JPH01234600A - Method for descaling band stainless steel - Google Patents

Abstract

PURPOSE:To remove the scales on the surface of a band stainless steel with an excellent capacity and to clean the surface by anodizing a cold-rolled and annealed band stainless steel in an aq. NaCl soln., and then pickling the steel with sulfuric-hydrofluoric acid and nitric-hydrofluoric acid. CONSTITUTION:The cold-rolled and then annealed band stainless steel 1 is passed through an electrolytic cell 2 filled with an electrolyte contg. 50-200g/l of NaCl and kept at 20-80 deg.C, then passed between anode plates 3 and 3 and between cathode plates 4 and 4, and anodized to mostly dissolve and remove the scales on the surface in the electrolyte. The product of the current density and electrolyzing time in the anodization is controlled to 200-800A, sec/cm<2>. The steel is then passed through a brush roll 12, the inside of a first pickling tank 10, and a pickling soln. contg. 150-250g/l sulfuric acid and 5-50g/l hydrofluoric acid and kept at 70-90 deg.C. The steel is then introduced into a second pickling tank 11 through a brush roll 12, passed through the pickling soln. contg. 50-100g/l nitric acid and 5-50g/l hydrofluoric acid and kept at 50-70 deg.C to completely remove the remaining scales and to dissolve the base metal immediately under the scales, and the surface is cleaned.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention allows easy management of the chemical solution used for scale removal and treatment of its waste liquid, and has a large scale removal ability and can be used even when the line speed is increased. This is a descaling method for stainless steel strips that can be traced, does not have to worry about pollution problems such as environmental pollution due to waste liquid and sludge generated in the line, and above all, improves the surface quality of the latest products. be.

[Conventional technology]

In general, hot-rolled stainless steel strip products such as Nα1 finish (surface finish) specified in JIS G4306 r hot-rolled stainless steel strip J are made from hot-rolled stainless steel strips that undergo heat treatment including annealing. In order to perform pickling or a treatment similar to pickling, the plate is manufactured by passing through a series of annealing and pickling processes in a line. A hot rolled stainless steel sheet product specified in JIS G43011 "Hot rolled stainless steel sheet" is manufactured by shearing the hot rolled stainless steel strip manufactured through this annealing and pickling process.

In addition, JIS G4307 r cold rolled stainless steel strip"
Nα2D defined by No. 28. Cold-rolled stainless steel strip products with various polishing finishes such as BA (surface finish 2) are produced using hot-rolled stainless steel strips produced through the annealing and pickling process as raw materials, and are made into lines. The cold rolling process, annealing and pickling process are repeated as necessary, and between these processes, an intermediate polishing process is conducted in line to remove scale residue and underground particles on the surface of the material. It is manufactured by being plated and then undergoing a refining process including a temper rolling process and a shearing and cutting process. and,
The cold-rolled stainless steel strip produced in this way is sheared to produce JIS G4305 r cold-rolled stainless steel sheet.
Cold-rolled stainless steel sheet products are manufactured as specified in the following.

As mentioned above, stainless steel strip products and steel sheet products are subjected to hot rolling, heat treatment including annealing after hot rolling, and softening annealing of the material that has been work hardened by cold rolling. Although there are some differences, scale mainly composed of oxides such as Fe and Cr is generated on the surface of the material each time. Unless the scale formed on the surface of the material is completely removed before proceeding with each process, it is not possible to obtain the highest quality product with good surface quality, so descaling treatment is performed each time.

However, the scale that forms on the material surface of stainless steel strips is generally dense and therefore extremely difficult to remove compared to other ordinary steels or special steels, that is, it is a solid wall for descaling.

Therefore, various descaling methods have been implemented or proposed in the past regarding the descaling of the scale generated on the surface of the stainless steel m-band material.

First of all, the most basic and widely practiced method for this treatment is sulfuric acid, nitric acid, and hydrochloric acid.

