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

Abstract

A cold-rolled steel sheet for a can, according to one embodiment of the present invention, comprises, by weight %: 0.0005% to 0.004% of carbon (C), 0.2% to 0.6% of manganese (Mn), 0.05% or less of silicon (Si), 0.030% or less of phosphorus (P), 0.030% or less of sulfur (S), 0.01% to 0.07% of aluminum (Al), and 0.0005% to 0.004% of nitrogen (N), with the remainder being iron (Fe) and other unavoidable impurities, wherein the cold-rolled steel sheet for a can comprises, by area %, 95% or more of deformed ferrite, and 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 between 1.5 and 2.0.

Description

Cold rolled steel sheet for cans and manufacturing method thereof

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

[0002] The tin-plated black plate, a steel material used for cans, is mostly thin, so the material is classified by the hardness indicated by the Rockwell surface hardness HR30T. In order to make a can for storing the contents using the tin-plated black plate, the surface of the tin-plated black plate is plated with tin, etc. to provide corrosion resistance, and then it is cut to a certain size and processed into a circular or square shape. The method of processing the container is divided into a method of processing without welding, such as a two-piece can, which is composed of a lid and a body, and a method of connecting the body by welding or bonding, such as a three-piece can, which is composed of a body, an upper lid, and a lower lid.

[0003] Among the tin-plated plates (SR-BP, single reduced black plate) manufactured by the single rolling method, the main use of soft tin-plated plates with a temper grade of T3 or lower is in areas requiring workability, while hard tin-plated plates with a temper grade of T4 to T6 are widely used in areas requiring the ability to withstand internal pressure from contents rather than workability, such as the body and lid of cans.

[0004] Secondary rolled steel plate refers to steel plate that has undergone hot rolling, primary cold rolling, and annealing processes, and has its strength increased by applying a relatively high reduction rate during the temper rolling process. The representative application of secondary rolled material, secondary rolled tin-plated plate (DR-BP, double reduced black plate), is classified according to the strength and hardness of the material. In the case of most secondary rolled materials, the strength increases through work hardening, but there is a problem that ductility decreases rapidly as a counteraction.

[0005] In particular, in the case of continuous annealing using low-carbon steel as a tin-plated plate for secondary rolling, aging occurs due to elements dissolved in the steel during the tin-melting step for alloying the tin layer in the tin-plating process or the baking step for drying organic substances such as lacquer in the can manufacturing process. This not only causes processing defects such as fluting, which causes the can to bend into a square shape, or stretcher strain, which causes stripe-shaped defects on the surface of the steel plate, but also causes strain aging after secondary rolling, which acts as a factor that further reduces the ductility of the material.

[0006] To suppress this type of deformation aging, a method of using annealed steel has been proposed, but even in the case of annealed steel, it has fundamental problems such as low productivity due to the long time required for annealing, uneven material quality of the product, and many surface defects in the secondary rolled steel plate, which reduces workability.

[0007] To solve such problems, a method of manufacturing secondary rolled tin-plated plates through continuous annealing, which has low production costs, uniform material, and excellent flatness and surface characteristics, is being actively considered.

[0008] In addition, the secondary rolling method that secures material through work hardening manufactures steel plates through processes such as hot rolling, primary cold rolling, annealing, temper rolling, and secondary cold rolling after steel is drawn, so compared to the conventional process of making products through annealing and temper rolling, there is an additional process, which causes a problem of increased manufacturing costs. Therefore, countermeasures for this are also being actively reviewed.

[0009] In one embodiment of the present invention, a cold-rolled steel sheet for cans and a method for manufacturing the same are provided. Specifically, in one embodiment of the present invention, a cold-rolled steel sheet for a portable butane gas can safety dome and a method for manufacturing the same are provided.

[0010] A cold-rolled steel sheet for a can according to one embodiment of the present invention contains, in wt%, carbon (C): 0.0005 to 0.004%, manganese (Mn): 0.2 to 0.6%, 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 remainder iron (Fe) and other unavoidable impurities, and in wt%, contains 95% or more of deformed ferrite, and 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 1.5 to 2.0.

