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

Abstract

A non-oriented electrical steel sheet according to an embodiment of the present invention comprises 2.0-4.0 wt% of silicon (Si), 0.5-2.0 wt% of manganese (Mn), 0.1 wt% or less (excluding 0 wt%) of aluminum (Al), 0.01 wt% or less (excluding 0 wt%) of vanadium (V), and the balance of iron (Fe) and other inevitable impurities, and satisfies equation 1, so that a non-oriented electrical steel sheet having low iron loss and a method for manufacturing the non-oriented electrical steel sheet can be implemented.

Description

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

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

[0002] In line with recent global policies to reduce carbon dioxide emissions to combat global warming, conventional internal combustion engine vehicles are rapidly being replaced by eco-friendly vehicles such as hybrid, electric, and hydrogen-powered vehicles. Eco-friendly vehicles utilize electric motors to generate the necessary driving force and significantly reduce harmful exhaust gas emissions, thereby minimizing environmental pollution.

[0003] As interest in and demand for eco-friendly vehicles grows, so does the demand for electric motors, which power these vehicles. Electric motors use electricity to generate the power needed for vehicles. Energy efficiency, which allows them to operate for longer periods of time using the same amount of energy, is a crucial technological element.

[0004] To improve the energy efficiency of such electric motors, it is essential to improve the magnetic performance of non-oriented electrical steel, which is used as the core material. Non-oriented electrical steel exhibits consistent magnetic properties in all directions, regardless of rolling direction. To improve energy efficiency, it is necessary to reduce core loss and increase magnetic flux density.

[0005] This magnetic flux density is determined by the arrangement of crystal grains. In particular, the magnetic anisotropy of iron (Fe) atoms makes it easy to magnetize. <100> It is desirable to uniformly generate a oriented aggregate structure throughout the sheet. Next, iron loss refers to the energy loss that occurs during the magnetization process of a material, and can be expressed as the energy loss occurring at a specific magnetic flux density and frequency.

[0006] The most effective way to improve these magnetic properties is to add silicon (Si). Adding silicon (Si), which has high resistivity, increases the material's inherent electrical resistance, thereby reducing core loss. However, while adding silicon (Si) can reduce core loss, adding large amounts can increase the material's brittleness, potentially leading to sheet fracture during cold rolling. Furthermore, increasing the amount of silicon (Si) added can lead to a decrease in saturation flux density.

[0007] To overcome the aforementioned problems, a method of adding aluminum (Al) or manganese (Mn), which have the second highest resistivity after silicon (Si), is commonly used. This minimizes brittleness and reduces iron loss. In particular, a method of reducing iron loss by adding large amounts of aluminum (Al) is used.

[0008] However, aluminum (Al) combines with nitrogen (N) present in steel to form fine precipitates. These fine precipitates lower iron loss and inhibit grain growth, thereby degrading magnetic properties. Furthermore, the addition of these alloying elements can be a major factor in increasing production costs.

[0009] Therefore, there is a need to develop a technology that improves magnetic properties by increasing the aggregate structure that is advantageous for magnetic properties without increasing the content of major alloying elements such as aluminum (Al).

[0010] [Patent Document]

[0011] (Patent Document 1) Republic of Korea Publication Patent No. 2023-0096881

[0012] 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 having excellent magnetic properties and a method for manufacturing a non-oriented electrical steel sheet by developing a grain structure advantageous for magnetic properties.

[0013] 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.

[0014] A non-oriented electrical steel sheet according to one embodiment of the present invention contains 2.0 to 4.0 wt% of silicon (Si), 0.5 to 2.0 wt% of manganese (Mn), 0.1 wt% or less of aluminum (Al) (excluding 0 wt%), 0.01 wt% or less of vanadium (V) (excluding 0 wt%), and the remainder iron (Fe) and other unavoidable impurities, and satisfies the following equation 1.

[0015] [Formula 1]

[0016]

[0017] (However, in the above formula 1, P{001} and P{112} represent the XRD peak intensities of the {001} and {112} directions, respectively, through XRD (X-ray diffraction) analysis.)

[0018] Additionally, the average grain size may be 2000 to 5000 μm.

[0019] Additionally, it may further include 0.01 wt% or less of carbon (C), 0.01 wt% or less of sulfur (S), and 0.01 wt% or less of nitrogen (N).

[0020] Additionally, it may further contain 0.2 wt% of phosphorus (P).

[0021] Also, iron loss (W 10 / 400 ) may be less than 11W / kg.

[0022] A non-oriented electrical steel sheet according to one embodiment of the present invention comprises a first step of preparing a steel material including the above-described alloy composition, a second step of hot-rolling the steel material to form a hot-rolled steel sheet, a third step of hot-rolling and annealing the hot-rolled steel sheet, a fourth step of cold-rolling the hot-rolled steel sheet subjected to the third step to form a cold-rolled steel sheet, and a fifth step of cold-rolling and annealing the cold-rolled steel sheet at 1000 to 1250°C for 8 to 16 hours.

[0023] In addition, the steel material that has undergone the above-mentioned fifth step can satisfy the above-mentioned equation 1.

