Hot-rolled non-oriented electrical steel sheet and its manufacturing method

Abstract

Provided are a hot-rolled non-oriented electrical steel sheet and a manufacturing method thereof, in which shot balls are projected onto the steel sheet in the manufacturing process to remove scale, and the surface and internal hardness is adjusted after the shot ball projection, thereby improving iron loss in all directions and iron loss after stress relief annealing. The hot-rolled non-oriented electrical steel sheet of the present invention contains, by weight %, 2.8 to 4.0% Si, 0.1 to 1.3% Al, 0.3 to 2.0% Mn, and the balance being Fe and unavoidable impurities, and satisfies the following formula 1: [Formula 1] 1.1≦Hv1 / HV2≦1.5 (In Equation 1, HV1 represents the hardness measured on the surface of the steel plate, and HV2 represents the hardness measured at a point halfway through the thickness of the steel plate.) It is characterized by further containing one or more of Cr: 0.2 wt % or less (excluding 0%), Sn: 0.06 wt % or less (excluding 0%), and Sb: 0.06 wt % or less (excluding 0%).

Description

[Technical Field]

[0001] The present invention relates to a hot-rolled non-oriented electrical steel sheet and a manufacturing method thereof, and more particularly to a hot-rolled non-oriented electrical steel sheet in which shot balls are projected onto the steel sheet during the manufacturing process to remove scale, and the surface and internal hardness is adjusted after the shot ball projection, thereby improving iron loss in all directions and iron loss after stress relief annealing, and a manufacturing method thereof. [Background technology]

[0002] Non-oriented electrical steel sheets are primarily used in motors that convert electrical energy into mechanical energy, and the excellent magnetic properties of non-oriented electrical steel sheets are required to achieve high efficiency in this process. In particular, with the recent rise in attention to environmentally friendly technologies, increasing the efficiency of motors, which account for more than half of total electrical energy consumption, is considered extremely important, and as a result, demand for non-oriented electrical steel sheets with excellent magnetic properties is also increasing.

[0003] The magnetic properties of non-oriented electrical steel sheets are primarily evaluated by iron loss and magnetic flux density. Iron loss refers to the energy loss that occurs at a specific magnetic flux density and frequency, while magnetic flux density refers to the degree of magnetization obtained under a specific magnetic field. Lower iron loss means that a motor with higher energy efficiency can be manufactured under the same conditions, while higher magnetic flux density means that motors can be made more compact and copper loss can be reduced. Therefore, it is important to create non-oriented electrical steel sheets with low iron loss and high magnetic flux density.

[0004] The characteristics of non-oriented electrical steel sheets that should be considered vary depending on the motor's operating conditions. Many motors consider W15 / 50, the iron loss when a 1.5T magnetic field is applied at a commercial frequency of 50Hz, to be the most important standard for evaluating the properties of non-oriented electrical steel sheets used in motors. However, not all motors for various applications consider W15 / 50 iron loss to be the most important, and iron loss at other frequencies or applied magnetic fields may be evaluated depending on the main operating conditions. In particular, for the non-oriented electrical steel sheets used in the drive motors of recent electric vehicles, magnetic properties are often important in low magnetic fields of 1.0T or less and high frequencies of 400Hz or more, so the properties of non-oriented electrical steel sheets are evaluated using iron loss such as W10 / 400.

[0005] Motor cores are divided into stator cores and rotor cores, and in order to satisfy the recent demand for smaller size and higher output for HEV drive motors and the like, there is a strong demand for non-oriented electrical steel sheets used in stator cores to have excellent magnetic properties, such as high magnetic flux density and low iron loss. Furthermore, as a means of achieving smaller size and higher output in motors such as the HEV drive motors, there is a trend toward higher motor rotation speeds. However, because HEV drive motors have large outer diameters, large centrifugal forces act on the rotor core. In addition, depending on the structure, there may be very narrow sections known as rotor core bridges. As a result, the non-oriented electrical steel sheets used in rotor cores are now required to be stronger than ever before.

[0006] Therefore, the ideal properties of non-oriented electrical steel sheets used in motor cores are not only excellent magnetic properties, but also high strength for rotor cores and higher magnetic flux density and lower iron loss for stator cores.Thus, even when using non-oriented electrical steel sheets for the same motor core, the required properties for rotor cores and stator cores are significantly different.However, from the perspective of increasing material yield, when manufacturing motor cores, it is preferable to simultaneously extract the rotor core material and the stator core material from the same steel sheet material, and then stack the respective core materials to assemble them into the rotor core or stator core. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a hot-rolled non-oriented electrical steel sheet and a manufacturing method thereof. More specifically, to provide a hot-rolled non-oriented electrical steel sheet in which shot balls are projected onto the steel sheet during the manufacturing process to remove scale and the surface and internal hardness are adjusted after the shot ball projection, thereby improving iron loss in all directions and iron loss after stress relief annealing, and a manufacturing method thereof. [Means for solving the problem]

[0008] The hot-rolled non-oriented electrical steel sheet of the present invention contains, by weight, 2.8-4.0% Si, 0.1-1.3% Al, 0.3-2.0% Mn, and the balance being Fe and unavoidable impurities, and satisfies the following formula 1.

[0009] [Formula 1] 1.1≦Hv1 / HV2≦1.5 (In Equation 1, HV1 represents the hardness measured on the surface of the steel plate, and HV2 represents the hardness measured at a point halfway through the thickness of the steel plate.)

