JP3221303B2 - Titanium or titanium alloy member with beautiful surface and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for re-acidifying reddish-brown colored spots (hereinafter sometimes referred to as "acid burn") generated on the surface of a titanium or titanium alloy member when the member is 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 the method.

[0002]

2. Description of the Related Art Generally, titanium or titanium alloy (hereinafter sometimes referred to as titanium) strips are manufactured through hot rolling or hot rolling and cold rolling. It is rarely shipped as is. In many cases, after rolling, annealing is performed in the air to remove strain, and then the scale or oxygen-enriched layer generated during rolling or annealing is treated by shot blasting, salt bath, etc. The strip surface is cleaned with a pickling solution containing hydrofluoric acid, for example, nitric hydrofluoric acid.

[0003] However, in this pickling step,
There is a drawback that sometimes a reddish brown acid burn occurs almost entirely or locally on the strip surface. Such acid burning does not pose a practical problem when the titanium strip is used for a structural material that is not visible, such as a heat exchanger, but is used for a material that is visible, such as a roofing material or a curtain wall. Sometimes the aesthetics will be impaired. Further, not only the strip but also the forged material may require a clean pickling surface for the final finish. In this case, the same problem as described above occurs.

[0004] The removal of acid pickling as described above is generally carried out by pickling again. However, in the re-picking method which has been carried out so far, acid pickling generated before re-picking is performed. Can be removed, but there is a problem that a new acid burn may occur when re-pickling is performed.

[0005]

SUMMARY OF THE INVENTION The present invention has been made under such a circumstance, and an object of the present invention is to reliably remove acid burns once generated by pickling to make titanium or titanium having a beautiful surface. An object of the present invention is to provide a method for manufacturing an alloy member, and a titanium or titanium alloy member obtained by such a method.

[0006]

According to the method of the present invention, which has attained the above object, a titanium or titanium alloy member having coloring spots generated by pickling is re-pickled to obtain a base titanium or titanium alloy. This is a method for producing a titanium or titanium alloy member having the gist of substantially removing only an oxide film on the surface while suppressing dissolution.

The specific constitution of the method of the present invention is as follows: (1) hydrofluoric acid: 0.1 to 5% by weight and nitric acid: 1 to 3
0% by weight, and the solution temperature is 5 to 70 ° C.
Re-pickling by dipping for 30 seconds, or (2)
Sulfuric acid: contains 0.1 to 80% by weight, liquid temperature is 5 to 100 ° C
Immersion in an aqueous solution for 1 to 300 seconds to perform re-acid washing. 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 using nitric hydrofluoric acid.

[0008] The titanium or titanium alloy member produced by the above method has a beautiful surface property without acid scorching. Specifically, the region where acid scorching occurs is 10% or less of the plate surface. It will be.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION
"Titanium fluoride is generated during pickling, which is the cause."
(Japanese Patent Application Laid-Open No. 1-123097) and "The activated titanium surface after the oxide film is removed by pickling is re-oxidized by the oxidizing action of nitric acid" (Japanese Patent Application Laid-Open No. 64-4491).
), But various opinions have not been clarified.

Therefore, the present inventors have conducted intensive studies on the actual conditions and causes of acid burning. As a result, the actual state of acid burning is an oxide film of titanium with a thickness of several hundred to several hundreds of square meters,
It was found to be generated by the following mechanism. That is, the pickling produces titanium ions and titanium fluoride ions during or immediately after the pickling (the pickling solution adheres to the surface even after being removed from the pickling solution).
Then, 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. The oxide film looks reddish brown due to the interference of light.

Based on these findings, the present inventors first suggested that in order to suppress the occurrence of acid burning, the pickling reaction should be caused at an appropriate rate to prevent excessive generation of titanium ions and titanium fluoride ions. It was thought that acid burning could be prevented or reduced. As a specific means for that, it was found that if the surface of the titanium member was cooled during the period from pickling to water washing, an extra pickling reaction was suppressed, and its technical significance was recognized. A separate application has been filed on the same date as the application.