[0024] Additionally, the steel material that has undergone the above-mentioned fifth step may have an average grain size of 2000 to 5000 μm.

[0025] Additionally, the steel may further include 0.01 wt% or less of carbon (C), 0.01 wt% or less of sulfur (S), and 0.01 wt% or less of nitrogen (N).

[0026] Additionally, the steel may further contain 0.2 wt% of phosphorus (P).

[0027] In addition, the steel that performed the above 5th step has a core loss (W 10 / 400 ) may be less than 11W / kg.

[0028] According to one embodiment of the present invention, by controlling the alloy composition and manufacturing process, a texture advantageous for magnetic properties can be formed, thereby realizing a non-oriented electrical steel sheet and a method for manufacturing a non-oriented electrical steel sheet having excellent magnetic properties.

[0029] The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

[0030] FIG. 1 is a flowchart schematically illustrating a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0031] Figure 2 is a drawing showing the XRD peak intensity measurement location and measurement results.

[0032] Figure 3 is a drawing showing a method for measuring average crystal grain size.

[0033] Figure 4 is a drawing showing a test piece for measuring iron loss.

[0034] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. However, the present invention is not limited or restricted by the following embodiments.

[0035] Additionally, when a component (or region, layer, portion, etc.) is referred to as being "on," "connected to," or "coupled to" another component, it means that it can be directly placed / connected / coupled to the other component, or that a third component may be placed between them.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] Unless otherwise specified, the notation 'A to 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.

[0040] Also, unless otherwise stated, 1 ppm is 0.0001 wt%.

[0041]

[0042] Non-oriented electrical steel sheet

[0043] A non-oriented electrical steel sheet according to one embodiment of the present invention contains 2.0 to 4.0 wt% of silicon (Si), 0.5 to 2.0 wt% of manganese (Mn), 0.1 wt% or less of aluminum (Al) (excluding 0 wt%), 0.01 wt% or less of vanadium (V) (excluding 0 wt%), and the remainder iron (Fe) and other unavoidable impurities.

[0044] Hereinafter, the role and content of alloy elements included in a non-oriented electrical steel sheet according to one embodiment of the present invention will be described in detail.

[0045]

[0046] Silicon (Si)

[0047] Silicon (Si) is a key additive in electrical steel, increasing the steel's resistivity and reducing core loss. However, too little silicon can insufficiently improve core loss. However, excessive silicon can reduce magnetic flux density and, due to increased brittleness, compromise cold-rollability. Therefore, appropriate adjustment of the silicon content is necessary.

[0048] If the silicon content is less than 2.0 wt%, the above-described effect cannot be expected, and if the silicon content exceeds 4.0 wt%, problems such as a decrease in magnetic flux density and an increase in brittleness may occur. Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain 2.0 to 4.0 wt% of silicon.

[0049]

[0050] manganese (Mn)

[0051] Manganese (Mn), like silicon (Si), is an element that improves magnetic properties by increasing resistivity and reducing iron loss. It can also enhance the fraction of aggregate structures with favorable magnetic properties.

[0052] In addition, manganese can combine with sulfur (S) present in steel to form sulfides such as MnS. If the MnS precipitates remain until the end of cold rolling annealing, the MnS precipitates may inhibit the growth of grains with a {001} orientation, making it difficult to secure a high orientation fraction favorable for magnetic properties. Therefore, the manganese content must be appropriately controlled to secure a high {001} orientation fraction.

[0053] When the manganese content exceeds 2.0 wt%, a large amount of MnS may be formed, and coarse-sized MnS precipitates may be formed, which may reduce the magnetic flux density. On the other hand, when the manganese content is less than 0.5 wt%, the above-described effect cannot be expected. In addition, since sulfur (S) in the steel is not precipitated as MnS but is dissolved in atomic form, sulfur (S) in the steel may be concentratedly segregated on the steel surface, which may hinder the growth of crystal grains with a {001} orientation.

[0054] Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain 0.5 to 2.0 wt% of manganese.

[0055]

[0056] Aluminum (Al)

[0057] Aluminum (Al), along with silicon (Si) and manganese (Mn), increases resistivity and reduces iron loss, making it a key additive in electrical steel. Aluminum can also play a role in reducing magnetic anisotropy, thereby reducing magnetic deviation.

[0058] Aluminum can combine with nitrogen to form nitrides, such as AlN. Furthermore, when combined with oxygen, it can form oxides, such as alumina (Al2O3). These nitrides and oxides can inhibit the growth of grains with the {001} orientation.

[0059] Therefore, in the present invention, in order to grow crystal grains having a {001} orientation that is advantageous for magnetic properties, the aluminum content that suppresses crystal grain growth and forms fine precipitates is controlled to an extremely small amount.

[0060] More specifically, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain 0.1 wt% or less of aluminum, and preferably may contain more than 0 wt% and 0.1 wt% or less of aluminum.

[0061]

[0062] Vanadium (V)

[0063] Vanadium (V) reacts with carbon (C) and nitrogen (N) in steel to form carbides and nitrides. These carbides and nitrides inhibit grain growth, thereby minimizing grain size. This suppresses excessive grain growth, and grain size can be controlled through the vanadium content.

