Galvanized steel sheet and method of manufacturing same

Abstract

One aspect of the present invention is to provide a galvanized steel sheet and a method of manufacturing same. Another aspect of the present invention is to provide a galvanized steel sheet having fine spangles and good painting quality and a method of manufacturing same.

Description

Hot-dip galvanized steel sheet and its manufacturing method

[0001] The present invention relates to a hot-dip galvanized steel sheet and a method for manufacturing the same.

[0002]

[0003] Typically, hot-dip galvanized steel sheets are manufactured by immersing steel sheets that have passed through an annealing furnace into a molten zinc plating bath, then allowing the applied molten zinc to solidify. As the molten zinc coated on the steel sheet cools, spangles, which are dendritic crystal grains, form on the surface of the plating layer. As the zinc solidifies, dendrites grow rapidly, driven by solidification nuclei in the early stages of solidification, forming a coarse spangle pattern. Therefore, the size of the spangles can be said to be determined in the early stages of solidification.

[0004]

[0005] Due to the coarse spangles formed on the surface of the plating layer, the corrosion resistance of the plating layer, paint adhesion, and surface appearance after painting deteriorate.

[0006]

[0007] Therefore, the quality of the galvanized steel sheet can be improved by reducing the spangle size formed on the galvanized steel sheet.

[0008]

[0009] Conventional methods for reducing the size of spangles include, for example, (1) using a plating bath that does not contain spangle-forming antimony (Sb) or lead (Pb), (2) applying pressure with a skin pass roll after plating, and (3) spraying water or a phosphate solution before the coated zinc solidifies.

[0010]

[0011] However, these conventional methods not only do not reduce the spangle size sufficiently, but also have the side effect of causing the phosphate component to remain, which deteriorates the coating quality in additional processes.

[0012]

[0013] Accordingly, there is a need for a method of precisely minimizing the spangle size of a hot-dip galvanized steel sheet while improving the surface appearance and quality without the aforementioned side effects.

[0014]

[0015] One aspect of the present invention is to provide a hot-dip galvanized steel sheet and a method for manufacturing the same.

[0016] Another aspect of the present invention is to provide a hot-dip galvanized steel sheet having fine spangles and good painting quality and a method for manufacturing the same.

[0017]

[0018] One embodiment of the present invention provides a hot-dip galvanized steel sheet comprising a base steel sheet and a hot-dip galvanized layer formed on at least one surface of the base steel sheet, wherein the average size of spangles formed on the surface of the hot-dip galvanized layer is 150 μm or less (excluding 0 μm), and the C content in a region within 2 μm in the thickness direction from the surface of the hot-dip galvanized layer is 0.2 wt% or less (including 0%).

[0019]

[0020] Another embodiment of the present invention provides a method for manufacturing a hot-dip galvanized steel sheet, comprising the steps of forming a hot-dip galvanized layer on at least one surface of a steel sheet; spraying an aqueous solution on the hot-dip galvanized layer; and cooling the hot-dip galvanized layer onto which the aqueous solution has been sprayed, wherein the step of spraying the aqueous solution includes spraying a mixed aqueous solution and air, wherein the mixed aqueous solution is composed of water, urea, and alcohol, and the average size of droplets upon spraying the mixed aqueous solution is 10 to 50 μm, the content of the urea is 0.1 to 5.0 wt%, and the content of the alcohol is 0.1 to 5.0 wt%.

[0021]

[0022] Between the step of forming the molten zinc-plated layer and the step of spraying the aqueous solution, a step of controlling the amount of adhesion of the molten zinc-plated layer may be additionally included.

[0023]

[0024] The above mixed aqueous solution can be sprayed with a steel plate temperature of 419°C to 419°C, which is the molten zinc plating temperature, as the spraying start temperature and a steel plate temperature of 417 to 415°C, as the spraying end temperature.

[0025]

[0026] The above mixed aqueous solution can be sprayed through a charging electrode.

[0027]

[0028] When the above mixed aqueous solution passes through the charging electrode, the voltage applied to the charging electrode may be -1 to -50 kV.

[0029]

[0030] The above alcohol may be at least one selected from the group consisting of ethanol, propanol, isopropanol, butanol, and isobutanol.

[0031]

[0032] The injection pressure of the above air can be 1.5 to 5.0 kgf / ㎠.

[0033]

[0034] The injection pressure of the above mixed aqueous solution may be 0.5 to 2.5 kgf / ㎠.

