KR20100033207A - Method for manufacturing hot-dipped aluminum coated steel sheet having improved surface appearance - Google Patents

Abstract

PURPOSE: A method for manufacturing hot-dipped aluminum plating steel plate of which surface appearance of the steel plate is improved is provided to differentiate a look of the hot-dipped aluminum plating steel plate by cooling and spraying metal powder on the surface of a plated steel plate with the air. CONSTITUTION: A method for manufacturing hot-dipped aluminum plating steel plate of which surface appearance of the steel plate comprises the following steps: plating a steel plate after dipping the steel plate on molten metal; spraying metal powder on the surface of the plated steel plate with the air; and cooling the steel plate. The metal powder is aluminum powder or alumina powder.

Description

Method for Manufacturing Hot-dipped Aluminum Coated Steel Sheet Having Improved Surface Appearance}

(1) immersing the plated steel sheet subjected to the continuous annealing and reducing process in a plating bath in which molten metal of Al-8 to 10wt% Si is molten and plating; (2) spraying a metal powder having a particle size of 20 to 60 µm and a water content of 0.01 to 0.30 wt% or less with air on the surface of the plated iron sheet; And (3) cooling the iron plate at a cooling rate of 40 ~ 80 ℃ / sec; relates to a method for producing a molten aluminum plated steel sheet with improved surface appearance.

Aluminum-based galvanized steel plate coated with aluminum on a base steel plate can be roughly classified into hot dipped and electrolytic depending on the manufacturing method. However, due to the characteristics of aluminum, electroplating is inferior in commercial production economics. Production by is preferred. The hot dip plating method is to immerse a base plate in an aluminum plating bath, which is a molten metal, and to coat an aluminum plating film on the surface thereof. The aluminum plating layer is thick and has excellent durability and heat resistance.

There are two types of aluminum plating baths, Type-I aluminum plated steel sheet composed of Al + 8 ~ 10wt% Si composition and Type-II aluminum plated steel sheet having Al single composition. Here, the inclusion of silicon (Si) has two major effects of suppressing the growth of the alloy layer between the plating layer and the base steel plate to improve workability and lower the temperature of the molten metal, thereby improving workability. It also has the negative effect of reducing heat and corrosion resistance. However, since most of the commercial production goes through a molding process such as bending or pressing after plating, Type-I having workability is used.

However, the plating bath composed of two or more components, such as Type-I aluminum plating, has a solid zone in which a solid and a liquid coexist, and due to the presence of the solid zone, the liquid solidifies completely into a solid. As the grain grows until it forms a pattern called sequins, the surface of the plated layer has a shiny speckle pattern to receive a low-grade image of the hot-dip galvanized steel sheet called dothan. In addition, irregularities are relatively large at the boundary between the sequins, resulting in a rough appearance of the surface, which may cause a poor appearance in the subsequent paint coating.

Therefore, in order to improve this problem, grain refinement methods have been studied. Specifically, the cooling time is faster, the passage time of the high-liquid section decreases the growth time of the grains, and the grain nucleation site is increased to increase the grain nucleation site. It's a way to use the principles that keep you from growing significantly. As a quenching method, a method of blowing a lot of air through a cooler, a method of blowing a water mist, a method of spraying zinc phosphate or ammonium phosphate solution, a method of spraying a metal powder, and the like are known. In theory, quenching results in zero spangles. In the case of wind or water mist, if quenching conditions are obtained to obtain complete zero spangles, it depends on the vibration of the iron plate or the impact of air on the surface of the plating layer. There is a problem in that the appearance quality is relatively lowered by causing a poor surface appearance.

In order to improve this problem, a method of spraying a metal powder with air or spraying zinc phosphate or ammonium phosphate solution may be applied. In this case, the cooling effect is relatively high due to the higher heat absorption capacity than the treatment with air or water alone, and the metal material itself acts as a nucleus of one grain to effectively suppress grain growth. However, when spraying the metal powder or phosphate solution, there is a problem in that the desired surface appearance cannot be obtained if the process conditions, such as the particle characteristics of the metal powder or the problem of powder storage, are not accompanied by suitable process conditions. In particular, problems such as a large increase in the production cost have been found, which resulted in a large amount of defective production in the recent high speed line of mass production equipment.

