Non-oriented electrical steel sheet and method for manufacturing non-oriented electrical steel sheet

Abstract

A non-oriented electrical steel sheet according to one embodiment of the present invention includes 2.8~3.8 wt% of silicon (Si), 0.2~0.5 wt% of manganese (Mn), 0.5~1.5 wt% of aluminum (Al), 0.005 wt% or less of carbon (C), 0.005 wt% or less of sulfur (S), 0.015 wt% or less of phosphorus (P), 0.005 wt% or less of nitrogen (N), 0.005 wt% or less of titanium (Ti), 0.08 wt% or less of tin (Sn), 0.07 wt% or less of nickel (Ni), 0.07 wt% or less of copper (Cu), and the balance of iron (Fe) and other inevitable impurities, and has a secondary phase volume fraction, which is a particle size of 1.1 µm or more, of 50% or more, and thus can have excellent mechanical properties and magnetic properties.

Description

[TECHNICAL FIELD]

[0001] The present invention relates to a non-oriented electrical steel sheet and a method for manufacturing a non-oriented electrical steel sheet.[BACKGROUND ART]

[0002] Recently, as environmental regulations have been strengthened globally, conventional internal combustion engine vehicles are being replaced by eco-friendly vehicles, such as hybrid vehicles, electric vehicles, or hydrogen vehicles. As the demand for the eco-friendly vehicles is increasing, interest in the efficiency of an electric motor used in the eco-friendly vehicles is increasing. Therefore, a higher quality non-oriented electrical steel sheet used as a core material of the electric motor is demanded.

[0003] Generally, the quality of the non-oriented electrical steel sheet may be determined by the magnetic properties and the magnetic properties may be mainly evaluated by a magnetic flux density and an iron loss.

[0004] First, the magnetic flux density is the number of magnetic field lines induced in a material under a specific magnetic field and is generally evaluated by a value B 50 induced under a magnetic field of 5000 A / m. A higher magnetic flux density is efficient to allow a stronger magnetic field to be induced with the same amount of energy. Factors which improve the magnetic flux density include a composition of alloying constituents, a grain size, and a texture.

[0005] Next, an iron loss may indicate an energy loss caused during the process of magnetizing a material and represent an energy loss caused at a specific magnetic flux density and a frequency. The iron loss may be divided into a hysteresis loss caused by the magnetization itself and an eddy current loss formed by an eddy current induced during the magnetization.

[0006] A representative method of improving the above-described magnetic properties includes a method of increasing specific resistance by adding elements, such as silicon (Si), aluminum (Al), and manganese (Mn) and a method of reducing a thickness of a steel sheet. However, when the elements, such as silicon (Si), aluminum (Al), and manganese (Mn), are added to increase the specific resistance, the magnetic flux density may be reduced and a rollability may be degraded, which makes it difficult to reduce the thickness. Further, when the thickness of the steel sheet is reduced, the productivity may be lowered, which may cause a problem of increased production cost due to the advanced production process.[DISCLOSURE] [TECHNICAL PROBLEM]

[0007] The present invention has been devised to solve the problems as described above and an object of the present invention is to provide a non-oriented electrical steel sheet having excellent mechanical properties and magnetic properties by controlling an alloying constituent and a manufacturing process and a method for manufacturing a non-oriented electrical steel sheet.

[0008] Objects of the present invention are not limited to the above-mentioned objects, and other objects, which are not mentioned above, can be clearly understood by those skilled in the art from the following descriptions.[TECHNICAL SOLUTION]

[0009] According to an aspect of the present invention, an electrical steel sheet includes 2.8 to 3.8 wt% of silicon (Si), 0.2 to 0.5 wt% of manganese (Mn), 0.5 to 1.5 wt% of aluminum (Al), 0.005 wt% or less of carbon (C), 0.005 wt% or less of sulfur (S), 0.015 wt% or less of phosphorus (P), 0.005 wt% or less of nitrogen (N), 0.005 wt% or less of titanium (Ti), 0.08 wt% or less of tin (Sn), 0.07 wt% or less of nickel (Ni), 0.07 wt% or less of copper (Cu), and the balance of iron (Fe) and other inevitable impurities, and a volume fraction of a secondary phase having a particle size of 1.1 µm or larger is 50% or higher.

[0010] Further, the secondary phase includes nitrides and oxides and a ratio of the number of nitrides to the number of oxides excluding CaO per unit area may satisfy the following Relation 1. 0.5 ≤ number of nitrides / number of oxides excluding CaO ≤ 4.5

[0011] Further, the yield strength YS may be 380 MPa or higher.

[0012] Further, the iron loss (W 10 / 400 ) is 13.5 W / kg or lower.

[0013] According to an aspect of the present invention, a method for manufacturing an electrical steel sheet includes: a first step of preparing a steel material which is a half-finished product; a second step of hot rolling the sheet material to form a hot-rolled steel sheet; a third step of hot rolling annealing the hot-rolled steel sheet; a fourth step of cold rolling the hot-rolled steel sheet which was subject to the third step to form a cold-rolled steel sheet; and a fifth step of cold rolling annealing the cold-rolled steel sheet, and the second step includes a step of reheating the steel material at 1100 to 1180°C.

[0014] Further, in the fifth step, the heat treatment may be performed at 925 to 1100°C.

