CN116635562A - Titanium plate - Google Patents

Abstract

The titanium plate has a predetermined chemical composition, the metallographic structure of which comprises an alpha phase, the average grain diameter of the alpha phase is 100.0 mu m or less, and the Euler angle g= { phi ₁ ,Φ,φ ₂ When the crystal orientation of the alpha phase is expressed, the maximum value of the crystal orientation distribution function f (g) is 14.0 or less, and the Euler angle is expressed as phi ₁ ：0～30°,Φ：30～90°,φ ₂ : the maximum value of the crystal orientation distribution function f (g) of the orientation group A expressed at 0 to 60 DEG is 1.0 or more, and phi is the Euler angle ₁ ：30～60°,Φ：30～90°,φ ₂ : the maximum value of the crystal orientation distribution function f (g) of the orientation group B expressed at 0 to 60 DEG is 1.0 or more, and phi is the Euler angle ₁ ：60～90°,Φ：30～90°,φ ₂ : the maximum value of the crystal orientation distribution function f (g) of the orientation group C expressed at 0 to 60 DEG is 1.0 or more.

Description

Titanium plate

Technical Field

The present invention relates to a titanium plate, and more particularly to a titanium plate having less processing anisotropy and excellent formability.

Background

Titanium plates are used in plate heat exchangers and the like. Since a high heat exchange rate is required for the plate heat exchanger, when the titanium plate is applied to the plate heat exchanger, the titanium plate is processed into a wave shape by press forming in order to increase the surface area. Therefore, the titanium plate for heat exchanger needs to have excellent formability in press forming.

In press forming, the titanium plate is required to be sufficiently and uniformly elongated in any direction without breaking. However, in a titanium plate, the mechanical properties (strength, elongation) in the rolling direction, that is, in the plate length direction (RD) are generally different from the mechanical properties (strength, elongation) in the plate width direction (TD) in the direction perpendicular to the direction RD in the plate surface (mechanical anisotropy is exhibited). This is because titanium sheets are usually manufactured by cold rolling in only one direction, resulting in formation of a texture oriented in a specific direction by cold rolling. The plate thickness direction (direction perpendicular to the plate surface) is hereinafter referred to as ND.

The texture formed by the cold rolling is only a recrystallized texture oriented in a specific azimuth even if annealed and recrystallized thereafter, and therefore the anisotropy of the texture is not eliminated. Therefore, conventional titanium sheets have anisotropy of mechanical properties derived from anisotropy of the structure before and after annealing.

The texture formed by cold rolling during the production of the titanium sheet will be described in more detail.

Titanium sheets manufactured by cold rolling in one direction under conventional conditions and annealing at an alpha domain temperature are formed with the following textures: the c-axis (axis parallel to the [0001] direction) of α -particles belonging to the hcp structure (hexagonal crystal) is often oriented in an azimuth inclined from ND (direction perpendicular to the plate surface) toward TD (plate width direction) by about 35 °. Because of this texture, conventional titanium sheets have processing anisotropy, which constitutes a cause of impairing the formability of the titanium sheets.

Various attempts have been made to improve the formability of titanium sheets as disclosed in patent documents 1 to 7.

Patent documents 1 and 2 describe the following: in order to improve strength and formability, the relationship between the grain size of the alpha-phase grains of the titanium plate and the area of the three oriented grains, which are expressed by the crystal orientation distribution function.

Patent document 1 discloses control of intermediate annealing conditions (performed in a recrystallization temperature range), final cold rolling conditions (the reduction ratio of final cold rolling is 20 to 87%), and final annealing conditions after cold rolling (the annealing temperature is not less than the β transformation point and lower than 950 ℃) for texture. The grain diameter of the alpha grains is also controlled by the final annealing conditions.

Patent document 2 discloses control of an intermediate annealing condition (performed in a recrystallization temperature range), a final cold rolling condition (the reduction ratio of the final cold rolling is 20 to 87%), and a final annealing condition after cold rolling (the annealing temperature is a temperature at which the β -phase content is 20% or more and lower than the β -transformation point) for a texture. The grain diameter of the α -grain is also controlled by the final annealing conditions and the final cold rolling reduction.

Patent document 3 describes the following: in order to improve strength and formability, the grain size of the alpha-phase grains of the titanium plate is set to a specific range, and the area ratio of the alpha-phase grains having a specific relationship with the (0001) plane axis orientation is set to a specific value. In patent document 3, in order to set the crystal orientation of the titanium plate and the equivalent circle diameter of the α -phase crystal grains within a predetermined range, the temperature rise rate (10 ℃/s or more) of the final annealing, the holding temperature (the temperature at which the area ratio of the β -phase to the α -phase reaches 50% or more and less than 950 ℃), the holding time (300 seconds or less), and the cooling rate (10 ℃/s or more) are controlled.

Patent document 4 describes the following: in order to reduce the anisotropy of strength, the grain size of alpha-phase grains of the titanium plate is set to a specific range, and the 0.2% yield strength in the direction in which the yield strength is minimized is YS _R A 0.2% yield strength in a direction perpendicular to the direction in which the yield strength is minimized is YS _T Ratio of time YS _T /YS _R At 1.17And (3) downwards. In patent document 4, the final cold rolling rate after the final intermediate annealing is set to 20 to 87%, and the annealing temperature of the final annealing is set to not less than the β transformation point (tβ) and less than 950 ℃, whereby the crystal orientation of the titanium sheet and the equivalent circular diameter of the α -phase crystal grains are controlled.

Patent document 5 describes the following: in order to reduce the anisotropy of strength, the average value of the aspect ratio of the alpha-phase grains of the titanium plate is set to 2.0 or more and the standard deviation is set to 0.70 or more, and the average value of the 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.

Patent document 6 describes a titanium sheet for press forming, which has an in-plane anisotropy of not less than 0.72, obtained by dividing the average r by the difference between the lankfield values (r values) obtained when the rolling direction is subjected to a tensile test at 90 ° and 0 ° by the elike value of not less than 12.9 by performing a rolling at a different peripheral speed under heat.

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.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 2016-108652

Patent document 2: japanese patent application laid-open No. 2017-137561

Patent document 3: japanese patent application laid-open No. 2015-63720

Patent document 4: japanese patent laid-open No. 2016-102237

Patent document 5: japanese patent application laid-open No. 2016-23215

Patent document 6: japanese patent application laid-open No. 2011-230171

Patent document 7: japanese patent application laid-open No. 63-130753

Non-patent literature

Non-patent document 1: three-dimensional crystal orientation distribution analysis method of well Boschy and its progress, recrystallization and texture and application in the control of this structure, japanese society for iron and steel, 3 rd month, 297-299 pages (well Boschy) method for analyzing 3-order member JI crystal orientation distribution, method for analyzing the size of the further layer of the crystal/aggregate composition, method for preparing the further layer of the coating of the そ layer of the crystal/aggregate composition, method for preparing the further layer of the coating of the earth by using the further layer of the Japanese Zhi Ji, chan 3, no. 297-299 )

Disclosure of Invention

Problems to be solved by the invention

As described above, the titanium plate manufactured by the conventional general method has a texture having a c-axis inclined from ND to TD by about 35 ° as a preferential orientation, and has mechanical anisotropy. In contrast, as a technique for improving the formability, various methods shown in the above-mentioned patent documents 1 to 7 have been proposed.

However, the titanium plates described in patent documents 1 to 3 have not been studied for mechanical anisotropy. The titanium plates described in patent documents 4 to 7 were studied for anisotropy of strength, but were not studied for anisotropy of elongation.