[0011] The dislocation density of deformed ferrite is 3 × 10 15 / m 2 6 × 10 15 / m 2 am.

[0012] According to one embodiment of the present invention, a cold-rolled steel sheet for a can has a tensile strength of 350 to 450 MPa, an elongation of 15% or more, a yield ratio of 0.7 to 1.0, and a load value of 110 to 150 MPa×mm.

[0013] A cold-rolled steel sheet for a can according to one embodiment of the present invention may further include a tin plating layer positioned on the surface of the steel sheet.

[0014] A method for manufacturing a cold-rolled steel sheet for cans according to one embodiment of the present invention includes the steps of: hot-rolling a slab containing, in wt%, carbon (C): 0.0005 to 0.004%, manganese (Mn): 0.2 to 0.6%, 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 remainder iron (Fe) and other unavoidable impurities to manufacture a hot-rolled steel sheet; a first cold-rolling step of first 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 second cold-rolling the annealed steel sheet at a reduction ratio of 9 to 14%.

[0015] A method for manufacturing a cold-rolled steel sheet for a can according to one embodiment of the present invention can satisfy the following equation 1.

[0016] [Formula 1]

[0017] [FDT]×[CT]×[RR1]×[AT] / 10 10 ≥3.2

[0018] (In Equation 1, [FDT] represents the finishing rolling temperature (℃) in the step of manufacturing hot-rolled steel sheets, [CT] represents the coiling temperature (℃) in the step of manufacturing hot-rolled steel sheets, [RR1] represents the reduction ratio (%) in the first cold rolling step, and [AT] represents the annealing temperature (℃) in the cold-rolled sheet annealing step.)

[0019] The slab may be heated to 1100 to 1300°C prior to the step of manufacturing the hot rolled steel plate.

[0020] The step of pickling the steel sheet before the first cold rolling step may further be included.

[0021] A step of tin plating the steel sheet after secondary cold rolling may be further included.

[0022] A cold-rolled steel sheet for cans according to one embodiment of the present invention has excellent strength, elongation, and load value at the same time, and can be used for a safety dome for a portable butane gas can.

[0023]

[0024] 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 only 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.

[0025] 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.

[0026] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0027] 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.

[0028] 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.

[0029] 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.

[0030]

[0031] In one embodiment of the present invention, the alloy composition, particularly the amount of C, Mn, etc. added to the steel components of the ultra-low carbon steel base, was controlled, and the microstructure was optimized to secure high tensile strength and high yield ratio characteristics at the same time.

[0032] This enables the production of ultra-thin steel sheets used in food / beverage containers, gas containers, and especially portable butane gas can safety domes, while also ensuring easy passability during the process and achieving the effect of shortening the process with excellent heat treatment efficiency.

[0033]

[0034] According to one embodiment of the present invention, in weight %, it contains carbon (C): 0.0005 to 0.004%, manganese (Mn): 0.2 to 0.6%, 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 remainder iron (Fe) and other unavoidable impurities.

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

[0036] Carbon (C): 0.0005 to 0.0040 wt%

[0037] Carbon (C) is an element generally added to steel sheets to improve their strength. It is a representative element that can cause aging when present in steel as a solid solution element. Excessive carbon content can harden the material, reducing cold-rolling properties and negatively impacting ductility. Conversely, too little carbon (C) can cause coarsening of the structure, making it difficult to secure hardness and strength, making it difficult to achieve the desired material quality. More specifically, carbon may be included in an amount of 0.0010 to 0.0030 wt%.

[0038] Manganese (Mn): 0.20 to 0.60 wt%,

[0039] Manganese (Mn) is a solid solution strengthening element that increases the strength of steel and improves hot workability. However, if excessive manganese sulfide (MnS) precipitates are formed, it is an element that can reduce the ductility and workability of steel. Therefore, if manganese (Mn) is added excessively, ductility is reduced and it can be a factor in the occurrence of atomic elevation and center segregation due to the addition of large amounts of alloying elements. However, if the manganese (Mn) content is too low, workability may be improved, but it can be a factor in the occurrence of red-hot embrittlement and it may be difficult to secure the target temper degree. More specifically, Mn may be included in an amount of 0.25 to 0.55 wt%.

