Non-oriented electrical steel sheet and its manufacturing method

Abstract

We provide a non-oriented electrical steel sheet and a manufacturing method thereof. Specifically, we provide a non-oriented electrical steel sheet and a manufacturing method thereof that suppresses the formation of fine carbonitrides by appropriately adding Mo, Ti, Nb, and V and adjusting the time within a specific temperature range during the cooling process after final annealing. [Solution] A non-oriented electrical steel sheet according to one embodiment of the present invention contains, by weight, Si: 3.3-4.0%, Al: 0.4-1.5%, Mn: 0.2-1.0%, C: 0.0015-0.0040%, N: 0.0005-0.0020%, S: 0.0005-0.0025%, Mo: 0.005-0.01%, Ti: 0.0005-0.0020%, Nb: 0.0005-0.0020%, and V: 0.0005-0.0020%, with the remainder being Fe and unavoidable impurities.

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 and a manufacturing method thereof, which is obtained by appropriately adding Mo, Ti, Nb, and V and controlling the time in a specific temperature range during the cooling process after final annealing to suppress the formation of fine carbonitrides. As a result, the present invention relates to a non-oriented electrical steel sheet and a manufacturing method thereof that has excellent magnetic properties and strength. [Background technology]

[0002] Non-oriented electrical steel sheets are primarily used in motors that convert electrical energy into mechanical energy, and excellent magnetic properties are required for them to achieve high efficiency in this process. In particular, environmentally friendly automobiles that are driven by motors instead of internal combustion engines have been attracting attention in recent years, and the demand for non-oriented electrical steel sheets used as the core material of drive motors is increasing. This has led to a demand for non-oriented electrical steel sheets that have both excellent magnetic properties and strength.

[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 allows for the production of more energy-efficient motors under the same conditions, while higher magnetic flux density allows for the miniaturization of motors or the reduction of copper loss. Therefore, using non-oriented electrical steel sheets with low iron loss and high magnetic flux density allows for the creation of drive motors with excellent efficiency and torque, thereby improving the mileage and power output of environmentally friendly vehicles.

[0004] The characteristics of non-oriented electrical steel that should be considered also vary depending on the operating conditions of the motor. The commonly used standard for evaluating the properties of non-oriented electrical steel used in motors is W15 / 50, which is the iron loss when a 1.5T magnetic field is applied at a commercial frequency of 50Hz. However, for non-oriented electrical steel sheets with a thickness of 0.35mm or less used in the drive motors of environmentally friendly automobiles, magnetic properties at low magnetic fields of 1.0T or less and high frequencies of 400Hz or more are often important, so the properties of non-oriented electrical steel sheets are often evaluated using W10 / 400 iron loss.

[0005] Non-oriented electrical steel sheets for the traction motors of environmentally friendly vehicles require strength as excellent as their magnetic properties. Traction motors for environmentally friendly vehicles are typically designed with permanent magnets inserted into the rotor. To ensure superior performance, inserted-magnet motors require the permanent magnets to be positioned on the outside of the rotor, as close to the stator as possible. However, if the strength of the electrical steel sheet is low when the motor rotates at high speeds, the permanent magnets inserted in the rotor will be dislodged by centrifugal force. Therefore, electrical steel sheets with high strength are required to ensure the performance and durability of the motor.

[0006] The most common way to simultaneously improve the magnetic properties and strength of non-oriented electrical steel is to add alloying elements such as Si, Al, and Mn. The addition of these alloying elements increases the steel's resistivity, reducing eddy current loss and overall iron loss. Furthermore, the alloying elements dissolve in iron as substitutional elements, strengthening the steel and increasing its strength. However, the more alloying elements such as Si, Al, and Mn are added, the lower the magnetic flux density and the greater the brittleness. Adding more than a certain amount of alloying elements makes cold rolling impossible, making commercial production impossible. While thinner electrical steel sheets offer better high-frequency iron loss, the reduced rollability due to brittleness is a critical issue.

[0007] Depending on the motor design objectives, electrical steel sheets with improved strength may be used, even if their magnetic properties are slightly compromised. Methods for manufacturing electrical steel sheets for such applications include the precipitation of interstitial elements and grain size reduction. Rotors manufactured with electrical steel sheets with significantly improved strength, even if their magnetic properties are slightly compromised, are primarily used to miniaturize motors and increase rotational speed, or to enhance the effectiveness of permanent magnets inserted into the rotor. While the formation of fine precipitates containing interstitial solid solution elements such as C, N, and S is effective in improving strength, it has the disadvantage of rapidly deteriorating core loss and reducing motor efficiency. Furthermore, grain size reduction has the disadvantage of increasing the non-uniformity of the steel sheet material due to the inclusion of unrecrystallized portions, resulting in greater quality deviations in mass-produced products.

