JPH09157872A - Titanium or titanium alloy member having beautiful surface and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent acid burning by repickling a titanium (alloy) member in which colored spots are produced by pickling and substantially removing only an oxidized film on the surface while the dissolution of the titanium (alloy) base is suppressed. SOLUTION: A titanium (alloy) member in which colored spots are generated by pickling is immersed in an aq. soln. of 5 to 70 deg.C soln. temp. contg., by weight, 0.1 to 5% hydrofluoric acid and 0.5 to 30% nitric acid for 1 to 30sec and is repickled. In the case the content of acid exceeds the upper limit, titanium ions and titanium fluoride ions are excessively formed to regenerate acid burning. In the case the content of acid is made smaller than the upper limit value, it takes a long time for removing an oxidized film. As for another method, it is immersed in an aq. soln. of 5 to 100 deg.C soln. temp. contg. 0.1 to 80% sulfuric acid for 1 to 300sec and is repickled. Sulfuric acid has high capacity of dissolving the oxidized film of titanium. In the case the content of acid exceeds the upper limit value, its oxidizability is made high, and the capacity of removing the oxidized film of titanium is deteriorated.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to reoxidation of reddish brown colored spots (hereinafter sometimes referred to as “acid burn”) generated on the surface of a titanium or titanium alloy member when pickled. The present invention relates to a useful method for producing a titanium or titanium alloy member having a beautiful surface by removing by washing, and a titanium or titanium alloy member obtained by this method.

[0002]

2. Description of the Related Art Titanium or titanium alloy (hereinafter sometimes referred to as titanium) strips are generally manufactured by hot rolling or hot rolling and cold rolling. It is rarely shipped as is. In many cases, after rolling, annealing is performed in the atmosphere for strain relief, and then the scale or oxygen-rich layer generated during rolling or annealing is treated by shot blasting or salt bath. To some extent, and the strip surface is cleansed with a pickling solution containing hydrofluoric acid, for example, nitric hydrofluoric acid.

However, in this pickling step,
Occasionally, there is a drawback that red-brown acid burning occurs almost or locally on the strip surface. This kind of acid burning has no practical problem when titanium strips are used for structural materials such as heat exchangers that are not visible to the human eye, but they are used for parts that are visible to humans such as roofing materials and curtain walls. In some cases, aesthetics will be lost. Further, not only strip but also forged material may require a clean pickling surface for the final finish, and in this case, the same problem as described above occurs.

The removal of the above-mentioned pickling is generally carried out by pickling again, but in the repickling methods that have been carried out up to now, the pickling that has occurred before the pickling has been carried out. Can be removed, but there is a problem that new acid burn may occur during re-pickling.

[0005]

SUMMARY OF THE INVENTION The present invention has been made under such circumstances, and its purpose is to reliably remove the acid scorch once generated by pickling and to provide titanium or titanium having a beautiful surface. It is to provide a method for manufacturing an alloy member and a titanium or titanium alloy member obtained by such a method.

[0006]

Means for Solving the Problems The method of the present invention capable of achieving the above object is to repickle a titanium or titanium alloy member in which coloring spots have been generated by pickling to obtain a base titanium or titanium alloy. It is a method for producing a titanium or titanium alloy member, which has the gist of substantially removing only the oxide film on the surface while suppressing dissolution.

Further, as a concrete constitution of the method of the present invention, (1) hydrofluoric acid: 0.1 to 5% by weight and nitric acid: 1 to 3
0% by weight, each of which has a liquid temperature of 5 to 70 ° C.
Re-pickling by soaking for 30 seconds, or (2)
Sulfuric acid: Contains 0.1 to 80% by weight, and the liquid temperature is 5 to 100 ° C.
Re-pickling by immersing in the aqueous solution for 1 to 300 seconds. Further, among the above methods, the method using sulfuric acid, which is relatively inexpensive, has an advantage that the cost can be reduced as compared with the case where nitric hydrofluoric acid is used.

Further, the titanium or titanium alloy member produced by the above method has a beautiful surface property without acid burning. Specifically, the area where acid burning occurs is 10% or less of the plate surface. Will be the one.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Regarding the cause of acid burn,
"Titanium fluoride is generated during pickling, which is the cause."
(JP-A 1-123097) or "The activated titanium surface after the oxide film is removed by pickling is reoxidized by the oxidizing action of nitric acid" (JP-A-64-4491).
Various opinions have been asserted, but it cannot be said that they have been clarified.

