Plated steel sheet and method for manufacturing the same

Abstract

An aspect of the present application is to provide a plated steel sheet. The plated steel sheet can include a base steel sheet; a Zn-Ni plated layer provided on at least one side of the base steel sheet; a Ni plated layer provided on one side of the Zn-Ni plated layer; and a Fe-Ni-Zn diffusion layer provided between the base steel sheet and the Zn-Ni plated layer, wherein an alloying degree of the diffusion layer can be 30% or more and less than 80%.

Description

Technical Field

[0001] This invention relates to a plated steel sheet and a method for manufacturing the same. More specifically, this invention relates to a plated steel sheet that can be used in secondary battery casings, etc., and a method for manufacturing the same. Background Technology

[0002] In recent years, as part of CO2 emission reduction efforts to protect the Earth's environment, the development and demand in the electric vehicle and electronic device sectors have increased significantly. Based on this technological development, the use of rechargeable batteries is increasing, and their applications are diversifying, including in mobile devices, power tools, energy storage devices, and electric vehicles.

[0003] Generally, there is an increasing demand for materials used in secondary battery casings to improve corrosion resistance in order to withstand the alkaline properties of the battery contents. For example, aluminum, plastics, or nickel-plated steel sheets with excellent corrosion resistance are being used as materials for such secondary battery casings.

[0004] Nickel-plated steel sheets can be manufactured by processing cold-rolled steel sheets through nickel plating, diffusion heat treatment, and leveling rolling. In this case, the amount of Ni plating, the degree of alloying of the Fe alloy layer formed by heat treatment, or the hardness of the Ni plating surface are important factors that determine the quality of the shell (e.g., corrosion resistance, machinability).

[0005] Furthermore, since nickel-plated steel sheets are used to manufacture the casing of secondary batteries through stamping, materials that ensure stamping workability are required in addition to corrosion resistance. Specifically, the strength of the base steel sheet, the elongation of the base steel sheet, and / or the hardness of the Ni coating are among the factors that determine stamping workability.

[0006] For example, if the hardness of the Ni coating is too high, defects or mold damage may occur during the stamping process due to coating peeling or cracking. Furthermore, if the strength of the base steel plate or the hardness of the Ni coating is too low, the coating may fuse to the mold during stamping, resulting in severe burrs and reduced productivity. Alternatively, after secondary battery manufacturing, short circuits or burr fragments reacting with the electrolyte inside the secondary battery may occur, leading to battery malfunction.

[0007] As prior art concerning the manufacture of secondary battery casings, Patent Document 1 discloses a method to improve corrosion resistance by enhancing the interfacial adhesion between the base steel plate and the coating through a Ni-Fe alloy layer and filling the cracked areas generated by the surface layer of nickel, which is a hard metal.

[0008] However, research is still needed on materials with sufficient corrosion resistance and processability for secondary battery casings that use steel plates.

[0009] (Patent Document 1) U.S. Patent Publication No. 5,587,248 Summary of the Invention

[0010] (a) Technical problems to be solved One aspect of the present invention is to provide a coated steel sheet with excellent corrosion resistance and processability, and a method for manufacturing the same.

[0011] The technical problems of this invention are not limited to the matters described above. Additional technical problems of this invention are described throughout the entire specification, and those skilled in the art will have no difficulty understanding these additional technical problems from the content of this specification.

[0012] (II) Technical Solution One aspect of the present invention is to provide a coated steel sheet. The coated steel sheet may include: a base steel sheet; a Zn-Ni coating disposed on at least one side of the base steel sheet; a Ni coating disposed on one side of the Zn-Ni coating; and an Fe-Ni-Zn diffusion layer disposed between the base steel sheet and the Zn-Ni coating, wherein the degree of alloying of the diffusion layer may be 30% or more and less than 80%.

[0013] Furthermore, in the aforementioned coated steel sheet, the Ni content relative to the total weight of the Zn-Ni coating can be 5-30% by weight.

[0014] Furthermore, in one of the aforementioned coated steel sheets, the thickness of the Zn-Ni coating can be 1-5 μm.

[0015] Furthermore, in one of the aforementioned coated steel sheets, the thickness of the Ni coating can be 1-5 μm.

[0016] Furthermore, in one of the aforementioned coated steel sheets, the average surface roughness (Ra) of the Ni coating can be greater than 1.0 μm and less than 2.0 μm.

[0017] Another aspect of the present invention is to provide a method for manufacturing a coated steel sheet. The method may include the following steps: performing Zn-Ni coating on at least one side of the base steel sheet; performing Ni coating on the Zn-Ni coated steel sheet; and annealing the Ni-coated steel sheet, wherein, in the annealing step, an Fe-Ni-Zn diffusion layer having an alloying degree of 30% or more and less than 80% may be formed.

