Nickel-plated steel sheet for cans and manufacturing method thereof

Abstract

A Ni-plated steel sheet for cans according to an embodiment of the present invention comprises: a base steel sheet; a Ni plating layer disposed on one surface or both surfaces of the base steel sheet; and an Fe-Ni alloy layer disposed between the base steel sheet and the Ni plating layer, wherein the base steel sheet contains, in wt%, 0.02-0.07% of C, 0.1-0.4% of Mn, 0.01-0.06% of Al, and 0.02-0.06% of Ti, with the remainder comprising Fe and inevitable impurities, the ASTM grain size number is at least 11.3, the tensile strength is at least 420 MPa, the elongation is at least 20%, the in-plane anisotropy Δr is at most 0.4, and the thickness of the Fe-Ni alloy layer is 0.5-2.5 µm.

Description

Nickel-plated steel sheet for cans and its manufacturing method

[0001] One embodiment of the present invention relates to a nickel-plated steel sheet for cans and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to a nickel-plated steel sheet with excellent strength and workability used in cylindrical battery cases for electric vehicles, and a method for manufacturing the same.

[0002] For cylindrical battery cans used in cylindrical battery cases, nickel (Ni) plating is typically applied to steel plates to resist corrosion caused by the electrolyte entering the battery. Recently, with the increasing demand for electric vehicles, demand for materials for cylindrical battery cases for electric vehicles has grown significantly.

[0003] Meanwhile, to ensure battery safety, demand for strength in battery can materials is increasing. Electric vehicle batteries can experience abnormal chemical reactions during operation due to various factors, such as overcurrent and external impact, which can generate large amounts of gas. This gas can increase internal pressure and even trigger a chain reaction of explosions within the battery. Therefore, battery can materials require high strength to withstand high pressures. Furthermore, using high-strength materials can further enhance battery performance by reducing can thickness and increasing internal space. Battery cans are manufactured through mechanical processing that reduces thickness by more than 30%. Even with the same yield strength, materials with high tensile strength exhibit higher work hardening rates, resulting in greater durability after processing. Therefore, battery can materials require particularly high tensile strength to achieve high strength after molding.

[0004] Battery can materials also require mechanical properties for processability. Cylindrical battery cans undergo processing processes such as drawing and ironing during molding, requiring a certain level of elongation in addition to strength. Furthermore, to minimize earing during cylindrical molding, a smaller in-plane anisotropy Δr is advantageous. High in-plane anisotropy not only increases the area of ​​earing that must be cut off after machining, but also creates thickness variations across different areas, making it difficult to fully utilize the internal space. Beyond mechanical properties, microstructure also influences processability. Finer grains allow for more uniform deformation, resulting in superior processed shapes. Coarse grains, however, can cause uneven deformation, resulting in not only shape distortion but also a surface roughness known as "orange peel."

[0005] Cylindrical battery cases are generally nickel-plated to prevent corrosion from the internal electrolyte or the atmosphere during processing. However, there are also specific requirements for the plating layer. Parts that come into contact with the processing mold are nickel-plated. To prevent the plating layer from peeling off during processing, a heat treatment is performed to form an Fe-Ni alloy layer at the interface through diffusion between the iron in the steel plate and the nickel in the plating layer, thereby improving adhesion. If the alloy layer is too thin, it is difficult to ensure adhesion between the steel plate and the plating layer. On the other hand, if it is too thick, the iron component is exposed to the surface of the plating layer, which can cause rust due to iron oxidation. Therefore, it is necessary to form an alloy layer of an appropriate thickness.

[0006] A method of performing secondary rolling at a high reduction rate on low-carbon steel to manufacture high-strength can steel sheets has been proposed. Performing secondary rolling after recrystallization annealing offers the advantage of significantly improving strength through work hardening. However, this high level of secondary rolling significantly reduces elongation, making it difficult to ensure can formability.

[0007] Additionally, a method is known for utilizing bake hardening by adding appropriate amounts of P and Nb to ultra-low carbon steel to secure strength and workability. However, because ultra-low carbon steel has a low C content, it has the disadvantage of requiring very strict simultaneous control of the C and Nb contents to ensure that some of the C remains in solution without precipitating NbC, enabling bake hardening.

[0008] Furthermore, a method has been proposed to enhance strength through solid solution strengthening by adding large amounts of nitrogen (greater than 130 ppm) to low-carbon steel, and to increase elongation by applying a relatively small secondary reduction ratio. However, the addition of large amounts of nitrogen, an interstitial element, can easily lead to compositional deviations, which in turn increase the likelihood of material deviations. Therefore, controlling compositional deviations to a low level requires additional effort during the steelmaking process.

[0009] Furthermore, a method was described to enhance strength by utilizing precipitation strengthening through the addition of Ti, and to further reduce the reduction in elongation due to work hardening by applying a secondary reduction ratio of 15% or less, thereby securing a balance between strength and ductility. However, the increase in strength due to work hardening leads to a decrease in elongation, making it difficult to secure workability.

[0010] In one embodiment of the present invention, a nickel-plated steel sheet for cans and a method for manufacturing the same are provided. Specifically, in one embodiment of the present invention, a nickel-plated steel sheet with excellent strength and workability, used for cylindrical battery cases for electric vehicles, and a method for manufacturing the same are provided.

