Plated steel sheet, manufacturing method thereof, and hot press formed member

Abstract

The present invention relates to a steel sheet suitable as a material for vehicle body members and, more specifically, to: a plated steel sheet suitable not only for hot forming but also for cold forming; a manufacturing method thereof; and a hot press formed member obtained from the plated steel sheet.

Description

galvanized steel sheet, method of manufacturing the same, and hot-formed part

[0001] The present invention relates to a steel sheet suitable as a material for automobile body parts, and more specifically, to a plated steel sheet, a method for manufacturing the same, and a hot-formed part obtained using the plated steel sheet.

[0002] Recently, as regulations regarding passenger protection and fuel efficiency improvement through vehicle lightweighting have become stricter, the application of components (parts) obtained through cold or hot forming as materials for automotive structural members is increasing to achieve these goals. Among these, hot-formed parts are obtained by applying a hot forming process to a specific steel sheet, and as a result, these parts can possess high strength. Therefore, hot-formed parts are particularly suitable for applications such as bumpers, doors, and pillar reinforcements where ultra-high strength or significant energy absorption capacity is required.

[0003] Meanwhile, Patent Document 1 proposes a technology regarding the hot forming of steel sheets. This document describes a method for securing ultra-high strength with high tensile strength by heating an Al-Si plated steel sheet to 850°C or higher, and then forming the microstructure of the manufactured component into martensite through hot forming and rapid cooling using a press. As such, since the hot-formed component is obtained by forming the steel sheet at a high temperature, it has the advantage of being easily formed when manufacturing components with complex shapes. Furthermore, since rapid cooling within the form can increase strength, a lightweighting effect resulting from increased strength can be expected.

[0004] Meanwhile, when Al-Zn-based plated steel sheets containing zinc were used as materials for hot forming to utilize the sacrificial mode of zinc, problems arose such as the occurrence of micro-cracks hundreds of micrometers in size due to the liquid metal embrittlement of zinc, or the adhesion of the plating layer to the rolls and molds inside the annealing furnace caused by liquefaction of the plating layer during hot forming. Additionally, there were issues such as deterioration in corrosion resistance as zinc volatilized instead of remaining during the heat treatment process for hot forming.

[0005] Accordingly, when applying galvanized steel sheets containing Al and Zn as hot forming materials, there is a need for a solution that can fundamentally resolve the aforementioned problems, and furthermore, there is a need for the development of materials suitable for cold forming as well.

[0006] (Patent Document 1) U.S. Patent Publication No. 6296805

[0007] One aspect of the present invention relates to a steel sheet suitable as a material for structural members for automobiles, and in particular aims to provide a plated steel sheet suitable for cold forming or hot forming processes and a method for manufacturing the same.

[0008] In addition, another aspect of the present invention is to provide a hot-formed part obtained from the aforementioned galvanized steel sheet, which has particularly ultra-high strength and excellent corrosion resistance and further weldability.

[0009] The problems of the present invention are not limited to those described above. A person skilled in the art will have no difficulty understanding additional problems of the present invention from the overall contents of this specification.

[0010] According to one aspect of the present invention, a plated steel plate comprising a base steel plate and a plating layer formed on the base steel plate is provided.

[0011] In one embodiment of the present invention, the plating layer may comprise: a first alloy layer formed on the substrate steel plate and comprising Al, Fe, Si, and optionally Zn; a second alloy layer formed on the first alloy layer and comprising Al, Fe, Si, and Zn; and a first alloy phase formed on or inside the second alloy layer and comprising Al, Fe, Si, and Zn.

[0012] In this way, a plated steel sheet can be provided in which the plating layer is composed of layers and phases according to specific components, and a hot-formed part obtained from this plated steel sheet can have excellent corrosion resistance and weldability.

[0013] In one embodiment of the present invention, the Zn content of the first alloy phase may be greater than the Zn content of the first alloy layer and the second alloy layer. Additionally, in one embodiment of the present invention, the first alloy phase may have an Al content greater than the Zn content, and the Zn content may be greater than the Fe content.

[0014] In one embodiment of the present invention, the first alloy layer may have a Fe content greater than the Al content, and the Al content greater than the Zn content.

[0015] In one embodiment of the present invention, the second alloy layer may have a greater content of Al than of Fe, and the greater content of Fe than of Zn.

[0016] In one embodiment of the present invention, the area fraction occupied by the first alloy phase in the thickness direction cross-section of the plating layer may be 4.0 to 25.0%.

[0017] In one embodiment of the present invention, the area fraction occupied by the first alloy layer in the thickness direction cross-section of the plating layer may be 4.0 to 20.0%.

[0018] In one embodiment of the present invention, a second alloy phase formed inside the second alloy layer and comprising Al, Zn, Fe, and Si may be further included. In this case, the content of Si in the second alloy phase may be greater than the content of Zn.

[0019] In one embodiment of the present invention, the first alloy phase may include an area exposed to the upper surface of the plating layer. Additionally, in one embodiment of the present invention, the second alloy layer may include an area exposed to the upper surface of the plating layer.

[0020] In one embodiment of the present invention, the base steel sheet comprises, in weight%, carbon (C): 0.02~0.60%, silicon (Si): 0.001~2.000%, aluminum (Al): 0.001~1.000%, manganese (Mn): 0.10~4.00%, phosphorus (P): 0.050% or less, sulfur (S): 0.0200% or less, nitrogen (N): 0.0200% or less, titanium (Ti): 0~1.0000%, niobium (Nb): 0~1.0000%, vanadium (V): 0~1.0000%, boron (B): 0~0.0100%, chromium (Cr): 0~1.00%, molybdenum (Mo): 0~1.00%, tungsten (W): 0~1.00%, copper (Cu): It may have a composition containing 0~1.0%, nickel (Ni): 0~1.0%, tin (Sn): 0~1.00%, calcium (Ca): 0~0.10%, magnesium (Mg): 0~0.10%, cobalt (Co): 0~1.00%, arsenic (As): 0~1.00%, zirconium (Zr): 0~1.00%, bismuth (Bi): 0~1.00%, rare earth elements (REM): 0~0.3%, and the remainder being Fe and other unavoidable impurities.

[0021] In one embodiment of the present invention, a surface treatment layer formed on the plating layer may be further included, wherein the surface treatment layer may be a resin layer containing Ti.

[0022] In one embodiment of the present invention, the surface treatment layer may have a thickness of 1.0 μm or less after drying.

[0023] According to another aspect of the present invention, a method for manufacturing a plated steel sheet is provided, comprising the steps of: preparing a base steel sheet; plating the base steel sheet to produce a plated steel sheet having a plating layer on the base steel sheet; and alloying the plated steel sheet. In this case, the base steel sheet may have the same alloy composition as the base steel sheet described above.

[0024] In one embodiment of the present invention, the alloying treatment may be a process of heat treatment performed by maintaining the plating at a heating temperature range of 800 to 850°C for 1 to 10 seconds after plating.

[0025] In one embodiment of the present invention, the plating may be performed by immersing the substrate steel plate in an aluminum-based plating bath comprising, in weight percent, silicon (Si): 6.0 to 15.0%, zinc (Zn): 30.0% or less (excluding 0%), and the remainder being aluminum (Al) and other unavoidable impurities.

[0026] In one embodiment of the present invention, the plating is 10 to 80 g / m² 2 It can be done with the amount of attachment.

[0027] In one embodiment of the present invention, the step of forming a surface treatment layer on the plating layer after the alloying treatment may be further included.

[0028] In one embodiment of the present invention, the surface treatment layer can be formed by applying a composition comprising a polymer binder resin.

[0029] In one embodiment of the present invention, the polymer binder resin may comprise, based on 100% by weight, 25-35% acrylic resin, 0.5-1.5% curing agent, 2.0-10.0% anti-corrosion agent, 0.10-0.30% Teflon-based wax, 2% or less silane coupling agent, 10.0% or less other additives, and the remainder being a solvent.

[0030] According to another aspect of the present invention, a hot-formed part comprising a base steel plate and a plating layer formed on the base steel plate is provided.

[0031] In one embodiment of the present invention, the plating layer may comprise: a first alloy layer formed on the substrate steel plate and comprising Al, Fe, Si, and Zn; a second alloy layer formed on the first alloy layer and comprising Al, Fe, Si, and Zn; a first alloy phase formed on or inside the second alloy layer and comprising Al, Fe, Si, and Zn; and a second alloy phase formed inside the second alloy layer and comprising Al, Fe, Si, and Zn.

