JP2577618B2 - Method and apparatus for descaling alloy steel strip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is easy to manage a chemical solution used for scale removal and to treat a waste liquid thereof, has a large scale removal capability, and follows even if the line speed is increased. Descaling of alloy steel strip containing at least nickel and / or chromium, which is possible, has no pollution problems such as environmental pollution with respect to waste liquid and sludge generated in the line, and above all, improves the surface quality of the final product The present invention relates to a method and an apparatus.

[Conventional technology]

Hot-rolled stainless steel strip products specified in JIS G 4306 "Hot-rolled stainless steel strip", which can be said to be representative of at least nickel and / or chromium-containing alloy steel strips, are generally hot-rolled stainless steel strips. It is manufactured by passing a steel strip through a series of lined annealing and pickling steps in order to perform a heat treatment including annealing, pickling or a treatment similar to this pickling. Then, a hot-rolled stainless steel strip specified in JIS G 4304 “Hot-rolled stainless steel sheet” is manufactured by shearing the hot-rolled stainless steel strip manufactured through the annealing and pickling step.

Further, the cold-rolled stainless steel strip products having various surface finishes such as No. 2D, No. 2B, No. 3, No. 4, BA specified in JIS G 4307 `` Cold rolled stainless steel strip '' The hot-rolled stainless steel strip produced through the annealing and pickling process is used as a material, and the strips are repeatedly passed through a cold rolling process and an annealing and pickling process, each of which is lined up, as necessary. In order to remove residual scale and flaws on the surface of the material, it is passed through a lined intermediate polishing process as necessary,
Further, it is manufactured through a temper rolling step and a refining step in which shearing, cutting, and the like are performed. Then, the cold-rolled stainless steel strip thus manufactured is sheared to JIS G 4305.
A cold-rolled stainless steel sheet product specified in “Cold-rolled stainless steel sheet” is being manufactured.

As described above, ferroalloy products such as stainless steel strip products and steel plate products are manufactured by hot rolling, heat treatment including annealing after the hot rolling, and softening and annealing of a work hardened by cold rolling. Therefore, a scale mainly composed of an oxide such as Fe or Cr is formed on the surface of the material each time to a greater or lesser degree. 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, scale formed on the surface of a material such as an alloyed steel strip, particularly a stainless steel strip, is generally very difficult to remove because of its denseness. Therefore, various descaling methods have been conventionally implemented or proposed for descaling of the scale generated on the material surface of the steel alloy strip.

First, the most basic and widely practiced treatment method since ancient times is to perform descaling by treating with sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid or a mixed acid chemical mixture of these, and to achieve a uniform and moderate passivation It was a pickling treatment for a chemical treatment. Also,
In recent years, a processing method for improving the descaling effect by immersing an alloy steel strip in a processing liquid obtained by adding a ferric salt to these pickling liquids has also been disclosed.

However, this treatment method using only the pickling treatment responds to the requirement that the steel alloy strip be processed at high speed to improve the productivity and to perform the complete descaling treatment to obtain a final product with good surface quality. Therefore, before the pickling treatment, a pretreatment mechanically, chemically, or a combination thereof is used. The mechanical pretreatment is a treatment method in which the scale layer is cracked by a shot blast or a scale breaker prior to the pickling treatment to facilitate descaling in the pickling treatment. As a pre-treatment, some components are altered by chemical treatment such as molten caustic treatment or anodic electrolysis in an aqueous solution using Na ₂ SO ₄ as the electrolyte, and the composition of the scale and the bonding strength with the metal base are changed. This is a processing method for weakening.