The present inventors have studied and found that the anisotropy of elongation is not necessarily small even when the anisotropy of strength is small. For example, as a conventional material, fig. 11A shows an S-S curve (stress-strain curve) for an α -annealed material obtained by subjecting a titanium plate manufactured by cold rolling to final annealing in an α temperature region (annealing temperature 800 ℃). As is clear from fig. 11A, even when the anisotropy of the strength of RD and TD is small, the anisotropy of elongation is not necessarily small. The S-S curve was also confirmed for a beta annealed material obtained by subjecting a titanium sheet produced by cold rolling to final annealing at a temperature equal to or higher than the beta transus point (annealing temperature 920 ℃ C.), and as a result, the same results as in FIG. 11A were obtained. That is, even when the anisotropy of the strength of RD and TD is small, the anisotropy of elongation is not necessarily small.

Further, if the anisotropy of the sheet is simply reduced, it is possible to make the c-axis and ND substantially coincide with each other by the different peripheral speed rolling as described in patent document 6 or the cross rolling as described in patent document 7 (Φ≡0, Φ) ₁ 、φ ₂ Arbitrary value). However, in these cases, although it is changedThe anisotropy of elongation is improved, but since the c-axis is oriented along ND, stretching from either direction becomes perpendicular to the c-axis, and the yield strength becomes lowest. In addition, in order to actually manufacture a thin titanium plate, it is necessary to roll the thin titanium plate with a cutting plate instead of coil stock in order to perform cross rolling, which is inefficient. Further, the rolling plate tends to curl and slip is large because the direction of friction between the two rolls is different in the rolling at the different peripheral speed, and the properties of the surface tend to deteriorate. Therefore, the techniques of patent documents 6 and 7 cannot sufficiently reduce the anisotropy of the titanium plate in practical operation.

In view of the above problems, an object of the present invention is to provide a titanium plate having a large elongation and a small anisotropy of elongation.

Solution for solving the problem

That is, the gist of the present invention is as follows.

[1]The titanium plate according to one embodiment of the present invention has the following chemical composition: comprises the following components in percentage by mass: 0 to 0.500 percent of O:0 to 0.400 percent, N:0 to 0.050 percent, C:0 to 0.080 percent, H:0 to 0.013 percent, al: 0-2.30%, cu:0 to 1.80 percent of Nb: 0-1.00%, si:0 to 0.50 percent of Zr:0 to 0.50 percent of Cr:0 to 0.50 percent of Mo:0 to 0.50% and Sn:0 to 1.50%, the balance being Ti and impurities, the metallographic structure comprising an alpha phase having an average grain diameter of 100.0 [ mu ] m or less and having an Euler angle g= { phi ] ₁ ,Φ,φ ₂ When the crystal orientation of the alpha phase is expressed, the maximum value of the crystal orientation distribution function f (g) calculated by the structural analysis of the spherical harmonic method using the electron back scattering diffraction method with the expansion index of 16 and the gaussian half-value width of 5 DEG is 14.0 or less, and the Euler angle is used as phi ₁ ：0～30°,Φ：30～90°,φ ₂ : the maximum value of the crystal orientation distribution function f (g) of the orientation group A expressed at 0 to 60 DEG is 1.0 or more, and phi is the Euler angle ₁ ：30～60°,Φ：30～90°,φ ₂ : the maximum value of the crystal orientation distribution function f (g) of the orientation group B expressed at 0 to 60 DEG is 1.0 or more, and phi is the Euler angle ₁ ：60～90°,Φ：30～90°,φ ₂ : the aforementioned crystals of orientation group C expressed at 0 to 60 DEGThe maximum value of the body orientation distribution function f (g) is 1.0 or more.

[2] The titanium plate according to the above [1], wherein the aforementioned chemical composition may contain O in mass%: 0.030 to 0.200 percent of Fe:0.020 to 0.200% of 1 or 2 kinds.

[3] The titanium plate according to the above [1] or [2], wherein the aforementioned chemical composition may contain Al in mass%: 0.10 to 2.30 percent of Cu:0.10 to 1.80% of 1 or 2 kinds.

[4] The titanium plate according to the above [3], wherein the aforementioned chemical composition may contain Fe in mass%: 0.100% or less, selected from Nb:0.10 to 1.00 percent of Si:0.10 to 0.50 percent of Zr:0.10 to 0.50% of more than 1 kind.

[5] The titanium sheet according to the above [3] or [4], wherein the chemical composition may contain, in mass%, a metal selected from the group consisting of Cr:0.05 to 0.50 percent of Mo:0.05 to 0.50 percent of Sn:0.05 to 1.50% of more than 1 kind.

[6] The titanium sheet according to any one of the above [1] to [5], wherein the average grain diameter of the largest 5 grains of the alpha phase may be 250 μm or less.

[7] The titanium sheet according to any one of the above [1] to [6], wherein the average crystal grain diameter of the alpha phase may be 2.0 to 100.0. Mu.m.

[8] The titanium sheet according to any one of the above [1] to [6], wherein the average crystal grain diameter of the alpha phase may be 8.0 to 100.0. Mu.m.

[9]According to [1] above]～[8]The titanium sheet according to any one of the preceding claims, wherein the ratio of the total elongation in the rolling direction to the total elongation in the sheet width direction is El _RD /El _TD May be 0.70 to 1.30.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the above aspect of the present invention, a titanium plate having a large elongation (hereinafter, the total elongation is indicated without any particular statement) and a small anisotropy of elongation can be provided. The titanium sheet is excellent in formability, and therefore is useful for producing a titanium product having a complicated shape by press forming.

Drawings

Fig. 1 is a diagram illustrating a method of expressing a crystal orientation in three dimensions based on euler angles.

Fig. 2 is a diagram illustrating a three-dimensional expression method for expressing the preferential orientation of the conventional material (α -annealed material) by using the euler angle.

Fig. 3 is a graph showing a contour line of the crystal orientation distribution function ODF in the euler angle space for the titanium plate of the present invention.

Fig. 4 is a graph showing a contour line of the crystal orientation distribution function ODF in the euler angle space for a titanium plate of the conventional example (α -annealed material).

Fig. 5 is a graph showing a contour line of the crystal orientation distribution function ODF in the euler angle space for a titanium plate of the conventional example (β annealed material).

Fig. 6 is a diagram illustrating regions of the alignment groups a to C in a three-dimensional representation of the euler angle.

Fig. 7 is a graph showing, in a contour line, the ODF of a region including a position where the ODF reaches the maximum value in each alignment group in the titanium plate of the present embodiment, points where (a) of fig. 7 includes alignment group a, (B) of fig. 7 includes alignment group B, and (C) of fig. 7 includes the ODF maximum value in alignment group C.

Fig. 8 is a graph showing, in a contour line, an ODF including a region where the ODF reaches the maximum value in each alignment group with respect to a conventional titanium plate, points where fig. 8 (a) includes alignment group a, fig. 8 (B) includes alignment group B, and fig. 8 (C) includes the ODF maximum value in alignment group C.

Fig. 9 is a graph showing quality indexes of the titanium plate according to the present embodiment, fig. 9 (a) is a graph showing strengths of TD and RD, and fig. 9 (B) is a graph showing total elongation and uniform elongation of TD and RD.

Fig. 10 is a view showing a structure (equiaxed structure) of the titanium plate of the present embodiment.

Fig. 11A is a graph showing an S-S curve of an annealed material of a titanium plate manufactured by conventional cold rolling.

Fig. 11B is a view showing an example of an S-S curve of the titanium plate of the present embodiment.

Fig. 12 is a diagram showing a structure (needle-like structure) of a titanium plate obtained by setting the final annealing to a β transformation point temperature or higher.

Fig. 13 is a diagram showing a process for manufacturing a titanium plate according to the present embodiment.

Fig. 14 is a diagram for explaining a method of calculating flow stress from an S-S curve.

