CN118632944A - Titanium - Google Patents

Abstract

In the titanium material, the average nitrogen concentration and the average carbon concentration in the range from the surface to the position where the oxygen concentration measured from the surface in the thickness direction by glow discharge spectrometry is 1/3 of the maximum value are respectively 14.0 atomic % or less, the average hydrogen concentration is 30.0 atomic % or less, and the difference between the lattice constant of the c-axis of Ti in the α-phase determined by X-ray diffraction measurement based on the parallel beam method at an incident angle of 0.3 degrees at the surface and the lattice constant of the c-axis of Ti in the α-phase determined by X-ray diffraction measurement based on the focusing method at the center of the plate thickness is the following.

Description

Titanium

Technical Field

The present invention relates to titanium materials.

Background Art

Titanium materials show extremely excellent corrosion resistance in the atmospheric environment, and are therefore used for building materials such as roofs and exterior walls of buildings. However, titanium materials that are used for a long time may discolor. Discoloration of titanium materials sometimes becomes a problem from the perspective of design. Therefore, titanium materials with excellent discoloration resistance and suppressed discoloration have been proposed.

For example, Patent Document 1 discloses a titanium material or titanium alloy material having excellent discoloration resistance, characterized in that a titanium material having a thickness of The surface oxide film has an amount of C of 30 atomic % or less, and the amount of C in the surface oxide film is 30 atomic % or less, and the amount of C in the base surface layer portion under the oxide film is 30 atomic % or less.

Patent Document 2 discloses titanium that is less likely to discolor in an atmospheric environment, characterized in that the average carbon concentration within a depth of 100 nm from the surface is 14 at % or less, and an oxide film with a thickness of 12 to 40 nm is present on the outermost surface.

Patent Document 3 discloses a titanium material that is less likely to discolor, wherein the amount of fluorine in the oxide film on the surface is 7 at % or less.

Patent document 4 discloses a method for manufacturing a titanium plate, which is characterized in that, in order to efficiently manufacture a titanium or titanium alloy plate with little discoloration under a light irradiation environment, the titanium plate is cold rolled using a lubricant in which the carbon content of the carbon-enriched layer on the surface of the titanium plate after cold rolling is less than 150 mg/ ^m2 , and then annealed in an oxidizing atmosphere, followed by descaling by molten salt immersion treatment and pickling using a nitric acid-hydrofluoric acid aqueous solution.

Patent document 5 discloses a titanium or titanium alloy that is not easily discolored in an atmospheric environment, characterized in that the average carbon concentration within a depth of 100 nm from the surface is less than 14 at %, an oxide film with a thickness of more than 12 nm and less than 30 nm is present on the surface, and the arithmetic mean height (Ra) of the titanium surface is less than 0.035 μm.

Prior art literature

Patent Literature

Patent Document 1: Japanese Patent Application Publication No. 2000-1729

Patent Document 2: Japanese Patent Application Publication No. 2002-12962

Patent Document 3: Japanese Patent Application Publication No. 2002-47589

Patent Document 4: Japanese Patent Application Publication No. 2002-60984

Patent Document 5: Japanese Patent Application Publication No. 2005-272870

Non-patent literature

Non-patent literature 1: Tsutomu Miyashita, "もう一时reviewしたい Surface Rough", Journal of the Society of Precision Engineering, Society of Precision Engineering, Vol.73, No.2, 2007, p.201-205

Summary of the invention

Problem that the invention aims to solve

In the techniques described in Patent Documents 1 to 5, the deterioration of the discoloration resistance of the titanium material is suppressed by reducing the carbon concentration on the surface. In addition, the discoloration resistance of the conventional titanium material is evaluated by the color difference after immersion in sulfuric acid at pH 3 at a temperature of 60°C for 14 days, as described in Patent Document 5. However, in recent years, titanium materials having better discoloration resistance than conventional titanium materials have been required.

The present invention has been made in view of the above problems, and its object is to provide a titanium material having excellent discoloration resistance and capable of suppressing discoloration for a long time compared with conventional titanium materials. The present invention also aims to provide a titanium material that does not discolor even when immersed for a longer period than the evaluation described in Patent Documents 1 to 5.

Solutions for solving problems

The gist of the present invention completed based on the above findings is as follows.

[1] A titanium material according to one embodiment of the present invention has an average nitrogen concentration and an average carbon concentration of 14.0 atomic % or less, respectively, and an average hydrogen concentration of 30.0 atomic % or less in a range from a surface to a position where an oxygen concentration measured along a thickness direction from the surface by glow discharge spectrometry is 1/3 of a maximum value, respectively.

The difference between the lattice constant of the c-axis of the α-phase Ti determined by X-ray diffraction measurement based on the parallel beam method at an incident angle of 0.3 degrees at the surface and the lattice constant of the c-axis of the α-phase Ti determined by X-ray diffraction measurement based on the focusing method at the center of the plate thickness is the following.

[2] The titanium material described in [1] above may include an oxide film having a thickness of 30.0 nm or less.

[3] The titanium material described in [1] or [2] above comprises: a titanium substrate, and an oxide film arranged on the surface of the titanium substrate, wherein the maximum value of the nitrogen concentration from the nitride in the oxide film when analyzed by X-ray photoelectron spectroscopy is 2.0 to 10.0 atomic %, the position where the nitrogen concentration from the nitride in the oxide film shows a maximum value exists in the range of 2 to 10 nm from the surface of the oxide film when converted to the sputtering rate of _SiO2 , the concentration of nitrogen from the nitride existing in the range from the position where the oxygen concentration becomes 1/2 of the maximum value to 20 nm on the titanium substrate side is less than the maximum value of the nitrogen concentration from the nitride in the oxide film and is less than 7 atomic %, and the maximum value of the nitrogen concentration from the nitride in the oxide film can be greater than or equal to the carbon concentration from the carbide at the position where the nitrogen concentration from the nitride in the oxide film becomes the maximum.

[4] The titanium material described in [1] or [2] above has a titanium substrate, wherein in the roughness profile of the titanium substrate in the direction in which the arithmetic mean roughness Ra becomes the maximum, the ratio of the arithmetic mean roughness Ra to the element length RSm, i.e. Ra/RSm, is 0.006 to 0.015, and the root mean square slope RΔq is 0.150 to 0.280, the kurtosis Rku of the titanium substrate is greater than 3, and the skewness Rsk of the titanium substrate can be greater than -0.5.

[5] The titanium material described in [3] above has a roughness profile in the direction in which the arithmetic mean roughness Ra of the titanium substrate becomes the largest, and the ratio of the arithmetic mean roughness Ra to the element length RSm, i.e. Ra/RSm, is 0.006 to 0.015, and the root mean square slope RΔq is 0.150 to 0.280, the kurtosis Rku of the titanium substrate is greater than 3, and the skewness Rsk of the titanium substrate can be greater than -0.5.

Effects of the Invention

According to the present invention, a titanium material having excellent discoloration resistance and capable of suppressing discoloration for a long period of time compared with conventional titanium materials can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic enlarged cross-sectional view showing a layer structure of a titanium material according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of changes in the depth direction of a spectrum of the titanium material according to the embodiment, which is obtained by X-ray photoelectron spectroscopy.

FIG. 3 is a diagram showing an example of changes in the depth direction of a spectrum of a conventional titanium material by X-ray photoelectron spectroscopy.

FIG. 4 is a diagram showing an example of element concentration distribution in the depth direction of the titanium material according to the embodiment and a conventional titanium material based on X-ray photoelectron spectroscopy.

5 is a graph showing the relationship between the maximum value of the concentration of nitrogen derived from titanium nitride in the oxide film and the color difference ΔE ^* ab before and after the color change test.

6 is a graph showing the relationship between the ratio of the arithmetic mean roughness Ra to the average width RSm of the profile unit, that is, Ra/RSm, the root mean square slope RΔq of the roughness profile unit, and the discoloration resistance.

FIG. 7 is a schematic diagram for explaining the kurtosis Rku.

DETAILED DESCRIPTION

Hereinafter, a titanium material according to an embodiment of the present invention will be described with reference to the drawings. In addition, the dimensions and ratios of the components in the drawings do not represent the actual dimensions and ratios of the components.

It should be noted that, in the numerical ranges described below including "to", the ranges include the lower limit and the upper limit. In the numerical values expressed as "less than" or "greater than", the numerical values are not included in the numerical range.

First, new findings obtained through studies by the inventors who completed the present invention will be described in detail.

It is believed that a titanium material is a structure in which an oxide film is arranged on the surface of a titanium base material, and the discoloration of the titanium material is caused by an increase in the thickness of the oxide film due to acid rain or the like. The carbon concentration near the surface of the titanium material affects the increase in the thickness of the oxide film, so in the conventional titanium material for the purpose of improving discoloration resistance, the carbon concentration on the surface is limited. The present inventors have conducted research to obtain a titanium material with excellent discoloration resistance that can suppress discoloration for a long time compared to the conventional titanium material.

First, the inventors measured the oxygen concentration, carbon concentration, and nitrogen concentration from the surface of the titanium material (in other words, the surface of the oxide film) along the thickness direction by glow discharge spectrometry (GDS). It is known that the titanium material has an oxide film, and the position where the oxygen concentration measured by GDS is 1/3 of the maximum value is located on the titanium substrate side near the interface between the oxide film and the titanium substrate. Hereinafter, the range from the surface of the titanium material to the position where the oxygen concentration measured by GDS along the thickness direction is 1/3 of the maximum value is referred to as the surface layer of the titanium material.

Next, the inventors immersed the titanium material in a sulfuric acid aqueous solution at pH 3 and 60°C for 4 weeks, and evaluated the discoloration resistance based on the color difference before and after the immersion. Comparing the titanium material that obviously changed color before and after the immersion with the titanium material that had almost no color change, it can be seen that there are differences in the carbon concentration and nitrogen concentration measured by GDS in the titanium material before the immersion. Specifically, it can be seen that in the case of the titanium material that obviously changed color when immersed in a sulfuric acid aqueous solution at pH 3 and 60°C for 4 weeks, in the titanium material before the immersion, nitrogen and carbon exist inside the oxide film and near the interface from the interface between the oxide film and the substrate to the interface on the substrate side. In the past, it was not believed that the nitrogen present in the oxide film and near the interface from the interface between the oxide film and the substrate to the interface on the substrate side would affect the discoloration of the titanium material. However, it is speculated that when the titanium material is exposed to an acid rain environment for a long time, the nitrogen present in the oxide film and its vicinity also becomes a starting point like carbon and the growth of the oxide film occurs.

In addition, the inventors of the present invention have obtained the following insights as a result of their research: the nitrogen concentration in the oxide film and its vicinity also affects the discoloration resistance of the titanium material in the same way as the carbon concentration, and the discoloration resistance is improved by limiting the nitrogen concentration. It is further known that in the range from the surface of the titanium material to the position where the oxygen concentration measured along the thickness direction by GDS is 1/3 of the maximum value, when the average nitrogen concentration and the average carbon concentration are respectively 14.0 atomic % or less, the discoloration resistance of the titanium material is improved compared with the past. The average carbon concentration of the surface layer of the titanium material can be reduced by increasing the annealing temperature or extending the annealing time. The average nitrogen concentration can be reduced by increasing the vacuum degree of the heat treatment.