[Problems to be solved by the invention]

The mechanical pretreatment such as the shot blast and the scale breaker described above has a defect that an indentation is left on the base material of the alloy steel strip or work hardening occurs. On the other hand, in chemical pretreatment such as molten caustic treatment, the amount of liquid taken out increases due to the high speed due to the high viscosity of molten caustic, and it follows the speed even when a wiping device is used. Therefore, it is difficult to prevent an increase in the amount of liquid taken out, resulting in a high cost. In addition, since it is difficult to increase the speed of the above pretreatment, the descaling ability cannot be weakened to increase the speed, and the acid concentration and the liquid temperature are adjusted to supplement and strengthen the weakened portion. A method of pickling by pickling is also adopted, but in this case, the aging of the pickling solution is accelerated, resulting in a disadvantage that the labor and cost for acid concentration control, additional acid, waste liquid treatment, and the like become large. . Furthermore, chemical pretreatment by anodic electrolysis in an aqueous solution containing Na ₂ SO ₄ as a neutral salt as an electrolyte is effective for a cold rolled material having a relatively small scale amount,
Less effective for hot-rolled material with large scale,
Moreover, when the ferromagnetic iron contains chromium, Cr ^{+ 6} ions are eluted, so that the waste liquid treatment is extremely troublesome in terms of pollution prevention. Therefore, even in the pretreatment by electrolysis in an aqueous solution of Na ₂ SO ₄ , it is difficult to increase the speed for hot-rolled materials, and if the speed is increased for both hot and cold-rolled materials,
The disadvantage is that the Cr ^{+ 6} ion extraction is increased to accelerate the aging of the electrolyte and to make the treatment more troublesome.

As described above, the descaling and the speeding-up, in which a good result can be obtained only by carefully performing at a low speed, have been difficult to achieve.

Therefore, the present invention provides a large scale removal capability in the pretreatment for any of the steel alloy strips of the hot-rolled material and the cold-rolled material, so that the speed can be increased and the problem of the waste liquid treatment is reduced, and the surface quality is improved. It is an object of the present invention to provide a descaling method and apparatus capable of obtaining an excellent steel alloy strip.

[Means for solving the problem]

The inventors of the present invention have conducted intensive studies in order to solve such problems, and as a final treatment, an acid using a pickling solution containing hydrofluoric acid, which has the advantage of positively removing the metal base just below the scale and cleaning the surface. If a rinsing treatment is adopted and the anodic electrolytic treatment is carried out in an electrolytic solution consisting mainly of an aqueous solution containing ferric chloride as a pretreatment, most of the scale is removed in this pretreatment stage, and In addition, the load of the final pickling process is reduced, and the speed can be increased.
The present invention was completed by investigating that the problem of waste liquid treatment was reduced because Cr ^{+ 6} ions were not generated, and that the alloy steel strip with excellent surface quality was obtained by removing the metal base just below the scale. .

[Description of configuration]

The alloy steel strip applicable in the present invention is at least
It is an alloy steel strip containing Ni and / or Cr, and may be any of a hot-rolled material and a cold-rolled material.

The electrolytic solution used for the pretreatment is mainly composed of an aqueous solution containing ferric chloride, and the pickling solution for the final treatment is composed of a mixed acid of hydrofluoric acid such as hydrofluoric acid and nitric acid and another acid. It is necessary.

By the way, the electrolytic solution comprising an aqueous solution containing ferric chloride used in the pretreatment of the present invention has a concentration of 250 to 400 g / l and a liquid temperature of 40 to 80 ° C. as described in detail below. Is preferred. That is, FIGS. 6 to 8 use a hot-rolled stainless steel strip SUS304 having a thickness of 3.8 mm and variously change the concentration and temperature of the aqueous solution containing ferric chloride (current density is 10 A / dm. reduction of alloy steel strip ² at constant) when electrolysis, the voltage is a graph showing the electrical conductivity, as is clear from these figures, the concentration of ferric chloride is 250 g / l or less,
In particular, the weight loss of the metal, which is reduced to 200 g / l or less, is reduced (the descaling ability is reduced), and pits are easily generated. On the other hand, when the concentration of ferric chloride exceeds 400 g / l, the descaling ability tends to decrease, and the supply voltage increases, so that the electrolytic efficiency decreases. In addition, the higher the electrolyte temperature, the higher the descaling ability, the lower the supply voltage, and the higher the conductivity, thereby improving the electrolysis efficiency. However, when the electrolyte temperature exceeds 80 ° C, the amount of water evaporation increases suddenly,
As the concentration changes (increases), the descaling ability and the electrolytic efficiency decrease for the above-described reason. On the other hand, when the liquid temperature decreases, the metal loss decreases, the supply voltage increases, the conductivity decreases, and the electrolytic efficiency decreases. Therefore, the liquid temperature is desirably 40 ° C. or higher from the viewpoint of descaling ability. Therefore, it is desirable that the concentration of the electrolyte is 250 to 400 g / l and the temperature of the electrolyte is in the range of 40 to 80 ° C. Furthermore, the concentration is 300 ± 30 g / l, considering the ferrous chloride carry-out phenomenon, the descaling ability decrease due to the concentration change, and the energy loss.
The liquid temperature is more preferably in the range of 60 ± 10 ° C.

