Non-oriented electrical steel sheet, its manufacturing method, and motor core including the same

Abstract

A non-oriented electrical steel sheet, a method for manufacturing the same, and a motor core including the same are provided. [Solution] The non-oriented electrical steel sheet of the present invention contains, by weight, 2.8-4.0% Si, 0.5-1.7% Al, and 0.3-2.0% Mn, with the remainder being Fe and unavoidable impurities. It is characterized by having a surface layer extending from the surface of the steel sheet toward the interior of the steel sheet, an insulating coating layer on the surface of the steel sheet, and a weight ratio of Al to Mn (Al / Mn) of 1-10 in the insulating coating layer and the surface layer.

Description

[Technical Field]

[0001] The present invention relates to a non-oriented electrical steel sheet, a manufacturing method thereof, and a motor core including the same, and more particularly to a non-oriented electrical steel sheet in which a surface layer formed on the steel sheet is controlled by appropriately controlling the dew point temperature during stress relief annealing (SRA), a manufacturing method thereof, and a motor core including the same. [Background technology]

[0002] Recently, as the damage caused by climate change increases, countries around the world have announced roadmaps for achieving carbon neutrality by 2050. Total carbon emissions are expected to reach 39 billion tons in 2020, of which internal combustion engines are expected to account for 24%, or 9.4 billion tons. This has led to a growing momentum to achieve carbon neutrality in this sector through the electrification of internal combustion engines. In the mobility sector, electrification, led by electric vehicles, is rapidly progressing. The driving motors required for new mobility vehicles must be able to increase mileage and top speed. This is directly related to the low iron loss characteristics of electrical steel sheets. Low iron loss in electrical steel sheets further improves efficiency and extends mileage. Therefore, low iron loss at high frequencies is essential for electrical steel sheets. To achieve this, electrical steel sheets typically contain large amounts of silicon and other elements, such as aluminum, manganese, and chromium, to ensure low iron loss at high frequencies.

[0003] However, in addition to the method of reducing iron loss by adding a large amount of resistivity elements such as Si, Al, Mn, and Cr, there is another method of improving iron loss by refining the grain size or by leaving unrecrystallized parts to increase strength, and then growing the grain size through the SRA process. Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a non-oriented electrical steel sheet, a manufacturing method thereof, and a motor core including the same. Specifically, an object of one embodiment of the present invention is to provide a non-oriented electrical steel sheet in which the surface layer formed on the steel sheet is controlled by appropriately adjusting the dew point temperature during stress relief annealing (SRA), a manufacturing method thereof, and a motor core including the same. [Means for solving the problem]

[0005] The non-oriented electrical steel sheet according to the present invention contains, by weight, 2.8-4.0% Si, 0.5-1.7% Al, and 0.3-2.0% Mn, with the remainder being Fe and unavoidable impurities. It is characterized in that a surface layer exists from the surface of the steel sheet toward the interior of the steel sheet, an insulating coating layer exists on the surface of the steel sheet, and the weight ratio of Al to Mn (Al / Mn) in the insulating coating layer and the surface layer is 1-10.

[0006] The non-oriented electrical steel sheet of the present invention preferably further contains one or more of C, N, S, Ti, Nb, and V in an amount of 0.005 wt % or less each. The steel sheet may further contain one or more of P: 0.005 wt% or less, Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Sn: 0.06 wt% or less, Sb: 0.06 wt% or less, Ni: 0.05 wt% or less, and Zn: 0.01 wt% or less.

[0007] The steel sheet preferably further contains one or more of Bi, Pb, Ge, and As in an amount of 0.200 wt % or less, respectively, or in a total amount thereof. The steel plate may further contain one or more of Mo: 0.03 wt % or less, B: 0.0050 wt % or less, Ca: 0.0050 wt % or less, and Mg: 0.0050 wt % or less. The steel plate preferably has a resistivity of 50 μΩ·cm or more. The steel sheet preferably has an average crystal grain size of 50 to 200 μm.

[0008] The manufacturing method includes the steps of hot-rolling a slab containing, by weight, 2.8 to 4.0% Si, 0.5 to 1.7% Al, and 0.3 to 2.0% Mn, with the remainder being Fe and unavoidable impurities, to produce a hot-rolled sheet, cold-rolling the hot-rolled sheet to produce a cold-rolled sheet, annealing the cold-rolled sheet, forming an insulating coating layer on the annealed cold-rolled sheet, and stress-relief annealing the steel sheet on which the insulating coating layer has been formed. The stress relief annealing step includes a temperature rise step of raising the temperature of the steel sheet to a cracking temperature and a cracking step, wherein the temperature rise step has a temperature rise rate of 10 to 50°C / min in the range of 300 to 500°C, the dew point of the temperature rise step is 10 to 50°C, and the dew point of the cracking step is 0 to 35°C.

