KR20150049991A - HOT DIP Al PLATED STEEL SHEET HAVING EXCELLENT SURFACE APPEARANCE AND HEAT RESISTANCE AND METHOD FOR MANUFACTURING THE SAME - Google Patents

Abstract

Disclosed are a hot-dip aluminum-plated steel sheet having excellent surface appearance and heat resistance and a manufacturing method thereof. According to one aspect of the present invention, the hot-dip aluminum-plated steel sheet having excellent surface appearance and heat resistance comprises a matrix steel sheet and a hot-dip aluminum-plated layer. The hot-dip aluminum-plated layer comprises: 5-15 wt% of silicon (Si); 1-3 wt% of iron (Fe); at least one among groups formed of 0.1-2.0 wt% of magnesium (Mg); 0.05-0.5 wt% of chrome (Cr); 0.1-1.0 wt% of titanium (Ti); and the rest being aluminum (Al) and inevitable impurities. The mean size of the spangles formed on the hot-dip aluminum-plated layer is 1.0 mm or less.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot dip galvanized steel sheet having excellent surface appearance and heat resistance,

The present invention relates to a molten aluminum plated steel sheet excellent in surface appearance and heat resistance widely used in boilers, heat exchangers, fireplaces, and the like, and a method of manufacturing the same.

Aluminum-plated steel sheet is made of cold-rolled steel sheet coated with aluminum-silicon alloy. It is made of an intermetallic compound which is a reaction product of aluminum plating layer and base iron and aluminum. It has excellent corrosion resistance of aluminum, , Oxidation resistance and heat reflectivity are also known to be far superior to those of galvanized steel sheets.

Therefore, it is widely used in general kitchen materials, kitchen appliances, boiler parts, heat exchangers, fireplaces, etc., which are used at a relatively high temperature. The aluminum-plated steel sheet is not easily corroded even at a high temperature due to the stable oxide film formed on the surface of the plating layer, and because of its low specific gravity, it exhibits a plating layer thickness three times closer to that of zinc even in the same plating amount.

In order to coat aluminum, various manufacturing methods are used depending on the application. However, hot dip galvanizing is mainly used as a manufacturing method for coating aluminum on the surface of a steel sheet in a large amount.

Continuous hot dip galvanizing can obtain the strength of a desired material by subjecting the cold-rolled steel sheet to a heat treatment at an elevated temperature for recrystallization in an annealing furnace in a reducing atmosphere. In addition, aluminum is plated on a large number of steel sheets continuously under the condition that the temperature of the steel sheet is similar to the temperature of the plating bath, thereby making it possible to mass-produce coated steel sheets having both corrosion resistance and strength. Such a hot-dip galvanized steel sheet undergoes a fine surface reduction and chemical treatment in order to impart uniform smoothness to the surface of the hot-dip coated steel sheet and to further improve the corrosion resistance.

However, since the above-described plating process proceeds in a plating bath maintained at about 660 ° C and the aluminum plating bath contains about 9 to 10% of silicon, the properties of the plating layer are significantly influenced by the plating process . Because aluminum and silicon, which are the main components of the plating bath component, form a process structure at a weight ratio of silicon at 577 ° C of 12.6%, the plating layer shows the aluminum single phase solidified structure and the process structure of aluminum silicon according to the cooling method after plating. Such a deviation of the solidification structure macroscopically shows a polygonal pattern on the surface of the plated steel sheet, and shows a deviation of the color of each part, thereby causing a problem that an excellent surface appearance can not be obtained.

In order to solve the above-mentioned problem, in Patent Document 1, aluminum powder having a particle size of 1 to 20 탆 is sprayed on the surface of the coated steel sheet before the aluminum in the plating layer formed by the hot-dip aluminum coating process is coagulated, To control the sequins on the surface of the plating layer and to produce an aluminum-plated steel sheet having an excellent surface appearance. However, if the spray amount of aluminum powder is excessive, the sprayed aluminum powder can not be effectively recovered and is released into the air, causing environmental pollution, and sticking to peripheral facilities, resulting in deteriorated workability.

Korean Patent Registration No. 10-0270083

One aspect of the present invention is to provide a molten aluminum-plated steel sheet having excellent surface appearance and heat resistance, which is produced by using a molten aluminum plating bath, and a method for producing the same.

In order to achieve the above object, a molten aluminum-plated steel sheet according to an embodiment of the present invention includes a base steel sheet and a molten aluminum plating layer, wherein the molten aluminum plating layer contains silicon (Si) 0.1 to 1.0% of titanium (Ti), the balance aluminum (Al) and inevitable impurities, and the average particle size of the sequins on the surface of the molten aluminum plating layer is 1.0 mm or less.

