JPH11158651A - Chromated stainless steel sheet excellent in resistant to rusting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To retard the rusting in the initial stage and to provide a stainless steel sheet at a low treating cost. SOLUTION: A stainless steel sheet in cleaned with an aq. soln. contg. one or both of phosphoric acid and a phosphorus compad and nitric acid to control the Fe2p2/3 peak strength ratio of Fe2 O3 /Fe to 0.1 to 0.9, then a chromating soln. contg. 1 to 40 g/1 total Cr at Cr<6+> /total Cr <=0.1 is applied, and the sheet is dried without being washed with water to form a chromatic film at 5 to 200 mg Cr/m<2> . The phosphoric acid or phosphorus compd. can be added to the chromating soln. to be in a ratio of P/total Cr=0.1 to 0.4, or a silica sol is added to be in a ratio of Si/total Cr=0.5 to 3.0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chromate-treated stainless steel sheet which does not cause the surface of the stainless steel sheet to be colored yellow by a chromate film and is effective in preventing initial rust.

[0002]

2. Description of the Related Art Stainless steel sheets have excellent corrosion resistance.
Since it has a beautiful appearance skin, when it is used for a building material, it is often used in a naked state using the appearance skin. For this reason, various surface finishes are prepared for the stainless steel plate for use in a bare state, so that it can meet the demands of consumers. However, when used for interior / exterior materials, there is a general demand for an HL finish with a rougher surface than a mirror finish with a high gloss. However, the corrosion resistance of the stainless steel plate changes depending on the finish even with the same steel type, and the corrosion resistance decreases as the skin becomes rougher. For this reason, when the HL finish is used, the generation of rust is faster than that of the smooth finish.

[0003] Therefore, various methods have been conventionally proposed to suppress the initial generation of rust. A typical method is to apply a clear paint on the surface of a stainless steel plate. However, when the clear coating is applied, the metallic luster is lost, giving the appearance of a coated steel plate, and even if the coating film is thinned, the original skin of the stainless steel plate is slightly changed.
Also, since the clear coating film does not contain a pigment that blocks ultraviolet rays, the weather resistance is generally inferior. In addition, since the stainless steel plate is also inferior in paintability, a clear paint having excellent corrosion resistance and weather resistance should be used. Even so, the coating film peels off in a relatively short time.

For this reason, even if the clear coating is applied, the generation of rust is simply delayed until the coating film is peeled off. In addition, since there is no demand for clear-painted stainless steel plates to provide a dedicated coating line, the coating uses continuous coating lines such as galvanized steel plates and aluminum-plated steel plates, but coating costs are still high. There was a problem.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a stainless steel sheet which can delay the generation of rust at an early stage and has a low processing cost.

[0006]

According to a first aspect of the present invention, a stainless steel sheet is washed with an aqueous solution containing one or both of phosphoric acid and a phosphoric acid compound and nitric acid.
F ₂ of Fe ₂ O ₃ and Fe at a depth within 10 nm from the surface
e2p _3/2 peak - 0.1 to 0 the click intensity ratio Fe ₂ O ₃ / Fe.
After setting to 9, the chromium having a total Cr content of 1 to 40 g / L and a hexavalent Cr content of 0.1 or less in a ratio of Cr ⁶⁺ / total Cr is 0.1 or less.
Coating solution and dry without washing with water
It is characterized in that a chromate film having an adhesion amount of 5 to 200 mg / m ² is formed.

In a second aspect of the present invention, in the first aspect, the chromate treatment solution is prepared by adding phosphoric acid or a phosphoric acid compound in a ratio of P / total Cr = 0.1 to 4.0. It is characterized by having. Further, the third invention is characterized in that, in the first invention or the second invention, the chromate treatment solution is obtained by adding silica sol in a ratio of Si / total Cr = 0.5 to 3.0. I have.

[0008]

The stainless steel sheet of the present invention has been subjected to chromate treatment. As the chromate film has a higher hexavalent Cr content, the rust resistance improves, and the yellow tint increases in proportion thereto. Becomes stronger. However, when a stainless steel sheet is used naked for interior and exterior materials, it uses a silver-white metal appearance and a finished skin. Will be lost.

The inventors of the present invention have studied the composition of a treatment solution capable of forming a colorless chromate film having excellent rust resistance, and found that the content of hexavalent Cr in the chromate treatment solution was limited to the conventional value. The amount was made extremely small to prevent coloring even if the amount of Cr adhering to the chromate film was increased to about 200 mg / m ² . That is, in the conventional chromate treatment solution, the maximum content of hexavalent Cr was about 50% of the total Cr regardless of the reaction type or the coating type.
The chromium content was made to be 0.1 or less in the ratio of Cr ⁶⁺ / total Cr so that the chromate film could be made colorless.