[0009] The slabs may further include one or more of C, N, S, Ti, Nb, and V in amounts of up to 0.005 wt. % each. The slab preferably further contains one or more of P: 0.005 wt% or less, Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Sn: 0.06 wt% or less, Sb: 0.06 wt% or less, Ni: 0.05 wt% or less, and Zn: 0.01 wt% or less. The slab may further contain one or more of Bi, Pb, Ge, and As in an amount of 0.200 wt % or less each or in total. The slab may further contain one or more of Mo: 0.03% by weight or less, B: 0.0050% by weight or less, Ca: 0.0050% by weight or less, and Mg: 0.0050% by weight or less.

[0010] In the cold-rolled sheet annealing step, the annealing temperature is preferably 750 to 850°C, and the annealing time is preferably 10 to 60 seconds. After annealing the cold-rolled sheet, the annealed cold-rolled sheet may have an average grain size of 10 to 30 μm. After annealing the cold-rolled sheet, the unrecrystallized fraction is preferably 1 to 15 area %.

[0011] After annealing the cold-rolled sheet, a surface layer exists from the surface of the cold-rolled sheet toward the interior of the cold-rolled sheet, and the thickness of the surface layer is preferably 0.0001 to 0.2 μm. After annealing the cold-rolled sheet, the following formula 1 can be satisfied. [Formula 1] 50≦[Average grain size (μm)]×[Cold-rolled plate annealing time (seconds)] / [Unrecrystallized area fraction (%)]≦500 In the temperature rising stage, it is preferable that the temperature rising rate and the dew point satisfy the following formula 2. [Formula 2] 0.7≦[Heating rate (℃ / min)] / [Dew point (℃)]≦2.5

[0012] The motor core of the present invention includes a rotor formed by stacking a plurality of non-oriented electrical steel sheets and a stator formed by stacking a plurality of non-oriented electrical steel sheets, wherein the non-oriented electrical steel sheets in the rotor contain, by weight, 2.8 to 4.0% Si, 0.5 to 1.7% Al, and 0.3 to 2.0% Mn, with the balance being Fe and unavoidable impurities; and the non-oriented electrical steel sheets in the stator contain, by weight, 2.8 to 4.0% Si, 0.5 to 1.7% Al, and 0.3 to 2.0% Mn, with the balance being Fe and unavoidable impurities, and wherein a surface layer exists from the surface of the steel sheet toward the interior of the steel sheet, and wherein the weight ratio of Al to Mn in the surface layer (Al / Mn) is 1 to 10. The non-oriented electrical steel sheets in the rotor preferably have an average crystal grain size of 10 to 30 μm. It is preferable that the difference in Si, Al, and Mn content between the non-oriented electrical steel sheets contained in the stator and rotor is 0.2 wt % or less. [Effects of the Invention]

[0013] The non-oriented electrical steel sheet according to the present invention has excellent uniformity in tensile strength after cold-rolled sheet annealing. Furthermore, the non-oriented electrical steel sheet according to the present invention is excellent in iron loss and insulation properties after SRA. Ultimately, the non-oriented electrical steel sheet of the present invention can be used to manufacture rotors without SRA treatment, and can be used to manufacture stators after SRA treatment, thereby contributing to environmental conservation by producing environmentally friendly motors for automobiles, highly efficient motors for home appliances, and super-premium motor cores. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic cross-sectional side view of a non-oriented electrical steel sheet according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] Terms such as "first," "second," and "third" are used to describe various portions, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one portion, component, region, layer, or section from another portion, component, region, layer, or section. Therefore, a first portion, component, region, layer, or section described below can be referred to as a second portion, component, region, layer, or section without departing from the scope of the present invention. The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. As used in the specification, the term "comprising" refers to the inclusion of certain features, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components. When a part is referred to as being "on" or "above" another part, it means that it is directly on or above the other part, or there may be other parts between them. In contrast, when a part is referred to as being "directly on" another part, there are no other parts between them. All terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains. Terms defined in commonly used dictionaries are additionally interpreted to have a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal sense unless specifically defined. Unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight.

[0016] In one embodiment of the present invention, the inclusion of an additional element means that the remaining iron (Fe) is replaced by the additional amount of the additional element. Although the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein, the present invention will be described in detail below so that those skilled in the art can easily practice the present invention. In one embodiment of the present invention, the dew point temperature is appropriately controlled during the stress relief annealing (SRA) process to control the surface layer and insulating coating layer formed on the steel sheet, thereby improving core loss and insulation properties at the same time.

[0017] A non-oriented electrical steel sheet according to one embodiment of the present invention contains, by weight, 2.8 to 4.0% Si, 0.5 to 1.7% Al, and 0.3 to 2.0% Mn, with the remainder being Fe and unavoidable impurities. First, the reasons for limiting the components of non-oriented electrical steel sheets will be explained.

[0018] Si::2.8~4.0wt% Silicon (Si) must be added in relatively large amounts because it increases the resistivity of the material and reduces iron loss. If too little Si is added, the effect of improving high-frequency iron loss may be minimal. On the other hand, if too much Si is added, the hardness of the material increases, which is undesirable as it reduces productivity and punchability. More preferably, the Si content is 3.0 to 3.7 wt %.