[0035]

[0036] The above mixed aqueous solution and air can be sprayed at a pressure ratio of 0.3 to 0.9.

[0037]

[0038] According to one aspect of the present invention, a hot-dip galvanized steel sheet and a method for manufacturing the same can be provided.

[0039] According to another aspect of the present invention, a hot-dip galvanized steel sheet having fine spangles and good paint quality, which can be preferably used as interior and exterior panels of automobile bodies, home appliances, and building materials, and a method for manufacturing the same can be provided.

[0040]

[0041] Figure 1 is a schematic diagram showing one embodiment of a hot-dip galvanized steel sheet manufacturing device applicable to the present invention.

[0042] Figure 2 is an EPMA analysis result for a molten zinc-plated layer of Invention Example 1 according to one embodiment of the present invention.

[0043] Figure 3 shows the EPMA analysis results for the molten zinc-plated layer of Comparative Example 6, which deviates from one embodiment of the present invention.

[0044]

[0045] Hereinafter, a hot-dip galvanized steel sheet according to one embodiment of the present invention will be described.

[0046]

[0047] According to one embodiment of the present invention, a hot-dip galvanized steel sheet includes a base steel sheet and a hot-dip galvanized layer formed on at least one surface of the base steel sheet. The present invention does not particularly limit the type of the base steel sheet, and any steel sheet for hot-dip galvanized steel sheets commonly used in the relevant technical field can be used. In addition, the present invention does not particularly limit the type of the hot-dip galvanized layer. However, as an example, the hot-dip galvanized layer may be formed of pure zinc (Zn), and may additionally include one or more of aluminum (Al), magnesium (Mg), antimony (Sb), and lead (Pb). More specifically, the hot-dip galvanized layer may include 0.13 to 0.3 wt% of Al and the remainder Zn, and may be a binary Zn-Al hot-dip galvanized layer or a ternary Zn-Al-Mg hot-dip galvanized layer. In the case of the above binary Zn-Al hot-dip galvanized layer, it may contain 40 to 95 wt% of Al, and in the case of the ternary Zn-Al-Mg hot-dip galvanized layer, it may contain 0.1 to 30 wt% of Al and Mg, respectively.

[0048]

[0049] It is preferable that the average size of the spangles formed on the surface of the hot-dip galvanized layer of the hot-dip galvanized steel sheet of the present invention is 150 ㎛ or less (excluding 0 ㎛). By forming such fine spangles, the corrosion resistance, paint adhesion, and surface appearance of the hot-dip galvanized steel sheet can be improved. If the average size of the spangles exceeds 150 ㎛, it may be difficult to sufficiently secure the aforementioned spangle refinement effect. Therefore, the average size of the spangles is preferably 150 ㎛ or less (excluding 0 ㎛). The average size of the spangles is more advantageously 140 ㎛ or less, more advantageously 130 ㎛ or less, and most advantageously 120 ㎛ or less.

[0050]

[0051] The hot-dip galvanized steel sheet of the present invention preferably has a C content of 0.2 wt% or less (including 0%) in a region within 2 μm in the thickness direction from the surface of the hot-dip galvanized layer. If C exists in the surface of the hot-dip galvanized layer, problems such as reduced weldability and paint adhesion may occur. In the present invention, by controlling the C content in the surface of the hot-dip galvanized layer as described above, the surface becomes more attractive and the usability of the steel sheet can be improved. However, in the present invention, the upper limit of the C content in the surface of the hot-dip galvanized layer is limited to 0.2 wt%, and if the C content exceeds 0.2 wt%, the above-mentioned problem may occur. Therefore, the C content in a region within 2 μm in the thickness direction from the surface of the hot-dip galvanized layer is preferably 0.2 wt% or less (including 0%). It is more advantageous for the C content in a region within 2 μm in the thickness direction from the surface of the hot-dip galvanized layer to be 0.1 wt% or less.

[0052]

[0053] Fig. 1 is a schematic diagram illustrating one embodiment of a hot-dip galvanized steel sheet manufacturing apparatus applicable to the present invention. Hereinafter, a method for manufacturing a hot-dip galvanized steel sheet according to one embodiment of the present invention will be described with reference to Fig. 1.

