JP7525784B2 - Titanium material and method for manufacturing titanium material - Google Patents

Description

The present invention relates to titanium materials and methods for manufacturing titanium materials.

Titanium materials used in building materials such as the walls and roofs of buildings (titanium materials for construction) are broadly divided into uncolored materials that have the silver color of titanium itself, and colored materials that have an interference color due to a certain thickness of oxide film applied to the surface by anodization.

Titanium is used as a building material even in coastal areas where salt accumulates due to its excellent corrosion resistance. More than 20 years have passed since titanium began to be used as a building material.

However, even uncolored materials may discolor if exposed to the atmosphere for a long period of time. It has been revealed that this discoloration is an interference color caused by an increase in the thickness of the oxide film on the surface of the titanium material due to an acidic environment of pH 4.5 or less, such as acid rain. This increase in the thickness of the oxide film does not impair the corrosion resistance of titanium. However, in areas where the appearance is important, such as the walls and roofs of buildings, there is a demand for titanium materials that are less susceptible to discoloration due to an increase in the thickness of the oxide film, and the development of such titanium materials is underway.

For example, Patent Document 1 discloses titanium that is resistant to discoloration in an atmospheric environment, characterized by an average carbon concentration of 14 at% or less within a range of 100 nm deep from the outermost surface, and an oxide film of 12 to 40 nm thickness on the outermost surface.

Patent document 2 discloses a titanium material that is resistant to discoloration and is characterized by having a fluorine content of 7 at % or less in the oxide film on the surface.

Patent Document 3 discloses titanium that is resistant to discoloration in an atmospheric environment, characterized in that, in an oxide film formed on the titanium surface and present within a range of 3 nm from the titanium surface, when the titanium oxide has a composition TiOx, x is in the range of 0.8 to 1.8, and the density of the oxide film is 4.2 g/cm ³ or more. In the technology disclosed in Patent Document 3, as the final step of pickling, the titanium surface is immersed in a nitric acid solution having a concentration of 18 to 40 mass% and a temperature of 45 to 80°C for 3 minutes or more by coating or immersion treatment, and then washed, thereby forming a film on the titanium surface.

Patent Document 4 discloses a pure titanium material for use as a building material, characterized in that the impurity elements Fe are restricted to 0.08 mass% or less, Nb to 0.02 mass% or less, and Co to 0.02 mass% or less. In the technology disclosed in Patent Document 4, the final process involves pickling followed by heating in air or in a vacuum at 130 to 280°C for a specified period of time.

Patent document 5 discloses pure titanium or titanium alloy that is resistant to discoloration in an atmospheric environment, characterized in that the average phosphorus content in a range of 40 nm from the surface of a titanium oxide layer formed on the titanium surface is 5.5 atomic % or less, and the average carbon concentration in a range of 100 nm deep from the titanium surface is 3 to 15 atomic %.

Patent Document 6 discloses titanium for use in acid rain atmospheric environments, characterized in that the base material is titanium or a titanium alloy, a nitrogen-enriched titanium layer having a thickness of 0.2 to 1.5 μm is formed on the surface of the base material, the nitrogen-enriched titanium layer contains 20 to 60 atomic % of nitrogen and 1 to 40 atomic % of oxygen in average atomic %, the ratio of Ti (average atomic % value)/N (average atomic % value) in the range of 0.1 μm from the outermost layer is in the range of 1.2 to 4.0, the average carbon concentration in the range of 0.2 μm deep from the surface of the base material toward the inside is 1 atomic % to 15 atomic %, and the color measurement values L ^* , a ^* , and b ^* are 40 to 80, -6 to 6, and -6 to 9, respectively, and the titanium material has a silvery appearance and is excellent in resistance to discoloration. The titanium material disclosed in Patent Document 5 is manufactured by an ion plating method.

As an example of technology that focuses on the roughness of the surface of titanium material, Patent Document 7 discloses an outdoor titanium or titanium alloy material with excellent resistance to discoloration, characterized by a surface roughness of 3 μm or less in center line average roughness Ra and a surface oxide film thickness of 20 Å (2 nm) or more. The titanium material disclosed in Patent Document 7 has a specified Ra in order to suppress physical adhesion of suspended matter in the air.

Patent document 8 discloses a titanium plate having an arithmetic mean roughness (Ra) in the range of 0.15 to 1.5 μm, a maximum height (Rz) in the range of 1.5 to 9.0 μm, a degree of distortion (Rsk) in the range of -3.0 to -0.5, and a Vickers hardness on the surface at a measurement load of 0.098 N that is higher than the Vickers hardness at a measurement load of 4.9 N, the difference being 45 or less.

Patent Document 9 discloses a titanium material with surface irregularities, characterized in that the arithmetic mean roughness Ra of the surface is 1.5 to 5.0 μm, and the ratio Ra to the mean spacing Sm of the irregularities is 0.018 to 0.05, in order to enhance lubricity.

JP 2002-12962 A JP 2002-47589 A JP 2005-154882 A JP 2004-300569 A JP 2006-336027 A JP 2010-265531 A Japanese Patent Application Publication No. 10-8234 JP 2010-255085 A JP 2005-298930 A

Hiroshi Kamio, Junko Imamura, Hideya Uenaka, Hideaki Yuki, C-111, "Effects of Environmental Factors on Crevice Corrosion Resistance of Titanium and Stainless Steel", Tokyo Denki University, May 13-15, 2013, Materials and Environment 2013 Lecture Collection, Japan Society of Corrosion Engineering, pp. 245-246 Tsutomu Miyashita, "Surface Roughness: A Review," Journal of the Japan Society for Precision Engineering, Vol. 73, No. 2, 2007, pp. 201-205

However, in recent years, global warming has progressed, causing rising temperatures and an acidic environment, making the environment in which titanium materials for construction are used harsher, and the oxide film thickness is more likely to increase. Therefore, if there is a titanium material that can suppress the increase in oxide film thickness and is less likely to exhibit interference colors even when the oxide film thickness increases, it can be used in buildings and other structures where appearance is even more important.

In Patent Documents 1 to 5, discoloration is evaluated as follows. The material is immersed in a sulfuric acid solution of pH 3 to 4 at 60°C for several days, and discoloration is evaluated based on the color difference before and after the immersion. The color difference is described as 3 to 7 or less when immersed in a sulfuric acid solution of pH 3 at 60°C for 7 or 14 days, and less than 5 or even less than 1 when immersed in a sulfuric acid solution of pH 4 at 60°C for 3 days. However, the above discoloration evaluation does not fully reflect use in higher temperature environments. In addition, when the titanium materials described in Patent Documents 1 to 5 are immersed in a sulfuric acid solution of pH 4 at 80°C for 4 days, the color difference before and after the immersion is about 15 or more, and conventional titanium materials do not have sufficient discoloration resistance under higher temperature conditions.

