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 satisfies expression 1 and contains 3.0-3.8 wt% of silicon (Si), 0.2-0.4 wt% of manganese (Mn), 0.8-1.5 wt% of aluminum (Al), 0.01 wt% or less of carbon (C), 0.01 wt% or less of sulfur (S), 0.08 wt% or less of phosphorus (P), 0.01 wt% or less of nitrogen (N), 0.01 wt% or less of titanium (Ti), and 0.01-0.1 wt% in total of at least one of tin (Sn) or antimony (Sb), with the remainder comprising iron (Fe) and other inevitable impurities. Accordingly, a non-oriented electrical steel sheet having low iron loss and a method for manufacturing the non-oriented electrical steel sheet can be achieved.

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, core loss must be reduced and magnetic flux density increased.

[0005] In particular, reducing iron loss is crucial. Iron loss represents 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. Iron loss can be divided into hysteresis loss, which occurs due to the magnetization process itself, and eddy current loss, which is generated by the eddy current induced during magnetization.

[0006] Conventionally, methods have been used to reduce iron loss by adding alloying elements that increase the resistivity of steel, such as silicon (Si), manganese (Mn), and aluminum (Al). However, in this case, the addition of the aforementioned alloying elements not only reduces magnetic flux density but also reduces rollability, making it difficult to thin the material. Furthermore, additive elements such as carbon (C), sulfur (S), nitrogen (N), and titanium (Ti) can combine with each other to form precipitates. At this time, the finely precipitated precipitates can hinder the movement of magnetic domains, which can act as a factor that deteriorates magnetic properties.

[0007] Therefore, there is a need for a technology to manufacture non-oriented electrical steel sheets with excellent magnetic and mechanical properties by controlling the amount of alloying elements added, precipitates, and process elements.

[0008] [Prior Art Literature]

[0009] [Patent Document]

[0010] Republic of Korea Patent No. 10-2297753

[0011] The present invention has been devised to solve the above problems, and the object of the present invention is to provide a non-oriented electrical steel sheet and a method for manufacturing a non-oriented electrical steel sheet having excellent magnetic properties by controlling the final heat treatment time and temperature.

[0012] 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.

[0013] A non-oriented electrical steel sheet according to one embodiment of the present invention contains 3.0 to 3.8 wt% of silicon (Si), 0.2 to 0.4 wt% of manganese (Mn), 0.8 to 1.5 wt% of aluminum (Al), 0.01 wt% or less of carbon (C), 0.01 wt% or less of sulfur (S), 0.08 wt% or less of phosphorus (P), 0.01 wt% or less of nitrogen (N), 0.01 wt% or less of titanium (Ti), and at least one of tin (Sn) and antimony (Sb) in a combined amount of 0.01 to 0.1 wt%, the remainder being iron (Fe) and other unavoidable impurities, and satisfying the following equation 1.

[0014] [Formula 1]

[0015] F s,i = (F s ) 2 + 3(F i ) ≤ 50

[0016] (However, in the above formula 1, F s represents the KAM (Kernel average misorientation) value, and F i represents the number of precipitates per unit area.)

[0017] Also, F, which represents the KAM value s The value may be less than 6.5.

[0018] Additionally, the number of precipitates with a diameter of 0.1㎛ or more is 15 / mm. 2 It could be as follows:

[0019] Also, iron loss (W 10 / 400 ) may be less than 14.5 W / kg.

[0020] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention includes a first step of preparing steel, a second step of hot-rolling the steel sheet 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, a fifth step of cold-rolling and annealing the cold-rolled steel sheet, and a sixth step of stress-relieving annealing the cold-rolled steel sheet subjected to the fifth step at 725 to 770°C for 1.5 to 2.5 hours.

[0021] In addition, the steel material that has undergone the above-mentioned sixth step can satisfy the above-mentioned equation 1.

[0022] In addition, the steel that performed the above 6th step has F indicating KAM value. s The value may be less than 6.5.

[0023] In addition, the steel material that performed the above 6th step has a number of precipitates with a diameter of 0.1㎛ or more of 15 / mm. 2 It could be as follows:

[0024] Also, iron loss (W 10 / 400 ) may be less than 14.5 W / kg.