[0032] In one embodiment of the present invention, the content of Zn in the first alloy may be greater than the content of Zn in the first alloy layer, the second alloy layer, and the second alloy layer.

[0033] In one embodiment of the present invention, the first alloy layer may have a Fe content greater than the Al content, and the Al content may be greater than the Zn content.

[0034] In one embodiment of the present invention, the second alloy layer may have a greater content of Al than of Fe, and the greater content of Fe than of Zn.

[0035] In one embodiment of the present invention, the first alloy phase may have a greater content of Al than of Zn, and the content of Zn may be greater than the content of Fe.

[0036] In one embodiment of the present invention, the second alloy phase may have a Si content greater than the Zn content.

[0037] In one embodiment of the present invention, the area fraction occupied by the first alloy phase in the cross-section in the thickness direction of the plating layer may be 5.0 to 35.0%.

[0038] In one embodiment of the present invention, the area fraction of the first alloy layer in the cross-section in the thickness direction of the plating layer may be 5.0 to 30.0%.

[0039] In one embodiment of the present invention, the first alloy phase may include an area exposed to the upper surface of the plating layer. Additionally, in one embodiment of the present invention, the second alloy layer may include an area exposed to the upper surface of the plating layer.

[0040] In one embodiment of the present invention, a surface treatment layer formed on the plating layer is included, and the surface treatment layer may be a resin layer comprising a Zn-Ti intermetallic compound.

[0041] According to the present invention, a plated steel sheet suitable for use as a material for parts of an automobile body can be provided, and a hot-formed part obtained using such a plated steel sheet can be provided.

[0042] In addition, according to the present invention, a hot-formed part having ultra-high strength and excellent corrosion resistance and weldability can be provided.

[0043] The various and beneficial advantages and effects of the present invention are not limited to those described above and may be more easily understood in the process of explaining specific embodiments of the present invention.

[0044] FIG. 1 shows a photograph of a cross-section of the plating layer of a plated steel sheet (Invention Example 1) according to one embodiment of the present invention ((a): optical microscope measurement result, (b): SEM measurement result).

[0045] FIG. 2 shows a photograph of a cross-section of a plating layer of a hot-formed part (inventive material 1) according to one embodiment of the present invention ((a): optical microscope measurement result, (b): SEM measurement result).

[0046] Preferred embodiments of the present invention will be described below with reference to the attached drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0047] In addition, embodiments of the present invention are provided to more fully explain the present invention to those with average knowledge in the relevant technical field.

[0048] In drawings, the shapes and sizes of elements may be exaggerated for clearer explanation.

[0049] In describing the embodiments of the present invention, if it is determined that a detailed description of known technology related to the present invention may unnecessarily obscure the essence of the present invention, such detailed description will be omitted. Furthermore, the terms described below are defined considering their functions in the present invention, and these may vary depending on the intentions or conventions of the user or operator. Therefore, such definitions should be based on the content throughout this specification. The terms used in the detailed description are merely for describing the embodiments of the present invention and should not be limited in any way. Unless explicitly stated otherwise, expressions in the singular form include the meaning of the plural form.

[0050] In this description, expressions such as “include” or “equipped” are intended to refer to certain characteristics, numbers, steps, actions, elements, parts or combinations thereof, and should not be interpreted to exclude the existence or possibility of one or more other characteristics, numbers, steps, actions, elements, parts or combinations thereof other than those described.

[0051] In addition, in the present invention, the term "steel plate" refers to a coil or sheet material that has not yet been processed into a specific shape, and the term "member" refers to a material that has been processed into a non-plate shape through a forming process.

[0052] It should be noted that in the present invention, when expressing the content of each element, the basis is weight (mass%) unless specifically otherwise specified. Additionally, the proportion of crystals or structures is based on area (area%) unless specifically otherwise expressed, and the gas content is based on volume unless specifically otherwise expressed.

[0053] The present invention will be described in detail below through each embodiment or example of the invention. It should be noted that each embodiment or example described in this specification is not limited to a single embodiment or example, but may also be combined with other embodiments or examples. Accordingly, the citation of claims in the patent claims is merely an example of an embodiment, and the technical concept of the present invention should not be interpreted as being limited only to a combination with the cited claims; rather, combinations with various claims are also included within the scope of the technical concept of the present invention.

[0054] The present invention will be described in detail below.

[0055] The inventors of the present invention have deeply investigated a method to fundamentally solve problems such as the failure to form an alloy phase and the volatilization of added elements during high-temperature heating for hot forming, which leads to reduced corrosion resistance, and the problem of the molten plating layer adhering to the mold during the hot forming process, in order to obtain hot-formed parts using steel sheets suitable for cold forming or hot forming, particularly Al-Zn-based plated steel sheets containing zinc (Zn).

[0056] As a result, the present invention has technical significance in providing a galvanized steel sheet capable of providing a hot-formed part with improved physical properties such as corrosion resistance and weldability, and a hot-formed part obtained from the galvanized steel sheet. Meanwhile, it should be noted that the galvanized steel sheet is also suitable for cold forming, and thus it is possible to obtain a cold-formed part from it.

[0057] According to one aspect of the present invention, a plated steel plate comprising a base steel plate and a plating layer formed on the base steel plate is provided.

[0058] In one embodiment of the present invention, the plating layer is an alloy plating layer comprising aluminum (Al) as a main component and further comprising zinc (Zn), silicon (Si), etc.

[0059] In one embodiment of the present invention, the plating layer may be alloyed. Although the alloying treatment conditions will be described in detail later, they may be a process of alloying heat treatment at a constant temperature continuously after the plating process to obtain the plating layer. Through the alloying heat treatment, the plating layer may be provided with multiple layers having various elements and alloy phases.

[0060] According to one embodiment of the present invention, the plating layer may include a first alloy layer formed on the base steel plate, a second alloy layer formed thereon, and a first alloy layer formed on the upper or inside of the second alloy layer.

[0061] In one embodiment of the present invention, the first alloy layer is a layer formed by combining Fe of the base steel sheet and a portion of Al, which is the main component of the plating layer, and may be a ferrite layer in which Al is dissolved.

[0062] In one embodiment of the present invention, the first alloy layer may include Al, Fe, and Si, and optionally Zn. In this case, the first alloy layer may have a Fe content greater than the Al content, and the Al content greater than the Zn content. As one example, the first alloy layer may have an iron (Fe) content of 60 to 95 weight%. As another example, the Fe content in the first alloy layer may be 65 weight% or more, and as yet another example, the Fe content may be 90 weight% or less. Meanwhile, excluding the iron (Fe), the first alloy layer may consist of Si: 10 weight% or less, the remainder being Al and other unavoidable impurities, and may further include Zn at 2 weight% or less.

[0063] In one embodiment of the present invention, the first alloy layer may include a second alloy layer.

[0064] In one embodiment of the present invention, the second alloy layer may include Al, Fe, Si, and Zn. In this case, the second alloy layer may have a greater content of Al than Fe, and a greater content of Fe than Zn.

[0065] In one embodiment of the present invention, the second alloy layer is a layer formed by Fe of the base steel sheet diffusing into the plating layer during the alloying process and forming an alloy phase with Al within the plating layer. Accordingly, the second alloy layer may be composed of an intermetallic compound of FeAl (e.g., FeAl3, Fe2Al5, etc.). As one example, the second alloy layer may contain 40% by weight or more of Al, and as another example, 40% to 55% by weight of Al. In addition to the Al, it may further include Fe, Si, Zn, etc. Meanwhile, the Fe content in the second alloy layer may be lower than the Fe content in the first alloy layer described above.

[0066] In one embodiment of the present invention, a first alloy phase may be formed on the upper or internal portion of the second alloy layer, and the first alloy phase may include Al, Fe, Si, and Zn.

[0067] In one embodiment of the present invention, the first alloy phase may have a greater content of Al than of Zn, and a greater content of Zn than of Fe.

[0068] In one embodiment of the present invention, the first alloy phase is a region with a relatively high Zn content, and the Zn content in the first alloy phase may be greater than the Zn content of the first alloy layer and the second alloy layer mentioned above. As one example, the first alloy phase may contain Zn in an amount of 24 to 45 weight%. As another example, the Zn content may be 27 weight% or more, and as yet another example, the Zn content may be 42 weight% or less. Meanwhile, excluding the Zn, the first alloy phase may further contain Si: 10 weight% or less and Fe: 15 weight% or less, and the remainder may be composed of Al and other unavoidable impurities.