The discoloration of the titanium material disclosed in Patent Document 6 is excellent, with a color difference of 4 or less after 14 days in a sulfuric acid aqueous solution of pH 3 at 80°C. However, the titanium material disclosed in Patent Document 6 is manufactured using an ion plating method. The ion plating method is a batch process using a vacuum furnace, and the degree of vacuum inside the vacuum furnace must be controlled, resulting in a long processing time. In addition, to use the ion plating method, the titanium material must be cut into sheets. Therefore, the manufacturing method of titanium material described in Patent Document 6 is expensive and takes a long time. Therefore, there is room for improvement in the technology disclosed in Patent Document 6.

In addition, the titanium material disclosed in Patent Document 7 specifies Ra in order to suppress the physical adsorption of suspended matter and improve stain resistance, but does not take into consideration the suppression of interference colors. The titanium materials disclosed in Patent Documents 8 and 9, like the titanium material disclosed in Patent Document 7, do not take into consideration the suppression of interference colors.

The present invention was made in consideration of the above problems, and the object of the present invention is to provide a titanium material that has excellent resistance to discoloration even at high temperatures and in an acidic environment, and a method for manufacturing the same.

The inventors conducted a detailed study of the relationship between the surface condition of titanium material and discoloration using surface analysis and discoloration tests, and discovered that by controlling the surface properties of the titanium material, it is possible to suppress discoloration caused by interference even if an oxide film grows. The inventors then discovered a method for producing such titanium material, leading to the present invention.

The gist of the present invention, which has been completed based on the above findings, is as follows.
[1]
The titanium material comprises a titanium base material in which, in a roughness curve in a direction in which the arithmetic mean roughness Ra is maximum, the ratio of the arithmetic mean roughness Ra to the element length RSm, Ra/RSm, is 0.006 to 0.015, and the root-mean-square slope RΔq is 0.150 to 0.280.
[2]
The titanium material according to [1], wherein the kurtosis Rku of the titanium base material is greater than 3 in a roughness curve in a direction in which the arithmetic mean roughness Ra is maximum.
[3]
The titanium material according to [1] or [2], wherein the skewness Rsk of the titanium base material is greater than −0.5 in a roughness curve in a direction in which the arithmetic mean roughness Ra is maximum.
[4]
F: 3 atomic % or less; and
C: 20 atomic% or less,
a titanium substrate having an oxide film on a surface thereof,
The titanium material according to any one of [1] to [3], wherein the thickness of the oxide film is 15 nm or less.
[5]
A polishing step of polishing the surface of the titanium material using abrasive fine powder having a grain size distribution of #320 or less in accordance with JIS R 6001-2:2017, and then
The method for producing a titanium material includes at least one of a laser cutting process in which the titanium material after the polishing process is laser cut by 3 μm or more from the surface with an aqueous solution containing 1 mass % or more of hydrofluoric acid and then heated to 300 to 880° C. in a non-oxidizing atmosphere, and a cold rolling process in which the titanium material after the polishing process is rolled down using a rolling roll having a surface roughness Ra of 0.5 μm or more so that the total rolling reduction is 0.10% or more.

As described above, the present invention makes it possible to provide a titanium material that has excellent resistance to discoloration even in high temperature and acidic environments, and a method for manufacturing the same.

FIG. 1 shows the effects of chloride ion concentration and temperature on crevice corrosion of pure titanium. FIG. 1 shows the effect of temperature on depassivation pH. FIG. 1 is a graph showing the relationship between the ratio Ra/RSm of the arithmetic mean roughness Ra to the average length RSm of the profile curve element, the root mean square slope RΔq of the roughness curve element, and discoloration resistance. FIG. 1 is a schematic diagram for explaining Kurtosis Rku.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings in the following order:
1. Background
<2. Titanium material>
<3. Manufacturing method of titanium material>

1. Background
First, the background of how the present inventors arrived at the present invention will be described with reference to Figures 1 and 2. Figure 1 is a diagram showing the influence of chloride ion concentration and temperature on crevice corrosion of pure titanium. Figure 2 is a diagram showing the influence of temperature on depassivation pH. Both Figures 1 and 2 are figures published in Hiroshi Kamio, Junko Imamura, Hideya Uenaka, Hideaki Yuki, C-111, "Effect of Environmental Factors on Crevice Corrosion Resistance of Titanium and Stainless Steel", Lecture Collection of Materials and Environment 2013, Japan Society of Corrosion and Protection, Tokyo Denki University, May 13-15, 2013, p. 246.

In FIG. 1, "◯" indicates a condition where the crevice corrosion resistance is good, and "×" indicates a condition where the crevice corrosion resistance is poor. As shown in FIG. 1, the effect of temperature on the crevice corrosion resistance of titanium materials is greater than that of the chloride ion concentration [Cl ^- ]. In addition, the depassivation pH (pHd) shown in FIG. 2 is a pH at which corrosion resistance cannot be exhibited, and in an environment below pHd, a stable passive film is not formed, making it difficult for the titanium material to exhibit good corrosion resistance. As shown in FIG. 2, as the temperature increases, the pHd of the titanium material also increases. As can be seen from FIGS. 1 and 2, the effect of temperature on the corrosion resistance of titanium materials is extremely significant, and it is easy to assume that the effect of temperature is also large in the discoloration of titanium materials, which is affected by the resistance of the oxide film, which is a passive film. Therefore, a titanium material is required that is suppressed from discoloring even in a higher temperature environment.

For example, in Patent Documents 1 to 4, as a condition for a discoloration acceleration test in which discoloration is accelerated in a laboratory to evaluate the degree of discoloration, a titanium material is immersed in a sulfuric acid aqueous solution of pH 3 or pH 4 at a temperature of 60°C. However, in the present invention, in view of the changes in the atmospheric environment today, a color difference indicating the degree of discoloration of 8 or less even when the test temperature is increased to 80°C is set as an index of discoloration resistance. When a conventional titanium material is immersed in a sulfuric acid aqueous solution of 80°C and pH 4 for 4 days, the color difference before and after immersion is about 15 or more, and the conventional titanium material does not have sufficient discoloration resistance. In order to obtain a titanium material that has excellent discoloration resistance even under high temperature and acidic environments, the inventors have closely studied the surface state of a titanium substrate and have come up with the present invention.
So far, the background that led the inventors to arrive at the present invention has been explained.

