JP2001348634A - Titanium sheet small in discoloration - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a titanium sheet hardly to be discolored even when used in the environment to be exposed to light such as outdoor. SOLUTION: In this titanium sheet obtained by subjecting a titanium cold rolled sheet to bright annealing or a titanium sheet obtained by annealing a titanium cold rolled sheet in an oxidizing atmosphere, subjecting the same to descaling and thereafter performing pickling finish, the content of carbon in a carbon concentrated layer in the surface layer of the titanium sheet is <=150 mg/m2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a titanium plate which is less discolored by light irradiation, and is suitable for roof materials and exterior materials of buildings.

[0002]

2. Description of the Related Art Titanium is a metal that is lighter and more excellent in corrosion resistance than iron and steel. In recent years, titanium plates have been often used outdoors as roof materials and exterior materials for buildings. The titanium plate used for such an application is usually manufactured by the following method.

That is, briquettes formed by pressing and mixing sponge-like titanium and crushed and refined titanium scrap are melted in a vacuum heating furnace and cooled to form ingots. Thereafter, the ingot is heated and stripped into a strip having a thickness of about 3 to 4 mm by hot rolling, and further subjected to an annealing treatment (annealing).
After that, after being shot blasted to remove oxide scale on the surface caused by hot rolling and annealing,
An acid washing treatment with nitric hydrofluoric acid (mixed acid of nitric acid and hydrofluoric acid) or the like is performed. Next, the thickness of 0.4 to 0.4
After rolling to about 1.0 mm, annealing is performed again.
This annealing includes bright annealing and annealing in an oxidizing atmosphere. In the case of bright annealing, it is used for various purposes after annealing. Further, when annealed in an oxidizing atmosphere, oxidized scale is generated on the surface. Therefore, descaling treatment is performed by immersion in a salt bath or the like, and the pickled finish is used.

[0004] However, as the amount of titanium thus produced increases as an exterior material, unexpected problems have become apparent. The problem is that the color tone of the surface changes as the period of use increases.

[0005] In other words, the silver-white color peculiar to titanium at the beginning of use outdoors has often changed to light brown or light purple after several months or years of use. Further, even in a titanium plate that has been used by being chemically colored from the beginning, there is an example in which the color tone gradually changes from the initial color tone. The cause of such discoloration of the titanium plate has not been elucidated at present, and there is no countermeasure at present, and the development of a titanium plate that does not change its color tone even when used outdoors for a long time is desired. .

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a titanium plate which does not easily discolor even when used in an environment where light is irradiated, such as outdoors.

[0007]

The present inventors analyzed the surface of a titanium plate after bright annealing or a surface of a titanium plate annealed in an oxidizing atmosphere and pickled to examine the chemical composition thereof, An atmospheric exposure test and an accelerated weather resistance test were performed using a titanium plate, and the relationship with discoloration was examined. After examining the results and conducting various tests, the following findings were obtained.

(A) A brightly annealed titanium plate and a titanium plate annealed in an oxidizing atmosphere and pickled to produce a carbon-enriched layer on the surface. The oxide layer affects the change in the color tone of the titanium plate surface.

(B) If the carbon-concentrated layer existing on the surface of the titanium plate is removed, the change in color tone becomes extremely small even when light is irradiated for a long time.

(C) The main cause of the formation of a carbon-enriched layer on the surface of the titanium plate is that the lubricating oil undergoes a mechanochemical reaction with the titanium surface in the course of cold rolling to form titanium carbide, which is dispersed in the surface layer. it is conceivable that. Cold rolling using a lubricant containing no carbon suppresses formation of a carbon-enriched layer.

(D) The cold-rolled sheet produced by cold rolling using a usual lubricant containing carbon is annealed in an oxidizing atmosphere, and the carbon content in the carbon-concentrated layer on the surface of the cold-rolled sheet is reduced. By annealing until the compound is sufficiently oxidatively decomposed, the carbon agricultural layer can be removed. In the case of bright annealing in which the cold-rolled sheet is annealed in a non-oxidizing gas or in a vacuum, the carbon-enriched layer can be removed by performing acid washing or polishing before or after the annealing. The present invention has been made based on such knowledge, and the gist is as follows.