[0054]

[0055] First, a hot-dip galvanized layer is formed on at least one surface of the base steel sheet. The present invention does not specifically limit the method for forming the hot-dip galvanized layer, and any hot-dip galvanized layer forming method commonly used in the relevant technical field can be used. For example, as illustrated in Fig. 1, a method of immersing the base steel sheet (2) in a hot-dip galvanizing bath (1) can be used.

[0056]

[0057] Meanwhile, after the formation of the hot-dip galvanized layer, a step of controlling the adhesion amount of the hot-dip galvanized layer may be additionally included. Through the process of controlling the adhesion amount of the hot-dip galvanized layer, the plating adhesion amount can be appropriately controlled by removing excess plating metal. The present invention does not particularly limit the method for controlling the adhesion amount of the hot-dip galvanized layer, and as an example, an air wiping process using an air knife (3) can be used. In addition, the present invention does not particularly limit the plating adhesion amount, and it can be appropriately controlled depending on the intended use of the hot-dip galvanized steel sheet. However, as an example, the plating adhesion amount may have a range of 20 to 500 g / ㎡ on one side.

[0058]

[0059] Thereafter, an aqueous solution is sprayed onto the hot-dip galvanized layer. When spraying the aqueous solution, it is preferable to spray a mixed aqueous solution and air. Generally, spangles are formed when solidification nuclei are generated and grow during the cooling of the molten zinc-plated layer. In order to refine the size of the spangles, the density of the solidification nuclei must be increased during the solidification reaction stage of the plating layer, and solidification must be completed without dendrite growth. Therefore, in the present invention, by spraying air together with the aqueous solution, the droplets of the aqueous solution are turned into a mist, thereby increasing the density of the solidification nuclei and allowing them to act as solidification nuclei on the surface of the steel sheet. Meanwhile, phosphate-based aqueous solutions have been used in the past to promote nucleation on the surface of the plating layer. However, these solutions contaminate surrounding equipment after drying or remain as a glassy film on the surface of the steel sheet, causing secondary deterioration of physical properties, thus limiting their use. In particular, the glassy phosphate remaining on the surface of the steel sheet can reduce paint adhesion during painting and cause low-temperature joint embrittlement. To improve this, the present invention is characterized by spraying a mixed aqueous solution composed of water, urea, and alcohol to increase the cooling rate of the plating layer when spraying the aqueous solution and to prevent residue from being generated after drying. The spraying of the mixed aqueous solution and air can be accomplished through a spray nozzle (5).

[0060]

[0061] That is, when a mixed aqueous solution composed of water, urea, and alcohol is sprayed instead of a conventional phosphate aqueous solution, the solidification speed of the steel plate surface is accelerated by the endothermic reaction heat of urea, the evaporation heat of alcohol, and the vaporization heat of water, as shown in [Equation 1], [Equation 2], and [Equation 3] below. In addition, the alcohol reduces the surface tension of the aqueous solution, so that the droplets become finer when sprayed compared to the phosphate aqueous solution, forming more solidification nuclei and allowing the molten zinc to cool quickly, resulting in finer spangle sizes. Meanwhile, the water and urea constituting the mixed aqueous solution may be added using a urea solution generally used in the relevant technical field. The present invention does not particularly limit the type of the urea solution, but for example, AdBlue® composed of 67.5% purified water and 32.5% urea ((NH2)2CO) may be diluted and used.

[0062]

[0063] [Equation 1] (NH2)2CO + H2O → 2NH3+ CO2ΔH°(heat of reaction) = 185.5 kJ / mol

[0064] [Formula 2] C2H5OH(l) → C2H5OH(g) ΔH°(heat of vaporization) = 39.3 kJ / mol

[0065] [Equation 3] H2O(l) → H2O(g) ΔH°(heat of vaporization) = 43.1 kJ / mol

[0066]

