JPH0611906B2 - 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 Aluminum-plated steel sheets whose surfaces are hot-dipped with aluminum are excellent in corrosion resistance and heat resistance, and have been widely used as various heat-appliance-based materials and automobile exhaust-system materials.

Such a 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., in the non-oxidizing furnace, and then introduces them into a reducing furnace.
The oxide film on the surface is reduced in a reducing atmosphere to activate the surface, and at the same time annealed to provide workability, and then cooled to a temperature suitable for plating, and then immersed in a plating bath for aluminum plating. It is applied, pulled up into the atmosphere, the amount of plating adhered is adjusted by gas wiping, cooled, and then wound.

The characteristics of the hot-dip aluminized steel sheet produced by such a plating method remarkably differ depending on the components of the base steel sheet to be plated, and as a method of increasing the oxidation resistance at high temperatures, the addition of Ti to the steel (JP-A-56-102523) Or, in order to improve the corrosion resistance, Cr is added to the steel (Japanese Patent Publication No. 52-33579).
Is known to be effective. In this way,
The improvement of the performance characteristics of the hot-dip aluminized steel sheet mainly depends on the adjustment of the components of the plated steel sheet.

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. 52-33579).
No. 6) or a stainless steel (Japanese Patent Laid-Open No. 62-274060) system is subjected to hot dip aluminum plating.
Although such a method also has a corresponding effect in improving the corrosion resistance, the protective effect of the plating layer is relatively short under the condition of strong corrosion such as an automobile muffler, and the plating original plate itself after the aluminum plating layer disappears. The service life will be determined by the corrosion resistance of. The present invention advantageously solves such drawbacks.

Means for Solving the Problems The present invention provides a hot-dip aluminized steel sheet in which the corrosion resistance of the aluminized layer is significantly improved. That is, the present invention has found that the corrosion resistance is remarkably improved by including Cr in the plating layer. Therefore, by adding 0.01% or more of Cr to the aluminum plating bath, Cr is contained in the plating layer and a remarkable effect of improving the corrosion resistance is exhibited.

The plating bath composition in the present invention is Si 1 to 12%, Cr 0.01 to
2%, with the balance consisting of Al and unavoidable impurities.

Thus, Si is added to suppress the growth of the alloy layer of the hot-dip aluminized steel sheet and impart plating adhesion, and the addition amount of 1% or more, preferably 5% or more is necessary. When the amount of Si in the plating bath exceeds 12%, the alloy layer suppressing effect is saturated, and the alloy layer has a sawtooth shape, which lowers the plating adhesion, so the upper limit was made 12%.

Next, as shown in Fig. 1, the amount of Cr added to the plating bath shows a gradual decrease in corrosion loss as the amount of Cr added increases. Stable and improve. However, when the amount of added Cr exceeds 0.4%, the plating bath temperature rises as the amount of added Cr increases because the Cr in the plating bath becomes oversaturated and becomes dross-like and adheres to the plating surface at the normal plating bath temperature. It is necessary to add 2% to the limit in the actual plating operation.

Fe, which is an unavoidable impurity in the plating bath, is eluted from the original plating plate, and its content is generally Si in the plating bath.
Although it depends on the amount and the plating bath temperature, it is about 1 to 3%, which does not hinder the purpose of the present invention.

Thus, by including Cr in the plating layer, the reason why the corrosion resistance is improved is considered to be that the aluminum plated steel plate 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. In addition, for aluminum plating of Cr-added steel, stainless steel plate, etc., Ni, Fe, Co or alloys of these can be applied per side to improve the hot-dip galvanizing property.
You may use what was pre-plated of 0.01-5 g / m < ² >.

Examples Examples of the present invention will be described below.

As shown in Table 1 in detail, low carbon steel is used as a plating base plate.
Ultra low carbon Ti added steel, Ultra low carbon Cr added steel (Cr content 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 by an oxidation-free furnace method.

For the plating bath composition, the Si target addition amount is 1.0%, 2.5%, 3.5%,
5.0%, 8.0%, 10%, and as the amount of Cr in the bath, no addition (comparative example), 0.01%, 0.05%, 0.1%, 1%, 2% addition aluminum plating is performed, and after plating, gas wiping After adjusting the coating weight to 100 g / m ² by the method, it was cooled and wound.

The plating bath temperature during plating is 50 to 70 ° C higher than the liquidus line in the Al-Si equilibrium diagram for the amount of Si added, and the amount of Cr added is 0.1% or less for the amount of Si added. Set the plating bath temperature according to the amount added and 700% for Cr 1% (Si addition amount 10%)
At ℃ and Cr2% (Si content 10%), aluminum plating was performed at 750 ℃, and good plating was obtained.

Table 1 shows the results of examining the corrosion resistance of the obtained aluminized steel sheet under various environments, such as an outdoor exposure test, a salt spray test, and a simulated exhaust gas condensate immersion test assuming a corrosion environment in an automobile muffler. In all the corrosion resistance tests, the corrosion weight loss was remarkably reduced as compared with the comparative example, and it is shown that the corrosion resistance becomes a steel sheet by adding Cr in the plating bath.

The corrosion resistance test method was performed as follows.

(1) Outdoor exposure test A test piece with a size of 50 × 200 mm was subjected to an outdoor exposure test for 3 years in a heavy industrial area with an inclination of 30 ° to the south, and the corrosion loss was measured.

(2) Salt spray test A test piece size of 70 × 150 mm was used, and a salt spray test was conducted for 30 days in accordance with JIS Z 2371 to measure the corrosion weight loss.

(3) Simulated exhaust gas condensate immersion test Specimen size 70 × 650 mm, soak the specimen in the beaker so that it will be submerged in the test solution, and test it at 80 ° C for 30 days in a semi-sealed state, then measure the corrosion loss did.

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, Si1.0-12
%, Cr 0.01 to 2%, it is possible to obtain an aluminum-plated steel sheet having excellent corrosion resistance, suppressing the growth of the alloy layer, and having good plating adhesion.

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 Co., Ltd. (72) Kunio Nishimura, Yawatahigashi, Kitakyushu, Fukuoka Prefecture 1-1-1 Kueda Mitsuda 1-1-1 Inside the Yawata Works, Nippon Steel Co., Ltd. (56) References JP-A-55-119161 (JP, A) JP-B 52-13774 (JP, B2)

Claims (1)

[Claims] 1. Si1.0-12%, Cr0.01-2 on the surface of the steel sheet.
%, With the balance being Al and unavoidable impurities, and a hot-dip aluminum-plated layer having excellent corrosion resistance.