Non-oriented electrical steel sheet and manufacturing method therefor

Abstract

A method for manufacturing a non-oriented electrical steel sheet, according to one embodiment of the present invention, comprises the steps of: (a) preparing steel that is a half-finished product comprising 2.5-3.8 wt% of silicon (Si), 1.45 wt% or more of nickel (Ni), 0.05 wt% or less of aluminum (Al) and the balance of iron (Fe) and other inevitable impurities; (b) hot rolling the steel, thereby forming a hot-rolled steel sheet; (c) cold rolling the hot-rolled steel sheet, thereby forming a cold-rolled steel sheet; and (d) cold roll annealing the cold-rolled steel sheet, wherein step (d) comprises the steps of: (d-1) increasing the temperature from room temperature to a first temperature at which austenite phase is stable, and then maintaining same for a first set time; (d-2) lowering the temperature to a second temperature at which a two-phase region where austenite phase and ferrite phase coexist is stable, and then maintaining same for a second set time; and (d-3) lowering the temperature to room temperature, and the phase transformation heat treatment in the cold rolling annealing step can improve the texture such that an orientation favorable to magnetism is developed, and can enhance magnetic properties.

Description

Non-oriented electrical steel sheet and manufacturing method thereof

[0001] The present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same, and more particularly, to a non-oriented electrical steel sheet and a method for manufacturing the same, in which the grain structure is improved to develop an orientation advantageous to magnetism through phase transformation heat treatment in a cold rolling annealing step, and magnetic properties are improved.

[0002] Non-oriented electrical steel is a material used as a core material for motors, generators, and small transformers, and is mainly used to convert electrical energy into kinetic energy, change voltage, or for other energy conversions.

[0003] These non-oriented electrical steel sheets are used as key materials for electric vehicle components, and demand is increasing further as interest in eco-friendly products grows due to recent global environmental issues.

[0004] The required properties of this non-oriented electrical steel are low core loss and high magnetic flux density. Conventionally, methods to lower the core loss of electrical steel have involved increasing the steel's resistivity or thinning the material. Increasing the addition of silicon (Si), aluminum (Al), manganese (Mn), and other elements in the steel increases the steel's resistivity and reduces core loss to a certain extent. However, this reduces the magnetic flux density and reduces rollability, making thinning difficult.

[0005] The magnetic flux density of electrical steel is determined by the fraction of iron (Fe) atoms in the steel and the arrangement of the steel grains. The magnetic anisotropy of iron atoms causes the magnetic field of iron single atoms to be <100> The aggregate tissue is easily magnetized, but <110> Collective organization and <111> Collective tissue is difficult to magnetize.

[0006] Therefore, the magnetization direction of the atomic arrangement within the steel is <100> When made parallel to the axis, the steel has a high magnetic flux density even at low magnetic fields. Conversely, high flux density can be achieved at low fields by either orienting the axis that is conducive to magnetization or avoiding the axis that is particularly difficult to magnetize.

[0007] In addition, research has been conducted on methods to control the grain structure by adjusting the composition or heat treatment temperature conditions to manufacture non-oriented electrical steel sheets with excellent magnetic properties.

[0008] Prior art document 1 discloses a heat treatment method based on a phase transformation from an austenite phase to a ferrite phase, but has the problem that secondary rolling for surface modification and secondary heat treatment for removing residual stress must be performed afterwards.

[0009] Prior art document 2 discloses a method for heat treatment in a ferrite single-phase region without undergoing phase transformation, but it has the problem of being difficult to apply in mass production because it requires high-temperature conditions of 1200°C and long-term heat treatment of at least 12 hours.

[0010] As described above, conventional processes and changes to component composition alone have minimal effects on improving properties through improvements in microstructure and texture. Furthermore, it is even more difficult to achieve significant improvements in texture, which significantly impacts magnetic properties, through additive elements or improvements in certain process conditions alone. Therefore, the development of alternative control methods and processes capable of enhancing magnetic properties is urgently needed.

[0011] [Prior Art Literature]

[0012] [Patent Document]

[0013] Prior Document 1: Korean Patent Publication No. 10-2009-0079056

[0014] Prior Document 2: Korean Patent No. 10-2376026

[0015] The present invention has been devised to solve the above problems, and the object of the present invention is to provide a non-oriented electrical steel sheet and a method for manufacturing the same, which improves the texture and magnetic properties by developing a magnetic orientation advantageous to magnetism through phase transformation heat treatment in the cold rolling annealing stage.

[0016] The tasks of the present invention are not limited to the tasks mentioned above, and other tasks not mentioned will be clearly understood by those skilled in the art from the description below.

[0017] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention comprises the steps of (a) preparing a steel material which is a semi-finished product containing 2.5 to 3.8 wt% of silicon (Si), 1.45 wt% or more of nickel (Ni), 0.05 wt% or less of aluminum (Al), the remainder being iron (Fe) and other unavoidable impurities, (b) hot-rolling the steel material to form a hot-rolled steel sheet, (c) cold-rolling the hot-rolled steel sheet to form a cold-rolled steel sheet, and (d) cold-rolling and annealing the cold-rolled steel sheet, wherein step (d) comprises (d-1) heating from room temperature to a first temperature at which an austenite phase is stable and then maintaining the temperature for a first set time, (d-2) cooling to a second temperature at which a two-phase region in which an austenite phase and a ferrite phase coexist is stable and then maintaining the temperature for a second set time, and (d-3) cooling to room temperature.

[0018] The above two-phase region may have a ratio of the peak of the {200} aggregate structure to the peak of the {112} aggregate structure, {200} / {112}, of 1.3 or more.

[0019] The above second temperature may be 930 to 970°C.

[0020] The above second setting time may be 5 seconds or more.

[0021] Between the above steps (b) and (c), a step of hot-rolling and annealing the hot-rolled steel sheet may be further included.

[0022] The above steel may further contain carbon (C) 0.005 wt% or less, sulfur (S) 0.005 wt% or less, nitrogen (N) 0.005 wt% or less, titanium (Ti) 0.005 wt% or less, and phosphorus (P) 0.015 wt%.

[0023] The above steel can satisfy the following equation 1.

