Nickel-plated heat-treated steel sheet for battery case having excellent corrosion resistance and method for manufacturing the same

Abstract

The present invention relates to a nickel-plated heat-treated steel sheet for a battery case having excellent corrosion resistance and a method of manufacturing the same. In one embodiment, the nickel-plated heat-treated steel sheet includes a base steel sheet and a nickel layer formed on one or more surfaces of the base steel sheet, wherein the nickel layer is laminated in two or more layers, and the weight per unit decreases in order from the base steel sheet toward the surface of the nickel layer.

Description

Technical Field

[0001] This invention relates to a nickel-plated heat-treated steel sheet for battery casings with excellent corrosion resistance and a method for manufacturing the same. Specifically, this invention provides a nickel-plated heat-treated steel sheet for battery casings with excellent corrosion resistance and a method for manufacturing the same by employing multiple nickel layers with nickel particles of different sizes and densities. Background Technology

[0002] In recent years, the battery market has been growing rapidly due to the increasing use of renewable energy and the accelerated transition of the automotive industry to electric vehicles. Cylindrical lithium-ion batteries, in particular, are widely used across various industries due to their standardized dimensions and rechargeability. Furthermore, cylindrical lithium-ion batteries require fewer manufacturing processes, resulting in lower production costs and facilitating mass production; these advantages have led to a rapid increase in their market share.

[0003] The cylindrical lithium-ion battery casing is made of nickel-plated heat-treated steel sheet. This is because nickel (Ni), the plating element of nickel-plated heat-treated steel sheet, is a precious metal, which is more beneficial for surface protection than iron (Fe), and has excellent spot weldability, formability, and corrosion resistance. In addition, iron (Fe) has high chemical resistance to alkaline media such as lithium ions, so the amount of nickel plating on the inner surface of the battery casing is less than that on the outer surface.

[0004] Recently, research has been underway to ensure the lightweighting of cylindrical lithium-ion batteries, thereby minimizing carbon dioxide (CO2) emissions to ensure environmental friendliness, while also increasing battery capacity. To ensure the lightweighting of these lithium-ion batteries, the thickness of the battery casing must be minimized; in particular, research is needed to ensure corrosion resistance even with a thin nickel plating layer.

[0005] The background technology related to this invention has been disclosed in Japanese Invention Patent No. 3594286 (November 24, 2004, Invention Title: Surface-treated steel plate for battery casing, battery casing using the same, method of manufacturing the same and battery). Summary of the Invention

[0006] One object of the present invention is to provide a nickel-plated heat-treated steel sheet with excellent corrosion resistance, strength and durability.

[0007] Another objective of this invention is to provide a nickel-plated heat-treated steel sheet that exhibits excellent corrosion resistance and lightweight properties even with a relatively thin plating thickness, thus providing excellent environmental friendliness and increased battery capacity.

[0008] Another object of the present invention is to provide a nickel-plated heat-treated steel sheet that minimizes defects such as cracks, pinholes and voids in the nickel layer, thereby achieving excellent corrosion resistance and surface quality. In addition, the excellent corrosion resistance provides excellent explosion resistance and structural safety when used in battery casings.

[0009] Another objective of this invention is to provide a nickel-plated heat-treated steel sheet with excellent surface conductivity and corrosion resistance, thereby maximizing battery life under external conditions.

[0010] Another object of the present invention is to provide a nickel-plated heat-treated steel sheet with excellent production efficiency and economy.

[0011] Another object of the present invention is to provide a method for manufacturing the nickel-plated heat-treated steel sheet.

[0012] This invention relates in one aspect to a nickel-plated heat-treated steel sheet. In one specific embodiment, the nickel-plated heat-treated steel sheet includes: a base steel sheet; and a nickel layer formed on one or more surfaces of the base steel sheet; wherein the nickel layer is stacked in two or more layers, and the unit weight decreases sequentially from the base steel sheet toward the surface of the nickel layer.

[0013] In one specific embodiment, the nickel layer is formed sequentially on one or more surfaces of the base steel plate as a base layer and a surface layer, wherein the base layer has a unit weight of 22 g / m². 2 Up to 50g / m 2 The surface layer has a unit weight of 4 g / m³. 2 Up to 10g / m 2 Furthermore, the unit weight of the nickel layer can be 26 g / m². 2 Up to 54g / m 2 .

