Composition for surface treatment of steel sheet, plated steel sheet surface-treated therewith, method for manufacturing the same, and hot-formed member

Abstract

The present invention relates to a surface-treated steel sheet suitable as a material for a sheet for a vehicle, and more particularly, to a composition for surface treatment of a plated steel sheet and a plated steel sheet surface-treated with the composition and a method for manufacturing the same, and a hot-formed member.

Description

Technical Field

[0001] This invention relates to a surface-treated steel sheet suitable for use as a material for automotive sheet metal, and more specifically, to a composition for surface treatment of plated steel sheets, a plated steel sheet surface-treated with the composition, a method for manufacturing the same, and thermoformed components. Background Technology

[0002] Typically, automotive sheet metal is made of galvanized steel sheet, which is inexpensive, has excellent corrosion resistance (resistance to pitting corrosion), and a beautiful surface appearance. Therefore, its use in automotive interior and exterior panels is gradually increasing.

[0003] The steel sheets used in automotive sheet metal are stamped and formed during the automobile manufacturing process, then assembled through welding and bonding, followed by degreasing, phosphate treatment, and coating. Therefore, galvanized steel sheets used in automotive sheet metal require specific physical properties such as lubricity, weldability, adhesion, release properties, and paintability.

[0004] In addition, the physical properties required for zinc-plated steel sheets vary depending on the type of plating, and supplementation is needed for those with relatively poor physical properties.

[0005] As an example, hot-dip galvanized (GI) and electro-galvanized (EG) steel sheets, due to their soft coatings, suffer from coating peeling and fusion issues at the ribs and other parts of the die during stamping processes involving high pressure and high speed friction. This results in defects such as scratches or dents on the steel sheet surface.

[0006] As another example, in the case of alloyed hot-dip galvanized steel sheet (GA), which has a high coefficient of surface friction, the low lubrication properties during stamping can lead to problems such as the raw material itself breaking or the hard coating peeling off and pulverizing.

[0007] To address this friction issue, a post-treatment process is being implemented for the surfaces of galvanized steel sheets and zinc-based alloy coated steel sheets used as automotive sheet metal.

[0008] As related technologies, techniques for forming a phosphate film on the surface of a zinc-plated layer (Patent Document 1 and Patent Document 2) and techniques for forming a metal oxide layer (Patent Document 3 and Patent Document 4) can be cited. However, these technologies are complex and have limitations in the types of zinc-plated steel sheets that can be applied.

[0009] Patent Documents 1 and 2 require processes such as surface conditioning, phosphate treatment, washing, and drying, which have drawbacks such as requiring considerable equipment space and solution management in actual operation. Furthermore, since the treatment method relies on the reactivity with the coating, there are inconveniences such as needing to change the solution composition depending on the type of zinc-plated steel sheet.

[0010] In the cases of Patent Documents 3 and 4, due to the limitation of the coating composition (metal composition), there is a limitation that it cannot be applied to all zinc-plated steel sheets.

[0011] Therefore, there is a need for a solution that can perform post-treatment (surface treatment) on zinc-coated steel sheets without requiring multiple processes, while effectively improving the lubricity (friction characteristics) of various zinc-coated steel sheets.

[0012] Furthermore, in recent years, automakers have continuously conducted research on lightweight vehicle bodies to improve fuel efficiency and meet CO2 emission regulations. As part of this effort, hot forming has been proposed to increase the strength of steel while maintaining the same weight. Hot forming involves processing steel with a certain strength in the austenitic single-phase region, followed by rapid cooling to a low temperature, thereby forming martensite and other low-temperature structures within the steel. This method can dramatically increase the strength of products, thus minimizing the reduced processability issues encountered when manufacturing high-strength (ultra-high-strength) components.

[0013] In addition, as efforts continue to achieve nationwide carbon neutrality, automakers and steel companies are jointly conducting various studies on technologies that can reduce CO2 emissions during hot forming.

[0014] To achieve this, a technique has been proposed to shorten the heating time to reach the target temperature during high-temperature heating for hot forming. As a related technology, Patent Document 5 discloses a method for coating a polymer on the surface of a steel sheet. As mentioned above, while coating a hydrocarbon polymer on the surface of a steel sheet can increase the heating rate during hot forming, residues are generated on the surface after hot forming, which may lead to problems such as reduced weldability.

[0015] Therefore, there is a need for a solution that can increase the heating rate during hot forming without reducing the physical properties, even when the surface treatment of steel sheets (coated steel sheets) suitable for hot forming is performed.

[0016] (Patent Document 1) Korean Patent Publication No. 2001-0074527 (Patent Document 2) Japanese Patent Publication No. 2003-206106 (Patent Document 3) Japanese Patent Publication No. 1990-190483 (Patent Document 4) Japanese Patent Publication No. 2014-185381 (Patent Document 5) Chinese Patent Publication No. 10616418 Summary of the Invention

[0017] (a) Technical problems to be solved One aspect of the present invention is to provide a composition for surface treatment of galvanized steel sheets, which not only improves the lubricity of the surface-treated zinc-plated steel sheets, but also shortens the heating time during high-temperature heating for hot forming of the surface-treated galvanized steel sheets for hot forming.

[0018] Furthermore, a plated steel sheet surface-treated using a surface treatment composition according to one aspect of the present invention and a method for manufacturing the same are provided.

[0019] As another aspect of the present invention, it is intended to provide a thermoformed component obtained by thermoforming a surface-treated coated steel sheet.

[0020] The technical problems to be solved in this invention are not limited to those mentioned above. Those skilled in the art to which this invention pertains can clearly understand other technical problems not mentioned from the following description.

