Non-oriented electrical steel sheet and its manufacturing method

Abstract

Hot rolling was carried out twice. <001> Provided is a non-oriented electrical steel sheet and a method for manufacturing the same, which suppresses texture, ensures the strength of the steel sheet before stress relief annealing, and ensures the magnetism of the steel sheet after stress relief annealing. The non-oriented electrical steel sheet of the present invention contains, by weight, 1.5 to 4% Si, 0.1 to 2% Al, and 0.05 to 2% Mn, with the remainder being Fe and unavoidable impurities, and has a {110} <001> The method for producing a non-oriented electrical steel sheet of the present invention is characterized in that the area fraction of crystal grains having an orientation within 15° from the center of the non-oriented electrical steel sheet is 10% or less. The method for producing a non-oriented electrical steel sheet of the present invention includes a first hot rolling step of hot rolling a slab containing, by weight, 1.5 to 4% Si, 0.1 to 2% Al, and 0.05 to 2% Mn, with the remainder being Fe and unavoidable impurities, to produce a first hot-rolled sheet; a step of coiling the first hot-rolled sheet; a second hot rolling step of hot rolling the first hot-rolled sheet at a temperature of 700 to 1000°C with a rolling reduction of 20 to 50% to produce a second hot-rolled sheet; a step of cold-rolling the second hot-rolled sheet to produce a cold-rolled sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet at a temperature of 710 to 820°C.

Description

[Technical Field]

[0001] One embodiment of the present invention relates to a non-oriented electrical steel sheet and a manufacturing method thereof. Specifically, one embodiment of the present invention relates to a non-oriented electrical steel sheet obtained by hot rolling twice to obtain a {110} <001> The present invention relates to a non-oriented electrical steel sheet that ensures the strength of the steel sheet before stress relief annealing and the magnetism of the steel sheet after stress relief annealing by suppressing the texture, and a method for manufacturing the same. [Background technology]

[0002] Non-oriented electrical steel is an important iron core material required for converting electrical energy into mechanical energy in rotating equipment, and its magnetic properties, namely low high-frequency iron loss and high magnetic flux density, are important for energy conservation. Here, iron loss is the energy that is converted into heat and lost during the energy conversion process, so the lower the iron loss, the more efficient it is, while magnetic flux density is the power that generates power, so the higher the efficiency. In addition, when rotating at thousands to tens of thousands of RPM, it is advantageous to reduce the thickness deviation of the electrical steel sheet along with its strength to produce a symmetrical core in order to suppress vibration and improve durability.

[0003] Recently, as a measure to combat the shortage of fossil fuels and reduce greenhouse gas emissions, there has been rapid development in the technology to convert existing internal combustion engine vehicles into HEVs (hybrid electric vehicles) / EVs (electric vehicles). These HEVs / EVs are vehicles that convert part or all of their drivetrain to an electric motor, reducing the amount of gasoline or diesel used as the fuel for existing internal combustion engines while achieving better fuel economy.

[0004] The motors used in these vehicles must produce high torque at low speeds and during acceleration, and rotate at high speeds during constant and high-speed driving. Therefore, the non-oriented electrical steel sheet used as the motor core material must have high magnetic flux density and high strength at low speeds, and high magnetic flux density and low high-frequency iron loss at high speeds, as well as small thickness deviation to suppress vibration. Generally, high-frequency iron loss refers to iron loss at frequencies above 200 Hz, and the value W10 / 400 is usually used for non-oriented electrical steel sheet for automobiles. Due to the characteristics of rotating equipment, iron loss and magnetic flux density in the circumferential direction are particularly important.

[0005] Generally, motor rotors require high magnetic flux density, strength, and thickness variation, while stators require low high-frequency core loss. However, reducing grain size to increase strength leads to lower core loss, which necessitates the use of different materials for the rotor and stator, resulting in increased costs. To address this issue, manufacturers can manufacture the rotor and stator using fine-grained electrical steel sheets and then heat-treat the stator at the customer's site, achieving high strength for the rotor and low high-frequency core loss for the stator. However, this process can result in texture degradation, resulting in excessively low magnetic flux density after the customer's heat treatment. Furthermore, non-resistive elements such as Si, Al, and Mn, which are added to improve high-frequency core loss, further reduce magnetic flux density. Therefore, materials with high magnetic flux density are required for applications requiring continuous weight reduction, such as the drive motors of environmentally friendly electric vehicles.

