Non-oriented electrical steel sheet and method for producing same

Abstract

A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, in wt%, 2.5 to 4.5% of Si, 0.1 to 1.5% of Al, and 0.1 to 0.5% of Mn, with the remainder comprising Fe and unavoidable impurities. The non-oriented electrical steel sheet according to one embodiment of the present invention has an orientation from {001} lt; 130gt, 130gt; and the angle is within 10 degrees.

Description

Technical Field

[0001] One embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same, which adjusts the thermal history during hot-rolled sheet annealing to develop grains with a specific orientation, thereby improving the magnetic properties. Background Art

[0002] Non-oriented electrical steel sheets are mainly used in motors that convert electrical energy into mechanical energy. In order to achieve high efficiency during the conversion process, non-oriented electrical steel sheets are required to have excellent magnetic properties. In particular, in recent years, as environmentally friendly vehicles that use motors instead of internal combustion engines have received attention, the demand for non-oriented electrical steel sheets used as core materials for drive motors has been increasing. Therefore, non-oriented electrical steel sheets that simultaneously have excellent magnetic properties and strength are needed.

[0003] The magnetic properties of non-oriented electrical steel are mainly 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, and magnetic flux density refers to the degree of magnetization obtained under a specific magnetic field. The lower the iron loss, the higher the energy efficiency of the motor that can be manufactured under the same conditions. The higher the magnetic flux density, the smaller the motor size or the lower the copper loss. Therefore, by using non-oriented electrical steel sheets with low iron loss and high magnetic flux density, a drive motor with excellent efficiency and torque can be manufactured, thereby improving the driving range and output of environmentally friendly vehicles.

[0004] According to the operating conditions of the motor, the characteristics of the non-oriented electrical steel sheet that need to be considered also change. As a conventional standard for evaluating the characteristics of non-oriented electrical steel sheets used in motors, the iron loss W15 / 50 when a magnetic field of 1.5 T is applied at a commercial frequency of 50 Hz is widely adopted. However, in non-oriented electrical steel sheets with a thickness of 0.35 mm or less used for environmentally friendly vehicle drive motors, the magnetic properties at a low magnetic field of 1.0 T or less and a high frequency of 400 Hz or more are often more important. Therefore, in many cases, the characteristics of non-oriented electrical steel sheets are evaluated by the W10 / 400 iron loss.

[0005] In order to improve the magnetic properties of non-oriented electrical steel sheets, the commonly adopted method is to add alloying elements such as Si, Al, and Mn. By adding these alloying elements, when the resistivity of the steel increases, the eddy current loss will decrease, thereby reducing the total iron loss. In addition, the alloying elements dissolve in iron as substitutional elements to exert a strengthening effect, thus improving the strength. On the other hand, as the addition amount of alloying elements such as Si, Al, and Mn increases, the magnetic flux density deteriorates, and there is a drawback of increased brittleness. If the addition amount exceeds a certain level, cold rolling cannot be carried out, and thus commercial production cannot be carried out. In particular, for electrical steel sheets, the thinner the thickness, the better the high-frequency iron loss, and the decrease in rollability caused by brittleness becomes a fatal problem. It is known that the maximum value of the sum of the Si, Al, and Mn contents that can be commercially produced is about 4.5%. In addition, by optimizing the trace element content, the highest-grade non-oriented electrical steel sheets with excellent magnetic properties and strength can be produced.

[0006] According to the design intention of the motor, sometimes electrical steel sheets with slightly worse magnetic properties but improved strength are used. There are two methods for manufacturing electrical steel sheets for this purpose. One is the method using the precipitation of interstitial elements, and the other is the method of reducing the grain size. When mainly improving the rotational speed by miniaturizing the motor or enhancing the effect of the permanent magnet inserted into the rotor, a rotor made of electrical steel sheets with slightly worse magnetic properties but significantly improved strength is used. At this time, if fine precipitates containing interstitial solid solution elements such as C, N, and S are formed, the strength improvement effect is good, but the iron loss deteriorates sharply, and there is a drawback of a decrease in motor efficiency. In addition, for the method of reducing the grain size, the drawback is that the non-recrystallized part is mixed in, resulting in an increase in the non-uniformity of the steel sheet material, and there is a drawback of a larger quality deviation in the mass-produced products.

