Non-oriented electrical steel sheet and its manufacturing method

Abstract

The present invention provides a non-oriented electrical steel sheet and a manufacturing method thereof, in which crystal grains having a specific orientation are developed by controlling the thermal history during annealing of the hot-rolled sheet, thereby improving magnetic properties. [Solution] A method for producing a non-oriented electrical steel sheet of the present invention includes the steps of hot rolling a slab containing, by weight, 2.5 to 4.5% Si, 0.1 to 1.5% Al, 0.1 to 0.5% Mn, and the balance being Fe and unavoidable impurities to produce a hot-rolled sheet, hot-rolling the hot-rolled sheet to produce a cold-rolled sheet, and cold-rolling the hot-rolled sheet to produce a cold-rolled sheet, The step of annealing the hot-rolled sheet includes a heating step of heating the hot-rolled sheet to a first soaking temperature (T1) of 980°C to 1100°C at a heating rate of 30°C / s or more, a first soaking step of maintaining the first soaking temperature (T1) within a 10°C range for 20 to 60 seconds, a cooling step of passing the first soaking temperature (T1) to a second soaking temperature (T2) of 750°C to 850°C within 30 seconds, and a second soaking step of maintaining the second soaking temperature (T2) within a 10°C range for 30 to 90 seconds, and the heating step is performed for 40 to 100 seconds.

Description

[Technical Field]

[0001] The present invention relates to a non-oriented electrical steel sheet and a manufacturing method thereof, and more particularly to a non-oriented electrical steel sheet in which crystal grains having a specific orientation are developed by controlling the thermal history during annealing of a hot-rolled sheet, thereby improving magnetic properties, 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 in order to achieve high efficiency in this process, they require excellent magnetic properties. In particular, as environmentally friendly automobiles that are driven by motors instead of internal combustion engines have recently gained attention, demand for non-oriented electrical steel sheets used as drive motor core materials has increased, resulting in 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 sheet 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 manufacture of more energy-efficient motors under the same conditions, while higher magnetic flux density allows for the manufacture of more compact motors or the reduction of copper loss. Therefore, non-oriented electrical steel sheet with low iron loss and high magnetic flux density can be used to manufacture drive motors with excellent efficiency and torque, thereby improving the mileage and power output of environmentally friendly automobiles.

[0004] The characteristics of non-oriented electrical steel sheets that must be considered also change depending on the operating conditions of the motor. The commonly used standard for evaluating the properties of non-oriented electrical steel sheets 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 environmentally friendly automobile drive motors, 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 often evaluated using W10 / 400 iron loss.

[0005] The most common method for improving the magnetic properties of non-oriented electrical steel sheets is to add alloying elements such as Si, Al, and Mn. The addition of these alloying elements increases the steel's resistivity, thereby 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, as the amount of alloying elements such as Si, Al, and Mn added increases, the magnetic flux density deteriorates and brittleness increases. Adding more than a certain amount of these elements makes cold rolling impossible, making commercial production impossible. In particular, the thinner the electrical steel sheet, the better its high-frequency iron loss becomes, and the reduced rollability due to brittleness becomes a critical issue. The maximum combined Si, Al, and Mn content that allows commercial production is known to be approximately 4.5%. By optimizing the amount of additional trace elements, the highest quality non-oriented electrical steel sheets with excellent magnetic properties and strength can be produced.

[0006] Depending on the motor design objective, electrical steel sheets with improved strength may be used, even if their magnetic properties are slightly degraded. Methods for manufacturing electrical steel sheets for such applications include precipitation of interstitial elements and grain size reduction. Rotors manufactured from electrical steel sheets with significantly improved strength, even if their magnetic properties are slightly degraded, are typically used when miniaturizing motors to 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 improves strength, it also has the disadvantage of rapidly degrading 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.

[0007] To solve these problems, attempts have been made to create non-oriented electrical steel sheets that have excellent both magnetic properties and strength by controlling the cooling rate during the cold-rolled sheet annealing process, but this has the problem of being difficult to apply to mass production due to increased material non-uniformity caused by the inclusion of unrecrystallized parts.Most of the technologies previously proposed to simultaneously improve magnetic properties and strength have not been put to use due to increased manufacturing costs, reduced productivity and yield, or insufficient improvement effects. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention provides a non-oriented electrical steel sheet and a manufacturing method thereof. Specifically, the present invention provides a non-oriented electrical steel sheet and a manufacturing method thereof in which crystal grains having a specific orientation are developed and magnetic properties are improved by controlling the thermal history during hot-rolled sheet annealing. [Means for solving the problem]

[0009] The non-oriented electrical steel sheet of the present invention is characterized by containing, by weight, 2.5 to 4.5% Si, 0.1 to 1.5% Al, 0.1 to 0.5% Mn, and the remainder being Fe and unavoidable impurities.