[0021] (II) Technical Solution According to one aspect of the present invention, a composition for surface treatment of steel plates is provided, the composition comprising an inorganic compound, an organic compound and a balance solvent, wherein the organic compound is a fatty acid-based organic compound or a dicarboxyl acid-based organic compound with a molecular weight of less than 1000.

[0022] In one embodiment of the invention, the content of organic compounds may be 0.15-7.50% based on 100% by weight of the total solids of the composition.

[0023] As described above, the composition for surface treatment of steel plates contains organic compounds, and in particular, by containing fatty acid-based organic compounds, the lubricity of surface-treated steel plates (especially galvanized steel plates) can be improved.

[0024] In one embodiment of the invention, the inorganic compound may be one or more selected from phosphorus (P), boron (B) and zirconium (Zr), and may further contain one or more selected from nickel (Ni), manganese (Mn), molybdenum (Mo), zinc (Zn) and silicon (Si).

[0025] According to another aspect of the present invention, a surface-treated zinc-coated steel sheet or aluminum-coated steel sheet is provided, comprising: a base steel sheet; a zinc-coated or aluminum-coated layer formed on at least one side of the base steel sheet; and a surface-treated thin film layer formed on the zinc-coated or aluminum-coated layer.

[0026] In one embodiment of the present invention, the surface treatment thin film layer formed on the zinc-based or aluminum-based coating may be formed by a composition of one embodiment of the present invention.

[0027] In one embodiment of the present invention, the surface treatment film layer consists of two layers, an upper layer and a lower layer, wherein the carbon (C) distribution of the upper and lower layers can satisfy the following relationship 1.

[0028] [Relation 1] (Top layer carbon content) / (bottom layer carbon content) > 1.0 Thus, according to one embodiment of the present invention, the surface-treated zinc-plated steel sheet or aluminum-plated steel sheet can have a surface-treated thin film layer containing organic compounds, wherein the content distribution of said organic compounds is obtained in the thickness (depth) direction, thereby achieving improved lubricity.

[0029] In one embodiment of the present invention, the surface treatment thin film layer formed on the zinc-based or aluminum-based coating may have a thickness of 0.1-1.0 μm.

[0030] According to another aspect of the present invention, a method for manufacturing a surface-treated coated steel sheet is provided, comprising the steps of: preparing a coated steel sheet on which a zinc-based coating or an aluminum-based coating is formed on at least one side of a base steel sheet; applying a surface treatment composition to the coating; and drying the coated steel sheet with the surface treatment composition to form a surface treatment film layer.

[0031] In one embodiment of the present invention, the step of coating the coating with a surface treatment composition can be performed using a solution composition of one embodiment of the present invention.

[0032] In one embodiment of the invention, the step of coating the surface treatment composition can be carried out at a concentration of 100-1000 mg / m³. 2 The amount of adhesion is determined.

[0033] In one embodiment of the invention, the post-coating drying step can be performed at a temperature range of 70-150°C, based on the PMT of the coated steel sheet.

[0034] According to another aspect of the present invention, a thermoformed component is provided, comprising: a base steel plate; an aluminum-based coating formed on at least one side of the base steel plate; and a surface treatment film layer formed on the aluminum-based coating.

[0035] (III) Beneficial Effects According to the present invention, a composition for surface treatment of steel plates composed of inorganic and organic compounds can be provided, which can be coated by a simple coating method, thus having an economic effect of reducing process costs.

[0036] Furthermore, when zinc-plated steel sheets or aluminum-plated steel sheets are surface-treated using the composition provided in this invention, the lubricity of the surface-treated zinc-plated steel sheets or aluminum-plated steel sheets can be improved, thus significantly improving the formability of cold forming or hot forming.

[0037] In particular, when processing surface-treated zinc-coated steel sheets or aluminum-coated steel sheets into parts with complex shapes or severe drawing processes, or under conditions of high stamping loads such as cold forming of high-strength steel materials, cracks in the steel sheets can be prevented, thereby improving formability.

[0038] Furthermore, even when surface-treating hot-formed coated steel sheets using the composition provided by the present invention, formability can be improved during blanking operations to form specific automotive parts. In particular, when manufacturing parts from surface-treated hot-formed coated steel sheets, the heating time during high-temperature heating for hot forming can be reduced, resulting in economic and environmentally beneficial effects. Attached Figure Description

[0039] Figure 1 This schematically illustrates the cross-sectional shape of a surface-treated steel sheet according to one embodiment of the present invention.

[0040] Figure 2 This is a side view showing a test piece for measuring adhesive strength according to an embodiment of the present invention. Best practice

[0041] Hereinafter, preferred embodiments of the present invention will be described with reference to various implementation schemes. However, the embodiments of the present invention can be modified into various other embodiments, and the scope of the present invention is not limited to the embodiments described below.

[0042] This invention provides a composition for surface treatment of steel plates, a plated steel plate for surface treatment using the composition, and a method for manufacturing the same. The invention will be described in detail below.

[0043] The inventors of this invention recognized the problem of insufficient lubrication properties when zinc-coated steel sheets are used as materials for automotive sheet metal, and conducted in-depth research to solve this problem.

[0044] Meanwhile, the inventors of this invention have conducted in-depth research on solutions that can meet the physical performance requirements of the automotive industry, where the hot-forming coated steel sheet is used, while reducing CO2 generation during the hot-forming process of the coated steel sheet. In particular, solutions that can improve the heating rate during the high-temperature heating for forming the hot-forming coated steel sheet have been investigated.

[0045] As a result, it was confirmed that a composition for surface treatment of steel sheets can be provided, which not only significantly improves the cold-pressing formability of zinc-plated steel sheets by increasing lubricity, but also ensures the physical properties required for the surface treatment layer of the plating steel sheet for hot forming, such as corrosion resistance and bending performance. At the same time, by reducing the heating time to the target temperature for high-temperature forming, it achieves the effects of improved productivity and reduced CO2. Thus, the present invention is completed.