[0010] However, the hexavalent Cr content of the processing solution is changed to Cr ⁶⁺
When the ratio of the total Cr is set to 0.1 or less, repelling is more likely to occur when applied to a stainless steel sheet than in the conventional chromate treatment solution. This repelling is caused by Fe ₂ O ₃ in the surface oxide film of the stainless steel sheet. The components were found to have a significant effect. The composition of the oxide film on the surface depends on the type and finish of the stainless steel sheet.
Fe ₂ O ₃ at a depth within 10 nm from the surface of the L-finished material
Results The components were analyzed by XPS, Fe2p _3/2 peak of Fe ₂ O ₃ and Fe - click intensity ratio 3.0 with Fe ₂ O ₃ / Fe
5.0.

Therefore, as a result of intensive studies on a method capable of removing the surface Fe ₂ O ₃ component without impairing the appearance of the stainless steel plate and making it hydrophilic, it was found that the stainless steel sheet contains one or both of phosphoric acid and a phosphoric acid compound. It has been found that washing with an aqueous solution is sufficient. However, the hydrophilization was still insufficient. For this reason, as a result of further studying a method capable of hydrophilizing, it was found that washing with an aqueous solution containing one or both of phosphoric acid and a phosphoric acid compound and nitric acid was sufficient. The principle that the surface of the stainless steel plate becomes hydrophilic by washing with the aqueous solution is based on the result of XPS analysis that in addition to the removal of the Fe ₂ O ₃ component, the water-repellent Cr oxide changes to Cr hydroxide as follows. Presumed.

FIG. 1 to FIG. 3 show XP of untreated material of stainless steel plate (SUS304, No. 4 finish), treated material of phosphoric acid aqueous solution, and treated material of mixed acid aqueous solution of phosphoric acid and nitric acid.
S Analysis Cha - but shows the bets, Fe2p _3/2 peak processing material Fe ₂ O ₃ than either the untreated material with an aqueous solution - click intensity decreases, Cr2p _3/2 peak reversed - click and Ni2p _3/2 peak - intensity clauses have increased, Fe ₂ O ₃ in the surface layer oxide film is seen to have been removed. Then, Cr2p _3/2 peak - the click intensity, Cr ₂ O ₃ peak was present in the untreated material - disappeared click is by washing, Cr (O
H) It has changed to ₃ · nH ₂ O. Also, comparing the peak strengths of the treatment materials depending on the type of the aqueous solution, it is clear that the mixed acid aqueous solution treatment of phosphoric acid and nitric acid has a higher Fe ₂ O 3 concentration than the phosphoric acid aqueous solution treatment material.
Fe2p _3/2 peak of O ₃ - click strength decreases, Ni2p
_3/2 peak strength or Cr2p _{3/2 of} Cr (OH) ₃ .nH ₂ O
The peak strength is large. Moreover, Cr (OH)
₃ · nH ₂ O in Cr2p _3/2 peak - click strength increase is remarkable.
From this, it is considered that the reason why the mixed acid aqueous solution treatment of phosphoric acid and nitric acid became more hydrophilic than the phosphoric acid aqueous solution treatment material was that most of the Cr oxide was changed to Cr hydroxide. Note that the same result can be obtained in the case of a treatment material using an aqueous solution containing a phosphoric acid compound and nitric acid.

[0013] However, phosphoric acid, washed with an aqueous solution containing the one or both nitric phosphate compound, Fe2p ₃ of Fe ₂ O ₃ and Fe at a depth within 10nm from the surface of the stainless steel plate _{/ 2} peak intensity ratio is Fe ₂ O
_If the ratio of ₃ / Fe is less than 0.1, the etching becomes partially excessive and the appearance is hindered. If the ratio exceeds 0.9, cissing cannot be prevented. Therefore, cleaning Fe2p _3/2 peak of Fe ₂ O ₃ and Fe - click intensity ratio is 0.1
This is performed so as to be in the range of 0.9. The concentration of phosphoric acid or nitric acid in the aqueous solution is not less than 1 g / L of phosphoric acid and 0.1 g of nitric acid.
When it is / L or more, the cleaning time can be shortened, and the workability is good. Further, it is preferable that after washing with an aqueous solution, washing with water or hot water is performed, and then a chromate film is formed subsequently.

