Steel sheet and method for manufacturing same

Abstract

The present invention relates to a steel sheet suitable for various uses including use in automobile parts and, more specifically, to a steel sheet and a method for manufacturing same.

Description

Steel plate and method for manufacturing the same

[0001] The present invention relates to a steel plate suitable for various purposes including automobile parts, and more specifically, to a steel plate and a method for manufacturing the same.

[0002] To address the global climate crisis, automakers are demanding steelmakers supply automotive steel with reduced CO2 emissions, aiming to achieve carbon neutrality by 2050. For this reason, steelmakers are currently developing automotive steel with reduced CO2 emissions through the recycling of scrap iron, utilizing existing blast furnace-converter furnace or electric arc furnace steelmaking processes.

[0003] When using scrap iron as a raw material, it is difficult to remove residual elements (tramp elements) such as Cu and Ni contained in the scrap iron during refining, so they end up being incorporated into the steel after refining. These residual elements have the problem of lowering the physical properties of the steel or deteriorating the surface quality. Therefore, until now, high-quality thin plate products, such as automotive steel plates, have been manufactured using molten iron as the main raw material and using a general blast furnace-converter process to greatly reduce the C and N in the steel while extremely controlling the content of residual elements.

[0004] Meanwhile, a technology for manufacturing automobile steel sheets with excellent processability from electric furnace steel containing residual elements using an electric furnace steelmaking method was proposed as follows.

[0005] Patent Documents 1 and 2 present techniques for manufacturing cold-rolled steel sheets with excellent workability. Specifically, the steel sheets disclose cold-rolled steel sheets with excellent cold workability despite containing a large amount of residual elements. However, these techniques do not consider the goal of improving the thermal plating adhesion of the steel sheets, nor do they address the means for achieving this goal.

[0006] In this way, although a technology for manufacturing automotive steel sheets containing residual elements has been proposed, automotive steel sheets with improved processability and plating adhesion despite containing residual elements have not yet been developed.

[0007] (Patent Document 1) Japanese Patent Publication No. 1995-118795

[0008] (Patent Document 2) Japanese Patent Publication No. 1998-025541

[0009] One aspect of the present invention is to provide a steel sheet having improved processability and plating adhesion while containing residual elements in manufacturing automotive steel sheets by recycling iron scrap, and a method for manufacturing the same.

[0010] The objectives of the present invention are not limited to the above-described content. Those skilled in the art will have no difficulty understanding the additional objectives of the present invention from the overall description of the present invention.

[0011] According to one aspect of the present invention, a steel sheet is provided, which includes, in wt%, carbon (C): more than 0% to 0.0700%, silicon (Si): more than 0% to 0.800%, manganese (Mn): more than 0% to 1.000%, aluminum (Al): more than 0% to 0.500%, phosphorus (P): 0% to 0.080%, sulfur (S): 0% to 0.0500%, nitrogen (N): 0% to 0.0300%, nickel (Ni): more than 0% to 1.000%, chromium (Cr): more than 0% to 1.000%, molybdenum (Mo): more than 0% to 1.000%, tin (Sn): more than 0% to 0.5000%, and at least one selected from the following groups (i) to (vi), the remainder being Fe and other unavoidable impurities.

[0012] (i) Copper (Cu): 0~1.000%

[0013] (ii) At least one of titanium (Ti): 0 to 0.500%, niobium (Nb): 0 to 0.500%, vanadium (V): 0 to 0.500%, and boron (B): 0 to 0.0200%.

[0014] (iii) Magnesium (Mg): 0~0.050%, calcium (Ca): 0~0.050%, and rare earth elements (REM) excluding yttrium (Y): 0~0.050%, at least one of these.

[0015] (iv) Tungsten (W): 0~0.50% and zirconium (Zr): 0~0.50%, at least one of these

[0016] (v) At least one of antimony (Sb): 0~0.5000% and cobalt (Co): 0~0.5000%

[0017] (vi) At least one of yttrium (Y): 0 to 0.200% and hafnium (Hf): 0 to 0.200%

[0018] In one embodiment of the present invention, when the average content (weight %) of (Cr+Ni+Mo+Sn) in the surface layer is A and the average content (weight %) of (Cr+Ni+Mo+Sn) in the center layer is B, a steel plate satisfying A / B of 0.15 to 30.00 can be provided.

[0019] In one embodiment of the present invention, a steel sheet having a microstructure of a single phase of ferrite can be provided, and the average crystal grain size of the ferrite can be 6 to 50 μm.

[0020] In one embodiment of the present invention, a steel sheet can be provided in which a value (I / II) obtained by dividing the average grain size (I) of a cold-rolled steel sheet by the average grain size (II) of a hot-rolled steel sheet satisfies 0.60 to 0.95.

[0021] The steel plate of the present invention has high strength and excellent processability, and can also have excellent plating adhesion when subjected to a subsequent plating process.

[0022] In one embodiment of the present invention, the steel plate may have a product of tensile strength (TS) and elongation (El) (TS×El) of 4.0 to 30.0 GPa·%, and a product of Lankford value (r-value) and elongation (r-value×El) of 20 to 200%.

[0023] In one embodiment of the present invention, the steel plate may include a plating layer formed on at least one surface, and the plating layer may have a powdering peeling width of less than 7 mm.

[0024] According to another aspect of the present invention, a method for manufacturing a steel sheet is provided, comprising the steps of: preparing a steel slab; heating the steel slab in a temperature range of 900 to 1300°C; finish-rolling the heated steel slab in an austenite region above the Ar3 transformation point or in a ferrite region below the Ar3 transformation point to obtain a hot-rolled steel sheet; coiling the hot-rolled steel sheet at 700°C or higher; cooling the coiled hot-rolled steel sheet to a temperature range of 250 to 350°C at a rate of 10.0°C / min or lower; cold-rolling the hot-rolled steel sheet after the cooling at a cold reduction ratio of 50% or higher to obtain a cold-rolled steel sheet; and annealing the cold-rolled steel sheet at 600°C or higher for 10 seconds or longer.

[0025] In one embodiment of the present invention, the steel slab may have the above-described alloy composition.

[0026] In one embodiment of the present invention, the steel slab may be obtained by continuously casting molten steel obtained through a steelmaking process in an electric furnace.

[0027] In one embodiment of the present invention, the annealing treatment step can be performed by heating the cold-rolled steel sheet obtained by cold rolling to the annealing temperature at a heating rate of 2 to 60°C / s.

[0028] In one embodiment of the present invention, a step of plating the cold rolled steel sheet after the annealing treatment may be further included, and the plating treatment may be hot dip plating or electroplating.

[0029] In one embodiment of the present invention, the molten zinc plating may be performed at a temperature range of 440 to 520°C, and an alloying heat treatment may be additionally performed after the molten zinc plating.