[0010] The non-oriented electrical steel sheet of the present invention has a {111} / / ND orientation fraction of 20 area % or less, where {111} / / ND means that the {111} plane of the crystal grain is parallel to the rolling surface (ND plane) and at an angle of 15° or less.

[0011] In the non-oriented electrical steel sheet of the present invention, when the texture is shown by ODF, the orientation with the highest strength is {001} <130> Located within 10 degrees of

[0012] The non-oriented electrical steel sheet of the present invention may further contain one or more of Sn, Sb, C, N, Ti, Nb, and V in an amount of 0.0050% by weight or less each.

[0013] The non-oriented electrical steel sheet of the present invention may further contain one or more of S: 0.0005 to 0.0050% by weight, Mg: 0.0025% by weight or less, and Cu: 0.01% by weight or less.

[0014] The non-oriented electrical steel sheet of the present invention may further contain one or more of P: 0.05 wt % or less, B: 0.002 wt % or less, Mo: 0.01 wt % or less, Cr: 0.5 wt % or less, and Zr: 0.005 wt % or less.

[0015] The non-oriented electrical steel sheet of the present invention may have an average grain size of 50 to 150 μm.

[0016] The non-oriented electrical steel sheet of the present invention has a distribution density of MgS precipitates with a diameter of 100 nm or less of 0.01 particles / μm 2 It may be the following:

[0017] The method for producing a non-oriented electrical steel sheet of the present invention is characterized by comprising the steps of: hot rolling a slab containing, by weight, 2.5 to 4.5% Si, 0.1 to 1.5% Al, 0.1 to 0.5% Mn, and the balance being Fe and unavoidable impurities to produce a hot-rolled sheet; hot-rolling the hot-rolled sheet to produce a cold-rolled sheet; and cold-rolling the hot-rolled sheet to produce a cold-rolled sheet.

[0018] The hot-rolled sheet annealing step includes a heating step of heating the hot-rolled sheet to a first soaking temperature (T1) of 980°C to 1100°C at a heating rate of 30°C / s or more, a first soaking step of maintaining the first soaking temperature (T1) within a 10°C range for 20 to 60 seconds, a cooling step of passing from the first soaking temperature (T1) to a second soaking temperature (T2) of 750°C to 850°C within 30 seconds, and a second soaking step of maintaining the second soaking temperature (T2) within a 10°C range for 30 to 90 seconds. The heating step can be carried out for 40 to 100 seconds.

[0019] The cold-rolled sheet annealing step can be carried out in an atmosphere of a mixed gas of hydrogen (H2) and nitrogen (N2) and having a dew point of 10°C or less.

[0020] The cold-rolled sheet annealing step may include a heating step in which heating is performed at a temperature increase rate of 25°C / s or more.

[0021] The cold-rolled sheet annealing step may include a soaking step of soaking at a soaking temperature of 900 to 1100°C. [Effects of the Invention]

[0022] The non-oriented electrical steel sheet of the present invention can have even better properties by optimizing the crystal orientation and improving the anisotropy of magnetic flux density. 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. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a graph showing a thermal history over time in a hot-rolled sheet annealing process according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] Terms such as "first," "second," and "third" are used to describe various portions, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one portion, component, region, layer, or section from another portion, component, region, layer, or section. Therefore, a first portion, component, region, layer, or section described below can be referred to as a second portion, component, region, layer, or section without departing from the scope of the present invention. The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. As used in the specification, the term "comprising" refers to the inclusion of certain features, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0025] When a part is referred to as being "on" or "above" another part, it means that it is directly on or above the other part, or there may be other parts between them. In contrast, when a part is referred to as being "directly on" another part, there are no other parts between them. Unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight. In one embodiment of the present invention, the inclusion of an additional element means that the remaining iron (Fe) is replaced by the additional amount of the additional element. 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.

