JP2021080489A - Titanium alloy thin plate and manufacturing method of titanium alloy thin plate - Google Patents

Abstract

To provide a titanium alloy thin plate having high strength and small anisotropy and a manufacturing method of the titanium alloy thin plate.SOLUTION: A titanium alloy thin plate according to the present invention has a texture that contains Al: 4.0 to 6.6 mass%, and in a (0001) pole view from a thickness direction, an angle between a direction showing a peak of integration degree calculated by a texture analysis of the inverse pole diagram using a spherical harmonic function method of the backscattered electron diffraction (EBSD) method (expansion index=16, Gauss half width value=5°) and a plate thickness direction is 30°or smaller, and, the maximum degree of integration of a (0001) plane is 4 or larger, in which a ratio of 0.2% proof stress in a plate width direction to 0.2% proof stress in a plate longer direction is 0.95 or larger and smaller than 1.05.SELECTED DRAWING: Figure 1

Description

The present invention relates to a titanium alloy thin plate and a method for producing a titanium alloy thin plate.

Titanium is a material that is lightweight, has high strength, and has excellent corrosion resistance, and is a material that can be applied to the aircraft field from the viewpoint of weight reduction and improvement of fuel efficiency. Therefore, titanium alloys are being actively developed according to the characteristics required for each component of the aircraft.

For example, Patent Document 1 discloses an α + β type titanium alloy wire rod composed of Fe of 1.4% or more and less than 2.1%, Al of 4.4% or more and less than 5.5%, residual titanium, and impurities. ..

Patent Document 2 discloses an α + β type titanium alloy rod composed of Fe of 0.5% or more and less than 1.4%, Al of 4.4% or more and less than 5.5%, residual titanium, and impurities.

Patent Document 3 describes a method for producing a thin plate in which one or a plurality of plate-shaped core materials are covered with a spacer material and a cover material to form a packed rolled material, and the packed material is rolled to reduce the thickness of the core material. The Ti-6Al-4V alloy thin plate by pack rolling is characterized in that the plate thickness of the cover material is set so that the ratio of the core material to the pack material is at least 0.25 or more for each initial plate thickness. The manufacturing method is disclosed.

Patent Document 4 describes a method for producing a thin plate in which one or a plurality of plate-shaped core materials are covered with a spacer material and a cover material to form a pack material, and the pack material is rolled to reduce the thickness of the core material. , Manufacture of Ti-6Al-4V alloy thin plate by pack rolling, characterized in that the rolling ratio per pass is 15% or more for rolling in which the rolling reduction ratio of the plate thickness before and after the thickness reduction of the pack material is 3 or more. The method is disclosed.

Patent Document 5 describes a hot-rolled annealed sheet of a titanium alloy composed of Al: 2.5 to 3.5%, V: 2.0 to 3.0%, the balance Ti and ordinary impurities in% by weight. A method for producing a titanium alloy sheet is disclosed, which comprises cold rolling in the same direction as the inter-rolling direction at a total rolling ratio of 67% or more, and then annealing at a temperature between 650 and 900 ° C.

In Patent Document 6, intermediate annealing performed after cold rolling in the manufacturing process of an α + β type titanium alloy cold-rolled plate is annealed in a temperature range below the β transformation point at an annealing temperature: [β transformation point -25 ° C] or higher. Time: 0.5 to 4 hours, cooling rate after heating and holding: 0.5 to 5 ° C./sec, temperature interval for cooling at the above cooling rate: 300 ° C. or less. , A method for producing an α + β type titanium alloy thin plate is disclosed.

Patent Document 7 states that at least one of the total rate solid-soluble β-stabilizing elements is 2.0 to 4.5% by mass in Mo equivalent, and at least one of the eutectoid β-stabilizing elements is 0 in Fe equivalent. An α + β type titanium alloy containing 3 to 2.0% by mass, at least one α-stabilizing element in an Al equivalent of more than 3.0% by mass and 5.5% by mass or less, and the balance being Ti and unavoidable impurities. In a thin plate, the average particle size of the α phase is 5.0 μm or less, the maximum particle size of the α phase is 10.0 μm or less, the average aspect ratio of the α phase is 2.0 or less, and α. An α + β type titanium alloy thin plate characterized by having a maximum phase ratio of 5.0 or less is disclosed.

Patent Document 8 describes an α + β type titanium alloy hot-rolled plate, wherein (a) the normal direction (plate thickness direction) of the hot-rolled plate is ND, the hot-rolling direction is RD, and the hot-rolled plate width direction. Let TD be the normal direction of the (0001) plane of the α phase, the c-axis orientation be the c-axis orientation, the angle between the c-axis orientation and ND be θ, and the angle between the c-axis orientation and the plane containing ND be the plane containing ND and TD. Let Φ be, and (b1) θ is 0 degrees or more and 30 degrees or less, and Φ is the highest among the (0002) reflection relative intensities of X-rays by crystal grains that enter the entire circumference (-180 degrees to 180 degrees). Let XND be the strong intensity, and the strongest intensity among the (0002) reflection relative intensities of X-rays by crystal grains with (b2) θ of 80 degrees or more and less than 100 degrees and Φ of ± 10 degrees is XTD. (C) An α + β type titanium alloy plate characterized by having an XTD / XND of 5.0 or more and having excellent cold rolling properties and cold handling is disclosed.

Patent Document 9 contains Fe: 0.8 to 1.5%, Al: 4.8 to 5.5%, N: 0.030% or less in mass%, and contains O (mass). %) Is [O], the content of N (% by mass) is [N], and Q (%) = 0.14 to 0. Defined by Q (%) = [O] +2.77 · [N]. It is a high-strength α + β type titanium alloy hot-rolled plate containing O and N in a range satisfying 38, and the balance is Ti and unavoidable impurities. The inter-rolling direction is RD, the hot-rolled plate width direction is TD, the normal direction of the (0001) plane of the α phase is the c-axis orientation, the angle formed by the c-axis orientation with ND is θ, and the c-axis orientation and ND are set. The angle formed by the surface containing ND and the surface containing TD is φ, and it depends on the crystal grains in which (b1) θ is 0 degrees or more and 30 degrees or less and φ is in the entire circumference (-180 degrees to 180 degrees). Of the (0002) reflected relative intensities of X-rays, the strongest intensity is XND, and (b2) θ of X-rays (b2) by crystal grains with θ of 80 degrees or more and less than 100 degrees and φ of ± 10 degrees. 0002) Among the relative reflection strengths, the strongest strength is XTD, and (c) a high-strength α + β-type titanium alloy plate having excellent cold coil handling characteristics, characterized in that XTD / XND is 4.0 or more. Is disclosed.

According to Patent Document 10, a thin plate of α + β type titanium alloy manufactured by rolling or forging is subjected to cold rolling with a rolling reduction ratio of 20% or more and then annealed at a temperature of 700 ° C. or higher and β transformation point or lower to obtain fineness. A method for producing an α + β type titanium alloy thin plate, which comprises obtaining a plate having an axial α structure, is disclosed.

Non-Patent Document 1 discloses an α + β titanium alloy thin plate having anisotropy in strength in a rolling direction and a direction perpendicular to the rolling direction.

Non-Patent Document 2 discloses an α + β titanium alloy thin plate in which hot rolling is performed at a temperature higher than the β transformation point to reduce the anisotropy of the strength in the rolling direction and the direction perpendicular to the rolling direction.

Japanese Unexamined Patent Publication No. 7-62474 Japanese Unexamined Patent Publication No. 7-70676 Japanese Unexamined Patent Publication No. 2001-300603 Japanese Unexamined Patent Publication No. 2001-300604 Japanese Unexamined Patent Publication No. 61-147864 Japanese Unexamined Patent Publication No. 1-127653 Japanese Unexamined Patent Publication No. 2013-227618 International Publication No. 2012/115242 International Publication No. 2012/115243 Japanese Unexamined Patent Publication No. 62-33750

Kobe Steel Technical Report / Vol. 59, No. 1 (2009), P.M. 81-84 Kobe Steel Technical Report / Vol. 60, No. 2 (2010), P.M. 50-54

By the way, titanium material used for a member requiring higher strength among the constituent members of an aircraft contains a large amount of Al, but has a large deformation resistance in hot rolling or cold rolling. The allowable load may be exceeded. Therefore, it is difficult to produce a high-strength titanium alloy thin plate by a conventional hot rolling method or a cold rolling method, and it is further difficult to produce a titanium alloy thin plate having a small anisotropy.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a titanium alloy thin plate having high strength and low anisotropy and a method for producing the titanium alloy thin plate. To do.

