WO2017175569A1

WO2017175569A1 - Titanium plate, heat exchanger plate, and fuel cell separator

Info

Publication number: WO2017175569A1
Application number: PCT/JP2017/011020
Authority: WO
Inventors: 良規伊藤; 浩司山下; 賢野原
Original assignee: 株式会社神戸製鋼所
Priority date: 2016-04-05
Filing date: 2017-03-17
Publication date: 2017-10-12
Also published as: JP2017186672A

Abstract

The present invention relates to a titanium plate and is characterized in that this titanium plate: contains 0.020 to 1.000 mass% of Fe and 0.020 to 0.200 mass% of O; contains an α-phase crystal grain structure that is an HCP structure; satisfies ([Fe]–0.020)/[O] ≥ 0.68; satisfies 1.5 ≤ (A3 + A4 + A5)/(A1 + A2) ≤ 30 where A1, A2, A3, A4, and A5 are, respectively, the area ratios for the crystal grains centered on respective orientations — an orientation 1 of φ1=0°, Φ=35°, φ2=0°, an orientation 2 of φ1=0°, Φ=35°, φ2=30°, an orientation 3 of φ1=90°, Φ=35°, φ2=30°, an orientation 4 of φ1=65°, Φ=30°, φ2=0°, and an orientation 5 of φ1=90°, Φ=90°, φ2=0° — in the representation of the crystal orientations of the α-phase crystal grains by a crystal orientation distribution function; and has an average value of 5-80 μm and a maximum value of not more than 300 μm for the circle-equivalent diameter of the α-phase crystal grains.

Description

Titanium plate, heat exchanger plate and fuel cell separator

The present invention relates to a titanium plate, a heat exchanger plate using the titanium plate, and a fuel cell separator.

In general, titanium plates are excellent in specific strength and corrosion resistance. Therefore, heat exchanger parts for chemical, electric power and food production plants, consumer products such as camera bodies and kitchen equipment, and transport equipment such as motorcycles and automobiles. It is used for exterior materials such as members and home appliances. Titanium plates are used in plate-type heat exchangers, which are being applied in recent years, among them, because high heat exchange efficiency is required. ing. Therefore, a titanium plate for a heat exchanger is required to have excellent formability in order to have a deep wave. Furthermore, a titanium plate for a heat exchanger is required to have a certain strength or more in order to realize durability improvement and weight reduction required as a heat exchanger.

Titanium plates that are frequently used for various applications are defined in the standard of JIS H4600 (2012). There are grades of JIS type 1, type 2, type 3, etc., depending on the concentration and strength of impurities such as Fe and O. As the number increases, the strength increases, and they are properly used according to the application. Conventionally, a JIS type 1 pure titanium plate (with a proof stress of 165 MPa or more) having a low concentration of Fe or O has been used as a member requiring high formability because of its low strength but high ductility. However, in recent years, in addition to improving the efficiency of heat exchangers, there is an increasing demand for higher strength and lighter weight. As a titanium plate that meets these requirements, for example, a JIS type 2 pure titanium plate (with a proof stress of 215 MPa or more) can be mentioned. However, when the strength level of such a pure titanium plate is reached, the formability is inferior, making it difficult to apply to a heat exchanger. In general, titanium materials can be increased in strength by increasing the concentration of impurities such as Fe and O and by making crystal grains finer. However, these methods may greatly reduce the formability.

Various techniques have been proposed for improving the formability of titanium plates.

For example, Patent Document 1 discloses a manufacturing method for obtaining a pure titanium plate having a low yield strength anisotropy by rolling so that the final rolling direction of hot rolling is perpendicular to the rolling direction of partial rolling. Has been. Patent Document 2 discloses a method of reducing in-plane anisotropy by using a Ti—Fe—O—N-based alloy and rolling only once in a direction orthogonal to the initial rolling direction. In Patent Document 3, the frequency of deformation twins at the time of press molding is increased by increasing the crystal grain size of the α-phase crystal grains. Also, after final annealing, skin pass rolling with a rolling reduction of 0.7 to 5% is performed, and the texture (C-axis deviation angle) is adjusted to obtain the specified accumulated strain, thereby maintaining the yield strength and press formability. A titanium plate is disclosed. In Patent Document 4, a balance between press formability and strength is achieved by applying a lubricating film to the surface, controlling the dynamic friction coefficient of the surface to less than 0.15, and satisfying a specific relational expression between elongation and r value. A method of taking is disclosed. Patent Document 5 discloses a titanium plate with improved formability by setting the Keynes factor f value defined by a predetermined formula to 0.60 or more.

However, the manufacturing method of Patent Document 1 is a cross rolling method in which rolling is performed in two directions perpendicular to each other, and generally a plate longer than the rolling roll width cannot be subjected to cross rolling. There are big restrictions on the shape. Furthermore, since the hexagonal C-axis is oriented in the vicinity of the normal to the plate surface, the strength anisotropy is reduced, but it is inferior in local deformability and is not suitable for bending or stretch forming.

The method of Patent Document 2 is considered to be less restrictive than the method of Patent Document 1, but in any case, there are significant restrictions on the plate shape that can be rolled. Also, the plate thickness is large. Furthermore, since the hexagonal C-axis is oriented in the vicinity of the normal to the plate surface, the strength anisotropy is reduced, but it is inferior in local deformability and is not suitable for bending or stretch forming.