[0026] Although the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein, the present invention will be described in detail below so that those skilled in the art can easily practice the present invention.

[0027] The non-oriented electrical steel sheet of the present invention contains, by weight, 2.5 to 4.5% Si, 0.1 to 1.5% Al, and 0.1 to 0.5% Mn.

[0028] The reasons for limiting the components of non-oriented electrical steel sheets will be explained below.

[0029] Si:2.5~4.5wt% Silicon (Si) increases the resistivity of the material, reduces iron loss, and increases strength through solid solution strengthening. If too little Si is added, the iron loss and strength improvement effects may be insufficient. If too much Si is added, the brittleness of the material increases, rolling productivity drops sharply, and a surface oxide layer and oxides that are harmful to magnetic properties may form. Therefore, Si may be contained in an amount of 2.5 to 4.5 wt. %. More specifically, it may be contained in an amount of 2.7 to 4.0 wt. More specifically, it may be contained in an amount of 3.0 to 3.7 wt.

[0030] Al: 0.1~1.5% by weight Aluminum (Al) increases the resistivity of the material, reduces iron loss, and increases strength through solid solution strengthening. If too little Al is added, fine nitrides are formed, making it difficult to achieve the magnetic improvement effect. 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, Al can be included at 0.1 to 1.5 wt. %. More specifically, it can be included at 0.3 to 1.2 wt. %. Even more specifically, it can be included at 0.5 to 1.0 wt. %.

[0031] Mn:0.1~0.5wt% Manganese (Mn) increases the resistivity of the material, improves iron loss, and forms sulfides. If too little Mn is added, fine sulfides are formed, causing magnetic deterioration. If too much Mn is added, fine MnS precipitates in large quantities, promoting the formation of a {111} texture that is unfavorable to magnetic properties and resulting in a rapid decrease in magnetic flux density. Therefore, Mn can be contained in an amount of 0.1 to 0.5 wt. %. More specifically, Mn can be contained in an amount of 0.2 to 0.4 wt. %.

[0032] The non-oriented electrical steel sheet of the present invention may further contain one or more of Sn, Sb, C, N, Ti, Nb, and V in an amount of 0.0050% by weight or less each.

[0033] One or more of Sn and Sb: 0.0050% by weight or less (excluding 0%) Tin (Sn) and antimony (Sb) preferentially segregate to grain boundaries, slowing the grain boundary segregation behavior of S and inducing surface defects due to excessive overall surface segregation. Therefore, in the present invention, it is advantageous to include small amounts of these elements in the steel composition. Excessive addition of Sn and Sb can cause surface defects. Therefore, at least one of Sn and Sb may be included in an amount of 0.0050 wt% or less. More specifically, each may be included in an amount of 0.0001 to 0.00050 wt%. Even more specifically, each may be included in an amount of 0.0010 to 0.0030 wt%.

[0034] C: 0.0050% by weight or less Carbon (C) causes magnetic aging and combines with other impurity elements to form carbides, which reduces magnetic properties, but it also hinders potential transfer and improves strength. If C is included in an excessive amount, the fraction of fine carbides increases, which can result in a deterioration of magnetic properties. Therefore, C can be contained in an amount of 0.0050 wt% or less. There is no particular lower limit for C, but considering productivity, it can be contained in an amount of 0.0010 wt% or more. That is, C can be contained in an amount of 0.0010 to 0.0050 wt%. More specifically, C can be contained in an amount of 0.0010 to 0.0030 wt%.

[0035] N: 0.0050% by weight or less Nitrogen (N) not only forms fine AlN precipitates inside the base material, but also combines with other impurities to form fine precipitates, suppressing grain growth and worsening iron loss. Therefore, N can be contained in an amount of 0.0050 wt% or less. There is no particular lower limit for N, but because N helps improve strength, the lower limit can be set to 0.0003 wt%. That is, N can be contained in an amount of 0.0003 to 0.0050 wt%. More specifically, N can be contained in an amount of 0.0010 to 0.0030 wt%.

[0036] Ti, Nb, V: 0.0050% by weight or less 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 deteriorating core loss. Therefore, the Ti, Nb, and V contents may each be 0.0050 wt.% or less. The lower limit is not particularly limited, but can be set to 0.0003 wt.% depending on steelmaking costs. That is, Ti, Nb, and V may each be contained in an amount of 0.0003 to 0.0050 wt.%. More specifically, Ti, Nb, and V may each be contained in an amount of 0.0003 to 0.0030 wt.%.

