Steel plate

Abstract

The titanium plate has a specified chemical composition, a metallographic structure including an α phase, an average grain size of the α phase of 100.0 μm or less, a maximum value of a crystal orientation distribution function f(g) of 14.0 or less when the crystal orientation of the α phase is expressed by the Euler angles g = {φ1, Φ, φ2}, an maximum value of the crystal orientation distribution function f(g) of orientation group A expressed by the Euler angles as φ1: 0 to 30°, Φ: 30 to 90°, and φ2: 0 to 60° is 1.0 or greater, an maximum value of the crystal orientation distribution function f(g) of orientation group B expressed by the Euler angles as φ1: 30 to 60°, Φ: 30 to 90°, and φ2: 0 to 60° is 1.0 or greater, and an maximum value of the crystal orientation distribution function f(g) of orientation group C expressed by the Euler angles as φ1: 60 to 90°, Φ: 30 to 90°, and φ2: 0 to 60° is 1.0 or greater.

Description

Technical Field

[0001] The present invention relates to a titanium plate, and in particular to a titanium plate having low processing anisotropy and excellent formability. Background Art

[0002] Titanium plates are used in plate heat exchangers and other applications. Because plate heat exchangers require high heat transfer rates, titanium plates are processed into a corrugated shape through press forming to increase their surface area. Therefore, titanium plates used in heat exchangers require excellent formability during press forming.

[0003] During press forming, titanium plates are required to be fully and uniformly elongated without breaking in any direction. However, for titanium plates, the mechanical properties (strength, elongation) in the rolling direction, i.e., the plate length direction (RD), are usually different from the mechanical properties (strength, elongation) in the plate width direction (TD) at right angles to the RD within the plate surface (having mechanical anisotropy). This is because titanium plates are usually manufactured by cold rolling only in one direction, resulting in a texture oriented in a specific direction by cold rolling. With respect to the plate thickness direction (the direction perpendicular to the plate surface), it is hereinafter referred to as ND.

[0004] The texture formed by cold rolling, even after annealing and recrystallization, can only form a recrystallized texture oriented in a specific direction, so the anisotropy of the structure is not eliminated. Therefore, conventional titanium plates have anisotropy in mechanical properties at any time before and after annealing, which is derived from the anisotropy of the structure.

[0005] The texture formed by cold rolling during the manufacturing process of the titanium plate will be described in more detail.

[0006] Titanium sheets manufactured under conventional conditions by cold rolling in one direction and annealing at α-range temperatures have a texture in which the c-axis (the axis parallel to the

[0001] direction) of the α grains in the hcp structure (hexagonal crystals) is often oriented approximately 35° from the ND (perpendicular to the sheet surface) toward the TD (sheet width direction). This texture causes conventional titanium sheets to exhibit processing anisotropy, which impairs their formability.

[0007] As disclosed in Patent Documents 1 to 7, various attempts have been made to improve the formability of titanium plates.

[0008] Patent Documents 1 and 2 describe that the relationship between the grain size of α-phase grains in a titanium plate and the area of ​​grains having three orientations expressed by a crystal orientation distribution function is set within a specific range in order to improve strength and formability.

[0009] Patent Document 1 controls the texture by controlling the intermediate annealing conditions (performed in the recrystallization temperature range), the final cold rolling conditions (setting the final cold rolling reduction to 20-87%), and the final annealing conditions after cold rolling (setting the annealing temperature to be above the β transformation point and below 950°C). The final annealing conditions also control the grain size of α grains.

[0010] Patent Document 2 controls the texture by controlling the intermediate annealing conditions (performed in the recrystallization temperature range), the final cold rolling conditions (setting the final cold rolling reduction ratio to 20-87%), and the final annealing conditions after cold rolling (setting the annealing temperature to a temperature above which the β phase content reaches 20% or more and below the β transformation point). The grain size of the α grains is also controlled by the final annealing conditions and the final cold rolling reduction ratio.

[0011] Patent Document 3 describes the following: To improve strength and formability, the grain size of the α-phase in the titanium plate is controlled within a specific range, and the area ratio of the α-phase grains, which form a specific relationship with the (0001) plane axis orientation, is controlled to a specific value. In Patent Document 3, to maintain the crystal orientation of the titanium plate and the equivalent circle diameter of the α-phase grains within the specified ranges, the final annealing temperature is controlled (10°C / s or higher), the holding temperature (above 50% and below 950°C), the holding time (300 seconds or less), and the cooling rate (10°C / s or higher).

[0012] Patent Document 4 states that in order to reduce the anisotropy of strength, the grain size of the α phase of the titanium plate is set to a specific range, and the 0.2% yield strength in the direction where the yield strength is minimized is set to YS R , let the 0.2% yield strength in the direction perpendicular to the direction in which the yield strength reaches the minimum be YS T The ratio of YS T / YS R In Patent Document 4, the crystal orientation of the titanium plate and the equivalent circle diameter of the α-phase grains are controlled by setting the final cold rolling ratio after the final intermediate annealing to 20 to 87% and the annealing temperature of the final annealing to be above the β transformation point (Tβ) and below 950°C.

[0013] Patent Document 5 describes that in order to reduce strength anisotropy, the average aspect ratio of the α-phase grains of the titanium plate is set to 2.0 or more, the standard deviation is set to 0.70 or more, and the average equivalent circle diameter is set to 5 μm or more and 100 μm or less, and the maximum value is set to 300 μm or less.

[0014] Patent Document 6 describes a titanium plate for press forming, which is rolled at a variable peripheral speed while hot and has an in-plane anisotropy of 12.9 or more and a value obtained by dividing the difference in Lankford values ​​(r-values) obtained in a tensile test at 90° and 0° relative to the rolling direction by the average r by 0.72 or less.

[0015] Patent Document 7 describes a titanium material obtained by cross rolling under predetermined hot rolling conditions and having a small anisotropy of 0.2% yield strength.

[0016] Prior art literature

[0017] Patent Literature

[0018] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-108652

[0019] Patent Document 2: Japanese Patent Application Laid-Open No. 2017-137561

[0020] Patent Document 3: Japanese Patent Application Laid-Open No. 2015-63720

[0021] Patent Document 4: Japanese Patent Application Laid-Open No. 2016-102237

[0022] Patent Document 5: Japanese Patent Application Laid-Open No. 2016-23315

[0023] Patent Document 6: Japanese Patent Application Laid-Open No. 2011-230171

[0024] Patent Document 7: Japanese Patent Application Laid-Open No. 63-130753

[0025] Non-patent literature

[0026] Non-Patent Literature 1: Hiroshi Inoue, "Three-Dimensional Crystal Orientation Distribution Analysis Method and Its Progress," Recrystallization, Texture, and Its Application in Microstructure Control, The Japan Iron and Steel Association, March 1999, pp. 297-299. Summary of the Invention

[0027] Problems to be solved by the invention

[0028] As mentioned above, titanium sheets manufactured using conventional methods have a texture with a preferred c-axis orientation of approximately 35° from the ND toward the TD, resulting in mechanical anisotropy. In contrast, various methods have been proposed as techniques for improving formability, as described in Patent Documents 1 to 7.

[0029] However, the titanium plates described in Patent Documents 1 to 3 have not been studied for mechanical anisotropy. Furthermore, the titanium plates described in Patent Documents 4 to 7 have been studied for strength anisotropy, but not for elongation anisotropy.

[0030] The present inventors have conducted research and found that even when the anisotropy of strength is small, the anisotropy of elongation is not necessarily small. For example, as an existing material, Figure 11A The SS curve (stress-strain curve) is shown for the α-annealed material obtained by final annealing in the α temperature range (annealing temperature 800°C) of a titanium plate manufactured by cold rolling. Figure 11A It is known that even when the anisotropy of strength in RD and TD is small, the anisotropy of elongation is not necessarily small. The SS curve was also confirmed for the β-annealed material obtained by final annealing (annealing temperature 920°C) at a temperature above the β transformation point of the titanium plate produced by cold rolling, and the result was the same as Figure 11A The same result was obtained. That is, even when the anisotropy of the strength in RD and TD is small, the anisotropy of the elongation is not necessarily small.