[0018] Furthermore, in the above method, when the base steel plate in the preparation step is an unannealed base steel plate, the annealing step can be carried out at 520-670°C.

[0019] Furthermore, in one of the above methods, when the base steel plate in the preparation step is an annealed base steel plate, the annealing step can be carried out at 380-520°C.

[0020] Furthermore, in one of the above methods, the Zn-Ni plating step can be performed at a rate of 3-20 g / m 2 The coating adhesion is achieved by Zn-Ni electroplating.

[0021] Furthermore, in one of the above methods, the Ni plating step can be performed at a concentration of 3-15 g / m 2 Ni electroplating is performed to determine the amount of plating adhesion.

[0022] Furthermore, in one of the above methods, the annealing step can be performed within a time period of more than 20 seconds and less than 100 seconds.

[0023] Furthermore, in one of the above methods, a step of leveling and rolling the annealed steel sheet may be further included.

[0024] Furthermore, in one of the above methods, the leveling rolling step can be performed with an elongation of 0.7-1.5%.

[0025] (III) Beneficial Effects According to the present invention, due to the inclusion of the Fe-Ni-Zn diffusion layer, the processability and corrosion resistance are improved, and it can be used as a material for secondary battery casings.

[0026] Furthermore, according to the present invention, the inclusion of a Zn-Ni coating can improve the interfacial adhesion and elongation between the base steel plate and the coating, thereby further improving the stamping processability.

[0027] The various and beneficial advantages and effects of the present invention are not limited to those described above, and can be more easily understood in the process of describing specific embodiments of the present invention. Attached Figure Description

[0028] To provide a fuller understanding of the accompanying drawings referenced in the detailed description of the invention, a brief description of each drawing is provided.

[0029] Figure 1 This is a flowchart of a method for manufacturing a coated steel sheet according to an embodiment of the present invention.

[0030] Figure 2This is a graph showing the GDS analysis of the coated steel sheet of Example 23.

[0031] Figure 3 This is a graph showing the GDS analysis of the coated steel sheet of Comparative Example 4. Best practice

[0032] The preferred embodiments of the present invention are described below. However, the embodiments of the present invention can be modified in many other ways, and the terminology used in this specification is for illustrative purposes only and is not intended to limit the invention. Furthermore, unless the relevant definitions explicitly indicate the opposite meaning, the singular form used in this specification also includes the plural form.

[0033] In this specification, unless otherwise stated, the term "comprising" does not exclude other constituent elements, but is used to indicate that other constituent elements may also be included.

[0034] Furthermore, unless otherwise specified, the % unit in this specification refers to weight.

[0035] Unless otherwise defined, all terms used in this specification, including technical and scientific terms, shall have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in dictionaries are interpreted as having meanings consistent with relevant technical literature and the present disclosure.

[0036] The present invention will now be described in detail.

[0037] According to one embodiment of the present invention, the coated steel sheet may include: a base steel sheet; a Zn-Ni coating disposed on at least one side of the base steel sheet; a Ni coating disposed on one side of the Zn-Ni coating; and an Fe-Ni-Zn diffusion layer disposed between the base steel sheet and the Zn-Ni coating.

[0038] First, the base steel plate will be described. There are no particular limitations on the type of steel plate, alloy composition, etc., of the base steel plate; steel plates commonly used for metal plating in this technical field can be used. For example, the base steel plate can be an extremely low carbon steel with excellent machinability. Furthermore, for example, the base steel plate can be an annealed cold-rolled (CR) steel plate or an unannealed cold-rolled steel plate (Full Hard; FH).

[0039] The base steel plate may contain carbon (C), silicon (Si), manganese (Mn), and phosphorus (P). The following is a brief description of each alloy composition. Unless otherwise stated, the content of each alloy composition refers to weight%.

[0040] Carbon (C): 0.005-0.05% Carbon (C) can improve the strength and hardenability of the base steel plate. When the C content is less than 0.005%, it may be difficult to manufacture because C is included as the least amount of impurity. Furthermore, when the C content exceeds 0.05%, the workability may decrease. That is, the C content can be 0.005-0.05%, specifically 0.005-0.050%, more specifically 0.015-0.050%, and even more specifically 0.025-0.050%.