[0015] Further, the steel material includes 2.8 to 3.8 wt% of silicon (Si), 0.2 to 0.5 wt% of manganese (Mn), 0.5 to 1.5 wt% of aluminum (Al), 0.005 wt% or less of carbon (C), 0.005 wt% or less of sulfur (S), 0.015 wt% or less of phosphorus (P), 0.005 wt% or less of nitrogen (N), 0.005 wt% or less of titanium (Ti), 0.08 wt% or less of tin (Sn), 0.07 wt% or less of nickel (Ni), 0.07 wt% or less of copper (Cu), and the balance of iron (Fe) and other inevitable impurities and a volume fraction of a secondary phase having a particle size of 1.1 µm or larger may be 50% or higher.

[0016] Further, the secondary phase includes nitrides and oxides and a ratio of the number of nitrides to the number of oxides excluding CaO per unit area may satisfy the following Relation 1. 0.5 ≤ number of nitrides / number of oxides excluding cao ≤ 4.5[ADVANTAGEOUS EFFECTS]

[0017] According to the embodiment of the present invention, a high strength and high efficient electrical steel sheet having excellent mechanical properties and magnetic properties and a method for manufacturing an electrical steel sheet may be implemented.

[0018] The effects of the present invention are not limited to the aforementioned effects, and other effects, which are not mentioned above, will be apparently understood by a person skilled in the art from the recitations of the claims.[DESCRIPTION OF DRAWING]

[0019] FIG. 1 is a flowchart illustrating a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention.[BEST MODE]

[0020] Hereinafter, the present invention will be described more fully with reference to the accompanying drawings, in which embodiments of the invention are shown. However, the present invention is not restricted or limited by the following embodiments.

[0021] When a component (or an area, a layer, or a portion) is described as being "placed on", "connected to" or "coupled to" another component, it should be understood that it may be directly placed on / connected to / coupled to the other component, but there may be another component therebetween.

[0022] It should be understood that a term "include" or "have" indicates that a feature, a number, a step, an operation, a component, a part or a combination thereof described in the specification is present, but does not exclude a possibility of presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof, in advance.

[0023] In order to clearly describe the present invention, detailed descriptions of parts which are unrelated to the description or well-known related technologies which may unnecessarily obscure the gist of the present invention will be omitted. Further, when reference numerals are denoted to components of each drawing in the present specification, throughout the specification, the same or like components are denoted by the same or like reference numerals.

[0024] Further, terms or words used in the specification and the claims should not be restrictively analyzed as a general and dictionary meaning and should be analyzed as a meaning and a concept which conform to the technical spirit of the present invention based on a principle that the inventor can appropriately define a concept of a term in order to describe his / her own invention by the most method.

[0025] Unless otherwise specified, the notation "A ~ B" with respect to numerical values A and B refers to A or more and B or less. In this notation, when a unit is attached only to the numerical value B, the corresponding unit is also applied to the numerical value A.

[0026] Further, unless otherwise specified, 1 ppm is 0.0001 wt%.

[0027] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.Non-oriented electrical steel sheet

[0028] A non-oriented electrical steel sheet according to one embodiment of the present invention includes 2.8 to 3.8 wt% of silicon (Si), 0.2 to 0.5 wt% of manganese (Mn), 0.5 to 1.5 wt% of aluminum (Al), 0.005 wt% or less of carbon (C), 0.005 wt% or less of sulfur (S), 0.015 wt% or less of phosphorus (P), 0.005 wt% or less of nitrogen (N), 0.005 wt% or less of titanium (Ti), 0.08 wt% or less of tin (Sn), 0.07 wt% or less of nickel (Ni), 0.07 wt% or less of copper (Cu), and the balance of iron (Fe) and other inevitable impurities.

[0029] Further, the non-oriented electrical steel sheet according to one embodiment of the present invention may form a secondary phase by controlling the above-described alloying constituent and a manufacturing method to be described below. Here, the secondary phase may refer to inclusion or precipitates which are dissolved in the steel and then re-precipitated and may include oxides and nitrides.

[0030] To be more specific, the non-oriented electrical steel sheet according to one embodiment of the present invention has a secondary phase having a particle size of 1.1 µm or larger and a volume fraction of 50% or more, among formed secondary phases. Here, when the volume fraction of the secondary phase having a particle size of 1.1 µm or larger is less than 50%, to the contrary, a volume fraction of minute secondary phase having a size of 1.1 µm or smaller is relatively high and the minute secondary phases interrupt the movement of magnetic domain, thereby degrading the magnetic property of the electric steel sheet.

[0031] Accordingly, in the electrical steel sheet according to the embodiment of the present invention, the alloying constituent and the manufacturing method are controlled to make a volume fraction of a secondary phase having a particle size of 1.1 µm or larger 50% or higher, thereby reducing a volume fraction occupied by minute secondary phases of 1.1 µm or smaller. By doing this, deterioration of the magnetic properties of the electrical steel sheet due to the interruption of the movement of the magnetic domain due to the minute secondary phases may be suppressed.

[0032] Further, in the non-oriented electrical steel sheet according to the embodiment of the present invention, a ratio of the number of nitrides to the number of oxides excluding CaO in the secondary phase per unit area may satisfy the following Relation 1. 0.5 ≤ number of nitrides / number of oxides excluding CaO ≤ 4.5

[0033] Here, the number of nitrides may be the number of nitrides formed per unit area of the electrical steel sheet according to the embodiment of the present invention and the number of oxides which do not include CaO may mean the number of oxides excluding CaO, among oxides which are secondary phases. Further, in Relation, the nitrides and the oxides are not limited to having a particle size of 1.1 µm or larger.