<2. Titanium material>
The titanium material according to this embodiment includes a titanium base material in which, in a roughness curve in a direction in which the arithmetic mean roughness Ra is maximum, the ratio of the arithmetic mean roughness Ra to the element length RSm, Ra/RSm, is 0.006 to 0.015, and the root-mean-square slope RΔq is 0.150 to 0.280. This will be described in detail below.

(2.1. Titanium substrate)
The titanium substrate of the titanium material of the present embodiment is made of either pure titanium or a titanium alloy, for example, pure titanium or a titanium alloy having a Ti content of 70 mass % or more.

Pure titanium includes, for example, commercially pure titanium as specified by JIS standards types 1 to 4 and the corresponding ASTM standards grades 1 to 4. In other words, the commercially pure titanium targeted in this invention consists of, by mass, C: 0.1% or less, H: 0.015% or less, O: 0.4% or less, N: 0.07% or less, Fe: 0.5% or less, with the balance being Ti and impurities. Note that for buildings, commercially pure titanium as specified by JIS standard type 1 or the equivalent ASTM Gr. 1, or equivalent materials, is mainly used.

Titanium alloys include alpha titanium alloys, alpha + beta titanium alloys, and beta titanium alloys.

Examples of alpha-type titanium alloys include highly corrosion-resistant alloys (titanium alloys specified in JIS standards 11-13, 17, 19-22, and ASTM standards Grades 7, 11, 13, 14, 17, 30, and 31, as well as titanium alloys containing small amounts of various other elements), Ti-0.5Cu, Ti-1.0Cu, Ti-1.0Cu-0.5Nb, and Ti-1.0Cu-1.0Sn-0.3Si-0.25Nb.

Examples of α+β type titanium alloys include Ti-3Al-2.5V, Ti-5Al-1Fe, and Ti-6Al-4V.

Furthermore, examples of β-type titanium alloys include Ti-11.5Mo-6Zr-4.5Sn, Ti-8V-3Al-6Cr-4Mo-4Zr, Ti-13V-11Cr-3Al, Ti-15V-3Al-3Cr-3Sn, Ti-20V-4Al-1Sn, and Ti-22V-4Al.

[Ra/RSm: 0.006 to 0.015]
[RΔq: 0.150 to 0.280]
The present inventors have studied in detail the relationship between the surface properties of titanium materials and their discoloration resistance, and have found that the discoloration resistance of titanium materials is determined by the arithmetic mean roughness Ra of the surface and the average length RSm of the contour curve elements. It has been found that the ratio Ra/RSm, and the root mean square slope RΔq of the roughness profile elements are extremely important.

The arithmetic mean roughness Ra, the average length of the profile curve element RSm, and the root mean square slope RΔq of the roughness curve element can be measured by a method conforming to JIS B 0601:2013. The kurtosis Rku and skewness Rsk described below can also be measured by a method conforming to JIS B 0601:2013.

The arithmetic mean roughness Ra in this embodiment is the arithmetic mean roughness Ra defined in JIS B 0601:2013, and is the average of the absolute values of the total coordinate values Zj in the reference length. The arithmetic mean roughness Ra is calculated by the following formula (1).
The roughness curve on which the arithmetic mean roughness Ra is calculated is obtained by applying a low-pass filter with a cutoff wavelength λc=0.8 mm to the measured cross-sectional curve of the oxide film to obtain a cross-sectional curve, and then applying a high-pass filter with a cutoff wavelength λs=2.667 μm to this step curve. The reference length of the roughness curve is the same as the cutoff wavelength λc, that is, 0.8 mm. λc is a filter that defines the boundary between the roughness component and the waviness component. λs is a filter that defines the boundary between the roughness component and a wavelength component shorter than that.

In the above formula (1), n is the number of measurement points, and Zj is the height of the jth measurement point on the roughness curve.

The average length RSm of the contour curve element is calculated using the following formula (2):

In the above formula (2), m is the number of measurement points, and Xsi is the length of the profile curve element in the reference length.

The root mean square slope RΔq of the roughness curve element is calculated using the following formula (3):

In the above formula (3), N is the number of measurement points. (dZj/dXj) is the local slope at the jth measurement point on the roughness curve, and is defined by the following formula (4).

In the above formula (4), ΔX is the measurement interval. In this embodiment, the measurement interval ΔX may be determined as follows. That is, the measurement interval ΔX is a value set by the surface roughness shape measuring instrument, and when the measurement length L is measured and N points of numerical data are obtained, ΔX is L/(N-1) on average at the measurement interval. For example, when a measurement length of 5 mm is measured using a SURFCOM 1900DX manufactured by Tokyo Seimitsu and software TIMS Ver. 9.0.3, if 25601 points of digital numerical data are obtained, ΔX is 5 mm/25600 points, which is about 0.195 μm on average.

The root mean square slope RΔq of a roughness curve element is a parameter that defines the slope angle (local slope dZ/dX) of the minute range formed by the surface irregularities relative to the reference length X of the roughness curve.

The inventors produced titanium materials with different Ra/RSm and RΔq, and investigated the effects of Ra/RSm and RΔq on discoloration resistance. Figure 3 shows the relationship between Ra/RSm, which is the ratio of the arithmetic mean roughness Ra to the average length RSm of the profile curve element, and the root-mean-square slope RΔq of the roughness curve element, and discoloration resistance.

The discoloration resistance can be evaluated by the color difference ΔE ^* ab and by observing the appearance.
The color difference ΔE ^* ab was calculated by immersing the titanium material in ^a sulfuric acid aqueous solution of pH 4 at 80° C. for 4 days, measuring the L ^* a ^* b ^* of the titanium material surface before and after immersion. The color difference was calculated from the differences ΔL ^* , Δa ^* , and Δb ^* in the lightness L ^* and chromaticity a ^* and b ^* before and after immersion, which are calculated in accordance with JIS Z 8730:2009.
Color difference ΔE ^* ab = [(ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² ] ^1/2
The larger the color difference ΔE ^* ab, the more the color changed before and after the test.

In the measurement of the color tone L ^* a ^* b ^* for evaluating the color difference ΔE ^* ab, light is irradiated from a daylight light source installed directly above the titanium plate. Therefore, the actual appearance may differ. In particular, for a titanium plate with a large RΔq, even if the color difference ΔE ^* ab is small, it may appear discolored when visually observed under sunlight. Therefore, visual observation under sunlight is also important for evaluating discoloration resistance.

