JP3411136B2 - Pickling method for Ni-based stainless steel sheet - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a pickling method for Ni (austenitic) stainless steel sheets.

[0002]

2. Description of the Related Art As a method for descaling a Cr-based stainless steel sheet, it is common to carry out sulfuric acid pickling, as disclosed in Japanese Patent Laid-Open No. 64-288.

However, when Ni-based stainless steel is washed with sulfuric acid, the finished surface is blackened, and it is difficult to secure quality. This black smut cannot be removed by a mechanical method such as brushing.

Therefore, as a method of removing the surface oxide scale after hot rolling of Ni-based stainless steel sheets, conventionally, hot derolled steel sheets are subjected to mechanical descaling such as shot blasting and then preheated to an appropriate temperature to obtain an appropriate concentration. The method of pickling with an aqueous solution of nitric hydrofluoric acid (Japanese Patent Application Laid-Open No. 61-245912, Japanese Patent Application Laid-Open No. 61-49706, etc.) and neutral salt electrolysis are used.

[0005]

However, in the method of pickling with an aqueous solution of nitric hydrofluoric acid, since a strong acid is used, it is necessary to provide the pickling tank and the circulation system with an acid resistant structure applicable to nitric hydrofluoric acid. The initial salt cost and the facility maintenance cost are high, and the neutral salt electrolysis method has a problem that the acid cost and the electrolysis cost are high.

The problem to be solved by the present invention is to enable the sulfuric acid pickling of Ni-based stainless steel at a low cost by enabling the whitening treatment after the sulfuric acid pickling in the Ni-based stainless steel.

[0007]

In order to solve the above problems, the method for pickling Ni-based stainless steel sheet according to the present invention is
(Sulfuric acid) / (nitric acid) =
The surface of the steel sheet is cleaned with a whitening pickling solution containing sulfuric acid and nitric acid having a concentration ratio of 2.5 to 100 (weight% ratio), and then washed with water.

The whitening pickling solution may further contain a substance that prevents dissolution of the ground iron, a surfactant that accelerates the pickling reaction, and a surfactant that contains a urea compound and an organic acid. it can.

[0009]

In the present invention, first, descaling was performed by sulfuric acid pickling, the blackened surface was washed with a mixed solution of sulfuric acid and nitric acid to remove the surface layer, and a silver-white surface peculiar to Ni-based stainless steel was obtained. After that, the residual acid is washed with water. At this time, by adding a surfactant to the whitening pickling solution, it is possible to improve the degree of whitening and suppress the generation of nitrogen oxide gas (NOx gas).

[0010]

【Example】

Example 1 Hereinafter, the present invention will be specifically described with reference to Examples.

FIG. 1 is a schematic view showing the pickling step of the present invention. In the figure, 1 is a hot coil around which a hot rolled steel plate 2 is wound, 3
Is a pickled coil. Between the hot coil 1 and the pickled coil 3, a mechanical descaling step I, a sulfuric acid pickling step II of the present invention, a whitening treatment step III and a hot water washing step IV are performed. In the mechanical descaling step I, the scale on the surface of the steel plate 2 is cracked by known shot blasting or the like to remove the coarse scale. In the next sulfuric acid pickling step II, the sulfuric acid concentration heated to 90 ° C was 300 g /
Immerse the steel sheet in 1 of acid or spray the steel sheet with acid. FIG. 2 shows the relationship between the pickling time and the amount of scraping, and the pickling is completed in about 60 seconds when the scraping of 4 μm is performed. Then, in an acid solution that mixes sulfuric acid and nitric acid, EO that prevents the dissolution of base iron
4% of a surfactant consisting of a PO copolymer compound, an ionic urea compound and an organic acid, and 5% of a surfactant consisting of a urea compound and an organic acid for suppressing the generation of nitrogen oxide gas (NOx gas).
The steel sheet is immersed in the whitening pickling solution containing the above or the whitening pickling solution is sprayed on the steel sheet. FIG. 3 shows changes in the color of the surface of the steel sheet when the concentrations of sulfuric acid and nitric acid were changed. The Cr-based stainless steel can be whitened by 5-20% nitric acid alone, but the Ni-based stainless steel was not whitened when sulfuric acid was 0%.