The current density during the anodic electrolytic treatment, 5A / dm ² smaller than descaling effect is reduced, since the electrolyte pattern tends to occur due to contrast 30A / dm ² larger than the current density nonuniformity, 5 It is desirable to be in the range of 30 A / dm ² .

Next, an apparatus for carrying out the method of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic view of an example of an apparatus for carrying out the method of the present invention, FIG. 2 is an enlarged plan view of the electrolytic solution tank of FIG. 1, and FIG. 3 is an apparatus for carrying out the method of the present invention. Schematic diagram of another example,
FIG. 4 is an enlarged plan view of the electrolytic solution tank of FIG. 3, and FIG. 5 is a schematic view of still another example of an apparatus for carrying out the method of the present invention.

In the drawings, in FIGS. 1 and 2, reference numeral 1 denotes at least heat-treated by an annealing furnace and a cooling device (not shown).
An alloy steel strip containing Ni and / or Cr, 2 is an electrolytic solution mainly composed of an aqueous solution containing ferric chloride, 3 is an electrolytic bath in which the electrolytic solution 2 is built, and 4 is an electrolytic bath in the electrolytic bath 3. The provided anode plate, 5 is a cathode plate also provided in the electrolytic solution tank 3, 6 is a DC power supply for electrolysis, and 7 is an acid pickling bath containing a pickling solution 8 composed of hydrofluoric acid and another acid. A tank, 9 is a feeding roll, 10 is a dipping roll, 11 is a brush roll, 12 is a back-up roll of the brush roll 11, and 13 is a washing nozzle. 3 and 4, reference numeral 14 denotes a conductive liquid such as sulfuric acid.
Reference numeral 15 denotes a conductive liquid tank in which a bath is built, 16 denotes an anode plate having acid resistance provided in the conductive liquid tank 14, and 17 denotes a cathode plate formed of an electrode plate. Numeral 18 denotes a cathode plate 17 in the electrolytic solution tank 3 and a conductive solution tank via a switching power supply 19 and a switching switch 19 for electrolysis.
The DC power source 6 for electrolysis, which is disposed so as to be connectable to the anode plate 16 (in the case of FIG. 3) 14 or the cathode plate 5 in the electrolytic solution tank 3 and an energizing roll 21 (in the case of FIG. 5) described later. This is another DC power supply for applying a small capacity voltage, and in FIG. 4, reference numeral 20 denotes a gas vent hole. Further, in FIG. 5, reference numeral 21 denotes an energizing roll provided between the electrolytic solution tank 3 and the pickling tank 7 and serving as an anode.

The descaling device for the steel alloy strip according to the present invention having the above-described configuration basically includes three devices as described in detail below. The first device is shown in FIGS.
This device is shown in FIGS. 3 and 4, and the third device is shown in FIG.