[0034] If a ratio of the number of nitrides to the number of oxides excluding CaO is less than 0.5, the improvement of the mechanical properties by precipitation enhancement may be insignificant so that it may be difficult to ensure a high yield strength (YS) characteristic of the non-oriented electrical steel sheet which is a finished product. In contrast, if the ratio of the number of nitrides to the number of oxides excluding CaO exceeds 4.5, it is advantageous to ensure the strength by the precipitation enhancement, but degradation of rollability may be caused. The degradation of the rollability may hinder the improvement of the magnetic property through the thickness reduction.

[0035] Further, the non-oriented electrical steel sheet according to the embodiment of the present invention may satisfy the following Relation 2. 3.0 < log T < 4.0

[0036] In Relation 2, T= 5·[S] + 12·[Ti] + 6·[P] +5·[Sn] +15·[Ni] + 11·[Cu]. [S], [Ti], [P], [Sn], [Ni], and [Cu] represent contents of S, Ti, P, Sn, Ni, and Cu and a content unit of each alloying element is ppm.

[0037] Log T is a relation of additive elements of the alloying constituents of the non-oriented electrical steel sheet according to the embodiment of the present invention excluding silicon (Si), manganese (Mn), and aluminum (Al). Here, the additive elements may be added to improve the strength of the non-oriented electrical steel sheet and form precipitates.

[0038] To be more specific, log T may be a relation in which a weight for each grain boundary strengthening element and embrittling element is used as a coefficient and a content of additive elements to be controlled to improve the magnetic property is formulated.

[0039] That is, in T, a coefficient which is multiplied before each element is a weight assigned to each element in consideration of heat of sublimation according to a bond energy based on iron (Fe).

[0040] In the non-oriented electrical steel sheet according to the embodiment of the present invention, according to Relation 2, log T may be larger than 3 and smaller than 4 to improve the magnetic property of the non-oriented electrical steel sheet. If log T is equal to or smaller than 3, it is difficult to achieve the improvement effect of the magnetic property in accordance with the improvement of the texture by the additive element. In contrast, if log T is equal to or larger than 4, the magnetic property may be degraded due to excessive contents of impurity elements.

[0041] The non-oriented electrical steel sheet according to the embodiment of the present invention satisfies Relation 2 so that the texture may be improved and the magnetic property may be improved.

[0042] Further, the non-oriented electrical steel sheet according to the embodiment of the present invention may satisfy the following Relation 3. 0.3 < Si + Mn + Al − log T < 1.3

[0043] In Relation 3, [Si], [Mn], and [Al] represent contents of Si, Mn, and Al, respectively, and the unit of content is wt%.

[0044] In Relation 3, {[Si] + [Mn] + [Al]} - log T is a relation representing correlation of a sum of silicon (Si), manganese (Mn), and aluminum (Al) and log T which is a relation of additive elements described above. To be more specific, {[Si] + [Mn] + [Al]} - log T may mean a relation in which a relationship between silicon (Si), manganese (Mn), and aluminum (Al) and the additive elements with respect to the strength and the rollability of the non-oriented electrical steel sheet is formulated by means of contents of the elements.

[0045] In the non-oriented electrical steel sheet according to the embodiment of the present invention, according to Relation 3, {[Si] + [Mn] + [Al]} - log T may be larger than 0.3 and smaller than 1.3. If {[Si] + [Mn] + [Al]} - log T is equal to or smaller than 0.3, the effect of improving the strength of the non-oriented electrical steel sheet which is a finished product is insignificant so that it may be difficult to implement the high strength property. In contrast, if {[Si] + [Mn] + [Al]} - log T is equal to or larger than 1.3, the strength of the steel material is excessively increased to deteriorate the rollability. The thin rolling may not be possible due to the deterioration of the rollability, which may hinder the improvement of the magnetic property by means of the thinning.

[0046] The electrical steel sheet according to the embodiment of the present invention satisfies Relation 3 so that the mechanical strength may be improved and more particularly, the high strength characteristic may be ensured in accordance with improvement of the mechanical strength without excessively hindering the rollability.

[0047] Hereinafter, a role and a content of each alloying element included in the non-oriented electrical steel sheet according to one embodiment of the present invention will be described in detail.Silicon (Si)

[0048] Silicon (Si) is a primary additive element of the electrical steel sheet which increases a specific resistance of steel, to lower an eddy current loss, among iron losses, thereby improving the magnetic property. If the content of silicon is too small, an amount of increased specific resistance is not sufficient so that the iron loss improvement effect may not be sufficient. In contrast, if the content of silicon is excessive, the brittleness of the material is increased to reduce the cold rollability. Further, as the content of silicon is increased, the brittleness increases to deteriorate the cold rollability, which may cause the degradation of the productivity.

[0049] Accordingly, the non-oriented electrical steel sheet according to the embodiment of the present invention may include 2.8 to 3.8 wt% of silicon and more desirably, include 2.8 to 3.65 wt%.Manganese (Mn)

[0050] Similar to silicon (Si), manganese (Mn) is an element which increases the specific resistance to lower the iron loss, thereby improving the magnetic property of the steel. Further, manganese may be added to improve the texture which is advantageous for the magnetic property. If the content of manganese is insufficient, the effect of increasing specific resistance is reduced, which may increase a high frequency iron loss.