[0024] [Formula 1]

[0025] [Ni] ≥ 2.52[Si] - 5.3

[0026] ([Ni] and [Si] represent the weight percent of Ni and Si, respectively.)

[0027] According to one embodiment of the present invention, a non-oriented electrical steel sheet is manufactured by hot-rolling a steel material containing 2.5 to 3.8 wt% of silicon (Si), 1.45 wt% or more of nickel (Ni), 0.05 wt% or less of aluminum (Al), the remainder being iron (Fe) and other unavoidable impurities, and then cold-rolling the steel material to form a cold-rolled steel sheet, and cold-rolling the cold-rolled steel sheet to manufacture a final product, wherein, during the cold-rolling annealing, the steel is heated from room temperature to a first temperature at which an austenite phase is stable, maintained for a first set time, and then cooled to a second temperature at which a two-phase region in which an austenite phase and a ferrite phase coexist is stable, maintained for a second set time, and then cooled to room temperature.

[0028] The above two-phase region may have a ratio of the peak of the {200} aggregate structure to the peak of the {112} aggregate structure, {200} / {112}, of 1.3 or more.

[0029] The above second temperature may be 930 to 970°C.

[0030] The above second setting time may be 5 seconds or more.

[0031] The above steel can satisfy the following equation 1.

[0032] [Formula 1]

[0033] [Ni] ≥ 2.52[Si] - 5.3

[0034] ([Ni] and [Si] represent the weight percent of Ni and Si, respectively.)

[0035] The above steel may further contain carbon (C) 0.005 wt% or less, sulfur (S) 0.005 wt% or less, nitrogen (N) 0.005 wt% or less, titanium (Ti) 0.005 wt% or less, and phosphorus (P) 0.015 wt%.

[0036] The sum of the {100} / ND fraction and the {110} / ND fraction of the above final product may be 46.0% or more.

[0037] The {100} / ND fraction of the above final product may be 28.8% or more, and the {112} / ND fraction may be 23.3% or less.

[0038] According to one embodiment of the present invention, a non-oriented electrical steel sheet contains 2.5 to 3.8 wt% of silicon (Si), 1.45 wt% or more of nickel (Ni), 0.05 wt% or less of aluminum (Al), the remainder being iron (Fe) and other unavoidable impurities, but has a magnetic flux density (B 50 ) value is 1.68 T or more, and the iron loss (W 10 / 400 ) value may be less than or equal to 11.88 W / kg.

[0039] The content of silicon and nickel in the non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following equation 1.

[0040] [Formula 1]

[0041] [Ni] ≥ 2.52[Si] - 5.3

[0042] ([Ni] and [Si] represent the weight percent of Ni and Si, respectively.)

[0043] According to one embodiment of the present invention, a non-oriented electrical steel sheet may have a sum of a {100} / ND fraction and a {110} / ND fraction of 46.0% or more.

[0044] According to one embodiment of the present invention, a non-oriented electrical steel sheet may have a {100} / ND fraction of 28.8% or more and a {112} / ND fraction of 23.3% or less.

[0045] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include carbon (C) 0.005 wt% or less, sulfur (S) 0.005 wt% or less, nitrogen (N) 0.005 wt% or less, titanium (Ti) 0.005 wt% or less, and phosphorus (P) 0.015 wt% or less.

[0046] A non-oriented electrical steel sheet and a manufacturing method thereof according to one embodiment of the present invention can improve the texture and magnetic properties by developing a {100} / ND orientation, which is advantageous to magnetism, through phase transformation heat treatment in a cold rolling annealing step.

[0047] FIG. 1 is a flowchart illustrating a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0048] FIG. 2 is a flowchart specifically illustrating a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0049] FIG. 3 is a drawing illustrating a cold rolling annealing step in a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0050] Hereinafter, with reference to the attached drawings, preferred embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be implemented in various different forms and is not limited or restricted by the following examples.

[0051] Terms such as "include" or "have" should be understood to specify the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but not to exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0052] In order to clearly explain the present invention, a detailed description of a part that is irrelevant to the description or a related known technology that may unnecessarily obscure the gist of the present invention has been omitted, and when adding reference signs to components of each drawing in this specification, the same or similar reference signs are attached to the same or similar components throughout the specification.

[0053] In addition, terms and words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0054] Unless otherwise specified, the notation 'A ~ B' for numerical values ​​A and B means 'A or more and B or less'. In such notation, if a unit is attached only to numerical value B, the unit shall be applied to numerical value A as well.

[0055] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0056]

[0057] Non-oriented electrical steel sheet

[0058] A non-oriented electrical steel sheet according to one embodiment of the present invention contains 2.5 to 3.8 wt% of silicon (Si), 1.45 wt% or more of nickel (Ni), 0.05 wt% or less of aluminum (Al), and the remainder being iron (Fe) and other unavoidable impurities. More specifically, a steel material having the above-described silicon (Si), nickel (Ni), and aluminum (Al) contents is hot-rolled and then cold-rolled to form a cold-rolled steel sheet, and the cold-rolled steel sheet is cold-rolled and annealed to manufacture a non-oriented electrical steel sheet as a final product. Therefore, it can be understood that the alloy components included in the semi-finished steel material are included within the same range in the cold-rolled steel sheet and the non-oriented electrical steel sheet as a final product.

[0059] According to one embodiment of the present invention, a non-oriented electrical steel sheet is manufactured by a method of heating, during cold rolling annealing, from room temperature to a first temperature at which an austenite phase is stable, maintaining the temperature for a first set time, cooling the steel sheet to a second temperature at which a two-phase region in which an austenite phase and a ferrite phase coexist is stable, maintaining the temperature for a second set time, and then cooling the steel sheet to room temperature.

[0060] In this way, the non-oriented electrical steel sheet according to one embodiment of the present invention can improve the aggregate structure to develop a magnetic orientation advantageous to magnetism through phase transformation heat treatment during cold rolling annealing, and can improve mechanical and magnetic properties.

[0061] That is, during cold rolling annealing, phase transformation heat treatment can be performed in the order of ferrite phase (α), austenite phase (γ), and ferrite phase (α). In particular, when the phase transformation from the austenite phase to the ferrite phase proceeds, nucleation can be induced in the temperature range where the {100} / ND orientation, which is advantageous for magnetism, is most developed, and this nucleation can be grown to improve the texture.

