JPH0526853A - Method for measuring main constituent concentration of neutral salt electrolytic bath for descaling stainless steel band - Google Patents

Abstract

PURPOSE:To enable sulfuric acid soda concentration and hexavalent chrome concentration which are especially important in management of composition of a neutral salt (sulfuric acid soda) electrolytic bath for descaling stainless steel to be measured readily, easily, frequently, and continuously. CONSTITUTION:An ultrasonic propagation speed and a liquid-solution conductivity are measured for a sample bath for measurement which is filtered through a neutral salt electrolytic bath and this relationship is subjected to temperature compensation for obtaining each constituent concentration by a set of measurement values consisting of a measurement value of the ultrasonic propagation speed and the liquid-solution conductivity which are created for each of a plurality of temperatures around a temperature at the time of measurement of a liquid solution of sulfuric acid soda and a hexavalent chrome where various kinds of concentration curve indicating a relationship between the calibration curve indicating a relationship between the sulfuric acid soda concentration and a the liquid-solution composition indicated by a hexavalent chrome concentration, thus enabling a work load required for controlling concentration of the electrolytic bath, bath conditions to be adjusted easily and descaling capacity to be stable, and quality to be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to measure the concentration of each component of sodium sulfate and hexavalent chromium, which are varied and formed as a neutral salt electrolytic bath consisting mainly of an aqueous solution of sodium sulfate is used for descaling of stainless steel strip. The present invention relates to a method for measuring the concentration of main components in a neutral salt electrolytic bath for descaling a stainless steel strip, which can be easily and quickly carried out.

[0002]

2. Description of the Related Art A stainless steel strip has a scale (metal oxide) on its surface due to annealing treatment in its manufacturing process.
Is generated, and there are various inconveniences in the state where the scale remains, so the descaling process is performed. As this descaling treatment method, electrolytic treatment in an aqueous solution of sodium sulfate (hereinafter sometimes simply referred to as neutral salt electrolytic treatment),
Alternatively, pretreatment such as immersion treatment in a mixed molten salt of caustic soda and sodium nitrate, followed by immersion in nitric hydrofluoric acid or electrolytic treatment in nitric acid aqueous solution, and further combining these are widely performed. ing. Among them, the neutral salt electrolysis treatment is a treatment method which has been widely adopted in recent years since it was disclosed in Japanese Patent Publication No. 38-12162. As described above, in this neutral salt electrolysis treatment, an aqueous solution of sodium sulfate is widely used as an electrolytic bath, and the bath is generally controlled in addition to pH, liquid temperature, and liquid volume, as well as sodium sulfate that changes during electrolysis. Composition control of the bath composition such as the concentration of Cr, the concentration of hexavalent chromium (also sometimes referred to as chromate ion) produced by dissolution from stainless steel, and the concentration of sludge.

Of these, the pH is determined by a method using a hydrogen ion electrode, the liquid temperature is determined by a thermocouple method, and the liquid amount is determined by a bath surface height obtained by using an ultrasonic liquid level gauge or the like. By the method of multiplying the cross-sectional area of the bath, continuous or automatic instrumental analysis is possible, respectively, and is generally performed. However, for the concentration of sodium sulfate, the concentration of chromate ions, and the concentration of sludge, the following representative methods have been generally used. That is, regarding the concentration of sodium sulfate, JI
SK0102, a method of precipitating sulfate as barium sulfate as described in 41.2 and measuring the mass thereof, and regarding the concentration of chromate ion, diphenylcarbazide absorptiometry or atomic absorption method described in JISK0102, 65.2, or Is a reducing agent (ferrous ammonium sulfate, which is commonly applied to measure the concentration of oxidizing substances in aqueous solutions containing oxidizing substances,
For reduction titration method and sludge concentration using sodium thiosulfate etc.) and an appropriate indicator, see JISK0102, 1
This is the filtration and drying method for suspended substances shown in Section 4.1.
All of these analysis operations require manpower and skill, and continuous or automatic instrumental analysis is almost impossible, and it is also difficult to measure them frequently.

