JP2517353B2 - Descaling method for stainless steel strip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention makes it easy to manage a chemical solution used for scale removal and to treat the waste solution thereof, and even if the scale removal capacity is large and the line speed is increased. It relates to a descaling method for stainless steel strips that can be followed, without worrying about pollution problems such as environmental pollution regarding waste liquid and sludge generated in the line, and above all, improving the surface quality of the final product. .

[Conventional technology]

Generally, hot-rolled stainless steel strip products such as No. 1 finish (surface finish) specified in JIS G4306 "Hot-rolled stainless steel strip" are made from hot-rolled stainless steel strip, which is annealed. It is manufactured by passing through a series of annealing pickling steps that are lined up in order to perform a heat treatment including pickling or a treatment similar to this pickling. The hot rolled stainless steel strip produced through this annealing pickling process is sheared to JIS G43
04 Hot-rolled stainless steel sheet products specified in “Hot-rolled stainless steel strip” are manufactured.

In addition, cold-rolled stainless steel strip products with various polishing finishes (surface finish) such as No. 2D, No. 2B, BA, etc. specified in JIS G4307 “Cold-rolled stainless steel strip” are subjected to the above-mentioned annealing pickling process. The manufactured hot-rolled stainless steel strip is repeatedly passed through the material and the cold-rolling process and the annealing pickling process, which are each made into a line, and the scale on the surface of the material is applied between these processes. In order to remove residue and ground defects, it is passed through an intermediate polishing process which is lined as necessary, and further subjected to a temper rolling process and a refining process in which shearing and cutting are performed. The cold-rolled stainless steel strip thus produced is sheared to produce a cold-rolled stainless steel sheet product defined in JIS G4305 “Cold-rolled stainless steel strip”.

As described above, the stainless steel strip product and the steel plate product are subjected to the hot rolling, the heat treatment including the annealing after the hot rolling, and the softening annealing of the work hardened material by the cold rolling. In each case, a scale mainly composed of oxides such as Fe and Cr is generated on the surface of the material. Unless the scale formed on the surface of the material is completely removed and the respective steps are carried out, a final product having good surface quality cannot be obtained, so that a descaling treatment is performed each time.

However, since the scale formed on the surface of the material of the stainless steel strip is generally dense, it is very difficult to remove, that is, descaling is difficult compared to other ordinary steel and special steel.

Therefore, with respect to the descaling of the scale formed on the surface of the material of the stainless steel strip, various descaling methods have been conventionally implemented or proposed.

First of all, the most basic and widely practiced method for this treatment has been to treat with sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid, or a mixed acid chemical solution containing these to perform descaling to achieve uniform and appropriate passivation. It was a pickling treatment. However, in the present treatment method using only this pickling treatment, the stainless steel strip is subjected to a high-speed treatment to improve productivity and yet a complete descaling treatment is performed, and there is a demand for obtaining a good surface quality as a final product. It is no longer possible to deal with this, and mechanical treatment, chemical treatment, or a pretreatment combining these has come to be used in combination before the pickling treatment which is the main treatment.

That is, the mechanical pretreatment is a machine for facilitating descaling by causing cracks in the scale layer by a shot blast or a scale breaker prior to pickling in the case of hot-rolled material with a large amount of scale. However, these mechanical pretreatments have drawbacks of leaving indentations on the base material of the stainless steel strip and causing work hardening.

In addition, some components are solute by chemical pretreatment such as electrolysis in an aqueous solution using Na ₂ SO ₄ as an electrolyte and a molten caustic treatment, and the composition of the scale and the base material Although a method of weakening the bonding force is also implemented, it is effective for cold-rolled material with a relatively small amount of scale, but less effective for hot-rolled material with a large amount of scale.