[0064] However, if the vanadium content exceeds 0.01 wt%, the aforementioned grain refinement may occur excessively, which may cause a problem of poor iron loss. Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain vanadium in an amount of 0.01 wt% or less, and preferably in an amount of more than 0 wt% and 0.01 wt% or less.

[0065] In addition, when the vanadium content is extremely low, grains may grow excessively, increasing eddy current loss and iron loss. Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain vanadium in an amount of 0.0001 wt% or more, and preferably, vanadium in an amount of 0.0003 wt% or more and 0.01 wt% or less.

[0066]

[0067] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include 0.01 wt% or less of carbon (C), 0.01 wt% or less of sulfur (S), and 0.01 wt% or less of nitrogen (N).

[0068]

[0069] carbon (C)

[0070] Carbon can increase iron loss by combining with vanadium (V) to form carbides. Furthermore, when the carbon content exceeds 0.01 wt%, it can expand the austenite (γ) region, inhibiting the growth of grains with the {001} orientation during cold rolling annealing. Furthermore, it can combine with iron (Fe), titanium (Ti), etc. to form carbides, thereby lowering the magnetic flux density and iron loss.

[0071] Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain carbon in an amount of 0.01 wt% or less.

[0072]

[0073] Yellow (S)

[0074] Sulfur (S) is an impurity element that is inevitably contained during the manufacturing process, and can combine with elements such as manganese (Mn) to form precipitates such as MnS. In particular, when a large amount of sulfur is added, MnS may be excessively precipitated during the cooling process after hot rolling and the cold rolling annealing process. Excessive precipitation of MnS may hinder the growth of grains with the {001} orientation and promote the growth of grains with the {110} orientation. In this case, the final microstructure may be formed of grains with the {110} orientation, resulting in the production of electrical steel sheets that are not suitable for motor cores.

[0075] Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain sulfur in an amount of 0.01 wt% or less.

[0076]

[0077] Nitrogen (N)

[0078] Nitrogen (N) can combine with aluminum (Al) or titanium (Ti) to form nitrides such as AlN and TiN, which can increase iron loss and inhibit the growth of grains with a {001} orientation. In addition, when the nitrogen content exceeds 0.01 wt%, it can expand the austenite (γ) region during cold rolling annealing, thereby inhibiting the growth of grains with a {001} orientation.

[0079] Therefore, it is desirable to add as little as possible, and the non-oriented electrical steel sheet according to one embodiment of the present invention may contain nitrogen in an amount of 0.01 wt% or less.

[0080]

[0081] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include 0.2 wt% or less of phosphorus (P).

[0082]

[0083] Person (P)

[0084] Phosphorus is a grain boundary segregation element, and if added excessively, problems such as grain growth inhibition, deterioration of magnetic properties, and reduction in cold rolling properties may occur due to the segregation effect. Therefore, it is preferable to add as little phosphorus as possible, and the non-oriented electrical steel sheet according to one embodiment of the present invention may contain phosphorus at 0.2 wt% or less.

[0085]

[0086] In addition to the aforementioned steel components, the remainder may contain iron and unavoidable impurities. Unavoidable impurities are impurities introduced during the steelmaking process and the manufacturing process of non-oriented electrical steel sheets. Since these impurities are widely known in the field, a detailed description will be omitted.

[0087] In one embodiment of the present invention, the addition of elements other than the aforementioned alloy components is not excluded, and various elements may be included within a range that does not impair the technical spirit of the present invention. When additional elements are included, they may be included to replace the remaining Fe.

[0088]

[0089] A non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following [Formula 1].

[0090] [Formula 1]

[0091]

[0092] However, in the above formula 1, P{001} and P{112} represent the XRD peak intensities of the {001} and {112} orientations, respectively, through XRD (X-ray diffraction) analysis. More specifically, P{001} and P{112} represent the peak intensity values ​​of the {001} orientation and the peak intensity values ​​of the {112} orientation, respectively, in the XRD analysis results of the non-oriented electrical steel sheet specimen. The method for measuring peak intensity through XRD will be described later.

[0093] Here, the {001} and {112} orientations may mean that the crystallographic {001} and {112} planes of the crystal orientations are parallel to the electrical steel plate surface. The electrical steel plate surface may mean the ND plane (Normal Direction Plane), and more specifically, when the rolling direction of the steel plate is the x-axis and the width direction is the y-axis, it may mean the xy plane.

[0094] The left side of the above equation 1 represents the fraction of the XRD peak intensity of the {001} orientation. More specifically, it represents the fraction of the XRD peak intensity values ​​of the {112} orientation and the {001} orientation that the {001} orientation occupies.

[0095] The above {001} orientation is a favorable orientation for magnetic properties, and the higher the {001} orientation fraction within the aggregate structure, the better the magnetic properties can be. On the other hand, the {112} orientation is a unfavorable orientation for magnetic properties, and the higher the {112} orientation fraction within the aggregate structure, the worse the magnetic properties can be.