[0008] To solve these problems, attempts have been made to produce non-oriented electrical steel sheets with excellent both magnetic properties and strength by controlling the cooling rate in the final annealing process, but this has the problem of making them difficult to apply to mass production due to increased material non-uniformity caused by the inclusion of unrecrystallized portions.In addition, many technologies that have been proposed to simultaneously improve magnetic properties and strength have not been used due to reasons such as increased manufacturing costs, reduced productivity and yield, and insufficient improvement effects. Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a non-oriented electrical steel sheet and a manufacturing method thereof, and more specifically, to provide a non-oriented electrical steel sheet and a manufacturing method thereof that suppresses the formation of fine carbonitrides by appropriately adding Mo, Ti, Nb, and V and controlling the time within a specific temperature range during the cooling process after final annealing. [Means for solving the problem]

[0010] A non-oriented electrical steel sheet according to one embodiment of the present invention contains, by weight, 3.3 to 4.0% Si, 0.4 to 1.5% Al, 0.2 to 1.0% Mn, 0.0015 to 0.0040% C, 0.0005 to 0.0020% N, 0.0005 to 0.0025% S, 0.005 to 0.01% Mo, 0.0005 to 0.0020% Ti, 0.0005 to 0.0020% Nb, and 0.0005 to 0.0020% V, with the remainder being Fe and unavoidable impurities, and satisfies the following formula 1: [Formula 1] 1.75≦([Mo]+[Ti]+[Nb]+[V]) / ([C]+[N])≦4.00 (In formula 1, [Mo], [Ti], [Nb], [V], [C], and [N] represent the contents (wt%) of Mo, Ti, Nb, V, C, and N, respectively.) The non-oriented electrical steel sheet according to one embodiment of the present invention has an average crystal grain size of 55 to 80 μm. The non-oriented electrical steel sheet according to one embodiment of the present invention has a distribution density of at least one of carbides, nitrides and carbonitrides having a grain size of 50 nm or less of 0.5 particles / mm 2 The following is the result.

[0011] The value calculated by the following formula 2 is 500 to 2000. [Formula 2] [Average grain size (μm)] 2 × [Distribution density of one or more of carbides, nitrides, and carbonitrides with a particle size of 50 nm or less (pieces / mm 2 )]

[0012] The non-oriented electrical steel sheet according to an embodiment of the present invention further contains one or more of Sn: 0.015 to 0.1 wt %, Sb: 0.015 to 0.1 wt %, and P: 0.005 to 0.05 wt %.

[0013] The non-oriented electrical steel sheet according to an embodiment of the present invention further contains one or more of Cu: 0.05 wt % or less, B: 0.002 wt % or less, Mg: 0.005 wt % or less, and Zr: 0.005 wt % or less.

[0014] The non-oriented electrical steel sheet according to one embodiment of the present invention has a resistivity of 50 μΩ·cm or more.

[0015] The non-oriented electrical steel sheet according to one embodiment of the present invention has a density of 7.55 g / cm 3 That's all.

[0016] The non-oriented electrical steel sheet according to one embodiment of the present invention has a 0.2% offset yield strength (Rp 0.2 ) is 440 MPa or more.

[0017] The non-oriented electrical steel sheet according to one embodiment of the present invention has a 0.2% offset yield strength (Rp 0.2 ) is 98.5% or more of the upper yield strength (ReH).

[0018] A method for producing a non-oriented electrical steel sheet according to an embodiment of the present invention includes the steps of producing a slab containing, by weight, 3.3-4.0% Si, 0.4-1.5% Al, 0.2-1.0% Mn, 0.0015-0.0040% C, 0.0005-0.0020% N, 0.0005-0.0025% S, 0.005-0.01% Mo, 0.0005-0.0020% Ti, 0.0005-0.0020% Nb, and 0.0005-0.0020% V, with the balance being Fe and unavoidable impurities, and satisfying the following formula 1: hot rolling the slab to produce a hot-rolled sheet; cold rolling the hot-rolled sheet to produce a cold-rolled sheet; and final annealing the cold-rolled sheet: [Formula 1] 1.75≦([Mo]+[Ti]+[Nb]+[V]) / ([C]+[N])≦4.00 (In formula 1, [Mo], [Ti], [Nb], [V], [C], and [N] represent the contents (wt%) of Mo, Ti, Nb, V, C, and N, respectively.) The final annealing step includes a step of soaking at a temperature of 910 to 1000°C and a step of cooling from the soaking temperature to 600°C within 25 seconds.