[0025] According to one embodiment of the present invention, by controlling the residual stress and the number of precipitates, a non-oriented electrical steel sheet with low iron loss and a method for manufacturing a non-oriented electrical steel sheet can be implemented.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] Unless otherwise specified, the notation 'A ~ B' for numerical values ​​A and B means 'A or more and B or less'. In such notation, if a unit is attached only to numerical value B, the unit shall be applied to numerical value A as well.

[0034] Also, unless otherwise stated, 1 ppm is 0.0001 wt%.

[0035]

[0036] Non-oriented electrical steel sheet

[0037] A non-oriented electrical steel sheet according to one embodiment of the present invention contains 3.0 to 3.8 wt% of silicon (Si), 0.2 to 0.4 wt% of manganese (Mn), 0.8 to 1.5 wt% of aluminum (Al), 0.01 wt% or less of carbon (C), 0.01 wt% or less of sulfur (S), 0.08 wt% or less of phosphorus (P), 0.01 wt% or less of nitrogen (N), 0.01 wt% or less of titanium (Ti), and at least one of tin (Sn) and antimony (Sb) in a combined amount of 0.01 to 0.1 wt%, with the remainder being iron (Fe) and other unavoidable impurities.

[0038] 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.

[0039]

[0040] Silicon (Si)

[0041] 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.

[0042] If the silicon content is less than 3.0 wt%, the above-described effects cannot be expected, and if the silicon content exceeds 3.8 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 3.0 to 3.8 wt% of silicon.

[0043]

[0044] manganese (Mn)

[0045] Manganese (Mn), like silicon (Si), is an element that improves magnetic properties by increasing resistivity and reducing iron loss. It is also added to enhance the fraction of textures with favorable magnetic properties. Furthermore, manganese can combine with sulfur (S) present in steel to form sulfides such as MnS.

[0046] When the manganese content is less than 0.2 wt%, fine MnS precipitates are formed to inhibit grain growth, and when the manganese content exceeds 0.4 wt%, coarse MnS precipitates are formed to reduce the magnetic flux density. Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain manganese in an amount of 0.2 to 0.4 wt%.

[0047]

[0048] Aluminum (Al)

[0049] 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.

[0050] When the aluminum content is less than 0.8 wt%, the increase in resistivity is not sufficient, which may increase high-frequency iron loss, and may form fine nitrides, which may increase the deviation of magnetic properties. When the aluminum content exceeds 1.5 wt%, excessive nitrides may be formed, which may reduce the magnetic flux density and cause a decrease in cold rolling properties. In addition, adding excessive aluminum may cause nozzle clogging problems during the casting process. Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain 0.8 to 1.5 wt% of aluminum.

[0051]

[0052] carbon (C)

[0053] Carbon can increase iron loss by combining with titanium (Ti) to form carbides such as TiC. If the carbon content exceeds 0.01 wt%, self-aging can occur, degrading magnetic properties. Therefore, a 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.

[0054]

[0055] Yellow (S)

[0056] Sulfur (S) is an impurity element that is inevitably contained during the manufacturing process, and adding large amounts can cause brittleness. Furthermore, it can combine with manganese (Mn), copper (Cu), and other elements to form precipitates such as MnS and CuS, thereby increasing iron loss. Therefore, it is desirable to add as little S as possible. A non-oriented electrical steel sheet according to one embodiment of the present invention may contain sulfur in an amount of 0.005 wt% or less.

[0057]

[0058] Person (P)

[0059] 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 as possible, and the non-oriented electrical steel sheet according to one embodiment of the present invention may contain phosphorus at 0.08 wt% or less.

[0060]

[0061] Nitrogen (N)

[0062] Nitrogen (N) can combine with aluminum (Al) or titanium (Ti) to form precipitates such as AlN and TiN, which can increase iron loss and inhibit grain growth. Therefore, it is desirable to add as little as possible. 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.

[0063]

[0064] Titanium (Ti)

[0065] Titanium (Ti) is an element with a strong tendency to form precipitates in steel, and combines with carbon (C) or nitrogen (N) to form precipitates such as TiC and TiN. These precipitates can inhibit grain growth. As the amount of titanium added increases, the fraction of precipitates increases, and this can form a texture that is unfavorable for magnetization, thereby deteriorating magnetic properties. Therefore, it is preferable to add as little as possible, and the non-oriented electrical steel sheet according to one embodiment of the present invention may contain titanium in an amount of 0.01 wt% or less.

