JP2974597B2 - Manufacturing method of dull finish stainless steel plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a dull-finished stainless steel sheet which is used by applying unpainted or transparent paint to interior and exterior building materials and vehicle exterior materials.

[0002]

2. Description of the Related Art The following two types of processes can be given as typical examples of a cold rolling production process for producing a dull-finished stainless steel sheet. [First Cold Rolling Manufacturing Process] (1) The hot rolled steel strip is subjected to an annealing and pickling step to obtain a hot rolled coil. (2) The above-mentioned hot rolled coil is subjected to a cold rolling step to obtain a cold rolled coil. Dull finishing is performed using a dull roll in the final pass of this cold rolling step. (3) After subjecting the cold-rolled coil to an annealing / pickling step, the coil is subjected to a refining step including temper rolling to obtain a dull-finished stainless steel sheet.

[Second Cold Rolling Manufacturing Process] (1) A hot rolled steel strip is subjected to an annealing and pickling step to obtain a hot rolled coil. (2) The above-mentioned hot rolled coil is subjected to a cold rolling step to obtain a cold rolled coil. However, in this cold rolling step, all passes are performed using smooth rolls, and dull finishing is not performed. (3) This cold-rolled coil is subjected to an annealing and pickling step. (4) Only one pass of cold rolling is performed using a dull roll, and dull finishing is performed. (5) The stainless steel plate subjected to the dull finish in the above process is further subjected to an annealing and pickling process, and then subjected to a refining process including temper rolling to obtain a dull finish stainless steel plate.

On the other hand, the pickling in the annealing / pickling step in the cold rolling production process of a general stainless steel having a smooth surface requires the stainless steel to have a beautiful surface. A light pickling treatment is performed to remove only the oxide scale formed on the surface and not to roughen the underlying steel surface as much as possible. In the cold rolling process of dull finish stainless steel, the pickling is the same as that of ordinary smooth stainless steel, from the viewpoint that the anti-glare property required for the product is imparted by dull rolling. Had been done.

[0005]

When a large number of dull-finished stainless steel plates manufactured by the above-described two processes are used on the same plane outdoors, the color tone difference between the steel plates is large, and in particular, between the production lots (coils). The difference in color tone is large and often aesthetically undesirable. An object of the present invention is to provide a method for producing a dull-finished stainless steel sheet having a small difference in color tone between production lots.

[0006]

The above objects and advantages of the present invention are as follows. First, (i) a pickling treatment in an annealing / pickling step performed after dull finish rolling of a stainless steel plate; or (ii) Performed after the cold rolling step, and at least one of the pickling treatment of the annealing and pickling step performed before and after the dull finish rolling of the stainless steel sheet,
(A) Sulfuric acid concentration is 50 to 250 g / l, temperature is 50 to 8
0 ° C., and the electrolytic current density is 100 to 300 mA / cm
Performed subsequent to electrolytic treatment and (ii) the electrolytic treatment in the aqueous solution of sulfuric acid takes place under conditions of ^2, the nitric acid concentration is 70~150g / l, temperature 50 to 80 ° C., and the electrolysis current density is 50 to This is achieved by a method for producing a dull-finished stainless steel sheet, which comprises electrolytic treatment in a nitric acid aqueous solution performed under a condition of 300 mA / cm ² . Hereinafter, this manufacturing method is also referred to as a first invention.

Further, the above objects and advantages of the present invention are as follows:
Secondly, (i) the pickling treatment in the annealing / pickling step performed after the dull finish rolling of the stainless steel sheet, or (ii) the pickling treatment is performed after the cold rolling step, and before and after the dull finish rolling of the stainless steel sheet. At least one of the pickling treatments in the annealing / pickling step performed later is as follows: (a) the sulfuric acid concentration is 50 to 250 g / l, the temperature is 50 to 80 ° C., and the electrolytic current density is 100 to 300 mA. / Cm ² , an electrolytic treatment in a sulfuric acid aqueous solution performed under the conditions of (b) and the electrolytic treatment described above, wherein the nitric acid concentration in the mixed acid aqueous solution is 30 to 150 g / l and the hydrofluoric acid concentration is 10 to 50 g. /
1, immersion treatment with a mixed acid aqueous solution performed under the condition that the weight ratio of hydrofluoric acid and nitric acid (hydrofluoric acid / nitric acid) is 1/8 or more, and the temperature of the mixed acid aqueous solution is 50 to 80 ° C. This is achieved by a method for manufacturing a dull-finished stainless steel sheet, which is a feature. Hereinafter, this manufacturing method is also referred to as a second invention.