[0019] After the step of producing the hot-rolled sheet, the method further includes the step of annealing the hot-rolled sheet at a temperature of 850 to 1150°C.

[0020] The final annealing step is performed in an atmosphere containing a mixture of hydrogen (H2) and nitrogen (N2). [Effects of the Invention]

[0021] According to one embodiment of the present invention, a non-oriented electrical steel sheet having improved magnetic properties and strength is provided, which contributes to improving the performance of drive motors for environmentally friendly automobiles. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a graph illustrating the temperature in a final annealing step in an example of the present invention. [Figure 2] This is a single-plane TEM photograph measured on steel type B1. [Figure 3] This is a single-plane TEM photograph taken on steel type B3. DETAILED DESCRIPTION OF THE INVENTION

[0023] 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 can be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0024] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. As used in the specification, the term "comprising" means to embody 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.

[0025] When a moiety is referred to as being "on" or "on top of" another moiety, it may be directly on or above the other moiety, with other moieties intervening. In contrast, when a moiety is referred to as being "directly on" another moiety, it does not mean that there are other moieties intervening. Also, unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight. In one embodiment of the present invention, further containing an additional element means that an additional amount of the additional element is included in place of the remaining iron (Fe).

[0026] 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 further analyzed to have a meaning that fits the relevant technical literature and the presently disclosed content, and are not interpreted as having an ideal or overly formal meaning unless otherwise defined.

[0027] While the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, the present invention will be described in detail below so that those skilled in the art can easily practice the present invention.

[0028] A non-oriented electrical steel sheet according to an embodiment of the present invention contains, by weight, 3.3 to 4.0% Si, 0.4 to 1.5% Al, 0.2 to 1.0% Mn, 0.0015 to 0.0040% C, 0.0005 to 0.0020% N, 0.0005 to 0.0025% S, 0.005 to 0.01% Mo, 0.0005 to 0.0020% Ti, 0.0005 to 0.0020% Nb, and 0.0005 to 0.0020% V, with the remainder being Fe and unavoidable impurities.

[0029] The reasons for limiting the components of the non-oriented electrical steel sheet will be explained below.

[0030] Si:3.30~4.00wt% Silicon (Si) increases the resistivity of a material, reducing iron loss, and increases strength through solid solution strengthening. If too little Si is added, the iron loss and strength improvement effects are insufficient. If too much Si is added, the brittleness of the material increases, rolling productivity drops sharply, and an oxide layer and oxides that are harmful to magnetism form on the surface, causing problems. Therefore, the Si content can be 3.3 to 4.0 wt. %. More specifically, the Si content can be 3.4 to 3.6 wt. %.

[0031] Al:0.40~1.50wt% Aluminum (Al) increases the resistivity of a material, reducing iron loss, and increases strength through solid solution strengthening. If too little Al is added, fine nitrides are formed or the oxide layer on the surface is not dense enough, making it difficult to achieve magnetic improvement. If too much Al is added, excessive nitrides are formed, degrading magnetic properties and causing problems in all processes, including steelmaking and continuous casting, significantly reducing productivity. Therefore, the Al content can be 0.4 to 1.5 wt. %. More specifically, the Al content can be 0.5 to 1.0 wt. %.

[0032] Mn:0.20~1.00wt% Manganese (Mn) increases the resistivity of the material, improving iron loss, and plays a role in forming sulfides. If too little Mn is added, fine MnS is formed, causing magnetic deterioration. If too much Mn is added, fine MnS is excessively precipitated, promoting the formation of a {111} texture that is unfavorable to magnetism and resulting in a rapid decrease in magnetic flux density. Therefore, Mn can be contained in an amount of 0.2 to 1.0 wt. %. More specifically, Mn can be contained in an amount of 0.30 to 0.70 wt. %.

[0033] C:0.0015~0.0040wt% Carbon (C) causes magnetic aging and combines with other impurity elements to form carbides, which reduces magnetic properties, but it also plays a role in improving strength by preventing potential transfer. If too little C is added, the strength improvement effect is insufficient. If too much C is added, the amount of fine carbides increases, causing a rapid deterioration of magnetic properties. Therefore, C can be contained in an amount of 0.0015 to 0.0040 wt. %. More specifically, C can be contained in an amount of 0.0020 to 0.0038 wt. %.

