.080%, N: 0% or more and 0.050% or less, O: 0% or more and 0.40% or less, Ni: 0% or more and less than 0.15%, Cr: 0% or more and less than 0.25%, and Mn: 0% or more and less than 0.25%, with the balance being Ti and impurities; and a final annealing process, wherein the titanium billet after the last cold rolling pass is annealed, wherein the average rolling rate of each cold rolling pass in the cold rolling process is greater than 30%, and the total rolling rate is greater than 60%.

[0054] The effects of the invention

[0055] As described above, according to this disclosure, it is possible to provide a titanium alloy plate and a titanium alloy coil with high strength, as well as a method for manufacturing the titanium alloy plate and the titanium alloy coil. Attached Figure Description

[0056] Figure 1 This is an example of a (0001) pole figure of a titanium alloy plate based on the thickness direction (ND) according to one embodiment of this disclosure.

[0057] Figure 2 This is a diagram used to illustrate the angle between the direction of the peak representing the degree of aggregation and the width direction.

[0058] Figure 3 This is an example of an optical microscope photograph of the titanium alloy plate involved in this embodiment.

[0059] Figure 4 An optical microscope photograph showing an example of a band-like tissue.

[0060] Figure 5 This is a schematic diagram illustrating the method for determining the average plate thickness. Detailed Implementation

[0061] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. It should be noted that the description will proceed in the following order.

[0062] 1. Titanium alloy plate

[0063] 2. Manufacturing method of titanium alloy plate

[0064] <1. Titanium Alloy Plate>

[0065] First, refer to Figures 1-5 The titanium alloy plate involved in this embodiment will be described. Figure 1 This is an example of a (0001) pole figure of the titanium alloy plate involved in this embodiment based on the thickness direction (ND). Figure 2 This is a diagram used to illustrate the angle between the direction of the peak representing the degree of aggregation and the width direction. Figure 2 The (0001) pole figure based on the thickness direction (ND) and Figure 1 same. Figure 3 This is a diagram illustrating an example of an optical microscope photograph of the titanium alloy plate involved in this embodiment. Figure 4 An optical microscope photograph showing an example of a band-like tissue. Figure 5 This is a schematic diagram illustrating the method for measuring the average plate thickness. It should be noted that, as will be explained in detail later, the titanium alloy plate involved in this embodiment can be manufactured using a method including a cold rolling process.

[0066] (1.1. Chemical Composition)

[0067] First, the chemical composition of the titanium alloy plate of this embodiment will be described. The titanium alloy plate involved in this embodiment contains, by mass%, Al: greater than 4.0% and less than 6.6%, Fe: 0% and less than 2.3%, V: 0% and less than 4.5%, Si: 0% and less than 0.60%, C: 0% and less than 0.080%, N: 0% and less than 0.050%, O: 0% and less than 0.40%, Ni: 0% and less than 0.15%, Cr: 0% and less than 0.25%, and Mn: 0% and less than 0.25%, with the balance being Ti and impurities. It should be noted that, unless otherwise specified, "%" in the following description of the chemical composition refers to "mass %".

[0068] Al is an α-phase stabilizing element and has high solid solution strengthening ability. Increasing the Al content increases the tensile strength at room temperature. High tensile strength can be obtained if the Al content is greater than 4.0%. Furthermore, the hot-rolled sheet before cold rolling can maintain high cold-rollability. The Al content is preferably 4.5% or more, more preferably 4.6% or more. On the other hand, when the Al content is greater than 6.6%, the cold-rollability of the hot-rolled sheet before cold rolling is significantly reduced, and regions of excessive Al dissolution due to solidification segregation, etc., are locally formed, resulting in Al regularization. Through these Al-regulated regions, the impact toughness of the titanium alloy sheet decreases. Therefore, the Al content is 6.6% or less, preferably 6.5% or less, more preferably 6.4% or less.

[0069] Fe is a β-phase stabilizing element. Fe has high solid solution strengthening ability, therefore, increasing the Fe content increases the tensile strength at room temperature. Furthermore, the β phase has higher workability compared to the α phase; therefore, increasing the Fe content improves the workability of the titanium alloy sheet and enhances dimensional accuracy. Fe is not essential in titanium alloy sheets, therefore its content is limited to 0%. However, to maintain good workability of the β phase at room temperature while obtaining the desired tensile strength, the Fe content is preferably 0.5% or more. More preferably, it is 0.7% or more. On the other hand, Fe is an element that is very prone to solidification and segregation; therefore, excessive Fe content can lead to localized Fe segregation, sometimes resulting in property differences between the segregated and unsegregated portions. Additionally, excessive Fe in titanium alloy sheets can sometimes reduce fatigue strength. Therefore, the Fe content is preferably 2.3% or less. More preferably, it is 2.1% or less, and even more preferably 2.0% or less. It should be noted that Fe is cheaper than β-phase stabilizing elements such as V or Si.

[0070] In this embodiment, the titanium alloy sheet may contain Fe, which can be replaced by V. V is a fully solid-solution β-phase stabilizing element and has solid-solution strengthening ability. V is not essential in the titanium alloy sheet, so its content has a lower limit of 0%. However, in order to obtain the same solid-solution strengthening ability as Fe, the V content is preferably 2.5% or more. The V content is more preferably 3.0% or more. If V is used instead of Fe, the cost increases, but since V is less prone to segregation than Fe, the deviation in properties caused by segregation is suppressed. As a result, stable properties are easily obtained in both the length and width directions of the titanium alloy sheet. In order to suppress the deviation in properties caused by V segregation, the V content is preferably 4.5% or less. As mentioned above, V is less prone to segregation than Fe, so it is preferable to contain V in the titanium billet when manufacturing large ingots.

[0071] Si is a β-phase stabilizing element, but it can also be dissolved in the α-phase, exhibiting high solid solution strengthening ability. As mentioned above, Fe sometimes segregates when it contains more than 2.3% in titanium alloy sheets, so Si can be included as needed to increase the strength of the titanium alloy sheets. In addition, Si has the opposite segregation tendency to O, and O is difficult to solidify and segregate, so by including appropriate amounts of Si and O in the titanium alloy sheets, it is expected to achieve both high fatigue strength and tensile strength. On the other hand, if the Si content is high, Si intermetallic compounds called silicides may sometimes form, reducing the fatigue strength of the titanium alloy sheets. If the Si content is 0.60% or less, the formation of coarse silicides is suppressed, and the reduction in fatigue strength is suppressed. Therefore, the Si content is preferably 0.60% or less. The Si content is more preferably 0.50% or less, and even more preferably 0.40% or less. Si is not essential in titanium alloy sheets, so its content has a lower limit of 0%, but the Si content can be, for example, 0.10% or more.

[0072] If titanium alloy sheets contain a large amount of carbon (C), it can sometimes reduce the ductility or workability of the sheets. Therefore, the C content is preferably less than 0.080%. C is not essential in titanium alloy sheets, so its lower limit is 0%. It should be noted that C is an unavoidable contamination, and its actual content is usually 0.0001% or more. A more preferred C content is 0.060% or less.

[0073] Similar to carbon (C), a high content of nitrogen (N) in titanium alloy sheets can sometimes reduce their ductility or workability. Therefore, the upper limit of the N content is preferably 0.050%. N is not essential in titanium alloy sheets, so the lower limit of its content is 0%. It should be noted that N is an unavoidable contamination, and its actual content is typically 0.0001% or more. More preferably, the N content is 0.04% or less.

[0074] Similar to carbon (C), a high content of oxygen (O) in titanium alloy sheets can sometimes reduce their ductility or workability. Therefore, the upper limit of the O content is preferably 0.40%, more preferably 0.38%, and even more preferably 0.35%. O is not essential in titanium alloy sheets, so its lower limit is 0%. It should be noted that O is an unavoidable contamination, and its actual content is usually 0.01% or more.

[0075] Similar to Fe or V, Ni is an element that improves tensile strength and processability. However, if the Ni content is 0.15% or more, the intermetallic compound Ti₂Ni, which forms as an equilibrium phase, can sometimes be formed, leading to a deterioration in the fatigue strength and room temperature ductility of the titanium alloy sheet. Therefore, the Ni content is preferably less than 0.15%. More preferably, the Ni content is 0.14% or less, 0.12% or less, and even more preferably 0.11% or less. Ni is not essential in titanium alloy sheets, so its content has a lower limit of 0%, but the Ni content can, for example, be 0.01% or more.

[0076] Similar to Fe or V, Cr is an element that improves tensile strength and processability. However, if the Cr content is 0.25% or more, the intermetallic compound TiCr2, which forms as an equilibrium phase, can sometimes be formed, leading to a deterioration in the fatigue strength and room temperature ductility of the titanium alloy sheet. Therefore, the Cr content is preferably less than 0.25%. The Cr content is more preferably 0.24% or less, or 0.21% or less. Cr is not essential in titanium alloy sheets, so its content has a lower limit of 0%, but the Cr content can, for example, be 0.01% or more.

[0077] Similar to Fe or V, Mn is an element that improves tensile strength and processability. However, if the Mn content is 0.25% or more, the intermetallic compound TiMn, which forms as an equilibrium phase, can sometimes be formed, leading to a deterioration in the fatigue strength and room temperature ductility of the titanium alloy sheet. Therefore, the Mn content is preferably less than 0.25%. More preferably, the Mn content is 0.24% or less, and even more preferably 0.20% or less. Mn is not essential in titanium alloy sheets, so its content has a lower limit of 0%, but the Mn content can, for example, be 0.01% or more.

[0078] When considering the effects of the above-mentioned chemical composition, the titanium alloy involved in this embodiment preferably contains, as optional elements, either Fe: 0.5 to 2.3% or V: 2.5 to 4.5%, Si: 0 to 0.60%, and also contains C: less than 0.080%, N: less than 0.050%, and O: less than 0.40%.

[0079] Furthermore, considering the effects of the aforementioned chemical composition, when the titanium alloy plate contains either Fe: 0.5 to 2.3% or V: 2.5 to 4.5%, the titanium alloy plate according to this embodiment preferably contains one or more of the following selected from the group consisting of Ni: less than 0.15%, Cr: less than 0.25%, and Mn: less than 0.25% to replace a portion of Fe or V.

[0080] In the case of the titanium alloy sheet according to this embodiment containing Fe, when it contains one or more elements selected from the group consisting of Ni: less than 0.15%, Cr: less than 0.25%, and Mn: less than 0.25%, the total amount of Fe, Ni, Cr, and Mn is preferably 0.5% or more and 2.3% or less. When the total amount of Fe, Ni, Cr, and Mn is 0.5% or more, high tensile strength can be obtained. In addition, when the total amount of Fe, Ni, Cr, and Mn is 0.5% or more, the β phase with good workability at room temperature can be maintained, and the workability of the titanium alloy sheet is improved, thereby improving dimensional accuracy. Furthermore, when the total amount of Fe, Ni, Cr, and Mn is 2.3% or less, the segregation of these elements is suppressed, thereby suppressing deviations in the properties of the titanium alloy sheet.