This was a pickling treatment in which the sample was treated with hydrofluoric acid or a mixed acid solution containing these to remove 4-scale and uniformly and appropriately passivate it. However, with this treatment method, which uses only pickling treatment, it is necessary to improve productivity by high-speed processing of stainless steel strips, and at the same time, to perform complete descaling treatment and obtain a final product with good surface quality. Mechanical, chemical, or a combination of these pretreatments have come to be used in combination before the main treatment, which is pickling treatment.

In other words, mechanical pretreatment is a machine that cracks the scale layer using Shot Plus 1 or a scale breaker prior to pickling in the case of hot-rolled materials with a large amount of scale to facilitate descaling. However, these mechanical pretreatments have the drawback of leaving impressions on the base of the stainless steel strip and causing work hardening.

In addition, conventional chemical pretreatments such as electrolysis in an aqueous solution using Na2SO4 as an electrolyte and molten caustic treatment can melt away some of the components and weaken the composition of the scale and its bonding strength with the substrate. Although methods have also been implemented,
Although it was effective for cold-rolled materials with a relatively small amount of scale, it was less effective for hot-rolled materials with a large amount of scale.

With this process, Na2S was used as a chemical pretreatment.
A descaling method is now performed in which anodic electrolysis is carried out in an O4 aqueous solution or molten caustic alkali treatment is carried out, followed by pickling with nitric-fluoric acid, nitric-fluoric acid, etc., or alternatively anodic electrolysis in an aqueous solution such as NaCl1. became.

On the other hand, in order to improve the productivity of stainless steel strips, in addition to rolling and annealing, it is required to perform descaling at high speed and with high efficiency.Therefore, it has become desirable to develop a descaling method with high scale removal capacity. It's here. However, when performing anodic electrolysis in a Na, SO4 aqueous solution as a chemical pretreatment, this pretreatment method has a large effect on cold rolled materials, but it is originally less effective on hot rolled materials. Moreover, since Cr" ions were eluted, the waste liquid treatment was extremely troublesome in terms of pollution prevention.
, pretreatment by electrolysis in an S04 aqueous solution is difficult to increase the speed of hot rolled materials, and when speeding up both hot and cold rolled materials, the amount of Cr" ion elution increases accordingly. This has the drawback of accelerating the aging of the electrolyte and making its treatment more troublesome.

In addition, when performing molten caustic treatment as another method of chemical pretreatment, since the molten caustic is highly viscous, increasing the speed increases the amount of liquid taken out, and the wiping device also follows the speed and liquid It has the disadvantage that it is difficult to prevent an increase in the amount taken out, resulting in high costs. As mentioned above, when pickling is performed by increasing the acid concentration and liquid temperature in order to weaken the pretreatment and strengthen the weakened portion, which is difficult to speed up, the aging of the pickling solution is accelerated. However, there was a drawback that the labor and cost required for acid concentration management, acid addition, waste liquid treatment, etc. were enormous. Also, instead of pickling, N
Even if anodic electrolysis is carried out in an aqueous solution containing aCl or the like as an electrolyte, if it is carried out strongly enough to become the main descaling agent, there is a drawback that pits are likely to occur in the stainless steel strip. In the past, it was difficult to achieve both descaling and high-speed descaling, which only yields good results when done carefully and at low speeds.

[Problem to be solved by the invention]

The object of the present invention is to provide a method for descaling stainless steel strips, which does not have the disadvantages of the prior art described above, has a large scale removal ability, can be carried out at high speed, has fewer problems in waste liquid treatment, and has a good quality surface. To this end, there was a problem that was difficult to solve as to what kind of treatment method and conditions should be used for the pretreatment and the subsequent main treatment.