Next, the inventors of the present invention focused on the hydrogen concentration in the surface of the titanium material and studied the effect of the hydrogen concentration in the surface of the titanium material on the discoloration resistance of the titanium material. As a result, it was found that when the average hydrogen concentration in the surface of the titanium material was 30.0 atomic % or less, the discoloration resistance was further improved. Titanium hydride is thermodynamically unstable compared to titanium oxide under the acid rain environment of the atmosphere. As the hydrogen concentration in the titanium material increases, it is possible to promote the formation of titanium oxide and reduce the discoloration resistance. However, it is believed that if the average hydrogen concentration in the surface of the titanium material is 30.0 atomic % or less, titanium hydride will not change into titanium oxide, and the reduction in discoloration resistance is suppressed.

Next, the present inventors paid attention to the change of the crystal structure of Ti on the surface of the titanium material. The present inventors found that the change of the c-axis of Ti, which is the α-phase of close-packed hexagonal crystals, affects the discoloration resistance of the titanium material.

According to the research conducted by the present inventors, it is known that if the difference between the lattice constant of the c-axis of the α-phase Ti obtained by X-ray diffraction measurement based on the parallel beam method at an incident angle of 0.3 degrees at the surface of the titanium material and the lattice constant of the c-axis of the α-phase Ti obtained by X-ray diffraction measurement based on the focusing method at the center of the plate thickness (also referred to as the center of the thickness) is The following can greatly improve the discoloration resistance. The above-mentioned X-ray diffraction measurement has different penetration levels of X-rays depending on the X-ray diffraction energy, but by performing the above-mentioned X-ray diffraction measurement on the surface of the titanium material and the center of the plate thickness of the titanium material, the lattice constant of the c-axis of Ti in each α-phase can be measured. In the present application, the increase in the lattice constant of the c-axis of the α-phase Ti in the surface layer is defined as follows. That is, the difference between the lattice constant of the c-axis of Ti in the α-phase obtained by X-ray diffraction measurement based on the parallel beam method with an incident angle of 0.3 degrees at the surface of the titanium material and the lattice constant of the c-axis of Ti in the α-phase obtained by X-ray diffraction measurement based on the focusing method at the center of the plate thickness is called the increase in the lattice constant of the c-axis of Ti in the α-phase in the surface layer. The measurement depth in X-ray diffraction measurement based on the parallel beam method at an incident angle of 0.3 degrees does not strictly correspond to the range in the thickness direction of the surface portion measured by GDS, but the increase in the c-axis lattice constant of α-phase Ti in the surface portion can be roughly measured.

It is believed that the increase in the lattice constant of the c-axis of the α-phase Ti in the surface portion of the titanium material is related to oxygen. If oxygen is dissolved in the α-phase Ti in the surface portion of the titanium material, the lattice constant of its c-axis becomes larger. It is speculated that if the lattice constant of the c-axis of the α-phase Ti present on the surface of the titanium material is greater than the lattice constant of the c-axis of the α-phase Ti present in the center of the thickness, titanium oxide with a high defect concentration is generated due to the effect of acid rain, the oxide film is easy to grow, and the discoloration resistance is deteriorated. The temperature, time, and vacuum degree of the heat treatment affect the crystal structure of the α-phase Ti in the surface portion of the titanium material. By increasing the vacuum degree in the atmosphere of the heat treatment, the amount of oxygen dissolved in the α-phase Ti in the surface portion of the titanium material is reduced, and the increase in the lattice constant of the c-axis of the α-phase Ti in the surface portion of the titanium material is suppressed. So far, the new insights obtained through the research of the inventors and others have been explained.

Next, a titanium material involved in one embodiment of the present invention is described with reference to FIG1. FIG1 is a schematic enlarged cross-sectional view showing the layer structure of the titanium material involved in the present embodiment. In the titanium material involved in the present embodiment, the average nitrogen concentration and the average carbon concentration in the range from the surface to the position where the oxygen concentration measured from the surface along the thickness direction by glow discharge spectrometry is 1/3 of the maximum value are respectively 14.0 atomic % or less, and the average hydrogen concentration is 30.0 atomic % or less, and the difference between the lattice constant of the c-axis of Ti in the α-phase determined by X-ray diffraction measurement based on the parallel beam method with an incident angle of 0.3 degrees at the surface and the lattice constant of the c-axis of Ti in the α-phase determined by X-ray diffraction measurement based on the focusing method at the center of the plate thickness is Hereinafter, the titanium material according to the present embodiment will be described in detail.

(Titanium material 1)

As shown in FIG1 , the titanium material 1 according to the present embodiment is a titanium material having an oxide film 20 formed on the surface of a titanium substrate 10. In other words, the titanium material 1 includes a titanium substrate 10 and an oxide film 20 formed on the surface of the titanium substrate 10. The surface layer 30 is a region from the surface of the titanium material 1 (in other words, the surface of the oxide film 20) to a position where the oxygen concentration measured by GDS in the thickness direction is 1/3 of the maximum value, and includes a portion of the titanium substrate 10.

(Titanium substrate 10)

The titanium substrate 10 of the titanium material 1 is pure titanium, industrial pure titanium or a titanium alloy. The titanium substrate 10 is, for example, pure titanium, industrial pure titanium or a titanium alloy having a Ti content of 70% by mass or more. Hereinafter, they are sometimes collectively referred to as "titanium". The crystal structure of pure titanium is a close-packed hexagonal α phase, and does not contain a body-centered cubic β phase. Industrial pure titanium is mainly composed of an α phase, and sometimes also contains a β phase depending on the chemical composition. The titanium alloy may be an α-type alloy having only an α phase, or an α+β-type alloy containing a body-centered cubic β phase. In addition, the titanium substrate 10 may be, for example, industrial titanium. For industrial titanium used for the titanium substrate 10, for example, various industrial titanium plates and strips described in JIS H4600: 2012, or various industrial titanium rods described in JIS H 4650: 2016 can be cited. When processability is required, industrial pure titanium of JIS Class 1 (for example, JIS H 4600: 2012) with reduced impurities is preferred. In addition, when strength is required, the titanium substrate 10 can be applied to JIS 2-4 industrial pure titanium. As titanium alloys, for example, in order to improve corrosion resistance, JIS 11-23 containing trace amounts of precious metal elements such as palladium, platinum, ruthenium, etc., or JIS 60 containing more elements such as Ti-6Al-4V alloy, 60E, 61 and 61F can be cited. It should be noted that in buildings, industrial pure titanium or equivalent materials specified in JIS 1 and ASTM Gr. 1 are mainly used.

Examples of titanium alloys mainly composed of α phase include highly corrosion-resistant alloys (titanium alloys specified in JIS standards 11 to 13, 17, 19 to 22, and Grade 7, 11, 13, 14, 17, 30, and 31 of ASTM standards, or titanium alloys further containing small amounts of various elements (Ti-Ru-Mm, etc.)), Ti-0.5Cu, Ti-1.0Cu, Ti-1.0Cu-0.5Nb, Ti-1.0Cu-1.0Sn-0.35Si-0.25Nb, etc. Mm represents a mixed rare earth metal.

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

When the titanium substrate 10 contains aluminum, such as the Ti-6Al-4V alloy, the corrosion resistance is deteriorated and the discoloration resistance is sometimes adversely affected. Therefore, when the oxide film 20 is formed on the surface of the titanium alloy as the titanium substrate 10, it is recommended to investigate the influence of the alloying elements on the application in advance and adjust the composition and thickness of each layer appropriately according to the titanium substrate 10.

For example, the titanium substrate 10 includes, in mass %,

Co: 0% or more and 1.0% or less,

Cr: 0% or more and 0.5% or less,

Ni: 0% or more and 1.00% or less,

Ta: 0% or more and 6.00% or less,

Al: 0% or more and 7.0% or less,

V: 0% or more and 5.0% or less,

S: 0% or more and 0.3% or less,

Cu: 0% or more and 1.50% or less,

Nb: 0% or more and 0.70% or less,

Sn: 0% or more and 1.40% or less,

Si: 0% or more and 0.55% or less,

Mo: 0% or more and 0.5% or less,

W: 0% or more and 0.5% or less,

Pd: 0% or more and 0.25%,

Ru: 0% or more and 0.15% or less,

Rh: 0% or more and 0.15% or less,

Os: 0% or more and 0.15% or less,

Ir: 0% or more and 0.15% or less,

Pt: 0% or more and 0.15% or less,

REM: 0% or more and 0.10% or less,

C: 0% or more and 0.18% or less,

H: 0% or more and 0.015% or less,

O: 0% or more and 0.40% or less,

N: 0% or more and 0.05% or less, and

Fe: 0% or more and 2.50% or less,

Industrially pure titanium or titanium alloy with the balance consisting of Ti and impurities.

Here, REM refers to rare earth elements, specifically, one or more elements selected from the group consisting of Sc, Y, light rare earth elements (La, Ce, Pr, Nd, Pm, Sm, Eu) and heavy rare earth elements (Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu).

In addition, the titanium substrate 10 contains, for example,

C: 0% or more and 0.10% or less,

H: 0% or more and 0.015% or less,

O: 0% or more and 0.40% or less,

N: 0% or more and 0.05% or less, and

Fe: 0% or more and 0.50% or less,

Industrial pure titanium with the balance consisting of Ti and impurities.

In addition, the titanium substrate 10 contains, for example,

Co: 0% or more and 0.80% or less,

Pd: 0% or more and 0.25% or less,

Cr: 0% or more and 0.2% or less,

Ru: 0% or more and 0.06% or less,

Ni: 0% to 0.60%, Ta: 0% to 6.0%, N: 0% to 0.05%, C: 0% to 0.08%, H: 0% to 0.015%, O: 0% to 0.35%, and

A titanium alloy containing Fe: 0% to 0.30% inclusive, with the balance being Ti and impurities.

The titanium substrate 10 includes, for example, in mass % Al: 2.0% to 7.0%, V: 1.0% to 5.0%, S: 0% to 0.3%, REM: 0% to 0.08%,

N: 0% to 0.05%, C: 0% to 0.10%, H: 0% to 0.015%,

O: 0% or more and 0.35% or less, and

A titanium alloy containing Fe: 0% to 2.5% inclusive, with the balance being Ti and impurities.

The titanium substrate 10 includes, for example, Cu: 0.3% to 1.50% inclusive, Nb: 0% to 0.70% inclusive, Sn: 0% to 1.40% inclusive, Si: 0% to 0.55% inclusive,

N: 0% to 0.05%, C: 0% to 0.10%, H: 0% to 0.015%,

O: 0% or more and 0.15% or less, and

Fe: 0% or more and 0.10% or less,

A titanium alloy in which the balance is composed of Ti and impurities.

In addition, the titanium substrate 10 contains, for example,

V: 0% or more and 0.5% or less,

Ni: 0% or more and 1.00% or less,

Cr: 0% or more and 0.5% or less,

Co: 0% or more and 1.0% or less,

Mo: 0% or more and 0.5% or less,

W: 0% or more and 0.5% or less,

Pd: 0% or more and 0.15% or less,

Ru: 0% or more and 0.15% or less,

Rh: 0% or more and 0.15% or less,

Os: 0% or more and 0.15% or less,

Ir: 0% or more and 0.15% or less,

Pt: 0% or more and 0.15% or less,

REM: 0.001% or more and 0.10% or less,

N: 0% or more and 0.03% or less,

C: 0% or more and 0.18% or less,

H: 0% or more and 0.015% or less,

O: 0% or more and 0.35% or less,

Fe: 0% or more and 0.30% or less, and

The total amount of Pd, Ru, Rh, Os, Ir and Pt: 0.01% or more and 0.15% or less,

A titanium alloy in which the balance is composed of Ti and impurities.