The present inventors have determined that the titanium alloy thin plate contains a predetermined amount of Al, and the peak of the degree of accumulation of crystal grains is predetermined with respect to the final rolled plate width direction in the (0001) pole diagram from the plate thickness direction. It was found that it exists within the angle of, and by increasing the maximum degree of integration, it has high strength and the anisotropy becomes small. Then, they have found a method for coldly cross-rolling a titanium alloy thin plate capable of achieving such a chemical composition and texture at the same time, and have arrived at the present invention.

The gist of the present invention completed based on the above findings is as follows.
(1) Al: contains 4.0 to 6.6% by mass,
Calculated by Texture analysis (expansion index = 16, Gaussian half width = 5 °) of the inverse pole diagram using the spherical harmonics method of backscattered electron diffraction (EBSD) method in the (0001) pole diagram from the plate thickness direction. It has an aggregate structure in which the angle between the direction showing the peak of the degree of integration and the thickness direction is 30 ° or less and the maximum degree of integration of the (0001) plane is 4 or more.
A titanium alloy thin plate in which the ratio of 0.2% proof stress in the plate width direction to 0.2% proof stress in the plate longitudinal direction is 0.95 or more and less than 1.05.
(2) It has a microstructure consisting of an equiaxed structure having an aspect ratio of 3.0 or less and a band structure having an aspect ratio of more than 3.0 and extending in the longitudinal direction of the plate.
The average particle size of the equiaxed structure is 0.1 μm or more and 10 μm or less.
The titanium alloy thin plate according to (1), wherein the area ratio of the band structure to the area of the microstructure is 10.0% or less.
(3) Furthermore, in% by mass,
Fe: 0.5 to 2.3% or V: 2.5 to 4.5%,
Si: 0-0.60%,
Containing, in addition
C: less than 0.08%,
N: 0.05% or less, and O: 0.40% or less,
The titanium alloy thin plate according to (1) or (2), which is limited to the above and the balance is composed of Ti and impurities.
(4) Instead of the Fe or a part of the V, by mass%,
Ni: less than 0.15%,
Cr: less than 0.25% and
The titanium alloy thin plate according to (3), which contains one or more selected from the group consisting of Mn: less than 0.25%.
(5) In any one of (1) to (4), wherein the average plate thickness is 2.5 mm or less and the dimensional accuracy of the plate thickness is 5.0% or less with respect to the average plate thickness. The titanium alloy thin plate described.
(6) In the tensile test, the r value, which is the ratio of _{the logarithmic strain ε t in} the plate thickness direction to the logarithmic strain ε _{W in} the plate width direction when the elongation in the plate longitudinal direction becomes 3%, is 2.0 or more and 10 The titanium alloy thin plate according to any one of (1) to (5), which is 0.0 or less.
(7) The titanium alloy thin plate according to any one of (1) to (6), which has a 0.2% proof stress at 25 ° C. of 700 MPa or more.
(8) The method for producing a titanium alloy thin plate according to any one of (1) to (7).
A cold cross rolling step of rolling a titanium material containing Al: 4.0 to 6.6% by mass in the longitudinal direction and the width direction of the titanium material, and
It has a final annealing step of annealing the titanium material after the cold cloth rolling step.
The total rolling ratio in the cold cross rolling step is 60% or more.
A method for producing a titanium alloy thin plate, wherein the cross-rolling ratio, which is the ratio of the rolling ratio in the longitudinal direction to the rolling ratio in the width direction, is 0.05 or more and 20.0 or less.
(9) The cold cross-rolling step includes an intermediate annealing step of annealing the titanium material between the plurality of cold rolling passes when a plurality of cold rolling passes are performed.
The annealing conditions in the intermediate annealing step and the final annealing step are as follows.
The annealing temperature is 600 ° C or higher (T _β- 50) ° C or lower, and
The method for producing a titanium alloy thin plate according to (8), wherein the annealing temperature T (° C.) and the holding time t (seconds) at the annealing temperature are conditions that satisfy the following formula (1).
22000 ≤ (T + 273.15) x (Log ₁₀ (t) + 20) ≤ 27000 ... Equation (1)
Here, T _β is the β transformation point (° C.).

As described above, according to the present invention, it is possible to provide a titanium alloy thin plate having high strength and low anisotropy and a method for producing the titanium alloy thin plate.

It is an example of the (0001) pole figure from the thickness direction (ND) of the titanium alloy thin plate which concerns on one Embodiment of this invention. It is a micrograph which shows an example of the band structure observed on the surface of a titanium alloy thin plate. It is a schematic diagram for demonstrating the measuring method of the average plate thickness.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The description will be given in the following order.
1. 1. Titanium alloy thin plate 2. Manufacturing method of titanium alloy sheet

<1. Titanium alloy thin plate ＞
First, the titanium alloy thin plate according to the present embodiment will be described with reference to FIGS. 1 to 3. FIG. 1 is an example of a (0001) pole figure from the thickness direction (ND) of the titanium alloy thin plate according to the present embodiment. FIG. 2 is a photomicrograph showing an example of a band structure observed on the surface of a titanium alloy thin plate. FIG. 3 is a schematic diagram for explaining a method of measuring the average plate thickness. Although the details will be described later, the titanium alloy sheet according to the present embodiment can be manufactured by a method including a cold rolling step.

(1.1. Chemical composition)
First, the chemical components contained in the titanium alloy thin plate according to the present embodiment will be described. The titanium alloy thin plate according to the present embodiment contains Al: 4.0 to 6.6% by mass. In the following, unless otherwise specified in the description of the chemical composition, the notation "%" shall represent "mass%".

Al is an α-phase stabilizing element and is an element having a high solid solution strengthening ability. As the Al content increases, the tensile strength at room temperature (25 ° C.) increases. When the Al content is 4.0% or more, high tensile strength can be obtained. Further, the hot-rolled plate before cold rolling can maintain high cold rollability. The Al content is preferably 4.5% or more. On the other hand, when the Al content exceeds 6.6%, the cold rollability of the hot-rolled sheet before cold rolling is remarkably lowered, and the region where Al is excessively dissolved due to solidification segregation or the like is locally localized. And Al is regularized. The region where Al is regularized reduces the impact toughness of the titanium alloy sheet. Therefore, the Al content is 6.6% or less.

The titanium alloy thin plate according to the present embodiment contains Fe: 0.5 to 2.3%, V: 2.5 to 4.5%, or Si: 0 to 0.60% as an optional element. Further, it is preferable that C: less than 0.08%, N: 0.05% or less, and O: 0.40% or less. Each element will be described below. Since Fe, V, Si, C, N and O are not essential in the titanium alloy thin plate, the lower limit of their contents is 0%.

Fe is a β-phase stabilizing element. Since Fe is an element having a high solid solution strengthening ability, increasing the Fe content increases the tensile strength at room temperature. Further, since the β phase has higher workability than the α phase, increasing the Fe content improves the workability of the titanium alloy thin plate. In order to obtain a desired tensile strength while maintaining a β phase having good workability at room temperature, the lower limit of the Fe content is preferably 0.5%. The lower limit of the Fe content is more preferably 0.7%. On the other hand, since Fe is an element that is very easily solidified and segregated, if Fe is excessively contained, Fe segregates locally, and the characteristics vary between the segregated portion and the non-segregated portion. There is. Further, if Fe is excessively contained in the titanium alloy thin plate, the fatigue strength may decrease. Therefore, the upper limit of the Fe content is preferably 2.3%. The upper limit of the Fe content is more preferably 2.1%. Fe is cheaper than β-phase stabilizing elements such as V or Si.

