JPH05106089A - Surface treatment method for stainless steel sheet - Google Patents

Abstract

PURPOSE:To provide the method for efficiently producing a stainless steel sheet excellent in corrosion resistance particularly in an acidic environment. CONSTITUTION:A stainless steel sheet is immersed in a liq. contg. 10 to 300g/l molybdenum trioxide, 5 to 300 g/l phosphoric acid and 0.5 to 200g/l hydrochloric acid and is subjected to anodic treatment and cathodic treatment under the conditions of 0 to 90 deg.C liquid temp. and 2 to 200Asec/dm<2> quantity of electricity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of dramatically improving the corrosion resistance of a stainless steel plate by subjecting the stainless steel plate to an electrolytic treatment.

[0002]

BACKGROUND OF THE INVENTION The present invention relates to a method for improving the corrosion resistance of a steel sheet while maintaining the luster and color tone of stainless steel by an electrochemical surface treatment. There are nitric acid electrolytic treatment for the material, or chromium plating using sulfuric acid and chromium trioxide.

Of these, the nitric acid electrolysis treatment has an effect of improving corrosion resistance at a low cost, but cannot significantly improve the corrosion resistance. On the other hand, the chrome plating has a drawback that it requires a large amount of chemicals and electric power, but it is extremely inferior in productivity, although it has a sufficient effect of improving corrosion resistance.

By the way, the corrosion resistance required when a stainless steel plate is used as a building material, a decorative article or the like has hitherto been mainly against salt damage in a neutral environment, but in recent years, there has been a problem such as acid rain. Along with this, high corrosion resistance in an acidic environment is also required. Then, as a method for dealing with this, Japanese Patent Publication No. 59-12755 was proposed.

That is, Japanese Patent Publication No. 59-12755 is
It is an invention made for the purpose of solving the problem with respect to such acid resistance together with the problem of manufacturing cost, specifically, the steel sheet, after phosphoric acid, after cathodic treatment in a liquid containing chromic acid, Disclosed is a method of performing cathodic treatment in a liquid containing phosphoric acid and molybdate. However, this method also has a problem in that it cannot be said that the corrosion resistance is sufficient and that the productivity is slightly inferior because two solutions are used.

Further, as a general problem when the surface treatment is performed on the stainless steel sheet, since a passivation film having an extremely minute structure having excellent corrosion resistance is present on the surface of the stainless steel sheet, the stainless steel sheet is electrochemically treated. In order to perform such a surface treatment, a pretreatment for removing the passive film and activating the surface may be necessary in advance.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and an object thereof is to provide a method for efficiently producing a stainless steel sheet having excellent corrosion resistance in an acidic environment. And

[0008]

DISCLOSURE OF THE INVENTION The present inventor investigated the corrosion resistance of a stainless steel plate in a solution containing various metal ions by cathodic treatment, and the steel plate after the cathodic treatment in an acidic environment having a pH of less than 5. did. As a result, it was found that molybdenum significantly improves corrosion resistance in an acidic environment, although the mechanism is unknown. Further, it was found that molybdenum trioxide is the best addition method of molybdenum to the solution for the cathode treatment in terms of the effect of improving the corrosion resistance.

When a steel sheet is subjected to cathodic treatment in a solution containing metal ions, it is necessary to add an electrolyte in addition to water to the solution. Therefore, molybdenum trioxide and sulfuric acid, hydrochloric acid, phosphoric acid or nitric acid are used. Cathodic treatment was carried out using various solutions containing, etc., and the effect of the type of electrolyte on the corrosion resistance was investigated. As a result, although it was possible to obtain good effects in any case, it was revealed that the use of phosphoric acid gave the best corrosion resistance.

Further, such an electrochemical treatment is
Since metal ions are deposited on the steel sheet, it is basically performed by cathodic treatment, but when phosphoric acid is used, it was found that the corrosion resistance is further improved by combining cathodic treatment and anodizing treatment. The reason for this is not clear, however, because such treatment elutes inclusions harmful to the corrosion resistance of the steel sheet surface or removes Mn-based oxides harmful to the corrosion resistance generated in bright annealing. I was wondering. It was also found that the order of the cathodic treatment and the anodizing treatment is that it is preferable to carry out the cathodic treatment after the anodizing treatment, because if the anodizing treatment is performed after the cathodic treating, the film formed by the cathodic treatment is destroyed.

As described above, the present inventor has found that the corrosion resistance of the stainless steel sheet can be remarkably improved by performing the anodization and the subsequent cathodic treatment in the solution containing molybdenum trioxide and phosphoric acid. But in the process,
It was also found that this method has a problem that the electrodeposition of molybdenum tends to be non-uniform. The cause of this is the passivation film existing on the surface of the stainless steel sheet before the treatment, so as a result of earnest research on the method of removing this passivation film without adding a new step, it was found in the treatment liquid of the electrochemical treatment. It was found that the addition of a small amount of hydrochloric acid to the anode can destroy the passivation film without deterioration of gloss during anodization, and that the cathode treatment can efficiently and uniformly deposit molybdenum. Then, the present invention has been completed.

