JPH11269677A - Pickling method of stainless steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily remove corrosion products on the surface of a stainless steel and to obtain a beautiful finish surface by treating a stainless steel with iron (III) chloride and then treating in an soln. containing hydrogen peroxide and an inorg. acid. SOLUTION: First, a stainless steel is treated by using iron (III) chloride at a specified dissolving rate under such conditions that the stainless steel can be dissolved for example, by using 30 to 45 wt.% iron (III) chloride at about 40 to 70 deg.C treatment temp. The treated stainless steel has corrosion products on its surface so that the surface is treated with a soln. containing hydrogen peroxide and an inorg. acid. As to the inorg. acid, hydrochloric acid, sulfuric acid or nitric acid is preferable. The soln. has to contain only 0.1 to 3 wt.% of hydrogen peroxide and 0.1 to 5 wt.% of inorg. acid. The treatment is carried out by spraying using a spray nozzle or the like or by dipping by using aeration means or pump, preferably at about 10 to 60 deg.C treating temp.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for pickling stainless steel to obtain an appropriate surface finish with a pickling solution at a predetermined pickling rate.

[0002]

2. Description of the Related Art Conventionally, pickling of stainless steel has been generally performed by using a mixed acid of hydrofluoric acid and nitric acid.
However, the use of nitric acid poses major environmental and pollution problems. That is, generation of NOx gas at the time of pickling, pollution of the sea area by a processing waste liquid containing a high concentration of nitrate ions, and the like are serious problems. To cope with such a problem, it is necessary to remove nitrate ions from the waste liquid. However, this technique requires large processing equipment and has a heavy burden on running costs, making it extremely difficult to implement. Also, the use of hydrofluoric acid is not preferred in terms of work hazard, environment, and pollution.

Under such circumstances, there is a strong demand for a pickling bath that does not use nitric acid and hydrofluoric acid. For example, Japanese Patent Publication No. 43-5
No. 201, JP-A-50-71524 and JP-A-50-74529 disclose a method of pickling stainless steel comprising ferric chloride-hydrochloric acid. As described above, there have been many reports on a method of pickling stainless steel with a solution composed of ferric chloride-hydrochloric acid, and this method is an effective method that does not use nitric acid or hydrofluoric acid. Japanese Patent Application Laid-Open No. 4-107279 discloses that when a stainless steel is etched with a ferric chloride solution, corrosion products adhere to the melt-processed surface.

[0004]

As described above, ferric chloride used for etching of stainless steel has a problem that corrosion products adhere to the melt-processed surface and generate stains on the processed surface. An object of the present invention is to provide a method for pickling stainless steel which can eliminate such difficulties.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies on a method for removing corrosion products generated on the surface of stainless steel in pickling of stainless steel in a bath of ferric chloride-hydrochloric acid. It has been found that corrosion products can be easily removed by immersion in a solution comprising hydrogen peroxide and an inorganic acid. That is, in the present invention, in pickling a stainless steel, (1) a step of treating the stainless steel with ferric chloride, and (2) a step of treating the treated stainless steel with a solution containing hydrogen peroxide and an inorganic acid. ,
And a method for pickling stainless steel.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The ferric chloride treatment as the first step is set under conditions that can melt stainless steel at a predetermined dissolution rate. For example, when treating SUS304 steel, a sufficient dissolution amount can be obtained if the ferric chloride is 30 to 45% by weight and the treatment temperature is 40 to 70 ° C.

[0007] The SUS304 steel melted in a predetermined amount has corrosion products on its surface. In the second stage, the SUS 304 steel in which the corrosion product has been generated is treated with a solution comprising hydrogen peroxide and an inorganic acid. The inorganic acid is preferably hydrochloric acid, sulfuric acid or nitric acid. The solution used here is hydrogen peroxide 0.1.
What is necessary is just to contain 1 to 3 weight% and to contain 0.1 to 5 weight% of inorganic acids.

In order to prevent metals other than the corrosion products of SUS304 steel from dissolving by performing the process for removing the corrosion products, the concentration of the inorganic acid is set to the minimum concentration at which the corrosion products can be removed. Is preferred. Also, the concentration of hydrogen peroxide is preferably set to the minimum concentration as in the case of the inorganic acid, in order to reduce the consumption by self-decomposition. That is, a concentration at which a desired corrosion product can be removed is previously obtained from a stainless steel test sample to be subjected to the removal of the corrosion product, and when the corrosion product is removed, the corrosion product removal process is performed while maintaining the obtained concentration. .

In the corrosion product removal procedure, a solution of a predetermined concentration of hydrogen peroxide and an inorganic acid is prepared, and the solution is sprayed on a stainless steel in which the corrosion product has been generated using a spray nozzle or the like, or aeration or pumping is performed. A desired method such as an immersion method using circulation may be appropriately selected. Processing temperature is 10-6
0 ° C. is preferred. The higher the treatment temperature, the shorter the corrosion product removal time, but the lower the treatment temperature, the more advantageous it is in suppressing the self-decomposition of hydrogen peroxide. Can be performed.

As the hydrogen peroxide used in the present invention, an aqueous solution of any concentration can be used, but 35% by weight or 60% by weight.
Are preferred because they are available as industrial chemicals.
Also, hydrochloric acid, sulfuric acid, and nitric acid as inorganic acids can be used in an aqueous solution of any concentration, but those having 35% by weight, 95% by weight, and 65% by weight are preferable because they can be obtained as industrial chemicals.

The method of the present invention can be applied regardless of the type of stainless steel and the manufacturing history. For example, it can be applied to austenitic and ferritic steels as well as hot-rolled steel sheets and cold-rolled steel sheets.

[0012]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to the examples.

Austenitic stainless steel SUS30
4 and a test piece (50 × 30 × 0.8 mm) of ferritic stainless steel SUS430 were immersed in a 30 to 45% by weight ferric chloride solution at 50 to 60 ° C.
A dissolution amount of 0 μm was obtained. The treated surfaces of all stainless steels were covered with black corrosion products. Corrosion product removal conditions include hydrogen peroxide concentration, inorganic acid concentration,
The processing time and the processing temperature were appropriately selected. Table 1 shows the processing results. Inorganic acid alone could not remove corrosion products under any conditions, but when treated with a mixed solution of hydrogen peroxide and inorganic acid, the corrosion products were removed and a surface with appropriate gloss was obtained.

[0014]

According to the present invention, corrosion products generated on the surface of stainless steel after ferric chloride treatment can be easily removed, and a clean finished surface can be obtained.

[0015]

[Table 1]

Claims (3)

[Claims] 1. When pickling a stainless steel, (1) a step of treating the stainless steel with ferric chloride, and (2) a step of treating the treated stainless steel with a solution containing hydrogen peroxide and an inorganic acid. A method for pickling stainless steel. 2. The method for pickling stainless steel according to claim 1, wherein the inorganic acid is hydrochloric acid, sulfuric acid or nitric acid. 3. The method of pickling stainless steel according to claim 1, wherein the solution contains 0.1 to 3% by weight of hydrogen peroxide and 0.1 to 5% by weight of an inorganic acid.