The present invention is to solve the problems of the prior art as described above and the technical problem that has been requested from the past.

Specifically, the present invention provides a method of manufacturing a molten aluminum plated steel sheet which can suppress sequin generation on the surface of a hot-dip galvanized steel sheet, enhance the appearance after coating, and provide a differentiation from the regular hot-dip galvanized steel sheet. In addition, the present invention provides a molten aluminum plated steel sheet having improved surface appearance.

In order to solve the above problems, the present inventors have conducted in-depth studies, and in the manufacture of Al-Si alloy hot-dip galvanized steel sheet, the metal powder is sprayed on the post-plating process, and the Al-Si is performed in a rapid cooling process. It was confirmed that the surface appearance was improved while suppressing the sequin pattern mainly existing on the surface of the alloy hot-dip steel sheet.

Accordingly, the present inventors, (1) the step of immersing the plated iron plate subjected to the continuous annealing and reduction process in a plating bath in which molten metal of Al-8 ~ 10wt% Si is molten; (2) spraying a metal powder having a particle size of 20 to 60 µm and a water content of 0.01 to 0.30 wt% or less with air on the surface of the plated iron sheet; And (3) cooling the iron plate at a cooling rate of 40 to 80 ° C./sec. To develop a method for manufacturing a molten aluminum plated steel sheet having an improved surface appearance.

Therefore, according to one embodiment of the present invention, (1) the step of immersing the plated iron plate subjected to the continuous annealing and reduction process in a plating bath in which molten metal of Al-8 ~ 10wt% Si is molten; (2) spraying a metal powder having a particle size of 20 to 60 µm and a water content of 0.01 to 0.30 wt% or less with air on the surface of the plated iron sheet; And (3) cooling the iron plate at a cooling rate of 40 ° C./80° C./sec. The manufacturing method of the molten aluminum plated steel sheet having improved surface appearance is provided.

In this case, the metal powder may be aluminum (Al) powder or alumina (Al ₂ O ₃ ) powder.

The air may be injected at a spray pressure of 2 ~ 10mbar.

The spraying may be performed from the spraying time point to the end point, and the spraying time may be a case where the surface temperature of the plating layer is a temperature directly above the solidification temperature of the molten metal. Preferably, the spraying time is the plating layer surface temperature of 650 ° C. It may be ~ 600 ℃, the injection end point may be that the surface temperature of the plating layer is 580 ℃ ~ 540 ℃.

In addition, the cooling in the step (3) is preferably carried out to 450 ℃ ~ 320 ℃.

In addition, after performing the step (1), the step of controlling the plating amount of the iron plate exiting the plating bath before the step (2) by the air knife may further include a step of 40 ~ 120g / m ² .

According to still another embodiment of the present invention, a molten aluminum plated steel sheet having improved surface appearance manufactured by the above-mentioned manufacturing method may be provided.

In addition, a molten aluminum plated steel sheet having an improved surface appearance having a sequin particle diameter of 0.5 mm or less on the surface of a plated steel sheet, an uneven size of 0.3 to 1.7 μm, and a coating amount of 40 to 120 g / m ² may be provided.

In particular, a molten aluminum plated steel sheet having a sequin particle diameter of 0.3 mm or less on the surface of a plated steel sheet, an uneven size of 0.3 to 1.7 μm, and a coating amount of 40 to 120 g / m ² may be provided.

The molten aluminum plating is characterized in that formed from a molten metal of Al-8 ~ 10wt% Si composition.

As discussed above, the present invention is (1) after the plating process by immersing the base steel plate subjected to the continuous annealing and reduction step in a plating bath in which a molten metal of Al-8 ~ 10wt% Si is molten, (2) the Spraying a metal powder having a particle size of 20 to 60 µm and a water content of 0.01 to 0.30 wt% or less with air on the surface of the plated iron sheet; And (3) further cooling the iron plate at a cooling rate of 40 to 80 ° C./sec, thereby providing a molten aluminum plated steel sheet having an improved surface appearance.