[0010] The hot-rolled non-oriented electrical steel sheet of the present invention may further contain one or more of Cr: 0.2% by weight or less (excluding 0%), Sn: 0.06% by weight or less (excluding 0%), and Sb: 0.06% by weight or less (excluding 0%).

[0011] The hot-rolled non-oriented electrical steel sheet of the present invention may further contain one or more of Cu: 0.01 to 0.2 wt %, P: 0.100 wt % or less (excluding 0%), Ni: 0.05 wt % or less (excluding 0%), and Zn: 0.01 wt % or less (excluding 0%).

[0012] The hot-rolled non-oriented electrical steel sheet 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 (excluding 0%), each or in total.

[0013] The hot-rolled non-oriented electrical steel sheet 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 (excluding 0%), either individually or in total.

[0014] The hot-rolled non-oriented electrical steel sheet of the present invention may further contain one or more of Mo: 0.03% by weight or less (excluding 0%), B: 0.0050% by weight or less (excluding 0%), V: 0.0050% by weight or less (excluding 0%), Ca: 0.0050% by weight or less (excluding 0%), Nb: 0.0050% by weight or less (excluding 0%), and Mg: 0.0050% by weight or less (excluding 0%).

[0015] The non-oriented electrical steel sheet of the present invention contains, by weight, 2.8 to 4.0% Si, 0.1 to 1.3% Al, 0.3 to 2.0% Mn, and the remainder Fe and unavoidable impurities, and satisfies the following formulas 2 and 3.

[0016] [Formula 2] 2|WL-WC| / (WL+WC)≦0.1

[0017] [Formula 3] 2|WL+WC-2WN| / (WL+WC)≦0.1 (In Equations 2 and 3, WL represents the iron loss (W10 / 1000, W / kg) measured in the rolling direction, WC represents the iron loss (W10 / 1000, W / kg) measured in a direction perpendicular to the rolling direction, and WN represents the iron loss (W10 / 1000, W / kg) measured in a direction forming a 45° angle with the rolling direction. W10 / 1000 represents the iron loss (W / kg) when a magnetic flux density of 1.0 T is induced at a frequency of 1000 Hz.)

[0018] The non-oriented electrical steel sheet of the present invention may further contain one or more of Cr: 0.2% by weight or less, Sn: 0.06% by weight or less, and Sb: 0.06% by weight or less.

[0019] The non-oriented electrical steel sheet of the present invention may have an average crystal grain size of 5 to 50 μm.

[0020] The non-oriented electrical steel sheet of the present invention can satisfy the following formula 4 after stress relief annealing.

[0021] [Formula 4] W10 / 1000≦20+t×150 (In Equation 4, W10 / 1000 represents the iron loss (W / kg) when a magnetic flux density of 1.0 T is induced at a frequency of 1000 Hz, and t represents the thickness of the steel plate (mm).)

[0022] The method for producing a hot-rolled non-oriented electrical steel sheet of the present invention includes the steps of hot-rolling a slab consisting of, by weight, 2.8-4.0% Si, 0.1-1.3% Al, 0.3-2.0% Mn, and the balance being Fe and unavoidable impurities to produce a hot-rolled sheet, and removing scale present on the surface of the hot-rolled sheet, wherein the step of removing scale includes a step of projecting shot balls onto the steel sheet to remove the scale, and after projecting the shot balls, the following formula 1 is satisfied:

[0023] [Formula 1] 1.1≦Hv1 / HV2≦1.5 (In Equation 1, HV1 represents the hardness measured on the surface of the steel plate, and HV2 represents the hardness measured at a point halfway through the thickness of the steel plate.)

[0024] The shot ball rate is 15-35 kg / (min·m 2 ) may also be used. The average particle size of the shot balls is 0.1 to 1 mm, and they can be projected for 1 to 60 seconds. The material of the shot balls may be an Fe-based alloy. The method may further include a step of annealing the hot-rolled sheet before the step of removing the scale.

[0025] The method for producing a non-oriented electrical steel sheet of the present invention includes the steps of hot rolling a slab containing, by weight, 2.8 to 4.0% Si, 0.1 to 1.3% Al, 0.3 to 2.0% Mn, and the balance being Fe and unavoidable impurities to produce a hot-rolled sheet, removing scale present on the surface of the hot-rolled sheet, cold-rolling the hot-rolled sheet from which the scale has been removed to produce a cold-rolled sheet, and cold-rolling the cold-rolled sheet, wherein the step of removing the scale includes a step of blasting shot balls at the steel sheet to remove the scale. After the shot ball is thrown, the following formula 1 is satisfied.

[0026] [Formula 1] 1.1≦Hv1 / HV2≦1.5 (In Equation 1, HV1 represents the hardness measured on the surface of the steel plate, and HV2 represents the hardness measured at a point halfway through the thickness of the steel plate.)

[0027] The slab may further contain one or more of Cr: 0.2 wt % or less, Sn: 0.06 wt % or less, and Sb: 0.06 wt % or less.

[0028] The shot ball rate is 15-35 kg / (min·m 2 ) may also be used. The average particle size of the shot balls is 0.1 to 1 mm, and they can be projected for 1 to 60 seconds. The material of the shot balls may be an Fe-based alloy.

[0029] The cold-rolled sheet may be annealed at a temperature of 700 to 850°C. The method may further include a step of annealing the hot-rolled sheet before the step of removing the scale. After the cold-rolled sheet annealing step, the steel sheet can satisfy Equation 2 and Equation 3.