[0069] Meanwhile, in one embodiment of the present invention, based on the cross-section in the thickness direction of the plating layer, the area fraction occupied by the first alloy phase (area of ​​the first alloy phase / total area of ​​the plating layer) may satisfy 4.0 to 25.0%. If the area fraction occupied by the first alloy phase is less than 4.0%, the sacrificial protection effect by Zn cannot be sufficiently obtained, and the corrosion resistance of the hot-formed part may be reduced. On the other hand, if the area fraction exceeds 25.0%, the contact resistance of the material increases, and as a result, the current range cannot be secured during the subsequent welding process, which may cause the resistance weldability to deteriorate. In another embodiment of the present invention, the area fraction occupied by the first alloy phase may be 9.0% or more.

[0070] In addition, in one embodiment of the present invention, based on the cross-section in the thickness direction of the plating layer, the area fraction occupied by the first alloy layer (area of ​​the first alloy layer / total area of ​​the plating layer) may satisfy 4.0 to 20.0%. If the area fraction occupied by the first alloy layer is less than 4.0%, Zn in the plating layer penetrates into the substrate steel during the hot forming process, increasing the likelihood of LME occurring. On the other hand, if the area fraction exceeds 20.0%, the thickness of the first alloy layer increases excessively, which increases the contact resistance of the material and consequently degrades weldability, and also lowers machinability due to the difference in hardness between phases. In another embodiment of the present invention, the area fraction occupied by the first alloy layer may be 9.0% or more.

[0071] Meanwhile, in one embodiment of the present invention, the first alloy phase may be exposed on the upper surface of the plating layer. If the first alloy phase includes an area exposed on the upper surface of the plating layer, it may contribute to the effect of improving the corrosion resistance of the plated steel sheet. However, the fraction of the area where the first alloy phase is exposed is not specifically limited.

[0072] Meanwhile, in one embodiment of the present invention, the second alloy layer may be exposed on the upper surface of the plating layer. If the second alloy layer includes an area exposed on the upper surface of the plating layer, it may contribute to the effect of preventing mold adhesion of the plating layer. However, the fraction of the area where the second alloy layer is exposed is not specifically limited.

[0073] In one embodiment of the present invention, the first alloy phase and the second alloy layer may be exposed on the upper surface of the plating layer. In this way, when the area in which the first alloy phase and the second alloy layer are exposed on the upper surface of the plating layer is included, it can contribute to preventing the plating layer from sticking to the mold during forming, along with the effect of improving the corrosion resistance of the plated steel sheet. However, the fraction of the respective area in which the first alloy phase and the second alloy layer are exposed is not specifically limited.

[0074] In one embodiment of the present invention, the second alloy layer may further include a second alloy phase, and the second alloy phase may include Al, Zn, Fe, and Si.

[0075] In one embodiment of the present invention, the second alloy phase may be formed by the diffusion of Si in the plating bath during the plating process, and such second alloy phase may consist of a Si enrichment phase. At this time, the Si enrichment phase forms a band shape connected to one another in a direction perpendicular to the thickness direction of the plating layer. As one example, the thickness of the band shape formed by the Si enrichment phase (based on the cross-section of the plating layer) may be 1 μm or less. If the thickness is formed to exceed 1 μm, the contact resistance of the member increases after hot forming, which may lead to a decrease in weldability.

[0076] In one embodiment of the present invention, the second alloy phase may have a Si content greater than the Zn content. As one example, the second alloy phase may contain 5 to 15 weight percent of Si. As another example, the Si may be 6 weight percent or more, and as yet another example, the Si may be 13 weight percent or less. Additionally, the second alloy phase may further contain 6 weight percent or less of Zn, excluding the Si, and the remainder may be composed of Al and other unavoidable impurities.

[0077] The plated steel sheet of the present invention, having a plating layer with a layered structure as described above, has the effect of providing excellent corrosion resistance when storing or transporting the material before and after the blanking process, which is a process of cutting a metal sheet into a specific shape and size before hot forming. Furthermore, as intermetallic compounds (e.g., FexAly) and metal oxides (e.g., ZnO, etc.) are formed within the plating layer, the surface of the material becomes blackened, and the effect of shortening the heating rate through radiant heat during heating for hot forming of such material can be obtained.

[0078] The base steel sheet constituting the plated steel sheet according to one embodiment of the present invention may include elements that can typically be added to steel, and the types and contents thereof are not specifically limited. However, non-limiting examples of elements that may be added to a base steel sheet according to one embodiment of the present invention are, in weight%, carbon (C): 0.02~0.60%, silicon (Si): 0.001~2.000%, aluminum (Al): 0.001~1.000%, manganese (Mn): 0.10~4.00%, phosphorus (P): 0.050% or less, sulfur (S): 0.0200% or less, nitrogen (N): 0.0200% or less, titanium (Ti): 0~1.0000%, niobium (Nb): 0~1.0000%, vanadium (V): 0~1.0000%, boron (B): 0~0.0100%, chromium (Cr): 0~1.00%, molybdenum (Mo): 0~1.00%, tungsten (W): It may contain 0~1.00%, copper (Cu): 0~1.0%, nickel (Ni): 0~1.0%, tin (Sn): 0~1.00%, calcium (Ca): 0~0.10%, magnesium (Mg): 0~0.10%, cobalt (Co): 0~1.00%, arsenic (As): 0~1.00%, zirconium (Zr): 0~1.00%, bismuth (Bi): 0~1.00%, rare earth elements (REM): 0~0.3%, and the remainder being Fe and other unavoidable impurities.

[0079] Among the alloy compositions described above, C, Mn, etc., may be added to ensure the strength of the steel; Si is effective not only for its deoxidation effect but also for reducing the segregation of Mn, etc., within the base steel sheet, and Al has a deoxidation effect. It should be noted that P, S, N, etc., may be elements inevitably introduced during the steel manufacturing process, but are not limited to these. Furthermore, it will be obvious to those skilled in the art that, in addition to the aforementioned composition, Ti, B, Cu, Mo, Cr, Ni, V, Ca, Nb, Sn, W, Sb, Mg, Co, As, Zr, Bi, REM, etc., may be additionally included in consideration of the target physical properties of the final product.

[0080] Meanwhile, the inventors of the present invention have conducted in-depth research on a method to further improve the anti-sintering properties of a plated steel sheet during hot forming according to one embodiment of the present invention and to improve the weldability of a hot-formed part, and have confirmed that the intended physical properties can be secured when a surface treatment layer containing a specific component is formed on the plating layer.

[0081] Accordingly, a plated steel sheet according to one embodiment of the present invention may further include a surface treatment layer on the aforementioned plating layer.

[0082] According to one embodiment of the present invention, the surface treatment layer can be formed by coating (surface treatment) the surface of the plating layer of the plated steel sheet, and at this time, the surface treatment layer can be formed using a solution composition.

[0083] In one embodiment of the present invention, the composition may be a composition comprising a polymer binder resin. As a preferred example, the polymer binder resin may comprise, based on 100% by weight: 25-35% acrylic resin, 0.5-1.5% curing agent, 2.0-10.0% anti-corrosion agent, 0.10-0.30% Teflon-based wax, 2% or less silane coupling agent, 10.0% or less other additives, and the remainder being a solvent.

[0084] The above acrylic resin serves as a binder component within the composition, and by adding a certain amount, physical properties such as chemical resistance and alkali resistance of the surface treatment layer can be secured. In one embodiment of the present invention, the content of the acrylic resin may be included in an amount of 25 to 35% based on 100% by weight of the total polymer binder resin. If the content of the acrylic resin is less than 25%, the viscosity of the composition decreases, making it difficult to control the thickness of the surface treatment layer. On the other hand, if the content exceeds 35%, the storage stability of the composition in a solution state may decrease. The type of acrylic resin is not specifically limited, and materials generally used in the field of steel plate surface treatment may be used.