[0062] According to one embodiment of the present invention, the steel can satisfy the alloy composition range of the following formula 1.

[0063] [Formula 1]

[0064] [Ni] ≥ 2.52[Si] - 5.3

[0065] ([Ni] and [Si] represent the weight percent of Ni and Si, respectively.)

[0066] As described above, the present invention is based on the phase transformation heat treatment from ferrite phase (α), austenite phase (γ), to ferrite phase (α) during cold rolling annealing, and maximizes the effect of improving the texture by utilizing the characteristic that the orientation that is preferentially formed is formed differently depending on the temperature conditions when the phase transformation from austenite phase (γ) to ferrite phase (α) progresses. At this time, since the phase transformation region disappears as the amount of silicon, which is a stabilizing element for the ferrite phase (α), increases, nickel (Ni), which is a stabilizing element for the austenite phase (γ), is added to enable the phase transformation heat treatment, and in the case of nickel (Ni), it is necessary to gradually increase the amount added as the silicon (Si) content increases.

[0067] Accordingly, the present invention derives the minimum addition amount of nickel (Ni) in relation to the content of silicon (Si) in the above-described [Formula 1], and more specifically, the minimum addition amount of nickel (Ni) is derived from [Formula 1] within the range of 2.5 to 3.8 wt% of silicon (Si). According to the present invention, nickel (Ni) must be included to satisfy [Formula 1] in order to secure the austenite phase (γ) region under temperature conditions of 1100°C.

[0068] Meanwhile, the steel may further contain carbon (C) 0.005 wt% or less, sulfur (S) 0.005 wt% or less, nitrogen (N) 0.005 wt% or less, titanium (Ti) 0.005 wt% or less, and phosphorus (P) 0.015 wt% or less.

[0069] In the two-phase region, the ratio of the peak of the {200} texture to the peak of the {112} texture, {200} / {112}, can be 1.3 or greater. Here, the two-phase region can mean the region where the austenite phase and the ferrite phase coexist. The larger {200} / {112}, the more improved magnetic properties can be obtained.

[0070] According to one embodiment of the present invention, the second temperature, which is a temperature at which the two-phase region is stable so that the ratio of the peak of the {200} texture to the peak of the {112} texture, {200} / {112}, satisfies 1.3 or more, may be 930 to 970°C, and the second set time may be 5 seconds or more. A detailed method for manufacturing a non-oriented electrical steel sheet according to the present invention, other than the second temperature and the second set time, will be described later.

[0071] Additionally, the sum of the {100} / ND fraction and the {110} / ND fraction of the final product may be 46.0% or more, the {100} / ND fraction of the final product may be 28.8% or more, and the {112} / ND fraction may be 23.3% or less.

[0072] Thus, according to one embodiment of the present invention, by improving the aggregate structure, a high magnetic flux density (B 50 ) and low iron loss (W 10 / 400 ) can provide a non-oriented electrical steel sheet with excellent magnetic properties. More specifically, the magnetic flux density (B 50 ) value is 1.68 T or more, and the iron loss (W 10 / 400 ) value may be less than or equal to 11.88 W / kg.

[0073] In addition, the non-oriented electrical steel sheet manufactured with the above-described alloy composition and manufacturing method may have a yield strength (YS) of 250 MPa or more and a tensile strength (TS) of 400 MPa or more.

[0074] Below, the lecture components and component ranges are explained.

[0075]

[0076] [Silicon (Si)]

[0077] Silicon (Si) is a component that increases resistivity and reduces eddy current loss. Furthermore, silicon is an element that improves the yield strength of steel and stabilizes ferrite and residual austenite at room temperature. If the silicon content is low, the core loss improvement effect may be insufficient. Furthermore, if the content is excessive, the alloying element composition may increase, which may reduce the magnetic flux density. More specifically, excessive silicon addition may increase brittleness, making cold rolling difficult and reducing productivity. Therefore, an appropriate amount of silicon must be added, and the steel according to one embodiment of the present invention may contain silicon in an amount of 2.5 wt% or more and 3.8 wt% or less.

[0078]

[0079] Nickel (Ni)

[0080] Nickel (Ni) is an element that stabilizes the austenite phase and can slightly increase resistivity. When silicon (Si) is added to steel at 1.5 wt% or more to improve iron loss, only a single ferrite phase region may exist. Therefore, nickel may be added to secure an austenite phase region at high temperatures. A steel according to one embodiment of the present invention may contain 1.45 wt% or more of nickel.

[0081] Additionally, in the present invention, the nickel (Ni) content can be adjusted in addition amount according to the silicon (Si) content so as to satisfy the above-described formula 1.

[0082]

[0083] [Aluminum (Al)]

[0084] Aluminum (Al) is an element that, together with silicon (Si), increases resistivity and reduces eddy current loss. Aluminum can react with nitrogen to induce AlN precipitation. Consequently, excessive aluminum content can deteriorate cold-rollability and magnetic flux density, degrading magnetic properties.

[0085] In addition, aluminum is an element that expands the ferrite phase region, reduces the phase transformation region, and forms a secondary phase such as AlN, which can deteriorate magnetic properties. The steel according to one embodiment of the present invention may contain aluminum in an amount of 0.05 wt% or less.

[0086]

[0087] [Carbon (C)]

[0088] Carbon (C) is an element that can combine with Ti, Nb, etc. to form carbides such as TiC, NbC, etc., and increase iron loss, thereby lowering magnetism. Therefore, the lower the carbon content, the more desirable it is. If the carbon content is excessive, it can act as an element that increases iron loss due to magnetic aging. More specifically, if the carbon content exceeds 0.005 wt% of the total weight, it can cause magnetic aging, thereby lowering magnetic properties. Therefore, the steel according to one embodiment of the present invention may have 0.005 wt% or less of carbon.