[0041] Silicon (Si): Less than 0.03% (except 0%) Silicon (Si) can improve strength as a solid solution strengthening element. However, when the Si content exceeds 0.03%, the strength increases excessively, which may be ineffective in terms of processability. That is, the Si content can be 0.03% or less, specifically 0.030% or less, more specifically 0.025% or less, and even more specifically 0.020% or less.

[0042] Manganese (Mn): 0.1-0.5% The solid solution strengthening effect of manganese (Mn) can ensure the strength of the target base steel plate. Manganese (Mn) combines with sulfur (S) to form MnS precipitates, which can suppress hot-rolling brittleness. When the Mn content is less than 0.1%, MnS precipitation is insufficient, and residual S may induce hot-rolling brittleness. Furthermore, when the Mn content exceeds 0.5%, the strength increases excessively, which may lead to unsatisfactory workability. That is, the Mn content can be 0.1-0.5%, specifically 0.10-0.50%, more specifically 0.1-0.4%, and even more specifically 0.1-0.3%.

[0043] Phosphorus (P): less than 0.02% (except 0%) Phosphorus (P) can improve the strength of steel plates as a material strengthening element. However, when the P content exceeds 0.02%, sufficient ductility cannot be guaranteed. That is, the P content can be less than 0.02%, specifically less than 0.020%, more specifically less than 0.018%, and even more specifically less than 0.016%.

[0044] The base steel plate contains the above-mentioned components, and iron (Fe) may be included as a residual component. Furthermore, during the normal manufacturing process, unintended impurities inevitably enter from the raw materials or the surrounding environment, and these impurities cannot be eliminated. These impurities are known to those skilled in the art during the normal manufacturing process, and therefore their details are not specifically mentioned in this specification.

[0045] By including the aforementioned alloy components in appropriate amounts, the base steel sheet ensures strength and mechanical-physical properties suitable for secondary battery casing applications. For example, a base steel sheet with a tensile strength of less than 400 MPa and / or an elongation of more than 30% ensures excellent strength and mechanical-physical properties.

[0046] The following is an explanation of the Zn-Ni coating.

[0047] Zn-Ni coating can improve the adhesion between the Ni coating and the base steel plate, as well as the corrosion resistance of the coated steel plate. Specifically, the Zn-Ni coating can be formed by electroplating on at least one side of the base steel plate. Typically, when Ni is plated onto the base steel plate, the Ni coating is too hard, resulting in slightly poor interfacial adhesion with the base steel plate. However, according to one embodiment of the present invention, the base steel plate is Zn-Ni plated before Ni plating, thus improving the interfacial adhesion between the Ni coating and the base steel plate, the ductility of the coated steel plate, and also improving its stamping workability.

[0048] The Ni content relative to the total weight of the Zn-Ni coating can be 5-30% by weight. When the Ni content is less than 5% by weight, sufficient corrosion resistance cannot be obtained. Furthermore, when the Ni content exceeds 30% by weight, the hardness is too high, and the processability may be reduced. That is, the Ni content can be 5-30% by weight, more specifically 7-25% by weight, and even more specifically 8-20% by weight.

[0049] The thickness of the Zn-Ni coating can be 1-5 μm. When the thickness of the Zn-Ni coating is less than 1 μm, sufficient corrosion resistance cannot be obtained. Furthermore, when the thickness of the Zn-Ni coating exceeds 5 μm, it leads to increased manufacturing costs and manufacturing difficulties. That is, the thickness of the Zn-Ni coating can be 1-5 μm, more specifically 2-5 μm, and even more specifically 3-5 μm.

[0050] The Zn-Ni coating may contain zinc (Zn) as a residual component. Furthermore, during normal manufacturing processes, unintended impurities (e.g., iron (Fe)) inevitably contaminate the material from raw materials or the surrounding environment, and these impurities cannot be eliminated. These impurities are known to those skilled in the art during normal manufacturing processes, and therefore, not all details are specifically mentioned in this specification.

[0051] The Ni coating will be explained below.

[0052] A Ni coating is formed on one side of a Zn-Ni coating, which can improve the corrosion resistance of the coated steel sheet. For example, the Ni coating can be formed by electroplating on one side of the Zn-Ni coating.

[0053] The thickness of the Ni coating can be 1-5 μm. When the thickness of the Ni coating is less than 1 μm, sufficient corrosion resistance cannot be obtained. Furthermore, when the thickness of the Ni coating exceeds 5 μm, it leads to increased manufacturing costs and manufacturing difficulties. That is, the thickness of the Ni coating can be 1-5 μm, more specifically 1.5-4.5 μm, and even more specifically 2-4 μm.