[0040] Silicon (Si): 0.050 wt% or less

[0041] Silicon (Si) combines with oxygen and other elements to form an oxide layer on the surface of steel plates, which deteriorates plating properties and reduces corrosion resistance. Therefore, its addition amount may be limited. However, considering that it is unavoidably included in steel, 0 wt% may be excluded. More specifically, it may be included in amounts of 0.001 to 0.040 wt%.

[0042] Phosphorus (P): 0.0300 wt% or less

[0043] Phosphorus (P) is an element that exists as a solid solution element in steel and enhances the strength and hardness of the steel by causing solid solution strengthening. If the content is too high, there is a concern that it will cause center segregation during casting and reduce workability. However, considering that it is unavoidably included in steel, 0% can be excluded. More specifically, P can be included in an amount of 0.0001 to 0.0100 wt%. More specifically, P can be included in an amount of 0.0005 to 0.0050 wt%.

[0044] Sulfur (S): 0.030 wt% or less

[0045] Sulfur (S) combines with manganese in steel to form non-metallic inclusions that serve as corrosion initiation sites and cause red shortness, so it is desirable to reduce its content as much as possible. In addition, it combines with manganese in steel to form manganese-sulfide precipitates, so if sulfur is too much, the size of these precipitates may become coarse, making it difficult to secure the target temper degree. However, considering that it is unavoidably included in steel, 0% can be excluded. More specifically, S may be included in an amount of 0.001 to 0.025 wt%. More specifically, S may be included in an amount of 0.005 to 0.020 wt%.

[0046] Aluminum (Al): 0.010 to 0.070 wt%

[0047] Aluminum (Al) is an element added to aluminum-killed steel to prevent material deterioration due to deoxidation and aging. To achieve the aforementioned effects, aluminum (Al) may be included in an appropriate amount. However, excessive addition of aluminum (Al) may saturate the deoxidation effect and rapidly increase the formation of surface inclusions such as aluminum oxide (Al2O3), which may deteriorate the surface properties of the hot-rolled material and reduce workability. More specifically, aluminum may be included in an amount of 0.015 to 0.050 wt%.

[0048] Nitrogen (N): 0.0005 to 0.0040 wt%

[0049] Nitrogen (N) is an element that exists in a solid solution state within steel and is effective in strengthening the material. To ensure the target tempering degree, it can be included at levels of 0.0005% or more. However, if its content exceeds 0.004%, not only will aging properties deteriorate significantly, but the burden of denitrification during the steelmaking process will also increase, potentially degrading steelmaking workability.

[0050] 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 Ti: 0.01 wt% or less, Mo: 0.01 wt% or less, V: 0.01 wt% or less, Ni: 0.1 wt% or less, Cr: 0.1 wt% or less, and Cu: 0.1 wt% or less.

[0051] A cold-rolled steel sheet for cans according to one embodiment of the present invention contains 95% or more of deformed ferrite in terms of area%.

[0052] Deformed ferrite means deformed ferrite. That is, the deformed ferrite of the present invention is deformed and has a dislocation density of 1x10 15 / m 2 This is ideal, and can be distinguished from other ferrites by the difference in dislocation density. In the present invention, the microstructure can be observed by an optical or electron microscope, and identified by measuring the dislocation density using XRD.

[0053] When the area fraction of deformed ferrite with high dislocation density is 90% or more, the material's variation range is small and its strength can reach the target level. More specifically, the deformed ferrite can be included in an amount of 95% or more. More specifically, the deformed ferrite can be included in an amount of 97 to 100%.

[0054] The ratio of the rolling direction average grain diameter to the thickness direction average grain diameter of the deformed ferrite (hereinafter referred to as the shape ratio) is 1.5 to 2.0. The shape ratio can be measured through optical microscopic observation of a steel sheet cross-section including the thickness direction and the rolling direction.

[0055] If the aspect ratio of the deformed ferrite is too small, it may be difficult to secure the strength level desired in the present invention. If the aspect ratio is too large, it may cause material deviation in the direction of the product. More specifically, the aspect ratio of the deformed ferrite may be 1.5 to 1.7.