Hereinafter, the present invention will be described in detail, by which other objects, advantages and effects of the present invention will become apparent.

In both cases of the first invention and the second invention, in the case of the above-described first cold rolling production process, the pickling treatment in the annealing / pickling step performed after the dull finish rolling is performed. Perform under strong pickling conditions. Further, in the case of the second cold rolling manufacturing process, the pickling treatment of at least one of the annealing and pickling steps performed before and after the dull finish rolling is performed after the cold rolling step, and the strong pickling conditions are used. Do it below. In the cold rolling step of the second cold rolling manufacturing process, dull finishing is not performed as described above.

According to the study of the present inventors, (a) the color tone variation of the dull finish steel sheet is caused by the variation in the surface properties formed by pickling before and after the dull finish rolling (this variation is caused by microscopic surface irregularities). Is the majority), and (b)
It has been found that the variation in the surface of the stainless steel sheet after pickling is smaller when strong pickling is performed than when light pickling is conventionally performed.

It will be apparent from Tables 1 and 2 below how the pickling conditions of the present invention are stronger than those of the conventional method.

[0012]

[Table 1]

[0013]

[Table 2]

The preferred conditions for the electrolytic treatment in the aqueous sulfuric acid solution employed in both the first and second inventions include a sulfuric acid concentration of 70 to 200 g / l, a temperature of 60 to 70 ° C.
An electrolysis current density of 150 to 250 mA / cm ² can be mentioned.

As preferred conditions for the electrolytic treatment in the aqueous nitric acid solution of the first invention, the nitric acid concentration is 80 to 120 g / l, the temperature is 60 to 70 ° C., and the electrolytic current density is 100 to 200 mA / cm.
² can be mentioned.

The preferred conditions for the immersion treatment with the mixed acid aqueous solution according to the second invention include a nitric acid concentration of 80 to 120.
g / l, hydrofluoric acid concentration of 20 to 50 g / l, hydrofluoric acid / nitric acid (weight ratio) of 1/5 to 1/2, and temperature of 60 to 70 ° C.

By adopting the pickling conditions of the present invention as described above, and more preferably, the unevenness of the color tone of the dull-finished stainless steel plate to be manufactured is improved, and the strong pickling causes the base iron to dissolve in acid. The unavoidable increase in loss can be kept within a small range.

The electrolysis time in the aqueous sulfuric acid solution and the electrolysis time in the aqueous nitric acid solution of the first invention are each preferably 2 to 10 seconds. Further, the duration of the electrolytic treatment in the sulfuric acid aqueous solution and the duration of the immersion treatment in the mixed acid aqueous solution performed in the second invention are preferably 2 to 10 seconds.

The electrolytic treatment in the aqueous sulfuric acid solution and the electrolytic treatment in the aqueous nitric acid solution according to the first invention can be performed using equipment known per se. Further, the electrolytic treatment in a sulfuric acid aqueous solution and the immersion treatment in a mixed acid aqueous solution, which are carried out in the second invention, can also be carried out using equipment known per se.

The treatment method of the first invention described above is a method suitable for ferritic stainless steel sheets, and the treatment method of the second invention is a method suitable for both ferritic and austenitic stainless steel sheets. is there.

In the treatment methods of the first and second inventions, a salt treatment (immersion treatment in a molten alkali salt containing sodium hydroxide and sodium nitrate as main components) often employed as a pretreatment for the pickling treatment. The object of the present invention is also achieved by adding.

In the treatment method of the second invention, the object of the present invention can be achieved even if an electrolytic treatment or an immersion treatment in a nitric acid aqueous solution is added after the immersion treatment with the mixed acid aqueous solution to enhance the passivation. Is done.

