JPH06330346A - Aluminum plated steel sheet - Google Patents

Abstract

PURPOSE:To produce an Al plated steel sheet excellent in appearance and corrosion resistance. CONSTITUTION:An Al plating layer having a gradient plating compsn. is formed on a steel sheet. The alloy layer part is a layer contg. Si at high concn. and the surface layer part is a plating layer having a compsn. similar to that of pure Al. The Al plating layer has the relation of Si% (1)>Si% (2)>Si% (3) among the Si content [Si% (1)] of an alloy layer existing at the interface between the plating layer and the steel sheet, the Si content [Si% (2)] of a plating film close to the alloy layer and the Si content [Si% (3)] of a plating film close to the surface of the plating layer. The Al plating layer also has the relation of Fe% (1)>Fe% (2) between the Fe content [Fe% (1)] of the plating film close to the alloy layer and the Fe content, [Fe% (2)] of the plating film close to the surface of the plating layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum plated steel sheet having excellent appearance and corrosion resistance.

[0002]

[Prior art and its problems] Since aluminum plated steel sheets are excellent in heat resistance, oxidation resistance, corrosion resistance, etc., they have traditionally been used as building material (fire doors, steam pipe parts), heat-resistant parts for household appliances (heat stoves). It is used in many fields such as reflectors, electric appliances) and automobile parts (radiators, mufflers). This aluminum-plated steel sheet is mainly manufactured by hot dipping method. There are two methods of hot dipping method, batch process and continuous process, but thin plating does not make a cut plate but increases the production amount as a coil. The continuous plating process has been adopted because of its advantages.

The continuous plating process is described in Japanese Examined Patent Publication No. 52-33.
No. 759, Japanese Unexamined Patent Publication No. 56-102523, Japanese Unexamined Patent Publication No. 60-262950 have been introduced in many technologies related to hot-dip aluminized steel sheet, but the surface is heat-treated in an atmosphere gas containing hydrogen. Of the strip steel sheet in which is activated and the wettability of the strip steel sheet is continuously passed through an aluminum plating bath maintained at a temperature of 600 ° C. or higher to react with the plating bath, and an intermetallic compound (alloy layer) is formed on the surface of the steel sheet. An aluminum-plated steel sheet is manufactured by a method of wiping to a predetermined coating weight while being generated. The aluminized steel sheet is composed of a steel surface layer in which a small amount of aluminum is solid-solved, an alloy intermediate layer of iron and an aluminized metal, and an aluminized outermost layer having substantially the same composition as the aluminizing bath.

However, although a steel plate plated with a pure aluminum layer has excellent corrosion resistance, a vigorous alloying reaction occurs during the plating operation to generate a large amount of alloy layer, resulting in heat resistance and workability of the plated product (bending process). Properties, drawing workability, bulging workability, compression workability and composite workability of these, etc.), the aluminum plating layer containing 5 to 10% of silicon causes Al to be contained in the steel. Aluminum-plated steel sheets of Al-Si alloys with reduced diffusion rate are generally manufactured.

The Al-Si alloy plated steel sheet has excellent heat resistance, and since the alloying reaction is suppressed by silicon, the workability does not deteriorate due to the cohesive failure of the alloy layer. However, when a large amount of silicon is contained, the plating layer itself becomes hard and there is a problem that minute cracks frequently occur due to insufficient ductility of the plating layer. In particular, when a large amount (1 to 3%) of iron eluted from the steel sheet into the plating bath is present in the plating layer, the plating layer becomes harder and cracks due to insufficient ductility occur. In order to solve such a problem, alloying heat treatment is performed to remove strain and recover workability at a temperature at which an alloy layer does not grow after plating. This method also has a problem that the heat treatment causes a cost burden. Further, although the addition of silicon is effective in suppressing the alloy layer as described above, it was desirable to avoid it from the problem of deteriorating the corrosion resistance.

[0006]

As described above, the present invention solves various problems such as workability deterioration due to an alloy layer, corrosion resistance deterioration due to silicon addition, workability deterioration due to the presence of silicon and iron, and the like. -To provide a steel sheet having both excellent heat resistance of a Si-based alloy layer and excellent corrosion resistance of a pure aluminum layer, the gist of which is to provide one or both sides of a steel sheet with an amount of Si from an inner layer to an outer layer. Depending on Fe
The amount of aluminum is gradually reduced, and the amount of Al is gradually increased.