[0046] According to one aspect of the present invention, a composition for surface treatment of steel plates comprising an inorganic compound, an organic compound, and a balance solvent is provided. The components constituting the composition are described in detail below. Furthermore, the component content within a thin film layer obtained by treatment with the composition is explained. Here, unless otherwise specified, the content of each component is based on 100% by weight of the total composition (solution composition) or 100% by weight of the dried thin film layer.

[0047] Inorganic compounds When a surface treatment composition is applied to the coating of a plated steel sheet to form a surface treatment film layer, it is necessary to improve the adhesion between the coating and the film layer. Therefore, the surface treatment composition for steel sheets according to one embodiment of the present invention comprises an inorganic compound.

[0048] In one embodiment of the invention, the inorganic compound may be one or more selected from phosphorus (P), boron (B) and zirconium (Zr), and may further contain one or more selected from nickel (Ni), manganese (Mn), molybdenum (Mo), zinc (Zn) and silicon (Si).

[0049] In one embodiment of the invention, the inorganic compound may be one or more of a substance composed of acetates, carbonates, alkali metal salts, ammonium salts or oxides or hydroxides of the aforementioned metals.

[0050] In one embodiment of the invention, the content of inorganic compounds in the composition is not particularly limited. That is, it is preferable to contain a level at which the surface treatment film layer does not peel off or fall off during the processing, forming, etc., of the surface-treated coated steel sheet and remains until the final part is manufactured. As an example, based on 100% by weight of the total composition, it may contain 5-15% by weight, where the content refers to the content in the solution composition.

[0051] organic compounds From the perspective of obtaining the target physical properties when performing surface treatment on coated steel sheets, the composition for surface treatment of steel sheets according to one embodiment of the present invention may contain organic compounds.

[0052] In one embodiment of the invention, the inorganic compound exists in the surface-treated film layer obtained by coating the composition as a high-hardness oxide or as a hydroxide with low resistance to shear forces, thereby contributing to lubricity. However, this is not a level conducive to molding. Therefore, it is technically significant that the composition according to one embodiment of the invention further comprises organic compounds in addition to the aforementioned inorganic compounds.

[0053] As described above, in the forming process of coated steel sheets surface-treated with a composition containing inorganic and organic compounds, for example, when stamping (cold forming) a surface-treated zinc-coated steel sheet using a die, the coated steel sheet can be imparted with significantly improved lubricity. This can prevent phenomena such as coating peeling or steel material breakage during stamping of the coated steel sheet. Furthermore, even better lubricity can be achieved under the high-load stamping conditions applied when processing high-strength steel coated steel sheets into parts.

[0054] In addition, when hot-formed coated steel sheets surface-treated with the above composition are used, for example, in the high-temperature heating of aluminum-based coated steel sheets for hot forming, the composition, having a high heat of combustion, can shorten the time required to reach the target temperature. As an example, when the solution used in the surface treatment contains a substance with a high heat of combustion, the surface temperature rises rapidly in the furnace during the hot forming of the coated steel sheet due to the heat of combustion of the substance in the coating solution. Therefore, the time required to reach the target temperature can be shortened.

[0055] Thus, the main objective of this invention is to improve the lubrication properties of surface-treated coated steel sheets while shortening the heating time during high-temperature heating of surface-treated hot-forming coated steel sheets. To achieve this, the organic compound preferably comprises a monocarboxyl acid system such as a fatty acid-based organic compound or a dicarboxylic acid-based organic compound having carboxyl groups at both ends.

[0056] In one embodiment of the invention, the organic compound has a melting point of 50°C or higher, is in a solid phase at room temperature, and has lower viscosity in the molten state, which is more advantageous. Therefore, a molecular weight of 1000 or lower is preferred. When the molecular weight is greater than 1000 and the viscosity in the molten state is high (viscous), it may contaminate the equipment during the production process and component processing.

[0057] In one embodiment of the present invention, the organic compound may be a fatty acid-based organic compound such as fatty acids, fatty acid salts, or fatty acid amides, or a dicarboxylic acid or a dicarboxylic acid salt.

[0058] As a non-limiting example, the fatty acid may be one or more selected from stearic acid, 12-hydroxystearic acid, 12-oxostearic acid, palmitic acid, and oleic acid. Furthermore, the fatty acid base salt may be sodium stearate, sodium laurate, sodium oleate, etc., and the fatty acid amide may be stearamide. In addition, the dicarboxylic acid group can be one or more of the following: adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, and dodecanedioic acid. The dicarboxylic acid salt can be one or more of the following: disodium adipate, diammonium adipate, disodium decanedioate, and diammonium decanedioate.

[0059] Additionally, the fatty acid-based organic compound may also comprise an ether of fatty acid and polyoxyethylene(n), an ester of fatty acid and polyoxyethylene(n), or a fatty acid ester. As a non-limiting example, the ether of fatty acid and polyoxyethylene(n) may be a polyoxyethylene(n) stearyl ether with n being 10 or less, and the ester of fatty acid and polyoxyethylene(n) may be a polyoxyethylene(n) stearate with n being 10 or less. Furthermore, the fatty acid ester may be one or more of ethylene glycol monostearate, sorbitan monostearate, and glycerol monostearate.

[0060] In one embodiment of the invention, the content of the organic compound can be 0.15-7.50% based on 100% by weight of the total composition. A higher content of the organic compound is more advantageous from the perspectives of improving the lubricity of the surface-treated coated steel sheet and increasing the heat of combustion.