[0066]

[0067] In particular, in the case of the above sulfur (S), nitrogen (N) and titanium (Ti), since they may form sulfides, nitrides and carbides, respectively, and thus have a negative effect on magnetism, it is preferable that their contents be controlled to 0.01 wt% or less.

[0068]

[0069] Tin (Sn) and antimony (Sb)

[0070] Tin (Sn) and antimony (Sb) are precipitate elements that form precipitates on the surface of steel sheets, and can be concentrated in the surface layer of the steel sheet. At this time, the concentrated tin and antimony can reduce iron loss by suppressing nitrogen adsorption and nitride formation. However, if the combined amount of any one or more of tin and antimony is less than 0.01 wt%, the above-described effect cannot be expected, and if it exceeds 0.1 wt%, excessive precipitate formation may cause grain boundaries to become embrittled, thereby reducing fatigue resistance. Therefore, a non-oriented electrical steel sheet according to an embodiment of the present invention may contain any one or more of tin and antimony in a combined amount of 0.01 to 0.1 wt%.

[0071]

[0072] 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.

[0073] 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.

[0074]

[0075] A non-oriented electrical steel sheet that satisfies the above-described alloy composition and according to the non-oriented electrical steel sheet manufacturing method described below satisfies the following formula 1.

[0076] [Formula 1]

[0077] F s,i = (F s ) 2 + 3(F i ) ≤ 50

[0078] However, F srepresents the KAM (Kernel average misorientation) value, and F i represents the number of precipitates with a diameter of 0.1㎛ or more per unit area. The above F s and F i The measurement method will be described later.

[0079] Above F s and F i are factors that affect the magnetic properties of non-oriented electrical steel sheets, more specifically, F s and F i can affect the iron loss in a complex manner. At this time, considering the relationship, F in the above equation 1 s,i can be expressed as

[0080] More specifically, F s and F i Each has a different degree of influence on iron loss. F s Wow F i When checking the change in iron loss according to F s The effect of F on iron loss i tends to be relatively higher than the effect on iron loss. At this time, F s The effect of F on iron loss is squared, and i It was experimentally determined that the effect of the iron loss is three times greater.

[0081] Thus, F calculated from the relationship between Fs and Fi s,i Through the values, the degree to which the KAM value and the number of precipitates with a diameter of 0.1㎛ or more affect the iron loss can be quantified.

[0082] If the above equation 1 is not satisfied, residual stress and precipitates, which have a negative effect on iron loss, increase, making it difficult to expect a low iron loss value. This will be explained in more detail below.

[0083] Above F sIt can refer to a quantified value through KAM analysis performed after measuring the residual stress of non-oriented electrical steel sheet with EBSD (Electron backscatter diffraction). KAM refers to the average of the crystal orientation difference between the crystal grain that is the measurement point and the crystal grains around the measurement point. Therefore, the higher the KAM value, the greater the crystal orientation difference with the surrounding crystal grains. At this time, a large crystal orientation difference with the surrounding crystal grains can be seen as a lot of deformation occurring in the crystal grain, and it can be seen as an increase in the residual stress as much as the deformation occurred.

[0084] In the present invention, the above F s is a value that quantifies the residual stress of non-oriented electrical steel sheets through KAM analysis. The higher the KAM value, the higher the residual stress. Residual stress can inhibit the movement of the magnetic domain wall and increase the iron loss. Therefore, F s It is important to lower the value, and the non-oriented electrical steel sheet according to one embodiment of the present invention is F s The value may be less than 6.5, and more preferably less than 3.5.

[0085] Also, the above F i is the number of precipitates, 1 mm of the surface layer of non-oriented electrical steel sheet 2 It refers to the number of precipitates with a diameter of 0.1㎛ or more within the region. The precipitates may be nitrides such as AlN and TiN, but are not limited thereto and may further include carbides and sulfides.

[0086] The above precipitates can interfere with the movement of the magnetic wall, thereby increasing the iron loss. Therefore, it is important to reduce the number of precipitates with a diameter of 0.1 ㎛ or more as much as possible, and the non-oriented electrical steel sheet according to one embodiment of the present invention has a number of precipitates with a diameter of 0.1 ㎛ or more of 15 / mm. 2 It may be less than or equal to 10 / mm, more preferably 10 / mm 2 It could be as follows:

[0087] Precipitates with a diameter of 0.1 μm or more can inhibit domain wall movement, and precipitates with a diameter of 0.1 μm or more have a similar effect on iron loss regardless of size. On the other hand, precipitates with a diameter of less than 0.1 μm have a minimal effect on iron loss and are therefore not considered in the present invention.

