JPH0790610A - Production of glavanized steel sheet excellent in resistance to blackening and corrosion and coating film adhesion - Google Patents

Abstract

PURPOSE:To impart excellent resistance to blackening and corrosion and coating film adhesion by cathodizing a galvanized steel sheet in an electrolyte contg. a specified metal and then chromating the sheet. CONSTITUTION:A galvanized steel sheet is electrolyzed in an electrolyte contg. one or more kinds of metals among Ni, Co and Fe with the sheet as a cathode to deposit the metals on the sheet surface at 1-50mum/m<2> and then chromated. Nickel sulfate, nickel chloride, nickel nitrate, cobalt sulfate, cobalt chloride, iron chloride and iron sulfate are used to prepare the electrolyte, and the electrolyte is preferably controlled to >=pH1.0 with sulfuric acid, hydrochloric acid, phosphoric acid, etc. Further, the cathode current density is preferably adjusted to >=2A/dm<2> in electrolysis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a zinc-based hot-dip galvanized steel sheet excellent in blackening resistance, coating adhesion and corrosion resistance.

[0002]

2. Description of the Related Art Recently, the use of surface-treated steel sheets has been rapidly increasing in response to the prolongation of service life of automobiles, home appliances, building materials and the like. Among these surface-treated steel sheets, the demand for zinc-based hot-dip galvanized steel sheets is increasing, and further, further improvement in performance such as appearance, corrosion resistance, paintability and workability is required for this steel sheet. ing.

Among these performances, the improvement of appearance is as follows.
After plating, before the solidification of the molten zinc layer is started, a zero spangle treatment for spraying water droplets in a mist state onto the surface of the molten zinc layer to reduce the size of zinc crystals is performed. In addition, skin pass rolling is performed to improve the appearance and plate shape.

Regarding the corrosion resistance, the conventional chromate treatment of coating the surface of the molten zinc layer with chromic anhydride or a mixed liquid of chromic anhydride and silicic acid colloid has been carried out. Method to improve corrosion resistance by treating each solution with phosphoric acid
No. 0018751), and a method of improving the corrosion resistance by adding phosphoric acid, a fluoride, a cobalt salt or the like to improve the corrosion resistance (Japanese Patent Application Laid-Open No. 57-174469).

However, a zinc-based hot-dip galvanized steel sheet, which has been plated and then skin-pass rolled, and then chromated to improve corrosion resistance, is stored in a warehouse or the like and is a processed product. There is a phenomenon that the plating surface discolors to black during the work in progress (this phenomenon is called black discoloration). This is a phenomenon that appears in the early stage of corrosion, and it is accelerated in the high temperature and high humidity atmosphere, and skin pass rolling is performed on chromate. It is often found in materials.

Next, a method for preventing blackening of the zinc-based hot-dip galvanized steel sheet will be described below. (1) A method of heating a steel sheet having a zinc-based hot-dip galvanized steel sheet to a temperature of 200 ° C. or higher before performing chromate treatment after treatments such as skin pass rolling and leveling (Japanese Patent Laid-Open No. 55-131178). Gazette).

(2) 17 after zinc-based hot dip plating
After heating to a temperature of 0 ° C or higher, Co or F on the surface
A method of performing chromate treatment after spraying an aqueous solution containing e ions (JP-A-1-129978).

(3) After performing zinc-based hot dip plating, Ni
Treated with a solution containing ions or Co ions,
After that, a method of performing chromate treatment (Japanese Patent Publication No. 3-049
982).

However, the method (1) has a problem that when it is carried out in a plating line, the heating equipment becomes large and it is difficult to control the oxide film on the plating surface.

Further, the method (2) has a problem that the effect of preventing blackening is remarkably reduced when the skin pass rolling is performed after spraying the aqueous solution on the plating surface.

In the method (3), Co or Ni is deposited on the surface of the plating layer in the form of metal or oxide by chemical substitution. This is because the oxide film on the surface of the plating is destroyed by skin pass rolling or the like. Since the metal is preferentially deposited on the exposed portion of the metal, it is non-uniform and the adhesion is weak, and the adhesiveness of the coating film deteriorates. Furthermore, if the amount of deposition changes greatly due to fluctuations in the treatment liquid and the amount of deposition increases, not only the appearance is impaired, but also the corrosion resistance and coating film adhesion are greatly degraded.

[0012]

DISCLOSURE OF THE INVENTION In order to solve the problems of the technique for preventing blackening in the conventional zinc-based hot-dip galvanized steel sheet described above, the present inventor conducted diligent research and studied. As a result of stacking, technical control is relatively easy, and it is possible to reliably prevent black discoloration under easy management. Zinc-based hot-dip galvanizing excellent in black resistance, coating adhesion and corrosion resistance. We developed a method for manufacturing steel sheets.