[0031] In addition, if the anisotropy of the plate is simply reduced, it is possible to expand the texture (Φ≈0, φ1 and φ2 are arbitrary values) in which the c-axis is basically consistent with ND by means of the variable-speed rolling described in Patent Document 6 and the cross-rolling described in Patent Document 7. However, in these cases, although the anisotropy of the elongation is improved, since the c-axis is oriented along the ND, stretching from any direction will become perpendicular to the c-axis, and the yield strength becomes the lowest. Furthermore, in reality, when manufacturing titanium thin plates, in order to implement cross-rolling, it is necessary to use cut plates for rolling instead of coils, which is inefficient. In addition, since the directions of friction between the two rollers in variable-speed rolling are different, the rolled plate is prone to curling and the slippage is large, so the surface properties are prone to deterioration. Therefore, the technologies of Patent Documents 6 and 7 cannot fully reduce the anisotropy of the titanium plate in actual operation.

[0032] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a titanium plate having a large elongation and a small anisotropy of elongation.

[0033] Solutions for solving problems

[0034] That is, the gist of the present invention is as follows.

[0035] [1] A titanium plate according to one embodiment of the present invention has the following chemical composition: in mass %, Fe: 0-0.500%, O: 0-0.400%, N: 0-0.050%, C: 0-0.080%, H: 0-0.013%, Al: 0-2.30%, Cu: 0-1.80%, Nb: 0-1.00%, Si: 0-0.50%, Zr: 0-0.50%, Cr: 0-0.50%, Mo: 0-0.50% and Sn: 0-1.50%, with the remainder being Ti and impurities, and a metallographic structure including an α phase, wherein the average grain size of the α phase is 100.0 μm or less, and when the crystal orientation of the α phase is represented by Euler angles g = {φ1, Φ, φ2}, by setting the expansion index to 16 and the height to The maximum value of the crystal orientation distribution function f(g) calculated by the spherical harmonics method of the electron backscatter diffraction method with a half-value width of 5° is 14.0 or less, the maximum value of the crystal orientation distribution function f(g) of the orientation group A expressed by the aforementioned Euler angles of φ1: 0 to 30°, Φ: 30 to 90°, and φ2: 0 to 60° is 1.0 or more, the maximum value of the crystal orientation distribution function f(g) of the orientation group B expressed by the aforementioned Euler angles of φ1: 30 to 60°, Φ: 30 to 90°, and φ2: 0 to 60° is 1.0 or more, and the maximum value of the crystal orientation distribution function f(g) of the orientation group C expressed by the aforementioned Euler angles of φ1: 60 to 90°, Φ: 30 to 90°, and φ2: 0 to 60° is 1.0 or more.

[0036] [2] The titanium plate according to [1], wherein the chemical composition may include, in mass %, one or two of O: 0.030 to 0.200% and Fe: 0.020 to 0.200%.

[0037] [3] The titanium plate according to [1] or [2], wherein the chemical composition may include, in mass %, one or both of Al: 0.10 to 2.30% and Cu: 0.10 to 1.80%.

[0038] [4] The titanium plate according to [3] above, wherein the chemical composition may include, in mass %, Fe: 0.100% or less, and one or more selected from Nb: 0.10-1.00%, Si: 0.10-0.50%, and Zr: 0.10-0.50%.

[0039] [5] The titanium plate according to [3] or [4] above, wherein the chemical composition may contain, in mass %, one or more selected from the group consisting of Cr: 0.05 to 0.50%, Mo: 0.05 to 0.50%, and Sn: 0.05 to 1.50%.

[0040] [6] The titanium plate according to any one of [1] to [5] above, wherein the average grain size of the five largest grains of the α phase can be 250 μm or less.

[0041] [7] The titanium plate according to any one of [1] to [6] above, wherein the average grain size of the α phase may be 2.0 to 100.0 μm.

[0042] [8] The titanium plate according to any one of [1] to [6] above, wherein the average grain size of the α phase may be 8.0 to 100.0 μm.

[0043] [9] The titanium plate according to any one of [1] to [8], wherein the ratio of the total elongation in the rolling direction to the total elongation in the plate width direction, i.e., El RD / El TD It can be 0.70 to 1.30.

[0044] Effects of the Invention

[0045] According to the above aspects of the present invention, a titanium plate having high elongation (hereinafter, total elongation unless otherwise specified) and low elongation anisotropy can be provided. This titanium plate has excellent formability and is therefore useful for manufacturing titanium products of complex shapes by press forming. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This figure explains the method of expressing crystal orientation three-dimensionally using Euler angles.

[0047] Figure 2 This figure explains a method of expressing the preferential orientation of a conventional material (α-annealed material) in three dimensions using Euler angles.

[0048] Figure 3 This is a diagram showing the crystal orientation distribution function ODF of the titanium plate of the present invention as contour lines in the Euler angle space.

[0049] Figure 4 This is a graph showing the crystal orientation distribution function ODF of a titanium plate of a conventional example (α-annealed material) as contour lines in the Euler angle space.

[0050] Figure 5 This is a graph showing the crystal orientation distribution function ODF of a titanium plate of a conventional example (β-annealed material) as contour lines in the Euler angle space.

[0051] Figure 6 This is a diagram illustrating the regions of orientation group A to orientation group C in a three-dimensional representation of Euler angles.

[0052] Figure 7 This is a diagram showing the ODF of the titanium plate of this embodiment as a contour line in a region including the position where the ODF reaches the maximum value in each orientation group. Figure 7 (A) includes orientation group A, Figure 7 (B) contains orientation group B, Figure 7 (C) contains the point of the ODF maximum value in orientation group C.

[0053] Figure 8 This is a diagram showing the ODF of a conventional titanium plate as a contour line in a region including the position where the ODF reaches the maximum value in each orientation group. Figure 8 (A) includes orientation group A, Figure 8 (B) contains orientation group B, Figure 8 (C) contains the point of the ODF maximum value in orientation group C.

[0054] Figure 9 is a graph showing the quality indexes of the titanium plate of this embodiment. Figure 9 (A) is a graph showing the strength of TD and RD, Figure 9 (B) is a graph showing the total elongation and uniform elongation in TD and RD.

[0055] Figure 10 This is a diagram showing the structure (isometric structure) of the titanium plate according to this embodiment.

[0056] Figure 11A This is a diagram showing an SS curve of an annealed titanium plate produced by conventional cold rolling.

[0057] Figure 11B This is a diagram showing an example of an SS curve of the titanium plate according to the present embodiment.

[0058] Figure 12 This is a diagram showing the structure (acicular structure) of a titanium plate obtained by setting the final annealing temperature to a β transformation point temperature or higher.

[0059] Figure 13 It is a diagram showing the manufacturing process of the titanium plate of this embodiment.

[0060] Figure 14 This is a diagram for explaining a method of obtaining flow stress from an SS curve. DETAILED DESCRIPTION

[0061] Hereinafter, a titanium plate according to one embodiment of the present invention (titanium plate according to this embodiment) will be described.

[0062] 1. Metallographic structure

[0063] <Contains α phase, average grain size of α phase is 100.0 μm or less>

[0064] The titanium plate of this embodiment has an α-phase as the primary crystal structure. The α-phase as the primary crystal structure means that the α-phase accounts for 95% or more of the entire evaluation surface by area. This percentage is preferably 97% or more, and more preferably 99% or more. The remaining structure besides the α-phase includes β-phase, Ti2Cu, TiFe, Ti3Al, and silicides.