[0067] The above mixed aqueous solution can be sprayed with the steel plate temperature of the hot-dip galvanizing treatment temperature ~ 419℃ as the spraying start temperature, and the steel plate temperature of 417-415℃ as the spraying end temperature. This is because it is effective to provide solidification nuclei from the outside in order to promote the formation of solidification nuclei. The above 'hot-dip galvanizing treatment temperature' means the temperature of the steel plate in a state in which the amount of deposited hot-dip galvanized layer is controlled, more specifically, in a state in which air-wiping treatment has been performed in the plating process. By spraying the aqueous solution on the steel plate from the hot-dip galvanizing treatment temperature, the steel plate is cooled and the molten zinc solidifies. However, experiments have shown that only droplets deposited around the steel plate temperature of 419℃ can act as solidification nuclei, and the aqueous solution sprayed on the steel plate before or after the solidification of the molten zinc begins only serves to take away the heat of the steel plate. Therefore, in order to form a large number of solidification nuclei, it is preferable to spray the aqueous solution on the steel plate at around 419℃. That is, if the steel plate temperature when starting to spray the aqueous solution is lower than 419℃, there is a risk that the spangles will increase and traces of dendrites will occur. However, since it is difficult to accurately measure the temperature of the steel plate being produced, spraying at 419℃ or higher, when the molten zinc-coated layer is completely molten, can prevent the plating structure from coarsening. Therefore, the spraying start temperature of the mixed aqueous solution may be a steel plate temperature of the molten zinc-coating treatment temperature to 419℃, more advantageously a steel plate temperature of 460 to 419℃, and even more advantageously a steel plate temperature of 430 to 419℃. In addition, if the spraying end temperature of the mixed aqueous solution exceeds 417℃, there is a risk that the solidification nuclei that have been generated will remelt, and if it is lower than 415℃, the solidification and cooling effects will be saturated. Therefore, the spraying end temperature of the mixed aqueous solution may be 417 to 415℃.

[0068]

[0069] It is important to ensure that as many droplets as possible are deposited on the steel plate within the above spray initiation and spray end temperature ranges. Considering this, smaller droplets are more advantageous than larger ones for the same amount of solution sprayed, as this increases the number of droplets.

[0070]

[0071] To this end, the mixed aqueous solution can be sprayed by passing it through a high-voltage charging electrode (6). This allows the aqueous solution droplets to be electrostatically charged and adhere to the steel plate through electrical attraction with the steel plate. Meanwhile, if a mesh-shaped charging electrode is used as the high-voltage charging electrode, a uniform electric field can be formed, thereby further enhancing the effect of the high voltage. Furthermore, since the droplets can be made fine, the pitting phenomenon that occurs when large droplets collide with the molten plating layer can be prevented, thereby preventing damage to the appearance.

[0072]

[0073] This effect becomes more pronounced as the applied voltage increases, and for this purpose, when the mixed aqueous solution passes through the charging electrode, the voltage applied to the charging electrode may be -1 to -50 kV. If the voltage is less than -1 kV, coarse spangles may be formed, and if the voltage is increased excessively, there is a possibility of electric sparks occurring between the charging electrode and the steel plate, so it is preferable to set it to -50 kV or less. Meanwhile, the charging electrode is for creating negatively charged droplets (mist), and the - sign of the voltage indicates polarity.

[0074]

[0075] When the above mixed aqueous solution is sprayed, the average size of the droplets is preferably 10 to 50 μm. By controlling the average size of the droplets in this way, spangles of a uniform size can be formed, thereby obtaining a more beautiful surface appearance. When the average size of the droplets is less than 10 μm, the amount of droplets reaching the steel sheet may be reduced, and when the average size of the droplets exceeds 50 μm, there may be a disadvantage in that the spangle refinement effect is reduced. Therefore, the average size of the droplets is preferably 10 to 50 μm. The lower limit of the average size of the droplets is more advantageously 15 μm, and 20 μm is even more advantageous. The upper limit of the average size of the droplets is more advantageously 45 μm, and 40 μm is even more advantageous.

[0076]

[0077] Meanwhile, as shown in [Equation 1], [Equation 2], and [Equation 3] mentioned above, the urea solution takes away the latent heat of the steel sheet through an endothermic reaction as the urea is decomposed along with the evaporation of alcohol and water, and temporarily remains on the surface to act as solidification nuclei, and the plating layer solidifies around these solidification nuclei. In addition, the alcohol reduces the surface tension of the aqueous solution, which plays a role in reducing the size of the droplets when sprayed and increases the cooling effect of the surface through the heat of evaporation. In general, one solidification nucleus forms one spangle, so when the droplets of the aqueous solution are smaller at the same amount of sprayed aqueous solution, the density of the solidification nuclei increases, which is advantageous for the production of a hot-dip galvanized steel sheet with a small spangle size. Therefore, it is desirable to spray a mixed aqueous solution of an appropriate concentration to further promote the formation of solidification nuclei in the solidification reaction.