[0019] Al: 0.5~1.7% by weight Aluminum (Al) must be added in large amounts because it increases the resistivity of the material and reduces iron loss. If too little Al is added, it is ineffective in reducing high-frequency iron loss and may cause the formation of fine nitrides, which may deteriorate magnetic properties. On the other hand, if too much Al is added, it may cause problems such as changing the physical properties of the mold flux during the continuous casting process, significantly reducing productivity. More preferably, the Al content is 0.7 to 1.5 wt.%.

[0020] Mn:0.3~2.0wt% Manganese (Mn) increases the resistivity of the material, improves iron loss, and plays a role in forming sulfides. If too little Mn is added, fine MnS precipitates, which may deteriorate the magnetic properties. On the other hand, if too much Mn is added, it may promote the formation of a

[0111] texture, which is unfavorable to magnetic properties, and may cause a sudden decrease in magnetic flux density. More preferably, the Mn content is 0.5 to 1.5 wt %. Specific resistance: 50 μΩ cm or more Higher resistivity is better for reducing eddy current loss in high-frequency rotating machines, but excessively high resistivity can result in poor magnetic flux density. The resistivity of the present invention can be calculated as 13.25 + 11.3 × ([Si] + [Al] + [Mn] / 2), where [Si], [Al], and [Mn] represent the Si, Al, and Mn contents (weight percent), respectively. Higher resistivity reduces iron loss. If resistivity is too low, poor iron loss will result, making it difficult to use as a high-efficiency motor. More specifically, the resistivity should be 50 to 90 μΩ·cm. Even more specifically, the resistivity should be 60 to 85 μΩ·cm.

[0021] The non-oriented electrical steel sheet according to one embodiment of the present invention may further contain one or more of P: 0.005 wt% or less, Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Sn: 0.06 wt% or less, Sb: 0.06 wt% or less, Ni: 0.05 wt% or less, and Zn: 0.01 wt% or less. P: 0.005% by weight or less Phosphorus (P) is a grain boundary segregation element, and if added in excess, it may delay recrystallization and deteriorate strength uniformity in the rolling direction and the direction perpendicular to the rolling direction. More preferably, P is contained in an amount of 0.0001 to 0.0030 wt %.

[0022] Cu:0.005~0.200wt% Copper (Cu) plays a role in forming sulfides together with Mn. If Cu is added in an excessively small amount, fine CuMnS may precipitate, deteriorating the magnetic properties. On the other hand, if Cu is added in an excessively large amount, high-temperature embrittlement may occur, which may cause cracks during continuous casting or hot rolling. More preferably, Cu is contained in an amount of 0.01 to 0.10 wt%.

[0023] Cr:0.010~0.50wt% Chromium (Cr) plays a role in increasing resistivity and improving iron loss. If too little Cr is added, the effect of increasing resistivity may be insufficient. On the other hand, if too much Cr is added, there is a risk of a decrease in magnetic flux density. More specifically, if Cr is further added, it is recommended that it be contained in an amount of 0.050 to 0.20 wt %.

[0024] Sn: 0.06% by weight or less Tin (Sn) is an element that segregates at grain boundaries and is added to suppress the diffusion of nitrogen through the grain boundaries, suppress the {111} texture that is harmful to magnetism, and increase the advantageous {100} texture, thereby improving magnetic properties. If too much Sn is added, it will hinder grain growth, reducing magnetism and worsening rolling properties. Therefore, it is best to add Sb within the above-mentioned range. A more preferred range is 0.005 to 0.060 wt. %, and even more preferred is 0.01 to 0.05 wt. %.

[0025] Sb: 0.06% by weight or less Antimony (Sb) is an element that segregates at grain boundaries and is added to suppress the diffusion of nitrogen through grain boundaries, suppress the {111} texture that is detrimental to magnetic properties, and increase the advantageous {100} texture, thereby improving magnetic properties. Adding excessive amounts of Sb can impede grain growth, reducing magnetic properties and worsening rolling properties. Therefore, it is recommended to add Sb within the aforementioned range. A more preferred range is 0.005 to 0.060 wt.%, and even more preferred is 0.01 to 0.05 wt.%.

[0026] Ni: 0.05% by weight or less Nickel (Ni) reacts with impurity elements to form fine sulfides, carbides, and nitrides, which can have a detrimental effect on magnetic properties. Specifically, it is preferable that the Ni content be 0.001 to 0.03 wt %.

[0027] Zn: 0.01% by weight or less If the zinc (Zn) content is excessive, it may act as an impurity and cause deterioration of magnetic properties. Therefore, it is preferable to add more Zn within the above range. More specifically, it can be contained in an amount of 0.001 to 0.005 wt %. The non-oriented electrical steel sheet according to one embodiment of the present invention may further contain one or more of Bi, Pb, Ge, and As in an amount of 0.200 wt % or less, respectively, or in a total amount thereof.