As a result of this process, Na ₂ SO ₄ was used as a chemical pretreatment.
A descaling method has been adopted in which anodic electrolysis is performed in an aqueous solution or molten caustic treatment is performed, and then pickling with sulfuric hydrofluoric acid, nitric hydrofluoric acid, or the like, or anodic electrolysis in an aqueous solution of NaCl or the like instead. It was

On the other hand, in order to improve the productivity of stainless steel strips, it is required to perform descaling at high speed and with high efficiency along with rolling and annealing. Therefore, the development of a descaling method with a large scale removing capability is desired. Came. However, when performing anodic electrolysis in an aqueous Na ₂ SO ₄ solution as a chemical pretreatment, this pretreatment method has a large effect on cold-rolled material, but it is originally so large on hot-rolled material. It has no effect and elutes Cr ⁺⁶ ions, so the treatment of the waste liquid is very troublesome in terms of pollution control. Therefore, pretreatment by electrolysis in Na ₂ SO ₄ aqueous solution is difficult to increase the speed for hot-rolled material, and Cr ⁺⁶ is the same for both hot-rolled and cold-rolled material. There is a drawback that the amount of ion elution increases and the aging of the electrolyte solution is accelerated and the treatment becomes more troublesome.

In addition, when performing molten caustic treatment as another method of chemical pretreatment, the molten caustic has a high viscosity, so that the amount of liquid taken out increases due to high speed, and the speed is also reduced by the wiping device. There is a drawback that it is difficult to follow up to prevent an increase in the amount of liquid taken out, resulting in an increase in cost.
When the pickling is carried out by increasing the acid concentration and the liquid temperature in order to weaken the pretreatment which is difficult to increase the speed as described above and to strengthen the weakened portion, the aging of the pickling solution is accelerated. However, there is a disadvantage that the labor and cost for controlling the acid concentration, adding acid, treating waste liquid, and the like are great. Also instead of pickling
Even if anodic electrolysis is carried out in an aqueous solution containing a mixture of NaCl and nitrate as an electrolyte, if it is performed so strongly that it becomes the main descaler, there is a drawback that pits are easily generated in the stainless steel strip. As described above, it has been difficult to achieve both descaling that achieves good results by carefully performing at low speed and high speed.

[Problems to be Solved by the Invention]

It is an object of the present invention to provide a method for descaling a stainless steel strip which has a large scale removing ability without the drawbacks of the above-mentioned prior art, can be speeded up, has less problems of waste liquid treatment, and has a good surface quality. For that purpose, there is a problem that it is difficult to solve what kind of processing method is to be performed for the pre-processing and the main processing performed thereafter.

[Means for solving the problem]

As a result of intensive studies to solve such problems, the present inventors have adopted, as the main treatment, pickling having the advantage of positively removing the metal base immediately below the scale to clean the surface, and the above-mentioned pickling. In order to reduce the drawbacks, pretreatment is performed.As pretreatment, anodic electrolysis in Na ₂ SO ₄ aqueous solution has advantages of self-regeneration ability of electrolyte and separation ability to separate scale as sludge. However, various investigations have been made to obtain processing conditions that do not cause the above-mentioned defects, but such conditions have not been obtained.