[0007] In order to solve the above problems, attempts have been made to manufacture non-oriented electrical steel sheets with excellent magnetic properties and strength at the same time by controlling the cooling rate of the cold-rolled sheet annealing process. However, due to the increase in material non-uniformity caused by the mixing of the non-recrystallized part, there is a problem that it is difficult to apply to the mass production process. In addition, in order to improve the magnetic properties and strength at the same time, most of the currently proposed technologies have not been adopted due to increased manufacturing costs, decreased productivity and yield, and poor improvement effects. Summary of the Invention

[0008] (I) Technical Problems to be Solved

[0009] An embodiment of the present invention aims to provide a non-oriented electrical steel sheet and a manufacturing method thereof. Specifically, an embodiment of the present invention aims to provide a non-oriented electrical steel sheet and a manufacturing method thereof, by adjusting the thermal history during hot-rolled sheet annealing, enabling the development of grains with a specific orientation, thereby improving the magnetic properties.

[0010] (II) Technical Solutions

[0011] The non-oriented electrical steel sheet according to an embodiment of the present invention contains, by weight %, Si: 2.5 to 4.5%, Al: 0.1 to 1.5%, Mn: 0.1 to 0.5%, and the balance contains Fe and inevitable impurities.

[0012] The non-oriented electrical steel sheet according to an embodiment of the present invention, wherein the {111} / / ND orientation fraction is 20 area % or less. Here, {111} / / ND refers to grains in which the {111} plane of the grains is parallel to the rolling plane (ND plane) within 15°.

[0013] The non-oriented electrical steel sheet according to an embodiment of the present invention, wherein when the texture is represented by ODF, the orientation with the highest strength is within 10° from {001}<130>.

[0014] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of Sn, Sb, C, N, Ti, Nb, and V, and their contents are each 0.0050% by weight or less.

[0015] The non-oriented electrical steel sheet according to an embodiment 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.

[0016] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of P: 0.05% by weight or less, B: 0.002% by weight or less, Mo: 0.01% by weight or less, Cr: 0.5% by weight or less, and Zr: 0.005% by weight or less.

[0017] The average grain size of the non-oriented electrical steel sheet according to an embodiment of the present invention may be 50 to 150 μm.

[0018] The non-oriented electrical steel sheet according to an embodiment of the present invention, wherein the distribution density of MgS precipitates having a diameter of 100 nm or less may be 0.01 pieces / μm 2 or less.

[0019] The manufacturing method of the non-oriented electrical steel sheet according to an embodiment of the present invention includes: a step of hot rolling a slab to manufacture a hot rolled sheet, wherein the slab contains, by weight %, Si: 2.5 to 4.5%, Al: 0.1 to 1.5%, Mn: 0.1 to 0.5%, and the balance contains Fe and inevitable impurities; a step of annealing the hot rolled sheet; a step of cold rolling the hot rolled sheet to manufacture a cold rolled sheet; and a step of annealing the cold rolled sheet.

[0020] The annealing process of 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 / second (s) or more; a first soaking step of maintaining within a range of 10°C of the first soaking temperature (T1) 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; a second soaking step of maintaining within a range of 10°C of the second soaking temperature (T2) for 30 to 90 seconds.

[0021] The heating step can be carried out for 40 to 100 seconds.

[0022] The annealing process of the cold-rolled sheet can be carried out in an environment of a mixed gas of hydrogen (H2) and nitrogen (N2) and a dew point temperature of -10°C or lower.

[0023] The annealing process of the cold-rolled sheet can include a heating step of heating at a heating rate of 25°C / second or more.

[0024] The annealing process of the cold-rolled sheet can include a soaking step of soaking at a soaking temperature of 900 to 1100°C.

[0025] (III) Beneficial Effects

[0026] For the non-oriented electrical steel sheet according to an embodiment of the present invention, by optimizing the crystal orientation to improve the anisotropy of the magnetic flux density, more excellent properties can be achieved.