[0028] When the above elements are added, they segregate at the grain boundaries, alleviating stress concentration at the grain boundaries during cold rolling and reducing the stress concentration during the subsequent recrystallization annealing process. <111> / / Magnetic flux density can be improved by suppressing the recrystallization of ND-oriented crystal grains. While the aforementioned effects can be obtained by adding these elements appropriately, excessive amounts can cause significant segregation, inhibiting grain growth and potentially resulting in poor magnetic flux density and core loss. More specifically, the alloy may further contain 0.0001 to 0.200 wt. % or a total of 0.001 to 0.100 wt. % or 0.005 to 0.05 ... More specifically, the alloy may further contain one or more of Bi, Pb, Ge, and As, each or in total. More preferably, the alloy further contains 0.001 to 0.100 wt. More preferably, the alloy further contains 0.005 to 0.050 wt. % or 0.005 to 0.050 wt. More specifically, the alloy may further contain one or more of Bi, Pb, Ge, and As, each or in total.

[0029] The non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of Mo: 0.03 wt % or less, B: 0.0050 wt % or less, Ca: 0.0050 wt % or less, and Mg: 0.0050 wt % or less. These react with the unavoidably contained C, S, N, etc. to form fine carbides, nitrides, or sulfides, which can adversely affect the magnetic properties, so it is preferable to set an upper limit as described above.

[0030] Other impurities In addition to the elements mentioned above, it may contain unavoidable impurities such as carbon (C), sulfur (S), nitrogen (N), titanium (Ti), niobium (Nb), and vanadium (V). It is preferable to limit the amounts of C, N, and Ti because they form carbonitrides and play a role in hindering magnetic domain movement, and it is also preferable to limit the amount of S because it forms sulfides and can hinder grain growth. It is preferable to include each of these elements in an amount of 0.0050 wt% or less. N combines with Ti, Nb, and V to form nitrides, which reduces grain growth. C reacts with N, Ti, Nb, V, etc. to form fine carbides, which play a role in hindering grain growth and magnetic domain movement. S forms sulfides and hinders grain growth. When impurity elements are further contained in this way, one or more of C, S, N, Ti, Nb, and V may be contained in an amount of 0.005 wt % or less each.

[0031] The non-oriented electrical steel sheet according to one embodiment of the present invention may have an average grain size of 50 to 200 μm. By appropriately adjusting the average grain size, magnetic properties can be further improved. In one embodiment of the present invention, the grain size may be measured in a plane parallel to the sheet surface of the steel sheet. More specifically, it may be measured in a thickness range of 1 / 4t to 3 / 4t, where t is the total thickness of the steel sheet. The grain size may be measured by imagining an imaginary circle having the same area as the grain, and then calculating the diameter of the circle. The average grain size may be measured by dividing the number of grains present within the area to be measured by the area to be measured. More specifically, the non-oriented electrical steel sheet according to one embodiment of the present invention may have an average grain size of 60 to 150 μm. In one embodiment of the present invention, unless otherwise specified, the average grain size refers to the average grain size after SRA.

[0032] 1 shows a schematic side cross-sectional view of a non-oriented electrical steel sheet according to an embodiment of the present invention. The non-oriented electrical steel sheet shown in FIG. 1 is merely for illustrating the present invention, and the present invention is not limited thereto. Therefore, the structure of the non-oriented electrical steel sheet can be modified in various ways. As shown in Figure 1, a non-oriented electrical steel sheet 100 according to an embodiment of the present invention includes a surface layer 20 extending from the surface of the steel sheet toward the interior of the steel sheet, and a steel sheet base material 10 in addition to the surface layer. An insulating coating layer 30 is present on the surface of the steel sheet.

[0033] In one embodiment of the present invention, the insulating coating layer 30 and the surface layer 20 are composed of Al and Mn oxides. When Al and Mn oxides are properly formed in the insulating coating layer 30 and the surface layer 20 during stress relief annealing, it is possible to simultaneously improve the insulating properties and magnetic properties. The insulating coating layer 30 may be composed mainly of Mn oxide, and the surface layer 20 may be composed mainly of Al oxide.

[0034] In one embodiment of the present invention, the insulating coating layer 30 and the surface layer 20 may have a weight ratio of Al to Mn (Al / Mn) of 10 or less. If the Mn content in the insulating coating layer 30 is too low and the Al / Mn ratio is too high, the bonding strength between the insulating coating layer 30 and the surface layer 20 may be weak. More specifically, the insulating coating layer 30 and the surface layer 20 may have a weight ratio of Al to Mn (Al / Mn) of 1-8.