First, as shown in FIG. 1 and FIG.
The anode plate 4 and the cathode plate 5 are both provided inside the electrolytic solution tank 3, and the pickling tanks 7, 7 are disposed after the electrolytic solution tank 3. Any one of platinum, ruthenium oxide, and lead oxide is applied. As the cathode plate 5, any one of platinum, titanium, which is a metal having a lower ionization tendency than the anode plate 4, and austenitic stainless steel is used. Or one type is applied. Among them, platinum is particularly preferable for the anode plate 4 and titanium is preferable for the cathode plate 5.
In such a first apparatus, an alloy steel strip 1 which has been heat-treated by an annealing furnace and a cooling device (not shown) is first passed through a feed roll 9 to form an electrolytic solution mainly composed of an aqueous solution containing ferric chloride. The solution 2 is sent to the electrolyte bath 3 in which the bath is built, and passes while being immersed in the electrolyte 2 by the front and rear immersion rolls 10, where the solution 2 mainly contains an aqueous solution containing ferric chloride. Most of the scale on the surface of the steel alloy strip 1 is dissolved and removed in the electrolytic solution 2 by the dissolving action and the anodic electrolytic action. Then, the alloy steel strip 1 from which most of the scale has been dissolved and removed passes through a feed roll 9 provided after the electrolytic solution tank 3 and a brush roll 11 and a back-up roll.
In this case, the anodic electrolysis removes most of the scale that has weakened the bonding force with the metal base but is still adhered and remained. Next, the alloy steel strip 1 is sent to the next pickling tank 7 via the sheet feeding roll 9 and then passed while being immersed by the front and rear immersion rolls 10, 10. The entire scale slightly remaining is dissolved, and at the same time, the metal base existing immediately below the scale layer is dissolved. Further, the alloy steel strip 1 is finished by melting the metal base immediately below the scale layer again while passing through the second pickling tank 7. After a while, alloy steel strip 1
Is passed between the brush roll 11 and the back-up roll 12 via the feed roll 9 to clean the metal adhered to the surface of the alloy steel strip 1 and the metal base remaining in a state where the bonding force is weak. Removed.

As shown in FIGS. 3 and 4, the second device is provided with a conductive liquid such as sulfuric acid in front of the electrolytic solution tank 3 in which the cathode plate 17 and immersion rolls 10 and 10 are provided before and after the cathode plate 17. A conductive liquid tank 14 in which a bath 15 is built is provided, and the conductive liquid tank 14
Anode plate 16 with acid resistance inside and dip roll 1 before and after
0, 10 are provided, and the pickling layer 7,
7 is provided. Further, an electrolytic direct-current power supply 6 and an applied voltage of a small capacity different from the electrolytic direct-current power supply 6 via a switch 19 for switching between an anode plate 16 and a cathode plate 17 having acid resistance. And a DC power supply 18 for connection to the power supply. In the second device as described above, the DC power source for electrolysis 6 is connected to the anode plate 16 and the cathode plate 17 via the switching switch 19 in a normal state,
The alloy steel strip 1 is composed of a feed roll 9 and front and rear immersion rolls 10
According to 0, the conductive liquid 15 is sent in a non-contact state between the anode plates 16 in the conductive liquid tank 14 in which the bath is built. At this time, the alloy steel strip 1 is charged to the cathode by the action of the anode plate 16, and oxygen gas is generated from the anode plate 16 at this time. On the other hand, hydrogen gas is generated from the alloy steel strip 1 charged on the cathode. Then, by the action of the hydrogen gas, a part of the scale having a weak bonding force is removed. As a result, the effect of the anodic electrolytic treatment with the next electrolytic solution 2 comprising an aqueous solution containing ferric chloride is further enhanced.

In the second device, since the anode and the cathode are not mixed in one electrolytic solution tank 3, there is no stray current between the electrodes, and the electrolytic current efficiency is improved. Platinum is used for the anode plate 16 and titanium is used for the cathode plate 17 as the respective materials. Similar to the above-mentioned reason, the generation of chlorine gas is small and the life is extended. It can be used, in which case it is cost effective.