A method for manufacturing a molten aluminum-plated steel sheet according to an embodiment of the present invention comprises: 5 to 15% of silicon (Si), 0.1 to 1.0% of titanium (Ti), and the balance aluminum (Al) and unavoidable impurities Preparing a molten aluminum plating bath containing the molten aluminum plating bath; Immersing the base steel sheet in the molten aluminum plating bath and performing plating to produce a plated steel sheet; And gas wiping and cooling the coated steel sheet.

In addition, the solution of the above-mentioned problems does not list all the features of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS The various features and advantages and effects of the present invention will become more fully understood with reference to the following specific embodiments.

According to an embodiment of the present invention, the average grain size of the sequins on the surface of the plating layer is 1.0 mm or less, and the surface appearance is excellent, and the growth of the Fe-Al intermetallic compound formed at the interface between the base steel sheet and the plating layer is slowed And a Fe-Al-Si-Ti intermetallic compound is formed, whereby a hot-dip coated steel sheet having excellent heat resistance can be provided.

The inventors of the present invention, while studying to solve the problems of the above-described prior arts, have succeeded in finely adding a small amount of Ti to a molten aluminum plating bath, thereby finishing the spangle on the surface of the plating layer to secure an excellent surface appearance of the coated steel sheet It is understood that the heat resistance of the coated steel sheet can be improved by slowing the growth of the Fe-Al-based intermetallic compound formed at the interface between the base steel sheet and the plated layer and forming the Fe-Al-Si-Ti based intermetallic compound And the present invention has been proposed.

Hereinafter, the present invention will be described in detail.

First, the molten aluminum plating bath used in the present invention will be described in detail.

The molten zinc alloy plating bath used in the present invention may contain silicon (Si) in an amount of 5 to 15%, titanium (Ti) in an amount of 0.1 to 1.0%, aluminum (Al) and unavoidable impurities.

Among the components in the molten zinc alloy plating bath, Si suppresses the growth of the Fe-Al intermetallic compound generated at the interface between the base steel sheet and the plating layer to improve the heat resistance of the coated steel sheet and improve the fluidity of the plating bath in the plating bath, It is an element that improves the quality. In order to exhibit such an effect in the present invention, it is preferable that the Si content is 5 wt% or more. On the other hand, when the content of Si is more than 15% by weight, Si segregation in the plating layer becomes serious, and a high-output post-plating cooling treatment is required to obtain a fine structure, and the color of the coated steel sheet becomes dark. Therefore, the Si content is preferably controlled to 5 to 15% by weight, and more preferably 6 to 12% by weight.

The Ti added together with the Si functions as a solidification nuclei in the plating layer to cause mutual interference between crystal boundaries of the sequins generated during cooling of the steel sheet to miniaturize the sequins, thereby improving the surface appearance of the coated steel sheet. Further, the Fe-Al-Si-Ti intermetallic compound is formed at the interface between the base steel sheet and the plated layer to prevent diffusion of Fe into the plated layer, thereby improving the heat resistance of the plated steel sheet. In order to exhibit such an effect in the present invention, it is preferable that the Ti content is 0.1 wt% or more. On the other hand, if the Ti content exceeds 1.0% by weight, the effect of improving the surface appearance and heat resistance is saturated, and the melting point is increased, so that the ingot is difficult to dissolve and the problem of the occurrence of the dross have. Therefore, the Ti content is preferably controlled to 0.1 to 1.0 wt%.

According to an embodiment of the present invention, one or more selected from the group consisting of Mg: 0.1 to 2.0% and Cr: 0.05 to 0.5% may be further included. The Mg and Cr serve to improve the corrosion resistance of the coated steel sheet by forming a dense passive oxidation film on the surface of the plating layer to prevent diffusion of oxygen into the plating layer.

Meanwhile, according to one embodiment of the present invention, the content of Fe in the plating bath is preferably controlled to 1 to 3 wt%. If the Fe content is less than 1% by weight, there is a problem that Fe is precipitated from various metal structures in the plating bath to cause erosion. On the other hand, when the Fe content exceeds 3% by weight, There is a problem in which the occurrence is rapidly increasing.

The remainder aluminum (Al) and unavoidable impurities. Addition of an effective component other than the above-mentioned composition is not excluded.

Hereinafter, a molten aluminum-plated steel sheet excellent in surface appearance and heat resistance, which is one aspect of the present invention, will be described in detail.

The molten aluminum plated steel sheet excellent in surface appearance and heat resistance, which is one aspect of the present invention, comprises a base steel sheet and a molten aluminum plated layer, wherein the molten aluminum plated layer contains 5 to 15% of silicon (Si) : 0.1 to 1.0%, the balance aluminum (Al) and unavoidable impurities.

Meanwhile, according to one embodiment of the present invention, the average particle size of the sequins on the surface of the molten aluminum plating layer has a value of 1.0 mm or less on average, and shows a beautiful surface appearance.

