Titanium plate and method for producing titanium plate

Abstract

The objective of the present disclosure is to provide a titanium plate with excellent shapeability, by virtue of which a greater amount of lower-purity scrap can be used, thus increasing the recycling rate. A titanium plate according to an aspect of the present disclosure has a plurality of protrusions formed on each of a pair of surfaces that oppose each other in the thickness direction, the plurality of protrusions having a maximum height Rz between 5 μm and 50 um inclusive and a maximum length in a plan view between 100 μm and 1000 μm inclusive, with a pitch of 1 mm or less between adjacent protrusions on each of the surfaces.

Description

Titanium plate and method for manufacturing titanium plate

[0001] The present disclosure relates to titanium plates and methods for manufacturing titanium plates.

[0002] Nowadays, in view of resource depletion, recycling of various things is progressing, and recycling of metals, which are consumed in large quantities, has been carried out for some time.

[0003] Pure titanium and titanium alloys are lighter and stronger than iron-based metal materials such as iron and its alloys, and are therefore widely used in sports equipment, leisure equipment, medical instruments, various plant components, aviation and space equipment, etc. Furthermore, because they exhibit extremely good corrosion resistance to seawater, they are also widely used in plate materials and welded pipes in heat exchangers that use seawater as a refrigerant.

[0004] Such members are formed by subjecting titanium plates to processes involving plastic deformation such as pressing, bending, drawing, etc. Therefore, titanium plates are required to have excellent formability during press working, etc.

[0005] Japanese Patent Application Laid-Open No. 2002-194591

[0006] Patent Document 1 describes improving the lubricity of a lubricant during press forming by controlling the surface hardness and the thickness of an oxide film. In this document, a brittle hardened layer containing large amounts of oxygen, carbon, nitrogen, etc., formed during cold rolling and subsequent heat treatment is removed, and then the thickness and surface hardness of the oxide film formed on the surface are controlled to prevent direct contact between the titanium metal and the tool, i.e., between the titanium metal and the mold surface, thereby preventing deterioration of the lubrication state. Because the brittle hardened layer in this document is removed by methods such as acid abrasion or grinding, this reduces yield and makes the removed titanium unrecyclable.

[0007] Meanwhile, the present inventors have intensively investigated ways to improve the formability of titanium plates from a different perspective than that of Patent Document 1. Furthermore, they have adopted a process within the manufacturing process that can prevent portions with reduced yield from becoming industrial waste, and have completed the present invention.

[0008] The present disclosure was made in light of these circumstances and aims to provide a titanium plate with excellent formability. When scrap is used as a recycled raw material, the amount of titanium impurity increases, which is expected to result in a deterioration of properties such as formability. The formability improvement provided by the present disclosure can be applied to scrap-based materials to complement the formability effect. Another aim of the present disclosure is to contribute to a carbon-neutral society by increasing the amount of scrap mixed, i.e., by increasing the metal recycling rate.

[0009] A titanium plate according to one embodiment of the present disclosure has a plurality of protrusions formed on each of a pair of surfaces facing each other in the plate thickness direction, the plurality of protrusions having a maximum height Rz of 5 μm or more and 50 μm or less and a maximum length in a planar view of 100 μm or more and 1000 μm or less, and the pitch between adjacent protrusions on each surface is 1 mm or less.

[0010] The titanium plate according to one embodiment of the present disclosure has excellent formability and can contribute to improving the metal recycling rate.

[0011] FIG. 1 is a schematic plan view of a titanium plate according to an embodiment of the present disclosure. FIG. 2 is a partially enlarged cross-sectional view of the cross section of the titanium plate of FIG. 1 cut in the plate thickness direction along line II-II. FIG. 3 is a schematic diagram showing a unit lattice in the titanium plate of FIG. 1. FIG. 4 is a flow diagram showing a method for manufacturing a titanium plate according to an embodiment of the present disclosure. FIG. 5 is a schematic diagram showing an example of the procedure for forming multiple protrusions on both sides in the forming step in the manufacturing method of the titanium plate of FIG. 4. FIG. 6 is a schematic diagram showing the procedure for forming multiple protrusions on one side in the forming step in the manufacturing method of No. 8 titanium plate. FIG. 7 is a schematic diagram for explaining the score as a press formability index.

[0012] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.

[0013] (1) A titanium plate according to one embodiment of the present disclosure has a plurality of protrusions formed on each of a pair of surfaces facing each other in the plate thickness direction, the plurality of protrusions having a maximum height Rz of 5 μm or more and 50 μm or less, a maximum length in a planar view of 100 μm or more and 1000 μm or less, and a pitch between adjacent protrusions on each surface of the titanium plate being 1 mm or less.

