JPS6376897A - Electrolytically chromated steel sheet having excellent weldability and its production - Google Patents

Abstract

PURPOSE:To develop the title electrolytically chromated steel sheet having a low contact resistance value and excellent weldability and appropriate for a can material by plating the surface of the steel sheet with Ni, and then forming a metallic Cr plated layer and a hydrated Cr oxide layer each having many protrusions on the surface. CONSTITUTION:An Ni plated layer is electroplated on one face of a steel sheet at 10-500mg/m<2>, the sheet is subsequently dipped in an electrolytic chromating soln. and electrolytically chromated with the steel sheet as a cathode, and the steel sheet is anodized at least once in the same soln. during the treatment. A metal Cr plated layer is formed on the Ni plated layer at 20-200mg/m<2>. and a hydrated Cr oxide layer is further formed thereon at 3-30mg/m<2>, expressed in terms of Cr. Both metal Cr layer and hydrated Cr oxide layer have many granular or angular protrusions on the surface. An electrolytically chromated layer consisting of a metal Cr plated layer and a hydrated Cr oxide layer is directly formed on the opposite face of the steel sheet.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention relates to an electrolytic chromate-treated steel sheet with excellent weldability, suitable as a material for cans produced by electric resistance seam welding, and a method for manufacturing the same. It is.

[Prior art and its problems]

Electrolytic chromate-treated steel sheets have a film formed on the surface of the steel sheet, consisting of a metallic chromium layer as a lower layer and a hydrated chromium oxide layer mainly composed of chromium oxide as an upper layer, and have excellent paintability and corrosion resistance. Since it is cheaper than tinplate, it is used in a wide range of fields as a material for cans such as food cans, bale cans, 181 cans, and oil cans.

Such electrolytic chromate-treated steel sheets have traditionally been used as materials for 2-piece cans processed by drawing 9, and for adhesive mortars (3-piece cans) whose joints are joined using organic resin, special cement, etc. However, it is not widely used as a material for welded cans whose seams are joined by electrical resistance seam welding. The reason for this is that the weldability of electrolytic chromate-treated steel sheets by electrical resistance seam welding is extremely poor.

However, in recent years, there has been an increase in demand for welded cans with high strength and reliability, and therefore there is a demand for improvement in the weldability of electrolytic chromate-treated steel sheets.

The reasons why the weldability of electrolytic chromate-treated steel sheets by electrical resistance seam welding is poor are as follows. That is, the metal chromium layer as the lower layer and the chromium hydrated oxide layer as the upper layer, which constitute the plating layer, have non-conductivity and non-thermal conductivity. Therefore, when electrical resistance seam welding is used to weld overlapping portions that are joints of can bodies, the metal chromium layer and the chromium hydrated oxide layer serve as an insulating film, resulting in a high contact resistance value.

The contact resistance value is a standard for evaluating whether local excessive current flows during welding. If the contact resistance value is high, the path through which the welding current flows is narrow, and therefore there is no local excessive current flowing. flows easily.

The contact resistance value of electrolytic chromate treated steel plate is 10 to 10
5 μΩ, which is extremely high compared to other surface-treated steel sheets for welded cans. Therefore, the welding current value immediately after welding is started is low, and only reaches a predetermined welding current value after a certain period of time has elapsed. As a result, the steel plate locally generates heat, causing dust to occur, and welding defects such as glow holes to occur in the welded portion.

For this reason, when welding electrolytically chromate-treated steel sheets, conventionally, the chromate treatment film on the welded portion had to be removed by polishing or the like, which required a lot of work.

As a method to solve the above-mentioned problem,
No. 3492 discloses a method for producing an electrolytically chromate-treated steel sheet comprising:

[After applying water glass to the parts of the steel plate that require welding and drying, chrome plating is applied to the surface, and welding is performed after peeling off the water glass.] Furthermore, JP-A No. 55-48406 discloses a method for producing an electrolytically chromate-treated steel sheet as follows.

``By applying temper rolling to a chrome-plated steel plate of 20 inches or less,
Weldability is improved by creating cracks in the plated surface and passing welding current through the countless cracks to the steel plate. However, the former method requires a process of applying water glass to the welding part of the electrolytic chromate-treated steel plate and drying it, while the latter method requires a process of subjecting the electrolytic chromate-treated steel plate to temper rolling. However, such pretreatment complicates the process and increases manufacturing costs.