In the chromate treatment liquid, the total Cr (total of trivalent and hexavalent Cr) is adjusted to 1 to 40 g / L from the viewpoints of the corrosion resistance of the film and the gelation of the treatment liquid. When it is less than 1 g / L,
Since the amount of hexavalent Cr is small, the corrosion resistance of the chromate film becomes insufficient, and if it exceeds 40 g / L, the treatment liquid tends to gel. The amount of Cr adhering to the chromate film is 5 to 200 mg / m ² . This is because if it is less than 5 mg / m ² , rust resistance is not sufficiently imparted to the stainless steel plate, and if it exceeds 200 mg / m ² , the adhesion of the chromate film is reduced. In the case of a chromate treatment, it is difficult to increase the amount of Cr adhering to the chromate film to 200 mg / m ² if it is a reaction type chromate treatment solution.

[0015] chromate - The preparative process liquid, chromic acid, chromates, but using an aqueous solution containing a water-soluble chromium compound such as bichromate, hexavalent Cr content Cr ⁶⁺ / total C
The ratio of r can be set to 0.1 or less by using an oxycarboxylic acid compound as the reducing agent without causing the treatment liquid to gel. Here, oxycarboxylic acid compounds include those having a hydroxyl group and a carboxyl group such as tartaric acid, malonic acid, citric acid, lactic acid, gluconic acid, glyceric acid, tropic acid, benzylic acid, hydroxyvaleric acid and the like. The hydroxyl group reduces hexavalent chromium to trivalent chromium, and the carboxyl group coordinates to the compound of trivalent chromium.
It is thought to prevent gelation.

When phosphoric acid or a phosphoric acid compound is added to the chromate treatment liquid, the formed chromate film becomes a hardly soluble chromium phosphate film, and the rust resistance of the stainless steel plate can be improved. it can. As the phosphoric acid compound, a water-soluble compound such as ammonium dihydrogen phosphate is used, and the amount of addition is adjusted so that P / total Cr = 0.1 to 4.0. If it is less than 0.1, the effect of improving the rust resistance due to insolubilization of the film is small, and if it is more than 4.0, the stability of the treatment liquid is reduced.

Further, when silica sol is added to the chromate treatment solution alone or together with the above-mentioned phosphoric acid or phosphoric acid compound, the rust resistance and moisture resistance of the chromate film can be enhanced. In any case, the addition of the silica sol is preferably in the range of 0.5 to 3.0 in the ratio of Si / total Cr. If it is less than 0.5, the effect of improving rust resistance is small, and if it exceeds 3.0, the adhesion of the film is reduced.

Chromate treatment liquid is applied to a stainless steel plate in the same manner as in the case of conventional coating type chromate treatment, such as a roll coating method, an air curtain method, and an electrostatic mist. It may be carried out by a chemical method, a squeeze roll coating method or the like, and a method of drying without washing with water.

[0019]

EXAMPLES Example 1 Tartaric acid was added to aqueous solutions of chromic anhydride having different total Cr concentrations to reduce most of hexavalent chromium to trivalent chromium, thereby preparing various chromate treatment solutions. This treatment liquid was sealed in a glass container and left in an atmosphere at 40 ° C. for 10 days. Thereafter, a stainless steel plate (SUS304, H
L finish, thickness 0.6 mm). First, a stainless steel plate is treated with an alkaline degreasing solution (pH 12.
5, liquid temperature 60 ° C) for 5 seconds, degreased, washed with water,
Next, a mixed acid aqueous solution of phosphoric acid and nitric acid (phosphoric acid 12 g / L,
Immersion in 1.7 g / L of nitric acid at a liquid temperature of 60 ° C. for 5 seconds (F of Fe ₂ O ₃ and Fe at a depth of 10 nm or less from the steel sheet surface)
e2p _3/2 peak intensity ratio: Fe ₂ O ₃ /Fe=0.1), washing with water, drying, and finally applying a treatment liquid with a roll coater. And after the application, the reached plate temperature 100
Dried at ° C. Table 1 shows the composition of the chromate treatment solution, the stability of the treatment solution carried out by the following method, and the performance of the chromate film.

(1) Stability test of chromate treatment solution The treatment solution was sealed in a glass container and left in an atmosphere of 40 ° C. to observe the number of days until gelation was observed. When no gelation or sedimentation was observed even when the mixture was allowed to stand, it was evaluated by the symbol ○, and when it was observed, it was evaluated by the symbol ×. (2) Color tone test The yellowness of the steel sheet was measured in accordance with JIS Z 8730 by Lab.
The b value was measured by the method, and those having a b value of less than 5.0
And those having a value of 5.0 or more were evaluated with the symbol x. In addition, yellowness is so strong that b value is large.

