JPH10273785A - Chromated stainless steel sheet excellent in rusting resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stainless steel sheet capable of retarding rusting in the initial stage and reduced in treatment costs. SOLUTION: A stainless steel sheet is washed with a phosphate-containing aqueous solution to regulate the Fe2P3/2 peak intensity ratio between Fe2 O3 and Fe, in the region between the surface and a position at a depth of 10 nm from the surface, so that Fe2 O3 /Fe becomes 0.1-0.9. Then, a chromating solution, in which total Cr content is regulated to (1 to 40) g/L and the content of sexivalent Cr is regulated so that the value of Cr<6+> /(total Cr) becomes <=0.1, is applied to the steel sheet, followed by drying without water washing. By this procedure, a chromate film, having (5 to 200) mg/m Cr coating weight, is formed. Further, phosphoric acid or phosphoric acid compound can be added to the chromating solution so that the value of P/(total Cr) becomes 0.1-4.0, and also silica sol can be added so that the value of S/(total Cr) becomes 0.5-3.0.

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 HL finishes with rougher skin than those with high gloss mirror finishes. 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.
In addition, since the clear coating film does not contain a pigment that blocks ultraviolet rays, the weather resistance is generally inferior, and the stainless steel plate is also inferior in paintability. Therefore, 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 for a period until the coating film is peeled off. In addition, since there is no demand for clear-painted stainless steel plates to have a dedicated coating line, continuous painting lines such as galvanized steel plates and aluminum-plated steel plates are used for painting, but the cost of painting is 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]

Means for Solving the Problems A first invention of the present invention is to wash a stainless steel plate with a phosphate-containing aqueous solution,
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 that, the chromium having a total Cr content of 1 to 40 g / L and a hexavalent Cr content of 0.1 or less in the ratio of Cr ⁶⁺ / total Cr was 0.1%.
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 plate is used naked for interior and exterior materials, it uses a silver-white metal appearance and a finished skin.If the appearance changes to yellow with a chromate film, the original appearance of the stainless steel plate is lost. 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⁺
The / 0.1 or less at a ratio of total Cr, conventional chromate when applied to a stainless steel plate - tend to cause cissing from preparative treatment solution, Fe ₂ O ₃ in this repelling in the surface oxide film of the stainless steel plate 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 Fe ₂ O ₃ component of the surface layer without impairing the appearance of the stainless steel plate, it was found that the stainless steel plate could be washed with a phosphate-containing aqueous solution. However, 10n from the surface of the stainless steel plate
Fe2p _3/2 peak of Fe ₂ O ₃ and Fe at a depth of up to m -
When cleaning is performed until the strength ratio of Fe ₂ O ₃ / Fe becomes less than 0.1, the etching becomes partially excessive and the appearance is hindered. When it exceeds 0.9, repelling cannot be prevented.
The range is 0.1 to 0.9. As the phosphate-containing aqueous solution, a commercially available zinc phosphate-based treating agent for a galvanized steel sheet or an iron phosphate-based treating agent for a cold-rolled steel sheet may be used. Further, it is preferable that after washing with the phosphate-containing 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 viewpoint of the corrosion resistance of the film, the gelation of the treatment liquid, and the like. 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 decreases. 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.

[0013] 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, the oxycarboxylic acid compound has 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 solution, the formed chromate film becomes a hardly soluble chromium phosphate film, and the rust resistance of the stainless steel plate can be enhanced. 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.

The coating of a chromate treatment solution on a stainless steel plate can be performed by a known method, for example, a roll coat method, an air-curtain method, or an electrostatic fog, as in the case of the conventional coating type chromate treatment. 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.

[0017]

【Example】

Example 1 Tartaric acid was added to aqueous solutions of chromic anhydride having different total Cr concentrations, and most of hexavalent chromium was reduced to trivalent chromium to prepare 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, it was immersed in a commercially available zinc phosphate treatment solution (concentration: 70 g / L, liquid temperature: 60 ° C.) for 5 seconds (Fe2p3 _{/ 2} peak of Fe ₂ O ₃ and Fe at a depth within 10 nm from the steel sheet surface). -Strength ratio: Fe ₂ O ₃ / Fe = 0.1), washing with water, drying, and finally applying a treatment liquid with a roll coater.
Then, after the application, the coating was dried at an ultimate plate temperature of 100 ° 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 adhered 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 without repelling were evaluated with a symbol ○, and those with repelling were evaluated with a symbol x.

[0020]

[Table 1] (Note 1) In Comparative Example 4, application was difficult due to gelation of the treatment liquid. (Note 2) Comparative Example 5 was not washed with the aqueous solution containing a phosphate, so that repelling occurred, and it was difficult to evaluate the performance.

Example 2 In Example 1, 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, it is changed to that to which phosphoric acid and silica sol are added, and the amount of Cr attached to the chromate film is 30 mg / m2. ² Change the zinc phosphate treatment solution to a concentration of 50 g / L and a solution temperature of 60 ° C. to reduce the concentration of Fe ₂ at a depth within 10 nm from the steel sheet surface.
O ₃ and Fe2p _3/2 peak of Fe - the click intensity ratio Fe ₂ O ₃ / F
e = 0.9, and a stainless steel plate made of SUS30
4, 2B finish, changed to 0.6 mm plate thickness. 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.

[0022]

[Table 2]

[0023]

As is evident from the foregoing description, the stainless steel plate was washed with phosphate-containing aqueous solution, Fe2p _3/2 peak of Fe ₂ O ₃ and Fe at the surface within 10nm depth - the click intensity ratio F
When the 0.1 to 0.9 in e ₂ O ₃ / Fe, colorless chromate - chromate hexavalent Cr content formed bet film was 0.1 or less at a ratio of Cr ⁶⁺ / total Cr - DOO Even if treated with a processing solution,
No repelling occurs. 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.

 ──────────────────────────────────────────────────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 a phosphate-containing aqueous solution, and the Fe ₂ O ₃ is removed at a depth within 10 nm 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.