Nickel-plated heat-treated steel sheet having excellent workability and method for producing the same

Abstract

A nickel-plated heat-treated steel plate having excellent workability and a method for manufacturing the same. The nickel-plated heat-treated steel plate comprises: a base steel plate; a nickel layer formed on one or both surfaces of the base steel plate; and a nickel-iron (Ni-Fe) alloy layer formed between the base steel plate and the nickel layer, and the nickel-plated heat-treated steel plate has a surface Rockwell hardness of 52 to 62.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Korean Patent Application No. 10-2020-0170950 filed on December 9, 2020, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to a nickel-plated heat-treated steel sheet having excellent workability and a method for producing the same. Background Art

[0004] The global battery market is growing due to the development of wireless electronic devices and eco-friendly vehicles. In particular, there is a growing demand for rechargeable (secondary) cylindrical lithium-ion batteries that are standardized in size and can be used in a variety of applications. In recent years, the application fields of such cylindrical lithium-ion batteries are expanding to various vehicles, such as motorcycles and trucks.

[0005] In the manufacture of cylindrical secondary batteries, first, steel sheets are used as substrates to produce materials for cylindrical secondary batteries through hot rolling, cold rolling, etc. This process determines the main quality factors of the final product, such as shape and strength. Then, the produced material is manufactured into nickel-plated heat-treated steel sheets through nickel (Ni) plating, diffusion heat treatment, and skin-pass rolling. This process determines important quality factors, such as nickel (Ni) plating amount (g / m 2 ), the content of the nickel-iron (Ni-Fe) alloy layer and the hardness of the nickel (Ni) layer (or pure Ni layer) forming the surface of the nickel plating layer.

[0006] In addition, the nickel-plated heat-treated steel sheet is processed by deep drawing (stamping and ironing (DNI) or stamping-thinning-re-stamping (DTR)) for use as a battery case. Here, if the strength (hardness) of the substrate and the strength (hardness) of the nickel (Ni) forming the outermost part (surface) of the nickel alloy layer (or nickel plating layer) are too high, process problems may occur during the multi-stage machining process for manufacturing the final product, such as the generation of a large amount of fine chips and dust and damage to the machining mold. On the contrary, if the strength (hardness) of the substrate and the strength (hardness) of the nickel (Ni) forming the surface of the nickel alloy layer are too low, the steel sheet material may stick to the machining mold during the machining operation, and severe burr formation may occur during the lug forming portion of the trimming battery case opening, which is the final process in the production of the battery case, resulting in a reduction in machining productivity.

[0007] In particular, if the strength of the substrate and the strength of the nickel on the surface forming the nickel alloy layer are too low, an electrical short circuit may occur due to the formation of burrs during the finishing process, which is performed after the battery electrolyte filling process performed by the final stage manufacturer of the battery (battery filling company), or secondary battery failure may occur due to the reaction between fine fragments (debris) originating from the burrs and the electrolyte in the secondary battery, thereby resulting in serious deterioration in product quality.

[0008] Therefore, the management of the strength (hardness) of the nickel-plated heat-treated steel sheet (product) used for the battery casing, the hardness of the nickel on the surface forming the nickel alloy layer, and the content of the nickel-iron (Ni-Fe) alloy layer (there is a correlation between the content of the nickel-iron alloy layer and the hardness of the surface nickel layer during the Ni-Fe alloy heat treatment process) ultimately has an important impact on the productivity and quality of the process of mechanically processing the nickel-plated heat-treated steel sheet into the battery casing and the battery filling process.

[0009] However, to date, quality control in the production of nickel-plated heat-treated steel sheets has mainly focused on improving corrosion resistance.

[0010] The background art of the present invention is disclosed in Japanese Patent Registration No. 3594286B2 (publication date: November 24, 2004, invention title: surface treated steel sheet for battery case, battery case using the same, manufacturing method thereof and battery). Summary of the invention

[0011] One aspect of the present invention is to provide a nickel-plated heat-treated steel sheet having excellent workability and corrosion resistance.

[0012] Another aspect of the present invention is to provide a nickel-plated heat-treated steel sheet including a nickel layer having excellent surface hardness and mechanical properties.

[0013] Another aspect of the present invention is to provide a nickel-plated heat-treated steel sheet that can prevent the formation of burrs and dust when machined into a secondary battery case, has good releasability, and can prevent a short circuit of the secondary battery.

[0014] Another aspect of the present invention is to provide a method for manufacturing the above-mentioned nickel-plated heat-treated steel sheet.

[0015] One aspect of the present invention relates to a nickel-plated heat-treated steel plate. In one embodiment, the nickel-plated heat-treated steel plate comprises: a base steel plate; a nickel layer formed on at least one surface of the base steel plate; and a nickel-iron (Ni-Fe) alloy layer formed between the base steel plate and the nickel layer, wherein the nickel-plated heat-treated steel plate has a surface Rockwell hardness of 52 to 62.