[0061] The content of this organic compound in the surface-treated thin film layer (dry thin film layer) obtained by surface treatment of the composition according to one embodiment of the present invention is important, and it can be present at 2-50% based on 100% by weight of the thin film layer. When the content of the organic compound in the thin film layer is 2% or more, the effect of adding the organic compound can be obtained. However, when the content of the organic compound is greater than 50%, the sealant adhesion will be significantly worse due to excessive reduction in shear resistance, which may cause other problems such as equipment contamination. In another embodiment of the present invention, the content of the organic compound can be 2-30% based on 100% by weight of the thin film layer, and as another embodiment, it can be 5-20%.

[0062] Furthermore, in a steel plate surface treatment composition according to one embodiment of the present invention, if the organic compound contained in the composition is a poorly soluble substance or has low dispersibility in solution under conditions of high content, additives such as emulsifiers may be further included. This is to ensure that the organic compound is sufficiently dispersed in a solvent such as water when the composition is prepared into a solution composition for coating treatment. In this case, the emulsifier may be appropriately selected and added in a certain amount depending on the type and amount of the organic compound.

[0063] Furthermore, according to one embodiment of the present invention, the composition for surface treatment of steel plates is a solution composition, in which the solvent used is not particularly limited and can be water. In this case, the water can be distilled water or deionized water. As described above, the solution composition can be prepared by adding the aforementioned inorganic and organic compounds to the solvent and then dissolving it. In one embodiment of the present invention, the solid content of the solution composition can be 8-15% by weight.

[0064] Hereinafter, a detailed description will be given of the coated steel sheet according to another aspect of the present invention, specifically a surface-treated zinc-coated steel sheet and a surface-treated hot-forming coated steel sheet.

[0065] According to one aspect of the present invention, a surface-treated zinc-coated steel sheet may include: a base steel sheet; a zinc coating formed on at least one side of the steel sheet; and a surface-treated thin film layer formed on the coating.

[0066] According to another aspect of the invention, a surface-treated thermoforming coated steel sheet may include: a base steel sheet; an aluminum-based coating formed on at least one side of the steel sheet; and a surface-treated thin film layer formed on the coating.

[0067] In one embodiment of the present invention, any steel plate can be used as long as it can be obtained by plating, and therefore its type and alloy composition are not particularly limited. The plating steel plate in this case includes not only zinc-plated steel plates but also aluminum-plated steel plates with aluminum coatings.

[0068] As a non-limiting example, the base steel plate may be carbon steel containing a certain amount of carbon (C), manganese (Mn), silicon (Si), phosphorus (P), sulfur (S), etc., which is well known in the art, and therefore the composition of alloying elements is not particularly limited.

[0069] In one embodiment of the invention, a zinc-based coating may be included on at least one side of the base steel plate. The zinc-based coating is a layer containing zinc (Zn) as the main component, for example, a coating containing 50% by weight or more Zn. Furthermore, the coating may be a zinc-based alloy coating that, in addition to zinc (Zn), further contains one or more elements such as aluminum (Al), magnesium (Mg), and silicon (Si). This coating can be applied not only to one side of the base steel plate but also to both sides.

[0070] In one embodiment of the invention, there is no particular limitation on the type of zinc-coated steel sheet having a zinc coating on at least one side of the base steel sheet. However, as a non-limiting example, it may be a hot-dip galvanized steel sheet manufactured by hot-dip galvanizing, an alloyed hot-dip galvanized steel sheet, or an electro-galvanized steel sheet manufactured by electro-galvanizing, or a zinc-based electro-alloy coated steel sheet.

[0071] Furthermore, in another embodiment of the invention, an aluminum-based coating may be included on at least one side of the base steel plate. It should be noted that this base steel plate is different from the base steel plate on which the zinc-based coating is formed. In other words, it does not mean that one side of the base steel plate includes a zinc-based coating and the other side includes an aluminum-based coating.

[0072] In one embodiment of the invention, the aluminum-based coating may be a coating containing aluminum (Al) as the main element. As an example, by weight percent, the aluminum-based coating may contain 0-27% zinc (Zn), 7.0-10.0% silicon (Si), the balance being aluminum (Al), and unavoidable impurities. Such a coating may be applied to one side of the base steel plate, or it may be applied to both sides.

[0073] In one embodiment of the invention, the aluminum coating can be formed by immersing the base steel plate in an aluminum molten plating bath, as will be described in detail later. It is known that the composition of the aluminum coating is determined by the composition of the aluminum molten plating bath.

[0074] In one embodiment of the invention, zinc (Zn) in the alloy composition of the aluminum-based coating is an element that helps ensure the corrosion resistance of the coating, achieving a sacrificial corrosion protection effect due to Zn. As an example, when the Zn content is greater than 27%, during the hot forming of the base steel sheet with the coating, the Zn diffuses into the interior of the base steel sheet, potentially causing cracks due to low metallization (LME). Therefore, the Zn content can be at most 27%, and even 0% does not pose a problem in ensuring the physical properties of the aluminum-based coating.

[0075] In one embodiment of the present invention, the silicon (Si) in the alloy composition constituting the aluminum-based coating can suppress the diffusion of Al present in the plating bath into the interior of the base steel plate during plating. As an example, to achieve the above effect, the Si content can be 7% or more. However, when the Si content is greater than 10%, the melting point of the plating bath may increase sharply, leading to a problem of a sharp increase in the amount of ash generated in the plating bath.

[0076] In one embodiment of the present invention, a surface-treated thin film layer may be included on the zinc-based plating layer. That is, a coating with a certain thickness may be formed on the zinc-based plating layer.