According to an embodiment of the present invention, the molten aluminum plated layer may be deposited with a plating amount of 10 to 500 g / m ² based on one side. When the plating amount is less than 10 g / m ² on the basis of one side, it is difficult to expect the effect of improving heat resistance and corrosion resistance. On the other hand, when the plating amount is more than 500 g / m ² on one side, it is disadvantageous from the economical point of view.

On the other hand, in general, in the hot-dip plating process, since skin pass is performed after plating, it is general to give an appropriate roughness (Ra) to the surface of the steel sheet. The surface roughness of the steel sheet needs to be managed as an important factor that affects the workability at the time of press forming and the post-coat post-coatability. For this purpose, the roughness of the roll can be transferred to the steel sheet by rough rolling using a roll having an appropriate surface roughness, so that the surface of the steel sheet can be illuminated.

If the surface of the plating layer formed after plating is roughened, the roughness of the roll during temper rolling becomes difficult to be uniformly transferred to the steel sheet, and the surface roughness after temper rolling is unevenly formed. That is, as the surface of the plating layer is not rough, the roughness of the roll during temper rolling tends to be uniformly transferred to the steel sheet, so it is desirable to reduce the roughness of the plating layer before temper rolling. Therefore, according to one embodiment of the present invention, it is preferable that the surface roughness (Ra) of the molten aluminum-plated steel sheet is controlled to be 1 占 퐉 or less.

Hereinafter, a method of manufacturing a molten aluminum-plated steel sheet excellent in surface appearance and heat resistance, which is another aspect of the present invention, will be described in detail.

A method of manufacturing a molten aluminum-plated steel sheet excellent in surface appearance and heat resistance, which is another aspect of the present invention, comprises the steps of: preparing a molten aluminum plating bath having the above composition; Immersing the base steel sheet in the molten aluminum plating bath and performing plating to produce a plated steel sheet; And gas wiping and cooling the coated steel sheet.

According to an embodiment of the present invention, the bath temperature of the molten aluminum plating bath may be 630 to 680 캜. When the bath temperature is lower than 630 DEG C, the flowability of the plating solution in the plating bath is lowered. On the other hand, when the bath temperature is higher than 680 DEG C, Fe precipitates from various metal structures in the plating bath, There is a problem in which the occurrence is rapidly increasing.

After completion of the plating, the deposition amount of the plating can be controlled by gas wiping the steel sheet having the plating layer formed thereon. The gas wiping is for adjusting the plating adhesion amount, and the method is not particularly limited.

According to an embodiment of the present invention, air or nitrogen may be used for the gas wiping, and nitrogen is more preferably used. This is because, when air is used, there is a problem that surface defects due to aluminum oxide occur in the post material plating.

According to an embodiment of the present invention, after the plating amount of the plating layer is adjusted by the gas wiping, the coated steel sheet may be cooled at a rate of 20 to 60 ° C / sec.

When the cooling rate is lower than 20 캜 / sec, the Fe-Al intermetallic compound is excessively generated at the interface between the base steel sheet and the plated layer, resulting in deterioration of the processability of the coated steel sheet. On the other hand, There is a problem that a defective surface appearance may occur due to excess cooling air injection amount.

As the cooling method during cooling, a usual cooling method that can cool the plating layer can be used. For example, cooling can be performed by using an air jet cooler, atomizing N ₂ wiping, water fog, or the like.

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

( Example  One)

In order to measure the size of the sequins in the aluminum plating layer due to addition of alloying elements in the plating bath, a plating bath having the composition shown in the following Table 1 was prepared, and a low-carbon cold-rolled steel sheet having a thickness of 1.2 mm, a width of 100 mm, , The base steel sheet was immersed in acetone and ultrasonically cleaned to remove foreign substances such as rolling oil present on the surface.

Before plating, all specimens were subjected to a reducing atmosphere heat treatment at 800 ° C in order to secure the mechanical properties of the steel sheet at the general hot dip galvanizing site.

The plating conditions after the heat treatment were all treated in the same manner, and the plating bath temperature was kept constant at 600 ° C.

After completion of the plating, the coating amount was adjusted to 60 g / m ² using N ₂ gas wiping, and the coating was cooled to a temperature of 200 캜 at a rate of 40 캜 / sec.

Thereafter, the average particle size of the sequins in the plating layer was measured, and the results are shown in Table 1 below. The average particle size of the sequins was measured by using an optical microscope to simulate the crystal grain size of the material (KS-D-0205).

division
Plating bath alloy composition (% by weight) Average particle size of sequins
(mm)
Si Fe Ti Mg Conventional example 9 2 - - 8.5 Comparative Example 1 9 2 0.01 - 8.5 Comparative Example 2 9 2 0.03 - 8.0 Comparative Example 3 9 2 0.05 - 6.0 Inventory 1 9 2 0.1 - 0.8 Inventory 2 9 2 0.3 - 0.5 Inventory 3 9 2 0.3 2 0.5

As shown in Table 1, Examples 1 to 3 satisfying the composition range of Ti of the present invention all exhibited excellent surface appearance with an average particle diameter of the sequins observed on the surface of the coating layer of 1.0 mm or less.

