JP2003286592A - Pickling process for stainless steel strip - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pickling process for obtaining a stainless steel strip showing an excellent surface quality and abrasion quality. <P>SOLUTION: In the pickling process, the stainless steel strip is annealed in the atmosphere, subjected to an alternation electrolysis by indirectly applying an electric current in an aqueous sodium sulfate solution or an aqueous sulfuric acid solution with a pH of 1-6 (a first aqueous solution), subjected to an alternation electrolysis by indirectly applying an electric current in an aqueous solution (a second aqueous solution) prepared by mixing sodium sulfate and nitric acid and soaked and pickled in an aqueous solution (a third aqueous solution) prepared by mixing nitric acid and hydrofluoric acid. The annealing process is performed with an in-furnace time of the stainless steel strip of 32-85 sec, a soaking time of 6-15 sec and a temperature of the stainless steel strip of 1,070-1,120°C. Preferably, the first aqueous solution has a sulfate ion concentration of 35-170 g/l and a solution temperature of 50-70°C, the second aqueous solution has a sodium sulfate concentration of 80-140 g/l, a nitric acid concentration of 80-140 g/l and a solution temperature of 20-60°C, and the third aqueous solution has a nitric acid concentration of 10-143 g/l, a hydrofluoric acid concentration of 22-33 g/l and a solution temperature of 40-60°C. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pickling method for a stainless steel strip which is excellent in surface quality after temper rolling and further excellent in surface quality after buffing (hereinafter referred to as polishing quality).

[0002]

2. Description of the Related Art Generally, a cold rolled stainless steel strip is manufactured by annealing and pickling in the manufacturing process.
This annealing is performed to soften or recrystallize the stainless steel strip, which has been work hardened by rolling.
The pickling is performed for the purpose of removing the oxide scale generated on the surface of the stainless steel strip by annealing. Further, among the cold rolled stainless steel strips, thin steel sheets used for building materials and decorations are usually annealed and pickled as described above, and then temper-rolled in some cases, and then buffed by buffing. Finished into a steel plate with a surface with high image clarity.

There are two methods of annealing, one is in a mixed gas atmosphere of hydrogen gas and nitrogen gas and the other is in air. The former method is more advantageous than the latter method because the oxide scale formed on the surface of the stainless steel strip is extremely thin and the pickling process after the annealing process can be performed with simple equipment. However, since hydrogen gas has a risk of explosion, there is a problem in maintenance management such as it is necessary to ensure sufficient work safety, and it is also expensive in terms of cost because it is expensive.

Under these circumstances, the latter method, which is performed in atmospheric gas, has often been used for annealing the stainless steel strip. However, a thick oxide scale is formed on the surface of the stainless steel strip annealed by this method, and it is difficult to completely remove this scale in the subsequent pickling treatment, resulting in poor surface quality of the product.

Particularly, when the scale remaining on the surface of the steel sheet during the temper rolling after pickling adheres to the rolling roll, unevenness is generated on the surface of the steel material, so that sufficient sharpness can be obtained even after buffing. I can't. Further, the annealing temperature as described above generally makes the steel material softer and the workability becomes better as it is set to a higher temperature. Therefore, in order to improve the mechanical properties of the steel material, the temperature of the steel material at the time of annealing is set high. Is desirable. However, if the temperature of the steel strip during annealing becomes too high, the crystal grain boundary groove becomes deep, and there is a problem that the crystal grain boundary groove remains on the surface of the steel material even after buffing and deteriorates the sharpness of the steel sheet.

On the surface of the stainless steel strip that has been annealed in atmospheric gas as described above, oxides (Fe ₂ O ₃ , Cr ₂ O ₃ ) containing Fe or Cr as a main component are formed on the outer layer of the surface. There is Si oxide in the inner layer. As a method for removing this oxide scale, a so-called salt treatment is carried out by immersing in a molten alkaline salt bath containing NaOH or NaNO ₃ as a main component,
A well-known method is to perform an anodic electrolysis treatment in a neutral salt aqueous solution, that is, to carry out so-called neutral salt electrolysis, and then immerse it in a nitric acid aqueous solution.

However, this method has problems such as bad atmosphere environment, high processing cost, difficult maintenance and management, and increase in the viscosity of the salt solution, so that the steel strip is often taken out. Recently, a method omitting the salt treatment is being adopted.