[0011] According to one embodiment of the present invention, a Ni-plated steel sheet for a can includes a base steel sheet, a Ni-plated layer positioned on one or both surfaces of the base steel sheet, and an Fe-Ni alloy layer positioned between the base steel sheet and the Ni-plated layer, wherein the base steel sheet contains, in wt%, C: 0.02 to 0.07%, Mn: 0.1 to 0.4%, Al: 0.01 to 0.06%, and Ti: 0.02 to 0.06%, the remainder being Fe and other unavoidable impurities, and has an ASTM grain size of 11.3 or more, a tensile strength of 420 MPa or more, an elongation of 20% or more, an in-plane anisotropy Δr of 0.4 or less, and a thickness of the Fe-Ni alloy layer of 0.5 to 2.5 ㎛.

[0012] The base steel plate may further include at least one of Si: 0.05 wt% or less, P: 0.015 wt% or less, S: 0.015 wt% or less, and N: 0.006 wt% or less.

[0013] The base steel plate may further include at least one of Nb: 0.01 wt% or less, Ni: 0.1 wt% or less, Cr: 0.1 wt% or less, Cu: 0.1 wt% or less, Mo: 0.01 wt% or less, and V: 0.01 wt% or less.

[0014] The base steel plate contains TiC precipitates, and the average particle size of the TiC precipitates may be 1 nm or more and 1 μm or less.

[0015] A method for manufacturing a Ni-plated steel sheet for a can according to one embodiment of the present invention comprises the steps of: hot-rolling a slab containing, in wt%, C: 0.02 to 0.07%, Mn: 0.1 to 0.4%, Al: 0.01 to 0.06%, and Ti: 0.02 to 0.06%, with the remainder being Fe and other unavoidable impurities, to manufacture a hot-rolled steel sheet; cold-rolling the hot-rolled steel sheet at a reduction ratio of 70 to 90% to manufacture a cold-rolled steel sheet; recrystallization annealing the cold-rolled steel sheet at a soaking temperature of 720 to 850°C; rectification rolling the recrystallization-annealed steel sheet at a reduction ratio of 0.5 to 1.8%; and plating Ni on one or both sides of the rectification-rolled steel sheet to manufacture a Ni-plated steel sheet. And it includes a step of alloying and annealing the Ni-plated steel sheet by maintaining it at a soaking temperature of 600 to 740°C for 5 to 60 seconds.

[0016] The slab may further include at least one of Si: 0.05 wt% or less, P: 0.015 wt% or less, S: 0.015 wt% or less, and N: 0.006 wt% or less.

[0017] The slab may further include at least one of Nb: 0.01 wt% or less, Ni: 0.1 wt% or less, Cr: 0.1 wt% or less, Cu: 0.1 wt% or less, Mo: 0.01 wt% or less, and V: 0.01 wt% or less.

[0018] Prior to the step of manufacturing the hot rolled steel plate, a step of heating the slab at 1200°C or higher may be further included.

[0019] The step of manufacturing a hot-rolled steel plate can be carried out by hot finishing rolling at Ar3 or higher and then coiling at a temperature of 580 to 720°C.

[0020] A Ni-plated steel sheet for a can according to one embodiment of the present invention has excellent durability and processability and can be usefully used in a cylindrical battery case.

[0021]

[0022] Fig. 1 is a schematic cross-section of a Ni-plated steel sheet for a can according to one embodiment of the present invention.

[0023] Figure 2 shows the GDS analysis results of the Ni-plated steel sheet manufactured in Invention Example 2.

[0024]

[0025] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0026] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0027] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0028] In one embodiment of the present invention, the inclusion of additional elements means including the remaining iron (Fe) in an amount equivalent to the additional amount of the additional elements.

[0029] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0030] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0031]

[0032] One embodiment of the present invention relates to a nickel-plated steel sheet used in an electric vehicle battery case after can molding. Materials for this application require a strength above an appropriate level to improve the pressure resistance of the battery. To ensure workability, an elongation above an appropriate level is required, and to obtain a normal shape, in-plane anisotropy and grain size below an appropriate level are required. Furthermore, the nickel-plated layer must have a certain level of corrosion resistance to prevent corrosion and adhesion to prevent peeling during processing.

[0033] FIG. 1 schematically illustrates a cross-section of a Ni-plated steel sheet (100) for a can according to one embodiment of the present invention. As shown in FIG. 1, the Ni-plated steel sheet (100) for a can includes a base steel sheet (10), a Ni-plated layer (30) positioned on one or both surfaces of the base steel sheet (10), and an Fe-Ni alloy layer (20) positioned between the base steel sheet (10) and the Ni-plated layer (30). In FIG. 1, the Fe-Ni alloy layer (20) and the Ni-plated layer (30) are shown as being positioned on one surface of the base steel sheet (10), but it is also possible for the Fe-Ni alloy layer (20) and the Ni-plated layer (30) to be positioned on both surfaces of the base steel sheet (100).

