Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/10—Alloys containing non-metals
  • C22C1/1026—Alloys containing non-metals starting from a solution or a suspension of (a) compound(s) of at least one of the alloy constituents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C14/00—Alloys based on titanium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
  • C22F1/18—High-melting or refractory metals or alloys based thereon
  • C22F1/183—High-melting or refractory metals or alloys based thereon of titanium or alloys based thereon
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/34—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/82—After-treatment

Definitions

• the present invention relates to a titanium material and a method for manufacturing a titanium material.
• Priority is claimed on Japanese Patent Application No. 2020-155144, filed in Japan on Sep. 16, 2020, the content of which is incorporated herein by reference.
• Titanium materials that are used as building materials for walls, roofs or the like of buildings are roughly classified into non-colored materials exhibiting silvery color that is the color of titanium itself and colored materials that are given an oxide film having a certain thickness on the surface by anode oxidation, thereby exhibiting interference color such as red or blue and having designability.
• titanium materials are also in use as a building material in seaside areas where salt adheres to titanium materials. Twenty years or more have passed since titanium materials began to be used as building materials, but there have been thus far no reports of corrosion that is considered as a problem. Both non-colored materials and colored materials exhibit excellent corrosion resistance.
• discoloration occurs when both non-colored materials and colored materials are exposed to the atmosphere or the like for a long period of time. It has been clarified that this discoloration is interference color that is generated by an increase in the thickness of an oxide film on the surface of a titanium material up to approximately several tens of nanometers due to an acidic environment with a pH of 4.5 or less, for example, acid rain or the like. Such an oxide film having a thickness of several tens of nanometers does not impair the corrosion resistance of titanium.
• Patent Document 1 discloses a titanium material that is less likely to discolor in the atmospheric environment, in which the average carbon concentration in a range from the outermost surface to a depth of 100 nm is 14 atom% or less, and an oxide film having a thickness of 12 to 40 nm is present on the outermost surface.
• Patent Document 2 discloses a titanium material that is less likely to discolor, in which the fluorine content in an oxide film on the surface is 7 atom% or less.
• Patent Document 3 discloses a titanium material that is less likely to discolor in the atmospheric environment, in which, in an oxide membrane formed on the titanium surface, in the oxide membrane that is present in a 3 nm range from the titanium surface, in a case where the composition of titanium oxide is indicated by TiOx, x is within a range of 0.8 to 1.8, and the density of the oxide membrane is 4.2 g/cm3 or more.
• the titanium material disclosed in Patent Document 3 is manufactured by a method or the like in which a titanium surface is treated with a mixed solution of nitric acid and hydrofluoric acid and then treated with a nitric acid solution.
• Patent Document 4 discloses a pure titanium material for building materials that is used as a building material, in which, as impurity elements, Fe is suppressed to 0.08 mass% or less, Nb is suppressed to 0.02 mass% or less, and Co is suppressed to 0.02 mass% or less.
• the titanium material disclosed in Patent Document 4 is manufactured by carrying out heating for a predetermined time at 130° C. to 280° C. in the atmosphere or in a vacuum following pickling in the final step.
• Non-colored materials are required to have high weather resistance by which interference color is not generated. Furthermore, in recent years, there has been a demand for a titanium material that is less likely to discolor in spite of an increase in temperature due to changes in the atmospheric environment and even in an acidic environment having a pH of 3.0 or less, which is even more severe than what has been described above.
• Patent Documents 1 to 4 weather resistance is evaluated as described below.
• the titanium material is immersed in a sulfuric acid aqueous solution having a pH of 3 to 4 at 60° C. for several days, and the weather resistance is evaluated with the color difference before and after the immersion.
• the color difference is 3 to 7 when the titanium material is immersed in a sulfuric acid aqueous solution having a pH of 3 at 60° C. for 7 days or 14 days and the color difference is less than 5, furthermore, less than 1 when the titanium material is immersed in a sulfuric acid aqueous solution having a pH of 4 at 60° C. for 3 days.
• the present invention has been made in view of the above problems, and an object of the present invention is to provide a titanium material having excellent weather resistance and a method for efficiently manufacturing the titanium material.
• the present inventors found that, in a case where a specific element is contained in the surface oxide films, the weather resistance is excellent.
• the present inventors found that the element content of the surface oxide film can be controlled by a cleaning step in which nitric hydrofluoric acid is used.
