JP7067543B2 - Steel sheet for cans and its manufacturing method - Google Patents

Description

The present invention relates to a steel sheet for cans and a method for manufacturing the same.

Patent Document 1 states that "a metal chromium layer and a chromium hydrated oxide layer are provided on the surface of a steel plate in this order from the steel plate side, and the amount of the metal chromium layer adhered is 50 to 200 mg / m ² . The chromium-equivalent adhesion amount of the chromium hydrated oxide layer is 3 to 30 mg / m ² , and the metal chromium layer is provided on the base portion having a thickness of 7.0 nm or more and the maximum. A steel plate for cans, comprising granular protrusions having a particle size of 200 nm or less and a number density of 30 pieces / μm ² or more per unit area ”is described (claim 1).

International Publication No. 2018/225739

As a result of the examination by the present inventors, the steel sheet for cans specifically described in Patent Document 1 may have insufficient weldability depending on the evaluation method. More specifically, when the contact resistance value between the steel sheet for cans and the electrode was measured under specific conditions, the value was large and it was sometimes judged that the weldability was insufficient.

Therefore, an object of the present invention is to provide a steel sheet for cans having excellent weldability and a method for manufacturing the same.

As a result of diligent studies by the present inventors, it has been found that the above object is achieved when the maximum particle size of the granular protrusions of the metallic chromium layer is within a specific range, and the present invention has been completed.

That is, the present invention provides the following [1] to [7].
[1] The surface of the steel plate has a metal chromium layer and a chromium hydrated oxide layer in this order from the steel plate side, and the amount of the metal chromium layer adhered is 65 mg / m ² or more and 200 mg / m ² or less. The adhered amount of the chromium hydrated oxide layer in terms of chromium is 7 mg / m ² or more and 30 mg / m ² or less, and the metallic chromium layer includes a base and granular protrusions provided on the base. A steel plate for cans, wherein the maximum particle size of the granular protrusions is more than 200 nm.
[2] The steel sheet for cans according to the above [1], wherein the maximum particle size of the granular protrusions is less than 1000 nm.
[3] The method for producing a steel plate for cans according to the above [1] or [2], wherein a cathode pulse electrolysis treatment is performed on the steel plate using an aqueous solution containing a hexavalent chromium compound and a fluorine-containing compound. And the anode pulse electrolysis treatment are alternately performed without causing a non-energized state. In the periodic back electrolysis treatment, the nth cathode pulse electrolysis treatment is set to Cn, and the _nth time. _A method for manufacturing a steel plate for a can, which is represented by any of the following (1) to (4) when the anode pulse electrolysis treatment is set to An.
(1) C ₁ A ₁ C ₂ A ₂ ... An C _{n + 1}
(2) C ₁ A ₁ C ₂ A ₂ ... C _{n An}
(3) A ₁ C ₁ A ₂ C ₂ ... _An C _n
(4) A ₁ C ₁ A ₂ C ₂ ... C _{n An + 1}
However, in the above (1) to (4), n is an integer of 3 or more.
[4] The method for producing a steel sheet for cans according to the above [3], wherein the aqueous solution has a Cr content of 0.5 mol / L or more and an F content of 0.2 mol / L or more.
[5] The steel sheet for cans according to the above [3] or [4], wherein the ratio of the electric quantity density of the anode pulse electrolytic treatment to the electric quantity density of the cathode pulse electrolysis treatment is 0.001 or more and less than 1. Manufacturing method.
[6] The method for producing a steel sheet for cans according to any one of [3] to [5] above, wherein the aqueous solution contains SO _4-2 of ^0.009 mol / L or more.
[7] The can for any of the above [3] to [6], wherein the energization time of the cathode pulse electrolysis treatment and the anode pulse electrolysis treatment is 0.01 seconds or more and 1.00 seconds or less, respectively. Manufacturing method of steel plate.

