Plated steel sheet and method for manufacturing same

Abstract

One aspect of the present invention provides a Zn-Mg-Al-based zinc alloy plated steel sheet having excellent surface appearance and excellent anti-glare properties, and a method for manufacturing same.

Description

Galvanized steel sheet and manufacturing method thereof

[0001] The present invention relates to a galvanized steel sheet and a method for manufacturing the same. More specifically, the present invention relates to a Zn-Mg-Al zinc alloy galvanized steel sheet having excellent surface appearance and anti-glare properties.

[0002] Zinc-based galvanized steel exhibits a sacrificial nature. When exposed to a corrosive environment, zinc, with a lower redox potential than iron, corrodes first, inhibiting corrosion of the steel. Furthermore, as the zinc in the plating layer oxidizes, it forms a dense corrosion product on the steel surface, shielding it from the oxidizing environment and enhancing its corrosion resistance. Thanks to these advantageous properties, zinc-based galvanized steel has recently been expanding its application to include building materials, home appliances, and automotive steel.

[0003] However, due to the increase in air pollution caused by industrialization, the corrosive environment is gradually worsening, and due to strict regulations on resource and energy conservation, there is a growing need to develop steel with better corrosion resistance than conventional galvanized steel.

[0004] To address these issues, research is being conducted on manufacturing technologies for zinc alloy-based galvanized steel sheets, which enhance the corrosion resistance of steel by adding elements such as aluminum (Al) and magnesium (Mg) to the zinc plating bath. A representative example is the Zn-Mg-Al zinc alloy-based galvanized steel sheet, which is prepared by adding magnesium to the Zn-Al plating composition.

[0005] However, in the case of Zn-Mg-Al type zinc alloy plated steel sheets, the plating bath surface is prone to oxidation due to the large content of Mg and Al components, and thus the surface quality is deteriorated due to the attachment of Mg and Al type oxides to the steel sheet surface.

[0006] In addition, although Zn-Mg-Al zinc alloy-coated steel sheets containing large amounts of Mg and Al have excellent corrosion resistance, they may cause glare when applied to infrastructure structures such as road noise barriers and guardrails, which can obstruct the driver's view.

[0007] Therefore, there is a recent demand for technology development that can meet the demand for Zn-Mg-Al galvanized steel sheets that have excellent corrosion resistance, surface appearance, and anti-glare properties.

[0008] [Prior Art Literature]

[0009] [Patent Document]

[0010] (Patent Document 1) Republic of Korea Patent Publication No. 2010-0073819

[0011] According to one aspect of the present invention, it is an object to provide a plated steel sheet having excellent surface appearance and anti-glare properties and a method for manufacturing the same.

[0012] The objectives of the present invention are not limited to the above-described scope. Those skilled in the art will have no difficulty understanding the additional objectives of the present invention from the overall content of this specification.

[0013] A plated steel sheet according to one aspect of the present invention comprises a base steel sheet; and a Zn-Mg-Al based plating layer provided on at least one surface of the base steel sheet; wherein the plating layer contains, in wt%, Mg: 4.0 to 6.3%, Al: 11.0 to 19.5%, the remainder Zn, and other unavoidable impurities, and the surface of the plated steel sheet can satisfy an average roughness Ra: 2.0 to 3.0 ㎛, a peak count RPc: 25 to 60 (1 / 10 mm), and a skewness Rsk: -0.5 to 0.5.

[0014] The above-described galvanized steel sheet may have a surface gloss B of 25 or more and 60 or less, and a surface whiteness L of 85 or more.

[0015] The above-described steel sheet contains, in weight %, C: more than 0% and 0.18% or less, Si: more than 0% and 1.5% or less, Mn: 0.010 to 2.7%, P: more than 0% and 0.0700% or less, S: more than 0% and 0.0150% or less, Al: more than 0% and 0.50% or less, Nb: more than 0% and 0.060% or less, Cr: more than 0% and 1.1% or less, Ti: more than 0% and 0.060% or less, and B: more than 0% and 0.03000% or less, and the remainder may be made of Fe and other unavoidable impurities.

[0016] The above-described Zn-Mg-Al plating layer may further include at least one selected from Si: 0.2% or less (including 0%) and Ca: 0.2% or less (including 0%) in weight %.

[0017] The above-described Zn-Mg-Al plating layer may further include one or more of the following groups (a) to (h).

[0018] (a) Ni: 0.5% or less

[0019] (b) La: 0.1% or less, Ce: 0.1% or less, Y: 0.1% or less, Sr: 1.0% or less, or more than one of the following

[0020] (c) Ti: 0.1% or less

[0021] (d) W: 0.5% or less

[0022] (e) Cu: 2.0% or less

[0023] (f) Cr: 0.5% or less, Mn: 0.5% or less, V: 0.5% or less, at least one of these

[0024] (g) B: 0.1% or less, P: 0.1% or less, at least one of these

[0025] (h) Sn: 1.0% or less, Sb: 1.0% or less, Bi: 1.0% or less, or at least one of these

[0026] The thickness of the Zn-Mg-Al plating layer described above can be 5 to 100 μm.