[0078]

[0079] The content of the above element is preferably 0.1 to 5.0 wt%. If the content of the above element is less than 0.1 wt%, the spangle refinement effect cannot be sufficiently obtained, and if it exceeds 5.0 wt%, not only does the manufacturing cost increase, but the element may become solid powder due to drying, which may contaminate surrounding equipment. In addition, since a large amount of C remains on the surface of the plating layer, problems such as poor weldability and paint adhesion may occur. Therefore, the content of the above element is preferably 0.1 to 5.0 wt%. The lower limit of the content of the above element is more advantageously 0.2 wt%, and even more advantageously 0.3 wt%. The upper limit of the content of the above element is more advantageously 4.5 wt%, and even more advantageously 4.0 wt%.

[0080]

[0081] The content of the alcohol is preferably 0.1 to 5.0 wt%. If the content of the alcohol is less than 0.1%, the spangle refinement effect cannot be sufficiently obtained, and if it exceeds 5.0%, not only does the manufacturing cost increase, but there may also be damage due to odor due to volatility. Therefore, the content of the alcohol is preferably 0.1 to 5.0 wt%. The lower limit of the content of the alcohol is more advantageously 0.3 wt%, and even more advantageously 0.5 wt%. The upper limit of the content of the alcohol is more advantageously 4.0 wt%, and even more advantageously 3.0 wt%. Meanwhile, the present invention does not particularly limit the type of the alcohol, but, for example, one or more selected from the group consisting of ethanol, propanol, isopropanol, butanol, and isobutanol may be used.

[0082]

[0083] Meanwhile, the spray pressure of the air may be 1.5 to 5.0 kgf / cm2. If the spray pressure of the air is less than 1.5 kgf / cm2, the spray pressure may be too low, making it difficult for the sprayed aqueous solution droplets to adhere to the steel plate. If the spray pressure of the air exceeds 5.0 kgf / cm2, the kinetic energy of the sprayed aqueous solution droplets may be too large, causing pitting marks to occur on the surface of the plating layer, thereby damaging the surface appearance.

[0084]

[0085] The spray pressure of the above mixed aqueous solution may be 0.5 to 2.5 kgf / cm2. If the spray pressure of the above mixed aqueous solution is less than 0.5 kgf / cm2, the spangle refinement effect may be reduced, and if the spray pressure of the above mixed aqueous solution exceeds 2.5 kgf / cm2, pitting marks may occur due to the aqueous solution droplets colliding with the steel plate surface, thereby damaging the appearance.

[0086]

[0087] The above mixed aqueous solution and air can be sprayed at a pressure ratio of 0.3 to 0.9. If the pressure ratio of the mixed aqueous solution and air is less than 0.3, the aqueous solution may not be sprayed, making it difficult to obtain the spangle refinement effect. If the pressure ratio of the mixed aqueous solution and air exceeds 0.9, drop marks may occur, damaging the surface appearance.

[0088]

[0089] Thereafter, the molten zinc plating onto which the aqueous solution has been sprayed is cooled. Through this cooling process, a molten zinc plating layer with finely divided spangles can be formed. The present invention does not specifically limit the cooling process, and any cooling conditions commonly used in the relevant technical field can be utilized.

[0090]

[0091] 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.

[0092]

[0093] (Example)

[0094] A base steel sheet having a thickness of 0.8 mm was immersed in a hot-dip galvanizing bath containing Al: 0.18 wt% and the balance Zn, containing C: 0.03%, Si: 0.01%, Mn: 0.15%, P: 0.008%, the balance Fe and other unavoidable impurities, at a moving speed of 80 m / min, and air-wiped to form a hot-dip galvanized layer on the base steel sheet so as to have a plating amount of 70 g / ㎡ per side. Thereafter, a mixed aqueous solution having the composition shown in Table 1 below and air were simultaneously sprayed onto the surface of the hot-dip galvanized layer through a two-fluid spray nozzle. At this time, the spraying start temperature of the mixed aqueous solution was a steel sheet temperature of 420°C, and the spraying end temperature was a steel sheet temperature of 417°C. Thereafter, the hot-dip galvanized layer on which the aqueous solution was sprayed was cooled. Meanwhile, in the case of Comparative Example 10, the mixed aqueous solution and air injection described above were not performed.

[0095]

[0096] The average spangle size, surface carbon content, corrosion resistance, paint adhesion, and surface appearance of the hot-dip galvanized layer of the hot-dip galvanized steel sheet manufactured in this manner were measured, and the results are shown in Table 2 below.