[0006] To address this issue, a method has been proposed in which hot-rolled sheets are thinned to 2.0 mm or less to improve properties. Another method has been proposed in which high-Al content is added and magnetic properties are improved through double annealing and double rolling. Another method has been proposed in which hot-rolled sheets are thinned through thin slab manufacturing. However, reducing the hot-rolled thickness is difficult to apply to mass production due to limitations on the roll force in the hot-rolling process. Furthermore, as the reduction ratio increases in the hot-rolling process, which is performed without load, there are problems with increased thickness deviation due to roll bending. While the double-annealing and double-rolling process has been shown to improve properties to some extent, it is a significant factor in increasing costs, and excessive development of Goss texture tends to deteriorate circumferential properties. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of one embodiment of the present invention is to provide a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, an object of one embodiment of the present invention is to provide a non-oriented electrical steel sheet that has been hot-rolled twice to form a {110} <001> The present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same, which ensures the strength of the steel sheet before stress relief annealing and the magnetism of the steel sheet after stress relief annealing by suppressing the texture. [Means for solving the problem]

[0008] A non-oriented electrical steel sheet according to one embodiment of the present invention contains, by weight, 1.5 to 4% Si, 0.1 to 2% Al, and 0.05 to 2% Mn, with the remainder being Fe and unavoidable impurities. <001> The area fraction of crystal grains having an orientation within 15° of the grain boundary is 10% or less.

[0009] The non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of Cr: 0.5 wt% or less, Cu: 0.2 wt% or less, P: 0.1 wt% or less, Sn: 0.06 wt% or less, and Sb: 0.06 wt% or less.

[0010] The non-oriented electrical steel sheet according to one embodiment of the present invention may further contain one or more of C, N, S, Ti, Nb, and V in an amount of 0.005 wt % or less.

[0011] The non-oriented electrical steel sheet according to one embodiment of the present invention may have an average grain size of 10 to 25 μm.

[0012] A non-oriented electrical steel sheet according to an embodiment of the present invention can satisfy the following formula 1. [Formula 1] Yield strength (MPa)≧140+100×[Si]+35×([Al]+[Mn]) (In formula 1, [Si], [Al], and [Mn] represent the contents (wt%) of Si, Al, and Mn, respectively.)

[0013] A non-oriented electrical steel sheet according to an embodiment of the present invention can satisfy the following formula 2. [Formula 2] Circumferential magnetic flux density (B 50 , Tesla)≧1.88+0.1×t-0.067×[Si]-0.0458×[Al]-0.022×[Mn] (In Equation 2, [Si], [Al], and [Mn] represent the contents (wt%) of Si, Al, and Mn, respectively, and t represents the thickness (mm) of the steel plate.)

[0014] The non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following formula 3 after stress relief annealing at a temperature of 700 to 850° C. for 10 to 300 minutes. [Formula 3] Circumferential magnetic flux density (B 50 , Tesla)≧1.85+0.1×t-0.067×[Si]-0.0458×[Al]-0.022×[Mn] Circumferential iron loss (W 10 / 400 , W / kg)≦6+4000×t 2 / (13+11×([Si]+[Al]+0.5×[Mn]) (In Equation 3, [Si], [Al], and [Mn] represent the contents (wt%) of Si, Al, and Mn, respectively, and t represents the thickness (mm) of the steel plate.)

[0015] A method for producing a non-oriented electrical steel sheet according to one embodiment of the present invention includes a first hot rolling step of hot rolling a slab containing, by weight, 1.5 to 4% Si, 0.1 to 2% Al, and 0.05 to 2% Mn, with the remainder being Fe and unavoidable impurities, to produce a first hot-rolled sheet; a step of coiling the first hot-rolled sheet; a second hot rolling step of hot-rolling the first hot-rolled sheet at a temperature of 700 to 1000°C with a reduction of 20 to 50% to produce a second hot-rolled sheet; a step of cold-rolling the second hot-rolled sheet to produce a cold-rolled sheet; and a cold-rolled sheet annealing step of the cold-rolled sheet at a temperature of 710 to 820°C.

[0016] The first hot rolling stage may include a rough rolling stage and a finish rolling stage.

[0017] The thickness of the first hot-rolled sheet may be 1.8 to 2.5 mm.

[0018] After the coiling step, the coiled coil can be cooled to below 700°C.

[0019] After the coiling step, a first hot-rolled sheet annealing step of annealing at a temperature of 700 to 1000°C may be further included.

[0020] The thickness of the second hot-rolled sheet may be 1.2 to 1.8 mm.

[0021] After the second hot rolling step, a second hot-rolled sheet annealing step of annealing the second hot-rolled sheet at a temperature of 850 to 1150°C may be further included.

[0022] After the cold-rolled sheet annealing step, the method may further include a step of stress relief annealing at a temperature of 700 to 850° C. for 10 to 300 minutes. [Effects of the Invention]

[0023] The non-oriented electrical steel sheet according to one embodiment of the present invention reduces thickness deviation in the width direction due to shape correction, and by reducing the cold rolling reduction rate and suppressing the generation of GOSS texture, it has excellent strength and circumferential mean magnetic flux density before customer heat treatment (stress relief annealing, SRA), and excellent circumferential mean magnetic flux density and high-frequency iron loss after customer heat treatment (stress relief annealing, SRA). Ultimately, the non-oriented electrical steel sheet according to one embodiment of the present invention contributes to the production of environmentally friendly motors for automobiles, highly efficient motors for home appliances, and super premium motor cores by using the same steel sheet as a rotor without SRA treatment and as a stator after SRA treatment. DETAILED DESCRIPTION OF THE INVENTION

[0024] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited to these. These terms are used to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Therefore, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0025] 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 form includes the plural form unless the context clearly dictates otherwise. As used in the specification, the meaning of "comprising" embodies certain properties, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other properties, regions, integers, steps, operations, elements, and / or components.