[0014] Another aspect of the present invention relates to a method for manufacturing the aforementioned nickel-plated heat-treated steel sheet. In one specific embodiment, the method for manufacturing the nickel-plated heat-treated steel sheet includes: electroplating one or more surfaces of a base steel sheet using a first plating solution comprising nickel sulfate, nickel chloride, and boric acid to form one or more first plating layers; electroplating the outermost surface of the first plating layer using a second plating solution comprising nickel sulfate, nickel chloride, boric acid, and additives to form a second plating layer, thereby manufacturing a plated sheet; and heat-treating the plated sheet; wherein the plating amount decreases sequentially from the base steel sheet toward the second plating layer, the nickel-plated heat-treated steel sheet includes a base steel sheet and nickel layers formed on one or more surfaces of the base steel sheet, the nickel layers being stacked in two or more layers, and the unit weight decreasing sequentially from the base steel sheet toward the surface of the nickel layers.

[0015] The nickel-plated heat-treated steel sheet for battery casings of the present invention has excellent corrosion resistance, strength, and durability. By minimizing defects such as cracks, pinholes, and voids in the nickel layer, it achieves excellent corrosion resistance and surface quality, exhibiting excellent corrosion resistance even with a relatively thin plating thickness. Its excellent lightweight properties bring environmental benefits and increased battery capacity. Furthermore, its excellent corrosion resistance provides superior explosion resistance and structural safety when used in battery casings. It can also provide a minimum plating thickness that ensures stability in corrosive environments. With excellent interlayer adhesion and surface conductivity, it can maximize battery life under external conditions, and also offers excellent production efficiency and economy.

[0016] In particular, the present invention can effectively delay the corrosion rate of the base material by forming two or more layers of nickel with different particle sizes while minimizing the thickness of the nickel layer. Furthermore, the nickel particles at the interface of the base steel plate are relatively coarse compared to the outermost nickel layer. By reducing the surface area between the nickel layer particles and the interface of the base steel plate, the accelerated diffusion of iron (Fe) and nickel (Ni) in the base steel plate during heat treatment is prevented, thereby minimizing the exposure of iron (Fe) in the nickel layer.

[0017] Furthermore, by making the nickel particles on the surface of the nickel layer finer than those at the interface of the base steel plate, defects such as surface cracks, pinholes, and voids can be minimized, thus preventing localized corrosion caused by the external environment. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a nickel-plated heat-treated steel sheet according to a specific embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram of a nickel-plated heat-treated steel sheet based on existing technology.

[0020] Figure 3 This is a SEM image showing the surface of the nickel-plated heat-treated steel plate in Experimental Example 1.

[0021] Figure 4 This is a SEM image showing the surface of the nickel-plated heat-treated steel plate in Experimental Example 9.

[0022] Figure 5 This is a photograph showing the corrosion resistance evaluation results of Experiment Example 1.

[0023] Figure 6 This is a photograph showing the corrosion resistance evaluation results of Experiment Example 9. Detailed Implementation

[0024] In describing this invention, if it is believed that relevant known technologies or specific descriptions of technical features may obscure the main points of this invention, then specific descriptions are omitted.

[0025] Furthermore, the following terms are defined according to their function in this invention, and may vary depending on the intention or habit of the user or operator; therefore, their definitions should be determined by the interpretation of the invention in this specification.

[0026] Nickel-plated heat-treated steel sheet

[0027] One aspect of the present invention relates to a nickel-plated heat-treated steel sheet. Figure 1 This is a schematic diagram of a nickel-plated heat-treated steel sheet according to a specific embodiment of the present invention. See also... Figure 1 The nickel-plated heat-treated steel sheet 100 includes: a base steel sheet 10; and a nickel layer 20 formed on at least one surface of the base steel sheet 10; wherein the nickel layer 20 is stacked in two or more layers, and the unit weight decreases sequentially from the base steel sheet toward the nickel layer surface.

[0028] Matrix steel plate

[0029] The base steel plate 10 may contain carbon (C), silicon (Si), manganese (Mn), phosphorus (P) and iron (Fe).

[0030] In one specific embodiment, the base steel plate may include 0.005 to 0.05 wt% carbon (C), more than 0 wt% to less than 0.05 wt% silicon (Si), 0.1 to 0.6 wt% manganese (Mn), more than 0 wt% to less than 0.01 wt% phosphorus (P), the balance iron (Fe), and other unavoidable impurities. When the above components and contents are included, the desired mechanical properties such as strength and hardness of the base steel plate can be ensured.

