Cold-rolled steel sheet for can and method for manufacturing the same

Abstract

A cold-rolled steel sheet for a can according to one embodiment of the present application, the cold-rolled steel sheet for a can comprising, in weight%, carbon (C): 0.0005 to 0.004%, manganese (Mn): 0.4 to 0.8%, silicon (Si): 0.05% or less, phosphorus (P): 0.030% or less, sulfur (S): 0.030% or less, aluminum (Al): 0.01 to 0.07%, nitrogen (N): 0.0005 to 0.004%, the balance of iron (Fe) and other inevitable impurities, the deformed ferrite comprising 95% or more in area%, and the ratio of the rolling direction average grain diameter of the deformed ferrite to the thickness direction average grain diameter being 1.1 or more and less than 1.5.

Description

Technical Field

[0001] One embodiment of the present invention relates to a cold-rolled steel sheet for tanks and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to a cold-rolled steel sheet for a safety dome of a portable butane gas tank and a method for manufacturing the same. Background Technology

[0002] The steel material used for cans is tinplate (black plate). Since most of this material is relatively thin, it is distinguished by its tempering degree, expressed as Rockwell hardness HR30T. To manufacture cans for storing contents, tinplate is plated onto its surface to impart corrosion resistance. It is then cut to specific dimensions and further processed into round or angular shapes. The methods for manufacturing containers are divided into those without welding, such as two-piece cans consisting of a lid and a body; and those that connect the can body through welding or joining, such as three-piece cans consisting of a body, a top lid, and a bottom lid.

[0003] In single-rolled tinplate (SR-BP), the main use of soft tinplate with a temper grade of T3 or below is for parts that require machinability, while hard tinplate with a temper grade of T4 to T6 is widely used for parts that require properties that can withstand the internal pressure of the contents rather than machinability, such as the body of a can, lid, etc.

[0004] Double-rolled steel sheet refers to steel sheet produced by applying a relatively high reduction rate to materials that have undergone hot rolling, one cold rolling, and annealing during a tempering and tempering process, thereby increasing the material's strength. As a representative application of double-rolled materials, double-rolled tinplate (DR-BP) is graded based on its strength and hardness. For most double-rolled materials, although the strength increases due to work hardening, there is a sharp decrease in ductility due to the reaction effect.

[0005] In particular, when low-carbon steel is used as the tin-plating base plate for secondary rolling and continuously annealed, the elements dissolved in the steel cause aging phenomena during the tin melting step used to alloy the tin layer in the tin plating process or the baking step used to dry organic materials such as paint in the can-making process. Therefore, during can processing, not only are there processing defects such as angular fringe (fluting) or tensile strain (stretcher strain) that causes stripe-like defects on the steel plate surface, but deformation aging also occurs after secondary rolling, further reducing the material's ductility.

[0006] Although the use of bell-type annealing materials has been proposed to suppress this deformation aging, bell-type annealing materials also have fundamental problems such as long annealing time leading to decreased productivity, uneven product material, and frequent surface defects in secondary rolled steel plates leading to decreased operability.

[0007] To address these issues, we are currently actively considering a solution to manufacture secondary rolled tin-plated substrates using a continuous annealing process that offers low production costs, uniform material quality, and excellent flatness and surface properties.

[0008] In addition, the secondary rolling method ensures material quality through work hardening. After steelmaking, the steel plate needs to be manufactured through processes such as hot rolling, first cold rolling, annealing, tempering rolling, and secondary rolling. Compared with the conventional process of manufacturing products through annealing and tempering rolling, the secondary rolling method adds processes, which leads to increased manufacturing costs. Countermeasures are being actively explored to address this issue. Summary of the Invention

[0009] (a) Technical problems to be solved One embodiment of the present invention provides a cold-rolled steel sheet for tanks and a method for manufacturing the same. Specifically, one embodiment of the present invention provides a cold-rolled steel sheet for a safety dome of a portable butane gas tank and a method for manufacturing the same.