[0030] [Formula 2] 2|WL-WC| / (WL+WC)≦0.1

[0031] [Formula 3] 2|WL+WC-2WN| / (WL+WC)≦0.1 (In Equations 2 and 3, WL represents the iron loss (W10 / 1000, W / kg) measured in the rolling direction, WC represents the iron loss (W10 / 1000, W / kg) measured in a direction perpendicular to the rolling direction, and WN represents the iron loss (W10 / 1000, W / kg) measured in a direction forming a 45° angle with the rolling direction. W10 / 1000 represents the iron loss (W / kg) when a magnetic flux density of 1.0 T is induced at a frequency of 1000 Hz.) After the step of annealing the cold-rolled sheet, the average grain size may be 5 to 50 μm. 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. After the stress relief annealing step, the steel sheet can satisfy the following formula 4.

[0032] [Formula 4] W10 / 1000≦20+t×150 (In Equation 4, W10 / 1000 represents the iron loss (W / kg) when a magnetic flux density of 1.0 T is induced at a frequency of 1000 Hz, and t represents the thickness of the steel plate (mm).) [Effects of the Invention]

[0033] According to the non-oriented electrical steel sheet of the present invention, the accumulated energy on the surface can be reduced during descaling, which affects the recrystallization behavior during the annealing process of the cold-rolled sheet, thereby reducing the variation in high-frequency iron loss in the directions of 0, 45, and 90 degrees relative to the rolling direction. Ultimately, the non-oriented electrical steel sheet of the present invention contributes to the production of environmentally friendly motors for automobiles, highly efficient motors for home appliances, and super premium class electric motors. DETAILED DESCRIPTION OF THE INVENTION

[0034] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only 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. 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 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" another part, it may be directly on top of the other part, or there may be other parts between them. In contrast, when a part is referred to as being "directly on top" of another part, there are no other parts between them.

[0035] 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 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 otherwise defined. 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 the remaining iron (Fe) is replaced by the additional amount of the additional element. While the present invention may be embodied in various different forms, it is to be understood that the invention is not limited to the specific embodiments set forth herein, and that the invention may be embodied in various different forms, without departing from the spirit or scope of the present invention.

[0036] The hot-rolled non-oriented electrical steel sheet of the present invention contains, by weight, 2.8-4.0% Si, 0.1-1.3% Al, 0.3-2.0% Mn, and the balance being Fe and unavoidable impurities, and satisfies the following formula 1.

[0037] [Formula 1] 1.1≦Hv1 / HV2≦1.5 (In Equation 1, HV1 represents the hardness measured on the surface of the steel plate, and HV2 represents the hardness measured at a point halfway through the thickness of the steel plate.)

[0038] The reasons for limiting the alloying elements are as follows.

[0039] Si:2.8~4.0wt% Silicon (Si) increases the resistivity of the material and reduces iron loss. If too little silicon is added, the effect of improving high-frequency iron loss may be insufficient. Conversely, if too much silicon is added, the hardness of the material increases, significantly impairing cold rolling properties, and deteriorating productivity and punchability. Therefore, Si can be added within the aforementioned range. More specifically, it can be contained in an amount of 3.0 to 3.8 wt. %. Even more specifically, it can be contained in an amount of 3.1 to 3.7 wt. %.

[0040] Al:0.10~1.30wt% Aluminum (Al) increases the resistivity of the material and reduces iron loss. If added in an excessively small amount, it is ineffective in reducing high-frequency iron loss and may cause the formation of fine nitrides, degrading magnetic properties. Conversely, if added in an excessively large amount, it may cause problems in all processes, including steelmaking and continuous casting, significantly reducing productivity. Therefore, Al can be added within the aforementioned range. More specifically, it can be contained in an amount of 0.50 to 1.10 wt. %. Even more specifically, it can be contained in an amount of 0.70 to 1.00 wt. %.

[0041] Mn:0.3~2.0wt% Manganese (Mn) is an element that increases the resistivity of a material, improves iron loss, and plays a role in forming sulfides. If too little Mn is added, fine sulfides may precipitate, reducing magnetic properties. Conversely, if too much Mn is added, it may promote the formation of a {111} texture, which is unfavorable to magnetic properties, resulting in a decrease in magnetic flux density. Therefore, Mn can be added within the aforementioned range. More specifically, Mn can be contained in an amount of 0.5 to 1.5 wt. %. Even more specifically, Mn can be contained in an amount of 0.7 to 1.3 wt. %. In the present invention, the resistivity may be 55 to 80 μΩ·cm.

[0042] The hot-rolled non-oriented electrical steel sheet of the present invention may further contain one or more of Cr: 0.2% by weight or less (excluding 0%), Sn: 0.06% by weight or less (excluding 0%), and Sb: 0.06% by weight or less (excluding 0%).

[0043] Cr: 0.20% by weight or less Chromium (Cr) plays a role in increasing the resistivity of the material and reducing iron loss. Therefore, Cr can be added within the ranges mentioned above. More specifically, 0.010 to 0.20 wt % can be contained. Even more specifically, 0.050 to 0.100 wt % can be contained. As mentioned above, when an additional element is further contained, it is contained in place of the remaining Fe.