[0085] The above-mentioned curing agent is effective in improving the corrosion resistance of the steel plate by reacting with the polymer resin, which is the main component of the composition, to increase the degree of crosslinking of the film. In one embodiment of the present invention, the curing agent may be included in an amount of 0.5 to 1.5% based on 100% by weight of the total polymer binder resin. If the content of the curing agent is less than 0.5%, the corrosion resistance may be reduced because a sufficient degree of crosslinking of the surface treatment layer is not secured. On the other hand, if the content exceeds 1.5%, the corrosion resistance may be reduced as a large amount of unbonded curing agent remains after the formation of the surface treatment layer. The type of the curing agent is not specifically limited, but as an example, it may be one or more selected from the group consisting of Highly Methylated Melamine Resins, Methylated High Imino Melamine Resins, Partially Methylated Melamine Resins, Highly Alkylated Melamine Resins, High Imino Melamine Resins, and mixtures thereof.

[0086] The above-mentioned anti-corrosion agent is a component added to impart corrosion resistance to the surface treatment layer and may include both titanium-based and phosphoric acid-based corrosion agents. Among these, the titanium-based corrosion agent exists in the form of a Ti compound within the surface treatment layer. During the hot forming process of the plated steel sheet forming the surface treatment layer, this Ti compound reacts with Zn in the Zn enrichment phase within the second alloy layer or the first alloy phase present on the surface of the plating layer to form Ti-Zn intermetallic compounds such as TiZn3 and Ti2Zn3. Due to the intermetallic compounds formed in this manner, sticking of the LME and molds / rolls can be suppressed. At this time, the Ti compound mainly reacts with the Zn enrichment phase within the first alloy phase.

[0087] In addition, the Ti compound present in the surface treatment layer by the titanium-based corrosion inhibitor may exist in an area of ​​5 to 50 percent based on the cross-sectional thickness of the surface treatment layer. Here, the shape of the Ti compound is not specifically limited, but as one example, the shape of the Ti compound may be a circular shape with a diameter of 50 to 500 mm based on a two-dimensional transmission electron microscope (TEM) image, and may exist in various shapes (round, square, etc.) having a size within 100 nm of the minor axis and 500 nm of the major axis based on the equivalent diameter of the circle.

[0088] In one embodiment of the present invention, the anti-corrosion agent may be included in an amount of 2.0 to 10.0% based on 100% by weight of the total polymer binder resin. If the content of the anti-corrosion agent is less than 2.0%, the corrosion resistance of the surface treatment layer may be reduced, and the formation of Ti-Zn intermetallic compounds may be insufficient, making it impossible to improve the weldability of the hot-formed part. On the other hand, if the content exceeds 10.0%, the content of Ti and P contained in the surface treatment layer becomes excessive, causing the surface treatment layer to become uneven and easily peel off. The anti-corrosion agent is not particularly limited, but as one example, titanium-polyphosphate or titanium-organic phosphate may be used.

[0089] The above Teflon-based wax may be added to provide lubricity to the surface treatment layer. In one embodiment of the present invention, the content of the Teflon-based wax may be 0.10 to 0.30% based on 100% by weight of the total polymer binder resin. If the content of the Teflon-based wax is less than 0.01%, the lubricity of the surface treatment layer becomes insufficient, and damage may occur in the surface treatment layer and / or the material during processing of the surface-treated steel plate. On the other hand, if the content exceeds 0.30%, lubricant particles may be excessively distributed in the surface treatment layer, which may instead lead to a decrease in corrosion resistance. The Teflon-based wax is not specifically limited, but as an example, polyethylene-Teflon-based wax or polyTeflon-based wax may be used.

[0090] The above silane coupling agent may be included to maintain a strong bond between the organic resin and the inorganic compound contained in the composition, and to modify the resin to induce a coupling reaction. In one embodiment of the present invention, the silane coupling agent may be included in an amount of 2.0% or less based on 100% by weight of the total polymer binder resin, and it may be 0%. If the content of the silane coupling agent exceeds 2.0%, the above-described effect becomes saturated, and it may instead cause an increase in manufacturing costs. The above silane coupling agent is not specifically limited, but as one example, it may be one or more selected from the group consisting of vinyl triethoxysilane, 3-glycidoxypropyl trimethoxysilane, 3-glycidoxypropyl triethoxysilane, 3-glycidoxypropylmethyl dimethoxysilane, N-2-(aminoethyl))-3-aminopropyl triethoxysilane, 3-aminopropyl trimethoxysilane, 3-aminopropyl triethoxysilane, and 2-perfluorooctyl ethyl trimethoxysilane.

[0091] The above-mentioned other additives may be added to improve workability during surface treatment. In one embodiment of the present invention, the content of the above-mentioned other additives may be 10.0% or less based on 100% by weight of the total polymer binder resin. If the content of the above-mentioned other additives exceeds 10.0%, the content of the aforementioned components becomes relatively insufficient, making it impossible to obtain the desired effect from the surface treatment layer. The above-mentioned other additives are not particularly limited, but as an example, BYK-333, etc., may be added to improve wettability and surface slip properties.

[0092] The polymer binder resin in the composition according to one embodiment of the present invention may include a solvent as the remainder excluding the aforementioned components. In this case, the solvent may be added to disperse the components constituting the polymer binder resin and to prepare a solution composition for surface treatment of plated steel sheets. Water may be used as the solvent, and in this case, the water may be deionized water or distilled water.

[0093] As such, a composition according to one embodiment of the present invention may include carbon (C), hydrogen (H), oxygen (O), nitrogen (N), silicon (Si), titanium (Ti), and phosphorus (P), etc., through a polymer binder resin composed of the aforementioned components. In this case, the silicon (Si) may be derived from a silane coupling agent which is a component of the polymer binder resin, and the titanium (Ti) and phosphorus (P) may be derived from a corrosion-preventive agent. Meanwhile, carbon (C), hydrogen (H), and oxygen (O) in the composition are components that naturally exist within the composition due to the components constituting the aforementioned composition. The content of each of these components is not specifically limited, and it is obvious that it will be appropriately controlled according to the content of each of the aforementioned components.

[0094] In one embodiment of the present invention, the surface treatment layer may have a dry thickness of 1.0 μm or less (excluding 0). If the thickness of the surface treatment layer exceeds 1.0 μm, the surface treatment layer may be formed too thick, resulting in inferior processability, weldability, etc. Although the lower limit of the thickness of the surface treatment layer is not specifically limited, it may have a thickness of 0.30 μm or more in order to provide an effect through the surface treatment layer.

[0095] Hereinafter, a method for manufacturing a plated steel sheet according to another aspect of the present invention will be described. However, it should be noted that the following method is merely one example for manufacturing a plated steel sheet, and that a plated steel sheet according to one embodiment of the present invention must not necessarily be manufactured by this manufacturing method. Furthermore, any manufacturing method that satisfies the claims of the present invention may be used without issue to implement each embodiment of the present invention.

[0096] According to one embodiment of the present invention, a plated steel sheet can be manufactured by including the steps of: preparing a base steel sheet; plating the base steel sheet to produce a plated steel sheet having a plating layer on the base steel sheet; and alloying the plated steel sheet.

[0097] In one embodiment of the present invention, the base steel sheet for obtaining the plated steel sheet may be the aforementioned base steel sheet, and it is noted that there are no particular limitations on its composition and that it is replaced by the aforementioned details.

[0098] In one embodiment of the present invention, the prepared steel sheet can be plated to produce a plated steel sheet, and the plating may be an aluminum-based plating. As one example, the aluminum-based plating may be performed by a molten aluminum plating method in which the steel sheet is immersed in a molten aluminum plating bath. At this time, the temperature of the molten aluminum plating bath may be set to a temperature range for normal aluminum plating, and as a non-limiting example, it may be performed in a temperature range of 620 to 680°C.

[0099] In one embodiment of the present invention, the molten aluminum plating bath is a plating bath containing aluminum (Al) as a main component, and as one example, the plating bath may contain silicon (Si) in an amount of 6.0 to 15.0 wt% and zinc (Zn) in an amount of 30.0 wt% or less (excluding 0%). In this way, by adding Si, effects such as improving the fluidity of the molten bath and suppressing the diffusion of Al into the substrate steel sheet during plating can be obtained, and by adding Zn, corrosion resistance can be improved.

[0100] In one embodiment of the present invention, the plating bath may further include iron (Fe) in addition to Al, Si, and Zn, and the content thereof may be 4.0 weight% or less. This iron (Fe) may partially flow into the plating layer during the plating process. In addition, the plating bath may further include one or more selected from Mg, Mn, Cr, Cu, Mo, Ni, Sb, Sn, Ti, Ca, and Sr.