• weather resistance in acidic environments can be obtained by carrying out the above-described cleaning step in the final step.
• the present inventors carried out additional studies based on the obtained knowledge and consequently attained the present invention.
• the gist of the present invention completed based on the above-described findings is as described below.
• a titanium material according to one aspect of the present invention in which, when a chemical composition of a surface is analyzed by X-ray photoelectron spectroscopy, the titanium material contains, as a composition of the surface, Zn:0.1 atom% or more and Ca: 0.5 atom% or more, and the titanium material contains, as a composition of a surface oxide film, C: 20.0 atom% or less and F: 5.0 atom% or less.
• the surface oxide film may have a thickness of 5 to 20 nm.
• a method for manufacturing a titanium material according to another aspect of the present invention having a cleaning step of cleaning a titanium raw material, in which the cleaning step includes an immersion treatment of immersing the titanium raw material in an aqueous solution having a temperature of 40° C. to 60° C. for 1.0 minutes or longer, where the aqueous solution contains a zinc salt: 0.00030 to 0.65000 mass% in terms of Zn, a calcium salt: 0.00060 to 0.40000 mass% in terms of Ca, HF: 1.0 to 6.0 mass%, and HNO 3 : 4.0 to 10.0 mass% and a water washing treatment of washing the titanium raw material lifted from the aqueous solution with water.
• the cleaning step includes an immersion treatment of immersing the titanium raw material in an aqueous solution having a temperature of 40° C. to 60° C. for 1.0 minutes or longer, where the aqueous solution contains a zinc salt: 0.00030 to 0.65000 mass% in terms of Zn, a calcium salt: 0.00060 to 0.40000
• the zinc salt may be 0.00030 to 0.00100 mass% in terms of Zn
• the calcium salt may be 0.00060 to 0.00108 mass% in terms of Ca.
• the zinc salt may be ZnCl 2 .
• the calcium salt may be CaCl 2 .
• the calcium salt may be CaCl 2 .
• the method for manufacturing a titanium material according to [3] or [4] may further have a heating step of heating the titanium raw material after the cleaning step to 300° C. to 900° C. in an inert atmosphere.
• the method for manufacturing a titanium material according to [5] may further have a heating step of heating the titanium raw material after the cleaning step to 300° C. to 900° C. in an inert atmosphere.
• the method for manufacturing a titanium material according to [6] may further have a heating step of heating the titanium raw material after the cleaning step to 300° C. to 900° C. in an inert atmosphere.
• the method for manufacturing a titanium material according to [7] may further have a heating step of heating the titanium raw material after the cleaning step to 300° C. to 900° C. in an inert atmosphere.
• Numerical limiting ranges expressed below using “to” include the lower limit and the upper limit in the ranges. Numerical values expressed with “more than” and “less than” are not included in numerical ranges.
• a titanium material according to the present embodiment includes a titanium bulk material (titanium substrate) and a surface oxide film disposed on the surface of the titanium bulk material.
• the titanium material according to the present embodiment will be described in detail below.
• the titanium bulk material in the titanium material of the present embodiment is made of any of pure titanium or a titanium alloy.
• the titanium bulk material is, for example, pure titanium or a titanium alloy having a Ti content of 70 mass% or more.
• Examples of the pure titanium include commercially pure titanium defined by Classes 1 to 4 of JIS standards and Grades 1 to 4 of ASTM standards, which correspond to Classes 1 to 4 of JIS standards. That is, commercially pure titanium that is a subject of the present embodiment contains, by mass%, C: 0.1% or less, H: 0.015% or less, O: 0.4% or less, N: 0.07% or less, Fe: 0.5% or less, and a remainder including Ti and impurities.
• commercially pure titanium defined by JIS Class 1 or ASTM Gr. 1, which is equivalent to JIS Class 1, or equivalent materials thereof are mainly used.
• titanium alloy examples include ⁇ -type titanium alloys, ⁇ + ⁇ -type titanium alloys, and ⁇ -type titanium alloys.
• Examples of the ⁇ -type titanium alloys include highly corrosion-resistant alloys (titanium alloys defined by Classes 11 to 13, 17, and 19 to 22 of JIS standards and Grades 7, 11, 13, 14, 17, 30, and 31 of ASTM standards or titanium alloys further containing a small amount of a variety of elements), Ti-0.5Cu, Ti-1.0Cu, Ti-1.0Cu-0.5Nb, Ti-1.0Cu-1.0Sn-0.3Si-0.25Nb, Ti-0.05 to 0.2Pd, and the like.