On the other hand, based on the above findings, the present inventor has been studying a solution for a case where acid burning is unfortunately caused by 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,
Since the regeneration of the oxide film is suppressed, it has been concluded that acid baking is unlikely to occur again, and the present invention has been completed.
Further investigations were made on the conditions for this. As shown in the above specific example, the composition, temperature,
I found that it was only necessary to strictly define the time.

According to the present invention, as described above, the titanium or titanium alloy member which has undergone pickling due to pickling is re-pickled to substantially suppress the dissolution of the base titanium or titanium alloy while substantially removing only the oxide film on the surface. The most characteristic feature is that it can be removed in various ways. For this purpose, various configurations can be considered. For example, in addition to hydrochloric acid, hydrofluoric acid, and phosphoric acid shown in Examples described later, oxalic acid, formic acid, etc. A pickling solution capable of dissolving an oxide film can be used as described above, or a mixture of these may be used. The object of the present invention can be achieved by strictly defining the composition, temperature, time, and the like of the pickling solution. Specific examples of the configuration include the following nitric hydrofluoric acid-containing aqueous solution and sulfuric acid-containing aqueous solution. .

The aqueous solution of nitric hydrofluoric acid shown as a specific example used in the 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 it exceeds the upper limit of, the pickling reaction rate will increase, and titanium ions and titanium fluoride ions will be excessively generated, thereby causing 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 are not generated, and it is difficult to regenerate acid burns. It takes too much time and productivity is reduced.

On the other hand, a sulfuric acid-containing aqueous solution shown as a specific example used for re-acidification 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 concentration and has a high ability to dissolve titanium film,
If sulfuric acid is excessively contained so as to exceed the upper limit, the oxidizing property gradually increases, and the ability to remove the titanium oxide film becomes weak. As the sulfuric acid content approaches the lower limit, excess titanium ions are not generated, and re-generation of acid burning is less likely to occur. Removal takes too long,
Productivity will be reduced.

Regardless of 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 aqueous solution containing nitric hydrofluoric acid is used, the liquid temperature needs to be 5 to 70 ° C, and when the aqueous solution containing sulfuric acid is used, the liquid temperature needs to 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 the productivity will be reduced. If the pickling temperature is higher than the upper limit, the pickling reaction will proceed too much, resulting in excessive titanium ions and fluoride. Titanium ions are generated, and acid burning occurs.

The immersion time of the strip must be 1 to 30 seconds when an aqueous solution containing nitric hydrofluoric acid is used, and 1 to 300 seconds when an aqueous solution containing sulfuric acid is used. That is, if the immersion time of the strip is shorter than these lower limits, the effect of the present invention of removing acid burns is not achieved, and if it is longer than the upper limit, acid burns occur. When another pickling solution is used, it is needless to say that the solution temperature and the strip immersion time must be appropriately set according to the type of the pickling solution.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples do not limit the present invention, and any design change based on the above and following points is not limited to the present invention. It is included in the technical scope.

[0019]

【Example】

Example 1 A pure titanium plate in which acid burning occurred was used.
A test piece of 5 mm square was prepared, and the test piece was pickled by variously changing the composition of the aqueous solution of nitric hydrofluoric acid, the temperature of the solution, and the immersion time, and then washed with water and dried. ) Was evaluated by visual observation according to the following five-grade criteria. Those whose evaluation is 1 to 3 are the rejection levels. The results are shown in Table 1 below together with the conditions for re-acid washing. (Relative evaluation criteria of acid burn occurrence degree) 5 ... The acid burn generated by the previous pickling is completely removed, and no acid burn occurs again. 4: Acid scorch occurs in the range of 1 to 10% of the plate surface.

3: An acid burn occurs in a range of 10 to 50% of the plate surface. 2: Acid scorch occurs in the range of 50 to 90% of the plate surface. 1: Acid burning occurs on almost the entire surface of the plate.

[0021]

[Table 1]

As is clear from Table 1, it can be seen that the examples of the present invention (Test Nos. 1 to 14) have very little or no re-generation of acid burns.
On the other hand, Test No. In Nos. 15 to 17, the composition and temperature of the aqueous solution of nitric hydrofluoric acid exceeded the upper limits specified in the present invention, so that acid burning occurred again.