[0026] When a part is referred to as being "on" another part, it can mean that it is directly on top of the other part, or there can 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. Unless otherwise defined, 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 belongs. Terms defined in commonly used dictionaries are additionally interpreted as having a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted as having an ideal or very formal meaning unless defined.

[0027] Furthermore, unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight. In one embodiment of the present invention, the term "additionally containing an additional element" means that an additional amount of the additional element is contained in place of the remaining iron (Fe).

[0028] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to exemplary embodiments thereof, so that those skilled in the art will be able to easily understand and practice the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein.

[0029] A non-oriented electrical steel sheet according to one embodiment of the present invention contains, by weight, 1.5 to 4% Si, 0.1 to 2% Al, and 0.05 to 2% Mn, with the remainder being Fe and unavoidable impurities. First, the reasons for limiting the components of the non-oriented electrical steel sheet will be explained.

[0030] Si::1.5~4.0wt% Silicon (Si) must be added in relatively large amounts to increase the resistivity of the material and reduce iron loss. If too little Si is added, the effect of improving high-frequency iron loss may be insignificant. If too much Si is added, the hardness of the material increases, which is undesirable as it reduces productivity and punchability. More specifically, the Si content may be 2.5 to 3.7 wt %.

[0031] Al:0.1~2.0wt% Aluminum (Al), together with Si, increases the resistivity of the material and reduces iron loss, and can form nitrides and oxides that are harmful to magnetic properties. If too little Al is added, it is ineffective in reducing high-frequency iron loss, and the formation of fine nitrides can degrade magnetic properties. If too much Al is added, it can cause problems by changing the physical properties of the mold flux during the steelmaking and continuous casting processes, significantly reducing productivity. More specifically, the Al content can be 0.5 to 1.5 wt%.

[0032] Mn:0.05~2.00wt% Manganese (Mn), along with Si and Al, increases the material's resistivity, improves core loss, and forms sulfides. If too little Mn is added, fine MnS precipitates, which can degrade magnetic properties. If too much Mn is added, it promotes the formation of a

[0111] texture, which is detrimental to magnetic properties, and Mn reduces the Fe fraction, which can cause a rapid decrease in magnetic flux density. More specifically, Mn can be contained in an amount of 0.5 to 1.5 wt%.

[0033] The non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of Cr: 0.5 wt% or less, Cu: 0.2 wt% or less, P: 0.1 wt% or less, Sn: 0.06 wt% or less, and Sb: 0.06 wt% or less.

[0034] Cr: 0.50% by weight or less Chromium (Cr) plays a role in increasing the resistance and improving core loss. If too much Cr is included, the magnetic flux density may decrease. More specifically, if Cr is further included, it may be contained in an amount of 0.01 to 0.50 wt %. Even more specifically, it may be contained in an amount of 0.050 to 0.20 wt %.

[0035] Cu: 0.200% by weight or less Copper (Cu) plays a role in forming sulfides together with Mn. If too much Cu is added, high-temperature brittleness occurs, which may lead to crack formation during continuous casting or hot rolling. More specifically, Cu may be contained in an amount of 0.005 to 0.200 wt. %. Even more specifically, Cu may be contained in an amount of 0.01 to 0.10 wt. %.

[0036] P: 0.10% by weight or less Phosphorus (P) is mostly dissolved in steel and has the effect of improving iron loss. When P is added in excess, it segregates at grain boundaries, reducing the toughness of the material and thereby degrading productivity and punchability. More specifically, P can be contained in an amount of 0.001 to 0.100 wt. %. Even more specifically, P can be contained in an amount of 0.005 to 0.050 wt. %.

[0037] Sn: 0.06% by weight or less Tin (Sn) can be added to improve magnetic properties by segregating at grain boundaries and surfaces, improving the texture of the material and suppressing surface oxidation. Adding excessive amounts of Sn can lead to severe grain boundary segregation, degrading surface quality, and increasing hardness, which can cause breakage of the cold-rolled sheet and reduce rollability. Therefore, additional Sn can be added within the aforementioned range. More specifically, Sn can be contained in an amount of 0.01 to 0.06 wt. %, and even more specifically, 0.02 to 0.05 wt. %.