The method of Patent Document 3 is considered to be inferior in productivity because the number of steps is increased in order to perform skin pass rolling. The method of Patent Document 4 requires a coating process and a film removal process, and is expensive. The method of Patent Document 5 cannot be said to have sufficient strength and formability, and further improvements in strength and formability are desired.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a titanium plate having excellent strength and formability, a heat exchanger plate using the titanium plate, and a fuel cell separator. And

JP 63-130753 A Japanese Patent No. 3481428 Japanese Patent No. 5385038 Japanese Patent No. 4452753 Japanese Patent No. 4088183

The titanium plate according to one aspect of the present invention has an alloy composition of Fe: 0.020 to 1.000 mass%, O: 0.020 to 0.200 mass%, the balance being composed of titanium and inevitable impurities, In the case of a titanium plate containing an α-phase crystal grain structure as a structure, the Fe concentration (mass%) is represented by [Fe], and the O concentration (mass%) is represented by [O]. Satisfied,
([Fe] −0.020) / [O] ≧ 0.68 (1)
When the crystal orientation of the α-phase crystal grains is expressed by a crystal orientation distribution function, φ1 = 0 °, φ = 35 °, φ2 = 0 ° is orientation 1, φ1 = 0 °, φ = 35 °, φ2 = 30 ° is azimuth 2, φ1 = 90 °, Φ = 35 °, φ2 = 30 ° is azimuth 3, φ1 = 65 °, Φ = 30 °, φ2 = 0 ° is azimuth 4, φ1 = 90 °, Φ = 90 °, φ2 = 0 ° as orientation 5, and the area ratios of the area of crystal grains having an orientation within 15 ° around each orientation with respect to the total area of all α-phase grains are A1, A2, A3, A4, respectively. , A5, the following formula (2) is satisfied,
1.5 ≦ (A3 + A4 + A5) / (A1 + A2) ≦ 30 (2)
The α-phase crystal grains have an average equivalent circle diameter of 5 to 80 μm and a maximum value of 300 μm or less.

A heat exchanger plate according to another aspect of the present invention is a plate for a heat exchanger using the above titanium plate, and when the plate thickness is t (mm), the pitch is 4t to 40t, and the depth is It is preferable to have one or more grooves of 5t to 15t.

Further, a fuel cell separator according to a further aspect of the present invention is a fuel cell separator using the above-described titanium plate, and the pitch is 4t to 40t and the depth is 5t when the plate thickness is t (mm). It is preferable to have one or more grooves of up to 15t.

FIG. 1 is a conceptual diagram showing the crystal orientation of α-phase crystal grains in one embodiment of the titanium plate of the present invention. FIG. 2A is a conceptual diagram showing the crystal orientation 1 of the α-phase crystal grains in one embodiment of the titanium plate of the present invention. FIG. 2B is a conceptual diagram showing the crystal orientation 2 of the α-phase crystal grains in one embodiment of the titanium plate of the present invention. FIG. 3 is a process flow diagram showing an embodiment of the method for producing a titanium plate of the present invention. FIG. 4 is a schematic plan view showing the shape of a molding die for evaluating formability in Examples. FIG. 5 is a schematic cross-sectional view taken along line EE of FIG. 4 showing the shape of a molding die for evaluating formability in the example.

As a result of intensive studies on the components of titanium and the like, the present inventors have made Fe and O a predetermined content, and in the control of the crystal grain structure of the α phase, which is the main phase of the titanium plate, how to orient the crystal orientation. It has been found that a titanium plate having high strength and excellent formability can be obtained by precisely controlling the present invention, and the present invention has been completed.

That is, the titanium plate of the present invention has an alloy composition of Fe: 0.020 to 1.000 mass%, O: 0.020 to 0.200 mass%, the balance being composed of titanium and inevitable impurities, and an HCP structure. Is a titanium plate containing an α-phase crystal grain structure, and when the Fe concentration (mass%) is represented by [Fe] and the O concentration (mass%) is represented by [O], the following formula (1) is satisfied. And
([Fe] −0.020) / [O] ≧ 0.68 (1)
When the crystal orientation of the α-phase crystal grains is expressed by a crystal orientation distribution function, φ1 = 0 °, φ = 35 °, φ2 = 0 ° is orientation 1, φ1 = 0 °, φ = 35 °, φ2 = 30 ° is azimuth 2, φ1 = 90 °, Φ = 35 °, φ2 = 30 ° is azimuth 3, φ1 = 65 °, Φ = 30 °, φ2 = 0 ° is azimuth 4, φ1 = 90 °, Φ = 90 °, φ2 = 0 ° as orientation 5, and the area ratios of the area of crystal grains having an orientation within 15 ° around each orientation with respect to the total area of all α-phase grains are A1, A2, A3, A4, respectively. , A5, the following formula (2) is satisfied,
1.5 ≦ (A3 + A4 + A5) / (A1 + A2) ≦ 30 (2)
The α-phase crystal grains have an average equivalent circle diameter of 5 to 80 μm and a maximum value of 300 μm or less.

With such a configuration, the titanium plate according to the present invention has excellent strength and formability. Further, by using this titanium plate, a heat exchanger plate and a fuel cell separator excellent in heat transfer efficiency and lightening effect can be obtained.

Hereinafter, embodiments of the present invention will be described in detail.

[Titanium plate]
As described above, the titanium plate according to the present embodiment contains Fe: 0.020 to 1.300% by mass, O: 0.020 to 0.400% by mass, and the balance is made of titanium and inevitable impurities. It includes an α-phase crystal grain structure that is an HCP structure (hexagonal close-packed structure). The titanium plate according to the present embodiment has a chemical composition according to industrial pure titanium such as 1 to 4 types of pure titanium specified in JIS H4600 (2012).

(Fe: 0.020 to 1.000 mass%, O: 0.020 to 0.200 mass%)
The strength of the titanium plate decreases when the content of Fe and O is small. Moreover, in order to manufacture a titanium plate having a Fe or O content of less than 0.020% by mass, high-purity sponge titanium is applied as a raw material, which increases costs. Therefore, each content of Fe and O is set to 0.020 mass% or more. The content of O is preferably 0.030% by mass or more. On the other hand, when a large amount of Fe is contained, segregation of the ingot increases and productivity decreases. Therefore, the Fe content is 1.000% by mass or less, preferably 0.800% by mass or less, and more preferably 0.500% by mass or less. Further, when a large amount of O is contained, the titanium plate becomes brittle and cracks during cold rolling tend to occur, resulting in a decrease in productivity and a decrease in formability. Therefore, the O content is 0.200% by mass or less, preferably less than 0.150% by mass, more preferably 0.130% by mass or less, and further preferably 0.100% by mass or less.