Therefore, NaCl, which was conventionally considered as an alternative to pickling,
Further studies on the pretreatment by anodic electrolysis in an aqueous solution containing a monobasic inorganic acid salt as an electrolyte revealed the following. That is, when NaF was used, the descaling capacity was larger than that of Na ₂ SO ₄ , but the viscosity of the produced sludge was high and it was difficult to remove it, and when NaNO ₃ was used, the descaling capacity was Na ₂ SO 4. _In the case of NaF and NaNO ₃ , both the same as in the case of No. ₄ and the generation of Cr ^{+ 6} ions in the electrolyte solution are the same as in the case of Na ₂ SO ₄ . It had a brown color mainly composed of iron, and when seawater was used, white scale adhered to the cathode, making it impossible to carry electricity.On the other hand, when NaCl was used, the descaling ability was Na ₂ SO. _It was found that the number of pits was much larger than that in the case of ₄ and the stainless steel strip, especially SUS304, had numerous pits, but the produced sludge was bluish green, and no Cr ⁺⁶ ions were found in the electrolyte. The descaling principle in this case was speculated to be an electrochemical reaction under non-oxidizing conditions. As a result of further study of electrolysis in this NaCl aqueous solution, usually, by adjusting the current density according to the electrolytic cell passage time, that is, the electrolysis time, which is determined by the speed of the line in which the annealing process is incorporated. Electrolysis in which the product (A · sec / dm ² ) of the current density (A / dm ² ) and the electrolysis time (sec) that can be kept within the specified range is below a certain value determined for each hot and cold rolled material. It has been found that electrolysis under the conditions can prevent the generation of the pits. As a result, in this way Na
The present inventors have completed the present invention by discovering that the above object can be achieved by performing pre-treatment by anodic electrolysis using Cl as an electrolyte and then performing pickling.

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

FIG. 1 is a process chart showing an example of an implementation state of the method of the present invention,
FIGS. 2 and 3 are graphs showing the upper limit of the product range of the current density and the electrolysis time defined in the method of the present invention for each hot and cold rolled stainless steel strip.

[Description of configuration]

In the method of the present invention, 50 to 200 g / l of Na is used as a pretreatment.
Electrolysis is performed by using a stainless steel strip as an anode in an electrolytic solution consisting of an aqueous solution of Cl.
The minimum concentration of Cl is 50 g / l because at low concentrations the conductivity of the electrolyte is low and the current efficiency is reduced.The higher the concentration of NaCl is, the higher the concentration of 200 g / l is. This is because the solubility in water was taken into consideration. The temperature of the electrolyte solution for this anodic electrolysis has a relatively small effect on the descaling result, so normal temperature (20 ° C) is not a problem, and higher temperature is preferable because the conductivity and NaCl solubility are higher. If the temperature exceeds ℃, problems such as complicated concentration control and energy loss due to an increase in the amount of evaporated water will occur, so 20 to 80 ℃ is the applicable range, and around 60 ℃ is optimal.

Anode electrolysis using NaCl of hot-rolled stainless steel strip (SUS304, SUS430) as the electrolyte was performed by changing the liquid temperature, current density (A / dm ² ) and electrolysis time (seconds), and the weight loss after treatment and Cr ⁺⁶ Table 1 shows the results of examinations for the presence or absence of ion generation and the presence or absence of pit generation. In addition, when the liquid temperature is high, it is shown in Table 3 as a part of Examples later.

From Tables 1 and 3, the influence of NaCl concentration and liquid temperature is not significant for the amount of weight loss by electrolytic treatment (which is greatly related to the descaling ability), the presence or absence of Cr ⁺⁶ , and the presence or absence of pits. I understand. Similar results were obtained for cold rolled stainless steel strip.

The product of the current density (A / dm ² ) during electrolysis and the electrolysis time (seconds) (A · second / dm ² , hereinafter sometimes referred to as the quantity of electricity per unit area) determines the descaling ability and the generation of pits. It has the most impact. The upper limit of the amount of electricity per unit area is at 800A · sec / dm ² in the case of hot-rolled stainless steel strip, in the case of cold-rolled stainless steel strip is 400A · sec / dm ^2, in each case If the above value is exceeded, pits will be generated when the stainless steel strip is SUS304. This upper limit is a little higher when the stainless steel strip is SUS430. Here, the difference between hot rolling and cold rolling is in accordance with the regulations of JIS G4304 and JIS G4305. Figures 2 and 3 show that hot-rolled stainless steel strips and cold-rolled stainless steel strips with various current densities (A /
dm ² ) and electrolysis time (sec) are combined (other conditions: NaCl concentration is 200 g / l, liquid temperature is constant at 60 ° C), and a graph shows the situation of pit generation during anodic electrolysis. hand,
It is shown that the above range is the upper limit of the electric quantity range per unit area when it is specified in common for SUS340 and SUS430.

