KR101560934B1 - GI Steel Plate Having Excellent Surface Smoothness and Method for preparing the Same, and Solution of Zn melts for the GI Steel Plate - Google Patents

Abstract

The present invention relates to a hot-dip zinc alloy plating solution which can obtain a plated steel sheet excellent in surface smoothness of a plating layer in hot-dip zinc-containing alloy plating containing Mg, comprising: 1-4 wt% Mg; Be 0.001-0.01 wt%; And 0.001-1% by weight of In, 0.001-1% by weight of Ga, 0.1-10% by weight of Sn, or a mixture of two or more thereof, and the balance of Zn and unavoidable impurities, And a plating layer formed by the plating solution, and a method of manufacturing the same.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a Zn-Al-Mg high corrosion resistant plating composition having excellent surface smoothness, a plated steel sheet plated using the above-mentioned plating composition, and a method for preparing the same. the GI Steel Plate}

The present invention relates to a coated steel sheet having improved smoothness of the surface of a plating layer in Zn-Al-Mg steel sheet having high corrosion resistance, a method for producing the same, and a galvanized zinc bath for use therein.

The fusion-bonded gold-plated steel sheet of Zn-Al-Mg has high corrosion resistance and is used in the manufacture of steel sheets requiring high corrosion resistance. However, the fused gold plating having such a composition has a problem that surface defects such as a hair line are formed during the solidification process of the plating layer, so that a smooth plating layer can not be obtained, thereby deteriorating the plating quality.

Such defects on the surface of the plating layer are caused by the growth of magnesium oxide due to the oxidation of magnesium contained in the plating liquid during solidification and the deterioration of the fluidity of the plating liquid. The plating solution adhering to the surface of the steel sheet is solidified to form a plating layer on the surface of the steel sheet. At this time, the magnesium in the plating solution is exposed to the atmosphere containing oxygen to grow thick magnesium oxide on the surface of the steel sheet, thereby deteriorating the smoothness of the plating layer do.

In addition, due to the characteristics of the ternary plated steel sheet, the solidification of the plated layer ends at a low temperature of about 340 캜, and is gradually drawn out from the plating tank of about 450 캜. The flowability of the plating layer becomes uneven as the temperature is lowered. Therefore, the plating solution is locally concentrated due to the lowering of the fluidity of the plating solution on the surface of the steel sheet during solidification, thereby hindering the smoothness of the plating layer. For this reason, it is not easy to form a plated layer having a smooth surface on the Zn-Al-Mg fused-alloy coated steel sheet.

In order to prevent the surface smoothness of the plating layer from deteriorating, it is necessary to prevent the oxidation of magnesium and ensure the uniform fluidity of the plating liquid at the time of solidification. Japanese Laid-Open Patent Publication No. 1999-140615 and International Patent Publication No. WO2010-130890 disclose a technique for improving the surface smoothness of such a plating layer.

The technique disclosed in these patent documents includes a configuration in which a sealing box is provided on the plating port to wipe and solidify the hot-dip coating layer adhered to the surface of the steel sheet drawn out from the plating port in the sealing box. That is, by performing wiping and solidification of the molten molten amount in a state where the oxygen concentration is minimized, formation of an oxide film of magnesium or the like on the surface of the plating layer is suppressed.

However, in the hot dip galvanizing process, the coating amount adjustment device of the plating port is often a part where the operator approaches and operates the knife lip cleaning and observation of the work situation for controlling the deposition amount. The surface smoothness of the plating layer can be improved by suppressing the oxidation of Mg by the above-mentioned method. However, since the deposition amount adjusting apparatus is located in the closed box, the worker can not access the apparatus and the operation becomes inconvenient. It is difficult to take measures, which may cause additional defects.

Zn-Al-Mg In the manufacture of a gold-plated steel sheet, magnesium oxide film is formed on the surface of the plating layer during the solidification process of the plating layer, thereby causing wrinkle-like defects such as hairline.

Accordingly, it is an object of the present invention to provide a hot-dip coating solution for obtaining a plated steel sheet excellent in surface smoothness of a plating layer in hot-dip galvanneal plating containing Mg.