[0037] The non-oriented electrical steel sheet of the present invention may further contain one or more of S: 0.0005 to 0.0050% by weight, Mg: 0.0025% by weight or less, and Cu: 0.01% by weight or less.

[0038] S:0.0005~0.0050wt% Sulfur (S) forms fine precipitates, MnS and CuS, which deteriorate magnetic properties and hot workability. Therefore, S may be contained in an amount of 0.0050 wt% or less. However, in one embodiment of the present invention, S helps develop crystal grains with a specific orientation and improves magnetic flux density, so in one embodiment of the present invention, S may be added in an amount of 0.0005 wt% or more. More specifically, S may be contained in an amount of 0.0010 to 0.0030 wt%.

[0039] Mg: 0.0025% by weight or less Magnesium (Mg) is an element that mainly combines with S to form sulfides, which can affect the oxide layer on the surface of the base steel. Therefore, Mg can be contained in an amount of 0.0025 wt% or less. The lower limit is not particularly limited, but can be set to 0.0001 wt% depending on steelmaking costs. That is, Mg can be contained in an amount of 0.0001 to 0.0025 wt%. More specifically, Mg can be contained in an amount of 0.0005 to 0.0020 wt%.

[0040] Cu: 0.01% by weight or less Copper (Cu) acts to form sulfides with Mn. If Cu is added in an excessively small amount, fine CuMnS precipitates, which can deteriorate magnetic properties. If Cu is added in an excessively large amount, high-temperature brittleness occurs, which can lead to cracks during continuous casting or hot rolling. More specifically, Cu can be contained in an amount of 0.001 to 0.01 wt%.

[0041] The non-oriented electrical steel sheet of the present invention may further contain one or more of P: 0.05 wt % or less, B: 0.002 wt % or less, Mo: 0.01 wt % or less, Cr: 0.5 wt % or less, and Zr: 0.005 wt % or less.

[0042] P: 0.050% by weight or less Phosphorus (P) deteriorates hot workability and reduces productivity rather than improving magnetic properties. Therefore, P can be contained in an amount of 0.050 wt.% or less. There is no particular lower limit, but it can be 0.005% because P segregates at the surface and grain boundaries of the steel sheet to suppress surface oxidation during annealing, hinders element diffusion through grain boundaries, and hinders recrystallization in the {111} / / ND orientation, thereby improving the texture. That is, P can be contained in an amount of 0.005 to 0.050 wt.%.

[0043] B: 0.002% by weight or less Adding excessive amounts of boron (B) can cause deterioration of magnetic properties through the formation of inclusions in the steel. Therefore, B can be contained in an amount of 0.002 wt% or less. The lower limit is not particularly limited, but can be set to 0.0001 wt% depending on steelmaking costs. In other words, B can be contained in an amount of 0.0001 to 0.0020 wt%.

[0044] Mo: 0.01% by weight or less If added in excess, molybdenum (Mo) may inhibit the segregation of Sn and P, reducing the texture improvement effect. Therefore, Mo can be contained in an amount of 0.01 wt% or less. There is no particular lower limit, but Mo can be contained in an amount of 0.001 wt% or more because it segregates to the surface and grain boundaries to improve the texture. In other words, Mo can be contained in an amount of 0.001 to 0.010 wt%.

[0045] Cr: 0.50% by weight or less Chromium (Cr) plays a role in increasing resistivity 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 included in an amount of 0.01 to 0.10 wt %.

[0046] Zr: 0.005% by weight or less Adding excessive amounts of zirconium (Zr) can cause deterioration of magnetic properties through the formation of inclusions in the steel. Therefore, Zr can be contained in an amount of 0.005 wt% or less. The lower limit is not particularly limited, but can be set to 0.0001 wt% depending on steelmaking costs. In other words, Zr can be contained in an amount of 0.0001 to 0.0050 wt%.

[0047] The balance is composed of Fe and unavoidable impurities. The unavoidable impurities are impurities that are mixed in during the steelmaking stage and the manufacturing process of the non-oriented electrical steel sheet, 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 as a substitute for the balance Fe.