Test No. In No. 18, acid burns could not be removed because the composition of the aqueous solution of nitric hydrofluoric acid was lower than the lower limit specified in the present invention. Test No. In No. 19, the acid temperature could not be removed because the liquid temperature was lower than the lower limit specified in the present invention. Test No. In No. 20, the acid temperature was higher than the upper limit specified in the present invention, so that acid burning occurred again. Test No. In No. 21, acid dipping could not be removed because the immersion time was below the lower limit specified in the present invention. Test No. In No. 22, since the immersion time was longer than the upper limit specified in the present invention, re-generation of acid burning occurred.

In the above embodiment, only pure titanium is employed. However, the occurrence of acid burning involves 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 only to pure titanium. The present invention can be applied not only to the case where the cut plate or the forged material shown in the above embodiment is pickled but also to a continuous process such as a continuous pickling line and a continuous annealing pickling line for strip.

EXAMPLE 2 In a continuous pickling line, after the 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, and the outer wall material was removed. Was examined visually.

As a result, the test No. 1-14
The titanium strip obtained by acid pickling under the same conditions as described above has a uniform surface gloss and color tone between the panels, has a very beautiful appearance, and has obtained optimal cleanliness as a panel material. Was. On the other hand, Test No. 15-22 The titanium strip obtained by pickling under the same conditions was processed into an outer wall panel in the same manner as described above, and mounted on the outer wall of the building. The luster and color tone between the panels differed greatly due to acid burning. Could not be used.

Example 3 Using pure titanium having undergone acid burning, thickness: 1 mm, 25
An mm square test piece was prepared, and the test piece was pickled with various changes in the composition (sulfuric acid concentration), solution temperature and immersion time of the aqueous solution containing sulfuric acid. The degree of removal was evaluated in the same manner as in Example 1.
The results are shown in Table 2 below together with the conditions for the re-acid cleaning.

[0028]

[Table 2]

As is evident from Table 2, it can be seen that the examples of the present invention (Test Nos. 23 to 36) have very little or no re-generation of acid burns. On the other hand, Test No. In No. 37, the acid burn could not be removed because the sulfuric acid concentration was lower than the lower limit specified in the present invention. Test No. In No. 38, since the sulfuric acid concentration exceeded the upper limit specified in the present invention, re-generation of acid burning occurred. Test No. In No. 39, the acid temperature could not be removed because the liquid temperature was lower than the lower limit specified in the present invention. Test No. In No. 40, since the liquid temperature was higher than the upper limit specified in the present invention, re-generation of acid burning occurred. Test No. In No. 41, since the immersion time was shorter than the lower limit specified in the present invention, the acid burn could not be removed. Test No. In No. 42, since the immersion time was longer than the upper limit specified in the present invention, re-generation of acid burning occurred.

In the above embodiment, only pure titanium was employed. However, as described above, the occurrence of acid burning involves titanium ions and fluoride ions generated by pickling. This is because the titanium alloy was pickled with sulfuric acid. The same goes for the case. Therefore, the above examples do not show that the present invention is applicable only to pure titanium. The present invention can be applied not only to the case where the cut plate or the forged material shown in the above embodiment is pickled but also to a continuous process such as a continuous pickling line and a continuous annealing pickling line for strip.

Example 4 After the pure titanium strip was pickled in the continuous pickling line 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, and the outer wall material was removed. Was examined visually.

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

[0033]

The present invention is constituted as described above. The titanium or the titanium alloy, in which colored spots (acid burns) are generated by the pickling, is re-pickled under appropriate conditions to obtain a base titanium or a titanium alloy. While suppressing the dissolution of acid, only the oxide film that caused acid burning was substantially removed, and the generation of excessive titanium ions and fluoride ions due to re-acidification could be prevented. As a result, it was possible to completely prevent or significantly reduce the occurrence of acid burning due to re-pickling. Further, the titanium or titanium alloy material obtained by the method of the present invention has no local unevenness in luster or color due to acid burning, and thus can be used as a noticeable member such as a building material requiring an aesthetic appearance.

Claims (4)

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