Further, when it is necessary to stop the power supply from the electrolytic DC power supply 6 due to, for example, failure of the electrolytic DC power supply 6 or regular repair, the anode plate 16 and the cathode plate 17 are required.
Between the anode plate 16 and the cathode plate 17 based on the potential difference between the metals constituting the cathode plate 17 → the electrolytic solution 2 → the alloy steel strip 1 → the conductive liquid 15 → the anode plate 16, that is, the direct current for electrolysis. The current flows through the anode plate 16 as a cathode and the cathode plate 17 as an anode, although weakly in the opposite direction to the state where power is supplied from the power supply 6, so that the anode plate 16 is made of ruthenium oxide or lead oxide. When it is an oxide, the oxide is reduced and dissolved to change the size of the anode, and the cathode plate 17 is dissolved by anodic electrolysis. However, one of the DC power supply 6 for electrolysis and the DC power supply 18 for applying a small capacity different from the DC power supply 6 for electrolysis is connected to the anode plate 16 and the cathode plate 17 via the switch 19 for switching. When the power supply from the DC power supply for electrolysis 6 is required, when the power supply from the DC power supply for electrolysis 6 needs to be stopped, a small capacity different from that of the DC power supply for electrolysis 6 can be applied via the switching switch 19. A DC power supply 18 for voltage is connected to the anode plate 16 and the cathode plate 17 so that a weak current flows from the anode plate 16 to the cathode plate 17 to prevent the anode plate 16 from becoming a cathode and the cathode plate 17 from becoming an anode. So the anode plate
It is possible to prevent the oxides constituting 16 from being reduced and dissolved to change the dimensions of the anode and to prevent the cathode plate 17 from being dissolved by anodic electrolysis. Since a certain degree of descaling occurs, the descaling action in the next electrolytic cell 3 is promoted.

As shown in FIG. 5, the third device is constructed by bathing an electrolytic solution 2 composed of an aqueous solution containing ferric chloride, and is provided with an electrolytic bath 3 having a cathode plate 5 and an pickling bath 7. , 7 are provided with an energizing roll 21 serving as an anode, and the electrolysis DC power supply 6 is connected to the energizing roll 21 and the cathode plate 5. In the third apparatus, as in the second apparatus, the DC power supply 6 for electrolysis and a small capacity different from the DC power supply 6 for electrolysis are provided via a switch 19 for switching between the cathode plate 5 and the energizing roll 21. Is connected so that the power supply from the electrolytic DC power supply 6 is stopped due to, for example, a failure or periodic repair of the electrolytic DC power supply 6. When the necessity arises, the potential difference between the metal constituting the cathode plate 5 and the energizing roll 21 between the cathode plate 5 and the energizing roll 21, that is, the cathode plate 5 → the electrolytic solution 2 → the alloy steel strip 1 → the energizing roll Although a weak current flows in the direction of 21, that is, in the opposite direction to the state where power is supplied from the DC power supply 6 for electrolysis, the current flows and the cathode plate 17 becomes an anode, so that the cathode plate 17 is melted by anodic electrolysis. Become. However, the DC power source for electrolysis 6 and the DC power source for electrolysis 6 are switched via the switch 19 between the cathode plate 5 and the energizing roll 21.
If any one of the DC power supply 18 for the applied voltage of another small capacity is connectably disposed, it becomes necessary to stop the power supply from the DC power supply 6 for electrolysis. A small-capacity DC power supply 18 for applying a voltage different from the DC power supply 6 for electrolysis is connected to the cathode plate 5 and the energizing roll 21 via the switching switch 19, and a weak current is supplied from the energizing roll 21 to the cathode plate 5. Since it is possible to prevent the cathode plate 5 from flowing and becoming an anode, it is possible to prevent the cathode plate 5 from being dissolved by anodic electrolysis. In the third apparatus as described above, in a normal state, the alloy steel strip 1 is fed to the feeder roll 21 and the cathode plate 5 with the direct current power source 6 for electrolysis connected thereto via the switch 19 for switching. Roll 9, Dipping roll 10,10
The plate is sent to the electrolytic solution tank 3 via the plate, and is sent between the cathode plates 5 in a non-contact state. At this time, the current-carrying roll 21 serves as an anode, and the alloy steel strip 1 comes into contact with this, so that the alloy steel strip 1 itself directly serves as an anode. In addition, power is supplied from a DC power supply 6 for electrolysis between the electrolytic solution tank 3 and the cathode plate 5. In this apparatus, it is important that the energizing roll 21 is disposed after the electrolytic solution tank 3. That is, since the conductivity of the scale is low, sparks are likely to be generated when current is directly applied to the alloy steel strip 1 having the scale. Therefore, it becomes important to directly supply electricity after removing most of the scale by the electrolytic treatment in the aqueous ferric chloride solution 2. Further, the energizing roll 21 is of a bridle type, and the more rough the roll surface, the more reliable power supply becomes possible.

