Non-oriented electrical steel sheet and method for manufacturing the same

Abstract

A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention includes the steps of: (a) preparing a steel material which is a semi-finished product containing 2.5 to 3.8% by weight of silicon (Si), 1.45% by weight or more of nickel (Ni), 0.05% by weight or less of aluminum (Al), and the remainder of 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. Step (d) includes (d-1) heating from room temperature to a first temperature at which the austenite phase is stable, and maintaining it for a first set time; (d-2) cooling to a second temperature at which the two-phase region where the austenite phase and the ferrite phase coexist is stable, and maintaining it for a second set time; and (d-3) cooling to room temperature. The phase transformation heat treatment in the cold rolling annealing step can improve the texture so that orientations favorable to magnetism develop, thereby improving the magnetic properties.

Description

[Technical Field]

[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, wherein the texture is improved by a phase transformation heat treatment in the cold rolling and annealing step so that orientations favorable to magnetism develop, thereby improving the magnetic properties. [Background technology]

[0002] Non-oriented electrical steel sheets are used as core materials for motors, generators, and small transformers, and are primarily used for converting electrical energy into kinetic energy, changing voltage, or other energy conversions.

[0003] These non-oriented electrical steel sheets are used as core materials in electric vehicle components, and demand has been increasing recently due to growing interest in environmentally friendly products in response to global environmental concerns.

[0004] The properties required for such non-oriented electrical steel sheets are low iron loss and high magnetic flux density. Conventionally, methods to reduce iron loss in electrical steel sheets include increasing the resistivity of the steel or thinning the material. Increasing the amount of silicon (Si), aluminum (Al), manganese (Mn), etc., added to the steel increases the resistivity of the steel and can reduce iron loss to a certain range, but this reduces the magnetic flux density and decreases rollability, making it difficult to thin the material.

[0005] The magnetic flux density of electrical steel sheets is determined by the fraction of iron (Fe) atoms in the steel and the arrangement of the steel's crystal grains. Due to the magnetic anisotropy of iron atoms, the magnetic flux density of single iron atoms is determined by the magnetic anisotropy of iron atoms. <100> Although magnetization easily occurs in textured materials, <110> collective organizations and <111> Texture is difficult to magnetize.

[0006] Therefore, the magnetization direction of the atomic arrangement within the steel <100> By orienting the steel parallel to its axis, it can achieve a high magnetic flux density even in a low magnetic field. On the other hand, it is also possible to obtain a high magnetic flux density in a low magnetic field by either orienting the axis that is useful for magnetization, or by not orienting the axis that is very difficult to magnetize.

[0007] In addition, conventional research has focused on methods for controlling the texture by adjusting the composition system or heat treatment temperature conditions, primarily in order to manufacture non-oriented electrical steel sheets with excellent magnetic properties.

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

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

[0010] As described above, simply changing the conventional process and component composition yields only minor improvements in microstructure and texture, and it is even more difficult to achieve a significant improvement in texture, which has a major impact on magnetic properties, by simply improving the added elements or some process conditions. Therefore, there is a need to develop other control methods and processes that can improve magnetic properties. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Korean Published Patent No. 10-2009-0079056 [Patent Document 2] Korean Registered Patent No. 10-2376026 [Overview of the project] [Problems that the invention aims to solve]

[0012] The present invention has been devised to solve the above problems, and an object of the present invention is to provide a non-oriented electrical steel sheet in which the microstructure is improved by a phase transformation heat treatment in a cold rolling and annealing step so that a magnetic advantageous orientation develops, and the magnetic properties are improved, and a method for producing the same.

[0013] The object of the present invention is not limited to the problems mentioned above, and other problems not mentioned should be clearly understood by those skilled in the art from the following description.

Means for Solving the Problems

[0014] A method for producing a non-oriented electrical steel sheet according to an embodiment of the present invention includes: (a) preparing a steel material, which is a semi-finished product containing 2.5 to 3.8% by weight of silicon (Si), 1.45% by weight or more of nickel (Ni), 0.05% by weight or less of aluminum (Al), and the balance of iron (Fe) and other inevitable 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. The step (d) includes: (d-1) heating from room temperature to a first temperature, which is a temperature at which the austenite phase is stable, and maintaining for a first set time; (d-2) cooling to a second temperature, which is a temperature at which a two-phase region where the austenite phase and the ferrite phase coexist is stable, and maintaining for a second set time; and (d-3) cooling to room temperature.

[0015] The two-phase region may have a ratio of {200} / {112}, which is the ratio of the peak of the {200} texture to the peak of the {112} texture, of 1.3 or more.

[0016] The second temperature may be 930 to 970 °C.

[0017] The second set time may be 5 seconds or more.

[0018] The step between step (b) and step (c) may further include a step of hot-rolling and annealing the hot-rolled steel sheet.

[0019] The steel material may further contain 0.005% by weight or less of carbon (C), 0.005% by weight or less of sulfur (S), 0.005% by weight or less of nitrogen (N), 0.005% by weight or less of titanium (Ti), and 0.015% by weight of phosphorus (P).

[0020] The aforementioned steel material may satisfy the following formula 1. [Formula 1] [Ni]≧2.52[Si]-5.3 ([Ni] and [Si] represent weight percentages of Ni and Si, respectively.)

[0021] An embodiment of the present invention involves hot-rolling a steel material containing 2.5 to 3.8% by weight of silicon (Si), 1.45% by weight or more of nickel (Ni), 0.05% by weight or less of aluminum (Al), and the remaining iron (Fe) and other unavoidable impurities, followed by cold-rolling to form a cold-rolled steel sheet. The cold-rolled steel sheet is then cold-rolled and annealed to produce the final product. During the cold-rolling and annealing process, the material is heated from room temperature to a first temperature at which the austenite phase is stable, maintained for a first set time, then cooled to a second temperature at which the two-phase region where the austenite and ferrite phases coexist is stable, maintained for a second set time, and finally cooled back to room temperature.