[0038] Sb: 0.06% by weight or less Antimony (Sb) can be added to improve magnetic properties by segregating at grain boundaries and surfaces, improving the texture of the material and suppressing surface oxidation. Addition of excessive Sb can lead to severe grain boundary segregation, degrading surface quality, and increasing hardness, which can lead to breakage of the cold-rolled sheet and reduced rollability. Therefore, additional Sb can be added within the aforementioned range. More specifically, Sb can be contained in an amount of 0.01 to 0.06 wt. %, and even more specifically, 0.02 to 0.05 wt. %.

[0039] The non-oriented electrical steel sheet according to one embodiment of the present invention may further contain one or more of C, N, S, Ti, Nb, and V in an amount of 0.005 wt % or less. C, N, and Ti can be limited because they form carbonitrides and play a role in hindering magnetic domain movement, and S can form sulfides and deteriorate grain growth, so its upper limit can be limited. Each of these elements can be contained 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 deteriorates grain growth. Specifically, the steel may contain one or more of C, S, N, Ti, Nb, and V in an amount of 0.0040 wt % or less each.

[0040] A 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, V: 0.0050 wt% or less, Ca: 0.0050 wt% or less, Nb: 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 magnetic properties, so the upper limit can be set as described above.

[0041] Other impurities In addition to the above elements, impurities may be inevitably mixed in. In one embodiment of the present invention, additional elements may be included in addition to the above elements, and if additional elements are included, they may be included in place of the remaining Fe.

[0042] The non-oriented electrical steel sheet according to one embodiment of the present invention has a {110} <001> The area fraction of crystal grains having an orientation within 15° of the grain boundary is 10% or less. This fine structure has an orientation that adversely affects magnetic properties, and by reducing this orientation and relatively increasing the number of crystal grains that have an orientation that is favorable for magnetic properties, magnetic properties are improved.

[0043] The formation of this microstructure is suppressed by performing the hot rolling process twice. When hot rolling is performed twice, the thickness of the second hot-rolled sheet becomes thinner after the second hot rolling, resulting in a smaller cold reduction ratio, which suppresses the formation of this microstructure. Even after the stress relief annealing process, the microstructure remains as it is without any additional change in fraction. More specific details will be described in relation to the manufacturing process.

[0044] The measurement method is not particularly limited, and can be measured by X-ray pole figure or EBSD (Electron Backscattering Diffraction). The measurement reference plane is not particularly limited, and can be a plane perpendicular to the rolling direction (TD plane).

[0045] The average grain size of the steel sheet may be 10 to 25 μm. If the average grain size is too small, the magnetic properties will be too poor, and the desired magnetic properties will not be achieved even after stress relief annealing. If the average grain size is too large, it will be difficult to ensure adequate strength. More specifically, the average grain size of the steel sheet may be 15 to 20 μm. In one embodiment of the present invention, the grain size of the grains may be measured in the rolling perpendicular plane (TD plane) of the steel sheet. More specifically, it may be measured in a thickness range of 1 / 4t to 3 / 4t of the total thickness t of the steel sheet. The grain size of the grains is determined by imagining a virtual circle having the same area as the area of ​​the grains, and the diameter of the circle is the grain size. The average grain size may be measured by dividing the area to be measured by the number of grains present within that area. In one embodiment of the present invention, unless otherwise specified, properties such as average grain size and yield strength refer to properties before SRA.

[0046] After stress relief annealing, the average grain size can be 30 to 300 μm. Stress relief annealing is a process in which, when manufacturing motors from non-oriented electrical steel sheets, the steel sheets are punched and laminated, and then heat-treated to remove residual stress. Specifically, stress relief annealing can be performed at a temperature of 700 to 850°C for 10 to 300 minutes.

[0047] As described above, the non-oriented electrical steel sheet according to one embodiment of the present invention has excellent strength and circumferential mean magnetic flux density before stress relief annealing, and has excellent circumferential mean magnetic flux density and high-frequency iron loss after stress relief annealing.

[0048] Specifically, the following formula 1 can be satisfied in relation to strength. [Formula 1] Yield strength (MPa)≧140+100×[Si]+35×([Al]+[Mn]) (In formula 1, [Si], [Al], and [Mn] represent the contents (wt%) of Si, Al, and Mn, respectively.) When Si, Al, and Mn are contained in a steel sheet, the yield strength is improved. In one embodiment of the present invention, in addition to the addition of Si, Al, and Mn, the {110} <001> By suppressing grain formation and adjusting the average grain size, the yield strength can be further improved.

[0049] More specifically, the yield strength may be 400 MPa or more. Even more specifically, it may be 400 to 600 MPa. Even more specifically, it may be 450 to 550 MPa. The yield strength may be measured by preparing three KS-13A specimens and performing a uniaxial tensile test, followed by measuring the yield strength under a 0.2% offset condition.

[0050] A non-oriented electrical steel sheet according to an embodiment of the present invention can satisfy the following formula 2. [Formula 2] Circumferential magnetic flux density (B 50 , Tesla)≧1.88+0.1×t-0.067×[Si]-0.0458×[Al]-0.022×[Mn] (In Equation 2, [Si], [Al], and [Mn] represent the contents (wt%) of Si, Al, and Mn, respectively, and t represents the thickness (mm) of the steel plate.)