Therefore, the present inventor has conducted extensive studies on the actual condition and the cause of acid burn. As a result, the actual condition of acid burning is an oxide film of titanium with a thickness of hundreds of tens to hundreds of liters.
It was found that this is generated by the following mechanism. That is, titanium ions and titanium fluoride ions are generated by pickling, but these are during pickling or immediately after pickling (even if taken out from pickling solution, pickling solution adheres to the surface).
In addition, it reacts with water and dissolved oxygen in the pickling solution to form titanium oxide, which is adsorbed on the titanium surface to form an oxide film. This oxide film looks reddish brown due to the interference of light.

From these findings, the inventors of the present invention first of all, in order to suppress the occurrence of acid burning, the pickling reaction is caused to occur at an appropriate rate and titanium ions and titanium fluoride ions are not excessively generated. It was thought that acid burn could be prevented or reduced. And as a specific means for that, it was found that if the surface of the titanium member is cooled during the period from pickling to water washing, the extra pickling reaction is suppressed, and its technical significance was recognized. Separately filed on the same date as the application.

On the other hand, the inventor of the present invention has made extensive studies based on the above findings as to a solution to a case where acid burning unfortunately occurs due to the first pickling. as a result,
If only the oxide film formed on the titanium surface is removed by re-pickling to minimize the dissolution of titanium,
The present inventors have completed the present invention by reaching the conclusion that acid burns are less likely to occur again because the regeneration of the oxide film is suppressed.
Then, further examination of the conditions therefor, as shown in the above specific example, the composition of the pickling solution, the temperature,
I found out that it is good to specify the time strictly.

According to the present invention, as described above, the titanium or titanium alloy member that has been acid-burned by pickling is re-pickled to substantially dissolve only the surface oxide film while suppressing the dissolution of the base titanium or titanium alloy. It has the greatest feature in that it is removed by the method described above, and various concrete structures can be considered for that purpose. For example, in addition to hydrochloric acid, hydrofluoric acid, phosphoric acid, oxalic acid, formic acid, etc. shown in the examples below. A pickling solution capable of dissolving the oxide film as described above can be used, or these may be mixed and used. Further, the object of the present invention can be achieved by strictly defining the composition, temperature, time, etc. of the pickling solution, and the specific configuration thereof will be described below with respect to the nitric hydrofluoric acid-containing aqueous solution and the sulfuric acid-containing aqueous solution. .

The nitric hydrofluoric acid-containing aqueous solution shown as a specific example for re-pickling in the present invention contains hydrofluoric acid: 0.1 to 5% by weight and nitric acid: 0.5 to 30% by weight. If the value exceeds the upper limit of, the pickling reaction rate increases, and titanium ions and titanium fluoride ions are excessively produced, which leads to the re-generation of acid burning. As the content of hydrofluoric acid and nitric acid approaches the lower limit, excess titanium ions and titanium fluoride ions will not be generated, and the re-generation of acid burning will be less likely to occur. It takes too much time, which reduces productivity.

On the other hand, the sulfuric acid-containing aqueous solution shown as a specific example for re-pickling in the present invention is sulfuric acid: 0.1 to 80% by weight.
Must be used. Sulfuric acid is a non-oxidizing acid at low concentrations and has a high ability to dissolve titanium films,
If the sulfuric acid is excessively contained to such an extent that the upper limit is exceeded, the oxidizing property gradually increases and the ability to remove the titanium oxide film becomes weak. As the content of sulfuric acid approaches the lower limit value, excess titanium ions will not be generated, and the re-generation of acid burning is less likely to occur. It takes too long to remove,
Productivity will be reduced.

Whether an aqueous solution containing nitric hydrofluoric acid or an aqueous solution containing sulfuric acid is used, it is necessary to appropriately control the pickling temperature. That is, when the nitric hydrofluoric acid-containing aqueous solution is used, the liquid temperature must be 5 to 70 ° C, and when the sulfuric acid-containing aqueous solution is used, the liquid temperature must be 5 to 100 ° C. If the pickling temperature is lower than these lower limits, the removal rate of the oxide film will be extremely reduced and productivity will be reduced, and if it is higher than the upper limit, the pickling reaction will proceed too much and excessive titanium ions and fluorination will occur. Titanium ions are generated, which causes acid burning.