[0022] The two-phase region may have a ratio of {200} / {112}, which is the ratio of the peak of the {200} texture to the peak of the {112} texture, of 1.3 or greater.

[0023] The second temperature may be 930 to 970°C.

[0024] The second setting time may be 5 seconds or more.

[0025] The aforementioned steel material may satisfy the following formula 1. [Formula 1] [Ni]≧2.52[Si]-5.3 ([Ni] and [Si] represent weight percentages of Ni and Si, respectively.)

[0026] The steel material may further contain 0.005% by weight or less of carbon (C), 0.005% by weight or less of sulfur (S), 0.005% by weight or less of nitrogen (N), 0.005% by weight or less of titanium (Ti), and 0.015% by weight of phosphorus (P).

[0027] The sum of the {100} / ND fraction and the {110} / ND fraction of the final product may be 46.0% or more.

[0028] 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.

[0029] An embodiment of the present invention provides a non-oriented electrical steel sheet containing 2.5 to 3.8% by weight of silicon (Si), 1.45% by weight or more of nickel (Ni), 0.05% by weight or less of aluminum (Al), the remainder of iron (Fe), and other unavoidable impurities, and has a magnetic flux density (B 50 The value is 1.68T or higher, and the iron loss (W) 10 / 400 The value may be 11.88 W / kg or less.

[0030] The silicon and nickel content of the non-oriented electrical steel sheet according to one embodiment of the present invention may satisfy the following formula 1. [Formula 1] [Ni]≧2.52[Si]-5.3 ([Ni] and [Si] represent weight percentages of Ni and Si, respectively.)

[0031] In one embodiment of the present invention, the non-oriented electrical steel sheet may have a sum of {100} / ND fraction and {110} / ND fraction of 46.0% or more.

[0032] In one embodiment of the present invention, the non-oriented electrical steel sheet has a {100} / ND fraction of 28.8% or more, and a {112} / ND fraction of 23.3% or less.

[0033] An embodiment of the present invention may further contain 0.005% by weight or less of carbon (C), 0.005% by weight or less of sulfur (S), 0.005% by weight or less of nitrogen (N), 0.005% by weight or less of titanium (Ti), and 0.015% by weight of phosphorus (P). [Effects of the Invention]

[0034] An embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same, in which the texture is improved by a phase transformation heat treatment in the cold rolling and annealing step, so as to develop a {100} / ND orientation that is advantageous for magnetism, thereby improving the magnetic properties. [Brief explanation of the drawing]

[0035] [Figure 1] This is a sequence diagram showing a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention. [Figure 2] This is a sequence diagram illustrating a method for manufacturing non-oriented electrical steel sheets according to one embodiment of the present invention. [Figure 3] This figure shows the cold rolling and annealing step in a method for manufacturing non-oriented electrical steel sheets according to one embodiment of the present invention. [Modes for carrying out the invention]

[0036] In the following, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be embodied in a variety of different forms and is not limited or restricted by the following embodiments.

[0037] Terms such as “includes” or “have” are intended to specify the presence of features, figures, steps, actions, components, parts, or combinations thereof as described in the specification, and should be understood not to preemptively exclude the presence or possibility of adding one or more other features, figures, steps, actions, components, parts, or combinations thereof.

[0038] In order to clearly explain the present invention, detailed descriptions of related prior art that are irrelevant to the description or that may unnecessarily obscure the essence of the invention have been omitted. In this specification, where reference numerals are assigned to components of each drawing, the same or similar reference numerals are assigned to identical or similar components throughout the specification.

[0039] Furthermore, the terms and words used in this specification and the claims shall not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that an inventor may appropriately define the concept of a term in order to best describe their invention.

[0040] Unless otherwise specified, the notation "A~B" for numerical values ​​A and B shall mean "A or greater and B or less". If a unit is attached only to numerical value B in such notation, that unit shall also apply to numerical value A.

[0041] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0042] Non-oriented electrical steel sheet An embodiment of the present invention provides for a non-oriented electrical steel sheet containing 2.5 to 3.8% by weight of silicon (Si), 1.45% or more by weight of nickel (Ni), 0.05% or less by weight of aluminum (Al), and the remaining iron (Fe) and other unavoidable impurities. More specifically, a steel material having the above-mentioned silicon (Si), nickel (Ni), and aluminum (Al) content is hot-rolled, then cold-rolled to form a cold-rolled steel sheet, and the cold-rolled steel sheet is cold-rolled and annealed to produce the final product, a non-oriented electrical steel sheet. Therefore, in the following, it can be understood that the alloy components contained in the semi-finished steel material are also contained within the same range in the cold-rolled steel sheet and the final product, the non-oriented electrical steel sheet.

[0043] According to one embodiment of the present invention, non-oriented electrical steel sheets are manufactured by cold rolling and annealing, in which the steel is heated from room temperature to a first temperature at which the austenite phase is stable, maintained for a first set time, then cooled to a second temperature at which the two-phase region where the austenite phase and ferrite phase coexist is stable, maintained for a second set time, and then cooled back to room temperature.

[0044] Thus, in one embodiment of the present invention, the non-oriented electrical steel sheet can be improved by a phase transformation heat treatment during cold rolling and annealing to improve its texture so that orientations favorable to magnetism develop, thereby improving its mechanical and magnetic properties.