On the other hand, in order to maintain the capacity of the neutral salt electrolytic bath, it is not sufficient to control the concentration of sodium sulfate alone, and at the same time, it is widely necessary to control the concentration of hexavalent chromium that accumulates as an aging product. Are known. From this background, it is possible to measure the concentration of sodium sulfate and hexavalent chromium easily and quickly at the same time with high reliability. In addition, it is frequently or continuously used to manage unexpected bath abnormalities. There has been a strong demand for a measurement method that can be carried out.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks of the prior art and particularly affects the neutral salt electrolytic treatment capacity in the composition control of the neutral salt electrolytic bath for descaling of stainless steel. Simultaneous and quick simultaneous measurement of neutral salt concentration and chromate ion concentration, which are main components, enables frequent measurement and continuous measurement by automatic instrumental analysis. The task is to let them do it.

[0006]

As a result of various investigations, the present inventor has completed the present invention by discovering that the above problems can be solved by combining ultrasonic wave propagation velocity measurement and solution conductivity measurement. The process will be described below. Generally, an ultrasonic densitometer for measuring solute concentration by ultrasonic wave propagation velocity measurement is widely used for alkali, water, salt, sugar, acid, resin, organic solvent, alcohol and the like. The principle of concentration measurement by ultrasonic wave propagation velocity measurement is that the propagation velocity of ultrasonic waves in a liquid is high, and this propagation velocity (hereinafter sometimes simply referred to as the speed of sound) is the type of liquid (type of solvent and solute), This is a property that changes greatly depending on the solute concentration and the liquid temperature. Ie the solute concentration of the liquid,
The relationship between the liquid temperature and the speed of sound is often complicated,
Although it changes variously depending on the type of liquid, if the type of liquid is constant, a constant relationship is established between them, so it is possible to know the solute concentration from the constant relationship by measuring the temperature and sound velocity of the target liquid. Can be done.

Therefore, it is known that the concentration of an aqueous solution containing only sodium sulfate as a solute can be measured by an ultrasonic densitometer. However, in the case of a neutral salt electrolytic bath for descaling of stainless steel, it contains a large amount of sodium sulfate, chromate ions and sludge, and these interfere with each other, making reliable measurement of concentration difficult. Has been said to be. Therefore, when ultrasonic wave propagation velocity and solution conductivity were both measured for an aqueous solution in which both sodium sulfate and hexavalent chromium were dissolved, the solution was prepared for the aqueous solution having a constant composition (sodium sulfate concentration and hexavalent chromium concentration). It was found that when the temperature was constant, almost constant values were obtained, and when the composition of the aqueous solution was different, different measurement values were obtained accordingly. This is sodium sulfate 6 in an aqueous solution
Valence chromium interferes with the measurement of ultrasonic wave propagation velocity and solution conductivity of coexisting partners, but the ultrasonic wave propagation velocity and solution conductivity of an aqueous solution containing both substances are considered to be one system. It indicates that each measurement value is always constant. Further, regarding the correspondence between the aqueous solution composition represented by the sodium sulfate concentration and the hexavalent chromium concentration and the measurement value set including the ultrasonic propagation velocity and the solution conductivity, the aqueous solution composition and the measurement value set each include two different items. From this, it was also found that the two-dimensional positioning of each compensates for the errors and the sharper correspondence is achieved as compared with the case where each consists of one item.

The above-mentioned aqueous solutions of sodium sulfate and hexavalent chromium are different from the neutral salt electrolytic bath of the actual line in the presence or absence of sludge. This difference is that the ultrasonic wave propagation velocity and the solution conductivity are simultaneously measured in the same manner as described above, and when the measurement value sets of both are the same, the aqueous solution composition and neutrality corresponding to the measurement value set in the aqueous solution are the same. After examining how it affects the comparison with the actual composition of the salt electrolysis bath,
When the concentration of sludge contained in the neutral salt electrolytic bath is 1 g / l or more, the aqueous solution composition corresponding to the set of measured values in the aqueous solution is lower than the actual bath composition, but the electrolytic bath was filtered to remove the sludge. It was found that both were the same if a sample was used. Therefore, the ultrasonic propagation velocity and the solution conductivity of an aqueous solution of sodium sulphate and hexavalent chromium of known various concentrations are measured at a plurality of temperatures in advance, and each of the above-mentioned measurements is used as reference data indicating the relationship between the aqueous solution composition and the set of measured values. By recording the value together with the temperature, it is possible to measure the ultrasonic propagation velocity and the solution conductivity of the filtrate of the bath whose concentration is to be measured, and to know the respective concentrations of sodium sulfate and hexavalent chromium from the reference data. Of.