As these measurement results show, (sulfuric acid)
The whitening treatment was good in the concentration ratio range of / (nitric acid) = 2.5 to 100 (weight% ratio).

FIG. 4 shows the nitric acid concentration when the sulfuric acid concentration is fixed at 30%, and the color of the plate surface depending on the presence or absence of the addition of a surfactant that prevents dissolution of the base iron. As shown in FIG. 4, in order to improve the degree of whitening, it is effective to add a surfactant that prevents the dissolution of base iron.

Example 2 In the pickling step of Example 1, 0.25% of monochloroacetic acid as a surfactant for promoting pickling was added to an acid solution obtained by mixing sulfuric acid and nitric acid at the time of whitening treatment, and nitrogen oxidizing gas ( It is also possible to use a whitening pickling solution containing a urea compound that suppresses the generation of NOx gas) and a 5% surfactant consisting of an organic acid, and dip the steel sheet in the same solution or spray the same onto the steel sheet. is there.

FIG. 5 is based on a whitening solution containing 30% sulfuric acid, 4% nitric acid, and 5% of a surfactant consisting of a urea compound and an organic acid, and shows the life of the solution depending on the presence or absence of addition of monochloroacetic acid for promoting pickling. It is an evaluation of change. As shown in FIG. 5, the addition of a surfactant that promotes pickling improves the liquid life, and the N generated during sulfuric acid pickling even when a large amount of steel sheet is treated.
The smut of i-type stainless steel can be removed.

[0016]

As described above, according to the present invention, the effective whitening treatment is performed later, which makes it possible to perform sulfuric acid pickling of Ni-based stainless steel, which is widely used in the stainless steel. Since the use of a mixture of nitric acid and hydrofluoric acid can be changed to sulfuric acid, which is widely used in Cr-based stainless steel, equipment construction costs can be reduced, pickling running costs can be reduced,
There are remarkable effects such as elimination of nitric hydrofluoric acid sludge treatment, avoidance of danger to hydrofluoric acid, and reduction of equipment maintenance cost. Further, in a line where both Cr and Ni-based stainless steel are produced, the equipment, working time, and cost required for liquid switching are unnecessary.

[Brief description of drawings]

FIG. 1 shows a hot coil pickling facility.

FIG. 2 shows the relationship between the pickling time and the amount of fusing when pickling Ni-based stainless steel with sulfuric acid.

FIG. 3 shows changes in the color of the surface of a steel sheet due to changes in sulfuric acid and nitric acid concentrations.

FIG. 4 shows changes in the color of the surface of the steel sheet with and without the addition of a surfactant that prevents the dissolution of base iron.

FIG. 5 shows changes in liquid life when a surfactant that promotes pickling is added.

[Explanation of symbols]

1 hot coil 2 steel plate 3 pickled coil

Continuation of the front page (56) Reference JP-A-8-35086 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C23G 1/08 B21B 45/06

Claims (3)

(57) [Claims] 1. A Ni-based stainless steel sheet is washed with sulfuric acid,
(Sulfuric acid) / (nitric acid) = 2.5 to 100 (% by weight ratio) The surface of the steel sheet is cleaned with a whitening pickling solution containing sulfuric acid and nitric acid, and then washed with water. A pickling method for a Ni-based stainless steel sheet, which is characterized in that 2. The pickling method for Ni-based stainless steel sheet according to claim 1, wherein a surfactant for preventing dissolution of base iron or a surfactant for promoting a pickling reaction is further added to the whitening pickling solution. 3. The whitening pickling solution contains nitrogen oxide gas (NO
The method for pickling Ni-based stainless steel according to claim 1, further comprising a surfactant composed of a urea compound and an organic acid for suppressing generation of (x gas).