(1) A titanium sheet obtained by bright annealing a cold-rolled titanium sheet, wherein the carbon content of the carbon-enriched layer on the surface of the titanium sheet is 15%.
A titanium plate with less discoloration by light irradiation of 0 mg / m ² or less. (2) annealing the cold rolled titanium sheet in an oxidizing atmosphere;
A titanium plate that has been desalted and then pickled and finished, wherein the carbon content of the carbon-concentrated layer on the surface of the titanium plate is 150 mg / m ² or less, and is less discolored by light irradiation.

Here, the carbon amount C of the carbon-enriched layer is an amount determined by the following equation.

C = TC-PC TC: After measuring the area of the rolled surface of an analytical sample cut out of a brightly annealed titanium plate or a titanium plate annealed in an oxidizing atmosphere, descaled and pickled and finished, and then subjected to the combustion method The amount of carbon per unit rolling surface area (1 m ² ) obtained by analyzing the amount of carbon in the sample and calculating based on the analysis value. PC: An analysis sample cut from a brightly annealed titanium plate or a titanium plate annealed in an oxidizing atmosphere, descaled, and pickled and finished, immersed in an aqueous nitric hydrofluoric acid solution to remove the carbon-enriched layer, and the rolled surface After measuring the area of 炭素, the amount of carbon in the sample per rolled surface area (1 m ² ) determined by analyzing the amount of carbon in the sample by the combustion method and calculating based on the analysis value.

[0015] Further, a carbon content of 150 mg / m ² or less includes 0. That is, a titanium plate in which the carbon concentration of the titanium plate surface layer is the same as the carbon concentration of the base metal is also included.

The inventor of the present invention alkali-degreases a titanium plate manufactured by performing normal hot rolling and cold rolling, and performs glow discharge mass spectrometry (GDMS) on its surface to remove carbon, hydrogen, oxygen, nitrogen and titanium. The amount of titanium was analyzed.

FIG. 1 shows the results of the analysis. As is clear from the figure, the surface layer of the titanium plate is a layer containing a high concentration of carbon, and the layer extends up to 1.2 μm from the surface.

This titanium plate was treated with 1% hydrofluoric acid (40%).
C) for 30 to 60 seconds, and the black smut adhered to the surface was rubbed off and dried while washing with water. As a result of X-ray diffraction analysis, a large amount of TiC was found in the carbon-enriched layer. I confirmed that.

In order to determine the amount of carbon in the carbon-concentrated layer of the cold-rolled titanium sheet having the chemical composition of the surface layer shown in FIG. 1 (hereinafter referred to as "concentrated carbon amount"), analysis is performed by the following method. Was. That is, after a cold rolled sheet sample is sufficiently degreased using a commercially available alkaline degreaser, it is immersed in an aqueous solution of nitric hydrofluoric acid (composition: 10% HNO ₃ -0.5% HF) adjusted to a temperature of 30 ° C. The immersion time was varied from 10 seconds to 60 seconds at 10 second intervals. After immersion, the sample was washed with water and dried. A sample for carbon analysis of about 0.5 g in weight was cut out from these pickled samples and samples not pickled after alkali degreasing,
Surface area other than end surface (cut surface), that is, rolled surface (2 surfaces)
After measuring the area of, the amount of carbon is analyzed by the combustion method,
The amount of carbon per unit rolling surface area (1 m ² ) was calculated based on the analysis values. The combustion method is a method in which an analytical sample is burned in an oxygen stream by a high-frequency induction heating method, and the concentration of carbon dioxide gas generated by the reaction between the carbon in the sample and oxygen in the atmosphere is determined by an infrared absorption method. Yes, the analyzer is L
A carbon-sulfur simultaneous determination device (HF-400 type) manufactured by eco was used.

[0020] FIG. 2 is a diagram showing the relationship between the surface carbon content of 1 m ² per calculated and pickling time. As apparent from FIG. 2, the carbon content of the sample not pickled was 26%.
The carbon content of the sample pickled at 3 mg / m ² was as follows.