[0089]

[0090] [Hwang (S)]

[0091] Sulfur (S) is an impurity element in steel that can impair the ductility and weldability of the steel. Sulfur can form precipitates such as MnS and CuS, which are detrimental to magnetic properties, thereby increasing iron loss and inhibiting grain growth, so it is desirable to add small amounts. The steel according to one embodiment of the present invention may contain 0.005 wt% or less of sulfur.

[0092]

[0093] [Nitrogen (N)]

[0094] Nitrogen (N) is an element that can contribute to the strength and corrosion resistance of steel. Specifically, nitrogen, along with carbon, stabilizes austenite, enhancing toughness. It is also an element that, like carbon, is particularly advantageous in enhancing strength through solid solution strengthening.

[0095] However, nitrogen can strongly combine with Al, Ti, Nb, etc. to form precipitates such as AlN, TiN, NbN, etc., thereby increasing iron loss and inhibiting grain growth, so it is preferable to add a small amount. The steel according to one embodiment of the present invention may have nitrogen at 0.005 wt% or less.

[0096]

[0097] Titanium (Ti)

[0098] Titanium (Ti) combines with carbon and nitrogen to form fine precipitates such as TiC and TiN, inhibiting grain growth. Titanium can reduce nitrogen in steel, but excessive titanium content can degrade the grain structure due to increased carbides and nitrides, resulting in poor magnetic properties. Because more titanium is added, magnetic properties deteriorate, so adding less titanium is recommended.

[0099] Therefore, the steel according to one embodiment of the present invention may contain titanium in an amount of 0.005 wt% or less.

[0100]

[0101] [P]

[0102] Phosphorus (P) is an impurity element in steel that can cause cracks during casting and reduce weldability. Excessive phosphorus content can deteriorate castability, increase the likelihood of steel becoming brittle, and increase the likelihood of dent defects. Therefore, it is preferable to add a small amount of phosphorus. According to one embodiment of the present invention, the steel may contain 0.015 wt% or less of phosphorus.

[0103] Meanwhile, in addition to the above elements, austenite phase stabilizing elements such as Mn, Co, and Cr may be added as needed to stabilize the austenite phase.

[0104] In addition to the aforementioned alloying elements, the remainder may include iron and unavoidable impurities. Unavoidable impurities are impurities introduced during the steelmaking process and the electrical steel sheet manufacturing process, and as these are widely known in the art, a detailed description thereof will be omitted. In one embodiment of the present invention, the addition of elements other than the aforementioned alloying elements is not excluded, and various elements may be included within a scope that does not impair the technical spirit of the present invention. When additional elements are included, they are included to replace the remaining iron.

[0105]

[0106] Method for manufacturing non-oriented electrical steel sheet

[0107] Hereinafter, a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention will be specifically described with reference to FIG. 1.

[0108] Referring to FIGS. 1 and 2, a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes the steps of (a) preparing a semi-finished steel product including 2.5 to 3.8 wt% of silicon (Si), 1.45 wt% or more of nickel (Ni), 0.05 wt% or less of aluminum (Al), the remainder being iron (Fe) and other unavoidable impurities, (b) hot-rolling the steel product to form a hot-rolled steel sheet, (c) cold-rolling the hot-rolled steel sheet to form a cold-rolled steel sheet, and (d) cold-rolling and annealing the cold-rolled steel sheet.

[0109] In addition, referring to FIGS. 2 and 3, in the method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention, (d) the step of cold-rolling and annealing the cold-rolled steel sheet includes (d-1) a step of heating from room temperature to a first temperature (T1) at which an austenite phase is stable and then maintaining the temperature for a first set time (t1), (d-2) a step of cooling to a second temperature (T2) at which a two-phase region where an austenite phase and a ferrite phase coexist is stable and then maintaining the temperature for a second set time (t2), and (d-3) a step of cooling to room temperature.

[0110] However, the embodiment is not necessarily limited thereto, and the method for manufacturing a non-oriented electrical steel sheet may further include a hot-rolling annealing step and a coating step, the relevant details of which will be described later. Hereinafter, each step of the method for manufacturing a non-oriented electrical steel sheet will be described in detail.

[0111] First, (a) the step of preparing a semi-finished steel product may be a step of manufacturing a steel product containing 2.5 to 3.8 wt% of silicon (Si), 1.45 wt% or more of nickel (Ni), 0.05 wt% or less of aluminum (Al), and the remainder iron (Fe) and other unavoidable impurities. The semi-finished product may be, for example, a slab, but is not necessarily limited thereto. In addition, the manufacturing of the slab may be performed by a process known in the relevant technical field, such as a steelmaking process, a steelmaking process, and a casting process.

[0112] The above steel may further contain carbon (C) 0.005 wt% or less, sulfur (S) 0.005 wt% or less, nitrogen (N) 0.005 wt% or less, titanium (Ti) 0.005 wt% or less, and phosphorus (P) 0.015 wt% or less.

[0113] Additionally, nickel (Ni) may be added to the steel according to the silicon (Si) content. Silicon is added to the steel to reduce iron loss in non-oriented electrical steel sheets. However, if the silicon content exceeds 1.7 wt%, the austenite region may disappear and only a ferrite single-phase region may exist. Therefore, a certain amount of nickel may be added to secure the austenite phase at high temperatures. The nickel content according to the silicon content may satisfy the following equation 1.

[0114] [Formula 1]

[0115] [Ni] ≥ 2.52[Si] - 5.3

[0116] ([Ni] and [Si] represent the weight percent of Ni and Si, respectively.)

[0117] Here, [Si] applied to the above formula 1 may be 2.5 wt% or more and 3.8 wt% or less. For example, when the silicon (Si) content of the steel is 2.5 wt%, the nickel (Ni) content may be included in a range of 1.45 wt% or more, but when the silicon (Si) content is 2.68 wt%, the nickel (Ni) content may be included in a range of 1.45 wt% or more to satisfy the above [Formula 1].

[0118] According to one embodiment of the present invention, the nickel (Ni) content can be adjusted as an austenite phase stabilizing element. However, this is not limited thereto, and a corresponding effect can be obtained by additionally using other austenite phase stabilizing elements such as manganese (Mn), cobalt (Co), and chromium (Cr), or by replacing nickel (Ni).