Advantages and features of the present invention and methods of performing the same will be understood more readily by reference to the following detailed description of the preferred embodiments and the accompanying drawings. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Method for producing a molten aluminum plated steel sheet with improved surface appearance according to an embodiment of the present invention (1) Plating the molten metal of Al-8 ~ 10wt% Si molten iron plate after the continuous annealing and reduction process Immersing in a bath and plating; (2) spraying a metal powder having a particle size of 20 to 60 µm and a water content of 0.01 to 0.30 wt% or less with air on the surface of the plated iron sheet; And (3) cooling the iron plate at a cooling rate of 40 ° C./80° C./sec. Hereinafter, in some cases, the step (1) is abbreviated as 'plating process', step (2) as 'spraying process', and step (3) as 'cooling process'.

As shown in FIG. 1, when a base steel sheet such as a low carbon steel plate to be plated is supplied in a continuous hot dip plating line, the surface layer is reduced after removing iron and oil from the surface through degreasing and heat treatment, and then the plating material metal is melted. The molten metal and the iron plate are diffused and plated from the moment when the molten metal is in contact with the iron plate by being immersed in the plating bath. Immediately after the iron plate passed through the plating bath is floated on the molten surface, the thickness of the plating layer is controlled by the air strength of the air knife, and it is solidified by forced cooling by a cooler, and then melted through a chemical treatment and a painting process. The plated steel sheet is completed.

The molten metal attached to the molten metal through the plating bath starts to cool immediately after the molten metal surface is floated. It must be completely solidified before reaching the top roll so that the plated metal does not adhere to the roll surface. There is no damage. Therefore, it is important to appropriately control the temperature up to the top roll.

In particular, in the case of a hot-dip galvanized metal material composed of two or more components such as a type I Al-8 ~ 10wt% Si plating bath, a sequin pattern is formed due to solidification due to the presence of a high liquid section, thereby inhibiting the surface appearance of the steel sheet. The inventors have discovered that the present invention provides the particle size and the particle size of the metal powder with air, in order to reduce the growth time of these grains and increase the number of grain nucleation sites to suppress grain growth. Efforts have been made to improve process conditions such as moisture content, or cooling rate.

The "metal powder" used in the spraying process according to the present invention is a spherical powder particle having a fine particle size formed by rapid cooling by dissolving a metal, and is well known in metallurgy or in the art.

The type of metal powder that can be used in the embodiments of the present invention may be any metal as long as it can act as a nucleation site while absorbing heat, but is preferably a plating material in consideration of corrosion resistance and other functional aspects after use. Use aluminum (Al) or alumina (Al ₂ O ₃ ) that is most similar to.

In the use of the metal powder, if the particle size is too small, the heat absorbing ability is reduced and melted before it becomes the nucleus of the grains. As it is difficult to uniformly spray during spraying, it causes clogging of the nozzle inlet and can cause more defects in the process of spraying powder. The possibility of contaminating the environment is also increased, and the heat absorbing ability is so low that a problem of not obtaining the desired appearance is not achieved unless the injection point is correctly aligned. In particular, as the continuous hot-dip plating equipment is rapidly increasing in size to improve productivity, and the product thickness of products is evolving into equipment that can be manufactured from thin plates to thick plates, the high speed of the line increases the particle size due to the inclusion of more latent heat. If the product is more affected, and if proper working conditions are not involved, it will result in a large quantity of defective production, which will greatly increase the production cost.

Accordingly, in one embodiment of the present invention, by controlling the particle size and the water content of the metal powder constant, it was intended to suppress the sequin generation of the surface of the hot-dip plating and lower the possibility of defective production.