[0054] The average surface roughness (Ra) of the Ni coating can be 1.0 μm or more and less than 2.0 μm. When the average surface roughness of the Ni coating is less than 1.0 μm, it may be difficult to manufacture using a flat rolling method. Furthermore, when the average surface roughness of the Ni coating is 2.0 μm or more, the required characteristics (e.g., processability, corrosion resistance, etc.) for secondary batteries cannot be adequately obtained. That is, the average surface roughness (Ra) of the Ni coating can be 1.0 μm or more and less than 2.0 μm, more specifically, it can be 1.0-1.8 μm, and even more specifically, it can be 1.0-1.6 μm.

[0055] The maximum roughness height (Ry) of the Ni coating can be 5-15 μm. When the maximum roughness height of the Ni coating is less than 5 μm, it may be difficult to manufacture using a flat rolling method. Furthermore, when the maximum roughness height of the Ni coating exceeds 15 μm, the required characteristics (e.g., processability, corrosion resistance, etc.) for secondary batteries cannot be adequately obtained. That is, the maximum roughness height (Ry) of the Ni coating can be 5-15 μm, more specifically 5-12 μm, and even more specifically 6-10 μm.

[0056] The Fe-Ni-Zn diffusion layer will be explained below.

[0057] The Fe-Ni-Zn diffusion layer is formed between the base steel sheet and the Zn-Ni coating, thereby improving processability. Typically, Ni coatings have high hardness and low elongation, leading to cracking issues during stamping. According to one embodiment of the invention, the coated steel sheet forms the Fe-Ni-Zn diffusion layer through annealing, thus improving the formability of the coated steel sheet and minimizing problems during machining (e.g., burr, chip, or dust generation, Ni coating adhesion to the die, die damage, etc.).

[0058] The alloying degree of the Fe-Ni-Zn diffusion layer can be 30% or more and less than 80%. Here, alloying degree can be used synonymously with the alloying degree of (Fe+Zn) in the Fe-Ni-Zn diffusion layer and the alloying degree of (Fe+Zn) / (Fe-Ni-Zn). Furthermore, alloying degree can refer to the content fraction of (Fe+Zn) in the Fe-Ni-Zn diffusion layer. When the alloying degree is less than 30%, processability and / or corrosion resistance may be insufficient. Furthermore, when the alloying degree is 80% or more, Fe components may be exposed on the surface, thus corrosion resistance may be insufficient. That is, the alloying degree can be 30% or more and less than 80%, more specifically 35-75%, and even more specifically 35-65%.

[0059] The thickness of the Fe diffusion layer in the Fe-Ni-Zn diffusion layer can be 30-80% of the total thickness of the Fe-Ni-Zn diffusion layer. The Fe diffusion layer can be formed by the diffusion of Fe components from the base steel plate into the Zn-Ni coating. Furthermore, the thickness of the Fe diffusion layer can refer to the thickness of the area where Fe components are detected during GDS analysis of the Fe-Ni-Zn diffusion layer. When the thickness of the Fe diffusion layer is less than 30%, processability may be insufficient. Furthermore, when the thickness of the Fe diffusion layer exceeds 80%, Fe components may be exposed on the surface, thus corrosion resistance may be insufficient. That is, the thickness of the Fe alloy layer can be 30-80%, more specifically 35-75%, and even more specifically 40-70%.

[0060] The following describes a method for manufacturing a coated steel sheet according to one embodiment of the present invention.

[0061] Figure 1 This is a flowchart of the method for manufacturing the coated steel sheet of the present invention. (Refer to...) Figure 1 The method for manufacturing a coated steel sheet may include: preparing a base steel sheet; performing Zn-Ni coating on at least one side of the base steel sheet; performing Ni coating on the Zn-Ni coated steel sheet; and annealing the Ni coated steel sheet.

[0062] The manufacturing process of galvanized steel sheets is explained in more detail.

[0063] [Preparation steps for the base steel plate] First, a base steel plate is prepared. As described above, the preparation of the base steel plate can be achieved by heating a slab that meets the aforementioned alloy composition, followed by hot rolling, coiling, and cold rolling. There are no particular limitations on the heating, hot rolling, coiling, and cold rolling conditions for the slab; conditions commonly used in this technical field can be applied. For example, cold-rolled steel sheet (CR) can be manufactured by annealing cold-rolled steel sheet (FH) at a high temperature. Both unannealed cold-rolled steel sheet (FH) and annealed cold-rolled steel sheet (CR) can be prepared as base steel plates.