According to the present invention, it is possible to provide a steel sheet for cans having excellent weldability and a method for manufacturing the same.

It is sectional drawing which shows typically the example of the steel plate for cans of this invention. It is a graph which shows an example of a periodic back electrolysis treatment.

[Steel sheet for cans]
FIG. 1 is a cross-sectional view schematically showing an example of a steel plate for cans of the present invention.
As shown in FIG. 1, it has a steel plate 2. The can steel plate 1 further has a metal chromium layer 3 and a chromium hydrated oxide layer 4 on the surface of the steel sheet 2 in this order from the steel plate 2 side.
The metal chromium layer 3 includes a flat plate-shaped base portion 3a that covers the steel plate 2 and granular protrusions 3b provided on the base portion 3a. The chromium hydrated oxide layer 4 is arranged on the metal chromium layer 3 so as to follow the shape of the granular protrusions 3b.

Hereinafter, each configuration of the steel sheet for cans of the present invention will be described in more detail.

<Steel plate>
The type of steel sheet is not particularly limited. Usually, a steel plate used as a container material (for example, a low carbon steel plate or an extremely low carbon steel plate) can be used. The manufacturing method and material of this steel sheet are not particularly limited. It is manufactured through processes such as hot rolling, pickling, cold rolling, annealing, and temper rolling from the normal steel piece manufacturing process.

<Metallic chrome layer>
The steel sheet for cans of the present invention has a metal chromium layer on the surface of the above-mentioned steel sheet.
Metallic chromium suppresses surface exposure of the steel sheet and improves corrosion resistance.
The amount of the metal chromium layer adhered is 65 mg / m ² or more, preferably 70 mg / m ² or more, and more preferably 80 mg / m ² or more because the steel sheet for cans has excellent corrosion resistance. The amount of adhesion is the amount of adhesion per one side of the steel sheet (hereinafter, the same applies).

On the other hand, if the amount of metallic chromium is too large, the high melting point metallic chromium covers the entire surface of the steel sheet, and the welding strength is significantly reduced and dust is generated significantly during welding, which may deteriorate the weldability.
The amount of the metal chromium layer adhered is 200 mg / m ² or less, preferably 180 mg / m ² or less, and more preferably 160 mg / m ² or less because the weldability of the steel sheet for cans is excellent.

<< Measurement method of adhesion amount >>
The amount of adhesion of the metallic chromium layer and the amount of adhesion of the chromium hydrated oxide layer described later in terms of chromium are measured as follows.
First, the amount of chromium (total amount of chromium) is measured for a steel sheet for cans on which a metallic chromium layer and a chromium hydrated oxide layer are formed, using a fluorescent X-ray apparatus. Next, the steel sheet for cans is subjected to an alkali treatment by immersing it in 7.5 N-NaOH at 90 ° C. for 10 minutes, and then the amount of chromium (the amount of chromium after the alkali treatment) is measured again using a fluorescent X-ray apparatus. .. The amount of chromium after the alkali treatment is defined as the amount of adhesion of the metallic chromium layer.
Next, (alkali-soluble chromium amount) = (total chromium amount)-(chromium amount after alkali treatment) is calculated, and the alkali-soluble chromium amount is used as the chromium-equivalent adhesion amount of the chromium hydrated oxide layer.

Such a metallic chromium layer includes a base and granular protrusions provided on the base. Next, each of these parts included in the metallic chromium layer will be described in detail.

《Base of metal chrome layer》
The base of the metal chromium layer mainly covers the surface of the steel sheet to improve corrosion resistance.
The base of the metal chrome layer has a sufficient uniform thickness so that when the steel sheets for cans inevitably come into contact with each other during handling, the granular protrusions provided on the surface layer destroy the base and the steel sheets are not exposed. Is preferable.
From such a viewpoint, the thickness of the base of the metal chromium layer is preferably 7 nm or more, more preferably 9 nm or more, still more preferably 10 nm or more.
On the other hand, although the upper limit is not particularly limited, the thickness of the base of the metallic chromium layer is, for example, 20 nm or less, preferably 15 nm or less.