When the particle size of the metal powder is less than 20 μm, the powder penetrates into the surface of the plating layer, and the particles stably settle in the plating layer to absorb and cool heat, and it is difficult to stably serve as a nucleation site. There is a problem that the probability of inhalation by the human body easily blown in the air. If the particle size exceeds 60㎛, even if mixed in the plating layer is too large compared to the thickness of the plating layer to generate fine irregularities in the plating layer even after the skin pass, causing fine pinholes after coating, and also fall off from the plating layer during skin pass It can contaminate the rolls and impair skin passability, causing secondary appearance defects on the plating surface. Therefore, it is preferable to use the particle size of metal powder 20-20 micrometers.

In addition, with the control of the particle size of the metal powder, the particles are entangled in the presence of moisture by the weight when the metal powder is stored in the hopper. Since it is impossible to spray uniformly, it causes a plating problem, which may cause a great damage in a large high speed continuous processing line. Since the smaller the particle size of the metal powder can be more easily entangled even at the same water content, when the particle size is 20 to 60㎛ as in one embodiment of the present invention, the water content is 0.01 to 0.30wt% based on the weight of the powder. It is desirable to manage as low as possible. At this time, the moisture content is a method of limiting the water content when purchasing powder, a method of packing the packaging material so that moisture does not penetrate, or a method of storing the package in a constant temperature and humidity warehouse by separating it from a hopper during unworking after opening the package. Can be managed by

According to one embodiment of the present invention, the injection strength of the air injected with the metal powder was also appropriately adjusted. Basically, in order to sufficiently penetrate the metal powder into the plating layer, it is necessary to blow a little wind. This may cause a bad appearance due to strong winds. However, if a weak wind is blown, the metal powder does not penetrate the plating layer sufficiently. It can also occur. Accordingly, in one embodiment of the present invention, the injection pressure of the wind was controlled to 2 to 10 mbar. If the injection pressure is too high exceeding 10 mbar, an air mark due to wind is generated or the plate is shaken due to plate shaking. If the injection pressure is too weak, less than 2 mbar, the metal powder will be attached only to the pole surface of the plating layer, so it will not be an internal element of the plating layer. It may also cause secondary defects and environmental pollution.

The starting point of the metal powder is preferably sprayed at the temperature immediately above the solidification temperature of the plated metal material. The injection timing may be different depending on the silicon content in the upper part of the solidification temperature in the metallurgical state diagram. Preferably, the powder is sprayed at the surface temperature of the plating layer at 650 ° C. to 600 ° C., and most preferably at 615 ° C. to 600 ° C. Do it. In addition, the end point of the spraying is preferably such that the plating layer surface temperature is 580 ° C to 540 ° C, more preferably 560 ° C to 540 ° C.

According to one embodiment of the present invention, in the cooling process, the steel plate cooling rate is 40 so that the grain growth is suppressed by allowing the liquid to quickly pass through the solid-state coexistence (mushy zone) of aluminum and silicon to implement zero sequining. It is preferable to control at -80 degreeC / sec. However, if the cooling rate is too fast exceeding 80 ℃ / sec, it may cause appearance defects depending on the amount of powder, air injection, and the latent heat of the iron plate in actual production, and when it is slowed below 40 ℃ / sec, grains grow Not enough time can be saved, and insufficient cooling capacity can cause problems in subsequent processes.

In order to prevent the metal plated on the iron plate from contacting the top roll with the plated layer sticking out and damaging the surface of the plated layer, the cooling is preferably performed using a cooler directly above the power sprayer. It is to be performed until the temperature of the top roll is 450 ℃ ~ 300 ℃, and more preferably cooled to 350 ℃ ~ 320 ℃.

According to a preferred embodiment of the present invention, it is preferable to include a step of controlling the plating amount of the iron plate exiting the plating bath before the spraying process after performing the plating process to 40 ~ 120g / m ² by using an air knife Do. The reason for controlling the coating amount in this manner is that when the coating is attached outside the numerical range, appearance defects occur due to uneven flow of the air knife, so that it is difficult to obtain a sound appearance.

In addition, according to a preferred embodiment of the present invention, there is provided a molten aluminum plated steel sheet with improved surface appearance manufactured by the above method.