[0021] Almost constant value for pickling time of 40-60 seconds, 50mg
/ M ² , this is the amount of carbon in the metal (PC)
it is conceivable that. Therefore, this value was subtracted from the carbon content (TC) of the sample not pickled and 263 mg / m ² , and 213 mg / m ² was the carbon content (C) of the carbon concentrated layer of the titanium cold-rolled sheet. It is. In the case of a sample with a small amount of concentrated carbon, one of the rolling surfaces is mechanically or / and
In addition, by adjusting the plate thickness to about 0.05 to 0.1 mm by chemically polishing, the amount of carbon in the base metal can be reduced, and the analysis accuracy of the amount of concentrated carbon can be increased. That is,
The plate thickness of the sample shown in FIGS. 1 and 2 is about 0.5 mm.
The area of the carbon-enriched surface of the analysis sample of 5 g is 0.5 m
The thickness is 5 times that in the case of a sheet thickness of m (because one rolled surface is polished), and the amount of concentrated carbon is also 5 times, so that the analysis accuracy is improved. In this case, at the time of pickling for removing the carbon-concentrated layer, it is necessary to seal the polished surface in advance with an adhesive tape or the like to prevent the polished surface from being dissolved.

FIG. 3 shows a sample of a titanium sheet which was obtained by annealing the cold-rolled titanium sheet shown in FIGS. 1 and 2 in an oxidizing atmosphere, descaling and pickling and finishing the sample. The relationship between the amount of surface carbon per 1 m ² and the pickling time calculated by the same method as in FIG. As is clear from FIG. 3, the carbon amount of the sample not pickled before the analysis was 28 mg / m ² , and the carbon amount of the pickled sample was as follows.

[0023] A constant value for pickling time of 40 to 60 seconds, 10 mg / m
^As shown in Fig. ² , this is considered to be the carbon content (PC) in the bullion. In addition, this value was reduced to about one-fifth of that in FIG. 2 because one of the rolling surfaces was polished to reduce the sheet thickness to about one-tenth, so that the amount of ingot was reduced to about one per unit rolling area. It is thought that it became 1/5. Therefore, this value was calculated based on the carbon content (TC) of the sample not pickled, 28 mg / m 2.
^The value, 18 mg / m ² , subtracted from ^2, is the carbon content (C) of the carbon-concentrated layer of the titanium plate which has been annealed in an oxidizing atmosphere, descaled, and pickled to finish. )
Although it is not fully understood why such a carbon-rich layer is formed, the rolling oil undergoes a mechanochemical reaction with the titanium surface in the course of cold rolling to form titanium carbide and form in the surface layer. Think to disperse.

Next, although the cause of the phenomenon of coloring or discoloration when the titanium plate is used outdoors as a roof material or an exterior plate of a building has not been elucidated at present, the titanium dioxide on the surface of the titanium plate has not been elucidated. This is considered to be a surface oxidation phenomenon caused by photocatalysis of the (TiO ₂ ) film.

That is, TiO ₂ has a wavelength of about 380 nm.
When the following light is irradiated, water and oxygen in the environment are chemically changed, and hydroxyl radicals with strong oxidizing power (・
OH) and superoxide anion (O ₂ ⁻ ) are known to be oxidizing agents. However, TiC dispersed in a carbon-concentrated layer on the surface of a titanium plate is chemically more unstable than TiO _2. Therefore, when these oxidizing agents act over a long period of time, they gradually decompose as shown in equation (1)
It is estimated to change to ₂ .

TiC + oxidizing agent → TiO ₂ + CO ₂ (1) At the same time as the above reaction, the titanium metal around TiC itself is oxidized by the oxidizing agent as shown in formula (2), and TiO ₂
Is estimated to change to

Ti + oxidant → TiO ₂ (2) The reason why the color tone of the titanium plate surface changes with time is that the carbon concentration in which TiC is dispersed Although the silicide layer does not show light interference, the reaction of the formulas (1) and (2) makes
It is considered that the thickness of the O ₂ film gradually increases, and the manner of light interference changes according to the thickness.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the carbon content of a carbon-concentrated layer on the surface of a titanium plate is specified to be 150 mg / m ² or less for the following reasons.

The discoloration of the titanium plate due to light irradiation proceeds more easily as the amount of carbon in the carbon-concentrated layer formed on the surface of the titanium plate increases, and the discoloration is suppressed unless the amount of concentrated carbon is 150 mg / m ² or less. This is because they cannot do it. Preferably 50 mg / m ² or less, more preferably 10 mg / m ²
/ M ² or less.