[0030] According to another aspect of the present invention, a steel sheet manufactured by the above-described manufacturing method can satisfy a value of 0.60 to 0.95 obtained by dividing the average grain size (I) of the cold-rolled steel sheet after the annealing treatment by the average grain size (II) of the hot-rolled steel sheet.

[0031] According to the present invention, it is possible to provide an automotive steel sheet having improved plating adhesion as well as processability despite containing residual elements.

[0032] The steel plate of the present invention is manufactured by recycling iron scrap, and has the advantage of excellent CO2 reduction effect when applied as a material for automobile bodies, etc.

[0033] The various advantageous and beneficial effects of the present invention are not limited to the above-described contents, and will be more easily understood in the course of explaining specific embodiments of the present invention.

[0034] The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the invention. As used herein, the singular forms also include the plural forms, unless the context clearly dictates otherwise.

[0035] The term "comprising" as used in the specification means specifying a particular characteristic, region, integer, step, operation, element and / or component, but does not exclude the presence or addition of other particular characteristics, regions, integers, steps, operations, elements, components and / or groups.

[0036] 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.

[0037] Hereinafter, a steel sheet according to one aspect of the present invention, particularly a steel sheet with excellent workability and plating adhesion, will be described in detail. It should be noted that, unless otherwise specified, the content of each element in the present invention refers to weight percent. Furthermore, unless otherwise specified, the ratio of crystals or structures is based on area.

[0038] Hereinafter, when explaining steel plates, it is clarified that cold rolled steel plates are meant unless otherwise specified.

[0039] A steel sheet according to one aspect of the present invention may include, in wt%, carbon (C): more than 0% to 0.0700%, silicon (Si): more than 0% to 0.800%, manganese (Mn): more than 0% to 1.000%, aluminum (Al): more than 0% to 0.500%, phosphorus (P): 0% to 0.080%, sulfur (S): 0% to 0.0500%, nitrogen (N): 0% to 0.0300%, nickel (Ni): more than 0% to 1.000%, chromium (Cr): more than 0% to 1.000%, molybdenum (Mo): more than 0% to 1.000%, and tin (Sn): more than 0% to 0.5000%.

[0040] Below, the reason for limiting the alloy composition of the steel plate provided in the present invention as described above is explained in detail.

[0041] Carbon (C): 0% to 0.0700%

[0042] Carbon (C) is an element that is effective in securing the strength of steel.

[0043] In one embodiment of the present invention, if the C content exceeds 0.0700%, it is difficult to secure the elongation and r-value value targeted by the present invention. Therefore, the C content may be 0.0700% or less. In another embodiment of the present invention, the C content may be 0.0650% or less, or 0.0600% or less.

[0044] Meanwhile, C is an essential element in steel manufacturing, and its content is greater than 0%. However, in one embodiment of the present invention, if the content is less than 0.0003%, the effect of reducing C is hardly obtained, and rather, it causes an increase in steel manufacturing cost, which is not preferable. Therefore, the C may be included in an amount of 0.0003% or more. In another embodiment of the present invention, the C may be included in an amount of 0.0010% or more, or 0.0015% or more.

[0045] Silicon (Si): 0% to 0.800%

[0046] Silicon (Si) is an element that enhances strength through solid solution strengthening, and is useful for strengthening ferrite and uniforming its structure, thereby improving workability. Furthermore, Si is an element necessary for deoxidation during steelmaking.

[0047] In one embodiment of the present invention, if the Si content exceeds 0.800%, there is a problem of causing plating defects such as underplating during plating and hindering the weldability of the steel sheet. Therefore, the Si content may be 0.800% or less. In another embodiment of the present invention, the Si content may be 0.700% or less.

[0048] Meanwhile, in one embodiment of the present invention, Si may be included in an amount exceeding 0%, and the content may be 0.001% or more in consideration of manufacturing costs.

[0049] Manganese (Mn): 0% to 1.000%

[0050] Manganese (Mn) is a useful element for simultaneously improving the strength and ductility of steel.

[0051] In one embodiment of the present invention, if the content of Mn exceeds 1.000%, processability deteriorates, which is not preferable. In another embodiment of the present invention, the Mn may be 0.900% or less, or 0.400% or less.

[0052] Meanwhile, in one embodiment of the present invention, Mn may be included in an amount exceeding 0%, and the content may be 0.001% or more in consideration of manufacturing costs.

[0053] Aluminum (Al): 0% to 0.500%

[0054] Aluminum (Al) is an element that combines with oxygen (O) in steel and acts as a deoxidizer. Similarly to Si, it is an element that strengthens ferrite, homogenizes the structure, and improves workability.

[0055] In one embodiment of the present invention, if the Al content exceeds 0.500%, there is a problem that the processability is reduced. Therefore, the Al may be contained at 0.500% or less. In another embodiment of the present invention, the Al may be contained at 0.400% or less.

[0056] Meanwhile, in one embodiment of the present invention, Al may be included in an amount exceeding 0%. However, since there is a problem of increased manufacturing costs in controlling the Al content to less than 0.001%, the content may be 0.001% or more in consideration of this.

[0057] Phosphorus (P): 0.080% or less

[0058] Phosphorus (P) is an element added to improve the strength of steel. In one embodiment of the present invention, if the P content exceeds 0.080%, there is a problem of hindering the workability of the steel and causing brittleness. Therefore, the P may be included in an amount of 0.080% or less. In another embodiment of the present invention, the P may be included in an amount of 0.070% or less.

[0059] Meanwhile, in one embodiment of the present invention, the P may be 0%, but the content may be limited to 0.001% or more in consideration of manufacturing cost.

[0060] Sulfur (S): 0.0500% or less

[0061] Sulfur (S) is an element that is inevitably added during the steel manufacturing process, and it combines with manganese (Mn) in the steel to form MnS inclusions, thereby inhibiting the ductility of the steel. Therefore, in one embodiment of the present invention, the S content may be limited to 0.0500% or less. In another embodiment of the present invention, S may be included at 0.0400% or less.

[0062] Meanwhile, in one embodiment of the present invention, the S content may be 0%, but since it may inevitably be contained in the steel, the content may exceed 0%. In one embodiment of the present invention, there is a problem that the manufacturing cost increases significantly in order to control the S content to less than 0.0010%. Therefore, the S content may be contained at 0.0010% or more.

[0063] Nitrogen (N): 0.0300% or less

[0064] Nitrogen (N) is an element that is inevitably added during the steel manufacturing process, and is an element that causes cracks in slabs by forming nitrides during the continuous casting process. Accordingly, in one embodiment of the present invention, N may be included at 0.0300% or less.

[0065] Meanwhile, in one embodiment of the present invention, the N content may be 0%, but since it may inevitably be contained in the steel, the content may exceed 0%. In one embodiment of the present invention, there is a problem that manufacturing costs significantly increase in order to control the N content to less than 0.0010%. Therefore, the N content may be contained at 0.0010% or more.