(([Fe] -0.020) / [O] ≧ 0.68)
When the Fe concentration (mass%) is represented by [Fe] and the O concentration (mass%) is represented by [O], when ([Fe] −0.020) / [O] is less than 0.68, it will be described later. Even if it goes through a rolling process and an annealing process, a desired texture is not formed. Therefore, ([Fe] −0.020) / [O] is set to 0.68 or more. ([Fe] −0.020) / [O] is preferably 0.70 or more, more preferably 0.75 or more. The upper limit of ([Fe] −0.020) / [O] is not particularly defined, but is practically 50 or less, preferably 20 or less, more preferably 10 or less.

(N: 0.050% by mass or less, C: 0.100% by mass or less, Al: 1.000% by mass or less)
The titanium plate according to the present embodiment exceeds the content as an unavoidable impurity described later, N: 0.050 mass% or less, C: 0.100 mass% or less, Al: 1.000 mass% or less. It is preferable to further contain one or more kinds.

When N, C, and Al are added in excess of the content as an unavoidable impurity, the strength of the titanium plate is improved, and further, Al improves the heat resistance. In order to obtain these effects, the contents of N, C, and Al are each preferably 0.001% by mass or more. On the other hand, if the titanium plate contains excessive amounts of N, C, and Al, cracking during cold rolling is likely to occur, and productivity is reduced. In particular, N tends to make the titanium plate brittle, so the N content is 0.050 mass% or less, preferably 0.014 mass% or less. The C content is 0.100% by mass or less, preferably 0.050% by mass or less. Moreover, Al content shall be 1.000 mass% or less, 0.400 mass% or less is more preferable, and 0.200 mass% or less is further more preferable.

(Remainder: titanium and inevitable impurities)
The remainder of the titanium plate according to this embodiment is made of titanium and inevitable impurities. Inevitable impurities include N, C, Al, H, Si, Cr, Ni and the like. N, C, and Al are as described above. The other elements are H: 0.005% by mass or less, and other elements: each 0.1% by mass or less are not hindered by the effects of the present invention and are allowed.

(Grain structure)
The titanium plate of this embodiment includes an α-phase crystal grain structure having an HCP structure (hexagonal close-packed structure). The α phase crystal grains have a hexagonal crystal structure, and the crystal structure itself has a strong anisotropy. Titanium plates manufactured by conventional rolling and annealing processes have a strong accumulation at an angular position where the α-phase grains are inclined by about 35 ° in the plate width direction from the normal direction of the rolling surface (perpendicular to the rolling surface). It forms a texture. In addition, there is no accumulation (peak) at an angular position inclined in the rolling direction, and there is a problem in that strong strength anisotropy is exhibited in the rolling surface due to higher strength in the sheet width direction than in the rolling direction. Yes.

Generally, the crystal orientation of a crystal grain in a material (sample) can be expressed using a Euler angle by a crystal orientation distribution function. The Euler angle is a method for expressing the crystal orientation relationship of crystal grains with respect to the coordinate system of the sample. Regarding the crystal orientation distribution function, see, for example, edited by Shinichi Nagashima, “texture”, Maruzen, published on January 20, 1984, p. 29-39.

FIG. 1 is a conceptual diagram showing the crystal orientation of α-phase crystal grains of the titanium plate of the present embodiment. As the sample coordinate system, three coordinate axes in an RD direction (rolling direction), a TD direction (plate width direction), and an ND direction (normal direction of the rolling surface), which are orthogonal to each other, are shown. In addition, as the crystal coordinate system, three coordinate axes of X axis, Y axis, and Z axis that are orthogonal to each other are shown. In FIG. 1, the X axis coincides with the [10-10] direction (the normal direction of the column surface), the Y axis coincides with the [-12-10] direction, and the Z axis coincides with the [0001] direction (C axis direction). Matches. In the Bunge notation method, a state in which the RD direction, the TD direction, and the ND direction of the sample coordinate system coincide with the X axis, the Y axis, and the Z axis of the crystal coordinate system is first considered. From there, the crystal coordinate system is rotated by φ1 around the Z axis, and is rotated by φ around the X axis (the state in FIG. 1) after the φ1 rotation. Finally, rotate φ2 around the Z axis after φ1 rotation and φ rotation. Using these three angles φ1, Φ, and φ2, the crystal orientation of the α-phase crystal grains (such as the C-axis direction) is defined.

That is, φ1 is the intersection of the RD-TD plane (rolling plane) of the sample coordinate system and the [10-10] [-12-10] plane of the crystal coordinate system and the RD direction (rolling direction) of the sample coordinate system. Is the angle between Φ is an angle formed by the ND direction (the normal direction of the rolling surface) of the sample coordinate system and the [0001] direction (the normal direction of the (0001) plane) of the crystal coordinate system. φ2 is the intersection of the RD-TD plane (rolling plane) of the sample coordinate system and the [10-10]-[-12-10] plane of the crystal coordinate system, and the [10-10] direction of the crystal coordinate system. Is the angle formed by

Here, using the Bunge notation, φ1 = 0 °, Φ = 35 °, φ2 = 0 ° is azimuth 1, φ1 = 0 °, Φ = 35 °, φ2 = 30 ° is azimuth 2, and φ1 = 90 ° Φ = 35 °, φ2 = 30 ° as azimuth 3, φ1 = 65 °, Φ = 30 °, φ2 = 0 ° as azimuth 4, φ1 = 90 °, Φ = 90 °, φ2 = 0 ° as azimuth 5 To do.

FIG. 2A is a conceptual diagram showing the crystal orientation 1 of the α phase crystal grains. FIG. 2B is a conceptual diagram showing the crystal orientation 2 of the α-phase crystal grains. Orientation 1 and orientation 2 are the orientations of the texture of the main α phase crystal grains recognized in the conventional material. These orientations indicate orientations in which the C axis of α-phase crystal grains (hexagonal crystals) is inclined by 35 ° from the normal direction of the rolling surface to the plate width direction (TD direction). The texture accumulated in these orientations causes the strength anisotropy of the titanium plate. 2A and 2B conceptually show the difference between the orientation 1 and the orientation 2 of the α-phase crystal grains for understanding the above crystal orientation, and are not necessarily shown accurately in terms of inclination and angle. Not a thing.