Further, the dipping time of the strip must be 1 to 30 seconds when the aqueous solution containing nitric hydrofluoric acid is used, and 1 to 300 seconds when the aqueous solution containing sulfuric acid is used. That is, if the dipping time of the strip becomes shorter than these lower limit values, the effect of the present invention of removing acid burn is not achieved, and if it becomes longer than the upper limit value, acid burn rather occurs. Needless to say, when another pickling solution is used, the temperature of the pickling solution and the strip immersion time need to be appropriately set according to the type of pickling solution.

The present invention will be described in more detail with reference to the following examples, but the following examples are not intended to limit the present invention, and any modification of the present invention can be made without departing from the spirit of the preceding and the following. It is included in the technical scope.

[0019]

【Example】

Example 1 Using a pure titanium plate with acid burning, thickness: 1 mm, 2
A test piece of 5 mm square was prepared, and the test piece was pickled by varying the composition of the aqueous solution containing nitric hydrofluoric acid, the solution temperature and the immersion time, and then washed with water and dried to determine the degree of acid burning (removal rate). ) Was evaluated by visual observation according to the following five-stage criteria. The evaluation level of 1 to 3 is the failure level. The results are shown in Table 1 below together with the conditions for re-pickling. (Relative Evaluation Criteria for Acid Burn Occurrence Level) 5 ... The acid burn generated by the previous pickling is completely removed, and the acid burn does not occur again. 4 ... Acid burn occurred in the range of 1 to 10% of the plate surface.

3 ... Acid burning occurs in the range of 10 to 50% of the plate surface. 2 ... Acid burning occurs in the range of 50 to 90% of the plate surface. 1 ... Acid burn occurred on almost the entire surface of the plate.

[0021]

[Table 1]

As is clear from Table 1, in the examples of the present invention (Test Nos. 1 to 14), re-generation of acid scorch is very little or no re-generation occurs.
On the other hand, Test No. In Nos. 15 to 17, the composition and temperature of the nitric hydrofluoric acid-containing aqueous solution exceeded the upper limits defined in the present invention, so that acid burn reoccurred.

Test No. In No. 18, the composition of the aqueous solution containing nitric hydrofluoric acid was below the lower limit defined by the present invention, and therefore acid burn could not be removed. Test No. In No. 19, since the liquid temperature was lower than the lower limit value defined in the present invention, acid burn could not be removed. Test No. In No. 20, since the liquid temperature exceeded the upper limit value defined in the present invention, re-generation of acid burning occurred. Test No. In No. 21, since the immersion time was less than the lower limit value defined in the present invention, acid burning could not be removed. Test No. In No. 22, since the immersion time exceeded the upper limit defined by the present invention, re-generation of acid scoring occurred.

Although only pure titanium is adopted in the above-mentioned embodiment, the occurrence of acid burning is related to titanium ions and fluoride ions generated by pickling, and the same applies to titanium alloys. Therefore, the above examples do not show that the present invention is applicable to pure titanium only. Further, the present invention can be applied not only to pickling the cut plate or forged material shown in the above-mentioned examples but also to continuous treatment such as a continuous pickling line for strips and a continuous annealing pickling line.

Example 2 In a continuous pickling line, after pure titanium strip was pickled under the conditions shown in Example 1, the titanium strip was processed into an outer wall panel and mounted on the outer wall of a building. The suitability for the above was visually examined.

As a result, the test No. 1-14
The titanium strip obtained by pickling under the same conditions as above has a uniform surface gloss and color tone between the panels, and has a very beautiful appearance. It was On the other hand, the test No. of Table 1 in Example 1 15-22 The titanium strip obtained by pickling under the same conditions was processed into an outer wall panel in the same manner as above and mounted on the outer wall of a building, and the gloss and color tone between the panels were significantly different due to acid burning. I couldn't use it.