[0016] In one embodiment, the nickel-iron alloy layer may have a nickel (Ni) content of 0.3 wt % to 25 wt %.

[0017] In one embodiment, the nickel layer may have a hardness of 150 to 250 measured using a micro Vickers hardness tester under a load of 10 gf.

[0018] Another aspect of the present invention relates to a method for manufacturing a nickel-plated heat-treated steel plate. In one embodiment, the method comprises: forming a nickel layer by electroplating at least one surface of a base steel plate with nickel (Ni); and forming a nickel-iron (Ni-Fe) alloy layer between the base steel plate and the nickel layer by diffusion heat treatment of the base steel plate and the nickel layer, wherein the nickel-plated heat-treated steel plate has a surface Rockwell hardness of 52 to 62.

[0019] The nickel-plated heat-treated steel sheet according to the present invention has good properties in terms of machinability such as cuttability and die-cutting, corrosion resistance and demouldability, and includes a nickel layer with excellent surface hardness and mechanical properties. Therefore, the nickel-plated heat-treated steel sheet according to the present invention can prevent burrs and dust (nickel, iron, etc.) from forming, damage to the machining mold, and adhesion of the steel sheet material to the machining mold when mechanically processed into a secondary battery housing, and can prevent the short circuit of the secondary battery. Therefore, the nickel-plated heat-treated steel sheet according to the present invention is suitable for use as a material for a secondary battery housing. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a view of a nickel-plated heat-treated steel sheet according to one embodiment of the present invention.

[0021] Figure 2 is a flow chart of a method for manufacturing a nickel-plated heat-treated steel sheet according to one embodiment of the present invention.

[0022] Figure 3 This is an image of a secondary battery case manufactured using Example 1.

[0023] Figure 4A is a diagram showing the measurement of the burr height of Example 2, and Figure 4B 1 is a diagram showing the measurement of the burr height in Comparative Example 3. DETAILED DESCRIPTION

[0024] Descriptions of known functions and configurations that may unnecessarily obscure the subject matter of the present invention will be omitted.

[0025] In addition, the terms to be described below are defined in consideration of the functions of the present invention, and these terms may vary depending on the intention or practice of a user or operator. Therefore, these terms should be defined based on the entire disclosure.

[0026] Nickel-plated heat-treated steel plate

[0027] One aspect of the present invention relates to a nickel-plated heat-treated steel sheet. Figure 1 is a view of a nickel-plated heat-treated steel sheet according to one embodiment of the present invention.

[0028] refer to Figure 1 The nickel-plated heat-treated steel sheet 100 includes: a base steel sheet 10 ; a nickel layer 20 formed on at least one surface of the base steel sheet; and a nickel-iron (Ni—Fe) alloy layer 30 formed between the base steel sheet 10 and the nickel layer 20 .

[0029] In one embodiment, the nickel-plated heat-treated steel plate 100 has a surface Rockwell hardness of 52 to 62. If the surface Rockwell hardness of the nickel-plated heat-treated steel plate is less than 52, the nickel may stick to the mold during the machining of the heat-treated steel plate, and the formation of burrs may be increased during the trimming of the end of the shell for the secondary battery, resulting in a short circuit of the secondary battery. On the contrary, if the hardness of the nickel-plated heat-treated steel plate exceeds 62, the heat-treated steel plate may have poor formability, resulting in mold damage, and a large amount of debris and dust may be generated during the manufacture of the secondary battery shell using the heat-treated steel plate. For example, the nickel-plated heat-treated steel plate 100 may have a surface Rockwell hardness of 52, 53, 54, 55, 56, 57, 58, 59, 60, 61 or 62.

[0030] Base steel plate

[0031] The base steel sheet 10 may include a steel sheet generally used for metal plating. In one embodiment, the base steel sheet may include carbon (C), silicon (Si), manganese (Mn), phosphorus (P), and iron (Fe).

[0032] For example, the base steel plate may include 0.005wt% to 0.05wt% of carbon (C), more than 0wt% to 0.05wt% or less of silicon (Si), 0.1wt% to 0.6wt% of manganese (Mn), more than 0wt% to 0.01wt% or less of phosphorus (P), and the remainder of iron (Fe) and other inevitable impurities, based on the total weight of the base steel plate. When the base steel plate includes the above elements in the above amounts, the base steel plate may have a desired level of mechanical properties (strength and hardness).

[0033] Based on the total weight of the base steel plate, the amount of carbon (C) may be 0.005 wt % to 0.05 wt %. Within this range, the base steel plate may have a desired level of mechanical properties, such as strength, hardness, etc. For example, the amount of carbon may be 0.01 wt % to 0.04 wt %. For example, 0.005, 0.006, 0.007, 0.008, 0.009, 0.010, 0.015, 0.020, 0.025, 0.030, 0.035, 0.040, 0.045, or 0.050 wt % of carbon may be included.