[0027] Ultimately, the non-oriented electrical steel sheet according to an embodiment of the present invention contributes to the manufacture of motors for environmentally friendly vehicles, motors for high-efficiency household appliances, and ultra-high-end electric motors. Description of the Drawings

[0028] Figure 1 is a graph schematically showing the thermal history over time in the annealing process of the hot-rolled sheet according to an embodiment of the present invention. Detailed Description of the Embodiment

[0029] The terms first, second, third, etc. are used to describe various parts, components, regions, layers, and / or segments, but these parts, components, regions, layers, and / or segments should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, or segment from another part, component, region, layer, or segment. Therefore, without departing from the scope of the present invention, the first part, component, region, layer, or segment described below can also be described as the second part, component, region, layer, or segment.

[0030] The terms used in this document are only for describing specific embodiments and are not intended to limit the present invention. Unless the context clearly indicates the contrary, the singular forms used herein are also intended to include the plural forms. The term "comprising" used in the specification may specifically refer to a certain property, field, integer, step, action, element, and / or component, but does not exclude the existence or addition of other properties, fields, integers, steps, actions, elements, and / or components.

[0031] If a part is described as being above another part, there may be other parts directly above or between the other parts. When a part is described as being directly above another part, there are no other parts therebetween.

[0032] In addition, unless otherwise specifically stated, % means weight %, and 1 ppm is 0.0001 weight %.

[0033] In one embodiment of the present invention, further comprising an additional element means that the additional element replaces the remaining iron (Fe), and the replacement amount is equivalent to the added amount of the additional element.

[0034] Although not otherwise defined, the meanings of all terms used herein (including technical terms and scientific terms) are the same as those commonly understood by those of ordinary skill in the art to which the present invention pertains. For terms defined in a dictionary, they should be interpreted as having a meaning consistent with the relevant technical literature and the content disclosed herein, and should not be interpreted in an idealized or overly formal sense.

[0035] Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement the present invention. However, the present invention can be implemented in various different ways and is not limited to the embodiments described herein.

[0036] An non-oriented electrical steel sheet according to an embodiment of the present invention, in weight %, comprises Si: 2.5 to 4.5%, Al: 0.1 to 1.5%, and Mn: 0.1 to 0.5%.

[0037] The reasons for the composition limitations of the non-oriented electrical steel sheet are described below.

[0038] Si: 2.5 to 4.5 wt%

[0039] Silicon (Si) plays a role in increasing the resistivity of the material to reduce iron loss and improving strength through solid solution strengthening. If too little Si is added, the improvement effects of iron loss and strength may be insufficient. If too much Si is added, the brittleness of the material increases, the rolling productivity drops sharply, and a surface oxidation layer and oxides harmful to magnetism may be formed. Therefore, Si can be contained in an amount of 2.5 to 4.5% by weight. More specifically, it can be contained in an amount of 2.7 to 4.0% by weight. More specifically, it can be contained in an amount of 3.0 to 3.7% by weight.

[0040] Al: 0.1 to 1.5% by weight

[0041] Aluminum (Al) plays a role in increasing the resistivity of the material to reduce iron loss and improving strength through solid solution strengthening. If too little Al is added, fine nitrides are formed, and it may be difficult to obtain the effect of magnetic improvement. If too much Al is added, excessive formation of nitrides occurs, leading to magnetic deterioration, problems in all processes such as steelmaking and continuous casting, and the productivity may drop significantly. Therefore, Al can be contained in an amount of 0.1 to 1.5% by weight. More specifically, it can be contained in an amount of 0.3 to 1.2% by weight. More specifically, it can be contained in an amount of 0.5 to 1.0% by weight.

[0042] Mn: 0.1 to 0.5% by weight

[0043] Manganese (Mn) plays a role in increasing the resistivity of the material to improve iron loss and forming sulfides. If too little Mn is added, fine sulfides are formed, leading to magnetic deterioration. If too much Mn is added, excessive precipitation of fine MnS occurs, promoting the formation of a {111} texture unfavorable to magnetism, resulting in a sharp decrease in magnetic flux density. Therefore, Mn can be contained in an amount of 0.1 to 0.5% by weight. More specifically, it can be contained in an amount of 0.2 to 0.4% by weight.

[0044] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of Sn, Sb, C, N, Ti, Nb, and V, and their contents are each 0.0050% by weight or less.