In Japanese Patent Laid-Open No. 11-61500, stainless steel strips and heat-resistant steel strips are subjected to anodic electrolysis in a neutral salt aqueous solution, and then subjected to anodic electrolysis and cathodic electrolysis in a sulfuric acid-nitric acid mixed aqueous solution. , A descaling method in which cathodic electrolysis in an aqueous nitric acid solution or immersion in an aqueous nitric acid-hydrofluoric acid mixture is performed.

According to this method, the Cr oxides in the oxide scale are anodic electrolyzed or in sulfuric acid in a neutral salt aqueous solution.
It is oxidized by anodic electrolysis in a nitric acid mixed aqueous solution to become Cr acid ions which are easily dissolved. On the other hand, the Fe oxide in the oxide scale is reduced by cathodic electrolysis in a sulfuric acid-nitric acid mixed aqueous solution to become divalent Fe ions which are easily dissolved. The Fe oxide in the oxide scale is further reduced by cathodic electrolysis in a nitric acid aqueous solution or by dipping in a nitric hydrofluoric acid mixed aqueous solution to become divalent Fe ions which are easily dissolved. Thus, the chromium oxide and the Fe oxide in the oxide scale are removed, but the removal of the Si oxide concentrated layer is insufficient, and as a result, the Si oxide remains on the surface of the steel strip.

In the above method, it is necessary to carry out anodic electrolysis and cathodic electrolysis in a sulfuric acid-nitric acid mixed aqueous solution. However, in a sulfuric acid-nitric acid mixed aqueous solution, when polypropylene-based materials are used for the equipment, deterioration of the equipment is accelerated. Therefore, there is a problem of cost increase such as burden of repair cost or high initial investment.

On the other hand, a method of manufacturing a steel sheet for the purpose of improving the buff polishing property has been studied. For example,
2000-288619 gazette is a method of annealing an austenitic stainless hot rolled steel sheet, mechanically descaling, pickling with an aqueous solution containing hydrochloric acid, nitric acid and hydrofluoric acid, and then cold rolling, Disclosed is a method for producing an austenitic stainless steel sheet having a good buffing property, which is characterized by controlling the immersion time in an aqueous pickling solution so that the residual area ratio of the grain boundary grooves is 3 to 6%. However, if the soaking time is specified in this way, the passing speed of the steel sheet is determined, and not only the production efficiency is limited, but even if the annealing and pickling conditions of the hot rolled steel sheet are specified as described above, the cold Polishing property deteriorates depending on annealing and pickling conditions after hot rolling.

[0012]

The present invention has been made in order to solve the above problems, and produces a stainless steel strip having excellent surface properties after pickling, particularly excellent polishing quality. An object is to provide a pickling method.

[0013]

Means for Solving the Problems The inventors of the present invention have made detailed studies on the annealing conditions of the stainless steel strip, the composition of the pickling solution and the electrolysis method. The present invention has been completed by finding a pickling method capable of producing a stainless steel strip having a different surface texture.

The gist of the present invention is "a pickling method for a stainless steel strip characterized by performing the following first pickling to third pickling after annealing the stainless steel strip in the atmosphere". And

First pickling: Pickling for performing alternating electrolysis in sodium sulfate aqueous solution or aqueous sulfuric acid solution having a pH of 1 to 6 by indirect energization. Second pickling: Alternating electrolysis in inducing energization in an aqueous solution containing sodium sulfate and nitric acid. Pickling No. 3 pickling: Pickling soaked in an aqueous solution of nitric acid and hydrofluoric acid mixed.
It is desirable that the temperature is 85 seconds, the soaking time is 6 to 15 seconds, and the temperature of the stainless steel strip is 1070 to 1120 ° C. The first pickling aqueous solution has a sulfate ion concentration of 35 to 170 g / l and a liquid temperature of 50 to 70 ° C., and the second pickling aqueous solution has a sodium sulfate concentration of 80 to 140 g / l. , Nitric acid concentration of 80-140g
/ l, the liquid temperature is 20 ~ 60 ℃, the aqueous solution of the third pickling, nitric acid concentration is 100 ~ 143g / l, hydrofluoric acid concentration is 22 ~ 3
The liquid temperature is preferably 3 g / l and the liquid temperature is 40 to 60 ° C. In the first pickling, the electric quantity density of alternating electrolysis is 60 to 400 C / dm.
² and the second pickling has an electric quantity density of alternating electrolysis of 50 to 20
It is preferably 0 C / dm ² .