The discoloration progression behavior also differs depending on the distribution state of carbon in the carbon-enriched layer. If the carbon-enriched layer is thin but the maximum carbon concentration is high, the discoloration proceeds in a relatively short time. On the other hand, when the carbon concentration layer is thick even if the maximum carbon concentration is low, the discoloration gradually proceeds over a long period of time.
Therefore, to effectively suppress discoloration, the maximum carbon concentration is preferably set to 10% by mass or less. It is preferably at most 5% by mass, more preferably at most 2% by mass. Further, the thickness of the carbon-concentrated layer is desirably 700 nm or less, preferably 500 nm or less, and more preferably 300 nm or less.

The titanium plate having the carbon-concentrated layer as described above can be manufactured as follows.

One method is a method in which a hot-rolled titanium sheet produced by a conventional method is cold-rolled using a carbon-free lubricant. As the lubricant containing no carbon, an aqueous solution containing 8 to 15% of a phosphate (potassium phosphate, sodium phosphate, or the like) can be used.

As another method, cold rolling is performed using a lubricant such as ordinary mineral oil. In this case, it is inevitable that a carbon-concentrated layer is formed on the surface of the titanium plate.
This is a method in which the subsequent annealing step is performed in an oxidizing atmosphere such as a hydrocarbon gas combustion heating furnace, and annealing is performed until the carbon-enriched layer is sufficiently oxidatively decomposed. Specifically, the carbon-enriched layer disappears by annealing at an annealing temperature of 750 to 800 ° C. for 3 to 5 minutes.

However, the higher the annealing temperature and the longer the annealing time, the thicker the oxide scale is formed on the surface, so that the subsequent desalting by salt bath treatment or pickling becomes more difficult. Therefore, conventionally, annealing has not been performed to the extent that the carbon-enriched layer is completely oxidized and decomposed, and only the minimum annealing necessary for recrystallization and softening of the titanium base metal is generally performed. is there. In the case of such an annealing, the carbon-enriched layer near the surface disappears and an oxide scale is generated instead, but the carbon-enriched layer often remains inside the oxide scale. If this is not removed in the next descaling step, a carbon-enriched layer will remain on the surface of the final product, so it is necessary to sufficiently remove it by the descaling step after annealing, that is, salt bath treatment and pickling. There is.

Since there are restrictions on the annealing temperature and the annealing time for other reasons, if it is unavoidable that many carbon-enriched layers remain after the annealing, the descaling step, that is, the salt bath treatment, is similarly performed. It is necessary to sufficiently dissolve and remove the carbon-concentrated layer by pickling.

The preferred method is 450 to 5
After being immersed in a molten alkali salt bath at 20 ° C. (for example, a melt of 90% sodium hydroxide and 10% sodium nitrate) for 5 to 30 seconds, a nitric acid pickling solution (nitric acid concentration of 8 to 15 ° C.) at 30 to 50 ° C. %, Aqueous solution with hydrofluoric acid concentration of 2-5%
This is a method of dipping for 0 to 200 seconds. Between the molten alkali salt bath treatment and the nitric acid hydrofluoric acid pickling treatment, alternating electrolysis (current density 10-20 A / dm ² , total anodic electrolysis time) in a 20-50 ° C. nitric acid aqueous solution (concentration 5-15%) (10-20 seconds), the carbon-enriched layer can be sufficiently removed.

The cold-rolled sheet having the carbon-concentrated layer may be annealed in a non-oxidizing gas such as nitrogen or argon or in a vacuum, but since the surface is not oxidized, the carbon-condensed layer on the cold-rolled sheet surface is not oxidized. Remains almost intact. And since the bright annealing material is not usually pickled after annealing, it has a carbon-enriched surface. Therefore, it is necessary to sufficiently remove the carbon-concentrated layer on the surface by pickling or polishing before or after annealing.

When removing the carbonized layer on the surface by pickling before annealing, hydrofluoric acid at a temperature of 30 to 50.degree.
2%) or nitric hydrofluoric acid (aqueous solution having a nitric acid concentration of 8 to 15% and a hydrofluoric acid concentration of 0.5 to 2%) for 30 to 150 seconds.