[0034] Based on the total weight of the base steel plate, the amount of silicon (Si) can be greater than 0wt% to less than 0.05wt%. Within this range, the base steel plate can have good ductility and workability. For example, the amount of silicon can be greater than 0wt% to less than 0.01wt%. For example, 0.00001, 0.0001, 0.0005, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.010, 0.015, 0.020, 0.025, 0.030, 0.035, 0.040, 0.045 or 0.050wt% of silicon (Si) can be included.

[0035] Based on the total weight of the base steel plate, the amount of manganese (Mn) may be 0.1wt% to 0.6wt%. Within this range, the base steel plate may have a desired level of strength and hardness after diffusion heat treatment. For example, the amount of manganese may be 0.2wt% to 0.5wt%. For example, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55 or 0.60wt% of manganese (Mn) may be included.

[0036] The amount of phosphorus (P) may be greater than 0 wt % to 0.01 wt % based on the total weight of the base steel sheet. Within this range, the base steel sheet may have good mechanical strength without defects such as segregation. For example, 0.00001, 0.0001, 0.0005, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009 or 0.01 wt % of phosphorus (P) may be included.

[0037] Alternatively, the base steel plate may be a material for tin plating (black steel plate (BP)), cold rolled (CR) steel, or full hard steel (non-annealed cold rolled steel).

[0038] Preferably, the base steel plate has a surface Rockwell hardness of 48 to 65. When the surface Rockwell hardness of the base steel plate falls within this range, the nickel-plated heat-treated steel plate (hereinafter referred to as "heat-treated steel plate") according to the present invention can have a desired level of nickel content in the nickel-iron alloy layer (or a desired level of thickness of the nickel-iron alloy layer) while having desired physical properties, in particular, a surface Rockwell hardness of 52 to 62. For example, the base steel plate may have a surface Rockwell hardness of 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64 or 65.

[0039] In one embodiment, before forming the nickel layer on the base steel plate by electroplating in a nickel bath, the base steel plate may be subjected to a pretreatment process. For example, the pretreatment process may include typical degreasing, water washing and pickling processes, but is not limited thereto.

[0040] Nickel layer

[0041] The nickel layer 20 is used to ensure the corrosion resistance of the heat-treated steel sheet according to the present invention. In one embodiment, the nickel layer 20 may be a pure Ni layer containing only nickel (Ni).

[0042] In one embodiment, the surface of the nickel layer 20 may have a hardness of 150 to 250 measured using a micro Vickers hardness tester under a load of 10 gf. Here, the surface of the nickel layer 20 may refer to the uppermost portion of the nickel layer 20. Within the range of this surface hardness, the heat-treated steel plate may have good properties in terms of machinability, formability, and demoldability, while preventing the nickel layer from sticking to the mold during mechanical processing of the heat-treated steel, and preventing the formation of burrs and the generation of dust and debris during the cutting process. For example, the surface of the nickel layer 20 may have a hardness of 150 to 250 measured using a micro Vickers hardness tester under a load of 10 gf and a retention time of 10 seconds. For example, the surface of the nickel layer 20 may have a hardness of 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 205, 210, 215, 220, 225, 230, 235, 240, 245, or 250.

[0043] Nickel-iron alloy layer

[0044] The nickel-iron alloy layer 30 may be formed between the base steel plate 10 and the nickel layer 20. The nickel-iron alloy layer 30 may be formed by diffusion heat treatment of the nickel layer 20 as described below.

[0045] In one embodiment, after the nickel layer 20 is removed from the heat-treated steel plate, the nickel-iron alloy layer 30 may have a nickel (Ni) content of 0.3 wt % to 25 wt % as measured by energy dispersive spectroscopy (EDS) or electron probe X-ray microanalysis (EPMA). For example, the nickel-iron alloy layer 30 may have 0.3 wt %, 0.4 wt %, 0.5 wt %, 0.6 wt %, 0.7 wt %, 0.8 wt %, 0.9 wt %, 1 wt %, 1.5 wt %, 2 wt %, 2.5 wt %, 3 wt %, 3.5 wt %, 4 wt %, 4.5 wt %, 5 wt %, 5.5 wt %, 6 wt %, 6.5 wt %, 7 wt %, 7.5 wt %, 8 wt %, 8.5 wt %, 9 wt %, 9.5 wt %, 10 wt %, 10.5 wt %, 11 wt %, 11.5 wt %, 12 wt %, 13 wt %, 14 wt %, 15 wt %, 16 wt %, 17 wt %, 18 wt %, 19 wt %, 20 wt %, 21 wt %, 22 wt %, 23 wt %, 24 wt %, 25 wt %, 26 wt %, 27 wt %, 28 wt %, 29 wt %, 30 wt %, 31 wt %, 32 %, 12wt%, 12.5wt%, 13wt%, 13.5wt%, 14wt%, 14.5wt%, 15wt%, 15.5wt%, 16wt%, 16.5wt%, 17wt%, 17.5wt%, 18wt%, 18.5wt%, 19wt%, 19.5wt%, 20wt%, 20.5wt%, 21wt%, 21.5wt%, 22wt%, 22.5wt%, 23wt%, 23.5wt%, 24wt%, 24.5wt% or 25wt% nickel content.