[0045] In other words, phase transformation heat treatment can be performed during cold rolling and annealing in the order of ferrite phase (α), austenite phase (γ), and ferrite phase (α). In particular, when the phase transformation proceeds from the austenite phase to the ferrite phase, nucleation can be induced in the temperature range where the {100} / ND orientation, which is favorable for magnetism, is most easily developed, and these can be grown to improve the texture.

[0046] According to one embodiment of the present invention, the steel material may satisfy the range of alloy components of the following formula 1.

[0047] [Ni]≧2.52[Si]-5.3 ([Ni] and [Si] represent weight percentages of Ni and Si, respectively.)

[0048] As described above, the present invention is based on a phase transformation heat treatment during cold rolling and annealing, which involves transitioning from a ferrite phase (α) to an austenite phase (γ) and then to another ferrite phase (α). When the phase transformation from austenite phase (γ) to ferrite phase (α) progresses, the present invention maximizes the effect of improving the texture by utilizing the characteristic that different orientations are preferentially formed depending on the temperature conditions. At this time, since the phase transformation region disappears as the amount of silicon, which is a stabilizing element of the ferrite phase (α), is increased, nickel (Ni), which is a stabilizing element of the austenite phase (γ), is added to enable the phase transformation heat treatment. In the case of nickel (Ni), it is necessary to gradually increase the amount added as the silicon (Si) content increases.

[0049] Accordingly, in the present invention, the minimum amount of nickel (Ni) to be added in the above-mentioned [Equation 1] is derived from its relationship with the silicon (Si) content. More specifically, the minimum amount of nickel (Ni) to be added is derived using [Equation 1] when the silicon (Si) content is in the range of 2.5 to 3.8% by weight. According to the present invention, the austenite phase (γ) region can only be secured under a temperature of 1100°C if nickel (Ni) is included in such a way that it satisfies [Equation 1].

[0050] On the other hand, steel materials may further contain 0.005% by weight or less of carbon (C), 0.005% by weight or less of sulfur (S), 0.005% by weight or less of nitrogen (N), 0.005% by weight or less of titanium (Ti), and 0.015% by weight or less of phosphorus (P).

[0051] In the two-phase region, the ratio of the peak of the {200} texture to the peak of the {112} texture, {200} / {112}, may be 1.3 or greater. Here, the two-phase region may refer to the region where the austenite phase and the ferrite phase coexist. The larger {200} / {112}, the more improved the magnetic properties can be obtained.

[0052] According to one embodiment of the present invention, the second temperature, which is the temperature at which the two-phase region is stable, may be 930 to 970°C, such that the ratio of {200} / {112}, which is the ratio of the peak of the {200} texture to the peak of the {112} texture, is 1.3 or more, and the second setting time may be 5 seconds or more. In addition to the second temperature and second setting time, a detailed manufacturing method of the non-oriented electrical steel sheet according to the present invention will be described later.

[0053] Furthermore, 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.

[0054] As a result, according to one embodiment of the present invention, by improving the texture, a high magnetic flux density (B 50 ) and low iron loss (W10 / 400 We can provide non-oriented electrical steel sheets with excellent magnetic properties having a magnetic flux density (B). More specifically, we can provide non-oriented electrical steel sheets with excellent magnetic properties having a magnetic flux density (B). 50 The value is 1.68T or higher, and the iron loss (W) 10 / 400 The value may be 11.88 W / kg or less.

[0055] Furthermore, the non-oriented electrical steel sheet manufactured using the alloy composition and manufacturing method described above may have a yield strength (YS) of 250 MPa or higher and a tensile strength (TS) of 400 MPa or higher.

[0056] The following describes the composition and range of steel.

[0057] [Silicon (Si)] Silicon (Si) is a component that increases resistivity and reduces eddy current losses. Furthermore, silicon is an element that can improve the yield strength of steel and stabilize ferrite and residual austenite at room temperature. If the silicon content is too low, the iron loss improvement effect may be insufficient. Conversely, if the content is too high, the alloying element component increases, potentially reducing the magnetic flux density. More specifically, excessive silicon addition can increase brittleness, making cold rolling difficult and reducing productivity. Therefore, an appropriate amount of silicon must be added, and in one embodiment of the present invention, the silicon content may be 2.5% by weight or more and 3.8% by weight or less.

[0058] [Nickel (Ni)] Nickel (Ni) is an element that can stabilize the austenite phase and partially increase its resistivity. When silicon (Si) is added to steel at a concentration of 1.5% by weight or more to improve iron loss, only a single-phase ferrite region may exist. Therefore, nickel can be added to ensure the austenite phase region at high temperatures. In one embodiment of the present invention, the nickel content may be 1.45% by weight or more.

[0059] Furthermore, the amount of nickel (Ni) added in the present invention can be adjusted according to the silicon (Si) content so as to satisfy the above formula 1.

[0060] [Aluminum (Al)] Aluminum (Al), along with Si, is an element that can increase resistivity and reduce eddy current losses. Aluminum can combine with nitrogen to induce AlN precipitation. This can lead to reduced cold rolling properties, decreased magnetic flux density, and degraded magnetic properties if the aluminum content is excessive.

[0061] Furthermore, aluminum is an element that expands the ferrite phase region, shrinks the phase transformation region, and can potentially inhibit magnetic properties by forming secondary phases such as AlN. In one embodiment of the present invention, the aluminum content may be 0.05% by weight or less.

[0062] [Carbon (C)] Carbon (C) is an element that can combine with Ti, Nb, etc., to form carbides such as TiC and NbC, which can increase iron loss and reduce magnetism. Therefore, a lower carbon content is preferable. 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% by weight of the total weight, it can cause magnetic aging and reduce magnetic properties. Therefore, the steel material according to one embodiment of the present invention may have a carbon content of 0.005% by weight or less.