(Thickness measurement method)
The thickness of the base of the metallic chromium layer is measured as follows.
First, a cross-sectional sample of a steel sheet for cans on which a metallic chromium layer and a chromium hydrated oxide layer are formed is prepared by a focused ion beam (FIB) method and observed with a scanning transmission electron microscope (TEM) at a magnification of 20,000. do. Next, in the cross-sectional shape observation in the bright field image, pay attention to the part where there are no granular protrusions and only the base, and in the line analysis by energy dispersive X-ray spectroscopy (EDX), the intensity curves of chromium and iron (horizontal axis). : Distance, vertical axis: strength) to obtain the thickness of the base. At this time, more specifically, in the strength curve of chromium, the point where the strength is 20% of the maximum value is set as the outermost layer, and the cross point with the strength curve of iron is set as the boundary point with iron, and the distance between the two points. Is the thickness of the base.

《Granular protrusions of metallic chrome layer》
The granular protrusions of the metal chromium layer are formed on the surface of the above-mentioned base portion, and reduce the contact resistance between the steel plates for cans to improve the weldability. The estimation mechanism for reducing contact resistance is described below.
Since the chromium hydrated oxide layer coated on the metallic chromium layer is a non-conductor film, it has a higher electrical resistance than metallic chromium and becomes an inhibitory factor for welding. When granular protrusions are formed on the surface of the base of the metal chromium layer, the granular protrusions destroy the chromium hydrated oxide layer due to the surface pressure at the time of contact between the steel plates for cans during welding, and the current-carrying point of the welding current. , And the contact resistance is greatly reduced.

The maximum particle size of the granular protrusions of the metallic chromium layer is more than 200 nm. As a result, the weldability of the steel plate for cans is excellent. It is presumed that the reason is that the granular protrusions having a certain size increase the effect of destroying the chromium hydrated oxide layer and make it easier to function as an energizing point.
The maximum particle size of the granular protrusions of the metal chromium layer is preferably 210 nm or more, more preferably 230 nm or more, further preferably 260 nm or more, particularly preferably 320 nm or more, and particularly preferably 340 nm or more, because the weldability of the steel sheet for cans is more excellent. Is the most preferable.

On the other hand, if the granular protrusions of the metallic chromium layer are too large, the surface appearance of the steel sheet for cans may be insufficient. Therefore, the maximum particle size of the granular protrusions of the metal chromium layer is preferably less than 1,000 nm, more preferably 800 nm or less, still more preferably 600 nm or less, because the surface appearance of the steel sheet for cans is excellent.

When there are many granular protrusions on the metallic chromium layer, the weldability is improved by increasing the number of current-carrying points. Therefore, the number density of the granular protrusions of the metal chromium layer per unit area is, for example, 10 pieces / μm ² or more, preferably 15 pieces / μm ² or more, more preferably 20 pieces / μm ² or more, and 30 pieces. / Μm ² or more is more preferable, 50 pieces / μm ² or more is particularly preferable, and 100 pieces / μm ² or more is most preferable.

On the other hand, the number density per unit area of the granular protrusions of the metal chromium layer is preferably 10,000 pieces / μm ² or less, more preferably 5,000 pieces / μm ² or less, because the surface appearance of the steel sheet for cans is excellent. It is preferable that 1,000 pieces / μm ² or less is more preferable, and 800 pieces / μm ² or less is particularly preferable.