[0066] Nickel (Ni): 0% to 1.000%

[0067] Nickel (Ni) is an element that stabilizes austenite and inhibits corrosion. Furthermore, Ni is a useful element for suppressing hydrogen-delayed fracture by concentrating on the surface of steel plates and preventing the intrusion of hydrogen into the steel.

[0068] In one embodiment of the present invention, if the content of Ni is excessive, processability may be poor, and as it is an expensive element, there is a concern that the manufacturing cost may increase. Therefore, the content may be limited to 1.000% or less. In another embodiment of the present invention, the Ni may be included at 0.900% or less.

[0069] Meanwhile, in one embodiment of the present invention, Ni may be included in an amount exceeding 0%, and may be included in an amount of 0.001% or more in order to sufficiently obtain the effect of Ni.

[0070] Chromium (Cr): 0% to 1.000%

[0071] Chromium (Cr) is an element that suppresses the decomposition of austenite and stabilizes austenite during alloying treatment of manufactured steel plates.

[0072] In one embodiment of the present invention, since excessive Cr content deteriorates processability, the Cr content may be limited to 1.000% or less in consideration of this. In another embodiment of the present invention, the Cr content may be included at 0.900% or less.

[0073] Meanwhile, in one embodiment of the present invention, Cr may be included in an amount exceeding 0%, and may be included in an amount of 0.001% or more in order to sufficiently obtain the effect of Cr.

[0074] Molybdenum (Mo): 0% to 1.000%

[0075] Molybdenum (Mo), similar to the Cr described above, is an element that suppresses the decomposition of austenite and stabilizes austenite during alloying treatment of manufactured steel plates.

[0076] In one embodiment of the present invention, since excessive Mo content reduces processability, the content may be limited to 1.000% or less in consideration of this. In another embodiment of the present invention, the Mo content may be included at 0.900% or less.

[0077] Meanwhile, in one embodiment of the present invention, Mo may be included in an amount exceeding 0%, and may be included in an amount of 0.001% or more in order to sufficiently obtain the effect of Mo.

[0078] Tin (Sn): 0% to 0.5000%

[0079] Tin (Sn) is an element that improves the plating wettability and adhesion of steel. In one embodiment of the present invention, if the tin content in the steel exceeds 0.5000%, there is a problem that the steel becomes brittle and cracks occur during hot or cold working. According to another embodiment of the present invention, the Sn may be included in an amount of 0.4000% or less.

[0080] Meanwhile, in one embodiment of the present invention, Sn may be included in an amount exceeding 0%, and in order to sufficiently obtain the effect by Sn, it may be included in an amount of 0.0005% or more.

[0081] In addition to the alloy composition described above, the steel sheet of the present invention may further include one or more elements selected from groups (i) to (vi) described below. Since all of the elements described below may be optionally added, it is noted that the content thereof is 0%. Meanwhile, the elements of groups (i) to (vi) may be referred to as residual elements.

[0082] (i) Copper (Cu): 0~1.000%

[0083] (ii) At least one of titanium (Ti): 0 to 0.500%, niobium (Nb): 0 to 0.500%, vanadium (V): 0 to 0.500%, and boron (B): 0 to 0.0200%.

[0084] (iii) Magnesium (Mg): 0~0.050%, calcium (Ca): 0~0.050%, and rare earth elements (REM) excluding yttrium (Y): 0~0.050%

[0085] (iv) Tungsten (W): 0~0.50% and zirconium (Zr): 0~0.50%, at least one of these

[0086] (v) At least one of antimony (Sb): 0~0.5000% and cobalt (Co): 0~0.5000%

[0087] (vi) At least one of yttrium (Y): 0 to 0.200% and hafnium (Hf): 0 to 0.200%

[0088] (i) Copper (Cu): 0~1.000%

[0089] Copper (Cu) is an element that stabilizes austenite and inhibits corrosion. Furthermore, Cu is a useful element for suppressing hydrogen-delayed fracture by concentrating on the surface of steel plates and preventing the intrusion of hydrogen into the steel.

[0090] In one embodiment of the present invention, since excessive Cu content results in poor processability, the content may be limited to 1.000% or less. In another embodiment of the present invention, the Cu content may be included at 0.900% or less.

[0091] Meanwhile, in one embodiment of the present invention, since Cu can achieve the purpose of the present invention without any problems even if it is not intentionally added, the content may be 0%. However, in order to obtain the aforementioned effect when adding Cu, the content may be 0.001% or more.

[0092] (ii) At least one of titanium (Ti): 0 to 0.500%, niobium (Nb): 0 to 0.500%, vanadium (V): 0 to 0.500%, and boron (B): 0 to 0.0200%.

[0093] Titanium (Ti), niobium (Nb), and vanadium (V) are elements that form precipitates in steel, and the strength and impact toughness of the steel can be improved by the formation of the precipitates. In particular, the Ti, Nb, and V can prevent the deterioration of workability caused by the dissolved carbon and dissolved nitrogen in the steel by precipitating the dissolved carbon and dissolved nitrogen in the form of carbides, nitrides, etc.

[0094] In one embodiment of the present invention, when the above elements are additionally added, each can be added at 0.001% or more, thereby obtaining the above-described effects. However, if the content of each element exceeds 0.500%, the effect of addition becomes saturated and the manufacturing cost increases, so the upper limit of each element can be limited to 0.500%. According to another embodiment of the present invention, when adding the above elements, each can be included at 0.400% or less.

[0095] Boron (B) is an element that improves the hardenability of steel, thereby increasing its strength, and inhibits nucleation at grain boundaries.

[0096] In one embodiment of the present invention, if the content of B exceeds 0.0200%, there is a concern that the deep drawability of the steel may deteriorate. Therefore, when adding B, the content may be limited to 0.0200% or less. According to another embodiment, the B may be included in an amount of 0.0100% or less. Meanwhile, in one embodiment of the present invention, when additionally adding B, in order to obtain the effect, it may be included in an amount of 0.0001% or more. According to another embodiment, when adding B, it may be included in an amount of 0.0005% or more or 0.0010% or more.

[0097] (iii) Magnesium (Mg): 0~0.050%, calcium (Ca): 0~0.050%, and rare earth elements (REM) excluding yttrium (Y): 0~0.050%

[0098] Rare earth elements (REMs), excluding magnesium (Mg), calcium (Ca), and yttrium (Y), are elements that improve the ductility of steel by spheroidizing sulfides in the steel. In one embodiment of the present invention, when adding the aforementioned elements, if the content of each element exceeds 0.050%, not only will the aforementioned effect be saturated, but the manufacturing cost will also increase. Therefore, the content may be limited to 0.050% or less.