[0014] Because the titanium plate has the plurality of protrusions formed on each of the pair of surfaces, lubricant can be distributed approximately uniformly around the plurality of protrusions on each surface, for example, during press forming. In particular, the protrusions have a maximum height Rz of 5 μm to 50 μm, a maximum length in plan view of 100 μm to 1000 μm, and a pitch between adjacent protrusions on each surface of 1 mm or less, which facilitates the retention of lubricant between adjacent protrusions. Furthermore, when the titanium plate contacts a mold, the tops of the generally evenly spaced protrusions come into contact, so stress is applied evenly over a wide area of ​​the plate surface even with a severe mold shape, thereby suppressing the promotion of localized deformation, which is characteristic of titanium. Therefore, the titanium plate has excellent formability. Furthermore, since the formation of the plurality of protrusions on each of the pair of surfaces improves lubricity, the range in which formability can be ensured in relation to the purity of titanium is broadened. In other words, the titanium plate is more likely to maintain formability even when the titanium purity is lowered. Therefore, the scope of application of recycled materials that are likely to have an increased impurity concentration can be expanded, and the titanium plate can increase the metal recycling rate.

[0015] (2) In the above (1), the titanium plate may be made of pure titanium material specified in JIS Class 1. With this configuration, the titanium plate can have improved formability.

[0016] (3) In the above (1) or (2), the plurality of protrusions may be arranged on lattice points on each of the pair of surfaces. With this configuration, it is easier to hold the lubricant more uniformly on the pair of surfaces.

[0017] (4) In the above (3), the protrusions may occupy an area ratio of 10% to 60% of the unit lattice. With this configuration, the lubricant can be more easily and uniformly held on the pair of surfaces.

[0018] (5) In any of (1) to (4) above, the protrusions may be circular or elliptical in plan view. This configuration facilitates more uniform retention of the lubricant on the pair of surfaces. The terms "circular" and "elliptical" encompass concepts such as "substantially circular" and "substantially elliptical," and include, for example, an "elliptical" shape having a pair of opposing straight lines and a pair of arcs connecting the ends of these straight lines. Furthermore, in the "elliptical" shape, "opposing" is not limited to opposing in the strict sense, and includes, for example, a configuration in which the pair of straight lines are non-parallel or a configuration in which the pair of arcs have different radii of curvature. Furthermore, in the "elliptical" shape, the length of the pair of straight lines is not limited.

[0019] (6) In any one of (1) to (5) above, the plurality of protrusions on the pair of surfaces may have the same shape and arrangement pattern. This configuration makes it easier to spread the lubricant more uniformly around the plurality of protrusions.

[0020] (7) In any of (1) to (6) above, the protrusions may have a flat or dome-shaped top. This configuration makes it easier to retain lubricant between adjacent protrusions. Furthermore, when the titanium plate contacts the mold, stress is more easily applied evenly over a wide area of ​​the plate surface, even with a severe mold shape, making it possible to more reliably suppress the promotion of localized deformation, which is characteristic of titanium. The terms "flat" and "dome-shaped" encompass the concepts of "approximately flat" and "approximately dome-shaped," and include, for example, shapes with partial irregularities.

[0021] (8) A method for producing a titanium plate according to another embodiment of the present disclosure includes the steps of: heat-treating a cold-rolled plate obtained by cold-rolling a titanium plate; forming a plurality of protrusions on each of a pair of surfaces of the cold-rolled plate that are opposite in the plate thickness direction after the heat-treating step; and subjecting the cold-rolled plate after the forming step to a finish heat treatment, wherein the plurality of protrusions have a maximum height Rz of 5 μm or more and 50 μm or less and a maximum length in a planar view of 100 μm or more and 1000 μm or less, and the pitch between adjacent protrusions on each of the surfaces is 1 mm or less.

[0022] The titanium plate manufacturing method includes the forming step, thereby forming the plurality of protrusions on each of the pair of surfaces. Therefore, the titanium plate obtained by this titanium plate manufacturing method can have a lubricant distributed approximately uniformly around the plurality of protrusions on each surface, for example, during press forming. In particular, the protrusions have a maximum height Rz of 5 μm to 50 μm, a maximum length in plan view of 100 μm to 1000 μm, and a pitch between adjacent protrusions on each surface of 1 mm or less, which facilitates the retention of lubricant between adjacent protrusions. Furthermore, according to this titanium plate manufacturing method, forming the plurality of protrusions on each of the pair of surfaces improves lubrication, enabling the molding of more complexly shaped components. Furthermore, according to this titanium plate manufacturing method, when the obtained titanium plate comes into contact with a mold, the tops of the protrusions, which are approximately evenly spaced, come into contact, so that stress is applied evenly over a wide area of ​​the plate surface, even with a severe mold shape, and the promotion of localized deformation, which is characteristic of titanium, is suppressed. Therefore, the titanium plate obtained by this titanium plate manufacturing method has excellent press formability. Furthermore, the titanium plate obtained by this titanium plate manufacturing method may have a reduced titanium purity to the extent that formability can be improved. In other words, titanium plates with an appropriately increased amount of scrap may be manufactured. Therefore, this titanium plate manufacturing method can increase the metal recycling rate.

[0023] In this disclosure, being able to increase the metal recycling rate means being able to use recycled materials, and is not intended to limit the titanium materials used to recycled materials.