Furthermore, the present invention is intended to provide a coated steel sheet comprising a plating layer formed by the plating solution and a method of manufacturing the same.

The present invention provides a hot-dip zinc alloy plating solution capable of obtaining a plated steel sheet excellent in surface smoothness, wherein the plating solution of the present invention comprises 1 to 4% by weight of Al; 1-4 wt% Mg; Be 0.001% by weight or more and less than 0.01% by weight; And 0.001-1% by weight of In, 0.001-1% by weight of Ga, 0.1-10% by weight of Sn or a mixture of two or more thereof, and the balance Zn and inevitable impurities.

According to an embodiment of the present invention, there is provided a method for manufacturing a high-corrosion-resisting hot-dip galvanized steel sheet, ; 1-4 wt% Mg; Be 0.001% by weight or more and less than 0.01% by weight; 0.001-1 wt% of In, 0.001-1 wt% of Ga, 0.1-10 wt% of Sn, or a mixture of two or more thereof; And the remainder Zn and inevitable impurities, a step of immersing the steel sheet in a plating bath containing a molten zinc alloy plating solution, the step of depositing a molten plating solution on the surface of the steel sheet, the step of regulating the amount of coating adhesion by gas wiping the steel sheet with the plating solution And cooling the steel sheet whose plating deposition amount is adjusted to solidify the plating solution to form a plating layer. The present invention also provides a method of manufacturing a hot-dip galvanized steel sheet.

Preferably, the gas wiping is performed using nitrogen gas containing 1% or less of oxygen in the air.

The plating adhesion amount may be in the range of 30 to 300 g / m 2 on the basis of one side of the steel sheet.

Further, the cooling can cool the steel sheet to 340 to 420 DEG C at a cooling rate of 5 to 10 DEG C / sec.

The present invention also provides a hot-dip galvanized hot-dip galvanized steel sheet excellent in surface smoothness, which comprises a Zn-Mg-Zn alloy hot-dip galvanized layer on one side or both sides of a steel sheet, ; 1-4 wt% Mg; Be 0.001% by weight or more and less than 0.01% by weight; And a hot-dip galvanized steel sheet comprising 0.001 to 1 wt% of In, 0.001 to 1 wt% of Ga, 0.1 to 10 wt% of Sn, or a mixture of two or more thereof and having a residual Zn and inevitable impurities, to provide.

According to the present invention, formation of an oxide film due to oxidation of magnesium or the like on the surface of a plating layer on a steel sheet can be minimized, smoothness of the plating surface can be improved, and surface defects such as unplated can be prevented.

Further, the flow of the plating liquid can be improved at the time of solidification of the molten molten amount, and it is possible to suppress the occurrence of wrinkle-like surface defects on the surface of the plating layer.

The present invention relates to a method for manufacturing a hot dip galvanized steel sheet, which comprises magnesium in a plating solution for imparting high corrosion resistance to a steel sheet, characterized in that the magnesium oxide film is grown on the surface of the plating layer due to high- Surface defects in the form of wrinkles on the surface of the plating layer due to deterioration are solved by improving the characteristics of the plating liquid.

The molten zinc alloy plating solution of the present invention contains Al, Mg, and Zn as a plating composition, and includes In, Ga, and Sn to improve the surface smoothness of the plating layer formed by the molten plating solution having the above composition. Hereinafter, the molten zinc alloy plating bath of the present invention will be described in detail, but includes zinc and inevitable impurities as the remainder in addition to the components described below.

As a component contained in the molten zinc alloy plating bath of the present invention, Al is added to improve the corrosion resistance of the plating layer and to inhibit the generation of dross on the surface layer of the plating bath due to the oxidation of magnesium, To 1% by weight of the total weight of the plating solution. When the content of Al is less than 1% by weight, the effect of improving the corrosion resistance is not sufficient and the effect of preventing magnesium oxidation in the surface layer of the plating bath is insufficient. On the other hand, when the content of Al exceeds 4% by weight, the iron elution of the base steel sheet is increased, and the weldability and the phosphate treatment property of the plating layer may be lowered. Do.