[0048] The non-oriented electrical steel sheet of the present invention may have an average grain size of 50 to 150 μm. When an appropriate average grain size is ensured, magnetic properties can be improved. In particular, high-frequency iron loss can be improved. In the present invention, the grain size refers to the diameter of a virtual circle having the same area as the grain area. The average grain size is calculated by 2 × (measured area ÷ number of grains ÷ π). 0.5 The grain size can be measured based on the rolling plane (TD plane). The measurement position is not particularly limited, but can be measured at a point 1 / 4 to 3 / 4 of the way through the entire thickness of the steel sheet. More specifically, the average grain size may be 60 to 95 μm.

[0049] The non-oriented electrical steel sheet of the present invention has a distribution density of MgS precipitates with a diameter of 100 nm or less of 0.01 particles / μm 2 It may be the following: MgS precipitates with a diameter of 100 nm or less segregate at grain boundaries, reducing the effective content of S, which improves texture, significantly reducing the texture improvement effect and adversely affecting magnetic properties. Therefore, it is advantageous to minimize their size. MgS precipitates refer to particles formed by the aggregation and precipitation of Mg and S, and refer to areas with higher Mg and S contents than the base level of the steel sheet. Precipitates can be measured using a transmission electron microscope (TEM). The diameter of an imaginary circle is assumed to represent the same as the grain size, and can be measured based on the rolling plane (TD plane). There is no particular lower limit for the diameter of precipitates, but it can be as low as 1 nm depending on the measurement limit. MgS precipitates exceeding 100 nm are coarse and do not significantly affect magnetic properties, so there is no particular limit. The distribution density of MgS precipitates is more specifically 0.001 to 0.007 particles / μm 2 may be.

[0050] The non-oriented electrical steel sheet of the present invention has an area fraction of {111} / / ND orientation of 20% or less, where {111} / / ND refers to crystal grains whose {111} planes are parallel to the rolling surface (ND plane) and within 15° of each other. As the {111} / / ND orientation fraction increases, the magnetocrystalline anisotropy energy increases, requiring more energy for magnetization, resulting in poor magnetic properties. Therefore, it is necessary to reduce the {111} / / ND fraction. The {111} / / ND fraction can be measured by EBSD over a sufficiently large area containing more than 10,000 crystal grains. More specifically, the {111} / / ND orientation fraction may be 3 to 16%.

[0051] In the non-oriented electrical steel sheet of the present invention, when the texture is shown by ODF, the orientation with the highest strength is {001} <130> This is located within 10 degrees of {001} <130> This means that a large amount of crystal grains with orientations close to {001} were formed. <130> is the orientation with the best circularly averaged magnetism, and among them, it has low anisotropy, which helps to exhibit excellent magnetism uniformly in all directions. The orientation with the highest strength can be confirmed by displaying the data measured by EBSD in ODF. More specifically, the orientation with the highest strength is {001} <130> It is positioned within a 2° to 8° range from the

[0052] The non-oriented electrical steel sheet of the present invention has excellent anisotropy of magnetic flux density and excellent high-frequency iron loss. When using the non-oriented electrical steel sheet of the present invention to manufacture environmentally friendly automobile drive motors, it is advantageous because it has uniformly excellent magnetic properties in all directions in the plane without adding elements such as Sn and Sb.

[0053] Specifically, the iron loss (W 10 / 400 ) is 13.5W / kg or less at a thickness of 0.25mm, and the magnetic flux density (B 50(90°) ) is 1.64T or more, and the magnetic flux density (B 50(55°) ) is 1.63T or more, and B50(55°) / B50(90°) can be 0.98 or more. Iron loss (W 10 / 400) is the iron loss when a magnetic flux density of 1.0T is induced at a frequency of 400Hz. 50 ) is the magnetic flux density induced in a magnetic field of 5000 A / m. More specifically, the iron loss (W 10 / 400 ) was 10.0 to 13.3 W / kg, and the magnetic flux density (B 50(90°) ) is 1.64 to 1.67 T, and the magnetic flux density (B 50(55°) ) is 1.63~1.66T, and B50(55°) / B50(90°) can be 0.990~0.999.