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an example of an apparatus for carrying out the present invention. As shown in the figure, in the pickling method of the present invention, the stainless steel strip 1 is first annealed in the annealing furnace 2 in the atmosphere and passed through an electrolytic pickling tank 3 filled with an aqueous sodium sulfate solution or an aqueous sulfuric acid solution. Then, the smut adhering to the surface of the steel strip is removed by the brush of the pickling and cleaning brush stand 4, and further passes through the electrolytic pickling tank 5 filled with an aqueous solution in which sodium sulfate and nitric acid are mixed, and is pickled and washed again. The brush of the brush stand 4 removes the smut. Then stainless steel strip 1
Passes through the pickling tank 6 filled with an aqueous solution of nitric acid and hydrofluoric acid, passes through the pickling cleaning brush stand 4 again, and is sent to the next step.

Here, electrolytic pickling tank 3 and electrolytic pickling tank 5
, A negative electrode 7 and a positive electrode 8 are installed so as to face the front and back surfaces of the stainless steel strip 1, and the negative electrode 7 and the positive electrode 8 are alternately arranged in the traveling direction of the stainless steel strip 1. is set up. The negative electrode 7 and the positive electrode 8 are
The stainless steel strip 1 is indirectly electrolyzed through an aqueous solution filled with a DC voltage and filled in each pickling tank. Such electrolysis by means of a device having at least two or more combinations of negative electrode 7 and positive electrode 8 is called alternating electrolysis. In addition, since the surface of the stainless steel strip 1 is usually not flawed, the negative electrode 7 and the positive electrode 8 are installed at positions where they do not come into contact with the stainless steel strip 1 and are energized. It is called energization.

In a normal stainless steel strip manufacturing process, a temper rolling mill 11 as shown in FIG. 1 is installed for the purpose of reducing yield stress. If it remains, defective surface properties (so-called roll coating) occur during temper rolling. This occurs because the oxide scale remaining on the surface of the steel strip is wound around the roll of the temper rolling mill and the uneven shape of the roll surface is transferred to the steel sheet. The concavo-convex shape generated on the surface of the steel plate itself not only deteriorates the appearance quality but also deteriorates the image clarity because the concavo-convex remains on the surface of the steel plate even if such a steel plate is buffed. Also, if roll coating occurs on the surface of the steel strip, the temper rolling mill must be opened and temper rolling must be performed again, which not only wastes the work, but also the part where roll coating occurs is a downgraded product or scrap. Since it becomes a product, it also causes a deterioration in yield.

However, even when temper rolling is performed on a steel strip from which Cr oxides and Fe oxides have been almost completely removed, it is not possible to suppress the occurrence of roll coating. However, as a result of the research conducted by the present inventors, it was found that the occurrence of roll coating can be suppressed by reducing the amount of Si oxide attached to the surface of the steel sheet.

As described above, when the cold-rolled stainless steel strip is subjected to high-temperature finish annealing, the grain boundary grooves of the steel sheet become deep, and the grain boundary grooves remain on the surface of the steel material even after buffing, so that the steel sheet becomes sharp. Deteriorates sex. The research conducted by the present inventors has revealed that the depth of the crystal grain boundary groove depends on the annealing conditions applied to the stainless steel strip after cold rolling. It was also found that the conventionally used pickling aqueous solution deepens the crystal grain boundary grooves because the crystal grain boundary grooves are preferentially etched together with the removal of scale adhering to the surface of the steel sheet. From these facts, the present inventors have found the optimum conditions for finish annealing of a cold rolled stainless steel strip, and have found pickling conditions that do not preferentially etch grain boundary grooves, and completed the present invention. .

(A) First pickling In the vicinity of a negative electrode placed in an aqueous solution of sodium sulfate or an aqueous solution of sulfuric acid, oxygen gas is generated by anodic electrolysis (anode reaction) on the surface of the steel strip, and Cr _{2 in} the scale is added. It is generally known that O ₃ (Cr is trivalent) is oxidized to Cr ₂ O ₇ ²⁻ (Cr is hexavalent) and Cr in the scale is dissolved in an aqueous solution.