[0099] In general, rare earth elements (REM) refer to a total of 17 metallic elements, including scandium (Sc), yttrium (Y), lanthanum (La), and cerium (Ce). However, according to one embodiment of the present invention, the content of yttrium (Y) is separately limited below, so in one embodiment of the present invention, REM refers to 16 elements excluding Y.

[0100] (iv) Tungsten (W): 0~0.50% and zirconium (Zr): 0~0.50%, at least one of these

[0101] Tungsten (W) and zirconium (Zr) are elements that enhance the hardenability of steel, thereby increasing its strength. In one embodiment of the present invention, if W and Zr are present in excess, not only will the aforementioned effects be saturated, but manufacturing costs will also increase. Therefore, when adding W and Zr, their contents may be limited to 0.50% or less, respectively.

[0102] (v) At least one of antimony (Sb): 0~0.5000% and cobalt (Co): 0~0.5000%

[0103] Antimony (Sb) and cobalt (Co) are elements that improve the plating wettability and plating adhesion of steel. In one embodiment of the present invention, when the content of the elements is added, if the content exceeds 0.5000%, the brittleness of the steel increases, which causes cracks during hot working or cold working, and therefore the content of each element may be limited to 0.5000% or less. According to another embodiment of the present invention, when these elements are added, they may be included at 0.4000% or less. Meanwhile, in order to sufficiently obtain the desired effect by adding these elements, they may be included at 0.0005% or more.

[0104] (vi) At least one of yttrium (Y): 0 to 0.200% and hafnium (Hf): 0 to 0.200%

[0105] Yttrium (Y) and hafnium (Hf) are elements that improve the corrosion resistance of steel. In one embodiment of the present invention, when the content of the elements is added, if the content exceeds 0.200%, there is a concern that the ductility of the steel may be reduced, so the content of each element may be limited to 0.200% or less.

[0106] In one embodiment of the present invention, the steel sheet may contain iron and other unavoidable impurities in addition to the aforementioned components. However, since unintended impurities may inevitably be mixed in from raw materials or the surrounding environment during the typical manufacturing process, they cannot be completely excluded. Since these impurities are readily apparent to anyone skilled in the art, not all of them are specifically mentioned herein. Furthermore, the addition of additional effective components other than the aforementioned components is not completely excluded.

[0107] According to one embodiment of the present invention, the content of some residual elements contained at a specific point based on the thickness direction of the steel plate can be controlled as follows, thereby improving the plating adhesion of the steel plate.

[0108] Specifically, in one embodiment of the present invention, when the average content (weight %) of (Cr+Ni+Mo+Sn) in the surface layer of the steel plate is A and the average content (weight %) of (Cr+Ni+Mo+Sn) in the center of the steel plate is B, A / B can satisfy 0.15 to 30.00.

[0109] In one embodiment of the present invention, A / B is significant in that it is utilized as an indicator of the plating adhesion of a steel plate. If the value of A / B is less than 0.15 or exceeds 30.00, there is a problem in that certain residual elements contained in the steel are not uniformly distributed.

[0110] Here, the center refers to the point t / 2 in the thickness direction. In addition, the surface layer refers to the inflection point, which is the point where the concentration of Cr, Ni, Mo, and Sn changes (or changes rapidly) when measuring the concentration gradient from the surface in the thickness direction.

[0111] In one embodiment of the present invention, the inflection point may refer to a point corresponding to 99% of the (Cr+Ni+Mo+Sn) content of the center in the concentration gradient measurement value when the (Cr+Ni+Mo+Sn) content of the polar surface is greater than the (Cr+Ni+Mo+Sn) content of the center, and may refer to a point corresponding to 1% of the (Cr+Ni+Mo+Sn) content of the center in the concentration gradient measurement value when the (Cr+Ni+Mo+Sn) content of the polar surface is less than the (Cr+Ni+Mo+Sn) content of the center. As a non-limiting example, the concentrations of the above-mentioned elements may be measured using FE-SEM or glow discharge spectroscopy (GDS).

[0112] As an example, when measuring the concentration of (Cr+Ni+Mo+Sn) in the thickness direction of the steel plate, the (Cr+Ni+Mo+Sn) content at the polar surface has the highest value, and the value tends to decrease linearly as it goes from the polar surface to the center.

[0113] As another example, when measuring the concentration of (Cr+Ni+Mo+Sn) in the thickness direction of the steel plate, the (Cr+Ni+Mo+Sn) content at the pole surface has the lowest value, and the value tends to increase linearly as it goes from the pole surface to the center.

[0114] Meanwhile, it is well known in the technical field of the present invention that steel sheets, i.e., cold-rolled steel sheets, are obtained through a series of rolling processes. That is, as will be described in detail later, the cold-rolled steel sheet according to the present invention is obtained through a cold rolling (and subsequent annealing heat treatment) process on a hot-rolled steel sheet obtained through a hot-rolling and coiling process.

[0115] For such hot-rolled steel sheets and cold-rolled steel sheets, in one embodiment of the present invention, it is preferable that the ratio of the average grain size of the hot-rolled steel sheet and the average grain size of the cold-rolled steel sheet obtained by cold-rolling and annealing the hot-rolled steel sheet satisfies the following.

[0116] Specifically, in one embodiment of the present invention, the value (I / II) obtained by dividing the average grain size (I) of the cold-rolled steel sheet by the average grain size (II) of the hot-rolled steel sheet can satisfy 0.60 to 0.95.

[0117] In this way, according to the present invention, by controlling the grain size of a hot-rolled steel sheet obtained by hot rolling, the grain size of a cold-rolled steel sheet obtained by subsequent cold rolling and annealing heat treatment can be secured, thereby obtaining excellent workability as well as strength.

[0118] If the value of the above I / II is less than 0.60, there is a problem that the rigidity increases significantly due to the grain size of the hot-rolled steel sheet becoming excessively fine, whereas if the value exceeds 0.95, the grain size becomes coarse, making it impossible to secure strength and workability.

[0119] In one embodiment of the present invention, the microstructure of the steel plate may be a single phase of ferrite.

[0120] That is, if the microstructure of the steel plate includes structures other than ferrite, such as pearlite, or bainite or martensite formed at low temperatures, the intended workability cannot be secured. However, it is not intended to exclude even extremely small amounts of impurity structures that are inevitably included during the process, and they are naturally included within the scope of the present invention.

[0121] In one embodiment of the present invention, the average grain size of the ferrite may be 6 to 50 μm. If the average grain size of the ferrite is less than 6 μm, there is a risk that the steel will become brittle due to increased rigidity, whereas if the size exceeds 50 μm, there is a risk that it will be detrimental to securing strength through grain refinement.

[0122] Meanwhile, it should be noted that the grain size of the hot-rolled steel sheet and cold-rolled steel sheet mentioned above refers to the grain size of ferrite.

[0123] A steel plate according to one embodiment of the present invention not only has high strength but also has excellent processability.