[0077] Furthermore, in one embodiment of the present invention, the aluminum-based coating may include a surface-treated thin film layer, which may also have a certain thickness.

[0078] In one embodiment of the present invention, the surface treatment thin film layer disposed on a zinc-based or aluminum-based coating can be formed from a steel plate surface treatment composition according to an embodiment of the present invention. That is, the thin film layer formed from the composition according to an embodiment of the present invention comprises inorganic compounds and organic compounds.

[0079] Therefore, surface-treated coated steel sheets can possess the desired physical properties. In particular, zinc-coated steel sheets can achieve a significant improvement in lubricity, and aluminum-coated steel sheets, as an example of coated steel sheets for hot forming, can not only shorten the heating time during high-temperature heating for hot forming, but also improve bending properties and resistance to hydrogen embrittlement (hydrogen absorption).

[0080] In one embodiment of the present invention, the surface treatment film layer may consist of two layers, an upper layer and a lower layer. That is, the film layer formed by the surface treatment composition according to one embodiment of the present invention has an organic compound content distribution in the depth direction, and the carbon (C) distribution of the upper and lower layers can satisfy the following relationship 1.

[0081] [Relation 1] (Top layer carbon content) / (bottom layer carbon content) > 1.0 As described above, according to one embodiment of the present invention, the surface-treated thin film layer is formed from a composition comprising inorganic and organic compounds, wherein the inorganic compounds are composed of metals such as P, B, and Zr, and the organic compounds may comprise fatty acid-based organic compounds, the types of which can be replaced by the contents described above.

[0082] As an example, when a composition according to an embodiment of the present invention is applied to the coating surface of a zinc-coated steel sheet, the coating components (e.g., Zn) within the coating are etched and oxidized through etching, and inorganic compounds in the composition precipitate at the surface (interface) of the coating to form a thin film. Furthermore, the organic compounds contained in the composition do not react with the coating, and therefore are mainly distributed in the upper part of the surface-treated thin film layer compared to the interface adjacent to the coating. As a result, the surface-treated thin film layer formed on the coating according to an embodiment of the present invention mainly contains inorganic compounds near the interface with the coating, and can consist of a lower layer with relatively fewer organic compounds and an upper layer composed of a relatively larger amount of organic compounds compared to the lower layer. This structure of upper and lower layers, as described above, can occur not only in zinc-coated steel sheets but also in aluminum-coated steel sheets used for hot forming.

[0083] In particular, the composition according to one embodiment of the present invention contains fatty acid-based organic compounds as organic compounds, so the carbon distribution of the upper and lower layers of the surface-treated thin film layer can satisfy Equation 1. Therefore, the lubrication characteristics of zinc-plated steel sheets and aluminum-plated steel sheets with surface treatment can be improved.

[0084] In one embodiment of the invention, the departure from Equation 1 corresponds to a situation where the upper layer of the surface-treated thin film layer does not primarily contain organic compounds. In this case, compared to the case where Equation 1 is satisfied with the same amount of added organic compounds, the lubricity of the plated steel sheet decreases. Furthermore, due to the large amount of organic compounds present in the lower layer, the adhesion between the surface-treated thin film layer and the plating interface decreases, potentially causing other problems such as reduced sealant adhesion.

[0085] In one embodiment of the invention, the carbon distribution in the thickness direction of the surface-treated thin film layer can be confirmed by measuring the amount of carbon in the upper and lower layers constituting the thin film layer using a glow discharge spectrometer (GDS) or by analyzing the cross-section of the thin film layer in the thickness direction using an energy dispersive spectrometer (EDS, such as an SEM-EDS device).

[0086] According to one embodiment of the present invention, the surface-treated thin film layer can have a thickness of 0.1-1.0 μm. This thickness is based on the thickness after drying. When the thickness of the thin film layer is less than 0.1 μm, the solution composition coating on the roughness protrusions of the plated steel sheet is too thin, resulting in deterioration in lubricity, corrosion resistance, flexibility, and resistance to hydrogen embrittlement. On the other hand, when the thickness of the thin film layer is greater than 1.0 μm, due to its excessive thickness, the adhesion of the sealant deteriorates, and the processing cost of the solution composition increases, which is economically disadvantageous.

[0087] Furthermore, in one embodiment of the present invention, the surface treatment thin film layer having an upper and lower layer structure can be defined as follows: the region from the outermost (extreme) surface towards the thickness (depth) direction where the value of Equation 1 is greater than 1.0 can be considered as the upper layer, and the other regions can be considered as the lower layer. In other words, based on the value of Equation 1, the point from which its value becomes less than 1.0 to the surface (interface) in contact with the coating can be considered as the lower layer.

[0088] Hereinafter, a method for manufacturing a zinc-plated steel sheet, i.e. a surface-treated zinc-plated steel sheet, according to another aspect of the present invention will be described.

[0089] Furthermore, a method for manufacturing a hot-formed coated steel sheet according to another aspect of the present invention, namely a surface-treated hot-formed coated steel sheet, will be described.

[0090] However, it should be noted that the following manufacturing methods correspond to an example of manufacturing surface-treated zinc-coated steel sheets and surface-treated hot-formed coated steel sheets, respectively.

[0091] Firstly, in one embodiment of the present invention, the surface-treated zinc-coated steel sheet can be manufactured by the following steps: preparing a coated steel sheet on at least one side of a base steel sheet having a zinc coating; applying a surface-treatment composition to the zinc coating of the coated steel sheet; and drying the coated steel sheet after the coating.

[0092] In one embodiment of the present invention, the surface-treated aluminum-coated steel sheet can be manufactured by the following steps: preparing a coated steel sheet having an aluminum coating formed on at least one side of a base steel sheet; applying a surface treatment composition to the aluminum coating of the coated steel sheet; and drying and curing the coated steel sheet after applying the composition to form a surface treatment film layer.