Impurities are components that exist in titanium regardless of the purpose of addition and are not necessary in the obtained titanium material. The term "impurities" is a concept that includes impurities mixed from raw materials or manufacturing environments when titanium is manufactured industrially. Examples of impurities include Cl, Na, Mg, Ca, and B. The content of each element of the impurities is preferably 0.1% by mass or less, and the total amount is preferably 0.4% by mass or less.

The titanium substrate 10 is generally a plate, a bar, a tube, a rod or a wire, or a shape obtained by processing these appropriately. The titanium substrate 10 may be in any shape, such as a spherical shape or a rectangular parallelepiped shape.

(Oxide film 20)

An oxide film 20 is formed on the surface of the titanium substrate 10. The thickness of the oxide film 20 is not particularly limited, but if it is greater than 30.0 nm, the color development of the titanium material 1 is sometimes affected by the interference of light. Therefore, the thickness of the oxide film 20 is preferably less than 30.0 nm. From the viewpoint of suppressing the color development caused by the interference of light, the thickness of the oxide film 20 is more preferably less than 25.0 nm, and further preferably less than 20.0 nm. The thickness of the oxide film 20 is greater than 0 nm, but for example, it can also be more than 10.0 nm. In addition, the discoloration resistance of the titanium material is improved by ensuring the thickness of the oxide film 20. Therefore, from the viewpoint of improving the discoloration resistance, the thickness of the oxide film 20 on the surface of the titanium material 1 is more preferably more than 12.0 nm.

The thickness of the oxide film 20 is measured by GDS. The measurement based on GDS is performed as follows. The measurement based on GDS uses JOBIN YVON GD-Profiler2 manufactured by Horiba, Ltd., in a constant power mode of 35W, the pressure of argon gas is set to 600Pa, and the discharge range is set to a diameter of 4mm. The measurement interval in the measurement based on GDS is 0.5nm. In the measurement based on GDS, O (oxygen), N (nitrogen), C (carbon), H (hydrogen) and Ti are analyzed from the surface of the titanium material 1. The concentration (atomic %) of each of the above elements is calculated by setting the sum of the above elements to 100 atomic %. The thickness of the oxide film 20 is calculated by the oxygen concentration measured by GDS. Specifically, the distance in the thickness direction from the surface to the position where the oxygen concentration is halved relative to the maximum value is the thickness of the oxide film 20. The average nitrogen concentration, the average carbon concentration and the average hydrogen concentration are the arithmetic mean of the values of the nitrogen concentration, the carbon concentration and the hydrogen concentration at each measurement point.

The nitrogen concentration from nitrides near the interface between the titanium substrate 10 and the oxide film 20 is preferably less than the maximum value of the nitrogen concentration in the oxide film 20 measured by XPS and is less than 7 atomic %. Nitrides are formed on the oxide film 20 by the manufacturing method of the titanium material 1 described later in this embodiment, but according to this method, the nitrides formed near the interface between the titanium substrate 10 and the oxide film 20 do not exist or are extremely small. The nitrogen content of the parent material of the titanium substrate 10 is about 0.05 to 0.07 mass % and at most about 0.20 atomic % as the value obtained in chemical analysis, which is an impurity level. This content is below the solid solubility limit of nitrogen in titanium, so nitrides will not be formed. Therefore, in the case where nitrides exist near the interface between the titanium substrate 10 and the oxide film 20, the nitrides are formed by nitrogen diffusing from the surface to the inside during the annealing treatment in one example of the manufacturing method of the titanium material 1 involved in this embodiment. Therefore, the nitrogen concentration derived from nitrides near the interface between the titanium substrate 10 and the oxide film 20 is preferably less than the maximum value of the nitrogen concentration in the oxide film 20 measured by XPS and is 7 atomic % or less. If the nitrogen concentration derived from nitrides near the interface between the titanium substrate 10 and the oxide film 20 is less than the maximum value of the nitrogen concentration in the oxide film 20 measured by XPS and is 7.0 atomic % or less, the growth of the oxide film when the titanium material 1 is exposed to an acid rain environment for a long time is suppressed, and discoloration is suppressed. The nitrogen concentration derived from nitrides near the interface between the titanium substrate 10 and the oxide film 20 is more preferably less than the maximum value of the nitrogen concentration in the oxide film 20 and is 3.0 atomic % or less. On the other hand, there is no restriction on the lower limit of the nitrogen concentration derived from nitrides near the interface between the titanium substrate 10 and the oxide film 20. Therefore, according to an example of a method for manufacturing the titanium material 1 involved in this embodiment, the lower limit of the nitrogen concentration from nitride near the interface between the titanium substrate 10 and the oxide film 20 is 0 atomic %, but if the nitrogen concentration caused by the peak separation of XPS (not 0) is also considered, it is sometimes around 0.5 atomic %.

It should be noted that the vicinity of the interface with the oxide film 20 in the titanium substrate 10 refers to the range from the interface when measured by XPS to 20 nm on the titanium substrate side. In the figure measured by XPS described later (for example, FIG. 4 ), the position where the oxygen concentration measured by XPS becomes 1/2 of the maximum value is taken as the interface. Therefore, the range from the position where the oxygen concentration measured by XPS becomes 1/2 of the maximum value to 20 nm on the titanium substrate side is taken as the vicinity of the interface with the oxide film 21 in the titanium substrate 10. The vicinity of the interface with the oxide film 20 in the titanium substrate 10 is a region different from the surface layer 30.

The oxide film 20 can be identified by GDS or XPS, but the thickness of the oxide film obtained by each measurement method is not strictly consistent due to the different measurement methods. However, in each measurement method, the definition of the oxide film is consistent in that the position where the oxygen concentration becomes 1/2 of the maximum value is the oxide film. In the present application, the oxide film is measured by XPS when the nitrogen concentration from nitride near the interface with the oxide film 20 in the titanium substrate 10 is measured.

The oxide film 20 preferably contains nitrogen from nitride. The nitrogen from nitride in the oxide film 20 is measured by X-ray photoelectron spectroscopy (XPS). FIG. 2 is a diagram showing an example of the change in the depth direction of the spectrum of the titanium material 1 according to the present embodiment based on X-ray photoelectron spectroscopy. FIG. 3 is a diagram showing an example of the change in the depth direction of the spectrum of a conventional titanium material based on X-ray photoelectron spectroscopy. FIG. 2 (A) and FIG. 3 (A) show the change in the depth direction of the N1s spectrum, FIG. 2 (B) and FIG. 3 (B) show the change in the depth direction of the C1s spectrum, FIG. 2 (C) and FIG. 3 (C) show the change in the depth direction of the O1s spectrum, and FIG. 2 (D) and FIG. 3 (D) show the change in the depth direction of the Ti2p spectrum. As shown in FIG. 2 (C), in the titanium material 1 according to the present embodiment, a clear peak from the nitride is sometimes confirmed at a depth corresponding to the oxide film 20. On the other hand, as shown in (C) of FIG. 3 , in conventional titanium materials, the peak derived from nitrides is extremely small. It can be seen from this that the titanium material 1 involved in the present embodiment preferably contains a specified amount of nitrogen derived from nitrides in the oxide film 20. The content of nitrogen derived from nitrides in the oxide film 20 is described in detail below. It should be noted that in the titanium material 1 involved in the present embodiment, as the peak intensity of nitrides (Nitride) in (C) of FIG. 2 increases, the intensity of the peak involved in TiN in (A) of FIG. 2 also increases, so it is considered that the nitrides in (C) of FIG. 2 come from titanium nitrides.

The nitrogen content from nitride in the oxide film 20 (the maximum value of nitrogen concentration) is preferably 2.0 to 10.0 atomic %. The nitrogen content from nitride in the oxide film 20 refers to the maximum value of the nitrogen concentration from nitride in the oxide film 20 measured by XPS. In the non-coloring material, if the oxide film 20 contains more than 2.0 atomic % of nitrogen from nitride, the color change resistance is further improved. The reason is not clear, but it is believed that this is because when nitrides exist in the oxide film 20, the atomic sequence is disordered, the strain distribution in the oxide film 20 changes, or the conductivity changes and the potential distribution at the nanometer level changes, etc., thereby changing the function of shielding ion penetration in the oxide film 20 (shielding function).

When the nitrogen content from the nitride in the oxide film 20 is 2.0 atomic % or more, the shielding function can be more reliably improved, and the effect of improving the color resistance can be more reliably obtained. If the stability in manufacturing is taken into consideration, the nitrogen content from the nitride in the oxide film 20 is more preferably 4.0 atomic % or more. On the other hand, when the nitrogen content from the nitride in the oxide film 20 is greater than 10.0 atomic %, the shielding function is sometimes reduced, and the effect of improving the color resistance cannot be obtained, but when the nitrogen content from the nitride in the oxide film 20 is 10.0 atomic % or less, the shielding function is maintained, and a higher effect of improving the color resistance can be obtained. If the stability in manufacturing is taken into consideration, the nitrogen content from the nitride in the oxide film 20 is more preferably 8.0 atomic % or less.

Furthermore, the inventors of the present invention have come up with the idea of improving the discoloration resistance by controlling the distribution of nitrogen from nitrides in the oxide film 20. FIG. 4 is a diagram showing an example of the element concentration distribution in the depth direction of the titanium material 1 (the present invention example) involved in the present embodiment and the conventional titanium material (the prior art example) based on X-ray photoelectron spectroscopy. The sputtering depth on the horizontal axis in FIG. 4 is the depth converted to the sputtering speed of SiO _2. The present invention example of FIG. 4 is about the element concentration distribution of the titanium material involved in the present embodiment shown in FIG. 2. The prior art example of FIG. 4 is about the element concentration distribution of the conventional titanium material (industrial pure titanium type 1) shown in FIG. 3.

As shown in FIG. 4 , the titanium material 1 involved in the present embodiment has a maximum nitrogen concentration from nitrides at a position where the sputtering depth is 2 to 10 nm when converted to the sputtering speed of SiO _2. On the other hand, in conventional titanium materials, the nitrogen concentration is extremely small. Therefore, the depth at which the nitrogen concentration from nitrides in the oxide film 20 becomes the maximum is preferably 2 to 10 nm when converted to the sputtering speed of SiO _2. It should be noted that the upper limit of the sputtering depth is preferably set to be above 30 nm including the range near the interface with the oxide film 20. In addition, it can also be changed according to the thickness of the oxide film 20, preferably about 3 times or more of the thickness of the oxide film 20.

Furthermore, the present inventors investigated the influence of the nitrogen concentration at the depth where the nitrogen concentration derived from nitrides in the oxide film 20 becomes maximum on the discoloration resistance. FIG5 is a graph showing the relationship between the maximum value of the nitrogen concentration derived from nitrides in the oxide film 20 and the color difference ΔE ^* ab before and after the discoloration test.

The color difference ΔE ^* ab was determined by the following method. The titanium material was immersed in a sulfuric acid aqueous solution at pH 3 for 4 weeks at 60°C, and the L ^* a ^* b ^* of the titanium material surface before and after the immersion was measured. The lightness L ^* and chromaticity a ^* and b* before and after the immersion were determined according to JIS Z 8730:2009. The differences ΔL ^* , Δa ^* , and Δb ^* were used to determine the color difference ΔE ^* ab.