[0081] Furthermore, when the titanium alloy sheet according to this embodiment contains V, when it contains one or more elements selected from the group consisting of Ni: less than 0.15%, Cr: less than 0.25%, and Mn: less than 0.25%, the total amount of V, Ni, Cr, and Mn is preferably 2.5% or more and 4.5% or less. When the total amount of V, Ni, Cr, and Mn is 2.5% or more, high tensile strength can be obtained. In addition, when the total amount of V, Ni, Cr, and Mn is 2.5% or more, the β phase with good workability at room temperature can be maintained, and the workability of the titanium alloy sheet is improved, thereby improving dimensional accuracy. In addition, when the total amount of Fe, Ni, Cr, and Mn is 4.5% or less, the segregation of these elements is suppressed, thereby suppressing deviations in the properties of the titanium alloy sheet.

[0082] The balance of the chemical composition of the titanium alloy plate according to this embodiment can be Ti and impurities. Impurities include, for example, H, Cl, Na, Mg, Ca, B mixed in during refining processes, and Zr, Sn, Mo, Nb, Ta, and Cu mixed in from waste materials. A total impurity level of 0.5% or less is considered acceptable. Furthermore, the H content is 150 ppm or less. B can potentially form large precipitates within the ingot. Therefore, even when contained as an impurity, it is preferable to suppress the B content as much as possible. In the titanium alloy plate according to this embodiment, it is preferable to set the B content to 0.01% or less.

[0083] It should be noted that when the titanium alloy plate involved in this embodiment contains 0.5 to 2.3% Fe, the V contained in the titanium alloy plate is sometimes only an amount considered as an impurity. When the titanium alloy plate involved in this embodiment contains 2.5 to 4.5% V, the Fe contained in the titanium alloy plate is sometimes only an amount considered as an impurity.

[0084] Furthermore, as long as the titanium alloy plate involved in this embodiment has high strength and excellent dimensional accuracy, it can naturally contain various elements instead of Ti. Similarly, for elements exemplified as impurities, as long as the titanium alloy plate has high strength and excellent dimensional accuracy, it can contain amounts that are considered impurities or more.

[0085] As described above, the titanium alloy plate involved in this embodiment can have the aforementioned chemical composition. More specifically, the chemical composition of the titanium alloy plate involved in this embodiment can be, for example, Ti-6Al-4V, Ti-6Al-4V ELI, or Ti-5Al-1Fe.

[0086] (1.2. Texture and Microstructure)

[0087] Next, the texture and microstructure of the titanium alloy plate involved in this embodiment will be described.

[0088] [Texture]

[0089] The titanium alloy sheet involved in this embodiment has the following texture: In the (0001) pole figure based on the thickness direction, the angle between the direction of the peak representing the degree of aggregation calculated by texture analysis using the spherical harmonic function method with an expansion factor of 16 and a Gaussian half-width of 5° for the inverse pole figure of electron backscatter diffraction (EBSD) and the thickness direction is less than 65°. Generally, if hot rolling is performed at high speed in one direction at a temperature in the α+β high-temperature region with a high proportion of β phase, the titanium alloy will form a hexagonal close-packed (hcp) texture with the c-axis oriented in the width direction perpendicular to the length direction when transforming from the β phase to the α phase, according to the variable selection rule. In the hcp texture with the c-axis oriented in the width direction, large anisotropy is generated in the tensile properties in the width and length directions. If the tensile properties in the width and length directions have large anisotropy, adverse conditions will occur during processing. The direction of the peak representing the degree of aggregation, calculated by texture analysis (expansion factor = 16, Gaussian full width at half maximum = 5°) of the inverse pole figure of the EBSD method using the spherical harmonic function method, corresponds to the direction of the highest orientation degree of the c-axis of hcp. In the titanium alloy plate of this embodiment, in the (0001) pole figure based on the plate thickness direction, the angle between the direction of the highest orientation degree of hcp's c-axis (the direction of the peak representing the degree of aggregation) and the plate thickness direction is 65° or less, thereby reducing anisotropy, ensuring high machinability, and thus improving dimensional accuracy. In the (0001) pole figure based on the plate thickness direction, the angle between the direction of the highest orientation degree of hcp's c-axis and the plate thickness direction is preferably 60° or less, more preferably 55° or less, and even more preferably 35° or less. There is no particular limitation on the lower limit of the angle between the direction of the highest orientation degree of hcp's c-axis and the plate thickness direction, but it is 0° or more. When manufacturing titanium alloy sheets by unidirectional rolling, the lower limit of the angle between the direction of the highest orientation of the c-axis of hcp and the sheet thickness direction is 20° or higher.

[0090] Furthermore, regarding the angle between the direction of the peak representing the degree of aggregation and the thickness direction, if unidirectional cold rolling is performed, a texture that is tilted in the width direction (TD) of the hcp axis (Split-TD type texture) may sometimes be formed. The Split-TD type texture has excellent formability, especially excellent bending performance. Therefore, the angle between the direction of the peak representing the degree of aggregation and the thickness direction is preferably 20° or more and 65° or less, which belongs to the Split-TD type texture.

[0091] (0001) Pole figures are obtained by chemically polishing the observation surface of a titanium alloy plate sample and performing crystal orientation analysis using EBSD. Specifically, a cross-section (L section) of the titanium alloy plate cut along the thickness direction in the length direction and at the center of the width direction (TD) is chemically polished. Crystal orientation analyses based on EBSD are performed at approximately 2 to 10 locations in a region of (total plate thickness) × 2 mm on this cross-section, at intervals of 1 to 2 μm, thereby creating (0001) pole figures. The aggregation peak positions of specific orientations in the (0001) pole figures are obtained using OIM Analysis software manufactured by TSL Solutions. TM The software (Ver. 8.1.0) calculates the texture using inverse pole figure analysis based on the spherical harmonic function method. The highest position of the contour lines is the peak position of the aggregation degree, and the value with the highest aggregation degree at the peak position is taken as the maximum aggregation degree. It should be noted that the aggregation degree of a specific orientation in the (0001) pole figure represents how many times the frequency of grains with that orientation is relative to the structure with a completely irregular orientation distribution (aggregation degree 1). It should also be noted that although the L-section at the center of the width direction is used as the observation surface in the above, the crystal orientation of the titanium alloy plate is uniformly distributed in the width direction; therefore, the L-section at any plate width position can also be used as the observation surface.

[0092] Figure 1 An example of a (0001) pole figure based on the thickness direction (ND) of the titanium alloy plate involved in this embodiment is shown. Figure 1 In the process, the poles of each detected crystal orientation cluster according to the slopes towards the final rolling direction (RD) and the final rolling width direction (TD), and contour lines of the degree of clustering are drawn in the pole figure (0001). Furthermore, the highest part of the contour line in the figure is the peak P1 of the grain. Therefore, in this embodiment, the angle between the direction representing the peak P1 of the grain and ND is 65° or less. Typically, the maximum degree of clustering is the degree of clustering of the peak P1 of the grain.

[0093] Furthermore, in the (0001) pole figure of the titanium alloy plate involved in this embodiment, the angle between the direction of the peak representing the aggregation degree and the width direction, calculated by texture analysis using the spherical harmonic function method of the inverse pole figure of electron backscatter diffraction with an expansion factor of 16 and a Gaussian half-width of 5°, can be less than 10°. The angle between the direction of the peak representing the aggregation degree and the width direction is as follows: Figure 2 The figure shows the angle θ2 between the direction from the center of the (0001) pole figure based on the plate thickness direction toward the position of the peak representing the degree of aggregation and the width direction (TD). From the perspective of manufacturing and observation of the structure, the angle is preferably 5° or less, and more preferably 3° or less.

[0094] Furthermore, in the titanium alloy plate involved in this embodiment, the angle between the direction of the peak representing the degree of aggregation and the plate thickness direction is less than 35°, which is calculated by texture analysis using the spherical harmonic function method for the inverse pole figure of electron backscatter diffraction with an expansion coefficient of 16 and a Gaussian half-width of 5°.

[0095] [Microstructure]

[0096] The titanium alloy sheet of this embodiment has an α-phase area ratio of 80% or more. The titanium alloy sheet of this embodiment contains a large amount of α-stabilizing elements to achieve high strength. Therefore, if the amount of β-stabilizing elements added is further increased, the strength will become too high, making cold rolling impossible. Therefore, the titanium alloy sheet of this embodiment has an α-phase area ratio of 80% or more. For example, the α-phase area ratio can be 82% or more. There is no particular upper limit to the α-phase area ratio; for example, it can be 100% or less, or 98% or less. The microstructure of the titanium alloy sheet of this embodiment consists of an α-phase and a balance microstructure, the balance microstructure including β-phase, TiFe, Ti3Al, and silicides.

[0097] In the titanium alloy plate of this embodiment, the area fraction of the α phase with a spherical equivalent diameter of 1 μm or more is greater than 53%. A high area fraction below 1 μm sometimes results in poor ductility at room temperature; therefore, the area fraction of the α phase with a spherical equivalent diameter of 1 μm or more is greater than 53%. The area fraction of the α phase with a spherical equivalent diameter of 1 μm or more can be 55% or more, or 60% or more. There is no particular upper limit to the area fraction of the α phase with a spherical equivalent diameter of 1 μm or more; for example, the area fraction can be 98% or less. The microstructure of the titanium alloy plate of this embodiment is, for example, [details omitted]. Figure 3 The structure shown. There is no particular upper limit to the circular equivalent diameter of the α phase; for example, the circular equivalent diameter of the α phase is less than 20 μm.

[0098] The area fraction of the α phase and the area fraction of the α phase with a circular equivalent diameter of 1 μm or more were determined by the following method. A section (L section) of a titanium alloy plate cut along the thickness direction in the length direction and at the center of the width direction (TD) was chemically polished. Crystal orientation analysis based on the EBSD method was performed on a region of (total plate thickness) × 200 μm of this section with a gradient of 1–5 μm for approximately 2–5 fields of view. The α phase was determined by this EBSD crystal orientation analysis. The area fraction of the α phase relative to the area of ​​the aforementioned region was taken as the area fraction of the α phase. Furthermore, the circular equivalent diameter of the α phase observed in the aforementioned fields of view (area A = π × (grain size D / 2)²) was calculated, and the total area of ​​the α phase with a circular equivalent diameter of 1 μm or more relative to the area of ​​the aforementioned region was taken as the area fraction of the α phase with a circular equivalent diameter of 1 μm or more. The grains of the α phase with a circular equivalent diameter of 1 μm or more contain the banded structure described later. It should be noted that although the area ratio of the α phase and the area ratio of the α phase with a circular equivalent diameter of 1 μm or more were measured based on the L-section at the center position in the width direction above, since the α phase is uniformly distributed in the width direction, the area ratio of the α phase and the area ratio of the α phase with a circular equivalent diameter of 1 μm or more can also be measured based on the L-section at any plate width position.