[0064] [Zn-Ni plating steps] Next, Zn-Ni plating can be performed on at least one side of the base steel plate. By performing Zn-Ni plating, a Zn-Ni coating can be formed on at least one side of the base steel plate. Specifically, the Zn-Ni plating step can be performed by electroplating the base steel plate with a Zn-Ni plating solution. There are no particular limitations on the electroplating conditions; conditions commonly used in this art can be applied.

[0065] The Zn-Ni plating process can be carried out at a concentration of 3-20 g / m 2 The Zn-Ni plating is performed to achieve a coating adhesion of less than 3 g / m. 2 At this point, excellent corrosion resistance cannot be guaranteed. Furthermore, when the Zn-Ni plating adhesion exceeds 20 g / m², [further issues arise]. 2 This can lead to increased manufacturing costs. Specifically, the Zn-Ni plating adhesion amount can be 3-20 g / m². 2 More specifically, it can be 5-18 g / m 2 More specifically, it can be 8-15g / m 2 .

[0066] As an example, the Zn-Ni plating solution in the Zn-Ni plating step can be prepared by dissolving 40-80 g / L of Zn metal and 40-80 g / L of Ni metal in sulfuric acid, adjusting the pH to 0.8-2.0, and dissolving 20-50 g / L of sodium sulfate (Na2SO4) in 1 L of total volume. By adjusting the Zn metal content, Ni metal content, pH value, and / or sodium sulfate content to the above ranges, the Ni content and the coating weight of the Zn-Ni plating layer can be adjusted.

[0067] As an example, the Zn-Ni plating step can be performed at 50-80°C. When the Zn-Ni plating temperature is below 50°C, the plating speed is slow, and productivity may decrease. Furthermore, when the Zn-Ni plating temperature exceeds 80°C, the plating speed is too fast, and the quality of the plating layer may decrease. That is, the Zn-Ni plating temperature can be 50-80°C, more specifically 55-75°C, and even more specifically 60-70°C.

[0068] As an example, the deposition efficiency in the Zn-Ni plating process can be above 85%. Deposition efficiency refers to the ratio of the actual deposition amount to the theoretical deposition amount, calculated based on the applied current.

[0069] [Ni plating steps] Next, Ni plating can be applied to the Zn-Ni coated steel sheet. By applying Ni plating, a Ni coating can be formed on one side of the Zn-Ni coating. When the order of the Zn-Ni plating and Ni plating steps is changed (i.e., when the Zn-Ni plating step is performed after the Ni plating step), it may be difficult to ensure the target level of corrosion resistance because a Ni coating exists on one side of the base steel sheet.

[0070] As an example, the Ni plating step can be performed by electroplating the base steel sheet using a Ni plating solution. There are no particular limitations on the electroplating conditions; conditions commonly used in this technical field can be applied.

[0071] The Ni plating process can be carried out at 3-15 g / m 2 Ni electroplating is performed to achieve a coating adhesion amount of less than 3 g / m. 2 At this stage, not only can the required processability and corrosion resistance in secondary batteries be not guaranteed, but the thickness of the Fe diffusion layer inside the Fe-Ni-Zn diffusion layer formed during subsequent annealing is also insufficient. Therefore, cracks may occur in the coated steel sheet during stamping, or the thickness reduction rate of the coated steel sheet may increase significantly. When the Ni coating adhesion exceeds 15 g / m 2 At this time, manufacturing costs may increase excessively. That is, the Ni plating adhesion amount can be 3-15 g / m. 2 More specifically, it can be 5-13 g / m 2 More specifically, it can be 7-12 g / m 2 .

[0072] The total amount of Zn-Ni plating and Ni plating (hereinafter, total plating amount) can be 5-40 g / m². 2 When the total coating adhesion is less than 5 g / m 2When the total coating thickness exceeds 40 g / m², it is difficult to adequately protect the base steel plate, thus potentially reducing corrosion resistance. 2 At this time, production costs may increase, or the stamping process may cause cracks in the hard Ni plating. That is, the total plating adhesion can be 5-40 g / m². 2 More specifically, it can be 8-30g / m 2 More specifically, it can be 10-25g / m 2 .

[0073] As an example, the Ni plating solution in the Ni plating step, based on a total volume of 1L, can contain 200-500 g / L of nickel sulfate (NiSO4), 30-100 g / L of nickel chloride (NiCl2), 20-80 g / L of boric acid (H3BO3), and the balance water. By adjusting the content of nickel sulfate, nickel chloride, and / or boric acid to the above ranges, the Ni coating can possess the target physical properties (e.g., corrosion resistance, processability, hardness, etc.).