The aluminum plated steel sheet of the present invention will be described in detail below. On one or both sides of the original plate softened by pretreatment such as heat treatment, from the inner layer on the steel plate side to the outermost layer of the plated layer, the amount of Si may be Fe.
An aluminum plating layer having a composition in which the amount is gradually reduced and the Al amount is gradually increased is applied. As described above, silicon is an effective component that reduces the diffusion of Al into the steel, suppresses Al-Si alloying, and improves heat resistance, and at the same time, it is a harmful component that deteriorates workability and corrosion resistance. It is an ingredient. However, in order for the present invention to provide an aluminum-plated steel sheet having the desired properties, silicon in the aluminum-plated layer is an essential component.

Therefore, according to the present invention, in order to effectively utilize the characteristics of silicon in an aluminum plated steel sheet, the inner layer side of the plated layer steel sheet has a high Si content and the outermost side of the plated layer has a low Si content. As described above, by gradually reducing the amount of Si from the inner layer to the outer layer of the plated layer, pure Al
It is intended to improve heat resistance while maintaining excellent workability and corrosion resistance of the plated layer. The composition of the plating layer and its thickness are not particularly limited, but Al-containing 10% to 20% of Si-for improving the heat resistance of the plating layer.
An inner layer having a thickness of about 1 to 3 μ of the Si-based alloyed layer, and an outermost layer having a thickness of about 5 to 15 μ of an aluminum plating layer containing Si: 5% or less for improving workability and corrosion resistance, and an intermediate between these intermediate compositions. Aluminized steel sheets consisting of layers are preferred.
Above all, it is preferable to thicken the highly pure aluminum plating layer as the outermost layer.

Further, in the present invention, in order to prevent minute plating cracks that occur when forming into various shapes, it is necessary to gradually reduce the iron mixed in the plating layer from the inner layer to the outer layer. Iron is eluted from a steel plate immersed in a plating bath during industrial aluminum plating, and usually about 2% is dissolved. The iron dissolved in the plating bath is naturally taken into the plating film and is supersaturated in aluminum to form a solid solution, which deteriorates the workability of the aluminum plating layer. Therefore, it is preferable that Fe content in the aluminum plating layer is as small as possible, and 1% or less in the outermost layer of the plating layer,
It is preferably 0.5% or less.

The aluminum-plated steel sheet of the present invention having the above-mentioned composition structure can be easily manufactured by various methods. For example, there is a step plating method. A steel plate to be plated is first immersed in an Al-Si alloy plating bath containing an arbitrary amount of Si and then an aluminum plating bath containing a small amount of Si while being passed, and each time wiping is performed using a gas wiping nozzle. A two-stage plating method in which the amount of plating applied is controlled using a device. Furthermore, the aluminum-plated steel sheet for which the present invention is intended can be manufactured by a three-step plating method in which a plating layer is formed in an aluminum plating bath having a further smaller amount of Si.
Furthermore, the aluminum-plated steel sheet of the present invention can be manufactured by other manufacturing methods such as a vacuum deposition method and a molten metal spray plating method. The aluminum-plated steel sheet of the present invention as described above is a plated layer having excellent heat resistance and corrosion resistance, and having excellent workability without fine cracks. Next, examples of the present invention will be described.

[0011]

【Example】

Example 1 A thin steel plate having a plate thickness of 0.8 mm was annealed in a nitrogen atmosphere containing 8% hydrogen, and then immersed in an aluminum plating bath containing 9.5% silicon to perform an initial alloying reaction. After the completion of the alloying reaction, the excess Al-Si alloy was pulled up from the bath and wiped off, and then immediately immersed in the second pure aluminum plating bath.
Immersion in the second plating bath was made as short as possible, the alloy layer formed in the first plating bath was left, and the pure aluminum plating layer was formed thereon. The total thickness of the plated steel sheet produced in this way is 1
It was 8 μm, and was composed of an alloy layer of about 2 μm and an aluminum plating layer of 16 μm. The silicon content in the alloy layer was 18.6%, and the silicon content in the aluminum plating layer 5 μm from the surface was 0.8%. Even if this steel sheet is subjected to Ot bending, no surface crack occurs in the bending portion,
It had extremely excellent workability. As a result of the atmospheric exposure test, almost no surface discoloration occurred, and the weight change due to corrosion was about 1/2 to 1/3 that of the conventional material.

