JPH0673597A - Highly corrosion resistant electroplated steel sheet and its production - Google Patents

Abstract

PURPOSE:To produce a composite-plated steel sheet electroplated with zinc- alumina, excellent in various properties, such as bare corrosion resistance and corrosion resistance after coating, plating adhesion, and weldability. CONSTITUTION:This highly corrosion resistant electroplated steel sheet has an electrogalvanizing layer of (10 to 50)g/m<2> coating weight at least on one side of a steel sheet. Moreover, this electrogalvanizing layer contains, by weight, 0.01-3% alumina sol expressed in terms of Al2O3 and 0.1-20% chromium expressed in terms of metallic Cr and further contains 0.001-20% of at least one element selected from the group consisting of Co, Ni, and Fe.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic zinc-alumina composite plated steel sheet excellent in various properties such as bare corrosion resistance, corrosion resistance after painting, plating adhesion and weldability, and a method for producing the same.

[0002]

2. Description of the Related Art Zn-based plated steel sheets are widely used as anticorrosion treated steel sheets in automobiles, home appliances, building materials and the like, which require corrosion resistance. This is because the pure zinc layer is base with respect to the iron of the steel sheet, so the zinc is first corroded to the exposed portion of the base metal caused by plating defects such as pinholes and processing, and the sacrificial anticorrosion effect. This is because it prevents the occurrence of red rust on the steel sheet. However, since pure zinc is active, there is a drawback that the corrosion of the zinc plating layer itself proceeds remarkably quickly in a corrosive environment such as salt spray. Further, since pure zinc easily forms conductive ZnO as a corrosion product, it is considered that the poor corrosion resistance by the corrosion product existing on the surface is also a cause of insufficient corrosion resistance. Therefore, various zinc-based alloy-plated steel sheets and zinc-based dispersion-plated steel sheets have been developed in place of the pure galvanized steel sheet.

Among them, the composite plating coating of aluminum-dispersed zinc described in JP-B-54-30649 is used as a material for suppressing the activity of the zinc plating layer and further suppressing the formation of the conductive corrosion product ZnO. A steel plate and a method for manufacturing the same can be given.

The publication is characterized in that metal Al particles are dispersedly contained during electrogalvanizing, whereby a plated steel sheet excellent in bare corrosion resistance can be obtained. However, in order to improve the plating adhesion, when rolling at a reduction rate of about 2% after plating causes deterioration of the work of the base steel sheet, and when a coating such as phosphate treatment or cationic electrodeposition coating is applied, There is a drawback that the coating film is likely to swell depending on the corrosion conditions. That is, since the water that has passed through the coating film reacts with oxygen to generate hydroxide ions, the lower part of the coating film becomes strongly alkaline, and the amphoteric metals alumina and zinc are dissolved. Especially when Al is present in the plating layer,
Since Al becomes an aluminum ion in a strong alkaline solution and quickly dissolves, it is considered to cause swelling of the coating film.

Japanese Patent Application No. 4-147296 discloses that a plating bath based on sulfate is used for Zn-Co-Cr-Al ₂
A method of manufacturing O ₃ dispersion plating is described. The present invention has a function of retaining basic zinc chloride by dispersing Al ₂ O ₃ in the Zn alloy layer, and as a result, improves corrosion resistance. By the way, in this publication, there is no description of the Cr existing form in the Zn alloy layer. That is, a local battery is formed in the plating layer depending on the presence state of Cr, and there is a drawback that corrosion is more likely to proceed. Therefore, intentionally defining the presence state of Cr in the Zn alloy layer is as follows. It is extremely important from the viewpoint of improving corrosion resistance.

[0006]

In the conventional zinc-based dispersion-plated steel sheet, in order to improve the adhesion of the plating, if a rolling reduction of about 2% is applied after plating, it causes deterioration of the work of the base steel sheet, and phosphorus When a coating such as acid treatment or cationic electrodeposition coating is applied, there is a drawback that the coating film is likely to swell depending on the corrosion conditions. That is, since the water that has passed through the coating film reacts with oxygen to generate hydroxide ions, the amphoteric metals alumina and zinc are dissolved.

