JP3092789B2 - Pickling liquid for stainless steel and method for pickling stainless steel using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pickling solution used for pickling stainless steel and a method for pickling stainless steel using the pickling solution.

[0002]

2. Description of the Related Art In the process of manufacturing stainless steel, in order to remove scale or a Cr-free layer generated during hot rolling or annealing, and to remove surface irregularities formed by various causes, for example, hot rolling. Acids such as sulfuric acid and hydrochloric acid to smooth out the scale digging and shot blast marks,
Alternatively, so-called pickling, in which steel is immersed in the mixed acid to dissolve the base iron, is performed.

[0003] This pickling is a very important step for improving gloss and corrosion resistance, which are important properties of stainless steel, and it is desirable to sufficiently dissolve the base iron. From such a viewpoint, in acid pickling of stainless steel, since the dissolution rate is slow with an acid such as sulfuric acid or hydrochloric acid, for example, 80 ° C.
For example, an acid pickling method of immersing in high-temperature, high-concentration acid having a large dissolving power for a long time, such as immersion in 20% sulfuric acid for 60 seconds, is used.

[0004] However, as the number of stainless steels having high corrosion resistance increases in recent years, there has been a problem that the conventional pickling method cannot sufficiently remove the scale and the Cr-free layer on the surface of the ground iron. In addition, as in recent years, when cold rolling is performed with a large-diameter roll in order to improve productivity,
Irregularities of the hot rolled sheet are likely to remain even after cold rolling, and the conventional pickling method has also caused a problem that gloss is reduced.

[0005] These problems are caused by insufficient dissolution of stainless steel during pickling. In order to increase the amount of dissolution during pickling, it is of course effective to increase the concentration and temperature of the acid and to lengthen the immersion time. However, as described above, under the current pickling conditions, since a high-concentration, high-temperature pickling solution has already been used, it is actually difficult to make further improvements, and the equipment has been significantly It is not economical because it requires remodeling.

[0006] Increasing the concentration of sulfuric acid is not economical because the slurry in waste acid treatment increases. JP-A-47-34122 discloses a method for increasing the amount of dissolution during pickling. In this method, a composition containing a reducing inorganic or organic compound and an aromatic or aliphatic compound having a -SO ₃ group (including -O-SO ₃ group) alone or in combination is added to an acid solution. And a method for accelerating the pickling of metals, which is characterized by adding a surfactant to the acid solution, in addition to the method.

The above compounds include sodium nitrite,
Examples include sodium thiosulfate, sodium sulfide, sodium sulfoxylate formaldehyde, anisaldehyde, benzaldehyde, acetaldehyde, formalin, ascorbic acid, toluenesulfonic acid, alkylsulfonic acid, cresolsulfonic acid, nitrosulfonic acid, naphthalenesulfonic acid, and glyoxal. It is listed in.

[0008] However, although these compounds do not always show a sufficient effect or have an effect of accelerating pickling, they generate toxic hydrogen sulfide at the time of addition and form colloidal S which causes clogging of piping. There is a problem that occurs.

[0009]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and can remove scales and the like in a short time of immersion in pickling of stainless steel, which had been required to have strict pickling conditions. Still another object of the present invention is to provide a pickling solution for stainless steel that does not generate toxic gas or colloidal S when a pickling accelerator is added, and a method for pickling stainless steel using the same.

[0010]

A first aspect of the present invention is a pickling solution for stainless steel containing an organic compound having a disulfide bond. In the first aspect, the organic compound preferably further has a carboxyl group and / or a hydroxyl group.

Preferably, the organic compound is an aliphatic compound and / or an aromatic compound. Further, the organic compound is preferably one or more selected from dithiodiacetic acid, dithiodipropionic acid, dithiosalicylic acid, and dithiodiethanol.

A second invention is a method for pickling stainless steel, comprising using the pickling solution of the first invention when pickling a hot-rolled stainless steel material. Further, in the first and second inventions, the acid of the pickling solution is preferably sulfuric acid, hydrochloric acid or a mixed acid of sulfuric acid and hydrochloric acid.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The present inventors have added the additives shown in the above publication to 80
As a result of examining the dissolution rate of SUS430 when added to 20% sulfuric acid at ℃, it was confirmed that the dissolution rate was increased by sodium thiosulfate and sodium sulfide.

However, sodium sulfide is used because harmful hydrogen sulfide is generated at the time of addition, and sodium thiosulfate is used because sodium is released in a colloidal state at the time of addition and causes clogging of piping. Can not do it.
Therefore, the present inventors have further proposed that an aqueous solution of sulfuric acid and an aqueous solution of hydrochloric acid containing various organic compounds further include hydrogen generated in the pickling solution according to the following formula (1) or (2) constituting the elementary reaction of the pickling reaction. Focusing on the behavior of the bubbles, the following [1] and [2] were found.