[0044] One or more of Sn: 0.06% by weight or less and Sb: 0.06% by weight or less Tin (Sn) and antimony (Sb) are segregating elements at grain boundaries. They are added to suppress nitrogen diffusion through grain boundaries, suppress the {111} texture that is detrimental to magnetism, and increase the advantageous {100} texture, thereby improving magnetic properties. Excessive addition of Sn and Sb hinders grain growth, reducing magnetic properties and worsening rolling properties. Therefore, Sn and Sb can be added within the aforementioned ranges. More specifically, Sn: 0.005 to 0.060 wt.% and Sb: 0.005 to 0.060 wt.% can be included. Even more specifically, Sn: 0.01 to 0.05 wt.% and Sb: 0.01 to 0.05 wt.% can be included.

[0045] The hot-rolled non-oriented electrical steel sheet of the present invention may further contain one or more of Cu: 0.01 to 0.2 wt %, P: 0.100 wt % or less (excluding 0%), Ni: 0.05 wt % or less (excluding 0%), and Zn: 0.01 wt % or less (excluding 0%).

[0046] Cu:0.01~0.20wt% 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 magnetic properties. If Cu is added in an excessively large amount, high-temperature brittleness may occur, which may lead to crack formation during continuous casting or hot rolling. More specifically, Cu may be contained in an amount of 0.05 to 0.10 wt%.

[0047] P: 0.100% by weight or less Phosphorus (P) can be added because it not only increases the resistivity of the material but also segregates to grain boundaries to improve the texture, increasing resistivity and reducing iron loss. However, if too much P is added, it can form a texture unfavorable to magnetic properties, resulting in no texture improvement effect, and excessive segregation to grain boundaries can reduce rollability and workability, making production difficult. Therefore, P can be added within the aforementioned range. More specifically, P can be contained in an amount of 0.001 to 0.090 wt. %. Even more specifically, P can be contained in an amount of 0.005 to 0.085 wt. %.

[0048] Ni: 0.05% by weight or less (excluding 0%) Nickel (Ni) reacts with impurity elements to form fine sulfides, carbides, and nitrides, which can have a detrimental effect on magnetic properties. More specifically, Ni can be contained in an amount of 0.001 to 0.03 wt %.

[0049] Zn: 0.01% by weight or less If the zinc (Zn) content is excessive, it may act as an impurity and deteriorate the magnetic properties. Therefore, Zn can be further added within the above-mentioned range. More specifically, Zn can be added in an amount of 0.001 to 0.005 wt %.

[0050] The hot-rolled non-oriented electrical steel sheet 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, respectively or in total.

[0051] C: 0.005% by weight or less When added in large amounts, carbon (C) expands the austenite region, widens the phase transformation interval, and inhibits ferrite grain growth during annealing, thereby increasing iron loss. It also bonds with Ti and other elements to form carbides, degrading magnetic properties and increasing iron loss due to magnetic aging during use after processing into electrical appliances. Therefore, C can be added within the aforementioned range. More specifically, C can be contained in an amount of 0.003 wt% or less. Even more specifically, C can be contained in an amount of 0.0001 to 0.003 wt%.

[0052] S: 0.005% by weight or less Sulfur (S) forms fine sulfides inside the base material, inhibiting grain growth and weakening iron loss, so it is preferable to add as little as possible. If S is included in large amounts, it may combine with Mn and other elements to form precipitates or induce high-temperature embrittlement during hot rolling. Therefore, S may be further included in an amount of 0.005 wt% or less. Specifically, S may be further included in an amount of 0.0030 wt% or less. Even more specifically, S may be further included in an amount of 0.0001 to 0.0030 wt%.

[0053] N: 0.005% by weight or less Nitrogen (N) strongly bonds with Al, Ti, etc. to form nitrides, which inhibit grain growth and prevent magnetic domain migration when precipitated, so it is preferable to add a small amount of N. Therefore, N can be added within the above-mentioned range. More specifically, N can be contained in an amount of 0.003 wt % or less. Even more specifically, N can be contained in an amount of 0.0001 to 0.003 wt %.

[0054] Ti, Nb, V: 0.005% by weight or less Titanium (Ti), niobium (Nb), vanadium (V), and the like are also strong carbonitride-forming elements, so it is preferable to avoid adding them as much as possible, and each of them should be contained in an amount of 0.005 wt% or less. More specifically, each of these can be contained in an amount of 0.0001 to 0.003 wt%.

[0055] The hot-rolled non-oriented electrical steel sheet 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 (excluding 0%), either individually or in total. When the above elements are added, they segregate at the grain boundaries, alleviating stress concentration at the grain boundaries during cold rolling, and in the subsequent recrystallization annealing process, <111> / / Improves magnetic flux density by suppressing recrystallization of ND-oriented crystal grains. When these elements are added appropriately, the aforementioned effects can be obtained. However, excessive amounts can cause significant segregation, suppressing grain growth and actually deteriorating magnetic flux density and core loss. More specifically, one or more of Bi, Pb, Ge, and As may be further included in an amount of 0.0001 to 0.200 wt %, individually or in total. More specifically, 0.001 to 0.100 wt % may be further included. 0.005 to 0.050 wt % may be further included.

[0056] The hot-rolled non-oriented electrical steel sheet of the present invention may further contain one or more of Mo: 0.03% by weight or less (excluding 0%), B: 0.0050% by weight or less (excluding 0%), Ca: 0.0050% by weight or less (excluding 0%), and Mg: 0.0050% by weight or less (excluding 0%). 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 the upper limit can be set as described above.