[0101] In one embodiment of the present invention, silicon (Si) in the plating bath not only lowers the melting point of the plating bath but also serves to prevent excessive alloying during high-temperature heating for hot forming. Accordingly, the Si may be included in an amount of 6.0% or more. However, if the content exceeds 15.0%, the plating layer is formed with a lamellar structure in which silicon particles are more distributed, resulting in inferior plating quality and excessive inhibition of the growth of the AlFe alloy layer, which may lead to the LME phenomenon.

[0102] In addition, zinc (Zn) in the plating bath is an element that is advantageous for improving the corrosion resistance of the plated steel sheet. If the content of Zn exceeds 30.0%, the melting point of the plating layer decreases and fluidity increases, which may lead to the occurrence of LME. Although there is no specific limit on the lower limit of the Zn content, it may be included at 10.0% or more to obtain the corrosion resistance effect due to Zn.

[0103] In one embodiment of the present invention, the aluminum-based plating is 10 to 80 g / m² 2 It can be performed with an attachment amount of . The above attachment amount is based on one side, and the above attachment amount is 10 g / m² 2 If it is less than that, surface quality and corrosion resistance may deteriorate. On the other hand, 80 g / m² 2 If it exceeds this amount, problems such as dust scattering and mold sticking may occur due to excessive plating, which may reduce productivity.

[0104] In one embodiment of the present invention, the plated steel sheet produced by the aluminum-based plating can be subjected to alloying heat treatment. The step of alloying heat treatment is not particularly limited, but can be performed by an on-line alloying heat treatment in which the plated steel sheet (aluminum-based plated steel sheet) obtained by the molten aluminum plating is heated while in motion.

[0105] As a non-limiting example, the alloying heat treatment may be performed continuously after the plating, known as diffusion annealing heat treatment. Diffusion annealing heat treatment is a process of performing heat treatment at a specific temperature to cause mutual diffusion between the base steel sheet and the plating layer. In one embodiment of the present invention, the diffusion annealing heat treatment may be a process of heating to a temperature range of 800 to 850°C and maintaining that temperature for 1 to 10 seconds.

[0106] In the alloying process described above, Fe within the base steel sheet may diffuse into the plating layer, and as a result, a first alloy layer containing ferrite and having Al dissolved at the interface between the base steel sheet and the plating layer may be formed, and a second alloy layer containing an intermetallic compound of FexAly may be formed on top of the first alloy layer.

[0107] Meanwhile, according to one embodiment of the present invention, the step of forming a surface treatment layer on the surface of the plating layer by surface treating the alloyed heat-treated plated steel sheet may be further included.

[0108] The above surface treatment layer can be formed by applying the aforementioned composition, namely a composition containing a polymer binder resin, to the surface of the plating layer, and the compositional composition of the above composition is replaced with the previously mentioned details.

[0109] In one embodiment of the present invention, the formation of the surface treatment layer may be performed by including the steps of applying the composition to the surface of the plating layer, followed by drying and curing. The method of applying the composition is not particularly limited, but any one coating method selected from the group consisting of bar coating, roll coating, spraying, immersion, spray squeezing, and immersion squeezing may be used.

[0110] In one embodiment of the present invention, the step of drying and curing after applying the composition may be performed in a temperature range of 80 to 150°C based on the Peak Metal Temperature (PMT), which is the final temperature reached by the plated steel sheet. If the drying temperature is below 80°C based on the PMT, drying may not be fully achieved, and the physical properties of the surface-treated plated steel sheet, such as corrosion resistance and alkali resistance, may be compromised. On the other hand, if the drying temperature exceeds 150°C based on the PMT, the organic components in the applied composition may carbonize, making it impossible to secure physical properties such as corrosion resistance and heat resistance. Furthermore, if the hardness of the surface treatment layer increases excessively, a problem may occur where the surface treatment layer cracks during processing.

[0111] Hereinafter, a hot-formed part according to another aspect of the present invention and a method for manufacturing the same will be described.

[0112] In one embodiment of the present invention, a hot-formed part can be obtained by hot-forming a steel sheet for hot forming, and the steel sheet for hot forming may be a plated steel sheet having the aforementioned plating layer according to one embodiment of the present invention.

[0113] A plated steel sheet according to one embodiment of the present invention comprises a base steel sheet; and a plating layer formed on the base steel sheet, wherein the plating layer may be composed of the aforementioned alloy layers.

[0114] A hot-formed part obtained from a plated steel sheet according to one embodiment of the present invention may also include a base steel sheet; and a plating layer formed on the base steel sheet.

[0115] A plating layer of a hot-formed part according to one embodiment of the present invention may include a first alloy layer formed on the base steel plate, a second alloy layer formed on the first alloy layer, a first alloy phase formed on the upper or internal portion of the second alloy layer, and a second alloy phase formed inside the second alloy layer.

[0116] The first alloy layer, the second alloy layer, and the first alloy phase constituting the plating layer of a hot-formed part according to one embodiment of the present invention may have properties similar to the alloy layer and alloy phase constituting the plating layer of the aforementioned plated steel sheet.

[0117] In one embodiment of the present invention, the first alloy layer constituting the plating layer of the hot-formed part may include Al, Fe, Si, and Zn, wherein the content of Fe is greater than the content of Al, and the content of Al is greater than the content of Zn.

[0118] In one embodiment of the present invention, the first alloy layer may include a second alloy layer comprising Al, Fe, Si, and Zn, wherein the second alloy layer may have a greater content of Al than of Fe and a greater content of Fe than of Zn.

[0119] In one embodiment of the present invention, the upper or inner part of the second alloy layer may include a first alloy phase comprising Al, Fe, Si, and Zn, wherein the first alloy phase may have an Al content greater than the Zn content and the Zn content greater than the Fe content. In particular, the Zn content of the first alloy phase may be greater than the Zn content of the first alloy layer and the second alloy layer, and may be greater than the Zn content in the second alloy phase described below.

[0120] In one embodiment of the present invention, the interior of the second alloy layer may include a second alloy phase comprising Al, Fe, Si, and Zn, and the second alloy phase may have a Si content greater than the Zn content.

[0121] In one embodiment of the present invention, when both the first alloy phase and the second alloy phase are formed within the second alloy layer, the first alloy phase may be formed above the second alloy phase.

[0122] Meanwhile, in one embodiment of the present invention, based on the cross-section in the thickness direction of the plating layer, the area fraction occupied by the first alloy phase (area of ​​the first alloy phase / total area of ​​the plating layer) may satisfy 5.0 to 35.0%. If the area fraction occupied by the first alloy phase is less than 5.0%, the sacrificial protection effect by Zn cannot be sufficiently obtained, and the corrosion resistance of the hot-formed part may be reduced. On the other hand, if the area fraction exceeds 35.0%, the contact resistance of the material increases, and as a current range is not secured during the subsequent welding process, it may cause the resistance weldability to be inferior. In another embodiment of the present invention, the area fraction occupied by the first alloy phase may be 10.0% or more.

[0123] In addition, in one embodiment of the present invention, based on the cross-section in the thickness direction of the plating layer, the area fraction occupied by the first alloy layer (area of ​​the first alloy layer / total area of ​​the plating layer) may satisfy 5.0 to 30.0%. If the area fraction occupied by the first alloy layer is less than 5.0%, Zn in the plating layer penetrates into the substrate steel during the hot forming process, increasing the likelihood of LME occurring. On the other hand, if the area fraction exceeds 30.0%, the contact resistance of the material increases, which not only degrades weldability but also degrades machinability due to the difference in hardness between phases. In another embodiment of the present invention, the area fraction occupied by the first alloy layer may be 10.0% or more.

[0124] Meanwhile, in one embodiment of the present invention, the first alloy phase may be exposed on the upper surface of the plating layer. If the first alloy phase includes an area exposed on the upper surface of the plating layer, it may contribute to the effect of improving the corrosion resistance of the hot-formed part. However, the fraction of the area where the first alloy phase is exposed is not specifically limited.

[0125] Meanwhile, in one embodiment of the present invention, the second alloy layer may be exposed on the upper surface of the plating layer. If the second alloy layer includes an area exposed on the upper surface of the plating layer, it may contribute to the effect of preventing the plating layer from sticking to the mold during molding. However, the fraction of the area where the second alloy layer is exposed is not specifically limited.