[0024] In this disclosure, "titanium" includes pure titanium and titanium alloys. "Maximum height Rz" refers to the maximum height Rz specified in JIS-B0601:2001. The maximum height Rz of multiple protrusions can be determined by setting a reference length that encompasses the profile (bottom-top-bottom) of at least one protrusion. "Planar view" refers to a view in the plate thickness direction. "Pitch between protrusions" refers to the distance between the centers of the protrusions in a planar view. "Multiple protrusions arranged on lattice points" refers to a configuration in which protrusions are arranged at the intersections of multiple first lattice lines arranged in parallel at equal intervals and multiple second lattice lines arranged in parallel at equal intervals so as to intersect with the multiple first lattice lines. "Unit lattice" refers to the smallest area defined by the first lattice lines and the second lattice lines (an area that does not include lattice points).

[0025] [Details of the Embodiments of the Present Disclosure] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings as appropriate. It should be noted that with respect to the numerical values ​​described in this specification, it is possible to adopt only one of the upper and lower limit values ​​described, or to arbitrarily combine the upper and lower limit values. In this specification, all combinable numerical ranges are described as suitable ranges. Furthermore, each figure is a schematic diagram and may not correspond to actual dimensions, ratios, etc.

[0026] 1 and 2, the titanium plate 10 has a pair of surfaces (a first surface 1 and a second surface 2) facing each other in the plate thickness direction. The titanium plate 10 has a plurality of protrusions 11, 12 formed on each of the pair of surfaces 1, 2 (specifically, a plurality of protrusions 11 are formed on the first surface 1, and a plurality of protrusions 12 are formed on the second surface 2). The plurality of protrusions 11, 12 each have a maximum height Rz of 5 μm or more and 50 μm or less, and a maximum length L in a plan view of 100 μm or more and 1000 μm or less. Furthermore, the pitch P between adjacent protrusions 11, 12 on each of the surfaces 1, 2 of the titanium plate 10 is 1 mm or less.

[0027] The titanium plate 10 has a pair of protrusions 11, 12 formed on each of the pair of surfaces 1, 2. Therefore, during press forming, for example, lubricant can be distributed approximately uniformly around the protrusions 11, 12 on each surface 1, 2. In particular, the protrusions 11, 12 have a maximum height Rz of 5 μm to 50 μm, a maximum length L in a plan view of 100 μm to 1000 μm, and a pitch between adjacent protrusions 11, 12 on each surface 1, 2 of 1 mm or less, which facilitates retention of lubricant between adjacent protrusions 11, 12. Furthermore, when the titanium plate 10 contacts a mold, the tops 11a, 12a of the protrusions 11, 12, which are approximately evenly spaced, come into contact. Therefore, even with a severe mold shape, stress is applied uniformly over a wide area of ​​the plate surface, suppressing the promotion of localized deformation, which is characteristic of titanium. Therefore, the titanium plate 10 has excellent formability. Furthermore, the lubricity of the titanium plate 10 can be improved by forming multiple protrusions 11, 12 on each of the pair of surfaces 1, 2, thereby broadening the range in which formability can be ensured in relation to the purity of titanium. In other words, the titanium plate 10 can easily maintain formability even when the purity of titanium is reduced. This expands the range of application of recycled materials that are likely to have an increased impurity concentration, and the titanium plate 10 can increase the metal recycling rate.

[0028] The titanium plate 10 is suitable for being given a three-dimensional shape by, for example, press molding. This press molding is performed with a lubricant applied between the titanium plate and the mold. The titanium plate 10 has a pair of protrusions 11, 12 formed on each of the surfaces 1, 2, so that the lubricant can be easily retained on both surfaces 1, 2.

[0029] The titanium plate 10 may be formed using a single material or a mixture of multiple materials with different chemical compositions. The material may be pure titanium or a titanium alloy. In particular, the titanium plate 10 is preferably formed using pure titanium, and more preferably using pure titanium as specified in JIS Class 1. By using pure titanium as specified in JIS Class 1, the multiple protrusions 11, 12 can be easily and reliably formed, and formability during press forming of the titanium plate 10 can be improved. The titanium plate 10 may be formed solely using pure titanium as specified in JIS Class 1 to enhance softness and further improve formability. In this case, the titanium plate 10 is configured as a pure titanium plate having a chemical composition specified in JIS Class 1. On the other hand, the titanium plate 10 may be manufactured by incorporating a large amount of titanium scrap as a melting raw material, as long as it is within the JIS specification range, in order to achieve metal recycling. Furthermore, the titanium scrap itself may have a chemical composition specified in JIS Class 1 to JIS Class 4. By controlling the shape of the multiple protrusions 11, 12, the titanium plate 10 can enhance the retention of lubricant on the surfaces 1, 2, ensuring formability even with a slightly lower purity. By using titanium scrap, the titanium plate 10 can promote resource recovery and waste recycling. Note that pure titanium specified in JIS Class 1 is the softest pure titanium, with the contents of elements other than titanium being N (nitrogen) ≦0.03 mass%, C (carbon) ≦0.08 mass%, H (hydrogen) ≦0.013 mass%, Fe (iron) ≦0.20 mass%, and O (oxygen) ≦0.15 mass%.