On the other hand, the pretreatment by anodic electrolysis using NaCl as the electrolyte is
Since this is a treatment that removes most of the scale to reduce the burden of pickling, the lower limit of the amount of electricity per unit area that is sufficient to fulfill this role is the result of various tests. It was 200 A · sec / dm ² for the steel strip and 100 A · sec / dm ² for the cold rolled stainless steel strip. Since descaling is usually performed in the form of a steel strip while traveling in the same line as the annealing process, the stripping speed adjusted to change the processing time required for annealing, that is, the annealing furnace passage time, depending on the size of the sheet thickness. Will directly determine the passage time of the electrolytic cell, that is, the electrolysis time, but by adjusting the current density (A / dm ² ) to keep the amount of electricity per unit area within the above range, the occurrence of pits can be prevented. In addition, sufficient pretreatment can be performed. According to the anodic electrolysis in a NaCl aqueous solution, the action of chlorine ions is added in addition to the reaction with the acid generated at the anode, so that the scale removing ability is large.

In the method of the present invention, as the acid used in the pickling treatment after the electrolytic treatment in the NaCl aqueous solution, there are at least hydrofluoric acid and sulfuric hydrofluoric acid mixed with at least hydrofluoric acid to remove even the metal base immediately below the scale layer. And either of
HF concentration of 5 to 50g / l, HNO ₃ concentration of 50 to 100g / l
Is suitable, and the sulfuric acid hydrofluoric acid pickling solution has an HF concentration of 5 to 50 g / l, H ₂ SO
_{4 A} concentration of 150 to 250 g / l is suitable, and a higher HF concentration is preferable in the above range.

Generally, when either one of the nitric hydrofluoric acid pickling solution and the sulfur hydrofluoric acid pickling solution is used, and when the two steps of pickling using both of them are used, From the viewpoint of the finished state and the passivation treatment, the nitric hydrofluoric acid pickling solution is preferably used at a liquid temperature of 50 to 70 ° C. In this way, SUS3 is used for the two-step pickling using sulfuric hydrofluoric acid in the first step and nitric hydrofluoric acid in the second step.
When applied to 04, SUS430, etc., in addition to the above effect by nitric hydrofluoric acid, if the acid temperature of the sulfuric acid hydrofluoric acid pickling solution used before is pickled at 70 to 90 ° C, descaling by sulfuric acid hydrofluoric acid and Very good results can be obtained by adding the etching effect. Table 2 shows the results of examining the weight loss when hot-rolled stainless steel strips (SUS304, SUS430) were treated with a pickling solution containing nitric hydrofluoric acid, sulfuric acid, and sulfur hydrofluoric acid alone.

It can be seen from Table 2 that the sulfuric acid hydrofluoric acid pickling solution is particularly excellent as the pre-stage pickling solution. Similar results were obtained with cold rolled stainless steel strip. The pre-stage pickling treatment with a pickling solution using H ₂ SO ₄ alone is preferably not carried out in the case of SUS 430 because it causes a large amount of weight loss in the case of SUS 304, but it may be carried out in the case of SUS 430.

Next, a specific example of the descaling step according to the method of the present invention will be described with reference to FIG. 1, including the operations that are performed in addition to electrolysis and pickling.