The plating bath of the present invention contains 1-4 wt% of Mg. When the content of Mg is less than 1% by weight, the effect of improving the corrosion resistance is not sufficient. When the content of Mg is more than 4% by weight, the magnesium is oxidized, It is difficult to manage the plating bath. Therefore, Mg is preferably contained in an amount of 1 to 4% by weight

The plating bath of the present invention includes Be. The Be is for inhibiting the magnesium oxide coating from growing on the surface of the plating layer due to oxidation of magnesium, and is preferably contained in an amount of 0.001 wt% or more. When the content of Be is less than 0.001% by weight, the effect of suppressing excessive oxidation of magnesium on the surface of the plating layer to be obtained by adding Be is not sufficient.

On the other hand, it is preferable that Be does not contain 0.01 wt% or more. When Be is contained in an amount of 0.01% by weight or more, unplating may occur, which may indicate a plating defect. The specific cause of the occurrence of such unplating is not clearly understood. However, in the case of a high-tensile steel sheet containing a large amount of components that inhibit plating ability such as Si, unplating may occur.

In addition, the plating bath of the present invention may contain In, Ga, or Sn. These added components improve the fluidity of the plating bath so as to spread uniformly on the surface of the steel sheet during solidification, thereby providing an effect of reducing the curvature of the plating layer.

As the added amount of the additive components increases, the effect is improved. However, In, Ga and Sn are expensive components, and the economical efficiency is decreased when the added amount is increased. Therefore, it is more preferable to add the additive components of In, Ga, and Sn in the range of 0.001-1 wt% of In, 0.001-1 wt% of Ga, and 0.1-10 wt% of Sn, respectively, in consideration of bendability improvement and economical efficiency. At this time, one of them may be added singly or two or more of them may be added in combination.

As described above, the addition of Be, In, Ga and Sn to the molten alloy of Zn-Al-Mg also suppresses the growth of the oxide film due to the oxidation of magnesium on the surface of the plating layer, It is possible to improve the fluidity of the plating liquid, and it is possible to suppress the generation of surface defects such as hair lines or wrinkles on the surface of the plating layer at the time of solidification. As a result, a Zn-Al-Mg alloy hot-dip galvanized steel sheet excellent in surface smoothness can be obtained.

By plating the steel sheet in the hot-dip galvanizing bath of the present invention as described above and pulling out the steel sheet, a plating layer having excellent smoothness can be formed on the surface of the steel sheet. At this time, gas wiping is performed using N ₂ gas on the steel sheet drawn out from the plating bath to control the coating amount of plating. At this time, the amount of plating adhered can be appropriately performed as required, and is not particularly limited. For example, the amount adhered to one side of the steel sheet may be in the range of 30 to 300 g / m 2.

The gas used for performing the gas wiping is preferably nitrogen. At this time, when the nitrogen gas contains oxygen, magnesium is preferentially oxidized on the surface of the plating layer, and fine surface defects such as a hair line can be generated on the surface of the plating layer along the moving direction of the gas. Do. And preferably 1% or less. For example, a nitrogen gas containing not more than 0.5% of oxygen is more preferable.

The plating layer may be formed by adjusting the plating amount by the above-described method, and then cooling the steel sheet to solidify the molten amount. The cooling of the plating layer can be performed by a conventional method, and is not particularly limited. For example, an air cooling method in which air is cooled can be applied. It is preferable that the cooling is performed from immediately after the gas wiping to the end of solidification, and the cooling is performed by spraying air.

At this time, the cooling rate of the steel sheet is preferably set in the range of 5-20 DEG C / sec. In the case of cooling at a rate lower than 5 deg. C / sec, the crystal structure of the plating layer becomes coarse, and it is preferable to cool at a rate of 5 deg. C / sec or more. The upper limit of the cooling rate can be appropriately adjusted, and is not particularly limited, but it is preferably carried out at a cooling rate of 20 DEG C / sec or less.

According to the present invention, it is possible to suppress the growth of the oxide film due to the oxidation of magnesium on the surface of the plating layer by using the molten plating solution containing magnesium on the surface of the steel sheet, The fluidity of the plating liquid can be ensured, and the smoothness of the plating surface can be enhanced.