When the carbonized layer on the surface is removed by pickling after annealing, nitric hydrofluoric acid (nitric acid concentration: 8 to 30 ° C. to 50 ° C.) is used.
~ 15%, aqueous solution of hydrofluoric acid concentration 1-4%)
It may be immersed for up to 200 seconds.

On the other hand, it is possible to remove the carbon-enriched layer on the surface by polishing. However, if a polishing oil containing carbon such as mineral oil is used as a lubricant for polishing, the carbon-enriched layer is removed from the surface by a mechanochemical reaction. Since a layer is formed, an aqueous solution containing 8 to 15% of a phosphate (potassium phosphate, sodium phosphate, or the like) is preferably used as the lubricant as in the case of cold rolling.

Next, when the titanium plate of the present invention is used for chemical coloring or high-temperature oxidation coloring in an aqueous solution or molten salt, a change in color tone is suppressed.

When using a titanium plate manufactured by an ordinary manufacturing method, it is necessary to sufficiently remove the carbon-concentrated layer on the surface of the material by pickling or polishing prior to the color forming treatment.

When the carbonized layer on the surface is removed by pickling, a hydrochloric acid aqueous solution (concentration: 5 to 15%) at 30 to 50 ° C. or nitric hydrofluoric acid (nitric acid concentration: 8 to 15%, hydrofluoric acid concentration: 0) (Aqueous solution of 0.5 to 2%) for 50 to 150 seconds.

[0044] In this way the concentrated carbon content of the titanium plate surface was produced should be below 150 mg / m ² as described above, preferably more preferably 50 mg / m ² is 10 mg / m ² or less. This tolerance also depends on the final surface finishing method. In other words, when the titanium plate is oxidized and colored in an aqueous solution or a molten salt, the outside of the carbon-concentrated layer is covered with a dense oxide film, and this is applied to the titanium plate of an oxidizing agent such as hydroxy radicals in the use environment. The amount of concentrated carbon is 50-150 mg / m
^{Even with 2} , the discoloration due to light irradiation tends to be small.

However, when the titanium plate is colored by high-temperature oxidation or when it is used without pickling or bright annealed skin, the oxide film outside the carbon-concentrated layer is very thin. Also, since it is not dense even if it is thick, it is impossible to prevent the oxidizing agent from penetrating into the use environment. Therefore, the amount of concentrated carbon is 50 mg / m ² or less, more preferably 10 m / m ² or less.
If it is not more than g / m ² , discoloration due to light irradiation can be sufficiently prevented.

[0046]

EXAMPLES (Example 1) Titanium (JI) having a thickness of 3.5 mm was used.
S1 type) hot-rolled strip is annealed using a continuous annealing pickling facility,
After pickling, a test material having a size of 120 × 200 mm was cut out and cold-rolled to a sheet thickness of 0.5 mm using a small four-high rolling mill.

At this time, as a cold rolling lubricant, 10
% Potassium phosphate aqueous solution and a mineral oil-based rolling oil were used.

A test specimen of 100 × 150 mm was cut out from the cold-rolled material, sufficiently degreased using a commercially available alkaline degreaser, and then annealed at 730 ° C. for 2 hours in argon gas.

After annealing, a 100 × 100 mm test piece was cut out and subjected to an atmospheric exposure test outdoors for one year to examine the presence and degree of discoloration. At the same time, a test piece which had been separately cut out before the atmospheric exposure test and a test piece from which the carbon agricultural layer had been removed by washing with nitric hydrofluoric acid were analyzed by a combustion method, and the amount of concentrated carbon per 1 m ^{2 of} the test piece surface was examined. These results are summarized in Table 1.

[0050]

[Table 1] As is clear from Table 1, the test piece of the present invention using a 10% aqueous solution of potassium phosphate as a lubricant did not discolor at all in an air exposure test for one year, whereas a mineral oil-based rolling oil was used. The test piece of the comparative example which had been cold rolled was discolored to light brown.

(Example 2) A hot-rolled titanium sheet (JIS class 1) manufactured in a usual process was cold-rolled using a mineral oil-based lubricant to a sheet thickness of 0.6 mm. A test material having a size of 150 × 200 mm was cut out from the titanium strip and sufficiently degreased using a commercially available alkaline degreaser.
Annealing was performed under various conditions using an experimental furnace that can be adjusted to the same atmosphere as a hydrocarbon gas combustion heating furnace.