[0099] The titanium alloy plate according to this embodiment has a microstructure consisting of an equiaxed structure with an aspect ratio of 3.0 or less and a banded structure with an aspect ratio greater than 3.0 extending in the length direction. The average grain diameter of the equiaxed structure is 0.1 μm or more and 20.0 μm or less, and the area ratio of the banded structure relative to the area of ​​the microstructure is preferably 10.0% or less. Each microstructure will be described below.

[0100] When hot rolling is performed at a temperature in the α+β domain or the β domain, such as Figure 4 As shown, titanium alloys sometimes form a structure known as "banding". Banding, as described here, is, for example, as shown in... Figure 4 The microstructure shown is a banded structure extending along the length direction. Specifically, it refers to grains with an aspect ratio greater than 3.0, expressed as the ratio of the major axis to the minor axis. The titanium alloy sheet according to this embodiment sometimes has a banded structure extending along the length direction. When a banded structure is formed, it can sometimes cause anisotropy in strength or defects during forming and processing. Therefore, it is preferable to have as little banded structure as possible. The area ratio of the banded structure relative to the area of ​​the microstructure is preferably 10.0% or less. The area ratio of the banded structure is more preferably 8.0% or less. On the other hand, since it is preferable to have no banded structure, the lower limit is 0%.

[0101] The aspect ratio and area ratio of the banded structure can be calculated as follows. A section (L-section) of a titanium alloy plate cut at the center of the width direction (TD) and along the thickness direction is chemically polished. Crystal orientation analysis based on the EBSD method is performed on a 200 μm region (total plate thickness) of this section with a gradient of 1–5 μm for approximately 2–5 fields of view. Based on the EBSD crystal orientation analysis results, the aspect ratio of each grain is calculated. Then, the area ratio of grains with an aspect ratio greater than 3.0 is calculated. It should be noted that although the aspect ratio and area ratio of the banded structure are calculated based on the L-section at the center of the width direction, since the banded structure is uniformly distributed in the width direction, the aspect ratio and area ratio of the banded structure can also be calculated based on the L-section at any position within the plate width.

[0102] The excess material other than the banded structure in the microstructure is preferably an equiaxed structure formed by recrystallization. From the perspective of formability, titanium alloy sheets preferably have an equiaxed structure, and in particular, since titanium alloy sheets are sometimes formed using superplastic properties, fine grains are preferred. From the perspective of formability and superplasticity, the average grain diameter of the equiaxed structure is preferably 20.0 μm or less. More preferably, the average grain diameter of the equiaxed structure is 15.0 μm or less, further preferably 10.0 μm or less, and even more preferably 8.0 μm or less. On the other hand, when the average grain diameter of the equiaxed structure is less than 0.5 μm, sometimes the effect of fine grains can lead to excessive strength and a significant decrease in ductility. As a result, particularly the workability at cold working (room temperature) can sometimes be reduced. Therefore, the average grain diameter of the equiaxed structure is preferably 0.5 μm or more. More preferably, the average grain diameter of the equiaxed structure is 1.0 μm or more.

[0103] It should be noted that more than 80% of equiaxed and banded tissues are α phase, while β phase exists between α phase and α phase.

[0104] The presence or absence of recrystallization can be determined by measuring the aspect ratio (ratio of major axis to minor axis) of the grains. If the aspect ratio is below 3.0, the grain can be identified as a recrystallized grain. It should be noted that the lower limit for the aspect ratio of equiaxed structures is 1.0.

[0105] The average grain diameter of equiaxed structures can be calculated as follows: Based on the grain area of ​​the equiaxed structure measured using EBSD, the round equivalent grain size (area A = π × (grain diameter D / 2)) can be determined. 2 The average value of this number of references is taken as the average grain diameter of the equiaxed structure.

[0106] (1.3-0.2% yield strength)

[0107] The smaller of the 0.2% yield strength in the length direction or the 0.2% yield strength in the width direction at 25°C for the titanium alloy sheet involved in this embodiment is preferably 700 MPa or more. Hereinafter, the smaller of the 0.2% yield strength in the length direction or the 0.2% yield strength in the width direction will be simply referred to as the 0.2% yield strength. In the aerospace industry and the like, a tensile strength close to that of Ti-6Al-4V, a common α+β type titanium alloy, at 25°C is generally required. If the 0.2% yield strength of the titanium alloy sheet at 25°C is 700 MPa or more, it can be used for applications requiring high strength. The 0.2% yield strength of the titanium alloy sheet at 25°C is more preferably 730 MPa or more. On the other hand, if the strength is too high, the strength of the hot-rolled sheet before cold rolling is also high, so it is sometimes difficult to cold roll the hot-rolled sheet, increasing the number of cold rolling passes and increasing costs. In addition, if the strength is too high, the cut sensitivity becomes high, and sheet breakage may occur. Therefore, the 0.2% yield strength of the titanium alloy sheet at 25°C is preferably 1200 MPa or less. More preferably, the 0.2% yield strength of the titanium alloy sheet at 25°C is 1150 MPa or less. Furthermore, if the 0.2% yield strength of the titanium alloy sheet at 25°C is 1000 MPa or less, it will further suppress cracking during rolling; therefore, the 0.2% yield strength of the titanium alloy sheet at 25°C is even more preferably 1100 MPa or less. The 0.2% yield strength can be determined using a method based on JIS Z2241:2011. That is, the 0.2% yield strength in the length direction and the 0.2% yield strength in the width direction can be determined using a method based on JIS Z2241:2011. It should be noted that the length direction mentioned here refers to the final rolling direction. For those skilled in the art, determining the final rolling direction is easy, and the final rolling direction is clear.

[0108] (1.4. Anisotropy)

[0109] The ratio of the 0.2% yield strength σT in the width direction to the 0.2% yield strength σL in the length direction at 25°C, i.e., the conditional yield strength ratio σT / σL, of the titanium alloy sheet according to this embodiment, is preferably 0.85 or more and 1.18 or less. As mentioned above, α+β type titanium has an hcp phase (α phase), and therefore exhibits higher anisotropy in the hcp direction. As mentioned above, anisotropy increases when forming a T-texture, and therefore, especially in the aircraft field, it is sometimes desirable to minimize anisotropy as much as possible. Therefore, although it is better for the conditional yield strength ratio σT / σL to be closer to 1.00, it is possible to obtain better formability if the conditional yield strength ratio σT / σL is 1.18 or less. The conditional yield strength ratio σT / σL is more preferably 1.16 or less, more preferably 1.15 or less, and even more preferably 1.14 or less. If cold cross-rolling is performed in both the length and width directions, the conditional yield strength ratio σT / σL can be 0.85 or higher and 1.10 or lower. The conditional yield strength ratio σT / σL of the titanium alloy sheet manufactured by cold cross-rolling is preferably 0.90 or higher, more preferably 0.95 or higher. Furthermore, the conditional yield strength ratio σT / σL of the titanium alloy sheet manufactured by cold cross-rolling is preferably 1.05 or lower. In the case of unidirectional cold rolling along the length direction, the conditional yield strength ratio σT / σL is unlikely to be less than 1.05 and can be 1.05 or higher. It should be noted that since unidirectional cold rolling can produce titanium alloy sheets with a conditional yield strength ratio σT / σL greater than 1.18, σT / σL can also be greater than 1.18.

[0110] (1.5. Average plate thickness)

[0111] The titanium alloy sheet according to this embodiment has an average thickness of 2.5 mm or less. For example, by using the titanium alloy sheet manufacturing method described later, a titanium billet containing the above-mentioned chemical composition can be used to achieve an average thickness of 2.5 mm or less. Titanium billets with an Al content greater than 4.0% and less than 6.6% have high deformation resistance, so ordinary rolling mills sometimes exceed the allowable load of the rolling mill during the manufacturing of thin sheets. Therefore, it is difficult to manufacture titanium alloy sheets containing the above-mentioned chemical composition with a thickness of 2.5 mm or less. In addition, when hot rolling is performed without using stacking rolling, if the sheet thickness is reduced, the temperature drops sharply, thereby increasing the deformation resistance. As a result, when hot rolling high-strength materials, the allowable load of the rolling mill is sometimes exceeded, making it difficult to achieve an average sheet thickness of 2.5 mm or less. On the other hand, although there is no particular limitation on the lower limit of the average sheet thickness of the titanium alloy sheet according to this embodiment, for titanium alloys with the above-mentioned strength, the average sheet thickness is actually mostly 0.1 mm or more. Therefore, the average sheet thickness of the titanium alloy sheet according to this embodiment is preferably 0.1 mm or more. The thickness of the titanium alloy plate involved in this embodiment is preferably 2.0 mm or less, more preferably 1.5 mm or less. Furthermore, the average thickness of the titanium alloy plate involved in this embodiment is more preferably 0.2 mm or more.

[0112] Here, refer to Figure 5 The method for determining the average plate thickness is explained below. At the center position in the width direction (TD) and at a distance of 1 / 4 of the plate width from each end in the width direction, the plate thickness is measured at more than 5 positions in the length direction at intervals of more than 1m using X-rays, a micrometer, or a vernier caliper. The average value of the measured plate thickness is taken as the average plate thickness.

[0113] (1.6. Plate thickness dimensional accuracy)

[0114] The dimensional accuracy of the titanium alloy sheet thickness according to this embodiment (hereinafter, the dimensional accuracy of sheet thickness is sometimes simply referred to as sheet thickness dimensional accuracy) is preferably 5.0% or less relative to the average sheet thickness. In lamination rolling, titanium alloy sheets are manufactured by hot rolling of multi-layered titanium materials sandwiched by steel. However, due to the large variation in deformation resistance of multi-layered titanium materials caused by temperature distribution, it is difficult to manufacture thin sheets with uniform thickness. However, the titanium alloy sheet according to this embodiment is manufactured by cold rolling as described below, and therefore is a titanium alloy sheet with excellent dimensional accuracy of sheet thickness. The dimensional accuracy of the titanium alloy sheet according to this embodiment is more preferably 4.0% or less relative to the average sheet thickness, and even more preferably 2.0% or less relative to the average sheet thickness.

[0115] The plate thickness dimensional accuracy is determined by the following method. Using X-rays, a micrometer, or a vernier caliper, plate thickness is measured at at least five locations along the length direction at intervals of at least 1 m, at the center position in the width direction (TD) and at positions one-quarter of the plate width from each end in the width direction. The maximum value of a', calculated using the actual measured plate thickness d and the aforementioned average plate thickness dave, is taken as the plate thickness dimensional accuracy a.