[0027] A method for manufacturing a galvanized steel sheet according to another aspect of the present invention may include the steps of preparing a base steel sheet; immersing the base steel sheet in a molten zinc plating bath to obtain a molten zinc-coated steel sheet; and wiping the molten zinc-coated steel sheet by supplying a mixed gas containing an inert gas and air, wherein the air may be included in the mixed gas in an amount of 5% by volume or more and 20% by volume or less based on the total volume of the mixed gas, and the molten zinc plating bath may include, in weight %, Mg: 4.0 to 6.3%, Al: 11.0 to 19.5%, the remainder Zn, and other unavoidable impurities, and in the step of obtaining the molten zinc-coated steel sheet, the inlet temperature A of the base steel sheet may satisfy the following relational expression 1.

[0028] [Relationship 1] (T B -40)℃ ≤ A ≤ (T B -10)℃

[0029] (In the above relational expression 1, T B represents the temperature (℃) of the above plating bath.)

[0030] The above-described steel sheet contains, in weight %, C: more than 0% and 0.18% or less, Si: more than 0% and 1.5% or less, Mn: 0.010 to 2.7%, P: more than 0% and 0.0700% or less, S: more than 0% and 0.0150% or less, Al: more than 0% and 0.50% or less, Nb: more than 0% and 0.060% or less, Cr: more than 0% and 1.1% or less, Ti: more than 0% and 0.060% or less, and B: more than 0% and 0.03000% or less, and the remainder may be made of Fe and other unavoidable impurities.

[0031] The above-described hot-dip galvanizing bath may further include, in weight %, at least one selected from Si: 0.2% or less (including 0%) and Ca: 0.2% or less (including 0%).

[0032] The above-described hot-dip galvanizing bath may further include one or more of the following groups (a) to (h).

[0033] (a) Ni: 0.5% or less

[0034] (b) La: 0.1% or less, Ce: 0.1% or less, Y: 0.1% or less, Sr: 1.0% or less, or more than one of the following

[0035] (c) Ti: 0.1% or less

[0036] (d) W: 0.5% or less

[0037] (e) Cu: 2.0% or less

[0038] (f) Cr: 0.5% or less, Mn: 0.5% or less, V: 0.5% or less, at least one of these

[0039] (g) B: 0.1% or less, P: 0.1% or less, at least one of these

[0040] (h) Sn: 1.0% or less, Sb: 1.0% or less, Bi: 1.0% or less, or at least one of these

[0041] Temperature T of the above-mentioned plating bath B It can be 440℃ or higher and 500℃ or lower.

[0042] The above-described inert gas may include at least one of argon gas and nitrogen gas.

[0043] According to one aspect of the present invention, a plated steel sheet having excellent surface appearance and anti-glare properties and a method for manufacturing the same can be provided.

[0044] The various advantageous and beneficial effects of the present invention are not limited to the above-described contents, and will be more easily understood in the course of explaining specific embodiments of the present invention.

[0045] Figure 1 is an image photograph showing the surface of (a) Invention Example 4 and (b) Comparative Example 4, respectively.

[0046] Figure 2 shows a comparative evaluation of the surface shape characteristics of (a) Invention Example 4 and (b) Comparative Example 4, respectively.

[0047] Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention may be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0048] In this specification, the term "including" is used to indicate that other components may be included rather than excluding other components unless specifically stated to the contrary.

[0049] Additionally, unless otherwise specifically provided in the specification of the present invention, the % unit means weight%.

[0050] In the conventional technology related to Zn-Mg-Al zinc alloy plating steel sheets, Mg was added to improve corrosion resistance. However, if Mg was added excessively, the generation of floating dross in the plating bath increased, and there was a problem that the dross had to be removed frequently, so the upper limit of the amount of Mg added was limited to 3.0%.

[0051] Accordingly, research was conducted to further improve corrosion resistance by increasing the amount of Mg added beyond 3.0%, but there was a problem in that the surface quality could not be secured due to adhesion of dross as the amount of Mg and Al added increased.

[0052] In addition to these surface quality issues, as described above, when the amount of Mg and Al added increases, the gloss of the plated steel sheet increases, which causes a problem in that glare cannot be prevented when applied to road facilities such as sound barriers and guardrails, which are infrastructure structures.

[0053] Therefore, in the prior art, it was technically difficult to provide a plated steel sheet that has corrosion resistance, an excellent surface appearance, and an anti-glare property through reduction in gloss.

[0054] Accordingly, the inventors of the present invention, after conducting a thorough study to solve the above-described problems, discovered that it is important to secure not only the composition of the plating layer but also the surface roughness characteristics of the plating steel sheet.

[0055] In addition, the inventors of the present invention also found that, as a means of securing the above-described characteristics, it is effective to control the inlet temperature of the base steel sheet during hot-dip galvanizing and the composition of the mixed gas supplied in the hot-dip galvanizing wiping step to an appropriate level.

[0056] The plated steel sheet of the present invention obtained as described above has an appropriate level of surface gloss and surface whiteness, thereby exhibiting excellent surface quality and anti-glare properties.