[0034] A base steel sheet (100) of a Ni-plated steel sheet for a can according to one embodiment of the present invention (100 includes, in wt%, C: 0.02 to 0.07%, Mn: 0.1 to 0.4%, Al: 0.01 to 0.06%, and Ti: 0.02 to 0.06%, and the remainder includes Fe and other unavoidable impurities.

[0035] Below, each component is explained in detail.

[0036] Carbon (C): 0.020 to 0.070 wt%

[0037] C is an element added to improve the strength of steel plates. If the content is low, the strength may be low, making it difficult to use as a structural material. Furthermore, if the content is too low, the load on the steelmaking process increases, which may reduce productivity. Conversely, if the C content is excessively high, the elongation may decrease, which may reduce formability. More specifically, C may be included in an amount of 0.030 to 0.065 wt%. More specifically, C may be included in an amount of 0.040 to 0.063 wt%.

[0038] In one embodiment of the present invention, some of the C is combined with a small amount of added Ti to exist in the form of fine TiC precipitates, which can contribute to effective strength enhancement by preventing excessive grain growth.

[0039] Manganese (Mn): 0.10 to 0.40 wt%

[0040] Manganese is an element that prevents hot shortness caused by solid solution S by combining with solid solution S in steel and precipitating as MnS. It also has the effect of increasing the strength of steel together with C by being solid solution in steel. However, the strength-enhancing effect is lower than that of Ti, and if too much Mn is included, the workability of the steel may be reduced. More specifically, Mn may be included in an amount of 0.13 to 0.30 wt%. More specifically, Mn may be included in an amount of 0.14 to 0.25 wt%.

[0041] Aluminum (Al): 0.010 to 0.060 wt%

[0042] Al is an element with a very strong deoxidizing effect, and reacts with nitrogen in steel to precipitate AlN, thereby preventing the formability from being reduced by the dissolved nitrogen. However, if added in large amounts, the effect of additional addition can be enhanced. More specifically, Al may be included in an amount of 0.015 to 0.055 wt%. More specifically, Al may be included in an amount of 0.020 to 0.050 wt%.

[0043] Titanium (Ti): 0.020 to 0.060 wt%

[0044] Ti can be combined with C to form stable, fine TiC precipitates. Fine TiC precipitates suppress grain growth and effectively hinder dislocation movement, contributing to strength enhancement. If the Ti content is too small, it is difficult to expect a sufficient strength-enhancing effect from TiC. If too much Ti is added, ductility decreases, which not only hinders workability but also easily causes nozzle clogging during continuous casting. More specifically, Ti may be included in an amount of 0.022 to 0.050 wt%. More specifically, Ti may be included in an amount of 0.023 to 0.045 wt%.

[0045] The base steel plate (10) may further include at least one of Si: 0.05 wt% or less, P: 0.015 wt% or less, S: 0.015 wt% or less, and N: 0.006 wt% or less.

[0046] Silicon (Si): 0.050 wt% or less

[0047] Si is an element that can be used as a decarburizing agent and can contribute to the improvement of strength through solid solution strengthening, so it is difficult to completely exclude it. However, if it is excessive, Si-based oxides are formed on the surface during annealing, which can cause defects during plating and reduce plating properties. Therefore, considering this, Si may be included at 0.05 wt% or less. More specifically, it may be included by 0.001 to 0.050 wt%. Even more specifically, it may be included by 0.005 to 0.035 wt%.

[0048] Phosphorus (P): 0.015 wt% or less

[0049] Addition of P below a certain amount is an element that can increase the strength without significantly reducing the ductility of the steel, but if too much P is added, it can segregate at grain boundaries, excessively hardening the steel and reducing the elongation. Therefore, P may be further included up to 0.015 wt%. More specifically, it may further include 0.001 to 0.015 wt%. More specifically, it may further include 0.003 to 0.013 wt%.

[0050] Sulfur (S): 0.015 wt% or less

[0051] Since S is an element that causes red-hot embrittlement during hot rolling when present in a solid solution state, the precipitation of MnS must be induced by the addition of Mn. The more S there is, the more additional Mn must be added at a corresponding level, so it is not desirable for it to be present in large amounts. Therefore, the upper limit of S can be limited to 0.015 wt% or less. More specifically, it can further include 0.001 to 0.015 wt%. More specifically, it can further include 0.003 to 0.013 wt%.

[0052] Nitrogen (N): 0.0060 wt% or less

[0053] Nitrogen is an element that inevitably remains in steel, but when present in a dissolved state, it causes aging, which significantly reduces workability. To minimize the decrease in ductility due to unnecessary aging, the upper limit may be limited to 0.006 wt% or less. More specifically, it may further include 0.0001 to 0.0060 wt%. More specifically, it may further include 0.0005 to 0.0055 wt%.

[0054] In addition to the above-mentioned alloy composition, the remainder includes Fe and inevitable impurities. However, in one embodiment of the present invention, the addition of other compositions is not excluded. The above-mentioned inevitable impurities may be unintentionally mixed from raw materials or the surrounding environment during a typical steel manufacturing process, and thus cannot be excluded. The above-mentioned inevitable impurities can be understood by those skilled in the art of typical steel manufacturing. For example, the alloy may further include one or more of Nb: 0.01 wt% or less, Ni: 0.1 wt% or less, Cr: 0.1 wt% or less, Cu: 0.1 wt% or less, Mo: 0.01 wt% or less, and V: 0.01 wt% or less.