In Fig. 3, "◯" indicates a condition where the color difference ΔE ^* ab is 8 or less and discoloration is not noticeable even when viewed with the naked eye, "△" indicates a condition where the color difference ΔE ^* ab is 8 or less but discoloration is noticeable when viewed with the naked eye, and "×" indicates a condition where the color difference ΔE ^* ab is more than 8 and discoloration is noticeable even when viewed with the naked eye. Here, the evaluation by visual observation was performed by arranging the titanium material not subjected to the discoloration acceleration test and the titanium material subjected to the discoloration acceleration test on a flat plate, comparing them from various angles under sunlight, and evaluating whether there is an angle at which discoloration is noticeable. This visual observation is performed under conditions assuming the roof or wall of an actual building, and is evaluated assuming that the color tone changes depending on the viewing angle.

As shown in Figure 3, it was found that the titanium material according to this embodiment has excellent resistance to discoloration when its surface has a ratio of arithmetic mean roughness Ra to the average length RSm of the contour curve element, Ra/RSm, of 0.006 to 0.015, and the root-mean-square slope RΔq of the roughness curve element is 0.150 to 0.280.

When Ra/RSm is less than 0.006, the unevenness of the titanium substrate surface is small and the intervals between the unevenness are wide. When RSm is less than 0.006, the surface of the titanium material is relatively smooth, and the color of the light that is intensified according to the optical path difference between the light reflected on the surface of the oxide film and the light reflected on the surface of the titanium substrate is recognized (i.e., the titanium material discolors). When Ra/RSm is 0.006 to 0.015, the optical path difference between the light reflected on the surface of the oxide film and the light reflected on the surface of the titanium substrate is small due to the relatively large inclination of the titanium material surface, and there is no light that is intensified in the visible light range, so discoloration is suppressed. Considering the mechanism by which discoloration is suppressed, there is no reason to limit the upper limit of Ra/RSm to 0.015, but it is difficult to industrially produce deep and narrow valley-like unevenness with a value of more than 0.015. Therefore, the upper limit of Ra/RSm is set to 0.015, at which the effects of the present invention are clearly obtained.

When RΔq is 0.150 or more, the inclination of the finer unevenness in the oxide film is large, and this local inclination suppresses the regular reflection of light irradiated on the titanium substrate surface, resulting in diffuse reflection. Therefore, the intensity of the reflected light on the titanium substrate surface that is reflected in the direction of the light reflected on the surface of the oxide film is reduced. As a result, the color of the intensified light is difficult to recognize. When RΔq is less than 0.150, the above action does not occur, and the titanium material discolors. On the other hand, when RΔq is more than 0.280, although the color difference is small at 8 or less, there may be angles at which the discoloration is noticeable under sunlight. This is thought to be because when RΔq is large, exceeding 0.280, there is an inclination that becomes the regular reflection direction when viewed from an oblique angle, and the interference color due to the increased oxide film thickness is intensified and becomes visible to the naked eye.

If Ra/RSm is 0.006 to 0.015 and the root mean square slope RΔq of the roughness curve element is 0.150 to 0.280, the above effects are obtained by superposition, and discoloration of the titanium material is suppressed. Furthermore, in the titanium material having the above surface state, even if an oxide film grows to about several tens of nm on its surface, the color tone change, i.e., discoloration, is suppressed. Therefore, in the roughness curve in the direction in which the arithmetic mean roughness Ra is maximum, the titanium base material has Ra/RSm, which is the ratio of the arithmetic mean roughness Ra to the element length RSm, of 0.006 to 0.015 and the root mean square slope RΔq of 0.150 to 0.280. The lower limit of Ra/RSm is preferably 0.007. Furthermore, RΔq is preferably 0.190 or more. When RΔq is between 0.190 and 0.0280, the color difference in this accelerated discoloration test is 6 or less, resulting in even greater effectiveness.

There are no particular limitations on the arithmetic mean roughness Ra and the average length of the contour curve element RSm as long as Ra/RSm is 0.006 to 0.015, but it is preferable that the arithmetic mean roughness Ra is 0.700 to 3.0 μm and the average length of the contour curve element RSm is 60 to 300 μm. The above preferred ranges for Ra and RSm have been set because they can be relatively easily achieved industrially using the manufacturing method described below.

[Kurtosis Rku: 3 Super]
Kurtosis Rku is an index representing the sharpness of the amplitude distribution curve. Fig. 4 is a diagram for explaining kurtosis Rku. Note that Fig. 4 is a diagram published in Tsutomu Miyashita, "Surface Roughness Reviewed Again," Journal of the Japan Society for Precision Engineering, Japan Society for Precision Engineering, Vol. 73, No. 2, 2007, p. 205. Kurtosis Rku represents the fourth-square mean of Zj in a reference length made dimensionless by the fourth power of the root-mean-square height Rq.

Zj is the height of the jth measurement point on the roughness curve. Rq is the root mean square height, which is expressed by the following formula (6).

Kurtosis Rku is an index that indicates the sharpness of the height distribution. When kurtosis Rku is 3, as shown in Figure 4, the height distribution is normal. As kurtosis Rku becomes smaller when the value is less than 3, the surface becomes flatter. As kurtosis Sku becomes larger when the value exceeds 3, the number of sharp peaks and valleys increases on the surface of the titanium material.

In the titanium substrate according to this embodiment, it is preferable that the kurtosis Rku is greater than 3 in the roughness curve in the direction in which the arithmetic mean roughness Ra is maximum. When the kurtosis Rku is greater than 3, the surface of the titanium substrate has sharp irregularities, and in a surface with sharp irregularities, the regular reflection component that manifests interference colors in the light reflected from the surface of the titanium substrate is further suppressed. As a result, even if the oxide film thickness increases, the interference colors become less noticeable, and discoloration of the titanium substrate is further suppressed.

[Surface roughness skewness Rsk: greater than -0.5]
The skewness Rsk is also called the degree of distortion and is an index that indicates the sharpness of the unevenness on the surface of a titanium material. The skewness Rsk represents the cube mean of Z(x) in a reference length that is made dimensionless by the cube of the root mean square height Rq, and is expressed by the following formula (7).

In the above formula (7), N is the number of measurement points, and Zj is the height of the jth measurement point on the roughness curve.