[0124] Specifically, according to one embodiment of the present invention, the steel plate can satisfy a product of tensile strength (TS) and elongation (El) (TS×El) of 4.0 to 30.0 GPa·%, and also a product of Lankford value (r-value) and elongation (r-value×El) of 20 to 200%.

[0125] A steel sheet according to one embodiment of the present invention may have a plating layer on at least one surface.

[0126] In one embodiment of the present invention, the plating layer may be a zinc-based plating layer, and the zinc-based plating layer is a plating layer containing zinc (Zn) as a main component, and a composition of the plating layer commonly applied in the relevant technical field may be applied in the same manner. In this case, the zinc-based plating layer may also include a zinc-based plating layer alloyed through alloying treatment.

[0127] In this way, a steel sheet having a zinc-based plating layer on at least one side of the steel sheet is a zinc-based plating steel sheet, and may be a galvanized steel sheet (GI), a galvanealed steel sheet (GA), an electrogalvanized steel sheet (EG), an electrogalvanized steel sheet, or the like.

[0128] In one embodiment of the present invention, the steel sheet having a zinc-based plating layer formed on at least one surface may be a steel sheet according to one embodiment of the present invention, and it is to be noted that the above-described description can be equally applied to the steel sheet.

[0129] Meanwhile, a steel sheet (cold rolled steel sheet) according to one embodiment of the present invention may have a concentration gradient of specific elements, for example, residual elements Cr, Ni, Mo, and Sn, in the thickness direction from the surface. When a plating layer (for example, a zinc-based plating layer) is formed on at least one surface of such a cold rolled steel sheet, the residual elements may further diffuse into the plating layer due to the influence of the temperature during plating or the temperature during alloying treatment. Accordingly, the concentration gradient of the residual elements in the plating steel sheet may be realized from the interface between the base material, which is the steel sheet, and the plating layer in the thickness direction of the base material, but may also be realized from an alloy layer formed at the interface between the base material and the plating layer.

[0130] That is, the residual elements may have a concentration gradient, previously represented by A / B, due to the difference in diffusion speed of the residual elements that diffuse toward the surface of the steel sheet during the process of manufacturing the cold-rolled steel sheet. This characteristic of the cold-rolled steel sheet also appears in the plated steel sheet.

[0131] A plated steel sheet according to one embodiment of the present invention has excellent powdering properties of the plating layer. Specifically, the plating layer may have a powdering peeling width of less than 7 mm.

[0132] Hereinafter, a method for manufacturing a steel plate (cold rolled steel plate) and a plated steel plate according to another aspect of the present invention will be described in detail.

[0133] First, the steel sheet according to the present invention, i.e., the cold-rolled steel sheet, can be obtained by going through a series of processes, for example, [steel slab heating - hot rolling - coiling - cooling - cold rolling - annealing]. Each process step is described in detail below, and it is to be noted that the following manufacturing process is an example for manufacturing the cold-rolled steel sheet of the present invention and the subsequent plated steel sheet.

[0134] According to one embodiment of the present invention, steel slabs or ingots can be manufactured through an electric furnace or a new blast furnace-converter process, and the raw materials used in the electric furnace or blast furnace-converter process include pig iron together with iron scrap. Here, pig iron refers to molten iron obtained from the blast furnace-converter process, or its cold material (Corrugate) or HBI (Hot Briquette Iron).

[0135] In the case of electric furnaces, desulfurization can be performed through ladle refining after the electric furnace discharge, and desulfurization and subsequent vacuum degassing can be performed. Furthermore, steel obtained from an electric furnace can be adjusted to achieve the desired final alloy composition by adding alloying elements during degassing. Common vacuum degassing methods include the RH and DH methods, but oxygen injection into the degassing tank can also be used. One such method is the oxygen injection method using a top blowing lance.

[0136] [Heating of steel slabs]

[0137] After preparing the steel slab, it can be heated. At this time, the steel slab may be a steel ingot. In one embodiment of the present invention, the steel slab may have the alloy composition described above, and thus, the alloy composition of the steel slab is replaced with the above-described content.

[0138] In one embodiment of the present invention, the heating temperature of the prepared steel slab or ingot may be in the range of 900 to 1300°C. If the heating temperature exceeds 1300°C, the steel may reach its melting point and melt, whereas if the temperature is lower than 900°C, the rolling load may increase during subsequent hot rolling, which may lower the stability of the hot rolling. In another embodiment of the present invention, the heating may be performed at 1160°C or lower.

[0139] [Hot rolling]

[0140] The above heated steel slab or ingot can be hot rolled to obtain a hot rolled steel sheet.

[0141] In one embodiment of the present invention, the finishing temperature during hot rolling can be either an austenite temperature above the Ar3 transformation point or a ferrite temperature below the Ar3 transformation point. However, if the finishing temperature is too low, the rolling load during hot rolling increases, so the lower limit temperature can be limited to 750°C or higher.

[0142] [Winding]

[0143] The hot-rolled steel sheet obtained by the above hot rolling can be wound into a coil shape.

[0144] In one embodiment of the present invention, the coiling process may be performed at a temperature of 700°C or higher. If the coiling temperature is lower than 700°C, the intended grain size of the hot-rolled steel sheet obtained after coiling cannot be secured. In another embodiment of the present invention, the coiling process may be performed at a temperature of 720°C or higher.

[0145] Meanwhile, there is no particular limitation on the upper limit of the above coiling temperature, but considering that scale may be excessively formed on the surface of the hot-rolled coil, the temperature may be limited to 800°C or lower.

[0146] The present invention can achieve a grain relationship of a hot-rolled steel sheet and a subsequent cold-rolled steel sheet, i.e., a range of I / II, by performing coiling at the above-described temperature.

[0147] [cooling]

[0148] The above-mentioned hot-rolled steel sheet can be cooled while uncoiling.

[0149] In one embodiment of the present invention, post-coiling cooling can be performed at a cooling rate of 10.0°C / min or less to a temperature range of 250 to 350°C. By performing cooling at such a relatively slow cooling rate, uniform crystal grains within the microstructure can be secured.

[0150] In one embodiment of the present invention, if the cooling rate exceeds 10.0°C / min during cooling, there is a possibility that the crystal grains will become coarser. Meanwhile, there is no particular limitation on the lower limit of the cooling rate during cooling. However, if the cooling rate is excessively low, it may put a strain on the cooling equipment and may also cause the crystal grains to become coarser. Therefore, taking this into consideration, the cooling rate may be limited to 0.2°C / min or more.

[0151] In one embodiment of the present invention, if the cooling end temperature is less than 250°C during cooling, there is a concern that the cooling time may be excessive and productivity may decrease, while if the cooling end temperature exceeds 350°C, there is a problem of causing a load during subsequent cold rolling.

[0152] [Cold rolling]

[0153] A cold rolled steel sheet can be obtained by cold rolling the above cooled uncoiled hot rolled steel sheet.