[Purpose of the invention]

Therefore, an object of the present invention is to provide an electrolytic chromate-treated steel sheet that has a low contact resistance value and excellent weldability and is suitable as a material for cans made by electric resistance seam welding, and a method for manufacturing the same. It is in.

[Summary of the invention]

The reason why the weldability of the electro-chromated steel sheet is poor is that the contact resistance value between the metal chromium layer and the chromium hydrated oxide layer is high, as described above. Therefore, in order to obtain sufficient welding strength, it is necessary to increase the welding current, and as a result, dust is generated due to localized abnormal heat generation of the steel plate, and welding defects such as glow holes occur in the welded portion.

As a result of intensive research aimed at improving the weldability of electrolytic chromate-treated steel sheets by electrical resistance seam welding, the inventors of the present invention discovered that, in the production of electrolytic chromate-treated steel sheets, the steel sheets were subjected to cathodic electrolytic chromate treatment. Anodic electrolysis treatment is performed at least once to form a large number of granular or angular protrusions on the surfaces of the metal chromium layer and the chromium hydrated oxide layer, thereby reducing the contact resistance value.
Developed a method for producing electrolytically chromate-treated steel sheets with excellent weldability, and filed a patent application (Japanese Patent Application 1987-192,614')
According to the method described above, when electrical resistance seam welding is performed, the contact resistance value is reduced, local abnormal heat generation of the steel plate is slight, and dust generation is reduced, but still. It wasn't necessarily enough.

Therefore, the inventors of the present invention have conducted extensive research to further improve weldability and develop a method that can obtain sufficient welding strength without increasing the welding current to the point where dust occurs. If a nickel film is formed on the steel plate, the steel plate with such a nickel film is subjected to cathodic electrolytic chromate treatment, and anodic electrolytic treatment is performed at least once during the cathodic electrolytic chromate treatment, the electrolytic chromate treated steel plate can be welded. It has been found that the lower limit current value to be obtained is lowered, and therefore, sufficient welding strength can be obtained without increasing the welding current to the point where dust occurs.

The electrolytic chromate-treated steel sheet of the present invention has been made based on the above findings, and includes a nickel layer with an amount of 10 to 500 η/R formed on at least one surface of the steel sheet, and a nickel layer on the nickel layer. 5-200m formed in
g/- of the gold maple chromium layer and the gold small chromium layer formed on the gold and small chromium layer, 3 to 30 μ/rrl in terms of metallic chromium.
The metallic chromium layer and the chromium hydrated oxide layer are characterized by having a large number of granular or angular projections on their surfaces. be.

[Structure of the invention]

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a diagram schematically showing a cross section of the coating of the electrolytically chromate-treated steel sheet of the present invention. A nickel layer 2 is formed on both surfaces of the steel plate 1, a metal chromium layer 3 is formed on the nickel layer 2, and a chromium hydrated oxide layer 4 is formed on the metal chromium layer 3. . A large number of granular or angular projections 5 are formed on the surface of the metal chromium layer 3, and these projections 5 cause the uppermost chromium hydrated oxide layer 4 to
It is formed into a protrusion.

The reason why weldability is improved by forming the nickel layer 2 on the surface of the steel plate 1 is estimated as follows. That is, nickel has excellent thermocompression bondability, while chromium has poor thermocompression bondability. Therefore, when electrolytically chromate-treated steel sheets are welded by electrical resistance seam welding, the heat and pressure bonding of the nickel layer 2 is added to the fusion of the steel sheet 1 on which the metallic chromium layer 3 and the chromium hydrated oxide layer 4 are formed. B, its weldability is improved.

The reason why weldability by electric resistance seam welding is improved by the protrusions 5 formed on the metallic chromium layer 3 and the protruding chromium hydrated oxide layer 4 on the surface thereof is presumed as follows.

(1) When the opposite ends of the copper plates are overlapped for electrical resistance seam welding, the contact area is increased by the protrusions 5, which improves electrical conductivity, making it easier for welding current to flow.

(2) Since the uppermost chromium hydrated oxide layer 4 cracks in the shape of a protrusion along the protrusion 5 formed on the metal chromium layer 3, it is easy to crack due to external pressure. As a result, when both ends of the steel plate are pressed together for welding, cracks occur in the chromium hydrated oxide layer 4, making it easier for welding current to flow.