[0057] The balance is composed of Fe and inevitable impurities. The inevitable impurities are impurities that are mixed in during the steelmaking stage and the manufacturing process of grain-oriented electrical steel sheets, and are widely known in the art, so a detailed description will be omitted. The present invention does not exclude the addition of elements other than the above-mentioned alloy components, and various elements may be included within a range that does not impair the technical concept of the present invention. When an additional element is further included, it is included to replace the balance Fe.

[0058] The hot-rolled non-oriented electrical steel sheet of the present invention satisfies the following formula 1, where the surface hardness is HV1 and the hardness at 1 / 2t in the depth direction is HV2.

[0059] [Formula 1] 1.10≦Hv1 / HV2≦1.50 (In Equation 1, HV1 represents the hardness measured on the surface of the steel plate, and HV2 represents the hardness measured at a point halfway through the thickness of the steel plate.)

[0060] By adjusting the hardness ratio between the surface and the interior, the accumulated energy on the surface can be reduced. This affects the recrystallization behavior during the annealing process of the cold-rolled sheet, and reduces the variation in high-frequency iron loss in the directions of 0, 45, and 90 degrees relative to the rolling direction. More specifically, the ratio of Hv1 / Hv2 may be 1.2 to 1.4. In this case, the hardness is a Vickers hardness, which can be measured using a micro Vickers hardness tester under a load of 10 g. Hv1 may be 250 to 400 Hv, and Hv2 may be 150 to 300 Hv.

[0061] The hot-rolled non-oriented electrical steel sheet of the present invention can be used as a material for a motor core by itself, or can also be used as a hot-rolled material for additionally performing the cold rolling and cold-rolled sheet annealing processes described below.

[0062] The non-oriented electrical steel sheet of the present invention contains, by weight %, 2.8 to 4.0% Si, 0.1 to 1.3% Al, 0.3 to 2.0% Mn, and the balance being Fe and unavoidable impurities. The reasons for limiting the addition ratio of each component in the non-oriented electrical steel sheet are the same as those for limiting the composition of the hot-rolled non-oriented electrical steel sheet described above, and therefore a repeated explanation will be omitted. Since the steel composition does not substantially change during additional manufacturing processes such as cold rolling and cold-rolled sheet annealing, the composition of the hot-rolled non-oriented electrical steel sheet is substantially the same as the composition of the non-oriented electrical steel sheet. The steel sheet can satisfy the formulas 2 and 3.

[0063] [Formula 2] 2|WL-WC| / (WL+WC)≦0.1

[0064] [Formula 3] 2|WL+WC-2WN| / (WL+WC)≦0.1 (In Equations 2 and 3, WL represents the iron loss (W10 / 1000, W / kg) measured in the rolling direction, WC represents the iron loss (W10 / 1000, W / kg) measured in a direction perpendicular to the rolling direction, and WN represents the iron loss (W10 / 1000, W / kg) measured in a direction forming a 45° angle with the rolling direction. W10 / 1000 represents the iron loss (W / kg) when a magnetic flux density of 1.0 T is induced at a frequency of 1000 Hz.)

[0065] Equations 2 and 3 are inventions that mathematically express the variation in high-frequency iron loss in the 0-, 45-, and 90-degree directions. The smaller the values ​​of Equations 2 and 3, the smaller the variation in iron loss. When a motor is manufactured using a non-oriented electrical steel sheet that satisfies these equations, the motor efficiency can be maximized. More specifically, the values ​​of Equations 2 and 3 may all be 0.09 or less. The lower limits of Equations 2 and 3 are not particularly limited and are 0.

[0066] The non-oriented electrical steel sheet of the present invention may have an average grain size of 5 to 50 μm. If the grains are excessively small, core loss may deteriorate. If the grains are excessively large, mechanical strength may decrease. More specifically, the average grain size may be 10 to 40 μm. The grain size may be measured by imagining a circle with the same area as the grain and measuring the grain size of that circle. The reference plane is a plane parallel to the rolled surface (ND plane), and may be measured at 1 / 4 to 3 / 4 of the thickness of the steel sheet. The average refers to the number average.

[0067] The non-oriented electrical steel sheet of the present invention can satisfy the following formula 4 after stress relief annealing at a temperature of 700 to 850°C for 10 to 300 minutes.

[0068] [Formula 4] W10 / 1000≦20+t×150 (In Equation 4, W10 / 1000 represents the iron loss (W / kg) when a magnetic flux density of 1.0 T is induced at a frequency of 1000 Hz, and t represents the thickness of the steel plate (mm).) Equation 4 mathematically expresses the relationship between W10 / 1000 and the thickness (t) of a steel sheet. It is known that iron loss (W10 / 1000) decreases in proportion to thickness, but the non-oriented electrical steel sheet of the present invention exhibits even lower iron loss (W10 / 1000) than a steel sheet of the same thickness due to its unique steel composition and hardness characteristics. The lower limit of Equation 4 is not particularly limited and is 0.

[0069] In the hot-rolled non-oriented electrical steel sheet of the present invention, shot balls are projected onto the steel sheet during the manufacturing process to remove scale, and the surface and internal hardness is adjusted after the shot ball projection, thereby improving iron loss in all directions and iron loss after stress relief annealing.