[Means to solve the problem]

As a result of intensive studies to solve such problems, the inventors of the present invention found that
This treatment uses pickling, which has the advantage of cleaning the surface by actively removing the metal base directly beneath the scale.
In order to alleviate the above-mentioned disadvantages of pickling, we decided to perform a pretreatment, and as the pretreatment, anodic electrolysis in an aqueous Na2SO4 solution has the advantages of the self-regeneration ability of the electrolyte and the separation ability of separating scale as sludge. Therefore, we conducted various studies and tried to find processing conditions that would avoid the above drawbacks.
No such conditions were obtained.

Therefore, Naω, which was conventionally considered as an alternative to pickling,
Further investigation into pretreatment by anodic electrolysis in an aqueous solution using a monobasic inorganic acid salt as an electrolyte revealed the following. That is, when using NaF, the descaling ability is greater than when using Na2SO4, but the viscosity of the generated sludge is high and it is difficult to remove it.
When O3 is used, the descaling ability is comparable to that of Na and SO4, and the generation of Cr'' ions in the electrolyte is the same for both NaF and NaNO3 as for Na2SO4. The sludge was mainly composed of ferric hydroxide and had a brown color; when seawater was used, white scale appeared on the cathode, making it impossible to conduct electricity; on the other hand, when NaCl was used, The descaling ability is much greater than that of Na25O, and countless bits occur on the surface of the stainless steel strip, especially 5US304, but the generated sludge has a bluish-green color and Cr""6 ions are observed in the electrolyte. It turns out there isn't.

The principle of descaling in this case was presumed to be an electrochemical reaction under non-oxidizing conditions. As a result of further studies on electrolysis in this NaCl aqueous solution, we found that the current density is usually adjusted within a predetermined range according to the electrolysis time, that is, the electrolysis time determined by the speed 1 of the line in which the annealing process is incorporated. The current density (
By electrolyzing under electrolytic conditions in which the sum of A/dII and the electrolysis time (seconds) is set to below a certain value determined for each hot-rolled and cold-rolled material, the P1- It has been found that it is possible to prevent the occurrence of the result,
In this way, the present invention was completed by discovering that the above object could be achieved by pre-treating with anodic electrolysis using NaCl as an electrolyte and then performing pickling.

Hereinafter, the method of the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a process diagram showing an example of the implementation state of the method of the present invention, and FIGS. 2 and 3 show the upper limits of the range of the product of current density and electrolysis time specified in the method of the present invention for hot and It is a graph shown for each cold rolled stainless steel strip.

[Explanation of configuration]

In the method of the present invention, 50 to 200 g/
Electrolysis is carried out using a stainless steel strip as an anode in an electrolytic solution consisting of an aqueous solution containing NaCl as the main component.
The reason why the NaCl concentration was set at 200 g/R was because at low concentrations frlM, the conductivity of the liquid becomes low and the current efficiency decreases, and the higher the NaCl concentration, the better, but the maximum value was set at 200 g/R.
This is because the solubility of Cl in water was considered.

The temperature of the electrolyte in this anodic electrolysis has a relatively small effect on the descaling results, so room temperature (20°C) is acceptable, and higher temperatures are preferable because they increase conductivity and NaCl solubility. If the temperature exceeds 80°C, problems such as complicated concentration management and energy loss will occur due to an increase in the amount of evaporated water, so the applicable range is 20 to 80°C, and 60°C in particular.
The best location is nearby.

Hot rolled stainless steel strip (SUS304.S, US4
30) anodic electrolysis using NaCl as an electrolyte was carried out by varying the liquid temperature, current density (A/d), and electrolysis time (seconds), and the results were shown in Table 3. Table 1 shows the results of the investigation regarding the presence or absence of occurrence.The case where the liquid temperature is high is shown in Table 3 later as part of the Examples.

From Tables 1 and 3 in the margin below, we can see the magnitude of weight loss due to electrolytic treatment (which is largely related to descaling ability), the influence of NaCρ concentration and liquid temperature on the presence or absence of Cr generation and the presence or absence of pill generation. It can be seen that this is not large.Similar results were also found for the cold-rolled stainless steel strip.