[0031] The carbon (C) content relative to the total weight of the base steel plate may be from 0.005% to 0.05% by weight. When contained within this range, the mechanical strength, such as strength and hardness, sought by this invention can be achieved. For example, the carbon content may be from 0.01% to 0.04% by weight.

[0032] The silicon (Si) may comprise more than 0% by weight and less than 0.05% by weight relative to the total weight of the base steel sheet. When contained within this range, the base steel sheet exhibits excellent ductility and processability. For example, the silicon may comprise more than 0% by weight and less than 0.02% by weight.

[0033] The manganese (Mn) content relative to the total weight of the base steel plate may be from 0.1% to 0.6% by weight. When contained within this range, the strength and hardness sought by the present invention can be easily ensured after heat treatment. For example, the manganese content may be from 0.2% to 0.5% by weight.

[0034] The phosphorus (P) content relative to the total weight of the base steel plate may be more than 0% by weight but less than 0.01% by weight. When it is included within this range, excellent mechanical strength can be achieved while preventing defects such as segregation in the base steel plate.

[0035] In another specific embodiment, the base steel plate may be a black plate (BP), a cold-rolled steel plate (CR), or a full-hard material that has not undergone annealing after cold rolling in the cold-rolled steel plate manufacturing process.

[0036] Nickel layer

[0037] The nickel layer consists of two or more layers stacked in a 20-layer configuration, with the weight per unit area decreasing sequentially from the base steel plate toward the nickel layer surface. Under these conditions, heat treatment can minimize the diffusion of iron (Fe) and nickel (Ni) in the base steel plate, resulting in an excellent effect in delaying the corrosion rate of the base steel plate. Furthermore, it can minimize the grain size of the outermost surface of the nickel layer, thereby minimizing the size of defects such as cracks, pinholes, and voids. This can prevent localized corrosion caused by the external environment and improve corrosion resistance.

[0038] For example, the nickel layer 20 can be stacked in two or more layers, and the average grain size and unit weight can be decreased sequentially from the base steel plate toward the surface of the nickel layer.

[0039] Reference Figure 1 The nickel layer 20 may be formed on one or more surfaces of the base steel plate, with one or more base layers 21, 22 and surface layers 24 in sequence.

[0040] Reference Figure 1 In this system, two or more base layers 21 and 22 decrease in weight per unit area from the base steel plate toward the nickel layer surface, and the weight per unit area of ​​the surface layer 24 can be lower than that of the base layer 22 adjacent to the surface layer 24. Under these conditions, heat treatment creates a corrosion potential difference, resulting in excellent corrosion resistance and minimizing the diffusion of iron (Fe) and nickel (Ni) in the base steel plate. This effectively delays the corrosion rate of the base steel plate and minimizes the grain size of the outermost surface of the nickel layer, thereby minimizing the size of defects such as cracks, pinholes, and voids. This prevents localized corrosion caused by the external environment and improves corrosion resistance.

[0041] Figure 2 This is a schematic diagram illustrating a prior art nickel-plated heat-treated steel sheet. (Refer to...) Figure 2 The nickel-plated heat-treated steel sheet 101 of the prior art forms a nickel layer 23 only on one or more surfaces of the base steel sheet 10. Unlike the nickel-plated heat-treated steel sheet of the present invention, it is difficult to form a corrosion potential difference. Compared with the present invention, which has two or more nickel layers with different unit weights, the effect of delaying the corrosion rate of the base steel sheet will be reduced, or the effect of preventing corrosion will be reduced because the outermost surface defects of the nickel layer are not prevented.

[0042] In one specific embodiment, the unit weight of the substrate layer may be 22 g / m². 2 Up to 50g / m 2 When included within this range, the grain coarsening effect is excellent, thereby minimizing the diffusion of iron (Fe) and nickel (Ni) in the base steel plate, resulting in an excellent effect in delaying the corrosion rate of the base steel plate.

[0043] In one specific embodiment, the unit weight of the surface layer may be 4 g / m². 2 Up to 10g / m 2 When included within this range, heat treatment can minimize grain size, thereby minimizing the size of defects such as cracks, pinholes, and voids, preventing localized corrosion caused by the external environment, and improving corrosion resistance.