The stainless steel strip 1 that has been running at the passing speed of the annealing furnace (not shown) is fed into the electrolytic bath 2 via the feed roll 15 and is fed back and forth by the dipping rolls 14 and 14. 2 passes between the anode plate 3 and the cathode plate 4 and the stainless steel strip 1 which are immersed in an electrolytic solution consisting of an aqueous NaCl solution and are connected to an electrolysis power source 5 while being immersed in the electrolytic solution. The stainless steel strip 1 is formed by a circuit formed so that the stainless steel strip 1 is charged to the cathode when passing between the anode plates 3 and the anode when passing between the cathode plates 4.
Undergoes anodic electrolysis, and most of the surface scale is dissolved and removed in the electrolytic solution. In this way, the scale dissolved in the electrolytic solution is combined with the hydroxide ions generated by the action of the cathode plate 4 and converted into sludge mainly composed of metal hydroxide. Since this sludge adheres to the stainless steel strip 1 and scratches the surface of the plate during feeding, it is successively withdrawn to the sludge liquid storage tank 7, and the sludge is separated from the electrolytic solution by the centrifugal separator 8 and discharged. Electrolyzer 2 by means of pumps 9 and 6
Return to. Since NaCl in the electrolytic cell 2 is constantly self-regenerating and does not generate Cr ⁺⁶ ions, the electrolytic solution is not aged. As described above, as the electrolysis conditions, the current density (A / dm ² ) is adjusted to the specified range according to the passage time of the stainless steel strip 1 through the electrolytic cell 2.

The stainless steel strip 1 that has passed through the electrolytic cell 2 is a plate feeding roll 15
And passes between the brush roll 12 and the back roll 13. At this time, the anodic electrolysis weakens the bonding force with the metal substrate, but most of the scale still adhering and remaining is removed.

Next, the stainless steel strip 1 is passed through the plate feed roll 15 and then pickled.
The plate is sent in 10, passed by the front and rear dipping rolls 14, 14 while being immersed in the above-mentioned pickling solution, while all the scale slightly remaining during the dissolution is removed, The metal base existing directly below the scale layer is melted. Since most of the scale layer is removed by the electrolytic treatment, the aging of the pickling solution in the pickling tank 10 is small by that much, so that descaling of the pickling solution and maintenance of the etching ability are easy.

The stainless steel strip 1 that has passed the pickling tank 10 is a plate feed roll 15
After passing between the brush roll 12 and the back-up roll 13 through, even if a small scale or metal base remains in a state where the bonding force with the metal base is weak, it is removed and a beautiful base material is obtained. Show up.

When the above-mentioned two types of pickling solutions are used for pickling, the above-mentioned pickling is carried out in the preceding stage, and subsequently, as shown in FIG. Wash tank 11
After passing through the brush roll 12 and the back-up roll 13, the subsequent pickling treatment and brushing treatment with another pickling solution may be performed. In the case of the two-step pickling treatment, the etching effect can be further enhanced as compared with the case of only one step, and the acid concentration can be adjusted for each step, so that the pickling ability can be easily maintained. What is preferably used as the front and rear pickling solution is as described above. Thus, the descaling step according to the method of the present invention is completed.

〔Example〕

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

A hot rolled stainless steel strip (SUS304 with a plate thickness of 3.8 mm, SUS340 with a plate thickness of 3.6 mm) that has traveled through the annealing process is temporarily wound around a coil for the purpose of experiment, and various feeding plates are carried out by the process shown in FIG. The descaling was carried out at various speeds, that is, by varying the electrolysis time and the pickling time. Other than NaCl as electrolyte, Na ₂ S
Pretreatments were carried out using various aqueous solutions of O ₄ , NaNO ₃ and NaF under various electrolysis conditions. Table 3 shows these electrolytic solutions and electrolysis conditions. As the pickling used in the subsequent two-step pickling treatment, the sulfuric acid hydrofluoric acid pickling solution with a H ₂ SO ₄ concentration of 228 g / l and an HF concentration of 10 g / l was used at a liquid temperature of 75 ° C for the previous pickling. Then, for the subsequent pickling, a nitric hydrofluoric acid pickling solution having a HNO ₃ concentration of 70 g / l and an HF concentration of 10 g / l was used at a liquid temperature of 60 ° C. Since the immersion lengths of the stainless steel strips in the electrolytic bath 2, pickling baths 10 and 11 used in this experiment were the same, the pre- and post-stage pickling treatment times were the same as the electrolysis time, and other pickling times were the same. Since the conditions of washing treatment are common to each experiment, they are omitted in the following table.