The present inventors, for these accumulations, α phase crystal grains in an orientation inclined in the rolling direction (RD direction) rather than the sheet width direction from the normal direction of the rolling surface, and the normal direction of the rolling surface In the conventional in-plane, the strength in the plate width direction is higher than that in the rolling direction by newly forming α phase crystal grains in an orientation inclined in the direction between the rolling direction and the plate width direction at a specific quantity ratio. It was found that the strength anisotropy of the steel plate can be effectively reduced to improve the formability of the titanium plate.

In addition to the α phase of the main phase that defines the crystal orientation of the crystal grains, the β phase of the BCC structure (body-centered cubic structure) may be included in an area ratio of about several percent, and the crystal orientation is not particularly specified.

Hereinafter, this embodiment will be described in more detail.

The titanium plate is generally rolled in one direction and produced in a coil shape.When the titanium plate is press-molded to produce a member, the longitudinal direction of the member is made to coincide with the rolling direction of the titanium plate, It is desired that the rolling direction (longitudinal direction of the member) be the main strain direction during molding.

However, the conventional material has excellent formability when the plate width direction is the main strain direction, and the formability is greatly reduced when the rolling direction is the main strain direction. In response to such a problem, the present invention improves the formability in the rolling direction with the rolling direction as the main strain direction.

The orientations of the texture of crystal grains recognized in conventional materials are mainly orientation 1 and orientation 2. These orientations indicate orientations in which the C axis of α-phase crystal grains (hexagonal crystals) is inclined by 35 ° in the plate width direction from the normal direction of the rolling surface. These textures improve the formability in the width direction of the sheet, and conversely reduce the formability in the rolling direction.Consider improving the texture and improving the formability. I found.

That is, the area ratio of the crystal grains having orientation 1 and orientation 2 is relatively reduced, and the C axis has an orientation inclined in the rolling direction from the normal direction of the rolling surface or in the direction between the rolling direction and the sheet width direction. A crystal grain structure was newly formed. And it discovered that the moldability of a rolling direction could be improved by fully increasing the area ratio of the crystal grain which has the newly formed direction rather than the crystal grain which has the direction 1 and the direction 2. FIG. There are several possibilities for the orientation of newly formed crystal grains, and it was assumed that the same effect of reducing strength anisotropy could be obtained. Therefore, as a result of repeated studies, the above-mentioned orientation 3, orientation 4, and orientation 5 are selected and defined.

That is, apart from the azimuth 1 and azimuth 2, the azimuth 3, which corresponds to the azimuth inclined in the rolling direction from the normal direction of the rolling surface, is inclined in the direction between the rolling direction and the sheet width direction from the normal direction of the rolling surface. Attention is paid to the azimuth 4 corresponding to the azimuth and the azimuth 5 corresponding to the C-axis being oriented parallel to the rolling direction. In these five orientations, the area ratio of the area of crystal grains each having an orientation within 15 ° to the total area of all α-phase crystal grains is calculated. The area ratio of the area of the crystal grains having an orientation within 15 ° centering on the obtained orientation 1, orientation 2, orientation 3, orientation 4, and orientation 5 with respect to the total area of all α-phase grains is defined as A1, A2, Let A3, A4, and A5.

At this time, if the present inventors satisfy the following formula (2), the in-plane strength anisotropy is reduced, and further, the strength in the rolling direction can be improved, and the formability in the rolling direction can be improved. I found it.
1.5 ≦ (A3 + A4 + A5) / (A1 + A2) ≦ 30 (2)

Here, the crystal grains having an orientation within 15 ° centered on each orientation mean all crystal grains within a range of 15 ° around each orientation.

(A1 + A2) indicates the total area ratio of crystal grains having the main texture orientation recognized in the conventional material. On the other hand, (A3 + A4 + A5) indicates the total area ratio of crystal grains having crystal orientations defined by orientation 3, orientation 4, and orientation 5, and contributes to improvement of formability in the rolling direction. When the ratio (A3 + A4 + A5) / (A1 + A2) is smaller than 1.5, sufficient formability in the rolling direction cannot be obtained. (A3 + A4 + A5) / (A1 + A2) is preferably more than 3.0, more preferably more than 6.0. On the other hand, (A3 + A4 + A5) / (A1 + A2) does not actually exceed 30, so it is set to 30 or less.

In addition, the present inventors have found that when the following formula (3) is satisfied, the formability in the rolling direction can be further improved.
1.0 <A3 / (A1 + A2) ≦ 10 (3)

A3 / (A1 + A2) represents the ratio of the area ratio of the crystal grains having the orientation defined by the orientation 3 to the area ratio of the crystal grains having the main texture orientation recognized in the conventional material. When A3 / (A1 + A2) is 1.0 or less, sufficient formability in the rolling direction cannot be obtained. A3 / (A1 + A2) is preferably greater than 2.0. On the other hand, A3 / (A1 + A2) does not actually exceed 10, and is 10 or less.

Furthermore, let φ1 = 50 °, Φ = 90 °, and φ2 = 0 ° be orientation 6. The azimuth 6 is an azimuth parallel to a direction in which the C axis is perpendicular to the normal line of the rolling surface and rotated by 40 ° from the rolling direction toward the sheet width direction. It has been found that the formability in the rolling direction can be further improved by making the degree of integration in the direction 5 higher than that in the direction 6.

That is, when the area ratio of the area of crystal grains having an orientation within 15 ° with respect to the orientation 6 to the total area of all α-phase crystal grains is A6, the A5 and A6 satisfy the following formula (4). It is preferable.
(A5-A6)> 0 ... (4)
(A5-A6) is preferably 1.0 or more.

The Euler angle represented by the crystal orientation distribution function can be obtained by orientation analysis using the SEM / EBSD measurement method (described later). Here, the Bunge notation method is used, and the C-axis of the α-phase crystal grain and the plate thickness direction of the rolled sheet (normal direction of the rolling surface) are parallel, and the [1010] direction (column surface method) of the α-phase crystal grain. The state in which the rolling direction of the rolled plate is parallel to the linear direction was defined as φ1 = 0 °, Φ = 0 °, and φ2 = 0 °.

Also, the rolling direction refers to the longitudinal direction of the material in the case of a coil shape. When the material is cut into a plate shape, the direction in which the 0.2% proof stress shows the maximum value when the tensile test is performed in the direction parallel to the plate surface is defined as the rolling direction for convenience.