Further, it is not necessary to perform the gas in a low-oxygen atmosphere which does not substantially contain oxygen as a gas used in the gasification and solidification process, and growth of the magnesium oxide film on the surface of the plating layer can be suppressed even if a certain level of oxygen is contained.

Example

Hereinafter, the present invention will be described in more detail with reference to examples. However, the following embodiments are illustrative of the present invention and are not intended to limit the present invention.

Comparative Example  1 to 6

After removing contaminants on the surface of a normal cold-rolled steel sheet having a thickness of 0.8 mm, the steel sheet was heated to a temperature of 820 ° C under a reducing atmosphere of N ₂ + H _{2 with} a hydrogen concentration of 10%, and then cooled to 460 ° C.

The steel sheet was immersed in a plating port having a temperature of 450 DEG C and containing a plating solution having the composition shown in Table 1 to adhere the plating solution to the surface of the steel sheet, By using a nitrogen gas having an oxygen concentration of 50 g / m < 2 >. Thereafter, the steel sheet was cooled at 350 DEG C at a cooling rate of 10 DEG C / sec to solidify the plated layer to produce a plated steel sheet.

The degree of surface bending of the plated steel sheet was observed and evaluated, and the corrosion resistance of the plated steel sheet was measured by a brine fraction test. The results are shown in Table 1.

At this time, the degree of surface bending was evaluated by evaluating the degree of the presence of the surface bending when the surface of the steel plate was touched with the hand, and when the surface smoothness was bad due to the touch, And a case in which the degree of tactile sensation was weak was denoted by DELTA, and a case in which the presence of surface curvature was not felt and the surface smoothness was excellent was evaluated as?.

The corrosion resistance evaluation was carried out by a salt spray test (SST, 5% NaCl atmosphere, 35 ° C, pH 6.5 to 7.2) in which 5% salt water was sprayed. The spraying time taken until the redness occurred by such a salt spray test was measured and recorded.

Comparative Example
No. Plating bath composition (% by weight) Wiping gas
Oxygen concentration (%) surface
Smoothness Corrosion resistance
(Hr) Al Mg Be Ga In Sn One 0.9 1.2 0.002 0.2 0 0 0.01 ○ 124 2 1.2 0.8 0.008 0 0.5 0 0.01 ○ 96 3 5 5 0.004 0 0.02 0 0.01 × 1200 4 4 4 0.01 0 0 0.9 0.9 △ 96 5 2.5 3 0 0.2 0.5 One 0.1 △ 480 6 3 3 0.005 0.2 0.4 8 1.2 x 480

The results of Table 1 indicate that Comparative Examples 1 and 2 had low Al or Mg concentrations and good surface curvature characteristics. However, the occurrence time of red rust was short and the corrosion resistance was insufficient.

Also, in Comparative Example 3, when the concentrations of Al and Mg were high, droplet-shaped particles adhered to the surface of the steel sheet and the surface was very rough.

In Comparative Example 4, when the amount of Be added was large, the surface of the plated steel sheet had a flat appearance without bending, but a small spot-uncoated region was present. Due to such unplating, the red rust in the salt spray test occurred at this part quickly.

On the other hand, in Comparative Example 5, a very thin hair-like wrinkle was formed on the surface when Be was not added. This is presumably because the plating layer is non-uniformly excessively oxidized when wiped by oxygen in the wiping gas.

In Comparative Example 6, a wiping gas having a high oxygen concentration was used. Although the plating solution contained Be, severe bending occurred in the width direction on the surface of the coated steel sheet, resulting in poor surface smoothness.

Example  1 to 5

After removing contaminants on the surface of a normal cold-rolled steel sheet having a thickness of 0.8 mm, the steel sheet was heated to a temperature of 820 ° C under a reducing atmosphere of N ₂ + H _{2 with} a hydrogen concentration of 10%, and then cooled to 460 ° C.