[0093] In one embodiment of the invention, any steel plate can be used for forming a zinc-based or aluminum-based coating on at least one side, as long as it can be manufactured as a coated steel plate through a coating process; therefore, its type is not particularly limited. Furthermore, the aforementioned basic steel plate can be used instead.

[0094] In one embodiment of the present invention, a zinc-based coating is a coating containing zinc (Zn) as the main component, without excluding the addition of other elements besides zinc. As an example, the other elements besides zinc may be one or more selected from aluminum (Al), magnesium (Mg), and silicon (Si). A coating containing these elements mixed with zinc can be called a zinc-based alloy coating. Furthermore, the aforementioned content regarding zinc-based coatings can be used instead.

[0095] In one embodiment of the invention, the aluminum-based coating can be formed by coating a base steel plate. As an example, this can be achieved by immersing the base steel plate in an aluminum-based plating bath containing unavoidable impurities of Si, Zn, and Fe, in addition to Al. As a non-limiting example, the aluminum-based plating bath may contain 7.0-10.0% silicon (Si). Adding Si can suppress the fluidity of the molten metal and the diffusion of Al into the base steel plate during plating. Furthermore, the aluminum-based plating bath may further contain: zinc (Zn): 0-27%, iron (Fe): up to 3%, with these contents replaced by the description above.

[0096] In one embodiment of the invention, the surface treatment composition can be applied to the surface and dried using a solution coating method, regardless of the type of coating. For example, any coating method selected from bar coating, roller coating, spraying, dipping, jet extrusion, and dip-squeeze can be used. Using the coating method described above results in a simple process and low operating costs, thus achieving economic benefits.

[0097] In one embodiment of the present invention, the surface treatment composition applied to a zinc-based or aluminum-based coating may be a steel plate surface treatment composition according to an embodiment of the present invention. In this case, the composition may be a solution composition; as an example of such a solution composition, it may be a surface treatment composition comprising 8-15% by weight of water as a solvent, based on solids. The water may be deionized water or distilled water.

[0098] As an example, when coating the above solution composition, a concentration of 100-1000 mg / m³ can be used. 2 The adhesion amount is determined. When the coating amount of the solution composition is less than 100 mg / m², the application rate is determined accordingly. 2 When the composition is applied thinly to the rough, protruding parts of the coating, reduced lubricity may occur. On the other hand, when the amount of the solution composition applied exceeds 1000 mg / m²... 2 If the dried surface-treated film layer becomes too thick, the physical properties of the sealant, such as adhesion, may deteriorate. More advantageously, the solution composition can be prepared at 150-500 mg / m³. 2 The amount of coating adhered.

[0099] In one embodiment of the present invention, the drying step of the coated steel sheet with the surface treatment composition can be performed at a temperature range of 70-150°C. When the drying temperature is below 70°C, drying cannot be completed, and the physical properties of the surface-treated coated steel sheet, such as corrosion resistance, film adhesion, and lubricity, may deteriorate. On the other hand, when the drying temperature is above 150°C, the ratio of hydroxides to oxides of inorganic compounds in the composition decreases, and lubricity, sealant adhesion, release properties, and phosphate treatment properties may decrease.

[0100] By performing the above-described process, a coated steel sheet with a surface-treated thin film layer can be obtained. This coated steel sheet can be not only zinc-based coated steel sheet, but also aluminum-based coated steel sheet suitable for use as a hot-forming coated steel sheet. In this case, the surface-treated thin film layer can be formed from a composition containing inorganic and organic compounds, resulting in a surface-treated thin film layer with a structure in which the organic compound has a content distribution in the thickness (depth) direction.

[0101] Furthermore, the surface-treated thin film layer having a content distribution in the thickness (depth) direction can be formed by chemical reactions that occur during coating and drying processes of a solution composition that simultaneously contains inorganic and organic compounds.

[0102] However, it should be noted that in order to obtain this surface-treated thin film layer, the method of first coating and drying a solution composition containing inorganic compounds, and then coating and drying a solution composition containing organic compounds a second time is not excluded. Detailed Implementation

[0103] The present invention will now be described in more detail through embodiments. However, these embodiments are merely illustrative of implementation of the invention, and the invention is not limited to these embodiments. The scope of the invention is determined by the matters set forth in the claims and those reasonably deduced therefrom.

[0104] (Example) Experimental Example 1. Zinc-coated steel sheet after surface treatment Prepare a zinc-based coating with a thickness of 0.8 mm, an elongation of 36-37%, and a g / m² content. 2 Alloyed hot-dip galvanized steel sheet (GA) with a coating amount. Then, a surface treatment composition in solution state is applied to the coating of the alloyed hot-dip galvanized steel sheet.

[0105] The surface treatment composition in solution state comprises boric acid (B) and ammonium molybdate (Mo) as inorganic compounds, and as organic compounds, the contents shown in Table 1 below. Each composition is prepared separately such that the content of organic compounds in the film layer formed by subsequent drying is as shown in Table 1. For example, when the content of organic compounds in the film layer is 20% by weight, the solution composition with a solid content of 10% by weight is composed of 9% by weight of inorganic compounds and 1% by weight of organic compounds. Water (distilled water) is used as the solvent.

[0106] The surface treatment compositions in various solution states were applied to the coating using a rod coating method, resulting in a film thickness of 400 mg / m² after drying. 2 Then, it is dried at 90°C to obtain alloyed hot-dip galvanized steel sheet with various surface treatment thin film layers.