In this invention, the amount of nickel layer 2 formed on at least one surface of steel plate 1 is 10 to 500 mg/m
It should be 2. If the total thickness of the nickel layer 2 is less than 10 cm/m2, the effect of improving heat-pressability is insufficient;
Is the amount of nickel layer 2 500m9/n? If it exceeds 100%, the effect of improving heat-pressability will be saturated and it will become uneconomical. Nickel layer 2
may be formed on both surfaces of the steel plate 1 or only on one surface.

In this invention, on the surface of the nickel layer 2 or on the steel plate 1
The amount of the Kinpeng chromium layer 3 formed on the surface of is 5 to 200
mg/m2, and the amount of the chromium hydrated oxide layer 4 formed on the metal chromium layer 3 is 3 to 30I in terms of metal chromium.
It should be ng/-. The amount of metal chromium layer 3 is 5 mg
/m2, the corrosion resistance of the film will be insufficient;
If the total amount of the metal chromium layer 3 exceeds 200 η/a, the amount of metal chromium becomes excessive, and no further improvement in weldability and corrosion resistance can be obtained. From the viewpoint of stable operation, the thickness after the metal chromium layer 3 is preferably 30 to 200/-. If the total thickness of the chromium hydrated oxide layer 4 is less than 3 m'i in terms of metal chromium, the corrosion resistance of the film will be insufficient. /m'', weldability deteriorates.

It is necessary that the protrusions 5 are formed on the entire surface of the gold chromium layer 3 in a granular or angular shape when viewed from above.

If the protrusions 5 are formed in a wide plate shape or are formed concentrated in a specific part, the desired effect cannot be expected.

Next, a method for producing an electrolytically chromate-treated steel sheet of the present invention will be described.

In this invention, before subjecting the steel plate 1 to cathodic electrolytic chromate treatment, 10
~500m9/? / of the nickel layer 2 is formed. Such a nickel layer 2 can be formed, for example, by subjecting the steel plate 1 to cathodic electrolysis treatment in a nickel plating bath. The nickel plating bath used may be a general plating bath such as a Watt bath mainly containing nickel sulfate, a nickel borofluoride bath, a nickel sulfamino acid bath, and is not limited to a specific plating bath.

Further, after nickel plating is performed using these plating baths, heat treatment may be performed to diffuse nickel into the steel.

The nickel layer 2 is not limited to plating as described above, and may be formed by means such as ion blating or vacuum deposition.

The plate 1 on which the nickel layer 2 was formed as described above,
A cathodic electrolytic chromate treatment is performed in an electrolytic chromate treatment bath. There are two main methods for cathodic electrolytic chromate treatment:

(a) contains at least one of chromic anhydride, chromate and dichromate as a main component, and F- and so
The process consists of subjecting the steel plate to cathodic electrolytic chromate treatment in a treatment bath containing 4"- to simultaneously form a metallic chromium layer as a lower layer and a hydrated chromium oxide layer as an upper layer on the surface of the steel plate. , the so-called one-liquid method.

(b) In the first treatment bath containing the above-mentioned 804'-, the steel plate is subjected to a first cathodic electrolytic chromate treatment to form only a fully bent chromium layer as a lower layer on the surface of the steel plate, and then the above-mentioned In a second treatment bath excluding 804'- from the treatment bath, a second cathodic electrolytic chromate treatment is applied to the steel plate on which the gold-marked chromium layer is formed, thereby forming a chromium hydrated oxide layer on the metallic chromium layer. The so-called two-liquid method consists of forming a

In electrolytic chromate treatment, the presence of 804'- is necessary for sufficient precipitation of metallic chromium;
When chromate treatment is carried out using a treatment bath containing 04'-, 8
There is good luck that 04'- is mixed in. This S04
It is difficult to completely remove it even by washing with water, and if it remains in the film, it is likely to cause corrosion or poor paint adhesion. According to the two-liquid method, as described above, it is possible to prevent 804'- from being mixed into the ROM hydrated oxide layer.

In the present invention, during the cathodic electrolytic chromate treatment using the one-liquid method described above, or during the first cathodic electrolytic chromate treatment of the two-liquid method, treatment with the same composition as the treatment bath is performed. Anodic electrolysis treatment is carried out at least once by means of a bath. Thus,
As shown in the drawings, on the nickel layer 2, a large number of granular or angular protrusions 5 are uniformly and densely distributed.
A protruding chromium hydrated oxide layer 4 with an amount of 3 to 30 my/m2 in terms of gold wire chromium is formed on the metal chromium layer 3. Ru.