[0030] Because the titanium plate 10 is made of titanium, it has excellent properties such as corrosion resistance, strength, and light weight. The titanium plate 10 can be used for components that require corrosion resistance, such as plate materials in plate heat exchangers and muffler components for motorcycles, as well as for sports equipment, leisure equipment, medical equipment, various plant components, and aviation and space equipment.

[0031] The upper limit of the thickness T of the titanium plate 10 (based on the tops 11a, 12a of the protrusions 11, 12) may be 4 mm or 1 mm. When the thickness T is equal to or less than the upper limit, the titanium plate 10 can be pressed from both sides in the thickness direction using a mold having a complementary shape, for example, to three-dimensionally deform the entire plate material in accordance with the mold. In such a configuration, it is desirable to be able to retain a lubricant on both surfaces 1, 2 during press forming. In this regard, the titanium plate 10 has multiple protrusions 11, 12 formed on the first surface 1 and the second surface 2, respectively, thereby enabling the lubricant to be appropriately retained on the first surface 1 and the second surface 2. The lower limit of the thickness T is not particularly limited, but may be 0.1 mm or 0.3 mm from the viewpoint of providing the titanium plate 10 with the necessary strength and from the viewpoint of the manufacturing limit for providing unevenness.

[0032] (Protrusions) The shape of the multiple protrusions 11, 12 can be, for example, circular, elliptical, rectangular, etc. in a plan view. Among these, circular and elliptical shapes are preferred from the viewpoint of preventing corners on the opposing surfaces of adjacent protrusions 11, 12 on each surface 1, 2. By configuring the multiple protrusions 11, 12 in this way, it becomes easier to retain the lubricant more uniformly around the multiple protrusions 11, 12.

[0033] The protrusions 11, 12 may have planar or dome-shaped tops 11a, 12a. In other words, the protrusions 11, 12 may have a shape other than a cone shape. When the tops 11a, 12a are planar, the shapes of the protrusions 11, 12 may be, for example, columnar or frustum-shaped. In this case, the tops 11a, 12a are formed by a top surface parallel to the surfaces 1, 2 on which the respective protrusions 11, 12 are formed. Examples of the columnar shape include a circular cylinder, an elliptical cylinder, and a rectangular column. Examples of the frustum shape include a circular truncated cone, an elliptical truncated cone, and a truncated pyramid. When the tops 11a, 12a are dome-shaped, the shapes of the protrusions 11, 12 may include, for example, a shape in which the top surface is curved convexly in the protruding direction of the protrusions 11, 12. Furthermore, when the tops 11a, 12a are dome-shaped, the entire protrusions 11, 12 may be configured in a dome shape. Protrusions 11, 12 have flat or dome-shaped tops 11a, 12a, which makes it easier to more reliably retain lubricant between adjacent protrusions 11, 12. Furthermore, when the titanium plate comes into contact with the mold, stress is more likely to be applied evenly over a wide area of ​​the plate surface, even with a severe mold shape, making it possible to more reliably suppress the promotion of localized deformation that is unique to titanium.

[0034] The shapes of the plurality of protrusions 11 formed on the first surface 1 may be different from each other, but are preferably the same. The shapes of the plurality of protrusions 12 formed on the second surface 2 may be different from each other, but are preferably the same. By making the shapes of the plurality of protrusions 11, 12 on each surface 1, 2 the same, it is easier to uniformly retain the lubricant on the first surface 1 and the second surface 2.

[0035] The heights H of the multiple protrusions 11 formed on the first surface 1 may be different from each other, but are preferably the same. The heights H of the multiple protrusions 12 formed on the second surface 2 may be different from each other, but are preferably the same. By making the heights H of the multiple protrusions 11, 12 on each surface 1, 2 the same, it is possible to prevent uneven stress and friction from the mold during press molding. As a result, the shapes of the protrusions 11, 12 can be reliably maintained, and the lubricant retention can be improved.

[0036] The lower limit of the maximum height Rz of the plurality of protrusions 11, 12 is 5 μm, preferably 7 μm, as described above, from the viewpoint of making it easier to fill the spaces between adjacent protrusions 11, 12 with lubricant. On the other hand, the upper limit of the maximum height Rz is 50 μm, preferably 30 μm, as described above, from the viewpoint of making it easier to form the plurality of protrusions 11, 12 into a desired shape and from the accuracy restrictions of the plate thickness tolerance.

[0037] The lower limit of the maximum length L of the plurality of protrusions 11, 12 in a plan view is 100 μm, preferably 180 μm, and more preferably 280 μm, as described above, from the viewpoint of easily forming the plurality of protrusions 11, 12 into a desired shape. On the other hand, the upper limit of the maximum length L is 1000 μm, preferably 700 μm, more preferably 500 μm, and even more preferably 450 μm, as described above, from the viewpoint of easily and uniformly spreading the lubricant over the first surface 1 and the second surface 2.

[0038] Adjacent protrusions 11, 12 are spaced apart on each of the first surface 1 and the second surface 2. That is, grooves 13, 14 (see FIG. 2 ) are provided between adjacent protrusions 11, 12. The grooves 13, 14 extend to the edges of the first surface 1 and the second surface 2.