The steel sheet was immersed in a plating pot having a temperature of 450 DEG C and containing a plating solution having the composition shown in Table 2, and a plating solution was attached to the surface of the steel sheet. Next, the steel sheet from the above-mentioned plating port was gas-wiped with air using a nitrogen gas having an oxygen concentration as shown in Table 2 in the air to adjust the adhesion amount of the plating solution adhering to the surface of the steel sheet to 50 g / m 2. Thereafter, the steel sheet was cooled at 350 DEG C at a cooling rate of 10 DEG C / sec to solidify the plated layer to produce a plated steel sheet.

The degree of surface bending of the plated steel sheet was observed and evaluated, and the corrosion resistance of the plated steel sheet was measured by a brine fraction test. The results are shown in Table 1.

At this time, the degree of surface bending was evaluated by evaluating the degree of the presence of the surface bending when the surface of the steel plate was touched with the hand, and the evaluation criteria were as follows.

X: Feeling is clearly felt by the touch, and the surface smoothness is poor

?: The presence of surface curvature is felt, but the degree of tactile sensation is weak

○: When the surface smoothness can not be felt and surface smoothness is excellent

The corrosion resistance evaluation was carried out by a salt spray test (SST, 5% NaCl atmosphere, 35 ° C, pH 6.5 to 7.2) in which 5% salt water was sprayed. The spraying time taken until the redness occurred by such a salt spray test was measured and recorded.

Example
No. Plating bath composition (% by weight) Oxygen concentration in wiping gas (%) surface
Smoothness Corrosion resistance
(Hr) Al Mg Be Ga In Sn One One One 0.002 0.2 0 0 0.01 ○ 240 2 4 4 0.008 0 0.5 0 0.01 ○ 1200 3 3 3 0.004 0 0.02 0 0.9 ○ 960 4 4 4 0.009 0 0 0.9 0.9 ○ 1200 5 2.5 3 0 0.2 0.5 One 0.01 ○ 480

As can be seen from Table 2, in Examples 1 to 5 which satisfied all the ranges of the present invention, there was a difference in corrosion resistance depending on the contents of Al and Mg, in particular, Mg content. However, It was found that red rust occurred only after that, and it was found that it had excellent corrosion resistance.

In addition, the smoothness of the surface of the plated layer showed a very smooth surface quality without bending of the surface.

Claims (6)

1-4 wt% of Al; 1-4 wt% Mg; Be 0.001% by weight or more and less than 0.01% by weight; And a mixture of 0.001-1 wt% of In, 0.001-1 wt% of Ga, and 0.1-10 wt% of Sn, and the balance of Zn and inevitable impurities.
1-4 wt% of Al; 1-4 wt% Mg; Be 0.001% by weight or more and less than 0.01% by weight; A mixture of 0.001-1% by weight of In, 0.001-1% by weight of Ga and 0.1-10% by weight of Sn; Depositing a plating solution on the surface of the steel sheet by immersing the steel sheet in a plating port including a hot-dip zinc alloy plating solution composed of the remaining Zn and inevitable impurities;
Adjusting the plating adhesion amount by gas wiping the steel sheet with the plating solution attached thereto;
Forming a plating layer by coagulating the plating solution by cooling the steel sheet whose plating deposition amount is adjusted;
Wherein the hot dip galvanized steel sheet has an excellent surface smoothness.
The method of manufacturing a hot-dip galvanized steel sheet according to claim 2, wherein the gas wiping is performed using nitrogen gas containing 1% or less of oxygen in air.
3. The method of producing a hot-dip galvanized steel sheet according to claim 2, wherein the amount of the plating is 30 to 300 g / m < 2 >
The method of manufacturing a hot-dip galvanized steel sheet according to claim 2, wherein the cooling is performed by cooling the steel sheet at 340 to 420 占 폚 at a cooling rate of 5 to 10 占 폚 / sec.
A Zn-Mg-Zn alloy hot dip galvanized layer on one side or both sides of the steel sheet,
The plating layer may contain Al in an amount of 1 to 4% by weight; 1-4 wt% Mg; Be 0.001-0.01 wt%; A mixture of 0.001-1% by weight of In, 0.001-1% by weight of Ga and 0.1-10% by weight of Sn; And the balance of Zn and unavoidable impurities.