JPH09111484A - Stainless steel acid cleaner - Google Patents

Abstract

(57) Abstract: An acid detergent containing hydrofluoric acid for stainless steel, which can increase the dissolution rate without increasing the concentration of hydrofluoric acid is provided. The dissolution rate is markedly increased by adding acetylacetone, sodium oxalate, and hydroxyquinoline, which have a larger complex formation constant with Fe ions than fluorine ions.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to stainless steel acid detergents.

[0002]

2. Description of the Related Art Stainless steel is pickled with sulfuric acid, hydrochloric acid, nitric acid, or nitric hydrofluoric acid (mixed acid of nitric acid and hydrofluoric acid) to produce scales and Cr-free layers produced during hot rolling or annealing, and various causes. The irregularities on the surface formed by (3), such as scale biting during hot rolling and shot blast marks, are removed. These pickling actions are extremely important in order to improve the luster and corrosion resistance which are important properties of stainless steel.

However, as in recent years, if the stainless steel having high corrosion resistance is increased or the plate passing speed of the pickling line is increased in order to improve the productivity, the conventional pickling method is not suitable for scale and descaling. There has been a problem that the Cr layer and surface irregularities formed due to various causes cannot be sufficiently removed. Further, as in recent years, when the cold rolling is performed with a large-diameter roll in order to improve productivity, the unevenness of the hot-rolled sheet is likely to remain even after cold-rolling, and with conventional acid detergents, there is also a problem that gloss decreases. Has occurred. These are caused by the insufficient dissolving power of the pickling solution.

In order to remove irregularities on the surface of stainless steel containing Ni and Mo, which have high corrosion resistance, it is necessary to dissolve base metal with nitric hydrofluoric acid because sulfuric acid and hydrochloric acid have a slow dissolution rate. It is known that increasing the concentration of hydrofluoric acid is effective for increasing the amount of dissolution during nitric hydrofluoric acid pickling, as disclosed in JP-A-60-248889. However, increasing the concentration of hydrofluoric acid means that hydrofluoric acid is a highly corrosive acid, which necessitates a major remodeling of the equipment and produces a large amount of sludge when compared with a constant amount of dissolved steel. It is difficult to realize due to problems. It is also difficult to raise the temperature of nitric hydrofluoric acid because the current pickling conditions are already high, which requires a major modification of the equipment.

[0005]

DISCLOSURE OF THE INVENTION The present invention promotes pickling of stainless steel with an acid containing hydrofluoric acid, and provides gloss and corrosion resistance due to residual surface defects such as scales, de-Cr layers on the surface of base steel and shots. The present invention provides an acid detergent containing hydrofluoric acid, which is capable of increasing the dissolution rate without increasing the concentration of hydrofluoric acid, for the purpose of preventing the decrease of the concentration.

[0006]

The present invention is directed to a stainless steel acid detergent containing hydrofluoric acid, wherein an additive having a complex formation constant with Fe ions larger than that of hydrofluoric acid is added. It is a detergent. As such an additive, one or more compounds selected from the group consisting of acetylacetone, benzoylacetone and furoylacetone are suitable. By the way, the complex formation constant of hydrofluoric acid with Fe ions is 25.5, and in the case of acetylacetone, benzoylacetone and furoylacetone, all are 26.2.
It is. The complex formation constant described here is a complex formation constant in an acid detergent at a pickling temperature, but it is also possible to relatively compare the complex formation constant described in a chemical data book or the like.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of investigations by the present inventors on the dissolution behavior of stainless steel with nitric hydrofluoric acid during pickling, it was found that fluorine ions promote dissolution, but fluorine ions do It was found that the complex was immediately formed with Fe ions and the promoting effect was lost. In particular, it was found that in the vicinity of the steel where the dissolution reaction has occurred, most of the fluorine ions form a complex, which makes it difficult for the dissolution to proceed.