[0057] From this point of view, a plated steel sheet according to one embodiment of the present invention may include a base steel sheet; and a Zn-Mg-Al-based plating layer provided on at least one surface of the base steel sheet; wherein the plating layer may contain, in wt%, Mg: 4.0 to 6.3%, Al: 11.0 to 19.5%, the remainder Zn, and other unavoidable impurities, and the surface of the plated steel sheet may satisfy an average roughness Ra: 2.0 to 3.0 ㎛, a peak count RPc: 25 to 60 (1 / 10 mm), and a skewness Rsk: -0.5 to 0.5. Hereinafter, each configuration will be described in detail.

[0058] First, a plated steel sheet according to an example of the present invention includes a base steel sheet; and a Zn-Mg-Al-based plated layer provided on at least one surface of the base steel sheet.

[0059] In the present invention, the type of the substrate steel sheet may not be particularly limited. For example, the substrate steel sheet may be an iron-based substrate steel sheet, i.e., a hot-rolled steel sheet or a cold-rolled steel sheet, commonly used as a substrate steel sheet for zinc-based galvanized steel sheets, but is not limited thereto. Alternatively, the substrate steel sheet may be, for example, carbon steel, ultra-low carbon steel, or high manganese steel used as a material for construction, home appliances, or automobiles.

[0060] However, as an example, the above-mentioned steel plate may have a composition including, in wt%, C: more than 0% and 0.18% or less, Si: more than 0% and 1.5% or less, Mn: 0.010 to 2.7%, P: more than 0% and 0.0700% or less, S: more than 0% and 0.0150% or less, Al: more than 0% and 0.50% or less, Nb: more than 0% and 0.060% or less, Cr: more than 0% and 1.1% or less, Ti: more than 0% and 0.060% or less, and B: more than 0% and 0.03000% or less, with the remainder being Fe and other unavoidable impurities.

[0061] Although not particularly limited, according to one embodiment of the present invention, a Zn-Mg-Al plating layer made of a Zn-Mg-Al alloy may be provided on at least one surface of the base steel sheet. The plating layer may be formed on only one surface of the base steel sheet, or may be formed on both surfaces of the base steel sheet. In this case, the Zn-Mg-Al plating layer refers to a plating layer that includes Mg and Al and mainly includes Zn (i.e., includes Zn at 50% or more).

[0062] Although not particularly limited, according to one embodiment of the present invention, the thickness of the Zn-Mg-Al-based plating layer may be 5 to 100 μm, more preferably 7 to 90 μm. If the thickness of the plating layer is less than 5 μm, the plating layer may become excessively thin locally due to errors arising from the thickness deviation of the plating layer, which may result in poor corrosion resistance. If the thickness of the plating layer exceeds 100 μm, the cooling of the molten plating layer may be delayed, and solidification defects such as flow patterns may occur on the surface of the plating layer, for example. In addition, the time required to solidify the plating layer may increase, which may lower the productivity of the steel sheet.

[0063] In addition, according to the present invention, the Zn-Mg-Al-based plating layer may include, in wt%, Mg: 4.0 to 6.3%, Al: 11.0 to 19.5%, the remainder Zn, and other unavoidable impurities. In addition, although not particularly limited, the plating layer may optionally further include, in wt%, at least one selected from Si: 0.20% or less (including 0%) and Ca: 0.200% or less (including 0%). Hereinafter, the reasons for adding each component and the reasons for limiting the content will be described in detail.

[0064] Mg: 4.0~6.3%

[0065] Mg is an element that improves the corrosion resistance of the plated steel sheet. In the present invention, the Mg content in the plated layer is controlled to 4.0% or more to secure the desired excellent corrosion resistance. On the other hand, if Mg is added excessively, dross may be generated, so the Mg content may be controlled to 6.3% or less. As another example, the Mg may be included in an amount of 4.5 to 6.0 wt%, and as another example, it may be included in an amount of 5.0 to 5.5 wt%.

[0066] Al: 11.0~19.5%

[0067] Generally, when Mg is added in an amount of 1.0% or more, the effect of improving corrosion resistance is exhibited, but when Mg is added in an amount of 2.0% or more, the generation of floating dross in the plating bath due to oxidation of Mg in the plating bath increases, and there is a problem that the dross must be removed frequently.

[0068] Due to these problems, in conventional technology, corrosion resistance was secured by adding Mg in an amount of 1.0% or more in Zn-Mg-Al zinc alloy plating, but the upper limit of the Mg content was set at 3.0% for commercialization.

[0069] However, in order to further improve corrosion resistance, it is necessary to increase the Mg content to 4.0% or more, but if the plating layer contains 4.0% or more of Mg, there is a problem of dross generation due to oxidation of Mg in the plating bath, so in order to suppress such dross generation, the Zn-Mg-Al plating layer according to an example of the present invention may have 11.0% or more of Al added.

[0070] However, if excessive addition of Al is made to suppress dross, the melting point of the plating bath increases, and the operating temperature becomes too high accordingly, which may cause problems due to high-temperature operation, such as erosion of the plating bath structure and deformation of the steel material. In addition, if the Al content in the plating bath is excessive, the Al reacts with the Fe of the base steel sheet and does not contribute to the formation of the Fe-Al suppression layer, and the reaction between Al and Zn occurs rapidly, causing excessive formation of a lump-shaped outburst phase, which may actually worsen the corrosion resistance. Therefore, it is preferable to control the upper limit of the Al content in the plating layer to 19.5%. As another example, the Al may be included in an amount of 13.0 to 17.5 wt%, and as another example, the Al may be included in an amount of 14.0 to 16.0 wt%.