In particular, when Al is present in the plating layer,
Since Al becomes an aluminum ion in a strong alkaline solution and quickly dissolves, it is considered to cause swelling of the coating film.

Further, as in Japanese Patent Application No. 4-147296, when the existence form of Cr in dispersion plating is unknown, its workability and corrosion resistance after working cannot be mentioned at all. That is, there is a concern that workability and corrosion resistance may be reduced depending on the form of Cr present.

Therefore, it is an object of the present invention to provide a zinc-alumina dispersion-plated steel sheet with high corrosion resistance and a method for producing the same, which solves the above-mentioned drawbacks of the prior art.

[0010]

The present inventors have arrived at the present invention through extensive studies in order to solve the above problems. That is, according to the first aspect of the present invention, a steel sheet having an electric Zn-based plating having an adhesion amount of 10 to 50 g / m ² on at least one surface of the steel sheet, wherein the electric zinc-based plating layer comprises: Alumina sol converted to Al ₂ O ₃ 0.0
1 to 3 wt% and contains chromium in an amount of 0.1 in terms of metallic Cr.
1 to 20 wt% and further contains at least one element selected from the group consisting of Co, Ni and Fe by 0.0
Provided is a highly corrosion-resistant electroplated steel sheet characterized by containing 0.1 to 20 wt%.

Here, it is preferable that Cr contained in the electrogalvanized layer is present in an oxide form, and a part or all thereof is present in the grain boundaries of Zn or Zn alloy crystals.

Further, according to the second aspect of the present invention, when zinc-based plating is applied to at least one surface of the steel sheet, zinc ions are contained in a zinc concentration of 0.5 to 2.5 mol / L,
Alumina sol having an Al ₂ O ₃ concentration of 0.01 to 0.5
mol / L, Chromium ion as chromium concentration 0.05
˜1 mol / L, and 0.1 to 1 m of at least one element selected from the group consisting of Co, Ni and Fe.
Using a sulfuric acid plating bath containing ol / L, the pH is 2 to
Provided is a method for producing a highly corrosion-resistant electroplated steel sheet, which comprises performing plating in a range of 4.5.

[0013]

The present invention will be described in more detail below. First book
The Zn-alumina dispersion-plated steel sheet of the invention will be described.
It In the present invention, Al addition to the zinc-based plating layer
As the compound, positively charged alumina sol is preferable.
Yes. That is, the plating layer is positively charged.
This is because it is easy to eutectoid into the inside. Also, alumina sol
Is completely Al₂O ₃Only exist as
It is not necessary to use, it is mixed as Al compound
May be used. That is, in general, alumina sol is 1
Since it is manufactured by a wet method at a low temperature of 00 ° C or less,
All Al₂O₃Is not, and most of them are A
1 hydroxide or hydrate or complex with Al salt
Because it exists as.

The content of alumina sol in the zinc-based plating layer is preferably 0.01 to ₃ wt% in terms of Al ₂ O ₃ . That is, if it is less than 0.01 wt%, the effect of improving the corrosion resistance is not sufficient, and if it exceeds 3 wt%, the plating appearance tends to turn black and the plating adhesion tends to decrease, and alumina sol is added to the plating bath. Because it is necessary to add a large amount, the concentration of alumina sol in the plating bath increases and the viscosity becomes high, which causes problems in operation.

Further, Cr is added to the electrogalvanized plating layer.
Is preferably contained in an amount of 0.1 to 20 wt% in terms of metallic Cr. In other words, the inclusion of Cr, which is more noble than zinc, suppresses the excessive activity of zinc in a corrosive environment, forms a passivation film at the initial stage of corrosion, prevents the elution of plating, and prevents the redox reaction. By improving corrosion resistance and evenly depositing Cr in the plating layer, even if the passivated film formed is broken, the broken portion has a slower elution rate of the plating due to the action of Due to the non-conductive Zn (O
This is because H) ₂ is produced and a passive film is formed again.

Further, when the Cr content in the zinc-based plating layer is less than 0.1 wt%, the effect of improving the corrosion resistance cannot be expected, and when it exceeds 20 wt%, the adhesion of the plating film is deteriorated and blackening occurs. Not preferable.