Detailed Description

Hereinafter, a titanium plate according to an embodiment of the present invention (titanium plate according to the present embodiment) will be described.

1. Metallographic structure

< average grain diameter of alpha phase is 100.0 μm or less >

The titanium plate of the present embodiment has a crystal structure mainly composed of an α phase. The alpha phase is the main crystal structure: the alpha phase fraction in the whole evaluation surface is 95% or more by area ratio. The fraction is preferably 97% or more, more preferably 99% or more. The rest of the tissues except the alpha phase comprise beta phase and Ti ₂ Cu、TiFe、Ti ₃ Al and silicide.

The average grain diameter of the alpha phase is 100.0 μm or less. If the average grain diameter of the α phase exceeds 100.0 μm, the ratio of grains of a specific crystal orientation increases, which constitutes a cause of anisotropy of elongation. In addition, the presence of coarse grains may cause wrinkles to be easily generated at the time of forming. The average crystal grain diameter of the α phase is preferably 90.0 μm or less, more preferably 80.0 μm or less.

On the other hand, the lower limit of the average grain diameter of the α phase is not limited, and when the average grain diameter is made fine, it is necessary to increase the reduction in cold rolling, and the texture is easily developed by cold rolling. Therefore, the average crystal grain diameter of the α phase may be 2.0 μm or more, or may be 5.0 μm or more or 8.0 μm or more.

The area ratio of the α phase was determined as follows.

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, by observing a titanium plateThe width 1/2 position (position from the width direction end to 1/2 of the width of the plate: width center) was measured on a plane (L cross section) perpendicular to the width direction of the plate. Specifically, an observation surface was prepared by polishing an L-section at a position 1/2 of the plate width of a titanium plate, and the concentration distribution of Fe and Cu was measured at a pitch of 1.0 μm (step: 1.0 μm) in a field of view of 500 μm×500 μm by SEM (Scanning Electron Microscopy, scanning electron microscope)/EPMA (Electron Probe Microanalyzer ). Since Fe and Cu are in beta phase or Ti ₂ Since the Cu portion is enriched, a region having a concentration of these elements 1.7 times or more the average of the entire field of view is defined as beta-phase or Ti ₂ Cu part, calculating the area ratio of the region to the whole view as beta phase or Ti ₂ Area ratio of Cu. Further, the area ratio of the α phase was calculated as a value obtained by subtracting the area ratio from 100%.

Since the α phase is uniformly distributed, the average grain size of the α phase can be measured on an arbitrary cross section of the titanium plate. For example, the measurement is performed by observing a plane (L-section) perpendicular to the plate width direction at a position 1/2 of the plate width of the titanium plate.

Specifically, an observation surface was formed by polishing an L-section at a position 1/2 of the plate width of a titanium plate, the EBSD pattern was measured by SEM at a pitch of 2.0 μm with respect to the total plate thickness of the observation surface X10 mm, and the observation surface was analyzed by recognizing boundaries having a difference in orientation of 15 DEG or more as grain boundaries and regions surrounded by the grain boundaries as crystal grains. Regarding the average crystal grain diameter, the average value of the equivalent circle diameter (circle equivalent diameter) of the crystal grains was evaluated as arithmetic average. The field of view is preferably set so that there are about 1000 or more crystal grains. However, when the average crystal grain diameter obtained by the above method is 5.0 μm or less, the average crystal grain diameter is determined by measuring again the field of view of total plate thickness×1mm at a pitch of 0.5 μm in order to improve accuracy.

<With Euler angle g= { phi ₁ ，Φ，φ ₂ The maximum value of the crystal orientation distribution function f (g) at the time of crystal orientation of alpha phase is 14.0 or less>

<Orientation group A (phi) ₁ ：0～30°,Φ：30～90°,φ ₂ : 0-60 °), orientation group B (Φ) ₁ ：30～60°,Φ：30～90°,φ ₂ : 0-60 °), orientation group C (Φ) ₁ ：60～90°,Φ：30～90°,φ ₂ : the maximum value of the crystal orientation distribution function f (g) of 0-60 DEG is 1.0 or more>

As described in patent documents 6 and 7, a structure (Φ.apprxeq.0, Φ) in which the c-axis is made to substantially coincide with ND has been studied conventionally ₁ 、φ ₂ Arbitrary value) to improve the anisotropy of elongation. However, these techniques have problems to be improved.

Accordingly, the present inventors have studied. As a result, it is thought that, based on the concept contrary to the prior art, the anisotropy of the elongation is reduced while having a sufficient elongation by making the proportion of specific tissues oriented in one direction small and making the tissues irregularly oriented in various directions mixedly exist. This is thought to be because the orientation dependence is reduced by making the tissue irregular, and a large number of twin systems are allowed to move in each tissue oriented in various directions, thereby causing an increase in elongation (total elongation).

In this embodiment, since the crystal orientation in the texture is expressed in three dimensions, an expression method based on euler angles is used. The expression method based on the euler angle (expression method of Bunge) is considered as 3 coordinate axes of RD, TD, and ND in an orthogonal relationship to each other as a sample coordinate system (coordinate system of a plate material). Then, as a crystal coordinate system (coordinate system based on the hcp tissue direction in the case of the α -phase of titanium), 3 coordinate axes of the X-axis, Y-axis, and Z-axis, which are orthogonal to each other, are considered. Z axis is [0001 ] ]Direction. X-axis is sometimes taken [10-10 ]]Direction (direction of normal to cylinder) is sometimes taken to be [1-210 ]]Direction. Here, the X-axis is [1-210 ]]Direction. In this case, the Y-axis is [10-10 ]]Direction (direction of normal to the cylinder). The X-axis was oriented in either direction, and the results were the same. In the euler angle expression method, as shown in fig. 1 a, a state in which the sample coordinate system coincides with the crystal coordinate system (X-axis coincides with RD, Y-axis coincides with TD, and Z-axis coincides with ND) is considered first. Then, as shown in FIG. 1 (B), the crystal coordinate system is rotated by φ about the Z-axis ₁ Degree (X ', Y', Z), then, as shown in FIG. 1 (C), rotate φ ₁ The X (X ') axis after the degree is rotated by phi degrees (X', Y ', Z'). Finally, as shown in FIG. 1 (D), the rotation φ is caused ₁ Rotation phi of Z (Z') axis after rotation phi and degree of degree ₂ Degree (not shown) (X ", Y '", Z'). Using the above phi ₁ °、Φ°、φ ₂ These 3 angles define the crystal orientation (direction of c-axis, etc.) of the crystal grains. The crystal structure of the alpha phase, which is the main phase structure of the titanium plate, is hexagonal and therefore can be composed of phi ₁ (0～90°)、Φ(0～90°)、φ ₂ (0-60 deg.).

The orientation of the conventional texture of the titanium plate manufactured by the conventional method, in which the c-axis is inclined from ND to TD by about 35 °, will be described further conceptually based on the expression method based on the euler angle. If the orientation in which the c-axis is inclined to the TD by about 35 ° is expressed by the expression method based on the euler angle, it is Φ=35°, Φ ₁ ＝0°、φ ₂ : arbitrary. Furthermore, if it is to [10-10 ]]The direction is defined as the orientation towards RD, then φ ₂ =0° becomes the preferential orientation. Fig. 2 shows an expression diagram based on euler angles, in which the preferential orientation of the existing material is expressed in three dimensions.

When a structure having a c-axis inclined by about 35 ° to the TD is stretched in the TD and stretched in the RD, the {10-10} plane, which is a main slip plane, the {11-22} plane, which is a twin plane, or the {10-12} plane has different angles from the stretching direction. The angles of the slip plane, the twin plane and the stretching direction are different: even if the stretching is performed with the same force, the degree of slip or twinning (deformation amount) obviously changes. Thus, in TD and RD, the mechanical properties create anisotropy.