[0045] One or more of Sn and Sb: each 0.0050% by weight or less and excluding 0%

[0046] Tin (Sn) and antimony (Sb) preferentially segregate at grain boundaries, slowing down the grain boundary segregation behavior of S, and excessive surface segregation leads to surface defects. Therefore, in one embodiment of the present invention, it is advantageous to contain a small amount of Sn and Sb in the steel composition. If too much Sn and Sb are added, surface defects may occur. Therefore, one or more of Sn and Sb can each be contained in an amount of 0.0050 wt% or less. More specifically, they can each be contained in an amount of 0.0001 to 0.00050 wt%. More specifically, they can each be contained in an amount of 0.0010 to 0.0030 wt%.

[0047] C: 0.0050 wt% or less

[0048] Carbon (C) causes magnetic aging, combines with other impurity elements to form carbides, which in turn leads to a decrease in magnetic properties or hinders dislocation movement, thereby increasing strength. If the C content is too high, the fraction of fine carbides increases, which may cause magnetic deterioration. Therefore, C can be contained in an amount of 0.0050 wt% or less. The lower limit of C is not particularly limited, 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, it can be contained in an amount of 0.0010 to 0.0030 wt%.

[0049] N: 0.0050 wt% or less

[0050] Nitrogen (N) not only forms fine AlN precipitates inside the base metal, but also combines with other impurities to form fine precipitates, which in turn inhibits grain growth, leading to deterioration of iron loss. Therefore, N can be contained in an amount of 0.0050 wt% or less. The lower limit of N is not particularly limited, but since N helps to increase strength, the lower limit can be 0.0003 wt%. That is, N can be contained in an amount of 0.0003 to 0.0050 wt%. More specifically, it can be contained in an amount of 0.0010 to 0.0030 wt%.

[0051] Ti, Nb, V: Each is 0.0050 wt% or less

[0052] Titanium (Ti), niobium (Nb), and vanadium (V) have a strong tendency to form precipitates in steel, and fine carbides, nitrides, or sulfides are formed inside the base metal, which in turn inhibits grain growth and magnetic domain wall movement, leading to deterioration of iron loss. Therefore, the contents of Ti, Nb, and V can each be 0.0050 wt% or less, and their lower limits are not particularly limited, but due to steelmaking costs, they can be 0.0003 wt%. That is, Ti, Nb, and V can each be contained in an amount of 0.0003 to 0.0050 wt%. More specifically, Ti, Nb, and V can each be contained in an amount of 0.0003 to 0.0030 wt%.

[0053] The non-oriented electrical steel sheet according to an embodiment 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.

[0054] S: 0.0005 to 0.0050% by weight

[0055] Sulfur (S) forms fine precipitates MnS and CuS, resulting in deterioration of magnetic properties and hot rolling workability. Therefore, S may be contained at 0.0050% by weight or less. However, in an embodiment of the present invention, it helps in the development of grains with a specific orientation and also helps in increasing the magnetic flux density. Therefore, in an embodiment of the present invention, 0.0005% by weight or more may be added. More specifically, S may be contained at 0.0010 to 0.0030% by weight.

[0056] Mg: 0.0025% by weight or less

[0057] Magnesium (Mg) is an element that mainly combines with S to form sulfides and may affect the oxide layer on the surface of the base iron. Therefore, Mg may be contained at 0.0025% by weight or less, and its lower limit is not particularly limited, but due to the steelmaking cost, it may be 0.0001% by weight. That is, Mg may be contained at 0.0001 to 0.0025% by weight. More specifically, it may be contained at 0.0005 to 0.0020% by weight.

[0058] Cu: 0.01% by weight or less

[0059] Copper (Cu) plays a role in forming sulfides together with Mn. When further adding Cu, if too little is added, fine precipitation of CuMnS may occur, leading to magnetic deterioration. If too much Cu is added, high-temperature brittleness will occur, and cracks may form during continuous casting or hot rolling. More specifically, Cu may be contained at 0.001 to 0.01% by weight.

[0060] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of P: 0.05% by weight or less, B: 0.002% by weight or less, Mo: 0.01% by weight or less, Cr: 0.5% by weight or less, and Zr: 0.005% by weight or less.