As will be described later, the texture of the crystal grains satisfying the above formulas (2), (3), and (4) is controlled at the time of production by chemical composition, final cold rolling conditions, and final annealing conditions. Can be obtained by:

It should be noted that the determination as to whether or not Expression (2), Expression (3), and Expression (4) are satisfied is usually as follows: thickness center portion (from thickness center to sheet thickness × (± 10)% ) Based on the measurement results. However, in principle, the equation is satisfied regardless of the thickness.

(Equivalent circle diameter of α phase crystal grains: average value 5 to 80 μm, maximum value 300 μm or less)
In the titanium plate according to this embodiment, if the α phase crystal grains are too coarse, the formability is deteriorated even if the strength anisotropy is reduced. In particular, as the plate thickness decreases, the number of crystal grains occupying in the plate thickness direction decreases, and the formability deteriorates significantly.

Therefore, the circle equivalent diameter of the α-phase crystal grains (the diameter of the circle having the same area as the cross section of the crystal grains) is 5 to 80 μm on the average and 300 μm or less on the maximum. The circle equivalent diameter of the α phase crystal grains is preferably 60 μm or less, more preferably 40 μm or less, on average. Further, the circle equivalent diameter of the α-phase crystal grains is preferably 250 μm or less, more preferably 200 μm or less, at the maximum value. Further, the maximum value of the equivalent circle diameter of the α-phase crystal grains also depends on the plate thickness, and is preferably about 1/4 or less of the plate thickness.

The crystal grain size of the α phase (the equivalent circle diameter of the α phase crystal grains) can be controlled by adjusting the final annealing conditions at the time of production, as will be described later. The α-phase crystal grain size can be measured in an arbitrary cross section of the titanium plate. In the case of a plate material, it is usually measured by observing a plane parallel to the rolling surface of the titanium plate. Specifically, the surface (plate surface) of the titanium plate is polished to form an observation surface, and an electron backscatter diffraction (EBSD) method is performed while scanning an electron beam on the surface with a scanning electron microscope (SEM). The EBSD pattern is measured and analyzed. A boundary having an orientation difference of 10 ° or more is recognized as a crystal grain boundary, and a region surrounded by the crystal grain boundary is defined as a crystal grain.

(Thickness: 1.0mm or less)
Since the titanium plate according to the present embodiment is suitable for forming a groove shape such as a heat exchanger plate, the plate thickness is preferably 1.0 mm or less. When the thickness of the titanium plate exceeds 1.0 mm, when a fine groove shape is provided by molding, wrinkles are likely to occur, and it becomes difficult to obtain a desired precise groove shape. Moreover, the deformation resistance at the time of shaping | molding becomes high, or cost increases. The thickness of the titanium plate is more preferably 0.7 mm or less from the viewpoint of moldability and cost. On the other hand, the thickness of the titanium plate is preferably 0.05 mm or more in order to easily obtain practical strength as a heat exchanger plate and a fuel cell separator. The thickness of the titanium plate is more preferably 0.07 mm or more from the viewpoint of further improving the strength.

Using the titanium plate of this embodiment, it is possible to form a heat exchanger plate and a fuel cell separator that are excellent in heat transfer efficiency and weight reduction effect.

Specifically, when the thickness of the titanium plate is set to t (mm), by providing one or more grooves having a pitch of 4t to 40t and a depth of 5t to 15t, it is more than conventional. Complex shapes can be formed. That is, it becomes possible to deepen the groove, narrow the groove width to narrow the pitch, or form an arbitrary pattern. As a result, the surface area of the formed titanium plate can be increased, the flow of the heat medium (liquid, gas) is homogenized, and a heat exchanger plate and a fuel cell separator exhibiting excellent heat transfer efficiency are obtained. Can do. Furthermore, even with the same heat transfer efficiency, the thickness can be reduced as the strength increases, and a lightweight heat exchanger plate and a fuel cell separator can be obtained.

[Production method of titanium plate]
The titanium plate according to the present embodiment, like the conventional titanium plate, is obtained by subjecting the ingot to ingot rolling and hot rolling to a desired thickness by a known method, and further annealing and cooling under specific conditions. It can be produced by hot rolling and final annealing.

FIG. 3 is a process flow diagram showing a method for manufacturing a titanium plate of the present embodiment. This will be described below based on this process flow chart. In addition, conventionally well-known conditions and methods can be applied except the conditions and methods specifically described below. In addition, in FIG. 3, each code | symbol is S1: Titanium material manufacturing process, S2: Hot rolling process, S3: Annealing process, S5: Cold rolling process, S6: Intermediate annealing process, S8: Final cold rolling process, S9: Shows the final annealing step.

(Titanium material manufacturing process S1)
First, in the titanium material manufacturing step S1, an ingot is manufactured by a conventionally known method, and the ingot is subjected to ingot forging or ingot rolling. For example, first, raw materials of predetermined components are melted by a consumable electrode type vacuum arc melting method (VAR method), a plasma arc melting method (PAM method), and an electron beam melting method (EB method), and then cast into a titanium ingot. Get. This ingot is subjected to block forging (hot forging) or block rolling into a block shape of a predetermined size. The chemical component such as Fe is as described above, and is adjusted to a predetermined component at the time of dissolution.

(Hot rolling process S2)
In the next hot rolling step S2, the block-shaped ingot is heated to, for example, 700 to 1050 ° C. and hot rolled to obtain a hot rolled sheet.

(Annealing step S3)
Next, in the annealing step S3, the obtained hot-rolled sheet is annealed while being held at 650 ° C. or higher and lower than 800 ° C. As other conditions, known conditions are applied.
In addition, when performing intermediate annealing process S6 mentioned later, annealing process S3 can be abbreviate | omitted as needed.

(Thickness determination S4)
Here, the plate thickness is determined (S4).
If the material is relatively soft, or if the desired plate thickness is relatively thick and the rolling reduction from annealing after hot rolling is small, there is no need to perform intermediate annealing. Therefore, after annealing process S3, it progresses to final cold rolling process S8 and final annealing process S9 which are mentioned later.

However, if the material is hard, or if the reduction ratio from the annealing after hot rolling becomes large, cracking is likely to occur during cold rolling, so intermediate annealing is required in the middle as described below.