<Sulfuric acid> Fe + H ₂ SO ₄ → FeSO ₄ + H ₂ ↑ (1) <Hydrochloric acid> Fe + 2HCl → FeCl ₂ + H ₂ 〔(2) [1] When pickling stainless steel, In addition, hydrogen bubbles adhering to the surface of the steel sheet hinder pickling.

[2] An organic compound such as an aliphatic compound having a disulfide bond, such as dithiodiacetic acid, dithiodipropionic acid, dithiosalicylic acid, dithiodiethanol, or an aromatic compound, is added in a very small amount to sodium thiosulfate, It has an effect of accelerating pickling more than sodium sulfide and does not generate hydrogen sulfide or colloidal S when added. The present invention has been made based on the above-mentioned newly found knowledge.

The mechanism by which the organic compound promotes pickling is considered as follows. That is, the hydrogen gas generated when the steel is melted during pickling remains attached to the steel sheet surface until bubbles of an appropriate size are formed, and no melting reaction occurs in the portion covered by the bubbles. Therefore, for example, in a pickling solution containing an organic compound having a disulfide bond that is a -SS- bond, the organic compound having a disulfide bond easily adheres to the surface of the steel sheet, and the wettability of the steel sheet to the pickling solution is significantly improved. Is done.

[0018] As a result, the pickling liquid helps the air to flow between the air bubbles and the steel sheet, the hydrogen gas is easily separated from the steel sheet surface, and the hydrogen bubbles adhering to the steel sheet surface are reduced to a small bubble diameter stage. Floats and separates quickly to accelerate the dissolution reaction. The organic compound having a disulfide bond in the present invention is more preferably a carboxyl group and / or
Alternatively, it preferably has a hydroxyl group.

This corresponds to the carboxyl group of the organic compound,
Hydroxyl groups are caused by OH caused by oxides on the metal surface
This is considered to be because hydrogen gas is easily separated from the steel sheet surface because of its good affinity with the base group and the COOH group, thereby promoting the dissolution reaction. As the organic compound, the following general formulas (3) and (4)
And an organic compound of at least one kind selected from aromatic compounds such as dithiosalicylic acid represented by the following formulas (5) and (6).

S ₂ (C _n H _2n COOH) ₂ ... (3) S ₂ (C _n H _2n OH) ₂ ... (4) Equations (3) and (4) , N represents an integer selected from 1 to 10,
More preferably, n is preferably an integer selected from 1 to 5.

[0021]

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[0022]

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The aliphatic compounds represented by the general formulas (3) and (4) include S ₂ (CH ₂ COOH) ₂ (dithiodiacetic acid) and S ₂ (CH ₂ CH ₂ COOH) ₂ ( Dithiodipropionic acid) and S ₂ (CH ₂ CH ₂ OH) ₂ (dithiodiethanol) are preferred. Also, the above equation
The dithiosalicylic acid represented by (5) or (6) may have a substituent such as an alkyl group.

Further, in the present invention, the hydrogen atom of the carboxyl group of the compound represented by the general formulas (3) and (5) before mixing with an acid is an alkali metal such as Na or K or Ca,
It may be substituted with an alkaline earth metal such as Mg. Examples of the acid of the pickling solution (acid aqueous solution) of the present invention include hydrofluoric acid, nitric acid, hydrochloric acid, sulfuric acid and a mixed acid of these acids, and more preferably hydrochloric acid, sulfuric acid or a mixed acid of hydrochloric acid and sulfuric acid. preferable.

The content of the organic compound having a disulfide bond (hereinafter referred to as an acid pickling accelerator) in the pickling solution (acid aqueous solution) of the present invention is 0.05 to 10 mmol / l (mmol / l). And more preferably 0.1
Preferably it is 5 mmol / l. If it is less than 0.05 mmol / l, the effect of accelerating pickling is small, and if it exceeds 10 mmol / l, no further effect of accelerating pickling is obtained, and in some cases, the effect of accelerating pickling is reduced and it is not economical. .

Further, a surfactant may be added to the pickling solution of the present invention. As surfactants, sodium laurate, sodium dodecylbenzenesulfonate,
Sodium dodecyl sulfate (SDS), stearylamine hydrochloride, stearyltrimethylammonium chloride,
Glycerin monostearate, polyoxyethylene nonylphenyl ether, polyethylene glycol oleate, lauric diethanolamide,
Lauryl dimethyl acetate betaine, 2-undecyl-N-
Carboxymethyl-N-hydroxyethylimidazolinium betaine is exemplified.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. SUS304, SUH409, SUS4 manufactured by normal method
10, SUS430, SUS436J1L hot rolled steel strip and after hot rolling,
The steel strips which were batch or continuously annealed under the conditions shown in the column of steel strip production conditions in Table 1 were shot blasted,
Pickling was performed under the conditions shown in Table 1.