[0046] In one embodiment, after the nickel layer 20 is removed using a nickel (Ni) removal solution including an acidic solution and an alkaline solution, the nickel (Ni) content of the nickel-iron (Ni—Fe) alloy layer may be measured.

[0047] When the nickel content of the nickel-iron alloy layer falls within the above range, the heat-treated steel plate can have good formability, thereby preventing mold damage, nickel layer sticking to the mold during machining of the heat-treated steel plate, and burr formation and dust and debris during the cutting process. For example, the ratio of the weight of nickel in the nickel-iron alloy layer 30 to the total weight of nickel and iron ((Ni / (Ni+Fe))×100) can be 0.3wt% to 25wt%, for example, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5 ... t%, 10wt%, 10.5wt%, 11wt%, 11.5wt%, 12wt%, 12.5wt%, 13wt%, 13.5wt%, 14wt%, 14.5wt%, 15wt%, 15.5wt%, 16wt%, 16.5wt%, 17wt%, 17 .5wt%, 18wt%, 18.5wt%, 19wt%, 19.5wt%, 20wt%, 20.5wt%, 21wt%, 21.5wt%, 22wt%, 22.5wt%, 23wt%, 23.5wt%, 24wt%, 24.5wt% or 25wt%.

[0048] Method for manufacturing nickel-plated heat-treated steel sheet

[0049] Another aspect of the present invention relates to a method for manufacturing a nickel-plated heat-treated steel sheet. Figure 2 1 is a flow chart of a method for manufacturing a nickel-plated heat-treated steel sheet according to one embodiment of the present invention. Figure 2 The method for manufacturing a nickel-plated heat-treated steel plate includes: a nickel layer forming step (S10); and a diffusion heat treatment step (S20).

[0050] More specifically, the method for manufacturing a nickel-plated heat-treated steel plate includes: forming a nickel layer (S10) by electroplating at least one surface of a base steel plate with nickel (Ni); and forming a nickel-iron (Ni-Fe) alloy layer (S20) between the base steel plate and the nickel layer by diffusion heat treatment of the base steel plate and the nickel layer, wherein the nickel-plated heat-treated steel plate (product) has a surface Rockwell hardness of 52 to 62.

[0051] Next, each step of the method for manufacturing a nickel-plated heat-treated steel sheet according to the present invention will be described in detail.

[0052] (S10) Nickel layer forming step

[0053] In the nickel layer forming step, a nickel layer is formed by electroplating at least one surface of the base steel plate with nickel (Ni).

[0054] The base steel plate may be the same as described above.

[0055] In one embodiment, electroplating (electrolytic plating) of nickel (Ni) can be performed by a typical electroplating method using a nickel plating solution (or a nickel plating bath). For example, a Watts bath or a sulfamate bath can be used as a plating solution.

[0056] In one embodiment, based on 1L of the bath, the Watt bath may include 150g / L to 400g / L of nickel sulfate (NiSO4), 20g / L to 60g / L of nickel chloride (NiCl2), 10g / L to 50g / L of boric acid (H3BO3) and the remainder of water, without being limited thereto. When a Watt bath having this composition is used for nickel electroplating, a nickel layer having desired physical properties can be easily formed. However, it should be understood that the present invention is not limited to the above bath composition.

[0057] For example, the amount of nickel sulfate based on 1 L of bath can be 150 g / L, 160 g / L, 170 g / L, 180 g / L, 190 g / L, 200 g / L, 210 g / L, 220 g / L, 230 g / L, 240 g / L, 250 g / L, 260 g / L, 270 g / L, 280 g / L, 290 g / L, 300 g / L, 310 g / L, 320 g / L, 330 g / L, 340 g / L, 350 g / L, 360 g / L, 370 g / L, 380 g / L, 390 g / L or 400 g / L.

[0058] For example, based on 1 L of bath, the amount of nickel chloride can be 20 g / L, 21 g / L, 22 g / L, 23 g / L, 24 g / L, 25 g / L, 26 g / L, 27 g / L, 28 g / L, 29 g / L, 30 g / L, 31 g / L, 32 g / L, 33 g / L, 34 g / L, 35 g / L, 36 g / L, 37 g / L, 38 g / L. , 39g / L, 40g / L, 41g / L, 42g / L, 43g / L, 44g / L, 45g / L, 46g / L, 47g / L, 48g / L, 49g / L , 50g / L, 51g / L, 52g / L, 53g / L, 54g / L, 55g / L, 56g / L, 57g / L, 58g / L, 59g / L or 60g / L.