Further, it is a feature of the present invention that all Cr in the zinc-based plating exists as an oxide. In other words, it is necessary to disperse the metal chromium fine particles in the plating solution in order to make them exist in the form of metal fine particles, but it is difficult to ensure the uniformity in the bath, and it is necessary to disperse them in the plating layer. In order to cause precipitation, the fine particles have to be several microns or less, and in some cases, submicron, but such fine particles are likely to be localized due to the aggregating action due to electrostatic force and intermolecular force, and uniform plating can be obtained. It's extremely difficult. Further, in order to obtain an alloy plating with zinc, trivalent chromium ions may be added to the plating bath. With respect to the production method according to the present invention, when the pH is 2 or more, the plating is burnt and all alloy plating is performed. Is extremely difficult to obtain.

For the above reason, it is preferable that the chromium is present in the plating layer in an oxide form. further,
It is preferable that a part or all of the chromium oxide is present at the grain boundaries of Zn or a Zn alloy crystal. That is,
This is because when the oxide is dispersed in the alloy layer, the alloy layer is likely to be porous and the plating adhesion is deteriorated, and the basic zinc chloride retaining function is deteriorated. As in the present invention, if the chromium oxide-like substance is present at the grain boundaries, the function of retaining the basic zinc chloride or zinc hydroxide generated by corrosion can be sufficiently exerted, which can contribute to the improvement of corrosion resistance. The plating adhesion and workability are also good because the oxide-like substance does not promote destruction from the grain boundaries.

The zinc-based plating preferably further contains 0.001 to 20 wt% of at least one element selected from the group consisting of Co, Ni and Fe.

The reason for adding one or more kinds of these alloying elements is the same as described in detail in the reason for adding chromium. Further, the content rate of these additional elements is 0.001 wt.
If it is less than%, it does not exert sufficient corrosion resistance effect, and conversely 2
If it exceeds 0 wt%, the sacrificial anticorrosive action of zinc decreases, which may cause a significant decrease in corrosion resistance depending on the corrosive environment, which is not preferable.

Next, the operation of the method for producing a highly corrosion-resistant plated steel sheet according to the present invention will be described in detail. In the method for producing a highly corrosion-resistant plated steel sheet of the present invention, the zinc ion concentration in the plating bath is preferably 0.5 to 2.5 mol / L. If the zinc ion concentration in the plating bath is less than 0.5 mol / L, supply of zinc ions to the surface of the steel sheet is delayed, plating burns occur, and the plating efficiency decreases, which is not preferable. Also, the zinc ion concentration in the plating bath is 2.5.
If it exceeds mol / L, the zinc compound is likely to precipitate in the plating bath, which causes a problem in managing the plating bath, which is not preferable.

Alumina sol in the plating bath is Al ₂ O ₃
It is required to be 0.01 to 0.5 mol / L in terms of conversion. If the concentration in the plating bath is less than 0.01 mol / L, alumina is not sufficiently dispersed in the plating layer and chromium precipitation is also suppressed, which is not preferable. Further, when the concentration in the plating bath exceeds 0.5 mol / L, the viscosity of the plating solution increases, and alumina easily gels in the plating solution, which is formed when continuous plating is performed for a long time. It is not preferable because the Al ₂ O ₃ and chromium contents in the plated layer cannot be kept constant.

In the plating bath, Cr ions are added in an amount of 0.05 to
Add 1 mol / L. The reason for this is that C in the plating layer
The r content is 0.1 wt% to 2 as metal chromium (Cr)
This is because it is necessary to set the content in the range of 0 wt%, and when the Cr ion content is less than 0.05 mol / L or exceeds 1 mol / L, the range deviates from these ranges.

Furthermore, at least one selected from Co, Ni and Fe is added to the plating bath in an amount of 0.1.
Add ~ 1 mol / L. The reason for this is, as described in the above-mentioned Cr ion addition amount, necessary to set the content of each element in the plating layer to 0.001 wt% to 20 wt%, and 0.1 mol / Less than L or 1
This is because it is difficult to maintain the content rate in these ranges if it exceeds mol / L.