Next, 100 × 150 m
A test piece having a size of m was cut out and subjected to descaling treatment in combination with a molten alkali salt immersion treatment, a nitric acid electrolytic treatment and a nitric acid hydrofluoric acid pickling. 100x12 cut out from this
Accelerated weathering test with a test piece of 0 mm size and 30 ×
The amount of concentrated carbon was analyzed using a 100 mm test piece.

The molten alkali salt had a composition of 90% sodium hydroxide and 10% sodium nitrate.
What was heated and melted at 0 degreeC was used. In addition, the nitric acid electrolytic treatment is performed at 50 ° C. in a 10% aqueous nitric acid solution at a current density of 15 A /
The pattern of anodic electrolysis at dm ² for 2 seconds followed by cathodic electrolysis for 2 seconds was repeated. The nitric acid pickling was carried out by immersing in a 40 ° C. nitric acid (10% HNO ₃ -2% HF) aqueous solution for a predetermined time.

Further, the accelerated weathering test was carried out for a total of 2,000 hours by a method of alternately repeating water wetting and light irradiation using a sunshine weather meter (one capable of irradiating light rays having a wavelength in the ultraviolet region as well as sunlight). Conduct,
The presence and degree of discoloration by the test were examined. Table 2 shows the results
Shown in

[0055]

[Table 2] As is evident from Table 2, No. 1 was subjected to sufficient annealing to make the carbon-enriched layer disappear almost completely. The 1 test material is
The amount of concentrated carbon was as low as 3 mg / m ^2, and no discoloration was observed in the accelerated weathering test for 2000 hours.

On the other hand, no. In all of the test materials 2 to 4, the carbon-enriched layer did not completely disappear by annealing, but the remaining carbon-enriched layer was removed to some extent by the descaling treatment. As a result, no. The test material of No. 2 had a concentrated carbon content of 6 mg / m ^{2 of} less than 10 mg / m ² , and had only a very pale golden color by the accelerated weathering test.
o. The test material of No. 3 has a concentrated carbon amount of less than 50 mg / m ^2.
3 mg / m ² , and only a pale golden color was obtained by the accelerated weathering test. On the other hand, no. 4
163mg The test material on the remaining number of carbon concentrated layer with short annealing time, since dissolution is also insufficient in descaling process, the concentrated carbon content is more than 50 mg / m ²
/ M ² . Then, the color changed to brown in the accelerated weather resistance test.

(Example 3) A hot-rolled titanium plate (JIS Class 1) manufactured in a normal process was cold-rolled using a mineral oil-based lubricant to form a 0.7 mm thick titanium (JIS Class 1) strip. A test material having a size of 150 × 200 mm was cut out from the plate and sufficiently degreased using a commercially available alkaline degreaser.

Thereafter, some of the test materials were immersed in nitric hydrofluoric acid (an aqueous solution having a nitric acid concentration of 10% and a hydrofluoric acid concentration of 1%) at 30 ° C., washed with water, dried, and placed in an argon atmosphere (dew point of −55 ° C.). ) At 720 ° C. for 2 hours.

Next, some of the test materials were immersed in an aqueous solution of nitric hydrofluoric acid (nitric acid concentration: 10%, hydrofluoric acid concentration: 2%) at 40 ° C., washed with water, dried, and cut out.
A one-year outdoor air exposure test was performed on a test piece having a size of 0 × 120 mm, and an analysis of the amount of concentrated carbon was performed on a test piece having a size of 30 × 100 mm. Table 3 shows the presence / absence and degree of discoloration in the air exposure test and the results of investigation of the amount of concentrated carbon by the combustion method.

[0060]

[Table 3] As is clear from Table 3, No. 1 was pickled before and after annealing. 1
The test material of 5 mg / m ^{2 with a} concentrated carbon amount of less than 10 mg / m ²
m ² , and did not discolor at all in the air exposure test.
In addition, No. 1 was pickled before or after annealing. 2 and N
o. 2 3 test material concentrated carbon content of less than 50 mg / m ²
7 and 35 mg / m ² , and only a very pale golden color was found in the air exposure test. In contrast, no pickling was performed after annealing, and the pickling before annealing was insufficient.
o. 4 of the test material is 87 mg / m ² Nearby concentrated carbon content is more than 50 mg / m ^2, a thin brown by atmospheric exposure test was colored. Also, N was not pickled at all before and after annealing.
o. 5 of the test material is 211 mg / m ² Nearby concentrated carbon content exceeds 150 mg / m ^2, becomes discolored purple by atmospheric exposure test was discolored purple by atmospheric exposure test.