[0055] The base steel plate (10) has an ASTM grain size number of 11.3 or more. The ASTM grain size number is an index that is correlated with the grain size and is measured by calculating it from an image obtained through optical microstructural observation according to the ASTM E112 standard (Standard Test Methods for Determining Average Grain Size). The ASTM grain size number can be measured for a cross-section including the thickness direction of the base steel plate (10). More specifically, it can be measured based on the TD plane.

[0056] A higher ASTM grain size indicates a smaller average grain size. A smaller ASTM grain size can lead to excessive strength increases and reduced elongation, making forming difficult. More specifically, the ASTM grain size is 11.3 to 13.0. More specifically, it is 11.3 to 12.0.

[0057]

[0058] Returning to the description of the Ni-plated steel sheet (100) for cans, the Fe-Ni alloy layer (20) is located between the base steel sheet (10) and the Ni plating layer (30). If only the Ni plating layer (30) exists without the Fe-Ni alloy layer (20), the adhesion to the base steel sheet (10) is not good and the layer may easily fall off during processing. The Fe-Ni alloy layer (20) is formed through Ni diffusion into the base steel sheet (10) and Fe diffusion into the Ni plating layer (30). In one embodiment of the present invention, the Fe-Ni alloy layer (20) means a region between a point where Fe becomes 5 wt% and a point where Ni becomes 5% in the thickness direction. The thickness of the Fe-Ni alloy layer (20) may be the distance between the aforementioned points. The thickness of the Fe-Ni alloy layer (20) can be measured through GDS (Glow Discharge Spectrometer) or EDS (Energy Disperse X-ray Spectrometer) measurement of the cross-section of the Ni-plated steel sheet (100) for cans. The Fe-Ni alloy layer (20) has an Fe and Ni concentration gradient, and the Fe concentration may have a concentration gradient in which the concentration increases from the outside of the steel sheet to the inside, and the Ni concentration may have a concentration gradient in which the concentration decreases from the outside of the steel sheet to the inside. The Fe-Ni alloy layer (20) may contain 35 to 65 wt% of Fe and 35 to 65 wt% of Ni on average in the thickness direction.

[0059] The thickness of the Fe-Ni alloy layer (20) may be 0.5 to 2.5 ㎛. If the thickness of the Fe-Ni alloy layer (20) is too thin, it is difficult to secure adhesion. If the thickness of the Fe-Ni alloy layer (20) is too thick, the Fe component existing in the base steel plate (10) may be exposed to the surface, which may result in poor corrosion resistance. More specifically, the thickness of the Fe-Ni alloy layer (20) may be 0.7 to 2.3 ㎛. Even more specifically, the thickness of the Fe-Ni alloy layer (20) may be 1.0 to 2.0 ㎛. In one embodiment of the present invention, the thickness of the Fe-Ni alloy layer (20) and the Ni plating layer (30) is the thickness for one side of the steel plate. When the Fe-Ni alloy layer (20) and the Ni plating layer (30) are present on both sides, at least one of the two sides may satisfy the aforementioned thickness.

[0060] The nickel plating layer (30) helps ensure corrosion resistance against battery electrolyte and atmosphere. The plating thickness may vary depending on the molding amount and electrolyte type, and at least one side where wear primarily occurs during molding may be plated to a thickness of 2.0 μm or more. In the case of hot dip plating, it is difficult to control the plating thickness below a certain level and the thickness deviation tends to be large, so plating may be performed through electroplating.

[0061] A nickel-plated steel sheet (100) for cans according to one embodiment of the present invention can simultaneously secure excellent strength, elongation, and in-plane anisotropy. Specifically, the tensile strength is 420.0 MPa or higher. More specifically, the tensile strength may be 420.0 to 600.0 MPa. More specifically, the tensile strength may be 425.0 to 550.0 MPa. More specifically, the tensile strength may be 430.0 to 500.0 MPa.

[0062] Specifically, the elongation is 20.0% or more. More specifically, the elongation may be 20.0% to 30.0%. More specifically, the elongation may be 20.5% to 28.0%. More specifically, the elongation may be 21.0% to 25.0%.

[0063] Specifically, the in-plane anisotropy Δr is 0.40 or less. More specifically, the in-plane anisotropy Δr may be 0.01 to 0.40. More specifically, the in-plane anisotropy Δr may be 0.10 to 0.35.

[0064] Tensile strength, elongation, and in-plane anisotropy Δr can be measured through conventional tensile tests at room temperature. In-plane anisotropy can be obtained through the following relationship 1.

[0065] (Relationship 1)

[0066] Δr = (r0+ r 90 - 2×r 45 ) / 2

[0067] (But, r0, r 45 , r 90 is the plastic anisotropy coefficient (Lankford value) when tensioned in the direction forming an angle of 0°, 45°, and 90° with the rolling direction, respectively.