[0034] N:0.0005~0.0020wt% Nitrogen (N) not only forms fine AlN precipitates inside the base material, but also combines with other impurities to form fine precipitates, which inhibit grain growth and worsen iron loss, but also improve strength. If too little nitrogen is added, strength cannot be sufficiently improved. If too much nitrogen is added, the number of fine nitrides increases, causing a rapid deterioration in iron loss. Therefore, N can be contained in an amount of 0.0005 to 0.0020 wt. %. More specifically, N can be contained in an amount of 0.0008 to 0.0018 wt. %.

[0035] S:0.0005~0.0025% by weight Sulfur (S) forms fine precipitates, MnS and CuS, which deteriorate magnetic properties and hot workability, so it is preferable to keep the content low. However, adding too little S reduces magnetic flux density. Therefore, S can be contained in an amount of 0.0005 to 0.0025 wt %. More specifically, S can be contained in an amount of 0.0010 to 0.0023 wt %.

[0036] Mo:0.0050~0.0100wt% Molybdenum (Mo) segregates to grain boundaries during annealing, suppressing the development of {111} texture, which is detrimental to magnetic properties, and forms fine carbides during cooling, improving strength. If too little Mo is added, this effect is insufficient. If too much Mo is added, it promotes the formation of carbides, deteriorating magnetic properties. Therefore, Mo can be contained in an amount of 0.005 to 0.01 wt. %. More specifically, it can be contained in an amount of 0.0060 to 0.0090 wt. %.

[0037] Ti, Nb, V: 0.0005 to 0.0020 wt% each Titanium (Ti), niobium (Nb), and vanadium (V) have a strong tendency to form precipitates in steel. They form fine carbides, nitrides, or sulfides within the base material, inhibiting grain growth and domain wall motion, thereby degrading core loss. Therefore, the upper limits of Ti, Nb, and V must be appropriately adjusted. On the other hand, if their contents are too low, the strength of the electrical steel sheet significantly decreases. Therefore, Ti, Nb, and V can each be contained in an amount of 0.0005 to 0.0020 wt. %. More specifically, each can be contained in an amount of 0.0007 to 0.0018 wt. %.

[0038] Ti+Nb+V:0.0030~0.0050wt% As mentioned above, Ti, Nb, and V play a role in strengthening the strength, so it is preferable to include them in a total amount of 0.0030 wt% or more. If these elements are included in excessive amounts, they form fine carbides, nitrides, or sulfides, which inhibit grain growth and domain wall motion, thereby deteriorating iron loss.

[0039] The non-oriented electrical steel sheet according to one embodiment of the present invention satisfies the following formula 1. [Formula 1] 1.75≦([Mo]+[Ti]+[Nb]+[V]) / ([C]+[N])≦4.00 (In formula 1, [Mo], [Ti], [Nb], [V], [C], and [N] represent the contents (wt%) of Mo, Ti, Nb, V, C, and N, respectively.)

[0040] When formula 1 is satisfied, the formation of fine carbonitrides can be minimized. That is, within the range of 1.75 to 4.00, the formation of fine carbonitrides is suppressed and the distribution density of carbonitrides is minimized, so it is controlled within this range. If the value of formula 1 is too low, problems arise in terms of strength. More specifically, the value of formula 1 is 2.00 to 3.50.

[0041] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of Sn: 0.015 to 0.1 wt %, Sb: 0.015 to 0.1 wt %, and P: 0.005 to 0.05 wt %.

[0042] Sn, Sb: 0.015 to 0.100% by weight each Tin (Sn) and antimony (Sb) segregate at the surface and grain boundaries of the steel sheet to suppress surface oxidation during annealing, prevent element diffusion through grain boundaries, and prevent recrystallization in the {111} / / ND orientation, improving the texture. If too little Sn or Sb is added, the above-mentioned effects are insufficient. If too much Sn or Sb is added, the amount of grain boundary segregation increases, reducing toughness and productivity, rather than improving magnetic properties. Therefore, Sn and Sb can be further added in an amount of 0.015 to 0.100 wt.% each. More specifically, they can be further added in an amount of 0.020 to 0.075 wt.% each.

[0043] P:0.005~0.050wt% Phosphorus (P) segregates at the surface and grain boundaries of the steel sheet to suppress surface oxidation during annealing, prevent element diffusion through grain boundaries, and prevent recrystallization in the {111} / / ND orientation, improving the texture. If too little P is added, these effects are insufficient. If too much P is added, hot working characteristics deteriorate, resulting in lower productivity compared to improved magnetic properties. Therefore, P can be further added at 0.005 to 0.050 wt. %. More specifically, P can be further added at 0.007 to 0.045 wt. %.