(Measuring method of particle size of granular protrusions and number density per unit area)
The particle size and the number density per unit area of the granular protrusions of the metallic chromium layer are measured as follows.
First, carbon vapor deposition is performed on the surface of a steel sheet for cans on which a metallic chromium layer and a chromium hydrated oxide layer are formed, and an observation sample is prepared by an extraction replica method. Then, a photograph is taken with a scanning transmission electron microscope (TEM) at a magnification of 20,000. By binarizing the photographed photograph using software (trade name: ImageJ) and performing image analysis, the area occupied by the granular protrusions is calculated back, and the particle size and the number density per unit area are obtained as a perfect circle conversion. The maximum particle size shall be the maximum particle size in the observation field of view taken in 5 fields at 20,000 times. The number density per unit area is the average of 5 fields of view.

<Chromium hydrated oxide layer>
Chromium hydrate precipitates on the surface of the steel sheet at the same time as metallic chromium, improving corrosion resistance and paint adhesion.

<< Adhesion amount >>
From the viewpoint of ensuring the corrosion resistance and paint adhesion of the steel sheet for cans, the adhesion amount of the chromium hydrated oxide layer in terms of chromium is 7 mg / m ² or more, preferably 16 mg / m ² or more.

On the other hand, chromium hydrated oxide is inferior in conductivity to metallic chromium, and if the amount is too large, it causes excessive resistance during welding, and various welding defects such as blow holes due to dust and splash generation and overfusion welding. In some cases, the weldability of the steel plate for cans is inferior.
Therefore, the adhesion amount of the chromium hydrated oxide layer in terms of chromium is 30 mg / m ² or less because the weldability of the steel sheet for cans is excellent, and the weldability of the steel sheet for cans is more excellent. 25 mg / m ² or less is preferable, and 20 mg / m ² or less is more preferable.

The method for measuring the amount of adhesion of the chromium hydrated oxide layer in terms of chromium is as described above.

[Manufacturing method of steel sheet for cans]
Next, the method for manufacturing the above-mentioned steel sheet for cans of the present invention (hereinafter, also simply referred to as “the manufacturing method of the present invention”) will be described.

<Periodic reverse electrolysis treatment>
In the production method of the present invention, a steel sheet is subjected to periodic reverse electrolysis treatment using an aqueous solution described later. FIG. 2 is a graph showing an example of periodic reverse electrolysis treatment. As shown in FIG. 2, in the periodic reverse electrolysis treatment, the cathode pulse electrolysis treatment (cathode electrolysis treatment with an extremely short energization time) and the anodic pulse electrolysis treatment (anode electrolysis treatment with an extremely short energization time) generate a non-energized state. Alternately without letting. The energization time of each pulse electrolysis treatment is preferably 1.00 seconds or less, more preferably 0.60 seconds or less.
On the other hand, the energization time of each pulse electrolysis treatment is preferably 0.01 seconds or longer, more preferably 0.10 seconds or longer, and 0.20 seconds or longer, because granular protrusions are easily formed and weldability is more excellent. Is more preferable.

That is, the periodic reverse electrolysis treatment is represented by any of the following (1) to (4) when the _nth cathode pulse electrolysis treatment is Cn and the _nth anode pulse electrolysis treatment is An. To.
(1) C ₁ A ₁ C ₂ A ₂ ... An C _{n + 1}
(2) C ₁ A ₁ C ₂ A ₂ ... C _{n An}
(3) A ₁ C ₁ A ₂ C ₂ ... _An C _n
(4) A ₁ C ₁ A ₂ C ₂ ... C _{n An + 1}

The first cathode pulse electrolysis treatment precipitates metallic chromium and chromium hydrated oxide. By the subsequent anodic pulse electrolysis treatment, metallic chromium is frequently melted on the entire surface of the steel sheet, and the starting point (precipitation site) of the granular protrusion is formed. Further, by the cathode pulse electrolysis treatment, granular protrusions of metallic chromium are deposited.
Even when the anodic pulse electrolysis treatment is first performed, the cathode pulse electrolysis treatment and the anodic pulse electrolysis treatment are repeatedly repeated to form granular protrusions in the same manner.
Therefore, the cathode pulse electrolysis process and the anode pulse electrolysis process are repeated a plurality of times. Specifically, in the above (1) to (4), n (hereinafter, also referred to as “repetition number n”) is an integer of 3 or more, preferably 5 or more, and more preferably 10 or more.
The upper limit is not particularly limited, but the number of repetitions n is, for example, 800 or less, preferably 500 or less, more preferably 300 or less, further preferably 100 or less, and particularly preferably 50 or less.