[0063] [Sulfur (S)] Sulfur (S) is an impurity element in steel and can inhibit the ductility and weldability of steel. Sulfur can increase iron loss and suppress grain growth by forming precipitates such as MnS and CuS, which are harmful to magnetic properties, so it is preferable to add it in small amounts. In one embodiment of the present invention, the sulfur content may be 0.005% by weight or less.

[0064] [Nitrogen (N)] Nitrogen (N) is an element that can contribute to the strength and corrosion resistance of steel. Specifically, nitrogen, along with carbon, stabilizes austenite and improves toughness, and is particularly advantageous for improving strength through solid solution strengthening, similar to carbon.

[0065] However, nitrogen can strongly bond with Al, Ti, Nb, etc., forming precipitates such as AlN, TiN, and NbN, which can increase iron loss and suppress grain growth, so it is preferable to add only a small amount. In one embodiment of the present invention, the nitrogen content may be 0.005% by weight or less.

[0066] [Titanium (Ti)] Titanium (Ti) can form fine precipitates such as TiC and TiN by bonding with C and N, which can suppress grain growth. Although titanium can reduce nitrogen in steel, if the titanium content is excessive, the increased carbides and nitrides can lead to a degraded texture and potentially inferior magnetic properties. Since the magnetic properties deteriorate as more titanium is added, it is preferable to add only a small amount.

[0067] Therefore, the steel material according to one embodiment of the present invention may contain 0.005% by weight or less of titanium.

[0068] [Lin(P)] Phosphorus (P) is an impurity element in steel that can cause cracks during casting and reduce weldability. If the phosphorus content is excessive, not only will the castability deteriorate and the likelihood of steel brittleness increase, but the likelihood of dent defects may also increase. Therefore, it is preferable to add a small amount of phosphorus. In one embodiment of the present invention, the phosphorus content may be 0.015% by weight or less.

[0069] On the other hand, in addition to the aforementioned elements, austenite phase stabilizing elements such as Mn, Co, and Cr can be added as needed to stabilize the austenite phase.

[0070] In addition to the steel components described above, the remainder may include Fe and unavoidable impurities. These unavoidable impurities are those introduced during the steelmaking process and the manufacturing process of electrical steel sheets, and since they are widely known in the relevant field, a detailed explanation will be omitted. In one embodiment of the present invention, the addition of elements other than the alloy components described above is not excluded, and a variety of elements may be included within a range that does not impair the technical concept of the present invention. If additional elements are further included, they may be included in place of the remainder Fe.

[0071] Manufacturing method of non-oriented electrical steel sheets In the following, a method for manufacturing non-oriented electrical steel sheets according to one embodiment of the present invention will be specifically described with reference to Figure 1.

[0072] Referring to Figures 1 and 2, a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention includes the steps of: (a) preparing a steel material which is a semi-finished product containing 2.5 to 3.8% by weight of silicon (Si), 1.45% by weight or more of nickel (Ni), 0.05% by weight or less of aluminum (Al), and the remaining 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.

[0073] Referring also to Figures 2 and 3, in a 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) heating from room temperature to a first temperature (T1) at which the austenite phase is stable, and maintaining it for a first set time (t1), (d-2) cooling to a second temperature (T2) at which the two-phase region where the austenite phase and the ferrite phase coexist is stable, and maintaining it for a second set time (t2), and (d-3) cooling to room temperature.

[0074] However, the examples are not necessarily limited to these, and the method for manufacturing non-oriented electrical steel sheets may further include a hot rolling and annealing step and a coating step, which will be described later. In the following, each step of the method for manufacturing non-oriented electrical steel sheets will be described in detail.

[0075] First, (a) the step of preparing a semi-finished steel material may be the step of manufacturing a steel material containing 2.5 to 3.8% by weight of silicon (Si), 1.45% by weight or more of nickel (Ni), 0.05% by weight or less of aluminum (Al), and the remainder being iron (Fe) and other unavoidable impurities. The semi-finished material may be, for example, a slab, but is not necessarily limited to this. Furthermore, the manufacturing of the slab may be carried out by processes known in the relevant art, such as a smelting process, a steelmaking process, or a continuous casting process.

[0076] The steel material may further contain 0.005% by weight or less of carbon (C), 0.005% by weight or less of sulfur (S), 0.005% by weight or less of nitrogen (N), 0.005% by weight or less of titanium (Ti), and 0.015% by weight or less of phosphorus (P).

[0077] Furthermore, nickel (Ni) may be added to the steel material depending on the silicon (Si) content. Although silicon is added to the steel material to reduce iron loss in non-oriented electrical steel sheets, if the amount of silicon added is 1.7% by weight or more, the austenite region may disappear, and only the ferrite single-phase region may exist. Therefore, in order to ensure the austenite phase at high temperatures, a certain amount of nickel may be added. The nickel content depending on the silicon content may satisfy the following formula 1. [Formula 1] [Ni]≧2.52[Si]-5.3 ([Ni] and [Si] represent weight percentages of Ni and Si, respectively.)

[0078] Here, the [Si] applied to Formula 1 may be 2.5% by weight or more and 3.8% by weight or less. For example, if the silicon (Si) content of the steel material is 2.5% by weight, the nickel (Ni) content may be in the range of 1.45% by weight or more, and if the silicon (Si) content is 2.68% by weight, the nickel (Ni) content may be in the range of 1.45% by weight or more so as to satisfy both of the above [Formula 1].

[0079] According to one embodiment of the present invention, the nickel (Ni) content can be adjusted as a stabilizing element of the austenite phase. However, the invention is not limited thereto, and corresponding effects can be obtained by further utilizing other austenite phase stabilizing elements such as Mn, Co, and Cr, or by substituting nickel (Ni).