[0051] When Si, Al, and Mn are contained in a steel sheet, the magnetic flux density decreases. In one embodiment of the present invention, even if a certain amount of Si, Al, and Mn is added, the {110} <001> By suppressing the formation of crystal grains and adjusting the average crystal grain size, the magnetic flux density can be improved.

[0052] More specifically, the circumferential magnetic flux density may be 1.62 T or more. Still more specifically, it may be 1.65 to 1.80 T. Even more specifically, it may be 1.68 to 1.75 T. The magnetic flux density (B 50 ) is the magnetic flux density induced in a magnetic field of 5000 A / m. The circumferential direction means the direction around the circle. In one embodiment of the present invention, ten ring samples with an outer diameter of 100 mm and an inner diameter of 90 mm are fabricated by electrical discharge machining, stacked, and then wound with copper wire to measure the magnetic properties.

[0053] The non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following formula 3 after stress relief annealing at a temperature of 700 to 850° C. for 10 to 300 minutes. [Formula 3] Circumferential magnetic flux density (B 50 , Tesla)≧1.85+0.1×t-0.067×[Si]-0.0458×[Al]-0.022×[Mn] Circumferential iron loss (W 10 / 400 , W / kg)≦6+4000×t 2 / (13+11×([Si]+[Al]+0.5×[Mn]) (In Equation 3, [Si], [Al], and [Mn] represent the contents (wt%) of Si, Al, and Mn, respectively, and t represents the thickness (mm) of the steel plate.)

[0054] Stress relief annealing tends to lower magnetic flux density and core loss. In one embodiment of the present invention, by appropriately adjusting the microstructure, it is possible to reduce core loss while minimizing deterioration in magnetic flux density.

[0055] More specifically, the circumferential magnetic flux density (B 50 ) can be 1.59 T or more. More specifically, the circumferential magnetic flux density (B 50 ) can be 1.62 to 1.78 T. More specifically, the circumferential magnetic flux density (B 50 ) can be 1.65 to 1.75T.

[0056] Circumferential iron loss after stress relief annealing (W 10 / 400 ) may be 13.2 W / kg or less. More specifically, it may be 8.0 to 13.0 W / kg. Even more specifically, it may be 8.5 to 12.5 W / kg. The non-oriented electrical steel sheet according to one embodiment of the present invention may have a thickness deviation of 2.0% or less. More specifically, the thickness deviation may be 1.0 to 1.8%. The thickness deviation may be calculated by measuring the thickness at the center of the steel sheet width direction and at points 15 mm from both sides of the width, and dividing the difference by the thickness at the center. The steel sheet thickness may be 0.10 to 0.35 mm. The non-oriented electrical steel sheet may further have an insulating coating on the base steel sheet. Since insulating coatings are widely known, a detailed description thereof will be omitted.

[0057] A method for producing a non-oriented electrical steel sheet according to one embodiment of the present invention includes a first hot rolling step of hot rolling a slab containing, by weight, 1.5 to 4% Si, 0.1 to 2% Al, and 0.05 to 2% Mn, with the remainder being Fe and unavoidable impurities, to produce a first hot-rolled sheet; a step of coiling the first hot-rolled sheet; a second hot rolling step of hot-rolling the first hot-rolled sheet at a temperature of 700 to 1000°C with a reduction of 20 to 50% to produce a second hot-rolled sheet; a step of cold-rolling the second hot-rolled sheet to produce a cold-rolled sheet; and a cold-rolled sheet annealing step of the cold-rolled sheet at a temperature of 710 to 820°C.

[0058] Each step will be explained in detail below. First, a slab is hot-rolled to produce a first hot-rolled sheet. 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 duplicated explanation will be omitted. The composition of the slab does not substantially change during manufacturing processes such as first hot rolling, second hot rolling, 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.

[0059] Before producing the first hot-rolled sheet, the slab can be heated. Specifically, the slab is placed in a heating furnace and heated to 1100-1250°C. When heated to a temperature above 1250°C, precipitates may remelt and precipitate finely after hot rolling. If the temperature is too low, deformation resistance during hot rolling may be too high, making it difficult to hot-roll to the appropriate thickness.

[0060] The first hot rolling step may include a rough rolling step and a finish rolling step. The rough rolling step is a step of producing a bar having a thickness of 20 to 50 mm. The finish rolling bar is rolled to produce a hot rolled sheet having a thickness of 1 to 3 mm. Rough rolling and finish rolling differ from the first hot rolling and second hot rolling steps of the present invention in that they are performed continuously without coiling. The temperature of the steel sheet in the finish rolling step may be 800 to 1000°C.

