JPH0733565B2 - Hot-dip aluminum plated steel sheet with excellent corrosion resistance - Google Patents

Description

TECHNICAL FIELD The present invention relates to a hot-dip aluminized steel sheet having excellent corrosion resistance.

2. Description of the Related Art A steel sheet having a surface coated with a molten aluminum plating has excellent corrosion resistance and heat resistance, and has been widely used as a material for various heat appliances and automobile exhaust systems.

Such hot-dip aluminized steel sheet is generally heated in a non-oxidizing furnace or an oxidizing furnace to oxidize and burn surface stains, rolling oil, etc., and then remove it, and then lead it to a reducing furnace in a reducing atmosphere. To reduce the oxide film on the surface to activate the surface, and at the same time to anneal it to give it workability, then cool it to a temperature suitable for plating, then immerse it in a plating bath and apply aluminum plating. It is manufactured by pulling it up, adjusting the amount of plating adhered by gas wiping, cooling, and then winding.

The characteristics of the hot-dip aluminized steel sheet produced by such a plating method remarkably vary depending on the components of the original steel sheet to be plated. It is known that the addition of Cr into steel (Japanese Patent Publication No. 52-33579) is effective in improving corrosion resistance.

In addition, type 2 is known in which pure aluminum is used for corrosion resistance and plating is performed to increase the amount of plating adhered.

As described above, the performance characteristics of the conventional hot-dip aluminized steel sheet have been improved mainly by adjusting the components of the base steel sheet to be plated or by increasing the amount of coating deposit.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in recent years, the need for improving the corrosion resistance of hot-dip aluminized steel sheets under various environments has been increasing. Therefore, as a means for improving the corrosion resistance, Cr-added steel (Japanese Patent Publication No.
579) or stainless steel (Japanese Patent Laid-Open No. 62-274060) system is hot-dip aluminum plated.

Although such a method also has a corresponding effect in improving the corrosion resistance, under strong corrosion conditions such as an automobile muffler, the protective effect of the plating layer is relatively short, and the useful life after the plating layer disappears. Will depend on the corrosion resistance of the plating base plate itself. Further, when it is used as a building material, a long life of the member is required, and it is preferable that the protective effect of the plating layer can be maintained for a long time.

Means for Solving the Problems The present invention provides a hot dip aluminized steel sheet with significantly improved corrosion resistance of the aluminized layer, the gist of which is to include Cr in the plated layer. It was found that the corrosion resistance is remarkably improved by this. For this reason, by adding 0.01% or more of Cr to the aluminum plating bath, Cr is contained in the plating layer, and a remarkable effect is obtained in improving the corrosion resistance.

The main additive element in the plating bath composition of the present invention is Cr
0.01 to 1%, other than 1% Si and 1 to 3% Fe are contained.

Therefore, as shown in FIG. 1, the amount of Cr gradually decreases as the amount of Cr added increases, and 0.01% or more is added in order to improve the corrosion resistance. However, if the amount of added Cr exceeds 0.4%, the Cr in the plating bath becomes oversaturated at the normal plating bath temperature, and even if it becomes dross, it adheres to the plating surface. It is necessary to raise the temperature (730-770 ℃). The upper limit of the Cr addition amount is
The limit is 1% from the actual plating operation.

Si is usually added to suppress the growth of the alloy layer of the aluminized steel sheet, but if the addition amount is less than 1%, the effect of suppressing the alloy layer becomes small. However, by raising the plating bath temperature, the reactivity of the plating base plate and the aluminum bath is increased, which is effective in preventing non-plating and pinholes, and it is advantageous for obtaining thick plating products due to the growth of the alloy layer. It is effective for obtaining the protective effect of the aluminum plating layer over a period. Si is easily mixed in the aluminum ingot refining process and is usually contained in 0.1 to 0.5%, so there are few plating defects.
The upper limit was set to less than 1% because there is no particular problem if Si is less than 1% in obtaining a thick plated product.

Inevitable impurity Fe is eluted from the original plating plate during aluminum refining or aluminum plating, and is generally saturated with respect to the plating bath. Its content varies depending on the plating bath temperature, but is about 1 to 3 % Included.