[0080] Next, (b) the step of hot-rolling the steel material to form a hot-rolled steel sheet is the step of hot-rolling the semi-finished product prepared in step (a) to form a hot-rolled steel sheet. Hot-rolling may include reheating, rough-rolling, finish-rolling, cooling, and winding processes.

[0081] First, the reheating process may involve reheating a semi-finished product for subsequent processes. The semi-finished product can be reheated under conditions where the SRT (Slab Reheating Temperature) is between 1110°C and 1150°C. If the SRT is below 1110°C, the deformation resistance during hot rolling will increase, potentially increasing the rolling load and reducing rollability. If it exceeds 1150°C, precipitates such as C, S, and N in the slab will be redissolved, potentially leading to the generation of fine precipitates during subsequent rolling and annealing processes. This could suppress grain growth and result in inferior magnetism. Therefore, in this invention, the semi-finished product can be reheated at a temperature between 1110°C and 1150°C.

[0082] Next, the rough rolling process may be used to produce semi-finished products into rolled material with appropriate shapes, thicknesses, and widths, and the finish rolling process may be used to adjust the semi-finished products to a specified thickness and width, and then roll them to a good surface and shape at a finishing temperature suitable for the intended use.

[0083] In this case, the FDT (Finishing Delivery Temperature) may be between 800°C and 900°C. If the FDT is below 800°C, rolling will occur in the two-phase region, forming a non-uniform structure that can significantly reduce impact toughness. If it exceeds 900°C, although ductility and toughness will be excellent, a problem may arise in which the strength decreases rapidly. Therefore, it is preferable that the FDT be between 800°C and 900°C.

[0084] Furthermore, the Coiling Temperature (CT) may be between 500°C and 700°C. If the CT is below 500°C, the crystal grain size may become too small, and the crystal grains may not grow sufficiently even after annealing. If the CT exceeds 700°C, there may be an increase in fine precipitates, which may reduce the magnetic properties. Therefore, it is preferable that the CT be between 500°C and 700°C.

[0085] (b) After step, the thickness of the hot-rolled steel sheet is preferably 2.6 mm or less. The thicker the hot-rolled steel sheet, the greater the reduction ratio of the cold rolling, and the inferior the texture may become, so the thickness of the hot-rolled steel sheet is preferably 2.6 mm or less.

[0086] However, if the thickness of the hot-rolled steel sheet is excessively thin, the thickness obtained after cold rolling may not be sufficient, which can lead to shape defects when the product is applied. Therefore, the thickness of the hot-rolled steel sheet may more preferably be 1.6 mm or more and 2.6 mm or less.

[0087] A hot rolling annealing step may be carried out between step (b) and step (c). The hot rolling annealing step may involve heat-treating the hot-rolled steel sheet at a temperature of 940°C to 1110°C for 30 to 180 seconds. Within the aforementioned heat treatment temperature range, the microstructure of the hot-rolled steel sheet can be uniformly formed with an average size of 50 to 200 mm. If the annealing temperature is too low, the stretched cast structure remaining after hot rolling may persist, inducing microstructure irregularities, resulting in smaller grain sizes and potentially reducing cold-rollability. On the other hand, if the annealing temperature is too high, it may induce an imbalance in the texture of the final product.

[0088] Therefore, the hot rolling annealing step can be carried out at a temperature of 940°C to 1110°C for 30 to 180 seconds. However, the hot rolling annealing step can be carried out selectively as needed, and the cold rolling step can be performed immediately after the hot rolling step without the hot rolling annealing step.

[0089] Cooling may be carried out after the hot rolling annealing step, and the cooling rate may be 20°C / initial or higher.

[0090] Furthermore, a pickling step may be performed after step (b). The pickling step may be a step in which an oxidizing scale layer formed on the surface of the hot-rolled steel sheet is removed with a pickling solution, and more specifically, it may be performed before step (c).

[0091] Subsequently, (c) the step of cold rolling the hot-rolled steel sheet to form a cold-rolled steel sheet may be carried out. (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 wound hot-rolled steel sheet at a temperature below the recrystallization temperature to further reduce the thickness of the steel sheet. Cold rolling may be a step of raising the temperature of the steel sheet to 75°C or more and 200°C or less in order to impart rollability to the pickled hot-rolled steel sheet, and then warm rolling with a reduction ratio of 50 to 90%. The thickness of the cold-rolled steel sheet formed in this way may be 0.1 mm or more and 0.5 mm or less.

[0092] After step (c), the step of cold-rolling annealing the cold-rolled steel sheet may be carried out. Cold-rolling annealing may be a process in which the steel material is exposed to and maintained at a temperature above the recrystallization temperature, and then cooled, thereby softening the material of the steel material that was hardened during cold rolling.

[0093] In a 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) heating from room temperature to a first temperature (T1) at which the austenite phase is stable, and maintaining it for a first set time (t1), (d-2) cooling to a second temperature (T2) at which the two-phase region where the austenite phase and the ferrite phase coexist is stable, and maintaining it for a second set time (t2), and (d-3) cooling to room temperature.

[0094] Steps (d-1), (d-2), and (d-3) described above will be explained in detail below.

[0095] First, step (d-1) involves heating from room temperature to a first temperature (T1) at which the austenite phase is stable, and then maintaining this temperature for a first set time (t1). Here, the first temperature (T1) may mean the temperature at which the austenite single-phase region is stable. The first temperature (T1) is preferably 1000 to 1200°C, but is not necessarily limited to this, and may include all cases where the austenite single-phase region is stable. The first set time (t1) may be 20 to 50 seconds.