[0074] As an example, the Ni plating step can be performed at a temperature of 40-80°C. When the Ni plating temperature is below 40°C, the plating speed is too slow, and the production speed may decrease. Furthermore, when the Ni plating temperature exceeds 80°C, the plating speed is too fast, and therefore the adhesion of the coating on the base steel plate may decrease. That is, the Ni plating temperature can be 40-80°C, more specifically 45-75°C, and even more specifically 50-70°C.

[0075] As an example, the Ni plating process can be performed at pH 3.0–5.0. Alternatively / alternatively, the Ni plating process can be performed at 5–40 A / dm². 2 The plating is performed at the specified current density. By adjusting the pH and / or current density values ​​to the ranges described above, excellent plating quality and an appropriate level of plating amount can be ensured.

[0076] [Annealing Steps] Next, the steel sheet with the Ni coating can be annealed. During the annealing step, an Fe-Ni-Zn diffusion layer can be formed between the base steel sheet and the Zn-Ni coating. The Fe-Ni-Zn diffusion layer is as described above.

[0077] As an example, when the base steel sheet in the preparation step is an unannealed base steel sheet (e.g., unannealed cold-rolled steel sheet (fully hard (FH))), the annealing step can be performed at 520-670°C. When the annealing temperature is below 520°C, Fe diffusion is slow, and the target alloying degree cannot be obtained. Furthermore, when the annealing temperature exceeds 670°C, the thickness of the Fe diffusion layer inside the Fe-Ni-Zn diffusion layer increases excessively, thus exposing Fe to the surface, potentially reducing corrosion resistance. That is, the annealing temperature can be 520-670°C, more specifically 540-650°C, and even more specifically 560-630°C.

[0078] As an example, when the base steel sheet in the preparation step is an annealed base steel sheet (e.g., an annealed cold-rolled (CR) steel sheet), the annealing step can be performed at 380-520°C. When the annealing temperature is below 380°C, Fe diffusion is slow, and the target alloying degree cannot be obtained. Furthermore, when the annealing temperature exceeds 520°C, the thickness of the Fe diffusion layer within the Fe-Ni-Zn diffusion layer increases excessively, thus exposing Fe to the surface, potentially reducing corrosion resistance. That is, the annealing temperature can be 380-520°C, more specifically 400-500°C, and even more specifically 420-480°C.

[0079] The annealing step can be performed within a time frame of more than 20 seconds but less than 100 seconds. When the annealing time is less than 20 seconds, Fe diffusion is slow, and the target alloying degree cannot be achieved. Furthermore, when the annealing time is more than 100 seconds, the thickness of the Fe diffusion layer within the Fe-Ni-Zn diffusion layer increases excessively, thus exposing Fe to the surface and potentially reducing corrosion resistance. In other words, the annealing time can be more than 20 seconds but less than 100 seconds, more specifically 30-90 seconds, and even more specifically 40-80 seconds.

[0080] The thickness of the Fe-Ni-Zn diffusion layer formed during the annealing step can be 15-70% of the combined thickness of the Zn-Ni coating and the Ni coating before annealing (hereinafter, the total coating thickness before annealing). When the thickness of the Fe-Ni-Zn diffusion layer is less than 15% of the total coating thickness before annealing, processability may be insufficient. Furthermore, when the thickness of the Fe-Ni-Zn diffusion layer exceeds 70% of the total coating thickness before annealing, corrosion resistance may be insufficient. That is, the thickness of the Fe-Ni-Zn diffusion layer can be 15-70% of the total coating thickness before annealing, more specifically 20-65%, and even more specifically 30-60%.

[0081] [Leveling and rolling steps] As an example, the process could further include a step of leveling and rolling the annealed steel sheet. Leveling and rolling allows for the adjustment of the steel sheet's thickness, shape, and surface roughness, while minimizing residual stress and ensuring uniform material properties.

[0082] The leveling rolling step can be performed with an elongation of 0.7-1.5%. When the elongation is less than 0.7%, the steel sheet shape may be undesirable. Furthermore, when the elongation exceeds 1.5%, the average surface roughness of the Ni coating may be slightly lower, thus potentially reducing corrosion resistance or workability. That is, the elongation can be 0.7-1.5%, more specifically 0.8-1.3%, and even more specifically 0.8-1.2%. Detailed Implementation

[0083] The present invention will now be described in more detail through embodiments. However, it should be noted that the following embodiments are merely illustrative of the invention and for more detailed description, and are not intended to limit the scope of the invention. This is because the scope of the invention is determined by the matters recorded in the claims and those reasonably inferred therefrom.