[0065] Furthermore, the average grain size of the α phase is set to 100.0 μm or less. If the average grain size of the α phase exceeds 100.0 μm, the ratio of grains with a specific crystal orientation increases, causing anisotropy in elongation. Furthermore, the presence of coarse grains can easily cause wrinkles during forming. The average grain size of the α phase is preferably 90.0 μm or less, and more preferably 80.0 μm or less.

[0066] On the other hand, there is no lower limit for the average grain size of the α phase. To reduce the average grain size, the cold rolling reduction ratio needs to be increased, which facilitates the development of the texture during cold rolling. Therefore, the average grain size of the α phase can be set to 2.0 μm or greater, or 5.0 μm or greater, or 8.0 μm or greater.

[0067] The area ratio of the α phase is determined by the following method.

[0068] Since the α phase is uniformly distributed, the area ratio of each phase constituting the metallographic structure of the titanium plate can be measured in any cross section of the titanium plate. In the present invention, for example, the measurement is performed by observing the surface perpendicular to the plate width direction (L cross section) at the 1 / 2 position of the plate width of the titanium plate (from the width end to the 1 / 2 position of the plate width: the width center). Specifically, the L cross section at the 1 / 2 position of the plate width of the titanium plate is polished to form an observation surface, and the concentration distribution of Fe and Cu is measured using SEM (Scanning Electron Microscopy) / EPMA (Electron Probe Microanalyzer) in a 500μm×500μm field of view with a spacing of 1.0μm (step size: 1.0μm). Since Fe and Cu are enriched in the β phase or Ti2Cu portion, the area where the concentration of these elements is 1.7 times or more of the average of the entire field of view is defined as the β phase or Ti2Cu portion, and the area ratio of this area relative to the entire field of view is calculated as the area ratio of the β phase or Ti2Cu. Furthermore, the value obtained by subtracting these area ratios from 100% was calculated as the area ratio of the α phase.

[0069] Since the α phase is uniformly distributed, the average grain size of the α phase can be measured at any cross section of the titanium plate. For example, it can be measured by observing a plane perpendicular to the plate width at a position 1 / 2 of the plate width (L cross section).

[0070] Specifically, the L section at the 1 / 2 position of the plate width of the titanium plate is ground to form an observation surface, and the EBSD pattern is measured with a SEM at a spacing of 2.0 μm for the field of view of the total plate thickness of the surface. The boundary with an orientation difference of more than 15° is identified as a grain boundary, and the area surrounded by the grain boundary is used as a grain. With respect to the average grain size, the average value of the equivalent circular diameter (circle equivalent diameter) of the grain is evaluated by arithmetic mean. The field of view is preferably set in a manner such that there are about 1000 or more grains. However, when the average grain diameter obtained by the above method is less than 5.0 μm, in order to improve the accuracy, the field of view of the total plate thickness × 1 mm is measured again at a spacing of 0.5 μm to obtain the average grain size.

[0071] <The maximum value of the crystal orientation distribution function f(g) when the crystal orientation of the α phase is expressed by Euler angles g = {φ1, Φ, φ2} is 14.0 or less>

[0072] The maximum value of the crystal orientation distribution function f(g) for orientation group A (φ1: 0-30°, Φ: 30-90°, φ2: 0-60°), orientation group B (φ1: 30-60°, Φ: 30-90°, φ2: 0-60°), and orientation group C (φ1: 60-90°, Φ: 30-90°, φ2: 0-60°) is 1.0 or greater.

[0073] As described in Patent Documents 6 and 7, studies have been conducted to improve elongation anisotropy by developing a texture in which the c-axis and ND are substantially aligned (Φ≈0, φ1 and φ2 are arbitrary values). However, these techniques have problems to be improved.

[0074] Therefore, the present inventors conducted research. As a result, they came up with the idea that, based on a concept contrary to the conventional ones, by reducing the proportion of a specific structure oriented in one direction and mixing structures oriented irregularly in various directions, the anisotropy of the elongation can be reduced while maintaining sufficient elongation. This is believed to be because the irregular structure reduces orientation dependence and enables the activation of a large number of twin systems in each structure oriented in various directions, thereby increasing the elongation (total elongation).

[0075] Since the crystal orientation in the texture is expressed in three dimensions in this embodiment, the representation method based on Euler angles is used. The representation method based on Euler angles (Bunge's representation method) considers the three coordinate axes RD, TD and ND as orthogonal to each other as the sample coordinate system (the coordinate system of the plate). Then, as the crystal coordinate system (in the case of the α phase of titanium, it is a coordinate system based on the direction of the hcp structure), the three coordinate axes X-axis, Y-axis and Z-axis are considered as orthogonal to each other. The Z axis is the

[0001] direction. The X axis sometimes takes the [10-10] direction (the normal direction of the cylinder) and sometimes takes the [1-210] direction. Here, the X axis adopts the [1-210] direction. In this case, the Y axis is the [10-10] direction (the normal direction of the cylinder). The results are the same regardless of whether any orientation is adopted as the X axis. In the representation method based on Euler angles, as Figure 1 As shown in (A), first consider the state where the sample coordinate system is consistent with the crystal coordinate system (X axis is consistent with RD, Y axis is consistent with TD, and Z axis is consistent with ND). Then, as Figure 1 As shown in (B), the crystal coordinate system is rotated φ1° (X', Y', Z) around the Z axis. Then, as Figure 1 As shown in (C), the X (X') axis after rotating φ1° is rotated Φ° (X', Y', Z'). Finally, as Figure 1 As shown in (D), the Z (Z') axis after rotating φ1° and Φ° is rotated by φ2° (not shown) (X", Y"', Z'). The three angles of φ1°, Φ°, and φ2° are used to define the crystal orientation of the grains (the direction of the c-axis, etc.). As for the crystal structure of the main phase of the titanium plate, that is, the α-phase, it is a hexagonal crystal and can be expressed by φ1 (0 to 90°), Φ (0 to 90°), and φ2 (0 to 60°).

[0076] The conventional texture of titanium plates manufactured using conventional methods, with the c-axis tilted approximately 35° from the ND toward the TD, will be further conceptually explained using the Euler angles. Expressing the c-axis tilted approximately 35° toward the TD using Euler angles, the following is true: Φ = 35°, φ1 = 0°, and φ2: arbitrary. Furthermore, limiting the [10-10] direction to the RD orientation, φ2 = 0° becomes the preferred orientation. Figure 2 A diagram showing the preferential orientation of this conventional material in three dimensions using Euler angles is shown.

[0077] When a structure with its c-axis tilted approximately 35° toward the TD is stretched in the TD and in the RD, the angles between the {10-10} plane, the main slip plane, and the {11-22} or {10-12} planes, which serve as twin planes, and the stretching direction differ. These differences in the angles between the slip and twin planes and the stretching direction mean that even with the same stretching force, the degree of slip and twinning (the amount of deformation) significantly changes. Consequently, mechanical properties become anisotropic in the TD and RD directions.

[0078] The crystal orientation distribution of a polycrystal is expressed by a function f(φ1, φ, φ2) using the aforementioned Euler angles (φ1, φ, φ2), and this function is called a crystal orientation distribution function (ODF).

[0079] If the crystal orientation (φ1, Φ, φ2) is g, then the ODF can be expressed as f(g). If the volume of the grains contained in the small orientation space dg of orientation g is dV, the volume ratio relative to the volume V of all grains is expressed using f(g) as "dV / V = f(g)dg". Therefore, once f(g) is known, the number of grains with a certain orientation can be determined. The value of f(g), which represents the orientation density, is 1 in the case of irregular orientation (see Non-Patent Document 1).