Therefore, the inventors of the present invention can increase the dissolution rate during pickling by adding an additive that is more likely to form a complex with Fe ions than with fluorine ions to inhibit the complex formation of fluorine ions. Therefore, various compounds that form complexes with Fe ions were added to nitric hydrofluoric acid, and the dissolution rates of stainless steels were compared. As a result, as shown in Table 1, it was found that the addition of acetylacetone, benzoylacetone, or furoylacetone, which has a larger complex formation constant with Fe ion than fluorine ion, as an additive has the effect of significantly increasing the dissolution rate. did. This effect is not observed with EDTA (complexation constant 25.1) and ammonium thiosulfate (complexation constant 3.25) whose complex formation constant with Fe ion is smaller than that of hydrofluoric acid. The effects of acetylacetone, benzoylacetone, and furoylacetone are exhibited only when hydrofluoric acid is present, as shown in Table 1 together with the case of nitric acid.

The present invention has been completed based on the above findings. The amount of the above additive added is 0.01 to 0.
It is good to use 5 mol / liter. If it is less than 0.01 mol / liter, the effect of promoting pickling of hydrofluoric acid is insufficient. Even if added in excess of 0.5 mol / liter, the effect will be saturated and it will be uneconomical. More preferably, the lower limit is 0.02 mol / liter or more, and optimally 0.03 mol / liter or more. The upper limit is preferably 0.2 mol / liter or less, and optimally 0.1 mol / liter or less.

[0010]

EXAMPLES The present invention will be described below based on examples. SUS304, SUS316 manufactured by the usual method
The hot-rolled steel strips of No. 1 and the steel strips annealed at 1150 ° C. in the combustion atmosphere of coke gas were shot blasted, and then the pickling loss when pickling under the conditions shown in Table 2 was investigated. . Furthermore, the dew point is -50 after cold rolling with a rolling reduction of 70% using a tandem rolling mill with a work roll diameter of 250 mm.
The gloss and corrosion resistance after bright annealing at 1100 ° C. in ammonia decomposed gas at 0 ° C. were investigated.

Further, SUS30 produced by a usual method
4, cold-rolled steel strip of SUS316 was continuously annealed at 1100 ° C. in a combustion atmosphere of propane gas, and the pickling weight loss when pickling under the conditions shown in Table 3 was investigated, and the corrosion resistance after pickling was further investigated. investigated. Acetylacetone, benzoylacetone, and furoylacetone were used as additives having a complex formation constant with Fe ions larger than that of hydrofluoric acid. Pickling with an acid detergent containing such additives, that is, 2, 3 in Table 2
4, 6, 7, 8, 10, 11, 12, 14, 15, 1
6 and 2, 3, 4, 6, 7, and 8 in Table 3, respectively, are pickling without addition of additives, that is, 1 in Table 2
Compared with Nos. 5, 9 and 13 and Nos. 1 and 5 in Table 3, the pickling weight loss is increased, and the glossiness and corrosion resistance are good.

[0012] The corrosion resistance is visually determined by a test method in which a 5% NaCl aqueous solution at 30 ° C is sprayed for 30 minutes, dried at 60 ° C for 1 hour, and held at 50 ° C in an atmosphere of 98% humidity for 1 hour. It was evaluated by the number of days until it was recognized, and the glossiness was evaluated by a method based on JIS Z8741.

[0013]

INDUSTRIAL APPLICABILITY According to the present invention, when pickling stainless steel containing Ni or Mo and hard to dissolve in acid, even if pickling for a short time, scales, de-Cr layers on the surface layer of base metal, shot eyes, etc. It is possible to remove surface defects and prevent deterioration of gloss and corrosion resistance due to their remaining.

In the examples, nitric hydrofluoric acid is shown, but the effect of the present invention is not limited to nitric hydrofluoric acid, and a pickling solution containing hydrofluoric acid, such as sulfuric acid, ferric nitrate, or fluorine. It is similarly exhibited by mixed acids of acids.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuhide Ishii 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Inside the Technical Research Institute of Kawasaki Steel Co., Ltd. (72) Susumu Sato Susumu 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Corp.

Claims (2)

[Claims] 1. A stainless steel acid detergent containing hydrofluoric acid, wherein an additive having a complex formation constant with Fe ions larger than that of hydrofluoric acid is added. 2. The stainless steel acid detergent according to claim 1, wherein the additive is one or more compounds selected from the group consisting of acetylacetone, benzoylacetone, and furoylacetone.