[0119] Next, the step (b) of hot-rolling the above steel to form a hot-rolled steel sheet is a step of hot-rolling the semi-finished product prepared in step (a) to form a hot-rolled steel sheet. The hot rolling may include reheating, rough rolling, sand rolling, cooling, and coiling processes.

[0120] First, the reheating process may be to reheat the semi-finished product for subsequent processing. The semi-finished product may be reheated under the condition of SRT (Slab Reheating Temperature) of 1110℃ or higher and 1150℃ or lower. If the SRT is lower than 1110℃, the deformation resistance during hot rolling increases and the rolling load increases, which may reduce the rollability. In addition, if the SRT exceeds 1150℃, precipitates such as C, S, and N in the slab may be re-dissolved, which may cause fine precipitates to be generated in the subsequent rolling and annealing processes, which may inhibit grain growth and result in poor magnetism. Therefore, in the present invention, the semi-finished product may be reheated at a temperature of 1110℃ or higher and 1150℃ or lower.

[0121] Next, the rough rolling process may be to make a semi-finished product into a rolled material having an appropriate shape, thickness, and width, and the finish rolling process may be to adjust the semi-finished product to a specified thickness and width and roll it at a finishing temperature suitable for the intended use to have a good surface and shape.

[0122] At this time, the Finishing Delivery Temperature (FDT) may be 800℃ or higher and 900℃ or lower. If the FDT is lower than 800℃, rolling occurs in an abnormal region, forming an uneven structure and significantly reducing impact toughness. Furthermore, if the FDT exceeds 900℃, ductility and toughness are excellent, but strength may decrease rapidly. Therefore, the FDT is preferably 800℃ or higher and 900℃ or lower.

[0123] Additionally, the CT (Coiling Temperature) may be 500°C or higher and 700°C or lower. If the CT is lower than 500°C, the grain size may become too small, preventing sufficient grain growth even after annealing. Furthermore, if the CT exceeds 700°C, the amount of fine precipitates may increase, degrading magnetic properties. Therefore, the CT is preferably 500°C or higher and 700°C or lower.

[0124] (b) After step, the thickness of the hot-rolled steel sheet is preferably 2.6 mm or less. As the thickness of the hot-rolled steel sheet increases, the cold rolling reduction rate increases, which may result in a deterioration of the texture, so the thickness of the hot-rolled steel sheet is preferably 2.6 mm or less.

[0125] However, if the thickness of the hot-rolled steel sheet is excessively thin, the thickness obtained after cold rolling may not be sufficient, which may cause shape defects when applied to the product. Therefore, the thickness of the hot-rolled steel sheet may be more preferably 1.6 mm or more and 2.6 mm or less.

[0126] (b) A hot-rolling annealing step may be performed between steps (c). The hot-rolling annealing step may be a heat treatment of the hot-rolled steel sheet at a temperature of 940°C or higher and 1110°C or lower for 30 to 180 seconds. Within the above heat treatment temperature range, the microstructure of the hot-rolled steel sheet can be uniformly formed with an average of 50 to 200 mm. If the annealing temperature is too low, the elongated cast structure remaining after hot rolling may remain, causing microstructure inhomogeneity, and the formation of small crystal grains may reduce cold-rollability. On the other hand, if the annealing temperature is too high, it may cause an imbalance in the texture of the final product.

[0127] Accordingly, the hot rolling annealing step can be performed at a temperature of 940°C or higher and 1110°C or lower for 30 to 180 seconds. However, the hot rolling annealing step can be performed selectively as needed, and the cold rolling step can be performed directly after the hot rolling step without the hot rolling annealing step.

[0128] After the hot rolling annealing step, cooling may be performed, at which time the cooling rate may be 20°C / sec or more.

[0129] Additionally, a pickling step may be performed after step (b). The pickling step may be a step of removing an oxidized scale layer formed on the surface of the hot-rolled steel sheet using a pickling solution, and more specifically, may be performed before step (c).

[0130] Thereafter, (c) a step of cold rolling the hot-rolled steel sheet to form a cold-rolled steel sheet may be performed. (c) The step of cold rolling the hot-rolled steel sheet to form a cold-rolled steel sheet may be a step of rolling the cooled and coiled hot-rolled steel sheet at a temperature below the recrystallization temperature to further thin the thickness of the steel sheet. The cold rolling may be a step of warm-rolling at a reduction ratio of 50 to 90% after increasing the temperature of the steel sheet to 75°C or higher and 200°C or lower in order to impart rollability to the pickled hot-rolled steel sheet. The thickness of the cold-rolled steel sheet thus formed may be 0.1 mm or higher and 0.5 mm or lower.

[0131] After the above step (c), the step (d) of cold rolling annealing the cold rolled steel sheet may be performed. Cold rolling annealing may be a process of exposing and maintaining the steel at a temperature higher than the recrystallization temperature and then cooling it to soften the material of the steel hardened during cold rolling.

[0132] In the method for manufacturing an electrical steel sheet according to one embodiment of the present invention, (d) the step of cold-rolling and annealing the cold-rolled steel sheet includes (d-1) a step of heating from room temperature to a first temperature (T1) at which an austenite phase is stable and then maintaining the temperature for a first set time (t1), (d-2) a step of cooling to a second temperature (T2) at which a two-phase region where an austenite phase and a ferrite phase coexist is stable and then maintaining the temperature for a second set time (t2), and (d-3) a step of cooling to room temperature.

[0133] Below, steps (d-1), (d-2), and (d-3) will be described in detail.

[0134] First, step (d-1) can be performed by heating from room temperature to a first temperature (T1) at which the austenite phase is stable, and then maintaining the temperature for a first set time (t1). Here, the first temperature (T1) may refer to a temperature at which the austenite single-phase region is stable. The first temperature (T1) may preferably be 1000 to 1200°C, but is not necessarily limited thereto, and may include all cases where the austenite single-phase region is stable at a temperature. In addition, the first set time (t1) may be 20 to 50 seconds.

[0135] Next, the (d-2) step may be a step of cooling to a second temperature (T2), which is a stable temperature for a two-phase region where an austenite phase and a ferrite phase coexist, and then maintaining the temperature for a second set time (t2). That is, the second temperature (T2) may mean a temperature at which the two-phase region of an austenite phase and a ferrite phase is stably maintained, and in this case, the ratio of the peak of the {200} texture to the peak of the {112} texture, {200} / {112}, may be 1.3 or more.