The molten aluminum plated steel sheet has zero surface sequins by minimizing the sequin pattern that may be formed on the surface of the plating layer by the aluminum-silicon alloy while maintaining corrosion resistance, which is an original property of aluminum, and molding processability of silicon. Appearance can be improved and appearance different from regular hot-dip steel sheet.

"Zero Spangle" refers to a level at which a pattern of sequins is generally not easily distinguished by the naked eye on the surface of an Al-Si hot-dip aluminum plated steel sheet, and does not produce grains of sequins themselves. Visually, the sequin grain size which can confirm sequins is about 90 micrometers. If the sequin size is less than this, the surface appearance will be the same color as a whole with a complete zero sequin such as no sequins with the naked eye. However, in commercial production, the ZEROS sequin means that the sequins have a particle diameter of 0.5 mm or less, and the visual appearance of the sequins does not have the same color tone but has a fine point color difference. In the embodiment of the present invention, the sequin particle diameter of the surface of the plated steel sheet is preferably 0.5 mm or less, and more preferably 0.3 mm or less.

In addition, according to a preferred embodiment of the present invention, according to the zero sequining, the size of the unevenness occurring in the boundary between the conventional sequins is also 0.3 to 1.7 탆, especially when the thickness of the sheet is less than 0.6 t, the thickness is 0.3 to 0.5 탆 and 0.6 t or more. It can be reduced to 0.5 ~ 1.7㎛ to prevent the appearance defects during the subsequent paint coating.

Example 1

Hereinafter, the present invention will be described in more detail with reference to Examples, but the scope of the present invention is not limited thereto.

1-1. Al - Si  Manufacturing of Molten Aluminum Plated Steel Sheet

Using the pilot apparatus shown in Fig. 1, the continuous hot dip plating line was performed at a plating bath temperature of 660 ° C., an inlet temperature of 655 ° C., and a line speed of 100 mpm which are typical Type-I molten aluminum plating working conditions. At this time, the composition of the plating bath was maintained at 91wt% Al and 9wt% Si. The iron plate introduced into the plating bath pot is 0.6t low carbon steel (chemical composition is C 0.0377wt%, Si 0.0099wt%, Mn 0.2153wt%, P 0.0127wt%, surface average roughness after cold rolling is 0.5㎛). The molten plated metal was attached to the iron plate surface while passing through, and the plating deposition amount was adjusted to 80 g / m ² based on both sides using an air knife device. The plated steel plate was adjusted by a non-contact thermometer, and aluminum powder was sprayed on both sides of the iron plate at various pressures of air using a metal powder spraying device at 615 ° C. Thereafter, the top roll was cooled to a temperature of 320 ° C. or less with a cooler located directly above the injector.

After that, the manufacturing of hot-dip galvanized steel sheet was completed through Skin Pass Mill, Tension Leveler, chemical post-treatment and oiling treatment.

1-2. Al - Si  Evaluation of Molten Aluminum Plated Steel Sheet

The surface appearance of the coated steel sheet was evaluated by variously controlling the metal powder particle size, water content, air injection pressure, and cooling rate of the steel sheet, and the results are shown in Table 1. Skin Pass Mill (SPM) work was performed with a rolling reduction of 220 tons using off-line to observe the presence of powdering.

Referring to Table 1, it can be seen that the surface appearance of the plated steel sheet in the invention examples 1 to 3, 9 to 11 is improved, and in the invention examples 4 to 8 to 16 to give a larger powder particle size and iron plate cooling rate value It can be seen that the appearance of the coated steel sheet is further improved.