The product of the current density (A/dragon) during electrolysis and the electrolysis time (seconds) (
The amount of electricity per unit area (hereinafter sometimes referred to as the amount of electricity per unit area) has the greatest influence on the descaling ability and the occurrence of pips. The upper limit of this amount of electricity per unit area is +1800A・sec/dJ for hot-rolled stainless steel strips, and 40OA・sec/dJ for cold-rolled stainless steel strips, and the above values are set in each case. If the stainless steel strip is 5US304, then pin 1~ will occur. When the stainless steel strip is 5O5430, these limits are a little higher. Here, the difference between hot rolling and cold rolling shall comply with the provisions of JIS G4304 and JIS G4305. Figures 2 and 3 show hot-rolled stainless steel strips and cold-rolled stainless steel strips using 5O5304, which is prone to pitting, at various current densities (A/c).
This is a graph showing the occurrence of P1- during anodic electrolysis under the conditions combining the electrolysis time (seconds) and the electrolysis time (other conditions: NaCl concentration 200g/l, liquid temperature 60℃ constant). and the above range is 5IJS340 and 5U
This indicates that this is the second limit of the range of the amount of electricity per unit area as defined in common with S430.

On the other hand, pretreatment by anodic electrolysis using NaCα as an electrolyte aims to remove most of the scale and reduce the burden of pickling, so the amount of electricity per unit area is sufficient to fulfill this role. As a result of various tests, the lower limit of the range was found to be 200 A·sec/plane for hot rolled stainless steel strip and 100 A·sec/dIIl for cold rolled stainless steel strip. Descaling is usually carried out in the form of a steel strip while it runs on the same line as the annealing process, so the processing time required for annealing, that is, the time it takes to pass through an annealing furnace, is adjusted to change the strip threading speed depending on the thickness of the strip. The time for passing through the electrolytic cell, that is, the electrolysis time, is determined by the current density (A
. NaC
According to anodic electrolysis in an aqueous solution, the action of chlorine ions is added in addition to the reaction with the acid generated at the anode, so the ability to remove scale is large.

In the method of the present invention, the acids used in the pickling treatment performed after the electrolytic treatment in the NaCl aqueous solution include nitric-fluoric acid mixed with at least hydrofluoric acid and nitric-fluoric acid mixed with at least hydrofluoric acid in order to remove even the metal base directly under the scale layer. For the nitrofluoric acid pickling solution, the HFfi degree is 5 to 50 g/l, and the HNO
A suitable 3'a degree is 50 to 100 g/l, and a HFlli degree of 5 to 50 g/l for a nitrofluoric acid pickling solution.

112SO4'a degrees 150-250 g/Q is appropriate, and within the above range, higher HF concentrations are preferred.

When using either the general nitric-fluoric acid pickling solution or the nitric-fluoric acid pickling solution, and when using either of them for two-stage pickling, the following are used: From the viewpoint of surface finish and passivation treatment, the nitric-fluoric acid pickling solution is preferably used at a temperature of 50 to 70°C. In this way, when applying two-stage pickling using nitric-fluoric acid in the first stage and nitric-fluoric acid in the second stage to 5US304.5O5430, etc., in addition to the above-mentioned effects of nitric-fluoric acid, the nitric-fluoric acid used first If pickling is carried out at a pickling solution temperature of 70 to 90°C, very good results can be obtained due to the added descaling and etching effects of nitric hydrofluoric acid. Table 2 shows hot rolled stainless steel strip (SUS3
04.

5IJS430) was treated with a pickling solution using nitric-fluoric acid, sulfuric acid, or nitric-fluoric acid alone.

From Table 2, it can be seen that the nitric-fluoric acid pickling solution is particularly excellent as a first-stage pickling solution. Similar results were obtained for cold rolled stainless steel strip. The pre-stage pickling treatment using a pickling solution using only H2SO4 is preferably not carried out in the case of S[15304, since it may cause smut although the weight loss is large, but it may be carried out in the case of 5US430.