[0039] The upper limit of the pitch P between adjacent protrusions 11, 12 on each of the first surface 1 and the second surface 2 is 1 mm, as described above, and preferably 800 μm, from the viewpoint of preventing the width of grooves 13, 14 from becoming too large or the planar area of ​​protrusions 11, 12 from becoming too large, thereby resulting in insufficient uniformity of the lubricant on surfaces 1, 2, and from the viewpoint of preventing grooves 13, 14 from hitting the mold surface due to the undulating shape of the mold. The lower limit of the pitch P can be set based on the size of the multiple protrusions 11, 12, etc., and can be, for example, 500 μm.

[0040] It is preferable that the plurality of protrusions 11, 12 are arranged on lattice points on each of the first surface 1 and the second surface 2. This configuration makes it easier to uniformly hold the lubricant on the first surface 1 and the second surface 2.

[0041] The plurality of protrusions 11, 12 may be arranged on the lattice points of a square lattice or on the lattice points of a triangular lattice, for example. It is particularly preferable that the plurality of protrusions 11, 12 are arranged on the lattice points of a triangular lattice. This configuration allows the plurality of protrusions 11, 12 to more reliably hold the lubricant on the first surface 1 and the second surface 2.

[0042] 3 , the lower limit of the occupied area ratio of the protrusions 11, 12 in the unit cell C is preferably 10%, more preferably 20%, from the viewpoint of preventing the protrusions 11, 12 that come into contact with the mold in the early stages of molding from buckling early and resulting in insufficient lubrication. On the other hand, the upper limit of the occupied area ratio is preferably 60%, more preferably 45%, from the viewpoint of ensuring the areas of the grooves 13, 14 that allow the lubricant to be easily and uniformly distributed on the first surface 1 and the second surface 2.

[0043] It is preferable that the shapes and arrangement patterns of the multiple protrusions 11, 12 on the first surface 1 and the second surface 2 are the same. This configuration makes it easier to spread the lubricant more uniformly around the multiple protrusions 11, 12. Furthermore, this configuration allows the multiple protrusions 11, 12 to evenly bear stress from the mold during press molding, making it easier to maintain the multiple protrusions 11, 12 in the desired shape. Note that the protrusions 11, 12 on the first surface 1 and the second surface 2 do not have to be arranged in positions facing each other. In other words, the arrangement pattern on the first surface 1 and the arrangement pattern on the second surface 2 may be misaligned overall in a plan view.

[0044] As described above, the titanium plate 10 can be used, for example, as a plate material in a plate-type heat exchanger. In such cases, it may be preferable for the titanium plate 10 to have superior stretch formability rather than deep draw formability. From this perspective, the r-value (Lankford value) of the titanium plate 10 in the direction perpendicular to the rolling direction may be less than 6.0. The upper limit of the r-value may be 5.0 or 4.5. Since components from deep draw forming inevitably occur in actual press-formed products, it is desirable for the titanium plate 10 to have an r-value of a certain level or higher. From this perspective, the lower limit of the r-value may be, for example, 2.0.

[0045] The lower limit of the n value in the direction perpendicular to the rolling direction of the titanium plate 10 may be 0.08 or 0.10 from the viewpoint of improving stretch formability. It is preferable that the r value and the n value of the titanium plate 10 are both within the above ranges. This configuration makes it possible to easily and reliably improve formability.

[0046] <Method of Manufacturing Titanium Plate> A method of manufacturing the titanium plate 10 shown in FIGS. 1 and 2 will be described with reference to FIG. 4. The method of manufacturing the titanium plate includes a step S1 of cold-rolling a hot-rolled plate, a step S2 of heat-treating the cold-rolled plate obtained by cold-rolling the hot-rolled plate, a step S3 of forming multiple protrusions 11, 12 on a pair of surfaces 1, 2 facing each other in the thickness direction of the cold-rolled plate after the heat-treating step S2, and a step S4 of subjecting the cold-rolled plate after the forming step S3 to a finish heat treatment. The multiple protrusions 11, 12 have a maximum height Rz of 5 μm to 50 μm and a maximum length L in a plan view of 100 μm to 1000 μm. The pitch between adjacent protrusions 11, 12 on each surface 1, 2 is 1 mm or less.