[0071] Si: 0.20% or less (including 0%)

[0072] When Si is added at 0.20% or less, it can prevent the formation of a thick Fe-Al alloy layer at the interface between the base steel and the plating layer, thereby preventing a decrease in the interface strength between the plating layer and the base steel. Therefore, addition is advantageous, but since there is little effect on the corrosion resistance in the present invention even if it is not added, the lower limit is set to 0%.

[0073] However, even if the Si addition amount exceeds 0.20%, the effect of suppressing the Fe-Al alloy layer at the interface reaches saturation, and as the Si addition amount increases, the melting point of the plating bath increases, so the plating bath temperature must be maintained high, which is not good from the perspective of equipment protection. According to one embodiment of the present invention, it may be 0.18% or less.

[0074] Ca: 0.200% or less (including 0%)

[0075] Although Ca does not necessarily need to be added, adding up to 0.200% can suppress the formation of MgO oxide in the plating bath. In addition, since small amounts are sometimes added for convenience in the production of ingots for plating bath production, small amounts may be present in the plating bath produced from such ingots. However, if the amount of Ca added exceeds 0.200%, the color of the steel sheet may darken, which is not preferred. According to one embodiment of the present invention, the amount of Ca may be 0.180% or less.

[0076] Residual Zn and other unavoidable impurities

[0077] In addition to the aforementioned components, the plating bath is composed of inevitable impurities and zinc components that are present during the ingot manufacturing process or components eluted from the steel sheet. The inevitable impurities include Sb, Sn, Pb, Sr, Cu, etc., which are components that are inevitably mixed in small amounts during the manufacturing of ingots for making plating solutions. Meanwhile, components that are inevitably eluted when the steel sheet is immersed in the plating bath and exist in small amounts in the plating bath include Mn, Ti, Ni, B, Nb, etc., but other components may also exist depending on the components of the steel sheet. However, even if they are inevitably added, it is not desirable for each component to be present in an amount of more than 0.01%.

[0078] According to one embodiment of the present invention, the plating layer may further include at least one of the following groups (a) to (h).

[0079] However, since the elements in each group below are not essential for achieving the tasks of the present invention, their lower limits of content are not limited. Therefore, even if not specifically mentioned below, the lower limit of the content of each element may be 0%.

[0080] (a) Ni: 0.5% or less

[0081] (b) La: 0.1% or less, Ce: 0.1% or less, Y: 0.1% or less, Sr: 1.0% or less, or more than one of the following

[0082] (c) Ti: 0.1% or less

[0083] (d) W: 0.5% or less

[0084] (e) Cu: 2.0% or less

[0085] (f) Cr: 0.5% or less, Mn: 0.5% or less, V: 0.5% or less, at least one of these

[0086] (g) B: 0.1% or less, P: 0.1% or less, at least one of these

[0087] (h) Sn: 1.0% or less, Sb: 1.0% or less, Bi: 1.0% or less, or at least one of these

[0088] Below, the reasons for adding each ingredient and limiting its content are explained in detail.

[0089] (a) Ni: 0.5% or less

[0090] Ni has the effect of preventing Fe diffusion by forming an Al-Ni alloy phase, but if its content exceeds 0.5%, there may be a problem of excessive increase in the cost of raw materials.

[0091] (b) La: 0.1% or less, Ce: 0.1% or less, Y: 0.1% or less, Sr: 1.0% or less, or more than one of the following

[0092] La, Ce, Y and Sr have the effect of preventing oxidation of Mg in the plating bath by forming an oxide film, but if their contents exceed 0.1%, 0.1%, 0.1% and 1.0%, respectively, there may be a problem of reduced plating properties due to an increase in the viscosity of the plating bath.

[0093] (c) Ti: 0.1% or less

[0094] Ti acts as a nucleation site for Ti-Al intermetallic compounds and has the effect of refining crystal grains (spangles), but if its content exceeds 0.1%, the melting point of the plating bath may increase and there may be a problem of increased dross.

[0095] (d) W: 0.5% or less

[0096] W forms W oxide on the surface, which improves corrosion resistance, but if its content exceeds 0.5%, there may be a problem of the melting point of the plating bath increasing.

[0097] (e) Cu: 2.0% or less

[0098] Cu has the effect of forming an Al-Cu process structure and lowering the hardness of the plating layer, but if its content exceeds 2.0%, there may be a problem of the spangles becoming coarser.

[0099] (f) Cr: 0.5% or less, Mn: 0.5% or less, V: 0.5% or less, at least one of these

[0100] Cr, Mn, and V have the effect of preventing electrode deterioration by suppressing alloying between zinc and the welding electrode due to rapid liquid loss, but if their content exceeds 0.5% each, there may be a problem of excessively increasing the melting point of the plating bath.

[0101] (g) B: 0.1% or less, P: 0.1% or less, at least one of these

[0102] B and P have the effect of suppressing LME cracks in welds, but if their contents exceed 0.1% each, there may be a problem of increased dross generation.