[0136] In the above step (d-2), the second temperature (T2) may be 930°C or more and 970°C or less to facilitate smooth nucleation of the ferrite phase. If the second temperature (T2) is less than 930°C, the grain size may be fine, which may increase hysteresis loss, and if the second temperature (T2) exceeds 970°C, the grain size may be coarse, which may increase eddy current loss. The second temperature (T2) may preferably be 935°C or more and 970°C or less.

[0137] Additionally, the second setting time (t2) may be 5 seconds or more, and preferably 5 to 45 seconds.

[0138] Next, (d-3) a step of cooling to room temperature can be performed.

[0139] Additionally, the coating of the cold-rolled steel sheet may be performed to secure the perforation and insulation properties, and may form an insulating film on the surface of the final annealed cold-rolled steel sheet.

[0140] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention designs an alloy composition so that sequential phase transformation into a ferrite phase, an austenite phase, and a ferrite phase is possible during cold rolling annealing, and a two-phase region where the austenite phase and the ferrite phase coexist is cooled to a stable temperature and then maintained, thereby improving the aggregate structure so that an orientation advantageous to magnetism is developed and improving magnetic and mechanical properties.

[0141] That is, by utilizing the characteristic that the orientation preferentially formed in each temperature range changes when the phase transformation from the austenite phase to the ferrite phase progresses, the effect of improving the texture can be maximized so that the {100} / ND orientation is developed.

[0142] The non-oriented electrical steel sheet according to one embodiment of the present invention manufactured by the above-described manufacturing method may have a sum of a {100} / ND fraction and a {110} / ND fraction of 46.0% or more, a {100} / ND fraction of 28.8% or more, and a {112} / ND fraction of 23.3% or less. Here, ND is an abbreviation for Normal Direction and may mean a direction perpendicular to a plane including a rolling direction, that is, a direction perpendicular to the surface of the sheet material.

[0143] In addition, the mechanical properties of the final product, non-oriented electrical steel sheet, can be a yield strength (YS) of 250 MPa or more and a tensile strength (TS) of 400 MPa or more.

[0144] In addition, a product with improved magnetic properties can be obtained compared to a product manufactured without going through a process of maintaining the two-phase region for a preset period of time during cold rolling annealing. At this time, the magnetic properties are determined by the iron loss (W 10 / 400 ) and magnetic flux density (B 50 ) means, more specifically (W10 / 400 ) means the iron loss at 400 Hz, 1.0 T, and B 50 It refers to the size of the magnetic flux density induced when a magnetic field of 5000 A / m is applied.

[0145]

[0146] Comparative and experimental examples

[0147] Below, the composition and operation of the present invention will be described in more detail through preferred comparative and experimental examples. However, these examples are provided as preferred examples to aid understanding of the present invention and are not intended to limit the present invention.

[0148] Table 1 shows the main alloy element compositions of the comparative examples and experimental examples, and Table 2 shows the results of in-situ XRD analysis of F / H samples having the compositions presented in Table 1 under the process conditions of Table 2. Process conditions not presented in Table 2 satisfied the method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention described above, and were controlled to be the same in all comparative examples and experimental examples.

[0149]

[0150] [Correction pursuant to Rule 91, August 29, 2024]

[0151] First, referring to Table 1, Comparative Examples 3, 6, 9, and 10 having alloy compositions of A1, A4, A7, and A8 do not satisfy Equation 1, which represents the minimum nickel content according to the silicon content according to an embodiment of the present invention. In addition, Comparative Example 7 having an alloy composition of A5 satisfies Equation 1, but the aluminum (Al) content exceeded 0.05 wt%. As a result, it can be confirmed that phase transformation does not occur in Comparative Examples 3, 6, 7, 9, and 10, and compared to the experimental examples, {100} / ND, which is favorable to magnetism, is formed less, and {112} / ND, which is unfavorable to magnetism, is formed more.

[0152] Next, referring to Table 2, in the case of Comparative Example 1, (d-2) the step of cooling to the second temperature, which is a stable temperature for a two-phase region where the austenite phase and the ferrite phase coexist, and then maintaining it for the second set time was not performed. Specifically, in Comparative Example 1, the texture and magnetic properties were confirmed under the condition that the A9 composition F / H sample was heated from room temperature to 965°C, maintained for 45 seconds, and then cooled. As a result, it was obtained that the texture properties were {100} / ND, which is a favorable orientation for magnetism, at 0.3%, and {112} / ND, which is a unfavorable orientation for magnetism, at 83.6%. And the magnetic properties B 50 = 1.58 T, W 10 / 400 = 13.58 W / kg, showing relatively inferior characteristics compared to the experimental example.

[0153] In the case of Comparative Example 2, it is outside the range of the second temperature according to the present invention. Specifically, Comparative Example 2 shows the texture and magnetic properties under the condition that the A0 composition F / H sample was heated from room temperature to the stable region of the austenite phase of 1100°C, maintained for 45 seconds, cooled to the stable temperature of the ferrite phase of 550°C, maintained again for 45 seconds, and then cooled to room temperature. Under the condition, {200} / {112} had a value of 0.77, which was less than 1.3, and {100} / ND, which was favorable to magnetism, was formed at 8.1%, and {112} / ND, which was unfavorable to magnetism, was formed at 41.9%. As a result, B, which is inferior to the experimental example, 50 = 1.68 T, W 10 / 400 = It exhibited magnetic properties of 13.21 W / kg.

[0154] In the case of Comparative Example 4, it is outside the range of the second temperature according to the present invention. Specifically, Comparative Example 4 shows the texture and magnetic properties under the condition that the A2 composition F / H sample was heated from room temperature to the stable region of the austenite phase of 1125°C, maintained for 40 seconds, cooled to the stable temperature of the ferrite phase of 550°C, maintained again for 45 seconds, and then cooled to room temperature. Under the condition, {200} / {112} was 0.77, which was less than 1.3, and {100} / ND, which was favorable for magnetism, was formed at 9.1%, and {112} / ND, which was unfavorable for magnetism, was formed at 37.2%. As a result, B, which is inferior to the experimental example, was obtained. 50 = 1.67 T, W 10 / 400 = It exhibited magnetic properties of 12.95 W / kg.