[0056] The dislocation density of the deformed ferrite is 3.0 ×10 15 / m 2 6.0 ×10 15 / m 2 It can be. In one embodiment of the present invention, the dislocation density can be measured through XRD.

[0057] If the dislocation density of deformed ferrite is too low, the desired level of strength cannot be secured. On the other hand, if the dislocation density of deformed ferrite is too high, brittleness may occur, and ductility and formability may be inferior. More specifically, the dislocation density of deformed ferrite is 3.1 × 10 15 / m 2 5.0 ×10 15 / m 2 It could be.

[0058] A cold-rolled steel sheet for cans according to one embodiment of the present invention can secure excellent strength characteristics, such as a tensile strength of 350 to 450 MPa, an elongation of 15% or more, and a yield ratio of 0.7 to 1.0.

[0059] According to one embodiment of the present invention, the cold-rolled steel sheet for cans is a high-strength material, and fields such as pressure-resistant tubes or can domes that utilize ultra-thin materials require that the tensile strength of the steel sheet be 350 MPa or higher, so that deformation due to the internal pressure of the can 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, it may be advantageous in terms of the pressure-resistant characteristics of the can, but the usability may be reduced due to the decrease in rollability caused by the increase in strength, and since very high pressure is required for dome deformation, it cannot satisfy the legal standard for safe DOME operating pressure. More specifically, the tensile strength may be 375 to 425 MPa.

[0060] If the overall elongation is less than 15%, the can's flange workability may be compromised, potentially leading to machining cracks. More specifically, the elongation may be between 20 and 35%.

[0061] Meanwhile, the yield ratio, which represents the ratio of a material's yield strength to its tensile strength, is a factor closely related to the material's strength and is defined as [yield strength / tensile strength]. To meet legal standards for safety dome operating pressure, high-strength materials are required, and for this purpose, the yield ratio can be between 0.70 and 1.00. More specifically, it can be between 0.80 and 0.95.

[0062] The load value, which is calculated by multiplying the tensile strength and thickness of the steel plate, is an index that is highly correlated with the operating pressure at which the dome is lifted when the internal pressure of the butane gas can increases. The cold-rolled steel plate for cans according to an embodiment of the present invention may have a load value of 110.0 to 150.0 MPa×mm. If the load value is too small, the dome is lifted even at a low internal pressure, so the legal safety standards cannot be satisfied. If the load value is too high, the dome can be operated only when a very high internal pressure is applied, so the risk of explosion may increase, and at the same time, the legal safety standards cannot be satisfied. Even if the tensile strength of the steel plate is satisfied, if the thickness of the steel plate is thin, the appropriate operating pressure cannot be satisfied, so the legal safety standards for the butane gas can safety dome can be satisfied when the combination of the tensile strength and thickness of the steel plate corresponds to a specific level. More specifically, the load value may be 130.0 to 145.0 MPa×mm.

[0063] The cold-rolled steel sheet for cans according to one embodiment of the present invention may further include a tin plating layer positioned on the surface of the steel sheet. The tin plating layer is not particularly limited, and tin plating may be performed under typical conditions applicable in the same technical field. Through tin plating, the steel sheet according to one embodiment of the present invention may include a tin plating layer on the surface.

[0064]

[0065] A method for manufacturing a cold-rolled steel sheet for cans according to one embodiment of the present invention includes the steps of: hot-rolling a slab containing, in wt%, carbon (C): 0.0005 to 0.004%, manganese (Mn): 0.2 to 0.6%, 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 remainder iron (Fe) and other unavoidable impurities to manufacture a hot-rolled steel sheet; a first cold-rolling step of first 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 second cold-rolling the annealed steel sheet at a reduction ratio of 9 to 14%.

[0066] Below, each step is explained in detail.

[0067] First, the slab is hot rolled to produce hot rolled steel plates.

