JPH10324984A - Acid pickling solution of stainless steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain acid pickling solution which can efficiently wash a stainless steel containing martensitic steel and ferritic steel without developing mist, harmful gas, etc., and also, eutrofication of the waste water by incorporating hydrofluoric acid, chloric acid and hydrochloric acid or sulfuric acid. SOLUTION: This acid pickling solution for stainless steel, containing 0.5-5 wt.% hydrofluoric acid, 0.5-30 wt.% chloric acid and 1-15 wt.% hydrochloric acid, 1-25% sulfuric acid or 1-25% hydrochloric acid + sulfuric acid, is avoided to use nitric acid generating the waste solution containing high concn. of the nitric acid ion and NOx gas and hydrogen peroxide which is poor in the washing effect to the martensitic steel and the ferritic steel and easily developes the mist. Since this acid pickling solution contains the hydrochloric acid and the sulfuric acid, etc., the chloric acid is added in the alkaline salt and the cost can be reduced. This acid pickling solution is used at <pH1 in the above component concns. and scale on the stainless steel is efficiently removed by contacting with this acid pickling solution at the room temp. - about 60 deg.C for about 1-60 min, and finished to the good outward appearance.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD OF THE INVENTION

The present invention relates to a pickling solution for stainless steel, and more particularly to a pickling solution for stainless steel without using nitric acid.

[0002]

2. Description of the Related Art Conventionally, pickling of stainless steel has been performed in a mixed acid bath in which two or more kinds of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid and the like are mixed. It is common to use a liquid.

However, the pickling solution containing nitric acid causes problems such as eutrophication at the time of drainage due to the high concentration of nitrate ions contained in the pickling treatment waste liquid. Therefore, there is a problem that the equipment and operation costs for this need to be increased. Further, there is a problem that nitric acid is decomposed during pickling to generate NOx gas.

[0004] Therefore, as a pickling method without using nitric acid, for example, Japanese Patent Application Laid-Open No. 60-243289 discloses a pickling solution for stainless steel composed of hydrofluoric acid-hydrochloric acid (or sulfuric acid) -hydrogen peroxide. This pickling solution can efficiently pickle general stainless steel without using nitric acid, but is inferior in cleaning effect on martensitic steel and ferritic steel. In addition, since hydrogen peroxide is decomposed during pickling, replenishment is required, and mist is easily generated.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to efficiently wash stainless steel including martensitic steel and ferrite steel without using nitric acid and hydrogen peroxide, and to remove mist during cleaning. An object of the present invention is to provide a pickling solution capable of preventing generation.

[0006]

The present invention relates to the following pickling solution. (1) A pickling solution for stainless steel, comprising hydrofluoric acid, chloric acid, hydrochloric acid or sulfuric acid. (2) Hydrofluoric acid 0.5-5% by weight, chloric acid 0.5-30
A pickling solution for stainless steel, comprising 1% to 15% by weight of hydrochloric acid, 1 to 25% by weight of sulfuric acid, or 1 to 25% by weight in total of both.

From the viewpoint of washing, hydrofluoric acid and chloric acid are preferably mixed in the form of an acid. However, it is sufficient that the acid is present in the pickling solution in the form of an acid. May be added in the form of a salt. In particular, since chloric acid is easily available in the form of a salt, it is more cost-effective to mix it in the form of a salt. When compounded in the form of a salt, an alkali metal salt such as a sodium salt and a potassium salt is preferable. Since hydrochloric acid and sulfuric acid are blended to ensure detergency, they are both blended in the form of an acid. Each of these components is dissolved in water to form a pickling solution.

[0008] The concentration of each component in the pickling solution is 0.1% for hydrofluoric acid.
5-5% by weight, preferably 2-4% by weight, chloric acid is 0.1%
5-30% by weight, preferably 5-15% by weight, hydrochloric acid 1
15% by weight, preferably 5 to 10% by weight, sulfuric acid 1 to 25
% By weight, preferably 5 to 15% by weight, and when both are used, the total amount of both is 1 to 25% by weight, preferably 5 to 15% by weight. It is preferable that the pH of the pickling solution is 1 or less.

The pickling solution of the present invention may contain, in addition to the above components, inorganic acids and organic acids and additives as other acids, but may not contain them, especially nitric acid and hydrogen peroxide. It is better not to mix them. In addition, as an additive,
Corrosion inhibitors, dissolution promoters, surfactants and the like can be added.

The above-mentioned pickling solution is prepared by dissolving each of the above-mentioned acid components and optionally added additives and the like in water.
In this case, a pickling solution can be prepared in advance in a factory or the like and subjected to pickling, but it can also be prepared at a pickling site and pickled as it is. In the case of preparing on-site, the pickling solution can be adjusted by adding each component to water while the object to be cleaned is in contact with water.