Example 3 Using pure titanium having acid burn, thickness: 1 mm, 25
A mm-square test piece was prepared, and this test piece was pickled by varying the composition of the aqueous solution containing sulfuric acid (sulfuric acid concentration), the solution temperature and the immersion time, and then washed with water and dried to determine the degree of acid burning ( The removal degree) was evaluated in the same manner as in Example 1.
The results are shown in Table 2 below together with the respective conditions for re-pickling.

[0028]

[Table 2]

As is apparent from Table 2, it can be seen that in the examples of the present invention (Test Nos. 23 to 36), re-generation of acid scoring is very little or not occurring at all. On the other hand, Test No. In No. 37, the sulfuric acid concentration was below the lower limit value specified in the present invention, and therefore acid burn could not be removed. Test No. In No. 38, the sulfuric acid concentration exceeded the upper limit value specified in the present invention, so that acid burn reoccurred. Test No. In No. 39, the liquid temperature was lower than the lower limit value specified in the present invention, and therefore acid burn could not be removed. Test No. In No. 40, the liquid temperature exceeded the upper limit value specified in the present invention, so that acid burn reoccurred. Test No. In No. 41, the acid burn could not be removed because the immersion time was less than the lower limit value defined in the present invention. Test No. In No. 42, the immersion time was longer than the upper limit value defined in the present invention, so that acid burn reoccurred.

In the above examples, only pure titanium was adopted, but as described above, the occurrence of acid burning is related to titanium ions and fluoride ions generated by pickling. This is because titanium alloy is pickled with sulfuric acid. Even if it is the same. Therefore, the above examples do not show that the present invention is applicable to pure titanium only. Further, the present invention can be applied not only to pickling the cut plate or forged material shown in the above-mentioned examples but also to continuous treatment such as a continuous pickling line for strips and a continuous annealing pickling line.

Example 4 In a continuous pickling line, after pure titanium strip was pickled under the conditions shown in Example 3, the titanium strip was processed into an outer wall panel and mounted on the outer wall of a building. The suitability for the above was visually examined.

As a result, the test No. shown in Table 2 was obtained. 23-3
The titanium strip obtained by pickling under the same conditions as in 6
The surface gloss and color tone were uniform between the panels, and the panels had a very beautiful appearance, and the optimum cleanliness was obtained as a panel material. On the other hand, Table 2 in Example 2
Test No. The titanium strip obtained by pickling under the same conditions as 37 to 42 was processed into an outer wall panel in the same manner as above and mounted on the outer wall of the building, and the gloss and color tone between the panels were large due to acid burning. I could not use it differently.

[0033]

EFFECTS OF THE INVENTION The present invention is constituted as described above. Titanium or titanium alloy in which colored spots (acid scoring) are generated by pickling is re-pickled under appropriate conditions to obtain a base titanium or titanium alloy. It was possible to substantially remove only the oxide film, which is the cause of acid burn, while preventing the dissolution of Al, and to prevent the generation of excessive titanium ions and fluoride ions due to re-pickling. As a result, it was possible to completely prevent or significantly reduce the occurrence of acid burning due to re-pickling. Further, since the titanium or titanium alloy material obtained by the method of the present invention does not have local unevenness of gloss and color tone due to acid burning, it can be used for a noticeable member such as a building material that requires an aesthetic appearance.

Claims (4)

[Claims] 1. A method of re-pickling a titanium or titanium alloy member in which colored spots have been generated by pickling to substantially remove only an oxide film on the surface while suppressing dissolution of the titanium or titanium alloy. A method of manufacturing a titanium or titanium alloy member having a beautiful surface. 2. Hydrofluoric acid: 0.1-5% by weight and nitric acid:
The method according to claim 1, further comprising re-pickling by immersing in an aqueous solution containing 0.5 to 30% by weight and having a liquid temperature of 5 to 70 ° C. for 1 to 30 seconds. 3. The production method according to claim 1, wherein re-pickling is performed by immersing in an aqueous solution containing sulfuric acid: 0.1 to 80% by weight and having a liquid temperature of 5 to 100 ° C. for 1 to 300 seconds. 4. A beautiful titanium or titanium alloy member having a surface produced by the method according to any one of claims 1 to 3, in which an area where acid burn occurs is 10% or less of the surface of the plate.