[0096] Next, step (d-2) may be a step in which the two-phase region where the austenite phase and the ferrite phase coexist is cooled to a second temperature (T2) which is a stable temperature, and then maintained for a second set time (t2). That is, the second temperature (T2) may mean the temperature at which the two-phase region of the austenite phase and the ferrite phase is maintained in a stable state, in which case the ratio of the peak of the {200} texture to the peak of the {112} texture, {200} / {112}, may be 1.3 or greater.

[0097] In step (d-2) above, the second temperature (T2) may be between 930°C and 970°C in order to facilitate the nucleation of the ferrite phase. If the second temperature (T2) is less than 930°C, the grain size is fine and hysteresis loss may increase, and if the second temperature (T2) is greater than 970°C, the grain size becomes coarser and eddy current loss may increase. Preferably, the second temperature (T2) may be between 935°C and 970°C.

[0098] Furthermore, the second setting time (t2) may be 5 seconds or more, and preferably 5 to 45 seconds.

[0099] Next, (d-3) the step of cooling to room temperature may be carried out.

[0100] Furthermore, the coating of the cold-rolled steel sheet may be carried out to ensure punchability and insulation, and may form an insulating film on the surface of the final annealed cold-rolled steel sheet.

[0101] In one embodiment of the present invention, a method for manufacturing non-oriented electrical steel sheets involves designing the alloy composition so that sequential phase transformations to ferrite phase, austenite phase, and ferrite phase are possible during cold rolling and annealing. By cooling the two-phase region where the austenite and ferrite phases coexist to a stable temperature and then maintaining that temperature, the texture is improved so that orientations favorable to magnetism develop, thereby improving both magnetic and mechanical properties.

[0102] In other words, by utilizing the characteristic that the orientation preferred for formation changes in each temperature range during the phase transformation from the austenite phase to the ferrite phase, the texture improvement effect can be maximized so that the {100} / ND orientation develops.

[0103] The non-oriented electromagnetic steel sheet according to an embodiment of the present invention manufactured by the above manufacturing method may have a sum of the {100} / ND fraction and the {110} / ND fraction of 46.0% or more, the {100} / ND fraction may be 28.8% or more, and the {112} / ND fraction may be 23.3% or less. Here, ND is an abbreviation for Normal Direction and may mean a direction perpendicular to the plane including the rolling direction, that is, a direction perpendicular to the surface of the sheet material.

[0104] Also, the mechanical properties of the non-oriented electromagnetic steel sheet as the final product thereof may be a yield strength (YS) of 250 MPa or more and a tensile strength (TS) of 400 MPa or more.

[0105] In addition, a product with improved magnetic properties can be obtained as compared with a product manufactured without going through the process of maintaining the time already set in the two-phase region during cold rolling and annealing. At this time, the magnetic properties mean iron loss (W 10 / 400 ) and magnetic flux density (B 50 ). More specifically, (W 10 / 400 ) means the iron loss at 400 Hz and 1.0 T, and B 50 means the size of the magnetic flux density induced when a magnetic field of 5000 A / m is applied.

[0106] Comparative Examples and Experimental Examples Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred comparative examples and experimental examples of the present invention. However, this is presented as a preferred exemplification for helping the understanding of the present invention, and the present invention is not limited thereby.

[0107] Table 1 shows the main alloy element compositions of this comparative example and experimental examples, and Table 2 shows the results of in-situ XRD analysis of the F / H samples of the compositions presented in Table 1 under the process conditions of Table 2. The process conditions not presented in Table 2 satisfy the manufacturing method of the non-oriented electromagnetic steel sheet according to an embodiment of the present invention described above and are controlled to be the same in the overall comparative examples and experimental examples.

[0108] [Table 1]

[0109] [Table 2]

[0110] First, referring to Table 1, Comparative Examples 3, 6, 9, and 10, which have alloy compositions A1, A4, A7, and A8, do not satisfy Formula 1, which shows the minimum amount of nickel added according to the silicon content in one embodiment of the present invention. Also, in the case of Comparative Example 7, which has an alloy composition A5, Formula 1 is satisfied, but the amount of aluminum (Al) added exceeds 0.05% by weight. As a result, no phase transformation occurred in Comparative Examples 3, 6, 7, 9, and 10, and when compared with the experimental example, it can be confirmed that fewer {100} / ND, which is advantageous for magnetism, are formed, and more {112} / ND, which is disadvantageous for magnetism, are formed.

[0111] Next, referring to Table 2, in the case of Comparative Example 1, the step of cooling the two-phase region where the austenite phase and ferrite phase coexist to a second temperature, which is a stable temperature, and then maintaining it for a second set time was not performed. Specifically, in Comparative Example 1, the texture and magnetic properties were confirmed under conditions in which an F / H sample with the component composition of A9 was heated from room temperature to 965°C, maintained for 45 seconds, and then cooled. As a result, the texture characteristics showed that 0.3% of {100} / ND, which is a magnetically favorable orientation, and 83.6% of {112} / ND, which is a magnetically unfavorable orientation, were formed. And the magnetic properties B 50 = 1.58T, W 10 / 400 The result is 13.58 W / kg, which, when compared to the experimental example, shows a relatively inferior characteristic.

[0112] In the case of Comparative Example 2, the temperature falls outside the range of the second temperature according to the present invention. Specifically, Comparative Example 2 shows the texture and magnetic properties of an A0 composition F / H sample heated from room temperature to 1100°C, where the austenite phase is stable, maintained for 45 seconds, cooled to 550°C, where the ferrite phase is stable, maintained again for 45 seconds, and then cooled back to room temperature. Under these conditions, {200} / {112} was 0.77, less than 1.3, {100} / ND, which is favorable for magnetism, was formed at 8.1%, and {112} / ND, which is unfavorable for magnetism, was formed at 41.9%. As a result, B exhibited inferior properties compared to the experimental example. 50 = 1.68T, W 10 / 400 It exhibited magnetic properties of 13.21 W / kg.