Next, a specific example of the descaling process according to the method of the present invention will be explained with reference to FIG. 1, including operations performed incidental to electrolysis and pickling.

The stainless steel tllF1, which has traveled at the same speed as it passes through the annealing furnace (not shown), is fed into the electrolytic cell 2 via the feeding roll 15, and is filled into the electrolytic cell 2 by dipping rolls 14 and 14 back and forth. The electrolytic power source 5
Anode plate 3 and cathode plate 4 connected to stainless steel #I! 8
1, the stainless steel strip 1 is charged as an anode by a circuit formed in such a way that when the stainless steel strip 1 passes between the anode plates 3, it becomes a cathode, and when it passes between the cathode plates 4, it becomes an anode. Under electrolytic action, most of the scale on the surface is dissolved and removed in the electrolytic solution. The scale thus dissolved in the electrolytic solution combines with hydroxide ions generated by the action of the cathode plate 4 and turns into sludge mainly composed of metal hydroxides. This sludge is made of stainless steel strip 1
The sludge adheres to the electrolyte and causes scratches on the surface during feeding, so the sludge is sequentially extracted into the liquid storage tank 7, and the sludge is separated from the electrolyte by a centrifuge 8 and discharged.
is returned to the electrolytic cell 2. NaCl in the electrolytic cell 2 is constantly self-regenerating and no Cr'''6 ions are generated, so there is no aging of the electrolytic solution.The electrolytic conditions include current density (A
/dJ) is adjusted to a specified range according to the passage time of the stainless steel strip 1 through the electrolytic cell 2, as described above.

The stainless steel strip 1 that has passed through the electrolytic bath 2 is transferred to a feeding roll 15.
It then passes between the brush roll 12 and the backup roll 13. At this time, the anodic electrolysis removes most of the scale that still remains attached, although its bonding force with the metal base is weakened.

Next, the stainless steel strip 1 is fed into the pickling tank 10 via the feeding rolls 15, and passes while being immersed in the above-described pickling solution by the front and rear dipping rolls 14, 14, during which time a small amount of the pickling liquid remains. In addition to dissolving and removing all of the scale that is present, the metal base that is present directly below the scale layer is also dissolved. Since most of the scale layer has been removed by the electrolytic treatment, the aging of the pickling solution in the pickling tank 10 is reduced accordingly, making it easy to maintain and manage the descaling and etching ability of the pickling solution. .

The stainless steel strip 1 that has passed through the pickling tank 1.0 passes through the feed roll 15 and is transferred to the brush roll 12 and the backup roll 1.
3, and at this time, even if a slight scale or metal base remains with a weak bonding force with the metal base, it is removed and a beautiful base is exposed.

When using the above two types of pickling liquids for pickling, the above-mentioned pickling is performed as the first step, and then, as shown in FIG. A pickling tank 11 and a brush roll 12 are provided. Backup roll 13
It is sufficient that the pickling process and the brushing process are performed in the subsequent stage using another type of pickling liquid. In the case of this two-stage pickling treatment, the etching effect can be further enhanced compared to the case of only one stage, and since the acid concentration can be adjusted for each stage, the pickling ability can be easily maintained. What is preferable to be used as the pickling liquid in the front and rear stages is as explained above. In this way, the descaling process according to the method of the present invention is completed.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples.

Hot rolled stainless steel strip (
5O5304 with a plate thickness of 3.8m, 5US with a plate thickness of 3.6mm
340) was once wound into a coil for an experiment, and descaling was performed at various plate feeding speeds, that is, by varying the electrolysis time and pickling time, according to the process shown in FIG.

In addition to NaCl, Na25o4. NaNO
3. Pretreatment was performed using an aqueous solution of NaF under various electrolytic conditions.