(3) Adhesion test of chromate film A tape to which a cellophane was once attached to a test piece and then peeled off
In the ping test, a symbol 皮膜 indicates that no film peeling was observed, and a symbol を indicates that some film peeling was observed.
In the above, those in which film peeling was observed on the entire surface were evaluated with the symbol x. (4) Rust resistance test The test piece was exposed outdoors and the number of days until rust was observed was observed. If no rust was observed for up to 1 month, mark ○; if no rust was observed for more than 1 month and 3 months, mark △; if rust was recognized by 1 month, mark x evaluated. (5) Repelling resistance The surface of the steel sheet after the application of the chromate treatment liquid was observed, and those with no repelling were evaluated with the symbol 、, and those with repelling were evaluated with the symbol x.

[0022]

[Table 1] (Note 1) In Comparative Example 4, application was difficult due to gelation of the treatment liquid. (Note 2) In Comparative Example 5, cleaning was not performed with a mixed acid aqueous solution of phosphoric acid and nitric acid, so that repelling occurred and performance evaluation was difficult. (Note 3) Comparative Example 6 was washed with an aqueous solution containing only 16 g / L of phosphoric acid, and Comparative Example 7 was washed with an aqueous solution containing only 3 g / L of nitric acid. there were.

Example 2 The same procedure as in Example 1 was repeated except that the chromate treatment solution was used when the total Cr concentration was 1%.
After reducing hexavalent chromium in an aqueous solution of 0 g / L ammonium chromate to trivalent chromium by adding tartaric acid, changing to a solution containing phosphoric acid and silica sol, washing for 1 minute, and adhering Cr to the chromate film The amount was kept constant at 30 mg / m ² . Further, the concentration of the mixed acid aqueous solution of phosphoric acid and nitric acid was changed to that of 1 g / L of phosphoric acid and 0.1 g / L of nitric acid, and Fe ₂ O ₃ and Fe at a depth of 10 nm or less from the steel sheet surface.
The 2p _3/2 peak strength ratio was Fe ₂ O ₃ /Fe=0.9, and the stainless steel plate was changed to SUS304, 2B finish, and 0.6 mm thick. Table 2 shows the composition of the chromate treatment solution and the chromate film performance of the tests (2) to (5) performed in Example 1.

[0024]

[Table 2]

[0025]

As described above, the stainless steel plate is washed with an aqueous solution containing one or both of phosphoric acid and a phosphoric acid compound and nitric acid, and the Fe ₂ O _{3 is} removed from the surface at a depth of 10 nm or less. Fe2p _3/2 peak of Fe and - the click intensity ratio 0.1 to 0.9 in the Fe ₂ O ₃ / Fe, colorless chromate -
No repelling occurs even when the coating is treated with a chromate treatment solution in which the hexavalent Cr content at which the coating film is formed is reduced to a Cr ⁶⁺ / total Cr ratio of 0.1 or less. Further, since the chromate film formed by the chromate treatment liquid is colorless even when the amount of the film is increased, the appearance of the stainless steel plate does not change and the stainless steel plate is excellent in rust resistance.

[Brief description of the drawings]

FIG. 1 shows the peak intensity of Fe2p _3/2 by XPS analysis.

FIG. 2 shows the Cr2p _3/2 peak intensity by XPS analysis.

FIG. 3 shows Ni2p _3/2 peak intensity by XPS analysis.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shinya Furukawa 5th Ishizu Nishimachi, Sakai-shi, Osaka Nisshin Steel Co., Ltd.

Claims (3)

[Claims] 1. A stainless steel sheet is washed with an aqueous solution containing one or both of phosphoric acid and a phosphoric acid compound and nitric acid, and the Fe ₂ O ₃ at a depth of 10 nm or less from the surface.
Fe2p _3/2 peak of the Fe - the click intensity ratio Fe ₂ O ₃ / Fe
After 0.1 to 0.9, the total Cr is 1 to 40 g / L,
A chromate treatment solution having a hexavalent Cr content of 0.1 or less in the ratio of Cr ⁶⁺ / total Cr is applied and dried without washing with water, so that the Cr adhesion amount is 5 to 200 mg / m 2.
^2. A chromate-treated stainless steel sheet having excellent rust resistance, characterized by forming a chromate film of ² . 2. The method according to claim 1, wherein the chromate treatment solution contains phosphoric acid or a phosphoric acid compound, wherein P / total Cr = 0.1 to 1.0.
A chromated stainless steel sheet having excellent rust resistance, characterized in that it is added so as to have a ratio of 4.0. 3. The method according to claim 1, wherein
A chromate-treated stainless steel sheet having excellent rust resistance, characterized in that a silica sol is added so that the ratio of Si / total Cr is 0.5 to 3.0.