[0116] a'=(d-dave) / dave×100...Formula (101)

[0117] The titanium alloy plate according to this embodiment has been described above. Due to its aforementioned chemical composition and metallographic structure, the titanium alloy plate according to this embodiment exhibits high strength. The titanium alloy plate according to this embodiment described above can be manufactured by any method; for example, it can also be manufactured by the manufacturing method of the titanium alloy plate according to this embodiment described below.

[0118] <2. Manufacturing Method of Titanium Alloy Plate>

[0119] The manufacturing method of titanium alloy sheet according to this embodiment includes: a slab manufacturing process for manufacturing titanium alloy slab blanks; a hot rolling process for hot rolling the titanium alloy slab blanks; a cold rolling process for cold rolling the titanium material after the hot rolling process; and a surface finishing or stretch straightening process for surface finishing or stretch straightening of the titanium material after the cold rolling process, as needed. Hereinafter, each step of the manufacturing method of titanium alloy sheet according to this embodiment will be described. In the cold rolling process, the titanium material after the hot rolling process is subjected to unidirectional cold rolling with at least one cold rolling pass in the length direction, or cold cross rolling with cold rolling passes in both the length and width directions. Hereinafter, as a first manufacturing method, the case of unidirectional cold rolling of the titanium material after the hot rolling process will be described, and as a second manufacturing method, the case of cold cross rolling of the titanium material after the hot rolling process will be described.

[0120] [First Manufacturing Method]

[0121] (2.1. Slab manufacturing process)

[0122] In the slab manufacturing process, titanium alloy slabs are manufactured. There are no particular restrictions on the manufacturing method of titanium alloy slabs; for example, they can be manufactured in the following order: First, sponge titanium ingots are made using various melting methods such as vacuum arc melting, electron beam melting, or plasma melting. Next, the resulting ingots are hot-forged at temperatures in the α-phase high-temperature domain, the α+β two-phase domain, or the β-phase single-phase domain to obtain the titanium alloy slab. It should be noted that pretreatments such as cleaning and cutting can be applied to the titanium alloy slabs as needed. Furthermore, when manufacturing hot-rollable rectangles using the furnace melting method, hot forging can be omitted, and the slabs can be supplied for hot rolling. The manufactured titanium alloy slab contains, by mass percent: Al: greater than 4.0% and less than 6.6%, Fe: greater than 0% and less than 2.3%, V: greater than 0% and less than 4.5%, Si: greater than 0% and less than 0.60%, C: greater than 0% and less than 0.080%, N: greater than 0% and less than 0.050%, O: greater than 0% and less than 0.40%, Ni: greater than 0% and less than 0.15%, Cr: greater than 0% and less than 0.25%, and Mn: greater than 0% and less than 0.25%.

[0123] (2.2. Hot rolling process)

[0124] In the hot rolling process, the titanium alloy slab is heated and then hot rolled. For example, the titanium alloy slab is heated to the β phase transformation point T. β After reaching a temperature range above ℃, rolling can be performed with a total reduction rate of 80% or more. However, when hot rolling begins at a temperature below the α+β phase temperature range, cracks form in the titanium alloy slab, or even without cracks, the aforementioned metallographic structure cannot be obtained. Therefore, in this process, hot rolling begins at the β phase temperature range. Furthermore, the temperature immediately after hot rolling, i.e., the final temperature, is set as the α+β phase temperature range, which varies depending on the composition of the titanium alloy slab, but for example, it can also be set as (T...). β -250)℃ or above and (T β The titanium material is hot-rolled at a temperature below -50°C, and the reduction rate is achieved in a single hot rolling operation. Alternatively, the reduction rate can be achieved through multiple hot rolling operations. The titanium material after this hot rolling process contains, by mass %: Al: greater than 4.0% and less than 6.6%, Fe: greater than 0% and less than 2.3%, V: greater than 0% and less than 4.5%, Si: greater than 0% and less than 0.60%, C: greater than 0% and less than 0.080%, N: greater than 0% and less than 0.050%, O: greater than 0% and less than 0.40%, Ni: greater than 0% and less than 0.15%, Cr: greater than 0% and less than 0.25%, and Mn: greater than 0% and less than 0.25%.

[0125] It should be noted that, in this specification, the "β phase transformation point" refers to the boundary temperature at which the α phase begins to form when the titanium alloy is cooled from the β-phase single-phase domain. The β phase transformation point can be obtained from a phase diagram. Phase diagrams can be obtained, for example, using the CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) method. Specifically, the β phase transformation point can be calculated using the Thermo-Calc integrated thermodynamic calculation system from Thermo-Calc Sotware AB and the specified database (TI3) to obtain the phase diagram of the titanium alloy using the CALPHAD method.

[0126] In the hot rolling process, known continuous hot rolling equipment can be used to continuously hot roll titanium alloy slabs. When using continuous hot rolling equipment, the titanium alloy slab is coiled by a coiler after hot rolling to form titanium alloy hot-rolled coils. Therefore, the titanium materials after the hot rolling process include plate-shaped titanium materials and coil-shaped titanium materials that are longer than plate-shaped titanium materials.

[0127] The titanium material after the hot rolling process can be subjected to annealing based on known methods, removal of oxide scale by pickling or cutting, or cleaning treatment, as needed. For example, the titanium material after the hot rolling process can be annealed at a temperature of 650°C or higher and 800°C for 20 to 90 minutes. This allows the non-recrystallized grains of the hot-rolled plate to precipitate as fine recrystallized grains, resulting in a more uniform and finer crystal structure in the final titanium alloy plate. It should be noted that the annealing can be carried out in an atmospheric atmosphere, an inactive atmosphere, or a vacuum atmosphere.

[0128] It should be noted that in the above-mentioned manufacturing method of titanium alloy plate, the titanium material after the hot rolling process corresponds to the titanium billet involved in this disclosure.

[0129] (2.3. Cold rolling process)

[0130] In this process, the titanium material after the hot rolling process undergoes at least one cold rolling pass along its length. The average rolling rate per cold rolling pass is greater than 30%, and the total rolling rate is greater than 60%. Through this cold rolling process, the c-axis of the hcp approaches the ND direction. However, if the average rolling rate per cold rolling pass and the total rolling rate are too small, the crystal orientation hardly changes, and the angle between the direction of the aggregation peak and the thickness direction is not less than 65°. In this case, the anisotropy of the titanium alloy sheet cannot be improved. Furthermore, while the aforementioned banded structure is formed through hot rolling, if the average cold rolling rate per cold rolling pass and the total cold rolling rate are small after hot rolling, the banded structure remains in the titanium material without being destroyed. Therefore, the average rolling rate per cold rolling pass in the cold rolling process is greater than 30%, and the total rolling rate is greater than 60%. The total rolling rate is preferably greater than 70%.

[0131] It should be noted that the term "one cold rolling pass" here refers to continuously performed cold rolling. Specifically, a cold rolling pass refers to the cold rolling from the end of the hot rolling process until the titanium material reaches the final product thickness, or, in the case of a surface finishing process described later after hot rolling, from the end of the hot rolling process to the beginning of the surface finishing process. When intermediate annealing is performed during the cold rolling process, the cold rolling from the end of the hot rolling process to the intermediate annealing process, the cold rolling from the intermediate annealing process to the final product thickness, or the cold rolling process to the beginning of the surface finishing process are respectively referred to as cold rolling passes. Furthermore, in the case of multiple intermediate annealing processes, the cold rolling from one intermediate annealing process to the next is also referred to as a cold rolling pass. It should be noted that the rolling rate of each cold rolling mill can be any ratio as long as the average rolling rate per pass is greater than 30%.

[0132] In this cold rolling process, manufacturing costs can be reduced by rolling long hot-rolled plates or hot-rolled coils that are long in the rolling direction, i.e., titanium materials.

[0133] The cold rolling temperature is preferably below 500°C. A cold rolling temperature below 500°C results in high dimensional accuracy, and the grains are refined during cold rolling, making it easier to exhibit superplastic properties. A cold rolling temperature below 400°C is more preferable. There is no particular limitation on the lower limit of the cold rolling temperature; for example, the cold rolling temperature can be set above room temperature. Room temperature here refers to above 0°C.

[0134] [Intermediate annealing process]

[0135] In the cold rolling process, when multiple cold rolling passes are performed, it is preferable to have an intermediate annealing process for annealing the titanium material between the multiple cold rolling passes. In the intermediate annealing process, it is preferable to have an annealing temperature T of 600°C or higher. βThe intermediate material in the cold rolling process is annealed at a temperature below -50°C, and the annealing temperature T (°C) and the holding time t (seconds) at annealing temperature T satisfy the following formula (102). It should be noted that in the following formula (102), (T+273.15)×(Log 10 (t)+20) is the Larsen-Miller parameter.

[0136] 22000≤(T+273.15)×(Log 10 (t)+20)≤27000…Equation (102)

[0137] In the formula, T β The β phase transition point (°C).

[0138] [Final annealing process]

[0139] The final annealing process is the annealing treatment of the titanium material after the final cold rolling pass. There are no particular restrictions on the annealing conditions in the final annealing process, but to improve the formability of the titanium alloy sheet, an annealing temperature T of 600°C or higher is preferred. β The annealing temperature is below -50℃, and the annealing temperature T (℃) and the holding time t (seconds) at the annealing temperature T satisfy the above formula (102).

[0140] By performing intermediate and final annealing processes under the aforementioned conditions, the uncrystallized particles recrystallize, causing the c-axis of the α-phase to approach the ND direction. This reduces the anisotropy of the titanium alloy sheet. Furthermore, recrystallization eliminates excess banded structures in the microstructure. On the other hand, the annealing temperature is the β-phase transformation point T. β At the above temperatures, a phase transformation from the β phase to the α phase occurs, resulting in a acicular structure. Furthermore, even if the annealing temperature is exactly below the β phase transformation point, a bimodal structure consisting of a mixture of equiaxed and acicular structures will still occur. Acicular and bimodal structures can sometimes lead to internal and end cracks during cold rolling. Moreover, acicular or bimodal structures often consist of coarse particles and are unlikely to exhibit superplastic properties. In the intermediate and final annealing processes, an annealing temperature T of 600°C or higher is preferred. β The annealing temperature T and annealing time t are determined by setting the annealing temperature T below -50℃ and satisfying the above equation (102). This allows the c-axis of the α-phase to approach the ND direction through recrystallization, further reducing the anisotropy of the titanium alloy plate and further reducing the banded structure in the microstructure. Furthermore, in the intermediate and final annealing processes, the annealing temperature T is set to 600℃ or higher and (T... βThe annealing temperature T and annealing time t are determined by means of the above formula (102) below -50℃, thereby increasing the fine equiaxed structure, suppressing internal and end cracks during cold rolling, and easily exhibiting superplastic properties.