[0068]

[0069] A method for manufacturing a Ni-plated steel sheet for a can according to one embodiment of the present invention comprises the steps of: hot-rolling a slab to manufacture a hot-rolled steel sheet; cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet; recrystallization annealing of the cold-rolled steel sheet; rectification rolling of the recrystallization-annealed steel sheet; nickel-plating of one or both sides of the rectification-rolled steel sheet to manufacture a nickel-plated steel sheet; and alloying annealing of the nickel-plated steel sheet.

[0070] Below, each step is explained in detail.

[0071] First, the slab is hot rolled to produce hot rolled steel plates.

[0072] Since the alloy composition of the slab has been described in the parent steel plate (10) of the Ni-plated steel plate for cans mentioned above, a duplicate description will be omitted. Since the alloy composition does not substantially change during the manufacturing process of the Ni-plated steel plate for cans, the alloy composition of the parent steel plate (10) and the alloy composition of the slab are substantially the same.

[0073] Prior to the step of manufacturing hot-rolled steel sheets, a step of heating the slabs at a temperature of 1200°C or higher may be further included. A temperature of 1200°C or higher is necessary because various precipitates formed in the steel during slab manufacturing must be re-dissolved. More specifically, the heating temperature may be between 1200 and 1350°C.

[0074] A hot rolled steel sheet can be manufactured by hot finishing rolling the reheated slab at a temperature of Ar3 or higher and then coiling it at 580 to 720°C. The reason why the hot rolling finishing temperature is limited to Ar3 or higher is to roll in the austenite single-phase region. If rolling is performed in this ideal region, rolling stability may deteriorate due to non-uniform material. The Ar3 temperature is widely known, and in one embodiment of the present invention, the Ar3 temperature can be calculated as 910 - (310 × [C]) - (80 × [Mn] ) - (0.35 × (25.4 - 8)). More specifically, the hot rolling finishing temperature can be 850°C to 1000°C.

[0075] The precipitation behavior of TiC varies depending on the coiling temperature during coiling after final rolling. If the coiling temperature is too low or too high, TiC is not properly precipitated. Therefore, the coiling temperature can be controlled to 580 to 720°C, which is convenient for precipitation. The thickness of the hot-rolled steel sheet can be 2 to 6 mm.

[0076] Next, the hot-rolled steel sheet is cold-rolled to produce cold-rolled steel sheets. An appropriate cold reduction ratio is crucial for both strength and workability. A higher reduction ratio facilitates recrystallization nucleation during annealing, resulting in finer grains and increased strength. Furthermore, a higher reduction ratio tends to reduce in-plane anisotropy. However, if the reduction ratio is too high, it not only reduces elongation, which adversely affects workability, but also increases deformation resistance, reducing productivity. Considering these factors, the cold reduction ratio is set to the range of 70 to 90%. More specifically, the reduction ratio can range from 73 to 85%. A pickling process prior to cold rolling can be added to remove scale generated during hot rolling. The thickness of the cold-rolled steel sheet can range from 0.3 to 1 mm.

[0077] Next, the cold-rolled steel sheet is subjected to recrystallization annealing. The primary purpose of recrystallization annealing is to remove internal stresses formed during cold rolling and ensure workability. To achieve this, an annealing process is required at a sufficiently high temperature to ensure complete recrystallization. To induce recrystallization in the cold-rolled steel sheet having the steel composition according to one embodiment of the present invention, a temperature of 720°C or higher is required, taking into account the increase in recrystallization temperature due to TiC. If the temperature is too low, recrystallization may not be complete and some deformation grains may remain, which may significantly reduce the ductility of the steel sheet and cause cracks during forming due to increased strength. However, if the annealing temperature is too high, it is difficult to secure strength through grain growth, and the decrease in strength during annealing may lead to fracture or shape defects. Therefore, the cold-rolled steel sheet may be subjected to recrystallization annealing at a soaking temperature of 720 to 850°C. More specifically, the annealing may be performed at a temperature of 725 to 835°C. The soaking time may be 10 to 120 seconds.

[0078] Next, the recrystallized annealed steel plate is subjected to rectification rolling.

[0079] Corrective rolling not only corrects the shape but also forms dislocations of appropriate density. These dislocations, formed during the corrective rolling process, facilitate the precipitation of carbides during the post-plating alloying annealing process, contributing to additional strength enhancement. To achieve this effect, a reduction ratio of 0.5% or greater is required. However, if the reduction ratio is too high, it provides a driving force for surface grain recrystallization and coarsening during the alloying annealing process. Locally coarse grains can cause workability problems such as local fractures due to uneven elongation. Therefore, a reduction ratio of 1.8% or less is recommended. More specifically, the reduction ratio can be between 0.6 and 1.7%.

[0080] Next, nickel-plated steel sheets are manufactured by nickel-plating one or both sides of the rectified rolled steel sheet. Ni plating is necessary to ensure corrosion resistance against battery electrolyte and atmosphere. The plating thickness may vary depending on the molding amount and electrolyte type, and at least one side where wear primarily occurs during molding may be plated to a thickness of 2.0 μm or more. More specifically, the plating may be plated to a thickness of 2.0 to 5.0 μm. Since it is difficult to control the plating thickness below a certain level in hot dip plating and the thickness deviation tends to be large, electroplating may be used. General conditions such as the nickel plating bath and current density during electroplating may be used, and a detailed description thereof will be omitted.