As described above, direct energization using the energizing roll 21 is the most preferable apparatus because of high electrolysis efficiency and excellent descaling effect. The reason why such a preferable current-carrying roll 21 can be adopted is that most of the scale can be removed in the pretreatment stage by performing the electrolytic treatment using the aqueous ferric chloride solution. is there.

[Action]

As described above, in the pretreatment of the pickling treatment as the final treatment, the alloy steel strip 1 is subjected to anodic electrolysis treatment in an aqueous solution 2 mainly containing ferric chloride, whereby the alloy steel strip 1 is treated. Most of the scale is removed, and in the subsequent pickling treatment, the remaining scale is removed and the metal base immediately below the scale is positively removed.

In other words, most of the scale is removed in the pretreatment of the pickling treatment, so that in the next pickling treatment, only a small amount of residual scale needs to be removed for finishing, which is different from various conventional descaling methods. As a result, the descaling load in the pickling treatment is greatly reduced, the etching action of the metal base of the alloy steel strip 1 is enhanced, and the product having excellent surface quality is obtained.

In addition, since the electrolytic solution is an aqueous ferric chloride solution 2, Cr ⁺⁶
Since there is no generation of ions, the treatment of Cr ⁺⁶ ions in the waste liquid discharged from the electrolytic solution tank 3 becomes unnecessary, and when anodic electrolytic treatment is performed in the aqueous solution, as shown in FIG. The descaling time is considerably shortened as compared with the case of immersion in the ferric aqueous solution 2, and it is possible to follow even if the line speed is increased. Furthermore, during the pickling process, the accumulation of scale in the pickling solution is reduced, so that the life of the pickling solution is extended and a long and high etching action is maintained. It becomes possible.

〔Example〕

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

Example 1 Three types of hot-rolled stainless steel strips (SUS304 having a thickness of 3.8 mm, SUS430 having a thickness of 3.6 mm, and SUS430 having a thickness of 3.6 mm) having traveled through the annealing process.
For a total of four types, namely, 3.6 mm SUS410) and a 4.0% thick 42% Ni alloy steel strip, descaling was performed under the following various conditions by the descaling method and apparatus shown in FIG. The results are shown in Table 1.

1.Electrolytic treatment (pretreatment) (1) Treatment solution: Ferric chloride aqueous solution (2) Liquid concentration: 300g / l (3) Liquid temperature: 60 ℃ (4) Electrolysis density: 20A / dm ² (5) Electrolysis Treatment time: 10, 20, 40, 80 seconds (6) Cathode plate: stainless steel 2. Pickling treatment (1) Treatment liquid and concentration: 70 g / l HNO ₃ + 10 g / l HF (2) Liquid temperature: 60 ° C Comparative Example 1 The apparatus shown in FIG. 5 was applied using the same stainless steel strip as in Example 1, and descaling was performed under the following conditions using a neutral salt electrolyte as an electrolytic treatment in the pretreatment. The results are shown in Table 2.

1.Electrolytic treatment (pretreatment) (1) Treatment liquid: aqueous sodium sulfate solution (2) Liquid concentration: 200g / l (3) Liquid temperature: 80 ° C (4) Electrolytic density: 20A / dm ² (5) Electrolytic treatment time : 10, 20, 40, 80 seconds (6) Cathode plate: stainless steel 2. Pickling treatment Treated under the same conditions as in Example 1.

The weight loss of the alloy steel strip was determined by taking a sample of 10 cm square, weighing the weight with a high-precision balance, and determining the weight loss per unit area before and after the processing.

Evaluation of the descaling state (judgment of presence / absence) is performed using
By visual inspection using 10), it was judged that there was a scale residue of 10 points or more per visual field, and that less than 10 was absent.