Fe that can be contained in the titanium alloy thin plate according to the present embodiment may be replaced with V. V is a total solid solution type β-phase stabilizing element, and is an element having a solid solution strengthening ability. In order to obtain the solid solution strengthening ability equivalent to that of Fe described above, the lower limit of the V content is preferably 2.5%. The lower limit of the V content is more preferably 3.0%. Substituting Fe for V increases the cost, but since V is less likely to segregate than Fe, variations in characteristics due to segregation are suppressed. As a result, it becomes easy to obtain stable characteristics in the plate longitudinal direction and the plate width direction of the titanium alloy thin plate. In order to suppress variations in characteristics due to segregation of V, the upper limit of the V content is preferably 4.5%. As described above, since V is less likely to segregate than Fe, it is preferable that V is contained in the titanium material when manufacturing a large ingot.

Si is a β phase stabilizing element, but it also dissolves in the α phase and exhibits a high solid solution strengthening ability. As described above, Fe may segregate when it is contained in the titanium alloy thin plate in an amount of more than 2.3%. Therefore, Si may be contained in the titanium alloy thin plate to increase the strength of the titanium alloy thin plate, if necessary. Further, Si tends to segregate in the opposite direction to O described below, and it is difficult to solidify and segregate as much as O. Therefore, by containing an appropriate amount of Si and O in the titanium alloy thin plate, high fatigue strength and tensile strength are achieved. Can be expected to be compatible. On the other hand, if the Si content is high, an intermetallic compound of Si called VDD may be formed, and the fatigue strength of the titanium alloy thin plate may decrease. When the Si content is 0.60% or less, the formation of coarse silicide is suppressed and the decrease in fatigue strength is suppressed. Therefore, the upper limit of the Si content is preferably 0.60%. The upper limit of the Si content is more preferably 0.50%.

If C is contained in a large amount in the titanium alloy thin plate, the ductility or workability of the titanium alloy thin plate may be lowered. Therefore, the C content is preferably less than 0.08%. C is an impurity that is unavoidably mixed, and its substantial content is usually 0.0001% or more. The C content is more preferably 0.06% or less.

Similar to C, when N is contained in a large amount in the titanium alloy thin plate, the ductility or processability of the titanium alloy thin plate may be lowered. Therefore, the upper limit of the N content is preferably 0.05%. In addition, N is an impurity unavoidably mixed, and the substantial content is usually 0.0001% or more. The N content is more preferably 0.04% or less.

Similar to C, when O is contained in a large amount in the titanium alloy thin plate, the ductility or processability of the titanium alloy thin plate may be lowered. Therefore, the upper limit of the O content is preferably 0.40%, more preferably 0.30%. Note that O is an impurity that is inevitably mixed in, and the substantial content is usually 0.01% or more.

When the titanium alloy thin plate according to the present embodiment contains either Fe: 0.5 to 2.3% or V: 2.5 to 4.5%, replace it with a part of Fe or V. It is preferable to contain one or more selected from the group consisting of Ni: less than 0.15%, Cr: less than 0.25%, and Mn: less than 0.25%. Hereinafter, Ni, Cr, and Mn will be described. Since Ni, Cr and Mn are not essential in the titanium alloy thin plate, the lower limit of their contents is 0%.

Like Fe or V, Ni is an element that improves tensile strength and workability. However, when the Ni content is 0.15% or more, the intermetallic compound Ti ₂ Ni, which is an equilibrium phase, is generated, and the fatigue strength and room temperature ductility of the titanium alloy thin plate may deteriorate. Therefore, the Ni content is preferably less than 0.15%. The Ni content is more preferably 0.10% or less.

Cr, like Fe or V, is an element that improves tensile strength and workability. However, when the Cr content is 0.25% or more, the intermetallic compound TiCr ₂ which is an equilibrium phase is generated, and the fatigue strength and room temperature ductility of the titanium alloy thin plate may deteriorate. Therefore, the Cr content is preferably less than 0.25%. The Cr content is more preferably 0.20% or less.

Mn, like Fe or V, is an element that improves tensile strength and workability. However, if the Mn content is 0.25% or more, the intermetallic compound Timn, which is an equilibrium phase, may be generated, and the fatigue strength and room temperature ductility of the titanium alloy thin plate may deteriorate. Therefore, the Mn content is preferably less than 0.25%. The Mn content is more preferably 0.20% or less.

When the titanium alloy thin plate according to the present embodiment contains Fe, it is selected from the group consisting of Ni: less than 0.15%, Cr: less than 0.25%, and Mn: less than 0.25%. When the seeds or two or more kinds are contained, 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. Further, when the total amount of Fe, Ni, Cr, and Mn is 0.5% or more, the β phase having good workability is maintained at room temperature, and the workability of the titanium alloy thin plate is improved. Further, when the total amount of Fe, Ni, Cr, and Mn is 2.3% or less, segregation of these elements is suppressed, and it is possible to suppress variations in the characteristics of the titanium alloy thin plate.

Further, when the titanium alloy thin plate according to the present embodiment contains V, it is selected from the group consisting of Ni: less than 0.15%, Cr: less than 0.25%, and Mn: less than 0.25%. When one kind or two or more kinds are contained, 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. When the total amount of Fe, Ni, Cr, and Mn is 4.5% or less, the β phase having good workability is maintained at room temperature, and the workability of the titanium alloy thin plate is improved. Further, when the total amount of Fe, Ni, Cr, and Mn is 4.5% or less, segregation of these elements is suppressed, and it is possible to suppress variations in the characteristics of the titanium alloy thin plate.

The balance of the chemical composition of the titanium alloy sheet according to the present embodiment may be Ti and impurities. Specific examples of the impurities include Cl, Na, Mg, Si, Ca mixed in the refining step and Fe, Zr, Sn, Mo, Nb, Ta, V and the like mixed in from scrap. If the total amount of impurities is 0.5% or less, there is no problem.

When the titanium alloy thin plate according to the present embodiment contains 0.5 to 2.3% of Fe, V contained in the titanium alloy thin plate may be contained in an amount regarded as an impurity, and the present embodiment. When the titanium alloy thin plate according to the above contains 2.5 to 4.5% of V, Fe contained in the titanium alloy thin plate may be contained in an amount regarded as an impurity.

Needless to say, the titanium alloy thin plate according to the present embodiment may contain various elements instead of Ti as long as it is a titanium alloy thin plate having high strength and exhibiting small anisotropy. .. Similarly, with respect to the elements exemplified as impurities, as long as the titanium alloy thin plate has high strength and exhibits small anisotropy, it may contain an amount equal to or greater than the amount regarded as an impurity. ..

As described above, the titanium alloy thin plate according to the present embodiment can have the above chemical components. More specifically, the chemical composition of the titanium alloy thin plate according to the present embodiment may be Ti-6Al-4V, Ti-6Al-4V ELI, Ti-5Al-1Fe.

(1.2. Aggregate structure and microstructure)
Next, the texture and microstructure of the titanium alloy sheet according to the present embodiment will be described.

[Aggregate organization]
The titanium alloy thin plate according to the present embodiment has a texture analysis (expansion index = 16) of the inverse pole diagram using the spherical harmonic method of the backscattered electron diffraction (EBSD) method in the (0001) pole diagram from the plate thickness direction. , Gaussian half-value width = 5 °), the angle between the direction showing the peak of the degree of integration and the plate thickness direction is 30 ° or less, and the maximum degree of integration of the (0001) plane is 4 or more. Have. Titanium alloys are generally hot-rolled in one direction at high speed in the β region or α + β high temperature region with a high β phase ratio, and when the phase is transformed from β phase to α phase, the plate width is determined by the variant selection rule. A structure (T-texture) in which the c-axis of the hexagonal close-packed (hcp) is oriented in the direction is formed. In the texture in which the c-axis of hcp is oriented in the plate width direction, a large anisotropy occurs in the tensile properties in the plate width direction and the plate longitudinal direction. If there is a large anisotropy in the tensile properties in the plate width direction and the plate longitudinal direction, molding processing is difficult and shape defects may occur. The c-axis of hcp is most oriented in the direction showing the peak of the degree of integration calculated by the Texture analysis (expansion index = 16, Gauss half width = 5 °) of the inverse pole diagram using the spherical harmonics method of the EBSD method. Corresponds to the direction. In the titanium alloy thin plate according to the present embodiment, in the (0001) pole figure from the plate thickness direction, the angle formed by the direction in which the c-axis of hcp is most oriented (the direction indicating the peak of the degree of integration) and the plate thickness direction is 30. When the temperature is less than or equal to °, the anisotropy can be reduced and high workability can be ensured. The angle formed by the direction in which the c-axis of hcp is most oriented (the direction indicating the peak of the degree of integration) and the plate thickness direction is preferably 28 ° or less.