As will be described later, in order to control the crystal grain structure of the titanium plate to a specific structure, it is preferable to perform the intermediate annealing.

(Cold rolling step S5, intermediate annealing step S6, plate thickness determination S7)
The hot-rolled sheet is usually formed into a desired sheet thickness by repeatedly performing the cold rolling process S5 and the intermediate annealing process S6 after the annealing process S3 after hot rolling. The necessity of intermediate annealing and the required number of times depend on the material and the cold rolling reduction ratio. The number of intermediate annealing is usually preferably 1 to 4 times, and more preferably 2 to 4 times.

(Intermediate annealing step S6)
Here, the case where intermediate annealing is performed once will be described as an example.
The intermediate annealing step S6 is mainly intended to soften the material in order to improve the subsequent cold rollability. Therefore, it is usually processed in the recrystallization temperature range (usually in the range of 500 ° C to 850 ° C), and processed at high temperature for a short time (about 820 ° C for several minutes) or low temperature for a long time (about 600 ° C for several tens of hours or more). Is done.

The intermediate annealing step S6 may be performed under any atmosphere of air, vacuum, inert gas, or reducing gas. Further, the intermediate annealing step S6 can be performed in either a batch furnace or a continuous furnace. In particular, when annealing (atmospheric annealing) is performed in an air atmosphere, the scale is attached to the surface of the titanium plate (hot rolled plate), so the process proceeds to the next step (the subsequent cold rolling step if intermediate annealing). Before the scale removal step, for example, salt heat treatment, pickling treatment, or the like is preferably performed.

(Cold rolling step S5, final cold rolling step S8)
The total rolling reduction (working ratio for the hot-rolled sheet) by cold rolling (cold rolling step S5, final cold rolling step S8) of the titanium plate according to this embodiment is set to 20 to 98%. The intermediate annealing may be performed a plurality of times during the cold rolling.

Further, the rolling reduction after the final intermediate annealing, that is, the rolling reduction in the final cold rolling step S8 is set to 20 to 87%. As a result, a desired texture of α-phase crystal grains is formed. At this time, if the rolling reduction exceeds 87%, a desired α-phase grain structure cannot be obtained even if the final annealing described below is performed. The rolling reduction in the final cold rolling step S8 is preferably 50 to 87%, and more preferably 50 to 70%.

Moreover, it is preferable that the rolling reduction in the cold rolling performed from the hot rolling step S2 to immediately before the final cold rolling step S8 does not exceed the rolling reduction in the final cold rolling step S8.

(Final annealing step S9)
In the final annealing step S9, the titanium plate according to the present embodiment preferably adjusts the temperature and time to control the crystal grain size and strength anisotropy of the α phase. Therefore, the annealing temperature is set to the β transformation point (Tβ) or more and less than 950 ° C. The β transformation point is the lowest temperature at which all of the α phase disappears and becomes the β phase, and changes depending on the chemical composition (Fe content, etc.) of the titanium material.

In the annealing step S3 and the intermediate annealing step S6 in the prior art, as described above, the general annealing condition of the pure titanium material is 600 ° C. or higher at which recrystallization proceeds and 850 ° C. or lower below the β transformation point. . Thus, by not increasing the fraction of β phase, the growth of α phase crystal grains is not hindered and grows in equiaxed granular form.

In contrast, in the final annealing according to the present embodiment, the entire cold-rolled sheet is transformed into the β phase by heating to the β transformation point or higher, that is, the β single phase region. Then, it transforms from the β phase to the α phase by cooling. By adopting such conditions, a desired α-phase crystal grain texture is formed, and strength anisotropy can be reduced. However, the higher the temperature in the β single-phase region, the more the growth of β-phase crystal grains is promoted. Further, as the holding time at the annealing temperature becomes longer, the β-phase crystal grains become larger and become coarser after 180 seconds. Accordingly, the annealing temperature (holding temperature) in the final annealing step is set to the β transformation point or higher and lower than 950 ° C., and the holding time in this temperature range is preferably 0 to 180 seconds. The cooling condition after the final annealing is preferably 10 ° C./second or more.

Note that the holding time of 0 seconds means that the cold rolled plate is heated and cooled as soon as the β transformation point is reached. The final annealing step S9 may be performed in any atmosphere of air, vacuum, inert gas, or reducing gas. In addition, when it anneals to air | atmosphere, it is preferable to perform a scale removal process as above-mentioned after cooling.

As described above, in the method for manufacturing a titanium plate according to the present embodiment, in controlling the α phase crystal grain structure of the titanium plate, particularly characteristic conditions are (1) titanium material manufacturing step S1. ([Fe] −0.020) / [O] is set to 0.68 or more, (2) In the final annealing step S9, the annealing temperature is set to the β transformation point or more and less than 950 ° C., and the holding time is 0 to 180 seconds. (3) The reduction ratio in the final cold rolling step S8 is set to 20 to 87%.

This specification discloses various modes of technology as described above, and the main technologies are summarized below.

The titanium plate of the present invention has an HCP structure in which the alloy composition is Fe: 0.020 to 1.000 mass%, O: 0.020 to 0.200 mass%, and the balance is composed of titanium and inevitable impurities. When the titanium plate includes an α-phase crystal grain structure and the Fe concentration (mass%) is represented by [Fe] and the O concentration (mass%) is represented by [O], the following formula (1) is satisfied:
([Fe] −0.020) / [O] ≧ 0.68 (1)
When the crystal orientation of the α-phase crystal grains is expressed by a crystal orientation distribution function, φ1 = 0 °, φ = 35 °, φ2 = 0 ° is orientation 1, φ1 = 0 °, φ = 35 °, φ2 = 30 ° is azimuth 2, φ1 = 90 °, Φ = 35 °, φ2 = 30 ° is azimuth 3, φ1 = 65 °, Φ = 30 °, φ2 = 0 ° is azimuth 4, φ1 = 90 °, Φ = 90 °, φ2 = 0 ° as orientation 5, and the area ratios of the area of crystal grains having an orientation within 15 ° around each orientation with respect to the total area of all α-phase grains are A1, A2, A3, A4, respectively. , A5, the following formula (2) is satisfied,
1.5 ≦ (A3 + A4 + A5) / (A1 + A2) ≦ 30 (2)
The α-phase crystal grains have an average equivalent circle diameter of 5 to 80 μm and a maximum value of 300 μm or less.