[0096] Therefore, when the above equation 1 is satisfied, the fraction of the {001} orientation is 70% or more, and an orientation fraction favorable to magnetic properties is secured, thereby enabling excellent magnetic properties. In addition, by confirming whether the above equation 1 is satisfied, the development of a set structure having the {001} orientation favorable to magnetic properties can be confirmed.

[0097] In the present invention, manganese (Mn) and vanadium (V) described above were added to satisfy the above formula 1.

[0098] This will be explained in more detail below.

[0099] When a large amount of sulfur (S) in steel is dissolved in an atomic state, sulfur (S) can be intensively segregated on the surface of the steel sheet during cold rolling annealing. At this time, the surface energy of grains with a {111} orientation is lower than that of grains with a {001} orientation, so the growth of grains with a {111} orientation can be promoted more than the growth of grains with a {001} orientation during cold rolling annealing. As a result, as grains with a {111} orientation grow, an electrical steel sheet composed of grains with a {111} orientation is formed, which can deteriorate the magnetic properties.

[0100] Therefore, in order to efficiently manufacture an electrical steel sheet composed of grains having a {001} orientation in a steel sheet containing sulfur (S) in the above-described content range, an appropriate amount of manganese addition is necessary. This activates the MnS precipitation reaction and minimizes the amount of sulfur (S) dissolved in an atomic state inside the steel sheet. At this time, since the surface energy of grains having a {001} orientation is low, grains having a {001} orientation can grow by encroaching on grains having a {111} or {110} orientation during cold rolling annealing.

[0101] More specifically, during cold rolling annealing in a reducing atmosphere, manganese (MnS) can react with hydrogen (H2) present in the atmosphere and decompose into hydrogen sulfide (H2S) and manganese (Mn). The generated hydrogen sulfide (H2S) is absorbed into the reducing atmosphere in gaseous form, and manganese (Mn) can be incorporated into the steel sheet. This reduces MnS precipitates and allows grains with a {001} orientation to grow.

[0102] At this time, the higher the temperature during cold rolling annealing, the faster the above-described reaction occurs, and as the temperature increases, the time required for MnS decomposition may decrease. More details will be described later in the section on the method for manufacturing non-oriented electrical steel sheets.

[0103] Meanwhile, as described above, MnS decomposes during cold rolling annealing, and grains with low surface energy grow explosively during cold rolling annealing. Excessive grain growth can lead to increased eddy current loss. Excessive grain growth degrades the mechanical properties of non-oriented electrical steel sheets. Furthermore, it reduces formability during punching or machining.

[0104] Therefore, it is necessary to suppress excessive grain growth, and a method of adding elements that form precipitates can be used to suppress excessive grain growth. The formed precipitates can inhibit excessive grain growth by hindering grain growth. Although iron loss may increase when precipitates are formed, suppressing excessive grain growth is more advantageous in improving iron loss and magnetic properties.

[0105] In the present invention, niobium (Nb) is added to suppress excessive grain growth, and the content of niobium satisfies the above-described range. Generally, niobium combines with nitrogen (N) or carbon (C) to form precipitates, and the formed precipitates can prevent excessive grain growth.

[0106] Additionally, the non-oriented electrical steel sheet according to one embodiment of the present invention may have an average grain size of 2000 to 5000 μm. A method for measuring the average grain size will be described later.

[0107] When the average grain size is less than 2000㎛, the growth of grains with the {001} orientation may not occur sufficiently. At this time, the area fraction of grains with the {001} orientation, which is advantageous for magnetic properties, may be insufficient, resulting in inferior magnetic properties. On the other hand, when the average grain size exceeds 5000㎛, the iron loss may increase due to increased eddy current loss caused by excessively large grains.

[0108] In this way, a non-oriented electrical steel sheet according to one embodiment of the present invention can have excellent magnetic properties by controlling the content of alloy elements to selectively grow crystal grains having an orientation advantageous for magnetic properties.

[0109] More specifically, by selectively growing crystal grains with {001} orientations that are favorable for magnetic properties, a grain structure favorable for magnetic properties can be formed. As a result, a low iron loss can be achieved, and preferably, an iron loss (W 10 / 400 ) may be less than 11W / kg.

[0110] Hereinafter, a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention will be described in detail.

[0111]

[0112] Method for manufacturing non-oriented electrical steel sheet

[0113] Hereinafter, a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention will be described with reference to FIG. 1.

[0114] FIG. 1 is a flowchart schematically illustrating a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0115] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention includes a first step (S1) of preparing steel, a second step (S2) of hot-rolling the steel sheet to form a hot-rolled steel sheet, a third step (S3) of hot-rolling and annealing the hot-rolled steel sheet, a fourth step (S4) of cold-rolling the hot-rolled steel sheet that has undergone the third step (S3) to form a cold-rolled steel sheet, and a fifth step (S5) of cold-rolling and annealing the cold-rolled steel sheet.

[0116] At this time, the steel contains 2.0 to 4.0 wt% of silicon (Si), 0.5 to 2.0 wt% of manganese (Mn), 0.1 wt% or less of aluminum (Al) (excluding 0 wt%), 0.01 wt% or less of vanadium (V) (excluding 0 wt%), and the remainder of iron (Fe) and other unavoidable impurities.