• highly corrosion-resistant alloys titanium alloys defined by Classes 11 to 13, 17, and 19 to 22 of JIS standards and Grades 7, 11, 13, 14, 17, 30, and 31 of ASTM standards or titanium alloys further containing a small amount of a variety of elements
• Examples of the a+ ⁇ type titanium alloys include Ti-3Al-2.5V, Ti-5Al-1Fe, Ti-6Al-4V, and the like.
• Examples of the ⁇ -type titanium alloys include Ti-11.5Mo-6Zr-4.5Sn, Ti-8V-3Al-6Cr-4Mo-4Zr, Ti-13V-11Cr-3Al, Ti-15V-3Al-3Cr-3Sn, Ti-20V-4Al-1Sn, Ti-22V-4Al, and the like.
• the composition of the surface of the titanium material when the chemical composition of the surface of the titanium material is analyzed by X-ray photoelectron spectroscopy, the composition of the surface is Zn: 0.1 atom% or more and Ca: 0.5 atom% or more, and the titanium material contains, as the composition of a surface oxide film, C: 20.0 atom% or less and F: 5.0 atom% or less.
• the Zn content on the surface is 0.1 atom% or more, and the Ca content is 0.5 atom% or more.
• Zn and Ca on the surface of the titanium material improve the weather resistance of the titanium material.
• the mechanism is not necessarily clear, but the present inventors assume that the improvement is attributed to any or a plurality of the inhibitor effect, oxygen deficiency repair effect, and bipolar film effect of Zn and Ca.
• the inhibitor effect is an effect of suppressing the growth of a surface oxide film by Zn and Ca on the surface of the titanium material preferentially dissolving in an acid rain environment to suppress the dissolution of titanium.
• the oxygen deficiency repair effect is an effect of suppressing the growth of the surface oxide film by the fact that the Ti 4+ sites in TiO 2 that configures the surface oxide film are doped with Zn 2+ and Ca 2+ , whereby oxygen deficiencies are repaired and, consequently, the elution of titanium is suppressed.
• the bipolar film effect is an effect of suppressing the growth of the surface oxide film by the fact that oxides (ZnO and CaO) having different semiconducting properties from TiO 2 are precipitated, and the migration of electrons from an acidic solution adhering to the surface of the surface oxide film is hindered.
• the weather resistance of the titanium material improves due to any or a plurality of the above-described effects.
• the Zn content is preferably 0.1 atom% or more or 0.2 atom% or more and more preferably 0.3 atom% or more.
• the Ca content is preferably 0.5 atom% or more or 0.6 atom% or more and more preferably 0.7 atom% or more.
• the Zn content is 1.0 atom% or less and the Ca content is 1.5 atom% or less, when the Zn content and the Ca content become higher than these values, the above-described effects tend to be saturated.
• the Zn content is more preferably 0.9 atom% or less.
• the Ca content is more preferably 1.4 atom% or less and still more preferably 1.3 atom% or less.
• the C content and the F content in the surface oxide film are 20.0 atom% or less and 5.0 atom% or less.
• discoloration is likely to occur. This is because the surface oxide film grows due to the fact that carbon, fluorine, or a compound thereof degrades the action of the surface oxide film that suppresses the elution of the titanium substrate, which makes it easy for titanium to be eluted or the fact that carbon or fluorine is present as a compound with titanium in the surface oxide film and the compound is likely to dissolve.
• carbon and fluorine in the surface oxide film may be present independently or may be present as a compound with titanium, hydrogen, oxygen, or the like.
• the C content is 20.0 atom% or less and the F content is 5.0 atom% or less, the elution of titanium and the growth of the surface oxide film in the titanium material are suppressed.
• the C content is preferably 18.0 atom% or less, 15.0 atom% or less, or 6.0 atom% or less.
• the F content is 4.9 atom% or less, 4.8 atom% or less, 4.5 atom% or less, or 4.0 atom% or less.
• the C content and the F content of the surface oxide film are as small as possible; however, substantially, the C content is 0.5 atom% or more, and the F content is 1.0 atom% or more in terms of production.
• C atoms are more preferably 1.0 atom% or more.
• the F content is more preferably 2.0 atom% or more.