Here, a method of drawing the (0001) pole figure will be described. (0001) The pole figure is obtained by chemically polishing the observation surface of the sample of the titanium alloy thin plate and analyzing the crystal orientation using EBSD. Specifically, a cross section obtained by cutting a titanium alloy thin plate in the plate thickness direction is chemically polished, and a region of (plate thickness) × 200 μm of the cross section is crystallized at about 2 to 5 places at intervals of 1 to 5 μm by the EBSD method. By performing the orientation analysis, the (0001) pole map can be drawn. (0001) The accumulation degree peak position of a specific direction in the pole figure is calculated by using the data of the OIM Analysis software manufactured by TSL Solutions by Texture analysis of the inverse pole figure using the spherical harmonic method. At this time, the position with the highest contour line is the peak position of the degree of integration, and the value with the highest degree of integration among the peak positions is the maximum degree of integration. It should be noted that the degree of accumulation of a specific orientation in the (0001) pole map is how many times the frequency of existence of crystal grains having that orientation is higher than that of a structure having a completely random orientation distribution (degree of integration 1). Is shown.

FIG. 1 shows an example of a (0001) pole figure from the thickness direction (ND) of the titanium alloy thin plate according to the present embodiment. In FIG. 1, the detected poles of each crystal orientation are accumulated according to the inclinations in the final rolling direction (RD) and the final rolled plate width direction (TD), and the contour lines of the degree of integration are shown in the (0001) pole diagram. It is drawn. The sites where the contour lines are highest in the figure are the peaks P1 and P2 of the crystal grains. Therefore, in the present embodiment, the angle formed by the directions indicating the peaks P1 and P2 of the crystal grains and the ND is 30 ° or less. Usually, the maximum degree of accumulation is the degree of accumulation of peaks P1 and P2 of crystal grains.

[Micro tissue]
The titanium alloy thin plate according to the present embodiment has a microstructure composed of an equiaxed structure having an aspect ratio of 3.0 or less and a band structure having an aspect ratio of more than 3.0 and extending in the longitudinal direction of the plate. It is preferable that the particle size of the equiaxed structure is 0.1 μm or more and 10 μm or less, and the area ratio of the band structure to the area of the microstructure is 10.0% or less. Each organization will be described below.

When the titanium alloy is hot-rolled at a temperature in the α + β region or β region, a structure called a “band structure” is formed as shown in FIG. The band structure referred to here specifically refers to a crystal grain having an aspect ratio of more than 3.0 represented by the major axis / minor axis of the crystal grain. The titanium alloy thin plate according to the present embodiment has a band structure extending in the longitudinal direction of the plate. When a band structure is formed, it may cause anisotropy of strength or a defect during molding. Therefore, it is better to have as few band structures as possible. The area ratio of the band structure to the area of the microstructure is preferably 10.0% or less. The area ratio of the band structure is more preferably 8.0% or less. On the other hand, since it is better not to have this band structure, the lower limit is 0%.

The aspect ratio and the area ratio of the band structure can be calculated as follows. A cross section of a titanium alloy thin plate cut perpendicularly in the plate width direction is chemically polished, and a region of (thickness) × 200 μm of the cross section is targeted at about 2 to 5 fields in steps 1 to 5 μm, and the crystal orientation by the EBSD method. Perform analysis. From the crystal orientation analysis result of this EBSD, the aspect ratio is calculated for each of the crystal grains. Then, the area ratio of the crystal grains having an aspect of more than 3.0 is calculated.

The rest of the microstructure other than the band structure is preferably an equiaxed structure formed by recrystallization. The titanium alloy thin plate preferably has an equiaxed structure from the viewpoint of moldability, and in particular, the titanium alloy thin plate is preferably fine particles because it may be formed by utilizing the superplastic property. From the viewpoint of formability and superplasticity, the average particle size of the equiaxed structure is preferably 10 μm or less. The average particle size of the equiaxed structure is more preferably 8 μm or less. On the other hand, if the average particle size of the equiaxed structure is less than 0.1 μm, the strength may become too large due to the grain fine effect, and the ductility may be significantly lowered. As a result, workability, especially in cold weather (room temperature), may decrease. Therefore, the average particle size of the equiaxed structure is preferably 0.1 μm or more. The average particle size of the equiaxed structure is more preferably 0.5 μm or more.

The presence or absence of recrystallization can be determined by measuring the aspect ratio (long-axis / short-axis ratio) of the crystal grains. If the aspect ratio is 3.0 or less, the crystal grains can be judged to be recrystallized grains. The lower limit of the aspect ratio of the equiaxed structure is 1.0.

The average crystal grain size of the equiaxed structure can be calculated as follows. For the equiaxed structure, the circle-equivalent particle size (area A = π × (particle size D / 2) ² ) was obtained from the crystal grain area measured by EBSD, and the average value based on this number was taken as the average crystal grain size of the equiaxed structure. To do.

(1.3. 0.2% proof stress in the longitudinal direction of the plate)
The 0.2% proof stress in the longitudinal direction of the titanium alloy thin plate according to the present embodiment at 25 ° C. is preferably 700 MPa or more. In the field of aircraft and the like, a tensile strength close to the tensile strength of Ti-6Al-4V, which is a general-purpose α + β type titanium alloy, at 25 ° C. is often required. If the 0.2% proof stress in the longitudinal direction of the titanium alloy thin plate at 25 ° C. is 700 MPa or more, it can be used in applications requiring high strength. The 0.2% proof stress in the longitudinal direction of the titanium alloy thin plate 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 plate before cold-rolling is also high, which makes it difficult to cold-roll the cold-rolled plate, which may increase the number of cold-rolled passes and increase the cost. is there. On the other hand, if the strength is too high, the notch sensitivity becomes high and the plate may break. Therefore, the 0.2% proof stress of the titanium alloy thin plate in the plate longitudinal direction at 25 ° C. is preferably 1200 MPa or less. The 0.2% proof stress in the longitudinal direction of the titanium alloy thin plate at 25 ° C. is more preferably 1150 MPa or less. Further, if the 0.2% proof stress of the titanium alloy thin plate in the plate longitudinal direction at 25 ° C. is 1100 MPa or less, cracking during cross rolling is further suppressed. The 2% proof stress is even more preferably 1100 MPa or less. The 0.2% proof stress in the longitudinal direction of the plate can be measured by a method according to JIS Z2241: 2011.

(1.4. Anisotropy)
The titanium alloy thin plate according to the present embodiment has a proof stress ratio σ _T / σ _{L, which is a ratio of 0.2% proof stress σ L} in the plate longitudinal direction at 25 ° C. to 0.2% proof stress σ _{T in the plate width direction at 25 ° C.} Is 0.95 or more and less than 1.05. Since α + β type titanium has an hcp phase (α phase) as described above, it exhibits higher anisotropy in the direction of hcp. As described above, since the anisotropy increases when the T-texture is formed, it may be desired to reduce the anisotropy as much as possible, especially in the field of aircraft. By performing cold cross rolling, yield strength ratio σ _{T /} σ _L can be produced titanium alloy sheet of less than 1.05. Further, when the proof stress ratio σ _T / σ _L is less than 1.05, excellent workability can be obtained. The proof stress ratio σ _T / σ _L is preferably 1.04 or less. On the other hand, when the proof stress ratio σ _T / σ _L is less than 0.95, the anisotropy becomes large.