[0051] Further, manganese reacts with sulfur (S) to form sulfide, such as MnS. If the content of manganese is less than 0.2 wt%, minute MnS precipitate is formed to suppress the grain growth, thereby deteriorating the magnetic property. In contrast, if the content of manganese exceeds 0.5 wt%, coarse MnS precipitate is formed to reduce a magnetic flux density, thereby deteriorating the magnetic property.

[0052] Accordingly, the non-oriented electrical steel sheet according to the embodiment of the present invention may include 0.2 to 0.5 wt% of manganese and desirably, include 0.2 to 0.32 wt%.Aluminum (Al)

[0053] Aluminum (Al) increases the specific resistance, together with silicon (Si) and manganese (Mn), to reduce the iron loss, thereby improving the magnetic property. Further, aluminum may serve to reduce magnetic anisotropy, thereby reducing the magnetic deviation. If the content of aluminum is too small, minute nitride is formed to increase magnetic property deviation. In contrast, if the content of aluminum is excessive, nitride is excessively formed to deteriorate the magnetic flux density.

[0054] Accordingly, the non-oriented electrical steel sheet according to the embodiment of the present invention may include 0.5 to 1.5 wt% of aluminum and more desirably, include 0.5 to 0.98 wt%.Carbon (C)

[0055] Carbon (C) is an element which is effective to increase the strength. However, carbon is coupled to titanium (Ti) or niobium (Nb) to form carbide, such as TiC or NbC, thereby increasing the iron loss. If the content of carbon exceeds 0.005 wt%, it causes magnetic aging, deteriorating the magnetic property. Accordingly, the non-oriented electrical steel sheet according to the embodiment of the present invention may include 0.005 wt% or less of carbon.Sulfur (S)

[0056] Sulfur (S) is an impurity element which is inevitably contained during the manufacturing process. If a large amount of sulfur is added, brittleness may be caused. Further, sulfur forms the precipitate, such as MnS or CuS, to increase iron loss and suppress the grain growth. Therefore, it is desirable to add sulfur as small as possible. Accordingly, the non-oriented electrical steel sheet according to the embodiment of the present invention may include 0.005 wt% or less of sulfur.Phosphorus (P)

[0057] Phosphorus (P) is a grain boundary segregated element which contributes to improvement of texture to increase the specific resistance and lower the iron loss. However, if a large amount of phosphorus which exceeds 0.015 wt% is added, excessive grain boundary segregation is generated to cause suppression of grain growth, deterioration of the magnetic property, and degradation of cold rollability. Accordingly, the non-oriented electrical steel sheet according to the embodiment of the present invention may include 0.015 wt% or less of phosphorus.Nitrogen (N)

[0058] Nitrogen (N) is an element which contributes to the strength and corrosion resistance of steel and stabilizes austenite to improve ductility of steel. However, nitrogen of the steel is coupled to aluminum (Al) or titanium (Ti) to form precipitate, such as AlN or TiN, thereby increasing iron loss. Further, nitrogen suppresses the grain growth so that the nitrogen is desirably added as small as possible. Accordingly, the non-oriented electrical steel sheet according to the embodiment of the present invention may include 0.005 wt% or less of nitrogen (N).Titanium (Ti)

[0059] Titanium (Ti) has a high tendency to form precipitate in the steel and is coupled to carbon (C) or nitrogen (N) to form minute precipitate, such as TiC or TiN, to suppress the grain growth. As the titanium is added, the fraction of precipitate is increased and a texture which is unfavorable to magnetization is formed to deteriorate the magnetic property. Accordingly, the non-oriented electrical steel sheet according to the embodiment of the present invention may include 0.005 wt% or less of titanium.Tin (Sn)

[0060] Tin (Sn) is an element which helps to form a texture which is advantageous for a magnetic property. Further, Tin (Sn) can suppress deterioration of the iron loss caused by permeating oxygen and nitrogen on a surface in the steel. However, if the content of tin exceeds 0.08 wt%, the grain growth is suppressed, thereby deteriorating the magnetic property and degrading the rollability. Accordingly, the non-oriented electrical steel sheet according to the embodiment of the present invention may include 0.08 wt% or less of tin.Nickel (Ni)

[0061] Nickel (Ni) is an element which improves the strength and improves the texture. Further, nickel is added together with copper (Cu) to suppress precipitation of sulfur (S) as minute CuS. However, when a content of nickel exceeds 0.07 wt%, the magnetic flux density may be reduced and the production cost may be increased due to a high price. Accordingly, the non-oriented electrical steel sheet according to the embodiment of the present invention may include 0.07 wt% or less of nickel.Copper (Cu)

[0062] Copper (Cu) is an element which is resistant to oxidation or corrosion and may improve the texture. However, if a content of copper exceeds 0.07 wt%, a precipitate phase, such as CuS, is formed to hinder the grain growth and deteriorate the iron loss. Accordingly, the non-oriented electrical steel sheet according to the embodiment of the present invention may include 0.07 wt% or less of copper.