[0010] (II) Technical Solution According to an embodiment of the present invention, the cold-rolled steel sheet for cans, by weight%, comprises: carbon (C): 0.0005 to 0.004%, manganese (Mn): 0.4 to 0.8%, silicon (Si): less than 0.05%, phosphorus (P): less than 0.030%, sulfur (S): less than 0.030%, aluminum (Al): 0.01 to 0.07%, nitrogen (N): 0.0005 to 0.004%, balance iron (Fe) and other unavoidable impurities. By area%, the wrought ferrite comprises more than 95%, and the ratio of the average grain diameter in the rolling direction to the average grain diameter in the thickness direction of the wrought ferrite is more than 1.1 and less than 1.5.

[0011] The dislocation density of deformed ferrite is 1×10 15 / m 2 Up to 5×10 15 / m 2 .

[0012] According to one embodiment of the present invention, the cold-rolled steel sheet for tanks has a tensile strength of 300 to 450 MPa, an elongation of 20% or more, and a yield ratio of 0.85 or more and 1 or less.

[0013] The cold-rolled steel sheet for cans in one embodiment of the present invention may further include a tin-plated layer located on the surface of the steel sheet.

[0014] A method for manufacturing a cold-rolled steel sheet for cans according to an embodiment of the present invention includes: a step of hot-rolling a slab to manufacture a hot-rolled steel sheet, wherein the slab contains, by weight percent, carbon (C): 0.0005 to 0.004%, manganese (Mn): 0.4 to 0.8%, silicon (Si): less than 0.05%, phosphorus (P): less than 0.030%, sulfur (S): less than 0.030%, aluminum (Al): 0.01 to 0.07%, nitrogen (N): 0.0005 to 0.004%, with the balance being iron (Fe) and other unavoidable impurities; a first cold rolling step of cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet; a step of cold-rolling the cold-rolled steel sheet; and a second cold rolling step of cold-rolling the annealed steel sheet at a reduction rate of 5% or more and less than 9%.

[0015] According to an embodiment of the present invention, a method for manufacturing cold-rolled steel sheet for tanks can satisfy the following formula 1.

[0016] [Formula 1] [FDT]×[CT]×[RR1]×[AT] / 10 10 ≥3.2 In Formula 1, [FDT] represents the final rolling temperature (°C) in the hot-rolled steel sheet manufacturing process, [CT] represents the coiling temperature (°C) in the hot-rolled steel sheet manufacturing process, [RR1] represents the reduction rate (%) in the first cold rolling step, and [AT] represents the annealing temperature (°C) in the cold-rolled sheet annealing step.

[0017] Before the step of manufacturing hot-rolled steel sheet, the slab can be heated to 1100 to 1300°C.

[0018] It may also include a pickling step of the steel sheet prior to a cold rolling step.

[0019] It may also include a step of tin plating the steel sheet after secondary cold rolling.

[0020] (III) Beneficial Effects According to an embodiment of the present invention, the cold-rolled steel sheet for tanks has excellent strength, elongation and load-bearing capacity, and can be used for safety domes of portable butane gas tanks. Detailed Implementation

[0021] The terms "first," "second," "third," etc., are used to describe parts, components, regions, layers, and / or segments, but these parts, components, regions, layers, and / or segments should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, or segment from another. Therefore, without departing from the scope of the invention, the first part, component, region, layer, or segment described below can also be described as a second part, component, region, layer, or segment.

[0022] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular forms used herein are intended to include the plural forms as well. The word "comprising" as used in the specification can specifically refer to a particular feature, domain, integer, step, action, element, and / or component, but does not exclude the presence or addition of other features, domains, integers, steps, actions, elements, components, and / or groups.

[0023] In addition, unless otherwise specified, % means weight, 1 ppm is 0.0001 weight.

[0024] In one embodiment of the present invention, the inclusion of additional elements refers to the replacement of a portion of the remaining iron (Fe) by additional elements, the replacement amount being equivalent to the amount of additional elements added.

[0025] Although not otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in dictionaries should be interpreted as having the same meaning as disclosed in relevant technical literature and herein, and should not be interpreted in an idealized or overly formal sense.

[0026] The embodiments of the present invention will be described in detail below to enable those skilled in the art to implement the invention. However, the present invention can be implemented in various different ways and is not limited to the embodiments described herein.