[0061] The thickness of the first hot-rolled sheet may be 1.8 to 2.5 mm. If the thickness of the first hot-rolled sheet is excessively large, the rolling load increases in the subsequent second hot-rolling and cold-rolling steps, resulting in the formation of a large amount of (111) recrystallization texture, which may adversely affect magnetic properties. It is difficult to further reduce the thickness in a single hot-rolling pass, and even if the thickness is reduced, the bending phenomenon of the rolling rolls increases the thickness deviation in the width direction, which affects the thickness deviation of the final steel sheet and causes shape defects. More specifically, the thickness of the first hot-rolled sheet may be 1.9 to 2.3 mm. Next, the first hot-rolled sheet is coiled. During the coiling step, the steel sheet temperature may be 500 to 700°C. After the coiling step, the coiled coil may be cooled to 700°C or less. By performing a second hot rolling after cooling, it is possible to further improve the isotropy.

[0062] After the coiling step, a first hot-rolled sheet annealing step may be further included, in which the sheet is annealed at a temperature of 700 to 1000°C for 1 second to 10 hours. The first hot-rolled sheet annealing step suppresses a strong cold-rolling deformation band structure in the subsequent rolling step, and suppresses a highly anisotropic Goss texture in the subsequent post-rolling annealing process, thereby achieving isotropy. More specifically, the sheet may be annealed for 10 to 600 seconds.

[0063] Next, in the second hot rolling step, the first hot-rolled sheet is hot-rolled at a temperature of 700-1000°C with a reduction of 20-50% to produce a second hot-rolled sheet. In one embodiment of the present invention, by adding the second hot-rolled sheet production step, the reduction in cold rolling can be reduced to improve magnetic properties and the shape can be corrected to reduce thickness deviation in the width direction of the final product sheet. The reduction can be calculated as (steel sheet thickness before reduction - steel sheet thickness after reduction) / steel sheet thickness before reduction x 100.

[0064] If the steel sheet temperature in the second hot rolling step is too low, a high rolling force is required, making it difficult to correct width thickness deviations. Furthermore, the GOSS texture may develop, causing a rapid deterioration in the magnetic properties of the final product sheet at around 45° from the rolling direction, resulting in poor circumferential characteristics. If the steel sheet temperature is too high, the rigidity of the roll itself may be weakened, resulting in severe bending. Furthermore, the flexibility of the hot-rolled sheet itself may be excessively weakened, making control difficult and even increasing thickness deviations. More specifically, the steel sheet temperature in the second hot rolling step may be 730 to 980°C. Even more specifically, it may be 750 to 950°C.

[0065] The reduction ratio during the second hot rolling may be 20 to 50%. If the reduction ratio is too small, the effect of the second hot rolling cannot be fully obtained. If the reduction ratio is too high, it is difficult to control the shape, and thickness deviation may actually increase. More specifically, the reduction ratio may be 25 to 45%. The thickness of the second hot-rolled sheet may be 1.2 to 1.8 mm. If the thickness of the second hot-rolled sheet is too thick, the rolling load in the subsequent cold rolling step increases, and a large amount of (111) recrystallization texture is formed, which may adversely affect magnetic properties. If the thickness is too thin, it is difficult to control the shape, and thickness deviation may actually increase. More specifically, the thickness of the second hot-rolled sheet may be 1.3 to 1.7 mm.

[0066] After the second hot rolling step, a second hot-rolled sheet annealing step may be further included in which the second hot-rolled sheet is annealed at a temperature of 850 to 1150°C for 3 to 600 seconds. If the annealing temperature for the second hot-rolled sheet is too low, the structure will not develop or will develop too finely, resulting in little effect in increasing magnetic flux density. If the annealing temperature is too high, the magnetic properties will deteriorate and the sheet shape will be distorted, resulting in poor rolling workability. More specifically, the temperature range may be 950 to 1125°C. The second hot-rolled sheet annealing is performed as needed to increase the orientation favorable for magnetic properties, and can be omitted.

[0067] The hot-rolled sheet is then pickled and cold-rolled to a desired thickness. Depending on the thickness of the hot-rolled sheet, a rolling reduction of 70-85% can be applied, and cold-rolled to a final thickness of 0.10-0.35 mm. To achieve the desired rolling reduction, cold-rolling can be performed once, or two or more times with intermediate annealing. More specifically, cold-rolling can be performed to a thickness of 0.15-0.30 mm.

[0068] The cold-rolled sheet is subjected to cold-rolled sheet annealing. In the cold-rolled sheet annealing step, the annealing temperature is 710 to 820°C. If the annealing temperature is too low, unrecrystallized portions may remain, making it difficult to ensure sufficient magnetic flux density. If the annealing temperature is too high, the crystal grains may become coarse, making it difficult to ensure adequate strength. More specifically, in the cold-rolled sheet annealing step, the annealing temperature may be 720 to 800°C, and the annealing time may be 10 to 60 seconds. Even more specifically, the annealing time may be 20 to 45 seconds.