In the roughness curve, when the valley length is greater than the peak length, the skewness Rsk is greater than 0. In other words, when the skewness Rsk is greater than 0, the ratio of concave portions is high in the average line of the roughness curve. In other words, the tips of the peaks (convex portions) in the roughness curve are sharply pointed, and the ends of the valleys (concave portions) are wide. The average line of the roughness curve refers to a curve that represents the long wavelength components that are blocked by the cutoff wavelength λc.
On the other hand, when the valley length is smaller than the peak length, the skewness Rsk is smaller than 0. In other words, when the skewness Rsk is smaller than 0, the ratio of concave portions to the average line of the roughness curve is high. In other words, the tips of the peaks (convex portions) in the roughness curve become wider, and the ends of the valleys (concave portions) become sharply pointed.
When the skewness Rsk is 0, the shape of the projections and recesses in the roughness curve is symmetrical with respect to the average plane.

In the titanium material according to this embodiment, it is preferable that the skewness Rsk is greater than -0.5 in the roughness curve in the direction in which the arithmetic mean roughness Ra is maximum. When the skewness Rsk is greater than -0.5, the tips of the peaks (convex portions) in the roughness curve become sharp, and the light reflected on the titanium base material surface is more likely to be scattered on the side closer to the light source, i.e., the peaks (convex portions), and discoloration is further suppressed. The side farther from the light source, i.e., the valleys (convex portions), is presumably less affected than the peaks (convex portions) because the shadow effect of the peaks (convex portions) makes it difficult to see the interference color that causes discoloration.

(2.2. Oxide film)
The titanium material according to the present embodiment preferably has an oxide film on the surface of the titanium base material that inhibits the growth of the oxide film. For example, such an oxide film has a thickness of 15 nm or less and contains F: 3 atomic % or less and C: 20 atomic % or less. The oxide film causes the titanium material to become an uncolored material that exhibits the silver color that is the color of titanium itself. The following is a detailed explanation.

First, an oxide film containing F: 3 atomic % or less and C: 20 atomic % or less will be described.
If the F content and C content of the oxide film are high, discoloration is likely to occur. This is because fluorine, carbon, or compounds thereof reduce the function of the oxide film that suppresses the dissolution of the titanium base material, making it easier for titanium to dissolve, or because they exist as compounds with titanium in the oxide film and the compounds are easily dissolved, which causes the oxide film to grow. Here, fluorine and carbon in the oxide film may exist alone or as compounds with titanium, hydrogen, oxygen, etc. If the F content is 3 atomic % or less and the C content is 20 atomic % or less, the dissolution of titanium from the titanium base material and the growth of the oxide film are suppressed. Therefore, the F content is preferably 3 atomic % or less and the C content is preferably 20 atomic % or less. More preferably, the F content is 1 atomic % or less and the C content is 15 atomic % or less.
The F content and C content of the oxide film are preferably small, but from a manufacturing standpoint, the practical lower limits are about 0 atomic % for the F content and about 6 atomic % for the C content.

The oxide film thickness and the F content and C content in the oxide film can be determined from the composition distribution in the depth direction obtained by Auger electron spectroscopy. The oxide film thickness is determined by multiplying the sputtering time at the position where the oxygen concentration is reduced by half relative to the measured oxygen concentration on the oxide film surface by the sputtering rate converted into _SiO2 and the basic sputtering time. _{The SiO2} -converted sputtering rate is, for example, the sputtering rate determined under the same measurement conditions using a _SiO2 film whose thickness has been measured in advance using an ellipsometer.

The maximum fluorine concentration in the oxide film is taken as the F content in the oxide film. In addition, since the outermost surface is affected by contamination, for carbon whose concentration decreases almost monotonically in the depth direction, the part where the oxygen concentration decreases at the outermost surface is considered to be affected by contamination, and the maximum carbon concentration after the depth where the oxygen concentration is maximum is taken as the C content in the oxide film.

The shape of the titanium material according to this embodiment is not particularly limited and may be a plate, coil, or strip. Up to this point, the titanium material according to this embodiment has been described.

<3. Manufacturing method of titanium material>
Next, the manufacturing method of the titanium material according to this embodiment will be described. The manufacturing method of the titanium material according to this embodiment has at least one of a polishing step of polishing the surface of the titanium material using abrasive powder having a grain size distribution of #320 or less according to JIS R 6001-2:2017, and then a spalling step of spalling the titanium material after the polishing step by 3 μm or more from the surface using an aqueous solution containing 1 mass % or more of hydrofluoric acid, or a cold rolling step of rolling down the titanium material after the polishing step by using a rolling roll having a surface roughness Ra of 0.5 μm or more so that the total rolling reduction is 0.10% or more. Hereinafter, the manufacturing method having the polishing step and the spalling step will be referred to as the first manufacturing method, the manufacturing method having the polishing step and the cold rolling step will be referred to as the second manufacturing method, and the manufacturing method having the polishing step, the spalling step, and the cold rolling step will be described as one example of a composite manufacturing method.
(3.1. First manufacturing method)
The first manufacturing method includes a polishing step of polishing the surface of a titanium material, and a machining step of machining a portion of the titanium material after the polishing step to a depth of 3 μm or more using an aqueous solution containing 1 mass % or more of hydrofluoric acid.

[Polishing process]
In this step, the surface of the titanium material is polished using abrasive powder having a particle size distribution of #320 or less in accordance with JIS R 6001-2: 2017. There are no particular limitations on the means for polishing the surface of the titanium material, and known means such as a brush roll or coil grinder can be used.

For example, when using a coil grinder, the surface of a plate coil-shaped titanium material is polished using the following method. The titanium material is polished using a polishing belt with a grit size of #320 or less, such as #320, #240, #100, #80, etc., on a coil line polishing machine. The abrasive powder used in the polishing belt is preferably one with a grit size of #100 or less. In order to obtain a more uniform polished surface, polishing may be performed multiple times using the same grit size or different grit sizes.

The titanium material to be subjected to the polishing process may be one manufactured by a known method. For example, a pure titanium or titanium alloy ingot having the above-mentioned composition is produced by various melting methods such as a vacuum arc melting method, an electron beam melting method, a hearth melting method such as a plasma melting method, etc., using sponge titanium or a mother alloy for adding alloy elements as a raw material. Next, the obtained ingot is divided and hot forged as necessary to form a slab. The slab is then hot rolled to form a hot-rolled coil of pure titanium or titanium alloy having the above-mentioned composition. This hot-rolled coil is cold rolled, and the polishing process is carried out on the titanium material after cold rolling.
The slab may be subjected to pretreatment such as polishing, cutting, etc., as necessary. When the slab is formed into a rectangular shape suitable for hot rolling by the hearth melting method, it may be subjected to hot rolling without performing blooming, hot forging, etc.
The cold rolling conditions are not particularly limited, and the cold rolling may be carried out under suitable conditions that provide the desired thickness, properties, etc.