[0141] (2.4. Surface rolling and stretching straightening process)

[0142] Titanium alloy sheets are manufactured through the aforementioned cold rolling process. However, the titanium alloy sheets after the cold rolling process are preferably subjected to surface rolling for adjusting mechanical properties or tensile straightening for correcting shape, as needed. The reduction rate in surface rolling is preferably 10% or less, and the elongation rate in tensile straightening is preferably 5% or less. It should be noted that surface rolling and tensile straightening may be omitted if not required.

[0143] According to the first manufacturing method, in the cold rolling process of hot-rolled plates manufactured using the above-mentioned titanium alloy plates, which are cold rolled more than once along the length direction, the average rolling rate per cold rolling is greater than 30%, and the total rolling rate is 60% or more. This results in a titanium alloy plate in which, in the (0001) pole figure based on the plate thickness direction, the angle between the direction of the peak representing the degree of aggregation calculated by texture analysis using the spherical harmonic function method with an expansion factor of 16 and a Gaussian half-width of 5° and the plate thickness direction is 65° or less. Furthermore, according to the first manufacturing method, the average plate thickness of the titanium alloy plate can be 2.5 mm or less, and the dimensional accuracy of the plate thickness relative to the average plate thickness can be 5.0% or less.

[0144] Furthermore, according to the first manufacturing method, the microstructure of the titanium alloy plate has a microstructure consisting of an equiaxed structure with an aspect ratio of 3.0 or less and a banded structure with an aspect ratio greater than 3.0 extending in the length direction. The average grain diameter of the equiaxed structure is 0.1 μm or more and 20.0 μm or less, and the area fraction of the banded structure relative to the area of ​​the microstructure is 10.0% or less. As a result, the anisotropy of the titanium alloy plate is further reduced.

[0145] Furthermore, according to the first manufacturing method, the ratio of 0.2% yield strength in the width direction to 0.2% yield strength in the length direction can be 1.05 or more and 1.18 or less.

[0146] In addition, according to the first manufacturing method, the grains are refined by cold rolling, which makes it easy to exhibit superplastic properties, and the titanium alloy sheet has excellent processability in thin sheet forming.

[0147] According to the manufacturing method of the titanium alloy sheet according to this embodiment, since it includes a unidirectional cold rolling process, it is possible to manufacture long strips of titanium alloy sheets and titanium alloy coils. Therefore, the above-described manufacturing method can also be referred to as a manufacturing method of titanium alloy coils. Therefore, it is obvious that the titanium alloy coils manufactured by the above-described manufacturing method have the same characteristics as the titanium alloy sheet of this disclosure. Specifically, the titanium alloy coils of this disclosure contain, by mass %: Al: greater than 4.0% and less than 6.6%, Fe: more than 0% and less than 2.3%, V: more than 0% and less than 4.5%, Si: more than 0% and less than 0.60%, C: more than 0% and less than 0.080%, N: more than 0% and less than 0.050%, O: more than 0% and less than 0.40%, Ni: more than 0% and less than 0.15%, Cr: more than 0% and less than 0.25%, and Mn: The content is above 0% and below 0.25%, with the balance being Ti and impurities. The area fraction of the α phase is above 80%, and the area fraction of the α phase with a circular equivalent diameter of 1 μm or more is greater than 53%. In the (0001) pole figure based on the plate thickness direction, the angle between the direction of the peak representing the aggregation degree and the plate thickness direction is below 65°, and the average plate thickness is below 2.5 mm.

[0148] It should be noted that, in the case of manufacturing titanium alloy coils, the above-mentioned "length direction" corresponds to the length direction of the titanium alloy coil, and the "width direction" corresponds to the direction perpendicular to the length direction of the rolled surface of the titanium alloy coil.

[0149] This concludes the explanation of the first manufacturing method.

[0150] [Second Manufacturing Method]

[0151] Next, the second manufacturing method will be described. The cold rolling process in the second manufacturing method differs from that in the first manufacturing method, while the other processes are the same as in the first manufacturing method. Therefore, the cold rolling process will be described in detail here, while the description of the other processes will be omitted.

[0152] The cold rolling process in the second manufacturing method is a cold cross-rolling process that performs cold rolling passes on the titanium material after the hot rolling process along the length and width directions.

[0153] The total rolling rate in this process, including rolling in both the length and width directions, is 60% or higher. The final rolling direction in this process is designated as the length direction, and the direction perpendicular to the length direction is designated as the width direction. If the total rolling rate is 60% or higher, the c-axis of the hcp phase is closer to the ND orientation, allowing for the production of titanium alloy sheets with low anisotropy. The higher the rolling rate, the closer the c-axis of the α-phase in the titanium alloy sheet is to the thickness direction and the greater the aggregation degree; therefore, there is no upper limit to the rolling rate.

[0154] There are no particular limitations on the cross-rolling ratio, for example, it can be 0.05 or more and 20.00 or less. The cross-rolling ratio referred to here is the rolling rate in the length direction relative to the rolling rate in the width direction (length direction rolling rate / width direction rolling rate) implemented until the sheet thickness changes from 4 mm to the target sheet thickness. If this cross-rolling ratio is 0.05 or more and 20.00 or less, the c-axis of the hcp is closer to the ND orientation, enabling the manufacture of thin sheets with low anisotropy. Furthermore, it can reduce the excessive banding structure. A cross-rolling ratio of 0.07 or more and 15.00 or less is more preferable.

[0155] If the total rolling rate is 60% or higher, there is no particular limitation on the average rolling rate per cold rolling pass. It should be noted that "one cold rolling pass" here refers to continuous cold rolling in the length or width direction of a hot-rolled sheet. Therefore, in this cold cross-rolling process, when multiple cold rolling operations are performed in the length and width directions on a hot-rolled sheet, the total number of passes is called the number of cold rolling passes. For example, if one cold rolling operation in the length direction and one cold rolling operation in the width direction are performed on a hot-rolled sheet, the number of cold rolling passes is 2. In the second manufacturing method, multiple rolling operations in the length or width direction can be performed. Furthermore, even if the sheet thickness is 4 mm or less, reheating can be performed. Alternatively, hot rolling in the width direction can be performed after one or more hot rolling operations in the length direction.

[0156] In addition, rolling along the width direction can be carried out at any time.

[0157] There is no particular limitation on the average rolling rate per cold rolling pass; for example, it can be set to 5% or more. The average rolling rate per cold rolling pass is preferably 10% or more, more preferably 20% or more. Furthermore, the average rolling rate per cold rolling pass can be 80% or less, or 75% or less.

[0158] The rolling temperature in the cold cross-rolling process is preferably below 500°C. A rolling temperature below 500°C results in high dimensional accuracy and grain refinement during rolling. A rolling temperature below 400°C is more preferable. There is no particular limitation on the lower limit of the cold rolling temperature; for example, the cold rolling temperature can be above room temperature. Room temperature here refers to 0°C or higher.

[0159] According to the second manufacturing method, the following titanium alloy plate can be obtained: In the (0001) pole figure based on the plate thickness direction, the angle between the direction of the peak representing the degree of aggregation calculated by texture analysis using the spherical harmonic function method of the inverse pole figure of electron backscatter diffraction with an expansion factor of 16 and a Gaussian half-width of 5° and the plate thickness direction is 35° or less; the ratio of the 0.2% yield strength in the width direction to the 0.2% yield strength in the length direction is 0.85 or more and 1.10 or less. By performing multiple rolling passes in the length direction and rolling passes in the width direction, the ratio of the 0.2% yield strength in the width direction to the 0.2% yield strength in the length direction can be made close to 1.00.

[0160] Furthermore, when the titanium billet contains a large amount of β-phase stabilizing elements such as V, high-speed hot rolling in a unidirectional direction at a temperature in the α+β high-temperature region with a high proportion of β-phase easily leads to the formation of T-texture, increasing the anisotropy of the titanium alloy sheet. However, according to the second manufacturing method, due to the implementation of cold cross-rolling, the formation of T-texture can be suppressed even when the titanium billet contains β-phase stabilizing elements such as V. As a result, it is possible to manufacture titanium alloy sheets with low anisotropy.

[0161] Furthermore, according to the second manufacturing method, the microstructure of the titanium alloy plate has a microstructure consisting of an equiaxed structure with an aspect ratio of 3.0 or less and a banded structure with an aspect ratio greater than 3.0 extending in the length direction. The average grain diameter of the equiaxed structure is 0.1 μm or more and 20.0 μm or less, and the area fraction of the banded structure relative to the area of ​​the microstructure is 10.0% or less. As a result, the anisotropy of the titanium alloy plate is further reduced.

[0162] Example

[0163] The embodiments of this disclosure will be described in detail below. It should be noted that the embodiments shown below are merely examples of this disclosure, and this disclosure is not limited to the following examples.

[0164] (Example 1)

[0165] 1. Manufacturing of titanium alloy plates

[0166] First, titanium alloy ingots with the chemical composition shown in Table 1 are manufactured as blanks for titanium alloy plates using any one of vacuum arc remelting (VAR), electron beam remelting (EBR), or plasma arc melting (PAM). Then, titanium alloy slab blanks with a thickness of 150 mm × width of 800 mm × length of 5000 mm are produced by primary rolling or forging. These titanium alloy slab blanks are then subjected to hot rolling, hot-rolled plate annealing, shot peening, and pickling to produce hot-rolled plates with a thickness of 4 mm. During hot rolling, the temperature is raised to 1050–1100 °C to bring the temperature of the titanium alloy slab blank to the β-phase transformation point T. β The above describes the process of hot rolling starting from this temperature, set at 800–950°C, to ensure the final temperature reaches the β-phase transformation point T. β The following should be noted: elements other than those listed in Table 1 are Ti and impurities.

[0167] The chemical composition of the hot-rolled plates was determined by ICP emission spectroscopy analysis of Al, Fe, Si, Ni, Cr, Mn, and V. O and N were determined using an oxygen-nitrogen simultaneous analysis apparatus via inactive gas melting, thermal conductivity, and infrared absorption. C was determined using a carbon-sulfur simultaneous analysis apparatus via infrared absorption. The chemical composition of each manufactured hot-rolled plate was equal to that of the titanium alloy slabs shown in Table 1. Furthermore, for the titanium slabs A to P shown in Table 1, the phase diagram of the titanium alloy was obtained using the Thermo-Calc integrated thermodynamic calculation system (TI3) from Thermo-Calc Sotware AB and the specified database, and the β-phase transformation point T was calculated using the CALPHAD method. β .