[0044] The non-oriented electrical steel sheet according to an embodiment of the present invention may further include one or more of Cu: 0.01 wt % or less, B: 0.002 wt % or less, Mg: 0.005 wt % or less, and Zr: 0.005 wt % or less.

[0045] Cu: 0.05% by weight or less Copper (Cu) is an element that can form sulfides at high temperatures, and when added in large amounts, it can cause surface defects during slab production. Therefore, when Cu is further contained, it can be contained in an amount of 0.05 wt% or less. More specifically, it can be contained in an amount of 0.001 to 0.05 wt%.

[0046] B: 0.002% by weight or less, Mg: 0.005% by weight or less, and Zr: 0.005% by weight or less B, Mg, and Zr are elements that adversely affect magnetism, and each may be further contained within the aforementioned range.

[0047] The balance includes Fe and unavoidable impurities. Unavoidable impurities are impurities that are mixed in during the steelmaking process and the manufacturing process of grain-oriented electrical steel sheets, and as they are widely known in the relevant field, detailed description thereof will be omitted. In one embodiment of the present invention, the addition of elements other than the alloy components described above is not excluded, and various elements may be included within a range that does not impair the technical concept of the present invention. When additional elements are further included, they are included in place of the balance of Fe.

[0048] The non-oriented electrical steel sheet according to one embodiment of the present invention has an average grain size of 55 to 80 μm. If the average grain size is too small, the core loss is poor. If the average grain size is too large, the strength is weak. More specifically, the average grain size is 58 to 75 μm.

[0049] The non-oriented electrical steel sheet according to one embodiment of the present invention has a density of at least one of carbides, nitrides, and carbonitrides having a grain size of 50 nm or less of 0.5 particles / mm 2 The following is the result.

[0050] In one embodiment of the present invention, the density of carbides, nitrides, or carbonitrides (hereinafter sometimes referred to as "carbonitrides") can be minimized by adding appropriate amounts of Mo, Ti, Nb, V, C, and N relative to the C and N contents while containing a certain amount of Mo, Ti, Nb, and V. Furthermore, by adjusting the cooling time during the final annealing process. The lower limit of the carbonitride particle size is 5 nm. Carbonitrides smaller than the above particle size have no substantial effect on magnetic properties. The particle size refers to the particle size of an imaginary circle with the same area as the carbonitride when observing the steel sheet. The carbonitrides are measured on the surface (ND plane) or cross section (TD plane, RD plane). Carbonitrides can be observed using a TEM. Carbonitrides refer to particulate regions with a higher C and / or N content than the steel sheet substrate.

[0051] The distribution density of carbonitrides is 0.5 pieces / mm 2 More specifically, it is 0.05 to 0.50 pieces / mm 2 More specifically, 0.10 to 0.40 pieces / mm 2 When carbides, nitrides, or carbonitrides are simultaneously contained, this is the distribution density of these in total.

[0052] In the non-oriented electrical steel sheet according to one embodiment of the present invention, the value of the following formula 2 is 500 to 2000. [Formula 2] [Average grain size (μm)] 2 × [Distribution density of one or more of carbides, nitrides, and carbonitrides with a particle size of 50 nm or less (pieces / mm 2 )] When the value of formula 2 satisfies 500 to 2000, it is possible to improve the strength as well as the magnetism.

[0053] The non-oriented electrical steel sheet according to one embodiment of the present invention has a resistivity of 50 μΩ·cm or more. More specifically, it is 53 μΩ·cm or more. Even more specifically, it is 58 μΩ·cm or more. There is no upper limit, but it is preferably 100 μΩ·cm or less.

[0054] The non-oriented electrical steel sheet according to one embodiment of the present invention has a density of 7.55 g / cm 3 That's all. In one embodiment of the present invention, it is possible to improve strength while maintaining an appropriate density. Specifically, the density is 7.55 to 8.00 g / cm. 3 The non-oriented electrical steel sheet according to an embodiment of the present invention is excellent in both strength and magnetic properties. Specifically, the non-oriented electrical steel sheet according to an embodiment of the present invention has a 0.2% offset yield strength (Rp 0.2 ) is 440 MPa or more. When a motor rotates at high speed, strong stress is applied from the inside to the outside of the motor. In particular, in the case of permanent magnet inserted motors, efficiency can be improved by placing the permanent magnets at the very end of the rotor, but if electrical steel sheets with low yield strength are used, the permanent magnets inserted into the rotor will cause deformation and destruction at the end of the rotor due to centrifugal force as the motor rotates, causing durability problems. For this reason, the mechanical properties of the steel sheets are important, and this is defined as the 0.2% offset yield strength (Rp 0.2 ) can be confirmed. More specifically, the 0.2% offset yield strength (Rp 0.2 ) is 440 to 460 MPa.