[0063] A balance other than the above-described components of steel may include Fe and inevitable impurities. The inevitable impurities are impurities mixed during a steelmaking step and a manufacturing process of a non-oriented electrical steel sheet and are well known in the art so that a detailed description thereof will be omitted.

[0064] In the embodiment of the present invention, addition of an element other than the above-described alloying constituents is not excluded, but various elements may be included without departing from the technical spirit of the present invention. When an additional element is further included, Fe which is the balance may be replaced.

[0065] The non-oriented electrical steel sheet including the alloying constituent according to one embodiment of the present invention may have excellent mechanical properties and has a yield strength (YS) of 380 MPa or higher, and a tensile strength (TS) of 480 MPa or higher. Desirably, the yield strength YS may be 392 MPa or higher.

[0066] Further, the non-oriented electrical steel sheet including the alloying constituent according to one embodiment of the present invention may have excellent magnetic properties and have an iron loss (W 10 / 400 ) of 13.5 W / kg or lower. More desirably, the iron loss (W 10 / 400 ) may be 13 W / kg or lower.

[0067] Hereinafter, a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention will be described in detail.Method for manufacturing non-oriented electrical steel sheet

[0068] Hereinafter, the method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention will be described with reference to FIG. 1.

[0069] The method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention includes a first step S1 of preparing a steel material which is a half-finished product, a second step S2 of hot rolling the sheet material to form a hot-rolled steel sheet, a third step S3 of hot rolling annealing the hot-rolled steel sheet, a fourth step S4 of cold rolling the hot-rolled steel sheet which was subject to the third step to form a cold-rolled steel sheet, and a fifth step S5 of cold rolling annealing the cold-rolled steel sheet.

[0070] Hereinafter, individual steps of the method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention will be described in detail.

[0071] The first step S1 of preparing a steel material which is a half-finished product is a step of preparing a steel material having the above-described alloying composition range to manufacture a non-oriented electrical steel sheet which is a finished product. To be more specific, the alloying constituent is designed in the above-described alloying composition range to manufacture a half-finished product. The half-finished product may be a slab, but is not limited thereto. Further, the slab may be manufactured by a known process in the art, such as a steelmaking process or a continuous casting process.

[0072] In the method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention, in the second step S2, the steel material on which the first step S1 is performed is hot-rolled to form a hot-rolled steel sheet.

[0073] To be more specific, the second step S2 may include a reheating step, a hot rolling step, and a winding step.

[0074] First, the reheating step may be performed prior to the hot rolling step to reheat the steel material for the subsequent process. To be more specific, in the reheating step, the steel material is charged into a heating furnace to uniformly heat the steel material to easily perform plastic deformation.

[0075] At this time, if the reheating temperature (slab reheating temperature, SRT) is lower than 1100°C, a rolling load is increased during the hot rolling so that the rollability may be deteriorated. In contrast, if the reheating temperature exceeds 1180°C, precipitate in the half-finished product, such as carbon (C), sulfur (S), and nitrogen (N), is resolved to form minute precipitate in a grain and a grain boundary during the cooling. This may be advantageous to improve the strength, but the grain growth is suppressed and the iron loss is deteriorated, to reduce the magnetic properties. Accordingly, in the reheating step according to the embodiment of the present invention, the reheating temperature may be 1100 to 1180°C.

[0076] Next, the hot rolling step may be performed. The hot rolling step may include rough rolling and finishing rolling processes. Here, during the rough rolling process, the steel material may be created as a rolled material with appropriate shape, thickness, and width and during the finishing rolling process, the steel material may be adjusted to have predetermined thickness and width and be rolled to have a satisfactory surface and shape at a correct finishing temperature.

[0077] At this time, the finishing temperature of the hot rolling step may be 800 to 900°C. If the finishing temperature is lower than 800°C, the rolling is performed in a secondary phase to form an irregular texture. In contrast, if the finishing temperature exceeds 900°C, there may be a problem in that the strength is sharply lowered.

[0078] Next, the winding step may be performed. At this time, a winding temperature is desirably 500 to 700°C. If the winding temperature is lower than 500°C, a size of the grain is too small so that the grain may not sufficiently grow even after annealing and if the winding temperature exceeds 700°C, minute precipitate is generated to degrade the magnetic property.

[0079] A thickness of the hot-rolled steel sheet which was subject to the second step S2 is desirably 1.6 to 2.6 mm. If the thickness of the hot-rolled steel sheet is too thin below 1.6 mm, a thickness obtained after the cold rolling is not sufficient, which may cause a shape defect when it is applied to the product. In contrast, if the thickness of the hot-rolled steel sheet exceeds 2.6 mm, a cold rolling thickness reduction ratio is increased to deteriorate the texture.

[0080] The method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may perform the third step S3 of annealing the hot-rolled steel sheet after the second step S2. To be more specific, the third step S3 is a hot rolling annealing step performed to ensure the uniformity and the cold rollability of a refined structure of the steel material on which the hot rolling is performed.

[0081] The hot rolling annealing step may be performed at a temperature at which an elongated cast structure is removed and a uniform refined structure having an average size of 50 to 200 µm is formed. To be more specific, the heat treatment may be performed at 900 to 1110°C for 30 to 180 seconds. At this time, a temperature rising rate may be 20°C / s or more and a cooling rate may be 20°C / s or more.