[0103] (h) Sn: 1.0% or less, Sb: 1.0% or less, Bi: 1.0% or less, or at least one of these

[0104] Sn, Sb, and Bi have the effect of uniformizing spangles and improving pot durability by lowering the plating bath temperature, but if their contents exceed 1.0% each, there may be a problem of coarsening of spangles.

[0105] Meanwhile, the surface of the plated steel sheet according to another embodiment of the present invention can satisfy an average surface roughness Ra: 2.0 to 3.0 ㎛, a peak count RPc: 25 to 60 (1 / 10 mm), and a skewness Rsk: -0.5 to 0.5.

[0106] Average surface roughness Ra: 2.0~3.0㎛

[0107] In one example of the present invention, in order to secure a surface quality that exhibits a luxurious white color without gloss, the average surface roughness may be 2.0㎛ or more. That is, if the average surface roughness is less than 2.0㎛, the presence of flat portions may induce light reflection, which may cause a glare problem. On the other hand, if the average surface roughness exceeds 3.0㎛, the surface may be very rough, which may adversely affect subsequent processing processes such as bending and roll forming. As another example, the average surface roughness may be 2.3 to 2.8㎛, and as another example, 2.5 to 2.6㎛.

[0108] Peak count RPc: 25~60 (1 / 10mm)

[0109] Throughout this specification, the peak count refers to the number of peaks present on the surface of the plated steel sheet per unit cm. That is, the peak count can be used as an indicator of the degree of unevenness of the surface of the plated steel sheet. If the peak count is less than 25 (1 / 10 mm), the surface may reflect unevenness, which may have a negative effect on the glare characteristics. If the peak count exceeds 60 (1 / 10 mm), the surface's high and low valleys may become excessively dense, which may cause a slipping phenomenon during processing. As another example, the peak count may be 35 to 50 (1 / 10 mm) or 40 to 45 (1 / 10 mm).

[0110] Skewness Rsk: -0.5 or more and 0.5 or less

[0111] Throughout this specification, the skewness Rsk value may refer to the degree of oil contained in the plating layer, and the skewness Rsk value may affect the processing characteristics of the plated steel sheet. If the skewness value is less than -0.5, it is difficult to maintain oil such as anti-rust oil or lubricant evenly in the width direction of the steel sheet, and there may be a problem in that local degreasing is not good even in subsequent degreasing processes. On the other hand, if the skewness value exceeds 0.5, there may be many peaks in the shape of a probe that rise upwards in the surface shape, so the surface shape may become distorted during processing. As another example, the skewness value of the surface of the plated steel sheet may be -0.3 to 0.3, and may be -0.1 to 0.1.

[0112] Meanwhile, according to one embodiment of the present invention, the plated steel sheet can secure corrosion resistance, as well as an excellent surface appearance and anti-glare properties at the desired level. More specifically, the plated steel sheet according to one example of the present invention can have a surface gloss B of 25 or more and 60 or less, and a surface whiteness L of 85 or more.

[0113] Surface gloss B: 25 or more and 60 or less

[0114] In order to prevent the problem that the color of the plated steel sheet appears dark due to the gloss being too low, one example of the present invention may set the lower limit of the surface gloss to 25 or more. On the other hand, if the surface gloss exceeds 60, there is a high possibility that it will cause glare to the driver's field of vision when applied to a road guardrail, so one embodiment of the present invention may set the surface gloss to 60 or less. That is, the plated steel sheet according to one example of the present invention can secure a target level of gloss while preventing glare by having the surface gloss of 25 or more and 60 or less. At this time, although not necessarily limited thereto, as one example, the surface gloss B may be measured with SHEEN's REF-260, and the angle of incidence at the time of measurement may be 60°. According to another example, the surface gloss may be 35 or more and 55 or less, and as another example, may be 40 or more and 50 or less.

[0115] Whiteness L: 85 or higher

[0116] In a non-limiting embodiment of the present invention, the whiteness may be set to 85 or higher for the purpose of securing the aesthetic appearance of the quality of the surface. Since the higher the whiteness, the more advantageous it is for achieving the purpose of the present invention, one example of the present invention does not specifically limit the upper limit of the whiteness. However, considering that implementing the whiteness exceeding 95 requires excessive time and effort in a practical process, a non-limiting example of the present invention may set the upper limit of the whiteness to 95. In this case, although not necessarily limited thereto, as one example, the whiteness may be measured with Minolta's CM-3700A, and in this case, the whiteness may appear in the range of 0 to 100. According to another example, the whiteness may be 90 or higher, and as another example, it may be 94 or higher.

[0117] Next, [a method for manufacturing a plated steel sheet] according to another aspect of the present invention will be described in detail. However, this does not necessarily mean that the plated steel sheet of the present invention must be manufactured by the following manufacturing method.

[0118] According to one embodiment of the present invention, a step of first preparing a base steel sheet may be included, and the type of the base steel sheet is not particularly limited. The base steel sheet may be an Fe-based base steel sheet used as a base steel sheet for a typical hot-dip galvanized steel sheet, i.e., a hot-rolled steel sheet or a cold-rolled steel sheet, but is not limited thereto. In addition, the base steel sheet may be, for example, carbon steel, ultra-low carbon steel, or high manganese steel used as a material for construction, home appliances, or automobiles, but is not limited thereto. In this case, the above-mentioned description may be equally applied to the base steel sheet.