There is no particular limitation on the method of supplying the plating components such as zinc, chromium and alumina sol to the plating bath, and a method of dissolving these sulfates or soluble compounds in the plating bath or a part or all of them being made of metal. It may be supplied and dissolved in the plating solution. Moreover, you may use together the chloride containing the said metal ion as needed. To supply the alumina sol to the plating bath, a commercially available boehmite-based alumina sol may be added as an aqueous solution. The particle size of the alumina sol used is preferably 10 to 100 nm. By setting the particle diameter of the alumina sol within the above range, preferable results are obtained in terms of stability of the plating solution, dispersibility in plating, plating adhesion, and the like.

In the plating manufacturing method of the present invention, the pH is preferably in the range of 2 to 4.5. That is,
If it is less than 2, the alumina sol will be aggregated and solidified, and if it exceeds 4.5, the productivity will be reduced due to the reduction in current efficiency, which is not preferable.

The plating bath temperature is preferably in the range of 40 ° C to 70 ° C. If the temperature is lower than 40 ° C., the current efficiency is lowered, and if the temperature exceeds 70 ° C., a black appearance is likely to occur, which is not preferable. By the above method, bare corrosion resistance,
It is possible to obtain a highly corrosion-resistant steel plate having excellent properties such as corrosion resistance after coating, plating adhesion and weldability.

The material to be plated, which is the object of the method for producing a plated steel sheet according to the present invention, is not particularly restricted with respect to the composition, production method, etc. of the steel sheet, and it may be either cold rolled steel sheet or rolled steel sheet. Well, various well-known steel plates such as low-carbon steel, ultra-low-carbon steel, high-tensile steel plate whose strength is improved by intentionally adding Si, Mn, P, Cr, Mo, Ti, Cu, etc. It can be used.

[0029]

EXAMPLES The present invention will be specifically described below based on examples. (Example 1) Zn and C produced by the following processing steps
The powdering resistance and the corrosion resistance after working of the plated steel sheet containing r, Al ₂ O ₃ , and at least one selected from Co, Ni and Fe were evaluated. Table 1 shows the experimental conditions and the evaluation results thereof.

1. Specimen Cold-rolled steel sheet for deep drawing; thickness 0.7 mm 2. Treatment process Degreasing → washing → pickling → plating → washing → drying → powdering resistance, corrosion resistance after processing 3. Conditions (1) Degreasing Sodium hydroxide 30g / L Surfactant (Brand name Pakuna) 1g / L Temperature 60 ° C Electrolyte at 20A / dm ^{2 using} steel plate as anode (2) Pickling sulfuric acid 10g / L Temperature 30 ° C Soaking time 5 seconds (3) Plating apparatus Method Liquid flow cell Anode (electrode) Zn Between electrodes 10 mm Plating solution flow rate 1 m / sec (4) Plating bath Zn ²⁺ 0.29 to 2.52 mol / L Cr ³⁺ 0.04 to 1 0.000 mol / L Al ₂ O ₃ (520 from Nissan Chemical Industries, Ltd.) 0.01 to 0.50 mol / L Co ²⁺ 0.08 to 0.97 mol / L Ni ²⁺ 0.43 mol / L Fe ²⁺ 0 .43 mol / L pH 2 to 4.5 (5) Plating condition Bath temperature 40 ° C. to 70 ° C. Current density 40 A / dm ^{2 to} 180 A / dm ² Energizing time 2 seconds to 30 seconds (6) Powdering resistance 180 inside Bend at an angle of (at that time, make sure there is no gap in the bent portion), then bend back so that it becomes almost flat, peel off the plating layer that floated with cellophane tape, and measure the amount of peeling with fluorescent X-ray The amount of peeling was evaluated. What peeling amount of 10 mg / m ² or less ◎, ○ those 10~100mg / m ^2, 100~1
000mg / m ² as the △, and as × 1000 mg / m ² or more. (7) Corrosion resistance 50 mm in diameter by press working of oil-coated plated steel sheet
A cup having a height of 30 mm was prepared by using a cellophane tape to remove the plating layer that had floated up after processing the outer surface of the cup, and the red rust generation period was investigated by the combined cycle corrosion test (CCT). The case where the occurrence of red rust was 100 days or more was evaluated as ⊚, the case of 50 to 100 days was evaluated as ○, the case of 20 to 50 days was evaluated as Δ, and the case within 20 days was evaluated as ×. One cycle of the combined cycle corrosion test is salt spray (35 ° C)
1Hr → dry (60 ℃) 5Hr → wet (50 ℃) 2Hr
Is. (8) Adhesion of coating material The test piece after plating was subjected to chemical conversion treatment (PBL3020 manufactured by Nippon Parkerizing Co., Ltd.), electrodeposition coating (Power Top 233E manufactured by Nippon Paint Co., Ltd.) 30 μm, intermediate coating (Luger Bake manufactured by Kansai Paint Co., Ltd.) KPX36) 35μ
m, topcoat (Kansai Paint Co., Ltd. Luger Bake White) 35 μm, and then the coating film is 5 mm wide and 100 m long
After making m scratches, a salt spray test was performed for 2 weeks, a tape peeling test was performed, and the adhesion of the coating film was evaluated by the peeling width from the scratched portion. The smaller the peeling width, the better the adhesion of the coating film, but the peeling width of 1 mm or less is ⊚, 1 to 2 mm is ◯, and 2 is
5 mm was evaluated as Δ, and 5 mm or more was evaluated as x.