[0044] In one specific embodiment, the average grain size of the substrate layer can be from 0.3µm to 20µm. Under these conditions, the nickel layer exhibits excellent formability and durability, while minimizing the diffusion of iron (Fe) and nickel (Ni) in the base steel plate, thus effectively delaying the corrosion rate of the base steel plate.

[0045] The base layer may have a larger average grain size and unit weight than the surface layer.

[0046] In one specific embodiment, the average grain size of the surface layer can be from 0.05µm to 10µm. Under this condition, excellent surface quality is achieved by minimizing the defect size on the nickel layer surface, while simultaneously minimizing corrosion caused by the external environment.

[0047] In one specific embodiment, the unit weight of the nickel layer may be 26 g / m². 2 Up to 54g / m 2 When included within this range, mechanical properties, corrosion resistance, and processability can be excellent.

[0048] In one specific embodiment, the thickness of the nickel layer can be from 0.1 µm to 10 µm. Under this thickness condition, the mechanical properties, corrosion resistance, and processability can be excellent.

[0049] In one specific embodiment, the total thickness of the substrate layer can be from 0.1µm to 8µm. Under these conditions, excellent durability and corrosion resistance are achieved, and the diffusion of iron (Fe) and nickel (Ni) in the base steel plate is minimized, resulting in an excellent effect in delaying the corrosion rate of the base steel plate.

[0050] In one specific embodiment, the thickness of each layer constituting the substrate layer can be from 0.05µm to 4µm. Under these conditions, excellent durability and corrosion resistance are achieved, and the diffusion of iron (Fe) and nickel (Ni) in the base steel plate is minimized, resulting in an excellent effect in delaying the corrosion rate of the base steel plate.

[0051] In one specific embodiment, the thickness of the surface layer can be from 0.01µm to 2µm. Under these conditions, the grain size can be minimized after heat treatment, thereby minimizing the size of defects such as cracks, pinholes, and voids, preventing localized corrosion caused by the external environment, and improving corrosion resistance.

[0052] Manufacturing method of nickel-plated heat-treated steel sheet

[0053] Another aspect of the present invention relates to a method for manufacturing the aforementioned nickel-plated heat-treated steel sheet. In one specific embodiment, the method for manufacturing the nickel-plated heat-treated steel sheet includes: step S10, forming a first coating layer; step S20, manufacturing a clad plate; and step S30, heat treatment. More specifically, the method for manufacturing the nickel-plated heat-treated steel sheet includes: step S10, electroplating one or more surfaces of a base steel sheet using a first plating solution containing nickel sulfate, nickel chloride, and boric acid to form one or more first coating layers; step S20, electroplating the outermost surface of the first coating layer using a second plating solution containing nickel sulfate, nickel chloride, boric acid, and additives to form a second coating layer, thereby manufacturing a clad plate; and step S30, heat-treating the clad plate; and the coating amount decreases sequentially from the base steel sheet toward the second coating layer.

[0054] (S10) First coating formation step

[0055] In the aforementioned step, electroplating is performed on one or more surfaces of the base steel plate using a first plating solution comprising nickel sulfate, nickel chloride, and boric acid to form one or more first plating layers.

[0056] In one specific embodiment, the first plating solution can be used for electroplating using conventional electroplating methods. For example, the plating solution can use a watt bath or a sulfamate bath.

[0057] In one specific embodiment, the first plating solution, based on 1L, may contain 200g / L to 250g / L of nickel sulfate (NiSO4), 30g / L to 50g / L of nickel chloride (NiCl2), 30g / L to 50g / L of boric acid (H3BO3), and the balance being water. When electroplating is performed using the first plating solution, the heat-treated steel plate exhibits excellent corrosion resistance and electrical conductivity, and also demonstrates excellent performance in delaying the corrosion rate of the base steel plate.

[0058] In one specific embodiment, electroplating using the first plating solution can be performed at a pH of 3.0 to 4.0 and a current density of 5 A / dm³. 2 Up to 30A / dm 2 The process is carried out under specific conditions. When electroplating is performed under these conditions, a nickel layer with the physical properties sought by this invention can be easily formed.

[0059] In one specific embodiment, the temperature of the first plating solution may be from 30°C to 70°C, but is not limited thereto.

[0060] In one specific embodiment, when two or more first coating layers are formed, the coating amount can be decreased sequentially from the base steel plate toward the surface. Under these conditions, a corrosion potential difference can be easily formed, resulting in excellent corrosion resistance, and the grain coarsening effect of the first coating layer (unit first coating layer) in contact with the base steel plate is excellent, thereby achieving an excellent effect in delaying the corrosion rate of the base steel plate.