[0088] As described above, the F s and F i is proportional to the iron loss of non-oriented electrical steel sheet, F s,i The lower the value, the lower the iron loss value can be expected. Through this, F in Equation 1 above s,i The iron loss of a non-oriented electrical steel sheet can be predicted using the value, and a low iron loss value can be expected when the above equation 1 is satisfied.

[0089] Accordingly, the non-oriented electrical steel sheet according to one embodiment of the present invention can have low iron loss, and preferably has iron loss (W 10 / 400 ) may be 14.5 W / kg or less, and more preferably 13.5 W / kg or less.

[0090] Hereinafter, a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention will be described in detail.

[0091]

[0092] Method for manufacturing non-oriented electrical steel sheet

[0093] 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.

[0094] 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.

[0095] 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 subjected to the third step (S3) to form a cold-rolled steel sheet, a fifth step (S5) of cold-rolling and annealing the cold-rolled steel sheet, and a sixth step (S6) of stress-relieving annealing the cold-rolled steel sheet subjected to the fifth step (S5).

[0096] At this time, the steel contains 3.0 to 3.8 wt% of silicon (Si), 0.2 to 0.4 wt% of manganese (Mn), 0.8 to 1.5 wt% of aluminum (Al), 0.01 wt% or less of carbon (C), 0.01 wt% or less of sulfur (S), 0.08 wt% or less of phosphorus (P), 0.01 wt% or less of nitrogen (N), 0.01 wt% or less of titanium (Ti), and 0.01 to 0.1 wt% of at least one of tin (Sn) and antimony (Sb), with the remainder containing iron (Fe) and other unavoidable impurities, and satisfies the above formula 1.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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 1150℃, 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.

[0103] Therefore, the reheating process according to one embodiment of the present invention can reheat the steel at a temperature of 1000 to 1150°C.

[0104] 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.

[0105] 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 800 to 900°C. If the finishing temperature is less than 800°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.

[0106] 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 500 to 600°C. If the coiling temperature is below 500°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 600°C, fine precipitates may form, increasing iron loss.

[0107] The thickness of the hot-rolled steel sheet formed through the second step (S2) is preferably 1.6 to 2.3 mm. If the thickness of the hot-rolled steel sheet is excessively thin, less than 1.6 mm, the thickness obtained after cold rolling may be insufficient, which may cause shape defects during product application. On the other hand, if the thickness of the hot-rolled steel sheet exceeds 2.3 mm, the cold rolling reduction rate increases, and the fraction of aggregate structures unfavorable to magnetic properties increases, which may result in inferior magnetic properties.

[0108] 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).

[0109] 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 3.0 wt% or more, hot-rolling annealing is preferably performed.

[0110] The reasons for performing hot-rolled annealing are as follows. When the silicon content exceeds 3.0 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.

[0111] 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.

[0112] The appropriate temperature for hot-rolling annealing according to the present invention may be 900 to 1100°C. If the hot-rolling annealing temperature is below 900°C, the elongated cast structure may remain after hot rolling, causing microstructural inhomogeneity. Conversely, if the hot-rolling annealing temperature exceeds 1100°C, it may cause an imbalance in the final product's texture and deteriorate its magnetic properties.

[0113] In addition, the hot-rolled annealing may be performed for 30 to 120 seconds to form an appropriate grain size under the above temperature conditions. At this time, the heating rate to the above temperature is preferably 10°C / s or higher, and the cooling rate after the heat treatment may be preferably 20°C / s or higher.

[0114] Furthermore, the third step (S3) according to the present invention can be performed in an atmosphere with a nitrogen fraction of 80 to 100%. At this time, the remaining gas excluding nitrogen can be filled with hydrogen (H2). At this time, if the hydrogen fraction is 10 to 20%, a surface denitrification reaction can occur. This reduces iron loss and improves magnetic properties. On the other hand, if the nitrogen (N) fraction is less than 80%, oxidation can occur during heat treatment, which can deteriorate magnetic properties.