[0081] Next, the Ni-plated steel plate is annealed.

[0082] The Ni plating layer (30) does not have excellent adhesion to the steel plate immediately after plating, and thus can easily fall off during processing. To prevent this, it is necessary to form an Fe-Ni alloy layer (20) between the Ni plating layer and the steel plate by diffusion through alloying annealing at high temperature.

[0083] At this time, it is maintained at a soaking temperature of 600 to 740℃ for 5 to 60 seconds. If the alloying annealing temperature is low or the time is too short, the Fe-Ni alloy layer is thin, making it difficult to secure adhesion. If the annealing temperature is too high or the time is too long, the alloy layer is thick, exposing the Fe component contained in the steel sheet to the surface of the plating layer, making it difficult to secure corrosion resistance. However, the correlation between the alloying annealing temperature and time and the alloy layer thickness is limited to the steel sheet manufactured by the components and manufacturing conditions described in the present invention, and may not be established for steel sheets with different components and manufacturing processes. More specifically, it can be maintained at a soaking temperature of 610 to 730℃ for 7 to 58 seconds.

[0084] In order to correct the shape of the steel plate after alloying annealing, additional cold rolling may be performed within the range of 2.0% or less.

[0085]

[0086] The present invention will be described in more detail below through examples. However, these examples are intended only to illustrate the present invention and are not intended to limit the present invention.

[0087]

[0088] Example 1

[0089] Steel plates having the compositions in Table 1 and the manufacturing conditions in Table 2 were manufactured. The components are actual values, and each slab having the corresponding components was manufactured. The slab was reheated to 1220℃, hot-rolled at 900℃ or higher to the same thickness of 4mm, and then coiled at 640℃ to manufacture a hot-rolled steel sheet. The coiled hot-rolled steel sheet was cold-rolled at the cold reduction ratio in Table 2, recrystallization annealing was performed for 30 seconds at the temperature in Table 2, and then constant rolling was performed at the constant reduction ratio in Table 2 to manufacture a recrystallization-annealed steel sheet. After nickel electroplating to a thickness of 3.0㎛ on the recrystallization-annealed steel sheet, alloying annealing was performed for 20 seconds at the temperature and time in Table 2 to manufacture the final nickel-plated steel sheet.

[0090] For each of the manufactured steel plates, the ASTM grain size, tensile strength, elongation, in-plane anisotropy, and alloy layer thickness were measured, and the results are shown in Table 3.

[0091] The ASTM grain size number was measured by calculating it from images obtained through optical microstructural observation according to ASTM E112 (Standard Test Methods for Determining Average Grain Size).

[0092] Tensile strength, elongation, and in-plane anisotropy Δr were measured through conventional tensile tests at room temperature. The in-plane anisotropy can be obtained using the following relationship 1.

[0093] (Relationship 1)

[0094] Δr = (r0+ r 90 - 2×r 45 ) / 2

[0095] (But, r0, r 45 , r 90 is the plastic anisotropy coefficient (Lankford value) when tensioned in the direction forming an angle of 0°, 45°, and 90° with the rolling direction, respectively.

[0096]

[0097] The alloy layer thickness was measured by Glow Discharge Spectrometer (GDS) measurement of the cross-section of the coated steel sheet. The length to the 5 wt% Fe point and the 5 wt% Ni point was measured.

[0098] The adhesion of the plating layer was judged to be good if there was no part of the plating layer that peeled off from the steel plate when the material was elongated by 20%, and the corrosion resistance was judged to be good if there was no surface discoloration when immersed in pure water for 20 minutes after molding and dried.

[0099]

[0100] (% by weight) CSiMnAlPSNTiInvention Example 10.0440.0160.190.0330.0070.0060.00280.042Invention Example 20.0610.0140.200.0350.0070.0060.00310.040Invention Example 30.0490.0140.210. 0320.0070.0060.00280.024 Invention Example 40.0510.0140.180.0350.0060.0060.00290.055 Invention Example 50.0480.0140.220.0350.0070.0060.00290.041 Invention Example 60.0500.01 50.190.0360.0070.0060.00310.039Invention Example 70.0480.0140.210.0340.0070.0060.00330.039Invention Example 80.0510.0160.220.0350.0070.0070.00280.036Invention Example 90. 0490.0140.210.0330.0070.0060.00310.037 Invention Example 100.0490.0140.180.0340.0070.0060.00310.037 Invention Example 110.0500.0140.220.0360.0080.0060.00290. 040 Invention Example 120.0510.0150.190.0370.0060.0070.00270.037 Invention Example 130.0480.0140.210.0330.0070.0060.00270.042 Invention Example 140.0500.0140.190.0370.0070.0 060.00300.041Comparative Example 10.0150.0160.190.0340.0070.0050.00320.040Comparative Example 20.0730.0150.220.0340.0080.0060.00320.038Comparative Example 30.0490.0150.200.0370 .0070.0060.00310.018Comparative Example 40.0500.0160.220.0320.0070.0060.00280.068Comparative Example 50.0520.0160.200.0370.0080.0060.00300.040Comparative Example 60.0490.0140.2 10.0340.0070.0060.00280.040Comparative Example70.0510.0150.190.0340.0080.0060.00270.041Comparative Example80.0490.0150.180.0330.0070.0060.00280.041Comparative Example90.0510.0160.180.0360.0080.0060.00320.044Comparative Example 100.0500.0150.200.0350.0070.0060.00290.043Comparative Example 110.0500.0140.210.0350.0070.0060.00290.043Comparative Example 120 .0490.0160.190.0350.0080.0060.00280.037Comparative Example 130.0490.0140.210.0350.0070.0060.00300.044Comparative Example 140.0510.0150.190.0340.0070.0060.00300.038.