[0055] In addition, in one embodiment of the present invention, the reduction in yield strength is small even when tension is applied compared to before tension is applied, so the strength of the motor can be maintained even when the motor rotates at a high speed. Specifically, the 0.2% offset yield strength (Rp 0.2 ) is 98.5% or more of the upper yield strength (ReH). More specifically, the 0.2% offset yield strength (Rp 0.2 ) is 98.5% to 99.9% of the upper yield strength (ReH). Yield strength can be measured according to the ISO 6892 standard by conducting a tensile test on a test piece with a parallel section length of 80 mm and measuring the yield strength with 0.2% tension or no tension.

[0056] The non-oriented electrical steel sheet according to one embodiment of the present invention has a magnetic flux density (B50) of 1.66 T or more. Here, B50 refers to the magnetic flux density induced in a magnetic field of 5000 A / m. More specifically, the magnetic flux density (B50) is 1.67 to 1.70 T. The non-oriented electrical steel sheet according to one embodiment of the present invention has an iron loss (W10 / 400) of 12.0 W / kg or less. W10 / 400 refers to the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz. More specifically, the iron loss (W10 / 400) is 10.5 to 11.5 W / kg. The reference thickness for measuring the iron loss is 0.30 mm.

[0057] A method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes the steps of: preparing a slab; hot-rolling the slab to prepare a hot-rolled sheet; cold-rolling the hot-rolled sheet to prepare a cold-rolled sheet; and final annealing the cold-rolled sheet.

[0058] Each step will be explained in detail below. First, the slab is manufactured.

[0059] The alloying elements of the slab have been explained in the section on the alloying elements of the non-oriented electrical steel sheet, so a duplicate explanation will be omitted. Since the alloying elements do not substantially change during the manufacturing process of the non-oriented electrical steel sheet, the alloying elements of the non-oriented electrical steel sheet and the slab are substantially the same.

[0060] Specifically, the slab contains, by weight, 3.3-4.0% Si, 0.4-1.5% Al, 0.2-1.0% Mn, 0.0015-0.0040% C, 0.0005-0.0020% N, 0.0005-0.0025% S, 0.005-0.01% Mo, 0.0005-0.0020% Ti, 0.0005-0.0020% Nb, and 0.0005-0.0020% V, with the remainder being Fe and unavoidable impurities, and can satisfy the following formula 1. [Formula 1] 1.75≦([Mo]+[Ti]+[Nb]+[V]) / ([C]+[N])≦4.00 (In formula 1, [Mo], [Ti], [Nb], [V], [C], and [N] represent the contents (wt%) of Mo, Ti, Nb, V, C, and N, respectively.)

[0061] The manufacturing process for the slabs is carried out by processes known in the art. After the slab is manufactured, it is heated. Specifically, the slab is placed in a heating furnace and heated to a temperature of 1,200°C or less. If the slab is heated to an excessively high temperature, precipitates such as AlN and MnS present in the slab are redissolved and then finely precipitated during hot rolling and annealing, suppressing grain growth and reducing magnetism.

[0062] Next, the slab is hot-rolled to produce a hot-rolled sheet. The thickness of the hot-rolled sheet is 2 to 2.3 mm. The finish rolling temperature in the hot-rolled sheet production step is 800°C or higher, specifically 800 to 1000°C. The hot-rolled sheet is coiled at a temperature of 700°C or lower. After the hot-rolled sheet production step, the process can further include a step of annealing the hot-rolled sheet. In this case, the annealing temperature of the hot-rolled sheet is 850 to 1150°C. If the annealing temperature of the hot-rolled sheet is too low, the texture does not grow or grows too fine, making it difficult to obtain a texture favorable for magnetic properties during annealing after cold rolling. If the annealing temperature is too high, magnetic crystal grains grow excessively, resulting in excessive surface defects in the sheet. Hot-rolled sheet annealing is performed as needed to increase the orientation favorable for magnetic properties, but it can also be omitted. The annealed hot-rolled sheet is then pickled. More specifically, the annealing temperature of the hot-rolled sheet is 950 to 1150°C.