[0080] The crystal orientation distribution function (ODF) can be determined using the electron backscattered diffraction (EBSD) method. The EBSD pattern is measured and analyzed while scanning electron beams through a scanning electron microscope (SEM). This pattern is then converted to angles relative to the plate surface using a computer. This yields the Euler angles (φ1, φ, φ2) of the crystal orientation at each measurement point. The ODF (f(φ1, φ, φ2)) can be calculated based on the data from the measurement points within the field of view.

[0081] In this embodiment, the crystal orientation distribution function (ODF) is obtained by the following method.

[0082] Since the α phase is evenly distributed, the crystal orientation distribution function can be measured in any cross section of the titanium plate. For example, the surface perpendicular to the plate width direction at the position of 1 / 2 of the plate width of the titanium plate (hereinafter also referred to as "L cross section") is ground to form a measurement surface, and the total plate thickness × 10mm field of view of this surface is measured with an electron beam backscatter diffraction (EBSD) method at a spacing of 5.0μm (step length 5.0μm) while scanning electron beams with a scanning electron microscope (SEM). The EBSD pattern is analyzed and converted into the α phase crystal of titanium by calculation on a computer. Figure 1 The data measured under the above conditions were analyzed using OIMAnalysis software manufactured by TSL Solutions Co., Ltd. TM (version 8.1.0) calculates the ODF of the α phase. ODF is calculated using the spherical harmonics method using electron backscatter diffraction (EBSD) for microstructure analysis (expansion index = 16, Gaussian half-width = 5°). Considering the symmetry of rolling deformation, calculations are performed to achieve linear symmetry in the thickness, rolling, and width directions.

[0083] The deformation characteristics of a titanium plate with α phase as the main phase depend on the orientation direction of each α grain constituting the α phase with an hcp structure. In addition, the mechanical anisotropy, especially the anisotropy of elongation, of a titanium plate with a large maximum value of f(g) is large. Therefore, in the titanium plate of this embodiment, the maximum value of the crystal orientation distribution function f(g) when the crystal orientation of the α phase of titanium is represented by the Euler angle g={φ1, Φ, φ2} is 14.0 or less. Since the maximum value of f(g) of the α phase as the main phase is 14.0 or less, the structure becomes irregular, and the anisotropy of the mechanical properties of the titanium plate can be reduced. Furthermore, since the c-axis is oriented in various directions, the yield strength can be made higher than that of the cross-rolled material. The maximum value of the crystal orientation distribution function f(g) is preferably less than 12.0, less than 10.0, and more preferably less than 9.0.

[0084] Regarding the texture of the titanium plate of this embodiment, a diagram showing the three-dimensional orientation distribution function f(φ1, φ, φ2) of φ1 (0 to 90°), φ(0 to 90°), and φ2 (0 to 60°) is shown in FIG. Figure 3 .

[0085] Figure 3 In the figure, f(g) at a specific φ2 is expressed as contour lines in the space of horizontal axis: φ1 (0-90°) and vertical axis: Φ (0-90°), and φ2 is selected at intervals of 5° from 0° to 55°, and summarized in one attached figure. Figure 3The values ​​of the f(g) contour lines in the figure are shown with 3 decimal places outside the column. The values ​​recorded with the guide lines in the figure are rounded to 1 decimal place for convenience. These points are for the following Figure 4 、 5 The same goes for 7 and 8.

[0086] exist Figure 3 The maximum value of f(φ1, Φ, φ2) is determined as follows. Specifically, cross sections are created, each sectioning φ2 at 1° intervals. The maximum value of f(g) in each section is measured, and the largest value is used. The maximum value of f(φ1, Φ, φ2) occurs at the position where φ1 = 0°, Φ = 35°, and φ2 = 0°. The maximum value of f(g) at this position is 7.0.

[0087] On the other hand, as a conventional material, the texture of an α-annealed material (having a texture with the c-axis tilted about 35° toward the TD as a preferred orientation) obtained by final annealing (annealing temperature 800°C) of a titanium plate manufactured by cold rolling in the α temperature region is compared with the texture of the α-annealed material. Figure 3 The same points are summarized in one figure, where φ2 is selected from 0° to 55° in 5° intervals. Figure 4 In this conventional example, f(φ1, Φ, φ2) reaches its maximum at the position of φ1 = 0°, Φ = 35°, and φ2 = 0°, and the maximum value of f(g) at this position is 14.6.

[0088] In addition, the texture of the conventional example (β annealed material) obtained by final annealing (annealing temperature 920°C) at a temperature above the β transformation point of the titanium plate produced by cold rolling was compared with the texture of the conventional example (β annealed material). Figure 3 、 Figure 4 The same points are summarized in one figure, where φ2 is selected from 0° to 55° in 5° intervals. Figure 5 In this example, f(φ1, Φ, φ2) reaches its maximum at the position where φ1 = 0°, Φ = 35°, and φ2 = 0°, and the maximum value of f(g) at this position is 51.0.

[0089] Even if the aforementioned f(g) is 14.0 or less, there is a possibility that the crystal orientation is concentrated in an orientation range close to the preferred orientation.

[0090] In addition to the above-mentioned provisions, the titanium plate of this embodiment further stipulates that the maximum value of the crystal orientation distribution function f(g) for orientation group A (φ1: 0-30°, Φ: 30-90°, φ2: 0-60°), orientation group B (φ1: 30-60°, Φ: 30-90°, φ2: 0-60°), and orientation group C (φ1: 60-90°, Φ: 30-90°, φ2: 0-60°) is 1.0 or greater. When the maximum value of the crystal orientation distribution function f(g) for orientation group A, orientation group B, and orientation group C is 1.0 or greater, the c-axis is oriented in various directions, the crystal orientation becomes irregular, and the anisotropy is reduced.

[0091] Orientation Group A, Orientation Group B, and Orientation Group C each represent orientation groups in which the c-axis is tilted by 30° or more from the ND in the directions within the sheet plane, 30° to 60°, and 60° to 90°. In other words, if the maximum value of f(g) in these orientation groups is 1.0 or greater, it indicates that a certain amount or more of the c-axis is tilted in each direction.

[0092] Figure 6 The figure shows the regions of the orientation group A, the orientation group B, and the orientation group C when the space of {φ1, Φ, φ2} is expressed as a three-dimensional solid space.

[0093] In addition, the titanium plate of the present embodiment and the titanium plate of the conventional example (the texture with the orientation of the c-axis tilted about 35 degrees toward the TD as the preferred orientation) Figure 7 、 Figure 8 The figure shows the ODF of the region where f(g) reaches its maximum value in each of orientation groups A, B, and C. The point where f(g) reaches its maximum value in the entire region (φ1, Φ, φ2) is the same as the point where f(g) reaches its maximum value in orientation group A.

[0094] Figure 7 (Titanium plate of this embodiment), Figure 8 (Conventional titanium plate) Three graphs (A), (B), and (C) are shown. Each graph shows the distribution of f(g) within the range (φ1: 0-90°, Φ: 0-90°) while maintaining φ2 at a specific angle. (A) The position where f(g) reaches its maximum is selected within orientation group A, (B) within orientation group B, and (C) within orientation group C. Each graph shows the point where f(g) reaches its maximum value in each of orientation groups A, B, and C.

[0095] Depend on Figure 7It can be seen that in the titanium plate of the present invention, in any of the orientation group A (φ1=0°, Φ=35°, φ2=0°, maximum value of f(g) 7.0), orientation group B (φ1=52°, Φ=44°, φ2=40°, maximum value of f(g) 2.8), and orientation group C (φ1=72°, Φ=60°, φ2=15°, maximum value of f(g) 2.7), the maximum value of the crystal orientation distribution function f(g) is all greater than 1.0.

[0096] In contrast, Figure 8 As shown, in the titanium plate of the comparative example, although the maximum value of f(g) of orientation group A (φ1=0°, Φ=35°, φ2=0°, maximum value of f(g) 14.6) and orientation group B (φ1=30°, Φ=30°, φ2=30°, maximum value of f(g) 3.0) is greater than 1.0, the maximum value of orientation group C (φ1=60°, Φ=90°, φ2=30°, maximum value of f(g) 0.9) is less than 1.0.