[0126] In one embodiment of the present invention, the first alloy phase and the second alloy layer may be exposed on the upper surface of the plating layer. In this way, when the area in which the first alloy phase and the second alloy layer are exposed on the upper surface of the plating layer is included, it can contribute to preventing the plating layer from sticking to the mold during forming, along with the effect of improving the corrosion resistance of the hot-formed part. However, the fraction of the respective area in which the first alloy phase and the second alloy layer are exposed is not specifically limited.

[0127] A hot-formed part according to one embodiment of the present invention, in which the plating layer is composed of the aforementioned layer structure, has excellent corrosion resistance. As one example, when evaluating corrosion resistance of a part that has undergone a predetermined hot forming process using a salt spray cycle test (ASTM D6899), no red rust occurs for 25 cycles (cycle, cy) or more. At this time, as a non-limiting example, 2 hours of salt spray, 4 hours of drying, and 2 hours of wetting can be considered as one cycle.

[0128] Meanwhile, a hot-formed part according to one embodiment of the present invention may further include a surface treatment layer on the plating layer. In this case, the surface treatment layer may be formed from a composition comprising a polymer binder resin according to one embodiment of the present invention. A hot-formed part including such a surface treatment layer may have excellent weldability in addition to the aforementioned corrosion resistance.

[0129] In one embodiment of the present invention, it is noted that the base steel sheet constituting the hot-formed part, the components within the plating layer, and furthermore the composition of the surface treatment layer can be replaced with the aforementioned details.

[0130] As previously mentioned, the surface treatment layer is formed on a plating layer according to an embodiment of the present invention, specifically a plating layer composed of several alloy layers and alloy phases. A first alloy phase containing a Zn enrichment phase exists on the outermost surface of the plating layer, and the Zn within this alloy phase reacts with Ti within the composition for forming the surface treatment layer to form a Ti-Zn intermetallic compound. More specifically, after the composition is applied to the surface of the plating layer to form the surface treatment layer, during the hot forming process following the blanking of the steel sheet for hot forming, the Zn in the Zn enrichment phase within the first alloy phase melts and diffuses into the composition, thereby causing the Ti-Zn intermetallic compound to exist within the surface treatment layer.

[0131] Accordingly, the surface treatment layer may include a Zn-Ti intermetallic compound. In one embodiment of the present invention, the Ti-Zn intermetallic compound is not specifically limited in type, but may be TiZn, TiZn2, Ti2Zn, Ti2Zn3, etc.

[0132] Meanwhile, the method for manufacturing a hot-formed part according to one embodiment of the present invention is not particularly limited, and as is widely known in the past, it can be manufactured through a process of heating a plated steel sheet to a temperature above the austenitizing temperature, maintaining it, and then forming it while rapidly cooling.

[0133] As one example of the present invention, after obtaining a blank using a plated steel sheet according to one embodiment of the present invention, the blank may be heated to a temperature range of 900 to 970°C and maintained for 3 to 15 minutes. After hot press forming the blank heated and maintained in this manner, the intended hot press formed part may be manufactured by undergoing a cooling step at a cooling rate greater than or equal to the critical cooling rate. As a non-limiting example, the cooling may be performed at a cooling rate of 30°C / s or more.

[0134] Meanwhile, according to one embodiment of the present invention, a plated steel sheet having a surface treatment layer on a plating layer can be applied as a steel sheet for hot forming, and the heating time during the heating process of a blank manufactured using this can be reduced. Therefore, compared to the manufacturing process for obtaining conventional hot-formed parts, a more economically advantageous manufacturing method can be provided.

[0135] The present invention will be explained in more detail below through examples. However, it should be noted that the following examples are intended merely to illustrate and explain the invention in more detail, and are not intended to limit the scope of the invention. This is because the scope of the invention is determined by the matters described in the patent claims and matters reasonably inferred therefrom.

[0136] (Example)

[0137] [Experimental Example 1-1]

[0138] A cold-rolled steel sheet (annealed steel sheet) having the composition of Table 1 below and a thickness of 1.2 mm was prepared as a base steel sheet, and then a plated steel sheet was manufactured by plating the base steel sheet under the conditions shown in Table 2 below. At this time, the temperature of the plating bath was applied uniformly at 630℃. Subsequently, the plated steel sheet was obtained by performing an alloying heat treatment under the conditions shown in Table 2 below, in succession to the plating process.

[0139] Composition: CsiMnAlCrBNBAl. Content (weight%): 0.22 0.26 1.13 0.03 0.20 0.028 0.0033 Fe and impurities

[0140] Specimen (No.) Plating Process Alloying Heat Treatment Process Plating Bath Composition (Wet%) Coating Amount (g / m²) 2Temperature (°C) Holding Time (s) ZnSibal.1 25.0 9.0 Al and impurities 5980052 25.0 9.0 Al and impurities 5985053 26.0 2.0 Al and impurities 5280014 26.0 2.0 Al and impurities 5285015 27.0 7.0 Al and impurities 6280076 27.0 7.0 Al and impurities 6285010 70 9.0 Al and impurities 42800580 9.0 Al and impurities 42900590 9.0 Al and impurities 429505

[0141] To analyze the plating layer of each hot-formed steel sheet manufactured according to the above, the cross-section in the thickness direction of each steel sheet was observed. Specifically, each cross-section in the thickness direction was observed using SEM to confirm the formation of each alloy layer within the plating layer, and for specific layers, the area ratio with the plating layer was calculated (Table 4). In addition, the component content within each alloy layer and each alloy phase was measured by point analysis at five random locations using the Energy Dispersive Spectroscopy (EDS) method, and the values ​​were presented from the minimum to the maximum (Table 3).

[0142] Specimen No. Plating Layer Structure Plating Layer Composition (Wet%) Classification AlZnFeSi 1 First Alloy Layer 8~110~283~873~6 Invention Example 1 Second Alloy Phase 43~463~638~436~11 Second Alloy Layer 44~465~736~436~12 First Alloy Phase 54~5936~391~42~82 First Alloy Layer 8~161~278~902~5 Invention Example 2 Second Alloy Phase 26~313~453~5812~13 Second Alloy Layer 26~452~1140~634~10 First Alloy Phase 45~5326~315~152~73 First Alloy Layer 4~29-64~941~6 Comparative Example 1 Second Alloy Phase 41~42-525~6 Second Alloy layer 49~54244~481~2 First alloy phase----4 First alloy layer 7~27-67~901~5 Comparative Example 2 Second alloy phase----Second alloy layer 36~52-45~711~5 First alloy phase----5 First alloy layer 5~170~172~913~10 Inventive Example 3 Second alloy phase 43~464~541~437~10 Second alloy layer 46~524~634~446~8 First alloy phase 54~5825~411~151~56 First alloy layer 4~281~258~931~11 Inventive Example 4 Second alloy phase 26~482~1040~593~12 Second alloy layer 46~489~1240~412~12 First Alloy phase 44~51 20~365~233~77 1st alloy layer----Comparative Example 3 2nd alloy phase 37~40 -47~48 11~15 2nd alloy layer 48~56 -37~47 1~5 1st alloy phase----8 1st alloy layer----Comparative Example 4 2nd alloy phase 39~41 -45~47 12~13 2nd alloy layer 49~57 -36~47 1~6 1st alloy phase----9 1st alloy layer----Comparative Example 5 2nd alloy phase 39~41 -45~48 10~13 2nd alloy layer 45~56 -35~48 2~8 1st alloy phase----

[0143] Specimen No. Area Fraction (%) Classification 1st Alloy Layer 1st Alloy Phase 17.4 9.5 Invention Example 12 10.7 5.4 Invention Example 23 17.2 - Comparative Example 14 29.2 - Comparative Example 25 9.6 22.7 Invention Example 36 11.3 24.7 Invention Example 47 - Comparative Example 38 - Comparative Example 49 - Comparative Example 5

[0144] As shown in Tables 3 and 4, the Zn and Si content in the plating bath satisfies the range according to one embodiment of the present invention, and in the examples of the invention in which alloying heat treatment was performed after plating using this plating bath, the first alloy layer, the second alloy layer, and the first alloy phase were clearly formed, and it can be confirmed that the content and area fraction of each element were formed as intended.

[0145] On the other hand, in Comparative Examples 1 and 2, in which plating was performed using a plating bath with a Si content of 2.0%, it can be confirmed that the first alloy phase was not formed because the diffusion of Fe by Si was not sufficiently suppressed. Furthermore, in Comparative Examples 3 to 5, in which plating was performed without containing Zn in the plating bath, the first alloy phase was not formed at all.