The crystal orientation distribution of the polycrystal is determined by using the Euler angle (phi) ₁ 、Φ、φ ₂ ) Is a function of f (phi) ₁ 、Φ、φ ₂ ) This function is referred to as a crystal orientation distribution function (Orientation Distribution Function, ODF).

If the crystal orientation (phi) is set ₁ 、Φ、φ ₂ ) G, ODF can be expressed as f (g). If the volume of the crystal grains contained in the minute orientation space dg of the orientation g is set to dV, the volume ratio of V relative to the volume of all the crystal grainsThe use of f (g) is denoted as "dV/v=f (g) dg", and therefore the presence of grains having a certain orientation can be known as long as f (g) is known. The value of f (g) representing the orientation density is 1 in the case of having irregular orientation (see non-patent document 1).

The crystal Orientation Distribution Function (ODF) can be obtained by an electron beam back scattering diffraction (Electron Back Scattered Diffraction Pattern: EBSD) method. For the inspection surface, an electron beam back scattering diffraction (EBSD) method was used to measure the EBSD pattern while scanning the electron beam with a Scanning Electron Microscope (SEM), analysis was performed, and the Euler angle (phi) of the crystal orientation at each measurement point was obtained by converting the calculation on a computer into an angle with respect to the plate surface ₁ 、Φ、φ ₂ ). Based on the data of the measurement points in the measured field of view, an ODF (f (Φ) ₁ 、Φ、φ ₂ ))。

In this embodiment, the crystal Orientation Distribution Function (ODF) is obtained as follows.

Since the α phase is uniformly distributed, the crystal orientation distribution function measurement can be performed in an arbitrary cross section of the titanium plate. For example, a surface perpendicular to the plate width direction (hereinafter also referred to as "L-section") at a position 1/2 of the plate width of a titanium plate is polished to form a measurement surface, the measurement surface is scanned with a total plate thickness x 10mm field of view, an electron beam is scanned with a Scanning Electron Microscope (SEM) while an EBSD pattern is measured by an electron beam back scattering diffraction (EBSD) method at a pitch of 5.0 μm, analysis is performed, and the angle with respect to the plate surface is converted into fig. 1 for an α -phase crystal of titanium by calculation on a computer, thereby obtaining the euler angle at each measurement point. As for the data measured under the above conditions, OIM Analysis software manufactured by TSL Solutions co., ltd ^TM (version 8.1.0) the ODF of the alpha phase was calculated. The ODF was calculated by a structural analysis using a spherical harmonic method using an electron beam back scattering diffraction (EBSD) method (expansion index=16, gaussian half-value width=5°). In this case, considering symmetry of rolling deformation, calculation is performed so as to form line symmetry for each of the plate thickness direction, the rolling direction, and the plate width direction.

Deformation characteristics of titanium plate with alpha phase as main phaseDepending on the orientation direction of the individual alpha grains constituting the alpha phase of the hcp structure. In addition, the titanium plate having a large maximum value of f (g) has a large mechanical anisotropy, particularly an anisotropy of elongation. Therefore, in the titanium plate of the present embodiment, the euler angle g= { Φ is used ₁ ，Φ，φ ₂ The maximum value of the crystal orientation distribution function f (g) at the time of crystal orientation of the alpha phase of titanium 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. Further, 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 12.0 or less and 10.0 or less, more preferably 9.0 or less.

Regarding the texture of the titanium plate of the present embodiment, phi will be expressed on a two-dimensional paper surface ₁ (0～90°)、Φ(0～90°)、φ ₂ Three-dimensional orientation distribution function f (phi) of (0-60 DEG) ₁ 、Φ、φ ₂ ) Is shown in fig. 3.

In FIG. 3, a specific phi is to be specified ₂ F (g) below is on the horizontal axis: phi (phi) ₁ (0-90 °), vertical axis: phi (0-90 DEG) is expressed by contour lines in the space, and phi is selected from 0 DEG to 55 DEG at intervals of 5 DEG ₂ The drawing is summarized in 1. The representation of the value of the contour line of f (g) in fig. 3 is shown as a number 3 bits after the decimal point outside the column. The numerical values shown in the figures together with the guide lines are, for convenience, numerical values 1 digit after rounding to decimal point. The same applies to fig. 4, 5, 7, and 8 described below.

In FIG. 3, f (φ) ₁ 、Φ、φ ₂ ) The maximum value of (2) was obtained as follows. Namely, the manufacture will phi ₂ The maximum value of f (g) in each section was examined by dividing the sections at 1 ° intervals, and the maximum value was used. f (phi) ₁ 、Φ、φ ₂ ) Maximum is at phi ₁ ＝0°、Φ＝35°、φ ₂ A position of=0°, where the maximum value of f (g) is 7.0.

On the other hand, as a conventional material, an α -annealing obtained by subjecting a titanium plate produced by cold rolling to final annealing (annealing temperature 800 ℃) in an α -temperature regionThe texture of the fire material (texture having a preferential orientation with the c-axis inclined at about 35 ° to the TD) was selected from 0 ° to 55 ° at 5 ° intervals in the same manner as in fig. 3 ₂ The drawing is summarized in FIG. 4, which is 1 drawing. In this prior art example, f (φ) ₁ 、Φ、φ ₂ ) Maximum is at phi ₁ ＝0°、Φ＝35°、φ ₂ A position of=0°, where the maximum value of f (g) is 14.6.

Further, regarding the texture of the conventional example (β annealed material) obtained by subjecting a titanium plate produced by cold rolling to final annealing at a temperature of β transformation point or higher (annealing temperature 920 ℃) was selected from the group consisting of 0 ° to 55 ° at a pitch of 5 ° in the same manner as in fig. 3 and 4 ₂ Fig. 5 is a summary of 1 drawing. In this example, f (φ) ₁ 、Φ、φ ₂ ) Maximum is at phi ₁ ＝0°、Φ＝35°、φ ₂ A position of=0°, where the maximum value of f (g) is 51.0.

Even if f (g) is 14.0 or less, there is a possibility that the crystal orientation concentrates on the orientation range near the preferential orientation.

The titanium plate of the present embodiment further defines, in addition to the above definition: orientation group A (phi) ₁ ：0～30°,Φ：30～90°,φ ₂ : 0-60 °), orientation group B (Φ) ₁ ：30～60°,Φ：30～90°,φ ₂ : 0-60 °), orientation group C (Φ) ₁ ：60～90°,Φ：30～90°,φ ₂ : the maximum value of the crystal orientation distribution function f (g) of 0 to 60 DEG is 1.0 or more. When the maximum value of the crystal orientation distribution function f (g) in each of the orientation groups a, B, and C is 1.0 or more, the C-axis is oriented in various directions, and the crystal orientation becomes irregular, and the anisotropy decreases.

The alignment groups a, B, and C each represent an alignment group in which the C-axis is inclined from ND by 30 ° or more in the direction of TD to 30 °, 30 ° to 60 °, and 60 ° to 90 °. That is, if the maximum value of f (g) in these alignment groups is 1.0 or more, the alignment indicating that the c-axis is inclined with respect to each direction is present by a certain amount or more.

FIG. 6 illustrates that { φ } ₁ ，Φ，φ ₂ The space of the three-dimensional space is expressed as a region of an orientation group a, an orientation group B, and an orientation group C.

Further, fig. 7 and 8 illustrate ODFs of regions where f (g) reaches the maximum value in each of the alignment groups a, B, and C, for the titanium plate of the present embodiment and the titanium plate of the conventional example (a texture having a C-axis inclined to the TD by about 35 ° as a preferential alignment). At (phi) ₁ 、Φ、φ ₂ ) The point at which f (g) reaches maximum in the entire region is the same as the point at which f (g) reaches maximum in the alignment group a.