[Surface cutting process]
In this process, the titanium material after the polishing process is eroded by 3 μm or more from its surface with an aqueous solution containing 1% or more by mass of hydrofluoric acid (erosion treatment), and then heated to 300 to 880 ° C. in a non-oxidizing atmosphere (heat treatment). Hereinafter, an aqueous solution containing 1% or more by mass of hydrofluoric acid may be simply referred to as an aqueous hydrofluoric acid solution. By eroding the titanium material after the polishing process by 5 μm or more with the aqueous hydrofluoric acid solution, the surface of the titanium material after the polishing process is given a more locally inclined unevenness. Examples of the aqueous solution include a nitric hydrofluoric acid solution and a sulfuric hydrofluoric acid solution containing 1% or more by mass of hydrofluoric acid. In addition to hydrofluoric acid, other chemicals such as nitric acid and sulfuric acid may be mixed. A mixed aqueous solution of hydrofluoric acid and nitric acid is preferable because it is the most versatile solution for eroding titanium, and more preferably, the nitric acid concentration is 1 to 8% by mass because color unevenness is suppressed.

The temperature of the hydrofluoric acid solution is preferably 20 to 60°C. If the temperature of the hydrofluoric acid solution is 20 to 60°C, it is relatively easy to control the amount of erosion. If the temperature exceeds 60°C, the erosion reaction becomes intense and it becomes difficult to suppress the temperature rise. The temperature of the hydrofluoric acid solution is more preferably 30 to 50°C.

The amount of erosion is 3 μm or more. If the amount of erosion is less than 3 μm, localized inclined unevenness is not sufficiently imparted, and RΔq may not reach 0.150. Therefore, the amount of erosion is 3 μm or more. The amount of erosion is preferably 5 μm or more.
On the other hand, the upper limit of the amount of scavenging is not particularly limited, but excessive scavenging only increases the yield loss, and may result in failure to obtain a titanium material of the desired thickness. Excessive scavenging also reduces the yield and increases the manufacturing cost. For example, the upper limit of the amount of scavenging is 20 μm, and preferably 10 μm.

The amount of swarf cutting can be confirmed, for example, by the following method. That is, in the case of a plate or a strip coil of a plate, for example, the mass before and after swarf cutting can be measured, and the amount can be calculated from the mass loss and the initial plate thickness, width, and length. In this calculation, if the density of the titanium material is required, for example, a value of 4.51 g/ ^cm3 can be used for commercially pure titanium.

Through the above polishing and surface-cutting processes, the Ra/RSm of the titanium substrate surface becomes 0.006 to 0.015, and the root-mean-square slope RΔq of the roughness curve element becomes 0.150 to 0.280.

Depending on the conditions of the laser cutting, the titanium material after the above-mentioned laser cutting process may contain a large amount of fluorine in the oxide film. If the oxide film contains a large amount of fluorine, discoloration may occur as described above. In order to reduce the F content of the oxide film, the titanium material after the laser cutting process is heated to 300 to 880°C in a non-oxidizing atmosphere. By heating the titanium material after the laser cutting process to 300 to 880°C in a non-oxidizing atmosphere, it is possible to reduce the F content in the oxide film. This is thought to be due to the diffusion and evaporation of fluorine. The non-oxidizing atmosphere is, for example, a vacuum atmosphere, an argon atmosphere, or a helium atmosphere. If the temperature is less than 300°C, the fluorine concentration may not be sufficiently reduced, and if the temperature exceeds 880°C, wrinkles may be formed on the surface due to transformation or grain growth, which may impair the above-mentioned surface characteristics. The heating temperature is preferably 320°C or higher. Also, the heating temperature is preferably 870°C or lower.

The vacuum atmosphere referred to here refers to an atmosphere with a degree of vacuum of 10 ^-2 Pa (approximately 10 ^-4 Torr) or lower. The argon atmosphere refers to an atmosphere made of argon gas with a purity of 99.99% or more, and the helium atmosphere refers to an atmosphere made of helium gas with a purity of 99.99% or more. The vacuum atmosphere may contain the argon gas or helium gas to the extent that the above-mentioned degree of vacuum is satisfied. The non-oxidizing atmosphere may be an atmosphere made of argon gas and helium gas. The above-mentioned atmosphere is used because it can prevent coloring due to oxidation of the titanium material during heating.

The heating time is sufficient as long as the fluorine concentration is below the desired level, and there is no reason to particularly limit the range of the heating time. Industrially, the heating time is preferably from 10 seconds to 8 hours.
This heating step may also serve as annealing of the titanium material.
Up to this point, the first manufacturing method has been described. Before and after each processing step, normal washing such as washing with water, washing with an alkali, or washing with a solvent may be carried out as appropriate.

(3.2. Second manufacturing method)
The second manufacturing method includes a polishing step of polishing the surface of the titanium material, and a cold rolling step of rolling the titanium material using a rolling roll having a surface roughness Ra of 0.5 μm or more so that the total rolling reduction is 0.10% or more. The polishing step is the same as the polishing step described in the first manufacturing method, and therefore a detailed description thereof will be omitted here.

[Cold rolling process]
In this process, the titanium material after the polishing process is rolled down using a rolling work roll (hereinafter referred to as the rolling roll) having an arithmetic mean roughness Ra of 0.5 μm or more. The titanium material after the polishing process is rolled down using the rolling roll so that the total reduction is 0.10% or more, so that the surface of the titanium material is given unevenness with a more localized incline. If the arithmetic mean roughness Ra of the rolling roll surface is too large, the uneven shape given in advance by the polishing process may change significantly, so the arithmetic mean roughness Ra of the rolling roll surface is preferably 2.0 μm or less.
The surface roughness of the rolling roll can be adjusted by polishing or shot blasting.

The total rolling reduction is 0.10% or more to provide localized inclined unevenness, and preferably 0.2% or more for the stability of the surface finish over the entire length of the coil. On the other hand, it is preferable to set the total rolling reduction to 1.5% or less so that the surface roughness formed by the polishing in the previous process is not crushed by cold rolling and the necessary uneven shape is not lost. In addition, although one pass of this cold rolling is sufficient to obtain the surface characteristics of the present invention, taking into account the need to finish the entire length of a long coil to a surface as uniform as possible, cold rolling may be performed multiple times, two or more passes. Taking this into consideration, the total rolling reduction is specified, and in the case of multiple passes, the total rolling reduction is the rolling reduction calculated from the difference between the initial and finished plate thicknesses.