• the thickness of the surface oxide film can be set to, for example, 100 nm or less and is more preferably 80 nm or less and still more preferably 5 nm or more and 20 nm or less. When the thickness of the surface oxide film is 20 nm or less, it is possible to suppress the generation of interference color by the surface oxide film.
• the thickness of the surface oxide film is more preferably 18 nm or less and still more preferably 12 nm or less.
• the thickness of the surface oxide film is preferably 5 nm or more.
• the thickness of the surface oxide film is 5 nm or more, the elution of Ti that is contained in the titanium material is suppressed, and higher weather resistance can be obtained.
• the thickness of the surface oxide film is more preferably 6 nm or more.
• the thickness of the surface oxide film refers to a range from the surface of the surface oxide film to a position where the oxygen concentration becomes the intermediate concentration between the maximum concentration and the base concentration.
• the base concentration refers to the average oxygen concentration in a range where the oxygen concentration curve becomes flat in a range where the oxygen concentration is 5 atom% or less after XPS analysis is carried out in the depth direction from the surface of the titanium material while carrying out sputtering.
• “Flat” mentioned herein refers to a place where the absolute value of the slope of an approximated straight line is 0.002 or less in an arbitrary depth range including a maximum of 5 or more quantitative values of the oxygen concentration that are measured by XPS analysis to be described below. The formula of the approximated straight line is calculated by the least-square method.
• the Zn content, the Ca content, the F content and the C content of the surface oxide film, and the thickness of the surface oxide film can be obtained from the composition distribution in the depth direction from the surface obtained by XPS carried out on the titanium material that has been immersed in acetone and cleaned with ultrasonic waves.
• the ultrasonic cleaning time may be, for example, 30 seconds or longer.
• the Zn content and the Ca content mentioned herein refer to the contents of the individual elements within a range from the surface of a sample to a depth of 8 nm or less in a state where sputtering is not carried out.
• As the composition analysis in the depth direction quantitative analysis of each element is carried out every 2 nm of sputtering depth in terms of SiO 2 , and the F content, the C content, and the O content are obtained from the surface of the titanium material to a depth at which the oxygen concentration reaches the base concentration.
• the thickness of the surface oxide film is a value obtained by multiplying the sputtering rate in terms of SiO 2 by the sputtering time, and the sputtering time is obtained at a position where the O content is halved with respect to the maximum value after XPS analysis is carried out until a depth where a baseline where the oxygen concentration curve becomes flat in a range where the oxygen concentration is 5 atom% or less.
• the sputtering rate in terms of SiO 2 is the sputtering rate obtained under the same measurement conditions using a SiO 2 film the thickness of which has been measured in advance using an ellipsometer.
• the baseline can be obtained by carrying out analysis from the surface to a position of 50 nm, but there are cases where the baseline can be obtained by carrying out analysis from the surface to a position of 100 nm depending on the surface state of the titanium material.
• the maximum fluorine concentration in the surface oxide film measured by the above-described method is regarded as the F content in the surface oxide film.
• the maximum value of the carbon concentration at the depth where the oxygen concentration is maximized or deeper is regarded as the C content.
• the shape of the titanium material according to the present embodiment is not particularly limited and is a plate, a coil, a strip, or the like. Hitherto, the titanium material according to the present embodiment has been described.
• a pickled surface such as nitric hydrofluoric acid pickling, for which nitric hydrofluoric acid is used, is an exemplary example. It is considered that pickling forms fine irregularities on the surface of titanium, these fine irregularities cause irregular reflection, and the whiteness of the titanium material increases.
• the titanium material having a pickled surface discolors. This is considered to be because an oxide film that is formed after pickling includes a large number of oxygen deficiencies and thus the elution of Ti ions in the atmospheric environment cannot be prevented.
• the present inventors found that a titanium material satisfying both weather resistance in acidic environments and whiteness can be provided by carrying out a cleaning step including the immersion treatment using nitric hydrofluoric acid in the final step.
• the titanium material preferably has a whiteness L * of 70 or higher on the surface. This makes it possible to satisfy both weather resistance and high whiteness, which is desirable from the viewpoint of designability.
• L * is preferably 90 or lower. L * is more preferably 80 or lower. A cleaning step to be described below makes it easy to achieve this whiteness.
• the whiteness is measured by, for example, the following method. That is, L * is measured in accordance with JIS Z 8730:2009 with a light source C using a color difference meter CR-200b manufactured by Konica Minolta Japan Inc., and the whiteness is evaluated.
