JPH08246185A - Electrogalvanized steel sheet excellent in surface appearance - Google Patents

Abstract

PURPOSE: To dissolve the difference in the initial electroanalysis for zinc caused by microflaws and stains which can not be recognized in the original sheet and to produce a steel sheet excellent in surface appearance, at the time of applying electrogalvanizing to a steel sheet, by previously forming a trace amt. of iron plating substrate and thereafter executing galvanizing. CONSTITUTION: At the time of applying electrogalvanizing to a steel sheet, it is applied with iron plating after pickling to form a substrate adhered with Fe by 5 to 500mg/m<2> . Fe is the main component in the steel sheet to be galvanized and gives no influence to the eluting rate of Zn by which sacrificial corrosion protection is aimed at. Thus, differed from Ni plating substrate treatment or the like, there is no fear of deteriorating the corrosion resistance of the electrogalvanized steel sheet. As for the coating weight of Fe in the iron plating, >=5mg/m<2> is needed from the effect of suppressing inferiority in the appearance, but, since, in the case of >500mg/m<2> , the effect is saturated, the upper limit is regulated to 500mg/m<2> . The coating weight of the galvanizing as the upper layer is not limited in particular, but, from the point of corrosion resistance which is the primary purpose, it is preferably regulated to >=5g/m<2> .

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 which has an excellent surface appearance and is suitable as a surface-treated steel sheet particularly used for home electric appliances and the like.

[0002]

2. Description of the Related Art The quality required for steel products is becoming higher year by year, and there is a great 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, for automobiles, Zn-based alloy plating and organic composite-plated steel sheets with an organic coating applied to it are developed. Has been converted.
As post-treatments for home appliances, chromate treatments and organic composite treatments that add an organic coating are the main
In many cases, electric Zn plating is adopted as the undercoat. Compared to 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 terms of cost, and has an advantage such as good compatibility with chromate treatment. There is. For this reason, the base plating is fixed to the electric Zn plating, and a post-treatment according to the needs is applied to this, thereby responding to diversifying needs such as corrosion resistance and omission of steps in the field of home appliances.

Under these circumstances, in post-processing household appliances, these post-treated steel sheets are often assembled and used as they are, and accordingly, the demand for appearance quality becomes strict, and the minute appearance that has been overlooked until now. Dirt is becoming ignorable. Appearance problems are classified into those caused in the electro-Zn plating process including post-treatment and those caused by the original plate. If the cause is identified, the solution is easy, but
In particular, in the case of the original plate, the manufacturing process is extremely complicated, and thus it is often difficult to specify, and even if it is possible, a fundamental solution is difficult to solve. Further, there are many problems that even if the cause is obviously the original plate, it cannot be confirmed at the stage of the original plate and can be confirmed only by performing electric Zn plating. As a method for producing an electric Zn-plated steel sheet having an excellent appearance, Japanese Patent Application No.
No. 222522 proposes a method of forming a lower layer by Ni plating and then forming an upper layer by Zn plating.

[0004]

However, a Zn-plated steel sheet having a lower layer formed by Ni plating and then an upper layer formed by Zn plating has Zn and Ni at a flaw or an end face.
Of Zn causes preferential dissolution reaction of Zn,
Corrosion resistance may deteriorate depending on the amount of plating adhered. Therefore, even when the amount of the lower layer plating is large, the electrical Zn having a stable and good surface appearance is not affected by the original plate state without impairing the original quality characteristics such as corrosion resistance.
Plated steel sheets are needed. The present invention is for solving the above problems, and an object thereof is to provide an electric Zn-plated steel sheet having an excellent surface appearance.

[0005]

The inventors of the present invention have found that the electric Z generated due to minute flaws or stains that cannot be confirmed on the original plate.
It was determined that the poor appearance of the n-plated steel sheet was due to a subtle difference in the initial Zn electrodeposition. Therefore, a thorough study was conducted on the uniformity of the initial electrodeposition of Zn, and a method that did not deteriorate the corrosion resistance of the Zn-plated steel sheet was searched for.
It was found that applying a small amount of plating is effective. The present invention has been made based on this finding, and the summary thereof is as follows. When the electric Zn plating is applied to the steel sheet, the Fe plating is preliminarily performed at 5 to 500 mg / m ²
Electric Zn excellent in surface appearance characterized by being adhered
Plated steel sheet.

[0006]

In the present invention, when performing electric Zn plating,
It is characterized in that a small amount of Fe plating is performed in advance.
The function and effect are to improve the poor appearance caused after the electric Zn plating due to minute scale flaws and stains on the surface of the steel sheet. It is possible to confirm that the defective appearance portion has a different color tone by visual observation and that the size and orientation of the plated crystal are not uniform when compared with the normal portion when microscopic observation is performed. At the micro-defects, Zn is not used due to the current situation or segregation of steel components.
It is considered that this is because the plating deposition, especially the initial deposition, becomes non-uniform. On the other hand, it is presumed that Fe plating is evenly deposited on the micro-defects as well as on the normal parts, and this serves as nuclei for Zn deposition to uniformly deposit Zn, and as a result, appearance stains are less likely to be observed. To be done. This is because the uniform precipitation property of Fe is higher than that of Zn.

Further, Fe is the main component of the base steel sheet and does not affect the elution rate of Zn which is responsible for sacrificial corrosion protection. Therefore, the corrosion resistance of the electric Zn plated steel sheet by the Fe plating treatment does not deteriorate. The lower limit of the amount of Fe plating deposited is 5 mg
/ M ² . If it is less than 5 mg / m ² , there is no effect of suppressing the appearance defect. Even if Fe plating is performed at 500 mg / m ² or more, the effect of suppressing the appearance defect is saturated and the performance is not changed. Therefore, the upper limit of the Fe plating adhesion amount is set to 500 mg / m ² . The amount of Zn plating deposited is not particularly limited, but we conducted a test in the range of 3 to 300 g / m ² and confirmed the effect of Fe plating. From the viewpoint of corrosion resistance, which is the original purpose of electroplated steel sheet, the Zn coating amount is 5
It is preferably g / m ² or more.

[0008]

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 obtain a plate thickness of 0.
It was set to 8 mm, and this was annealed to obtain a plating original plate. When such an original plate was electroplated with 20 g / m ² of electric Zn using a sulfuric acid bath containing 1 mol / l of Zn ions, appearance stain was generated on all 10 sheets. On the contrary,
After performing Fe plating using the sulfuric acid bath containing Fe ions 1 mol / l, shows the results of electrical Zn plating Table 1, which was conducted Fe coating weight 5 to 500 mg / m ² appearance dirt is There was nothing.

The appearance defect occurrence rate is ⊚: Appearance stain occurrence rate is less than 5% ◯: Appearance stain occurrence rate is 5% or more and less than 20% △: Appearance stain occurrence rate is 20% or more and less than 40% ×: Appearance stain occurrence rate The evaluation was made at 40% or more.

[0010]

[Table 1]

[0011]

Industrial Applicability As described above, the present invention provides a method for improving the microscopic appearance stain after the electric Zn plating caused by the original plate. In particular, it is suitable as a method for manufacturing a base Zn plating of a surface-treated steel sheet for home electric appliances which is used as it is after being assembled and processed, and is very effective in meeting the increasingly strict requirements for appearance quality.

Claims (1)

[Claims] 1. An electric Zn-plated steel sheet having an excellent surface appearance, which comprises depositing Fe plating in an amount of 5 to 500 mg / m ^{2 in} advance when performing electric Zn plating on the steel sheet.