In addition, the evaluation of the removal state of the metal base after descaling is performed by observing each target sample whose area has been sufficiently polished as a comparison material with an electron microscope (× 1000) and using a metal different from the metal base (this is referred to as a subscale). Went by the presence or absence.

As is clear from Tables 1 and 2, the method according to the present invention is shorter in time than the one by the neutral salt electrolysis such as sodium sulfate which is one of the conventional chemical pretreatment methods. It can be seen that the descaling is completed and the loss of treatment of the alloy steel strip is large and the descaling effect is excellent.

Example 2 A hot-rolled stainless steel strip was manufactured and cold-rolled to obtain three types of stainless steel strips of SUS304, SUS430, and SUS410 each having a thickness of 1.0 mm. 42% N
The descaling of i-alloy was performed in the same manner as in Example 1 by the descaling method and apparatus shown in FIG. 5 under exactly the same conditions as in Example 1. The results are shown on the third surface.

Comparative Example 2 The four steel strips used in Example 2 were descaled under exactly the same conditions as in Comparative Example 1. The results are shown in Table 4.

The evaluation of the descaling state and the removal state of the metal base were performed in exactly the same manner as in Example 1 and Comparative Example 1.

As apparent from Tables 3 and 4, the results obtained by the method of the present invention can be completed in a shorter time than in the case of the conventional method as in the case of Example 1 as in Example 1, and the processing weight can be reduced. Showed a large descaling effect.
In addition, they were all superior in uniformity of surface gloss, rough skin, etc., as compared with those obtained by the method of the present invention.

[Effects of the Invention] The method and apparatus for descaling an alloy steel strip according to the present invention as described in detail above have various advantages as listed below, and their industrial value is very large. is there.

1) Since most of the scale was removed in a short time by the pretreatment, the descaling load in the pickling tank was reduced, the life of the pickling solution was extended, and the descaling ability was stabilized. Accordingly, the labor and cost required for controlling the concentration of the pickling solution and for adding acid are reduced, and the descaling can be sped up.

2) Since the same line can be used for both hot-rolled material and cold-rolled material to obtain sufficient descaling capability, the production capacity was improved.

3) As the pretreatment, anodic electrolysis using an aqueous solution containing mainly ferric chloride is adopted, so that the treatment of Cr ⁺⁶ ions in the waste liquid discharged from the electrolytic cell becomes unnecessary, and the treatment cost is reduced. Was.

4) Since the pretreatment has sufficient descaling ability and is not highly viscous like a molten salt and has little liquid take-out,
Excellent in cost.

5) Since most of the scale can be removed in the pretreatment, the remaining scale is surely removed in the pickling treatment, and at the same time, the metal base immediately below the scale is dissolved. Therefore, it was possible to reduce surface roughness and uneven gloss, which are surface defects of the alloy steel strip due to insufficient descaling.

6) Regarding the equipment aspect when carrying out the present invention, since both the electrolytic cell and the pickling tank can be used as they are, almost no equipment modification is required, and the descaling ability is low. Improved.

7) With respect to the apparatus of the present invention, when a conductive liquid tank provided with an anode plate is provided in front of an electrolyte tank provided with a cathode plate, the alloy liquid steel is used in the conductive liquid tank. In order to cause a preliminary descaling action in the band, an effect of further increasing descaling in the next electrolytic solution tank was achieved.

8) In the case where an energizing roll serving as an anode is provided after the electrolytic solution tank to supply power directly to the alloy steel strip, the electrolytic efficiency and descaling can be further improved.

9) A configuration in which either one of a main DC power supply for electrolysis and a DC power supply for an applied voltage having a small capacity different from the DC power supply for electrolysis is connected via a switching switch. In this case, the electrodes are protected even when power cannot be supplied from the main DC power supply for electrolysis, and the life of the electrodes is extended.