[0117] Additionally, the steel may further contain 0.01 wt% or less of carbon (C), 0.01 wt% or less of sulfur (S), and 0.01 wt% or less of nitrogen (N), and may further contain 0.2 wt% of phosphorus (P).

[0118] The alloy composition has been previously described, so a detailed explanation will be omitted. Furthermore, since the alloy composition does not substantially change during the manufacturing process described below, the alloy composition of the steel material and the alloy composition of the final product, the non-oriented electrical steel sheet, are substantially identical.

[0119] Hereinafter, each step of a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention will be described in detail.

[0120] The first step (S1) of preparing steel is the step of preparing a semi-finished product for manufacturing the final product, a non-oriented electrical steel sheet. More specifically, this step may be a step of manufacturing a semi-finished product by designing the alloy components within the alloy composition range according to one embodiment of the present invention. The semi-finished product may be a slab, but is not necessarily limited thereto. Furthermore, the slab may be manufactured using a steelmaking process known in the art, such as a casting process.

[0121] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may, after the first step (S1), perform a second step (S2) of hot-rolling the steel material to form a hot-rolled steel sheet. More specifically, the second step (S2) may include a reheating process, a hot-rolling process, and a coiling process.

[0122] First, the reheating process may be performed prior to the hot rolling process to reheat the steel for subsequent processing. Specifically, this may be a step of loading the steel into a heating furnace and uniformly heating it, thereby facilitating plastic deformation.

[0123] At this time, if the reheating temperature is below 1000℃, the rolling load increases, which can make hot rolling difficult. On the other hand, if the reheating temperature exceeds 1200℃, precipitates formed by carbon (C), sulfur (S), nitrogen (N), etc. in the steel are re-dissolved, which can lead to the formation of fine precipitates during the subsequent rolling and annealing processes. These fine precipitates can inhibit grain growth and increase iron loss.

[0124] Therefore, the reheating process according to one embodiment of the present invention can reheat the steel at a temperature of 1000 to 1200°C.

[0125] Next, a hot rolling process may be performed to form a hot-rolled steel sheet by hot-rolling the reheated steel. The hot rolling process may include rough rolling and finish rolling. Here, rough rolling may refer to forming the steel into a rolled material with an appropriate shape, thickness, and width, and finish rolling may refer to adjusting the steel to a specified thickness and width and rolling it at a finishing temperature suitable for the intended use to achieve a good surface and shape.

[0126] At this time, the finishing temperature of the hot rolling process may be carried out at a temperature for uniform tissue formation and appropriate strength enhancement, and preferably, the finishing temperature may be 860 to 900°C. If the finishing temperature is lower than 860°C, rolling may be performed in a two-phase region, which may result in the formation of an uneven tissue. If the finishing temperature exceeds 900°C, the problem of a rapid decrease in the strength of the steel may occur.

[0127] Afterwards, a coiling process can be performed to coil the hot-rolled steel sheet formed through the hot rolling process. At this time, the coiling temperature is preferably 550 to 650°C. If the coiling temperature is below 550°C, brittleness increases, potentially leading to sheet fracture. Furthermore, the grain size may become too small, preventing sufficient grain growth even after annealing. Conversely, if the coiling temperature exceeds 650°C, fine precipitates may form, increasing iron loss.

[0128] The thickness of the hot-rolled steel sheet formed through the second step (S2) is preferably 1.8 to 3.0 mm. If the thickness of the hot-rolled steel sheet is excessively thin, less than 1.8 mm, the thickness obtained after cold rolling is insufficient, which may cause shape defects during product application. On the other hand, if the thickness of the hot-rolled steel sheet exceeds 3.0 mm, the cold rolling reduction ratio increases, and the fraction of aggregate structures unfavorable to magnetic properties increases, which may result in inferior magnetic properties.

[0129] According to one embodiment of the present invention, a non-oriented electrical steel sheet can perform a third step (S3) of hot-rolling and annealing the hot-rolled steel sheet after the second step (S2).

[0130] The third step (S3) may be a hot-rolling annealing step performed to ensure uniformity of the microstructure of the steel material subjected to hot rolling. When the silicon content is 2.0 wt% or more, hot-rolling annealing is preferably performed.

[0131] The reasons for performing hot-rolled annealing are as follows. When the silicon content exceeds 2.0 wt%, the α-ferrite single phase is maintained without phase transformation into a solid state during heating from room temperature to the melting point. However, dynamic recrystallization (DRX) does not occur during this process, resulting in the formation of elongated unrecrystallized parts. These unrecrystallized parts have high internal residual stresses and are unstable, which can lead to increased anisotropy and plate failure.

[0132] Therefore, the third step (S3) may be a hot rolling annealing step that performs heat treatment at an appropriate temperature to promote recrystallization of unrecrystallized grains and thereby obtain a uniform equiaxed grain.

[0133] The appropriate temperature for hot-rolling annealing according to the present invention may be 800 to 1250°C. If the hot-rolling annealing temperature is below 800°C, the elongated cast structure may remain after hot rolling, causing microstructural inhomogeneity. Conversely, if the hot-rolling annealing temperature exceeds 1250°C, it may cause an imbalance in the final product's texture and deteriorate its magnetic properties.