[0047] The titanium plate manufacturing method includes a forming step S3, which allows multiple protrusions 11, 12 to be formed on each of the pair of surfaces 1, 2. Therefore, the titanium plate 10 obtained by this titanium plate manufacturing method can have a lubricant distributed approximately uniformly around the multiple protrusions 11, 12 on each of the surfaces 1, 2, during press forming, for example. In particular, the protrusions 11, 12 have a maximum height Rz of 5 μm to 50 μm, a maximum length in a plan view of 100 μm to 1000 μm, and a pitch between adjacent protrusions 11, 12 on each of the surfaces 1, 2 of 1 mm or less, which facilitates retention of lubricant between adjacent protrusions 11, 12. Furthermore, according to this titanium plate manufacturing method, forming multiple protrusions 11, 12 on each of the pair of surfaces 1, 2 improves lubrication, enabling the titanium plate to be molded into components with more complex shapes. Furthermore, according to this titanium plate manufacturing method, when the obtained titanium plate 10 comes into contact with the mold, the tops 11a, 12a of the roughly evenly arranged protrusions 11, 12 come into contact, so stress is applied evenly over a wide area of ​​the plate surface even with a severe mold shape, suppressing the promotion of localized deformation that is unique to titanium. Therefore, the titanium plate 10 obtained by this titanium plate manufacturing method has excellent press formability. Furthermore, the titanium purity of the titanium plate 10 obtained by this titanium plate manufacturing method may be reduced to the extent that formability can be enhanced. In other words, a titanium plate 10 with an appropriately increased amount of scrap may be manufactured. Therefore, this titanium plate manufacturing method can increase the metal recycling rate.

[0048] (Cold Rolling Step) The cold rolling step S1 may be performed after the hot-rolled sheet has been subjected to heat treatment, pickling, etc. The lower limit of the reduction in the cold rolling step S1 may be 0.5 or 0.8. Furthermore, heat treatment and pickling may be performed along the way until the finished sheet thickness is reached. On the other hand, the upper limit of the reduction is not particularly limited, but may be 0.9 or 0.85 from the viewpoint of preventing edge cracks from occurring at the end of the sheet. Note that the "reduction rate" refers to a value calculated by (h1-h2) / h1, where h1 is the sheet thickness before rolling and h2 is the sheet thickness after rolling.

[0049] (Heat Treatment Step) In the heat treatment step S2, the cold-rolled sheet obtained in the cold rolling step S1 is subjected to a recrystallization heat treatment. That is, in the heat treatment step S2, heat treatment is performed to form fine recrystallized grains. The heating temperature in the heat treatment step S2 can be, for example, 550°C or higher and lower than 900°C. Furthermore, the heating time in the heat treatment step S2 can be, for example, 10 seconds or higher and 10 minutes or lower.

[0050] In the heat treatment step S2, it is also preferable to pickle the surface of the cold-rolled sheet obtained in the cold rolling step S1. That is, in the heat treatment step S2, the cold-rolled sheet is subjected to a recrystallization heat treatment, and at the same time, the cold-rolled sheet is pickled to reduce the surface oxide layer, deposits, and residual stress generated during the heat treatment process. By pickling the cold-rolled sheet in the heat treatment step S2, the oxide film and oxygen-affected layer on the surfaces 1 and 2 of the cold-rolled sheet sent to the forming step S3 can be removed, resulting in a uniformly blunted and smooth surface. As a result, the multiple protrusions 11 and 12 can be easily and reliably formed in the forming step S3.

[0051] (Forming Step) In the forming step S3, the cold-rolled sheet after the heat treatment step S2 is subjected to transfer rolling to form multiple protrusions 11, 12 on the surfaces 1, 2. In the forming step S3, the protrusions 11, 12 are formed on the surfaces 1, 2 using, for example, a pair of rolling rolls 20 and a pair of protrusion-forming dies 21 as shown in FIG. 5 . The pair of protrusion-forming dies 21 have an inverted shape of the multiple protrusions 11, 12 on their surfaces (the surfaces facing the cold-rolled sheet 22). This inverted shape has an indentation deeper than the height H of the protrusions 11, 12. In the forming step S3, the cold-rolled sheet 22 is sandwiched between the pair of protrusion-forming dies 21 and passed between the pair of rolling rolls 20 to form the multiple protrusions 11, 12 on the surfaces 1, 2. Note that the method of forming the multiple protrusions 11, 12 in the forming step S3 is not limited to transfer rolling. For example, in the forming step S3, the plurality of protrusions 11, 12 may be formed by laser engraving, additive manufacturing, or the like.

[0052] In the forming step S3, for example, the cold-rolled sheet is reduced in one go by a pair of upper and lower rolls having the above-described inverted shape, thereby thinning the cold-rolled sheet, thereby easily forming the height H of the multiple protrusions 11, 12. The upper limit of the reduction rate of the cold-rolled sheet 22 in the forming step S3 is preferably 0.25, and more preferably 0.20, from the viewpoint of suppressing the occurrence of twisting or wrinkles in the cold-rolled sheet 22 when the multiple protrusions 11, 12 are formed in a single rolling. On the other hand, the lower limit of the reduction rate is preferably 0.05, and more preferably 0.10, from the viewpoint of sufficiently ensuring the height H of the multiple protrusions 11, 12.

[0053] The upper limit of the thickness of the cold-rolled sheet 22 after the forming step S3 may be 3 mm or 1 mm. The lower limit of the thickness may be 0.1 mm or 0.3 mm. In the titanium sheet manufacturing method, the thickness of the cold-rolled sheet 22 after the forming step S3 may be the same as the thickness T of the obtained titanium sheet 10.