[0059] For example, based on 1 L of bath, the amount of boric acid can be 10 g / L, 11 g / L, 12 g / L, 13 g / L, 14 g / L, 15 g / L, 16 g / L, 17 g / L, 18 g / L, 19 g / L, 20 g / L, 21 g / L, 22 g / L, 23 g / L, 24 g / L, 25 g / L, 26 g / L, 27 g / L, 28 g / L, 29g / L, 30g / L, 31g / L, 32g / L, 33g / L, 34g / L, 35g / L, 36g / L, 37g / L, 38g / L, 39g / L, 40g / L, 41g / L, 42g / L, 43g / L, 44g / L, 45g / L, 46g / L, 47g / L, 48g / L, 49g / L or 50g / L.

[0060] In one embodiment, electroplating using a plating bath may be performed at a pH of 3.0 to 4.8, a bath temperature of 45° C. to 70° C., and 2 A / dm 2 Up to 40A / dm 2 When electroplating using a bath is performed under these conditions, a nickel layer having desired physical properties can be easily formed.

[0061] For example, electroplating using a bath may be performed under the following conditions: a pH of 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7 or 4.8, a bath temperature of 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C or 70°C, and a current density of 2 A / dm 2 、3A / dm 2 , 4A / dm 2 , 5A / dm 2 、6A / dm 2 , 7A / dm 2 , 8A / dm 2 , 9A / dm 2 、10A / dm 2 、11A / dm 2 、12A / dm 2 、13A / dm 2 、14A / dm 2 、15A / dm 2 、16A / dm 2 、17A / dm 2 、18A / dm 2、19A / dm 2 、20A / dm 2 、21A / dm 2 、22A / dm 2 、23A / dm 2 、24A / dm 2 、25A / dm 2 、26A / dm 2 、27A / dm 2 、28A / dm 2 、29A / dm 2 、30A / dm 2 、31A / dm 2 、32A / dm 2 、33A / dm 2 、34A / dm 2 、35A / dm 2 、36A / dm 2 、37A / dm 2 、38A / dm 2 、39A / dm 2 or 40A / dm 2 .

[0062] An additive may be used to impart brightness to the nickel plating. Preferably, the additive does not contain sulfur. If a sulfur-containing brightener is used in bright nickel plating, the heat-treated steel plate may be easily cracked during machining due to the increased hardness of the nickel plating, resulting in reduced corrosion resistance of the heat-treated steel plate. In addition, the heat-treated steel plate may be scratched by debris accumulated on the machining tool during machining of the heat-treated steel plate.

[0063] In one embodiment, the total amount of nickel (Ni) used for electroplating may be 2.7 g / m 2 Up to 44.5g / m 2 .

[0064] A deep drawing process is used in manufacturing a secondary battery housing using the heat-treated steel sheet according to the present invention. Through this process, the thickness of the heat-treated steel sheet is reduced by 10% to 50% (i.e., the heat-treated steel sheet is stretched). If the total amount of nickel used for electroplating is less than 2.7 g / m 2 , the heat-treated steel sheet cannot exhibit sufficient corrosion resistance due to the lack of nickel required to cover the base steel sheet containing iron (Fe). On the contrary, if the total amount of nickel used for electroplating exceeds 44.5 g / m 2 , which can lead to machining problems such as the formation of nickel dust and cracking of the nickel plating during the manufacture of the secondary battery housing using the heat-treated steel sheet, as well as increased production costs due to excessive use of nickel. For example, the total amount of nickel (Ni) used for electroplating can be 2.7 g / m 2, 2.8g / m 2 , 2.9g / m 2 , 3g / m 2 , 4g / m 2 , 5g / m 2 , 6g / m 2 , 7g / m 2 , 8g / m 2 , 9g / m 2 , 10g / m 2 , 11g / m 2 , 12g / m 2 , 13g / m 2 , 14g / m 2 , 15g / m 2 , 16g / m 2 , 17g / m 2 , 18g / m 2 , 19g / m 2 , 20g / m 2 , 21g / m 2 , 22g / m 2 , 23g / m 2 , 24g / m 2 , 25g / m 2 , 26g / m 2 , 27g / m 2 , 28g / m 2 , 29g / m 2 , 30g / m 2 , 31g / m 2 , 32g / m 2 , 33g / m 2 , 34g / m 2 , 35g / m 2 , 36g / m 2 , 37g / m 2 , 38g / m 2 , 39g / m 2 , 40g / m 2 , 41g / m 2 , 42g / m 2 , 43g / m 2 , 44g / m 2 , 44.1g / m 2 , 44.2g / m 2 , 44.3g / m 2 44.4g / m 2 or 44.5g / m 2 .

[0065] (S20) Diffusion Heat Treatment Step

[0066] In the diffusion heat treatment step, a nickel-iron (Ni—Fe) alloy layer is formed between the base steel plate and the nickel layer through diffusion heat treatment of the base steel plate and the nickel layer.

[0067] The nickel layer formed by electroplating has high hardness and low elongation. If the nickel layer is formed into a secondary battery case without additional treatment, this may cause the nickel layer forming the surface of the battery case to crack or rust, and cause deterioration of secondary battery performance.