On the other hand, in the vicinity of the positive electrode installed in this aqueous solution
In the steel strip surface, the cathodic electrolysis (cathode reaction)
More hydrogen gas is generated. This gas adheres to the steel strip surface
Has a function to remove the Cr oxide or Fe oxide
It Especially when these aqueous solutions are in the acidic region,
Near the positive electrode, the surface of the steel strip is scaled by cathodic electrolysis.
Fe_TwoO_ThreeOf the trivalent Fe of is reduced to divalent Fe,
Fe in aqueous solution²⁺Dissolves. Furthermore, the exact reason is
Although it is not certain, this trivalent Fe is Fe in the aqueous solution. ²⁺age
When dissolved by melting, the Si oxide that had been concentrated on the steel plate surface was released.
escape.

However, when the pH of the aqueous solution of sodium sulfate or the aqueous solution of sulfuric acid is less than 1, cathodic electrolysis (cathode reaction) is sufficiently promoted and Si oxide is easily released, but the surface of the steel sheet is roughened. , The surface quality deteriorates. On the other hand, if the pH exceeds 6, cathodic electrolysis (cathodic reaction) does not occur and Cr in the scale is only dissolved in the aqueous solution by anodic electrolysis (anode reaction), so the scale loss on dissolution decreases. However, Si oxide is not released.

As described above, the effect of removing oxides such as Cr and Fe appears in both the anodic electrolysis and the cathodic electrolysis in the sodium sulfate aqueous solution or the sulfuric acid aqueous solution. This effect is further enhanced by repeating such electrolysis and performing alternating electrolysis. Therefore, in the present invention,
The stainless steel strip was subjected to alternating electrolysis by indirect energization in a sodium sulfate aqueous solution having a pH of 1 to 6 or a sulfuric acid aqueous solution.

(B) Second pickling method In general, a method of performing electrolytic pickling in an aqueous solution of sodium sulfate and then electrolytic pickling in an aqueous solution of nitric acid is widely used. The principle is that the trivalent Fe of Fe ₂ O _{3 in} the scale is reduced to divalent Fe by cathodic electrolysis in an aqueous nitric acid solution, and is dissolved as Fe ^{2 + in the} aqueous solution, so that sodium sulfate in the previous stage is dissolved. It is to remove the scale remaining in the electrolytic pickling in the aqueous solution.

However, according to the research conducted by the present inventors, electrolytic pickling in a mixed solution thereof is preferable to electrolytic pickling in a nitric acid aqueous solution and electrolytic pickling in a sodium sulfate aqueous solution, respectively. It has become clear that the amount of descaling can be increased. Further, by carrying out alternating electrolysis in which a combination of anodic electrolysis and cathodic electrolysis is repeated at least two times or more in this mixed aqueous solution, a larger effect can be obtained. Therefore, in the present invention, following the above pickling treatment, it is necessary to perform alternating electrolysis by indirect energization in an aqueous solution in which sodium sulfate and nitric acid are mixed.

(C) Third pickling The scale picked up on the surface of the steel strip can be almost completely removed by the above two pickling treatments.
Divalent Fe is reduced to trivalent Fe to form iron fluoride complex ions, which precipitate in the liquid. Here, hydrofluoric acid acts to break the passivation film on the surface of the steel strip to promote dissolution, and nitric acid acts to form a passivation film on the surface of the steel sheet to improve corrosion resistance. Therefore, in this mixed solution, the active dissolution of the stainless steel itself, that is, the dissolution of the crystal grain boundaries is not preferentially performed and the dissolution within the crystal grains is promoted. And a stainless steel strip with excellent polishing quality is obtained.

(D) Annealing in air At the time of annealing in air, the in-furnace time of the stainless steel strip was measured.
If it is less than 32 seconds, the plate temperature cannot be raised to the target plate temperature, and if the soaking time is less than 6 seconds or if the plate temperature is less than 1070 ° C, sufficient tempering is not performed. Therefore, in any case, the required mechanical properties cannot be obtained. On the other hand, when the in-furnace time of the stainless steel strip exceeds 85 seconds, the soaking time exceeds 15 seconds, or the plate temperature exceeds 1120 ° C, grain boundary oxidation is promoted and the quality after polishing is adversely affected. Will be given.