• a cleaning step is carried out as the final step in the manufacturing step of the titanium material.
• an ingot step, a hot rolling step, a cold rolling step, an annealing step, and a temper rolling/stretch straightening step are sequentially carried out, and then a cleaning step is carried out.
• the cleaning step is carried out after the annealing step in a case where the temper rolling/stretch straightening step is skipped.
• sponge titanium, a mother alloy for adding an alloying element, or the like is used as a raw material, and an ingot of pure titanium or a titanium alloy having the above-described components is produced by a variety of melting methods such as hearth melting methods such as a vacuum arc melting method, an electron beam melting method, and a plasma melting method.
• hearth melting methods such as a vacuum arc melting method, an electron beam melting method, and a plasma melting method.
• the obtained ingot is bloomed and hot-forged as necessary to produce an ingot.
• the ingot may be heated to 600° C. to 850° C. and rolled at a temperature of the transformation point or lower.
• the rolling reduction may be determined depending on the properties of a final product.
• the heating temperature is preferably 700° C. to 850° C.
• the heating temperature is preferably 700° C. or higher from the viewpoint of deformation resistance.
• the heating temperature is preferably 850° C. or lower since the thickness of an oxide film on the titanium raw material after hot rolling can be reduced and it becomes possible to carry out descaling after hot rolling under mild conditions.
• the titanium raw material after the hot rolling needs to be rolled under conditions where desired thickness or properties can be obtained.
• the titanium raw material may be annealed between the cold rolling passes.
• this titanium raw material may be annealed in an inert atmosphere after removing impurities such as a lubricating oil adhering in the cold rolling step in an alkali cleaning line.
• impurities such as a lubricating oil adhering in the cold rolling step in an alkali cleaning line.
• atmospheric annealing, salt bath descaling, and pickling may be sequentially carried out on the titanium raw material after the cold rolling step.
• the temper rolling/stretch straightening step may be appropriately carried out for the purpose of, for example, straightening the shape of the titanium raw material after the annealing step.
• the aqueous solution that is used in the immersion treatment contains 0.00030 to 0.65000 mass% of a zinc salt in terms of Zn.
• the zinc salt include ZnCl 2 , ZnSO 4 , Zn(NO 3 ) 2 , Zn 3 (PO 4 ) 2 , and ZnCO 3 .
• ZnCl 2 is preferable since the solubility in water is the highest.
• the zinc salt content is 0.00030 to 0.65000 mass% in terms of Zn.
• zinc salt content is less than 0.00030 mass% in terms of Zn, zinc oxide is not formed on the surface of the titanium material, which is the final product, to an extent that the growth of the surface oxide film can be suppressed. Therefore, the weather resistance becomes poor.
• the zinc salt content is 0.65000 mass% or less in terms of Zn.
• the zinc salt content is preferably 0.00150 mass% or less in terms of Zn; however, when the zinc salt content is more than 0.00100 mass% in terms of Zn, the weather resistance is favorable, but there are cases where zinc oxide formed in the surface oxide film aggregates. Since the aggregated zinc oxide makes the surface of the titanium material nonuniform, color unevenness is caused on the surface of the titanium material, designability becomes a problem, and there are cases where the titanium material cannot be used as building materials.
• the zinc salt content is more preferably 0.00100 mass% or less or 0.00080 mass% or less in terms of Zn.
• the zinc salt content is preferably 0.00060 mass% or more in terms of Zn.
• the aqueous solution that is used in the immersion treatment contains 0.00060 to 0.40000 mass% of a calcium salt in terms of Ca.
• the calcium salt include CaCl 2 , CaSO 4 , Ca(NO 3 ) 2 , and CaCO 3 .
• CaCl 2 is preferable since the solubility in water is high and the deliquescency is low.
• the calcium salt content is 0.00060 to 0.40000 mass% in terms of Ca.
• the calcium salt content is less than 0.00060 mass% in terms of Ca, calcium oxide is not formed on the surface of the titanium material, which is the final product, to an extent that the growth of the surface oxide film can be suppressed. Therefore, the weather resistance becomes poor.
• the calcium salt content is 0.40000 mass% or less.
• the calcium salt content may be 0.00200 mass% or less in terms of Ca.