[0027] In one embodiment of the present invention, by controlling the amount of C, Mn, etc. added to the alloy composition (especially the steel composition of very low carbon steel base) and optimizing the microstructure, high tensile strength is ensured, while high yield strength ratio is also ensured.

[0028] This allows for the manufacture of extremely thin steel plates for food / beverage cans, gas containers, and especially portable butane gas cylinder safety domes, ensuring seamless plate flow during the process and achieving excellent process reduction through efficient heat treatment operations.

[0029] According to one embodiment of the present invention, the material comprises, by weight percent: carbon (C): 0.0005 to 0.004%, manganese (Mn): 0.4 to 0.8%, silicon (Si): less than 0.05%, phosphorus (P): less than 0.030%, sulfur (S): less than 0.030%, aluminum (Al): 0.01 to 0.07%, nitrogen (N): 0.0005 to 0.004%, with the balance being iron (Fe) and other unavoidable impurities.

[0030] The ingredients are described in detail below.

[0031] Carbon (C): 0.0005 to 0.0040% by weight Carbon (C) is typically added to increase the strength of steel sheets and is a representative element that can cause aging when present in steel as a solid solution. Excessive carbon content will harden the material, reducing cold rollability and potentially negatively impacting ductility. Conversely, insufficient carbon (C) content can lead to coarsening of the microstructure, making it difficult to ensure hardness and strength, thus potentially compromising the desired material quality. More specifically, a carbon content of 0.0010 to 0.0030% by weight is acceptable.

[0032] Manganese (Mn): 0.40 to 0.80% by weight Manganese (Mn), as a solid solution strengthening element, can improve the strength and hot workability of steel. However, if excessive manganese sulfide (MnS) precipitates form, it will impair the ductility and workability of the steel. Therefore, excessive addition of manganese (Mn) will reduce ductility and may contribute to atomic rise and center segregation due to the large amount of alloying elements added. However, if the manganese (Mn) content is too low, although workability is improved, it will contribute to hot brittleness, making it difficult to ensure the target quenching and tempering degree. More specifically, it can contain 0.45 to 0.60% by weight of Mn.

[0033] Silicon (Si): less than 0.050% by weight Silicon (Si) combines with oxygen and other elements to form an oxide layer on the surface of steel plates, which contributes to poor tin plating and reduced corrosion resistance; therefore, its addition should be limited. However, considering its unavoidable presence in the steel, 0% by weight can be excluded. More specifically, it can be included in the range of 0.001 to 0.040% by weight.

[0034] Phosphorus (P): less than 0.0300% by weight Phosphorus (P) exists as a solid-solution element in steel, increasing its strength and hardness by inducing solid-solution strengthening. Excessive P content can cause center segregation during casting, potentially reducing machinability. However, considering its unavoidable presence in steel, 0% can be excluded. More specifically, 0.0001 to 0.0100% by weight of P may be included. More specifically, 0.0005 to 0.0050% by weight of P may be included.

[0035] Sulfur (S): less than 0.030% by weight Sulfur (S) combines with Mn in steel to form non-metallic inclusions that act as corrosion initiation points and contribute to red shortness; therefore, its content is preferably minimized. Furthermore, since it combines with manganese in steel to form manganese-sulfide precipitates, excessive sulfur can lead to coarse-sized precipitates, potentially making it difficult to ensure the target quenching and tempering. However, considering its unavoidable presence in the steel, 0% can be excluded. More specifically, 0.001 to 0.025% by weight of S may be included. More specifically, 0.005 to 0.020% by weight of S may be included.

[0036] Aluminum (Al): 0.010 to 0.070% by weight Aluminum (Al) is an element added to aluminum-killed steel to prevent material degradation caused by deoxidizers and aging. To achieve this effect, it can be contained in appropriate amounts or more. However, if excessive aluminum (Al) is added, the deoxidation effect will saturate and surface inclusions such as alumina (Al₂O₃) will increase dramatically, potentially leading to deterioration of the surface properties and reduced processability of the hot-rolled material. More specifically, it can contain 0.015 to 0.050% by weight of Al.