In the acid cleaning method, cleaning is performed by bringing an object to be cleaned into contact with an acid cleaning solution. As the contact method, any method such as immersion, jet, spray, etc. can be adopted, but stirring, pump circulation,
It is preferable to make contact by applying physical force by jet, spray or the like.

The conditions of the pickling vary depending on the type of the object to be cleaned, the type of scale, the state of adhesion, etc., but the temperature of the pickling solution is from room temperature to 60 ° C., preferably 40 to 50 ° C., and the contact time is 1 to 1.
It is suitable for 60 minutes, preferably about 5 to 15 minutes.
The pressure may be normal pressure, but it is 0.1 to 1 MPa, preferably 0.3 to 0.5 MPa when jetting or spraying.
It is preferable to inject the acid solution at a pressure of the order.

In the present invention, the concentration of each component of the pickling solution may be at the above-mentioned concentration before the start of the pickling, and the acid may be consumed during the continuation of the pickling to lower the concentration outside the above range.
When the concentration decreases, the detergency can be maintained by supplying the decreased component to maintain the concentration.

When the stainless steel is washed with the pickling solution of the present invention, the scale is partially dissolved by fluoride ions, and the metal base material is dissolved by the addition of hydrofluoric acid, chloric acid and hydrochloric acid or sulfuric acid. It is presumed that this weakens the adhesive force between the metal material and the scale, and the scale is easily peeled off and removed.

Here, the reaction of dissolution of the metal base material by chloric acid and another acid is presumed to be based on the following reaction formula when the metal is iron.

Embedded image Fe + ClO ₃ ⁻ + 3H ⁺ → Fe ²⁺ + HClO ₂ + H ₂ O (1)

The scale attached to the stainless steel is removed by such a reaction, and the general scale of stainless steel including martensite steel and ferrite steel can be efficiently removed, and the finished appearance is good. This tendency is more remarkable when using sulfuric acid than when using hydrochloric acid. Further, unlike the case of hydrogen peroxide during the acid cleaning, no mist is generated due to the generation of bubbles due to self-decomposition, and the working environment is less contaminated.

The pickling effluent produced by the washing can be neutralized by adding sodium hydroxide, slaked lime, etc., to render it harmless.

[0018]

As described above, since the acid washing of the present invention comprises hydrofluoric acid, chloric acid, hydrochloric acid or sulfuric acid, it does not need to use nitric acid which leads to eutrophication or hydrogen peroxide which is highly self-decomposing. Accordingly, stainless steel including martensite steel and ferrite steel can be efficiently cleaned, and generation of mist during cleaning can be prevented.

[0019]

Embodiments of the present invention will be described below. In each case,% is% by weight.

Examples 1 and 2, Comparative Examples 1 and 2 As pickling solutions of Examples 1 and 2 and Comparative Examples 1 and 2, aqueous solutions of the following components were prepared. Example 1: Hydrofluoric acid 2% + sodium chlorate 5% + hydrochloric acid 5
% Example 2: 2% hydrofluoric acid + 5% sodium chlorate + 1 sulfuric acid
0% Comparative Example 1: 4% hydrofluoric acid + 3% hydrogen peroxide + 2% hydrochloric acid Comparative Example 2: 2% hydrofluoric acid + 13% nitric acid

With these pickling solutions, pickling was performed by the following operation. First, stainless steel SUS3 with scale attached
04, SUS430, SUS403 steel plate 2cm x 2
The test piece was cut into a size of cm, and 500 ml of the cleaning solution was prepared as described above to obtain a cleaning solution. Each washing solution was transferred to a 500 ml polyethylene beaker, adjusted to 40 ° C. in a thermostat, and the test piece was immersed in the washing solution. After 10 minutes, the test piece was taken out, washed with water, and water and dirt were removed with gauze. Finally, the surface condition was observed. Further, after washing, the washing effluent was neutralized with sodium hydroxide. Table 1 shows the results.

[0022]

[Table 1]

Notes in Table 1 SUS403 = Martensitic steel SUS430 = Ferritic steel SUS304 = Austenitic steel Scale removal ○: All scales removed △: Most scales removed ×: Some scales remain Finished ○: Glossy Beautiful finish ×: Dark finish

From the results shown in Table 1, it can be seen that the example of the present invention is superior to the comparative example 1 using hydrogen peroxide in the detergency of martensite steel and ferritic steel, and the example 2 using sulfuric acid is particularly excellent. It turns out that it has detergency. In the example, no mist was generated.

Claims (2)

[Claims] 1. A pickling solution for stainless steel, comprising hydrofluoric acid, chloric acid, hydrochloric acid or sulfuric acid. 2. 0.5 to 5% by weight of hydrofluoric acid, 0.5 to 30% by weight of chloric acid, 1 to 15% by weight of hydrochloric acid, 1 to 25% by weight of sulfuric acid, or 1 to 2 in total of both.
A pickling solution for stainless steel, comprising 5% by weight.