Example 2 A sulfuric acid bath having the following composition was prepared. Plating bath (sulfuric acid bath) composition Zinc sulfate (heptahydrate) 400 g / l (Zn ion amount 1.4 mol / l) Cobalt sulfate (heptahydrate) 100 g / l (Co ion amount 0.36 mol / l) 40% sulfuric acid Chromium aqueous solution 70 g / l (Cr ion amount 0.14 mol / l) 20% alumina sol solution 40 g / l (alumina amount 0.08 mol / l) (Nissan Chemical Co., Ltd. alumina sol AS-520)

A Zn-alumina-based dispersion-plated steel sheet was produced by plating the cold-rolled steel sheet, which had been subjected to alkali degreasing, pickling with 5% hydrochloric acid and then water washing, using the above plating bath under the following conditions. Plating conditions Plating bath temperature 50 ° C pH 2.8 Anode material 5% Sn-Pb Current density 75A / dm ²

When a Zn-alumina-based dispersion-plated steel sheet was manufactured under the above conditions (Example of the present invention), the aging of the plating bath and Cr, Al and Co in the plating layer of the obtained Zn-alumina-based dispersion plating steel sheet. The relationship with the content of is shown in FIG. In addition, as a comparative example, when a Zn-alumina-based dispersion-plated steel sheet was manufactured under exactly the same conditions except that the pH was set to 1.5, the time of the plating bath and the plating of the obtained Zn-alumina-based dispersion plating steel sheet The relationship with the contents of Cr, Al and Co in the layer is also shown in FIG. In addition, in FIG. 1, the solid line and the white line show the example of the present invention, and the dotted line and the black line show the comparative example. The ○ and ● marks indicate the Cr content,
△ and ▲ marks show Al content, and □ and ■ marks show Co content.

As shown in FIG. 1, in the comparative example, which is a conventional manufacturing method, the contents of Cr and Al in the plated layer are reduced over a period of about 1 week. For example, the contents of Cr and Al in the plating layer are stable even after the plating bath has been aged for 8 weeks.

Example 3 A sulfuric acid bath having the following composition was prepared. Plating bath (sulfuric acid bath) composition Zinc sulfate (heptahydrate) 343 g / l (Zn ion amount 1.2 mol / l) Cobalt sulfate (heptahydrate) 83 g / l (Co ion amount 0.3 mol / l) 40% sulfuric acid Chromium aqueous solution 450 g / l (Cr ion amount 0.9 mol / l) 20% alumina sol solution 150 g / l (alumina amount 0.3 mol / l) (Nissan Chemical Co., Ltd. alumina sol AS-520)

A Zn-alumina dispersion-plated steel sheet was produced by plating the cold-rolled steel sheet, which had been degreased with alkali, pickled with 5% hydrochloric acid and then washed with water, using the above plating bath under the following conditions. Plating conditions Plating bath temperature 50 ° C pH 3.0 Anode material 5% Sn-Pb Current density 75A / dm ²