The present invention has been completed based on these findings. That is, according to the present invention, when a neutral salt electrolytic bath mainly composed of an aqueous solution of sodium sulfate is used for descaling of a stainless steel strip, the amount of the sodium sulfate and hexavalent chromium, which are produced in variable amounts, are measured. The ultrasonic wave propagation velocity and the solution conductivity are measured for a measurement sample bath obtained by filtering the electrolytic bath, and an aqueous solution of sodium sulfate and hexavalent chromium having various known concentrations is prepared in advance for each of a plurality of temperatures around the temperature at the time of the measurement. The two-dimensional calibration curve showing the relationship between the measured value set consisting of the measured ultrasonic wave propagation velocity and the measured value of the solution conductivity and the aqueous solution composition represented by the sodium sulfate concentration and the hexavalent chromium concentration is used to correct the above temperature by the temperature correction. The present invention relates to a method for measuring the concentration of main components in a neutral salt electrolytic bath, which is characterized by knowing the concentration of each component.

The method for measuring the concentration of main components of the neutral salt electrolytic bath for descaling stainless steel strip according to the present invention will be described in detail below with reference to the drawings. 1 and 2 are diagrams showing the relationship between the aqueous solution composition represented by the sodium sulfate concentration and the hexavalent chromium concentration and the measurement value set consisting of the ultrasonic wave propagation velocity and the solution conductivity for two different temperatures, FIG. FIG. 4 is a diagram showing the degree of error due to temperature correction of each of the sodium sulfate concentration and the hexavalent chromium concentration obtained by the method of the present invention, and FIG.
FIG. 1 is a diagram showing an embodiment of the method of the present invention together with an apparatus suitable for the embodiment.

The reference data for preparing the two-dimensional calibration curve used in the present invention is obtained by the following experiment. First, aqueous solutions having various concentrations of sodium sulfate and hexavalent chromium are prepared. The liquid to be measured by the present invention is a neutral salt electrolytic bath in a real line. Therefore, the respective concentrations of sodium sulfate and hexavalent chromium are usually 0 to 200 g / liter for sodium sulfate and 0 to 50 g / liter for hexavalent chromium in consideration of the concentration variation range on the actual line. It is preferable to prepare each aqueous solution. This is because the concentration control range of the neutral salt electrolytic bath is preferably such that the concentration of sodium sulfate is 50 to 200 g / liter and the hexavalent chromium concentration is 50 g / liter or less. The reason for this is that sodium sulfate has a low solubility in water, and when a bath is prepared to a concentration of more than 200 g / liter, undissolved sodium sulfate remains in the bath and various adverse effects are caused. Producing 50 g /
This is because if it is less than 1 liter, the electrolytic treatment effect cannot be expected. The concentration of hexavalent chromium is 50 grams /
This is because if the amount exceeds liters, the electrolytic treatment effect cannot be expected and the solubility of sodium sulfate further decreases.

Next, the measured temperature is determined. Both the ultrasonic wave propagation velocity and the conductivity are greatly affected by the liquid temperature. Therefore, it is preferable to set the measurement temperature of the aqueous solution to be the same as the measurement temperature of the concentration measurement target bath. However, the measured temperature of the concentration measurement target bath in the actual line is different depending on whether the measurement location is close to the electrolytic cell or at a remote location where it is guided from the electrolytic cell through some flow paths. In addition, the bath temperature itself is not always constant because it fluctuates within a certain range or changes intentionally. The temperature is predicted within the predicted temperature range (often close to the temperature range in the electrolytic cell) so that the temperature can be corrected by interpolation or extrapolation. A plurality of temperatures including at least both ends of the measured temperature range (these temperatures are the ambient temperature in terms of the measured temperature)
Is defined as the measured temperature of the aqueous solution for creating the reference data.
For example, 70 [deg.] C. and 90 [deg.] C. are set as the aqueous solution measurement temperatures for creating the reference data applied to the actual line where the liquid temperature control value of the neutral salt electrolytic bath is 80 ± 10 [deg.].