[0113] In the case of Comparative Example 4, the temperature falls outside the range of the second temperature according to the present invention. Specifically, Comparative Example 4 shows the texture and magnetic properties of an F / H sample of composition A2 under the following conditions: heated from room temperature to 1125°C, where the austenite phase is stable, maintained for 40 seconds, cooled to 550°C, where the ferrite phase is stable, maintained again for 45 seconds, and then cooled back to room temperature. Under these conditions, {200} / {112} was 0.77, less than 1.3, {100} / ND, which is favorable for magnetism, was formed at 9.1%, and {112} / ND, which is unfavorable for magnetism, was formed at 37.2%. As a result, B exhibited inferior properties compared to the experimental example. 50 = 1.67T, W 10 / 400 It exhibited magnetic properties of 12.95 W / kg.

[0114] In the case of Comparative Example 5, the temperature falls outside the range of the second temperature according to the present invention. Specifically, Comparative Example 5 shows the texture and magnetic properties of an A3 composition F / H sample heated from room temperature to a region where the austenite phase is stable at 1100°C, maintained for 45 seconds, cooled to a temperature where the ferrite phase is stable at 550°C, maintained again for 45 seconds, and then cooled back to room temperature. Under these conditions, {200} / {112} was 0.75, less than 1.3, {100} / ND favorable for magnetism was formed at 8.8%, and {112} / ND unfavorable for magnetism was formed at 36.7%. As a result, B exhibited inferior properties compared to the experimental example. 50 = 1.67T, W 10 / 400 It exhibited a magnetic property of 12.87 W / kg.

[0115] In the case of Comparative Example 8, the temperature falls outside the range of the second temperature according to the present invention. Specifically, Comparative Example 8 shows the texture and magnetic properties of an F / H sample of composition A6 under the following conditions: heated from room temperature to 1100°C, where the austenite phase is stable, maintained for 45 seconds, cooled to 550°C, where the ferrite phase is stable, maintained again for 45 seconds, and then cooled back to room temperature. Under these conditions, {200} / {112} was 0.74, less than 1.3, {100} / ND, which is favorable for magnetism, was formed at 7.5%, and {112} / ND, which is unfavorable for magnetism, was formed at 36.6%. As a result, B exhibited inferior properties compared to the experimental example. 50 = 1.67T, W 10 / 400 It exhibited magnetic properties of 12.32 W / kg.

[0116] In the case of Comparative Example 11, the temperature falls outside the range of the second temperature according to the present invention. Specifically, Comparative Example 11 shows the texture and magnetic properties of an F / H sample of composition A9 under the following conditions: heated from room temperature to 1150°C, where the austenite phase is stable, maintained for 40 seconds, cooled to 550°C, where the ferrite phase is stable, maintained again for 45 seconds, and then cooled back to room temperature. Under these conditions, {200} / {112} was 0.73, less than 1.3, {100} / ND, which is favorable for magnetism, was formed at 8.2%, and {112} / ND, which is unfavorable for magnetism, was formed at 39.0%. As a result, B exhibited inferior properties compared to the experimental example. 50 = 1.66T, W 10 / 400 It exhibited magnetic properties of 12.32 W / kg.

[0117] In the case of Comparative Example 12, the temperature falls outside the range of the second temperature according to the present invention. Specifically, Comparative Example 12 shows the texture and magnetic properties of an F / H sample of composition A10 under the following conditions: heated from room temperature to 1150°C, where the austenite phase is stable, maintained for 45 seconds, cooled to 550°C, where the ferrite phase is stable, maintained again for 45 seconds, and then cooled back to room temperature. Under these conditions, {200} / {112} was 0.72, less than 1.3, {100} / ND, which is favorable for magnetism, was formed at 6.7%, and {112} / ND, which is unfavorable for magnetism, was formed at 39.7%. As a result, B exhibited inferior properties compared to the experimental example. 50 = 1.65, W 10 / 400 It exhibited magnetic properties of 12.25 W / kg.

[0118] In the case of Comparative Example 13, the temperature falls outside the range of the second temperature according to the present invention. Specifically, Comparative Example 13 shows the texture and magnetic properties of an F / H sample of composition A10 under the following conditions: heated from room temperature to 1150°C in the region where the austenite phase is stable, maintained for 45 seconds, cooled to a temperature of 920°C, maintained again for 45 seconds, and then cooled to room temperature. Under these conditions, {200} / {112} was 0.75 and less than 1.3, {100} / ND favorable for magnetism was formed at 7.2%, and {112} / ND unfavorable for magnetism was formed at 38.4%. As a result, B exhibited inferior properties compared to the experimental example.50 = 1.67, W 10 / 400 It exhibited magnetic properties of 12.58 W / kg.

[0119] In the case of Comparative Example 14, the temperature falls outside the range of the second temperature according to the present invention. Specifically, Comparative Example 14 shows the texture and magnetic properties of an F / H sample of composition A10 under the following conditions: heated from room temperature to 1150°C in the region where the austenite phase is stable, maintained for 45 seconds, cooled to a temperature of 980°C, maintained again for 45 seconds, and then cooled to room temperature. Under these conditions, {200} / {112} was 0.73, less than 1.3, {100} / ND favorable for magnetism was formed at 9.0%, and {112} / ND unfavorable for magnetism was formed at 38.6%. As a result, B exhibited inferior properties compared to the experimental example. 50 = 1.66, W 10 / 400 It exhibited a magnetic property of 12.47 W / kg.