[0115] The method for manufacturing a non-oriented electrical steel sheet according to the present invention may, after the third step (S3), 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. More specifically, it may be a process in which the hot-rolled steel sheet is rolled to a thickness and width that meet the specifications of the final product.

[0116] The above cold rolling process preferably has a first pass reduction ratio of 40 to 50%, a reduction ratio for each of the remaining passes of 30 to 45%, and a total reduction ratio of 81 to 96%. The sheet thickness of the cold rolled steel sheet formed by cold rolling at the above-described reduction ratio may be 0.2 to 0.25 mm.

[0117] 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.

[0118] At this time, the appropriate temperature for cold rolling annealing may be 950 to 1100℃. If the cold rolling annealing temperature is lower than 950℃, the crystal grain size after annealing may be small, resulting in poor magnetic flux density and iron loss. On the other hand, if the cold rolling annealing temperature exceeds 1100℃, the precipitates may re-dissolve, forming fine precipitates, which may result in poor magnetic properties, and excessive grain growth may cause a decrease in strength.

[0119] In addition, the cold rolling annealing according to the present invention can be maintained for 30 to 90 seconds under the above temperature conditions, the heating rate to the above temperature is preferably 10°C / s or more, and the cooling rate after heat treatment is preferably 10°C / s or more.

[0120] The fifth step (S5) may be performed in a mixed atmosphere consisting of hydrogen (H2) and nitrogen (N2). More preferably, the process may be performed in an atmosphere in which the hydrogen (H2) fraction is 20% or more and the remainder is nitrogen (N2). When the hydrogen (H2) fraction is less than 20%, nitrogen (N) may penetrate the surface of the steel sheet to form nitrides, thereby increasing iron loss. Here, the fraction may refer to a volume fraction.

[0121] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may perform a coating step and a punching 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 relevant technical field.

[0122] In addition, the above-mentioned punching step is a step of punching a non-oriented electrical steel sheet into the shape of a motor core, and can be performed by a process known in the relevant technical field.

[0123] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may perform a sixth step (S6) of removing residual stress of a cold-rolled steel sheet that has undergone the fifth step (S5) after the fifth step (S5).

[0124] The above sixth step (S6) is a stress relief annealing (SRA) heat treatment step for removing residual stress remaining inside the steel sheet, and may be a stress relief annealing step performed to remove residual stress of the cold rolled steel sheet or the cold rolled steel sheet that has undergone the coating step and the punching step.

[0125] At this time, the preferred temperature range for stress relief annealing is 725 to 770°C, and more preferably, the temperature range may be 730 to 770°C.

[0126] If the stress-relief annealing temperature is below 725℃, the temperature is insufficient to evenly flatten the shape of the non-oriented electrical steel sheet, reducing the flatness of the non-oriented electrical steel sheet and potentially reducing the space factor during motor manufacturing. On the other hand, if the stress-relief annealing temperature exceeds 770℃, sooting may occur on the surface of the non-oriented electrical steel sheet, which may lead to increased core loss.

[0127] Furthermore, the holding time within the above-described temperature range is preferably 1.5 to 2.5 hours. If the heat treatment is performed for less than 1.5 hours, the residual stress within the steel sheet may not be sufficiently reduced, which may adversely affect iron loss. Conversely, if the heat treatment is performed for more than 2.5 hours within the above-described temperature range, precipitates may grow within the steel sheet, and these precipitates may inhibit magnetic domain movement, thereby increasing iron loss.

[0128] At this time, the heating rate within the above-described temperature range is preferably 20°C / min or more, and the cooling rate after heat treatment is preferably 5°C / min or more.

[0129] Accordingly, the non-oriented electrical steel sheet according to one embodiment of the present invention can have low iron loss, and preferably has iron loss (W 10 / 400 ) may be 14.5 W / kg or less, and more preferably 13.5 W / kg or less.

[0130]

[0131] Experimental example

[0132] 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.

[0133]

[0134] (Method for manufacturing non-oriented electrical steel sheet specimens)

[0135] The specimen of the non-oriented electrical steel sheet of the present invention contains 3.3 wt% of silicon (Si), 0.25 wt% of manganese (Mn), 0.9 wt% of aluminum (Al), 0.0019 wt% of carbon (C), 0.0017 wt% of sulfur (S), 0.0008 wt% of phosphorus (P), 0.0017 wt% of nitrogen (N), 0.0016 wt% of titanium (Ti), 0.0008 wt% of tin (Sn), 0.0092 wt% of antimony (Sb), and the remainder of iron (Fe).