The reason why the corrosion resistance is improved by containing Cr in the plating layer is that the aluminum-plated steel sheet forms a dense passivation film by the effect of Cr in the plating layer in a corrosive environment.

The effect of improving the corrosion resistance of the aluminum plating layer by adding Cr to the plating bath and including it in the plating layer is not limited to general low carbon steel, but also to Cr-added steel, stainless steel, etc., regardless of steel type and steel composition. It is something that can be obtained. Also, as a means for improving the hot-dip aluminum plating property of Cr-added steel, stainless steel, etc., Ni, F
You may pre-plate 0.01 to 5 g / m ^{2 of} e, Co or these alloys on one side.

Examples Examples of the present invention will be described below.

Low carbon steel as plating base plate, ultra low carbon Cr added steel (Cr in steel
2.5%, 5.1%, 7.3%), YUS409D, SUS430, 22% Cr steel, etc. were cold-rolled to a plate thickness of 0.8 mm, and this was used for aluminum plating in an oxidation-free furnace method.

Plating bath composition is Si0.05, 0.16, 0.53, 0.96%, Cr content is
No addition (comparative example), aluminum plating was performed in a 0.01, 0.05, 0.1, 0.5, 1% addition bath, and after plating, the coating adhesion amount was adjusted to 270 g / m ² by a gas wiping method, and after cooling, it was wound.

The bath temperature during plating was 720 ° C. when the Cr content was 0.5% or less, and 760 ° C. when the Cr content was 1%, and good plating was obtained.

Table 1 shows the results of examining the obtained aluminum-plated steel sheets for corrosion resistance under various environments, such as an outdoor exposure test, a salt spray test, and a simulated exhaust gas pseudo-condensation liquid immersion test assuming a corrosion environment in an automobile muffler. It can be seen that in any of the corrosion resistance tests, the corrosion weight loss is remarkably reduced as compared with the comparative example, and the corrosion resistance is improved by adding Cr to the plating bath.

Corrosion resistance test method (1) Outdoor exposure test Specimen size was sheared to 50 x 200 mm, with an inclination angle of 30 ° to the south,
An outdoor exposure test was conducted for 3 years in a heavy industrial area to measure and evaluate the corrosion weight loss.

(2) Salt Water Spray Test A salt water spray test was conducted for 30 days in accordance with JIS Z 2371 with a specimen size of 70 × 150 mm, and corrosion loss was measured and evaluated.

(3) Simulated exhaust gas pseudo-condensation liquid immersion test The size of the test piece was 70 x 150 mm, and the test piece was immersed in the test solution so that it would be submerged in the beaker. It was measured and evaluated.

Test solution composition _{^{So 4 -2 0.1% NO 3 -}} 0.015% Cl - 0.03% CO 3 -2 0.4% NH 4 - 0.3% HCOOH 0.1% CH 3 COOH 0.1% pH8 Effects of the Invention As described above, according to the present invention, the Al bath contains less than 1% Si, C
By adding 0.01 to 1% of r, it is possible to obtain an aluminum-plated steel sheet having excellent corrosion resistance and good surface properties.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the relationship between the Cr content in a molten aluminum plating bath and the corrosion resistance of an aluminum plated steel sheet (salt spray test for 30 days).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keishi Ichikawa 1-1-1 Edamitsu, Yawatahigashi-ku, Kitakyushu, Fukuoka Prefecture (1-1) Inside the Yawata Works, Nippon Steel Corporation (72) Fumihiko Suga, Yawatahigashi, Kitakyushu, Fukuoka Prefecture 1-1-1 Kueda Mitsue 1-1-1 Inside Nippon Steel Co., Ltd. Yawata Works (56) Reference JP-A-55-119161 (JP, A) JP-A-64-21061 (JP, A) JP-A-61-272389 (JP, A) Japanese Patent Publication Sho 52-13774 (JP, B2)

Claims (1)

[Claims] 1. A steel sheet surface having less than 1% Si and 0.01 to 1% Cr.
A hot-dip aluminized steel sheet having excellent corrosion resistance, characterized in that a hot-dip aluminium-plated layer containing Al and unavoidable impurities is contained in the balance.