Fig. 7 (titanium plate of the present embodiment) and fig. 8 (titanium plate of the conventional example) show 3 diagrams of (a), (B) and (C), respectively. All will phi ₂ Fix at a specific angle and fix (phi) ₁ : 0-90 degrees, phi: the distribution of f (g) in the range of 0 to 90 deg. is illustrated with a contour line. (A) selecting phi at which f (g) reaches maximum in the orientation group A, (B) selecting phi in the orientation group B, and (C) selecting phi at which f (g) reaches maximum in the orientation group C ₂ . Then, in each of the figures, the point at which f (g) reaches the maximum value in each of the alignment groups a, B, and C is illustrated.

As can be seen from FIG. 7, in the titanium plate of the present invention, the titanium plate is formed in the orientation group A (φ ₁ ＝0°、Φ＝35°、φ ₂ Maximum value of =0°, f (g) 7.0), orientation group B (Φ ₁ ＝52°、Φ＝44°、φ ₂ Maximum value of =40°, f (g) 2.8), orientation group C (Φ ₁ ＝72°、Φ＝60°、φ ₂ In any of the values of=15°, the maximum value of f (g) 2.7), the maximum value of the crystal orientation distribution function f (g) is 1.0 or more.

On the other hand, as shown in FIG. 8, in the titanium plate of the comparative example, although the orientation group A (φ ₁ ＝0°、Φ＝35°、φ ₂ Maximum value of =0°, f (g) 14.6), orientation group B (Φ ₁ ＝30°、Φ＝30°、φ ₂ The maximum value of f (g) of =30°, the maximum value of f (g) of 3.0) is 1.0 or more, but the orientation group C (Φ) ₁ ＝60°、Φ＝90°、φ ₂ Maximum value of =30°, maximum value of f (g) 0.9) is less than 1.0.

Fig. 11B shows an example of an S-S curve of the titanium plate of the present embodiment. As shown in the S-S curve of fig. 11B, the titanium plate of the present embodiment has small anisotropy of elongation (total elongation) and flow stress, compared to the conventional titanium plate (fig. 11A).

< average grain diameter of 5 grains having the largest grain diameter of alpha phase is 250 μm or less >

In the titanium plate of the present embodiment, when the grain diameter (equivalent circular diameter) of the largest 5 grains among the grains included in the α -phase as the main phase is averaged, it is preferably 250 μm or less. When the average grain diameter of the largest 5 grains is 250 μm or less, occurrence of wrinkles due to the presence of coarse grains can be suppressed.

The average grain diameter of the maximum 5 grains is obtained by: the crystal grain diameter in the visual field was measured in the same manner as the measurement of the average crystal grain diameter of the α phase, and the equivalent circle diameters of the maximum 5 crystal grains were averaged to obtain the crystal grain diameter. (counting as 1 grain in the case where there are a plurality of grains of the same grain size.)

2. Chemical composition

Next, the chemical composition of the titanium plate of the present embodiment will be described. Hereinafter, the content% of each element is referred to as mass%. The range indicated by the term "to" includes the values at both ends thereof as the lower limit and the upper limit.

The titanium plate of the present embodiment may have the following chemical composition: comprises Fe:0 to 0.500 percent of O:0 to 0.400 percent, N:0 to 0.050 percent, C:0 to 0.080 percent, H:0 to 0.013 percent, and the balance of Ti and impurities, and further can have the following chemical composition: instead of a part of Ti, 1 or more kinds of Al, cu, nb, si, zr, cr, mo, sn which are arbitrary elements are further contained.

The impurities are elements that may be mixed from raw materials and production steps, and Cl, na, mg, ca, ta, V is exemplified. These elements are acceptable without impairing the working effect of the titanium plate of the present embodiment. If the respective impurities are limited to less than 0.1 mass%, and the total amount of the impurities is further limited to 0.5 mass% or less, the level is a level where there is no problem. Further, any of the above elements may be contained as impurities.

The chemical composition in the absence of any element corresponds to the standard of industrial pure titanium (1 to 4) of "titanium and titanium alloy-plate and strip" of Japanese Industrial Standard JIS H4600 (2007). Pure titanium sheets are easy to form because of low alloying elements.

On the other hand, when the strength and oxidation resistance are to be improved, it is preferable to contain any of the above elements in the range described below. Since any element is not necessarily contained, the lower limit is 0%.

Fe：0～0.500％

If the Fe content is excessive, β phase remains after intermediate annealing in β region, and twin crystal formation becomes difficult in the subsequent cold rolling, resulting in failure to obtain a desired texture. Therefore, the Fe content is set to 0.500% or less. From the viewpoint of texture control, the Fe content is preferably 0.350% or less, more preferably 0.250% or less, still more preferably 0.200% or less, and still more preferably 0.150% or less. Further, if the Fe content exceeds 0.100%, there is a fear that the oxidation resistance is lowered. Therefore, the Fe content is preferably 0.100% or less in consideration of oxidation resistance.

The Fe content may be 0%, but Fe is an element that may be contained in titanium, and if the Fe content is less than 0.001%, the refining cost increases, so the Fe content may be set to 0.001% or more. Further, fe is also an element having an effect of improving the yield strength by 0.2%. In order to obtain this effect, the Fe content is preferably 0.020% or more, more preferably 0.030% or more.

O：0～0.400％

If the O content is too large, the twinning deformation is suppressed, and the texture described above cannot be obtained. Therefore, the O content is set to 0.400% or less. From the viewpoint 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 still further preferably 0.150% or less. The content of O may be 0%, but O is an element that may be contained in titanium, and if the content of O is less than 0.001%, refining costs increase, so the content of O may 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 effect, the O content is preferably set to 0.020% or more. The O content is more preferably 0.030% or more.

N：0～0.050％

C：0～0.080％

H：0～0.013％

If the N content, the C content, and the H content are excessive, the elongation decreases. 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%.

These elements may be contained in an amount of 0%, but the smelting costs are significantly increased by making the content of N less than 0.0001%, the content of C less than 0.0001% and the content of H less than 0.00001%. Therefore, the N content may be set to 0.0001% or more, the C content to 0.0001% or more, and/or the H content to 0.00001% or more. The N content may be set to 0.001% or more, the C content may be set to 0.001% or more, and/or the H content may be set to 0.001% or more.

Al：0～2.30％

Al is an element that increases the 0.2% yield strength, and the more the Al content, the greater the 0.2% yield strength. And thus may be contained. In order to obtain the 0.2% yield strength improving effect, the Al content is preferably 0.10% or more, more preferably 0.30% or more.

On the other hand, if the Al content is too large, the movement of the specific twin system is suppressed and the elongation is lowered. From the viewpoint 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%.

Cu：0～1.80％

Cu is an element that increases the 0.2% yield strength without inhibiting twin deformation, and the more Cu content, the greater the 0.2% yield strength. And thus may be contained. In order to obtain the 0.2% yield strength improving effect, the Cu content is preferably 0.10% or more, more preferably 0.30% or more.

On the other hand, if the Cu content is too high, ti will precipitate ₂ Cu, elongation decreases. From Ti ₂ The Cu content is preferably 1.80% or less in terms of Cu precipitation,more preferably 1.60% or less, still more preferably 1.50% or less, still more preferably 1.20% or less.

In the case of an increase in yield strength of 0.2%, it preferably comprises Al:0.10% or more and 2.30% or less and Cu: 1 or 2 of 0.10% or more and 1.80% or less.