In the conventional method (particularly, the method using an industrial continuous line), the steel sheet conveyed in the aqueous solution is subjected to cathode electrolysis treatment or anodic electrolysis treatment for each of a plurality of distant electrodes. Therefore, a non-energized state (a state in which the steel sheet is immersed in the aqueous solution without energization) is inevitably generated between the cathode electrolysis treatment and the anodic electrolysis treatment.
Ions that dissociate from the fluorine ^- containing compound contained in the aqueous solution used for electrolysis (for example, F- ^, SiF _6-2- ) and optionally the sulfate ion ₍ ^SO4-2 ) are steel plates even when they are not energized. The chromium hydrated oxide formed on the surface layer of the above is non-uniformly dissolved. This dissolution site becomes a site where granular protrusions of metallic chromium are deposited in the subsequent cathode electrolysis treatment.
That is, in the conventional method, the precipitation sites of the granular protrusions are formed non-uniformly not only by the anodic electrolysis treatment but also by the immersion in a non-energized state. Therefore, it is considered that the granular protrusions are dispersed and the particle size becomes finer.

On the other hand, the cathode pulse electrolysis process and the anode pulse electrolysis process are alternately repeated without causing a non-energized state. As a result, it is considered that granular protrusions can be grown intensively at a limited site and can be coarsened.
Further, in the periodic reverse electrolysis treatment, the polarity is reversed in a short time and the electrolysis treatment is repeated. Therefore, it is expected that the electrolytic treatment is switched before the reactants in the aqueous solution used for the electrolytic treatment are electrically transferred, and it is presumed that the reaction substance is in a diffusion rate-determining state. If the diffusion is rate-determining (mass transfer is rate-determining), dissolution and precipitation are repeated on the granular protrusions where the current tends to concentrate, so it is considered that the granular protrusions are more likely to be coarsened than the conventional method. .. On the other hand, if the energization time of each pulse electrolysis treatment is too short, it may be difficult to form granular protrusions.

The cathode pulse electrolysis treatment precipitates metallic chromium and chromium hydrated oxide, and forms granular protrusions from the starting point of the granular protrusions. At this time, if the cathode pulse electrolysis treatment is too strong or too weak, the number density of the granular protrusions may decrease.
The anodic pulse electrolysis process forms the starting point of the granular protrusions. At this time, if the dissolution in the anode pulse electrolysis treatment is too strong or too weak, the starting point of the granular protrusions may decrease, the dissolution may proceed unevenly, and the distribution of the granular protrusions may vary, or the base of the metal chromium layer may be formed. The thickness of the may decrease.
Therefore, the ratio of the electric quantity density of the anode pulse electrolysis treatment to the electric quantity density of the cathode pulse electrolysis treatment (anodic pulse electrolysis treatment / cathode pulse electrolysis treatment) is preferably 0.001 or more and less than 1, and 0.003 or more and 0. It is more preferably 090 or less, and further preferably 0.005 or more and 0.075 or less.
When the ratio of the electric quantity density (anode pulse electrolysis treatment / cathode pulse electrolysis treatment) is within the above range, the number density of the granular protrusions in the metal chromium layer and the thickness of the base can be easily set in an appropriate range.
The electric energy density (unit: C / dm ² ) is the product of the current density (unit: A / dm ² ) and the energization time (unit: sec.).

<Aqueous solution>
The aqueous solution used for the periodic back electrolysis treatment contains at least a hexavalent chromium compound and a fluorine-containing compound.