When a Zn-alumina-based dispersion-plated steel sheet was manufactured under the above conditions (Example of the present invention), the aging of the plating bath and Cr, Al and Co in the plating layer of the obtained Zn-alumina-based dispersion plating steel sheet The relationship with the content of is shown in FIG. In addition, as a comparative example, when a Zn-alumina-based dispersion-plated steel sheet was manufactured under exactly the same conditions except that the pH was set to 1.5, the time of the plating bath and the plating of the obtained Zn-alumina-based dispersion plating steel sheet The relationship with the contents of Cr, Al and Co in the layer is also shown in FIG. In FIG. 2, the solid line and the white line show the examples of the present invention, and the dotted line and the black line show the comparative examples. The ○ and ● marks indicate the Cr content,
△ and ▲ marks show Al content, and □ and ■ marks show Co content.

As shown in FIG. 2, in the comparative example, which is a conventional manufacturing method, the contents of Cr and Al in the plated layer are decreased over a period of about 1 week. For example, the contents of Cr and Al in the plating layer are stable even after the plating bath has been aged for 7 weeks.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

[Table 4]

[0043]

[Table 5]

[0044]

[Table 6]

[0045]

[Table 7]

[0046]

[Table 8]

[0047]

As described in detail above, the Zn-alumina dispersion-plated steel sheet of the present invention has a plating layer containing a predetermined amount of alumina and Cr and at least one of Co, Ni, and Fe. , Bare corrosion resistance, corrosion resistance after painting,
Zn-alumina dispersion-plated steel sheet is used for a long period of time by using a sulfuric acid bath which has excellent characteristics such as plating adhesion and workability and is suitable for high-speed mass production of plated steel sheet by the method of the present invention at an appropriate pH. It is possible to manufacture stably across.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the aging of a plating bath and the contents of Cr, Al and Co in a plating layer in the present invention and the conventional method for producing a Zn-alumina-based dispersion plated steel sheet.

FIG. 2 is a graph showing the relationship between the aging of the plating bath and the contents of Cr, Al and Co in the plating layer in another example of the present invention and the conventional method for producing a Zn-alumina-based dispersion-plated steel sheet. .

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Mochizuki 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Technical Research Division (72) Inventor Hiroki Nakamaru Chuo-ku, Chiba-shi, Chiba Kawasaki-cho, No. 1 Kawasaki Steel Co., Ltd., Technical Research Headquarters (72) Inventor, Tomokatsu Katagiri, Kawasaki-machi, Chuo-ku, Chiba, Chiba Prefecture Kawasaki Steel Co., Ltd., Technical Research Headquarters (72) Inventor, Morito Extension 1, Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Technical Research Division

Claims (3)

[Claims] 1. A steel sheet having an adhesion amount of at least one surface of 10
~ 50g / m²With a steel plate with electric Zn-based plating that is
Alumina sol is added as Al to the electrogalvanized plating layer.
₂O ₃It contains 0.01 to 3 wt% in conversion and contains chromium.
Contains 0.1 to 20 wt% in terms of metallic Cr, and further contains C
at least selected from the group consisting of o, Ni and Fe
Also contains 0.001 to 20 wt% of one element
Characterized high corrosion resistance electroplated steel sheet. 2. The Cr contained in the electrogalvanized plating layer exists in an oxide form, and a part or all of it is Zn or Z.
The highly corrosion-resistant electroplated steel sheet according to claim 1, which is present in a grain boundary of an n-alloy crystal. 3. When zinc-based plating is applied to at least one surface of a steel sheet, zinc ion has a zinc concentration of 0.5 to 0.5.
2.5 mol / L, alumina sol having an Al ₂ O ₃ concentration of 0.01 to 0.5 mol / L, chromium ions having a chromium concentration of 0.05 to 1 mol / L, and further Co and Ni.
And high corrosion resistance characterized by performing plating in a pH range of 2 to 4.5 using a sulfuric acid plating bath containing 0.1 to 1 mol / L of at least one element selected from the group consisting of Fe and Fe. Manufacturing method of electroplated steel sheet.