[0069] After annealing the cold-rolled sheet, the unrecrystallized fraction may be 3 to 13 area %. If the unrecrystallized fraction of the cold-rolled sheet is properly formed, it is possible to simultaneously ensure magnetic properties and strength. In one embodiment of the present invention, the unrecrystallized fraction can be classified by the orientation distribution in the lattice using EBSD. More specifically, the unrecrystallized fraction may be 5 to 10 area %.

[0070] Next, the annealed cold-rolled steel sheet is subjected to stress relief annealing. After annealing the cold-rolled steel sheet, the insulating coating, punching, and lamination processes can be performed. These processes are well known, so a detailed description will be omitted. 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 the remaining stress in the steel sheet, thereby 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. In other words, 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.

[0071] The stress relief annealing step can be carried out at a temperature of 700 to 850°C for 10 to 300 minutes. A motor core according to an embodiment of the present invention includes a rotor formed by laminating a plurality of non-oriented electrical steel sheets, and a stator formed by laminating a plurality of non-oriented electrical steel sheets. The rotor may be laminated with the non-oriented electrical steel sheets before stress relief annealing, and the stator may be laminated with the non-oriented electrical steel sheets after stress relief annealing. 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.

[0072] In one embodiment of the present invention, the rotor and the stator can be manufactured simultaneously using the same non-oriented electrical steel sheet, which further improves manufacturing efficiency. The motor core may have an insulating coating interposed between the steel plates. Since insulating coatings are widely known, a detailed description thereof will be omitted. Preferred examples and comparative examples of the present invention will be described below. However, the following examples are merely preferred examples of the present invention, and the present invention is not limited to the following examples.

[0073] Example 1 Slabs were manufactured having the compositions shown in Table 1 below. The components other than those listed in Table 1, such as Ti, Nb, and V, were each controlled to 0.003 wt % or less, with the remainder being Fe. The slabs were heated to 1150°C and first hot-rolled to the entry thickness listed in Table 2 below. Second hot-rolling was performed under the conditions listed in Table 2, followed by second hot-roll annealing at 1100°C for 60 seconds. The hot-rolled and annealed sheets were pickled and then cold-rolled to the thickness listed in Table 2. They were then annealed for 1 minute in 20% hydrogen and 80% nitrogen by volume at the annealing temperature listed in Table 2, after which the circumferentially averaged magnetic properties, strength, and thickness deviation were measured. Subsequently, heat treatment (stress relief annealing) was performed at 800°C for 1 hour in a nitrogen atmosphere, and the circumferentially averaged magnetic properties were measured again. The circumferentially averaged magnetic properties were measured by electrical discharge machining to prepare ring samples with an outer diameter of 100 mm and an inner diameter of 90 mm. Ten of these samples were stacked and then wound with copper wire to measure the magnetic properties. Yield strength was measured by performing uniaxial tensile tests on three KS-13A specimens, followed by a 0.2% offset. The thickness deviation was calculated by measuring the thickness at the center of the coil and at points 15 mm from both sides of the width, and dividing the difference by the thickness at the center.

[0074] The GOSS fraction was measured (15 degree offset) by EBSD (Electron Backscattering Diffraction) on the steel sheet before stress relief annealing.

[0075] [Table 1]

[0076] [Table 2]

[0077] [Table 3]

[0078] As shown in Tables 1 to 3, when the temperature and reduction rate during the second hot rolling are properly adjusted and the temperature during the cold-rolled sheet annealing is properly adjusted, the {110} <001> The texture was minimal, the thickness deviation was appropriate, and the magnetic flux density and yield strength before SRA were excellent, as were the magnetic flux density and core loss after SRA. On the other hand, when the annealing temperature of the cold-rolled sheet was low, the magnetic flux density before SRA was poor. When the annealing temperature of the cold-rolled sheet was high, the yield strength before SRA was poor. When the temperature during the second hot rolling was low, the magnetic flux density before and after SRA was poor. When the temperature during the second hot rolling was high, the thickness deviation increased. When the reduction rate during the second hot rolling was small, the magnetic properties before and after SRA were poor. When the reduction rate during the second hot rolling was large, the thickness deviation increased.

[0079] Example 2 Slabs were manufactured with the compositions shown in Table 4 below. Components other than those listed in Table 4, such as C, S, N, Ti, Nb, and V, were each controlled to 0.003 wt % or less, with the remainder being Fe. The slab was heated to 1130°C and subjected to first hot rolling to 2.3 mm. The wound coil was then reheated to 730°C using induction heating, then second hot rolling to 1.6 mm, and hot-rolled sheet annealing at 1050°C. The hot-rolled annealed sheet was pickled, cold-rolled to 0.25 mm, and cold-rolled sheet annealed for 1 minute in 20% hydrogen by volume, 80% nitrogen by volume, and 790°C. It was then heat-treated (stress-relief annealing) for 1 hour in a nitrogen atmosphere at 800°C, and the magnetic properties and yield strength before and after SRA were measured in the same manner as in Example 1.