[0155] In the case of Comparative Example 5, it is outside the range of the second temperature according to the present invention. Specifically, Comparative Example 5 shows the texture and magnetic properties under the condition that the A3 composition F / H sample was heated from room temperature to the stable region of the austenite phase of 1100°C, maintained for 45 seconds, cooled to the stable temperature of the ferrite phase of 550°C, maintained again for 45 seconds, and then cooled to room temperature. Under the condition, {200} / {112} had a value of 0.75, which was less than 1.3, and {100} / ND, which was favorable for magnetism, was formed at 8.8%, and {112} / ND, which was unfavorable for magnetism, was formed at 36.7%. As a result, B, which is inferior to the experimental example, was formed. 50 = 1.67 T, W 10 / 400 = It exhibited magnetic properties of 12.87 W / kg.

[0156] In the case of Comparative Example 8, it is outside the range of the second temperature according to the present invention. Specifically, Comparative Example 8 shows the texture and magnetic properties under the condition that the A6 composition F / H sample was heated from room temperature to a stable austenite phase region of 1100°C, maintained for 45 seconds, cooled to a stable ferrite phase temperature of 550°C, maintained again for 45 seconds, and then cooled to room temperature. Under the condition, {200} / {112} was 0.74, which was less than 1.3, and {100} / ND, which was favorable for magnetism, was 7.5%, and {112} / ND, which was unfavorable for magnetism, was formed at 36.6%. As a result, B, which is inferior to the experimental example, was formed. 50 = 1.67 T, W 10 / 400 = It exhibited magnetic properties of 12.32 W / kg.

[0157] In the case of Comparative Example 11, it is outside the range of the second temperature according to the present invention. Specifically, Comparative Example 11 shows the texture and magnetic properties under the condition that the A9 composition F / H sample was heated from room temperature to the stable region of the austenite phase of 1150°C, maintained for 40 seconds, cooled to the stable temperature of the ferrite phase of 550°C, maintained again for 45 seconds, and then cooled to room temperature. Under the condition, {200} / {112} had a value of 0.73, which was less than 1.3, and {100} / ND, which was favorable for magnetism, was formed at 8.2%, and {112} / ND, which was unfavorable for magnetism, was formed at 39.0%. As a result, B, which is inferior to the experimental example, was formed. 50 = 1.66 T, W 10 / 400 = It exhibited magnetic properties of 12.32 W / kg.

[0158] In the case of Comparative Example 12, it is outside the range of the second temperature according to the present invention. Specifically, Comparative Example 12 shows the texture and magnetic properties under the condition that the A10 composition F / H sample was heated from room temperature to a stable austenite phase region of 1150°C, maintained for 45 seconds, cooled to a stable ferrite phase temperature of 550°C, maintained again for 45 seconds, and then cooled to room temperature. Under the condition, {200} / {112} had a value of 0.72, which was less than 1.3, and {100} / ND, which was favorable for magnetism, was formed at 6.7%, and {112} / ND, which was unfavorable for magnetism, was formed at 39.7%. As a result, B, which is inferior to the experimental example, was formed. 50 = 1.65, W 10 / 400 = It exhibited magnetic properties of 12.25 W / kg.

[0159] In the case of Comparative Example 13, it is outside the range of the second temperature according to the present invention. Specifically, Comparative Example 13 shows the texture and magnetic properties under the condition that the A10 composition F / H sample was heated from room temperature to a stable region of 1150°C in the austenite phase, maintained for 45 seconds, cooled to a temperature of 920°C, maintained for another 45 seconds, and then cooled to room temperature. Under the condition, {200} / {112} was 0.75, which was less than 1.3, and {100} / ND, which was favorable for magnetism, was 7.2%, and {112} / ND, which was unfavorable for magnetism, was formed at 38.4%. As a result, B, which is inferior to the experimental example, was formed. 50 = 1.67, W 10 / 400 = It exhibited magnetic properties of 12.58 W / kg.

[0160] In the case of Comparative Example 14, it is outside the range of the second temperature according to the present invention. Specifically, Comparative Example 14 shows the texture and magnetic properties under the condition that the A10 composition F / H sample was heated from room temperature to a stable region of 1150°C in the austenite phase, maintained for 45 seconds, cooled to a temperature of 980°C, maintained for another 45 seconds, and then cooled to room temperature. Under the condition, {200} / {112} was 0.73, which was less than 1.3, and {100} / ND, which was favorable for magnetism, was 9.0%, and {112} / ND, which was unfavorable for magnetism, was formed at 38.6%. As a result, B, which is inferior to the experimental example, was formed. 50 = 1.66, W 10 / 400 = It exhibited magnetic properties of 12.47 W / kg.

[0161] In the case of Comparative Example 15, it is outside the range of the second setting time according to the present invention. Specifically, Comparative Example 15 shows the texture and magnetic properties under the condition that the A10 composition F / H sample was heated from room temperature to a stable region of 1150°C in the austenite phase, maintained for 45 seconds, cooled to a temperature of 980°C, maintained for 3 seconds again, and then cooled to room temperature. Under the condition, {200} / {112} was 0.76, which was less than 1.3, and {100} / ND, which was favorable for magnetism, was 8.7%, and {112} / ND, which was unfavorable for magnetism, was formed at 36.9%. As a result, B, which is an inferior characteristic compared to the experimental example, 50 = 1.67, W 10 / 400 = It exhibited magnetic properties of 12.11 W / kg.

[0162] On the other hand, Experimental Examples 1 to 7 performed a cold rolling annealing process that performed a two-phase region phase transformation heat treatment while satisfying the alloy composition and Equation 1 according to an embodiment of the present invention. As a result, the texture was improved so that a magnetically advantageous orientation was developed, and specifically, it was confirmed that the sum of the {100} / ND fraction and the {110} / ND fraction was 46.0% or more, the {100} / ND fraction was 28.8% or more, and the {112} / ND fraction was 23.3% or less, and the magnetic flux density (B ) which is a magnetic characteristic 50 ) value is 1.68 T or more, and the iron loss (W 10 / 400 ) It can be confirmed that the value satisfies 11.88 W / kg or less.