ΔE ^* ab=[(ΔL ^* ) ²⁺ (Δa ^* ) ²⁺ (Δb ^* ) ² ] ^1/2 . The smaller the color difference ΔE ^* ab is, the smaller the degree of discoloration before and after the test is, and the more excellent the discoloration resistance is.

As shown in FIG. 5 , when the nitrogen concentration at the depth where the nitrogen concentration from the nitride in the oxide film 20 becomes the maximum is less than 2.0 atomic %, the shielding property cannot be fully improved, and the color difference is sometimes greater than 8. On the other hand, if the nitrogen concentration from the nitride is greater than 10.0 atomic %, the shielding property is reduced, and the color difference is sometimes greater than 8. In addition, when the nitrogen concentration at the depth where the nitrogen concentration from the nitride in the oxide film 20 becomes the maximum is greater than 10.0 atomic %, it sometimes becomes a golden or yellowish hue. When it becomes a golden or yellowish hue, the hue changes, so it is sometimes not suitable for applications that require the silver color of titanium itself. It is speculated that the change in hue is due to the appearance of the material color of titanium nitride. Therefore, the nitrogen concentration at the depth where the nitrogen concentration from the nitride in the oxide film 20 becomes the maximum is 2.0 to 10.0 atomic %.

Furthermore, as shown in FIG. 5 , if the nitrogen concentration at the depth where the nitrogen concentration from nitrides in the oxide film 20 becomes maximum is lower than the carbon concentration from carbides at the same depth, the color difference may be greater than 8. This is also considered to be caused by the influence of strain distribution in the oxide film 20, the influence of the potential distribution at the nanometer level due to the change in conductivity, etc. as described above. Therefore, the nitrogen concentration at the depth where the nitrogen concentration from nitrides in the oxide film 20 becomes maximum is preferably equal to or greater than the carbon concentration from carbides at the position where the nitrogen concentration from nitrides in the oxide film 20 becomes maximum.

The concentrations of N, C, O and Ti from nitrides, carbides and oxides in the titanium substrate 10 and the oxide film 20 can be calculated by using X-ray photoelectron spectroscopy, and Ar ion sputtering is performed on the surface of the titanium material. Specifically, the analysis conditions are set to X-ray source: mono-AlKα (hν: 1486.6 eV), beam diameter: 200 μmΦ (≈ analysis area), detection depth: a few nm, collection angle: 45°, sputtering conditions: Ar ⁺ , sputtering rate 4.3 nm/min. (SiO ₂ conversion value). The SiO ₂ conversion value refers to the sputtering rate when the SiO ₂ film whose thickness has been measured in advance by an ellipsometer is obtained under the same measurement conditions.

The peak appearing at a binding energy of about 393 to 408 eV is measured as the peak of N1s, and N from organic matter is separated at about 399 to 401 eV and N from nitride at about 397±1 eV. The peak appearing at a binding energy of about 280 to 395 eV is measured as the peak of C1s, and C from organic matter is separated at about 284 to 289 eV and C from carbide at about 281.5±1 eV. The peak appearing at a binding energy of about 525 to 540 eV is measured as the peak of O1s, and O from organic matter is separated at about 399 to 401 eV and O from metal oxide at about 529.5 to 530.5 eV. The peak appearing at a binding energy of 450 to 470 eV is measured as the peak of Ti2p. The binding energies of the above substances are normal values and may vary depending on the charge of the measurement sample, etc. As one of the charge correction methods, a method of performing correction based on the peak position of the C-C bond in C derived from organic matter can be used.

As a conventional analysis method using these peaks, the element concentration and the concentration of each chemical state can be analyzed using the analysis software MultiPak. The conventional steps are described below. The background is corrected based on the Shirley method. Next, the Gauss-Lorents function is used for the compound, and the Asymmetric function is used in the case of metals to fit the peaks of each element according to the chemical state. Then, the area ratio of the peaks from each chemical state is multiplied by the concentration (atomic %) of the element to calculate the concentration (atomic %) of each chemical state. Such steps are used to calculate the nitrogen content from nitrides and the carbon content from carbides. It should be noted that the concentration of the element is calculated in each element detected by XPS, including the (unseparated) peak area of all peaks involved in the element, and it is divided by the sensitivity coefficient of each element as a percentage.

The content of nitrogen derived from nitride in the oxide film 20 has been described in detail above.

(Surface layer 30)

The discoloration resistance of the titanium material 1 is improved by reducing the average nitrogen concentration and the average carbon concentration of the surface portion 30. From the viewpoint of discoloration resistance, the average nitrogen concentration and the average carbon concentration of the surface portion 30 measured along the thickness direction from the surface of the titanium material 1 by GDS of the above method are respectively 14.0 atomic % or less. The average nitrogen concentration of the surface portion 30 of the titanium material 1 is preferably 12.0 atomic % or less, and more preferably 10.0 atomic % or less. The average carbon concentration of the surface portion 30 of the titanium material 1 is preferably 13.0 atomic % or less, more preferably 12.0 atomic % or less, and further preferably 10.0 atomic % or less. The average nitrogen concentration of the surface portion 30 of the titanium material 1 can be 0 atomic % or more than 1.0 atomic %. The average carbon concentration of the surface portion 30 of the titanium material 1 can be 0 atomic % or more than 1.0 atomic %.

The discoloration resistance of the titanium material 1 is further improved by reducing the average hydrogen concentration of the surface portion 30. The hydrogen concentration of the surface portion 30 of the titanium material 1 is 30.0 atomic % or less, preferably 25.0 atomic % or less, and more preferably 20.0 atomic % or less. Titanium is a metal with a high affinity for hydrogen, and the hydrogen concentration of the surface portion 30 may be 10.0 atomic % or more.

(Difference in lattice constant of c-axis of α-phase Ti in surface layer portion 30)

The crystal structure of the α-phase Ti in the surface portion 30 of the titanium material 1 affects the discoloration resistance. Specifically, if the lattice constant of the c-axis of the α-phase Ti in the surface portion 30 of the titanium material 1 increases, the discoloration resistance deteriorates. The increase in the lattice constant of the c-axis of the α-phase Ti in the surface portion 30 of the titanium material 1 is evaluated by the difference between the lattice constant of the c-axis of the α-phase Ti determined at the surface of the titanium material 1 by X-ray diffraction measurement based on the parallel beam method with an incident angle of 0.3 degrees and the lattice constant of the c-axis of the α-phase Ti determined at the center of the plate thickness by X-ray diffraction measurement based on the focusing method. From the viewpoint of discoloration resistance, the increase in the lattice constant of the c-axis of the α-phase Ti in the surface portion 30 of the titanium material 1 is The following are preferably The smaller the increase in the c-axis lattice constant of the α-phase Ti on the surface of the titanium material 1, the better. If the increase is negative, it is due to measurement error and the increase is regarded as

The c-axis lattice constant of the α-phase Ti in the surface layer 30 of the titanium material 1 was determined by X-ray diffraction measurement using the parallel beam method on the surface of the titanium material. In the X-ray diffraction measurement using the parallel beam method, an X-ray diffraction device SmartLab manufactured by Rigaku Corporation was used, and the X-ray source was Co-Kα (wavelength ). In order to remove Kβ rays, a W/Si multilayer mirror is used on the incident side of the X-ray. The X-ray source load power (tube voltage/tube current) is 5.4kW (40kV/135mA). The incident angle of the X-ray on the sample is 0.3 degrees, and the scanning diffraction angle is 2θ. In the measurement, a sample with a size of 25mm (length) × 50mm (width) cut from titanium material by mechanical processing is used. The light beam is irradiated with 12.5mm (length) × 25mm (width) of the sample as the center, and the measurement is carried out on the surface of the sample. It should be noted that the cut sample may have dirt attached to the measured surface, so it is cleaned with acetone and ethanol.

The crystal structure of the α-phase Ti at the center of the titanium plate thickness is measured by X-ray diffraction using a focusing method. The sample used to analyze the crystal structure of the α-phase Ti at the center of the titanium plate thickness is finely processed by mechanical grinding and electrolytic grinding in such a way that the center of the titanium plate thickness becomes the measurement surface for X-ray diffraction measurement. In the X-ray diffraction measurement using the focusing method, the X-ray diffraction device used in the X-ray diffraction measurement using the parallel beam method can be used, and the X-ray source, the Kβ-ray removal filter, and the X-ray source load power can also be the same as the conditions of the above-mentioned parallel beam method. As long as it is in the center of the plate thickness, the crystal structure of Ti is consistent, so the sample can be made from any part of the plate width and rolling direction. Here, the sample was made from approximately one-quarter of the plate width to the center, and the experiment was carried out.

The lattice constant of the c-axis of the α-phase Ti at the surface and the center of the plate thickness of the titanium material was calculated from the diffraction peak of the (0002) plane using software (Xpert Highscore Plus) manufactured by SPECTRIS Co., Ltd. When the titanium substrate is of α+β type, the lattice constant of the c-axis of the α-phase Ti is also calculated from the diffraction peak of the α-phase Ti.

(Ra/RSm: 0.006～0.015)

(RΔq: 0.150～0.280)

Furthermore, the inventors conducted a detailed study on the relationship between the surface properties and discoloration resistance of titanium materials and found that for the discoloration resistance of titanium materials, the ratio of the arithmetic mean roughness Ra of the surface of the titanium substrate to the average width RSm of the profile unit, i.e. Ra/RSm, and the root mean square slope RΔq of the roughness profile unit will affect the discoloration resistance.

The arithmetic mean roughness Ra, the average width RSm of the profile element, and the root mean square slope RΔq of the roughness profile element can be measured by a method in accordance with JIS B 0601: 2013. It should be noted that the kurtosis Rku and skewness Rsk described below can also be measured by a method in accordance with JIS B 0601:2013.

The arithmetic mean roughness Ra of the present embodiment is the arithmetic mean roughness Ra specified 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).

It should be noted that the roughness profile used as the basis for calculating the arithmetic mean roughness Ra is a roughness profile obtained by using a low-frequency filter with a cutoff wavelength λc=0.8mm on the measured cross-sectional curve of the oxide film, and further using a high-frequency filter with a cutoff wavelength λs=2.667μm on the cross-sectional curve. In addition, the reference length of the roughness profile is set to a length equal to the cutoff wavelength λc, that is, 0.8mm. 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 the wavelength component shorter than it.

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 profile.

The average width RSm of the contour unit is calculated according to the following formula (2).

In the above formula (2), m is the number of measurement points, and Xsi is the length of the contour unit on the reference length.

The root mean square slope RΔq of the roughness profile element is calculated according to 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 profile and is defined by the following formula (4).

In the above formula (4), ΔX is the measurement interval. In the present embodiment, the measurement interval ΔX can be determined as follows. That is, the measurement interval ΔX is a value set by the surface roughness shape measuring instrument. When taking N points of numerical data when measuring its measurement length L, the average ΔX is L/(N-1) based on the measurement interval. For example, using Tokyo Seimitsu SURFCOM1900DX and software TIMS Ver.9.0.3, when taking 25601 points of digital display data when measuring a measurement length of 5 mm, ΔX is 5 mm/25600 points, and the average is about 0.195 μm.