Through the above-mentioned polishing and cold rolling steps, the titanium substrate surface has an Ra/RSm of 0.006 to 0.015 and a root-mean-square slope RΔq of the roughness profile element of 0.150 to 0.280.
So far, the second manufacturing method has been described.

(3.3. Examples of composite types)
The method for producing a titanium material according to the present invention may include both the spalling step in the first production method and the cold rolling step in the second production method, in which case either step may be carried out first. By carrying out the spalling step and the cold rolling step, it is possible to produce a titanium material having an Ra/RSm of 0.006 to 0.015 and a root-mean-square slope RΔq of the roughness curve element of 0.150 to 0.280.
In the above, the heat treatment in the laser cutting step is described as a step following the laser cutting step, but when both the laser cutting step and the cold rolling step are performed, either the heat treatment or the cold rolling step may be performed first after the laser cutting step. In other words, the steps may be performed in the order of the laser cutting step, the heat treatment, and the cold rolling step, or the laser cutting step, the cold rolling step, and the heat treatment. Regardless of whether the heat treatment or the cold rolling step is performed first, it is possible to produce a titanium material having an Ra/RSm of 0.006 to 0.015 and a root-mean-square slope RΔq of the roughness curve element of 0.150 to 0.280.

The produced titanium may be subjected to temper rolling to adjust the mechanical properties or stretch straightening to correct the shape, as necessary.
The method for producing a titanium material according to this embodiment has been described above.

The following provides a detailed explanation of the embodiment of the present invention, with reference to examples. Note that the examples shown below are merely examples of the present invention, and the present invention is not limited to the examples below.

Example 1
In this example, titanium materials were manufactured based on the first manufacturing method. In this example, JIS type 1 plate (equivalent to ASTM Gr. 1) conforming to JIS H 4600:2012, JIS type 2 plate (equivalent to ASTM Gr. 2), Ti-0.05Pd plate (equivalent to JIS type 17 (ASTM Gr. 7)), Ti-0.15Pd plate (equivalent to JIS type 11 (ASTM Gr. 11)), Ti-0.5Ni-0.05Ru plate (equivalent to JIS type 21 (ASTM Gr. 13)), Ti-3Al-2.5V plate (equivalent to JIS type 61 (ASTM Gr. 9)), Ti-6Al-4V plate (equivalent to JIS type 60 (ASTM Gr. 5)), Ti-15v-3Cr-3Sn-3Al plate (equivalent to JIS type 61 (ASTM Gr. 6)), Ti-2.5V ... The following plates were used: Ti-0.03Ru-0.002Mm, Ti-5Al-1Fe, and Ti-20V-4Al-1Sn. The Mm in Ti-0.03Ru-0.002Mm plate indicates misch metal.

The JIS Class 1 plate, JIS Class 2 plate, Ti-0.05Pd plate, Ti-0.15Pd plate, Ti-0.5Ni-0.05Ru plate, Ti-3Al-2.5V plate, and Ti-Ru-Mm plate were obtained by cold rolling, alkaline washing, and annealing at a temperature of 650° C. for 4 hours in a vacuum atmosphere, and had a plate thickness of 0.5 mm.
The Ti-6Al-4V plate, the Ti-15V-3Cr-3Sn-3Al plate, the Ti-5Al-1Fe plate, and the Ti-20V-4Al-1Sn plate were obtained by cold rolling, annealing at 800° C. for 5 minutes in an air atmosphere, and then pickling, and had a plate thickness of 1.0 mm.

Tables 1 to 4 show the conditions for the polishing process and the surface-cutting process in the manufacturing conditions for titanium material. In Table 4, Ti-0.03Ru-0.002Mm plate is described as Ti-Ru-Mm plate. Also, the "number of polishing passes" shown in Tables 1 to 4 indicates the number of times the titanium material was passed through a coil grinder line consisting of three polishing stands with polishing belts.

The surface roughness parameters of the manufactured titanium material (arithmetic mean roughness Ra, average length of profile curve element RSm, root mean square slope RΔq of roughness curve element, kurtosis Rku, and skewness Rsk) were measured in accordance with JIS B 0601:2013 under the following conditions.
Equipment: Surface roughness and shape measuring instrument (SURFCOM 1900DX manufactured by Tokyo Seimitsu Co., Ltd., analysis software: TiMS Ver. 9.0.3)
Probe: Tokyo Seimitsu Co., Ltd. shape probe (model: DT43801)
Parameter calculation standard: JIS-01 standard Measurement type: Roughness measurement Cutoff type: Gaussian Tilt correction: Least squares linear correction Measurement distance: 5.0 mm
Cutoff wavelength λc: 0.8 mm
Measurement range: ±64.0 μm
Measurement speed: 0.3mm/sec
Movement and return speed: 0.6 mm/sec
Return setting: Normal measurement Pre-drive length: (Cutoff wavelength/3) x 2
Measurement interval Δx: 0.195μm
λs cutoff ratio: 300
λs cutoff wavelength: 2.667 μm
Pickup type: Standard pickup Polarity: Forward

Measurements were taken at three points in the direction in which Ra was maximum, and the average value was calculated. In the case of titanium plate, the direction parallel to the rolling direction was set as 0°, and roughness was measured in four directions: 22.5°, 45°, and 90° (perpendicular to the rolling direction), and the direction in which Ra was maximum was determined. When titanium material was rolled using a rolling roll, or when a roll with embedded abrasive grains was rotated in the rolling direction to polish the plate surface, Ra was maximum in the 90° direction, which is perpendicular to the rolling direction.

The oxide film thickness and the F, C, P and S contents in the oxide film were determined from the composition distribution in the depth direction obtained by Auger electron spectroscopy. The oxide film thickness was determined by multiplying the sputtering rate in terms of _SiO2 by the basic sputtering time, which was calculated based on the measured oxygen concentration on the oxide film surface and the sputtering time, at which the oxygen concentration was reduced by half.

The maximum fluorine concentration in the oxide film was taken as the F content in the oxide film. In addition, since the outermost surface is affected by contamination, for carbon, whose concentration decreases almost monotonically in the depth direction, the part where the oxygen concentration decreases at the outermost surface was considered to be affected by contamination, and the maximum carbon concentration after the depth where the oxygen concentration is maximum was taken as the C content in the oxide film. The P content and S content of the oxide film were analyzed in the same way as the F content.