[0082] If the hot rolling annealing temperature is lower than 900°C, the elongated cast structure remaining after the hot rolling remains to cause the refined structure and at this time, the small grains are formed to serve as an obstacle to the cold rolling. In contrast, if the annealing temperature exceeds 1110°C, an imbalanced texture of the finished product is caused to reduce the magnetic property. Further, the hot rolling annealing time may be ranged from 30 to 180 seconds so as to form an appropriate grain size at each temperature condition.

[0083] Next, the method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may perform the fourth step S4 to cold roll the hot-rolled steel sheet which was subject to the third step S3 to form a cold-rolled steel sheet. The fourth step S4 may be a process of rolling the hot-rolled steel sheet which was subject to the third step S3 at a recrystallization temperature or lower to further reduce a thickness of the steel sheet. To be more specific, the fourth step S4 may be a process of rolling the hot-rolled steel sheet to have a thickness and a width which satisfy the specification of the finished product.

[0084] The fourth step S4 may be performed with a thickness reduction rate of 50 to 96% and the thickness of the cold-rolled steel sheet formed by the cold rolling may be 0.35 mm or smaller. Further, if necessary, for easiness of the rolling, warm rolling may be performed at the recrystallization temperature or lower by raising the sheet temperature to 100 to 200°C.

[0085] Next, the method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may perform the fifth step S5 of cold rolling annealing the cold-rolled steel sheet. The cold rolling annealing step may be performed to soften the cold-rolled steel sheet which is hardened by the recrystallization while being subject to the cold rolling step. Further, the cold rolling annealing step may be performed at a temperature at which an optimal grain size is derived by considering the reduction of the iron loss and the mechanical property. If the cold rolling annealing temperature is below a reference temperature, a grain size is minute, which may cause a hysteresis loss. In contrast, if the cold rolling annealing temperature exceeds the reference temperature, the grain size becomes coarse and the eddy current loss is increased.

[0086] Accordingly, the fifth step S5 according to the embodiment of the present invention may be performed by raising the temperature of the cold-rolled steel sheet to 925 to 1100°C and then maintaining it for 30 to 120 seconds, and then cooling the cold-rolled steel sheet. At this time, a temperature rising rate may be 10°C / s or more and a cooling rate may be 20°C / s or more.

[0087] Further, the fifth step S5 may be performed under the mixed atmosphere of nitrogen and hydrogen to suppress oxidation or nitration of a surface of the cold-rolled steel sheet. By doing this, the surface quality of the cold-rolled steel sheet may be improved.

[0088] The method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may further include a coating step after the fifth step S5. The coating step may be performed to ensure the insulation property of the non-oriented electrical steel sheet and improve a punching property and mean that an insulating film is formed on the surface of the cold-rolled steel sheet which was subject to the fifth step S5.

[0089] The non-oriented electrical steel sheet manufactured by the method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may have excellent mechanical properties and have a yield strength (YS) of 380 MPa or higher, and a tensile strength (TS) of 480 MPa or higher. Desirably, the yield strength YS may be 392 MPa or higher.

[0090] Further, the non-oriented electrical steel sheet including the alloying constituent according to one embodiment of the present invention may have excellent magnetic properties and have an iron loss (W 10 / 400 ) of 13.5 W / kg or lower. More desirably, the iron loss (W 10 / 400 ) may be 13 W / kg or lower.

[0091] By doing this, according to the method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention, a reheating temperature and a cold rolling annealing temperature are controlled to improve the magnetic property and the mechanical strength.

[0092] Further, the present invention may provide a high strength and highly efficient non-oriented steel sheet having a high mechanical strength and an excellent magnetic property and a method for manufacturing a non-oriented steel sheet.Comparative Example and Experimental Example

[0093] Hereinafter, desirable comparative examples and experimental examples are proposed for better understanding of the present invention. However, the following comparative examples and experimental examples are provided to help the understanding of the present invention, but the present invention is not limited by the following experimental examples.

[0094] In Table 1, alloying element compositions of Comparative Examples and Experimental Examples are represented. In Table 2, results of measuring a volume fraction of a secondary phase having a size of 1.1 µm or larger of Comparative Examples and Experimental Examples, whether to satisfy Relation 1, a reheating temperature, a cold rolling annealing condition, and a mechanical property and a magnetic property depending on whether to satisfy Relation 2, and whether to satisfy Relation 2 are represented.

[0095] In the Comparative Examples and the Experimental Examples, the steel material having the allying composition represented in Table 1 was used. Further, the manufacturing process of Comparative Examples and Experimental Examples of the present invention was controlled by the same condition within the range described in the above-described method for manufacturing a non-oriented electrical steel sheet according to the embodiment of the present invention with the control variable, other than the process conditions represented in Table 2.

[0096] The mechanical properties of the Comparative Examples and the Experimental Examples were measured based on International Standard ISO 6892-1. Further, the magnetic properties of Comparative Examples and Experimental Examples were measured using an Epstein band with a length of 300 mm and a width of 30 mm based on Epstein frame test based on International Standard IEC 60404-2.