Therefore, the annealing in the atmosphere, the in-furnace time of the stainless steel strip is 32-85 seconds, the soaking time is 6-15 seconds,
Moreover, it is desirable that the temperature of the stainless steel strip is 1070 to 1120 ° C.

(E) Concerning the first pickling aqueous solution If the concentration of sulfate ions in the aqueous solution is less than 35 g / l, descaling is not completed, which may cause Si oxide to remain on the surface of the steel strip. . On the other hand, its sulfate ion concentration is 17
Above 0 g / l, not only the descaling effect saturates,
In particular, when using an aqueous solution of sodium sulfate, sodium sulfate that cannot be completely dissolved is precipitated, and further crystallized,
Indentation occurs on the surface of steel strip. Therefore, it is desirable that the sulfate ion concentration in the aqueous solution is 35 to 170 g / l.

When the liquid temperature of the aqueous solution is less than 50 ° C., the electrolysis efficiency is lowered and Si oxide remains. on the other hand,
If the liquid temperature exceeds 70 ° C, not only the descaling effect will be saturated, but especially when using an aqueous solution of sodium sulfate, undissolved sodium sulfate will precipitate, and further crystallize to form on the surface of the steel strip. Indentation occurs. Therefore,
The liquid temperature of the aqueous solution is preferably 50 to 70 ° C.

(F) Regarding the second pickling aqueous solution If the concentration of sodium sulfate in the aqueous solution is less than 80 g / l, descaling is not completed, which may cause the Si oxide to remain on the surface of the steel strip. . On the other hand, when the sodium sulfate concentration exceeds 140 g / l, the electrolytic action is strong, so that electrolytic pits are formed on the surface and the surface properties deteriorate. Therefore,
It is desirable that the sodium sulfate concentration in the aqueous solution be 80 to 140 g / l. The nitric acid concentration in the aqueous solution is 80 g / l.
If it is less than the above, descaling is not completed, which may cause Si oxide to remain on the surface of the steel strip. On the other hand, when the nitric acid concentration exceeds 140 g / l, the electrolytic action is strong, so that electrolytic pits are formed on the surface and the surface properties deteriorate. Therefore,
The nitric acid concentration in the aqueous solution is preferably 80 to 140 g / l.

When the liquid temperature of the aqueous solution is less than 20 ° C., the electrolysis efficiency is lowered and Si oxide remains. on the other hand,
When the liquid temperature exceeds 60 ° C., the water content in the aqueous solution evaporates, sodium sulfate precipitates and is further crystallized, causing indentation flaws on the surface of the steel strip. Therefore, it is desirable to set the liquid temperature of the aqueous solution to 20 to 60 ° C.

(G) About the third pickling aqueous solution When the nitric acid concentration in the mixed solution is less than 100 g / l, the passivation of the steel strip surface becomes insufficient and the corrosion resistance deteriorates. On the other hand, when the nitric acid concentration in the mixed solution exceeds 143 g / l, the surface of the steel strip becomes excessively passivated and the dissolution action is suppressed. Further, when the concentration of hydrofluoric acid in the mixed solution is less than 22 g / l, descaling is not completed and scale remains on the surface of the steel strip. On the other hand, when the concentration of hydrofluoric acid in the mixed solution exceeds 33 g / l, the dissolution of the steel strip surface becomes excessive and rough skin occurs. Moreover, the acid resistant equipment accompanying this is required, and the cost increases.

(H) Electricity Density of Electrolysis in the First Pickling This means that when the electric quantity density of electrolysis is less than 60 C / dm ² .
This is because Cr oxides and Fe oxides cannot be sufficiently removed, and it becomes difficult to completely remove Si oxides in the subsequent pickling, and the electric energy density is 400 C / dm ² . This is because if it exceeds the above range, the melting of the steel strip itself is promoted and the surface becomes rough. Therefore, it is desirable that the electric quantity density of the alternating electrolysis performed by the indirect energization in the sodium sulfate aqueous solution or the sulfuric acid aqueous solution is 60 to 400 C / dm ² .