If the titanium plate has such a structure, the in-plane strength anisotropy is small, and a titanium plate having both strength and formability can be obtained. The titanium plate of the present invention may further have any one or more of the structures listed below. Thereby, in addition to the above advantages, it is considered that further effects can be achieved.

The titanium plate described above preferably satisfies the following formula (3).
1.0 <A3 / (A1 + A2) ≦ 10 (3)

If the titanium plate has such a configuration, it can be a titanium plate with improved formability in the rolling direction.

In addition, any one of the titanium plates described above has φ1 = 50 °, φ = 90 °, φ2 = 0 ° as an orientation 6, and an entire α phase of crystal grains having an orientation within 15 ° with the orientation 6 as the center. When the area ratio with respect to the total area of the crystal grains is A6, it is preferable to satisfy the following formula (4).
(A5-A6)> 0 ... (4)

If the titanium plate has such a configuration, it can be a titanium plate that is further excellent in formability in the rolling direction.

Any of the titanium plates described above may further contain one or more of N: 0.050 mass% or less, C: 0.100 mass% or less, and Al: 1.000 mass% or less. preferable.

If the titanium plate has such a configuration, the strength of the titanium plate can be further improved. Furthermore, heat resistance can be improved by adding Al.

Furthermore, it is preferable that any of the titanium plates described above has a plate thickness of 1.0 mm or less. If it is a titanium plate of such a structure, the improvement of a further moldability and weight reduction can be achieved.

The heat exchanger plate of the present invention is a heat exchanger plate using any of the titanium plates described above, and when the plate thickness is t (mm), the pitch is 4t to 40t and the depth is 5t. It is preferable to have one or more grooves of up to 15t.

Such a heat exchanger plate is excellent in heat transfer efficiency and weight reduction effect.

The fuel cell separator of the present invention is a fuel cell separator using any of the titanium plates described above, and when the plate thickness is t (mm), the pitch is 4t to 40t and the depth is 5t. It is preferable to have one or more grooves of up to 15t.

Such a fuel cell separator is excellent in heat transfer efficiency and weight reduction effect.

As mentioned above, although the form for implementing this invention was described, the Example which confirmed the effect of this invention is demonstrated concretely compared with the comparative example which does not satisfy | fill the requirements of this invention below. It should be noted that the present invention is not limited by this embodiment, and can be implemented with modifications within the scope of the claims, all of which are included in the technical scope of the present invention. .

[Production of test materials]
Pure titanium (JIS H4600 (2012)) ingot and pure titanium ingot contain Fe, O, etc., and the raw material consisting of titanium and inevitable impurities is melted by CCIM (Cold Crucible Induction Melting Method) Thus, a titanium ingot having the composition shown in Table 1 was obtained. This titanium ingot was subjected to partial forging (hot forging), hot rolling and annealing under known conditions to obtain a hot rolled sheet having a thickness of 4.0 mm. The scale of the surface of the hot-rolled sheet is removed, intermediate annealing is performed at 750 ° C., final cold rolling and final annealing are performed under the conditions shown in Table 1, and descaling processing is performed by salt bath treatment and pickling. .45 mm test materials (test materials No. 1 to 12) were obtained. Further, based on the composition of the test material, the β transformation point (Tβ) was calculated using the thermodynamic calculation software “ThermoCalc” and is also shown in Table 1.

(Measurement of α phase texture and crystal grain size)
The surface (sheet surface) of the test material is polished, and the area is 1.6 mm square (1.6 mm each in the rolling direction and the rolling width direction) on the rolled surface having a thickness of 1/2 part (the center of the sheet thickness). On the other hand, tissue observation by EBSD was performed. The EBSD measurement was performed by the FE-SEM / EBSD method. The measurement data was analyzed using EBSD data analysis software, and the texture and crystal grain size were measured. Note that the minimum grain size of the crystal grains to be subjected to EBSD measurement was 1.5 μm.

The texture is analyzed by SEM-EBSD analysis software using a crystal orientation distribution function (Orientio Distribution Function: ODF), and crystal orientations of specific crystal grains expressed by six Euler angles (azimuth 1, azimuth 2). , Azimuth 3, azimuth 4, azimuth 5, azimuth 6) with respect to the total area of all α-phase grains (A1, A2, A3, A4, A5, A6) was measured. From the numerical values, (A3 + A4 + A5) / (A1 + A2), A3 / (A1 + A2), and (A5-AA6) were calculated. The results are shown in Table 2.

Here, Bunge's notation method is used for Euler angle notation, and the C-axis of the α-phase crystal grain and the plate thickness direction of the rolled sheet (normal direction of the rolling surface) are parallel, and [10− 10] The state in which the direction (normal direction of the column surface) and the rolling direction of the rolled sheet are parallel was defined as φ1 = 0 °, Φ = 0 °, and φ2 = 0 °. On the other hand, the crystal grain size was similarly calculated based on the SEM / EBSD measurement result as a circle equivalent diameter of a crystal grain by setting a boundary having an orientation difference of 10 ° or more as a crystal grain boundary.

In calculating the average value of the equivalent circle diameter of α phase crystal grains, based on the EBSD measurement results, based on the data points identified as α phase, the boundary with an orientation difference of 10 ° or more is recognized as the grain boundary. The region surrounded by the crystal grain boundary was defined as a crystal grain, and the equivalent circle diameter of each crystal grain was calculated by image analysis. At this time, noise (measurement points that were not accurately identified) is included in the measurement result, so in order to remove the influence, extraction is performed in order from large crystal grains, and 95 of the total area identified as α phase. % Up to the crystal grain size when it exceeded the area for the first time was used as the calculated parameter of the average grain size.

In the calculation of the maximum value of the equivalent circle diameter of the α-phase crystal grains, the average value of the fifth crystal grains in order from the largest crystal grains was taken as the maximum value based on the same data.

The average and maximum values of equivalent circle diameters are shown in Table 2. In Tables 1 and 2, the numbers underlined indicate that the values deviate from the definition of the present invention.