[0054] (Finishing Heat Treatment Step) In the finishing heat treatment step S4, the cold-rolled sheet after the forming step S3 is subjected to finishing annealing. The heat treatment temperature in the finishing heat treatment step S4 may be any temperature that allows recrystallization, and may be, for example, 550°C or higher and lower than 900°C.

[0055] [Other Embodiments] The above-described embodiments do not limit the configuration of the present invention. Therefore, the above-described embodiments may include omissions, substitutions, or additions of components based on the description in this specification and common general technical knowledge, and all of these should be construed as falling within the scope of the present invention.

[0056] The arrangement of the plurality of protrusions on each surface is not limited to the arrangement described in the above embodiment, and for example, the plurality of protrusions may be arranged randomly on each surface.

[0057] As described above, the shape and arrangement pattern of the plurality of protrusions on the pair of surfaces are preferably the same, however, the shape and arrangement pattern of the plurality of protrusions on the first surface and the shape and arrangement pattern of the plurality of protrusions on the second surface may be different, as long as the titanium plate is capable of distributing the lubricant over each surface.

[0058] The present disclosure will be described in detail below based on examples, but the present disclosure should not be construed as being limited based on the description of these examples.

[0059] (No. 1 to No. 6) For No. 1 to No. 6, adjacent portions of pure titanium sheets (hot-rolled sheets) from the same lot that had undergone the same process were cut out, pickled, and then subjected to the cold-rolling step S1. The cold-rolled sheets obtained in the cold-rolling step S1 were heat-treated (heat-treating step S2). For No. 1 to No. 5, multiple protrusions were formed on each of a pair of surfaces facing each other in the thickness direction of the cold-rolled sheet after the heat-treating step S2, using the procedure described below (forming step S3), and the cold-rolled sheet after the forming step S3 was subjected to a finish heat treatment (finish heat treatment step S4) to obtain a titanium sheet. On the other hand, for No. 6, the forming step S3 was not performed, and the cold-rolled sheet after the heat-treating step S2 was subjected to the finish heat treatment step S4 to obtain a titanium sheet. The compositions of the obtained titanium plates are shown in Table 1 (note that, for No. 2 to No. 6, adjacent portions of the same pure titanium plate as No. 1 were used, and therefore, they are considered to have the same composition as No. 1 and are listed in Table 1). Table 2 also shows the plate thickness, rolling reduction, heat treatment temperature [°C] in the cold rolling step S1, and the heat treatment type and heat treatment temperature [°C] in the finish heat treatment step S4 during the manufacturing process. Table 3 also shows the configuration of the protrusions formed in the forming step S3 (note that for No. 6, the maximum height Rz of the plate surface is shown). In Table 1, all elements other than O, Fe, N, and C are Ti (titanium). In Table 3, the maximum height Rz of the multiple protrusions was measured using a MITSUTOYO "SURFTEST SJ-210" in accordance with JIS-B0601:2001, with a reference length of 0.8 mm and an evaluation length of 4 mm. The maximum height Rz in Table 3 is a value determined by setting a reference length so as to include the profile (bottom-top-bottom) of one or more protrusions.

[0060] (Forming step) For No. 1 to No. 5, in the forming step S3, a protrusion-forming die was used, which was made of a flat thin plate made of SUS316 and having a thickness of 0.3 mm, and which had holes arranged in the arrangement shown in Fig. 1, the holes having a diameter equal to the maximum length of the protrusions in a plan view and a pitch between adjacent protrusions. As shown in Fig. 5, the cold-rolled sheet was sandwiched between the die from above and below, and pressed into a rolling mill to perform transfer rolling.

[0061] (No. 7) A titanium plate was produced using a pure titanium plate (hot-rolled plate) from a different lot than Nos. 1 to 6, using the same procedure as No. 6. The composition of the obtained titanium plate is shown in Table 1. Table 2 also shows the plate thickness, rolling reduction, and heat treatment type and heat treatment temperature [°C] in the finish heat treatment step S4 during the production process. Table 3 also shows the maximum height Rz of the plate surface.

[0062] (No. 8) A titanium plate was produced using a pure titanium plate (hot-rolled plate) from a different lot than Nos. 1 to 6. In No. 8, a titanium plate having the chemical composition shown in Table 1 was produced using the same procedures as Nos. 1 to 5, except that the heat treatment step S2 was not performed and multiple protrusions were formed on only one side of the cold-rolled plate in the forming step S3. In the forming step S3, a protrusion-forming roll 31 was used, which had holes on its surface arranged as shown in FIG. 1, each having a diameter equal to the maximum length of the protrusions in a plan view and a pitch between adjacent protrusions. This protrusion-forming roll 31 was then placed on the upper side of the rolling mill as shown in FIG. 6, and a 0.8 mm-thick cold-rolled plate was sandwiched between the protrusion-forming roll 31 and a lower smooth-surfaced rolling roll 30 to perform transfer rolling. The plate thickness, reduction, and heat treatment type and heat treatment temperature [°C] in the finish heat treatment step S4 during the production process are shown in Table 2. The configuration of the protrusions formed in the forming step S3 is shown in Table 3 (for the first surface on which multiple protrusions are not formed, the maximum height Rz of the plate surface is shown).