[0168] [Table 1]

[0169]

[0170] Next, the obtained hot-rolled sheet is subjected to a cold rolling process under the conditions shown in Table 2. Examples 1-18, 30 of the invention and Comparative Example 3 in Table 2 are examples of repeatedly performing cold rolling with an average rolling rate of 35-60% per cold rolling pass and intermediate annealing under the conditions shown in Table 2, cold rolling until the total rolling rate reaches 70-94%. Example 19 of the invention is an example of repeatedly performing cold rolling with an average rolling rate of 35% per cold rolling pass and intermediate annealing under the conditions shown in Table 2, cold rolling until the total rolling rate reaches 60%. Example 20 of the invention is an example of cold rolling at a temperature of 300°C. Example 21 of the invention is an example of repeatedly performing cold rolling with an average rolling rate of 40% per cold rolling pass and intermediate annealing under the conditions shown in Table 2, cold rolling until the total rolling rate reaches 78%. The intermediate annealing process in Example 21 is an example that does not satisfy the above formula (102). Examples 22 and 23 are examples of cold rolling with rolling rates of 75% and 60%, respectively, without intermediate annealing. Examples 24-26 are examples of cold rolling with a first cold rolling pass having a rolling rate of 75%, followed by intermediate annealing under the conditions shown in Table 2, and then cold rolling with a second cold rolling pass having a rolling rate of 50%, resulting in a total rolling rate of 88%. Examples 27-29 are examples of cold rolling with a first cold rolling pass having a rolling rate of 50%, followed by a first intermediate annealing under the conditions shown in Table 2, then cold rolling with a second cold rolling pass having a rolling rate of 50%, followed by a second intermediate annealing under the conditions shown in Table 2, and finally cold rolling with a third cold rolling pass having a rolling rate of 60%, resulting in a total rolling rate of 90%. A reference example is a hot-rolled plate without a cold rolling process. Comparative Example 1 is an example with an average rolling rate of 20% per pass and a total rolling rate of 59%. Comparative Example 2 is an example with a total rolling rate of 50%. In Comparative Example 4, which uses titanium billet O with a high Al content, surface cracks and severe end cracks occurred during cold rolling after hot rolling. Therefore, in Comparative Example 4, intermediate annealing and final annealing were not performed. It should be noted that in Table 2, "T"... β "T" represents the β phase transition point, and the "Larsen-Miller parameter" is (T+273.15)×(Log). 10 The value of (t)+20). Additionally, in Table 2, "Mode A" indicates a cold rolling mode where the rolling rate of the first cold rolling pass is set to 75%, and the rolling rate of the second cold rolling pass is set to 50%. In Table 2, "Mode B" indicates a cold rolling mode where the rolling rate of the first cold rolling pass is set to 50%, the rolling rate of the second cold rolling pass is set to 50%, and the rolling rate of the third cold rolling pass is set to 60%.

[0171] [Table 2]

[0172]

[0173] 2. Evaluation

[0174] The titanium alloy plates involved in the various inventive examples, reference examples, and comparative examples were evaluated in the following aspects.

[0175] 2.1.Chemical composition

[0176] The chemical composition of the titanium alloy plates involved in each of the invention examples, reference examples, and comparative examples was determined using the same method as that used for determining the chemical composition of hot-rolled plates.

[0177] 2.2. Location of Aggregation Peak

[0178] The observation surfaces of the titanium alloy plates involved in each of the invention examples, reference examples, and comparative examples were chemically polished, and crystal orientation analysis was performed using electron backscatter diffraction (EBSD) to obtain (0001) pole figures. Specifically, the L-section at the center of the width direction (TD) of each sample was chemically polished, and crystal orientation analysis based on EBSD was performed on a region of (total plate thickness) × 2 mm at intervals of 1 to 2 μm for approximately 2 to 10 fields of view to create (0001) pole figures. The data on the aggregation peak positions of specific orientations in the (0001) pole figures were calculated using OIMAnalysis software manufactured by TSL Solutions, using texture analysis of inverse pole figures using the spherical harmonic function method (expansion factor = 16, Gaussian half-width = 5°).

[0179] 2.3. Area fraction of the α phase and area fraction of the α phase with a circular equivalent diameter of 1 μm or more

[0180] The area fraction of the α phase and the area fraction of the α phase with a circular equivalent diameter of 1 μm or more were determined using the following method. A section of a titanium alloy sheet cut perpendicular to the width direction (TD) at its center was chemically polished. Crystal orientation analysis based on the EBSD method was performed on a region of 200 μm (total sheet thickness) of this section, with a gradient of 1–5 μm, across approximately 2–5 fields of view. The area fraction of the α phase relative to the area of ​​this region was taken as the area fraction of the α phase. Furthermore, the circular equivalent diameter of the α phase observed in the aforementioned fields of view was calculated (area A = π × (grain size D / 2)). 2 The total area of ​​the α phase with a circular equivalent diameter of 1 μm or more relative to the area of ​​the aforementioned region is taken as the area ratio of the α phase with a circular equivalent diameter of 1 μm or more. The grains of the α phase with a circular equivalent diameter of 1 μm or more contain the banded structure described later.

[0181] 2.4. Aspect ratio and area ratio of banded tissue

[0182] A cross-section of a titanium alloy plate cut perpendicular to the width direction (TD) at its center was chemically polished. Crystal orientation analysis based on EBSD was performed on a 200 μm region (total plate thickness) of this cross-section, with a gradient of 1–5 μm across approximately 2–5 fields of view. Based on the EBSD crystal orientation analysis results, the aspect ratio of each grain was calculated. The area fraction of grains with an aspect ratio greater than 3.0 was calculated as the area fraction of the banded structure.

[0183] 2.5. Average grain diameter of equiaxed structures

[0184] For the average grain diameter of equiaxed structures, the round equivalent grain size is calculated based on the grain area measured by EBSD for equiaxed structures (area A = π × (grain diameter D / 2)). 2 The average value of this number of references is taken as the average grain diameter of the equiaxed structure.

[0185] 2.6.02% Yield Strength

[0186] The 0.2% yield strength of the titanium alloy plates involved in each of the inventive examples, reference examples and comparative examples at 25°C was determined according to JIS Z 2241:2011.

[0187] 2.7. Average plate thickness (dave)

[0188] The average plate thickness dave of the titanium alloy plates involved in each of the inventive examples, reference examples, and comparative examples was determined by the following method. For each manufactured titanium alloy plate, the plate thickness was measured at five or more locations at intervals of more than 1 m along the length direction, at the center position in the width direction and at a distance of 1 / 4 of the plate width from each end in the width direction, using X-rays, a micrometer, or a vernier caliper. The average value of the measured plate thicknesses was taken as the average plate thickness dave.

[0189] 2.8. Plate thickness dimensional accuracy a

[0190] The thickness dimensional accuracy a of the titanium alloy plate involved in each of the inventive examples, reference examples and comparative examples uses the plate thickness d actually measured by the above method and the above average plate thickness dave, and the maximum value of a' calculated by the following formula (101) is taken as the dimensional accuracy a.

[0191] a'=(d-dave) / dave×100...Formula (101)

[0192] 3. Results

[0193] The evaluation results are shown in Table 3. It should be noted that "θ" in Table 3 refers to the angle between the direction of the peak representing aggregation degree and the plate thickness direction in the (0001) pole figure based on the plate thickness direction, calculated through texture analysis using the spherical harmonic function method for the inverse pole figure of electron backscatter diffraction with an expansion factor of 16 and a Gaussian half-width of 5°. Additionally, "θ2" in Table 3 refers to the angle between the direction of the peak representing aggregation degree originating from the center of the pole figure and the plate width direction in the (0001) pole figure based on the plate thickness direction, calculated through texture analysis using the spherical harmonic function method for the inverse pole figure of electron backscatter diffraction with an expansion factor of 16 and a Gaussian half-width of 5°.

[0194] [Table 3]

[0195]

[0196] With regard to any one of the Invention Examples 1 to 30, the Reference Examples, and the Comparative Examples 1 to 4, the contents of Al, Fe, Si, Ni, Cr, Mn, V, O, N, and C in the manufactured titanium alloy plate are equal to the contents of the aforementioned elements contained in the respective hot-rolled plates used.

[0197] Regarding Examples 1 to 20 of the invention, (0001) the angle θ between the direction of the peak representing the degree of aggregation in the pole figure and the plate thickness direction is 65° or less, and the angle θ2 between the direction of the aforementioned peak representing the degree of aggregation and the width direction is 0°. Furthermore, the average grain diameter of the equiaxed structure is 0.1 μm or more and 20.0 μm or less, and the area fraction of the banded structure is 10% or less. The area fraction of the α phase is 80% or more, and the area fraction of the α phase with a circular equivalent diameter of 1 μm or more is greater than 53%. The average plate thickness is 1.0 to 1.2 mm, and the dimensional accuracy is 0.8 to 4.5%. Additionally, the 0.2% yield strength in the length direction at 25°C is 700 MPa or more, and the ratio of the 0.2% yield strength σT in the width direction at 25°C to the 0.2% yield strength σL in the length direction at 25°C, i.e., the conditional yield strength ratio σT / σL, is 1.05 or more and 1.18 or less.

[0198] Regarding Invention Example 21, (0001) the angle θ between the direction of the peak representing the degree of aggregation in the pole figure and the plate thickness direction is 49°, and the angle θ2 between the direction of the aforementioned peak representing the degree of aggregation and the width direction is 0°. Furthermore, the average grain diameter of the equiaxed structure is 1.8 μm, and the area fraction of the banded structure is 5.0%. The area fraction of the α phase is 88% or more, and the area fraction of the α phase with a circular equivalent diameter of 1 μm or more is 88%. The average plate thickness is 0.9 mm, and the dimensional accuracy is 2.0%. Additionally, the 0.2% yield strength at 25°C is 805 MPa, and the conditional yield strength ratio σT / σL is 1.12.

[0199] Regarding Invention Examples 22 and 23, (0001) the angle θ between the direction of the peak representing the degree of aggregation and the plate thickness direction in the pole figure is 50°, and the angle θ2 between the direction of the aforementioned peak representing the degree of aggregation and the width direction is 0°. Furthermore, the average grain diameter of the equiaxed structure in Invention Example 22 is 3.5 μm, and the average grain diameter of the equiaxed structure in Invention Example 23 is 10.5 μm. The area fractions of the banded structures are 15.0% and 20.0%, respectively. The area fraction of the α phase is 80% or more in both examples, and the area fraction of the α phase with a circular equivalent diameter of 1 μm or more is greater than 53%. The average plate thickness is 1.0 mm and 1.6 mm, and the dimensional accuracy is 2.0% and 2.5%, respectively. Additionally, the 0.2% yield strength at 25°C is 700 MPa or more, and the conditional yield strength ratio σT / σL is 1.11 and 1.15, respectively.