The above-mentioned anodic electrolytic treatment is performed by cathodic electrolytic chromate treatment to form a gold β-chromium layer of at least 20 mv/1r? It is desirable to perform this after the formation.

When a copper strip is continuously subjected to cathodic electrolytic chromate treatment using a plating device consisting of a plurality of vertical plating baths arranged in series, the copper strip is intermittently in contact with the zinc roll of each plating bath. As a result, the cathodic electrolytic chromate treatment also becomes intermittent. As a result, the above-described protrusions tend to form on the surface of the metallic chromium layer, and as the interval between cathodic electrolytic chromate treatments becomes longer, protrusions inevitably form.

However, the protrusions produced in this way are extremely non-uniform. Therefore, good weldability cannot be expected due to this.

On the other hand, in the present invention, since the anodic electrolytic treatment is performed during the cathodic electrolytic chromate treatment, the protruding metallic chromium is uniformly and densely formed. The reason why such protruding metallic chromium is uniformly and densely formed is considered to be due to the following reason. That is, by the cathodic electrolytic chromate treatment before the anodic electrolytic treatment, a full-fat chromium layer and a chromium hydrated oxide layer are formed on the surface of the nickel layer of the steel sheet. Since the chromium hydrated oxide layer is in a colloidal state, by performing anodic electrolytic treatment during the cathodic electrolytic chromate treatment, the surface of the gold chromium layer is oxidized by the oxidizing electrolyte and changed to chromium oxide. Since chromium oxide and metallic chromium have different lattice constants, many defects with disordered atomic arrangements are generated in the chromium oxide layer. The electrical resistance of this part is low because the chromium oxide film is thinner than other parts or the metallic chromium layer is exposed. Therefore, it is considered that metallic chromium is preferentially deposited during the re-cathodic electrolytic chromate treatment, so that a large number of protruding metal chromium particles are formed uniformly and densely.

In order to grow gold-chromium protrusions, it is necessary to perform cathodic electrolytic chromate treatment after anodic electrolytic treatment, and anodic electrolytic treatment must be performed at a position that satisfies this requirement.

Such an anodic electrolytic treatment is essential for uniformly and densely forming protruding metallic chromium, but it also has the effect of improving the chromium electrolytic efficiency.

In the case of the two-component method, anodic electrolytic treatment is performed during the cathodic electrolytic chromate treatment in the first treatment bath, but this is necessary to properly form protrusions in the entire chromium layer. This is because it is necessary to perform the anodic electrolytic treatment during the cathodic electrolytic chromate treatment by the first treatment bath in which most of the chromate is formed.

During cathodic electrolytic chromate treatment, chromium is difficult to precipitate on the nickel layer in the low current density range. Therefore, it is preferable that the current density in the cathodic electrolytic chromate treatment is not lower than 15 A/dm'. That is, if the current density is less than 15 A/dm'', even if anodic electrolytic treatment is performed, it is difficult to obtain metallic chromium protrusions with a uniform distribution.

The electrolyte in the anodic electrolytic treatment is preferably within the range of 0.01 to 5 coulombs/d m'. If the electric bond is less than 0.01 coron/dm', the effect of the anodic electrolytic treatment cannot be obtained, while if the electric bond exceeds 5 coron/dm', metallic chromium will be eluted.

In the method of the present invention, when using a plating apparatus consisting of a plurality of vertical plating tanks arranged in series, the anodic electrolytic treatment is performed in one vertical plating tank in the middle of the cathodic electrolytic chromate treatment. It can be implemented by

In addition, when using a plating apparatus consisting of a horizontal plating tank, the supply current can be temporarily reversed during the cathodic electrolytic chromate treatment to perform the anodic electrolytic treatment.

[Embodiments of the invention]

Next, this invention will be compared with examples and comparative examples.
I will explain in detail.