[0013]

Means for Solving the Problems Black resistance to blackening according to the present invention,
A method for producing a zinc-based hot-dip galvanized steel sheet having excellent coating film adhesion and corrosion resistance is described below.
Blackening resistance, coating adhesion and corrosion resistance, characterized by performing chromate treatment after electrolytic treatment using a zinc-based fused-plated steel sheet as a cathode in an aqueous solution containing one or more types of Fe The method for producing a zinc-based hot-dip galvanized steel sheet having excellent properties is defined as the first invention, and the zinc-based hot-dip galvanized steel sheet is coated with a zinc-based hot-dip plated in an aqueous solution containing one or more of Ni, Co, and Fe. Electrolytic treatment is performed using a steel plate as a cathode, and Ni on the surface of the zinc-based galvanized steel plate,
1 or 50m of the amount of one or more of Co and Fe deposited
The method for producing a zinc-based hot-dip galvanized steel sheet excellent in blackening resistance, coating adhesion and corrosion resistance, which comprises g / m ² and then chromate treatment, is the second invention. It will be.

The method for producing a zinc-based hot-dip galvanized steel sheet which is excellent in blackening resistance, coating adhesion and corrosion resistance according to the present invention will be described in detail below.

That is, in the method for producing a zinc-based hot-dip galvanized steel sheet excellent in blackening resistance, coating adhesion and corrosion resistance according to the present invention, one or more of Ni, Co and Fe are zinc-based melted. Ni, C when effectively attached to a coated steel plate
The electrolytic treatment is carried out in an aqueous solution containing one or more of Fe and Fe using the zinc-based fused steel sheet as the cathode.

And, one or two of Ni, Co and Fe.
As the aqueous solution containing at least one species, nickel sulfate, nickel chloride, nickel nitrate, cobalt sulfate, cobalt chloride, cobalt nitrate, iron sulfate, iron chloride, iron nitrate can be used. Sulfuric acid, hydrochloric acid, phosphoric acid, etc. are added in order to adjust the electric conductivity and the like.

The use conditions of this aqueous solution are not particularly limited, but the metal salt concentration is 10 to 200 g / l, the aqueous solution temperature is 20 to 60 ° C., and the aqueous solution pH is 1.0.
The above is appropriate. If the pH is less than 1.0, the zinc-base fused steel sheet is etched, which is not preferable.

The electrolytic treatment using the zinc-based hot-dip galvanized steel sheet as a cathode with this aqueous solution is preferably carried out at a cathode current density of 2 A / dm ² or more. If the cathode current density is less than 2 A / dm ² , etching of the zinc-based fused plated steel sheet may occur.

By the electrolytic treatment using a zinc-based hot-dip galvanized steel sheet as a cathode, the amount of one or more of Ni, Co and Fe deposited is in the range of 1 to 50 mg / m ² . And 1m
If it is less than g / m ² , the blackening preventing effect cannot be expected, and if it exceeds 50 mg / m ² , the gloss of the steel sheet surface deteriorates.

Thus electrolytically treated, Ni, C on the surface
The zinc-based fused-plated steel sheet to which one or more of o and Fe are attached is then subjected to chromate treatment.
This chromate treatment method may be performed by any treatment liquid, treatment method and treatment condition, and the same effect can be obtained.

By the method for producing a zinc-based hot-dip galvanized steel sheet excellent in blackening resistance, coating adhesion and corrosion resistance according to the present invention, a zinc-based hot-dip galvanized steel sheet excellent in blackening resistance, coating adhesion and corrosion resistance is obtained. Although it is not clear theoretically that Ni can be produced, Ni that precipitates on the plating surface due to electrolytic treatment,
It is considered that the adhesion of Co, Fe, etc. is strong, and that it is uniform and dense, and that the good appearance is due to less etching of the plating surface.

In the method for producing a zinc-based hot-dip galvanized steel sheet excellent in blackening resistance, coating adhesion and corrosion resistance according to the present invention, the zinc-based hot-dip galvanized steel sheet is a pure zinc-plated steel sheet or a zinc-based alloy. It means a steel plate that is fused.

[0023]

[Examples] Examples of a method for producing a zinc-based hot-dip galvanized steel sheet excellent in blackening resistance, coating adhesion and corrosion resistance according to the present invention will be described together with comparative examples.

[0024]

[Example] A fine spangle (zero spangle) hot-dip galvanized steel sheet with a zinc adhesion of 60 g / m ^{2 on} one side was used as a plated steel sheet, and after skin pass rolling with an elongation rate of 0.8%, The electrolytic treatment described below was performed.

Electrolytic treatment of Nos. 1 to 6 of the present invention and Comparative Example No. 1 in Table 1 Sulfuric acid was added to a 20 g / l aqueous solution of nickel sulfate to adjust pH.
= 2 and the current density in an aqueous solution at a liquid temperature of 30 ° C,
By controlling the electrolysis time, the Ni deposition amount, the present invention No.1 is 1.2 mg / m ^2, No.2 is 3.5 mg / m ^2, No.3 is 12.3 mg / m ^2, No.4 Is 28.4 mg / m ² , No.
No. 5 is 39.8 mg / m ² and No. 6 is 45.5 mg / m 2.
² and Comparative Example No. 1 were subjected to an electrolytic treatment of 55.3 mg / m ² .