Next, the ultrasonic wave propagation velocity and the solution conductivity of each of the prepared various aqueous solutions are measured at the measurement temperature of the aqueous solution defined above, for example, 70 ° C. and 90 ° C. For measurement, it is convenient to use a measuring instrument equipped with sensors for measuring ultrasonic wave propagation velocity, solution conductivity and solution temperature. One example of the reference data of the aqueous solution composition (sodium sulfate concentration and hexavalent chromium concentration) thus obtained and the corresponding measurement value set (ultrasonic wave propagation velocity and solution conductivity) (aqueous solution composition range and measurement) Two-dimensional calibration curves are shown in the graphs with the temperatures as examples) in FIG. 1 (when the measured temperature is 70 ° C.) and FIG. 2 (when the temperature is also 90 ° C.). These figures show scales in the coordinates so that the corresponding aqueous solution composition can be understood at the position indicating a certain set of measured values in the Cartesian coordinate system with the ultrasonic propagation velocity as the horizontal axis and the solution conductivity as the vertical axis. It is attached. The relationship between the set of measured values and the composition of the aqueous solution in such a two-dimensional calibration curve can be stored in the storage operation device of the multi-component concentration meter described later.

After the relationship between the set of measured values and the composition of the aqueous solution is obtained in this way, next, the ultrasonic wave propagation velocity and the solution conductivity are measured together with the measured temperature for the concentration measurement target bath, that is, the actual line neutral salt electrolytic bath. measure. The measurement of these three items does not necessarily have to be performed at the same time unless the bath suddenly changes, but it is preferable to perform the measurement at almost the same time with as little time as possible. As mentioned above, these measurements are performed on the filtrate from which the sludge has been removed by once filtering the bath. This removal of sludge is necessary to prevent the measuring device or the sensor of the multi-component densitometer from being contaminated by the sludge, and was also performed when the sensor was used in a method other than the method of the present invention. That is. As for the degree of filtration in the method of the present invention, it is sufficient to remove 90% or more of sludge having a particle size of 1 μm or more, and it is preferable to use a filtration device having such performance.

When the ultrasonic wave propagation velocity and the solution conductivity of the filtrate as described above are measured, the concentration of sodium sulfate in the concentration measurement target bath is determined from the relationship between the set of measurement values based on the reference data prepared in advance and the aqueous solution composition. And know the hexavalent chromium concentration. The method will be specifically described. The case of using the two-dimensional calibration curve will be described with reference to FIG. 1 and FIG. 2, for example. When the actual measured temperature is exactly the temperature of the two-dimensional calibration curve, for example, 70 ° C., the measured value obtained using FIG. 1 is used. The position of the set is found on the coordinates by the scales of the horizontal axis and the vertical axis, and the concentration of each component is read according to what numerical value the scale corresponds to the scale indicating the concentration of sodium sulfate and the concentration of hexavalent chromium. If the actual measured temperature and the temperature of the two-dimensional calibration curve do not match, each component concentration corresponding to the same measurement value set as the actual measurement value set is read from the two two-dimensional calibration curves and read. Each component concentration corresponding to the actual measured concentration is calculated by interpolation or extrapolation from the two concentrations, the temperatures of the two two-dimensional calibration curves, and the actual measured temperature. The concentration of each component obtained in this way, that is, the composition of the aqueous solution and the measurement value set obtained by measurement, is the relationship between the measurement value set previously obtained from the reference data and the solution composition at the actual measurement temperature. This is the case when the temperature is corrected to. The concentration of each component thus obtained is the concentration of the component to be measured. When using a multi-component densitometer equipped with a sensor for measuring ultrasonic wave propagation velocity, solution conductivity and solution temperature, and a memory operation unit, store the relationship of the two-dimensional calibration curve. It is also possible to know the concentration of each component by the same temperature correction as in the case of the graph by inputting the measured value manually or automatically.