In the above descaling experiment, anodic electrolysis (treatment 1),
The weight loss (mg / dm ² ) after each treatment of the first-stage pickling (treatment 2) and the second-stage pickling (treatment 3) was measured and totaled, and the descaling ability at each treatment stage and the total removal of the process were performed. Expressed scale ability. This weight loss is measured in advance by weight, width,
Processing that involves changing the processing conditions for a coil of known length 1,
After the treatment 2 and the treatment 3, the weight, width and length are measured again, and the weight difference is divided by the product of the plate width (dm) and the treatment length (dm) to reduce the weight per unit length. Method, and before performing treatment 1, treatment 2 and treatment 3 including changes in treatment conditions, a 10 cm square (1 dm square) sample is taken from the coil, and after each treatment the sample under that condition is also the same. The weight difference was divided by the sample area, and the weight loss per unit length was calculated. In addition, after the process was completed, the presence or absence of scale residue was visually observed. In addition to the above, detection work of Cr ⁺⁶ ions in the electrolytic solution during electrolysis was performed to examine the presence or absence of the generation. Furthermore, the presence or absence of pits was also examined, and if pits were present, they were generated by anodic electrolysis. The results are shown in Table 3.

From Table 3, for weight loss in anodic electrolysis (treatment 1),
It was found that the use of NaCl as the electrolyte was the largest compared to other cases, and it was possible to reduce the aging of the pickling solution during pickling by that much, and the generation of Cr ^{+ 6} ions was also found in other cases (however, in the case of seawater, However, in the case of NaCl, it is not. In the case of NaCl, no pit is generated when the amount of electricity per unit area (a × b) is less than or equal to the upper limit of the range specified in the method of the present invention, but otherwise pit is generated. I understand. When the amount of electricity per unit area (a × b) in the anode electrolysis using Nacl as the electrolyte is within the range specified in the method of the present invention, as shown in Table 3, the weight loss in Treatment 1 is considerably large and the electrolysis time is long. Although a stainless steel strip with a beautiful surface was obtained by pickling for the same time as above, when the amount of electricity per unit area (a x b) was smaller than the lower limit of the range specified in the method of the present invention, It has been found that pickling requires a lot of time, and the aging of the pickling solution is accelerated and its management becomes troublesome. When electrolysis was performed using seawater, it was difficult to carry out because the electrode had a white scale, so pickling was omitted.

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

〔effect〕

The descaling method for a stainless steel strip according to the present invention as described in detail above has various advantages as listed below, and its industrial value is very large.

1. Since most of the descaling is possible by pretreatment, the descaling load in the pickling tank is reduced, the life of the pickling solution is extended, and the descaling ability is stable. Therefore, the labor required for the concentration control of the pickling solution and the additional acid,
The cost can be reduced and the descaling can be speeded up.

2. Both hot-rolled material and cold-rolled material can be used on the same line to obtain sufficient descaling capacity, which will improve the production capacity.

3. By adopting anodic electrolysis using sodium chloride solution as a pretreatment method, treatment of Cr ⁺⁶ ions in the waste liquid discharged from the electrolytic cell is not necessary and the treatment cost is reduced. Further, since there is no generation of Cr ^{+ 6} ions in the electrolytic solution and the removed scale is a sludge made of a metal hydroxide, it is separated from the liquid phase, so that deterioration of the liquid is small, and sodium chloride which is an electrolyte is also included. Since it is relatively inexpensive, stable pretreatment is possible at low cost.

4. The pretreatment in the method of the present invention has a sufficient descaling ability, and since it does not have high viscosity like molten salt and little liquid is taken out, it is excellent in cost.