The root mean square slope RΔq of the roughness profile unit is a parameter that defines the inclination angle of a micro range formed by surface irregularities with respect to the reference length X of the roughness profile (local slope dZ/dX).

The inventors of the present invention prepared titanium materials with changed Ra/RSm and RΔq, and studied the influence of Ra/RSm and RΔq of the titanium substrate on the discoloration resistance. FIG6 is a graph showing the relationship between Ra/RSm, which is the ratio of the arithmetic mean roughness Ra to the average width RSm of the profile unit of the titanium substrate, and the root mean square slope RΔq of the roughness profile unit, and the discoloration resistance.

As described above, the color change resistance can be evaluated by color difference ΔE ^* ab and appearance observation. However, in the measurement of the color tone L ^* a ^* b ^* used to evaluate the color difference ΔE ^* ab, light is irradiated from a sunlight light source set just above the titanium plate. Therefore, it may be different from the actual appearance. In particular, for titanium plates with large RΔq, even if the color difference ΔE ^* ab is small, it may appear to be discolored in visual observation under sunlight. Therefore, in the evaluation of color change resistance, visual observation under sunlight is also important.

The "0" in Figure 6 indicates that the color difference ΔE ^* ab is less than 5 and the proportion of people who think that the color change is not obvious in the sensory evaluation based on visual observation is more than 80%, and the "×" indicates that the color difference ΔE ^* ab is less than 5 but the proportion of people who think that the color change is not obvious in the sensory evaluation based on visual observation is less than 80%. Here, in the sensory evaluation based on visual observation, the titanium material that has not been used for the previous formal color change accelerated test and the titanium material after the formal color change accelerated test are pre-arranged on a flat plate, and 10 evaluators observe and compare from various angles under sunlight to determine whether there is an angle where the color change is obviously visible. The ratio of people who think that the color change is not obvious is compared. It should be noted that this visual observation assumes the conditions of the roof and walls of the actual building, and it is also an evaluation that assumes that the color tone changes according to the observation angle.

As shown in FIG6 , it was found that the titanium material involved in the present embodiment has excellent discoloration resistance even in a higher temperature and acidic environment when the ratio of the arithmetic mean roughness Ra to the average width RSm of the profile unit, i.e., Ra/RSm, is 0.006 to 0.015 and the root mean square slope RΔq of the roughness profile unit is 0.150 to 0.280. This titanium material having excellent discoloration resistance even in a high temperature and acidic environment can further suppress long-term discoloration.

When Ra/RSm is less than 0.006, the concavoconvexity on the surface of the titanium substrate is small, and the interval between the concavoconvexity is wide. When Ra/RSm is less than 0.006, the surface of the titanium material is relatively smooth, and due to the optical path difference between the light reflected by the surface of the oxide film and the light reflected by the surface of the titanium substrate, the color of the light enhanced according to the optical path difference is sometimes recognized. That is, sometimes the titanium material changes color. It is believed that if Ra/RSm is 0.006-0.015, the optical path difference between the light reflected by the surface of the oxide film and the light reflected by the surface of the titanium substrate becomes smaller due to the larger slope of the titanium material surface, and there is no light enhanced within the range of visible light, so the discoloration is suppressed. Considering the mechanism by which the discoloration is suppressed, although there is no reason to limit the upper limit of Ra/RSm to 0.015, it is difficult to produce deep and narrow valley-shaped concavoconvexities greater than 0.015 in industry. Therefore, the upper limit of Ra/RSm is preferably 0.015, which can clearly obtain the effect of the present invention.

When RΔq is above 0.150, the slope of the finer concavoconvex in the oxide film is large. Due to the local slope, the specular reflection of the light irradiated to the surface of the titanium substrate is suppressed and diffusely reflected. Therefore, the intensity of the reflected light on the surface of the titanium substrate reflected in the direction of the light reflected from the surface of the oxide film decreases. As a result, it is difficult to identify the color of the enhanced light. When RΔq is less than 0.150, the above effect will not occur, so sometimes the titanium material looks discolored. On the other hand, when RΔq is greater than 0.280, although the color difference is as small as less than 5, there is sometimes an angle where the discoloration looks obvious under sunlight. It is believed that this is because when RΔq is greater than 0.280, when the titanium material is viewed from an oblique direction, there is an inclination in the direction of specular reflection, and the interference color is enhanced due to the increase in the thickness of the oxide film, which can be visually identified.

If Ra/RSm is 0.006 to 0.015, and the root mean square slope RΔq of the roughness profile unit is 0.150 to 0.280, the above-mentioned effects can be obtained in an additive manner, so the discoloration of the titanium material is further suppressed. Furthermore, even if the oxide film grows to about tens of nm on the surface of the titanium material having the above-mentioned surface state, the change in hue, i.e., discoloration, is suppressed. Therefore, the titanium substrate preferably has a ratio of the arithmetic mean roughness Ra to the element length RSm, i.e., Ra/RSm, of 0.006 to 0.015 in the roughness profile in the direction in which the arithmetic mean roughness Ra becomes the largest, and the root mean square slope RΔq is 0.150 to 0.280. The lower limit of Ra/RSm is more preferably 0.007. In addition, RΔq is more preferably 0.190 or more. When RΔq is 0.190 to 0.0280, the color difference in the accelerated discoloration test is less than 6, and a higher effect can be obtained.

The arithmetic mean roughness Ra and the average width RSm of the contour unit are as described above, and Ra/RSm is preferably 0.006 to 0.015, but the arithmetic mean roughness Ra is more preferably 0.700 to 3.0 μm, and the average width RSm of the contour unit is more preferably 60 to 300 μm. Setting the arithmetic mean roughness Ra to 0.700 to 3.0 μm and the average width RSm of the contour unit to 60 to 300 μm can be easily achieved industrially by the manufacturing method described below.

[Kurtosis Rku: greater than 3]

Kurtosis Rku is an index indicating the sharpness of the amplitude distribution curve. FIG. 7 is a diagram for explaining the kurtosis Rku. It should be noted that FIG. 7 is a diagram published in Tsutomu Miyashita, "Surface Roughness by One-step Reconstruction", Journal of the Society for Precision Engineering, The Society for Precision Engineering, Vol. 73, No. 2, 2007, p. 205. Kurtosis Rku represents the fourth-power average of Zj on the reference length dimensionless by the fourth power of the root mean square height Rq.

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

Kurtosis Rku is an indicator of the sharpness of the height distribution. When the kurtosis Rku is 3, as shown in Figure 7, the height distribution is a normal distribution. As the kurtosis Rku is less than 3, the value becomes smaller and the surface becomes flatter. As the kurtosis Sku is greater than 3, the value becomes larger and there are more sharp peaks and valleys on the surface of the titanium material.

In the roughness profile in the direction where the arithmetic mean roughness Ra becomes maximum, the kurtosis Rku of the titanium substrate is preferably greater than 3. When the kurtosis Rku is greater than 3, the surface of the titanium substrate has sharp irregularities, and on the surface with sharp irregularities, the component of specular reflection showing interference color in the light reflected from the surface of the titanium substrate is further suppressed. As a result, even if the thickness of the oxide film increases, the interference color does not become more obvious, and the discoloration of the titanium material is further suppressed.

[Skewness Rsk: greater than -0.5]

Skewness Rsk is also called skewness and is an index indicating the sharpness of surface irregularities. Skewness Rsk represents the cubic average of Z(x) on a reference length dimensionless by the cube of the root mean square height Rq, and is expressed by the following equation (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 profile.

In the roughness profile, when the valley length is greater than the peak length, the skewness Rsk becomes greater than 0. In other words, if the skewness Rsk is greater than 0, the ratio of the concave portion in the average line of the roughness profile is high. That is, the peak (convex portion) in the roughness profile has a sharp tip and the valley (concave portion) has a wide tip. The average line of the roughness profile refers to the curve of the long wavelength component blocked by the cutoff wavelength λc.

On the other hand, when the valley length is shorter than the peak length, the skewness Rsk becomes less than 0. In other words, when the skewness Rsk is less than 0, the proportion of the concave portion in the average line of the roughness profile is high. That is, the peak (convex portion) in the roughness profile has a wide front end, and the valley (concave portion) has a sharp end.

When the skewness Rsk is 0, the shapes of the concavities and convexities in the roughness profile are symmetrical with respect to the average plane.

In the roughness profile in the direction where the arithmetic mean roughness Ra becomes the maximum, the skewness Rsk of the titanium substrate is preferably greater than -0.5. When the skewness Rsk is greater than -0.5, the front end of the peak (convex portion) in the roughness profile becomes sharper, and the light reflected from the surface of the titanium substrate is more easily scattered on the side close to the light source, that is, on the peak (convex portion), and the color change is further suppressed. Since the shadow effect caused by the peak (convex portion) makes it difficult to see the interference color that is the cause of the color change, it is estimated that the side far from the light source, that is, the valley (convex portion) is not as affected as the peak (convex portion).

So far, the titanium material involved in the present embodiment has been described. The thickness of the titanium material involved in the present embodiment can be, for example, 0.2 mm or more, or 0.3 mm or more. In addition, the thickness of the titanium material involved in the present embodiment is not particularly limited, for example, it can be 5.0 mm or less, or 3.0 mm or less, or 2.0 mm or less.

In the titanium material according to the present embodiment, the average nitrogen concentration and the average carbon concentration in the range from the surface to the position where the oxygen concentration measured from the surface in the thickness direction by glow discharge spectrometry is 1/3 of the maximum value are respectively 14.0 atomic % or less, and the average hydrogen concentration is 30.0 atomic % or less, and the difference between the lattice constant of the c-axis of Ti in the α-phase determined by X-ray diffraction measurement based on the parallel beam method at an incident angle of 0.3 degrees at the surface and the lattice constant of the c-axis of Ti in the α-phase determined by X-ray diffraction measurement based on the focusing method at the center of the plate thickness is As described below, the titanium material according to the present embodiment can suppress discoloration for a long period of time compared with conventional titanium materials and has excellent discoloration resistance.

In addition, if the maximum value of the nitrogen concentration from the nitride in the oxide film when analyzed by X-ray photoelectron spectroscopy is 2.0 to 10.0 atomic %, the position where the nitrogen concentration from the nitride in the oxide film shows the maximum value exists in the range of 2 to 10 nm from the surface of the oxide film when converted to the sputtering rate of SiO ₂ , the concentration of nitrogen from the nitride present in the titanium substrate near the interface with the oxide film is less than the maximum value of the nitrogen concentration from the nitride in the oxide film and is 7.0 atomic % or less, and the maximum value of the nitrogen concentration from the nitride in the oxide film is greater than or equal to the carbon concentration from the carbide at the position where the nitrogen concentration from the nitride in the oxide film becomes the maximum, then the discoloration resistance is excellent even in a high temperature and acidic environment. Moreover, the titanium material having excellent discoloration resistance even in a high temperature and acidic environment can further suppress long-term discoloration.

(Method for manufacturing titanium material)

An example of a method for manufacturing a titanium material according to the present embodiment is described. However, the titanium material according to the present embodiment is not limited to the titanium material manufactured by the manufacturing method described below. In addition, pure titanium and titanium alloys used in building materials such as exterior materials are mostly in the form of plates, so an example of a method for manufacturing a plate-shaped titanium material is described below.