[0101] Cold reduction ratio (%) Recrystallization annealing temperature (℃) Constant reduction ratio (%) Alloying annealing temperature (℃) Alloying annealing time (sec) Invention example 1807501.067020 Invention example 2807501.067020 Invention example 3807501.067020 Invention example 4807501.067020 Invention example 5757501.067020 Invention example 6857501.067020 Invention example 7807301.0670 20 inventions 8808301.067020 inventions 9807500.667020 inventions 10807501.667020 inventions 11807501.062020 inventions 12807501.072020 inventions 13807501.067010 inventions 14807501.067 055Comparative Example 1807501.067020Comparative Example 2807501.067020Comparative Example 3807501.067020Comparative Example 4807501.067020Comparative Example 5657501.067020Comparative Example 6937501.067020Comparative Example 7807101.067020Comparative Example 8808601.067020Comparative Example 9807500.367020Comparative Example 10807501.967020Comparative Example 11807501.058020Comparative Example 12807501.076020Comparative Example 13807501.06703Comparative Example 14807501.067065

[0102] ClassificationASTMGrain sizeTensile strength(MPa)Elongation(%)In-plane anisotropy(△r)Alloy layer thickness(μm)AdhesionCorrosion resistanceInvention example111.4445.422.60.241.4GoodGoodInvention example211.5482.521.10.251.5GoodGoodInvention example311.4442.423.10.251.5GoodGoodInvention example411.4464.622.60.251.4GoodGoodInvention example511.4425.623.60.281.5GoodGoodInvention example611.5466.122.10.161.5GoodGoodInvention example711.4470. 621.40.251.6 Good Good Invention Honor 811.6466.723.60.251.5 Good Good Invention Honor 911.3440.522.10.251.4 Good Good Invention Honor 1011.7470.622.60.241.5 Good Good Invention Honor 1111.6470.121.90.231.2 Good Good Invention Honor 1211.3461.022.20.251.9 Good Good Invention Honor 1311.6470.722.20.260.9 Good Good Invention Honor 1411.6463.82 2.20.252.0GoodGoodComparisonExample111.2386.523.10.201.6GoodGoodComparisonExample211.6500.619.30.281.6GoodGoodComparisonExample310.8416.224.60.261.6GoodGoodComparisonExample411.7499.418.30.211.4GoodGoodComparisonExample511.0402.125.60.481.6GoodGoodComparisonExample611.7480.619.50.201.4GoodGoodComparisonExample7-577.410.6-1.5Good Good Comparison Example 8 11.24 10.0 25.00 20 1.5 Good Good Comparison Example 9 11.5 39 5.4 21.40 25 1.5 Good Good Comparison Example 10 11.6 49 9.4 19.50 25 1.5 Good Good Comparison Example 11 11.5 46 7.3 22.00 25 0.4 Poor Good Comparison Example 12 11.3 45 3.6 22.50 25 2.6 Good Bad Comparison Example 13 11.5 47 3.5 22.10 25 0.3 Poor Good Comparison Example 14 11.5 46 7.6 21.80 25 2.6 Good Bad

[0103] As shown in Tables 1 to 3, Inventive Examples 1 to 14 satisfy all the steel components and manufacturing conditions, and it can be confirmed that tensile strength, elongation, and in-plane anisotropy are all excellent. In addition, it can be confirmed that the Fe-Ni alloy layer is formed with an appropriate thickness, and thus adhesion and corrosion resistance are also excellent.

[0104] Comparative Example 1 was a case where the C content was low, and sufficient strength was not secured due to the low C content. In addition, due to the low C content, the crystal grains were formed large with an ASTM crystal grain size of 11.1, and the tensile strength was low. On the other hand, Comparative Example 2 was a case where the C content was excessive, and the crystal grains were formed small, and sufficiently high tensile strength was obtained, but the elongation was low, resulting in poor processability.

[0105] Comparative Example 3 is a case where the Ti content is low, and the Ti content is insufficient to form a sufficient amount of TiC. As a result, the grains are formed large and the tensile strength is low. Comparative Example 4 is a case where the Ti content is high, and the grains are formed small, and the tensile strength is excellent, but the elongation is low.

[0106] Comparative Example 5 exhibited low cold reduction ratios, resulting in large grain sizes and low tensile strength. Furthermore, in-plane anisotropy Δr was significantly inferior. As in Comparative Example 6, when the cold reduction ratio was excessively high, elongation was reduced, which also reduced processability.