[0200] Regarding Examples 24-26 of the invention, (0001) the angle θ between the direction of the peak representing the degree of aggregation and the plate thickness direction in the pole figure is 65° or less, and the angle θ2 between the direction of the peak representing the degree of aggregation and the width direction is 0°. Furthermore, the average grain diameter of the equiaxed structure is 0.1 μm or more and 20.0 μm or less, and the area fraction of the banded structure is 10% or less. The area fraction of the α phase is 80% or more, and the area fraction of the α phase with a circular equivalent diameter of 1 μm or more is greater than 53%. The average plate thickness is 0.5 mm, and the dimensional accuracy is 1.0. Additionally, the 0.2% yield strength in the length direction at 25°C is 700 MPa or more, and the conditional yield strength ratio σT / σL is 1.05 or more and 1.18 or less.

[0201] Regarding Examples 27-29 of the invention, (0001) the angle θ between the direction of the peak representing the degree of aggregation and the plate thickness direction in the pole figure is 65° or less, and the angle θ2 between the direction of the peak representing the degree of aggregation and the width direction is 0°. Furthermore, the average grain diameter of the equiaxed structure is 0.1 μm or more and 20.0 μm or less, and the area fraction of the banded structure is 10% or less. The area fraction of the α phase is 80% or more, and the area fraction of the α phase with a circular equivalent diameter of 1 μm or more is greater than 53%. The average plate thickness is 0.4 mm, and the dimensional accuracy is 1.0% or less. Additionally, the 0.2% yield strength in the length direction is 700 MPa or more, and the conditional yield strength ratio σT / σL is 1.05 or more and 1.18 or less.

[0202] Regarding Invention Example 30, (0001) the angle θ between the direction of the peak representing the degree of aggregation in the pole figure and the plate thickness direction is 45°, and the angle θ2 between the direction of the aforementioned peak representing the degree of aggregation and the width direction is 0°. Furthermore, the average grain diameter of the equiaxed structure is 3.5 μm, and the area fraction of the banded structure is 5.0%. The area fraction of the α phase is 85% or more, and the area fraction of the α phase with a circular equivalent diameter of 1 μm or more is 80%. The average plate thickness is 1.0 mm, and the dimensional accuracy is 1.5%. Additionally, the 0.2% yield strength is 800 MPa, and the conditional yield strength ratio σT / σL is 1.14.

[0203] Regarding the reference example, in the (0001) pole figure, the angle θ between the direction of the peak representing the degree of aggregation and the plate thickness direction is greater than 65°. Therefore, the conditional yield strength ratio σT / σL is greater than 1.18, exhibiting strong anisotropy.

[0204] In Comparative Example 1, the average rolling rate per pass was as low as 20%, and the total rolling rate was also as low as 59%. Therefore, the angle θ between the direction of the peak representing the degree of aggregation in the (0001) pole figure and the plate thickness direction was greater than 65°. Therefore, the conditional yield strength ratio σT / σL was greater than 1.18, exhibiting strong anisotropy. In Comparative Example 2, although the average rolling rate per pass was 50%, intermediate annealing and cold rolling were not repeated, and the total rolling rate was as low as 50%. Therefore, the angle θ between the direction of the peak representing the degree of aggregation in the (0001) pole figure and the plate thickness direction was greater than 65°. Therefore, the conditional yield strength ratio σT / σL was greater than 1.18, exhibiting strong anisotropy. In Comparative Example 3, due to the low Al content, the 0.2% yield strength was as low as 598 MPa. In Comparative Example 4, as described above, surface cracks and severe end cracks occurred during cold rolling.

[0205] (Example 2)

[0206] A hot-rolled sheet with a thickness of 4 mm was manufactured in the same manner as in Example 1, having the chemical compositions shown in Table 1 (A, B, C, E, and M).

[0207] Next, the obtained hot-rolled sheet is subjected to a cold rolling process under the conditions shown in Table 4. Examples 31-37 in Table 2 involve multiple cold rolling passes with an average rolling rate of 5% or more per cold rolling pass to achieve the total rolling rate shown in Table 4. Examples 31-35 in Table 4 involve repeated cold rolling passes at a rolling temperature of 25°C and intermediate annealing under the conditions shown in Table 2 until the total rolling rate reaches 60-75% through cold cross-rolling. Intermediate annealing is performed at a temperature of 680-900°C for 60-28800 s, and final annealing is performed at a temperature of 650-930°C for 120-28800 s. The cross-rolling ratio in Examples 32-36 is 0.4-7.0. Example 36 involves repeated cold rolling passes at a rolling temperature of 400°C and intermediate annealing under the conditions shown in Table 4 until the total rolling rate reaches 75% through cold cross-rolling. Intermediate annealing is performed at 800°C for 120 seconds, and final annealing is performed at 850°C for 120 seconds. The cross-rolling ratio of Invention Example 36 is 13.0. Invention Example 37 is an example of cold cross-rolling by repeatedly performing multiple cold rolling passes at a rolling temperature of 25°C and intermediate annealing under the conditions shown in Table 4 until the total rolling yield reaches 62%. Intermediate annealing is performed at 800°C for 120 seconds, and final annealing is performed at 850°C for 120 seconds. The cross-rolling ratio of Invention Example 37 is 0.17. In this case, in order to achieve the rollable dimensions, the rolls are appropriately cut according to the width of the rolls, and rolling is performed in the cross directions simultaneously.

[0208] [Table 4]

[0209]

[0210] For the titanium alloy plates involved in each invention example, the same evaluation methods as in Example 1 were used for the same items as in Example 1. The evaluation results are shown in Table 5.

[0211] [Table 5]

[0212]

[0213] Regarding Examples 31-37 of the Invention, (0001) the angle θ between the direction of the peak representing the degree of aggregation in the pole figure and the plate thickness direction is 35° or less. Furthermore, the average grain diameter of the equiaxed structure is 0.1 μm or more and 10.0 μm or less, and the area fraction of the banded structure is 10% or less. The area fraction of the α phase is 80% or more, and the area fraction of the α phase with a circular equivalent diameter of 1 μm or more is greater than 53%. The average plate thickness is 1.0 to 1.8 mm, and the dimensional accuracy is 1.5% to 3.5% or less. Additionally, the 0.2% yield strength at 25°C is 700 MPa or more, and the ratio of the 0.2% yield strength σT in the width direction at 25°C to the 0.2% yield strength σL in the length direction at 25°C, i.e., the conditional yield strength ratio σT / σL, is 0.85 or more and 1.10 or less.

[0214] The preferred embodiments of this disclosure have been described in detail above, but this disclosure is not limited to the examples described. Obviously, those skilled in the art to which this disclosure pertains can conceive of various modifications or variations within the scope of the technical concept recorded in the claims, and these examples naturally also fall within the technical scope of this disclosure.

Claims

1. A titanium alloy plate, which contains, by mass % Al: Greater than 4.0% and less than 6.6% Fe: 0% or more and 2.3% or less V: Above 0% and below 4.5% Si: 0% or more and 0.60% or less C: 0% or more and less than 0.080% N: 0% or more and less than 0.050% O: Above 0% and below 0.40% Ni: 0% or more and less than 0.15% Cr: 0% or more and less than 0.25%, and Mn: 0% or more and less than 0.25%, The balance consists of Ti and impurities. The α-phase area fraction of the titanium alloy plate is over 80%. The area fraction of the α phase with a spherical equivalent diameter of 1 μm or more is greater than 53%. In the (0001) pole figure based on the plate thickness direction, for the inverse pole figure of electron backscatter diffraction using the spherical harmonic function method, the angle between the direction of the peak representing the aggregation degree and the plate thickness direction, calculated by texture analysis with an expansion coefficient of 16 and a Gaussian half-width of 5°, is less than 65°. The average thickness of the titanium alloy plate is less than 2.5 mm.

2. The titanium alloy plate according to claim 1, wherein the microstructure comprises an equiaxed structure with an aspect ratio of 3.0 or less and a banded structure with an aspect ratio greater than 3.0 and extending in the length direction. The average grain diameter of the equiaxed structure is greater than 0.1 μm and less than 20.0 μm. The area fraction of the banded tissue relative to the area of ​​the microstructure is 10.0% or less.

3. The titanium alloy plate according to claim 1 or 2, wherein it contains, by mass %, either Fe: 0.5% or more and 2.3% or less, or V: 2.5% or more and 4.5% or less.

4. The titanium alloy plate according to claim 3, wherein, by mass percent, it contains one or more elements selected from the group consisting of Ni: less than 0.15%, Cr: less than 0.25%, and Mn: less than 0.25%. When the titanium alloy plate contains Fe, the total amount of Fe, Ni, Cr, and Mn is 0.5% or more and 2.3% or less. When the titanium alloy plate contains V, the total amount of V, Ni, Cr and Mn is more than 2.5% and less than 4.5%.

5. The titanium alloy plate according to claim 1 or 2, wherein, The smaller of the 0.2% yield strength in the length direction or the 0.2% yield strength in the width direction at 25°C is above 700 MPa and below 1200 MPa.

6. The titanium alloy plate according to claim 3, wherein, The smaller of the 0.2% yield strength in the length direction or the 0.2% yield strength in the width direction at 25°C is above 700 MPa and below 1200 MPa.

7. The titanium alloy plate according to claim 4, wherein, The smaller of the 0.2% yield strength in the length direction or the 0.2% yield strength in the width direction at 25°C is above 700 MPa and below 1200 MPa.

8. The titanium alloy plate according to claim 1 or 2, wherein, In the (0001) pole figure based on the plate thickness direction, for the inverse pole figure of electron backscatter diffraction using the spherical harmonic function method, the angle between the direction of the peak representing the aggregation degree and the width direction is less than 10°, calculated by texture analysis with an expansion coefficient of 16 and a Gaussian half-width of 5°. The ratio of the 0.2% yield strength in the width direction to the 0.2% yield strength in the length direction is greater than 1.05 and less than 1.

18.

9. The titanium alloy plate according to claim 3, wherein, In the (0001) pole figure based on the plate thickness direction, for the inverse pole figure of electron backscatter diffraction using the spherical harmonic function method, the angle between the direction of the peak representing the aggregation degree and the width direction is less than 10°, calculated by texture analysis with an expansion coefficient of 16 and a Gaussian half-width of 5°. The ratio of the 0.2% yield strength in the width direction to the 0.2% yield strength in the length direction is greater than 1.05 and less than 1.

18.

10. The titanium alloy plate according to claim 4, wherein, In the (0001) pole figure based on the plate thickness direction, for the inverse pole figure of electron backscatter diffraction using the spherical harmonic function method, the angle between the direction of the peak representing the aggregation degree and the width direction is less than 10°, calculated by texture analysis with an expansion coefficient of 16 and a Gaussian half-width of 5°. The ratio of the 0.2% yield strength in the width direction to the 0.2% yield strength in the length direction is greater than 1.05 and less than 1.