[0163] Although the present invention has been described above with reference to limited embodiments and drawings, the present invention is not limited thereto, and various embodiments are possible within the scope equivalent to the technical idea of ​​the present invention and the patent claims to be described below by a person having ordinary skill in the art to which the present invention pertains.

Claims

1. (a) A step of preparing a steel semi-finished product containing 2.5 to 3.8 wt% of silicon (Si), 1.45 wt% or more of nickel (Ni), 0.05 wt% or less of aluminum (Al), the remainder being iron (Fe) and other unavoidable impurities; (b) a step of hot rolling the above steel to form a hot-rolled steel plate; (c) a step of cold rolling the hot-rolled steel sheet to form a cold-rolled steel sheet; and (d) including a step of cold rolling annealing the cold rolled steel sheet, Step (d) above, (d-1) A step of heating from room temperature to a first temperature at which the austenite phase is stable and then maintaining the temperature for a first set period of time; (d-2) a step of cooling to a second temperature, which is a stable temperature in a two-phase region where an austenite phase and a ferrite phase coexist, and then maintaining the temperature for a second set time; and (d-3) A method for manufacturing a non-oriented electrical steel sheet, comprising a step of cooling to room temperature.

2. In paragraph 1, The above two-phase region is, A method for manufacturing a non-oriented electrical steel sheet in which the ratio of the peak of the {200} texture to the peak of the {112} texture, {200} / {112}, is 1.3 or more.

3. In paragraph 1, The above second temperature is, A method for manufacturing non-oriented electrical steel sheets having a temperature of 930 to 970°C.

4. In paragraph 1, The above second setting time is, A method for manufacturing a non-oriented electrical steel sheet having a curing time of 5 seconds or longer.

5. In paragraph 1, Between steps (b) and (c) above, A method for manufacturing a non-oriented electrical steel sheet further comprising a step of hot-rolling and annealing the hot-rolled steel sheet.

6. In paragraph 1, The above steel is, A method for manufacturing a non-oriented electrical steel sheet further comprising carbon (C) 0.005 wt% or less, sulfur (S) 0.005 wt% or less, nitrogen (N) 0.005 wt% or less, titanium (Ti) 0.005 wt% or less, and phosphorus (P) 0.015 wt% or less.

7. In paragraph 1, The above steel is, A method for manufacturing a non-oriented electrical steel sheet satisfying the following equation 1. [Formula 1] [Ni] ≥ 2.52[Si] - 5.3 ([Ni] and [Si] represent the weight percent of Ni and Si, respectively.) 8. Cold-rolled steel sheet is formed by hot-rolling and then cold-rolling steel containing 2.5 to 3.8 wt% of silicon (Si), 1.45 wt% or more of nickel (Ni), 0.05 wt% or less of aluminum (Al), and the remainder of iron (Fe) and other unavoidable impurities. The above cold rolled steel sheet is cold rolled and annealed to manufacture the final product, A non-oriented electrical steel sheet manufactured by a method of heating from room temperature to a first temperature at which the austenite phase is stable during the above cold rolling annealing, maintaining the temperature for a first set time, cooling the steel sheet to a second temperature at which the two-phase region where the austenite phase and the ferrite phase coexist is stable, maintaining the temperature for a second set time, and then cooling the steel sheet to room temperature.

9. In paragraph 8, The above two-phase region is, Non-oriented electrical steel sheet having a ratio of the peak of the {200} texture to the peak of the {112} texture, {200} / {112}, of 1.3 or more.

10. In paragraph 8, The above second temperature is, Non-oriented electrical steel sheet with a temperature of 930 to 970℃.

11. In paragraph 8, The above second setting time is, Non-oriented electrical steel sheet for more than 5 seconds.

12. In paragraph 8, The above steel is, A non-oriented electrical steel sheet satisfying the following equation 1. [Formula 1] [Ni] ≥ 2.52[Si] - 5.3 ([Ni] and [Si] represent the weight percent of Ni and Si, respectively.) 13. In paragraph 8, The above steel is, Non-oriented electrical steel sheet further comprising carbon (C) 0.005 wt% or less, sulfur (S) 0.005 wt% or less, nitrogen (N) 0.005 wt% or less, titanium (Ti) 0.005 wt% or less, and phosphorus (P) 0.015 wt% or less.

14. In paragraph 8, A non-oriented electrical steel sheet having a sum of the {100} / ND fraction and the {110} / ND fraction of the final product of the above-mentioned type of steel being 46.0% or more.

15. In paragraph 8, A non-oriented electrical steel sheet having a {100} / ND fraction of the above final product of 28.8% or more and a {112} / ND fraction of 23.3% or less.

16. Contains 2.5 to 3.8 wt% of silicon (Si), 1.45 wt% or more of nickel (Ni), 0.05 wt% or less of aluminum (Al), the remainder being iron (Fe) and other unavoidable impurities. Magnetic flux density (B 50 ) value is 1.68 T or more, and the iron loss (W 10 / 400 ) Non-oriented electrical steel sheet with a value of 11.88 W / kg or less.

17. In paragraph 16, A non-oriented electrical steel sheet having the above silicon and nickel contents satisfying the following formula 1. [Formula 1] [Ni] ≥ 2.52[Si] - 5.3 ([Ni] and [Si] represent the weight percent of Ni and Si, respectively.) 18. In paragraph 16, Non-oriented electrical steel sheet having a sum of {100} / ND fraction and {110} / ND fraction of 46.0% or more.

19. In paragraph 16, Non-oriented electrical steel sheet having a {100} / ND fraction of 28.8% or more and a {112} / ND fraction of 23.3% or less.

20. In paragraph 16, Non-oriented electrical steel sheet further comprising carbon (C) 0.005 wt% or less, sulfur (S) 0.005 wt% or less, nitrogen (N) 0.005 wt% or less, titanium (Ti) 0.005 wt% or less, and phosphorus (P) 0.015 wt% or less.

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