[0037] Nitrogen (N): 0.0005 to 0.0040% by weight Nitrogen (N) exists in a solid solution state inside steel and is an effective element for strengthening the material. To ensure the target tempering degree, it can be contained at a level of 0.0005% or higher. On the other hand, if its content exceeds 0.004%, not only will the aging performance deteriorate drastically, but it will also increase the denitrification burden in the steelmaking process, which may lead to a deterioration in steelmaking operability.

[0038] In addition to the aforementioned alloy components, the balance includes Fe and unavoidable impurities. However, in one embodiment of the invention, the addition of other components is not excluded. The unavoidable impurities are those that may be unintentionally introduced from raw materials or the surrounding environment during conventional steel manufacturing processes, and therefore, the possibility of impurity contamination cannot be ruled out. These unavoidable impurities are understood by those skilled in the art of conventional steel manufacturing. For example, it may also contain one or more of the following: Ti: less than 0.01 wt%, Mo: less than 0.01 wt%, V: less than 0.01 wt%, Ni: less than 0.1 wt%, Cr: less than 0.1 wt%, and Cu: less than 0.1 wt%.

[0039] According to one embodiment of the present invention, the cold-rolled steel sheet for tanks contains more than 95% deformed ferrite by area percentage.

[0040] Deformed ferrite refers to ferrite that has been deformed. Specifically, the deformed ferrite of this invention, after deformation, has a dislocation density of 1 x 10⁻⁶. 15 / m 2As described above, it can be distinguished from other ferrites by the difference in dislocation density. In this invention, the fine structure can be observed using optical or electron microscopy, and identification can be performed by measuring the dislocation density using XRD.

[0041] When the area fraction of deformed ferrite with high dislocation density is above 90%, the material properties exhibit smaller fluctuations, and the strength can reach the target level. More specifically, deformed ferrite can comprise more than 95%. More specifically, deformed ferrite can comprise 97% to 100%.

[0042] The ratio of the average grain diameter in the rolling direction to the average grain diameter in the thickness direction of the deformed ferrite (hereinafter also referred to as the shape ratio) is greater than or equal to 1.1 and less than 1.5. The shape ratio can be measured by observing the cross-section of the steel plate including both the thickness and rolling directions using an optical microscope.

[0043] If the shape ratio of the deformed ferrite is too small, there are problems in ensuring the desired strength level of the invention; if the shape ratio is too large, it may cause material deviations in all directions of the product. More specifically, the shape ratio of the deformed ferrite can be from 1.2 to 1.4.

[0044] The dislocation density of deformed ferrite can be 1.0 × 10⁻⁶. 15 / m 2 Up to 5.0×10 15 / m 2 In one embodiment of the invention, dislocation density can be measured by XRD.

[0045] If the dislocation density of wrought ferrite is too low, the target strength level cannot be guaranteed; conversely, if the dislocation density is too high, brittleness may occur, and ductility and formability may deteriorate. More specifically, the dislocation density of wrought ferrite can be 2.0 × 10⁻⁶. 15 / m 2 Up to 4.5×10 15 / m 2 .

[0046] According to one embodiment of the present invention, the cold-rolled steel sheet for tanks has a tensile strength of 300 to 450 MPa, an elongation of more than 20%, and a yield ratio of 0.85 to 1.00, which can ensure excellent strength properties.

[0047] According to one embodiment of the present invention, cold-rolled steel sheet for tanks is used as a high-strength material. In fields where extremely thin materials are used (such as pressure pipes or tank domes), since the tensile strength of the steel sheet is set to 300 MPa or higher, deformation caused by internal tank pressure only occurs above a certain pressure. Therefore, the lower limit of the tensile strength can be limited to 350 MPa. On the other hand, if the tensile strength exceeds 450 MPa, although it may be advantageous in terms of the tank's pressure resistance, the increased strength leads to a decrease in cold-rollability, thus potentially reducing performance. Furthermore, very high pressure is required to prevent dome deformation, which cannot meet the legal standards for safe dome operating pressure. More specifically, the tensile strength can be between 375 and 425 MPa.

[0048] If the total elongation is less than 20%, the can's flange will have poor workability and may crack during processing. More specifically, the elongation can be between 23% and 35%.