[0107]

[0108] In Comparative Example 7, the recrystallization annealing temperature was low, preventing proper recrystallization. Consequently, the elongation was low, resulting in significantly reduced workability. This is likely due to the extremely fine precipitation of TiC. When the recrystallization annealing temperature was too high, as in Comparative Example 8, large grains and low tensile strength resulted. Furthermore, when the recrystallization annealing temperature was high, as in Comparative Example 8, the risk of fracture increased due to low strength at high temperatures, requiring a relatively reduced sheet speed, which also resulted in reduced productivity.

[0109] Comparative Example 9 was formed with a low tensile strength due to a very low static pressure reduction. In Comparative Example 10, when the static pressure reduction was excessively high, problems occurred in which the elongation was low and the surface grains became coarser.

[0110] Comparative Example 11 had a low alloying annealing temperature, and Comparative Example 13 had a short alloying time, resulting in a thin Fe-Ni alloy layer. In both cases, the bonding strength between the steel sheet and the plating layer was low, resulting in the plating layer peeling off during battery can forming. Comparative Example 12 had a high alloying annealing temperature, and Comparative Example 14 had a long alloying annealing time, resulting in a thick Fe-Ni alloy layer in both cases. This resulted in Fe being exposed to the surface, causing rust to easily occur after water washing and drying.

[0111]

[0112] The present invention is not limited to the embodiments described herein, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

[0113] [Explanation of symbols]

[0114] 100: Ni-plated steel sheet

[0115] 10: Base steel plate

[0116] 20: Fe-Ni alloy layer

[0117] 30: Ni plating layer

Claims

1. Comprising a base steel plate, a Ni plating layer positioned on one or both surfaces of the base steel plate surface, and an Fe-Ni alloy layer positioned between the base steel plate and the Ni plating layer, The above base steel plate contains, in wt%, C: 0.02 to 0.07%, Mn: 0.1 to 0.4%, Al: 0.01 to 0.06%, and Ti: 0.02 to 0.06%, with the remainder being Fe and other inevitable impurities. The ASTM grain size number is 11.3 or greater, The tensile strength is 420 MPa or more, The elongation rate is 20% or more, The in-plane anisotropy Δr is less than 0.4, A nickel-plated steel sheet for cans having a Fe-Ni alloy layer thickness of 0.5 to 2.5 ㎛.

2. In paragraph 1, The above-mentioned base steel sheet is a nickel-plated steel sheet for cans further containing at least one of Si: 0.05 wt% or less, P: 0.015 wt% or less, S: 0.015 wt% or less, and N: 0.006 wt% or less.

3. In paragraph 1, The above-mentioned base steel sheet is a nickel-plated steel sheet for cans, further comprising at least one of Nb: 0.01 wt% or less, Ni: 0.1 wt% or less, Cr: 0.1 wt% or less, Cu: 0.1 wt% or less, Mo: 0.01 wt% or less, and V: 0.01 wt% or less.

4. In paragraph 1, The above-mentioned base steel sheet is a Ni-plated steel sheet for cans, which contains TiC precipitates and has an average particle size of 1 nm or more and 1 μm or less of the TiC precipitates.

5. A step of manufacturing a hot-rolled steel sheet by hot-rolling a slab containing C: 0.02 to 0.07%, Mn: 0.1 to 0.4%, Al: 0.01 to 0.06%, and Ti: 0.02 to 0.06% by weight, with the remainder being Fe and other unavoidable impurities; A step of manufacturing a cold rolled steel sheet by cold rolling the hot rolled steel sheet at a reduction ratio of 70 to 90%; A step of recrystallizing the cold rolled steel sheet at a soaking temperature of 720 to 850°C; A step of performing a re-rolling process on a recrystallized steel sheet at a reduction ratio of 0.5 to 1.8%; A step for manufacturing a Ni-plated steel sheet by plating Ni on one or both sides of a straight-rolled steel sheet; and A method for manufacturing a Ni-plated steel sheet for cans, comprising the step of alloying and annealing the Ni-plated steel sheet by maintaining it at a soaking temperature of 600 to 740°C for 5 to 60 seconds.

6. In paragraph 5, A method for manufacturing a Ni-plated steel sheet for cans, wherein the above slab further includes at least one of Si: 0.05 wt% or less, P: 0.015 wt% or less, S: 0.015 wt% or less, and N: 0.006 wt% or less.

7. In paragraph 5, A method for manufacturing a Ni-plated steel sheet for cans, wherein the above slab further contains at least one of Nb: 0.01 wt% or less, Ni: 0.1 wt% or less, Cr: 0.1 wt% or less, Cu: 0.1 wt% or less, Mo: 0.01 wt% or less, and V: 0.01 wt% or less.

8. In paragraph 5, Prior to the step of manufacturing the above hot rolled steel plate, A method for manufacturing a Ni-plated steel sheet for cans, further comprising the step of heating the above slab at 1200°C or higher.

9. In paragraph 5, The steps for manufacturing the above hot rolled steel plate are A method for manufacturing a nickel-plated steel sheet for cans, which is coiled at a temperature of 580 to 720°C after hot finishing rolling at Ar3 or higher.

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