[0084] (Example) Annealed steel sheet (CR) or unannealed steel sheet (FH) with a thickness of 0.30 mm containing C: 0.03 wt%, Si: 0.01 wt%, Mn: 0.15 wt%, P: 0.008 wt%, and the balance iron (Fe) and other unavoidable impurities are prepared as the base steel sheet.

[0085] The base steel plate was subjected to alkaline degreasing, pickling with sulfuric acid aqueous solution, and water washing, followed by Zn-Ni electroplating using a Zn-Ni plating solution. Specifically, the Zn-Ni plating solution was prepared by dissolving 60 g / L of Zn metal and 60 g / L of Ni metal in sulfuric acid in 1 L of solution, adjusting the pH to 1.5, and then dissolving 40 g / L of sodium sulfate (Na2SO4). The Zn-Ni plating was carried out at 60°C, and the Zn-Ni plating amount and the Ni content relative to the total weight of the Zn-Ni plating layer were performed under the conditions described in Table 1 below.

[0086] Subsequently, Ni electroplating was performed on the steel sheet with the Zn-Ni coating using a Ni plating solution. The Ni plating solution, based on a 1L volume, contained 400g / L nickel sulfate (NiSO4), 80g / L nickel chloride (NiCl2), 60g / L boric acid (H3BO3), and the balance water. Ni plating was performed at pH 4.0, a temperature of 60℃, and a current density of 20A / dm³. 2 The Ni plating was carried out under the conditions described in Table 1 below.

[0087] Finally, the steel sheet with the Ni coating is annealed under the conditions described in Table 1 below, and after forming an Fe-Ni-Zn diffusion layer between the base steel sheet and the Zn-Ni coating, it is leveled and rolled to manufacture the coated steel sheet.

[0088] [Table 1] The degree of alloying, average surface roughness (Ra), corrosion resistance, and processability of the Fe-Ni-Zn diffusion layers of the manufactured examples and comparative examples were evaluated and are then described in Table 2 below.

[0089] The degree of alloying was calculated using the formula [(Fe+Zn) / (Fe+Ni+Zn)×100] (where each element refers to its content (by weight%) in the Fe-Ni-Zn diffusion layer). The content of each element was measured using GDS analysis.

[0090] The average surface roughness (Ra) was measured using a MITUTOYO SV502 2D surface roughness meter.

[0091] Corrosion resistance was evaluated according to JIS Z-2371 through a 4-hour salt spray test. Specifically, each steel plate was machined into a cylindrical battery casing of grade 2170 (21 mm in diameter and 70 mm in height) and then subjected to a salt spray test. The presence or absence of white and red rust on the surface was used to evaluate corrosion resistance (◎: excellent, ○: good, △: average, ×: poor).

[0092] Machinability was evaluated through bending tests on each steel plate. Specifically, a 25mm thick sample was clamped in the plate and bent 180° (1T bending). Machinability was then evaluated by the presence or absence of cracks in the coating cross-section using FE-SEM (JEOL JSM-7000F) image analysis. A complete absence of cracks on the machined surface and a coating thickness reduction rate of less than 20% was rated ◎ (Excellent); a complete absence of cracks on the machined surface but a coating thickness reduction rate of 20% or more but less than 60% was rated ○ (Good); a complete absence of cracks on the machined surface but a coating thickness reduction rate of 60% or more was rated △ (Average); and a complete presence of cracks on the machined surface was rated × (Poor).

[0093] [Table 2] As can be seen from Tables 1 and 2 above, under the manufacturing conditions proposed in Examples 1 to 64 of this invention, an appropriate level of alloying degree and average surface roughness of the Ni coating are ensured, and excellent corrosion resistance and processability are also observed.

[0094] Furthermore, as a representative example, the GDS analysis chart of Example 23 is shown in... Figure 2 As shown. Specifically, Figure 2 (A) is a graph showing the GDS analysis of the total coating (Zn-Ni coating and Ni coating) and the Fe, Ni, and Zn content in the diffusion layer before annealing in Example 23. Furthermore, Figure 2 (B) is a graph showing the content of Fe, Ni and Zn in the total coating and diffusion layer after annealing in Example 23 using GDS analysis.

[0095] Reference Figure 2 It was confirmed that the alloying degree of the diffusion layer after annealing in Example 23 was achieved at an appropriate level.

[0096] On the other hand, in Comparative Examples 1 and 7, the annealing time was set too short, resulting in insufficient alloying of the diffusion layer, causing coating cracks, and reducing corrosion resistance and processability. Furthermore, in Comparative Examples 2 and 8, the annealing time was set too long, resulting in excessive alloying of the diffusion layer, reducing both corrosion resistance and processability.