[0097] In the following Table, a secondary phase volume fraction of 1.1 µm or larger refers to a volume fraction of a secondary phase having a size of 1.1 µm or larger, among secondary phases generated in the non-oriented electrical steel sheet according to the embodiment of the present invention. Further, in the following Table, an iron loss is W 10 / 400 , and means an iron loss at 400 Hz and 1.0 T and the unit thereof is W / kg. Further, in the following Table 2, O for whether to satisfy means that it satisfies Relation and X means that it does not satisfy Relation. [Table 1]ClassificationAdditive element (wt%)Additive element (ppm)SiMnAlCNSTiPSnNiCuA02.80.310.652122282512030050120A12.840.290.892010191410534511030A22.910.260.9830151818125200310650A33.120.240.91141020109722515060A43.320.321.125151818125350420880A53.340.250.919918138848013040A63.410.260.8728182521150220450900A73.520.210.7916161916773009080A83.550.220.7125221835128190800480A93.650.210.8325181412862804075 [Table 2] Classificati onComposit ionSecondary phaseReheatin g temperat ure (°C)Cold rolling annealing[Relation 2][Relation 3]Yield strengt h (Mpa)Iron loss (W / kg )Secondary phase volume fraction (%) of 1.1 µm or largerWheth er to satisfy[Relat ion 1]Wheth er to satisfyTemperat ure (°C)Duratio n (S)ValueWheth er to satisfyValueWheth er to satisfyComp. Ex. 1A046X0.25X1130975453.67O0.09X34013.9Experi. Ex. 1A155O1.33O11501000453.66O0.36O39212.9Comp. Ex. 2A238X1.35O1130925304.14X0.01X42014.5Experi. Ex. 2A352O1.52O1140980403.68O0.59O41512.7Comp. Ex. 3A442X1.06O1190925304.27X0.47O46014.8Experi. Ex. 3A560O0.58O11301000453.75O0.74O44512Comp. Ex. 4A535X0.45X12501110803.75O0.74O41013.9Comp. Ex. 5A641X2.4O1180900304.28X0.26X50314.3Experi. Ex. 4A752O0.61O1130950403.65O0.87O46811.8Comp. Ex. 6A838X2.8O1160930404.29X0.19X51014.2Experi. Ex. 5A957O0.83O1150990503.55O1.14O47511.6

[0098] Referring to Tables 1 and 2, Comparative Examples 1 and 4 are manufactured by alloying compositions A0 and A5, respectively, and satisfy the alloying constituents according to the embodiment of the present invention. In contrast, it is confirmed that Comparative Examples 1 and 4 do not satisfy 50% or more of the volume fraction of the secondary phase having a size of 1.1 µm or larger and do not satisfy [Relation 1].

[0099] At this time, it is confirmed that Comparative Examples 1 and 4 do not satisfy an iron loss (W 10 / 400 ) of 13.5 W / kg or lower which is a target magnetic characteristic value of the present invention. Further, it is confirmed that Comparative Example 1 does not satisfy a yield strength (YS) of 380 MPa or higher which is a target mechanical characteristic value of the present invention.

[0100] Continuously, referring to Tables 1 and 2, Comparative Example 2 is manufactured by an alloying composition A2 to satisfy the alloying constituent according to the embodiment of the present invention and satisfy [Relation 1], but does not satisfy 50% or more of a volume fraction of a secondary phase having a size of 1.1 µm or larger. Further, Comparative Examples 3, 5, and 6 satisfy [Relation 1], but do not satisfy 50% or more of a volume fraction of a secondary phase having a size of 1.1 µm or larger. Further, Comparative Examples 3, 5, and 6 are manufactured by alloying compositions A4, A6, and A8, respectively, and do not satisfy the alloying constituent according to the embodiment of the present invention.

[0101] At this time, it is confirmed that Comparative Examples 2, 3, 5 and 6 do not satisfy an iron loss (W 10 / 400 ) of 13.5 W / kg or lower which is a target magnetic characteristic value of the present invention.

[0102] Continuously, referring to Tables 1 and 2, Comparative Example 3 is manufactured by an alloying composition A4 and does not satisfy a content of copper (Cu) and a reheating temperature range of the present invention. Further, Comparative Example 4 is manufactured by a composition A5 to satisfy an alloying composition range of the present invention, but does not satisfy the reheating temperature range.

[0103] As a result, it is confirmed that an iron loss (W 10 / 400 ) of Comparative Example 3 is 14.8 W / kg and an iron loss (W 10 / 400 ) of Comparative Example 4 is 13.9 W / kg, which do not satisfy an iron loss (W 10 / 400 ) of 13.5 W / kg or lower which is a target magnetic characteristic value of the present invention.

[0104] Referring to Tables 1 and 2, Comparative Example 4 is manufactured by an alloying composition A5 to satisfy the alloying composition range of the present invention, but does not satisfy a cold rolling annealing temperature range of the present invention. Further, Comparative Example 5 is manufactured by an alloying composition A6, which is out of a content of copper (Cu) and is out of a cold rolling annealing temperature range.

[0105] At this time, it is confirmed that Comparative Examples 4 and 5 do not satisfy an iron loss (W 10 / 400 ) of 13.5 W / kg or lower which is a target magnetic characteristic value of the present invention.

[0106] Referring to Tables 1 and 2, Comparative Example 2 is manufactured by an alloying composition A2 to satisfy the alloying constituent of the present invention, but does not satisfy [Relation 2] which is a relation according to a content of the additive element. Further, Comparative Examples 3 and 5 are comparative examples manufactured by alloying compositions A4 and A6, respectively, and are out of a content of copper (Cu) according to the embodiment of the present invention, and do not satisfy [Relation 2]. Comparative Example 6 is a comparative example manufactured by alloying composition A8 and is out of a content of nickel (Ni) of the present invention, and does not satisfy [Relation 2].