Next, the degree of error when the temperature is corrected as described above will be empirically described. Among the aqueous solutions of various compositions in which sodium sulfate and hexavalent chromium were mixed and mixed, which were used when the reference data of the two-dimensional calibration curves of FIGS. 1 and 2 were obtained, the sodium sulfate concentration was 0 g / l, 100 g / l , 150 g / l, 200 g / l, and 3 cases of hexavalent chromium concentration of 0 g / l, 20 g / l, 50 g / l
For each of the 12 aqueous solutions in total, the ultrasonic propagation velocity and the solution conductivity at 75 ° C, 80 ° C, and 85 ° C were measured, and three sets of actual measurements were made for each aqueous solution. Got a price set. Then, the method of the present invention was applied on the assumption that the compositions of these 12 kinds of aqueous solutions were unknown, and a total of 36 sets of concentration measurement values were obtained in the same manner as the above-mentioned method. The concentration range of these concentrations was measured for each of the sodium sulfate concentration and the hexavalent chromium concentration, that is, the distribution range of the measured concentration with respect to each actual concentration, that is, the error degree due to the temperature correction in the method of the present invention was examined. 4) (in the case of hexavalent chromium concentration). Figure 3
As can be seen from FIG. 4 and FIG. 4, the error of the method of the present invention due to the temperature correction is about 5%, which is sufficiently reliable.

The method of the present invention can easily and rapidly measure the sodium sulfate concentration and the hexavalent chromium concentration of the neutral salt electrolytic bath in a real line, and frequently or continuously using instrumental analysis. Can be carried out. Such an embodiment will be described with reference to FIG. 5 together with an example of a device suitable for it. In this embodiment, ultrasonic wave propagation velocity, solution conductivity and solution temperature are measured from the middle of the circulation path in which a part of the neutral salt electrolytic bath is taken out from the electrolytic cell and sent to the original electrolytic cell. Further, the measurement is carried out in the measuring tank guided by the branched flow path through the filtering device while avoiding the influence of ultrasonic waves generated in the electrolytic tank. In the embodiment, a multi-component densitometer equipped with a sensor for measuring ultrasonic wave propagation velocity, solution conductivity and solution temperature, a memory operation device, and a display device is used as the densitometer.

The stainless steel strip S is continuously fed to the electrolytic bath 1 in which the electrolytic bath 1b is stored by way of the inlet side feed roll 1a and the inlet side dipping roll 1c so as to face the stainless steel strip S. After being electrolyzed by the action of the electrode 1d for electrolysis arranged in the electrolysis tank 1a, it is continuously fed through the exit-side dipping roll 1c and the exit-side feed roll 1a. on the other hand,
The electrolytic solution 1b is forcibly circulated between the electrolytic cell 1 and the circulation tank 1e through the pipe 1g and the circulation pump 1f, and the electrolytic solution 1b is branched from the circulation path in the middle of the forced circulation path. The liquid is sent to the sample collecting tank 2 through 2d, the filtering device 2e, and the metering pump 2f, and is returned to the circulation tank 1e through the pipe 2g. The reason why the sample collecting tank 2 is provided here is that ultrasonic waves generated when bubbles of hydrogen gas or oxygen gas generated in the electrolytic tank 1 are destroyed because the concentration meter measures ultrasonic wave propagation speed. This is to avoid disturbance. The temperature sensor 2a, the ultrasonic wave propagation velocity sensor 2b, and the conductivity sensor 2c of the densitometer are immersed in the electrolytic solution 1b sampled in the sample collecting tank 2. The outputs of these sensors 2a, 2b, and 2c are processed by a memory computing unit 2h that stores the relationship of the two-dimensional calibration curve in advance, and the temperature of the electrolyte 1b, the concentration of sodium sulfate, and 6
The valent chromium concentration is continuously displayed on the display device 2i.

The electrolytic solution 1b supplied to the sample collecting tank 2
The contained sludge is removed by the filtration device 2e having the ability to remove 90% or more of sludge having a particle size of 1 μm or more. When the method of the present invention is carried out using such an apparatus, simultaneous and rapid measurement of the sodium sulfate concentration and the hexavalent chromium concentration of the neutral salt electrolyte is frequently and automatically or continuously carried out. It is extremely easy to do.

[0020]

【Example】

Example 1 Sodium sulfate concentrations obtained by the method of the present invention and the conventional method (comparative example) were measured for the same neutral salt electrolytic bath immediately after the bath was built and after 6 months had elapsed while being used in the actual line after bath building, and 6
Table 1 shows the valent chromium concentration. The measured value is the average value of 10 repeated measurements, and the standard deviation is shown in parentheses.