[0097] Figure 11B An example of the SS curve of the titanium plate of this embodiment is shown. Figure 11B As shown in the SS curve, compared with the existing titanium plate ( Figure 11A ), the anisotropy of elongation (total elongation) and flow stress is small.

[0098] <The average grain diameter of the five largest grains of the α phase is 250 μm or less>

[0099] The titanium plate of this embodiment preferably has an average grain diameter (equivalent circle diameter) of the five largest grains among the grains contained in the α phase as the main phase, which is 250 μm or less. When the average grain diameter of the five largest grains is 250 μm or less, the generation of wrinkles caused by the presence of coarse grains can be suppressed.

[0100] The average grain size of the five largest grains is obtained by measuring the grain size in the field of view in the same manner as for the average grain size of the α phase described above, and averaging the equivalent circle diameters of the five largest grains. (If there are multiple grains of the same grain size, each is counted as a single grain.)

[0101] 2. Chemical composition

[0102] Next, the chemical composition of the titanium plate of this embodiment will be described. Hereinafter, the percentages of the contents of each element are expressed as mass %. In addition, ranges expressed with "to" include both end values ​​as lower and upper limits.

[0103] The titanium plate of this embodiment can have the following chemical composition: containing Fe: 0-0.500%, O: 0-0.400%, N: 0-0.050%, C: 0-0.080%, H: 0-0.013%, and the remainder is Ti and impurities, and can further have the following chemical composition: replacing part of the above-mentioned Ti, further containing one or more of Al, Cu, Nb, Si, Zr, Cr, Mo, and Sn, which are arbitrary elements.

[0104] Impurities refer to elements that may be introduced from raw materials or during the manufacturing process. Examples include Cl, Na, Mg, Ca, Ta, and V. These elements are acceptable as long as they do not impair the effects of the titanium plate of this embodiment. Limiting the amount of each impurity to less than 0.1% by mass, and limiting the total amount of impurities to 0.5% by mass or less, is a non-problematic level. Furthermore, any of the above elements may be included as impurities.

[0105] The chemical composition without any elements corresponds to the standards for industrial pure titanium (types 1 to 4) in Japanese Industrial Standard JIS H4600 (2007), "Titanium and titanium alloys - Sheet and strip." Pure titanium sheet is easy to form due to its low alloying element content.

[0106] On the other hand, when it is desired to improve strength and oxidation resistance, it is preferable to contain the above-mentioned optional elements within the range described below. Since the optional elements are not necessarily contained, the lower limit is 0%.

[0107] Fe: 0~0.500%

[0108] If the Fe content is too high, the β phase will remain after the intermediate annealing in the β region, making it difficult to form twins during the subsequent cold rolling, resulting in the inability to obtain the desired texture. Therefore, the Fe content is set to 0.500% or less. From the perspective of texture control, the Fe content is preferably 0.350% or less, more preferably 0.250% or less, further preferably 0.200% or less, and even more preferably 0.150% or less. In addition, if the Fe content exceeds 0.100%, there is a risk of reduced oxidation resistance. Therefore, considering oxidation resistance, the Fe content is preferably 0.100% or less.

[0109] The Fe content can be 0%, but since Fe is an element that may be present in titanium, reducing the Fe content to less than 0.001% increases refining costs. Therefore, the Fe content should be set to 0.001% or higher. Furthermore, Fe has the effect of increasing the 0.2% yield strength. To achieve this effect, the Fe content is preferably 0.020% or higher, and more preferably 0.030% or higher.

[0110] O: 0~0.400%

[0111] If the O content is too much, the twin deformation is suppressed and the above-mentioned texture cannot be obtained. Therefore, the O content is set to 0.400% or less. From the perspective of twin suppression, the O content is preferably 0.350% or less, more preferably 0.250% or less, further preferably 0.200% or less, and further preferably 0.150% or less. The O content can be 0%, but O is an element that may be contained in titanium. If the O content is to be less than 0.001%, the refining cost will increase, so the O content can be set to 0.001% or more. In addition, O is also an element that increases the 0.2% yield strength. In order to obtain the above-mentioned effect, it is preferred to set the O content to 0.020% or more. The O content is more preferably 0.030% or more.

[0112] N: 0~0.050%

[0113] C: 0~0.080%

[0114] H: 0~0.013%

[0115] Excessive N, C, and H contents will reduce elongation. Therefore, the N content is set to 0.050% or less, the C content is set to 0.080% or less, and the H content is set to 0.013% or less. The C content is preferably less than 0.050%.

[0116] The contents of these elements may be 0%, but reducing the N content to less than 0.0001%, the C content to less than 0.0001%, and the H content to less than 0.00001% significantly increases smelting costs. Therefore, the N content may be set to 0.0001% or higher, the C content to 0.0001% or higher, and / or the H content to 0.00001% or higher. The N content may be set to 0.001% or higher, the C content to 0.001% or higher, and / or the H content to 0.001% or higher.

[0117] Al: 0-2.30%

[0118] Al is an element that increases the 0.2% yield strength. The higher the Al content, the higher the 0.2% yield strength. Therefore, Al can be contained. To achieve this effect of increasing the 0.2% yield strength, the Al content is preferably 0.10% or more, and more preferably 0.30% or more.

[0119] On the other hand, if the Al content is too high, the activity of the specific twin system is suppressed, and the elongation is reduced. From the perspective of twin suppression, the Al content is set to 2.30% or less. The Al content is preferably 2.00% or less, more preferably 1.95%, and even more preferably 1.60%.

[0120] Cu: 0-1.80%

[0121] Cu is an element that increases the 0.2% yield strength without inhibiting twinning. The higher the Cu content, the higher the 0.2% yield strength. Therefore, it is acceptable to include Cu. To achieve the 0.2% yield strength-enhancing effect, the Cu content is preferably 0.10% or more, and more preferably 0.30% or more.

[0122] On the other hand, if the Cu content is too high, Ti2Cu will precipitate and the elongation will decrease. From the perspective of Ti2Cu precipitation, the Cu content is preferably 1.80% or less, more preferably 1.60% or less, further preferably 1.50% or less, and even more preferably 1.20% or less.

[0123] In order to increase the 0.2% yield strength, it is preferable to contain one or both of Al: 0.10% to 2.30% and Cu: 0.10% to 1.80%.

[0124] Nb: 0-1.00%

[0125] Nb is an element that improves oxidation resistance and may be contained when use at high temperatures is anticipated. To achieve an effect of improving oxidation resistance, the Nb content is preferably 0.10% or more, more preferably 0.15% or more.

[0126] On the other hand, if the Nb content is too high, the β phase will remain after intermediate annealing in the β region, making it difficult to form twins during subsequent cold rolling. In this case, the desired texture may not be formed. Therefore, from the perspective of texture control, the Nb content is set to 1.00% or less. The Nb content is preferably 0.85% or less, and more preferably 0.80% or less.

[0127] Si: 0-0.50%

[0128] Si is an element that improves oxidation resistance and may be contained when use at high temperatures is anticipated. To achieve an effect of improving oxidation resistance, the Si content is preferably 0.05% or more, more preferably 0.10% or more.

[0129] On the other hand, if the Si content is too high, silicides may precipitate and the elongation may decrease. Therefore, the Si content is set to 0.50% or less. The Si content is preferably 0.45% or less, and more preferably 0.40% or less.

[0130] Zr: 0~0.50%

[0131] Zr is an element that improves oxidation resistance and may be contained when use at high temperatures is anticipated. To achieve an effect of improving oxidation resistance, the Zr content is preferably 0.10% or more, more preferably 0.15% or more.