After degreasing, pickling, and rinsing both sides of a cold-rolled steel plate with a thickness of 0.221 mm, the cold-rolled steel plate is cathodic electrolytically treated using the nickel plating bath shown below to coat both surfaces. A nickel layer was formed. Next, the cold-rolled steel sheet on which the nickel layer has been formed is treated with the first electrolytic chromate treatment bath shown below, or with the first electrolytic chromate treatment bath and the second electrolytic chromate treatment bath shown below.
A cathodic electrolytic chromate treatment is performed using an electrolytic chromate treatment bath, and in the middle of the cathodic electrolytic chromate treatment, an anodic electrolytic treatment is performed using a treatment bath having the same composition as the first electrolytic chromate treatment bath to produce the nickel shown in Table 1. A specimen of an electrolytically chromate-treated steel sheet according to the present invention having a coating amount and a chromium deposition amount (hereinafter referred to as "the specimen of the present invention")
41 to 12 (referred to as "comparative specimen" hereinafter), and comparative electrolytic chromate-treated steel sheet specimens prepared by a method outside the scope of the present invention.

) &1 to 7 were prepared. The composition and treatment conditions of each bath are shown below.

(1) Nickel plating bath composition - N15Oi: 240P/1NiCfz:
45 y/l! Boric acid: 30y/1 Bath temperature...50℃...2.8 Current density: 2A/drr? (2) First electrolytic chromate treatment bath composition = -Cry3: 175 y71 Na2SiF6: 5! /l Na2SO4: 0.9P/1) Bath temperature...45°C Current density -30A/dtr? Current application time: 0.3 seconds No current application time: 0.3 seconds Total current application time: 1.5 seconds (3) Second electrolytic chromate treatment bath composition - Cr03: 50y/l NH4F: 21/1 Bath temperature: 40°C Current density: 30A/dm Current time: 0.3 seconds No current time: 0.3 seconds Total energization time: 0.9 seconds As described above For test specimens 1 to 12 of the present invention and comparison specimens 1 to 7 prepared by The results are also shown in Table 1.

(1) Contact resistance value A specimen was heated at a temperature of 205°C for 23 minutes, and a +25 tin-plated cleaning plate was placed on both sides of the heated specimen, and this was used for contact resistance measurement. Place it between the upper and lower copper chips and measure its resistance.

Next, the above-mentioned two heated specimens were stacked so that the front and back sides were in contact with each other, and +25 tin-plated steel plates were stacked on both sides of the stacked specimens in the same manner as above to resist the resistance. Measure. Measured in this way,
The contact resistance value was obtained by subtracting the value of one specimen from the value of the two-ply specimen.

(2) Appropriate welding current range The specimen was heated at a temperature of 205°C for 23 minutes, and the two specimens heated in this way were resistance welded under the following conditions.
The range of welding current between the lower limit of the welding current value that provides sufficient welding strength and the upper limit of the welding current value that does not cause dust was determined as the appropriate welding current range.

Welding speed: 19.2m/min Wrap width of welded part: 0.41B Pressure crab of welded part 601). f Frequency of welding power source: 200 Hz As is clear from Table 1, comparative specimens A1 and 2 do not have a nickel layer on the surface of the steel sheet and are not subjected to anodic electrolytic treatment during the cathodic electrolytic chromate treatment. However, the contact resistance value was high, the appropriate welding current range was 0, and it was impossible to weld the desired welding strength due to the generation of dust.

Comparative specimens No. 3 and No. 4, in which no nickel layer was formed on the surface of the steel sheet even if anodic electrolytic treatment was performed during cathodic electrolytic chromate treatment, had low contact resistance values, but the appropriate welding current range was low. It was narrow and had poor weldability.

Although a nickel layer is formed on the surface of the steel plate, the thickness of the nickel layer is low beyond the scope of the present invention, and the comparative specimen 5 does not perform anodic electrolytic treatment during the cathodic electrolytic chromate treatment. The resistance value was high, the appropriate welding current range was extremely narrow, and weldability was poor. Even though a nickel layer was formed on the surface of the steel sheet and an anodic electrolytic treatment was performed during the cathodic electrolytic chromate treatment, the comparative specimen JIL6, which had a low total nickel layer outside the range of the present invention, was not subject to contact. Although the resistance value was low, the appropriate welding current range was narrow and weldability was poor.

Even though a hazy nickel layer within the range of the present invention is formed on the surface of the steel plate, comparative specimen A7, which was not subjected to anodic electrolytic treatment during the cathodic electrolytic chromate treatment, had a high contact resistance value and an appropriate value. The welding current range was also narrow and weldability was poor.