The titanium material is produced by cold-rolling pure titanium or a titanium alloy as a blank, and then performing annealing and cooling treatments.

The titanium billet for cold rolling can use materials manufactured by known methods. For example, a master alloy for adding sponge titanium and alloying elements is used as a raw material, and various melting methods such as vacuum arc melting, electron beam melting, or plasma melting are used to produce an ingot of pure titanium or titanium alloy having the above composition. Then, the obtained ingot is initially rolled and hot forged into a slab as required. Then, the slab is hot rolled to produce a hot-rolled coil of pure titanium or titanium alloy having the above composition.

It should be noted that the slab may be subjected to pre-treatment such as cleaning and cutting as required. In addition, when the slab is made into a hot-rollable rectangular shape by the hearth melting method, it may be directly subjected to hot rolling without hot forging or the like.

Next, the hot rolled coil is subjected to cold rolling. Lubricating oil is used in cold rolling, but the lubricating oil used sometimes becomes the cause of increasing the carbon concentration on the surface of the titanium material during annealing. Therefore, it is preferred to remove the oil on the surface of the titanium billet by alkali degreasing, rolling with rough rollers, i.e., rough rolling, coil grinder, or grinding before annealing. It should be noted that when lubricating oil is applied to the surface of the titanium billet and cold rolling is performed, the surface of the titanium billet contains carbon due to a mechanochemical reaction. The cold titanium billet subjected to the final annealing treatment can be appropriately pickled and annealed.

The titanium billet after cold rolling or the titanium billet after oil removal treatment is subjected to final annealing. The final annealing is generally a process for reducing the strain introduced into the pure titanium or titanium alloy as the titanium billet by cold rolling, so as to soften the titanium billet. In the manufacture of the titanium material involved in the present embodiment, the final annealing and its subsequent cooling treatment are processes for the purpose of controlling the average nitrogen concentration and average carbon concentration, average hydrogen concentration, lattice constant of the c-axis of Ti of the α-phase in the surface of the titanium material, and thickness of the oxide film. It is believed that by increasing the temperature of the final annealing, the nitrogen and carbon of the surface of the titanium material brought by impurities diffuse in the thickness direction, and the average nitrogen concentration and average carbon concentration of the surface of the titanium material are reduced. It is believed that the average hydrogen concentration of the surface of the titanium material and the lattice constant of the c-axis of Ti of the α-phase in the surface of the titanium material are reduced by increasing the vacuum degree of the final annealing. Therefore, the final annealing is carried out in an inert gas (except nitrogen) atmosphere after forming a vacuum atmosphere or directly in a vacuum. The heating temperature of the final annealing treatment and the atmosphere of the final annealing treatment are described below. Here, the inert gas refers to a gas that is inert to titanium, and refers to argon, helium, or neon.

From the viewpoint of reducing the average nitrogen concentration and the average carbon concentration of the surface layer of the titanium material, the heating temperature (annealing temperature) of the final annealing treatment is 630°C or more. From the viewpoint of reducing the average carbon concentration of the surface layer of the titanium material, the annealing temperature is preferably 650°C or more. The upper limit of the annealing temperature is not particularly set, but from the viewpoint of manufacturing cost, it is preferably 750°C or less. The annealing temperature mentioned here is the temperature in the heating furnace used in the annealing treatment, which is measured using a thermocouple set in the heating furnace. From the viewpoint of reducing the average nitrogen concentration and the average carbon concentration of the surface layer of the titanium material, the annealing time is preferably 5 hours or more. The annealing time is more preferably 10 hours or more. From the perspective of the ability to anneal the titanium material in the cold-rolled state, the annealing time can be 3 hours or more. On the other hand, from the viewpoint of productivity, the annealing time is preferably 48 hours or less. In addition, if the annealing time exceeds 10 hours, there are sometimes disadvantages such as the grain diameter becoming too coarse, resulting in a decrease in tensile strength, and wrinkles caused by processing. Therefore, from the viewpoint of maintaining the tensile strength, the annealing time is preferably 10 hours or less. It should be noted that the annealing time referred to here is the time for maintaining the temperature in the heating furnace having the titanium material therein at the annealing temperature.

The final annealing treatment is carried out in an inert gas atmosphere into which an inert gas other than nitrogen is introduced after forming a vacuum atmosphere, an inert gas atmosphere (except nitrogen) or a vacuum atmosphere. The vacuum degree of the vacuum atmosphere is, for example, 1.0×10 ^{- 2} Pa or less. The inert gas atmosphere is preferably a rare gas atmosphere, more preferably an Ar atmosphere. From the viewpoint of suppressing the increase of the lattice constant of the c-axis of the α-phase Ti in the surface portion of the titanium material and reducing the average hydrogen concentration and the average nitrogen concentration of the surface portion of the titanium material, the vacuum degree before the inert gas atmosphere is formed in the final annealing treatment is preferably 1.0×10 ^-2 Pa or less. From the viewpoint of reducing the average hydrogen concentration of the surface portion of the titanium material, the vacuum degree before the inert gas atmosphere is formed in the final annealing treatment is more preferably 5.0×10 ^-3 Pa or less. In addition, the inert gas atmosphere can be set to an atmosphere containing, for example, 99.99% by volume or more of Ar in the heating furnace. The inert atmosphere can be an atmosphere containing 99.99% by volume or more of He (helium). The inert gas atmosphere may be formed after forming a vacuum atmosphere in the heating furnace before starting heating for the final annealing treatment, or the vacuum atmosphere may be formed in the heating furnace before starting heating and then changed to an inert gas atmosphere during the period from the start of heating to the start of cooling.

The final annealing treatment is performed at the above-mentioned annealing temperature and annealing time in a vacuum atmosphere or an inert gas atmosphere (except nitrogen) in which an inert gas other than nitrogen is introduced after the vacuum atmosphere is formed, so that a state with low oxygen, nitrogen, carbon and hydrogen is formed on the surface of the titanium material. By making the surface of such a titanium material a surface state with high cleanliness in the final annealing treatment, it is opened to the atmosphere, nitrogen atmosphere, and inert gas atmosphere containing more than 10% nitrogen during the subsequent cooling treatment, and a specified amount of nitride can be generated in the oxide film by the nitrogen contained in these atmospheres. For the titanium material that is cooled and then opened to the atmosphere in the final annealing treatment, even if it is heated again in a nitrogen-containing atmosphere, the specified nitride cannot be generated in the oxide film.

The annealing atmosphere is an inert gas with a nitrogen concentration of 0.005 volume % or less. It should be noted that nitrogen accounts for less than half of the impurities in general industrial pure gases, so the atmosphere of the annealing process in this embodiment using the inert gas is sufficiently pure.

The final annealing atmosphere is maintained until the titanium material after annealing has no tempering color, for example, 300° C. or less. The annealing atmosphere can be maintained until it cools to room temperature, or the heating furnace can be opened to the atmosphere at 300° C. or less.

After the final annealing treatment, the titanium billet is cooled. The cooling atmosphere is, for example, the same atmosphere as the annealing atmosphere at the beginning of cooling, and when the temperature in the heating furnace is below 300° C., an atmosphere consisting of nitrogen, a mixed atmosphere of argon or helium containing 10% by volume or more of nitrogen, or air.

There is no particular restriction on the cooling rate after the final annealing treatment. However, below 300°C when open, in order to make the amount of nitrogen from nitrides present in the oxide film within a specified range, it is preferably set to the following conditions. In addition, from the perspective of suppressing the disorder of the shape caused by the thermal shrinkage of the titanium material during cooling, the cooling rate until opening (below 300°C) is preferably 50°C/minute or less, more preferably 30°C/minute or less, and further preferably 1°C/minute when cooling a large titanium material of more than 1 ton.

In the cooling after the final annealing treatment, it is preferred to introduce nitrogen into the heating furnace or open the heating furnace to the atmosphere at the moment when the temperature in the heating furnace becomes a temperature below 300°C, so that a nitrogen atmosphere containing more than 10% by volume of nitrogen is formed in the heating furnace. The amount of nitrogen from nitrides present in the oxide film varies according to the cleanliness of the titanium surface in addition to the temperature and atmosphere. It is believed that this is because trace amounts of carbon, oxygen, hydrogen, and nitrogen present on the surface of the titanium blank compete to react on the surface of the titanium material, but the amount of reaction between nitrogen and titanium varies depending on which reaction occurs first, and the amount of nitride generated also changes accordingly. However, if the temperature when the atmosphere is changed (opened) is below 300°C, the reaction between titanium and nitrogen occurs fully, and the generated nitrides will not be excessive. Therefore, by cooling treatment after annealing, the maximum value of the nitrogen concentration from nitrides present in the oxide film can be 2.0 to 10.0 atomic%. On the other hand, when the temperature when the atmosphere is changed is lower than 200°C, the nitrogen content from nitrides in the oxide film will be less than 2.0 atomic%. This is because the reaction between nitrogen and titanium slows down when the temperature is low. The temperature is preferably 250° C. or higher, and more preferably 280° C. or higher.

After forming a nitrogen atmosphere in the heating furnace, the cooling time until reaching 200° C. is preferably set to 1.5 hours or more, and more preferably to 2.0 hours or more. By setting the cooling time until reaching 200° C. to 1.5 hours or more after forming a nitrogen atmosphere in the heating furnace, the maximum value of the nitrogen concentration derived from the nitride in the oxide film when analyzed by X-ray photoelectron spectroscopy becomes 2.0 to 10.0 atomic %, and the position where the nitrogen concentration derived from the nitride in the oxide film shows the maximum value exists in the range of 2 to 10 nm from the surface of the oxide film when converted to the sputtering rate of SiO ₂ .

It should be noted that even if the titanium material after the cooling treatment is subjected to cold rolling including rolling using a matte roll at a reduction ratio of 5% or less, the characteristics of the titanium material according to the present embodiment can be maintained.

In the manufacturing method of the titanium material involved in the present embodiment, it is preferred to have: a grinding process, using grinding powder with a particle size distribution of a particle size number of #320 or less according to JISR 6001-2:2017 to grind the surface of the titanium billet; and a roughening rolling process, using a roller with a surface roughness Ra of 0.5μm or more, to press the titanium billet in a manner such that the total reduction rate becomes 0.10% or more. The above-mentioned grinding process is implemented before the above-mentioned final annealing treatment, and the above-mentioned roughening rolling process is performed after the above-mentioned final annealing treatment. Through the above-mentioned grinding process and roughening rolling process, the Ra/RSm of the surface of the titanium substrate becomes 0.006 to 0.015, and the root mean square slope RΔq of the roughness profile unit becomes 0.150 to 0.280. The above-mentioned grinding process and roughening rolling process are described below.

[Polishing process]

In this step, the surface of the titanium blank is ground using a grinding fine powder having a particle size distribution of #320 or less according to JIS R 6001-2: 2017. The means for grinding the surface of the titanium blank is not particularly limited, and for example, a known means such as a brush roll and a coil grinder can be used.

For example, when a coil grinder is used, the surface of a coiled titanium blank is ground by the following method. The titanium material is ground using a wire grinder using a grinding belt with a particle size of #320 or less, such as #320, #240, #100, #80, etc. The grinding powder used in the grinding belt is preferably a grinding powder with a particle size of #100 or less. In order to obtain a more uniformly ground surface, sometimes multiple grindings are performed with the same particle size or with different particle sizes.