Nb：0～1.00％

Nb is an element for improving oxidation resistance, and may be contained in the case where use at high temperature is anticipated, for example. In order to obtain the oxidation resistance improving effect, the Nb content is preferably 0.10% or more, more preferably 0.15% or more.

On the other hand, if the Nb content is excessive, β phase remains after intermediate annealing in β region, and it becomes difficult to form twin crystal in the subsequent cold rolling. In this case, a desired texture may not be formed. Therefore, from the viewpoint of texture control, the Nb content is set to 1.00% or less. The Nb content is preferably 0.85% or less, more preferably 0.80% or less.

Si：0～0.50％

Si is an element that improves oxidation resistance, and may be contained in the case where use at high temperature is anticipated, for example. In order to obtain the oxidation resistance improving effect, the Si content is preferably 0.05% or more, more preferably 0.10% or more.

On the other hand, if the Si content is too large, silicide may be precipitated and the elongation may be lowered. Therefore, the Si content is set to 0.50% or less. The Si content is preferably 0.45% or less, more preferably 0.40% or less.

Zr：0～0.50％

Zr is an element for improving oxidation resistance, and may be contained in the case where use at high temperature is anticipated, for example. In order to obtain the oxidation resistance improving effect, the Zr content is preferably 0.10% or more, more preferably 0.15% or more.

On the other hand, if the Zr content is too large, there is a possibility that grain growth is greatly suppressed, grain refinement occurs, and elongation decreases. Accordingly, the Zr content was set to 0.50% or less. The Zr content is preferably 0.45% or less, more preferably 0.40% or less.

In the case of improving oxidation resistance, it is preferable to contain a material selected from the group consisting of Nb:0.10 to 1.00 percent of Si:0.10 to 0.50 percent of Zr:0.10 to 0.50% of more than 1 kind.

Cr：0～0.50％

Cr is an element that increases the yield strength by 0.2%. And thus may be contained. In the case of obtaining the effect of improving the yield strength by 0.2%, the Cr content is preferably 0.05% or more, more preferably 0.10% or more.

On the other hand, if the Cr content is excessive, β phase remains after intermediate annealing in β region, and it becomes difficult to form twin crystal in the subsequent cold rolling. In this case, a desired texture may not be formed. Therefore, from the viewpoint of texture control, the Cr content is set to 0.50% or less. The Cr content is preferably 0.45% or less, more preferably 0.40% or less.

Mo：0～0.50％

Mo is an element that increases the yield strength by 0.2%. And thus may be contained. In the case of obtaining the effect of improving the yield strength by 0.2%, the Mo content is preferably 0.05% or more, more preferably 0.10%.

On the other hand, if the Mo content is excessive, β phase remains after intermediate annealing in β region, and it becomes difficult to form twin crystal in the subsequent cold rolling. In this case, a desired texture may not be formed. Therefore, from the viewpoint of texture control, the Mo content is set to 0.50% or less. The Mo content is preferably 0.45% or less, more preferably 0.40% or less.

Sn：0～1.50％

Sn is an element that increases the 0.2% yield strength. And thus may be contained. In the case of obtaining the effect of improving the yield strength by 0.2%, the Sn content is preferably 0.05% or more, more preferably 0.10% or more.

On the other hand, if the Sn content is too large, grain growth may be greatly suppressed, grain refinement may occur, and elongation may be reduced. 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 still more preferably 1.00% or less.

In the case of an increase in yield strength of 0.2%, it preferably comprises a metal selected from the group consisting of Cr:0.05 to 0.50 percent of Mo:0.05 to 0.50 percent of Sn:0.05 to 1.50% of more than 1 kind.

The titanium sheet of the present embodiment is preferably a cold-rolled annealed sheet obtained by subjecting a cold-rolled sheet to final annealing. Further, the sheet subjected to the finish annealing may be subjected to tempering by a tension leveler, a temper mill or the like. The sheet is preferably a thin sheet, and the thickness is preferably 1.5mm or less. The thickness of the sheet is more preferably 1.2mm or less, still more preferably 1.0mm or less, and still more preferably 0.8mm or less.

3. Characteristics of

The titanium plate of the present embodiment has a sufficient elongation and has a small anisotropy in elongation.

For example, the elongation (total elongation) at the time of stretching in RD (rolling direction) and TD (sheet width direction) is preferably 20% or more.

Further, elongation El when stretched in RD (Rolling direction) _RD Elongation El when stretched in TD (sheet width direction) _TD Ratio (El) _RD /El _TD ) The closer to 1.0, the less anisotropic will be. Elongation El of the titanium plate of the present embodiment when stretched in RD (Rolling direction) _RD Elongation El when stretched in TD (sheet width direction) _TD Ratio (El) _RD /El _TD ) Preferably 0.70 to 1.30. (El) _RD /El _TD ) More preferably 0.75 or more, still more preferably 0.80 or more, still more preferably 0.85 or more. Furthermore, (El) _RD /El _TD ) More preferably 1.25 or less, and still more preferably 1.20 or less.

In the titanium sheet of the present embodiment, from the viewpoint of anisotropy, the ratio of flow stress is preferably 0.90 to 1.10 at the 1/4 position, the 1/2 position, and the 3/4 position of the strain in the S-S curve at the time of stretching in the RD (rolling direction) and the TD (sheet width direction), respectively, in the total elongation (at break).

Tensile test according to JIS Z2241 (1998) "metallic material tensile test method", elongation of RD, TD was measured using test piece No. 13B specified in JIS Z2201 (1998) "metallic material tensile test piece". Specifically, the gauge length was set to 50mm, the strain rate was set to 0.5%/min until the strain rate reached 2% strain, and the strain rate was set to 30%/min thereafter, and the tensile was performed until the fracture.

The ratio of the flow stress at the 1/4 position, the 1/2 position, and the 3/4 position of the strain to the total elongation (at break) of the S-S curve was determined as follows. For example, in the tensile test, when the S-S curve shown in fig. 14 is obtained for RD and TD, the strain of the smaller of the total elongation of RD and TD (strain of TD, 0.420 in fig. 14) is obtained. The flow stress of RD and TD was obtained at the 1/4 (0.105), 1/2 (0.210) and 3/4 (0.315) positions of the strain. At each location, the flow stress ratio was calculated by dividing the flow stress of RD by the flow stress of TD.

4. Method of manufacture

Next, a preferred method for producing the titanium plate of the present embodiment will be described. The titanium plate of the present embodiment is preferable because the effect can be obtained by having the above-described features, regardless of the manufacturing method, but can be stably manufactured by the manufacturing method including the following steps.

(I) A smelting process, (II) a cogging process, (III) a hot rolling process, (IV) a cold rolling process, and (V) a final annealing process.

Hereinafter, each step will be described.

[ smelting Process ]

The titanium ingot produced to have a predetermined purity is melted by a known method to produce a predetermined cast slab. Specifically, a vacuum arc melting method (VAR method) and an electron beam melting method (EB method) can be applied.

[ procedure of cogging ]

The shape of the slab is formed by known cogging rolling and forging.

[ Hot Rolling Process ]

This is carried out in a known manner.

For example, the slab is heated to 700 to 1000 ℃ and rolled at a rolling rate of 60 to 98% to obtain a hot rolled plate. In this case, if the temperature is heated to a temperature exceeding the β transformation point, the formation of oxide scale is intensified, and therefore the heating temperature is preferably set to be equal to or lower than the β transformation point.

[ annealing Process of Hot rolled sheet ]

Annealing (hot-rolled sheet annealing) may be performed as needed after the hot rolling step and before the cold rolling step. In this case, the annealing is performed for a predetermined time while the temperature is kept at 600 ℃ or higher and at most the beta transus temperature.