[0136] A slab having the above-described alloy composition was manufactured, and after reheating the slab to 1050°C, hot rolling was performed to manufacture a hot-rolled steel sheet having a thickness of 2 mm. The hot-rolled steel sheet was coiled at 550°C, hot-rolled and annealed at 1000°C for 60 seconds in an atmosphere with a nitrogen fraction of 100%, and then cold-rolled to manufacture a cold-rolled steel sheet having a thickness of 0.25 mm. Cold-rolled and annealed at 1000°C for 100 seconds were then cooled. After coating and stamping the cold-rolled steel sheet, the temperature was increased at a rate of 20°C / min to the annealing temperature described in Table 2 below, stress-relief annealing was performed for 3 h, and then cooled at a rate of 5°C / min to manufacture a specimen.

[0137] Other process conditions not described in Table 2 below were controlled as control variables and were controlled identically within the range described in the method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0138]

[0139] (Method for measuring the properties of non-oriented electrical steel sheets)

[0140] 1. KAM(Kernel average misorientation)

[0141] In order to measure the KAM value of the experimental example, EBSD (Electron backscatter diffraction) measurement specimens were manufactured and measured so that the ND (Normal direction) plane of the steel sheet was observed, and the EBSD measurement values ​​were measured using Kernel average misorientation maps in the OIM Analysis program, an analysis software. More specifically, the KAM values ​​of five regions with an area of ​​1 mm × 0.3 mm were obtained using the above-described method, and the average value of the KAM values ​​of the five regions was calculated and used as the KAM value of the non-oriented electrical steel sheet specimen.

[0142] 2. Number of precipitates

[0143] 1 mm on the surface of the non-oriented electrical steel sheet specimen 2 Five areas with a size were observed using a SEM (Scanning Electron Microscope), and the number of precipitates with a diameter of 0.1 ㎛ or more within the areas was measured to calculate an average value. At this time, the diameter of the precipitate can mean the diameter of a virtual circle having the same area as the area of ​​the observed precipitate when the virtual circle is formed.

[0144] 3. Iron hand

[0145] Iron loss (W) of the non-oriented electrical steel sheet specimen of the present invention 10 / 400) was measured using the Epstein frame test method according to the IEC 60404-2 international standard. At this time, non-oriented electrical steel sheets were manufactured into specimens with a length of 300 mm and a width of 30 mm and measured.

[0146]

[0147] (Evaluation results of non-oriented electrical steel sheets)

[0148] Experimental Example F s , F i , F s,i and iron loss (W 10 / 400 ) values ​​are shown in Table 1 below. In Table 1 below, 'W 10 / 400 ' means the iron loss value at 400Hz, 1.0T, and the unit is W / kg.

[0149] Experimental Example No. SRA Temperature F s F i F s,i W 10 / 40017107.8266.8415.727851.52268.2515.683750362712.647286.1346.2114.3257831.62062.5615.268031278216.177522.8728.8412.887157.7265.2916.298080.529 87.2516.38107058.2273.2415.72118050.82781.6416.1127256.2347.4414.38137652.31035.2913.4148001.12679.2116.08157236.1346.2114.19167722.21652.841 4.56177582.5933.2513.2187702.11549.4114.4197453.1524.6112.33207206.5351.2514.6217751.91857.6114.78227483.2525.2412.38237801.71959.8914.882473 05.8342.6413.9257771.81960.2414.9826727634514.1277493.3525.8912.5287991.22576.4415.88297911.32576.6915.98307187.5365.2516.2317552.6727.7612.7

[0150] Referring to Table 1 above, it can be confirmed that Experimental Examples 1, 8, 10, 20, and 30 are experimental examples in which the stress relief annealing temperature is less than 725°C. At this time, F s It can be confirmed that the value exceeds 6.5 and does not satisfy the above equation 1. In addition, it can be confirmed that the iron loss value does not satisfy the target of 14.5 W / kg or less in the present invention. Continuing to refer to Table 1, it can be confirmed that the stress relief sodon temperature exceeds 770℃ in the cases of Experimental Example 2, Experimental Example 5, Experimental Example 6, Experimental Example 9, Experimental Example 11, Experimental Example 14, Experimental Example 16, Experimental Example 21, Experimental Example 23, Experimental Example 25, Experimental Example 28 and Experimental Example 29. In addition, F i The value is 15 / mm2 It can be confirmed that it exceeds and does not satisfy the above equation 1. At this time, the iron loss (W ) targeted by the present invention 10 / 400 ) It can be confirmed that the value of 14.5W / kg or less is not satisfied.