[0097]

[0098] The average spangle size was measured as follows. Ten straight lines were drawn at equal intervals vertically and horizontally on the photographs of the hot-dip galvanized layer using an optical microscope and SEM, and the total number of spangles passing through these straight lines was counted. After that, the sum of the straight line lengths was calculated and divided by the total number of spangles to determine the average length of one spangle. This was regarded as the equivalent diameter of a circle and measured as the average spangle size (sum of straight line lengths / total number of spangles = average length of one spangle).

[0099]

[0100] The carbon content of the surface layer of the hot-dip galvanized layer was measured using the EDS carbon atom surface analysis method, which is the C content in an area within 2 ㎛ in the thickness direction from the surface of the hot-dip galvanized layer.

[0101]

[0102] Meanwhile, in order to evaluate the corrosion resistance and coating adhesion after painting, specimens were manufactured from the hot-dip galvanized steel sheet manufactured above. The specimens were manufactured by coating the hot-dip galvanized steel sheet with melamine alkyd resin to a thickness of approximately 20 μm using a roll-coater coating tester, baking the resultant at a plate temperature (PMT) of 160°C for 30 seconds, and then cooling it to room temperature with water.

[0103]

[0104] After painting, the corrosion resistance was tested by spraying 5% NaCl at 35℃ at 1 kg / m using a salt spray device (Japanese Industrial Standard Test Method JIS E2731) on the above specimen. 2 After spraying at a spray pressure of , the time required for 5% white rust generation was evaluated. At this time, if it took 480 hours or more but less than 680 hours, it was evaluated as ○ (excellent), if it took 360 hours or more but less than 480 hours, it was evaluated as △ (average), and if it took less than 360 hours, it was evaluated as × (poor).

[0105]

[0106] The adhesion of the coating was evaluated by immersing the above-mentioned specimen in distilled water at 50℃ for 240 hours, naturally drying it, making 100 checkerboard-shaped marks at 1 mm intervals on the surface of the coating, and then peeling the coating with Scotch tape, counting the number of coatings that peeled off the tape. At this time, if there was no peeling, it was evaluated as ○ (excellent), if the peeling rate was more than 0% but less than 3%, it was evaluated as △ (average), and if it was more than 3%, it was evaluated as × (poor).

[0107]

[0108] The surface appearance was evaluated by measuring the color difference (ΔE) compared to Comparative Example 10, and if it was 0.5 or more, it was evaluated as ○, if it was 0.3 or more but less than 0.5, it was evaluated as △ (normal), and if it was less than 0.3, it was evaluated as × (poor).

[0109]

[0110] Composition of mixed solution (weight%)Average droplet size (㎛)Air injection pressure (kgf / ㎠)Mixed solution injection pressure (kgf / ㎠)Mixed solution and air Pressure ratio urea alcohol water invention example 150.1 residue 501.50.90.6 invention example 230.1 residue 501.50.90.6 invention example 310.1 residue 501.50.90.6 invention example 40.50.1 residue 501.50.90.6 invention example 553 residue 401.50.90.6 invention example 633 residue 401.50.90.6 invention example 713 residue 401.50.90.6 invention example 80.53 residue 401.50.90.6 invention example 951.5 residue 401.50.90.6 invention example 1031.5 residue 401.50.90.6 invention example 1111.5 Residue 401.50.90.6 Invention Example 120.51.5 Residue 401.50.90.6 Comparative Example 100 Residue 1002.51.50.6 Comparative Example 203 Residue 902.51.50.6 Comparative Example 301 Residue 902.51.50.6 Comparative Example 403 Residue 702.51.50.6 Comparative Example 501 Residue 702.51.50.6 Comparative Example 673 Residue 602.51.50.6 Comparative Example 773 Residue 402.51.50.6 Comparative Example 80.13 Residue 802.51.50.6 Comparative Example 90.13 Residue 702.51.50.6 Comparative Example 10-------

[0111]