[0035] The Mn and Al contents in the insulating coating layer 30 and the surface layer 20 can be measured using GDS. The amounts of Al and Mn can be defined by the area of ​​the GDS peak. The boundary between the surface layer 20 and the steel sheet substrate 10 can be defined as the intersection of the point where the oxygen peak decreases and the point where the Fe peak increases. The distinction between the insulating coating layer 30 and the surface layer 20 is not necessary in one embodiment of the present invention, but can be defined by the inflection point where the slope of the Al peak changes. The Al and Mn contents in the insulating coating layer 30 and the surface layer 20 can be appropriately adjusted by adjusting the temperature rise rate and dew point during the stress relief annealing process, which will be described in detail later in the description of the method for manufacturing a non-oriented electrical steel sheet.

[0036] Specifically, the non-oriented electrical steel sheet according to one embodiment of the present invention may have an insulation value of 500 mA or more. More specifically, the insulation value may be 550 to 900 mA. The insulation value may be measured by the Franklin test method. Furthermore, the non-oriented electrical steel sheet according to one embodiment of the present invention preferably has an iron loss (10 / 400) of 10.50 W / kg or less. More specifically, it is preferably 9.0 to 10.0 W / kg. The magnetic property can be measured by the Epstein method or the SST (single sheet test) method. In this case, the thickness is preferably 0.25 mm.

[0037] A method for producing a non-oriented electrical steel sheet according to one embodiment of the present invention includes the steps of hot-rolling a slab containing, by weight, 2.8 to 4.0% Si, 0.5 to 1.7% Al, and 0.3 to 2.0% Mn, with the remainder being Fe and unavoidable impurities, to produce a hot-rolled sheet, cold-rolling the hot-rolled sheet to produce a cold-rolled sheet, annealing the cold-rolled sheet, and stress-relief annealing the annealed cold-rolled sheet. Each stage will be explained in detail below.

[0038] First, a slab is manufactured. The reasons for limiting the addition ratio of each component in the slab are the same as those for limiting the composition of the non-oriented electrical steel sheet described above, so a repeated explanation will be omitted. The composition of the slab does not substantially change during manufacturing processes such as hot rolling, hot-rolled sheet annealing, cold rolling, cold-rolled sheet annealing, and stress-relief annealing, which will be described later, so the composition of the slab and the composition of the non-oriented electrical steel sheet are substantially the same.

[0039] The slab can be heated before producing the hot-rolled sheet. Specifically, the slab is placed in a heating furnace and heated at 1100-1250°C. When heated at a temperature above 1250°C, precipitates may re-melt and precipitate finely after hot rolling. The heated slab is hot-rolled to 2 to 2.3 mm to produce a hot-rolled sheet. In the stage of producing the hot-rolled sheet, the finish rolling temperature is preferably 800 to 1000°C.

[0040] After the step of producing the hot-rolled sheet, the method may further include a step of annealing the hot-rolled sheet. The annealing temperature for the hot-rolled sheet is preferably 850 to 1150°C. If the annealing temperature for the hot-rolled sheet is less than 850°C, the structure does not grow or grows finely, resulting in little effect in increasing magnetic flux density. If the annealing temperature exceeds 1150°C, the magnetic properties may deteriorate and the rolling workability may be impaired due to deformation of the sheet. More specifically, the temperature range is preferably 950 to 1125°C. More specifically, the annealing temperature for the hot-rolled sheet is 900 to 1100°C. Hot-rolled sheet annealing is performed to increase orientation favorable for magnetic properties as needed, and may be omitted.

[0041] The hot-rolled sheet is then pickled and cold-rolled to the desired thickness. Depending on the thickness of the hot-rolled sheet, a reduction of 70-95% can be applied, and cold-rolling can be performed to a final thickness of 0.2-0.65 mm. To achieve the desired reduction, cold rolling can be performed once, or two or more times with intermediate annealing. The cold-rolled sheet is subjected to cold-rolled sheet annealing.

[0042] In the cold-rolled sheet annealing step, the annealing temperature is preferably 750-850°C and the annealing time is preferably 10-60 seconds. If the annealing temperature is higher and the cracking time is longer, the unrecrystallized portions disappear, the average grain size becomes larger, and sufficient strength cannot be secured, which may result in poor directional strength uniformity. If the annealing temperature is low and the cracking time is short, the grains may not grow properly, which may result in poor magnetic properties. More specifically, in the cold-rolled sheet annealing step, the annealing temperature is preferably 7700-830°C and the annealing time is preferably 20-45 seconds. After annealing the cold-rolled sheet, the annealed cold-rolled sheet preferably has an average grain size of 10 to 30 μm. When the average grain size of the cold-rolled sheet is properly formed, both magnetic properties and strength can be ensured. The average grain size of the cold-rolled sheet preferably is 15 to 25 μm.