[0061] In one specific embodiment, the coating weight of the first coating layer can be 22 g / m². 2 Up to 50g / m 2 When included within this range, the grain coarsening effect is excellent, thereby minimizing the diffusion of iron (Fe) and nickel (Ni) in the base steel plate, resulting in an excellent effect in delaying the corrosion rate of the base steel plate.

[0062] In one specific embodiment, the total thickness of the first coating can be from 0.1µm to 8µm. Under these conditions, excellent durability and corrosion resistance are achieved, and the diffusion of iron (Fe) and nickel (Ni) in the base steel plate is minimized, resulting in an excellent effect in delaying the corrosion rate of the base steel plate.

[0063] In one specific embodiment, the thickness of each layer constituting the first coating can be from 0.05µm to 4µm. Under these conditions, excellent durability and corrosion resistance are achieved, and the diffusion of iron (Fe) and nickel (Ni) in the base steel plate is minimized, resulting in an excellent effect in delaying the corrosion rate of the base steel plate.

[0064] (S20) Steps for manufacturing coated plates

[0065] In the above steps, a second plating layer is formed on the outermost surface of the first plating layer by electroplating with a second plating solution containing nickel sulfate, nickel chloride, boric acid and additives, thereby manufacturing a plated plate.

[0066] In one specific embodiment, the second plating solution, based on 1L, may contain 200g / L to 250g / L of nickel sulfate (NiSO4), 30g / L to 50g / L of nickel chloride (NiCl2), 30g / L to 50g / L of boric acid (H3BO3), 0.1g / L to 20g / L of additives, and the balance being water. When electroplating is performed using the second plating solution, the heat-treated steel sheet exhibits excellent corrosion resistance and electrical conductivity, preventing surface layer defects and minimizing defect size, thus achieving excellent corrosion resistance.

[0067] In one specific embodiment, the additive may comprise one or more of a non-sulfur-based wetting agent and an organic additive. For example, it may comprise one or more of a non-sulfur-based wetting agent at a concentration of 0.1 g / L to 50 g / L and an organic additive at a concentration of 0.1 g / L to 10 g / L.

[0068] In one specific embodiment, the non-sulfur-based wetting agent is a sulfur-free substance that can prevent the surface layer from hardening, thereby preventing cracks from occurring during processing and reducing corrosion resistance.

[0069] In one specific embodiment, the organic additive may comprise one or more of a gloss agent, a pH adjuster, and a surfactant. In one specific embodiment, the gloss agent may be an aliphatic unsaturated alcohol such as a polyoxyethylene adduct of an alcohol, an unsaturated carboxylic acid, formaldehyde, coumarin, etc., but is not limited thereto.

[0070] In one specific embodiment, electroplating using the second plating solution can be performed at a pH of 3.0 to 4.0 and a current density of 5 A / dm³. 2 Up to 30A / dm 2 The process is carried out under specific conditions. When electroplating is performed under these conditions, a nickel layer with the physical properties sought by this invention can be easily formed.

[0071] In one specific embodiment, the temperature of the second plating solution can be from 30°C to 70°C, but is not limited thereto.

[0072] In one specific embodiment, the coating weight of the second coating layer can be 4 g / m². 2 Up to 10g / m 2 When included within this range, heat treatment can minimize grain size, thereby minimizing the size of defects such as cracks, pinholes, and voids, preventing localized corrosion caused by the external environment, and improving corrosion resistance.

[0073] In one specific embodiment, the thickness of the second coating can be from 0.01µm to 2µm. Under this condition, the grain size can be minimized after heat treatment, thereby minimizing the size of defects such as cracks, pinholes, and voids, preventing localized corrosion caused by the external environment, and improving corrosion resistance.

[0074] In one specific embodiment, the combined thickness of the first and second coatings can be from 0.1 µm to 10 µm. Under this thickness condition, excellent mechanical properties, corrosion resistance, and processability can be achieved.

[0075] In one specific embodiment, the sum of the coating weights of the first and second coatings can be 26 g / m². 2 Up to 54g / m 2 When included within this range, mechanical properties, corrosion resistance, and processability can be excellent.

[0076] (S30) Heat treatment steps

[0077] The step described is to heat-treat the plated sheet. For example, an intermediate can be manufactured by heat-treating the plated sheet.