[0070] The method for producing a hot-rolled non-oriented electrical steel sheet of the present invention includes the steps of hot-rolling a slab containing, by weight, 2.8 to 4.0% Si, 0.1 to 1.3% Al, 0.3 to 2.0% Mn, and the balance being Fe and unavoidable impurities to produce a hot-rolled sheet, and removing scale present on the surface of the hot-rolled sheet. Each step will be explained in detail below.

[0071] First, a slab is hot-rolled to produce a hot-rolled sheet. The steel composition of the slab has been described in the hot-rolled non-oriented electrical steel sheet, so a detailed description will be omitted. The steel composition does not substantially change during the processes of heating the slab, hot-rolling, and annealing the hot-rolled sheet, which will be described later. The slab can be heated before hot rolling. There are no restrictions on the heating temperature of the slab, but it can be heated to 1100 to 1250°C. If the heating temperature of the slab is too high, precipitates that inhibit magnetism may re-melt and precipitate finely after hot rolling. The thickness of the hot-rolled sheet after hot rolling may be 2 to 3.0 mm.

[0072] After the step of producing the hot-rolled sheet, the method may further include a step of annealing the hot-rolled sheet. Hot-rolled sheet annealing is preferably performed when producing a high-quality electrical steel sheet that does not undergo phase transformation, and is effective in improving the texture of the cold-rolled annealed sheet and increasing the magnetic flux density. In this case, the step of annealing the hot-rolled sheet can be performed at a temperature of 850 to 1200°C. If the annealing temperature of the hot-rolled sheet is too low, the structure will not grow or will grow too fine, making it difficult to expect an increase in magnetic flux density. If the annealing temperature of the hot-rolled sheet is too high, the magnetic properties may deteriorate and the rolling workability may be impaired due to deformation of the sheet shape. Annealing of the hot-rolled sheet is performed as necessary to increase the orientation favorable for magnetic properties, but it can be omitted. The annealed hot-rolled sheet can be pickled.

[0073] Next, scale present on the surface of the hot-rolled steel sheet is removed. In the present invention, scale is removed using shot ball blasting, and the shot volume is adjusted to increase the number of nucleation sites during recrystallization, thereby ensuring a fine recrystallization fraction. The scale removal step involves projecting an appropriate amount of shot balls. Shot balls accumulate energy on the surface of the material, increasing surface hardness. During this process, shot balls are projected onto the steel plate in an amount that suppresses surface hardness, removing scale but preventing surface hardening. If the surface hardness after shot ball projection is HV1 and the hardness at 1 / 2t in the depth direction is HV2, then the following formula 1 is satisfied.

[0074] [Formula 1] 1.10≦Hv1 / HV2≦1.50 (In Equation 1, HV1 represents the hardness measured on the surface of the steel plate, and HV2 represents the hardness measured at a point halfway through the thickness of the steel plate.)

[0075] By adjusting the surface and internal hardness ratio after shot ball projection, the accumulated energy on the surface during descaling can be reduced. This affects the recrystallization behavior during the final annealing process, reducing the variation in high-frequency iron loss in the 0, 45, and 90 degree directions relative to the rolling direction. More specifically, the Hv1 / Hv2 ratio may be 1.2 to 1.4. In this case, the hardness is a Vickers hardness, which can be measured using a micro Vickers hardness tester under a load of 10 g. Hv1 may be 250 to 400 Hv, and Hv2 may be 150 to 300 Hv. The shot ball rate is 15-35 kg / (min·m 2 ) can be used. By appropriately adjusting the shot ball projection rate, the nucleation sites during recrystallization can be increased, thereby ensuring the fraction of fine recrystallization. More specifically, the shot ball projection rate is 17 to 32 kg / (min·m 2 ) may also be used.

[0076] The average particle size of the shot balls is 0.1 to 1 mm, and they can be projected for 1 to 60 seconds. More specifically, the average particle size of the shot balls is 0.3 to 0.8 mm, and they can be projected for 5 to 30 seconds. The average particle size of the shot balls and the projection time of the shot balls can also affect the nucleation sites on the surface. The material of the shot balls is not particularly limited, but an Fe-based alloy can be used. After shot ball blasting, the steel sheet surface can be smoothed by immersion in a pickling solution. The pickling solution is not particularly limited, and hydrochloric acid can be used. If the concentration of the pickling solution or the immersion time is too low or too short, the steel sheet will become rough due to the increased blast rate, which can lead to surface problems. Conversely, if the concentration of the pickling solution or the immersion time is too high or too long, the steel sheet surface may be severely damaged. More specifically, the steel sheet can be pickled by immersion in the pickling solution for 10 to 60 seconds.

[0077] The method for producing a non-oriented electrical steel sheet of the present invention includes the steps of hot rolling a slab consisting of, by weight, 2.8 to 4.0% Si, 0.1 to 1.3% Al, 0.3 to 2.0% Mn, and the balance being Fe and unavoidable impurities to produce a hot-rolled sheet, removing scale present on the surface of the hot-rolled sheet, cold-rolling the hot-rolled sheet from which the scale has been removed to produce a cold-rolled sheet, and cold-rolling the cold-rolled sheet. The steps of producing a hot-rolled sheet and removing scale present on the surface of the hot-rolled sheet have been described in the method for producing a hot-rolled non-oriented electrical steel sheet, so a duplicated description will be omitted.