[0134] In addition, the hot-rolled annealing may be performed for 60 to 180 seconds to form an appropriate grain size under the above temperature conditions. At this time, the heating rate to the heat treatment temperature is preferably 10°C / min or higher, and the cooling rate after the heat treatment may be preferably 20°C / s or higher.

[0135] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may further include a shot blast and acid pickling process after the third step (S3).

[0136] Specifically, shot blasting can be performed by spraying fine particles with a size of 2 to 1200 μm at a high speed of 50 to 120 m / s while rotating at a speed of 2000 rpm or more. Pickling can be performed by supplying 18% hydrochloric acid to a pickling tank where it reacts with the steel plate, thereby reacting with fine residual scale that cannot be removed by mechanical methods.

[0137] Thereafter, the method for manufacturing a non-oriented electrical steel sheet according to the present invention may perform a fourth step (S4) of cold rolling the hot-rolled steel sheet that has undergone the third step (S3) to form a cold-rolled steel sheet. The fourth step (S4) may be a cold rolling process in which the hot-rolled and annealed hot-rolled steel sheet is rolled at a temperature below the recrystallization temperature to further reduce the thickness of the steel sheet.

[0138] More specifically, it may be a process for rolling a hot-rolled steel sheet to a thickness and width that meet the specifications of the final product. The fourth step (S4) according to the present invention may cold-roll the hot-rolled steel sheet into a cold-rolled steel sheet having a thickness of 0.35 mm or less. At this time, the reduction ratio is preferably 70 to 95%.

[0139] If the thickness of cold-rolled steel sheet exceeds 0.35 mm, its magnetic properties may deteriorate, and the space factor of the motor may decrease during production. Furthermore, prolonged annealing may be required to decompose the manganese sulfide precipitated within the steel, which can lead to increased production costs and reduced productivity.

[0140] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may perform a fifth step (S5) of cold-rolling annealing the cold-rolled steel sheet after the fourth step (S4). The cold-rolling annealing may be performed at an appropriate temperature to improve magnetic and mechanical properties.

[0141] In addition, the above cold rolling annealing can be performed in a reducing atmosphere, and more specifically, it can be performed in a reducing atmosphere mixed with hydrogen and nitrogen. At this time, as described above, MnS precipitated in the steel reacts with hydrogen present in the reducing atmosphere and decomposes into gaseous hydrogen sulfide (H2S) and manganese (Mn). As a result, MnS, which had been impeding the growth of grains with a {100} orientation, is decomposed, and grains with a {100} orientation, which are advantageous for magnetic properties, can explosively grow.

[0142] The above-described reaction occurs more rapidly at higher cold rolling annealing temperatures, and higher temperatures can reduce the time required for MnS decomposition. Therefore, it is important to control the temperature to an appropriate level where the above-described reaction can occur.

[0143] At this time, the appropriate temperature for cold rolling annealing may be 1000 to 1250°C. If the cold rolling annealing temperature is lower than 1000°C, MnS precipitates that impede the growth of grains with a {100} orientation may be slowly decomposed, making it difficult to obtain a non-oriented electrical steel sheet with a maximized {100} orientation. In addition, the grain size after annealing may be small, resulting in poor magnetic flux density and iron loss.

[0144] On the other hand, if the cold rolling annealing temperature exceeds 1250℃, excessive grain growth may result in deterioration of magnetic and mechanical properties. Specifically, precipitates may re-dissolve, forming fine precipitates, which may deteriorate magnetic properties, and excessive grain growth may result in reduced strength.

[0145] In addition, the cold rolling annealing according to the present invention can control the heat treatment time depending on the final annealing temperature. Preferably, the temperature can be maintained for 8 to 16 hours within the aforementioned temperature range, and the heating rate up to the above temperature is preferably 5 to 20°C / min or more, and the cooling rate after the heat treatment is preferably 30°C / s or more.

[0146] If the heat treatment time during cold rolling annealing is less than 8 hours, the growth of grains with {001} orientation may be insufficient due to the insufficient cold rolling annealing time, which may result in poor magnetic properties. On the other hand, if the heat treatment time during cold rolling annealing exceeds 16 hours, excessive grain growth may occur, resulting in eddy current loss, and the increased eddy current loss may result in poor magnetic properties.

[0147] Therefore, the cold rolling annealing process according to the present invention can appropriately control the average grain size while maximizing the {100} orientation by maintaining the steel sheet having the above-described composition ratio at 1000 to 1250°C / s for 8 to 16 hours.

[0148] That is, by cold-rolling and annealing a steel sheet having the above-described composition ratio for 8 to 16 hours, a non-oriented electrical steel sheet satisfying the above-described formula 1 and having an average grain size of 2000 to 5000 μm can be manufactured.

[0149] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may further include a coating step after the fifth step (S5). The coating step may be performed to secure the insulation properties and improve the punchability of the non-oriented electrical steel sheet, and may mean forming an insulating film on the surface of the cold-rolled steel sheet on which the fifth step (S5) has been performed. The coating step may be performed using a process known in the art.