[0021] The multi-component densitometer used is a multi-component ultrasonic densitometer MOD.
It was a modification of EL-50 (manufactured by Suzuki Corporation). From Table 1, the concentration of sodium sulfate and the concentration of hexavalent chromium obtained by the method of the present invention are almost the same as those of the conventional method, and the variations are also the same. Moreover, the measurement can be performed extremely quickly and easily.

[0022]

As described in detail above, the method for measuring the concentration of main components of the neutral salt electrolytic bath for descaling a stainless steel strip according to the present invention has the effects listed below.
Its industrial value is enormous. Since the concentration control of sodium sulfate and hexavalent chromium in the neutral salt electrolytic bath can be performed quickly and easily and frequently or continuously, the workload required for these analyzes is reduced. Since bath information can be quickly obtained, bath conditions can be adjusted easily, and as a result, the neutral salt electrolytic treatment action is stabilized and the quality is improved by stabilizing the descaling ability of the stainless steel strip. . As a result of stabilizing the neutral salt electrolysis treatment, the amount of subsequent use of nitric hydrofluoric acid was reduced, and it became possible to reduce the manufacturing cost and the emission of environmental pollutants.

[Brief description of drawings]

FIG. 1 and FIG. 2 are diagrams showing a relationship between an aqueous solution composition represented by a sodium sulfate concentration and a hexavalent chromium concentration and a set of measurement values composed of an ultrasonic wave propagation velocity and a solution conductivity for two different temperatures.

FIG. 3 and FIG. 4 are diagrams showing the error levels due to temperature correction of the sodium sulfate concentration and the hexavalent chromium concentration obtained by the method of the present invention.

FIG. 5 is a diagram showing an embodiment of the method of the present invention together with an apparatus suitable for the embodiment.

[Explanation of symbols]

1 electrolysis tank 1a Sending plate roll 1b Electrolysis bath 1c dipping roll 1d Electrode for electrolysis 1e Circulation tank 1f circulation pump 1g piping 2 sample collection tank 2a Temperature sensor 2b Ultrasonic wave velocity sensor 2c Solution conductivity sensor 2d sampling pipe 2e Filtration device 2f Sampling pump 2g piping 2h Memory operation device 2i display device S stainless steel strip

Claims (4)

[Claims] 1. A neutral salt electrolytic bath mainly consisting of an aqueous solution of sodium sulfate is used for descaling of a stainless steel strip, and when the concentration of each component of sodium sulfate and hexavalent chromium produced is varied, the neutral salt is used. The ultrasonic wave propagation velocity and the solution conductivity are measured for a measurement sample bath obtained by filtering the electrolytic bath, and an aqueous solution of sodium sulfate and hexavalent chromium having various known concentrations is prepared in advance for each of a plurality of temperatures around the temperature at the time of the measurement. By the two-dimensional calibration curve showing the relationship between the measured value set consisting of the measured ultrasonic wave propagation velocity and the measured value of the solution conductivity and the aqueous solution composition represented by the sodium sulfate concentration and the hexavalent chromium concentration,
A method for measuring the concentration of main components of a neutral salt electrolytic bath for descaling a stainless steel strip, which comprises temperature-correcting the above relationship to know the concentration of each component. 2. A storage operation for storing a relationship between a sensor for measuring an ultrasonic wave propagation velocity, a solution conductivity and a solution temperature and the two-dimensional calibration curve according to claim 1 and calculating a concentration from the measured value. A method for measuring the concentration of main components of a neutral salt electrolytic bath for descaling a stainless steel strip according to claim 1, wherein a multicomponent concentration meter provided with a device is used. 3. The ultrasonic wave propagation velocity, the solution conductivity and the solution temperature are measured from the middle of the circulation path in which a part of the neutral salt electrolytic bath is taken out of the electrolytic cell and sent to the original electrolytic cell. The neutral salt for descaling of a stainless steel strip according to claim 1 or 2, which is carried out in a measuring tank guided by a branching flow path through a filtration device while avoiding the influence of ultrasonic waves generated in the electrolytic tank. Measuring method of concentration of main components of electrolytic bath. 4. The sample bath from which the sludge is substantially removed by filtering the neutral salt electrolytic bath with a filter having an ability to remove sludge having a particle size of 1 μm or more by 90% or more is to be measured. 13. A method for measuring the concentration of main components of a neutral salt electrolytic bath for descaling a stainless steel strip according to any one of 1.