[0119] Next, the base steel sheet prepared as described above is immersed in a hot-dip galvanizing bath containing, in wt%, Mg: 4.0 to 6.3%, Al: 11.0 to 19.5%, and the balance Zn and other unavoidable impurities, to obtain a hot-dip galvanized steel sheet. At this time, with respect to the reasons for adding the components in the above-described plating bath and the reasons for limiting the contents, the description of the components of the above-described plating layer may be equally applied, except for the small amount of impurity content that may flow in from the base steel sheet. Therefore, according to one aspect of the present invention, the plating bath may optionally further include, in wt%, at least one selected from Si: 0.20% or less (including 0%) and Ca: 0.200% or less (including 0%).

[0120] At this time, the explanation of the components of the plating layer described above can be applied equally to the reasons for adding components and limiting the content in the plating bath described above, except for the small amount of Fe content that may flow in from the base steel sheet.

[0121] Meanwhile, in order to manufacture the plating bath of the aforementioned composition, a composite ingot containing a predetermined amount of Zn, Al, and Mg, or a Zn-Mg, Zn-Al ingot containing individual components, can be used. To replenish the plating bath consumed by molten plating, the ingot is additionally melted and supplied. In this case, a method of directly immersing the ingot in the plating bath and melting it can be adopted, or a method of melting the ingot in a separate pot and then replenishing the molten metal to the plating bath can be adopted.

[0122] In addition, according to a non-limiting example of the present invention, when obtaining the hot-dip galvanized steel sheet, the inlet temperature A of the base steel sheet can satisfy the following relational expression 1.

[0123] [Relationship 1] (T B -40)℃ ≤ A ≤ (T B -10)℃

[0124] (In the above relational expression 1, T B represents the temperature (℃) of the above plating bath.)

[0125] That is, if the inlet temperature A of the steel plate derived by the above relational expression 1 is T B If it is below -40℃, there may be a problem that the crystal phase is not dense, and the inlet temperature A of the above steel plate is T B If it exceeds -10℃, there may be a problem with the plating adhesion. As another example, the inlet temperature A of the above steel plate is (T B -30)℃ to (T B -10)℃, and as another example, (T B -20)℃ to (T B -10)℃ may be.

[0126] At this time, although not particularly limited, as an example, the plating bath temperature (T) mentioned above B ) can be in the range of 440 to 500°C. Meanwhile, more preferably, the plating bath temperature (T B) may be 455°C, or the plating bath temperature (T B ) may have an upper limit of 490℃.

[0127] Next, a method for manufacturing a galvanized steel sheet according to a non-limiting example of the present invention may include a step of wiping the galvanized steel sheet by supplying a mixed gas containing an inert gas and air.

[0128] In addition, according to the method for manufacturing a plated steel sheet according to one embodiment of the present invention, the air may be included in the mixed gas in an amount of 5% by volume or more and 20% by volume or less based on the total volume thereof.

[0129] That is, as a result of the above-described study, the inventors of the present invention found that when wiping is performed by mixing 5% to 20% by volume of air with an inert gas, unlike the conventional method, the surface of the plated steel sheet can exhibit excellent whiteness in a milky form through mild oxidation, and the gloss disappears, resulting in excellent anti-glare properties.

[0130] If the air content is less than 5 vol% based on the total fraction of the mixed gas, the above-described weak oxidation effect may be minimal, and as a result, it may be difficult to improve the whiteness of the steel sheet. On the other hand, if the air content exceeds 20 vol% based on the total fraction of the mixed gas, serious peroxidation defects may be induced on the surface of the steel sheet. Therefore, in a non-limiting embodiment of the present invention, the air content included in the mixed gas may be maintained at 5 to 20 vol%. In another example, the air content included in the mixed gas may be 5 to 15 vol%, and in another example, 5 to 10 vol%.

[0131] Meanwhile, although not particularly limited, according to one embodiment of the present invention, the inert gas may be argon (Ar) gas, nitrogen (N2) gas, or a mixed gas of argon and nitrogen, but from an economical perspective, it may be more preferable to use nitrogen gas.

[0132] Hereinafter, the present invention will be described in more detail through examples. However, it should be noted that the following examples are intended only to illustrate and further illustrate the present invention and are not intended to limit the scope of the invention. This is because the scope of the invention is determined by the matters set forth in the patent claims and matters reasonably inferred therefrom.

[0133] (Example)

[0134] A base steel sheet having a thickness of 1.5 mm and a width of 1200 mm is prepared, having a composition of C: 0.018%, Si: 0.010%, Mn: 0.20%, P: 0.009%, S: 0.005%, Al: 0.1%, Nb: 0.02%, Cr: 0.20%, Ti: 0.020%, B: 0.015%, and the remainder of Fe and impurities. The base steel sheet is immersed in a hot-dip galvanizing bath under the conditions of Table 1 below to obtain a hot-dip galvanized steel sheet. The composition of the hot-dip galvanizing bath in Table 1 below excludes the content of a small amount of Fe that may be introduced from the base steel sheet.