No Particle size Water content Air injection pressure Cooling rate Exterior SPM Results Comparative Example 1 One 0.05 1.8 20 Ⅹ no problem Comparative Example 2 5 0.08 2.0 24 Ⅹ no problem Comparative Example 3 10 0.10 2.5 32 △ no problem Comparative Example 4 15 0.12 3.0 38 ◇ no problem Inventive Example 1 20 0.15 3.5 45 ○ no problem Inventory 2 25 0.18 4.0 48 ○ no problem Inventory 3 30 0.20 4.5 50 ○ no problem Inventive Example 4 35 0.22 5.0 52 ◎ no problem Inventive Example 5 40 0.24 5.5 53 ◎ no problem Inventive Example 6 45 0.26 6.0 57 ◎ no problem Inventive Example 7 50 0.28 6.5 65 ◎ no problem Inventive Example 8 55 0.30 7.0 72 ◎ no problem Comparative Example 5 60 0.32 7.5 83 ◇ no problem Comparative Example 6 65 0.35 8.0 87 ◇ Powder ring Comparative Example 7 70 0.40 8.5 93 ◇ Powder ring Comparative Example 8 3 0.38 8.0 45 ◇ Powder ring Comparative Example 9 8 0.36 7.5 45 ◇ Powder ring Comparative Example 10 13 0.34 7.0 47 ◇ Powder ring Comparative Example 11 18 0.32 6.5 48 ◇ Powder ring Inventive Example 9 23 0.30 6.0 51 ○ no problem Inventive Example 10 28 0.28 5.5 50 ○ no problem Inventive Example 11 33 0.26 5.0 50 ○ no problem Inventive Example 12 38 0.24 4.5 52 ◎ no problem Inventive Example 13 43 0.22 4.0 55 ◎ no problem Inventive Example 14 48 0.20 3.5 52 ◎ no problem Inventive Example 15 53 0.18 3.0 52 ◎ no problem Inventive Example 16 58 0.16 2.5 50 ◎ no problem Comparative Example 12 63 0.14 2.0 40 ○ Powder ring Comparative Example 13 68 0.12 1.5 35 △ Powder ring Comparative Example 14 73 0.10 1.0 30 Ⅹ Powder ring

Legend) ◎: Sequin size 0.3mm or less ○: Sequin size 0.5mm or less, △: 1.0mm or less, ⅹ: Sequin size 2.0mm or less, ◇: Sequin size unevenness

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

1 is a schematic diagram of a process for manufacturing a molten aluminum plated steel sheet according to an embodiment of the present invention.

Claims (13)

(1) immersing the plated steel sheet subjected to the continuous annealing and reducing process in a plating bath in which molten metal of Al-8 to 10wt% Si is molten and plating; (2) spraying a metal powder having a particle size of 20 to 60 µm and a water content of 0.01 to 0.30 wt% or less with air on the surface of the plated iron sheet; And (3) cooling the iron plate at a cooling rate of 40 ~ 80 ℃ / sec; manufacturing method of molten aluminum plated steel sheet with improved surface appearance. The method of claim 1, wherein the metal powder is aluminum powder or alumina powder. The method of claim 1, wherein the air is injected at an injection pressure of 2 to 10 mbar. The method of claim 1, wherein the injection is performed from the injection time point to the end point. The method of claim 4, wherein the spraying point is a case where the surface temperature of the plating layer is a temperature directly above the solidification temperature of the molten metal. The method of claim 4, wherein the spraying point is a plating layer surface temperature of 650 ° C. to 600 ° C. 6. The method of claim 4, wherein the injection end point is a plating layer surface temperature is 580 ℃ ~ 540 ℃. The method of claim 1, wherein the step (3) is a cooling to 450 ℃ to 300 ℃. The method of claim 1, further comprising the step of controlling the plating amount of the iron plate which exited the plating bath before step (2) after performing step (1) to 40 to 120 g / m ² by an air knife. Manufacturing method. 10. A molten aluminum plated steel sheet having an improved surface appearance produced by the method according to any one of claims 1 to 9. Hot-dip aluminum plated steel sheet with an improved surface appearance with a sequin particle diameter of 0.5 mm or less, unevenness of 0.3 to 1.7 μm, and plating amount of 40 to 120 g / m ² . Hot-dip galvanized steel sheet with a sequin particle diameter of 0.3mm or less, uneven size of 0.3-1.7 μm, and plating amount of 40-120 g / m ^{2 on the surface} of the coated steel sheet. The molten aluminum plating is a molten aluminum plated steel sheet formed from a molten metal of Al-8 ~ 10wt% Si.

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