[0063] Next, the hot-rolled sheet is cold-rolled to produce a cold-rolled sheet. At this time, the reduction is adjusted to 70-85%. If necessary, the cold-rolling step can include one cold-rolling step or two or more cold-rolling steps with intermediate annealing in between. At this time, the intermediate annealing temperature is 850-1150°C. The thickness of the cold-rolled sheet is 0.10-0.35 mm. Next, the cold-rolled sheet is subjected to final annealing. There are no significant restrictions on the annealing temperature in the process of annealing the cold-rolled sheet, as long as it is a temperature normally used for non-oriented electrical steel sheets. Since the iron loss of non-oriented electrical steel sheets is closely related to the size of the crystal grains, a soaking temperature (T) of 910-1000°C is used.max The soaking temperature means a state where there is almost no temperature fluctuation. The soaking time is 100 seconds or less, so that the annealing is performed in a short time.

[0064] Then, the soaking temperature (T max ) to 600°C within 25 seconds (t). By cooling in such a short time, it is possible to minimize the formation of fine carbonitrides and to suppress the irregular growth of crystal grains. More specifically, the soaking temperature (T max ) to 600°C in 15 to 23 seconds (t). Fig. 1 shows a schematic diagram of the soaking temperature and cooling time (t) according to one embodiment of the present invention.

[0065] The final annealing step is performed in an atmosphere containing a mixture of hydrogen (H2) and nitrogen (N2). Specifically, the atmosphere contains 5-40% by volume of hydrogen and 60-95% by volume of nitrogen. Annealing in this atmosphere has the advantage of preventing the formation of fine oxides that are harmful to magnetism and are formed at high temperatures. During the final annealing process, the average grain size can be 55-80 μm, and all (i.e., more than 99%) of the processed structure formed in the previous cold rolling step is recrystallized.

[0066] After final annealing, an insulating coating is formed. The insulating coating can be an organic, inorganic, or organic / inorganic composite coating, or it can be an insulating coating. The present invention will be described in more detail below with reference to examples. However, these examples are merely for illustrative purposes and are not intended to limit the scope of the present invention. [Example]

[0067] Slabs were produced with the chemical composition shown in Table 1, with the remainder consisting of Fe and unavoidable impurities. The slabs were heated to 1,150°C and hot rolled at a finishing temperature of 880°C to produce hot-rolled sheets with a thickness of 2.0 mm. The hot-rolled sheets were annealed at 1,020°C for 100 seconds and then cold-rolled to a thickness of 0.25 mm. These were then subjected to final annealing at the temperatures shown in Table 2 for 100 seconds.

[0068] The calculated value of relational expression 1 for each test piece, the cooling time from the soaking temperature to 600°C during final annealing, the distribution density of (Mo, Ti, Nb, V) (C, N) precipitates with a diameter of 50 nm or less, the average grain size, the upper yield strength (ReH), the 0.2% offset yield strength (Rp 0.2 ), Rp 0.2 The values ​​of / ReH and magnetic properties are shown in Table 2.

[0069] The content of each element was measured by ICP wet analysis. The cooling time from the maximum temperature to 600°C was measured by attaching TC to the surface of the test piece and directly measuring the sheet temperature. Precipitates were measured by replicating TEM test pieces and measuring 0.5 mm at high magnification. 2 When carbides or nitrides with a diameter of 50 nm or less containing Mo, Ti, Nb, or V were found over the above area, the number of particles was divided by the observed area to calculate the distribution density. The grain size was calculated by polishing and etching the cross section of the test piece perpendicular to the rolling direction, and photographing an area sufficient to contain 1,500 or more grains with an optical microscope, and dividing the measured area by the number of grains. 0.5 The yield strength was calculated using the formula: tensile test was conducted on a test piece with a parallel section length of 80 mm in accordance with the ISO 6892 standard, and the results are shown. For magnetic properties such as magnetic flux density and iron loss, five test pieces measuring 60 mm wide x 60 mm long were cut from each test piece, and measurements were taken in the rolling direction and perpendicular to the rolling direction using a single sheet tester, and the average values ​​are shown.

[0070] [Table 1]

[0071] [Table 2]

[0072] [Table 3]

[0073] As shown in Tables 1 to 3, in the examples in which the alloying elements were appropriately adjusted and the cooling time during final annealing was adjusted to be short, the distribution and grain size of carbonitrides were suitably controlled, resulting in a high Rp of 440 MPa or more. 0.2 It can be seen that excellent magnetic properties are achieved. It can be seen that A1 and D2 have poor strength properties because the values ​​of Equation 1 are too small. It can be seen that B2 and C2 have poor magnetic properties because the values ​​of Equation 1 are too large, resulting in the generation of a large amount of carbonitrides.