(1.5. R value)
The r value (Rankford value) is a characteristic value representing anisotropy, and the r value in the present embodiment is the logarithm in the plate thickness direction when the elongation in the plate longitudinal direction becomes 3% in the tensile test. is the ratio of strain in the plate width direction with respect to epsilon _t logarithmic strain _{ε W (ε W / ε t} ). Generally, in titanium, the r value in the width direction is smaller than that in the longitudinal direction, but the r value in the longitudinal direction can be increased by performing cross rolling. When the r value is high, material flow tends to occur in the inward direction of the plate surface. Further, when the proof stress ratio σ _T / σ _L is 0.95 or more and less than 1.05 and the r value in the longitudinal direction is large, the deep drawing formability is excellent. The titanium alloy thin plate according to the present embodiment preferably has an r value of 2.0 or more and 10.0 or less. When the r value is 2.0 or more, excellent deep drawing workability can be obtained. The r value is more preferably 2.2 or more, and even more preferably 2.5 or more. On the other hand, if the r value exceeds 10.0, the bending workability may be extremely lowered. The r value is more preferably 9.0 or less.

The r value can be calculated by, for example, the following method. That is, a JIS13B tensile test piece was prepared in the longitudinal direction of the plate, the strain rate was set in the range of 0.15 to 15 mm / min, and a tensile load was applied to the test piece until the elongation in the longitudinal direction of the plate became 3%. After that, the load is unloaded, and the amount of deformation is obtained from the distance between the reference points before and after tensioning and the change in plate width. Since the volume is constant, the plate thickness is calculated. The r value, which is the ratio of _{the logarithmic strain ε W} in the width direction obtained thereby and the logarithmic strain ε _{t of the plate thickness, can be calculated.}

(1.6. Average plate thickness)
The average thickness of the titanium alloy thin plate according to the present embodiment is preferably 2.5 mm or less. According to the method for producing a titanium alloy thin plate described later, the average thickness of the titanium alloy thin plate can be set to 2.5 mm or less by using a titanium material containing Al of 4.0% or more and 6.6% or less. Titanium material with an Al content of 4.0% or more and 6.6% or less has a large deformation resistance, and therefore exceeds the allowable load of the rolling mill when manufacturing a thin plate in a general rolling mill. According to the method, it is difficult to produce a titanium alloy thin plate having an Al content of 4.0% or more and 6.6% or less and a plate thickness of 2.5 mm or less. Further, even when hot rolling is performed without using pack rolling, when the plate thickness becomes thin, the temperature drops sharply and the deformation resistance increases. As a result, when hot rolling a high-strength material, the allowable load of the rolling mill may be exceeded, and it is difficult to reduce the average plate thickness to 2.5 mm or less. On the other hand, although there is no particular limitation on the lower limit of the average plate thickness of the titanium alloy thin plate according to the present embodiment, the average plate thickness of the titanium alloy having the above strength is actually 0.1 mm or more. There are many. Therefore, the average thickness of the titanium alloy thin plate according to the present embodiment is preferably 0.1 mm or more. The upper limit of the thickness of the titanium alloy thin plate according to the present embodiment is more preferably 2.0 mm. Further, the lower limit of the average plate thickness of the titanium alloy thin plate according to the present embodiment is more preferably 0.2 mm.

Here, a method of measuring the average plate thickness will be described with reference to FIG. For the center position in the plate width direction (TD) and the position at a distance of 1/4 of the plate width from both ends in the plate width direction, the plate thickness at each position is measured at 5 or more points, and the average value of the measured plate thickness is averaged. The plate thickness.

(1.7. Plate thickness dimensional accuracy)
The thickness dimensional accuracy of the titanium alloy thin plate according to the present embodiment is preferably 5.0% or less with respect to the average plate thickness. In pack rolling, which can produce titanium alloy thin plates, a plurality of laminated titanium materials wrapped in steel are hot-rolled to produce titanium alloy thin plates, but the deformation resistance of the multiple laminated titanium materials due to the temperature distribution It is difficult to manufacture a thin plate with a uniform plate thickness because it changes greatly. However, since the titanium alloy thin plate according to the present embodiment is manufactured through cold rolling as described later, it is possible to obtain a titanium alloy thin plate having excellent plate thickness dimensional accuracy. The dimensional accuracy of the titanium alloy thin plate according to the present embodiment is more preferably 4.0% or less with respect to the average plate thickness. The dimensional accuracy of the titanium alloy thin plate according to the present embodiment is even more preferably 2.0% or less with respect to the average plate thickness.

The plate thickness dimensional accuracy is the maximum value of a calculated by the following formula (101) using the actually measured plate thickness d and the above average plate thickness _dave.
a = (d-d- _ave ) / d- _ave × 100 ... Equation (101)

The titanium alloy thin plate according to the present embodiment has been described above. The titanium alloy thin plate according to the present embodiment contains Al: 4.0 to 6.6% by mass and has the above-mentioned metal structure, and therefore has high strength and small anisotropy. The titanium alloy thin plate according to the present embodiment described above may be produced by any method, but can also be produced, for example, by the method for producing a titanium alloy thin plate according to the present embodiment described below.

<2. Manufacturing method of titanium alloy thin plate ＞
The method for manufacturing a titanium alloy thin plate according to the present embodiment is a slab manufacturing step for manufacturing a titanium alloy slab, a hot rolling step for hot rolling a titanium alloy slab, and a cold cloth for a titanium material after the hot rolling step. It includes a cold cross rolling step of rolling and, if necessary, a temper rolling / tensile straightening step of temper rolling or tensile straightening the titanium material after the cold cross rolling step. Hereinafter, each step of the method for manufacturing a titanium alloy thin plate according to the present embodiment will be described.

(2.1. Slab manufacturing process)
In the slab manufacturing process, a titanium alloy slab is manufactured. The method for producing the titanium alloy slab is not particularly limited, and for example, it can be produced by the following procedure. First, an ingot is prepared from titanium sponge by various melting methods such as a vacuum arc melting method, an electron beam melting method, and a hearth melting method such as a plasma melting method. Next, a titanium alloy slab can be obtained by hot forging the obtained ingot at a temperature in the α-phase high temperature region, the α + β two-phase region, or the β-phase single-phase region. The titanium alloy slab may be subjected to pretreatment such as cleaning treatment and cutting, if necessary. Further, when a rectangle that can be hot-rolled by the hearth melting method is formed, it may be subjected to hot rolling without hot forging or the like. The produced titanium alloy slab contains 4.0% or more and 6.6% or less of Al.

(2.2. Hot rolling process)
In the hot rolling step, the titanium alloy slab is heated and then hot rolled. The hot rolling conditions are not particularly limited, and the titanium alloy slab may be hot rolled under known conditions. For example, the titanium alloy slab may _{be heated to a temperature of β transformation point T β} ° C. or higher and then rolled so that the total reduction ratio is 80% or higher. Further, the finishing temperature can be, for example, (T _β −250) ° C. or higher and (T _β- 50) ° C. or lower. Further, the reduction rate may be hot-rolled so as to have the above-mentioned reduction rate in one hot rolling, or hot-rolled so as to have the above-mentioned reduction rate by a plurality of hot rollings. May be good. The titanium material after the main hot rolling step contains Al in an amount of 4.0% or more and 6.6% or less.

In the present specification, the “β transformation point” means the boundary temperature at which the α phase begins to be generated when the titanium alloy is cooled from the β phase single phase region. The β transformation point can be obtained from the phase diagram. The phase diagram can be obtained by, for example, the CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) method. Specifically, the phase diagram of the titanium alloy is obtained by the CALPHAD method using Thermo-Calc, which is an integrated thermodynamic calculation system of Thermo-Calc Waterare AB, and a predetermined database (TI3), and the β transformation point is determined. Can be calculated.

In the hot rolling step, the titanium alloy slab can be continuously hot rolled using a known continuous hot rolling facility. When a continuous hot rolling facility is used, the titanium alloy slab is hot rolled and then wound by a winder to form a titanium alloy hot rolled coil.

