JPH08165593A - Electrogalvanized steel sheet excellent in uniform surface appearance - Google Patents

Abstract

PURPOSE: To provide an electrogalvanized steel sheet excellent in uniform surface appearance by applying flash plating of the iron-family metals, Ni, Co and Fe, on the lower layer to cover the defective appearance of an electrogalvanized steel sheet due to the minute crack and dust not recognized on the original sheet, increasing the number of the stable plating nuclei in the initial galvanizing stage and making the plating uniform. CONSTITUTION: An original sheet degreased and pickled is electrogalvanized. In this case, the flash plating of one kind among the iron-family metals, Ni, Co and Fe, is applied on the lower layer at >=10mg/m<2> , then the number of plating nuclei in the initial galvanizing stage is increased to >=10<6> units/mm<2> , and an electrogalvanized steel sheet excellent in uniform surface appearance is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric Zn-plated steel sheet, and more particularly to an electric Zn-plated steel sheet having a uniform surface appearance for household appliances or automobile outer panels.

[0002]

2. Description of the Related Art The quality requirements for steel products are becoming higher year by year, and there is a strong need for improving corrosion resistance, especially for automobiles and home appliances, and the demand for surface-treated steel sheets is increasing accordingly. As surface-treated steel sheets, Zn-based plating and organic composite-plated steel sheets with an organic coating applied to automobiles have been developed and put to practical use in post-treatment steel sheets not only for corrosion resistance but also for omitting process steps for home appliances. There is. Chromate treatment and organic composite treatment for applying an organic film are mainly used as post-treatments for home appliances, but electric Zn plating is often used as the undercoat. Compared with Zn-based alloy plating developed for automobiles, electro-Zn plating is inferior in corrosion resistance at the same deposition amount, but is easy to manufacture and advantageous in cost, and has good compatibility with chromate treatment. There are advantages. Therefore, the base plating is fixed to the electric Zn plating, and the post-treatment according to the needs is applied to this to meet the diversifying needs such as corrosion resistance and the omission of steps in the field of home appliances.

Under these circumstances, for post-treatment of home appliances, these post-treated steel sheets are often assembled and used as they are, and accordingly, the demand for appearance quality becomes strict.
The minute appearance stains that have been overlooked are becoming ignorable. As a method for producing an electric Zn-plated steel sheet having an excellent appearance, JP-A-4-74887, 74
Japanese Patent No. 888 discloses a method of forming a lower layer plating in an acidic electric Zn plating bath containing a conductivity auxiliary agent and then forming an upper layer plating in another Zn plating bath containing no conductivity auxiliary agent. It has not been possible to improve the appearance stains.

[0004]

The appearance problems are classified into those occurring in the electric Zn plating process including post-treatment and those caused by the original plate. If the cause is identified, the solution is easy, but especially in the case of the original plate, the manufacturing process is extremely complicated, so it is often difficult to identify,
Even if they can be identified, it is difficult to reach a fundamental solution. Also, even if obviously due to the original plate,
There are many problems that cannot be confirmed at the original plate stage and can be confirmed only by performing electric Zn plating. For this reason, there has been a need for a method capable of obtaining a stable and good surface appearance without being affected by the original plate state without impairing the original quality characteristics such as corrosion resistance in the electric Zn plating process.

[0005]

The inventors of the present invention have found that electric Zn generated due to minute flaws or stains that cannot be confirmed on the original plate.
It was found that the poor appearance of the plated steel sheet was due to the non-uniformity of the grown crystal due to the insufficient amount of nucleation of the initially deposited Zn crystal. Then, as a result of studying the increase of the initial nucleation nuclei of Zn, it was found that flash plating with an iron group metal is effective for increasing the number of plating nuclei generated during the subsequent Zn plating. The present invention has been made based on this finding, and its gist is as follows. Electric Zn was applied to the plating base plate that had been pretreated with degreasing and pickling.
At the time of plating, any one of the iron group metals of Ni, Co, and Fe is used as flash plating to form 10 mg in the lower layer.
/ M ² or more, and the amount of initial Zn plating nuclei generated during Zn plating is set to 10 ⁶ pieces / mm ² or more, which is an electric Zn plated steel sheet excellent in uniform surface appearance.

[0006]

In the present invention, when performing electric Zn plating, first, flash plating of Ni, Co, Fe was performed at 10 mg / m 2.
Do ² or more. The effect of this is that by performing high overvoltage flash plating, a large number of uniform plating stable nuclei can be obtained irrespective of the original plate state.
In n plating, stable Zn plating nuclei at the initial stage of plating are 1
0 ⁶ pieces / mm ² or more are generated, and a uniform plating appearance can be obtained. If the amount of flash plating is less than 10 mg / m ² , the number of stable nuclei generated is insufficient and a uniform appearance cannot be obtained.
The upper limit is not particularly specified, but 500 mg / m ² or less is preferable from the viewpoint of operating cost and workability.

[0007]

[Example] A hot rolled material of low carbon steel having a plate thickness of 4 mm was pickled so that the scale remained thin and then cold rolled to a plate thickness of 0.8 mm, which was annealed to form a plating original plate. did. Such a plate was subjected to flash plating using a flash plating bath of an iron group metal shown in Table 1, and then a sulfuric acid bath having a pH of 1 containing Zn ions of 65 g / l and a bath temperature of 60 ° C. was used to obtain a relative flow rate. Electric Zn plating was performed at 1 m / sec. The relationship between the number of Zn plating nuclei generated and the appearance stain generation rate at that time is shown in FIGS. From this result, it is found that the number of stable nuclei generated by Zn plating after 10 mg / m ² or more of the iron group metal flash plating is 10 ⁶ / mm ² or more, and the plating has an excellent uniform appearance and other quality. It can be seen that there is no deterioration in performance.

[0008]

[Table 1]

[0009]

Industrial Applicability As described above, the present invention provides a steel sheet which efficiently improves minute appearance stains after electric Zn plating caused by an original plate. In particular, it is suitable as a base electroplated Zn steel sheet for surface-treated steel sheets for home appliances that are assembled and used as they are. is there.

[Brief description of drawings]

1] Ni flash plating amount and initial Z according to the present invention
A diagram showing the relationship between the amount of n-plating nuclei generated and the appearance contamination rate,

FIG. 2 is a Co flash plating amount and initial Z according to the present invention.
A diagram showing the relationship between the amount of n-plating nuclei generated and the appearance contamination rate,

FIG. 3 Fe flash plating amount and initial Z according to the present invention
It is a figure which shows the relationship between the amount of n-plating nuclei generated, and the appearance stain generation rate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsutoshi Enyama 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corp. Kimitsu Steel Co., Ltd.

Claims (1)

[Claims] 1. When electroplating Zn on a plating original plate which has been subjected to pretreatment such as degreasing and pickling, Ni, Co,
The present invention is characterized in that the amount of initial Zn plating nuclei generated during Zn plating is set to 10 ⁶ pieces / mm ² or more after the lower layer is subjected to 10 mg / m ² or more by flash plating with any one of Fe iron group metals. Electric Zn plated steel sheet with excellent uniform surface appearance.