[0023]

The present invention will be described below in detail with reference to examples. Example 1 (First Invention) and Comparative Example 1 Many lots (coils) of ferritic dull-finished stainless steel sheets (SUS430) were manufactured by the first and second cold rolling manufacturing processes described above. The pickling treatment conditions are shown in Table 3 below.

[0024]

[Table 3]

In the second cold rolling manufacturing process, the pickling conditions in the annealing / pickling step performed after the dull finish rolling were the conditions shown in Table 3. The produced stainless steel sheets were given a seven-point color tone rating of 1 to 7 (a darker color tone as the number was smaller, and a whitish color tone as the number was larger) by outdoor visual observation. In addition,
The range of the variation means that when the value is, for example, 4, the color tone score of the stainless steel sheet is, for example, 3 to 6 or 1 to 4.
It means that it spreads during four stages like four. Therefore, the smaller the value, the more uniform the color tone.

[0026]

[Table 4]

Example 2 (Second Invention) and Comparative Example 2 Austenitic dull-finished stainless steel sheet (SUS304) by the first and second cold rolling production processes described above.
Lots (coils) were manufactured. The pickling treatment conditions are shown in Table 5 below.

[0028]

[Table 5]

In the second cold rolling production process, the pickling conditions in the annealing / pickling step performed after the dull finish rolling were the conditions shown in Table 5.

The produced stainless steel sheets were given a color tone score in the same manner as in the examples, and the range of variation is shown in Table 6.

[0031]

[Table 6]

From the results in Tables 4 and 6, it can be seen that the color tone between the coils of the dull-finished stainless steel sheet obtained by the processing method of the present invention is more uniform.

[0033]

According to the production method of the present invention, the dull-finished stainless steel sheet obtained has reduced color tone variation between coils. As a result, the occurrence of defective products of the dull-finished stainless steel sheet was reduced, and the frequency of replacing the building material due to color tone variation after the steel sheet was used as a building material was reduced.

Claims (4)

(57) [Claims] 1. An acid pickling treatment in an annealing / pickling step performed after dull finish rolling of a stainless steel sheet, or (ii) performed after a cold rolling step and before dull finish rolling of a stainless steel sheet. And at least one of the pickling treatments of the annealing / pickling step performed later,
(A) Sulfuric acid concentration is 50 to 250 g / l, temperature is 50 to 8
0 ° C., and the electrolytic current density is 100 to 300 mA / cm
² ) an electrolytic treatment in a sulfuric acid aqueous solution performed under the condition of (2), and (b) the electrolytic treatment is performed subsequent to the electrolytic treatment described above. A method for producing a dull-finished stainless steel sheet, comprising: performing an electrolytic treatment in an aqueous nitric acid solution under a condition of about 300 mA / cm ² . 2. The method according to claim 1, wherein the stainless steel sheet is ferrite. 3. An acid pickling treatment in an annealing / pickling step performed after the dull finish rolling of the stainless steel sheet, or (ii) performed after the cold rolling step and before the dull finish rolling of the stainless steel sheet. And at least one of the pickling treatments of the annealing / pickling step performed later,
(A) Sulfuric acid concentration is 50 to 250 g / l, temperature is 50 to 8
0 ° C., and the electrolytic current density is 100 to 300 mA / cm
Electrolytic treatment in the aqueous solution of sulfuric acid takes place under conditions of ^2, and (ii) performed subsequent to the electrolytic process, the nitric acid concentration in the mixed acid solution is 30 to 150 g / l, hydrofluoric acid concentration of 10
５０50 g / l, weight ratio of hydrofluoric acid to nitric acid (hydrofluoric acid / nitric acid) is 1
/ 8 or more, and the temperature of the mixed acid aqueous solution is 50 to 80.
Immersion treatment with a mixed acid aqueous solution performed at a temperature of
A method for producing a dull-finished stainless steel sheet, comprising: 4. The method according to claim 3, wherein the stainless steel sheet is a ferritic or austenitic stainless steel sheet.