[0080] [Table 4]

[0081] As shown in Table 4, when the Si, Al, and Mn contents were appropriately adjusted, the magnetic flux density and yield strength before SRA were excellent, and the magnetic flux density and core loss after SRA were excellent. On the other hand, when the Si, Al, and Mn contents are too low or too high, it was confirmed that the sheet fracture occurs, the magnetic properties before / after SRA are poor, or the yield strength before SRA is poor.

[0082] The present invention is not limited to the above-described embodiments, and can be manufactured in various different forms, and a person skilled in the art to which the present invention pertains should 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 are not limiting.

Claims

1. The alloy contains, by weight, 1.5 to 4% Si, 0.1 to 2% Al, and 0.05 to 2% Mn, with the remainder being Fe and unavoidable impurities; A non-oriented electrical steel sheet, characterized in that the area fraction of crystal grains having an orientation within 15° of {110}<001> is 10% or less.

2. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of Cr: 0.5 wt% or less (excluding 0%), Cu: 0.2 wt% or less (excluding 0%), P: 0.1 wt% or less (excluding 0%), Sn: 0.06 wt% or less (excluding 0%), and Sb: 0.06 wt% or less (excluding 0%).

3. The non-oriented electrical steel sheet according to claim 1, further comprising 0.005% by weight or less (excluding 0%) of one or more of C, N, S, Ti, Nb, and V.

4. The non-oriented electrical steel sheet according to claim 1, wherein the average grain size is 10 to 25 μm.

5. The non-oriented electrical steel sheet according to claim 1, which satisfies the following formula 1: [Formula 1] Yield strength (MPa)≧140+100×[Si]+35×([Al]+[Mn]) (In formula 1, [Si], [Al], and [Mn] represent the contents (wt%) of Si, Al, and Mn, respectively.)

6. The non-oriented electrical steel sheet according to claim 1, which satisfies the following formula 2: [Formula 2] Circumferential magnetic flux density (B ５０ , Tesla) ≧1.88+0.1×t-0.067×[Si]-0.0458×[Al]-0.022×[Mn] (In Equation 2, [Si], [Al], and [Mn] represent the contents (wt%) of Si, Al, and Mn, respectively, and t represents the thickness (mm) of the steel plate.)

7. 2. The non-oriented electrical steel sheet according to claim 1, which satisfies the following formula 3 after stress relief annealing at a temperature of 700 to 850°C for 10 to 300 minutes: [Formula 3] Circumferential magnetic flux density (B ５０ , Tesla) ≧1.85+0.1×t-0.067×[Si]-0.0458×[Al]-0.022×[Mn] Circumferential iron loss (W １０／４００ , W / kg)≦6+4000×t ２ / (13 + 11 × ([Si] + [Al] + 0.5 × [Mn]) (In Equation 3, [Si], [Al], and [Mn] represent the contents (wt%) of Si, Al, and Mn, respectively, and t represents the thickness (mm) of the steel plate.)

8. a first hot rolling step of hot rolling a slab containing, by weight, 1.5 to 4% Si, 0.1 to 2% Al, and 0.05 to 2% Mn, with the remainder being Fe and unavoidable impurities, to produce a first hot-rolled sheet; coiling the first hot-rolled strip; a second hot rolling step of hot rolling the first hot-rolled sheet at a temperature of 700 to 1000°C and a rolling reduction of 20 to 50% to produce a second hot-rolled sheet; cold-rolling the second hot-rolled sheet to produce a cold-rolled sheet; and The method for manufacturing a non-oriented electrical steel sheet comprises a cold-rolled sheet annealing step of annealing the cold-rolled sheet at a temperature of 710 to 820°C.

9. The method for manufacturing a non-oriented electrical steel sheet according to claim 8 , wherein the first hot rolling step includes a rough rolling step and a finish rolling step.

10. The method for producing a non-oriented electrical steel sheet according to claim 8, wherein the first hot-rolled sheet has a thickness of 1.8 to 2.5 mm.

11. The method for manufacturing a non-oriented electrical steel sheet according to claim 8, wherein after the coiling step, the coiled coil is cooled to 700°C or less.

12. The method for manufacturing a non-oriented electrical steel sheet according to claim 8, further comprising a first hot-rolled sheet annealing step of annealing the sheet at a temperature of 700 to 1000°C after the coiling step.

13. The method for producing a non-oriented electrical steel sheet according to claim 8, wherein the second hot-rolled sheet has a thickness of 1.2 to 1.8 mm.

14. The method for manufacturing a non-oriented electrical steel sheet according to claim 8, further comprising, after the second hot rolling step, a second hot-rolled sheet annealing step of annealing the second hot-rolled sheet at a temperature of 850 to 1150°C.

15. The method for manufacturing a non-oriented electrical steel sheet according to claim 8, further comprising the step of performing stress relief annealing at a temperature of 700 to 850°C for 10 to 300 minutes after the step of cold-rolled sheet annealing.

Images