[0068] In one embodiment, the nickel layer may have a surface hardness of 200 to 300 measured using a micro Vickers hardness tester under a load of 10 gf. For example, the nickel layer may have a surface hardness of 200, 205, 210, 215, 220, 225, 230, 235, 240, 245, 250, 255, 260, 265, 270, 275, 280, 285, 290, 295, or 300.

[0069] When a nickel-iron (Ni-Fe) alloy layer is formed between the nickel layer and the base steel plate by diffusion heat treatment to soften the nickel layer, the heat-treated steel plate can have good machinability due to the softness of the nickel layer and the nickel-iron (Ni-Fe) alloy layer, and the secondary battery casing manufactured using the heat-treated steel plate can have good corrosion resistance.

[0070] The diffusion heat treatment may include a diffusion heat treatment in a continuous annealing furnace (CAF) and a diffusion heat treatment in a batch annealing furnace (BAF), but is not limited thereto.

[0071] Regardless of the type of diffusion heat treatment used, by appropriately combining the heat treatment temperature with the heat treatment time, the following physical properties can be ultimately ensured by the diffusion heat treatment step.

[0072] (1) The heat-treated steel plate has a surface Rockwell hardness of 52 to 62.

[0073] (2) A nickel-iron (Ni—Fe) alloy layer having a nickel (Ni) content of 0.3 wt % to 25 wt % is formed between the nickel layer (pure Ni) and the base steel plate.

[0074] (3) The nickel layer (pure Ni) has a surface hardness of 150 to 250 measured using a micro Vickers hardness tester under conditions of a load of 10 gf and a holding time of 10 seconds.

[0075] In one embodiment, the atmosphere gas used in the diffusion heat treatment may include any gas that does not cause oxidation of the heat-treated steel sheet during the heat treatment without limitation. The diffusion heat treatment temperature and the diffusion heat treatment time may vary depending on whether the diffusion heat treatment is performed in a continuous annealing furnace (CAF) or a batch annealing furnace (BAF). In addition, the diffusion heat treatment temperature and the diffusion heat treatment time may vary depending on the initial strength (hardness) of the base steel sheet and the properties required for the final heat-treated steel sheet product.

[0076] In one embodiment, when the diffusion heat treatment is performed in a continuous annealing furnace, the diffusion heat treatment may be performed at 520°C to 630°C for 5 to 60 seconds. When the diffusion heat treatment in the continuous annealing furnace is performed under these conditions, the desired mechanical properties of the heat-treated steel sheet may be easily obtained. For example, the diffusion heat treatment in the continuous annealing furnace may be performed at 520°C to 600°C for 5 to 25 seconds.

[0077] For example, the diffusion heat treatment in the continuous annealing furnace can be carried out at 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, 600°C, 610°C, 620°C or 630°C for 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59 or 60 seconds.

[0078] In one embodiment, when the diffusion heat treatment is performed in a batch annealing furnace, the diffusion heat treatment may be performed at 380°C to 510°C for 1 to 15 hours. When the diffusion heat treatment in the batch annealing furnace is performed under these conditions, the desired mechanical properties of the heat-treated steel sheet may be easily obtained. For example, the diffusion heat treatment in the batch annealing furnace may be performed at 400°C to 500°C for 1 to 15 hours.

[0079] For example, the diffusion heat treatment in a batch annealing furnace can be carried out at 380°C, 390°C, 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C or 510°C for 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15 hours.

[0080] refer to Figure 2The method for manufacturing a nickel-plated heat-treated steel plate according to the present invention may further include, after the diffusion heat treatment step (S20), performing temper rolling on the diffusion heat-treated steel plate.

[0081] (S30) Tempering rolling step

[0082] In the temper rolling step, the diffusion heat treated steel sheet is temper rolled. The purpose of temper rolling is to control the thickness, shape and surface roughness of the heat treated steel sheet, minimize the residual stress in the heat treated steel sheet, and ensure uniform material properties throughout the heat treated steel sheet.

[0083] In one embodiment, the temper rolling of the diffusion heat treated steel plate can be carried out at an elongation of 0.5% to 3.0%. Within this elongation range, the residual stress in the heat treated steel plate can be minimized while ensuring uniform material properties throughout the heat treated steel plate. For example, the temper rolling of the diffusion heat treated steel plate can be carried out at an elongation of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9% or 3.0%.

[0084] The method for manufacturing nickel-plated heat-treated steel plates according to the present invention can reduce the generation of nickel dust and the sticking of heat-treated steel plate materials to the machining mold when mechanically processed into secondary battery shells, can prevent severe burr formation during the trimming of the open ends of the secondary battery shells, and can improve the corrosion resistance of the secondary battery.

[0085] Then, the present invention will be described in more detail with reference to some embodiments.It should be understood that these embodiments are provided only for illustration and should not be interpreted as limiting the present invention in any way.For the sake of clarity, the description of the details that those skilled in the art can easily think of will be omitted.