[0063]

[0064]

[0065]

[0066] (Formability) The formability of titanium plates No. 1 to No. 8 was evaluated using a "press formability score" according to the following procedure. First, titanium plates No. 1 to No. 8 were press-formed from both sides using a pair of dies having complementary press surfaces, and these titanium plates were deformed to have the uneven shape (herringbone pattern) shown in Figure 7. This press forming was performed with a lubricant applied between the titanium plate and the pair of dies. In Figure 7, four V-shaped uneven portions are provided at intervals in the X direction (the vertical direction on the paper). To calculate the press formability score, as shown in Figure 7, four measurement points M1-M4 were set on the front and back of the formed titanium plate. For each measurement point, 0 points were assigned if cracks were observed, 1 point if clear necking was present, 2 points if signs of necking were present, and 3 points if the titanium plate was uniformly deformed, resulting in a total score out of 24 points. In this formability test, the indentation depth [mm] of the mold was changed, and the maximum indentation depth at which a total score of 24 points could be maintained was evaluated as the forming limit. The evaluation results are shown in Table 4. Measurement points M1-M4 are empirically the parts most susceptible to cracking.

[0067] (0.2% Yield Strength, Tensile Strength, Elongation, r-Value, and n-Value) For titanium plates No. 1 to No. 8, tensile tests and r-value measurements were performed at a 90° angle relative to the rolling direction. The tensile tests were performed in accordance with ASTM-E8, and the 0.2% yield strength (YS), tensile strength (TS), elongation (El), and n-value were determined. The n-value was calculated within a nominal strain range of 2 to 4%. The r-value was calculated by stopping the test at an elongation strain of 8%, measuring the plate width and elongation at five locations at 10 mm intervals within a 50 mm gauge range. The results are shown in Table 4. The plate thickness was measured using a micrometer to determine the thickness between the parallel top surfaces of the protrusions.

[0068] (Yield Ratio) For titanium plates No. 1 to No. 8, the yield ratio (YR) was calculated by dividing YS by TS and multiplying the result by 100. The results are shown in Table 4.

[0069]

[0070] (Evaluation Results) As shown in Table 4, titanium plates No. 1 to No. 5, which have multiple protrusions formed on both sides, have plates with different protrusion heights and areas, but the forming limit is large, at 4.6 mm or more. Since the strength levels are also approximately the same, titanium plates No. 1 to No. 5 are superior in formability to plates No. 6 and No. 7, which are smooth plates without protrusions. Furthermore, titanium plates No. 1 to No. 5 have small r-values ​​of 4.0 or less and large n-values ​​of 0.12 or more. This indicates that titanium plates No. 1 to No. 5 have excellent stretch formability and are suitable for use as plate materials in plate-type heat exchangers, for example. Titanium plate No. 8 has multiple protrusions formed on one side, a small r-value of 3.5, and a small n-value of 0.04, resulting in poor stretch formability. It is also suggested that the formation of irregularities on both sides is advantageous for formability.

[0071] REFERENCE SIGNS LIST 1 First surface 2 Second surface 10 Titanium plate 11, 12 Protrusions 11a, 12a Top surface 13, 14 Groove 20, 30 Rolling roll 21 Protrusion forming die 22 Cold-rolled plate 31 Protrusion forming roll M1-M4 Measurement point C Unit lattice H Protrusion height L Maximum length of top surface of protrusion P Pitch between protrusions T Thickness of titanium plate

Claims

1. A titanium plate having a pair of surfaces facing each other in the thickness direction, each of which has a plurality of protrusions formed thereon, the plurality of protrusions having a maximum height Rz of 5 μm or more and 50 μm or less and a maximum length in a plan view of 100 μm or more and 1000 μm or less, and the pitch between adjacent protrusions on each of the surfaces being 1 mm or less.

2. The titanium plate according to claim 1, which is made of pure titanium material specified in JIS Class 1.

3. The titanium plate according to claim 1 or 2, wherein the plurality of protrusions on each of the pair of surfaces are arranged on lattice points.

4. The titanium plate according to claim 3, wherein the area ratio of the protrusions in the unit lattice is 10% or more and 60% or less.

5. A titanium plate according to claim 1 or 2, wherein the protrusions are circular or elliptical in plan view.

6. A titanium plate according to claim 1 or 2, wherein the shape and arrangement pattern of the plurality of protrusions on the pair of surfaces are the same.

7. A titanium plate according to claim 1 or claim 2, wherein the protrusions have flat or dome-shaped tops.

8. A method for manufacturing a titanium plate, comprising: a step of heat treating a cold-rolled plate obtained by cold-rolling a titanium plate; a step of forming a plurality of protrusions on each of a pair of surfaces opposing in the plate thickness direction of the cold-rolled plate after the heat treating step; and a step of finish heat treating the cold-rolled plate after the forming step, wherein the plurality of protrusions have a maximum height Rz of 5 μm or more and 50 μm or less and a maximum length in a plan view of 100 μm or more and 1000 μm or less, and the pitch between adjacent protrusions on each of the surfaces is 1 mm or less.

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