Examples of the hexavalent chromium compound include chromium trioxide (CrO ₃ ); dichromate such as potassium dichromate (K ₂ Cr ₂ O ₇ ); and chromate such as potassium dichromate (K ₂ CrO ₄ ). ; Etc. can be mentioned.
The amount of Cr in the aqueous solution is preferably 0.5 mol / L or more, more preferably 0.7 mol / L or more, still more preferably 1.0 mol / L or more.
On the other hand, the amount of Cr in the aqueous solution is preferably 5.0 mol / L or less, more preferably 3.0 mol / L or less.

Fluorine-containing compounds include, for example, hydrofluoric acid (HF), potassium fluoride (KF), sodium fluoride (NaF), silicate hydrofluoric acid (H2 _{SiF 6 )} and / or salts thereof. Examples of the salt of sodium fluorosilicate include sodium silica (Na ₂ SiF ₆ ), potassium fluorosilicate (K ₂ SiF ₆ ), ammonium silica fluoride ((NH ₄ ) ₂ SiF ₆ ) and the like.
The amount of F in the aqueous solution is preferably 0.2 mol / L or more, more preferably 0.25 mol / L or more.
On the other hand, the amount of F in the aqueous solution is preferably 5.0 mol / L or less, more preferably 4.0 mol / L or less, and even more preferably 3.0 mol / L or less.

The aqueous solution may further contain ^SO _4-2 .
SO _{4-2 is contained in the aqueous solution in the manner of, for example, sulfuric acid (H 2 SO 4); sulfate such as sodium sulfate (Na 2 SO 4} ⁾ _{, calcium sulfate (} Ca SO ₄ ); and the like. It is preferably contained in an aqueous solution in the form of sulfuric acid.
The amount of SO _4-2 in the aqueous solution is preferably ^0.009 mol / L or more.
On the other hand, the amount of SO _4-2 in the aqueous solution is preferably ^0.090 mol / L or less, more preferably 0.080 mol / L or less, and even more preferably 0.070 mol / L or less.

The liquid temperature of the aqueous solution in the periodic reverse electrolysis treatment is preferably 20 ° C. or higher and 80 ° C. or lower, and more preferably 40 ° C. or higher and 60 ° C. or lower.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples.

<Making steel sheets for cans>
A steel sheet having a tempering degree of T4CA manufactured with a plate thickness of 0.22 mm was subjected to normal degreasing and pickling. Next, an aqueous solution containing CrO ₃ , NaF, and H ₂ SO ₄ was placed in a stationary cell, and a steel sheet was subjected to periodic reverse electrolysis treatment using a lead electrode to prepare a steel sheet for cans. .. The prepared steel sheet for cans was washed with water and dried at room temperature using a blower.
The Cr amount, F amount, and _SO4-2 ^amount of the aqueous solution are shown in Table 1 below.
The types of periodic reverse electrolysis treatment (any of (1) to (4) described above), the number of repetitions n, and the ratio of the electric quantity density (anode pulse electrolysis treatment / cathode pulse electrolysis treatment) are shown in Table 1 below. show.

However, in Comparative Example 1, a steel sheet for cans was produced in the same manner as in Example 43 of Patent Document 1 (International Publication No. 2018/225739).

<Adhesion amount and maximum particle size of granular protrusions>
With respect to the produced steel sheet for cans, the amount of adhesion of the metallic chromium layer and the amount of adhesion of the chromium hydrated oxide layer in terms of chromium (indicated simply as "adhesion amount" in Table 1 below) were measured. The measuring method is as described above.
In addition, the maximum particle size of the granular protrusions was measured for the metallic chromium layer of the produced steel sheet for cans. The measuring method is as described above.
The results are shown in Table 1 below.

<evaluation>
The following evaluations were made on the produced steel sheets for cans. The evaluation results are shown in Table 1 below.