(I) Electricity Density of Electrolysis of Second Pickling This means that when the electric quantity density of electrolysis is less than 50 C / dm ² .
This is because Cr oxides and Fe oxides cannot be removed sufficiently, and it becomes difficult to completely remove Si oxides in the subsequent pickling. On the other hand, the electric energy density of 200C / dm ² is reduced. If it exceeds, the melting of the steel strip itself is promoted and the surface becomes rough. Therefore, it is desirable that the electric quantity density of the alternating electrolysis performed by indirect energization in an aqueous solution in which sodium sulfate and nitric acid are mixed is 50 to 200 C / dm ² .

[0038]

Example 1 A 1.5 mm thick SUS304 cold rolled stainless steel sheet was annealed and pickled in a direct heating type annealing furnace (radiation heating method) in the atmosphere under the conditions shown in Table 1. gave.

[0039]

[Table 1]

After annealing and pickling under the conditions shown in Table 1,
For each test piece that was further temper rolled,
Using Light # 1200, polishing speed 30mpm, pressing force 5kg
/cm ^TwoPolished 5 times.

FIG. 2 is a view showing the SEM observation results of the surface of each test piece before and after polishing, (a) shows the surface properties and sharpness of Example 1 of the present invention, and (b) ) And (c) show the surface properties and image clarity for Comparative Examples 1 and 2.

The image clarity is the intensity of the light observed by the light receiver after the light emitted from the light source is reflected by the sample surface and passes through the filter with the slit as shown in FIG. Such a sharpness measuring method is called ICM, and one in which one of the slit sizes is 0.5 is expressed as ICM0.5.

As shown in FIG. 2, in Example 1 of the present invention, the grain boundary grooves were shallow even before polishing, and no grain boundary grooves were observed after polishing. Also, regarding the sharpness,
High values of 76.9 before polishing and 84.2 after polishing were obtained. On the other hand, in Comparative Examples 1 and 2, deep grain boundary grooves existed on the surface of the steel strip before polishing, and the grain boundary grooves remained after polishing. Further, the image clarity was as low as 60.2 before polishing in Comparative Example 1 and 41.0 after polishing, and in Comparative Example 2 was 63.5 before polishing and 48.2 after polishing, which were low values.

Example 2 A SUS304 cold-rolled stainless steel sheet having a thickness of 0.2 to 2.0 mm was annealed and pickled in a direct-fired heating annealing furnace (radiation heating method) in the atmosphere under the conditions shown in Table 2. Then, temper rolling was performed.

[0045]

[Table 2]

The appearance of each of the test pieces was inspected with sharpness and uniformity as evaluation items.

Here, the "vividness" means the result based on the value measured by ICM0.5. In this evaluation, "◎" indicates a test piece with ICM 0.5 of 80 or more,
"○" indicates a test piece with ICM 0.5 of 60 or more and less than 80,
“△” indicates a test piece with ICM 0.5 of 40 or more and less than 60,
“X” indicates a test piece having an ICM of 0.5 and less than 40.

"Uniformity" means the result of visual observation based on the presence or absence of unevenness on the surface of the steel strip. In this evaluation, “◎” indicates a test piece in which the steel strip surface where no unevenness was generated was 80% or more of the whole, and “○” was 60% or more of the steel strip surface where no unevenness was generated. The test piece was less than 80%, and “△” means the test piece in which the unevenness of the steel strip surface was 40% or more and less than 60% of the whole,
“X” indicates a test piece in which the surface of the steel strip in which unevenness did not occur was less than 40% of the whole.

3A and 3B are diagrams showing the results of the appearance inspection for each test piece. FIG. 3A shows the result of the "vividness" inspection, and FIG. 3B shows the result of the "uniformity" inspection. .

Inventive Example 2 is an example in which the annealing conditions are the same as those in Comparative Example 3 but the pickling conditions are different. In the evaluation result of “vividness” shown in FIG. 3 (a), in the invention example 2, the total of “⊚” and “∘” was 96%, and in the comparative example 3, there was no “∘”, Only 15% of "○". Further, in the evaluation result of “uniformity” shown in FIG.
And the total of “◯” was 37%, Comparative Example 3 had no “⊚”, and “O” was only 10%. in this way,
Inventive Example 2 has remarkably improved surface properties as compared with Comparative Example 3.