[0150] Accordingly, according to one embodiment of the present invention, crystal grains having a (001) orientation that is advantageous for magnetic properties can be grown, thereby achieving excellent magnetic properties. More specifically, the iron loss (W 10 / 400 ) may be less than 11 W / kg.

[0151]

[0152] Experimental example

[0153] Below, the composition and operation of the present invention will be explained through experimental examples. However, these examples are provided to aid understanding of the present invention and are not intended to limit the present invention.

[0154]

[0155] (Method for manufacturing non-oriented electrical steel sheet specimens)

[0156] The specimen of the non-oriented electrical steel sheet of the present invention includes the alloy components described in Table 1 below, and the remainder other than the alloy components described in Table 1 below includes iron (Fe).

[0157]

[0158] A specimen of the non-oriented electrical steel sheet of the present invention can be manufactured as follows.

[0159] A slab having the alloy composition described in Table 1 above was manufactured, the slab was reheated to 1150°C, and then hot rolled to manufacture a hot-rolled steel sheet having a thickness of 2 mm. The hot-rolled steel sheet was hot-rolled and annealed, and the hot-rolled steel sheet subjected to hot-rolling and annealing was pickled.

[0160] Afterwards, a cold-rolled steel sheet with a final thickness of 0.2 mm was manufactured through cold rolling, and the manufactured cold-rolled steel sheet was cold-rolled and annealed at 1200°C for the time period shown in Table 2 below. At this time, the heating rate was 10°C / min, and it was performed in a reducing atmosphere containing hydrogen (H2) and (N2). The cold-rolled steel sheet that was cold-rolled and annealed was coated to manufacture a final non-oriented electrical steel sheet specimen.

[0161] The manufacturing method described above and other process conditions not described in Table 2 were controlled as control variables and were identically controlled within the range described in the method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0162]

[0163] (Method for measuring the properties of non-oriented electrical steel sheets)

[0164] 1. XRD peak intensity

[0165] The XRD peak intensity measurement method will be described in more detail with reference to Fig. 2.

[0166] Fig. 2 is a drawing showing the XRD peak intensity measurement location and measurement results. Fig. 2 (a) is a drawing showing an example of an XRD peak intensity measurement test piece, and Fig. 2 (b) is a drawing showing an example of an XRD measurement result.

[0167] In order to measure the XRD peak of a non-oriented electrical steel sheet specimen, a test piece with a size of 60 mm × 60 mm was manufactured, and the XRD peak was measured in the ND (Normal direction) direction of the test piece. When measuring the XRD peak, the measurement is made in the angle range of 20 to 90°, and is performed at 9 points (P) within the test piece as shown in Fig. 2 (a). Thereafter, the direction and peak intensity value corresponding to each peak are derived from the measured result values.

[0168] For example, the XRD measurement result values ​​derived as in (b) of Fig. 2 are displayed in the form of a graph, and intensity values ​​according to angle are derived. At this time, a peak appears on the graph, and the angle and intensity values ​​at the corresponding peak can be derived.

[0169] The XRD peak intensity value used in the above formula 1 was the peak intensity value measured using the above-described method, and more specifically, the average value of the XRD peak intensity values ​​measured in three test pieces was calculated and used.

[0170] 2. Average grain size

[0171] To measure the average grain size, non-oriented electrical steel specimens measuring 60 mm × 60 mm were prepared and etched in a natal solution. The grain size was then measured using the linear intercept method.

[0172] As shown in Fig. 3, an imaginary line was drawn parallel to the width or length of the specimen, the number of interfaces in contact with the imaginary line was counted, and the length or width was divided by the number of interfaces to determine the value as the grain size.

[0173] The virtual line (L) is composed of 7 lines parallel to each of the horizontal and vertical directions, and the grain size was measured on a total of 14 virtual lines, and the average value of these was used as the average grain size of one specimen.

[0174] 3. Iron hand

[0175] Iron loss (W) of the non-oriented electrical steel sheet specimen of the present invention 10 / 400 ) was measured according to the test method specified in the IEC 60404-2 international standard, and was measured using the Epstein frame test method.

[0176] Referring to Fig. 4, a more detailed explanation will be given. Fig. 4 is a drawing showing a test piece for measuring iron loss.

[0177] In this experiment, a non-oriented electrical steel sheet was cut into sizes of (300±0.5) mm in length and (30±0.2) mm in width to prepare a core loss measurement test piece (10). When cutting, half of the core loss measurement test piece (10) was cut in a direction parallel to the rolling direction (RD, Rolling direction), and the other half was cut in a direction perpendicular to the rolling direction (TD, Transverse direction).

[0178] Afterwards, the prepared iron loss measurement test pieces (10) were prepared in multiples of 4, and measured after being laminated in a double-overlapping manner as shown in Fig. 4. At this time, the iron loss measurement test pieces (10) were measured by inserting iron loss measurement test pieces (10) cut in the same direction into the coil former so that they face each other.