[0120] In the case of Comparative Example 15, the range of the second set time according to the present invention falls outside the specified range. Specifically, Comparative Example 15 shows the texture and magnetic properties of an F / H sample of composition A10 under the following conditions: heated from room temperature to 1150°C to a region where the austenite phase is stable, maintained for 45 seconds, cooled to a temperature of 980°C, maintained again for 3 seconds, and then cooled to room temperature. Under these conditions, {200} / {112} was 0.76, less than 1.3, {100} / ND favorable for magnetism was formed at 8.7%, and {112} / ND unfavorable for magnetism was formed at 36.9%. As a result, B exhibited inferior properties compared to the experimental example. 50 = 1.67, W 10 / 400 It exhibited magnetic properties of 12.11 W / kg.

[0121] On the other hand, in Experimental Examples 1 to 7, the alloy composition according to one embodiment of the present invention satisfies formula 1, and a cold rolling annealing process was performed to perform phase transformation heat treatment in the two-phase region. As a result, the texture was improved so that orientations favorable to magnetism developed, and 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 properties, such as magnetic flux density (B), were improved. 50 The value is 1.68T or higher, and the iron loss (W) 10 / 400 The value can be confirmed to be 11.88 W / kg or less.

[0122] Although the present invention has been described above by limited embodiments and drawings, it is not limited thereto, and can be implemented in various ways by persons with ordinary skill in the art to which the present invention pertains, within the equivalent scope of the technical concept of the present invention and the claims described below.

Claims

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

2. The aforementioned two-phase region is A method for manufacturing a non-oriented electrical steel sheet according to claim 1, wherein the ratio of the peak of the {200} texture to the peak of the {112} texture, {200} / {112}, is 1.3 or greater.

3. The second temperature is, A method for manufacturing a non-oriented electrical steel sheet according to claim 1, wherein the temperature is 930 to 970°C.

4. The second setting time is A method for manufacturing a non-oriented electrical steel sheet according to claim 1, wherein the time is 5 seconds or more.

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

6. The aforementioned steel material is A method for producing a non-oriented electrical steel sheet according to claim 1, further comprising 0.005% by weight or less of carbon (C), 0.005% by weight or less of sulfur (S), 0.005% by weight or less of nitrogen (N), 0.005% by weight or less of titanium (Ti), and 0.015% by weight or less of phosphorus (P).

7. The aforementioned steel material is A method for manufacturing a non-oriented electrical steel sheet according to claim 1, satisfying the following formula 1. [Formula 1] [Ni]≧2.52 [Si]-5.3 ([Ni] and [Si] represent weight percentages of Ni and Si, respectively.)

8. A steel material containing 2.5 to 3.8% by weight of silicon (Si), 1.45% by weight or more of nickel (Ni), 0.05% by weight or less of aluminum (Al), and the remaining iron (Fe) and other unavoidable impurities is hot-rolled, and then cold-rolled to form a cold-rolled steel sheet. The cold-rolled steel sheet is cold-rolled and annealed to produce the final product. Non-oriented electrical steel sheet manufactured by the cold rolling and annealing process described above, in which the material is heated from room temperature to a first temperature at which the austenite phase is stable, maintained for a first set time, then cooled to a second temperature at which the two-phase region where the austenite and ferrite phases coexist is stable, maintained for a second set time, and then cooled back to room temperature.

9. The aforementioned two-phase region is The non-oriented electrical steel sheet according to claim 8, wherein the ratio of the peak of the {200} texture to the peak of the {112} texture, {200} / {112}, is 1.3 or greater.

10. The second temperature is, The non-oriented electrical steel sheet according to claim 8, wherein the temperature is 930 to 970°C.

11. The second setting time is The non-oriented electrical steel sheet according to claim 8, wherein the time is 5 seconds or more.

12. The aforementioned steel material is A non-oriented electrical steel sheet according to claim 8, satisfying the following formula 1. [Formula 1] [Ni]≧2.52 [Si]-5.3 ([Ni] and [Si] represent weight percentages of Ni and Si, respectively.)

13. The aforementioned steel material is The non-oriented electrical steel sheet according to claim 8, further comprising 0.005% by weight or less of carbon (C), 0.005% by weight or less of sulfur (S), 0.005% by weight or less of nitrogen (N), 0.005% by weight or less of titanium (Ti), and 0.015% by weight or less of phosphorus (P).

14. The non-oriented electrical steel sheet according to claim 8, wherein the sum of the {100} / ND fraction and the {110} / ND fraction of the final product is 46.0% or more.

15. The non-oriented electrical steel sheet according to claim 8, wherein the {100} / ND fraction of the final product is 28.8% or more, and the {112} / ND fraction is 23.3% or less.

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

17. The non-oriented electrical steel sheet according to claim 16, wherein the content of silicon and nickel satisfies the following formula 1. [Formula 1] [Ni]≧2.52 [Si]-5.3 ([Ni] and [Si] represent weight percentages of Ni and Si, respectively.)

18. The non-oriented electrical steel sheet according to claim 16, wherein the sum of the {100} / ND fraction and the {110} / ND fraction is 46.0% or more.

19. The non-oriented electrical steel sheet according to claim 16, wherein the {100} / ND fraction is 28.8% or more and the {112} / ND fraction is 23.3% or less.

20. The non-oriented electrical steel sheet according to claim 16, further comprising 0.005% by weight or less of carbon (C), 0.005% by weight or less of sulfur (S), 0.005% by weight or less of nitrogen (N), 0.005% by weight or less of titanium (Ti), and 0.015% by weight or less of phosphorus (P).

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