[0132] On the other hand, if the Zr content is too high, grain growth may be significantly inhibited, grains may become finer, and elongation may decrease. Therefore, the Zr content is set to 0.50% or less. The Zr content is preferably 0.45% or less, and more preferably 0.40% or less.

[0133] In order to improve the oxidation resistance, it is preferable to contain one or more selected from the group consisting of Nb: 0.10 to 1.00%, Si: 0.10 to 0.50%, and Zr: 0.10 to 0.50%.

[0134] Cr: 0~0.50%

[0135] Cr is an element that increases the 0.2% yield strength, so it may be contained. To obtain the effect of increasing the 0.2% yield strength, the Cr content is preferably 0.05% or more, more preferably 0.10% or more.

[0136] On the other hand, if the Cr content is too high, the β phase will remain after intermediate annealing in the β region, making it difficult to form twins during subsequent cold rolling. In this case, the desired texture may not be formed. Therefore, from the perspective of texture control, the Cr content is set to 0.50% or less. The Cr content is preferably 0.45% or less, and more preferably 0.40% or less.

[0137] Mo: 0~0.50%

[0138] Mo is an element that increases the 0.2% yield strength, so it may be contained. To obtain the effect of increasing the 0.2% yield strength, the Mo content is preferably 0.05% or more, more preferably 0.10%.

[0139] On the other hand, if the Mo content is too high, the β phase will remain after intermediate annealing in the β region, making it difficult to form twins during subsequent cold rolling. In this case, the desired texture may not be formed. Therefore, from the perspective of texture control, the Mo content is set to 0.50% or less. The Mo content is preferably 0.45% or less, and more preferably 0.40% or less.

[0140] Sn: 0~1.50%

[0141] Sn is an element that increases the 0.2% yield strength, so it may be contained. To obtain the effect of increasing the 0.2% yield strength, the Sn content is preferably 0.05% or more, more preferably 0.10% or more.

[0142] On the other hand, if the Sn content is too high, grain growth may be significantly inhibited, grains may become finer, and elongation may decrease. Therefore, the Sn content is set to 1.50% or less. The Sn content is preferably 1.30% or less, more preferably 1.10% or less, and even more preferably 1.00% or less.

[0143] In order to increase the 0.2% proof stress, it is preferable to contain one or more selected from the group consisting of 0.05% to 0.50% of Cr, 0.05% to 0.50% of Mo, and 0.05% to 1.50% of Sn.

[0144] The titanium plate of this embodiment is preferably a cold-rolled and annealed plate obtained by subjecting a cold-rolled plate to a final annealing step. Alternatively, the plate may be tempered using a tension leveler, skin-pass mill, or the like after the final annealing step. Furthermore, a thin plate is preferred, preferably having a thickness of 1.5 mm or less. A thickness of 1.2 mm or less is more preferred, 1.0 mm or less is even more preferred, and 0.8 mm or less is even more preferred.

[0145] 3. Features

[0146] The titanium plate of this embodiment has sufficient elongation and small anisotropy of elongation.

[0147] For example, the elongation (total elongation) in both RD (rolling direction) and TD (sheet width direction) when stretched is preferably 20% or more.

[0148] In addition, the elongation El when stretched along RD (rolling direction) RD Elongation El when stretched along TD (sheet width direction) TD The ratio (El RD / El TD ) is closer to 1.0, the smaller the anisotropy will be. The elongation El of the titanium plate when stretched along RD (rolling direction) of this embodiment is RD Elongation El when stretched along TD (sheet width direction) TD The ratio (El RD / El TD ) is preferably 0.70 to 1.30. (El RD / El TD ) is more preferably 0.75 or more, further preferably 0.80 or more, and still further preferably 0.85 or more. RD / El TD ) is more preferably 1.25 or less, and further preferably 1.20 or less.

[0149] In addition, with respect to the titanium plate of this embodiment, from the perspective of anisotropy, the flow stress ratio is preferably 0.90 to 1.10 at the 1 / 4 position, the 1 / 2 position, and the 3 / 4 position of the strain on the smaller side of the total elongation (at fracture) of the SS curve when stretched along the RD (rolling direction) and TD (plate width direction), respectively.

[0150] Tensile testing was conducted in accordance with JIS Z2241 (1998), "Metallic Materials Tensile Testing Methods," using a No. 13B test piece specified in JIS Z2201 (1998), "Metallic Materials Tensile Test Specimens." Elongation in the RD and TD directions was measured. Specifically, the gauge length was set to 50 mm, and the strain rate was set to 0.5% / min until a strain of 2% was reached, and then to 30% / min thereafter, with the specimen stretched until fracture.

[0151] In addition, the flow stress ratio at the 1 / 4 position, 1 / 2 position, and 3 / 4 position, which are the smaller strains until the total elongation (at break) of the SS curve, is determined by the following method. For example, in a tensile test, when the following values ​​are obtained for RD and TD: Figure 14 In the case of the SS curve shown in FIG, the strain of the smaller of the total elongation of RD and TD is obtained ( Figure 14 (where TD is the strain, 0.420). Calculate the flow stresses in RD and TD at 1 / 4 of the strain (0.105), 1 / 2 (0.210), and 3 / 4 (0.315). At each position, divide the flow stress in RD by the flow stress in TD to calculate the flow stress ratio.

[0152] 4. Manufacturing Method

[0153] Next, a preferred method for manufacturing the titanium plate of this embodiment will be described. The titanium plate of this embodiment can achieve its effects as long as it has the above-mentioned characteristics, regardless of the manufacturing method. However, a manufacturing method including the following steps is preferred because it can be stably manufactured.

[0154] (I) Melting step, (II) Coiling step, (III) Hot rolling step, (IV) Cold rolling step, (V) Final annealing step.

[0155] Hereinafter, each step will be described.

[0156] [Smelting process]

[0157] A titanium billet produced to a predetermined purity is melted by a known method to form a predetermined ingot. Specifically, vacuum arc melting (VAR) or electron beam melting (EB) can be used.

[0158] [Blanking process]

[0159] The slab is processed into a slab shape by known bloom rolling and forging.

[0160] [Hot rolling process]

[0161] Proceed according to a known method.

[0162] For example, a slab is heated to 700-1000°C and rolled at a reduction ratio of 60-98% to obtain a hot-rolled sheet. At this time, heating to a temperature exceeding the β transformation point accelerates scale formation, so the heating temperature is preferably set below the β transformation point.

[0163] [Hot-rolled plate annealing process]

[0164] Annealing (hot-rolled sheet annealing) may be performed as needed after the hot rolling process and before the cold rolling process. In this case, annealing is performed for a predetermined time while maintaining a temperature of 600° C. or higher and a β transformation point temperature or lower.

[0165] The β-transition point temperature can be obtained from a phase diagram. The phase diagram can be obtained, for example, using the CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) method, for example using Thermo-Calc, a comprehensive thermodynamic calculation system from Thermo-Calc Software AB, and a specified database (TI3).

[0166] When manufacturing the titanium plate of this embodiment, the most characteristic feature is the combination of the cold rolling process, the intermediate annealing in the cold rolling process, and the conditions of the final annealing process. Therefore, in the cold rolling process, the conditions of the final cold rolling and the intermediate annealing immediately before the final cold rolling (hereinafter referred to as "final intermediate annealing") are set to predetermined conditions. The cold rolling, final intermediate annealing, final cold rolling, and final annealing processes of the titanium plate manufacturing process of this embodiment are schematically shown in FIG. Figure 13 .

[0167] [Cold rolling process]

[0168] Cold rolling up to final intermediate annealing may be performed under known conditions. Intermediate annealing may be performed between each pass of cold rolling.