[0054] The method for producing a non-oriented electrical steel sheet of the present invention includes the steps of hot rolling a slab to produce a hot-rolled sheet, hot-rolling the hot-rolled sheet to produce a cold-rolled sheet, and cold-rolling the cold-rolled sheet to produce a cold-rolled sheet. First, the slab is hot rolled. The alloy composition of the slab has been explained in the alloy composition of the non-oriented electrical steel sheet, so a duplicate explanation will be omitted. Since the alloy composition does not substantially change during the manufacturing process of the non-oriented electrical steel sheet, the alloy composition of the non-oriented electrical steel sheet and the slab is substantially the same.

[0055] Specifically, the slab contains, by weight, 2.5 to 4.5% Si, 0.1 to 1.5% Al, 0.1 to 0.5% Mn, and the remainder Fe and unavoidable impurities. Other additional elements have been explained in the alloy components of the non-oriented electrical steel sheet, so a duplicate explanation will be omitted.

[0056] 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 1200°C or less. If the slab heating temperature is too high, precipitates such as AlN and MnS present in the slab will re-dissolve and then finely precipitate during hot rolling and annealing, which may inhibit grain growth and reduce magnetic properties.

[0057] Next, the slab is hot-rolled to produce a hot-rolled sheet. The thickness of the hot-rolled sheet may be 1.8 to 2.3 mm. In the step of producing the hot-rolled sheet, the finish rolling temperature may be 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 is manufactured, it is annealed. Figure 1 is a graph showing a schematic time-dependent thermal history in the hot-rolled sheet annealing process.

[0058] As shown in FIG. 1, the hot-rolled sheet annealing step includes a heating step of heating the hot-rolled sheet to a first soaking temperature (T1) of 980°C to 1100°C at a heating rate of 30°C / s or more, a first soaking step of maintaining the first soaking temperature (T1) within a 10°C range for 20 to 60 seconds, a cooling step of passing from the first soaking temperature (T1) to a second soaking temperature (T2) of 750°C to 850°C within 30 seconds, and a second soaking step of maintaining the second soaking temperature (T2) within a 10°C range for 30 to 90 seconds.

[0059] Here, the temperature at each stage means the temperature of the steel sheet surface at each stage. The hot-rolled sheet is heated to a first soaking temperature (T1) of 980°C to 1100°C at a heating rate of 30°C / s or more. Rapidly heating the hot-rolled sheet at a heating rate of 30°C / s or more helps improve the texture. More specifically, the temperature can be raised at a heating rate of 35 to 150°C / s. It is also possible to heat the sheet to a first soaking temperature (T1) or higher and then cool it to the first soaking temperature (T1). The heating step can be carried out for 40 to 100 seconds from an initial temperature of 10 to 50°C. At this time, the temperature increase rate may be an average temperature increase rate per time from the initial temperature to the final temperature. At temperatures below the initial temperature, the temperature can be increased at a general rate of less than 30°C / s, followed by a rapid increase in temperature.

[0060] Next, in the first soaking step, the first soaking temperature (T1) is maintained within a 10°C range for 20 to 60 seconds. The first soaking temperature (T1) may be any temperature between 980°C and 1100°C, and annealing can be performed for 20 to 60 seconds while maintaining a constant temperature within a 10°C range. If the first soaking temperature is too low or the time is too short, the grains may not grow sufficiently, and the {111} / / ND orientation may develop strongly during the recrystallization annealing step after cold rolling, resulting in a deterioration in magnetic properties. If the first soaking temperature is too high or the time is too long, the {001} orientation may develop strongly during the recrystallization annealing step after cold rolling, resulting in a deterioration in magnetic properties. <130> The magnetic orientation may develop far away from the target temperature, resulting in deterioration of the magnetic property. More specifically, the first soaking temperature (T1) is 1000°C to 1050°C, and can be maintained for 30 to 50 seconds. The temperature can be maintained within a 5°C range from the first soaking temperature.

[0061] Next, in the cooling step, the material is cooled from the first soaking temperature (T1) to the second soaking temperature (T2) of 750°C to 850°C within 30 seconds. If the cooling step time is too long, the texture may not be improved sufficiently. More specifically, the cooling step can be performed for 5 to 20 seconds. Next, in the second soaking step, the second soaking temperature (T2) is maintained within a 10°C range of 750°C to 850°C for 30 to 90 seconds. If the second soaking temperature is too low or the time is too short, S may not be sufficiently segregated to the grain boundaries, resulting in a decrease in the texture improvement effect. If the second soaking temperature is too high or the time is too long, fine MgS precipitates may form, resulting in a deterioration in magnetic properties. More specifically, the second soaking temperature (T2) is 780°C to 830°C, and can be maintained for 45 to 80 seconds. It can be maintained within a 5°C range from the second soaking temperature. After the second soaking step, the mixture is cooled as necessary.