[0107] As a result, it is confirmed that Comparative Examples 2, 3, 5 and 6 do not satisfy an iron loss (W 10 / 400 ) of 13.5 W / kg or lower which is a target magnetic characteristic value of the present invention.

[0108] Continuously, referring to Tables 1 and 2, Comparative Examples 1 and 2 are manufactured by alloying compositions A0 and A2, respectively, to satisfy the alloying constituent range according to the embodiment of the present invention, but do not satisfy [Relation 3] which is a relation according to a content of the additive element. Further, Comparative Example 5 is manufactured by an alloying composition A6, which is out of a content of copper (Cu) and does not satisfy [Relation 3]. Comparative Example 6 has an alloying composition A8 and does not satisfy a nickel (Ni) content range and [Relation 3].

[0109] At this time, it is confirmed that Comparative Examples 1, 2, 5 and 6 do not satisfy an iron loss (W 10 / 400 ) of 13.5 W / kg or lower which is a target magnetic characteristic value of the present invention.

[0110] In contrast, it is confirmed that Experimental Examples 1 to 5 according to the embodiment of the present invention have 50% or more of a volume fraction of a secondary phase having a size of 1.1 µm, which satisfy a target volume fraction of the secondary phase and satisfy [Relation 1]. Further, it is confirmed through Tables 1 and 2 that both the reheating temperature range and the cold rolling annealing temperature range are satisfied.

[0111] As a result, Experimental Examples 1 to 5 satisfy a yield strength (YS) of 380 MPa or higher which is a target mechanical property of the present invention and satisfy an iron loss (W 10 / 400 ) of 13.5 W / kg or lower which is a target magnetic property of the present invention.

[0112] By doing this, it is confirmed that the non-oriented steel sheet according to the embodiment of the present invention has a high strength and excellent magnetic property.

[0113] As described above, the embodiments of the present invention have been described and it is obvious to those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or scope of the present invention. Therefore, it should be understood that the embodiment is not restrictive, but is illustrative and thus the present invention is not limited to the above-described embodiment but may be modified within the scope of the accompanying claims and the equivalent range.

Claims

1. An electrical steel sheet comprising 2.8 to 3.8 wt% of silicon (Si), 0.2 to 0.5 wt% of manganese (Mn), 0.5 to 1.5 wt% of aluminum (Al), 0.005 wt% or less of carbon (C), 0.005 wt% or less of sulfur (S), 0.015 wt% or less of phosphorus (P), 0.005 wt% or less of nitrogen (N), 0.005 wt% or less of titanium (Ti), 0.08 wt% or less of tin (Sn), 0.07 wt% or less of nickel (Ni), 0.07 wt% or less of copper (Cu), and balance of iron (Fe) and other inevitable impurities, wherein a volume fraction of a secondary phase having a particle size of 1.1 µm or larger is 50% or higher.

2. The electrical steel sheet of claim 1, wherein the secondary phase includes nitrides and oxides and a ratio of the number of nitrides per unit area to the number of oxides excluding CaO per unit area satisfies the following Relation 1: 0.5 ≤ number of nitrides / number of oxides excluding CaO ≤ 4.5 .

3. The electrical steel sheet of claim 1, wherein a yield strength (YS) is 380 MPa or higher.

4. The electrical steel sheet of claim 1, wherein an iron loss (W10 / 400) is 13.5 W / kg or lower.

5. A method for manufacturing an electrical steel sheet, comprising: a first step of preparing a steel material which is a half-finished product; a second step of hot rolling the sheet material to form a hot-rolled steel sheet; a third step of hot rolling annealing the hot-rolled steel sheet; a fourth step of cold rolling the hot-rolled steel sheet which was subject to the third step to form a cold-rolled steel sheet; and a fifth step of cold rolling annealing the cold-rolled steel sheet, wherein the second step includes a step of reheating the steel material at 1100 to 1180°C.

6. The method for manufacturing an electrical steel sheet of claim 5, wherein in the fifth step, heat treatment is performed at 925 to 1100°C.

7. The method for manufacturing an electrical steel sheet of claim 5, wherein the steel material includes 2.8 to 3.8 wt% of silicon (Si), 0.2 to 0.5 wt% of manganese (Mn), 0.5 to 1.5 wt% of aluminum (Al), 0.005 wt% or less of carbon (C), 0.005 wt% or less of sulfur (S), 0.015 wt% or less of phosphorus (P), 0.005 wt% or less of nitrogen (N), 0.005 wt% or less of titanium (Ti), 0.08 wt% or less of tin (Sn), 0.07 wt% or less of nickel (Ni), 0.07 wt% or less of copper (Cu), and balance of iron (Fe) and other inevitable impurities, and a volume fraction of a secondary phase having a particle size of 1.1 µm or larger is 50% or higher.

8. The method for manufacturing an electrical steel sheet of claim 7, wherein the secondary phase includes nitrides and oxides and a ratio of the number of nitrides per unit area to the number of oxides excluding CaO per unit area satisfies the following Relation 1: 0.5 ≤ number of nitrides / number of oxides excluding CaO ≤ 4.5 .

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