[0086] Examples and Comparative Examples

[0087] Example 1

[0088] (1) Preparation of base steel plate: A slab containing 0.03 wt% (300 ppm) of carbon (C), more than 0 wt% and less than 0.001 wt% (10 ppm) of silicon (Si), 0.31 wt% (3,100 ppm) of manganese (Mn), more than 0 wt% and less than 0.001 wt% (10 ppm) of phosphorus (P), and the balance of iron (Fe) and other inevitable impurities is preheated and then hot-rolled and cold-rolled to prepare a base steel plate with a thickness of 0.30 mm and a surface Rockwell hardness of 57.

[0089] (2) Nickel electroplating: The base steel sheet was pretreated by alkaline degreasing, alkaline electrolytic degreasing and pickling (in a sulfuric acid aqueous solution), and then nickel was electroplated. Specifically, a bath containing 225 g / L of nickel sulfate (NiSO4), 45 g / L of nickel chloride (NiCl2), 45 g / L of boric acid (H3BO3) and the balance of water and a temperature of 60°C and a pH of 3.2 to 4.5 was prepared, and then electroplating was performed in the bath at a current density of 10 ASD. Here, the amount of nickel adhering to the upper and lower surfaces of the base steel sheet was 10 g / m 2 and 10 g / m 3 respectively measured using an X-ray fluorescence analyzer (XRF). 2 and 30g / m 2 .

[0090] (3) Diffusion heat treatment and temper rolling: The steel sheet on which the nickel layer was formed was subjected to diffusion heat treatment in an intermittent annealing furnace (BAF) in an inert gas atmosphere at 400°C for 15 hours, and then temper rolled using a high temper rolling mill at an elongation of 1.2%, thereby manufacturing a nickel-plated heat-treated steel sheet.

[0091] Example 2 to Example 5

[0092] A nickel-plated heat-treated steel sheet was produced in the same manner as in Example 1, except that the diffusion heat treatment was performed under the batch annealing furnace (BAF) conditions listed in Table 1.

[0093] Example 6 to Example 9

[0094] A nickel-plated heat-treated steel sheet was produced in the same manner as in Example 1, except that the diffusion heat treatment was performed in a continuous annealing furnace in an inert gas atmosphere under the conditions listed in Table 1.

[0095] Comparative Example 1

[0096] A nickel-plated heat-treated steel sheet was produced in the same manner as in Example 1, except that the diffusion heat treatment was not performed.

[0097] Comparative Example 2

[0098] A nickel-plated heat-treated steel sheet was produced in the same manner as in Example 1, except that the diffusion heat treatment was performed under the batch annealing furnace (BAF) conditions listed in Table 1.

[0099] Comparative Example 3

[0100] A nickel-plated heat-treated steel sheet was produced in the same manner as in Example 6, except that the diffusion heat treatment was performed under the continuous annealing furnace conditions listed in Table 1.

[0101] Experimental example

[0102] The following properties of each of the nickel-plated heat-treated steel sheets produced in Examples and Comparative Examples were evaluated.

[0103] 1) Surface hardness of nickel-plated heat-treated steel sheet: The hardness of each nickel-plated heat-treated steel sheet manufactured in Examples and Comparative Examples was measured using a superficial Rockwell hardness tester.

[0104] 2) Nickel (Ni) content (wt%) in nickel-iron (Ni-Fe) alloy layer: The nickel layer (pure Ni) was selectively removed from the surface of each nickel-plated heat-treated steel plate manufactured in the embodiments and comparative examples using a nickel removal solution including an acidic solution and an alkaline solution, and then the nickel content ((Ni / (Ni+Fe))×100) in the nickel-iron (Ni-Fe) alloy layer was measured using a scanning electron microscope (SEM) and an energy dispersive spectrometer (EDS) under the following conditions: magnification: 200; acceleration voltage: 20 kV; and the number of photons of secondary energy incident on the EDS device: 2 kCPS or more.

[0105] 3) Surface hardness of nickel layer: The surface hardness of the nickel layer of each of the nickel-plated heat-treated steel sheets produced in Examples and Comparative Examples was measured using a micro Vickers hardness tester under the conditions of a load of 10 gf and a holding time of 10 seconds.

[0106] 4) Formability into secondary battery case: Each nickel-plated heat-treated steel sheet manufactured in the examples and comparative examples was deep drawn (drawing and ironing (DNI), drawing-iron-redrawing (DTR)) using a deep drawing device (Asahi-Seiki Manufacturing Co., Ltd.) to manufacture a cylindrical secondary battery case. Figure 3 : is an image of a cylindrical secondary battery case manufactured using the nickel-plated heat-treated steel sheet manufactured in Example 1. Figure 3 As shown in , the length of the burr formed during the trimming of the end portion (A) of the secondary battery case was measured using a profile measurement system (CONTRACER CV-3200, MITUTOYO Corporation). The results are shown in Table 1 and FIG.