5.Because most of the scale can be removed by the pretreatment, the residual scale is removed by the pickling treatment, and at the same time, the metal base directly under the scale is also dissolved. , The surface defects of the stainless steel strip due to insufficient descaling, such as rough skin and uneven gloss, could be reduced.

6. Regarding the facility side when carrying out the method of the present invention, since both the electrolytic bath and the pickling bath can use the conventional ones as they are, almost no facility remodeling is required, and the descaling ability is high. Was improved.

[Brief description of drawings]

FIG. 1 is a process chart showing an example of an implementation state of the method of the present invention, and FIGS. 2 and 3 show the upper limit of the product range of the current density and the electrolysis time defined in the method of the present invention, respectively, for hot and It is a graph shown for each cold rolled stainless steel strip. 1 …… Stainless steel strip 2 …… Electrolysis tank 3 …… Anode plate 4 …… Cathode plate 5 …… Electrolysis electrode 6 …… Liquid feeding pump 7 …… Sludge liquid storage tank 8 …… Centrifuge 9 …… Liquid feeding Pump 10 …… Pickling tank 11 …… Pickling tank 12 …… Brush roll 13 …… Back up roll 14 …… Immersion roll 15 …… Plate roll

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-61-266588 (JP, A) JP-A-54-142140 (JP, A) JP-B-53-23245 (JP, B2)

Claims (8)

(57) [Claims] 1. A liquid temperature of 20 to 80 ° C. and a product of a current density and an electrolysis time of 200 in an electrolytic solution composed of an aqueous solution of NaCl of 50 to 200 g / l.
Electrolytic treatment is performed using hot rolled stainless steel strip as an anode under the condition of ~ 800 A · sec / dm ² , and then at least either nitric hydrofluoric acid or sulfur hydrofluoric acid is pickled to reach the metal substrate directly under the scale. A method for descaling a stainless steel strip characterized by removing. 2. The method for descaling a stainless steel strip according to claim 1, wherein the pickling treatment is carried out by a two-stage treatment of first with sulfur hydrofluoric acid and then with nitric hydrofluoric acid. 3. A hydrofluoric acid having a H ₂ SO ₄ concentration of 150 to 250 g / l.
The method for descaling a stainless steel strip according to claim 1 or 2, wherein an HF concentration of 5 to 50 g / l is used at a liquid temperature of 70 to 90 ° C. 4. HF as nitric hydrofluoric acid having a HNO ₃ concentration of 50 to 100 g / l
The method for descaling a stainless steel strip according to claim 1 or 2, wherein a solution having a concentration of 5 to 50 g / l is used at a liquid temperature of 50 to 70 ° C. 5. A liquid temperature of 20 to 80 ° C. and a product of current density and electrolysis time of 100 in an electrolytic solution composed of an aqueous solution of NaCl of 50 to 200 g / l.
Electrolytic treatment was performed using a stainless steel strip annealed after cold rolling under the condition of ~ 400 A · sec / dm ² as an anode, and then subjected to pickling treatment with at least either nitric hydrofluoric acid or sulfur hydrofluoric acid. A descaling method for a stainless steel strip, which is characterized by removing even the metal base immediately below the scale. 6. The method of descaling a stainless steel strip according to claim 5, wherein the pickling treatment is carried out by a two-step treatment of first with sulfuric hydrofluoric acid and then with nitric hydrofluoric acid. 7. A hydrofluoric acid having a H ₂ SO ₄ concentration of 150 to 250 g / l.
The method for descaling a stainless steel strip according to claim 5 or 6, wherein an HF concentration of 5 to 50 g / l is used at a liquid temperature of 70 to 90 ° C. 8. HF as nitric hydrofluoric acid having a HNO ₃ concentration of 50 to 100 g / l
The method for descaling a stainless steel strip according to claim 5 or 6, wherein a solution having a concentration of 5 to 50 g / l is used at a liquid temperature of 50 to 70 ° C.