[0062] Next, the hot-rolled sheet is cold-rolled to produce a cold-rolled sheet. The cold rolling is performed as a final rolling to a thickness of 0.1 mm to 0.35 mm. In the cold rolling step, the reduction ratio can be adjusted to 85% or more. More specifically, the reduction ratio can be 85 to 95%. If the reduction ratio is too low, thickness variations in the width direction of the steel sheet may occur.

[0063] Next, the cold-rolled sheet is annealed. The cold-rolled sheet annealing step can be performed in an atmosphere containing a mixed gas of hydrogen (H2) and nitrogen (N2) and having a dew point of 10°C or less. Annealing in an atmosphere with a low dew point can suppress surface oxidation and promote surface segregation of S, thereby forming an excellent texture throughout the entire thickness. More specifically, the dew point can be -10 to -50°C. Even more specifically, it can be -15 to -45°C. The mixed gas can contain 40% or less by volume of hydrogen and 60% or more by volume of nitrogen. The same atmosphere can be used in the heating step and soaking step described below.

[0064] The cold-rolled sheet annealing step includes a heating step in which the sheet is heated from a starting temperature of 20 to 50°C to a soaking temperature at a temperature increase rate of 25°C / s or more. The texture can be improved by rapidly increasing the temperature during the cold-rolled sheet annealing. More specifically, the temperature can be increased at a temperature increase rate of 35 to 150°C / s. The cold-rolled sheet annealing step may include a soaking step at a soaking temperature of 900 to 1100°C. If the soaking temperature is too low, the grains may not grow sufficiently or the deformed structure may remain, resulting in poor core loss. If the soaking temperature is too high, the eddy current loss increases and the {001} <130> The orientation may decrease, and the magnetic properties may deteriorate. More specifically, the soaking temperature may be 950 to 1050°C. Annealing may be performed at the soaking temperature for 30 to 50 seconds. During the annealing process of the cold-rolled sheet, all (i.e., 99% or more) of the worked structure formed during the cold rolling stage is recrystallized.

[0065] After annealing the cold-rolled sheet, an insulating coating can be formed. The insulating coating can be organic, inorganic, or organic-inorganic composite coating, or it can be other insulating coating agents.

[0066] The present invention will be described in more detail below through examples, but these examples are merely for illustrative purposes and are not intended to limit the scope of the present invention. [Example]

[0067] Slabs were produced from the components shown in Tables 1 and 2, with the balance consisting of Fe and unavoidable impurities. These were heated to 1150°C and hot rolled at a finishing temperature of 880°C to produce hot-rolled sheets with a thickness of 2.0 m. The hot-rolled sheets were subjected to first and second hot-rolled annealing under the conditions in Table 3 below, and then cold-rolled to a thickness of 0.25 mm. These were then cold-rolled under the conditions in Table 4. Average grain diameter, MgS precipitate density of 100 nm or less, {111} / / ND orientation fraction, {001} <130> The angle differences are summarized in Table 4.

[0068] The average grain size of the crystal grains was measured by polishing the TD cross section of the specimen to 100 mm 2 After measuring with EBSD to obtain the above area, the average number and area fraction values ​​were used, which were merged using the Merge function of the OIM software and calculated using the Grain Size (diameter) function. The density of MgS precipitates less than 100 nm was measured by replicating the final annealed sheet to prepare a TEM specimen. 2 Among the precipitates that appear when observing the above areas with a TEM, the number of precipitates for which the length of the longest line segment across the shape is 100 nm or less and for which peaks for Mg and S appear simultaneously when the components are analyzed with EDS was divided by the measured area to obtain the area.