[0146] FIG. 1 shows a cross-section of the plating layer of Invention Example 1 taken using an optical microscope (a) and a scanning electron microscope (SEM) (b). As shown in FIG. 1, it can be confirmed that a first alloy phase containing a Zn enrichment phase is formed on the surface of the plating layer (outermost layer) (a). In addition, it can be confirmed that a second alloy phase containing a Si enrichment phase is formed at the midpoint in the thickness direction of the plating layer (b).

[0147] [Experimental Example 1-2]

[0148] Each hot-formed part was manufactured by heating the galvanized steel sheet prepared from Experimental Example 1-1 to 900°C, maintaining it for 3 minutes, and then hot-forming it with a flat plate mold.

[0149] Subsequently, the corrosion resistance of each hot-formed part was evaluated. First, specimens measuring 120 mm in width × 75 mm in length were prepared, and a salt spray cycle test was conducted. In this test, one cycle was defined as 2 hours of salt spraying, 4 hours of drying, and 2 hours of wetting, and the number of cycles at which red rust began to appear was measured (salt conditions: 5% NaCl and 35℃±2℃; drying conditions: 60℃±2℃ and <35% relative humidity; wetting conditions: 50℃±2℃ and >95% relative humidity).

[0150] Specimen No. Titration Generation Cycle Count Classification 130 cy Abnormal Invention Example 1227 cy Invention Example 233 cy Comparative Example 143 cy Comparative Example 2530 cy Abnormal Invention Example 3630 cy Abnormal Invention Example 476 cy Comparative Example 383 cy Comparative Example 493 cy Comparative Example 5

[0151] As shown in Table 5, in the case of hot-formed parts (Invention Examples 1 to 4) obtained by hot-forming a plated steel sheet according to one embodiment of the present invention, the number of cycles for the occurrence of red rust is 25 cy or more, confirming that the corrosion resistance is excellent.

[0152] In addition, to analyze the plating layer of each hot-formed part, the cross-section in the thickness direction of each part was observed. At this time, the process was carried out in the same manner as the method used to analyze the plating layer of the steel sheet, and the results for each content are shown in Table 6 below. Furthermore, for specific layers, the area ratio with respect to the plating layer was calculated and is shown in Table 7.

[0153] Specimen No. Plating Layer Structure Plating Layer Composition (Wet%) Classification AlZnFeSi 1 First Alloy Layer 6~180~275~9 11~6 Inventive Material 1 Second Alloy Phase 25~282~358~6 18~13 Second Alloy Layer 45~47 11~1239~412~3 First Alloy Phase 74~76 21~281~41~52 First Alloy Layer 6~150~279~9 21~5 Inventive Material 2 Second Alloy Phase 27~343~650~639~10 Second Alloy Layer 42~47 10~1239~452~3 First Alloy Phase 66~72 14~213~171~93 First Alloy Layer 5~110~275~850~2 Comparative Material 1 Second Alloy Phase 30~352~456~614~6 Second Alloy Layer 44~45 13~14 41~430~1 First Alloy Phase----4 First Alloy Layer 5~100~17 4~8 81~2 Reference Material 2 Second Alloy Phase 35~39 -5 7~60 3~4 Second Alloy Layer 50~5 42~34 4~470~1 First Alloy Phase----5 First Alloy Layer 9~101~27 4~8 60~2 Inventive Material 3 Second Alloy Phase 30~380~348~5 311~18 Second Alloy Layer 49~5 25~7 35~44 2~6 First Alloy Phase 64~7 219~26 2~140~26 First Alloy Layer 7~100~18 7~90 2 Inventive Material 4 Second Alloy Phase 30~360~349~5 111~12 Second Alloy Layer 46~486~835~452~10 First Alloy Phase 65~7513~173~52~57 First Alloy Layer 5~7-89~911~2 Reference Material 3 Second Alloy Phase 30~35-57~597~10 Second Alloy Layer 52~56-44~461~2 First Alloy Phase----8 First Alloy Layer 5~7-89~921~2 Reference Material 4 Second Alloy Phase 30~36-56~616~8 Second Alloy Layer 44~55-44~531~3 First Alloy Phase----9 First Alloy Layer 3~5-92~941~6 Reference Material 5 Second Alloy Phase 30~34-57~615~8 Second Alloy Layer 50~53-42~481~2 First Alloy Phase----

[0154] Specimen No. Area Fraction (%) Classification 1st Alloy Layer 1st Alloy Phase 117.0 10.3 Inventive Material 12 26.0 6.0 Inventive Material 23 33.1 - Comparative Material 14 33.6 - Comparative Material 25 10.8 26.8 Inventive Material 36 10.9 11.8 Inventive Material 47 31.5 - Comparative Material 38 35.7 - Comparative Material 49 37.9 - Comparative Material 5

[0155] As shown in Tables 6 and 7, the hot-formed parts (Inventive Materials 1 to 4) obtained by hot-forming a plated steel sheet according to one embodiment of the present invention have an alloy layer and an alloy phase formed as intended within the plating layer.

[0156] On the other hand, hot-formed parts (Comparative Materials 1 to 5) obtained by hot-forming a plated steel sheet that does not have a plating layer structure according to one embodiment of the present invention did not satisfy the range according to one embodiment of the present invention for the alloy layer and alloy phase within the plating layer.

[0157] FIG. 2 shows a cross-section of the plating layer of the inventive material 1 taken using an optical microscope (a) and a scanning electron microscope (SEM) (b). As shown in FIG. 2, it can be confirmed that a first alloy layer exists in the area in contact with the substrate steel plate, a first alloy phase exists near the surface of the second alloy layer formed thereon, and a second alloy phase exists below the first alloy phase.

[0158] [Experimental Example 2-1]

[0159] A surface treatment layer was formed on the surface of the plating layer of the plated steel sheet prepared from Experimental Example 1-1. At this time, the composition for surface treatment consisted of 30% acrylic resin (acrylic acid-ethylene copolymer), 0-15% colloidal silica, 0-0.5% silane coupling agent (3-Aminopropyltriethoxysilane), 0.5% imide-based curing agent (Highly Methylated Melamine Resins), 2-10% rust-preventive corrosion-resistant agent (Titanium-Polyphosphate), 0.5% Teflon-based wax, 5% additive (BYK-333), and the remainder being a solution (water), based on 100% by weight of the total. The above composition was coated onto the surface of the plating layer of each steel sheet using a roll coating method, and then dried and cured at 120°C based on PMT. The thickness of the surface treatment layer was measured using a non-destructive coating thickness gauge (Betascope®).

[0160] Next, each plated steel sheet with a surface treatment layer formed thereon was heated to 900°C and held for 3 minutes, and then hot-formed using a flat plate mold to manufacture each hot-formed part.

[0161] Subsequently, the weldability of each hot-formed part was evaluated. The weldability was expressed as a value calculated as a percentage of the difference based on the maximum welding current of an untreated galvanized steel sheet (Invention Example 3 of [Table 3]) when tested according to ISO 18278-2 (2016) and RNES-B-00010v3 (2016) standards.

[0162] Meanwhile, the time required to reach the target heating temperature during the heating for the above-mentioned hot forming was also measured. Specifically, the time required for heating was expressed as a percentage of the time saved, based on the time taken to raise the temperature of an untreated galvanized steel sheet to the target temperature.

[0163] Specimen No. Composition Components (Weight%) Surface Treatment Layer Dry Thickness (㎛) Weldability Improvement Rate (%) Heating Time Reduction Rate (%) Classification Silica SCAT i-based 115 0.5 70.45 -37 Comparative Example A 2100 0.5 101.40 -36 Comparative Example B 300 70.45 613 Inventive Example A 400 20.8 1311 Inventive Example B 500 100.78 312 Inventive Example C 600 71.1 3010 Comparative Example C 700 0.5 50.5 1-67 Comparative Example D 800 0.5 30.6 2-68 Comparative Example E

[0164] As shown in Table 8, it can be confirmed that the weldability of a hot-formed part obtained using a plated steel sheet surface-treated with a surface treatment composition according to one embodiment of the present invention is improved compared to a hot-formed part obtained using a plated steel sheet that has not undergone surface treatment (control example).