18.

11. The titanium alloy plate according to claim 5, wherein, In the (0001) pole figure based on the plate thickness direction, for the inverse pole figure of electron backscatter diffraction using the spherical harmonic function method, the angle between the direction of the peak representing the aggregation degree and the width direction is less than 10°, calculated by texture analysis with an expansion coefficient of 16 and a Gaussian half-width of 5°. The ratio of the 0.2% yield strength in the width direction to the 0.2% yield strength in the length direction is greater than 1.05 and less than 1.

18.

12. The titanium alloy plate according to claim 6 or 7, wherein, In the (0001) pole figure based on the plate thickness direction, for the inverse pole figure of electron backscatter diffraction using the spherical harmonic function method, the angle between the direction of the peak representing the aggregation degree and the width direction is less than 10°, calculated by texture analysis with an expansion coefficient of 16 and a Gaussian half-width of 5°. The ratio of the 0.2% yield strength in the width direction to the 0.2% yield strength in the length direction is greater than 1.05 and less than 1.

18.

13. The titanium alloy plate according to claim 1 or 2, wherein, In the (0001) pole figure based on the plate thickness direction, for the inverse pole figure of electron backscatter diffraction using the spherical harmonic function method, the angle between the direction of the peak representing the aggregation degree and the plate thickness direction, calculated by texture analysis with an expansion coefficient of 16 and a Gaussian half-width of 5°, is less than 35°. The ratio of the 0.2% yield strength in the width direction to the 0.2% yield strength in the length direction is greater than 0.85 and less than 1.

10.

14. The titanium alloy plate according to claim 3, wherein, In the (0001) pole figure based on the plate thickness direction, for the inverse pole figure of electron backscatter diffraction using the spherical harmonic function method, the angle between the direction of the peak representing the aggregation degree and the plate thickness direction, calculated by texture analysis with an expansion coefficient of 16 and a Gaussian half-width of 5°, is less than 35°. The ratio of the 0.2% yield strength in the width direction to the 0.2% yield strength in the length direction is greater than 0.85 and less than 1.

10.

15. The titanium alloy plate according to claim 4, wherein, In the (0001) pole figure based on the plate thickness direction, for the inverse pole figure of electron backscatter diffraction using the spherical harmonic function method, the angle between the direction of the peak representing the aggregation degree and the plate thickness direction, calculated by texture analysis with an expansion coefficient of 16 and a Gaussian half-width of 5°, is less than 35°. The ratio of the 0.2% yield strength in the width direction to the 0.2% yield strength in the length direction is greater than 0.85 and less than 1.

10.

16. The titanium alloy plate according to claim 5, wherein, In the (0001) pole figure based on the plate thickness direction, for the inverse pole figure of electron backscatter diffraction using the spherical harmonic function method, the angle between the direction of the peak representing the aggregation degree and the plate thickness direction, calculated by texture analysis with an expansion coefficient of 16 and a Gaussian half-width of 5°, is less than 35°. The ratio of the 0.2% yield strength in the width direction to the 0.2% yield strength in the length direction is greater than 0.85 and less than 1.

10.

17. The titanium alloy plate according to claim 6 or 7, wherein, In the (0001) pole figure based on the plate thickness direction, for the inverse pole figure of electron backscatter diffraction using the spherical harmonic function method, the angle between the direction of the peak representing the aggregation degree and the plate thickness direction, calculated by texture analysis with an expansion coefficient of 16 and a Gaussian half-width of 5°, is less than 35°. The ratio of the 0.2% yield strength in the width direction to the 0.2% yield strength in the length direction is greater than 0.85 and less than 1.

10.

18. The titanium alloy plate according to claim 1 or 2, wherein, The dimensional accuracy of the plate thickness is less than 5.0% relative to the average plate thickness.

19. The titanium alloy plate according to claim 3, wherein, The dimensional accuracy of the plate thickness is less than 5.0% relative to the average plate thickness.

20. The titanium alloy plate according to claim 4, wherein, The dimensional accuracy of the plate thickness is less than 5.0% relative to the average plate thickness.

21. The titanium alloy plate according to claim 5, wherein, The dimensional accuracy of the plate thickness is less than 5.0% relative to the average plate thickness.

22. The titanium alloy plate according to claim 6 or 7, wherein, The dimensional accuracy of the plate thickness is less than 5.0% relative to the average plate thickness.

23. The titanium alloy plate according to claim 8, wherein, The dimensional accuracy of the plate thickness is less than 5.0% relative to the average plate thickness.

24. The titanium alloy plate according to any one of claims 9 to 11, wherein, The dimensional accuracy of the plate thickness is less than 5.0% relative to the average plate thickness.

25. The titanium alloy plate according to claim 12, wherein, The dimensional accuracy of the plate thickness is less than 5.0% relative to the average plate thickness.

26. The titanium alloy plate according to claim 13, wherein, The dimensional accuracy of the plate thickness is less than 5.0% relative to the average plate thickness.

27. The titanium alloy plate according to any one of claims 14 to 16, wherein, The dimensional accuracy of the plate thickness is less than 5.0% relative to the average plate thickness.

28. The titanium alloy plate according to claim 17, wherein, The dimensional accuracy of the plate thickness is less than 5.0% relative to the average plate thickness.

29. A titanium alloy coil, which contains, by weight % Al: Greater than 4.0% and less than 6.6% Fe: 0% or more and 2.3% or less V: Above 0% and below 4.5% Si: 0% or more and 0.60% or less C: 0% or more and less than 0.080% N: 0% or more and less than 0.050% O: Above 0% and below 0.40% Ni: 0% or more and less than 0.15% Cr: 0% or more and less than 0.25%, and Mn: 0% or more and less than 0.25%, The balance consists of Ti and impurities. The area fraction of the α phase in the titanium alloy coil is over 80%. The area fraction of the α phase with a spherical equivalent diameter of 1 μm or more is greater than 53%. In the (0001) pole figure based on the plate thickness direction, for the inverse pole figure of electron backscatter diffraction using the spherical harmonic function method, the angle between the direction of the peak representing the aggregation degree and the plate thickness direction, calculated by texture analysis with an expansion coefficient of 16 and a Gaussian half-width of 5°, is less than 65°. The average thickness of the titanium alloy coil is less than 2.5 mm.

30. A method for manufacturing a titanium alloy plate according to any one of claims 1 to 28, comprising the following steps: A hot rolling process in which a titanium alloy slab is heated to a temperature range of 900 to 1,000°C or higher, and then hot-rolled from the temperature range of the β phase to a total reduction of 80% or more β after which hot rolling is performed from the temperature range of the β phase to a total reduction of 80% or more The cold rolling process involves performing at least one cold rolling pass along the length of the hot-rolled titanium billet. The titanium billet, by mass percent, contains Al: greater than 4.0% and less than 6.6%, Fe: greater than 0% and less than 2.3%, V: greater than 0% and less than 4.5%, Si: greater than 0% and less than 0.60%, C: greater than 0% and less than 0.080%, N: greater than 0% and less than 0.050%, O: greater than 0% and less than 0.40%, Ni: greater than 0% and less than 0.15%, Cr: greater than 0% and less than 0.25%, and Mn: greater than 0% and less than 0.25%, with the balance being Ti and impurities. The final annealing process involves annealing the titanium billet after the last cold rolling pass. In the cold rolling process, the average rolling rate of each cold rolling pass is greater than 30%, and the total rolling rate is greater than 60%.

31. The method for manufacturing a titanium alloy plate according to claim 30, wherein, When the cold rolling process is performed by a plurality of the cold rolling passes, an intermediate annealing process for annealing the titanium material between the plurality of the cold rolling passes is included, and annealing conditions of the intermediate annealing process and the final annealing process are conditions in which an annealing temperature is 600°C or higher and (T β -50) °C or lower, and the annealing temperature T (°C) and a holding time t (sec) at the annealing temperature satisfy the following equation (1), -50) °C or lower, and the annealing temperature T (°C) and a holding time t (sec) at the annealing temperature satisfy the following equation (1), 22000≤(T+273.15)×(Log 10 (t) + 20) ≤ 27000 … Equation (1) In the formula, T β The β phase transition point (°C).

32. A method for manufacturing a titanium alloy plate according to any one of claims 1 to 28, comprising the following steps: The cold cross-rolling process involves cold rolling passes in both the length and width directions of a titanium billet. The titanium billet, by mass percent, contains Al: greater than 4.0% and less than 6.6%, Fe: greater than 0% and less than 2.3%, V: greater than 0% and less than 4.5%, Si: greater than 0% and less than 0.60%, C: greater than 0% and less than 0.080%, N: greater than 0% and less than 0.050%, O: greater than 0% and less than 0.40%, Ni: greater than 0% and less than 0.15%, Cr: greater than 0% and less than 0.25%, and Mn: greater than 0% and less than 0.25%, with the balance being Ti and impurities. The final annealing process involves annealing the titanium billet after the cold cross-rolling process. The total rolling rate in the cold cross-rolling process is over 60%. The ratio of the rolling rate in the length direction to the rolling rate in the width direction, i.e., the cross rolling ratio, is 0.05 or more and 20.00 or less.

33. The method for manufacturing a titanium alloy plate according to claim 32, wherein, When the cold cross-rolling process performs multiple cold rolling passes, an intermediate annealing process for annealing the titanium billet is included between the multiple cold rolling passes. The annealing conditions for the intermediate annealing process and the final annealing process are as follows: the annealing temperature is above 600°C and (T β The annealing temperature T (°C) is below -50°C, and the holding time t (seconds) at the annealing temperature satisfies the following formula (1). 22000≤(T+273.15)×(Log 10 (t) + 20) ≤ 27000 … Equation (1) In the formula, T β The β phase transition point (°C).

34. A method for manufacturing the titanium alloy coil according to claim 29, comprising the following steps: The cold rolling process involves performing at least one cold rolling pass along the length of the titanium billet. The titanium billet contains, by mass%, Al: greater than 4.0% and less than 6.6%, Fe: greater than 0% and less than 2.3%, V: greater than 0% and less than 4.5%, Si: greater than 0% and less than 0.60%, C: greater than 0% and less than 0.080%, N: greater than 0% and less than 0.050%, O: greater than 0% and less than 0.40%, Ni: greater than 0% and less than 0.15%, Cr: greater than 0% and less than 0.25%, and Mn: greater than 0% and less than 0.25%, with the balance being Ti and impurities. The final annealing process involves annealing the titanium billet after the last cold rolling pass. In the cold rolling process, the average rolling rate of each cold rolling pass is greater than 30%, and the total rolling rate is greater than 60%.

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