[0068] The alloy composition of the slab has been described in the previously mentioned cold-rolled steel sheet for cans, so a duplicate description will be omitted. Since the alloy composition does not substantially change during the manufacturing process of the cold-rolled steel sheet for cans, the alloy composition of the cold-rolled steel sheet for cans and the alloy composition of the slab are substantially identical.

[0069] Prior to the step of manufacturing a hot-rolled steel sheet, a step of heating the slab to 1100 to 1300°C may be further included. The slab heating may be performed to smoothly perform the subsequent rolling process and sufficiently obtain the target physical properties of the steel sheet. The present invention is not particularly limited to these reheating conditions, and any typical reheating conditions are possible. More specifically, the heating may be performed at 1150 to 1250°C.

[0070] The heated slab can be hot-finished rolled at a finishing rolling temperature of 900 to 950°C. If the finishing rolling temperature is too low, grain mixing may rapidly occur as hot rolling is completed in the low-temperature region, which may result in a decrease in rollability and workability. On the other hand, if the finishing rolling temperature is too high, uniform hot rolling may not occur across the entire thickness, resulting in insufficient grain refinement, which may result in a decrease in impact toughness due to grain coarsening. More specifically, hot rolling can be performed at a finishing rolling temperature of 905 to 935°C.

[0071] Hot-rolled hot-rolled steel sheets can be coiled at a coiling temperature of 550 to 700°C. Hot-rolled hot-rolled steel sheets can be coiled after cooling at the run-out-table (ROT) stage. If the coiling temperature is too low, the formation behavior of low-temperature precipitates may differ due to the transverse temperature unevenness during cooling and holding, which may cause material deviation and adversely affect workability. On the other hand, if the coiling temperature is too high, the final product's structure may become coarser, which may lead to material softening and reduced corrosion resistance. More specifically, the coiling temperature can be 580 to 650°C.

[0072] Next, the hot-rolled steel sheet is first cold-rolled to produce a cold-rolled steel sheet. At this time, the reduction ratio during the first cold rolling may be 80 to 94%. The reduction ratio can be calculated by (steel sheet thickness before rolling) - (steel sheet thickness after rolling) / (steel sheet thickness before rolling) × 100. If the cold reduction ratio is too low, the hot-rolled steel sheet thickness must be reduced to produce the target ultra-thin material, which not only significantly reduces the hot-rolling workability but also makes it difficult to secure grains for securing the final product material due to the low reduction ratio. On the other hand, if the cold reduction ratio is too high, the material is hardened, but there may be a problem in that the cold workability is significantly reduced due to the load of the rolling mill. More specifically, the reduction ratio during the first cold rolling may be 85 to 93%.

[0073] In one embodiment of the present invention, a step of pickling the steel sheet prior to cold rolling after coiling may be further included. The pickling conditions are not particularly limited, but may be performed under typical conditions applicable in the same technical field.

[0074] Next, the cold-rolled steel sheet is annealed. The annealing temperature can range from 600 to 800°C. The annealing process can reduce the strength from the increased strength achieved by the strain introduced during cold rolling to the target strength by performing annealing.

[0075] In this regard, if the annealing temperature is too low, deformation will not be sufficiently released, resulting in high strength but significantly reduced workability. Conversely, if the annealing temperature is too high, recrystallization will rapidly progress during the annealing process, reducing the fraction of deformed ferrite and softening the material, potentially preventing the desired strength from being achieved. Furthermore, there is a risk of equipment failure due to material defects, such as sheet fracture, within continuous equipment. More specifically, the annealing temperature can range from 650 to 780°C.

[0076] A method for manufacturing a cold-rolled steel sheet for a can according to one embodiment of the present invention can satisfy the following equation 1.

[0077] [Formula 1]

[0078] [FDT]×[CT]×[RR1]×[AT] / 10 10 ≥3.20

[0079] (In Equation 1, [FDT] represents the finishing rolling temperature (℃) in the step of manufacturing hot-rolled steel sheets, [CT] represents the coiling temperature (℃) in the step of manufacturing hot-rolled steel sheets, [RR1] represents the reduction ratio (%) in the first cold rolling step, and [AT] represents the annealing temperature (℃) in the cold-rolled sheet annealing step.)

