JPH07258814A - Galvannealed steel sheet excellent in corrosion resistance - Google Patents

Abstract

PURPOSE:To produce a galvannealed steel sheet excellent in corrosion resistance by forming a plating layer, where specific percentages of Mn, Fe, and Al are incorporated into Zn, on the surface of a steel sheet. CONSTITUTION:A plating layer 1, having a composition consisting of, by weight, 0.5-2.5% Mn, 8-12% Fe, 0.05-0.5% Al, and the balance Zn, is formed on a steel sheet 2 as a base material and then subjected to heating treatment, by which galvannealed steel sheet is obtained. By this method, the defects, such as increase in weight and deterioration in workability, caused by increasing coating weight in order to improve corrosion resistance can be removed, and the galvannealed steel sheet having high corrosion resistance even if coating weight is not increased can be obtained by adding Mn to a plating layer.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a galvannealed steel sheet having excellent corrosion resistance.

[0002]

2. Description of the Related Art In recent years, there has been a demand for reducing the weight of automobiles from the viewpoint of exhaust gas regulation, and therefore, a steel plate having a thin plate thickness and high corrosion resistance is required. Therefore, conventionally, the base steel sheet is subjected to hot dip galvanization containing Al, but under severe environmental conditions such as salt damage environment and high temperature and high humidity, white rust due to corrosion of zinc and the like deteriorate the appearance. Therefore, in order to further provide corrosion resistance, hot-dip galvannealing after hot dip galvanizing and various post-treatments after galvanizing have been performed to improve corrosion resistance.

[0003]

In order to further improve the corrosion resistance, the plating layer becomes thick, resulting in a problem that workability and weldability are deteriorated. In addition, post-processing increases costs and causes work loss.

[0004]

SUMMARY OF THE INVENTION The present invention advantageously solves the problems of the prior art and has an Mn of 0.5 to 2.5.
%, Fe 8 to 12%, Al 0.05% to 0.5%, and the remaining Zn is a galvannealed steel sheet having excellent corrosion resistance.

[0005]

The present invention will be described below with reference to the drawings. Figure 1
FIG. 1 is a schematic view of a galvannealed steel sheet according to the present invention. One layer has Mn: 0.5 to 2.5%, Fe: 8 to 1
2% and Al: 0.05-0.5% Remaining Zn plating layer 1
Is. The two layers are base material steel plates 2. A feature of the present invention is an alloyed hot-dip galvanized steel sheet that contains 0.01 to 2.5% of Mn in the plating layer and has excellent corrosion resistance.

The reasons for setting the content of each element in the plating layer will be described below. Mn: If the Mn content in the plating layer is less than 0.5%, the effect of corrosion resistance does not appear. Further, when Mn is contained in an amount of 2.5% or more, the powdering resistance is reduced. Therefore, the Mn content in the plating layer is 0.01 to 2.5.
%.

Fe: When the Fe content in the plating layer is 8% or less, the effect of corrosion resistance after coating, which is an advantage of alloying hot-dip galvanizing, cannot be seen. On the other hand, if it is 12% or more, the ratio of the brittle Γ layer in the plating layer increases, and the powdering resistance decreases. Therefore, the Fe content in the plating layer is 8 to 12
%.

Al: Al in the plating bath is necessary for improving the powdering resistance of the obtained plated steel sheet.
However, if it is 0.2% or more, alloying is remarkably suppressed and the alloy is not alloyed. As a result, the Al content in the plating layer obtained from this plating bath is 0.05 to 0.5%.

[0009]

[Examples] The bare corrosion resistance of the steel sheet of the present invention is shown. The Mn content in the plating layer was changed, and a steel sheet having a thickness of 0.8 mm was subjected to the zinc alloy plating of the present invention with an adhesion amount of 45 g / m ² . After performing 500 cycles of cycle corrosion test on the obtained material (5% salt water immersion 10 minutes → 50 ° C., RH 95% or more wet 10 minutes → 60 ° C., RH 40% or less drying 1 minute), 500 cycles, The amount of reduction in plate thickness was measured and evaluated according to the following criteria. As a result, as shown in Table 1, the corrosion resistance became more effective as the amount of Mn in the plating layer increased. Thus, Mn has an effect on the corrosion resistance because Mn has a sacrificial anticorrosion property against Zn. As a result, peeling of the plating is prevented and the progress of corrosion is suppressed. Good ◎ (0.3mm) -〇 (0.5mm)-△ (0.7mm)
− × (perforated) inferior

[0010]

[Table 1]

[0011]

EFFECTS OF THE INVENTION The present invention solves the drawbacks such as weight increase and workability deterioration caused by increasing the coating amount in order to increase the corrosion resistance. It was possible to obtain an alloyed hot-dip galvanized product showing high corrosion resistance.

[Brief description of drawings]

FIG. 1 is a diagram showing a plating structure according to the present invention.

[Explanation of symbols]

 1 Plating layer 2 Base steel plate

Claims (1)

[Claims] 1. Mn 0.5 to 2.5%, Fe 8 to 12%
And an alloyed hot-dip galvanized steel sheet having excellent corrosion resistance, characterized in that it has a plating layer consisting of Al 0.05% to 0.5% and the balance Zn.