A discoloration test was conducted on the obtained titanium material sample. In the discoloration test, the titanium material was immersed in a sulfuric acid aqueous solution of pH 4 at 80°C for 4 days, and the L ^* a ^* b ^* of the titanium material surface was measured before and after immersion to obtain the color difference ΔE ^* ab. The color difference was measured from the differences ΔL ^* , Δa ^* , and Δb ^* in the lightness L ^* and chromaticity a ^* and b ^* before and after immersion, which are calculated in accordance with JIS Z 8730:2009.
Color difference ΔE ^* ab = [(ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² ] ^1/2
The color difference was measured using a color difference meter CR-200b manufactured by Minolta Co., Ltd. under light source C.
When the color difference ΔE ^* ab was 6.0 or less, the discoloration resistance was judged to be extremely good (◎); when the color difference ΔE ^* ab was more than 6.0 and less than 8.0, the discoloration resistance was judged to be good (◯); and when the color difference ΔE ^* ab was more than 8.0, the discoloration resistance was judged to be poor (×).
For the visual observation, titanium materials that had not been subjected to this discoloration acceleration test and titanium materials that had been subjected to this discoloration acceleration test were placed on a flat plate and compared from various angles under sunlight, and if there was an angle at which discoloration was noticeably visible, it was judged as failing (x), and if there was no such angle, it was judged as passing (○). Note that this visual observation was performed under conditions that simulated the roofs and walls of an actual building, and the evaluation was also made assuming that the color tone would change depending on the viewing angle.
From the evaluation of the color difference and visual observation described above, the resistance to discoloration was judged comprehensively as follows and in the table below. When the color difference ΔE ^* ab is 6.0 or less "◎" and the visual observation is pass "◯", it is judged as very good (◎); when the color difference ΔE ^* ab is more than 6.0 and 8.0 or less "◯" and the visual observation is pass "◯", it is judged as good (◯); when the color difference ΔE ^* ab is more than 8.0 "×" or when the color difference ΔE ^* ab is 8.0 or less but the visual observation is fail "×", it is judged as unsatisfactory (×). The above evaluation criteria are shown in Table 2.

Tables 6 to 9 show the characteristics of the obtained titanium materials (each parameter of the surface roughness of the sample, the thickness of the oxide film, the F content and the C content of the oxide film), the color difference ΔE ^* ab, and the visual evaluation results.

As shown in Tables 1 to 9, when Ra/RSm was 0.006 to 0.015 and the root mean square slope RΔq of the roughness curve element was 0.150 to 0.280, discoloration resistance was good. In addition, when kurtosis Rku was greater than 3 or skewness Rsk was greater than -0.5, discoloration resistance was extremely good.

In addition, when the oxide film contained 3 atomic % or less of F and 20 atomic % or less of C, the discoloration resistance was extremely good.

Example 2
In this example, a titanium material was manufactured based on the second manufacturing method. The titanium material used was a plate obtained through the same process as in Example 1. Tables 10 and 11 show the conditions of the polishing process and the cold rolling process among the manufacturing conditions of the titanium material.

Measurement of each parameter of the surface roughness of the prepared samples, calculation of the oxide film thickness and the F content and C content in the oxide film, and color difference ΔE ^* ab and visual evaluation were performed in the same manner as in Example 1. Tables 12 and 13 show each characteristic of the obtained titanium material (each parameter of the surface roughness of the sample, the oxide film thickness, the F content and C content of the oxide film), the color difference ΔE ^* ab, and the visual evaluation results.

As shown in Tables 10 to 13, when Ra/RSm was 0.006 to 0.015 and the root mean square slope RΔq of the roughness curve element was 0.150 to 0.280, discoloration resistance was good. In addition, when kurtosis Rku was greater than 3 or skewness Rsk was greater than -0.5, discoloration resistance was extremely good.

In addition, when the oxide film contained 3 atomic % or less of F and 20 atomic % or less of C, the discoloration resistance was extremely good.

Example 3
In this example, titanium materials were manufactured based on a composite manufacturing method including a spalling process and a cold rolling process. Nos. A1, A2*, A3*, A4*, and C11 to C23 in Example 1 were used and subjected to the cold rolling process shown in Table 14. Nos. B1 to B4 and D11 to D13 in Example 2 were used and subjected to the spalling process shown in Table 15.

Measurement of each parameter of the surface roughness of the prepared samples, calculation of the oxide film thickness and the F content and C content in the oxide film, and color difference ΔE ^* ab and visual evaluation were performed in the same manner as in Example 1. Tables 16 and 17 show each characteristic of the obtained titanium material (each parameter of the surface roughness of the sample, the oxide film thickness, the F content and C content of the oxide film), the color difference ΔE ^* ab, and the visual evaluation results.

As shown in Tables 14 to 17, the samples produced by both the surface cutting process and the cold rolling process had Ra/RSm of 0.006 to 0.015 and a root-mean-square slope RΔq of the roughness curve element of 0.150 to 0.280, demonstrating good resistance to discoloration.

In addition, when the oxide film contained 3 atomic % or less of F and 20 atomic % or less of C, the discoloration resistance was extremely good.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited to such examples. It is clear that a person with ordinary knowledge in the technical field to which the present invention pertains can conceive of various modified or revised examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

Claims (5)

A titanium material having a titanium base material in which, in a roughness curve in the direction in which the arithmetic mean roughness Ra is maximum, the ratio of the arithmetic mean roughness Ra to the element length RSm, Ra/RSm, is 0.006 to 0.015, and the root-mean-square slope RΔq is 0.150 to 0.280. The titanium material according to claim 1, wherein the kurtosis Rku of the titanium substrate is greater than 3 in the roughness curve in the direction in which the arithmetic mean roughness Ra is maximum. The titanium material according to claim 1 or 2, wherein the skewness Rsk of the titanium base material is greater than -0.5 in the roughness curve in the direction in which the arithmetic mean roughness Ra is maximum. F: 3 atomic % or less; and
C: 20 atomic% or less,
a titanium substrate having an oxide film on a surface thereof,
The titanium material according to any one of claims 1 to 3, wherein the oxide film has a thickness of 15 nm or less. A polishing step of polishing the surface of the titanium material using abrasive fine powder having a grain size distribution of #320 or less in accordance with JIS R 6001-2:2017, and then
The method for producing a titanium material includes at least one of a laser cutting process in which the titanium material after the polishing process is laser cut by 3 μm or more from the surface with an aqueous solution containing 1 mass % or more of hydrofluoric acid and then heated to 300 to 880° C. in a non-oxidizing atmosphere, and a cold rolling process in which the titanium material after the polishing process is rolled down using a rolling roll having a surface roughness Ra of 0.5 μm or more so that the total rolling reduction is 0.10% or more.

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