[0154] In one embodiment of the present invention, cold rolling may be performed at a cold reduction ratio of 50% or more. If the cold reduction ratio is less than 50%, it may be difficult to secure the target thickness and shape correction of the steel sheet may be difficult. According to one embodiment of the present invention, there is no particular limitation on the upper limit of the cold reduction ratio during cold rolling, but if it is too excessive, cold rolling load may be induced, and therefore, taking this into consideration, it may be limited to 95% or less.

[0155] [Sodun]

[0156] The cold rolled steel sheet manufactured above can be annealed and heat treated.

[0157] In one embodiment of the present invention, the annealing heat treatment may be performed in a general continuous annealing furnace, and may be performed under the condition that the cold-rolled steel sheet is heated to 600°C or higher and then heat-treated for 10 seconds or longer. If the temperature is lower than 600°C or the annealing heat treatment time is shorter than 10 seconds, recrystallization may not sufficiently occur during the annealing process, which may lead to the generation of unrecrystallized structures. In this case, the workability of the steel sheet may be poor.

[0158] According to one embodiment of the present invention, the upper limits of temperature and time for the annealing heat treatment are not particularly limited. However, considering the risk of equipment troubles due to high-temperature annealing and the inferiority of powdering properties, the upper limits may be set to 960°C and 15 minutes, respectively.

[0159] Meanwhile, when heating the cold-rolled steel sheet to a temperature for annealing, heating can be performed at a constant heating rate. As an example, the heating rate can be 2 to 60°C / s. If the heating rate is too slow or too fast, the grain characteristics intended for the present invention may not be secured.

[0160] The cold rolled steel sheet manufactured through the above-described series of processes can have the strength and workability targeted in the present invention.

[0161] In particular, the cold-rolled steel sheet according to one embodiment of the present invention may have a product of tensile strength (TS) and elongation (El) (TS×El) of 4.0 to 30.0 GPa·%, and a product of Lankford value (r-value) and elongation (r-value×El) of 20 to 200%.

[0162] Meanwhile, according to one aspect of the present invention, a plated steel sheet can be obtained by plating a steel sheet, i.e., a cold-rolled steel sheet. The cold-rolled steel sheet may be a cold-rolled steel sheet manufactured through a series of processes according to one embodiment of the present invention. Accordingly, the plated steel sheet may have a plated layer on at least one surface of the aforementioned cold-rolled steel sheet.

[0163] In one embodiment of the present invention, the plating process may be a hot dip plating process or an electroplating process, and each plating process may be performed under conditions commonly practiced in the relevant technical field.

[0164] As an example, the above-mentioned hot-dip galvanizing can be performed by immersing the cold-rolled steel sheet, which has undergone the above-mentioned annealing heat treatment, in a hot-dip galvanizing bath containing zinc as the main component. The conditions for the hot-dip galvanizing treatment can be based on typical conditions, and are not specifically limited in this specification. However, as one implementation example, the GI hot-dip galvanizing can be performed under typical conditions in the temperature range of 440 to 520°C.

[0165] In addition, according to one embodiment of the present invention, an alloyed hot-dip galvanized steel sheet (GA) can be obtained by selectively performing alloying heat treatment on a galvanized steel sheet having a zinc-based plating layer formed thereon. The alloying heat treatment can also be performed under typical conditions and is not specifically limited thereto. However, as an example, the alloying heat treatment can be performed at a temperature range of 500 to 560°C.

[0166] In addition, as another example, the electroplating can be performed by placing a base steel sheet (cold rolled steel sheet) on the cathode of a vertical plating cell type electroplating simulator, and then circulating a plating solution containing zinc (Zn) to form a zinc-based plating layer on at least one surface of the base steel sheet (cold rolled steel sheet).

[0167] Hereinafter, the present invention will be described in more detail through examples. However, it should be noted that the following examples are intended solely to illustrate the present invention and are not intended to limit the scope of the invention. This is because the scope of the invention is determined by the matters set forth in the patent claims and matters reasonably inferred therefrom.

[0168] (Example)

[0169] Steel slabs having the alloy compositions shown in Table 1 below were prepared. Hot-rolled steel sheets were manufactured from the steel slabs through the [reheating - hot rolling - coiling - cooling] process according to the respective conditions shown in Table 2 below. Thereafter, cold-rolled steel sheets were obtained by performing a series of subsequent processes (cold rolling - annealing) shown in Table 2 below for each hot-rolled steel sheet. At this time, the cooling process after coiling was performed in the temperature range of 250 to 350°C.

[0170] The above steel slab was obtained through the following process. First, iron scrap mixed with molten iron from a conventional blast furnace was introduced into an electric furnace to obtain molten steel. This molten steel was then transferred to a ladle and vacuum degassing was performed in an RH degassing furnace (0.1 torr). At the same time, alloying components were added to produce molten steel having the desired composition. Thereafter, the molten steel was manufactured into a slab by continuous casting.

[0171] The microstructure and mechanical properties of the manufactured steel sheets were measured and evaluated, and all results are presented in Table 3 below. The phase types and properties of the microstructure were measured and evaluated for the cold-rolled steel sheets, and the grain size was measured for both the hot-rolled steel sheets and the cold-rolled steel sheets. The cold-rolled steel sheets in this case correspond to the cold-rolled steel sheets after annealing.

[0172] First, the microstructure of each cold-rolled steel sheet was examined by taking specimens at t / 4 in the thickness direction, polishing them, and then observing the cross-sections of the polished specimens by nital etching them using a scanning electron microscope (SEM). After the nital etching, the structure without irregularities on the surface of the specimens was determined to be ferrite, and the structure with a spherical or lamellar structure was determined to be cementite. In addition, in order to confirm the grain size characteristics of the ferrite, the average grain size was measured using an optical microscope for each specimen taken at t / 4 in the thickness direction of the hot-rolled and cold-rolled steel sheets and the cross-sections of which were nital etched.

[0173] In addition, a tensile test was conducted to evaluate the physical properties of each cold-rolled steel sheet. The tensile test was evaluated using specimens collected according to the JIS No. 5 standard at a 90-degree angle to the rolling direction of the rolled plate, and the product of tensile strength (TS) and elongation (El) (TS × El) was calculated. In addition, the Lankford value (r-value) for the same specimen was measured using the three-point method after 15% tensile prestrain, and the average values ​​in the rolling direction (L direction), the direction perpendicular to the rolling direction (C direction), and the direction at 45 degrees to the rolling direction (D direction) were calculated using the following formula.

[0174] r-value = (r L + 2r D + r C ) / 4

[0175] Meanwhile, in order to confirm the content (wt%) of specific elements (Cr, Ni, Mo, and Sn) at specific points in the thickness direction of the cold-rolled steel sheet, the cross-section of each specimen was removed with FIB and then measured by component analysis using FE-SEM. At this time, according to the definition of the surface layer, the content within the surface layer and the point at the center (t / 2) in the thickness direction were measured, and each was repeated 30 times at random points. After removing the maximum and minimum values ​​of the analyzed values ​​for each element, the content was calculated as the average value.