The titanium blank provided for the grinding process can use materials manufactured by known methods. For example, a master alloy for adding sponge titanium and alloying elements is used as a raw material, and various melting methods such as a hearth melting method such as a vacuum arc melting method, an electron beam melting method or a plasma melting method are used to make an ingot of pure titanium or a titanium alloy having the above-mentioned composition. Then, the obtained ingot is initially rolled and hot-forged into a slab as required. Then, the slab is hot-rolled to form a hot-rolled coil of pure titanium or a titanium alloy having the above-mentioned composition. The hot-rolled coil is cold-rolled, and the cold-rolled titanium blank is subjected to a grinding process. The cold-rolled titanium blank provided for the grinding process can be appropriately annealed.

It should be noted that the slab may be subjected to pre-treatment such as grinding and cutting as required. In addition, when a hot-rollable rectangular shape is produced by a hearth melting method, it may be directly subjected to hot rolling without performing initial rolling, hot forging, etc.

The cold rolling conditions are not particularly limited, and the cold rolling may be carried out under conditions that appropriately obtain desired thickness, characteristics, etc.

[Texturing rolling process]

In this process, a titanium billet is pressed using a rolling work roll (hereinafter referred to as a rolling roll) having a surface arithmetic mean roughness Ra of 0.5 μm or more. By using the above-mentioned rolling roll, the titanium billet is pressed in such a way that the total reduction rate becomes 0.10% or more, and a more locally inclined concavity and convexity is applied to the surface of the titanium billet. When the arithmetic mean roughness Ra of the surface of the rolling roll is too large, the concavity and convexity shape applied in advance by the grinding process may sometimes change significantly, so the arithmetic mean roughness Ra of the surface of the rolling roll is preferably 2.0 μm or less.

The surface roughness of the roll can be adjusted by grinding and shot peening.

In order to apply locally inclined concavoconvexo, the total reduction rate is 0.10% or more, and preferably 0.2% or more in terms of the stability of the surface shaping over the entire length of the coil. On the other hand, in order to prevent the surface roughness formed in the previous grinding process from being destroyed by cold rolling and causing the desired concavoconvex shape to disappear, it is preferably set to 1.5% or less. In addition, in order to obtain the surface characteristics of the present invention, even one pass of cold rolling is sufficient, but considering that the entire length of the long coil is finished into a uniform surface as much as possible, multiple cold rollings of more than 2 passes can be implemented. Taking this into consideration, the total reduction rate is specified, and in the case of multiple passes, the total reduction rate is set to the reduction rate calculated based on the difference between the initial and finished plate thicknesses.

Example

(Example 1)

The titanium blanks shown in Table 1 were cold rolled to a thickness of 0.4 mm, and then degreased using an alkali or organic solvent to remove oil from the surface of the titanium blanks. In this embodiment, JIS1 pure titanium (equivalent to ASTM Gr.1), JIS2 pure titanium (equivalent to ASTM Gr.2), JIS3 pure titanium (equivalent to ASTM Gr.3), JIS4 pure titanium (equivalent to ASTM Gr.4), JIS11 titanium alloy (equivalent to ASTM Gr.11, Ti-0.15Pd), JIS21 titanium alloy (equivalent to ASTM Gr.13, Ti-0.5Ni-0.05Ru), JIS17 titanium alloy (equivalent to ASTM Gr.7, Ti-0.05Pd), Ti-Ru-Mm, Ti-3Al-2.5V, Ti-5Al-1Fe, and JIS60 titanium alloy (equivalent to ASTM Gr.5, Ti-6Al-4V) according to JIS H 4600:2012 were used. Mm in Ti-Ru-Mm represents mixed rare earth metal.

Then, in Examples 1 to 23 of the present invention, each titanium billet was annealed under the conditions shown in Table 1. The open temperature shown in Table 1 is the temperature when the furnace is opened during the cooling process after holding at each annealing temperature for each annealing time. The temperature at this time is the temperature in the furnace measured using a thermocouple.

In Examples 1 to 13, 19 to 23 of the present invention and Comparative Examples 1 to 3, heating was started in the vacuum atmosphere shown in "Vacuum Degree" of Table 1, and 99.99% by volume or more of Ar gas was introduced into the annealing furnace until cooling started. During the cooling process after each titanium billet was kept in the furnace at each annealing temperature for only each annealing time, each annealing atmosphere was maintained until the opening temperature shown in Table 1, and the furnace was opened when the temperature in the furnace dropped to the opening temperature.

In Examples 14 and 15 of the present invention, heating was started in an Ar atmosphere, and the Ar atmosphere was maintained until the furnace was opened.

In Examples 16 to 18 of the present invention, heating was started in the vacuum atmosphere shown in "Degree of Vacuum" in Table 1, and the vacuum degree was maintained until the furnace was opened.

In Comparative Examples 4 and 5, the titanium billets shown in Table 1 were cold rolled to a thickness of 0.4 mm, degreased using an alkali or organic solvent, etc., and then pickled and finished with nitric acid and hydrofluoric acid without final annealing.

[Table 1]

The average nitrogen concentration, average carbon concentration, and average hydrogen concentration of the surface layer were determined by the following method. O, N, C, H, and Ti were analyzed by GDS. The measurement was performed using JOBIN YVON GD-Profiler2 manufactured by Horiba, Ltd. The measurement conditions were set to a constant power mode of 35 W, an argon pressure of 600 Pa, and a discharge range of 4 mm in diameter. In the measurement based on GDS, the measurement interval was 0.5 nm.

The concentrations (atomic %) of the above-mentioned elements are calculated by setting the sum of the above-mentioned elements to 100 atomic %. The range from the surface of the titanium material to the position where the oxygen concentration measured in the thickness direction by GDS is 1/3 of the maximum value is regarded as the surface layer of the titanium material. The average nitrogen concentration, average carbon concentration and average hydrogen concentration are the arithmetic mean values of the nitrogen concentration, carbon concentration and hydrogen concentration at each measurement point.

The lattice constant of the c-axis of the α-phase Ti in the surface of the titanium material is obtained by X-ray diffraction measurement using the parallel beam method. In the X-ray diffraction measurement using the parallel beam method, an X-ray diffraction device SmartLab manufactured by Rigaku Corporation is used, and the X-ray source is Co-Kα (wavelength ). In order to remove Kβ rays, a W/Si multilayer mirror is used on the incident side of the X-ray. The X-ray source load power (tube voltage/tube current) is 5.4kW (40kV/135mA). The incident angle of the X-ray on the sample is 0.3 degrees, and the scanning diffraction angle is 2θ. For the measurement sample, a titanium material with a thickness of 0.4mm is cut into a size of 25mm (length) × 50mm (width) by mechanical processing, and the light beam is irradiated with the center position of the titanium surface, in other words, the position of 12.5mm (length) × 25mm (width) on the surface of the measurement sample as the center, and the measurement is carried out. It should be noted that the cut sample may have dirt attached to the surface to be measured, so it is cleaned with acetone.

The lattice constant of the c-axis of the α-phase Ti at the center of the plate thickness of the titanium material is measured by X-ray diffraction using the focusing method. The sample used to analyze the crystal structure of the α-phase Ti at the center of the plate thickness of the titanium material is finely processed by mechanical grinding and electrolytic grinding in such a way that the center of the plate thickness of the titanium material becomes the measurement surface for X-ray diffraction measurement. In the X-ray diffraction measurement using the focusing method, the X-ray diffraction device used in the X-ray diffraction measurement using the parallel beam method is used, and the X-ray source, the Kβ-ray removal filter, and the X-ray source load power are also the same as the conditions of the above-mentioned parallel beam method.

The lattice constant of the c-axis of the α-phase Ti at the surface and the center of the thickness of the titanium material was calculated from the diffraction peak of the (0002) plane.

The difference in the lattice constant of the c-axis of the α-phase Ti in the surface of the titanium material is obtained from the difference between the lattice constant calculated at the surface of the titanium material and the lattice constant calculated at the center of the plate thickness.

The thickness of the oxide film was determined from the oxygen concentration measured by the GDS method described above. Specifically, the distance in the thickness direction from the surface to the position where the oxygen concentration was reduced to half of the maximum value was taken as the thickness of the oxide film.

The content of nitrogen derived from nitrides contained in the oxide film is measured by the following method: That is, based on the distribution of nitrogen concentration derived from nitrides in the depth direction measured by the following method, the maximum value in the oxide film is taken as the content of nitrogen derived from nitrides contained in the oxide film.

The distribution of the nitrogen concentration from nitrides and the carbon concentration from carbides in the depth direction (film thickness direction) in the oxide film, and the nitrogen concentration from nitrides near the interface with the oxide film in the titanium substrate (20 nm from the interface to the titanium substrate side) are measured by the following method. That is, XPS is used to measure the concentration distribution in the depth direction by Ar ion sputtering on the surface of the titanium material, and the state of each element of each peak position of N1s, C1s, O1s and Ti2p is analyzed to calculate the concentration of N, C, O and Ti from nitrides, carbides and oxides. The details are calculated according to the above steps. The analysis conditions of XPS are as follows.

Device: Quantera SXM manufactured by ULVAC-PHI

X-ray source: mono-AlKα (hν: 1486.6eV)

Beam diameter: 200μmΦ(≈Analysis area)

Detection depth: a few nm

Collection angle: 45°

Sputtering conditions: Ar ⁺ , sputtering rate 4.3 nm/min. (SiO ₂ conversion value)

The SiO ₂ conversion value refers to the sputtering rate obtained under the same measurement conditions using a SiO ₂ film whose thickness has been measured in advance using an ellipsometer.

The surface roughness parameters of the manufactured titanium material (arithmetic mean roughness Ra, average width of profile element RSm, root mean square slope RΔq of roughness profile element, kurtosis Rku, skewness Rsk) were measured under the following conditions in accordance with JIS B 0601:2013.

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 straight line correction

Measuring distance: 5.0mm

Cut-off wavelength λc: 0.8mm

Measuring range: ±64.0μm

Measuring speed: 0.3mm/sec

Moving/returning speed: 0.6mm/sec

Return setting: Normal measurement

Pre-drive length: (cut-off wavelength/3)×2

Measurement interval Δx: 0.195 μm

λs cutoff ratio: 300

λs cut-off wavelength: 2.667μm

Pickup type: Standard pickup

Polarity: Forward

The measurement position is to measure 3 points in the direction where Ra becomes the maximum, and find the average value. Here, the direction where Ra becomes the maximum is when the titanium material is a plate, and the direction parallel to the rolling direction is taken as 0°, and the roughness is measured in 4 directions of 22.5°, 45°, and 90° (direction perpendicular to the rolling direction) to determine the direction where Ra becomes the maximum. In the case where a titanium material is made by rolling a titanium billet with a rolling roller, or when a roller embedded with abrasive grains is rotated along the rolling direction to grind the plate surface, Ra becomes the maximum in the direction perpendicular to the rolling direction, that is, the 90° direction.

The manufactured titanium material was immersed in a sulfuric acid aqueous solution at pH 3 and 60°C for 4 weeks, and the color difference before and after the immersion was calculated. Based on the color difference value, the color resistance was evaluated. The color difference ΔE of 0 or more and 5 or less was considered to be extremely good (A) for color resistance, greater than 5 and less than 10 for good (B) for color resistance, and greater than 10 for poor (C). It should be noted that the color difference ΔE before and after the test was calculated by the following formula.

