JPH08277450A - Hot dip pure galvanized steel sheet excellent in corrosion resistance - Google Patents

Abstract

PURPOSE: To produce a hot dip pure galvanized steel sheet excellent in the corrosion resistance of the edge faces in the steel sheet even under the condition of a severe corrosive environment by forming a pure galvanizing layer contg. a specified amt. of alkali metals on the steel sheet. CONSTITUTION: A pure galvanizing layer contg. 0.01 to 1mol% of one or more kinds among alkali metals such as lithium, sodium, potassiussm is formed on a steel sheet. This galvanizing layer can be obtd. by mixing a prescribed amt. of alkali metals to a pure galvanizing bath of about 450 deg.C, melting the same and immersing the steel sheet therein, and the layer thickness may ordinarily be regulated to about 8 to 40μm. Thus, the generation of red rust on the edge faces can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip galvanized steel sheet which is excellent in corrosion resistance, especially in red rust resistance of end faces.

[0002]

2. Description of the Related Art Since a steel sheet is corroded as it is, a surface-treated steel sheet whose surface is hot-dipped is generally used. However, if corrosion progresses even if the surface is plated, the plating corrosion product covers the end face, and the sacrificial anticorrosion effect on the end face is lost. The degree of progress of this end surface corrosion depends on the type of plating, and if the coating amount is the same, pure zinc plating has the slowest corrosion progress and excellent red rust resistance. Becomes Even with the above-mentioned pure zinc plating, the anticorrosion effect on the end face is not perfect, and especially in places where the exposure and corrosion environment is harsh, such as Okinawa or similar areas, the occurrence of red rust can be seen in several years.

[0003]

Therefore, according to the present invention,
It is an object of the present invention to provide a hot-dip galvanized steel sheet having excellent corrosion resistance on the end surface of the steel sheet even under severe corrosive environment.

[0004]

The hot-dip galvanized steel sheet according to the present invention contains one or more kinds of alkali metals such as lithium, sodium or potassium in a pure galvanized layer in an amount of 0.0 or more.
It is characterized by containing 0 to 1 mol%.

[0005]

The present invention will be further described below. In the hot dip galvanized steel sheet of the present invention, the pure galvanized layer contains 0.001 to 1 mol% of one or more of lithium, sodium or potassium as an alkali metal as a total amount. If the content of the above-mentioned alkali metal is less than 0.001 mol%, the sacrificial anticorrosion effect is not exerted. On the other hand, if it is more than 1 mol%, the corrosion rate of the plating layer is high and the sacrificial anticorrosion effect is not obtained efficiently.

The sacrificial anticorrosion effect of the alkali metal contained in the pure galvanized layer of the present invention is caused by the inclusion of the alkali metal in the plating corrosion product when the end face is covered with the plating corrosion product. It is considered that the substance exhibits alkalinity of pH 8 or less to be passivated and suppresses the progress of corrosion of the end face.

The mixing ratio of the above lithium, sodium or potassium is not particularly limited, and it is possible to select a single content or a plurality of mixing ratios for each.
The method of mixing the alkali metal in the pure zinc plating layer is not particularly limited, and for example, the alkali metal may be mixed and dissolved in a hot dip galvanizing bath at about 450 ° C. The plating conditions and the like may follow conventional methods.

The film thickness of the pure zinc plating layer containing the alkali metal may be appropriately selected according to the conditions of the operating environment. Usually, the thickness of the pure zinc plating layer is 8 to 40 μm. The base material of the hot-dip galvanized steel sheet of the present invention may be any material, but normally it is preferable to degrease and pickle the base material to improve the adhesion of the plating.

[0009]

Embodiments of the present invention will be described below. After degreasing and pickling a cold rolled plate having a thickness of 0.8 mm, the plate is passed through a molten pure galvanizing bath containing various alkali metals to obtain a molten pure galvanized steel sheet having a pure galvanized layer thickness of 20 μm. Manufactured. The conditions for adding the alkali metal are as shown in Table 1. On the other hand, as a comparative example, a normal hot-dip galvanized steel sheet without addition of alkali metal (same coating thickness)
Also manufactured. Next, a polyester-based coating material was applied to the produced pure galvanized steel sheet so as to have a film thickness of 20 μm and dried. These steel sheets were cut for an exposure corrosion test, samples were prepared, and an atmospheric exposure test was conducted for three years in Okinawa. The evaluation of the sample was performed by measuring the width of red rust generation on the end surface. The results of the exposure test are shown in Table 1. As is clear from Table 1, generation of red rust on the end face can be suppressed by incorporating an appropriate amount of alkali metal into the pure zinc plating layer.

[0010]

[Table 1]

[0011]

The hot-dip galvanized steel sheet of the present invention contains one or more alkali metals such as lithium, sodium or potassium in the pure galvanized layer in a specific amount.
In particular, it is possible to suppress the occurrence of red rust on the end surface of the steel plate,
The effect that the service life of the plated steel sheet is extended can be obtained.

Claims (1)

[Claims] 1. One or more kinds of alkali metals such as lithium, sodium or potassium on a steel plate in an amount of 0.001
A hot dip galvanized steel sheet having an excellent corrosion resistance formed with a pure galvanized layer containing 1 to 1 mol%.