The hot-rolled plate after the hot-rolling step may be subjected to annealing by a known method, removal of oxide scale or the like by pickling or cutting, or cleaning treatment, if necessary. For example, the hot-rolled plate after the hot-rolling step is annealed at a temperature of 650 ° C. or higher and 800 ° C. or lower for a time of 20 minutes or more and 90 minutes or less. As a result, the unrecrystallized grains of the hot-rolled sheet can be precipitated as fine recrystallized grains, and the crystals in the metal structure of the finally obtained titanium alloy thin plate can be made more uniform and fine. Annealing may be performed in an air atmosphere, an inert atmosphere, or a vacuum atmosphere.

(2.3. Cold cross rolling process)
In this step, the titanium material containing Al: 4.0 to 6.6% by mass after the hot rolling step is rolled in the plate longitudinal direction and the plate width direction.

The total rolling ratio including both rolling in the plate longitudinal direction and rolling in the plate width direction is 60% or more. When the total rolling ratio is 60% or more, the c-axis of hcp is more oriented toward ND, and it is possible to manufacture a titanium alloy thin plate having a small anisotropy. As the rolling ratio increases, the c-axis of the α phase of the titanium alloy thin plate becomes closer to the plate thickness direction and the degree of integration increases, so that the upper limit of the rolling ratio is not limited.

The cross-rolling ratio is 0.05 or more and 20.0 or less. The cross-rolling ratio referred to here is the rolling rate in the plate longitudinal direction (rolling rate in the plate longitudinal direction / rolling rate in the plate width direction) with respect to the rolling rate in the plate width direction applied from the plate thickness of 4 mm to the target plate thickness. To tell. When this cross-rolling ratio is 0.05 or more and 20.0 or less, the c-axis of hcp becomes more oriented toward ND, and it is possible to manufacture a thin plate having a small anisotropy. In addition, it is possible to reduce the excessive band structure. The cross-rolling ratio is more preferably 0.07 or more and 15.0 or less.

The rolling rate per cold rolling pass is not particularly limited as long as the total rolling rate is 60% or more. The single cold rolling pass referred to here refers to cold rolling in the longitudinal direction of the plate or cold rolling in the width direction of the plate, which is continuously performed on the hot rolled plate. Therefore, in the main cold cross rolling process, when cold rolling in the plate longitudinal direction and cold rolling in the plate width direction are performed a plurality of times on the hot rolled plate, the total number of times is the number of cold rolling passes. Become. For example, when a hot-rolled plate is subjected to one cold rolling in the plate longitudinal direction and one cold rolling in the plate width direction, the number of cold rolling passes is two. Rolling in the longitudinal direction of the plate or rolling in the width direction of the plate may be performed a plurality of times. Further, even if the plate thickness is 4 mm or less, reheating or the like may be performed. Further, the hot rolling in the plate width direction may be performed every time the hot rolling in the plate longitudinal direction is performed once or several times.

The rolling ratio per cold rolling pass is not particularly limited and may be, for example, 5% or more. The rolling ratio per cold rolling pass is preferably 10% or more, more preferably 20% or more.

The rolling temperature in the cold cross rolling step is preferably 500 ° C. or lower. When the rolling temperature is 500 ° C. or lower, high dimensional accuracy can be obtained and the crystal grains are refined during rolling. The rolling temperature is more preferably 400 ° C. or lower.

[Intermediate annealing process]
In the cold cross rolling step, when performing a plurality of cold rolling passes, it is preferable to have an intermediate annealing step of annealing the titanium material (hot rolled plate after the cold rolling pass) between the cold rolling passes. .. In the intermediate annealing step, the annealing temperature T is 600 ° C. or higher (T _β- 50) ° C., and the annealing temperature T (° C.) and the holding time t (seconds) at the annealing temperature T are expressed by the following formula (102). ) Is preferably annealed in the intermediate material in the cold rolling process. In addition, (T + 273.15) × (Log ₁₀ (t) +20) of the following formula (102) is a Larson mirror parameter.
22000 ≦ (T + 273.15) × (Log ₁₀ (t) + 20) ≦ 27000 ... (102) Equation Here, T _β is a β transformation point (° C.).

[Final annealing process]
The cold cross-rolling step has a final annealing step of annealing the titanium material after the final cold rolling pass. The annealing conditions in the final annealing step are not particularly limited, but in order to improve the moldability of the titanium alloy plate, the annealing temperature T is 600 ° C. or higher (T _β- 50) ° C. and the annealing temperature is T (° C.). It is preferable that the holding time t (seconds) at the annealing temperature T satisfies the above formula (102).

By carrying out the intermediate annealing step and the final annealing step under the above conditions, the uncrystallized grains are recrystallized and the c-axis of the α phase approaches the ND direction. This makes it possible to further reduce the anisotropy of the titanium alloy thin plate. In addition, recrystallization eliminates an excessive amount of band structure in the microstructure. On the other hand, when the annealing temperature is equal to _{or higher than the β transformation point T β} , a phase transformation from the β phase to the α phase occurs, and the α phase generated thereby becomes a needle-like structure. Further, even if the annealing temperature is just below the β transformation point, the bimodal structure is a mixture of equiaxed structure and acicular structure. Needle-like and bimodal structures can cause internal cracks and ear cracks during cold rolling. Further, the needle-like structure or the bimodal structure often has coarse particles, which makes it difficult to develop superplastic properties. In the intermediate annealing step and the final annealing step, the annealing temperature T is 600 ° C. or higher (T _β- 50) ° C., and the annealing temperature T and the annealing time t satisfy the above equation (102). By determining T and the annealing time t, the c-axis of the α phase approaches the ND direction due to recrystallization, further reducing the anisotropy of the titanium alloy thin plate, and further reducing the band structure in the microstructure. It is possible to reduce it. Further, in the intermediate annealing step and the final annealing step, the annealing temperature T is 600 ° C. or higher (T _β- 50) ° C., and the annealing temperature T and the annealing time t satisfy the above formula (102). By determining the annealing temperature T and the annealing time t, fine equiaxed structures are increased, internal cracks and ear cracks during cold rolling are suppressed, and superplastic properties are easily exhibited.

(2.4. Tempered rolling / tensile straightening process)
A titanium alloy sheet is manufactured through the above cold rolling process, and the titanium alloy sheet after the cold rolling process is used for temper rolling for adjusting mechanical properties or for correcting the shape, if necessary. It is preferable that tensile straightening is performed. The rolling reduction in temper rolling is preferably 10% or less, and the elongation in tensile straightening is preferably 5% or less. It should be noted that temper rolling and tensile straightening may not be performed if it is not necessary. The method for manufacturing the titanium alloy thin plate according to the present embodiment has been described above.

According to the method for producing a titanium alloy sheet according to the present embodiment, the total rolling ratio of the hot-rolled sheet produced using the above-mentioned material of the titanium alloy sheet is 60% or more, and the cross-rolling ratio is 0. By cold cross-rolling of 05 or more and 20.0 or less, in the (0001) pole diagram from the plate thickness direction, the Texture analysis of the inverse pole diagram using the spherical harmonic function method of the EBSD method (expansion index = 16, Aggregate structure in which the angle between the direction showing the peak of the degree of integration calculated by Gaussian half-price width = 5 °) and the thickness direction is 30 ° or less, and the maximum degree of integration of the (0001) plane is 4 or more. A titanium alloy thin plate having a ratio of 0.2% strength in the plate width direction to 0.2% strength in the longitudinal direction of the plate of 0.95 or more and less than 1.05 can be obtained.

Further, according to the method for producing a titanium alloy thin plate according to the present embodiment, the annealing conditions in the intermediate annealing step and the final annealing step are such that the annealing temperature is 600 ° C. or higher (T _β- 50) ° C. and the annealing temperature. By setting T (° C.) and the holding time t (seconds) at the annealing temperature to satisfy the above formula (102), a fine equiaxed structure in the titanium material after the intermediate annealing step or the final annealing step. The ratio of As a result, even when the titanium material contains 4.0 to 6.6% of Al, internal cracks and ear cracks are suppressed.