[0061] P: 0.050% by weight or less

[0062] Phosphorus (P) deteriorates the hot rolling process characteristics and reduces productivity compared to magnetic improvement. Therefore, P can be contained at 0.050 wt% or less. Its lower limit is not particularly restricted, but due to segregation at the surface and grain boundaries of the steel plate, it suppresses surface oxidation during annealing, thereby hindering the diffusion of elements through the grain boundaries and the recrystallization of the {111} / / ND orientation, and also plays a role in improving the texture. Therefore, it can be 0.005%. That is to say, P can be contained at 0.005 to 0.050 wt%.

[0063] B: 0.002 wt% or less

[0064] If an excessive amount of boron (B) is added, it may cause magnetic deterioration due to the formation of inclusions in the steel. Therefore, B can be contained at 0.002 wt% or less. Its lower limit is not particularly restricted, but due to the steelmaking cost, it can be 0.0001 wt%. That is to say, B can be contained at 0.0001 to 0.0020 wt%.

[0065] Mo: 0.01 wt% or less

[0066] If an excessive amount of molybdenum (Mo) is added, it suppresses the segregation of Sn and P and may reduce the texture improvement effect. Therefore, Mo can be contained at 0.01 wt% or less. Its lower limit is not particularly restricted, but it segregates at the surface and grain boundaries, thereby playing a role in improving the texture. Therefore, it can be contained at 0.001 wt% or more. That is to say, Mo can be contained at 0.001 to 0.010 wt%.

[0067] Cr: 0.50 wt% or less

[0068] Chromium (Cr) plays a role in improving iron loss by increasing the resistivity. If the Cr content is too high, the magnetic flux density may decrease. More specifically, when further containing Cr, it can be contained at 0.01 to 0.10 wt%.

[0069] Zr: 0.005 wt% or less

[0070] If an excessive amount of zirconium (Zr) is added, it may cause magnetic deterioration due to the formation of inclusions in the steel. Therefore, Zr can be contained at 0.005 wt% or less. Its lower limit is not particularly restricted, but due to the steelmaking cost, it can be 0.0001 wt%. That is to say, Zr can be contained at 0.0001 to 0.0050 wt%.

[0071] The remainder contains Fe and inevitable impurities. Regarding the inevitable impurities, they are impurities mixed in during the steelmaking process and the manufacturing process of the non-oriented electrical steel sheet, which are well-known in the art, so specific descriptions are omitted. In one embodiment of the present invention, in addition to the aforementioned alloy components, the addition of other elements is not excluded, and the inclusion method can be different within the scope of not damaging the technical idea of the present invention. If additional elements are further included, they replace a part of the Fe in the remainder.

[0072] For the non-oriented electrical steel sheet according to one embodiment of the present invention, its average grain size can be 50 to 150 μm. When an appropriate average grain size is ensured, the magnetic properties can be improved. In particular, the high-frequency iron loss can be improved. In one embodiment of the present invention, for the grain size, assuming there is a virtual circle with the same area as the grain area, the diameter of this circle is the grain size. The average grain size can be calculated by 2×(measured area÷number of grains÷π) 0.5 . The grain size can be measured based on the rolling vertical plane (TD plane). The measurement position is not particularly limited, but it can be measured at 1 / 4 to 3 / 4 of the overall thickness of the steel sheet. More specifically, the average grain size can be 60 to 95 μm.

[0073] For the non-oriented electrical steel sheet according to one embodiment of the present invention, the distribution density of MgS precipitates with a diameter of 100 nm or less can be 0.01 particles / μm 2 or less.

[0074] MgS precipitates with a diameter of 100 nm or less segregate at the grain boundaries, resulting in a reduction in the effective content of S that improves the texture, and the texture improvement effect is significantly reduced, thus having an adverse effect on the magnetic properties. Therefore, it is preferably suppressed as much as possible. MgS precipitates refer to particles formed by the aggregation of Mg and S, indicating the part where the contents of Mg and S are higher than the base level of the steel sheet. The precipitates can be measured using a transmission electron microscope (TEM). Similar to the grain size, assuming there is a virtual circle, the diameter of this circle is the diameter of the precipitate, and it can be measured based on the rolling vertical plane (TD plane). The lower limit of the diameter of the precipitate is not restricted, but due to measurement limitations, it can be 1 nm. MgS precipitates with a diameter exceeding 100 nm are coarse and have little impact on the magnetic properties, so they will not be restricted separately. For the distribution density of MgS precipitates, more specifically, it can be 0.001 to 0.007 particles / μm 2 .