[0078] In one specific embodiment, the heat treatment can be performed at 600°C to 730°C. At this temperature, nickel layers with different particle sizes are formed, thereby creating a corrosion potential difference to delay the corrosion rate of the base steel plate, and minimizing defects on the nickel layer surface, resulting in excellent surface quality and corrosion resistance. For example, the heat treatment can be performed at 680°C to 710°C.

[0079] The heat treatment can be carried out in a reducing atmosphere. The reducing atmosphere can be provided by using an atmosphere gas containing one or more of nitrogen (N2) and hydrogen (H2). The atmosphere gas may contain 1 to 20 volume percent nitrogen and 1 to 15 volume percent hydrogen. For example, it may contain 5 to 15 volume percent nitrogen and 1 to 10 volume percent hydrogen. Under these conditions, the heat-treated steel sheet exhibits excellent durability and corrosion resistance.

[0080] In one specific embodiment, the heat treatment can last from 10 seconds to 30 minutes. When heat treatment is performed under these conditions, the heat-treated steel sheet exhibits excellent corrosion resistance and electrical conductivity. For example, the heat treatment can last from 30 seconds to 5 minutes or from 30 seconds to 1 minute.

[0081] (S40) Leveling and rolling steps

[0082] In one specific embodiment, a skin-pass rolling step may be included. In this step, the intermediate is skin-pass rolled to produce a skin-pass rolled material (or a nickel-plated heat-treated steel sheet). The purpose of the skin-pass rolling is to adjust the thickness, shape, and surface roughness of the steel sheet to minimize residual stress in the heat-treated steel sheet and ensure uniform material properties.

[0083] The rolling process can be achieved by placing the intermediate into a rolling mill and performing leveling rolling using an upper workroll and a lower workroll.

[0084] The nickel-plated heat-treated steel sheet includes a base steel sheet and nickel layers formed on one or more surfaces of the base steel sheet. The nickel layers are stacked in two or more layers, and the unit weight decreases sequentially from the base steel sheet toward the surface of the nickel layers. For example, the nickel layers may be stacked in two or more layers, and the average grain size and unit weight may decrease sequentially from the base steel sheet toward the surface of the nickel layers.

[0085] Reference Figure 1 The nickel layer 20 may be formed on one or more surfaces of the base steel plate, with one or more base layers 21, 22 and surface layers 24 in sequence.

[0086] Reference Figure 1 In this system, two or more base layers 21 and 22 decrease in weight per unit area from the base steel plate toward the nickel layer surface, and the weight per unit area of ​​the surface layer 24 can be lower than that of the base layer 22 adjacent to the surface layer 24. Under these conditions, a corrosion potential difference can be formed during heat treatment, resulting in excellent corrosion resistance and minimizing the diffusion of iron (Fe) and nickel (Ni) in the base steel plate. This significantly delays the corrosion rate of the base steel plate and minimizes the grain size of the outermost surface of the nickel layer, thereby minimizing the size of defects such as cracks, pinholes, and voids, and preventing localized corrosion caused by corrosion resistance and the external environment.

[0087] In one specific embodiment, the unit weight of the substrate layer may be 22 g / m². 2 Up to 50g / m 2When included within this range, the grain coarsening effect is excellent, minimizing the diffusion of iron (Fe) and nickel (Ni) in the base steel plate, and can be very effective in delaying the corrosion rate of the base steel plate.

[0088] In one specific embodiment, the unit weight of the surface layer may be 4 g / m². 2 Up to 10g / m 2 When included within this range, heat treatment can minimize grain size, thereby minimizing the size of defects such as cracks, pinholes, and voids, preventing localized corrosion caused by the external environment, and improving corrosion resistance.

[0089] In one specific embodiment, the average grain size of the substrate layer can be from 0.3µm to 20µm. Under these conditions, the nickel layer exhibits excellent formability and durability, while minimizing the diffusion of iron (Fe) and nickel (Ni) in the base steel plate, resulting in excellent performance in delaying the corrosion rate of the base steel plate.

[0090] In one specific embodiment, the average grain size of the surface layer can be from 0.05µm to 10µm. Under this condition, excellent surface quality is achieved by minimizing the defect size on the nickel layer surface, while simultaneously minimizing corrosion caused by the external environment.

[0091] The base layer may have a larger average grain size and unit weight than the surface layer.