[0078] The hot-rolled sheet is cold-rolled to produce a cold-rolled sheet. The final cold rolling is performed to a thickness of 0.15 mm to 0.65 mm. If necessary, a second cold rolling can be performed after the first cold rolling and intermediate annealing, with a final reduction of 50 to 95%. Next, the cold-rolled sheet is annealed. The cold-rolled sheet is annealed at a temperature in the range of 700 to 850°C for 10 to 1000 seconds so that the grain size in the cross section of the steel sheet is 5 to 50 μm. If the annealing temperature of the cold-rolled sheet is too low, the grains may be small and the core loss may deteriorate. If the temperature is too high, the grains may become coarse and the mechanical strength may decrease. More specifically, the annealing can be performed in the range of 740 to 820°C. After cold-rolling and annealing, the steel sheet can recrystallize 80% or more of the structure processed by cold rolling.

[0079] In the present invention, the recrystallization behavior during the annealing of the cold-rolled sheet can be affected to reduce the variation in high-frequency iron loss in the directions of 0, 45, and 90 degrees relative to the rolling direction. Specifically, after the cold-rolled sheet annealing step, the steel sheet can satisfy Equations 2 and 3.

[0080] [Formula 2] 2|WL-WC| / (WL+WC)≦0.1

[0081] [Formula 3] 2|WL+WC-2WN| / (WL+WC)≦0.1 (In Equations 2 and 3, WL represents the iron loss (W10 / 1000, W / kg) measured in the rolling direction, WC represents the iron loss (W10 / 1000, W / kg) measured in a direction perpendicular to the rolling direction, and WN represents the iron loss (W10 / 1000, W / kg) measured in a direction forming a 45° angle with the rolling direction. W10 / 1000 represents the iron loss (W / kg) when a magnetic flux density of 1.0 T is induced at a frequency of 1000 Hz.)

[0082] Equations 2 and 3 are inventions that mathematically express the variation in high-frequency iron loss in the 0-, 45-, and 90-degree directions. The smaller the values ​​of Equations 2 and 3, the smaller the variation in iron loss. When a motor is manufactured using a non-oriented electrical steel sheet that satisfies these equations, the motor efficiency can be maximized. More specifically, the values ​​of Equations 2 and 3 may all be 0.09 or less. The lower limits of Equations 2 and 3 are not particularly limited and are 0.

[0083] Next, after annealing the cold-rolled sheet, an insulating coating can be formed. The insulating coating can be an organic, inorganic, or organic-inorganic composite coating, or it can be formed with other insulating coating agents. For example, the insulating coating can be formed by applying an insulating coating-forming composition containing 40 to 70 wt % of a metal phosphate and 0.5 to 10 wt % of silica. After annealing the cold-rolled sheet, the process may further include a step of punching, laminating, and then stress relief annealing. The stress relief annealing step can further improve magnetic properties by removing stress applied to the non-oriented electrical steel sheet during punching and laminating. The stress relief annealing can be performed at a temperature of 700 to 850°C for 10 to 300 minutes. More specifically, it can be performed at a temperature of 750 to 800°C for 30 to 180 minutes. After the stress relief annealing step, the steel sheet can satisfy the following formula 4.

[0084] [Formula 4] W10 / 1000≦20+t×150 (In Equation 4, W10 / 1000 represents the iron loss (W / kg) when a magnetic flux density of 1.0 T is induced at a frequency of 1000 Hz, and t represents the thickness of the steel sheet (mm).) Equation 4 mathematically expresses the relationship between W10 / 1000 and the thickness (t) of the steel sheet. It is known that iron loss (W10 / 1000) decreases in proportion to thickness, but the non-oriented electrical steel sheet of the present invention has a further reduction in iron loss (W10 / 1000) compared to steel sheets of the same thickness due to its unique steel composition and hardness characteristics. The lower limit of Equation 4 is not particularly limited and is 0.

[0085] 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. Example 1 Slabs were manufactured containing the components shown in Table 1 below, with the balance being Fe and other unavoidably added impurities. The slabs were heated to 1150°C and hot-rolled at 850°C to produce hot-rolled sheets with a thickness of 2.3 mm. The hot-rolled sheets were then annealed at 1100°C for 4 minutes. Next, they were blasted with steel shot balls with an average diameter of 0.5 μm at the dose shown in Table 2 below to remove scale, and then pickled. They were then cold-rolled to a thickness of 0.27 mm and annealed at 800°C for 5 minutes. The content of each component was measured using ICP wet analysis. Five test pieces measuring 60 mm wide x 60 mm long were cut from each test piece and measured for iron loss characteristics using a single sheet tester. Iron loss after stress relief annealing was measured after annealing the test pieces at 750°C for 120 minutes. The hardness of the test piece after blasting was measured using a micro Vickers hardness tester under a load of 10 g.

[0086] [Table 1]

[0087] [Table 2]

[0088] [Table 3]

[0089] As shown in Tables 1 to 3, it can be confirmed that steel types 1 to 7 and 14 to 19, in which the alloying components and hardness after shot blasting were appropriately adjusted, had improved iron loss and iron loss anisotropy. In contrast, it can be confirmed that the iron loss and iron loss anisotropy deteriorate in steel types 8 to 13 that do not satisfy the alloy composition, and that the iron loss and iron loss anisotropy deteriorate in steel types 8, 20 to 23 that do not satisfy the hardness ratio of the hot-rolled sheet. It can be confirmed that steel types 14 to 19 do not contain the appropriate amount of Cr, Sn, or Sb, and that the magnetic properties are partially deteriorated.