Further, when the titanium material contains a large amount of β-phase stabilizing elements such as V, T-texture is formed by hot rolling in one direction at high speed in the β region or the α + β high temperature region having a high β phase ratio. It is easy, and the anisotropy of the titanium alloy thin plate tends to increase. However, according to the method for producing a titanium alloy sheet according to the present embodiment, since cold cross rolling is carried out, the formation of T-texture is suppressed even when the titanium material contains a β-phase stabilizing element such as V. To. As a result, it is possible to manufacture a titanium alloy thin plate having a small anisotropy.

Further, according to the method for producing a titanium alloy thin plate according to the present embodiment, the titanium alloy thin plate having an r value of 2.0 or more and 10.0 or less is excellent in deep drawing workability.

Further, according to the method for producing a titanium alloy thin plate according to the present embodiment, the crystal grains are refined by cold rolling and the superplastic characteristics are easily exhibited, and the titanium alloy thin plate is excellent in processability in thin plate molding. It becomes.

Hereinafter, embodiments of the present invention will be specifically described with reference to examples. The examples shown below are merely examples of the present invention, and the present invention is not limited to the following examples.

1. 1. Manufacture of Titanium Alloy Thin Plate First, the titanium alloy shown in Table 1 by either vacuum arc remelting (VAR: Vacuum Arc Remelting), electron beam melting (EBR: Electron Beam Remelting), or plasma melting (PAM: Prasma Arc Melting). After manufacturing the ingot, a titanium alloy slab having a thickness of 150 mm, a width of 800 mm, and a length of 5000 mm was manufactured by bulk rolling or forging. Then, these titanium alloy slabs were hot-rolled, hot-rolled, annealed, shot-blasted, and pickled to obtain a hot-rolled plate having a thickness of 4 mm. In Table 1, "Bal." Represents the rest.

Regarding the chemical composition of the hot-rolled plate, Al, Fe, Si, Ni, Cr, Mn, and V were measured by IPC emission spectroscopy. O and N were measured by an inert gas melting method and a thermal conductivity / infrared absorption method using an oxygen / nitrogen simultaneous analyzer. C was measured by an infrared absorption method using a carbon-sulfur simultaneous analyzer. The chemical composition of each of the produced hot-rolled plates was the same as the chemical composition of the titanium alloy slab shown in Table 1. Further, regarding the titanium materials A to M shown in Table 1, the state of the titanium alloy was obtained by the CALPHAD method using the Thermo-Calc, which is an integrated thermodynamic calculation system of Thermo-Calc Storage AB, and a predetermined database (TI3). The figure was acquired and the β transformation point was calculated.

Next, the obtained hot-rolled plate was cold-rolled under the conditions shown in Table 2. In Invention Examples 1 to 15 and 17 to 19, and Comparative Examples 1 and 2, a plurality of cold rolling ratios are obtained so as to have a total rolling ratio shown in Table 2, assuming that the rolling ratio per cold rolling pass is 5% or more. A rolling pass was made. In Invention Examples 1 to 15 in Table 2, a plurality of cold rolling passes at a rolling temperature of 25 ° C. and intermediate annealing under the conditions shown in Table 2 are repeated, and cold until the total rolling ratio reaches 60 to 92%. This is an example of cross-rolling. The intermediate annealing was performed at a temperature of 800 to 900 ° C. for 60 to 28800 s, and the final annealing was performed at a temperature of 650 to 900 ° C. for 60 to 28800 s. The cross-rolling ratio of Invention Examples 1 to 15 was 0.15 to 7.00. In Invention Examples 16 to 18, a plurality of cold rolling passes at a rolling temperature of 400 ° C. and intermediate annealing under the conditions shown in Table 2 were repeated, and cold cross-rolling was performed until the total rolling ratio became 70 to 90%. This is an example. The intermediate annealing was carried out at a temperature of 680 to 850 ° C. for 120 to 28800 s, and the final annealing was carried out at a temperature of 700 to 900 ° C. for 120 to 28800 s. The cross-rolling ratio of Invention Examples 16 to 18 was 15.00. A reference example is a hot-rolled sheet that has not been cold-rolled. Comparative Example 1 is an example in which a plurality of cold rolling passes having a rolling temperature of 25 ° C. and intermediate annealing under the conditions shown in Table 2 are repeated, and cold rolling is performed until the total rolling ratio reaches 50%. In Comparative Example 1, cross rolling was not performed. Comparative Example 2 is an example in which a plurality of cold rolling passes having a rolling temperature of 25 ° C. and intermediate annealing under the conditions shown in Table 2 were repeated, and cold rolling was performed until the total rolling ratio reached 66%. The cross-rolling ratio of Comparative Example 2 was 0.02. In Table 2, "T _β " is a β transformation point, and "Larson mirror parameter" is a value of (T + 273.15) × (Log ₁₀ (t) + 20).

2. Evaluation The following items were evaluated for the titanium alloy thin plates according to each invention example, reference example, and comparative example.

2.1. Chemical Composition The chemical composition of the titanium alloy thin plate according to each invention example, reference example and comparative example was measured by the same method as the method for measuring the chemical composition of the hot-rolled plate.

2.2. Maximum degree of integration and degree of accumulation Peak position By chemically polishing the observation surface of the sample of the titanium alloy thin plate according to each invention example, reference example and comparative example, and analyzing the crystal orientation using the electron backscatter diffraction method (0001). ) I got a polar diagram. Specifically, a cross section obtained by cutting each sample in the plate thickness direction is chemically polished, and in the cross section, an EBSD method is applied to a region of (plate thickness) × 200 μm at intervals of 1 to 5 μm for about 2 to 5 fields of view. The crystal orientation was analyzed by (0001) and a pole figure was drawn. (0001) For the peak position of the degree of integration in a specific direction in the pole figure, the data is analyzed by using the OIM Analysis software manufactured by TSL Solutions and the inverse pole figure using the spherical harmonic method (expansion index = 16, Gaussian and a half). Price range = 5 °).

2.3. Aspect ratio and band structure area ratio A cross section of a titanium alloy thin plate cut perpendicularly in the plate width direction is chemically polished, and a region of (plate thickness) x 200 μm of the cross section is about 2 to 5 visual fields in steps 1 to 5 μm. The crystal orientation was analyzed by the EBSD method. From the crystal orientation analysis result of this EBSD, the aspect ratio was calculated for each of the crystal grains. As the band structure area ratio, the area ratio of crystal grains having an aspect of more than 3.0 was calculated.

2.4. Average crystal grain size of equiaxed structure The average crystal grain size of equiaxed structure is the equivalent grain size of a circle (area A = π × (particle size D / 2) ² ) from the crystal grain area measured by EBSD for the equiaxed structure. The average value based on the number was used as the average crystal grain size of the equiaxed structure.

2.5. 0.2% proof stress The 0.2% proof stress of the titanium alloy thin plate according to each invention example, reference example and comparative example at 25 ° C. was measured in accordance with JIS Z 2241: 2011.

2.6. r-value The r-value of the titanium alloy sheet according to each of the invention examples, reference examples and comparative examples was calculated by the following method. That is, a JIS13B tensile test piece was prepared in the longitudinal direction of the plate, the strain rate was set in the range of 0.15 to 15 mm / min, and a tensile load was applied to the test piece until the elongation in the longitudinal direction of the plate became 3%. After that, the tensile load was unloaded, and the amount of deformation was obtained from the distance between the reference points before and after the tension and the change in plate width. Since the volume is constant, the plate thickness was calculated. The r value, which is the ratio of _{the logarithmic strain ε W} in the width direction obtained by this to the logarithmic strain ε _{t of the plate thickness, was calculated.}

2.7. Average plate thickness The average plate thickness of the titanium alloy thin plates according to each invention example, reference example, and comparative example was measured by the following method. The thickness of each of the manufactured titanium alloy thin plates was measured at five or more locations at the center position in the plate width direction and at a distance of 1/4 of the plate width from both ends in the plate width direction. The average value of was taken as the average plate thickness.