[Performance evaluation]
(Tensile test)
A No. 13 test piece specified in JIS Z2201 (2011) was cut out from the test material. Based on JIS H4600 (2012), a room temperature tensile test was performed at room temperature with the rolling direction (RD) as the load axis direction, and 0.2% yield strength (YS) was measured. The results are shown in Table 2. 170 MPa or more was accepted.

(Evaluation of formability)
The moldability was evaluated by performing press molding using a molding die simulating a heat exchange part (plate) of a plate heat exchanger for each test material. FIG. 4 is a schematic plan view showing the shape of a molding die for evaluating moldability. FIG. 5 is a schematic cross-sectional view taken along the line EE of FIG. 4 showing the shape of a molding die for evaluating moldability. As shown in FIG. 4 and FIG. 5, the shape of the molding die is 100 mm × 100 mm in the molded part, four twill lines with a pitch of 17 mm and a maximum depth of 6.5 mm, and each twill line is apex. Further, it has an R shape with R = 2.5 mm.

Using this molding die, press molding was performed by an 80-ton press. In press molding, rust preventive oil was applied to both surfaces of each test material for lubrication, and the test material was placed on the lower mold so that the rolling direction of each test material coincided with the vertical direction of FIG. And after constraining the flange portion with a plate press, the mold was pushed in under the condition of a press speed of 1 mm / sec. The mold was pushed in at intervals of 0.1 mm, and the maximum amount of indentation depth (E: unit mm) at which no cracks occurred was determined by experiment. Then, the formability index (F) was calculated by the following formula. The results are shown in Table 2. When the moldability index (F) is a positive value, it indicates that the balance between strength and moldability is excellent, and it was determined to be acceptable.
F = E- (GH × YS)
G = 7.70, H = 0.0120
YS = Numerical value of 0.2% proof stress in the RD direction (rolling direction) E = Numerical value of the maximum indentation depth

As shown in Table 1 and Table 2, test material No. which is an example of the present invention. In Nos. 1 to 6, the equivalent-circle diameter and texture state of the α-phase crystal grains (numerical values in the formulas (2), (3), and (4)) are within the scope of the present invention, and have excellent strength and molding He had a good balance of sex.

In contrast, test material No. In No. 7, the final annealing temperature was below the β transformation point, the average value of the circle equivalent diameter of the α phase crystal grains was small, the texture was not sufficiently developed, and the formability was low. Test material No. In Nos. 8 and 11, ([Fe] -0.020) / [O] was below the lower limit, the final annealing temperature was below the β transformation point, the texture was not sufficiently developed, and the moldability was low. . In addition, test material No. No. 11 was low in 0.2% proof stress because the O and Fe contents were relatively small. Test material No. No. 9, ([Fe] -0.020) / [O] is below the lower limit, the final annealing temperature is above the upper limit, and the maximum equivalent circle diameter of the α phase grains exceeds the upper limit. The texture was not sufficiently developed and the moldability was low. Test material No. In Nos. 10 and 12, although final annealing was performed properly, ([Fe] -0.020) / [O] was below the lower limit, the texture was not sufficiently developed, and the formability was low.

This application is based on Japanese Patent Application No. 2016-076112 filed on Apr. 5, 2016, the contents of which are included in the present application.

In order to express the present invention, the present invention has been described appropriately and sufficiently through the embodiments with reference to specific examples and the like. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized that this is possible. Therefore, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not limited to the scope of the claims. To be construed as inclusive.

The present invention has wide industrial applicability in the technical fields related to titanium plates, heat exchangers, fuel cell separators, and the like.

Claims

The alloy composition is Fe: 0.020 to 1.000% by mass, O: 0.020 to 0.200% by mass, the balance is composed of titanium and inevitable impurities, and the crystal grain structure of the α-phase having the HCP structure Including a titanium plate,
When the Fe concentration (mass%) is represented by [Fe] and the O concentration (mass%) is represented by [O], the following formula (1) is satisfied:
([Fe] −0.020) / [O] ≧ 0.68 (1)
When the crystal orientation of the α-phase crystal grain is expressed by a crystal orientation distribution function, φ1 = 0 °, φ = 35 °, φ2 = 0 ° is orientation 1, φ1 = 0 °, φ = 35 °, φ2 = 30 ° Azimuth 2, φ1 = 90 °, Φ = 35 °, φ2 = 30 ° azimuth 3, φ1 = 65 °, Φ = 30 °, φ2 = 0 ° azimuth 4, φ1 = 90 °, Φ = 90 °, φ2 = 0 ° is the orientation 5, and the area ratio of the area of the crystal grains having the orientation within 15 ° around each orientation to the total area of all α-phase grains is A1, A2, A3, A4, and A5, respectively. Sometimes the following formula (2) is satisfied,
1.5 ≦ (A3 + A4 + A5) / (A1 + A2) ≦ 30 (2)
A titanium plate, wherein an average equivalent circle diameter of the α-phase crystal grains is 5 to 80 μm and a maximum value is 300 μm or less.
The titanium plate according to claim 1, wherein the following formula (3) is satisfied.
1.0 <A3 / (A1 + A2) ≦ 10 (3)
The area ratio of the area of the crystal grains having an orientation within 15 ° around the orientation 6 with φ1 = 50 °, φ = 90 °, and φ2 = 0 ° as the center and the total area of all α-phase crystal grains as A6 The titanium plate according to claim 1, wherein the following formula (4) is satisfied.
(A5-A6)> 0 ... (4)
The titanium plate further contains any one or more of N: 0.050 mass% or less, C: 0.100 mass% or less, and Al: 1.000 mass% or less. The titanium plate described in 1.
The titanium plate according to claim 1, wherein the plate thickness is 1.0 mm or less.
A heat exchanger plate using the titanium plate according to any one of claims 1 to 5, wherein when the plate thickness is t (mm), the pitch is 4t to 40t and the depth is 5t to 15t. A heat exchanger plate having one or two or more grooves.
A fuel cell separator using the titanium plate according to any one of claims 1 to 5, wherein when the plate thickness is t (mm), the pitch is 4t to 40t and the depth is 5t to 15t. A fuel cell separator having one groove or two or more grooves.