Figure 2 is a 10,000x micrograph showing the gold structure of the whole French chromium layer in specimen A3 of the present invention, and Figure 3 is the metallic chromium layer of comparison specimen A1 that was not subjected to anodic electrolysis treatment. This is a 10,000x micrograph showing the metallographic structure of . As is clear from comparing Figures 2 and 3,
In the case of specimen 1 of the present invention shown in FIG. 2, a large number of granular protrusions (black dots) are uniformly and densely formed on the entire surface of the chromium layer, whereas gold In the case of comparative specimen A1 shown in FIG. 3, only sparse projections were formed on the surface of the goldstone chromium layer.

[Effects of the Invention] As described above, the present invention provides an electrolytic chromate treatment suitable as a material for cans made by electric resistance seam welding, which has a low contact resistance value and extremely excellent tS contact properties. An industrially excellent effect is brought about in that a copper plate can be easily manufactured.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing a cross section of the film of the electrolytically chromate-treated steel sheet of the present invention, and FIG. 2 is a diagram showing the metal structure of the metallic chromium layer of the electrolytically chromate-treated cast sheet of the present invention.
FIG. 3 is a 10,000x micrograph showing the metal structure of the metallic chromium layer of a conventional electrolytically chromate-treated steel sheet. In the drawings, 1... steel plate 2... nickel layer 3...
Total bending chromium layer 4...Chromium hydrated oxide layer 5...
protrusion.

Claims (8)

[Claims] (1) formed on at least one surface of the steel plate;
a nickel layer in an amount of 0 to 500 mg/m^2, a metallic chromium layer formed on the nickel layer in an amount of 5 to 200 mg/m^2, and a metallic chromium layer formed on the metallic chromium layer. , a chromium hydrated oxide layer with an amount of 3 to 30 mg/m^2 in terms of metallic chromium, and the metallic chromium layer and the chromium hydrated oxide layer have many granular or angular projections on their surfaces. An electrolytic chromate-treated steel sheet with excellent weldability, characterized by having. (2) Welding according to claim (1), characterized in that the nickel layer, the metal chromium layer, and the chromium hydrated oxide layer are formed on both surfaces of the steel plate. Electrolytic chromate treated steel sheet with excellent properties. (3) The nickel layer, the metallic chromium layer, and the chromium hydrated oxide layer are formed on one surface of the steel plate, and the metallic chromium layer and the chromium hydrated oxide layer are formed on the other surface of the steel plate. The electrolytic chromate-treated steel sheet with excellent weldability according to claim (1), characterized in that a layer is formed. (4) On at least one surface of the steel plate, 10 to 500
A nickel layer with an amount of mg/m^2 is formed, and the steel sheet on which the nickel layer has been formed is subjected to cathodic electrolytic chromate treatment in an electrolytic chromate treatment bath. 5-200 mg/m^2, subjected to at least one anodic electrolytic treatment by the same treatment bath as the chromate treatment bath, thus having a large number of granular or angular protrusions on the nickel layer.
and a chromium hydrated oxide layer with an amount of 3 to 30 mg/m^2 in terms of metallic chromium, on the metallic chromium layer. A method for manufacturing an electrolytically chromate-treated steel sheet. (5) The anodic electrolytic treatment is carried out in the middle of the cathodic electrolytic chromate treatment, which consists of simultaneously forming a metallic chromium layer and a chromium hydrated oxide layer using one type of electrolytic chromate treatment bath. A method for manufacturing an electrolytically chromate-treated steel sheet with excellent weldability as set forth in claim (4), characterized in that: (6) The anodic electrolytic treatment is performed by forming only a metallic chromium layer using a first electrolytic chromate treatment bath, and then forming a chromium hydrated oxide layer on the metallic chromium layer using a second electrolytic chromate treatment bath. The electrolytic chromate treatment with excellent weldability as set forth in claim (4) is carried out during the cathodic electrolytic chromate treatment using the first electrolytic chromate treatment bath to form a A method for producing chromate-treated steel sheets. (7) Claims (4) to (6) characterized in that the nickel layer, the metal chromium layer, and the chromium hydrated oxide layer are formed on both surfaces of the steel plate.
A method for producing an electrolytically chromate-treated steel sheet with excellent weldability according to any one of the items. (8) forming the nickel layer, the metal chromium layer, and the chromium hydrated oxide layer on one surface of the steel plate;
Any one of claims (4) to (6), characterized in that the metal chromium layer and the chromium hydrated oxide layer are formed on the other surface of the copper plate.
A method for producing an electrolytically chromate-treated steel sheet with excellent weldability as described in .