Example 3 of the present invention is an example in which the pickling conditions are the same as those of Comparative Example 4 but the annealing conditions are different. In the evaluation result of "vividness" shown in FIG. 3 (a), in the invention example 3, the total of "◎" and "○" was 100%, and in the comparative example 3, there was no "◎", "○" was only 12%. Also, FIG. 3 (b)
In the evaluation result of “uniformity” shown in FIG.
The total of “⊚” and “∘” was 67%, and Comparative Example 3 did not have “⊚” and “∘” at all. As described above, the present invention example 3 has an excellent effect of improving the surface properties as compared with the comparative example 4.

[0052]

According to the pickling method of the present invention, a stainless steel strip having excellent surface quality and polishing quality can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of an apparatus for carrying out the present invention.

FIG. 2 is an SEM of the surface of each test piece before and after polishing.
It is a figure which shows the observation result, (a) shows the surface texture and image clarity about this invention example 1, (b) and (c) shows the surface texture and image clarity about comparative examples 1 and 2. Indicates.

3A and 3B are diagrams showing the results of the appearance inspection of each test piece, in which FIG. 3A shows the “visibility” inspection result, and FIG. 3B shows the “uniformity” inspection result.

FIG. 4 is a diagram showing a method for measuring sharpness.

[Explanation of symbols]

1. Stainless steel strip, 2. Annealing furnace, 3. 3. An electrolytic pickling tank filled with an aqueous solution of sodium sulfate or an aqueous solution of sulfuric acid, Pickling and cleaning brush stand, 5. 5. An electrolytic pickling tank filled with an aqueous solution in which sodium sulfate and nitric acid are mixed; 6. A pickling tank filled with an aqueous solution in which nitric acid and hydrofluoric acid are mixed, Negative electrode, 8. Positive electrode, 9. Hot rinse tank, 10. Dryer, 11. Temper rolling mill

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 4K037 EA12 FF03 FM01 GA08 HA05                 4K053 PA03 PA12 QA01 RA15 RA16                       RA17 RA25 SA06 TA04 TA15                       TA16 YA02 YA03

Claims (7)

[Claims] 1. A method for pickling a stainless steel strip, which comprises subjecting a stainless steel strip to annealing in the atmosphere and then performing the following first pickling to third pickling. First pickling: Pickling for alternating electrolysis by indirect energization in sodium sulfate aqueous solution or sulfuric acid solution having pH of 1 to 6 Second pickling: Acid pickling for alternating electrolysis in aqueous solution mixed with sodium sulfate and nitric acid Third pickling: Pickling soaking in an aqueous solution of a mixture of nitric acid and hydrofluoric acid 2. The annealing as described above, wherein the in-furnace time of the stainless steel strip is 32 to 85 seconds, the soaking time is 6 to 15 seconds, and the stainless steel strip is 1070 to 1120 ° C. The pickling method for a stainless steel strip according to claim 1, which is characterized in that. 3. The aqueous solution of the first pickling has a sulfate ion concentration of 35.
~ 170 g / l, and the liquid temperature is 50 ~ 70 ℃, the pickling method for stainless steel strip according to claim 1 or 2, characterized in that. 4. The second pickling aqueous solution has a sodium sulfate concentration of 80 to 140 g / l, a nitric acid concentration of 80 to 140 g / l, and a liquid temperature of 20 to 60 ° C. The method for pickling a stainless steel strip according to any one of claims 1 to 3. 5. The third pickling aqueous solution has a nitric acid concentration of 100 to 143.
g / l, hydrofluoric acid concentration is 22-33 g / l, and liquid temperature is 40-
It is 60 degreeC, The pickling method of the stainless steel strip in any one of Claim 1 to 4 characterized by the above-mentioned. 6. The first pickling has an electric quantity density of 60 to 60 in alternating electrolysis.
The pickling method for a stainless steel strip according to claim 1, wherein the pickling method is 400 C / dm ² . 7. The second pickling has an electric quantity density of 50 to 50 in alternating electrolysis.
It is 200 C / dm ² , The pickling method of the stainless steel strip in any one of Claim 1 to 6 characterized by the above-mentioned.