The beta transus temperature can be obtained from the phase diagram. The phase diagram can be obtained, for example, by the calhad (Computer Coupling of Phase Diagramsand Thermochemistry, phase diagram coupled with thermochemical computer) method, for which, for example, a Thermo-Calc integrated thermodynamic computing system from Thermo-Calc Software AB company, thermo-Calc, and a predetermined database (TI 3) can be used.

In the production of the titanium sheet of the present embodiment, the most characteristic is a combination of conditions of the cold rolling step and the intermediate annealing and final annealing steps in the cold rolling step. Therefore, in the cold rolling step, the conditions for the final cold rolling and the conditions for the intermediate annealing immediately before the final cold rolling (hereinafter referred to as "final intermediate annealing") are set to predetermined conditions. Fig. 13 schematically shows the steps of cold rolling, final intermediate annealing, final cold rolling, and final annealing in the process of producing a titanium sheet according to the present embodiment.

[ Cold Rolling Process ]

The cold rolling to the final intermediate annealing may be performed under known conditions. Intermediate annealing may be performed between the passes of cold rolling.

Heating temperature of final intermediate annealing: above the beta-phase transition temperature

In the final intermediate annealing (final annealing in the intermediate annealing), when the temperature is equal to or higher than the β transformation point temperature, the α phase temporarily changes to the β phase, and when the temperature is cooled, the α phase changes to the α phase, so that the texture becomes irregular. As a result, the anisotropy of the titanium plate can be reduced. If the heating temperature is lower than the beta transus temperature, the maximum of the crystal orientation distribution function f (g) in the final product may exceed 14.0. As a result, the anisotropy of the titanium plate increases. Therefore, the heating temperature of the final intermediate annealing is set to be equal to or higher than the β transformation point temperature.

On the other hand, from the viewpoint of oxidation resistance, the temperature of the final intermediate annealing is preferably 1000 ℃ or lower.

In addition, the annealing time is preferably 0 to 10 minutes from the viewpoint of oxidation resistance. Here, the annealing time of 0min means a case where cooling starts immediately after the annealing temperature is reached.

Final cold rolling: the rolling rate is 5-50%

If the rolling reduction of the final cold rolling (rolling reduction of the cold rolling after the final intermediate annealing and before the final annealing) is 5 to 50%, the twin deformation is also active in addition to the slip deformation, and the texture becomes irregular. If the rolling reduction of the final cold rolling is less than 5%, coarse needle-like unrecrystallized grains remain in the subsequent annealing, and the maximum value of the crystal orientation distribution function f (g) exceeds 14.0. In addition, the average grain diameter may also exceed 100.0. Mu.m. On the other hand, if the rolling reduction of the final cold rolling exceeds 50%, twinning is less likely to occur, orientation in a specific direction due to slip deformation is enhanced, orientation in a specific direction still occurs after the final annealing, and the maximum value of the crystal orientation distribution function f (g) in the final product may exceed 14.0. As a result, the anisotropy of the titanium plate increases. Therefore, in the final cold rolling, the rolling reduction is set to 5% or more and 50% or less. In the final cold rolling, the rolling reduction is preferably 10% or more and 40% or less.

The cold rolling at this rolling rate may be performed in 1 pass or in a plurality of passes. That is, the total rolling reduction of the cold rolling (no-pass annealing) performed between the final intermediate annealing and the final annealing may be a predetermined rolling reduction.

If the crystal orientation is irregular at a point of time before the final cold rolling, the crystal orientation is further irregular eventually, and therefore, it is preferable to perform intermediate annealing in the β region (temperature equal to or higher than the β transformation point) so that the orientations are varied.

[ final annealing Process ]

Heating temperature: 475 ℃ and below beta transformation point temperature

In the final annealing, if the heating temperature is lower than 475 ℃, recrystallization is not ended and anisotropy increases. Further, there is a possibility that the elongation is lowered. Therefore, the heating temperature of the final annealing is set to 475 ℃.

On the other hand, if the heating temperature exceeds the β transformation point temperature, the structure becomes a needle-like structure, coarse grains are formed, and the maximum value of the crystal orientation distribution function f (g) exceeds 14.0. In addition, wrinkles are easily generated during molding. Therefore, the heating temperature is set to be equal to or lower than the β transformation point temperature.

The heating time for the final annealing is not particularly limited, but is preferably set to 0.5min or more in view of the stability of the structure in which the structure is assuredly recrystallized. On the other hand, from the viewpoint of preventing coarsening of crystal grains, it is preferably set to 480min or less.

According to the above production method, the crystal orientation of the product is various, the texture is irregular, and the anisotropy of strength and elongation is reduced.

Examples

After producing titanium alloy ingots having the chemical compositions shown in tables 1 and 2 by vacuum arc melting (VAR: vacuum Arc Remelting), slabs having a thickness of 150 mm. Times.800 mm in width. Times.5000 mm in length were produced by cogging rolling or forging. Subsequently, these slabs were heated to 850 ℃ and hot rolled, and titanium plate materials having a thickness of 4.0mm and the composition shown in tables 1 and 2 were prepared. And (3) carrying out hot rolled plate annealing on a part of the titanium plate blank at 780 ℃ for 2 min. The titanium sheet material was subjected to cold rolling, final intermediate annealing, final cold rolling, and final annealing under the conditions shown in tables 1 and 2, and a titanium sheet (cold rolled annealed sheet) having a sheet thickness of 0.5mm was produced.

TABLE 1

TABLE 2

The area ratio of the α phase, the average grain diameter of the α phase, and the average grain diameter of the maximum 5 grains of the α phase were measured as described above using the plane (L section) perpendicular to the plate width direction at the 1/2 position of the plate width of the titanium plate as an observation plane.

Furthermore, regarding the euler angle g= { Φ ₁ ，Φ，φ ₂ The "crystal orientation distribution function f (g) and its maximum value at the time of crystal orientation of the α phase" were obtained by the above-described method using a plane (L cross section) perpendicular to the plate width direction at the 1/2 position of the plate width of the titanium plate as an observation plane.

In addition, the Euler angle is calculated as phi according to the method ₁ ：0～30°,Φ：30～90°,φ ₂ : orientation group A expressed in phi of 0-60 DEG ₁ ：30～60°,Φ：30～90°,φ ₂ : orientation group B expressed in phi of 0-60 DEG ₁ ：60～90°,Φ：30～90°,φ ₂ : a maximum value of the crystal orientation distribution function f (g) of the orientation group C expressed at 0 to 60 deg..

Further, from the obtained titanium plate, a test piece No. 13B specified in JIS Z2201 (1998) "Metal tensile test piece" was taken, and a tensile test was performed according to JIS Z2241 (1998) "Metal tensile test method", and elongation (El) of RD and TD was measured _RD 、El _TD ). Specifically, the total elongation was obtained by setting the gauge length to 50mm, setting the strain rate to 2% strain to 0.5%/min, setting the strain rate to 30%/min thereafter, stretching to fracture, abutting the fracture surfaces after fracture, and measuring the amount of change in the gauge length (50 mm before stretching). In addition, el for anisotropy _RD /El _TD Is evaluated.

Further, a test piece No. 13B prescribed in JIS Z2201 (1998) "metallic material tensile test piece" was further taken out of the obtained titanium plate, and according to JIS Z2241 (1998) "metallic material tensile test method", tensile test was performed at a strain rate of 30%/min in the rolling direction to a strain amount of 20%, and then appearance was confirmed to visually evaluate the occurrence of wrinkles. The wrinkles herein refer to orange peel caused by the irregularities accompanying plastic deformation. Specifically, the surface was observed, and the titanium plate having obvious wrinkles visually was judged to have wrinkles.