[0179]

[0180] (Evaluation results of non-oriented electrical steel sheet specimens)

[0181] Cold rolling annealing time in the production of non-oriented electrical steel sheet specimens, the value of the left side of the above equation 1, satisfaction of the above equation 1, average grain size and iron loss (W 10 / 400 ) values ​​are shown in Table 2 below. In Table 2 below, '[Formula 1] value' means the value of the left side of the above formula 1, and whether the above formula 1 is satisfied is shown on the right side. In addition, in Table 2 below, 'W 10 / 400 ' means the iron loss value at 400 Hz, 1.0 T, and the unit is W / kg.

[0182]

[0183] Referring to Table 1 and Table 2 above, in the case of an experimental example that is not satisfied with the cold rolling annealing time of the present invention, the iron loss (W) targeted in the present invention 10 / 400 ) does not satisfy the value of 11W / kg or less. In particular, it can be confirmed that the above equation 1 is not satisfied when the cold rolling annealing time is less than 6 hours. At this time, the iron loss (W 10 / 400 ) can be confirmed to exceed 11W / kg.

[0184] Continuing to refer to Table 1 and Table 2 above, it can be confirmed that in the case of experimental examples that do not satisfy the alloy composition of the present invention, the above formula 1 is not satisfied. At this time, the iron loss (W) targeted in the present invention 10 / 400 ) It can be confirmed that the value of 11W / kg or less is not satisfied.

[0185] On the other hand, in the case of an experimental example that satisfies the alloy composition and manufacturing method according to one embodiment of the present invention, it can be confirmed that the above formula 1 and the crystal grain size according to the present invention are satisfied. At this time, the iron loss (W 10 / 400 ) It can be confirmed that the value satisfies the target of 11 W / kg or less in the present invention.

[0186] As described above, preferred embodiments of the present invention have been described. It will be apparent to those skilled in the art that the present invention may be embodied in other specific forms, in addition to the embodiments described above, without departing from the spirit or scope thereof. Therefore, the above-described embodiments should be considered illustrative rather than restrictive, and accordingly, the present invention is not limited to the above description, but may be modified within the scope of the appended claims and their equivalents.

Claims

1. Contains 2.0 to 4.0 wt% of silicon (Si), 0.5 to 2.0 wt% of manganese (Mn), 0.1 wt% or less of aluminum (Al) (excluding 0 wt%), 0.01 wt% or less of vanadium (V) (excluding 0 wt%), and the remainder iron (Fe) and other unavoidable impurities. A non-oriented electrical steel sheet satisfying the following equation 1. [Formula 1] (However, in the above formula 1, P{001} and P{112} represent the XRD peak intensities of the {001} and {112} directions, respectively, through XRD (X-ray diffraction) analysis.) 2. In paragraph 1, Non-oriented electrical steel sheet with an average grain size of 2000 to 5000㎛.

3. In paragraph 1, Non-oriented electrical steel sheet further containing 0.01 wt% or less of carbon (C), 0.01 wt% or less of sulfur (S), and 0.01 wt% or less of nitrogen (N).

4. In paragraph 3, Non-oriented electrical steel sheet further containing 0.2 wt% of phosphorus (P).

5. In paragraph 1, Iron Loss (W 10 / 400 ) Non-oriented electrical steel sheet with a strength of 11 W / kg or less.

6. A first step of preparing steel containing 2.0 to 4.0 wt% of silicon (Si), 0.5 to 2.0 wt% of manganese (Mn), 0.1 wt% or less of aluminum (Al) (excluding 0 wt%), 0.01 wt% or less of vanadium (V) (excluding 0 wt%), and the remainder iron (Fe) and other unavoidable impurities; A second step of hot rolling the above steel to form a hot-rolled steel plate; The third step of hot-rolling and annealing the above hot-rolled steel sheet; A fourth step of forming a cold-rolled steel sheet by cold rolling the hot-rolled steel sheet that has undergone the third step; and A method for manufacturing a non-oriented electrical steel sheet, comprising a fifth step of cold-rolling and annealing the cold-rolled steel sheet at 1000 to 1250°C for 8 to 16 hours.

7. In paragraph 6, A method for manufacturing a non-oriented electrical steel sheet that satisfies the following equation 1, wherein the steel material that has undergone the above-mentioned fifth step is [Formula 1] (However, in the above formula 1, P{001} and P{112} represent the XRD peak intensities of the {001} and {112} directions, respectively, through XRD (X-ray diffraction) analysis.) 8. In paragraph 6, A method for manufacturing a non-oriented electrical steel sheet having an average grain size of 2000 to 5000 ㎛, wherein the steel sheet has undergone the above 5th step.

9. In paragraph 6, A method for manufacturing a non-oriented electrical steel sheet, wherein the steel further contains 0.01 wt% or less of carbon (C), 0.01 wt% or less of sulfur (S), and 0.01 wt% or less of nitrogen (N).

10. In paragraph 9, A method for manufacturing a non-oriented electrical steel sheet, wherein the steel further contains 0.2 wt% of phosphorus (P).

11. In paragraph 6, The steel that has undergone the above 5 steps has a core loss (W 10 / 400 ) A method for manufacturing a non-oriented electrical steel sheet having a strength of 11 W / kg or less.

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