[0107] In addition, for partially alloyed hot-dip galvanized steel sheets, after preparing inorganic compound solutions and organic compound solutions respectively, one of the two solutions is first coated, and then the other solution is coated a second time to form a surface treatment thin film layer.

[0108] Friction tests and sealant adhesion evaluations were conducted on alloyed hot-dip galvanized steel sheets with various surface treatment thin film layers, and the results are shown in Table 1 below.

[0109] Friction testing was conducted using a pin-on-disk method. A 3mm diameter steel ball was used as the fixed pin, and the frictional force (mN) was measured under conditions of a 50g load, a 10mm rotation radius, and a linear velocity of 20mm / s. The average value was taken over a measurement period of 5 to 100 seconds. The results showed that lower frictional force indicated better lubrication (friction characteristics).

[0110] The sealant adhesion evaluation involves preparing two 25×100mm test pieces. Then, on one test piece, 10mm inward from the end, apply a 25mm (width) × 25mm (length) × 3mm (height) application of sealant (mastic sealer; adhesion strength standard (Spec): 4.0 kgf / cm²). 2 Adhesive. Afterwards, as... Figure 2 Another test piece was stacked on top of the previous one, and then baked at 170°C for 20 minutes. The adhesive shear strength of the upper and lower test pieces was then measured. The shear strength was measured at a rate of 50 mm / min, and the maximum shear force was divided by 6.25 cm. 2 The bond strength (kgf / cm²) is expressed as a value derived from the bonded area. 2 ).

[0111] In addition, to confirm the carbon distribution along the thickness direction of the surface-treated thin film, the carbon content of the upper and lower layers constituting the surface-treated thin film was measured using SEM-EDS surface analysis. Then, the carbon distribution degree was calculated according to Equation 1. Here, the carbon content (weight % (wt%)) obtained through surface analysis from the outermost surface of the surface-treated thin film to a position t / 2 in the thickness direction (where t corresponds to the thickness of the thin film) is taken as the carbon content of the upper layer, and the carbon content (weight %) obtained through surface analysis from position t / 2 to the interface between the thin film and the coating is taken as the carbon content of the lower layer.

[0112] [Table 1] As shown in Table 1, it can be confirmed that in Comparative Example 1, which was not surface treated, and Comparative Example 2, which was surface treated with a composition consisting only of inorganic compounds, the friction force was 40 mN or more, and the lubricity was significantly worse.

[0113] On the other hand, compared with Comparative Examples 1 and 2, the friction force was significantly reduced in Invention Examples 1 to 15, which used a composition containing inorganic compounds and a certain amount of fatty acid-based organic compounds for surface treatment. This can be attributed to the presence of fatty acid-based organic compounds within the surface-treated thin film layer, which forms a structure with an organic compound content distribution in the thickness (depth) direction, thereby achieving a carbon distribution that satisfies Equation 1.

[0114] In addition, although the surface treatment composition contains organic compounds, the adhesive strength of Comparative Examples 3 to 6, which contain excessive amounts of organic compounds, is poor despite satisfying the carbon distribution of Formula 1.

[0115] In addition, in Comparative Examples 8 and 9 where the content of organic compounds in the composition was insufficient, the adhesive strength was excellent due to the relatively high content of inorganic compounds, but the friction increased and the lubricity decreased.

[0116] In addition, Comparative Example 7 shows a case where the carbon distribution in the surface-treated thin film layer is excessive in the lower layer compared to the upper layer. It can be seen that when there are too many organic compounds in the lower layer of the thin film layer, the adhesion between the thin film layer and the base steel plate is reduced, which may cause problems with the adhesion of the sealant.

[0117] On the other hand, in Examples 7 and 13, where the carbon distribution in the surface-treated thin film layer is significantly less than that in the upper layer, excellent lubricity is confirmed, based on the abundant organic compounds present in the upper layer. Furthermore, the good adhesive strength characteristics can be predicted to be due to the organic compounds in the upper layer within the thin film layer melting and becoming fluid at the sealant baking temperature, thus being absorbed to the sealant side.

[0118] Experimental Example 2. Surface-treated aluminum-coated steel sheet An aluminum-coated steel sheet was prepared, with an aluminum-based coating consisting of 9% silicon, the balance Al, and unavoidable impurities by weight on both sides of a base steel sheet. Then, a solution-state surface treatment composition was applied to the coating of the aluminum-coated steel sheet. The solution-state surface treatment composition used was the same as that used in Experimental Example 1.

[0119] The surface treatment compositions in various solution states were applied to the coating using a bar coating method, resulting in a dried film layer with an adhesion weight of 400 mg / m². 2 Then, it is dried at 90°C to obtain an aluminum-coated steel sheet with various surface treatment thin film layers.

[0120] Subsequently, the aluminum-based coated steel sheets with thin film layers formed on the coating as described above were heated to 900°C and then held for 5 minutes. They were then stamped (formed) using a die while being cooled to obtain a hot-formed component. The corrosion resistance, bending properties, and hydrogen absorption of the hot-formed component were then measured, and the results are shown in Table 2 below.

[0121] Corrosion resistance was evaluated according to ISO 14993:2018, also as a relative area of ​​red rust formation compared to untreated aluminum-coated steel sheets.

[0122] Bending performance (in both the C and L directions) was measured five times using a three-point bending evaluation (VDA238-100), and the average value of the outer bending angle calculated from the maximum bending strength was recorded.

[0123] The diffusive hydrogen content was evaluated using Bruker's G8 GALILEO product. The sample was heated from room temperature to 400°C, and the amount of hydrogen released was quantitatively measured. Considering that the hydrogen contained in the component naturally releases to the outside over time, samples that have been in use for the same period of time since the component was manufactured were used to measure the hydrogen content.