[0080] Equation 1 is a combination of temperature conditions and reduction ratio conditions at each stage. In one embodiment of the present invention, the finishing rolling temperature, coiling temperature, first cold rolling reduction ratio, and annealing temperature are all set relatively high, thereby obtaining the desired strength and material properties. If any one of these values ​​is small, the value of Equation 1 becomes small, and it becomes difficult to obtain the desired strength and material properties. More specifically, the value of the left side of Equation 1 may be 3.50 to 4.00. More specifically, the value of the left side of Equation 1 may be 3.55 to 3.80.

[0081] Next, the annealed steel plate is subjected to a second cold rolling process at a reduction ratio of 9 to 14%. Secondary cold rolling can be performed to control the shape of the plate after annealing, impart roughness, and ultimately achieve the desired material quality. If the reduction ratio is too low, it may be difficult to secure the desired material quality through the second rolling process. If the reduction ratio is too high, work hardening may progress rapidly, making it difficult to secure the desired elongation and tensile strength. More specifically, the reduction ratio for the second cold rolling process can be 10 to 13%.

[0082] Next, a step of tin-plating the secondary cold-rolled steel sheet may be further included. At this time, tin (Tin) plating may be performed at a temperature range of 250 to 350°C, and the tin-plated steel sheet may be cooled to room temperature. The tin-plating conditions are not particularly limited, and tin-plating may be performed under typical conditions applicable in the same technical field.

[0083]

[0084] 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.

[0085]

[0086] Example 1

[0087] A slab having the composition shown in Table 1 below was manufactured, and after heating the slab to 1250°C, hot rolling, pickling, primary cold rolling, annealing, and secondary cold rolling were performed according to the processes listed in Table 2 below to manufacture a cold-rolled steel sheet for cans with a thickness listed in Table 3 below.

[0088] The microstructure was observed using an optical microscope after etching each specimen with nital, and the dislocation density was measured through XRD, and the area fraction of deformed ferrite and the dislocation density of the microstructure were expressed. The grain shape ratio of deformed ferrite represents the ratio of the average grain diameter in the rolling direction to the average grain diameter in the thickness direction, and could be measured through optical microscope observation.

[0089] Yield strength and elongation were measured through tensile tests at room temperature. Tensile specimens were manufactured by processing standard specimens according to ASTM standards (ASRM E-8 standard). Yield strength (YS) and elongation (El) were measured using a tensile tester (INSTRON, Model 6025). Yield ratio was calculated by dividing yield strength by tensile strength. Load value was obtained by multiplying tensile strength and thickness.

[0090] Steel grade (weight%)CMnSiPSAlNA0.00200.250.0250.00150.0150.0250.0010B0.00250.550.0250.00150.0150.0250.0010C0.01000.250.0250.00150.0150.0250.0015D0.01000.750.0250.00150.0150.0250.0015E0.01000.250.0250.00150.0150.0250.0055

[0091] No. Steel gradeHot rolling finish temperature (℃)Coiling temperature (℃)1st cold rolling reduction ratio (%)Annealing temperature (℃)Formula 1 Value2nd cold rolling reduction ratio (%)1A910600897403.60102B910610897403.66103A750610897403.01104A920450907402.76105B930620647402.73106A910610895502.72107B920610 887403.65168C910600897403.60109D910600887403.561010E910600897403 .601011C750610887402.981012D910610885502.691013E920610897403.705

[0092] No. Thickness (mm) Deformed ferrite (area %) Shape Specific dislocation density (10 15 / m 2 )10.355991.53.420.355991.63.330.220982.26.240.210981.56.150.210991.71.560.210981.57.570.450992.38.580.210981.46.290.355991.76.5100.355971.67.2110.230971.66.3120.420962.57.8130.350981.66.2

[0093] No. Tensile strength (MPa) Elongation (%) Yield ratio Load value (MPa × mm) Safety dome operation Pass / Fail Classification 1380310.92134.9 Pass invention example 12400250.91142.0 Pass invention example 23480100.93105.6 Failed comparison example 14475120.9099.8 Failed comparison example 25340330.8071.4 Failed comparison example 36465130.9297.7 Failed comparison example 4749080.95220 .5Failure comparison example 58460110.9096.6Failure comparison example 69475100.89168.6Failure comparison example 71048090.89170.4Failure comparison example 811460140.90105.8Failure comparison example 91250050.96210.0Failure comparison example 1013470100.90164.5Failure comparison example 11