[0176] In addition, to evaluate powdering properties, each cold-rolled steel sheet was plated in a hot-dip galvanizing bath at 440 to 480°C, and a 45-degree V-bend test was performed on the obtained plated steel sheet. At this time, the evaluation surface was placed on the inner side of the bend, and after bending at 60 degrees using a mold with a curvature radius of 1 mm at the tip, tape was attached to the inner side, and the tape was removed, and the powdering properties of the plating layer peeled off together with the tape were evaluated on a full score of 5. The specific evaluation criteria were set as follows, and a score of 2 or higher was evaluated as passing.

[0177] Peeling width less than 2 mm: 5 points

[0178] Peeling width 2 mm or more but less than 3 mm: 4 points

[0179] Peeling width 3 mm or more but less than 5 mm: 3 points

[0180] Peeling width 5 mm or more but less than 7 mm: 2 points

[0181] Peeling width 7mm or more: 1 point

[0182] Steel alloy composition (weight %) CSiMnPSAlNCrNiMoSnTiOther A0.00080.0040.0550.0030.00160.0230.00130.8100.6500.8200.3300.014Hf 0.004B0.00150.0030.0940.0040.00600.0260.00370.6400.8700.4400.2000.035Nb 0.056Y 0.005C0.00270.0140.1630.0120.00700.0310.00540.4800.3700.4700.1100.053W 0.02D0.00390.0230.2040.0250.01300.0340.00630.3600.2700.3400.0400.055Mg 0.003E0.01560.0260.2530.0370.01600.0360.00880.2900.2200.2300.0500.076Cu 0.26Zr 0.02F0.02830.0270.2920.0480.02200.0350.00960.1600.1300.1300.0100.096B 0.0024Sb 0.002G0.05020.0340.3720.0620.03400.0310.01650.0020.0020.0010.0010.145Ca 0.005REM 0.001XA0.07440.0230.2350.0250.02100.0300.00450.1900.2400.1800.0230.037 - 550.2400.2100.2100.0240.054-XC0.00220.0231.0680.0180.03300.0320.00630.2100.2500.1600.0220.055-XD0.00230.0250. 2260.0200.03200.5330.00680.2300.1800.1900.0170.064-XE0.00210.0240.2230.0250.02700.0320.03430.2000.2000.1700.0 200.296 - XF0.00240.0280.2090.0240.02300.0350.00571.1100.2200.2400.0220.051 -00510.2401.0400.2600.0210.047-Xh0.00230.0260.2770.0280.02400.0260.00460.3000.2501.1900.0240.041-XI0.00210.0240.2400.0240.02300.0280.00450.3200.2400.1600.5210.039- In Table 1, REM means REM excluding Y.

[0183]

[0184] Steel heating temperature (℃) Finish rolling temperature (℃) Coiling temperature (℃) Cooling after coiling (℃ / min) Cold rolling reduction rate (%) Heating rate (℃ / s) Annealing temperature (℃) Annealing time (s) I / II specimen No.A11608807500.67647930400.971B11608807500.67640820400.582A12809308200.576469306000.943B10507804000.57638750200.5 74A11608807500.37656880400.735B11608807500.57634880400.766B13109507500.67627880400.837B8806204600.67625880400.778B 12709508200.87633880400.629B11608806800.77634880400.8910B11608807500.84733880400.5311B11608807501.17636570400.3612 B11608807500.97634970400.9713B11608807500.8762688050.3514B11608807500.8762788010000.9815B11608807000.17619860400.9 716B116088070010.57623860400.5417B11608807000.8761880400.9818B11608807500.67663880400.5119C10508807500.77624860400 .8320D10508807501.17616920400.9021E11608807201.3767900400.6322F12508807802.5766900400.7123G11608807805.7762880400. 7424XA11608807501.07616880400.3825XB11608807500.77621880400.5326XC11608807500.67624880400.4527XD11608807500.876238 80400.4328XE11608807500.97625880400.5429XF11608807500.67627880400.563067617880400.4632XI11608807500.97623880400.4733 In Table 2, I / II refers to the value (I / II) obtained by dividing the average grain size (I) of cold-rolled steel sheets by the average grain size (II) of hot-rolled steel sheets.

[0185]

[0186] Specimen No. A / B cold rolled steel sheet average grain size (㎛) TS × El (GPa%) r-value × El (%) powdering property 10.5 147 28 194 4 20.50 24 199 0 43 31.24 54 34 21 1 1 4 0.48 53.7 18 4 5 0.16 36 26 19 9 5 6 0.37 34 24 15 8 5 7 0.38 17 3.8 18 4 8 0.50 9 3.5 16 39 32.20 33 22 15 2 1 1 0 0.47 14 3.31 6 31 1 0.56 15 5.6 13 31 2 0.13 8 3.41 4 1 1 3 0.39 38 24 18 13 1 4 0.12 10 3.5 15 1 1 5 0.27 34 23 15 8 31 6 0.44 43261752170.38123.4163180.4336241392190.35133.6153200.8627271305212.592218984228.5519165942317.2146.93532429.274.32232516.052.61422625.493.71622723.863.51532820.182.81332921.752.61433022.8113.61723124.3133.41223218.5102.91523316.8122.6182 votes In 3, A / B means the value (A / B) obtained by dividing the average content (weight%, A) of (Cr+Ni+Mo+Sn) in the surface layer by the average content (weight%, B) of (Cr+Ni+Mo+Sn) in the center.

[0187] As shown in Tables 1 to 3 above, in the case of specimens that satisfy both the alloy composition and manufacturing conditions proposed in the present invention, the microstructure was formed to have the intended crystal grains, and both strength and processability were excellent.

[0188] On the other hand, in the case of specimens that deviate from one or more of the alloy composition and manufacturing conditions of the present invention, the crystal grains of the microstructure are not formed as intended, or specific elements are distributed unevenly, resulting in at least one or more properties such as strength, processability, and plating adhesion being inferior.

[0189] In this way, the present invention has a technical significance in that it can achieve both excellent processability and plating adhesion by controlling the crystal grain size characteristics and the content ratio of specific elements in each thickness direction.