These electrolytic solutions and electrolytic conditions are shown in Table 3. The pickling used in the subsequent two-stage pickling treatment was 117 [iA
Ni+; 1H7sOJi degree power 228 g/Q TeI+
Use a nitrofluoric acid pickling solution with F11 degrees F10 g/l at a liquid temperature of 75°C, and the subsequent pickling L knee HNO31 degrees Cuff 0 g.
/Q A nitric-fluoric acid pickling solution with an HF concentration of 10 g/l was used at a solution temperature of 60°C. Electrolytic cell used in this experiment 2. Since the immersion length of the stainless steel strip in the pickling tanks 10 and 1 is the same, the pickling treatment time in the 111i stage and the subsequent stage is the same as the electrolysis time, and the other pickling treatment conditions are the same for each experiment. Since these are common to all, they are omitted from the table below.

In the above descaling experiment, positive pi electrolysis (treatment)),
Measure the weight loss (■/dJ) after each of the first-stage pickling (treatment 2) and the second-stage pickling (treatment 3), and add them up.
The descaling ability at each processing stage and the overall descaling ability were shown. This method of measuring weight loss is as follows:
Process 1 including changing processing conditions for a coil whose width and length are known. After applying treatment 2 and treatment 3, measure the weight, width, and length again, and divide the weight difference by the product of plate width (dm) and treatment length (dm) to calculate the weight loss per unit length. Process 1, which includes the method of determining the value and changing the processing conditions. Before applying treatment 2 and treatment 3, take a 100m square (ldm square) sample from the coil, and after each treatment take a sample under the same conditions, and divide the weight difference by the sample area to calculate the unit. It was measured by any method that calculates the weight loss per length. In addition, after the process was completed, the presence or absence of scale remaining was visually observed. In addition to the above, Cr” in the electrolyte during electrolysis
We performed ion detection work to determine whether or not they occur. Furthermore, the presence or absence of occurrence of pin 1~ was investigated, and if present, it was caused by anodic electrolysis. These results are shown in Table 3.

From Table 3 in the margin below, regarding the weight loss in anodic electrolysis (treatment 1), N
It was found that the use of aCl as an electrolyte is the most common compared to other cases, and the aging of the pickling solution during pickling can be reduced accordingly, and Cr+G ions are also generated in other cases (excluding seawater). It can be seen that this is observed in the case of NaCl, whereas it is absent in the case of NaCl.

In the case of NaCl, if the amount of electricity per unit area (aXb) is below the upper limit of the range specified in the method of the present invention, no pits will occur, but if not, pits 1~ will occur. I understand that. In addition, the amount of electricity per unit area (a
When X b) is within the range specified in the method of the present invention, the weight loss in treatment 1 is quite large as shown in Table 3, and the stainless steel has a beautiful surface after pickling for the same time as the electrolysis time. fF
However, if the amount of electricity per unit area (a x b) is smaller than the lower limit of the range specified in the method of the present invention, pickling must take longer than the electrolysis time, It can be seen that the aging of the pickling solution is accelerated and its management becomes troublesome. When electrolysis was performed using seawater, white scale formed on the electrodes, making it difficult to carry out the electrolysis, so pickling was omitted.

From the above table, it can be seen that the method of the present invention is extremely excellent as a descaling method.

〔effect〕

The method for descaling a stainless steel band according to the present invention as detailed above has various advantages as listed below, and its industrial value is extremely large.

1. Since most of the scale can be removed by pretreatment, the descaling load in the pickling tank is reduced, the life of the pickling solution is extended, and the descaling ability is stabilized. Therefore, the labor required for controlling the concentration of the pickling solution and adding acid,
This reduced costs and enabled faster descaling.

2. Production capacity can be improved because it is now possible to obtain sufficient descaling ability for both hot-rolled and cold-rolled materials on the same line.

3. By adopting anodic electrolysis using an aqueous sodium chloride solution as a pretreatment method, it is no longer necessary to treat Cr" ions in the waste liquid discharged from the electrolytic tank, reducing the cost of treatment. There is no generation of Cr" ions in the process, and the removed scale is separated from the liquid phase as sludge made of metal hydroxide, so there is little deterioration of the liquid, and the electrolyte, sodium chloride, is relatively inexpensive. This has made possible low-cost and stable pretreatment.