[0169] Final intermediate annealing heating temperature: above β transformation point

[0170] During the final intermediate annealing (the final annealing within the intermediate annealing), heating to a temperature above the β transformation point causes the α phase to temporarily transform into the β phase, and upon cooling, it transforms back into the α phase, causing the texture to become irregular. This results in a reduced anisotropy of the titanium plate. If the heating temperature is below the β transformation point, the maximum value of the crystal orientation distribution function f(g) in the final product will exceed 14.0. This results in increased anisotropy of the titanium plate. Therefore, the heating temperature for the final intermediate annealing is set above the β transformation point.

[0171] On the other hand, from the viewpoint of oxidation resistance, the temperature of the final intermediate annealing is preferably 1000° C. or lower.

[0172] In addition, from the viewpoint of anti-oxidation, the annealing time is preferably 0 to 10 minutes. Here, the annealing time of 0 minutes refers to the case where cooling is started immediately after reaching the annealing temperature.

[0173] Final cold rolling: rolling rate 5-50%

[0174] If the final cold rolling reduction (the cold rolling reduction performed after the final intermediate annealing and until the final annealing) is 5-50%, twinning deformation will also be active on the basis of slip deformation, and the texture will become irregular. If the final cold rolling reduction is lower than 5%, coarse needle-shaped unrecrystallized grains will remain in the subsequent annealing, and the maximum value of the crystal orientation distribution function f(g) will exceed 14.0. In addition, the average grain size will also exceed 100.0μm. On the other hand, if the final cold rolling reduction exceeds 50%, twinning is unlikely to occur, and the orientation along a specific direction based on slip deformation is enhanced. After the final annealing, the orientation along a specific direction still appears, and the maximum value of the crystal orientation distribution function f(g) will exceed 14.0 in the final product. As a result, the anisotropy of the titanium plate increases. Therefore, in the final cold rolling, the rolling reduction is set to be greater than 5% and less than 50%. In the final cold rolling, the rolling reduction is preferably greater than 10% and less than 40%.

[0175] The cold rolling at this rolling reduction rate may be performed in one pass or in multiple passes. That is, the total rolling reduction rate of the cold rolling performed between the final intermediate annealing and the final annealing (without annealing between passes) may be such that it reaches the predetermined rolling reduction rate.

[0176] If the crystal orientation is made irregular before the final cold rolling, it will eventually become further irregular. Therefore, it is preferable to perform intermediate annealing in the β region (temperature equal to or higher than the β transformation point) to make the orientation varied.

[0177] [Final annealing process]

[0178] Heating temperature: above 475℃ and below β-transformation point

[0179] If the heating temperature during final annealing is lower than 475°C, recrystallization will not be completed, anisotropy will increase, and elongation may decrease. Therefore, the heating temperature for final annealing is set to 475°C or higher.

[0180] On the other hand, if the heating temperature exceeds the β transformation point, the microstructure becomes acicular, resulting in coarse grains and a maximum value of the crystal orientation distribution function f(g) exceeding 14.0. Furthermore, wrinkles are more likely to form during forming. Therefore, the heating temperature should be set below the β transformation point.

[0181] The heating time of the final annealing is not particularly limited, but is preferably set to 0.5 min or longer from the perspective of ensuring the stability of the structure by recrystallization, and is preferably set to 480 min or shorter from the perspective of preventing coarsening of crystal grains.

[0182] According to the above-mentioned manufacturing method, the crystal orientation of the product is varied, the texture is irregular, and the anisotropy of strength and elongation is reduced.

[0183] Example

[0184] After manufacturing titanium alloy ingots having the chemical composition shown in Tables 1 and 2 by vacuum arc melting (VAR), slabs having a thickness of 150 mm × a width of 800 mm × a length of 5000 mm are manufactured by bloom rolling or forging. Subsequently, these slabs are heated to 850°C and hot rolled to prepare titanium plate billets having a thickness of 4.0 mm and a composition shown in Tables 1 and 2. A portion of the titanium plate billets is annealed by hot rolling at 780°C for 2 minutes. The titanium plate billets are subjected to cold rolling, final intermediate annealing, final cold rolling, and final annealing under the conditions shown in Tables 1 and 2 to manufacture titanium plates (cold rolled annealed plates) having a thickness of 0.5 mm.

[0185] [Table 1]

[0186]

[0187] [Table 2]

[0188]

[0189] For the obtained titanium plate, the surface perpendicular to the plate width direction at the 1 / 2 position of the titanium plate (L section) is used as the observation surface, and the area ratio of the α phase, the average grain size of the α phase, and the average grain size of the five largest grains of the α phase are measured according to the above method.

[0190] In addition, regarding the crystal orientation distribution function f(g) and its maximum value when the crystal orientation of the α phase is represented by the Euler angle g = {φ1, Φ, φ2}, the surface (L cross section) perpendicular to the width direction of the titanium plate at the position of 1 / 2 of the plate width is used as the observation surface and is calculated according to the above method.

[0191] In addition, according to the above method, the maximum values ​​of the crystal orientation distribution function f(g) of the orientation group A expressed by the above Euler angles as φ1: 0~30°, Φ: 30~90°, φ2: 0~60°, the orientation group B expressed by φ1: 30~60°, Φ: 30~90°, φ2: 0~60°, and the orientation group C expressed by φ1: 60~90°, Φ: 30~90°, φ2: 0~60° are calculated.

[0192] Furthermore, a No. 13B test piece specified in JIS Z2201 (1998) "Metallic Material Tensile Test Specimen" was taken from the obtained titanium plate, and a tensile test was performed according to JIS Z2241 (1998) "Metallic Material Tensile Test Method" to measure the elongation (Elongation) in RD and TD. RD 、El TD Specifically, the gauge length was set to 50 mm, the strain rate was set to 0.5% / min until the strain reached 2%, and then to 30% / min, and the specimen was stretched to break. After the break, the fracture surface was butt-jointed, and the change in gauge length (50 mm before stretching) was measured to determine the total elongation. RD / El TD The value of .

[0193] Furthermore, a No. 13B test piece, as specified in JIS Z2201 (1998), "Metallic Materials Tensile Test Specimens," was taken from the resulting titanium plate and subjected to a tensile test in accordance with JIS Z2241 (1998), "Metallic Materials Tensile Test Methods," at a strain rate of 30% / min in the rolling direction until the strain reached 20%. The appearance of the plate was then confirmed and visually evaluated for the presence of wrinkles. Wrinkles here refer to the appearance of an orange peel caused by the unevenness associated with plastic deformation. Specifically, the surface was observed, and titanium plates with visible wrinkles were judged to have wrinkles.

[0194] In addition, for some examples, when stretching along RD (rolling direction) and TD (sheet width direction) to measure the elongation, the flow stress ratio was calculated at the 1 / 4 position, 1 / 2 position, and 3 / 4 position of the strain until the total elongation (at fracture) on the SS curve.

[0195] The results are shown in Tables 3 and 4.

[0196] [Table 3]

[0197]

[0198] [Table 4]

[0199]

[0200] Regarding Examples 1 to 36 of the present invention, the total elongation in either RD or TD was 20% or more, and El RD / El TD The values ​​of are all close to 1.00, and the anisotropy is small. For example, the crystal orientation distribution function f(g) of the titanium plate of Inventive Example 6 in three-dimensional Euler angle is as follows: Figure 3 、 Figure 7 As shown. Figure 3 It can be seen that in the three-dimensional space of Euler angles, f(g) is dispersed without showing a tendency to increase locally. As a result, the maximum value of f(g) appears at φ1 = 0°, Φ = 35°, and φ2 = 0°, and the maximum value of f(g) at this position is 7.0. The structure of Example 6 of the invention was analyzed and the results were as follows: Figure 10 The average grain size is 65 μm. As a result, it is confirmed that the elongation in either RD or TD direction is high, and the mechanical anisotropy including strength is eliminated ( Figure 9 ).