[0112] Classification Spangle average size (㎛) Surface carbon content (weight %) Corrosion resistance after coating Coating adhesion Surface appearance Invention example 11500.1○○○Invention example 21500.1○○○Invention example 31500.1○○○Invention example 41500.1○○○Invention example 51200.1○○○Invention example 61200.1○○○Invention example 71200.1○○○Invention example 81200.1○○○Invention example 91200.1○○○Invention example 101200.1○○○Invention example 111200. 1○○○Invention Example 121200.1○○○Comparative Example 13000.1○○△Comparative Example 22500.1○○△Comparative Example 32600.1○○△Comparative Example 42000.1○○△Comparative Example 52000.1○○△Comparative Example 61800.5△△○Comparative Example 71200.5△△○Comparative Example 82400.1○○△Comparative Example 92000.1○○△Comparative Example 105000.1○○×

[0113]

[0114] As can be seen from Tables 1 and 2 above, in the case of Inventive Examples 1 to 12, which satisfy the conditions proposed by the present invention, it can be seen that the corrosion resistance, paint adhesion, and surface appearance are good. On the other hand, in the case of Comparative Examples 1 to 10, which do not satisfy the conditions proposed by the present invention, it can be seen that at least one of the corrosion resistance, paint adhesion, and surface appearance is not good.

[0115]

[0116] Figure 2 shows the EPMA analysis results for the hot-dip galvanized layer of Invention Example 1. Figure 3 shows the EPMA analysis results for the hot-dip galvanized layer of Comparative Example 23. As can be seen from Figures 2 and 3, in the case of Invention Example 1, almost no carbon is observed, but in the case of Comparative Example 6, a relatively large amount of carbon is observed.

[0117]

[0118] [Explanation of symbols]

[0119] 1: Hot-dip galvanizing bath

[0120] 2: Steel plate

[0121] 3: Air knife

[0122] 4: Spray tank

[0123] 5: Injection nozzle

[0124] 6: Electrode

[0125] 7: Air curtain

[0126] 8: Intake hood

[0127] 9: Pyrometer

Claims

1. Including a steel plate and a hot-dip galvanized layer formed on at least one surface of the steel plate, The average size of the spangles formed on the surface of the above molten zinc plating layer is 150㎛ or less (excluding 0㎛), A hot-dip galvanized steel sheet having a C content of 0.2 wt% or less (including 0%) in a region within 2 ㎛ in the thickness direction from the surface of the hot-dip galvanized layer.

2. A step of forming a molten zinc plating layer on at least one surface of the steel plate; A step of spraying an aqueous solution onto the molten zinc-plated layer; and It includes a step of cooling the molten zinc plating onto which the above aqueous solution is sprayed, The step of spraying the above aqueous solution includes spraying a mixed aqueous solution and air, The above mixed aqueous solution is composed of water, urea and alcohol, When the above mixed aqueous solution is sprayed, the average size of the droplets is 10 to 50 μm. The content of the above elements is 0.1 to 5.0 wt%, A method for manufacturing a hot-dip galvanized steel sheet wherein the alcohol content is 0.1 to 5.0 wt%.

3. In claim 2, A method for manufacturing a hot-dip galvanized steel sheet, further comprising a step of controlling the adhesion amount of the hot-dip galvanized layer between the step of forming the hot-dip galvanized layer and the step of spraying the aqueous solution.

4. In claim 2, A method for manufacturing a hot-dip galvanized steel sheet, wherein the above mixed aqueous solution is sprayed at a steel sheet temperature of 419°C to 419°C, which is the hot-dip galvanizing treatment temperature, as the spraying start temperature, and at a steel sheet temperature of 417 to 415°C, which is the spraying end temperature.

5. In claim 2, A method for manufacturing a molten galvanized steel sheet in which the above mixed aqueous solution is sprayed through a charging electrode.

6. In claim 5, A method for manufacturing a hot-dip galvanized steel sheet, wherein when the above mixed aqueous solution passes through a charging electrode, the voltage applied to the charging electrode is -1 to -50 kV.

7. In claim 2, A method for manufacturing a hot-dip galvanized steel sheet, wherein the alcohol is at least one selected from the group consisting of ethanol, propanol, isopropanol, butanol, and isobutanol.

8. In claim 2, A method for manufacturing a hot-dip galvanized steel sheet wherein the air injection pressure is 1.5 to 5.0 kgf / ㎠.

9. In claim 2, A method for manufacturing a hot-dip galvanized steel sheet wherein the spray pressure of the above mixed aqueous solution is 0.5 to 2.5 kgf / ㎠.

10. In claim 2, A method for manufacturing a hot-dip galvanized steel sheet, wherein the above mixed aqueous solution and air are sprayed at a pressure ratio of 0.3 to 0.9.

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