[0049] On the other hand, the yield ratio, which represents the ratio of a material's yield strength to its tensile strength, is a factor closely related to material strength and is defined as [yield strength / tensile strength]. To meet legal standards for working pressure in safety domes, high-strength materials are required. Therefore, the yield ratio can range from 0.85 to 1.00. More specifically, it can range from 0.87 to 0.95.

[0050] According to one embodiment of the present invention, the cold-rolled steel sheet for cans may further include a tin-plated layer on the surface of the steel sheet. The tin-plated layer is not particularly limited and can be applied under conventional conditions applicable in the same technical field. By tin plating, the steel sheet according to one embodiment of the present invention can include a tin-plated layer on its surface.

[0051] A method for manufacturing a cold-rolled steel sheet for cans according to an embodiment of the present invention includes: a step of hot-rolling a slab to manufacture a hot-rolled steel sheet, wherein the slab contains, by weight percent, carbon (C): 0.0005 to 0.004%, manganese (Mn): 0.4 to 0.8%, silicon (Si): less than 0.05%, phosphorus (P): less than 0.030%, sulfur (S): less than 0.030%, aluminum (Al): 0.01 to 0.07%, nitrogen (N): 0.0005 to 0.004%, with the balance being iron (Fe) and other unavoidable impurities; a first cold rolling step of cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet; a step of cold-rolling the cold-rolled steel sheet; and a second cold rolling step of cold-rolling the annealed steel sheet at a reduction rate of 5% or more and less than 9%.

[0052] The following describes each step in detail.

[0053] First, the slab is hot-rolled to produce hot-rolled steel sheets.

[0054] The alloy composition of the slab has already been described in the section on cold-rolled steel sheets for cans, so it will not be repeated here. The alloy composition does not substantially change during the manufacturing process of cold-rolled steel sheets for cans; therefore, the alloy composition of the cold-rolled steel sheets for cans is substantially the same as that of the slab.

[0055] Prior to the step of manufacturing the hot-rolled steel sheet, a step of heating the slab to 1100 to 1300°C may be included. This slab heating can be performed to ensure smooth execution of subsequent rolling processes and to fully obtain the physical properties of the target steel sheet. The invention is not particularly limited to these reheating conditions, as long as conventional reheating conditions are applicable. More specifically, the temperature can be heated to 1150 to 1250°C.

[0056] For heated slabs, hot rolling can be performed at a final rolling temperature of 900 to 950°C. If the final rolling temperature is too low, grain mixing will intensify as hot rolling ends in the low-temperature region, potentially leading to reduced rollability and processability. On the other hand, if the final rolling temperature is too high, uniform hot rolling cannot be achieved across the entire thickness range, resulting in insufficient grain refinement, which may lead to a decrease in impact toughness due to grain coarsening. More specifically, hot rolling can be performed at a final rolling temperature of 905 to 935°C.

[0057] For hot-rolled steel sheets, coiling can be performed at a coiling temperature of 550 to 700°C. Alternatively, coiling can be performed after cooling at the run-out table (ROT) stage. If the coiling temperature is too low, uneven temperature distribution in the width direction during cooling and holding will lead to variations in the formation behavior of low-temperature precipitates, inducing material deviations and adversely affecting processability. On the other hand, if the coiling temperature is too high, material softening and reduced corrosion resistance may occur as the final product's microstructure coarsens. More specifically, coiling can be performed at a coiling temperature of 580 to 650°C.

[0058] Next, the hot-rolled steel sheet undergoes a single cold rolling process to produce a cold-rolled steel sheet. In this case, the reduction rate during the single cold rolling can be between 80% and 94%. The reduction rate can be calculated as ((steel sheet thickness before rolling) - (steel sheet thickness after rolling)) / (steel sheet thickness before rolling) × 100. If the cold reduction rate is too low, the thickness of the hot-rolled steel sheet must be reduced to produce the extremely thin material of the target thickness. This not only significantly reduces hot rolling operability but also makes it difficult to ensure the grain structure required to guarantee the final product material due to the low reduction rate. On the other hand, if the cold reduction rate is too high, although the material will harden, there may be a significant reduction in cold operability due to the mill load. More specifically, the reduction rate during a single cold rolling process can be between 85% and 93%.