• the calcium salt content is more than 0.00108 mass% in terms of Ca, similar to the zinc oxide, there are cases where calcium oxide aggregates. Since the aggregated calcium oxide makes the surface of the titanium material nonuniform, color unevenness is caused on the surface of the titanium material, and there are cases where designability becomes a problem.
• the calcium salt content is 0.00108 mass% or less in terms of Ca, it is possible to suppress color unevenness.
• the calcium salt content is preferably 0.00108 mass% or less and more preferably 0.00100 mass% or less in terms of Ca.
• the calcium salt content is preferably 0.00072 mass% or more in terms of Ca.
• the aqueous solution that is used in the immersion treatment contains HF: 1.0 to 6.0 mass% and HNO 3 : 4.0 to 10.0 mass%.
• the aqueous solution that is used in the cleaning step contains HF: 1.0 to 6.0 mass% and HNO 3 : 4.0 to 10.0 mass%, fine irregularities are formed on the surface of the titanium material.
• the HF content is preferably 5.0 mass% or less.
• the HNO 3 content is preferably 8.0 mass% or less.
• the HF content is preferably 1.5 mass% or more.
• the HNO 3 content is preferably at least 4.5 mass% or more.
• the temperature of the aqueous solution is 40° C. to 60° C.
• the temperature of the aqueous solution is lower than 40° C., there are cases where the titanium material is unevenly pickled and the color becomes uneven on the surface of the titanium material.
• the temperature of the aqueous solution is higher than 60° C., fumes of HNO 3 are generated, and manufacturing facilities are adversely affected. Therefore, the temperature of the aqueous solution is 40° C. to 60° C.
• the temperature of the aqueous solution is preferably 50° C. or lower.
• the immersion time is 1.0 minutes or longer.
• the immersion time is 1.0 minutes or longer, the color is uniform and fine irregularities are formed on the surface of the titanium material.
• the upper limit of the immersion time is not particularly limited, but is preferably 2.0 minutes. When the immersion time is 2.0 minutes or shorter, it is possible to carry out the treatment while maintaining the productivity of the continuous line.
• the immersion treatment makes Zn 2+ and Ca 2+ in the aqueous solution adsorbed onto the surface of the titanium raw material.
• the titanium raw material is washed with water.
• the water washing method is not particularly limited, and the titanium raw material may be washed with water using immersion in a water washing bath, spray washing, or the like. Water washing removes the excess aqueous solution on the surface of the titanium raw material and makes a surface oxide film formed on the surface of the titanium material. At this time, oxides of Zn 2+ and Ca 2+ adsorbed onto the surface of the titanium raw material are formed.
• the titanium raw material after the cleaning step is preferably heated at 300° C. to 900° C. in an inert atmosphere as necessary.
• the heating of the titanium raw material after the cleaning step to 300° C. to 900° C. in an inert atmosphere makes it possible to decompose fluorotitanic acid ions that have been incorporated into the surface oxide film by heating, discharge F to the outside of the surface oxide film, and reduce the F content in the surface oxide film.
• the inert atmosphere is, for example, a vacuum atmosphere, an argon atmosphere, a helium atmosphere, or the like.
• the vacuum atmosphere mentioned herein refers to an atmosphere having a degree of vacuum of 7.0 ⁇ 10 -4 to 2.5 ⁇ 10 -2 Pa.
• the argon atmosphere refers to an atmosphere containing 90 vol% or more of argon
• the helium atmosphere refers to an atmosphere containing 90 vol% or more of helium.
• the heating time is preferably 0.5 to 10.0 (hours). When the heating time is within the above-described range, fluorotitanic acid in the surface oxide film that has been incorporated during the immersion treatment is sufficiently decomposed.
• the lower limit of the heating time is more preferably 1.0 hour, and the upper limit of the heating time is more preferably 5.0 hours.
• Table 1 is an example of the quantitative analysis results by XPS of the surface of the titanium material according to the present embodiment and an example of the quantitative analysis results by XPS of the surface of an ordinary titanium material. “-” in Table 1 indicates that the value was the detection limit or less.
• the Zn content was 0.3 atom%
• the Ca content was 0.7 atom%
• both contents increased compared with those of the conventional materials.
• Titanium cold-rolled sheets (titanium substrates) of types shown in Table 2 were manufactured, a plurality of samples having a variety of sizes were cut out from each of these cold-rolled sheets, and an immersion treatment was carried out under conditions shown in Table 2.
• Table 2 shows the immersion treatment conditions.