[Brief description of the drawings]

FIG. 1 is a process diagram of an example of an apparatus for carrying out the method of the present invention, FIG. 2 is an enlarged plan view of the electrolytic solution tank of FIG. 1, and FIG. 3 is an apparatus for carrying out the method of the present invention. FIG. 4 is an enlarged plan view of the electrolytic solution tank of FIG. 3, FIG. 5 is a process diagram of still another example of the apparatus for carrying out the method of the present invention, and FIG.
FIG. 7 is a graph showing the relationship between the ferric chloride concentration of the electrolytic solution and the weight loss of the alloy steel strip according to the electrolytic solution temperature according to the method of the present invention and the method not according to the present invention, and FIG. FIG. 8 is a graph showing the relationship between the concentration and the supply voltage for each electrolyte temperature, and FIG. 8 is a graph showing the relationship between the ferric chloride concentration of the electrolyte and the conductivity for each electrolyte temperature. DESCRIPTION OF SYMBOLS 1 ... Alloy steel strip 2 ... Electrolyte 3 ... Electrolyte tank 4 ... Anode plate 5 ... Cathode plate 6 ... DC power supply for electrolysis 7 ... Pickling tank 8 ... Pickling solution 9 ... Sending Plate roll 10 Dipping roll 11 Brush roll 12 Back-up roll 13 Cleaning nozzle 14 Conductive liquid tank 15 Conductive liquid 16 Anode plate 17 having acid resistance 17 Acid resistance Negative electrode plate 18 DC power supply for applied voltage 19 Switching switch 20 Gas vent hole 21 Electric roll

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-60900 (JP, A) JP-A-63-161194 (JP, A) JP-A-49-67836 (JP, A) JP-A-63-1986 216999 (JP, A)

Claims (7)

(57) [Claims] An anodic electrolysis treatment is performed on an alloy steel strip containing at least nickel and / or chromium in an electrolytic solution consisting mainly of an aqueous solution containing ferric chloride, followed by a pickling solution containing hydrofluoric acid. A method for descaling an alloyed steel strip, comprising removing the metal base immediately below the scale by pickling. 2. A ferric oxide having a concentration of 250 to 400 g / l and a liquid temperature of 4 g / l.
5 to 30 A / dm ² using an electrolyte consisting of an aqueous solution at 0 to 80 ° C.
2. The method for descaling an alloy steel strip according to claim 1, wherein an anodic electrolysis treatment is performed at a current density of not more than 3, and then a pickling treatment comprising a nitric acid and a hydrofluoric acid is carried out to remove the metal base immediately below the scale. 3. An anode plate made of any one of platinum, ruthenium oxide and lead oxide and a cathode plate made of any one of platinum, titanium and austenitic stainless steel mainly contain ferric chloride. An electrolytic solution comprising an aqueous solution is contained inside the electrolytic solution tank, and an acid pickling treatment tank containing a pickling solution containing hydrofluoric acid is provided after the electrolytic solution tank. A descaling device for an alloy steel strip. 4. A conductive liquid tank provided with an anode plate is provided in front of an electrolytic tank provided with a cathode plate and containing an electrolyte mainly comprising an aqueous solution containing ferric chloride. An acid pickling treatment tank in which a pickling solution containing hydrofluoric acid is provided after the electrolytic solution tank is provided, and a DC power supply for electrolysis is connected to the cathode plate and the anode plate. A descaling device for an alloy steel strip, which is characterized in that: 5. A DC power source for electrolysis and a small-capacity applied voltage different from the DC power source for electrolysis via a switching switch between a cathode plate in the electrolyte bath and an anode plate in the electroconductive bath. The descaling device for an alloy steel strip according to claim 4, wherein any one of the DC power sources is connected to the DC power source. 6. An electrolytic bath in which an electrolytic solution mainly composed of an aqueous solution containing ferric chloride, in which a cathode plate is provided, and an acid bath in which a pickling solution containing hydrofluoric acid is built. A descaling device for an alloy steel strip, wherein an energizing roll serving as an anode is provided between the treatment tank and the electrolytic roll, and a DC power supply for electrolysis is connected to the energizing roll and the cathode plate. 7. A DC power source for electrolysis and a DC power source for applying a small voltage different from the DC power source for electrolysis can be connected to the energizing roll and the cathode plate via a switching switch. The descaling device for an alloy steel strip according to claim 6, which is provided.