[0059] In one embodiment of the invention, a pickling process may also be included, whereby the steel sheet is pickled after coiling and before cold rolling. The pickling conditions are not particularly limited and can be performed under conventional conditions applicable in the same technical field.

[0060] Next, the cold-rolled steel sheet undergoes cold-rolled sheet annealing. The annealing temperature can be between 600 and 800°C. Annealing reduces the strength to the target strength by annealing the material, which is in a state of increased strength due to deformation introduced during cold rolling. From this perspective, if the annealing temperature is too low, the deformation cannot be fully released, resulting in higher strength but potentially significantly reduced workability. On the other hand, if the annealing temperature is too high, recrystallization during annealing intensifies, reducing the fraction of deformed ferrite and softening the material, potentially preventing the achievement of the target strength. Furthermore, there are concerns about material defects such as sheet breakage in continuous rolling mills, leading to equipment malfunctions. More specifically, the annealing temperature can be between 650 and 780°C.

[0061] According to an embodiment of the present invention, a method for manufacturing cold-rolled steel sheet for tanks can satisfy the following formula 1.

[0062] [Formula 1] [FDT]×[CT]×[RR1]×[AT] / 10 10 ≥3.20 In Formula 1, [FDT] represents the final rolling temperature (°C) in the hot-rolled steel sheet manufacturing process, [CT] represents the coiling temperature (°C) in the hot-rolled steel sheet manufacturing process, [RR1] represents the reduction rate (%) in the first cold rolling step, and [AT] represents the annealing temperature (°C) in the cold-rolled sheet annealing step.

[0063] Equation 1 is a combination of temperature and reduction conditions in each step. In one embodiment of the invention, the final rolling temperature, coiling temperature, single-stage cold rolling reduction, and annealing temperature are all set relatively high to obtain the target strength and material properties. When any of these conditions is small, the value of Equation 1 becomes smaller, making it difficult to obtain the target strength and material properties. More specifically, the left-hand side of Equation 1 can be between 3.50 and 4.00. More specifically, the left-hand side of Equation 1 can be between 3.55 and 3.80.

[0064] Next, the annealed steel sheet undergoes a second cold rolling process with a reduction rate of 5% to less than 9%. This second cold rolling can be performed to control the sheet shape after annealing, impart surface roughness, and ultimately achieve the target material quality. If the reduction rate is too low, it may be difficult to ensure the required material quality through a second rolling process. If the reduction rate is too high, work hardening is exacerbated, potentially making it difficult to ensure the target elongation and tensile strength. More specifically, the second cold rolling reduction rate can be between 6% and 8%.

[0065] The next step may include tin plating on the steel sheet after secondary cold rolling. Tin plating can be performed at a temperature range of 250 to 350°C, and the tin-plated steel sheet can be cooled to room temperature. Tin plating conditions are not particularly limited and can be performed under conventional conditions applicable in the same technical field.

[0066] The present invention will be further described in detail below by way of examples. However, the following examples are merely illustrative of the invention, and the invention is not limited to the following examples.

[0067] Example 1 A slab with the composition shown in Table 1 was manufactured. After the slab was heated to 1250°C, it was hot rolled, pickled, cold rolled once, annealed, and cold rolled twice according to the process in Table 2 to produce a cold-rolled steel sheet for cans with a thickness of 0.35 mm.

[0068] For the fine microstructure, each sample was etched with nitric acid and alcohol, and then observed using an optical microscope. The dislocation density was measured by XRD, and the area fraction of deformed ferrite and the dislocation density of the fine microstructure were expressed. The grain shape ratio of deformed ferrite, representing the ratio of the average grain diameter in the rolling direction to the average grain diameter in the thickness direction, can be measured by observation using an optical microscope.

[0069] Yield strength and elongation were measured by room temperature tensile testing, with the tensile specimens prepared to conform to ASTM specifications (ASRM E-8 standard). The yield strength (YS) and elongation (El) of the tensile specimens were measured using a tensile testing machine (Instron, Model 6025). The yield ratio was calculated by dividing the yield strength by the tensile strength.