• the cold-rolled sheets after the immersion treatment were washed with water by the following method. That is, the cold-rolled sheets after the immersion treatment were immersed in a water washing bath at room temperature (25° C.) for 1 minute, thereby removing a pickling liquid on the surfaces.
• No. 1 in Table 2 is an example in which a cleaning step was not carried out (an example of a sheet as cold-rolled and annealed), and No. 2 is an example in which a zinc salt and a calcium salt were not contained in an aqueous solution that was used in the immersion treatment in the cleaning step.
• CP1 shown in the item of the titanium raw material type in Table 2 indicates commercially pure titanium of JIS Class 1
• CP2 indicates commercially pure titanium of JIS Class 2
• CP3 indicates commercially pure titanium of JIS Class 3.
• Underlined conditions in Table 2 indicate that the conditions are outside the scope of the present invention.
• Example 21 CP3 ZnCl 2 0.00096 CaCl 2 0.00108 2.0 4.5 40 3.0 - Present Invention
• Example 22 Ti-1Cu ZnCl 2 0.00096 CaCl 2 0.00108 2.0 4.5 40 3.0 - Present Invention
• Example 23 Ti-3Al-2.5V ZnCl 2 0.00096 CaCl 2 0.00108 2.0 4.5 40 3.0 - Present Invention
• Example 24 Ti-5Al-1Fe ZnCl 2 0.00096 CaCl 2 0.00108 2.0 4.5 40 1.0 - Present Invention
• Example 25 Ti-0.05Pd ZnCl 2 0.00096 CaCl 2 0.00108 2.0 4.5 40 1.0 - Present Invention
• Example 26 Ti-0.35Pd ZnCl 2 0.00096 CaCl 2 0.00108 2.0 4.5 40 1.0 - Present Invention
• Example 27 Ti-15V-3Al-3Cr-3Sn ZnCl 2 0.00096 CaCl 2 0.00108 2.0 4.5 40 1.0 - Present Invention
• the SiO 2 conversion value is the sputtering rate obtained under the same measurement conditions using a SiO 2 film the thickness of which has been measured in advance using an ellipsometer.
• L*, a ⁇ , and b ⁇ were measured in accordance with JIS Z 8730: 2009 at a total of 10 points (5 points on each of the front and rear surfaces: 1 point at the sample central part and 4 points at the sample corner portions) on a 200 mml, ⁇ 300 mmw ⁇ 0.3 mmt sample after a water washing treatment, and color differences ⁇ E*ab between the measurement points were used as evaluation criteria.
• the color differences were measured with a light source C using a color difference meter CR-200b manufactured by Konica Minolta Japan Inc. Specifically, samples where the maximum value of the color differences AE*ab between the measurement points was 5 or less were determined to have favorable evaluation results (OK), and samples where the maximum value of the color differences AE*ab was more than 5 were determined to have poor evaluation results (NG).
• a 50 mmL ⁇ 25 mmw ⁇ 0.3 mmt piece was cut out from the water-washed sample, and a discoloration acceleration test was carried out thereon.
• the sample was immersed in a sulfuric acid aqueous solution having a pH of 3 at 80° C. for 4 days.
• L*a*b* of the surface of the titanium material before and after the discoloration acceleration test was measured to obtain color differences AE*ab before and after the discoloration acceleration test.
• the color differences were measured and calculated in the same manner as described above. The color differences were measured on the front and rear surfaces at 1 point in the central part and 4 points in the corner portions of the sample, and the color difference AE*ab obtained on average from a total of 10 points was used for the evaluation of weather resistance.
• the threshold value of the color difference AE*ab at which discoloration is visually recognized is 8.0
• the weather resistance was determined as favorable (OK)
• the weather resistance was determined as poor (NG).
• L ⁇ , a ⁇ , and b ⁇ were measured in accordance with JIS Z 8730:2009, and the whiteness was evaluated by comparing L ⁇ , a ⁇ , and b ⁇ with L ⁇ before the cleaning step.
• the whiteness was measured on the front and rear surfaces at 1 point in the central part and 4 points in the corner portions of the sample in the same manner as described above, and L ⁇ obtained on average from a total of 10 points was used for the evaluation of whiteness.
• the titanium materials were favorable in terms of weather resistance. Furthermore, the samples where the thickness of the surface oxide film was 5 to 20 nm were also favorable in terms of evaluation results of the color unevenness and the whiteness L*.

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