4. The pretreatment in the method of the present invention has a sufficient descaling ability, and is also excellent in terms of loss because it is not as viscous as molten salt and has little liquid carry-out.

5. Since it is now possible to remove most of the scale during pre-treatment, the pickling process removes the remaining scale and at the same time dissolves the metal base directly under the scale. It was possible to reduce surface roughness and uneven gloss, which are surface defects of stainless steel strips caused by insufficient descaling.

6. With regard to equipment when implementing the method of the present invention, conventional electrolytic cells and pickling tanks can be used as they are, so almost no equipment modification is required, and the descaling ability is improved. The results were improved.

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing an example of the implementation state of the method of the present invention, and FIGS. 2 and 3 show the upper limits of the range of the product of current density and electrolysis time specified in the method of the present invention for hot and It is a graph shown for each cold rolled stainless steel strip. 1... Stainless steel strip 2... Electrolytic cell 3... Anode plate 4... Cathode plate 5... Electrolyte for electrolysis 6... Liquid feed pump 7... Sludge liquid storage tank 8 Centrifugal separator 9... Liquid feed pump 10, pickling tank 11, pickling tank 12, brush roll 13, backup roll 14... dipping roll 15... feed plate roll

Claims (1)

[Claims] 1. In an electrolytic solution consisting of an aqueous solution containing 50 to 200 g/l of NaCl as a main component, the solution temperature is 20 to 80°C, and the product of current density and electrolysis time is 200 to 800 A·sec/dm. The feature is that electrolytic treatment is performed under the conditions of ^2 using a hot rolled stainless steel strip as an anode, and then pickling treatment is performed with at least either nitric-fluoric acid or sulfuric-fluoric acid to remove even the metal substrate immediately below the scale. A method for descaling stainless steel strips. 2. The method for descaling a stainless steel strip according to claim 1, wherein the pickling treatment is carried out in two steps, first with sulfuric and then with nitric and hydrofluoric acid. 3 As sulfuric acid, H_2SO_4 concentration is 150-25
0 g/l and HF concentration of 5 to 50 g/l at a liquid temperature of 70
The method for descaling a stainless steel strip according to claim 1 or 2, wherein the method is used at a temperature of ~90°C. 4 As nitric hydrofluoric acid, HNO_3 concentration is 50 to 100 g/
1 with an HF concentration of 5 to 50 g/l at a liquid temperature of 50 to 70 g/l.
The method for descaling a stainless steel strip according to claim 1 or 2, wherein the method is used at a temperature of .degree. 5 In an electrolytic solution consisting of an aqueous solution containing 50 to 200 g/l of NaCl as the main component, the solution temperature is 20 to 80°C, and the product of current density and electrolysis time is 100 to 400 A・sec/dm^2. It is characterized by performing electrolytic treatment using a cold-rolled and annealed stainless steel strip as an anode, and then pickling with at least either nitric-fluoric acid or sulfuric-fluoric acid to remove even the metal substrate immediately below the scale. A method for descaling stainless steel strips. 6. The method for descaling a stainless steel strip according to claim 5, wherein the pickling treatment is carried out in two steps, first with sulfuric and then with nitric and hydrofluoric acid. 7 As sulfuric acid, H_2SO_4 concentration is 150-25
0 g/l and HF concentration of 5 to 50 g/l at a liquid temperature of 70
The method for descaling a stainless steel strip according to claim 5 or 6, wherein the method is used at a temperature of ~90°C. 8 As nitric hydrofluoric acid, HNO_3 concentration is 50 to 100 g/
1 with an HF concentration of 5 to 50 g/l at a liquid temperature of 50 to 70 g/l.
The method for descaling a stainless steel strip according to claim 5 or 6, wherein the method is used at a temperature of .degree.