[0043] After annealing the cold-rolled sheet, the unrecrystallized fraction is preferably 1 to 15 area %. When the unrecrystallized fraction of the cold-rolled sheet is properly formed, both magnetic properties and strength can be ensured. In one embodiment of the present invention, the unrecrystallized fraction refers to elongated grain sizes, similar to elongated grains, when observed through structural observation, and can be distinguished from spherical recrystallized grain sizes. More specifically, the unrecrystallized fraction is preferably 3 to 13 area %. After annealing the cold-rolled sheet, a surface layer exists from the surface toward the interior of the cold-rolled sheet, and the thickness of the surface layer is preferably 0.001 to 0.2 μm. During the annealing process of the cold-rolled sheet, the surface of the steel sheet is partially oxidized to form the surface layer. More specifically, the thickness of the surface layer is preferably 0.01 to 0.1 μm.

[0044] After annealing the cold-rolled sheet, the difference in tensile strength between the rolling direction and other directions becomes 15 MPa or less, ensuring uniformity of tensile strength (ratio of tensile strength in the rolling direction / tensile strength in the 45-degree direction > 98%). After annealing the cold-rolled sheet, the following formula 1 can be satisfied. [Formula 1] 50≦[Average grain size (μm)]×[Cold-rolled plate annealing time (seconds)] / [Unrecrystallized area fraction (%)]≦500 When the above formula 1 is satisfied, a tensile strength of 630 MPa or more can be obtained, and the directional strength ratio (tensile strength in the rolling direction / tensile strength in the 45-degree direction) can be uniform at 98.0% or more.

[0045] Next, an insulating coating layer is formed on the annealed cold-rolled steel sheet. Methods for forming an insulating coating layer are widely known, so a detailed description will be omitted. Specifically, the insulating coating layer can be formed by applying an insulating coating layer-forming composition containing metal phosphate and silica as its main components, followed by heat treatment. In one embodiment of the present invention, since Mn in the steel sheet diffuses into the insulating coating layer during stress relief annealing, it is preferable that the insulating coating layer have a very low Mn content after formation. Specifically, it should be 0.01 wt % or less.

[0046] Next, the steel sheet with the insulating coating layer is subjected to stress relief annealing. After the insulating coating is formed, punching and lamination processes can be performed. This process is well known and will not be described in detail. Stress is generated in the non-oriented electrical steel sheet during the punching process, which adversely affects the magnetic properties of the non-oriented electrical steel sheet. In the case of a stator, where magnetic properties are relatively important among motor cores, stress relief annealing is performed to remove residual stress in the steel sheet, improving the magnetic properties of the steel sheet. On the other hand, in the case of a rotor, where strength properties are relatively more important than magnetic properties, stress relief annealing can be omitted. That is, even if the same steel sheet is used, it can be used for different purposes as a stator and a rotor depending on whether or not it is subjected to stress relief annealing.

[0047] The stress relief annealing step includes a temperature rise step in which the steel sheet is heated to a cracking temperature and a cracking step, and the temperature rise step is in the range of 300 to 500°C at a temperature rise rate of 10°C / min or more, the dew point in the temperature rise step is 10 to 50°C, and the dew point in the cracking step is 10°C or more. Under the above conditions, an appropriate insulating coating layer 30 and surface layer 20 are formed, thereby simultaneously improving insulation and magnetic properties.

[0048] The temperature-raising step is a step in which the steel sheet is heated to a crack temperature. The starting temperature is not particularly limited, but may be from room temperature (25°C) to 300°C. During the temperature-raising step, the temperature-raising rate in the range of 300 to 500°C is preferably 10°C / min or more. Only by ensuring an appropriate temperature-raising rate can Al and Mn be appropriately contained in the insulating coating layer and the surface layer. More specifically, during the temperature-raising step, the temperature-raising rate in the range of 300 to 500°C may be 10°C / min to 50°C / min.

[0049] The dew point during the temperature rise stage is 10°C to 50°C. If the dew point is too low, the surface layer 20 may not be formed properly. If the dew point is too high, a large amount of Al and Mn oxides may be formed in the coating layer and the surface layer 20, causing deep internal oxidation of the base steel and resulting in poor magnetic properties. More specifically, the dew point during the temperature rise stage is preferably 15°C to 46°C. In the temperature rising stage, the temperature rising rate and the dew point can satisfy the following formula 2: [Formula 2] 0.7≦[Heating rate (℃ / min)] / [Dew point (℃)]≦2.5 When the relationship between the heating rate and the dew point is properly adjusted, the insulating coating layer 30 and the surface layer 20 are more properly formed, and the insulating property and the magnetic property can be further improved at the same time.

[0050] The cracking stage is a stage in which the steel sheet is maintained at a constant cracking temperature. The cracking temperature is preferably 700 to 850°C. The cracking time is preferably 10 to 300 minutes. The dew point at the cracking stage is preferably 10°C or higher. By adjusting the temperature rise stage and the dew point temperature, the insulating coating layer 30 and the surface layer 20 can be properly formed. More specifically, the dew point at the cracking stage is preferably 10 to 50°C.