In some examples, when stretching in RD (rolling direction) and TD (sheet width direction) for measuring elongation, the ratio of flow stress was determined at the 1/4 position, the 1/2 position, and the 3/4 position of the strain up to the total elongation (at break) of the S-S curve.

The results are shown in tables 3 and 4.

TABLE 3

TABLE 4

In the examples 1 to 36 of the present invention, the total elongation was 20% or more in both RD and TD, and El _RD /El _TD The values of (2) are also sufficiently close to 1.00, and the anisotropies are small. For example, the crystal orientation distribution function f (g) of the titanium plate of invention example 6 in three dimensions of euler angles is shown in fig. 3 and 7. As is clear from fig. 3, f (g) is dispersed in the space in three dimensions of the euler angle without showing a tendency to increase locally. As a result, the maximum value of f (g) is at phi ₁ ＝0°、Φ＝35°、φ ₂ =0°, the maximum value of f (g) at this position being 7.0. The structure of this invention example 6 was analyzed, and as a result, an equiaxed structure having an average grain diameter of 65 μm was obtained as shown in FIG. 10. As a result, it was confirmed that the elongation in both directions of RD and TD was high, and the mechanical anisotropy including strength was eliminated (fig. 9).

In contrast, in comparative example 101, since the temperature of the final intermediate annealing was low, a strongly oriented structure having a maximum value of f (g) of more than 14.0 was formed, and as a result, el _RD /El _TD The value of (2) is also large, and the anisotropy of the titanium plate is large.

In comparative example 102, the rolling reduction of the final cold rolling was low, and a structure in which unrecrystallized grains remained was formed, and a structure in which f (g) had a maximum value exceeding 14.0 and had a strong orientation was formed. As a result, el _RD /El _TD The value of (2) is also large, and the anisotropy of the titanium plate is large. In addition, in the case of the optical fiber,the average grain diameter exceeds 100.0 μm, and wrinkles are generated upon deformation.

Comparative example 103 has a structure in which f (g) has a maximum value exceeding 14.0 and is strongly oriented due to a high rolling yield in the final cold rolling, and thus El is obtained _RD /El _TD The value of (2) is also large, and the anisotropy of the titanium plate is large.

In comparative example 104, the final annealing temperature was low to form a structure in which unrecrystallized grains remained, and thus El _RD /El _TD The value of (2) is also large, and the anisotropy of the titanium plate is large.

Comparative examples 105 and 109 formed needle-like structures having a small roundness including coarse structures due to a high temperature of the final annealing. As a result, a strongly oriented structure in which the maximum value of f (g) exceeds 14.0 was formed, el _RD /El _TD The value of (2) is also large. In addition, wrinkles are generated.

In comparative example 106, the final intermediate annealing was not performed, and the cold rolling yield at the time of final cold rolling was high, so that the maximum value of f (g) in the alignment group C was less than 1.0. Results El _RD /El _TD The value of (2) is also large, and the anisotropy of the titanium plate is large.

In comparative example 107, since the final intermediate annealing was not performed, the cold rolling rate at the time of final cold rolling was high, and thus a strongly oriented structure having a maximum value of f (g) exceeding 14.0 was formed, and as a result El _RD /El _TD The value of (2) is also large, and the anisotropy of the titanium plate is large. In addition, the final annealing temperature is high, and the α phase has a needle-like structure with a small average roundness, and as a result, wrinkles are generated.

Comparative example 108 formed a strongly oriented structure having a maximum value of f (g) exceeding 14.0 due to a low temperature of the final intermediate annealing, and resulted in El _RD /El _TD The value of (2) is also large, and the anisotropy of the titanium plate is large. In addition, the final annealing temperature is high, and the α phase has a needle-like structure with a small average roundness, and as a result, wrinkles are generated.

Comparative example 110 formed a strongly oriented structure in which the maximum value of f (g) exceeded 14.0, since the final cold rolling was not performed. Furthermore, el _RD /El _TD The value of (2) is also large, and the anisotropy of the titanium plate is large. In addition, the α phase forms a needle-like structure with a small average roundness, and as a result, wrinkles are generated.

Comparative example 111 was not subjected to final annealing. As a result, elongation is reduced, and El _RD /El _TD The value of (2) is also large.

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, resulting in El _RD /El _TD The value of (2) is also large, and the anisotropy of the titanium plate is large.

The O content of comparative example 113 exceeds the upper limit, the maximum value of f (g) of the alignment group C is less than 1.0, and the elongation is also reduced.

The Al content of comparative example 114 exceeds the upper limit, and the elongation decreases.

The Cu content of comparative example 115 exceeds the upper limit, and the elongation decreases.

Industrial applicability

According to the present invention, a titanium plate having a large elongation and a small anisotropy of elongation can be provided. The titanium sheet is excellent in formability, and therefore is useful for producing a titanium product having a complicated shape by press forming.

Claims (9)

1. A titanium plate is characterized in that,

has the following chemical composition: comprises in mass percent

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 to 0.50%, and

Sn：0～1.50％，

the balance of Ti and impurities,

the metallographic structure comprises an alpha phase,

the alpha phase has an average crystal grain diameter of 100.0 μm or less,

with Euler angle g= { phi ₁ ,Φ,φ ₂ When the alpha phase crystal orientation is expressed, the maximum value of the crystal orientation distribution function f (g) calculated by the structural analysis of the spherical harmonic method using the electron back scattering diffraction method with the expansion index of 16 and the Gaussian half-value width of 5 DEG is 14.0 or less,

with the Euler angle phi ₁ ：0～30°,Φ：30～90°,φ ₂ : the maximum value of the crystal orientation distribution function f (g) of the orientation group A expressed at 0 to 60 DEG is 1.0 or more,

With the Euler angle phi ₁ ：30～60°,Φ：30～90°,φ ₂ : the maximum value of the crystal orientation distribution function f (g) of the orientation group B expressed at 0 to 60 DEG is 1.0 or more,

with the Euler angle phi ₁ ：60～90°,Φ：30～90°,φ ₂ : the maximum value of the crystal orientation distribution function f (g) of the orientation group C expressed at 0 to 60 DEG is 1.0 or more.

2. The titanium plate according to claim 1, wherein,

the chemical composition comprises the following components in mass percent

O:0.030 to 0.200 percent of Fe:0.020 to 0.200% of 1 or 2 kinds.

3. The titanium plate according to claim 2, wherein,

the chemical composition comprises the following components in mass percent

Al:0.10 to 2.30 percent of Cu:0.10 to 1.80% of 1 or 2 kinds.

4. The titanium plate according to claim 3, wherein,

the chemical composition comprises the following components in mass percent

Fe:0.100% or less, and

selected from Nb:0.10 to 1.00 percent of Si:0.10 to 0.50 percent of Zr:0.10 to 0.50% of more than 1 kind.

5. The titanium plate according to claim 3 or 4, wherein,

the chemical composition comprises the following components in mass percent

Selected from Cr:0.05 to 0.50 percent of Mo:0.05 to 0.50 percent of Sn:0.05 to 1.50% of more than 1 kind.

6. The titanium sheet according to any one of claims 1 to 5, characterized in that,

The average grain diameter of the largest 5 grains of the alpha phase is 250 [ mu ] m or less.

7. The titanium sheet according to any one of claims 1 to 6, characterized in that,

the average grain diameter of the alpha phase is 2.0-100.0 mu m.

8. The titanium sheet according to any one of claims 1 to 6, characterized in that,

the average grain diameter of the alpha phase is 8.0-100.0 mu m.

9. The titanium sheet according to any one of claim 1 to 8, characterized in that,

the ratio of the total elongation in the rolling direction to the total elongation in the sheet width direction, el _RD /El _TD 0.70 to 1.30.