[0092] In one specific embodiment, the unit weight of the nickel layer may be 26 g / m². 2 Up to 54g / m 2 When included within this range, mechanical properties, corrosion resistance, and processability can be excellent.

[0093] In one specific embodiment, the thickness of the nickel layer can be from 0.1 µm to 10 µm. Under this thickness condition, the mechanical properties, corrosion resistance, and processability can be excellent.

[0094] In one specific embodiment, the total thickness of the substrate layer can be from 0.1 µm to 8 µm. Under these conditions, excellent durability and corrosion resistance are achieved, and the diffusion of iron (Fe) and nickel (Ni) in the base steel plate is minimized, resulting in excellent performance in delaying the corrosion rate of the base steel plate.

[0095] In one specific embodiment, the thickness of each layer constituting the substrate layer can be from 0.05µm to 4µm. Under these conditions, excellent durability and corrosion resistance are achieved, and the diffusion of iron (Fe) and nickel (Ni) in the base steel plate is minimized, resulting in excellent performance in delaying the corrosion rate of the base steel plate.

[0096] In one specific embodiment, the thickness of the surface layer can be from 0.01µm to 2µm. Under these conditions, the grain size can be minimized after heat treatment, thereby minimizing the size of defects such as cracks, pinholes, and voids, preventing localized corrosion caused by the external environment, and improving corrosion resistance.

[0097] Existing technologies have failed to identify a minimum coating thickness in corrosive environments, but this invention, through defect control of the coating, can provide a stable minimum coating thickness. Furthermore, by improving the corrosion resistance of the nickel plating layer, this invention ensures the explosion resistance and structural safety of the nickel-plated heat-treated steel sheet used for battery casings, and improves corrosion resistance in the most economical way without altering the specifications required for battery casing manufacturing, affecting the steel sheet material and properties of subsequent processes, or the manufacturing process itself.

[0098] The technical features and effects of the present invention are further described in detail below through preferred experimental examples. However, the illustrated embodiments are preferred examples of the present invention and should not be construed as limiting the present invention. Those skilled in the art can deduce from the technical aspects what is not described in this specification, therefore, related descriptions will be omitted.

[0099] Experimental Example 1

[0100] (1) Preparation of base steel plate: A steel billet containing 0.03% by weight (300ppm) carbon (C), more than 0 to 0.001% by weight (10ppm) silicon (Si), 0.31% by weight (3100ppm) manganese (Mn), more than 0 to 0.001% by weight (10ppm) phosphorus (P), balance iron (Fe) and other unavoidable impurities is reheated and hot rolled and cold rolled to prepare a base steel plate (cold rolled carbon steel plate) with a thickness of 0.30mm.

[0101] (2) Forming the first coating: Electroplating is performed on both sides of the base steel plate in a first plating solution containing 220 g / L nickel sulfate, 40 g / L nickel chloride and 40 g / L boric acid, and with a pH of 3.8, to form one or more first coatings.

[0102] (3) Preparation of the plated plate: On the outermost surface of the first coating layer, electroplating is performed in a second plating solution containing 220 g / L nickel sulfate, 40 g / L nickel chloride, 40 g / L boric acid, 5 g / L non-sulfur wetting agent (Shinto Metals Co., Ltd. WA129), and 1 g / L organic additive (glosser, Shinto Metals Co., Ltd. GL6000C), with a pH of 3.8, to form a second coating layer, thereby producing the plated plate. The coating weight of the second coating layer of the plated plate is lower than that of the first coating layer.

[0103] (4) Heat treatment and leveling rolling: The clad plate was heat-treated at 700°C for less than 1 minute in a reducing atmosphere (a mixture of 10% nitrogen (N2) and 3% hydrogen (H2) by volume) to produce an intermediate. The intermediate was then fed into a leveling mill and leveled in one pass with a reduction rate of 1% to produce a nickel-plated heat-treated steel plate.

[0104] The nickel-plated heat-treated steel sheet includes a base steel sheet and a nickel layer formed on one or more surfaces of the base steel sheet, wherein the nickel layer sequentially forms a base layer (average grain size: 3µm, unit weight 22g / m²) on both surfaces of the base steel sheet. 2 ) and surface layer (average grain size: 0.5µm, unit weight 4g / m) 2 The base layer is formed to have a larger average grain size and unit weight than the surface layer.