[0151] On the other hand, in the case of Experimental Example 3, Experimental Example 4, Experimental Example 7, Experimental Example 12, Experimental Example 13, Experimental Example 15, Experimental Example 17, Experimental Example 18, Experimental Example 19, Experimental Example 22, Experimental Example 24, Experimental Example 26, Experimental Example 27 and Experimental Example 31, it can be confirmed that the stress relief annealing temperature satisfies 720 to 770°C. In addition, F s and F i It can be confirmed that the value satisfies the range targeted in the present invention and satisfies the above equation 1, and the iron loss (W 10 / 400 ) It can be confirmed that the value satisfies 14.5 W / kg or less.

[0152] 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 3.0 to 3.8 wt% of silicon (Si), 0.2 to 0.4 wt% of manganese (Mn), 0.8 to 1.5 wt% of aluminum (Al), 0.01 wt% or less of carbon (C), 0.01 wt% or less of sulfur (S), 0.08 wt% or less of phosphorus (P), 0.01 wt% or less of nitrogen (N), 0.01 wt% or less of titanium (Ti), and at least one of tin (Sn) and antimony (Sb) in a combined amount of 0.01 to 0.1 wt%, with the remainder containing iron (Fe) and other unavoidable impurities. A non-oriented electrical steel sheet satisfying the following equation 1. [Formula 1] F s,i = (F s ) 2 + 3(F i ) ≤ 50 (However, in the above formula 1, F s represents the KAM (Kernel average misorientation) value, and F i (Indicates the number of precipitates with a diameter of 0.1㎛ or more per unit area.) 2. In paragraph 1, F indicating KAM value s Non-oriented electrical steel sheet with a value of less than 6.

5.

3. In paragraph 1, The number of precipitates with a diameter of 0.1㎛ or more is 15 / mm 2 Below is the non-oriented electrical steel sheet.

4. In paragraph 1, Iron Loss (W 10 / 400 ) Non-oriented electrical steel sheet having a strength of 14.5 W / kg or less.

5. A first step of preparing a steel material containing 3.0 to 3.8 wt% of silicon (Si), 0.2 to 0.4 wt% of manganese (Mn), 0.8 to 1.5 wt% of aluminum (Al), 0.01 wt% or less of carbon (C), 0.01 wt% or less of sulfur (S), 0.08 wt% or less of phosphorus (P), 0.01 wt% or less of nitrogen (N), 0.01 wt% or less of titanium (Ti), and 0.01 to 0.1 wt% of at least one of tin (Sn) and antimony (Sb), with the remainder being 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; A fifth step of cold rolling annealing the above cold rolled steel sheet; and A method for manufacturing a non-oriented electrical steel sheet, comprising a sixth step of performing stress relief annealing on the cold-rolled steel sheet having performed the fifth step above at 720 to 770°C for 1.5 to 2.5 hours.

6. In paragraph 5, 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 6th step is [Formula 1] F s,i = (F s ) 2 + 3(F i ) ≤ 50 (However, in the above formula 1, F s represents the KAM (Kernel average misorientation) value, and F i (Indicates the number of precipitates with a diameter of 0.1㎛ or more per unit area.) 7. In paragraph 5, The steel that has undergone the above 6 steps has an F value indicating the KAM value. s A method for manufacturing a non-oriented electrical steel sheet having a value of less than 6.

5.

8. In paragraph 5, The steel material that has undergone the above 6th step has a number of precipitates with a diameter of 0.1㎛ or more of 15 / mm. 2 Method for manufacturing non-oriented electrical steel sheet below.

9. In paragraph 5, Iron Loss (W 10 / 400 ) A method for manufacturing a non-oriented electrical steel sheet having a strength of 14.5 W / kg or less.

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