2.8. Plate thickness dimensional accuracy For the plate thickness dimensional accuracy of the titanium alloy thin plate according to each invention example, reference example and comparative example, the plate thickness d actually measured by the above method and the above average plate thickness _dave are used. The maximum value of a calculated by the following formula (101) was taken as the dimensional accuracy.
a = (d-d- _ave ) / d- _ave × 100 ... Equation (101)

2.9. Deep drawing workability The deep drawing workability of the titanium alloy thin sheet according to each invention example, reference example and comparative example was evaluated by the following method. That is, a circular blank having a blank diameter of φ80 mm was cut out from the manufactured titanium alloy thin plate, and a cylindrical punch diameter of φ40 mm, a radius of curvature of the punch shoulder of 4 mm, a clearance of 1 mm, a radius of curvature of the die shoulder of 6 mm, and a wrinkle pressing load of 1.1 tons. Lubrication was evaluated by performing a deep drawing test under the conditions of a Teflon (registered trademark) sheet and a speed of 20 mm / min. × (defective) when cracks occur during deep drawing, Δ (good) when ears with a height of more than 5 mm occur without cracks, and 5 mm or less in height without cracks. The case where ears were generated was marked as ◯ (extremely good). △ The above was accepted. The difference between the maximum value of the axial length and the minimum value of the axial length of the cylindrical titanium material after the deep drawing test was defined as the ear height.

3. 3. Results Table 3 shows the above evaluation results. In addition, "θ" shown in Table 4 is a Texture analysis (expansion index =) of the inverse pole diagram using the spherical harmonic method of the backscattered electron diffraction (EBSD) method in the (0001) pole diagram from the plate thickness direction. 16. Gaussian full width at half maximum = 5 °) is the angle formed by the direction indicating the peak of the degree of integration and the plate thickness direction.

Regarding Examples 1 to 15, the peak of the degree of integration (maximum degree of integration) in the (0001) pole figure is 6 or more, and the angle between the direction showing the peak of the degree of integration and the plate thickness direction is 15 to 27 °. Met. The average particle size of the equiaxed structure was 1.5 to 6.7 μm, and the area ratio of the band structure was 0.0 to 8.0%. The final plate thickness was 0.3 to 1.8 mm, and the dimensional accuracy was 1.1 to 3.5%. Further, the 0.2% proof stress σL in the plate longitudinal direction at 25 ° C. was 700 MPa or more, and the proof stress ratio σT / σL was 0.95 or more and less than 1.05. The r value was 2.0 or more and 10.0 or less. The deep drawing workability was extremely good in each case.

In Invention Examples 16 to 18, the peak of the degree of integration (maximum degree of integration) in the (0001) pole figure is 7, and the angle between the direction showing the peak of the degree of integration and the plate thickness direction is 25 °. there were. The average particle size of the equiaxed structure was 1.7 to 3.5 μm, and the area ratio of the band structure was 0.0%. The final plate thickness was 0.4 to 1.2 mm, and the dimensional accuracy was 1.5 to 2.1% or less. Further, the 0.2% proof stress σL in the plate longitudinal direction at 25 ° C. was 700 MPa or more, and the proof stress ratio σT / σL was 0.95 or more and less than 1.05. The r value was 2.0 or more and 10.0 or less. The deep drawing workability was extremely good in each case.

For the reference example, the angle formed by the direction showing the peak of the degree of integration and the plate thickness direction in the (0001) pole figure was 30 ° or more. Therefore, the proof stress ratio σT / σL was 1.05 or more, showing strong anisotropy. The r value was less than 2.0. The deep drawing workability was poor.

Further, the titanium alloy thin plate of Comparative Example 1 has an angle formed by the direction showing the peak of the degree of integration in the (0001) pole figure and the plate thickness direction of 30 ° or more, and the proof stress ratio σT / σL is 1.05 or more. , Showed strong anisotropy. The r value was less than 2.0. The deep drawing workability was poor.

Further, in the titanium alloy thin plate of Comparative Example 2, the angle formed by the direction showing the peak of the degree of integration in the (0001) pole figure and the plate thickness direction is 30 ° or more, and the proof stress ratio σT / σL is 1.05 or more. , Showed strong anisotropy. The r value was less than 2.0. Although the deep drawing workability was good, it was inferior to Invention Examples 1 to 18.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such examples. It is clear that a person having ordinary knowledge in the field of technology to which the present invention belongs can come up with various modifications or modifications within the scope of the technical idea described in the claims. , These are also naturally understood to belong to the technical scope of the present invention.

Claims (9)

Al: contains 4.0 to 6.6% by mass,
Calculated by Texture analysis (expansion index = 16, Gaussian half width = 5 °) of the inverse pole diagram using the spherical harmonics method of backscattered electron diffraction (EBSD) method in the (0001) pole diagram from the plate thickness direction. It has an aggregate structure in which the angle between the direction showing the peak of the degree of integration and the thickness direction is 30 ° or less and the maximum degree of integration of the (0001) plane is 4 or more.
A titanium alloy thin plate in which the ratio of 0.2% proof stress in the plate width direction to 0.2% proof stress in the plate longitudinal direction is 0.95 or more and less than 1.05. It has a microstructure consisting of an equiaxed structure having an aspect ratio of 3.0 or less and a band structure having an aspect ratio of more than 3.0 and extending in the longitudinal direction of the plate.
The average particle size of the equiaxed structure is 0.1 μm or more and 10 μm or less.
The titanium alloy thin plate according to claim 1, wherein the area ratio of the band structure to the area of the microstructure is 10.0% or less. In addition, in% by mass,
Fe: 0.5 to 2.3% or V: 2.5 to 4.5%,
Si: 0-0.60%,
Containing, in addition
C: less than 0.08%,
N: 0.05% or less, and O: 0.40% or less,
The titanium alloy thin plate according to claim 1 or 2, wherein the titanium alloy thin plate is limited to and the balance is composed of Ti and impurities. In place of the Fe or a part of the V, in% by mass,
Ni: less than 0.15%,
Cr: less than 0.25% and
The titanium alloy thin plate according to claim 3, which contains one or more selected from the group consisting of Mn: less than 0.25%. The titanium alloy thin plate according to any one of claims 1 to 4, wherein the average plate thickness is 2.5 mm or less, and the dimensional accuracy of the plate thickness is 5.0% or less with respect to the average plate thickness. .. _{In the tensile test, the r value, which is the ratio of the logarithmic strain ε t in} the plate thickness direction to the logarithmic strain ε _{W in} the plate width direction when the elongation in the plate longitudinal direction becomes 3%, is 2.0 or more and 10.0 or less. The titanium alloy thin plate according to any one of claims 1 to 5. The titanium alloy thin plate according to any one of claims 1 to 6, wherein the 0.2% proof stress at 25 ° C. is 700 MPa or more. The method for manufacturing a titanium alloy sheet according to any one of claims 1 to 7.
A cold cross-rolling step of rolling a hot-rolled plate containing Al: 4.0 to 6.6% by mass in the plate longitudinal direction and the plate width direction, and
It has a final annealing step of annealing the titanium material after the cold cloth rolling step.
The total rolling ratio in the cold cross rolling step is 60% or more.
A method for producing a titanium alloy thin plate, wherein the cross-rolling ratio, which is the ratio of the rolling ratio in the plate longitudinal direction to the rolling ratio in the plate width direction, is 0.05 or more and 20.0 or less. The cold cross-rolling step includes an intermediate annealing step of annealing the titanium material between the plurality of cold rolling passes when a plurality of cold rolling passes are performed.
The annealing conditions in the intermediate annealing step and the final annealing step are as follows.
The annealing temperature is 600 ° C or higher (T _β- 50) ° C or lower, and
The method for producing a titanium alloy thin plate according to claim 8, wherein the annealing temperature T (° C.) and the holding time t (seconds) at the annealing temperature are conditions that satisfy the following formula (1).
22000 ≤ (T + 273.15) x (Log ₁₀ (t) + 20) ≤ 27000 ... Equation (1)
Here, T _β is the β transformation point (° C.).

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