Next, regarding the obtained steel strip after pickling, (1) weight loss of pickling, and (2) the steel strip after the above-mentioned pickling and after further performing the following post-treatment, according to the steel type. It was investigated how glossiness and corrosion resistance are changed by the addition of the pickling accelerator in the present invention. [SUS304:] (1) Loss of acid pickling (2) After pickling, and then cold rolled at a rolling reduction of 70% using a tandem rolling mill with a work roll diameter of 250 mm, in an ammonia decomposition gas with a dew point of -50 ° C, 1150 Gloss and corrosion resistance after bright annealing at ℃.

[SUH409:] (1) Loss on pickling (2) After pickling, the roll was rolled at a rolling reduction of 70% using a tandem rolling mill having a work roll diameter of 250 mm, and 5% hydrogen with a dew point of -40 ° C was added. Corrosion resistance after annealing at 880 ° C. in nitrogen gas containing and electrolytic pickling at 40 C / dm ² in 15% HNO ₃ and 1% HCl.

[SUS410:] (1) Loss on pickling (2) Corrosion resistance after pickling. [SUS430:] (1) Loss of pickling (2) After pickling, cold rolled at a rolling reduction of 70% using a tandem rolling mill with a work roll diameter of 250 mm and then decomposed in ammonia decomposition gas with a dew point of -50 ° C. Gloss and corrosion resistance after bright annealing at ℃.

[SUS436J1L:] (1) Loss of pickling (2) After pickling, after cold rolling at a rolling reduction of 70% in a tandem rolling mill with a work roll diameter of 250 mm, in a propane gas combustion atmosphere at 1000 ° C. Annealing in 20% Na ₂ SO ₄ aqueous solution 1
And neutral salt electrolyte of 20C / dm ^2, pickled in a mixed acid of 10% HNO ₃ and 3% HF, the corrosion resistance after the nitric acid electrolysis of 40C / dm ² in 10% HNO _3.

The corrosion resistance was determined by adding an aqueous solution of 5% NaCl at 30 ° C. for 30 mi.
n Spraying, drying at 60 ° C for 1 hour, 50% at 98% humidity
The test method was repeated by holding for h, and evaluated by the number of days until rust was visually observed. The glossiness is JISZ
It was evaluated by a method based on 8741. The evaluation results are shown in Table 1 together with the steel strip production conditions and the pickling conditions.

As shown in Table 1, Experiment Nos. 2, 4, and 4 using the pickling solution to which the pickling accelerator according to the present invention was added.
6, 8, 9, 11, 13, 15, 17, 19, 20, 22, 24, and 26 (Examples 1 to 14) of Experiment Nos. 1 and 3, respectively, in which no pickling accelerator was added. , 5,7,10,12,14,16,18,2
Compared with 1, 23, 25 (Comparative Examples 1 to 12), the pickling effect, glossiness, and corrosion resistance are significantly superior.

Further, as a result of adding the pickling accelerator according to the present invention to the pickling solution and using it, no odor of hydrogen sulfide was detected in any of the above-mentioned experiments. Further, no colloidal products were found in the piping system such as a heat exchanger, and a smooth operation was possible.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

According to the present invention, the rate of dissolution during pickling is extremely slower than that of ordinary steel, and the scale and ground iron surface layer are removed in the pickling of stainless steel, which had previously been required to have strict pickling conditions. Surface defects such as a Cr layer and shots can be removed by immersion for a short time, and a decrease in gloss and corrosion resistance due to their remaining can be prevented very effectively.

Further, the present invention has an industrially superior effect that does not cause environmental and operational disadvantages such as generation of toxic gas or colloidal S when an acid pickling accelerator is added.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinji Yamazaki 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Chiba Works (58) Field surveyed (Int. Cl. ⁷ , DB name) C23G 1 / 08 C23G 5/032

Claims (4)

(57) [Claims] 1. A pickling solution for stainless steel, comprising an organic compound having a disulfide bond. 2. The pickling solution for stainless steel according to claim 1, wherein the organic compound further has a carboxyl group and / or a hydroxyl group. 3. The pickling solution for stainless steel according to claim 1, wherein the organic compound is one or more selected from dithiodiacetic acid, dithiodipropionic acid, dithiosalicylic acid, and dithiodiethanol. 4. A method for pickling stainless steel, comprising using the pickling solution according to claim 1 when pickling a hot-rolled stainless steel material.