[0201] In contrast, in Comparative Example 101, the final intermediate annealing temperature was low, and a strongly oriented structure with a maximum value of f(g) exceeding 14.0 was formed. As a result, El RD / El TD The value of is also large, and the anisotropy of the titanium plate is large.

[0202] Comparative Example 102 had a structure with residual unrecrystallized grains due to the low reduction ratio of the final cold rolling, and a strongly oriented structure with a maximum value of f(g) exceeding 14.0 was formed. RD / El TD The value of is also large, indicating that the titanium plate has a large anisotropy. In addition, the average grain size exceeds 100.0 μm, causing wrinkles during deformation.

[0203] Comparative Example 103 had a high reduction ratio in the final cold rolling, and thus a strongly oriented structure with a maximum value of f(g) exceeding 14.0 was formed. RD / El TD The value of is also large, and the anisotropy of the titanium plate is large.

[0204] Comparative Example 104 had a structure with residual unrecrystallized grains due to the low temperature of the final annealing. RD / El TD The value of is also large, and the anisotropy of the titanium plate is large.

[0205] Comparative Examples 105 and 109 formed a small acicular structure with coarse structure due to the high temperature of the final annealing. As a result, a strongly oriented structure with a maximum value of f(g) exceeding 14.0 was formed. RD / El TD The value of is also large. In addition, wrinkles are generated.

[0206] In Comparative Example 106, since the final intermediate annealing was not performed, the cold rolling ratio during the final cold rolling was high, and therefore the maximum value of f(g) of the orientation group C was less than 1.0. RD / El TD The value of is also large, and the anisotropy of the titanium plate is large.

[0207] Comparative Example 107 did not undergo final intermediate annealing, and the cold rolling ratio during final cold rolling was high, so a strongly oriented structure with a maximum value of f(g) exceeding 14.0 was formed. RD / El TD The value of is also large, and the anisotropy of the titanium plate is large. In addition, the final annealing temperature is high, and the α phase becomes a needle-shaped structure with a small average roundness, resulting in wrinkles.

[0208] Comparative Example 108 had a strong orientation structure with a maximum value of f(g) exceeding 14.0 due to the low temperature of the final intermediate annealing. RD / El TD The value of is also large, and the anisotropy of the titanium plate is large. In addition, the final annealing temperature is high, and the α phase becomes a needle-shaped structure with a small average roundness, resulting in wrinkles.

[0209] Comparative Example 110 did not undergo final cold rolling, resulting in a strongly oriented structure with a maximum value of f(g) exceeding 14.0. RD / El TD The value of is also large, and the anisotropy of the titanium plate is large. In addition, the α phase becomes a needle-shaped structure with a small average roundness, resulting in wrinkles.

[0210] Comparative Example 111 did not undergo final annealing. As a result, the elongation decreased, and RD / El TD The value of is also large.

[0211] The Fe content of Comparative Example 112 exceeded the upper limit, and a strongly oriented structure with a maximum value of f(g) exceeding 14.0 was formed. RD / El TD The value of is also large, and the anisotropy of the titanium plate is large.

[0212] In Comparative Example 113, the O content exceeded the upper limit, the maximum value of f(g) of orientation group C was less than 1.0, and the elongation was also reduced.

[0213] In Comparative Example 114, the Al content exceeded the upper limit, and the elongation decreased.

[0214] In Comparative Example 115, the Cu content exceeded the upper limit, and the elongation decreased.

[0215] Industrial applicability

[0216] According to the present invention, a titanium plate having high elongation and low elongation anisotropy can be provided. This titanium plate has excellent formability and is therefore useful for producing titanium products of complex shapes by press forming.

Claims

1. A titanium plate, characterized in that: The chemical composition is as follows: Fe: 0-0.500%, O：0～0.400％、 N：0～0.050％、 C：0～0.080％、 H：0～0.013％、 Al：0～2.30％、 Cu: 0-1.80%, Nb: 0-1.00%, Si: 0-0.50%, Zr：0～0.50％、 Cr：0～0.50％、 Mo: 0~0.50%, and Sn: 0~1.50%, The balance is Ti and impurities. The α phase fraction of the metallographic structure in the entire evaluation surface is 95% or more by area. The average grain size of the α phase is 100.0 μm or less, When the crystal orientation of the α phase is represented by the Euler angle g = {φ1, Φ, φ2}, the maximum value of the crystal orientation distribution function f(g) calculated by the structure analysis using the spherical harmonic method of the electron backscatter diffraction method with an expansion index of 16 and a Gaussian half-value width of 5° is 14.0 or less. The maximum value of the crystal orientation distribution function f(g) of the orientation group A expressed by the Euler angles φ1: 0 to 30°, Φ: 30 to 90°, and φ2: 0 to 60° is 1.0 or greater, The maximum value of the crystal orientation distribution function f(g) of the orientation group B expressed by the Euler angles φ1: 30 to 60°, Φ: 30 to 90°, and φ2: 0 to 60° is 1.0 or greater, The maximum value of the crystal orientation distribution function f(g) of the orientation group C expressed by the Euler angles of φ1: 60 to 90°, φ: 30 to 90°, and φ2: 0 to 60° is 1.0 or greater.

2. The titanium plate according to claim 1, characterized in that The chemical composition comprises by mass % One or two of O: 0.030 to 0.200% and Fe: 0.020 to 0.200%.

3. The titanium plate according to claim 2, characterized in that The chemical composition comprises by mass % One or two of Al: 0.10 to 2.30% and Cu: 0.10 to 1.80%.

4. The titanium plate according to claim 3, characterized in that The chemical composition comprises by mass % Fe: 0.100% or less, and One or more selected from the group consisting of Nb: 0.10 to 1.00%, Si: 0.10 to 0.50%, and Zr: 0.10 to 0.50%.

5. The titanium plate according to claim 3, characterized in that The chemical composition comprises by mass % One or more selected from the group consisting of Cr: 0.05 to 0.50%, Mo: 0.05 to 0.50%, and Sn: 0.05 to 1.50%.

6. The titanium plate according to claim 4, characterized in that The chemical composition comprises by mass % One or more selected from the group consisting of Cr: 0.05 to 0.50%, Mo: 0.05 to 0.50%, and Sn: 0.05 to 1.50%.

7. The titanium plate according to any one of claims 1 to 6, characterized in that The average grain size of the five largest grains of the α phase is 250 μm or less.

8. The titanium plate according to any one of claims 1 to 6, characterized in that The average grain diameter of the α phase is 2.0 to 100.0 μm.

9. The titanium plate according to claim 7, characterized in that The average grain diameter of the α phase is 2.0 to 100.0 μm.

10. The titanium plate according to any one of claims 1 to 6, characterized in that The average grain diameter of the α phase is 8.0 to 100.0 μm.

11. The titanium plate according to claim 7, characterized in that The average grain diameter of the α phase is 8.0 to 100.0 μm.

12. The titanium plate according to any one of claims 1 to 6, characterized in that The ratio of the total elongation in the rolling direction to the total elongation in the plate width direction is El RD / El TD It is 0.70~1.

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13. The titanium plate according to claim 7, characterized in that The ratio of the total elongation in the rolling direction to the total elongation in the plate width direction is El RD / El TD It is 0.70~1.

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14. The titanium plate according to claim 8, characterized in that The ratio of the total elongation in the rolling direction to the total elongation in the plate width direction is El RD / El TD It is 0.70~1.

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15. The titanium plate according to claim 9, characterized in that The ratio of the total elongation in the rolling direction to the total elongation in the plate width direction is El RD / El TD It is 0.70~1.

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16. The titanium plate according to claim 10, characterized in that The ratio of the total elongation in the rolling direction to the total elongation in the plate width direction is El RD / El TD It is 0.70~1.

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17. The titanium plate according to claim 11, characterized in that The ratio of the total elongation in the rolling direction to the total elongation in the plate width direction is El RD / El TD It is 0.70~1.30.

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