[0105] Experimental Examples 2 to 8

[0106] Except for the nickel layer that is subject to the conditions of base layer unit weight and surface layer unit weight in Table 1 below, nickel-plated heat-treated steel sheets were produced by the same method as in Experimental Example 1 above.

[0107] Experimental Examples 9 to 12

[0108] Except for the base layer with the unit weight conditions in Table 1 below, and without forming a second coating (surface layer) during heat treatment, nickel-plated heat-treated steel sheets were produced by the same method as in Experimental Example 1 above.

[0109] Experimental Example

[0110] Corrosion resistance evaluation: For the above experimental examples, corrosion resistance evaluation (potassium ferrocyanide test) was conducted according to JIS-H-8617 standard. Potassium ferrocyanide solution reacts with the iron (Fe) component of nickel-plated heat-treated steel plate to turn blue, thus evaluating corrosion resistance.

[0111] Specifically, prepare an 80mm x 80mm (width x length) sample for the above-mentioned experimental example. Immerse analytical filter paper in an aqueous solution of potassium ferrocyanide (1 wt%), ferric chloride (potassium hexacyanoferrate(III)), and NaCl (6 wt%). Attach the filter paper to the sample surface and leave it for 30 minutes. Then peel off the filter paper and visually evaluate whether there are blue spots on the sample surface in contact with the filter paper. The results are shown in Table 1 below (A: no potassium ferrocyanide reaction, B: 1 to 5 reactions, C: more than 6 reactions).

[0112] Table 1

[0113]

[0114] As can be seen from the results in Table 1 above, Experimental Examples 1 to 8 exhibit superior corrosion resistance compared to Experimental Examples 9 and 11, which only use a base layer without a surface layer.

[0115] The following Figure 3 This is a SEM image showing the surface of Experimental Example 1. Figure 4 This is a SEM image showing the surface of Experimental Example 9. (Refer to...) Figure 3 and Figure 4 It can be seen that, compared with Experimental Example 9, Experimental Example 1, which uses the nickel layer according to the present invention, has a superior surface quality. Conversely, compared with Experimental Example 1, Experimental Example 9, which does not use the surface layer of the present invention, shows a significant increase in defects such as surface cracks and voids, indicating a decrease in surface quality and durability.

[0116] The following Figure 5 This is a photograph showing the corrosion resistance evaluation results of Experimental Example 1. Figure 6 This is a photograph showing the corrosion resistance evaluation results of Experimental Example 9. (Refer to...) Figure 5 and Figure 6 It can be seen that Experimental Example 1 has better corrosion resistance than Experimental Example 9.

[0117] The present invention has been described above with reference to embodiments. Those skilled in the art will understand that the invention can be implemented in various modifications without departing from its essential characteristics. Therefore, the disclosed embodiments should be considered exemplary rather than restrictive. The scope of the invention is defined by the claims rather than the foregoing description, and any differences within the equivalent scope should be considered to be included in the invention.

Claims

1. A nickel-plated heat-treated steel sheet, characterized in that, include: Matrix steel plate; and A nickel layer is formed on one or more surfaces of the base steel plate; The nickel layer consists of two or more layers, and the unit weight decreases sequentially from the base steel plate toward the surface of the nickel layer.

2. The nickel-plated heat-treated steel sheet according to claim 1, characterized in that, The nickel layer is formed sequentially on one or more surfaces of the base steel plate as a base layer and a surface layer. The base layer has a unit weight of 22g / m³. 2 Up to 50g / m 2 The surface layer has a unit weight of 4 g / m³. 2 Up to 10g / m 2 The unit weight of the nickel layer can be 26 g / m². 2 Up to 54g / m 2 .

3. A method for manufacturing a nickel-plated heat-treated steel sheet, characterized in that, Includes the following steps: On one or more surfaces of a base steel plate, electroplating is performed using a first plating solution containing nickel sulfate, nickel chloride and boric acid to form one or more first plating layers; On the outermost surface of the first coating layer, a second coating layer is formed by electroplating using a second plating solution containing nickel sulfate, nickel chloride, boric acid, and additives, thereby producing a plated plate; and The plated plate is heat-treated. In this configuration, the coating thickness decreases sequentially from the base steel plate towards the second coating layer. The nickel-plated heat-treated steel sheet includes a base steel sheet and a nickel layer formed on one or more surfaces of the base steel sheet. The nickel layer is stacked in two or more layers, and the unit weight decreases sequentially from the base steel plate toward the surface of the nickel layer.

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