《Weldability》
The produced steel sheet for cans was subjected to a heat treatment simulating the heat treatment during coating baking, and then the contact resistance was measured.
More specifically, first, for each example, two steel plates for cans were placed in a gas furnace set at 210 ° C., and after reaching 205 ° C., heat treatment was performed for 10 minutes. At this time, a temperature measurement sample to which a thermocouple was welded was placed in a gas furnace together with a steel plate for a can, and the temperature was monitored.
After the heat treatment, two steel plates for cans were overlapped. The two stacked steel plates for cans were sandwiched between electrodes (DR type 1 mass% Cr—Cu electrode processed with a tip diameter of 6 mm and a curvature of R40 mm) and held at a pressing force of 1 kgf / cm ² for 15 seconds. Then, 10 A was energized, and the contact resistance value (R) between the steel plate for can and the electrode was measured. 10 points were measured, and the average value was taken as the contact resistance value and evaluated according to the following criteria. Practically, if it is "◎◎", "◎" or "○", it can be evaluated that the weldability is excellent.

◎ ◎: R is 500 μΩ or less ◎: R is more than 500 μΩ, 1000 μΩ or less ○: R is more than 1000 μΩ, 1500 μΩ or less △: R is more than 1500 μΩ, 2000 μΩ or less ×: R is more than 2000 μΩ

<Summary of evaluation results>
As shown in Table 1 above, the steel sheets for cans of Invention Examples 1 to 18 were superior in weldability to Comparative Example 1.

1: Steel plate for cans 2: Steel plate 3: Metallic chromium layer 3a: Base 3b: Granular protrusions 4: Chromium hydrated oxide layer

Claims (6)

A metal chromium layer and a chromium hydrated oxide layer are provided on the surface of the steel sheet in this order from the steel sheet side.
The amount of the metal chromium layer adhered is 65 mg / m ² or more and 200 mg / m ² or less.
The chromium-equivalent adhesion amount of the chromium hydrated oxide layer is 7 mg / m ² or more and 30 mg / m ² or less.
The metallic chromium layer comprises a base and granular protrusions provided on the base.
A steel sheet for cans in which the maximum particle size of the granular protrusions is more than 200 nm and 350 nm or less . The method for manufacturing a steel sheet for cans according to claim 1 .
Using an aqueous solution containing a hexavalent chromium compound and a fluorine-containing compound, the steel sheet is subjected to periodic reverse electrolysis treatment in which cathode pulse electrolysis treatment and anodic pulse electrolysis treatment are alternately performed without causing a non-energized state. ,
The periodic reverse electrolysis treatment is represented by any of the following (1) to (4) when the _nth cathode pulse electrolysis treatment is Cn and the _nth anode pulse electrolysis treatment is An. A method for manufacturing steel sheets for cans.
(1) C ₁ A ₁ C ₂ A ₂ ... An C _{n + 1}
(2) C ₁ A ₁ C ₂ A ₂ ... C _{n An}
(3) A ₁ C ₁ A ₂ C ₂ ... _An C _n
(4) A ₁ C ₁ A ₂ C ₂ ... C _{n An + 1}
However, in the above (1) to (4), n is an integer of 3 or more. The method for producing a steel sheet for cans according to claim 2 , wherein the aqueous solution has a Cr content of 0.5 mol / L or more and an F content of 0.2 mol / L or more. The method for producing a steel sheet for cans according to claim 2 or 3 , wherein the ratio of the electric quantity density of the anode pulse electrolytic treatment to the electric quantity density of the cathode pulse electrolysis treatment is 0.001 or more and less than 1. The method for producing a steel sheet for cans according to any one of claims 2 ^to ₄ , wherein the aqueous solution contains SO 4-2 of 0.009 mol / L or more. The method for manufacturing a steel sheet for cans according to any one of claims 2 to 5 , wherein the energization time of the cathode pulse electrolysis treatment and the anode pulse electrolysis treatment is 0.01 seconds or more and 1.00 seconds or less, respectively. ..

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