Electrolytic treatment of Nos. 7 to 9 of the present invention and Comparative Examples No. 2 and No. 3 in Table 1 A 50 g / l cobalt chloride aqueous solution was treated with phosphoric acid to pH =
It was adjusted to 2.5, the current density and the electrolysis time were controlled in an aqueous solution at a liquid temperature of 50 ° C., and the Co deposition amount was determined according to the present invention No.
No. 7 is 9.8 mg / m ² , No. 8 is 25.7 mg / m ² , N
No. 9 is 48.3 mg / m ² , Comparative Example No. 2 is 0.6 mg.
/ M ² and Comparative Example No. 3 were subjected to an electrolytic treatment of 78.1 mg / m ² .

No. 10 to No. 12 in Table 1 and Comparative Example N
o.4, No.5 electrolytic treatment 50 g / l ferrous sulfate aqueous solution with sulfuric acid pH = 1.
5, the current density and the electrolysis time were controlled in an aqueous solution having a liquid temperature of 30 ° C., and the Fe deposition amount was 2.
3mg / m ^2, No.11 is 11.2mg / m ^2, No.1
2 is 29.2 mg / m ² , Comparative Example 4 is 0.6 mg / m ² , N
No. 5 was subjected to an electrolytic treatment of 60.0 mg / m ² .

Electrolytic treatment of No. 13 and No. 14 of the present invention in Table 1 An aqueous solution of 30 g / l nickel sulfate and 10 mg / m ² cobalt chloride was adjusted to pH = 2 with sulfuric acid, and the solution temperature was 30 ° C. In the present invention, the current density and the electrolysis time were controlled so that the present invention No. 13 had a Ni deposition amount of 1.5 mg / m ² , C
o Adhesion amount 0.5 mg / m ² , No. 14 is Ni adhesion amount 21.
7 mg / m ^2, was subjected to electrolytic treatment of Co deposition amount 3.1 mg / m ^2.

Electrolytic treatment of Comparative Examples No. 6 and No. 7 in Table 1 A 40 g / l cobalt sulfate aqueous solution was treated with sulfuric acid to pH = 4.
The liquid temperature at 50 ° C. and controlling the immersion time,
Immersion treatments of the adhesion amount of Comparative Example No. 6 were 15.1 mg / m ² and those of No. 7 were 45.4 mg / m ² .

Chromate treatment is performed with chromic anhydride 20 g /
1, a phosphoric acid 8 g / l, and a silicic acid colloid 20 g / l were used, various temperatures were 30 ° C., the treatment time was 2 seconds, the rolls were squeezed, and hot air drying was performed at 90 ° C. Chromium amount is 20-30
It was mg / m ² .

Table 1 shows the evaluation results of the characteristics. 1) Blackening resistance A 70 mm × 150 mm test piece was held at an angle of 60 ° and left in an atmosphere of 50 ° C. and a humidity of 98% for 10 days,
The blackening of the plated surface was visually determined. ◎: No change at all, ○: Very slight discoloration, △: Discoloration is noticeable, ×: Significant discoloration

2) Adhesion of coating film An acrylic paint was applied and baked to a coating film thickness of 20 μm. The evaluation of the adhesiveness was made by making a burs pattern on the test piece to reach the base material at intervals of 1 mm, performing Erichsen extrusion of 6 mm at the extrusion height, and evaluating the number of coating film residuals after taping. ⊚: 100 remaining marks, ◯: 99 to 95, Δ: 94 to 9
0, ×: 89 to 50, XX: 49 to 0

3) Corrosion resistance A 6 mm high Erichsen processed test piece was subjected to a salt spray test for 120 hours. The area of white rust after the test was evaluated. ⊚: No rust, ○: 5% or less, Δ: 20% or less, ×: 50
% Or less, XX: 51% or more

4) Appearance The appearance after the chromate treatment was visually evaluated. ○: White / glossy surface, △: White / low-gloss surface, ×: Gray, yellow-blue, low-gloss surface

[0035]

[Table 1]

[0036]

As described above, the method for producing a zinc-based hot-dip galvanized steel sheet excellent in blackening resistance, coating adhesion and corrosion resistance according to the present invention has the above-mentioned constitution, and therefore, good blackening resistance. And has the effect that a zinc-based hot-dip galvanized steel sheet having excellent coating film adhesion and corrosion resistance can be manufactured with stable productivity.

Claims (2)

[Claims] 1. A zinc-based hot-dip galvanized steel sheet made of Ni, Co, F
In an aqueous solution containing one or more of e,
Blackening resistance, which is characterized by performing chromate treatment after performing electrolytic treatment with a zinc-based fused steel sheet as the cathode,
A method for producing a zinc-based hot-dip galvanized steel sheet having excellent coating film adhesion and corrosion resistance. 2. A zinc-based hot-dip galvanized steel sheet made of Ni, Co, F
In an aqueous solution containing one or more of e,
Electrolytic treatment is performed using a zinc-based galvanized steel sheet as a cathode, and the amount of one or more of Ni, Co, and Fe deposited on the surface of the galvanized galvanized steel sheet is set to 1 to 50 mg / m ^2, and then chromate treatment is performed. Blackening resistance, which is characterized by
A method for producing a zinc-based hot-dip galvanized steel sheet having excellent coating film adhesion and corrosion resistance.