(Example 4) A hot rolled titanium sheet (JIS Class 1) manufactured in a usual process was cold-rolled with a mineral oil-based lubricant to form a 0.5 mm thick titanium (JIS Class 1) strip. After cutting out a test material having a size of 150 × 200 mm from the plate and sufficiently degreased using a commercially available alkaline degreaser,
Annealing was performed at 720 ° C. for 2 hours in an argon atmosphere (dew point: −55 ° C.).

Next, some of the test materials were immersed in nitric hydrofluoric acid (aqueous solution having a nitric acid concentration of 10% and a hydrofluoric acid concentration of 2%) at 40 ° C. for 120 seconds, washed with water, and dried. afterwards,
Molten salt electrolytic coloring, aqueous electrolytic coloring or high-temperature oxidation coloring were performed, and accelerated weathering test was performed on a test piece of 100 × 120 mm cut out from this, and analysis of the amount of concentrated carbon was performed on a 30 × 100 mm test piece. .

The molten salt electrolytic coloration was 33% at 320 ° C.
In a mixed salt bath of sodium nitrate and 67% potassium nitrate, a positive voltage of 8 volts
Seconds. In addition, for the aqueous electrolysis coloring, a positive voltage of 10 volts was applied for 30 seconds in a 5% aqueous solution of sodium phosphate at 40 ° C. using a platinum plate as a cathode. Furthermore, high-temperature oxidation coloring was performed by heating at 300 ° C. for 5 minutes in the atmosphere, and a titanium plate colored golden was obtained by any of the methods. The accelerated weather resistance test was conducted for a total of 3000 times by using a sunshine weather meter (which can irradiate light rays having a wavelength in the ultraviolet region as well as sunlight) by alternately repeating water wetting and light irradiation. The presence and degree of discoloration were examined. Table 4 shows the results of the investigation of the presence and degree of discoloration by the accelerated weathering resistance test and the amount of concentrated carbon by the combustion method.

[0064]

[Table 4] As is evident from Table 4, pickling was performed before coloring to remove most of the carbon-enriched layer. All of the test materials 1 to 3 have 3 to 4 mg / m ^{2 in which the} amount of concentrated carbon is less than 10 mg / m ^2.
And no discoloration was observed in the accelerated weather resistance test. On the other hand, No. 1 in which the pickling before coloring was omitted. The test materials Nos. 4 to 6 differed in the amount of concentrated carbon depending on the coloring method. 4 and no.
The test material of No. 5 has a concentrated carbon content of less than 150 mg / m ²
And 100 mg / m ² , with only slight or slight discoloration in the accelerated weathering test. On the other hand, in the case of No. 1 which developed high-temperature oxidation color. 6 of the test material concentrated carbon content is more than 150mg / m ² 203mg / m ^2, and the large discolored by accelerated weathering test became violet.

[0065]

According to the present invention, a titanium plate having a small change in color tone can be easily obtained even when used outdoors for a long time, and the industrial effect is great.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an analysis result of a GDMS method on the surface of a cold-rolled titanium sheet.

FIG. 2 is a diagram showing the relationship between the pickling time and the calculated amount of surface carbon.

FIG. 3 is a diagram of another example showing the relationship between the pickling time and the calculated amount of surface carbon.

Claims (2)

[Claims] 1. A titanium sheet obtained by bright annealing a cold-rolled titanium sheet, wherein the carbon content of the carbon-concentrated layer on the surface of the titanium sheet is 150 mg.
/ M ² or less, the titanium plate having little discoloration due to light irradiation. 2. A titanium sheet which is obtained by annealing a cold-rolled titanium sheet in an oxidizing atmosphere, descaling and finishing with pickling, wherein the carbon content of the carbon-concentrated layer on the surface of the titanium sheet is 150 mg / m ² or less. Titanium plate with less discoloration due to light irradiation.