[0165] In addition, it can be confirmed that the heating time can be reduced by more than 10% compared to the control example when heating to a high temperature for hot forming the surface-treated plated steel sheet. These results suggest that the efficiency of the hot forming process can be increased and that the energy generated during the manufacture of parts, etc. by hot forming can be reduced.

Claims

1. Includes a base steel plate and a plating layer formed on the base steel plate, and The above plating layer is, A first alloy layer formed on the above-mentioned base steel plate and comprising Al, Fe, Si, and optionally Zn; A second alloy layer formed on the first alloy layer and comprising Al, Fe, Si, and Zn; and A first alloy phase formed on or inside the second alloy layer and comprising Al, Fe, Si, and Zn; and The Zn content of the first alloy layer is greater than the Zn content of the first alloy layer and the second alloy layer, and The above-mentioned first alloy phase is a plated steel sheet in which the content of Al is greater than the content of Zn, and the content of Zn is greater than the content of Fe.

2. In Paragraph 1, The above-mentioned first alloy layer is a plated steel sheet in which the content of Fe is greater than the content of Al and the content of Al is greater than the content of Zn.

3. In Paragraph 1 or 2, The above second alloy layer is a plated steel sheet in which the content of Al is greater than the content of Fe, and the content of Fe is greater than the content of Zn.

4. In any one of paragraphs 1 to 3, A plated steel sheet in which the area fraction occupied by the first alloy phase in the thickness direction cross-section of the plating layer is 4.0 to 25.0%.

5. In any one of paragraphs 1 through 4, A plated steel sheet in which the area fraction of the first alloy layer occupies 4.0 to 20.0% in the cross-section in the thickness direction of the plating layer.

6. In any one of paragraphs 1 through 5, A plated steel sheet further comprising a second alloy phase formed inside the second alloy layer and including Al, Zn, Fe, and Si.

7. In any one of paragraphs 1 through 6, The above second alloy phase is a plated steel sheet in which the Si content is greater than the Zn content.

8. In any one of paragraphs 1 through 7, A plated steel sheet comprising a region in which the first alloy phase is exposed on the upper surface of the plating layer.

9. In any one of paragraphs 1 through 8, A plated steel sheet comprising a region in which the second alloy layer is exposed on the upper surface of the plating layer.

10. In any one of paragraphs 1 through 9, The above base steel sheet comprises, in weight%, Carbon (C): 0.02~0.60%, Silicon (Si): 0.001~2.000%, Aluminum (Al): 0.001~1.000%, Manganese (Mn): 0.10~4.00%, Phosphorus (P): 0.050% or less, Sulfur (S): 0.0200% or less, Nitrogen (N): 0.0200% or less, Titanium (Ti): 0~1.0000%, Niobium (Nb): 0~1.0000%, Vanadium (V): 0~1.0000%, Boron (B): 0~0.0100%, Chromium (Cr): 0~1.00%, Molybdenum (Mo): 0~1.00%, Tungsten (W): 0~1.00%, Copper (Cu): A plated steel sheet having a composition comprising 0~1.0%, nickel (Ni): 0~1.0%, tin (Sn): 0~1.00%, calcium (Ca): 0~0.10%, magnesium (Mg): 0~0.10%, cobalt (Co): 0~1.00%, arsenic (As): 0~1.00%, zirconium (Zr): 0~1.00%, bismuth (Bi): 0~1.00%, rare earth elements (REM): 0~0.3%, and the remainder being Fe and other unavoidable impurities.

11. In any one of paragraphs 1 through 10, It further includes a surface treatment layer formed on the above plating layer, and A plated steel sheet in which the above surface treatment layer is a resin layer containing Ti.

12. In any one of paragraphs 1 through 11, A plated steel sheet having a surface treatment layer having a thickness of 1.0㎛ or less after drying.

13. Step of preparing the steel sheet base; A step of manufacturing a plated steel plate having a plating layer on the base steel plate by plating the above-mentioned base steel plate; and The above-mentioned plated steel sheet includes the step of alloying; A method for manufacturing a plated steel sheet, wherein the alloying treatment is a step of heat treating by maintaining the plating at a heating temperature range of 800 to 850°C for 1 to 10 seconds after plating.

14. In Paragraph 13, A method for manufacturing a plated steel sheet, wherein the plating is performed by immersing the above-mentioned steel sheet in an aluminum-based plating bath containing, in weight percent, silicon (Si): 6.0~15.0%, zinc (Zn): 30.0% or less (excluding 0%), and the remainder being aluminum (Al) and other unavoidable impurities.

15. In Paragraph 13 or 14, The above plating is 10~80g / m² 2 A method for manufacturing plated steel sheets, performed with an amount of coating.

16. In any one of paragraphs 13 through 15, The above base steel sheet comprises, in weight%, Carbon (C): 0.02~0.60%, Silicon (Si): 0.001~2.000%, Aluminum (Al): 0.001~1.000%, Manganese (Mn): 0.10~4.00%, Phosphorus (P): 0.050% or less, Sulfur (S): 0.0200% or less, Nitrogen (N): 0.0200% or less, Titanium (Ti): 0~1.0000%, Niobium (Nb): 0~1.0000%, Vanadium (V): 0~1.0000%, Boron (B): 0~0.0100%, Chromium (Cr): 0~1.00%, Molybdenum (Mo): 0~1.00%, Tungsten (W): 0~1.00%, Copper (Cu): A method for manufacturing a plated steel sheet having a composition comprising 0~1.0%, nickel (Ni): 0~1.0%, tin (Sn): 0~1.00%, calcium (Ca): 0~0.10%, magnesium (Mg): 0~0.10%, cobalt (Co): 0~1.00%, arsenic (As): 0~1.00%, zirconium (Zr): 0~1.00%, bismuth (Bi): 0~1.00%, rare earth elements (REM): 0~0.3%, and the remainder being Fe and other unavoidable impurities.

17. In any one of paragraphs 13 through 16, A method for manufacturing a plated steel sheet, further comprising the step of forming a surface treatment layer on the plating layer after the alloying treatment.

18. In any one of paragraphs 13 through 17, The above surface treatment layer is formed by applying a composition containing a polymer binder resin, and The above polymer binder resin is, based on 100 weight%, A method for manufacturing a plated steel sheet comprising 25~35% acrylic resin, 0.5~1.5% curing agent, 2.0~10.0% rust-prevention / corrosion-resistant agent, 0.10~0.30% Teflon-based wax, 2% or less silane coupling agent, 10.0% or less other additives, and the remainder being a solvent.

19. A base steel plate and a plating layer formed on the base steel plate, and The above plating layer is, A first alloy layer formed on the above-mentioned base steel plate and comprising Al, Fe, Si, and Zn; A second alloy layer formed on the first alloy layer and comprising Al, Fe, Si, and Zn; A first alloy phase formed on or inside the second alloy layer and comprising Al, Fe, Si, and Zn; and A second alloy phase formed inside the second alloy layer and comprising Al, Fe, Si, and Zn; and The Zn content of the first alloy is greater than the Zn content of the first alloy layer, the second alloy layer, and the second alloy layer, and A hot-formed part in which the first alloy layer has a Fe content greater than the Al content, and the Al content greater than the Zn content.

20. In Paragraph 19, The above second alloy layer is a hot-formed part in which the content of Al is greater than the content of Fe and the content of Fe is greater than the content of Zn.

21. In Paragraph 19 or Paragraph 20, The above first alloy phase is a hot-formed part in which the content of Al is greater than the content of Zn, and the content of Zn is greater than the content of Fe.

22. In any one of paragraphs 19 through 21, The above second alloy phase is a hot-formed part in which the Si content is greater than the Zn content.

23. In any one of Paragraphs 19 through 22, A hot-formed part in which the area fraction occupied by the first alloy phase in the thickness direction cross-section of the plating layer is 5.0 to 35.0%.

24. In any one of paragraphs 19 through 23, A hot-formed part in which the area fraction of the first alloy layer occupies 5.0 to 30.0% in the cross-section in the thickness direction of the plating layer.

25. In any one of paragraphs 19 through 24, A hot-formed part comprising a region in which the first alloy phase is exposed on the upper surface of the plating layer.

26. In any one of paragraphs 19 through 25, A hot-formed part comprising a region in which the second alloy layer is exposed on the upper surface of the plating layer.

27. In any one of paragraphs 19 through 26, It includes a surface treatment layer formed on the above plating layer, and A hot-formed part, wherein the surface treatment layer is a resin layer containing a Zn-Ti intermetallic compound.

Images