[0090] 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 will understand that the present invention can be embodied in other specific forms without changing the technical idea or essential characteristics of the present invention. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and not limiting.

Claims

1. In weight percent, Si: 2.8 to 4.0%, Al: 0.1 to 1.3%, Mn: 0.3 to 2.0%, and the balance being Fe and inevitable impurities; A hot-rolled non-oriented electrical steel sheet characterized by satisfying the following formula 1: [Formula 1] 1.1≦Hv1 / HV2≦1.5 (In Equation 1, HV1 represents the hardness measured on the surface of the steel plate, and HV2 represents the hardness measured at a point halfway through the thickness of the steel plate.)

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

3. 2. The hot-rolled non-oriented electrical steel sheet according to claim 1, further comprising one or more of Cu: 0.01 to 0.2 wt %, P: 0.100 wt % or less (excluding 0%), Ni: 0.05 wt % or less (excluding 0%), and Zn: 0.01 wt % or less (excluding 0%).

4. 2. The hot-rolled non-oriented electrical steel sheet according to claim 1, further comprising one or more of C, N, S, Ti, Nb, and V in an amount of 0.005% by weight or less (excluding 0%), each or in total.

5. 2. The hot-rolled 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% by weight or less (excluding 0%), either individually or in total.

6. 2. The hot-rolled non-oriented electrical steel sheet according to claim 1, further comprising one or more of Mo: 0.03% by weight or less (excluding 0%), B: 0.0050% by weight or less (excluding 0%), Ca: 0.0050% by weight or less (excluding 0%), and Mg: 0.0050% by weight or less (excluding 0%).

7. A non-oriented electrical steel sheet comprising, by weight%, 2.8 to 4.0% Si, 0.1 to 1.3% Al, 0.3 to 2.0% Mn, and the balance being Fe and unavoidable impurities, and satisfying the following formulas 2 and 3: [Formula 2] 2|WL-WC| / (WL+WC)≦0.1 [Formula 3] 2|WL+WC-2WN| / (WL+WC)≦0.1 (In Equations 2 and 3, WL represents iron loss (W10 / 1000, W / kg) measured in the rolling direction, WC represents iron loss (W10 / 1000, W / kg) measured in a direction perpendicular to the rolling direction, and WN represents iron loss (W10 / 1000, W / kg) measured in a direction forming an angle of 45° with the rolling direction. W10 / 1000 represents iron loss (W / kg) when a magnetic flux density of 1.0 T is induced at a frequency of 1000 Hz.)

8. 8. The non-oriented electrical steel sheet according to claim 7, wherein the average crystal grain size is 5 to 50 μm.

9. 8. The non-oriented electrical steel sheet according to claim 7, which satisfies the following formula 4 after stress relief annealing: [Formula 4] W10 / 1000≦20+t×150 (In Equation 4, W10 / 1000 represents the iron loss (W / kg) when a magnetic flux density of 1.0 T is induced at a frequency of 1000 Hz, and t represents the thickness of the steel sheet (mm).)

10. A step of producing a hot-rolled sheet by hot-rolling a slab consisting of, in weight percent, 2.8 to 4.0% Si, 0.1 to 1.3% Al, 0.3 to 2.0% Mn, and the balance being Fe and unavoidable impurities; and removing scale present on the surface of the hot-rolled sheet. the removing of the scales includes removing the scales by projecting shot balls onto the steel plate, A method for producing a hot-rolled non-oriented electrical steel sheet, characterized in that the following formula 1 is satisfied after shot ball projection: [Formula 1] 1.1≦Hv1 / HV2≦1.5 (In Equation 1, HV1 represents the hardness measured on the surface of the steel plate, and HV2 represents the hardness measured at a point halfway through the thickness of the steel plate.)

11. The amount of shot balls projected is 15 to 35 kg / (min.m ２ 11. The method for producing a hot-rolled non-oriented electrical steel sheet according to claim 10, wherein the non-oriented electrical steel sheet is

12. The method for manufacturing a hot-rolled non-oriented electrical steel sheet according to claim 10, wherein the average particle size of the shot balls is 0.1 to 1 mm, and the shot balls are projected for 1 to 60 seconds.

13. The method for producing a hot-rolled non-oriented electrical steel sheet according to claim 10, wherein the material of the shot balls is an Fe-based alloy.

14. The method for manufacturing a hot-rolled non-oriented electrical steel sheet according to claim 10, further comprising the step of annealing the hot-rolled sheet before the step of removing the scale.

15. A step of producing a hot-rolled sheet by hot-rolling a slab consisting of, in weight percent, 2.8 to 4.0% Si, 0.1 to 1.3% Al, 0.3 to 2.0% Mn, and the balance being Fe and unavoidable impurities; removing scale present on the surface of the hot-rolled sheet; cold-rolling the descaled hot-rolled sheet to produce a cold-rolled sheet; annealing the cold-rolled sheet; the removing of the scales includes removing the scales by projecting shot balls onto the steel plate, A method for producing a non-oriented electrical steel sheet, characterized in that the following formula 1 is satisfied after shot ball projection: [Formula 1] 1.1≦Hv1 / HV2≦1.5 (In Equation 1, HV1 represents the hardness measured on the surface of the steel plate, and HV2 represents the hardness measured at a point halfway through the thickness of the steel plate.)

16. 16. The method of claim 15, wherein the cold-rolled sheet is annealed at a temperature of 700 to 850°C.

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

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