[0051] A motor core according to one embodiment of the present invention includes a rotor formed by stacking a plurality of non-oriented electrical steel sheets, and a stator formed by stacking a plurality of non-oriented electrical steel sheets, wherein the non-oriented electrical steel sheets in the rotor contain, by weight, 2.8 to 4.0% Si, 0.5 to 1.7% Al, and 0.3 to 2.0% Mn, with the remainder being Fe and unavoidable impurities; the non-oriented electrical steel sheets in the stator contain, by weight, 2.8 to 4.0% Si, 0.5 to 1.7% Al, and 0.3 to 2.0% Mn, with the remainder being Fe and unavoidable impurities; a surface layer exists from the surface of the steel sheet toward the interior of the steel sheet; and an insulating coating layer exists on the surface of the steel sheet, and a weight ratio of Al to Mn (Al / Mn) in the insulating coating layer and the surface layer is 1 to 10. The rotor has the same properties as the non-oriented electrical steel sheet before SRA annealing, and the stator has the same properties as the non-oriented electrical steel sheet after SRA annealing, so a detailed description thereof will be omitted.

[0052] In one embodiment of the present invention, the rotor and the stator can be manufactured simultaneously using the same non-oriented electrical steel sheet, further improving manufacturing efficiency. The rotor and the stator may be manufactured simultaneously using the same non-oriented electrical steel sheets, and the difference in Si, Al, and Mn content between the non-oriented electrical steel sheets contained in the stator and the rotor may be 0.2% or less. The motor core is made of steel sheets with an insulating coating between them. Since insulating coatings are widely known, a detailed explanation will be omitted. Preferred examples and comparative examples of the present invention will be described below. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples. [Example]

[0053] Example 1 The slabs were manufactured as shown in Table 1 below. All of the elements other than those listed in Table 1, such as C, S, N, Ti, Nb, and V, were controlled to 0.003 wt % or less, with the remainder being Fe. The slab was heated to 1150°C and hot-rolled to a thickness of 2.0 mm by finish rolling at 850°C. The hot-rolled sheet was annealed at 1100°C for 4 minutes and then pickled. It was then cold-rolled to a thickness of 0.25 mm, and cold-rolled sheet annealing was performed under the conditions shown in Table 2 below. After cold rolling and annealing, the properties of the steel sheets (i.e., rotors) are shown in Table 2. The grain size was investigated using an optical microscope, and the unrecrystallized fraction was measured using SEM-EBSD.

[0054] The tensile strength was measured using a tensile tester according to the JIS standard. The annealed cold-rolled sheet was then coated with a Cr-free phosphate-based insulating coating composition to form an insulating coating, and then subjected to SRA annealing under the conditions shown in Table 3. The properties of the steel sheet (i.e., stator) after SRA annealing are shown in Figure 3. The insulating properties were measured using a Franklin tester. The magnetic properties were measured using a single sheet test machine. The composition of the insulating coating layer and the surface layer was measured using GDS. The amounts of Al and Mn were defined by the area of ​​the GDS peak.

[0055] [Table 1]

[0056] [Table 2]

[0057] [Table 3]

[0058] As shown in Tables 1 to 3, when the alloy components and surface layer properties are appropriately adjusted, it can be seen that core loss and insulation properties are improved simultaneously. In addition, it can be confirmed that the tensile strength before SRA and the uniformity of the tensile strength can be secured after annealing the cold rolled sheet. In the case of the inventive example, Mn-O was mainly present in the insulating coating layer, and Al-O was mainly present in the surface layer. Looking at the area ratio of GDS, when Al / Mn exceeded 10, there was almost no Mn oxide in the insulating coating layer and surface layer. When Mn-O was sufficiently formed in the insulating coating layer and surface layer, the Al / Mn value fell within the appropriate range, resulting in excellent insulation and magnetic properties.

[0059] The present invention is not limited to the above-described embodiments, and can be manufactured in various different forms, and those skilled in the art will understand that the present invention can be embodied in other specific forms without changing the technical concept or essential features of the present invention. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and not limiting.

Claims

1. The alloy contains, by weight, 2.8 to 4.0% Si, 0.5 to 1.7% Al, and 0.3 to 2.0% Mn, with the balance being Fe and unavoidable impurities; There is a surface layer extending from the surface of the steel plate toward the interior of the steel plate, an insulating coating layer is present on the surface of the steel sheet; The non-oriented electrical steel sheet is characterized in that the weight ratio of Al to Mn in the insulating coating layer and the surface layer is 1 to 10.

2. 2. The non-oriented electrical steel sheet according to claim 1, further comprising at most 0.005 wt. % of one or more of C, N, S, Ti, Nb, and V.

3. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of P: 0.005 wt % or less, Cu: 0.005 to 0.2 wt %, Cr: 0.01 to 0.5 wt %, Sn: 0.06 wt % or less, Sb: 0.06 wt % or less, Ni: 0.05 wt % or less, and Zn: 0.01 wt % or less.

4. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of Bi, Pb, Ge, and As in an amount of 0.200% or less by weight each or in a total amount thereof.

5. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of Mo: 0.03 wt % or less, B: 0.0050 wt % or less, Ca: 0.0050 wt % or less, and Mg: 0.0050 wt % or less.

6. 2. The non-oriented electrical steel sheet according to claim 1, wherein the resistivity is 50 μΩ·cm or more.

7. 2. The non-oriented electrical steel sheet according to claim 1, wherein the average crystal grain size is 50 to 200 μm.

8. a step of producing a hot-rolled sheet by hot-rolling a slab containing, in weight percent, 2.8 to 4.0% Si, 0.5 to 1.7% Al, and 0.3 to 2.0% Mn, with the balance being Fe and unavoidable impurities; cold-rolling the hot-rolled sheet to produce a cold-rolled sheet; a cold-rolled sheet annealing step of annealing the cold-rolled sheet; forming an insulating coating layer on the annealed cold-rolled sheet; and stress-relief annealing the steel sheet on which the insulating coating layer is formed; The stress relief annealing step includes a temperature increasing step of increasing the temperature of the steel sheet to a cracking temperature and a cracking step, The temperature rising step is in the range of 300 to 500°C at a temperature rising rate of 10 to 50°C / min, The method for manufacturing a non-oriented electrical steel sheet, wherein the dew point in the temperature rising step is 10 to 50°C, and the dew point in the cracking step is 0 to 35°C.

9. The method for producing a non-oriented electrical steel sheet according to claim 8, wherein the slab further contains one or more of C, N, S, Ti, Nb, and V in an amount of 0.005% by weight or less, respectively.

10. 9. The method for producing a non-oriented electrical steel sheet according to claim 8, wherein the slab further contains one or more of P: 0.005 wt% or less, Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Sn: 0.06 wt% or less, Sb: 0.06 wt% or less, Ni: 0.05 wt% or less, and Zn: 0.01 wt% or less.

11. The method for producing a non-oriented electrical steel sheet according to claim 8, wherein the slab further contains one or more of Bi, Pb, Ge, and As in an amount of 0.200 wt % or less, respectively, or in a total amount thereof.

12. 9. The method for producing a non-oriented electrical steel sheet according to claim 8, wherein the slab further contains one or more of Mo: 0.03 wt% or less, B: 0.0050 wt% or less, Ca: 0.0050 wt% or less, and Mg: 0.0050 wt% or less.

13. 9. The method of claim 8, wherein the annealing step comprises annealing the cold-rolled sheet at a temperature of 750 to 850° C. for a time of 10 to 60 seconds.

14. The method for manufacturing a non-oriented electrical steel sheet according to claim 8, wherein the annealed cold-rolled sheet has an average grain size of 10 to 30 μm after the cold-rolled sheet annealing.

15. The method for producing a non-oriented electrical steel sheet according to claim 8, wherein the unrecrystallized fraction after the cold-rolled sheet annealing is 1 to 15 area %.

16. 9. The method for manufacturing a non-oriented electrical steel sheet according to claim 8, wherein after the cold-rolled sheet annealing, a surface layer exists from the surface of the cold-rolled sheet toward the inside of the cold-rolled sheet, and the thickness of the surface layer is 0.0001 to 0.2 μm.

17. 9. The method for producing a non-oriented electrical steel sheet according to claim 8, wherein the following formula 1 is satisfied after the cold-rolled sheet is annealed: [Formula 1] 50≦[Average grain size (μm)]×[Cold-rolled plate annealing time (seconds)] / [Unrecrystallized area fraction (%)]≦500

18. 9. The method for producing a non-oriented electrical steel sheet according to claim 8, wherein in the heating step, the heating rate and the dew point satisfy the following formula 2: [Formula 2] 0.7≦[heating rate (°C / min)] / [dew point (°C)]≦2.5

19. The rotor is made of a plurality of laminated non-oriented electromagnetic steel sheets, and the stator is made of a plurality of laminated non-oriented electromagnetic steel sheets, the non-oriented electrical steel sheets in the rotor contain, by weight %, 2.8 to 4.0% Si, 0.5 to 1.7% Al, and 0.3 to 2.0% Mn, with the remainder being Fe and unavoidable impurities; the non-oriented electrical steel sheets in the stator contain, by weight, 2.8 to 4.0% Si, 0.5 to 1.7% Al, and 0.3 to 2.0% Mn, with the remainder being Fe and unavoidable impurities; a surface layer exists from the surface of the steel sheet toward the interior of the steel sheet; and an insulating coating layer exists on the surface of the steel sheet; The insulating coating layer and the surface layer have a weight ratio of Al to Mn (Al / Mn) of 1 to 10.

20. 20. The motor core according to claim 19, wherein the non-oriented electrical steel sheets in the rotor have an average crystal grain size of 10 to 30 μm.

21. 20. The motor core according to claim 19, wherein the difference in Si, Al, and Mn content between the non-oriented electrical steel sheets included in the stator and the rotor is 0.2 wt % or less.

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