[0069] The {111} / / ND orientation fraction was measured by EBSD measurement data using OIM software, with the ND error angle being within 15 degrees. <111> When a partition is generated to have a direction, the fractional value shown in the partition summary information is used. {001} <130> The angle difference was calculated by calculating the ODF from the EBSD data to determine the orientation with the maximum intensity, and then comparing the orientation with {001} <130> The misorientation value with respect to the direction was calculated. For magnetic properties such as magnetic flux density and iron loss, five 60mm wide x 60mm long specimens were cut from each specimen, and iron loss was measured using a single sheet tester in the rolling direction and perpendicular to the rolling direction, with the average value being shown. Magnetic flux density was measured in the direction perpendicular to the rolling direction and at a 55° angle to the rolling direction. At this time, W 10 / 400 is the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz, and B 50 means the magnetic flux density induced in a magnetic field of 5000 A / m.

[0070] [Table 1]

[0071] [Table 2]

[0072] [Table 3]

[0073] [Table 4]

[0074] [Table 5]

[0075] As shown in Tables 1 to 5, when the annealing temperature and time of the hot-rolled sheet are appropriately adjusted, the {001} <130> It can be seen that the crystal orientation is developed, the magnetic flux density and iron loss are excellent, and the anisotropy of the magnetic flux density is excellent. On the other hand, if the temperature and time during annealing of the hot-rolled sheet are not properly controlled, the {001} <130> It can be seen that the crystal orientation is small, the magnetic flux density and core loss are relatively poor, and the anisotropy of the magnetic flux density is relatively poor.

[0076] The present invention is not limited to the examples, and can be manufactured in various different forms, and it should be understood by those skilled in the art 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-described examples are illustrative in all respects and not limiting.

Claims

1. In weight percent, Si: 2.5 to 4.5%, Al: 0.1 to 1.5%, Mn: 0.1 to 0.5%, and the balance being Fe and unavoidable impurities; The {111} / / ND orientation fraction is 20 area % or less, where {111} / / ND means that the {111} plane of the crystal grain is parallel to the rolling surface (ND plane) and within 15°; A non-oriented electrical steel sheet characterized in that, when the texture is expressed as ODF, the orientation having the highest strength is located within 10° from {001}<130>.

2. 2. The non-oriented electrical steel sheet according to claim 1, further comprising at most 0.0050 wt. % of one or more of Sn, Sb, C, N, Ti, Nb, and V.

3. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of S: 0.0005 to 0.0050 wt %, Mg: 0.0025 wt % or less, and Cu: 0.01 wt % or less.

4. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of P: 0.05 wt% or less, B: 0.002 wt% or less, Mo: 0.01 wt% or less, Cr: 0.5 wt% or less, and Zr: 0.005 wt% or less.

5. 2. The non-oriented electrical steel sheet according to claim 1, wherein the average grain size is 50 to 150 μm.

6. The distribution density of MgS precipitates with a diameter of 100 nm or less is 0.01 particles / μm ２ 2. The non-oriented electrical steel sheet according to claim 1, wherein:

7. a step of producing a hot-rolled sheet by hot-rolling a slab consisting of, in weight percent, 2.5 to 4.5% Si, 0.1 to 1.5% Al, 0.1 to 0.5% Mn, and the balance being Fe and unavoidable impurities; annealing the hot-rolled sheet; cold-rolling the hot-rolled sheet to produce a cold-rolled sheet; and annealing the cold-rolled sheet; The step of annealing the hot-rolled sheet comprises: The hot-rolled sheet is heated to a first soaking temperature (T １ ) heating stage, The first soaking temperature (T １ a first soaking step of maintaining the temperature within a 10°C range of 20 to 60 seconds; The first soaking temperature (T １ ) to a second soaking temperature (T ２ ) a cooling step in 30 seconds or less; The second soaking temperature (T ２ ) in a 10°C range for 30 to 90 seconds.

8. 8. The method for manufacturing a non-oriented electrical steel sheet according to claim 7, wherein the heating step is performed for 40 to 100 seconds.

9. The cold-rolled sheet annealing step is carried out using hydrogen (H ２ ) and nitrogen (N ２ 8. The method for producing a non-oriented electrical steel sheet according to claim 7, wherein the heating is carried out in an atmosphere of a mixed gas of the above-mentioned components (a) and (b) having a dew point of 10° C. or less.

10. The method for manufacturing a non-oriented electrical steel sheet according to claim 7, wherein the cold-rolled sheet annealing step includes a heating step of heating at a temperature rising rate of 25°C / s or more.

11. The method for manufacturing a non-oriented electrical steel sheet according to claim 7, wherein the cold-rolled sheet annealing step includes a soaking step of soaking at a soaking temperature of 900 to 1100°C.

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