On the other hand, the conventional examples and Comparative Examples 1 to 3 did not contain Ti, or the content thereof was insufficient, and the average particle size of the sequins was out of the range controlled by the present invention, and the surface appearance was poor.

( Example  2)

In order to evaluate the effect on the corrosion resistance and the heat resistance of the coated steel sheet by the addition of the alloying element in the molten aluminum plated layer, the specimen having the composition of Example 1 was subjected to a salt spray test and heat resistance evaluation at 400 ° C, Respectively. Specific test methods and evaluation criteria are as follows.

1. Evaluation of corrosion resistance

Each plating material was subjected to a corrosion promotion test using a salt water spray test (salt spray standard test according to KS-C-0223), and the time elapsed until the area of the generated red rust became 5% on the surface of the plating layer was measured.

◎: When exceeding 1500 hours

○: 500 to 1500 hours.

?: 200 to 500 hours.

X: less than 200 hours.

2. Evaluation of heat resistance

Each of the plating materials was heated to 400 DEG C and held for 24 hours to visually evaluate the degree of discoloration of the surface.

◎: Very good,

Good: Excellent,

?: Usually,

X: Bad

division Heat resistance Corrosion resistance Conventional example △ △ Comparative Example 1 △ △ Comparative Example 2 △ △ Comparative Example 3 △ △ Inventory 1 ○ ○ Inventory 2 ◎ ○ Inventory 3 ◎ ◎

As shown in Table 2, Examples 1 to 3 satisfying the composition range of Ti of the present invention all exhibited excellent heat resistance after heating to 400 占 폚 and good surface discoloration when held for 24 hours. In Examples 1 to 3, corrosion resistance test was also performed after the corrosion accelerated test was performed by the salt spray test, and the elapsed time from the surface of the plating layer to the reduction area of 5% was 500 hours or more. Particularly, in the case of Inventive Example 3, corrosion resistance was improved by Mg addition, which is an element for improving corrosion resistance.

On the other hand, the conventional example and the comparative examples 1 to 3 do not contain Ti, or the content thereof is insufficient, and the heat resistance and the corrosion resistance are shown to be excellent.

Claims (9)

A base steel sheet and a molten aluminum plated layer,
Wherein the molten aluminum plating layer contains 5 to 15% of silicon (Si), 0.1 to 1.0% of titanium (Ti), the balance aluminum (Al) and unavoidable impurities,
Wherein the average particle diameter of the sequins on the surface of the molten aluminum plated layer is 1.0 mm or less.
The method according to claim 1,
Wherein the molten aluminum plated layer contains at least one selected from the group consisting of magnesium (Mg): 0.1 to 2.0% and chromium (Cr): 0.05 to 0.5% in weight% .
3. The method according to claim 1 or 2,
Wherein the molten aluminum plated layer has a surface appearance of 10 to 500 g / m < ² > and an excellent heat resistance.
3. The method according to claim 1 or 2,
The surface of the molten aluminum-plated steel sheet has a surface roughness (Ra) of 1 탆 or less and excellent in surface appearance and heat resistance.
Preparing a molten aluminum plating bath containing 5 to 15% of silicon (Si), 0.1 to 1.0% of titanium (Ti), aluminum (Al) and unavoidable impurities in terms of% by weight;
Immersing the base steel sheet in the molten aluminum plating bath and performing plating to produce a plated steel sheet; And
And a step of wiping and cooling the coated steel sheet by gas, and cooling the coated steel sheet.
6. The method of claim 5,
Wherein the molten aluminum plating bath is a molten aluminum plating bath having a surface appearance and excellent heat resistance, further comprising at least one member selected from the group consisting of magnesium (Mg): 0.1 to 2.0% and chromium (Cr): 0.05 to 0.5% A method of manufacturing a steel sheet.
The method according to claim 5 or 6,
Wherein the molten aluminum plating bath is further provided with 1 to 3% of iron (Fe) by weight, and the surface appearance and heat resistance of the steel plate are excellent.
The method according to claim 5 or 6,
Wherein the bath temperature of the molten aluminum plating bath is 630 to 680 DEG C, and the surface appearance and heat resistance of the steel plate are excellent.
The method according to claim 5 or 6,
Wherein the gas used for the gas wiping is nitrogen (N ₂ ), and the surface appearance and heat resistance of the steel plate are excellent.