[0124] Furthermore, even with the aforementioned excellent physical properties, the equipment may be difficult to use if the film detaches and contaminates during the manufacturing, transportation, and blanking processes of the steel sheet in coil form. Therefore, before thermoforming, strong adhesive tape was applied to the surface of the coated steel sheet test piece and then removed for tape testing. The test piece with increased tape weight was used as a benchmark to distinguish test pieces that were expected to cause equipment contamination. These results are shown together in Table 2 below.

[0125] In addition, the time required to reach the target heating temperature was also measured. Specifically, the time required to reach the target temperature was expressed as a relative shrinkage rate (%), based on the time required to heat the untreated aluminum-coated steel sheet to the target temperature.

[0126] [Table 2] As shown in Table 2, it can be confirmed that the physical properties of the thermoformed components (Examples a to o) obtained by thermoforming aluminum-coated steel sheets surface-treated with a surface-treatment composition according to an embodiment of the present invention are improved in terms of corrosion resistance, bending and hydrogen absorption compared to the thermoformed component without surface treatment (Comparative Example a).

[0127] In particular, it can be confirmed that the heating time for hot forming of the surface-treated aluminum-coated steel sheet can be significantly shortened compared to Comparative Example a. This result suggests that the efficiency of the hot forming process can be improved, and energy costs can be reduced when manufacturing parts by hot forming.

[0128] Furthermore, although the surface treatment composition contains organic compounds, the excessive amounts in Comparative Examples c to f and the excessive carbon distribution in the lower layer compared to the upper layer in Comparative Example g are expected to cause equipment contamination during raw material processing, and therefore are deemed unsuitable for practical application. Additionally, in Comparative Examples h and i, where the organic compound content in the composition is insufficient, corrosion resistance deteriorates, and hydrogen absorption is not improved.

[0129] [Explanation of reference numerals in the attached figures] 1... Foundation steel plate 2... Zinc-based or aluminum-based coatings 3... Surface treatment thin film layer 4...lower level 5... Upper level

Claims

1. A composition for surface treatment of steel plates, comprising an inorganic compound, an organic compound, and a balance solvent, wherein the organic compound is a fatty acid-based organic compound or a dicarboxylic acid-based organic compound with a molecular weight of less than 1000.

2. The composition for surface treatment of steel plates according to claim 1, wherein, Based on the total 100% by weight of the composition, the content of the organic compound is 0.15-7.50%.

3. The composition for surface treatment of steel plates according to claim 1, wherein, The organic compound is selected from one or more of the following: stearic acid, 12-hydroxystearic acid, 12-oxostearic acid, palmitic acid, oleic acid, sodium stearate, sodium lauryl oleate, stearamide, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, undecanoic acid, dodecanoic acid, disodium adipic acid, diammonium adipic acid, disodium sebacic acid, diammonium sebacic acid, ethers of fatty acids and polyoxyethylene(n), esters of fatty acids and polyoxyethylene(n), and fatty acid esters.

4. The composition for surface treatment of steel plates according to claim 1, wherein, The inorganic compound is selected from one or more of phosphorus (P), boron (B) and zirconium (Zr).

5. The composition for surface treatment of steel plates according to claim 4, wherein, The inorganic compound further comprises one or more selected from nickel (Ni), manganese (Mn), molybdenum (Mo), zinc (Zn) and silicon (Si).

6. A surface-treated coated steel sheet, comprising: Foundation steel plate; A coating, said coating being formed on at least one side of the base steel plate; as well as A surface-treated thin film layer, the surface-treated thin film layer being formed on the coating. The surface treatment film layer is formed from the surface treatment composition according to any one of claims 1 to 5.

7. The surface-treated plated steel sheet according to claim 6, wherein, The surface-treated thin film layer contains 2-50% organic compounds on a total basis of 100% by weight.

8. The surface-treated plated steel sheet according to claim 6, wherein, The surface-treated thin film layer consists of two layers, an upper layer and a lower layer, and the carbon (C) distribution of the upper and lower layers satisfies the following relationship 1. [Relation 1] (Top layer carbon content) / (bottom layer carbon content) > 1.

0.

9. The surface-treated plated steel sheet according to claim 6, wherein, The surface-treated thin film layer has a thickness of 0.1-1.0 μm.

10. The surface-treated plated steel sheet according to claim 6, wherein, The coating is a zinc-based coating or an aluminum-based coating.

11. A method for manufacturing a surface-treated coated steel sheet, comprising the following steps: Prepare to form a coated steel sheet on at least one side of the base steel sheet; A surface treatment composition is applied to the coating; as well as The plated steel sheet coated with the surface treatment composition is dried to form a surface treatment film layer. The surface treatment composition is the composition according to any one of claims 1 to 5.

12. The method for manufacturing a surface-treated coated steel sheet according to claim 11, wherein, The step of applying the surface treatment composition is at a concentration of 100-1000 mg / m³. 2 The amount of adhesion is determined.

13. The method for manufacturing a surface-treated coated steel sheet according to claim 11, wherein, The coating step is performed by any one of the following methods: bar coating, roller coating, spraying, dipping, jet extrusion, and dipping squeeze-drying.

14. The method for manufacturing a surface-treated coated steel sheet according to claim 11, wherein, The drying step is carried out at a temperature range of 70-150°C, based on the PMT of the coated steel sheet.

15. The method for manufacturing a surface-treated coated steel sheet according to claim 11, wherein, The coating is a zinc-based coating or an aluminum-based coating.

16. A thermoformed component, comprising: Foundation steel plate; An aluminum-based coating is formed on at least one side of the base steel plate; as well as A surface-treated thin film layer is formed on the aluminum-based coating. The thin film layer is formed from the composition of any one of claims 1 to 5.

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