That is, according to the present invention, a stainless steel plate is made of molybdenum trioxide (10 to 300 g / l) and phosphoric acid (5 to 300).
It is characterized in that it is immersed in a liquid containing g / l and hydrochloric acid 0.5 to 20 g / l, and anodizing is followed by cathodic treatment under the conditions of a liquid temperature of 0 to 90 ° C. and an electric quantity of ^{2 to} 200 Asec / dm ^2. The present invention provides a surface treatment method for a stainless steel sheet.

The present invention will be described in detail below. In the present invention, the material to be treated may be a stainless steel plate.

In the present invention, a stainless steel plate is subjected to electrochemical treatment, and the treatment liquid is molybdenum trioxide 1
A liquid containing 0 to 300 g / l, phosphoric acid 5 to 300 g / l and hydrochloric acid 0.5 to 20 g / l is used.

As described above, molybdenum is effective for improving the corrosion resistance of the stainless steel sheet in an acidic environment, and it is particularly preferable to add molybdenum as molybdenum trioxide to the treatment liquid. And the addition amount is 10
~ 300 g / l. If it is less than 10 g / l, a sufficient amount of film for improving the corrosion resistance cannot be formed, and if it exceeds 300 g / l, the effect of improving the corrosion resistance is saturated and the steel sheet turns yellow.

As described above, it is preferable to select phosphoric acid as the electrolyte, and the addition amount is 5 to 300 g.
/ L. If it is less than 5 g / l, the steel sheet after treatment will not have a sufficient effect of improving corrosion resistance, and if it exceeds 300 g / l,
It becomes uneconomical because the effect of improving corrosion resistance is saturated.

Hydrochloric acid is effective for removing the passive film as described above, and the addition amount thereof is 0.5 to 20 g / l. If it is less than 0.5 g / l, the passivation film removing effect is insufficient, and if it exceeds 20 g / l, the steel sheet is eluted during the anodization and the gloss deteriorates.

In the present invention, a stainless steel plate is immersed in the above-mentioned treatment liquid, the liquid temperature is 0 to 90 ° C., and the electricity amount is 2 to 200 Asec.
Anodization and subsequent cathodic treatment are performed under the condition of / cm ² .

The reason for limiting the liquid temperature to 0 to 90 ° C. is 0 ° C.
If the temperature is less than 90 ° C, a film sufficient to improve corrosion resistance is not formed and
This is because if it exceeds the above range, the formed film becomes thick and the steel sheet is discolored.

The reason why the amount of electricity during the anodizing and cathodic treating is limited to ² to 200 Asec / dm ² is that when it is less than ² sec / dm ² , a film sufficient to improve the corrosion resistance is not formed and 200 As
The ec / dm ² greater, resulting film becomes thick, because the steel sheet is discolored.

The reason why the anodizing is followed by the anodizing is that if the anodizing is performed after the anodizing, not only the film formed by the anodizing is destroyed by the anodizing, but also the passivation by the anodizing is performed before the anodizing. This is because the effect of uniform electrodeposition of molybdenum obtained because the film can be destroyed cannot be obtained.

[0022]

EXAMPLES The present invention will be described below in greater detail by giving Examples.

(Example) As a stainless steel material, JI
S-standard SUS430 was selected and brightly annealed to prepare a 1.0 mm thick stainless steel plate as a material to be treated. The material to be treated was electrochemically treated under the conditions shown in Table 1, washed with water and dried to obtain a test piece. About them,
After measuring the glossiness (JIS Z8741 measuring angle 20 °), a corrosion test was conducted under the conditions of Table 2. After the corrosion test, the corrosion resistance was evaluated by measuring the rusting area ratio. The results are shown in Table 3, and the steel sheet treated by the method of the present invention is superior in corrosion resistance and gloss to the steel sheet treated by the comparative method.

[0024]

[Table 1]

[Table 2]

[0025]

[0026]

[0027]

As described above, according to the present invention, by subjecting a stainless steel sheet to an electrochemical treatment, it is possible to efficiently produce a highly corrosion-resistant steel sheet that can be used in a harsh acidic environment. Therefore, its industrial effect is extremely large.

Claims (1)

[Claims] 1. A stainless steel plate made of molybdenum trioxide 1
Immersed in a liquid containing 0 to 300 g / l, phosphoric acid 5 to 300 g / l and hydrochloric acid 0.5 to 20 g / l, and liquid temperature 0 to 90
A method for surface treatment of a stainless steel sheet, which comprises performing anodization and then cathodic treatment under conditions of a temperature of ^{2 to} 200 Asec / dm ² .