[0107] Table 1

[0108]

[0109] Figure 4A is a diagram showing the measurement of the burr height of Example 2, and Figure 4B is a graph showing the measurement of burr height of Comparative Example 3. Referring to Table 1 and FIG4 , it can be seen that the nickel-plated heat-treated steel sheets of Examples 1 to 9 achieve desired levels of surface Rockwell hardness, Vickers surface hardness of the nickel layer, and nickel content in the nickel-iron alloy layer.

[0110] In addition, it can be seen that the nickel-plated heat-treated steel plates of Examples 1 to 9 can prevent the generation of fine chips and dust, damage to the machining mold, and sticking of the steel plate material to the machining mold when machined into a secondary battery case, and can minimize burr formation during trimming of the lug forming portion of the end opening of the secondary battery case (which is the final process in the production of the secondary battery case).

[0111] These results indicate that the heat-treated steel sheet according to the present invention can prevent a decrease in workability and productivity, and can significantly reduce the possibility of secondary battery failure due to electrical short circuits caused by burrs during a finishing process performed after the battery electrolyte filling process performed by the final stage manufacturer of the battery (battery filling company).

[0112] On the contrary, compared with Examples 1 to 9, the nickel-plated heat-treated steel sheet of Comparative Example 1 cannot reduce the generation of fine chips and dust when mechanically processed into a secondary battery housing due to the excessively high surface hardness of the nickel (Ni) layer, thereby increasing the possibility of mechanical processing defects (such as dents and scratches) and production losses due to frequent mold cleaning procedures. In addition, due to the high mold wear rate, it is expected that the maintenance cost will increase.

[0113] In addition, compared with Examples 1 to 9, the nickel-plated heat-treated steel sheets of Comparative Examples 2 and 3 cannot prevent the steel sheet material from sticking to the machining mold during machining due to the relatively large thickness of the nickel-iron alloy layer, the high nickel content of the nickel-iron alloy layer, and the low hardness of the nickel layer. In addition, the nickel-plated heat-treated steel sheets of Comparative Examples 2 and 3 cannot prevent serious burr formation during the lug forming portion of the opening of the secondary battery case when machined into a secondary battery case, thereby resulting in reduced machining productivity and increased likelihood of serious problems with product quality, such as electrical short circuits due to burrs during the finishing process and secondary battery failure due to the reaction between fragments originating from the burrs and the electrolyte in the secondary battery, which is performed after the battery electrolyte filling process performed by the final stage manufacturer of the battery (battery filling company).

[0114] Although some embodiments have been described herein, it will be appreciated by those skilled in the art that various modifications, changes and variations may be made without departing from the spirit and scope of the present invention. Therefore, it will be appreciated that these embodiments are provided only for illustration and should not be interpreted as limiting the present invention in any way. The scope of the present invention should be limited by the appended claims rather than the above description, and the claims and their equivalents are intended to cover such modifications that will fall within the scope of the present invention, etc.

Claims

1. Nickel-plated heat-treated steel plate, including: Base steel plate; a nickel layer formed on at least one surface of the base steel plate; as well as A nickel-iron (Ni—Fe) alloy layer is formed between the base steel plate and the nickel layer by diffusion heat treatment of the base steel plate and the nickel layer, The nickel-plated heat-treated steel plate has a surface Rockwell hardness of 52 to 62. The total amount of nickel contained in the nickel layer and the nickel-iron alloy layer is 11 g / m 2 Up to 44.5g / m 2 , The diffusion heat treatment is carried out in a continuous annealing furnace (CAF) or a batch annealing furnace (BAF), When the diffusion heat treatment is performed in the batch annealing furnace, the diffusion heat treatment is performed at 380° C. to 500° C. for 1 to 15 hours. When the diffusion heat treatment is performed in the continuous annealing furnace, the diffusion heat treatment is performed at 520° C. to 630° C. for 5 to 25 seconds. 2 . The nickel-plated heat-treated steel sheet according to claim 1 , wherein the nickel-iron alloy layer has a nickel (Ni) content of 0.3 wt % to 25 wt %. 3 . The nickel-plated heat-treated steel sheet according to claim 1 , wherein the nickel layer has a hardness of 150 to 250 measured using a micro Vickers hardness tester under a load of 10 gf.

4. A method for manufacturing a nickel-plated heat-treated steel plate, comprising: forming a nickel layer by electroplating at least one surface of a base steel plate with nickel (Ni); as well as Through diffusion heat treatment of the base steel plate and the nickel layer, a nickel-iron (Ni—Fe) alloy layer is formed between the base steel plate and the nickel layer. The nickel-plated heat-treated steel plate has a surface Rockwell hardness of 52 to 62. The diffusion heat treatment is carried out in a continuous annealing furnace (CAF) or a batch annealing furnace (BAF), When the diffusion heat treatment is performed in the batch annealing furnace, the diffusion heat treatment is performed at 380° C. to 500° C. for 1 to 15 hours. When the diffusion heat treatment is performed in the continuous annealing furnace, the diffusion heat treatment is performed at 520° C. to 630° C. for 5 to 25 seconds.

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