Claims

1. Containing, in wt%, carbon (C): more than 0% to 0.0700%, silicon (Si): more than 0% to 0.800%, manganese (Mn): more than 0% to 1.000%, aluminum (Al): more than 0% to 0.500%, phosphorus (P): 0 to 0.080%, sulfur (S): 0 to 0.0500%, nitrogen (N): 0 to 0.0300%, nickel (Ni): more than 0% to 1.000%, chromium (Cr): more than 0% to 1.000%, molybdenum (Mo): more than 0% to 1.000%, tin (Sn): more than 0% to 0.5000%, and at least one selected from the following groups (i) to (vi), the remainder being Fe and other unavoidable impurities, (i) Copper (Cu): 0~1.000%, (ii) At least one of titanium (Ti): 0 to 0.500%, niobium (Nb): 0 to 0.500%, vanadium (V): 0 to 0.500%, and boron (B): 0 to 0.0200%; (iii) Magnesium (Mg): 0 to 0.050%, Calcium (Ca): 0 to 0.050%, and Rare Earth Elements (REM) excluding Yttrium (Y): 0 to 0.050%, at least one of these; (iv) Tungsten (W): 0 to 0.50% and zirconium (Zr): 0 to 0.50%, at least one of these; (v) At least one of antimony (Sb): 0 to 0.5000% and cobalt (Co): 0 to 0.5000%. (vi) At least one of yttrium (Y): 0 to 0.200% and hafnium (Hf): 0 to 0.200%; When the average content (weight%) of (Cr+Ni+Mo+Sn) in the surface layer is A and the average content (weight%) of (Cr+Ni+Mo+Sn) in the center is B, A / B satisfies 0.15 to 30.00, The above center refers to a point t / 2 in the thickness direction, and the above surface refers to an inflection point where the concentration of Cr, Ni, Mo, and Sn changes when the concentration gradient is measured in the thickness direction from the surface, and the inflection point refers to a point corresponding to 99% of the (Cr+Ni+Mo+Sn) content of the center in the concentration gradient measurement value when the (Cr+Ni+Mo+Sn) content of the polar surface is greater than the (Cr+Ni+Mo+Sn) content of the center, or refers to a point corresponding to 1% of the (Cr+Ni+Mo+Sn) content of the center in the concentration gradient measurement value when the (Cr+Ni+Mo+Sn) content of the polar surface is smaller than the (Cr+Ni+Mo+Sn) content of the center. Steel plate with an average grain size of 6 to 50 ㎛.

2. In paragraph 1, The above steel plate is a cold rolled steel plate manufactured by cold rolling and annealing heat treatment of a hot rolled steel plate obtained by hot rolling. A steel sheet characterized in that the value (I / II) obtained by dividing the average grain size (I) of the cold rolled steel sheet by the average grain size (II) of the hot rolled steel sheet satisfies 0.60 to 0.

95.

3. In paragraph 1, The above steel plate is a steel plate whose microstructure is a single phase ferrite.

4. In paragraph 1, The above steel plate is a steel plate whose product of tensile strength (TS) and elongation (El) (TS × El) is 4 to 30 GPa·%.

5. In paragraph 1, The above steel plate is a steel plate having a product of the Lankford value (r-value) and the elongation (r-value × El) of 20 to 200%.

6. In paragraph 1, The above steel plate is a steel plate including a plating layer formed on at least one surface.

7. In paragraph 6, A steel plate having a powdering peeling width of the above plating layer of less than 7 mm.

8. A step for preparing a steel slab including, by weight%, carbon (C): more than 0% but not more than 0.0700%, silicon (Si): more than 0% but not more than 0.800%, manganese (Mn): more than 0% but not more than 1.000%, aluminum (Al): more than 0% but not more than 0.500%, phosphorus (P): 0% but not more than 0.080%, sulfur (S): 0% but not more than 0.0500%, nitrogen (N): 0% but not more than 0.0300%, nickel (Ni): more than 0% but not more than 1.000%, chromium (Cr): more than 0% but not more than 1.000%, molybdenum (Mo): more than 0% but not more than 1.000%, tin (Sn): more than 0% but not more than 0.5000%, and at least one selected from the following groups (i) to (vi), the remainder being Fe and other unavoidable impurities; (i) Copper (Cu): 0~1.000%, (ii) At least one of titanium (Ti): 0 to 0.500%, niobium (Nb): 0 to 0.500%, vanadium (V): 0 to 0.500%, and boron (B): 0 to 0.0200%; (iii) Magnesium (Mg): 0 to 0.050%, Calcium (Ca): 0 to 0.050%, and Rare Earth Elements (REM) excluding Yttrium (Y): 0 to 0.050%, at least one of these; (iv) Tungsten (W): 0 to 0.50% and zirconium (Zr): 0 to 0.50%, at least one of these; (v) Antimony (Sb): 0~0.5000% and cobalt (Co): 0~0.5000%, at least one of these; (vi) At least one of yttrium (Y): 0 to 0.200% and hafnium (Hf): 0 to 0.200%; A step of heating the above steel slab in a temperature range of 900 to 1300℃; A step of obtaining a hot rolled steel sheet by finish rolling the above heated steel slab in the austenite range above the Ar3 transformation point or in the ferrite range below the Ar3 transformation point; A step of coiling the above hot-rolled steel plate at 700℃ or higher; A step of cooling the above-mentioned coiled hot-rolled steel sheet to a temperature range of 250 to 350°C at a rate of 10.0°C / min or less; A step of obtaining a cold rolled steel sheet by cold rolling the hot rolled steel sheet after the cooling at a cold reduction ratio of 50% or more; and A method for manufacturing a steel plate, comprising a step of annealing the cold rolled steel plate at 600°C or higher for 10 seconds or longer.

9. In paragraph 8, A method for manufacturing a steel sheet, characterized in that the value (I / II) obtained by dividing the average grain size (I) of the cold rolled steel sheet after the annealing treatment by the average grain size (II) of the hot rolled steel sheet after the coiling satisfies 0.60 to 0.

95.

10. In paragraph 8, The above steel slab is a method for manufacturing a steel plate by continuously casting molten steel obtained through a steelmaking process in an electric furnace.

11. In paragraph 8, The above annealing process step is: A method for manufacturing a steel plate, comprising heating the cold rolled steel plate to an annealing temperature at a heating rate of 2 to 60°C / s.

12. In paragraph 8, It further includes a step of plating the cold rolled steel sheet after the above annealing treatment. The above plating treatment is a method for manufacturing a steel plate that is a hot-dip plating or electroplating process.

13. In paragraph 12, The above-mentioned method for manufacturing a steel sheet is a method for manufacturing a steel sheet by performing a molten zinc plating process at a temperature range of 440 to 520°C.

14. In paragraph 13, A method for manufacturing a steel sheet further comprising a step of performing alloying heat treatment after the above molten zinc plating.

15. In a steel plate manufactured by any one of the manufacturing methods of Articles 8 to 14, A steel sheet having a value of 0.60 to 0.95, obtained by dividing the average grain size (I) of the cold rolled steel sheet after the above annealing treatment by the average grain size (II) of the hot rolled steel sheet.

16. In paragraph 15, A steel plate comprising a plating layer formed on at least one surface of the steel plate.

17. In paragraph 16, A steel plate having a powdering peeling width of the above plating layer of less than 7 mm.