[0097] In Comparative Examples 3, 4, 9, and 10, the alloying degree of the diffusion layer was excessively increased due to the annealing temperature being set too high, resulting in reduced corrosion resistance and workability. Furthermore, in Comparative Examples 5, 6, 11, and 12, the workability was insufficient due to the excessively high annealing temperature being set.

[0098] Furthermore, as a representative comparative example, the GDS analysis chart of Comparative Example 4 is shown in... Figure 3 As shown. Specifically, Figure 3 (A) is a graph showing the GDS analysis of the total coating (Zn-Ni coating and Ni coating) and the Fe, Ni, and Zn content in the diffusion layer before annealing in Comparative Example 4. Furthermore, Figure 3 (B) is a graph showing the content of Fe, Ni and Zn in the total coating and diffusion layer after annealing of Comparative Example 4 using GDS analysis.

[0099] Reference Figure 3 It was confirmed that in Comparative Example 4, the alloying degree of the diffusion layer after annealing was excessively high.

[0100] Comparative Examples 13, 17, 21 and 22 did not form a Zn-Ni coating, so the degree of alloying increased excessively after annealing or the interfacial adhesion between the Ni coating and the base steel plate decreased, thus reducing the stamping workability and corrosion resistance.

[0101] In Comparative Examples 14, 18, and 19, the annealing temperature was set very low, resulting in insufficient alloying of the diffusion layer and failure to form a sufficient alloy layer, thus reducing corrosion resistance and processability.

[0102] In Comparative Examples 15 and 19, the elongation rate was set very low during leveling rolling, resulting in excessively high average surface roughness and reduced quality in areas such as corrosion resistance and processability. Furthermore, in Comparative Examples 16 and 20, the elongation rate was set very high during leveling rolling, resulting in excessively low average surface roughness and poor quality in areas such as corrosion resistance and processability.

[0103] The above embodiment is an example, and the present invention is not limited thereto. Any content having a substantially the same structure and achieving the same effect as the technical concept described in the claims of the present invention is included within the technical scope of the present invention.

Claims

1. A galvanized steel sheet, comprising: Foundation steel plate; A Zn-Ni coating is disposed on at least one side of the base steel plate; A Ni coating, wherein the Ni coating is disposed on one side of the Zn-Ni coating; and The Fe-Ni-Zn diffusion layer is disposed between the base steel plate and the Zn-Ni coating. The degree of alloying of the diffusion layer is above 30% and less than 80%.

2. The galvanized steel sheet according to claim 1, wherein, The Ni content relative to the total weight of the Zn-Ni coating is 5-30% by weight.

3. The galvanized steel sheet according to claim 1, wherein, The thickness of the Zn-Ni coating is 1-5 μm.

4. The galvanized steel sheet according to claim 1, wherein, The thickness of the Ni coating is 1-5 μm.

5. The coated steel sheet according to claim 1, wherein, The average surface roughness Ra of the Ni coating is greater than 1.0 μm and less than 2.0 μm.

6. A method for manufacturing a galvanized steel sheet, comprising the following steps: Prepare the foundation steel plate; Zn-Ni plating is performed on at least one side of the base steel plate; Ni plating is performed on the steel sheet that has been Zn-Ni coated; and The Ni-plated steel sheet is then annealed. In the annealing step, an Fe-Ni-Zn diffusion layer with an alloying degree of 30% or more but less than 80% is formed.

7. The method for manufacturing galvanized steel sheet according to claim 6, wherein, When the base steel plate in the preparation step is an unannealed base steel plate, the annealing step is carried out at 520-670°C.

8. The method for manufacturing galvanized steel sheet according to claim 6, wherein, When the base steel plate in the preparation step is an annealed base steel plate, the annealing step is carried out at 380-520°C.

9. The method for manufacturing galvanized steel sheet according to claim 6, wherein, The Zn-Ni plating step is performed at a concentration of 3-20 g / m 2 The coating adhesion is achieved by Zn-Ni electroplating.

10. The method for manufacturing galvanized steel sheet according to claim 6, wherein, The Ni plating step is performed at a concentration of 3-15 g / m 2 Ni electroplating is performed to determine the amount of plating adhesion.

11. The method for manufacturing galvanized steel sheet according to claim 6, wherein, The annealing step is performed within a time frame of more than 20 seconds and less than 100 seconds.

12. The method for manufacturing galvanized steel sheet according to claim 6, wherein, The manufacturing method further includes a step of leveling and rolling the annealed steel plate.

13. The method for manufacturing galvanized steel sheet according to claim 12, wherein, The leveling and rolling step is carried out with an elongation of 0.7-1.5%.

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