[0074] It can be seen that B1 and C1 have poor magnetic properties due to the excessively long cooling time, which resulted in the formation of large amounts of carbonitrides. It can be seen that A2 has poor strength properties due to the excessively high soaking temperature, which resulted in large crystal grains. It can be seen that D1 has poor strength and magnetic properties due to the excessively low soaking temperature, which resulted in the formation of small crystal grains. It can be seen that D5 and D6 have poor strength and magnetic properties due to the low content of Mo, Ti, Nb, and V.

[0075] The present invention is not limited to the examples, and can be manufactured in various different forms, and a person skilled in the art to which the present invention pertains can understand that the present invention can be embodied in other specific forms without changing the technical idea or essential features of the present invention. Therefore, it should be understood that the above example is illustrative in all respects and not limiting.

Claims

1. containing, by weight percent, 3.3 to 4.0% Si, 0.4 to 1.5% Al, 0.2 to 1.0% Mn, 0.0015 to 0.0040% C, 0.0005 to 0.0020% N, 0.0005 to 0.0025% S, 0.005 to 0.01% Mo, 0.0005 to 0.0020% Ti, 0.0005 to 0.0020% Nb, and 0.0005 to 0.0020% V, with the balance being Fe and unavoidable impurities; Satisfies the following formula 1: The average crystal grain size is 55 to 80 μm, The total distribution density of one or more of carbides, nitrides, and carbonitrides having a particle size of 50 nm or less is 0.5 particles / mm ２ A non-oriented electrical steel sheet characterized by the following: [Formula 1] 1.75≦([Mo]+[Ti]+[Nb]+[V]) / ([C]+[N])≦4.00 (In formula 1, [Mo], [Ti], [Nb], [V], [C] and [N] represent the contents (wt%) of Mo, Ti, Nb, V, C and N, respectively.)

2. The non-oriented electrical steel sheet according to claim 1, wherein the value calculated by the following formula 2 is 500 to 2000: [Formula 2] [Average grain size (μm)] ２ × [distribution density (pieces / mm ２ )]

3. 3. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of Sn: 0.015 to 0.1 wt %, Sb: 0.015 to 0.1 wt %, and P: 0.005 to 0.05 wt %.

4. 4. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of Cu: 0.05 wt % or less, B: 0.002 wt % or less, Mg: 0.005 wt % or less, and Zr: 0.005 wt % or less.

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

6. Density is 7.55 g / cm ３ The non-oriented electrical steel sheet according to any one of claims 1 to 5, wherein the non-oriented electrical steel sheet is as described above.

7. 0.2% offset yield strength (Rp ０．２ 7. The non-oriented electrical steel sheet according to claim 1, wherein the tensile strength (T) of the non-oriented electrical steel sheet is 440 MPa or more.

8. 0.2% offset yield strength (Rp ０．２ 8. The non-oriented electrical steel sheet according to claim 1, wherein the upper yield strength (ReH) is 98.5% or more of the upper yield strength (ReH).

9. a step of producing a slab containing, in weight percent, 3.3 to 4.0% Si, 0.4 to 1.5% Al, 0.2 to 1.0% Mn, 0.0015 to 0.0040% C, 0.0005 to 0.0020% N, 0.0005 to 0.0025% S, 0.005 to 0.01% Mo, 0.0005 to 0.0020% Ti, 0.0005 to 0.0020% Nb, and 0.0005 to 0.0020% V, with the balance being Fe and unavoidable impurities, and satisfying the following formula 1: hot rolling the slab to produce a hot-rolled sheet; cold-rolling the hot-rolled sheet to produce a cold-rolled sheet; final annealing of the cold-rolled sheet; 9. The method of manufacturing a non-oriented electrical steel sheet according to claim 1, wherein the final annealing step includes a step of soaking at a soaking temperature of 910 to 1000°C and a step of cooling from the soaking temperature to 600°C within 25 seconds. [Formula 1] 1.75≦([Mo]+[Ti]+[Nb]+[V]) / ([C]+[N])≦4.00 (In formula 1, [Mo], [Ti], [Nb], [V], [C] and [N] represent the contents (wt%) of Mo, Ti, Nb, V, C and N, respectively.)

10. 10. The method of claim 9, further comprising the step of annealing the hot-rolled sheet at a temperature of 850 to 1150° C. after the step of producing the hot-rolled sheet.

11. The final annealing step is carried out in a hydrogen (H ２ ) and nitrogen (N ２ 11. The method for producing a non-oriented electrical steel sheet according to claim 9, wherein the steel sheet is annealed in an atmosphere containing a mixture of:

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