[0094] As shown in Tables 1 to 4, Invention Examples 1 and 2 are cases where both the steel composition and manufacturing conditions are satisfied, and it can be confirmed that the shape ratio of the deformed ferrite is appropriately formed and the tensile strength, elongation, yield ratio, and load value are all excellent, thereby satisfying the legal requirements required for a safety dome.

[0095] On the other hand, if the steel composition is not satisfied or the manufacturing conditions are not met, it can be confirmed that the deformed ferrite is not properly formed, the dislocation density is not properly formed, and the tensile strength, elongation, yield ratio, or load value are somewhat inferior, so that the legal requirements required for a safety dome are not satisfied.

[0096]

[0097] 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.

Claims

Contains, in wt%, carbon (C): 0.0005 to 0.004%, manganese (Mn): 0.2 to 0.6%, silicon (Si): 0.05% or less (excluding 0%), phosphorus (P): 0.030% or less (excluding 0%), sulfur (S): 0.030% or less (excluding 0%), aluminum (Al): 0.01 to 0.07%, nitrogen (N): 0.0005 to 0.004%, the remainder iron (Fe) and other inevitable impurities, Contains more than 95% of deformed ferrite by area %, A cold rolled steel sheet for cans having a ratio of the average grain diameter in the rolling direction to the average grain diameter in the thickness direction of the above-mentioned deformed ferrite of 1.5 to 2.

0. In the first paragraph, The dislocation density of the above-mentioned modified ferrite is 3 × 10 15 / m 2 Inside 6 × 10 15 / m 2 Cold rolled steel sheet for cans. In the first paragraph, The above steel plate is a cold rolled steel plate for cans having a tensile strength of 350 to 450 MPa, an elongation of 15% or more, a yield ratio of 0.7 to 1, and a load value of 110 to 150 MPa×mm. In the first paragraph, A cold rolled steel sheet for cans further comprising a tin plating layer positioned on the surface of the steel sheet. A step of manufacturing a hot-rolled steel sheet by hot-rolling a slab containing, in wt%, carbon (C): 0.0005 to 0.004%, manganese (Mn): 0.2 to 0.6%, silicon (Si): 0.05% or less (excluding 0%), phosphorus (P): 0.030% or less (excluding 0%), sulfur (S): 0.030% or less (excluding 0%), aluminum (Al): 0.01 to 0.07%, nitrogen (N): 0.0005 to 0.004%, the remainder iron (Fe) and other unavoidable impurities; A first cold rolling step of manufacturing a cold rolled steel sheet by first cold rolling the above hot rolled steel sheet; A step of annealing the cold rolled steel sheet; and It includes a second cold rolling step of second cold rolling the annealed steel plate at a reduction ratio of 9 to 14%, A method for manufacturing a cold rolled steel sheet for cans satisfying the following equation 1. [Formula 1] [FDT]×[CT]×[RR1]×[AT] / 10 10 ≥3.2 (In Equation 1, [FDT] represents the finishing rolling temperature (℃) in the step of manufacturing hot-rolled steel sheets, [CT] represents the coiling temperature (℃) in the step of manufacturing hot-rolled steel sheets, [RR1] represents the reduction ratio (%) in the first cold rolling step, and [AT] represents the annealing temperature (℃) in the cold-rolled steel sheet annealing step.) In paragraph 5, A method for manufacturing a cold rolled steel sheet for cans, further comprising a step of heating the slab to 1100 to 1300°C prior to the step of manufacturing the hot rolled steel sheet. In paragraph 5, A method for manufacturing a cold rolled steel sheet for cans, further comprising a step of pickling the steel sheet before the first cold rolling step. In paragraph 5, A method for manufacturing a cold rolled steel sheet for cans, further comprising the step of plating the steel sheet with tin after the secondary cold rolling.