[0135] Next, a wiping process was performed using a mixed gas of nitrogen (N2) gas and air. At this time, the air content in the mixed gas is as shown in Table 1 below. Next, the surface gloss, whiteness, surface roughness, number of surface peaks, and skewness of the manufactured plated steel sheet were measured, and the measured values ​​are shown in Table 2 below. The thickness of the Zn-Mg-Al-based plating layer of the manufactured plated steel sheet was 5 to 100 μm.

[0136] At this time, the surface gloss B was measured using SHEEN's REF-260, and the measured surface gloss is the gloss at an incident angle of 60°.

[0137] Additionally, the L (lightness) value in the above whiteness was measured with Minolta's CM-3700A.

[0138] Surface roughness, surface peak number, and skewness Rsk were measured using a contact-type roughness measuring device manufactured by KOSAKA in accordance with the JIS2013 standard.

[0139] No. Plating Conditions Wiping Gas Plating Bath Composition [wt%] Plating Bath Temperature [℃ Base Iron Inlet Temperature [℃ Air Content in Mixed Gas [vol%] MgAl Other Invention Example 14.0 11.0 Balance Zn4404305 Invention Example 24.4 11.4 Balance Zn4504406 Invention Example 34.9 12.2 Balance Zn4554458 Invention Example 45.4 14.4 Balance Zn4604509 Invention Example 55.7 17.5 Balance Zn47546511 Invention Example 66.1 19.2 Balance Zn49047012 Invention Example 74.6 11.6 Balance Zn46044014 Invention Example 85.1 12.3 Balance Zn45542517 Invention Example 96.319.5 Balance Zn49045020 Comparative Example 13.89.1 Balance Zn4404400 Comparative Example 26.410.2 Balance Zn4504501 Comparative Example 35.77.9 Balance Zn4704702 Comparative Example 47.114.4 Balance Zn4904903 Comparative Example 53.78.9 Balance Zn4404504 Comparative Example 66.310.2 Balance Zn4504607 Comparative Example 75.67.9 Balance Zn4704609 Comparative Example 87.220.0 Balance Zn49047010 Comparative Example 97.619.1 Balance Zn49048013 Comparative Example 104.38.0 Balance Zn47045015 Comparative Example 114.86.5 Residue Zn4604308 Comparative Example 126.710.8 Residue Zn47045014 Comparative Example 137.821.0 Residue Zn51051021 (Many defects occurred) Comparative Example 146.510.7 Residue Zn46047025 (Many defects occurred) Comparative Example 156.97.8 Residue Zn49049027 (Many defects occurred) Comparative Example 164.912.5 Residue Zn50052015

[0140] No. Surface gloss B Whiteness L Surface roughness Surface peak number Distortion Glossness [60 degree incident] Whiteness [℃] Ra [㎛] Rpc [cm -1 ]Rsk invention example 160853.025-0.5 invention example 255862.830-0.3 invention example 346872.735-0.1 invention example 443892.4470.0 invention example 532902.5510.1 invention example 627922.5500.1 invention example 734912.4520.2 invention example 828932.3540.3 invention example 925952.2600.5 comparison example 1254400.8100-0.8 comparison example 2232431.092-0.8 comparison example 3221451.195-0.7 comparison example 4185481.290-0.7 comparison example 5120521.487-0.6Comparative Example 6117541.488-0.6Comparative Example 7113571.487-0.5Comparative Example 8105601.580-0.5Comparative Example 9101631.683-0.4Comparative Example 1099371.682-0.4Comparative Example 1198731.774-0.3Comparative Example 1276771.775-0.3Comparative Example 1374771.774-0.3Comparative Example 1468791.873-0.3Comparative Example 1566811.872-0.1Comparative Example 1661821.865-0.8

[0141] In the case of Comparative Examples 1 to 16, at least one of the plating composition and manufacturing conditions specified in the present invention was not satisfied, so that the surface roughness, number of surface peaks, or skewness were outside the range suggested by the present invention, and as a result, the plated steel sheets of Comparative Examples 1 to 16 exhibited poor performance in terms of surface appearance quality and anti-glare characteristics. On the other hand, in the case of Inventive Examples 1 to 9, the plating composition and manufacturing conditions specified in the present invention were satisfied, and thus excellent surface appearance quality and anti-glare characteristics were exhibited.

[0142] Figure 1 is an image photograph showing the surface of (a) Invention Example 4 and (b) Comparative Example 4, respectively. Looking at Figure 1, it can be confirmed that Invention Example 4 exhibits a higher whiteness value than Comparative Example 4, and has superior aesthetics in terms of surface quality appearance.

[0143] In addition, Fig. 2 compares and evaluates the surface shape characteristics of (a) Invention Example 4 and (b) Comparative Example 4, respectively. Looking at Fig. 2, it can be confirmed that Comparative Example 4 has lower surface roughness than Invention Example 4, and as a result, Comparative Example 4 has a higher possibility of causing glare due to the presence of flat portions compared to Invention Example 4. In addition, it can be confirmed through Fig. 2 that Invention Example 4 has a smaller number of surface peaks than Comparative Example 4. Therefore, Invention Example 4 can secure a surface quality that exhibits a luxurious white color without gloss.