[0070] Table 1 Table 2 Table 3 As shown in Tables 1 to 3, Examples 1 and 2 of the invention simultaneously satisfy the steel composition and manufacturing conditions. It can be confirmed that the shape ratio of the deformed ferrite is appropriately formed, and the tensile strength, elongation and yield strength ratio are all excellent, which meets the requirements for a safety dome.

[0071] On the other hand, if the steel composition or manufacturing conditions are not met, it can be confirmed that the deformed ferrite cannot be properly formed, or the dislocation density is not properly formed, and the tensile strength, elongation, or yield ratio is partially inferior, so as not to meet the conditions required as a safety dome.

[0072] This invention is not limited to the embodiments described above and can be manufactured in various different ways. Those skilled in the art should understand that other specific methods can be used without altering the technical concept or essential features of the invention. Therefore, it should be understood that the above embodiments are exemplary in all respects and not restrictive.

Claims

1. A cold-rolled steel sheet for cans, wherein, The cold-rolled steel sheet for cans, by weight percent, comprises: carbon (C): 0.0005 to 0.004%, manganese (Mn): 0.4 to 0.8%, silicon (Si): Less than 0.05%, phosphorus (P): less than 0.030%, sulfur (S): less than 0.030%, aluminum (Al): 0.01 to 0.07%, nitrogen (N): 0.0005 to 0.004%, balance iron (Fe) and other unavoidable impurities. By area percentage, deformed ferrite comprises more than 95%. The ratio of the average grain diameter in the rolling direction to the average grain diameter in the thickness direction of the deformed ferrite is greater than 1.1 and less than 1.

5.

2. The cold-rolled steel sheet for cans according to claim 1, wherein, The dislocation density of the deformed ferrite is 1×10⁻⁶. 15 / m 2 Up to 5×10 15 / m 2 .

3. The cold-rolled steel sheet for cans according to claim 1, wherein, The cold-rolled steel sheet for the tank has a tensile strength of 300 to 450 MPa, an elongation of more than 20%, and a yield strength ratio of more than 0.85 and less than 1.

4. The cold-rolled steel sheet for cans according to claim 1, wherein, The cold-rolled steel sheet for cans also includes a tin-plated layer on the surface of the steel sheet.

5. A method for manufacturing a cold-rolled steel sheet for cans, comprising: The step of hot rolling a slab to produce a hot-rolled steel sheet, wherein the slab comprises, by weight %, carbon (C): 0.0005 to 0.004%, manganese (Mn): 0.4 to 0.8%, silicon (Si): less than 0.05%, phosphorus (P): less than 0.030%, sulfur (S): less than 0.030%, aluminum (Al): 0.01 to 0.07%, nitrogen (N): 0.0005 to 0.004%, balance iron (Fe) and other unavoidable impurities; A cold rolling step to manufacture cold-rolled steel sheets by performing a single cold rolling process on the hot-rolled steel sheet; The steps of cold-rolled steel sheet annealing; and The secondary cold rolling step involves performing a second cold rolling on annealed steel sheets with a reduction rate of 5% or more but less than 9%. And it satisfies the following equation 1: [Formula 1] [FDT]×[CT]×[RR1]×[AT] / 10 10 ≥3.2 In Formula 1, [FDT] represents the final rolling temperature (°C) in the hot-rolled steel sheet manufacturing process, [CT] represents the coiling temperature (°C) in the hot-rolled steel sheet manufacturing process, [RR1] represents the reduction rate (%) in the first cold rolling step, and [AT] represents the annealing temperature (°C) in the cold-rolled sheet annealing step.

6. The method for manufacturing cold-rolled steel sheet for cans according to claim 5, further comprising: The step of heating the slab to 1100 to 1300°C prior to the step of manufacturing the hot-rolled steel sheet.

7. The method for manufacturing cold-rolled steel sheet for cans according to claim 5, further comprising: The steel sheet is pickled before the first cold rolling step.

8. The method for manufacturing cold-rolled steel sheet for cans according to claim 5, further comprising: The step of tin plating the steel sheet after the second cold rolling is as follows.

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