Example 2 A thin steel plate having a plate thickness of 0.8 mm was cleaned on its surface and then introduced into a vacuum chamber for plating by a vacuum deposition method. As the plating, 1.5% Al-Si alloy with a silicon content of 7.5% is used.
μ formation, then gradually reduce the silicon content,
As the surface layer, a 5.0 μ pure aluminum layer was formed. The total plating thickness was adjusted to 20 μm. Even when the plated steel sheet was heated at 450 ° C. for 30 minutes and then subjected to Ot bending, no surface cracks were generated in the bent portion, and the workability was extremely excellent. As a result of the atmospheric exposure test, almost no surface discoloration occurred, and the weight change due to corrosion was about 1/2 to 1/3 that of the conventional material.

Example 3 A thin steel sheet having a thickness of 0.8 mm was annealed in a nitrogen atmosphere containing 8% hydrogen, and then 3 μm of an Al—Si alloy containing 8.5% silicon was used.
Spray plated. Further, about 15 μ of pure aluminum having a (Fe + Si) content of 0.5% or less was spray-plated on the upper layer. The plated steel sheet was subjected to cylindrical drawing at a working ratio of 1.8 and the surface after processing was observed. No crack was found on the surface of the steel sheet after processing corresponding to the punch corner R portion (R = 3.0) and the die corner R portion (R = 4.0), and it had extremely excellent workability. In addition, as a result of the atmospheric exposure test of the steel sheet before processing, almost no surface discoloration occurred, and the weight change due to corrosion was 1 / th that of the conventional material.
It was about 2 to 1/3.

Comparative Example 1 A thin steel plate having a plate thickness of 0.8 mm was annealed in a nitrogen atmosphere containing 8% hydrogen, immersed in an aluminum plating bath containing 9.5% silicon, and then lifted from the bath to remove excess Al by a gas wiping method. The -Si alloy was wiped off, and the adhesion amount was adjusted to a plating thickness of 20μ. This plating bath contained 1.9% iron eluted from the steel sheet due to a long-time plating operation.
When this plated steel sheet was subjected to Ot bending, and many cracks were found in the bent portion, it was subjected to a humidity tank test,
The cracked portion was covered with red rust and was of little practicality.

Comparative Example 2 An Al-Si alloy (Si8.5%) containing no iron was plated by 20 μm by a vacuum deposition method. Even when the plated steel sheet was heated at 450 ° C. for 30 minutes and then subjected to Ot bending, no surface cracks were generated in the bent portion, and the workability was extremely excellent. When an air exposure test was conducted, surface discoloration was likely to occur, and the weight change due to corrosion was inferior to that of pure aluminum-plated steel sheet by 2 to 3 times.

Comparative Example 3 A thin steel plate having a thickness of 0.8 mm was annealed in a nitrogen atmosphere containing 8% hydrogen, immersed in a pure aluminum plating bath, and then lifted up from the bath to wipe excess aluminum by a gas wiping method to obtain 20 μm. The adhesion amount was adjusted to the plating thickness. This plating bath contained 2.5% of iron eluted from the steel sheet due to long-term plating work. The plated steel sheet was subjected to cylindrical drawing at a working ratio of 1.8, and the surface after processing was observed. Swelling occurred on the surface of the steel sheet after processing corresponding to the punch corner R portion (R = 3.0) and the die corner R portion (R = 4.0), and the plating film easily peeled off in the tape test.

[0017]

As described above in detail, the plated steel sheet of the present invention is an excellent aluminum-plated steel sheet having both unprecedented workability and corrosion resistance, and requires severe workability and long-term weather resistance. It is used as the most suitable product for the intended use and the use requiring excellent heat resistance.

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Claims (2)

[Claims] 1. An aluminum-plated steel sheet, characterized in that one or both surfaces of the steel sheet are provided with an aluminum-plated layer having a composition in which the amount of Si gradually decreases and the amount of Al gradually increases from the inner layer to the outer layer. 2. An aluminum-plated steel sheet, characterized in that one or both surfaces of the steel sheet are provided with an aluminum-plated layer having a composition in which the amounts of Si and Fe gradually decrease and the amount of Al gradually increases from the inner layer to the outer layer.