Claims

1. Steel plate; and Including a Zn-Mg-Al based plating layer provided on at least one surface of the above steel plate; The above plating layer contains, in weight %, Mg: 4.0 to 6.3%, Al: 11.0 to 19.5%, the remainder Zn and other unavoidable impurities. A coated steel sheet whose surface satisfies the average roughness Ra: 2.0 to 3.0 ㎛, peak count RPc: 25 to 60 (1 / 10 mm), and skewness Rsk: -0.5 to 0.

5.

2. In paragraph 1, A galvanized steel sheet having a surface gloss B of 25 or more and 60 or less and a surface whiteness L of 85 or more.

3. In paragraph 1, The above-mentioned steel sheet is a plated steel sheet comprising, in weight%, C: more than 0% but not more than 0.18%, Si: more than 0% but not more than 1.5%, Mn: 0.010 to 2.7%, P: more than 0% but not more than 0.0700%, S: more than 0% but not more than 0.0150%, Al: more than 0% but not more than 0.50%, Nb: more than 0% but not more than 0.060%, Cr: more than 0% but not more than 1.1%, Ti: more than 0% but not more than 0.060%, and B: more than 0% but not more than 0.03000%, with the remainder being Fe and other unavoidable impurities.

4. In paragraph 1, A plated steel sheet, wherein the Zn-Mg-Al-based plating layer further comprises at least one selected from, in weight %, Si: 0.2% or less (including 0%) and Ca: 0.2% or less (including 0%).

5. In paragraph 1, A plated steel sheet, wherein the Zn-Mg-Al-based plating layer further comprises at least one of the following groups (a) to (h). (a) Ni: 0.5% or less (b) La: 0.1% or less, Ce: 0.1% or less, Y: 0.1% or less, Sr: 1.0% or less, or at least one of these (c) Ti: 0.1% or less (d) W: 0.5% or less (e) Cu: 2.0% or less (f) Cr: 0.5% or less, Mn: 0.5% or less, V: 0.5% or less, at least one of these (g) B: 0.1% or less, P: 0.1% or less, at least one of these (h) Sn: 1.0% or less, Sb: 1.0% or less, Bi: 1.0% or less, or at least one of these 6. In paragraph 1, A plated steel sheet having a thickness of the Zn-Mg-Al-based plating layer of 5 to 100 ㎛.

7. Step for preparing the steel plate; A step of immersing the above-mentioned steel sheet in a molten zinc plating bath to obtain a molten zinc-coated steel sheet; and A step of wiping by supplying a mixed gas containing an inert gas and air to the molten zinc-coated steel sheet; The above air is contained in the above mixed gas in an amount of 5% by volume or more and 20% by volume or less with respect to the total volume thereof, The above-mentioned hot-dip galvanizing bath contains, in weight %, Mg: 4.0 to 6.3%, Al: 11.0 to 19.5%, the remainder Zn and other unavoidable impurities. A method for manufacturing a galvanized steel sheet, wherein in the step of obtaining the above-described hot-dip galvanized steel sheet, the inlet temperature A of the base steel sheet satisfies the following relational expression 1. [Relationship 1] (T B -40)℃ ≤ A ≤ (T B -10)℃ (T in the above relation 1 B represents the temperature (℃) of the above plating bath.) 8. In paragraph 7, A method for manufacturing a plated steel sheet, wherein the above-mentioned steel sheet contains, in wt%, C: more than 0% but not more than 0.18%, Si: more than 0% but not more than 1.5%, Mn: 0.010 to 2.7%, P: more than 0% but not more than 0.0700%, S: more than 0% but not more than 0.0150%, Al: more than 0% but not more than 0.50%, Nb: more than 0% but not more than 0.060%, Cr: more than 0% but not more than 1.1%, Ti: more than 0% but not more than 0.060%, and B: more than 0% but not more than 0.03000%, with the remainder being Fe and other unavoidable impurities.

9. In paragraph 7, A method for manufacturing a galvanized steel sheet, wherein the above-mentioned molten zinc plating bath further contains, in wt%, at least one selected from Si: 0.2% or less (including 0%) and Ca: 0.2% or less (including 0%).

10. In paragraph 7, A method for manufacturing a galvanized steel sheet, wherein the above-mentioned molten zinc plating bath further comprises at least one of the following groups (a) to (h). (a) Ni: 0.5% or less (b) La: 0.1% or less, Ce: 0.1% or less, Y: 0.1% or less, Sr: 1.0% or less, or at least one of these (c) Ti: 0.1% or less (d) W: 0.5% or less (e) Cu: 2.0% or less (f) Cr: 0.5% or less, Mn: 0.5% or less, V: 0.5% or less, at least one of these (g) B: 0.1% or less, P: 0.1% or less, at least one of these (h) Sn: 1.0% or less, Sb: 1.0% or less, Bi: 1.0% or less, or at least one of these 11. In paragraph 7, Temperature T of the above plating bath B A method for manufacturing a plated steel sheet having a temperature of 440℃ or higher and 500℃ or lower.

12. In paragraph 7, A method for manufacturing a plated steel sheet, wherein the inert gas comprises at least one of argon gas and nitrogen gas.

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