ΔE＝((L ^* 2-L ^* 1) ²⁺ (a ^* 2-a ^* 1) ²⁺ (b ^* 2-b ^* 1) ² )1/2

Here, L*1, a*1, and b*1 are the measurement results of color before the color change test, and L ^* 2, a ^* 2, and b ^* 2 are the measurement results of color after the color change test, which are based on the L ^* a ^* b ^* colorimetric method specified in JIS Z 8729.

The color difference was measured using CR400 manufactured by Konica Minolta, Inc., with the diameter of the measurement area being 8 mm and a light source of D65.

In addition, each titanium material manufactured was subjected to sensory evaluation based on visual observation. The evaluation based on visual observation is to arrange the titanium materials that have not been subjected to the formal accelerated discoloration test and the titanium materials after the formal accelerated discoloration test on a flat plate in advance, and 10 evaluators observe and compare them from various angles under sunlight to determine whether there is an angle where the discoloration is obviously visible. The case where 90% or more of the 10 evaluators judge that the discoloration is not obvious is A+++, the case where 80% or more and less than 90% of the 10 evaluators judge that the discoloration is not obvious is A++, the case where 70% or more and less than 80% of the 10 evaluators judge that the discoloration is not obvious is A+, the case where 50% or more and less than 70% of the 10 evaluators judge that the discoloration is not obvious is A0, the case where 30% or more and less than 50% of the 10 evaluators judge that the discoloration is not obvious is B, the case where less than 30% of the 10 evaluators judge that the discoloration is not obvious is C, and the case evaluated as C is unqualified. It should be noted that this visual observation assumes the conditions of the roof and walls of an actual building and is also an evaluation that assumes that the color tone changes depending on the observation angle.

The results are shown in Tables 2 and 3. The underlined elements in Tables 2 and 3 are outside the scope of the present invention.

[Table 2]

[Table 3]

In Examples 1 to 23 of the present invention, the average nitrogen concentration and the average carbon concentration in the surface layer were both 14.0 atomic % or less, the average hydrogen concentration was 30.0 atomic % or less, and the difference in the lattice constant of the c-axis of the α-phase Ti between the surface of the titanium material and the center of the plate thickness was Hereinafter, the color difference evaluation results thereof were B or higher, and the sensory evaluation results based on visual observation were B or higher.

In Comparative Example 1, the vacuum degree during annealing was as low as 1.0×10 ^-1 Pa, so the average nitrogen concentration in the surface layer was high. As a result, the titanium material of Comparative Example 1 was unacceptable in both the color difference evaluation results and the sensory evaluation results based on visual observation.

In Comparative Example 2, the annealing temperature was low and the average carbon concentration of the surface layer was high. As a result, the color difference evaluation results and the sensory evaluation results based on visual observation of the titanium material of Comparative Example 2 were both unacceptable.

In Comparative Example 3, the vacuum degree during annealing was as low as 8.0×10 ^-2 Pa, so it is estimated that the oxygen concentration in the surface layer of the titanium material increased, the lattice constant of the c-axis of the α-phase Ti in the surface layer increased, and the difference in lattice constants increased. As a result, the color difference evaluation results and the sensory evaluation results based on visual observation of the titanium material of Comparative Example 3 were both unacceptable.

In Comparative Examples 4 and 5, the average hydrogen concentration in the surface layer was high, and the titanium material of Comparative Example 3 was unacceptable in both the color difference evaluation result and the sensory evaluation result based on visual observation.

As shown above, the titanium material according to the present embodiment has excellent color change resistance for a long time even in a sulfuric acid aqueous solution of pH 3 simulating severe acid rain. It can be said that the present invention is particularly effective in outdoor applications such as roofs or wallboards, and its industrial value is extremely high.

(Example 2)

After the titanium billets shown in Table 4 were cold rolled to a thickness of 0.4 mm, they were degreased using an alkali or organic solvent to remove the oil on the surface of the titanium billets. Then, each titanium billet was annealed under the conditions shown in Table 4. The open temperature shown in Table 4 is the temperature when the furnace is opened during the cooling process after each annealing time is maintained at each annealing temperature. The temperature at this time is the temperature in the furnace measured using a thermocouple.

[Table 4]

The same evaluation as in Example 1 was performed on each of the produced titanium materials. The results are shown in Tables 5 and 6.

[Table 5]

[Table 6]

As shown in Tables 5 and 6, in Examples 24 to 39 of the present invention, the maximum value of the nitrogen concentration from nitrides in the oxide film when analyzed by X-ray photoelectron spectroscopy was 2.0 to 10.0 atomic %, the position where the nitrogen concentration from nitrides in the oxide film showed the maximum value existed in the range of 2 to 10 nm from the surface of the oxide film when converted to the sputtering rate of SiO ₂ , the concentration of nitrogen from nitrides in the titanium substrate near the interface with the oxide film was less than the maximum value of the nitrogen concentration from nitrides in the oxide film and was 7 atomic % or less, and the maximum value of the nitrogen concentration from nitrides in the oxide film was equal to or greater than the carbon concentration from carbides at the position where the nitrogen concentration from nitrides in the oxide film became the maximum. The color difference evaluation results were A, and the sensory evaluation results based on visual observation were all A++, and the color change resistance was excellent.

(Example 3)

The titanium billets shown in Table 7 were cold rolled to a thickness of 0.4 mm, and then subjected to a grinding process, cleaning, annealing, and roughing rolling process in sequence under the conditions shown in Tables 7 and 8. The "number of grinding passes" shown in Table 7 refers to the number of times the titanium billets were passed through the production line of the coil grinding machine composed of three grinding machine racks equipped with grinding belts.

In Examples 40 to 72 of the present invention, each titanium billet was subjected to final annealing treatment under the conditions shown in Table 8. The open temperature shown in Table 8 is the temperature when the furnace is opened during the cooling process after holding at each annealing temperature for each annealing time. The temperature at this time is the temperature in the furnace measured using a thermocouple.

In Examples 40 to 61 and 63 to 72 of the present invention, heating was started in a vacuum atmosphere shown in "Vacuum Degree" of Table 8, and 99.99% by volume or more of Ar gas was introduced into the annealing furnace until cooling started. During the cooling process after each titanium billet was kept in the furnace at each annealing temperature for only each annealing time, each annealing atmosphere was maintained until the opening temperature shown in Table 8, and the furnace was opened when the temperature in the furnace dropped to the opening temperature.

In Example 62 of the present invention, heating was started in the vacuum atmosphere shown in the "vacuum degree" in Table 8, and the vacuum degree was maintained until the furnace was opened.

In Comparative Example 6, the titanium billet was cold-rolled to a thickness of 0.4 mm, degreased using an alkali or organic solvent, etc., and then pickled and finished with nitric acid and hydrofluoric acid without final annealing.

[Table 7]

[Table 8]

The produced titanium materials were evaluated in the same manner as in Example 1. The results are shown in Tables 9 and 10. The underlined elements in Table 9 are outside the scope of the present invention.

[Table 9]

[Table 10]

As shown in Tables 7 to 10, it can be seen that as long as the heat treatment temperature, time, heat treatment atmosphere, and cooling atmosphere are controlled, in the roughness profile in the direction where the arithmetic mean roughness Ra becomes the maximum, the ratio of the arithmetic mean roughness Ra to the element length RSm, i.e., Ra/RSm, can be made 0.006 to 0.015, and the root mean square slope RΔq is 0.150 to 0.280, the peak Rku of the titanium substrate is greater than 3, and the skewness Rsk of the titanium substrate is greater than -0.5, and the evaluation results are more excellent. In particular, in Examples 59 to 61 of the present invention, the average nitrogen concentration and the average carbon concentration of the surface layer are both less than 14.0 atomic %, the average hydrogen concentration is less than 30.0 atomic %, and the difference in the lattice constant of the c-axis of the α-phase Ti at the surface of the titanium material and the center of the plate thickness is Hereinafter, the maximum value of the nitrogen concentration from nitrides in the oxide film when analyzed by X-ray photoelectron spectroscopy is 2.0 to 10.0 atomic %, the position where the nitrogen concentration from nitrides in the oxide film shows the maximum value exists in the range of 2 to 10 nm from the surface of the oxide film when converted to the sputtering rate of SiO ₂ , the concentration of nitrogen from nitrides in the titanium substrate near the interface with the oxide film is less than the maximum value of the nitrogen concentration from nitrides in the oxide film and is 7 atomic % or less, and the maximum value of the nitrogen concentration from nitrides in the oxide film is equal to or greater than the carbon concentration from carbides at the position where the nitrogen concentration from nitrides in the oxide film becomes the maximum. As a result, the color difference evaluation results of these are A, and the sensory evaluation results based on visual observation are A+++, and the color change resistance is extremely excellent.

Description of Reference Numerals

1 Titanium

10 Titanium substrate

20 Oxide coating

30 Surface

Claims (5)

1. A titanium material having an average nitrogen concentration and an average carbon concentration of 14.0 at% or less and an average hydrogen concentration of 30.0 at% or less, respectively, in a range from a surface to a position at which an oxygen concentration measured from the surface in a thickness direction is 1/3 of a maximum value by glow discharge spectrometry,

The difference between the lattice constant of the c-axis of the alpha-phase Ti obtained by the X-ray diffraction measurement by the parallel beam method with an incident angle of 0.3 degrees at the surface and the lattice constant of the c-axis of the alpha-phase Ti obtained by the X-ray diffraction measurement by the focusing method at the center of the plate thickness isthe following

2. The titanium material according to claim 1, which comprises an oxide film having a thickness of 30.0nm or less.

3. The titanium material according to claim 1 or 2, which has:

Titanium substrate

An oxide film disposed on the surface of the titanium substrate,

When the analysis is performed by X-ray photoelectron spectroscopy,

The maximum value of the nitrogen concentration from the nitride in the oxide film is 2.0 to 10.0 at%,

The position of the oxide film where the nitrogen concentration from the nitride shows the maximum value is present in a range of 2 to 10nm from the surface of the oxide film when converted at the sputtering rate of SiO ₂,

The concentration of nitrogen from the nitride existing in the range from the position where the oxygen concentration becomes 1/2 of the maximum value to the 20nm on the titanium substrate side is less than the maximum value of the nitrogen concentration from the nitride in the oxide film and 7 at% or less,

The maximum value of the nitrogen concentration from the nitride in the oxide film is larger than or equal to the carbon concentration from the carbide at the position where the nitrogen concentration from the nitride in the oxide film becomes maximum.

4. The titanium material according to claim 1 or 2, comprising a titanium substrate having a roughness profile in a direction in which an arithmetic average roughness Ra is maximum, wherein a ratio of the arithmetic average roughness Ra to a component length RSm, that is, ra/RSm, is 0.006 to 0.015, and a root mean square slope RΔq is 0.150 to 0.280,

The kurtosis Rku of the titanium substrate is greater than 3,

The skewness Rsk of the titanium substrate is greater than-0.5.

5. The titanium material according to claim 3, wherein the titanium base material has a ratio of the arithmetic average roughness Ra to the element length RSm, that is, ra/RSm, of 0.006 to 0.015 and a root mean square slope RΔq of 0.150 to 0.280 in a roughness profile in a direction in which the arithmetic average roughness Ra is maximum,

The kurtosis Rku of the titanium substrate is greater than 3,

The skewness Rsk of the titanium substrate is greater than-0.5.