[0075] An non-oriented electrical steel sheet according to an embodiment of the present invention has an area fraction of {111} / / ND orientation of 20 area% or less. Here, {111} / / ND refers to grains in which the {111} plane of the grains is parallel to the rolling plane (ND plane) within 15°. As the orientation fraction of {111} / / ND increases, the magnetocrystalline anisotropy energy increases, and more energy is required for magnetization, so the magnetic properties deteriorate, and it is necessary to reduce the {111} / / ND fraction. For the {111} / / ND fraction, a sufficiently wide area containing more than 10,000 grains is measured by EBSD. More specifically, the {111} / / ND orientation fraction can be 3 to 16 area%.

[0076] An non-oriented electrical steel sheet according to an embodiment of the present invention, when the texture is represented by ODF, the orientation with the highest intensity can be within 10° from {001}<130>. This means that a large number of grains with orientations near {001}<130> are formed. {001}<130> is the orientation with the most excellent circumferential average magnetism. Due to the low anisotropy, it can contribute to the uniform exhibition of excellent magnetism in all directions. For the orientation with the highest intensity, it is confirmed by using the data measured by EBSD and represented by ODF. More specifically, the orientation with the highest intensity can be in the range of 2° to 8° from {001}<130>.

[0077] An non-oriented electrical steel sheet according to an embodiment of the present invention has excellent anisotropy of magnetic flux density and excellent high-frequency iron loss. When manufacturing a motor for environmentally friendly vehicle drive using the non-oriented electrical steel sheet according to an embodiment of the present invention, without adding elements such as Sn and Sb, it will also have excellent magnetic properties uniformly in all in-plane directions, so it has advantages.

[0078] Specifically, for a thickness of 0.25 mm, the iron loss (W 10 / 400 ) of the non-oriented electrical steel sheet is 13.5 W / kg or less, the magnetic flux density (B 50(90°) ) measured in the direction perpendicular to rolling is 1.64 T or more, and the magnetic flux density (B 50(55°) ) measured in the direction forming a 55-degree angle with the rolling direction is 1.63 T or more. B50(55°) / B50(90°) can be 0.98 or more. The iron loss (W 10 / 400 ) is the iron loss when excited by a magnetic flux density of 1.0 T at a frequency of 400 Hz. The magnetic flux density (B 50 ) is the magnetic flux density induced under a magnetic field of 5000 A / m. More specifically, the iron loss (W 10 / 400 ) of the non-oriented electrical steel sheet is 10.0 to 13.3 W / kg, the magnetic flux density (B 50(90°) ) measured in the direction perpendicular to rolling is 1.64 to 1.67 T, and the magnetic flux density (B50(55°) ) is from 1.63 to 1.66 T, and B50(55°) / B50(90°) can be from 0.990 to 0.999.

[0079] A method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes: a step of hot rolling a slab to manufacture a hot-rolled sheet; a step of annealing the hot-rolled sheet; a step of cold rolling the hot-rolled sheet to manufacture a cold-rolled sheet; and a step of annealing the cold-rolled sheet.

[0080] First, the slab is hot rolled.

[0081] Regarding the alloy composition of the slab, it has been described in the alloy composition of the aforementioned non-oriented electrical steel sheet, so repeated description is omitted. During the manufacturing process of the non-oriented electrical steel sheet, the alloy composition does not substantially change, so the alloy compositions of the non-oriented electrical steel sheet and the slab are substantially the same.

[0082] Specifically, in terms of weight %, the slab contains Si: 2.5 to 4.5%, Al: 0.1 to 1.5%, Mn: 0.1 to 0.5%, and the balance contains Fe and inevitable impurities.

[0083] Regarding other additional elements, it has been described in the alloy composition of the non-oriented electrical steel sheet, so repeated description is omitted.

[0084] Before hot rolling the slab, heating can be performed. The heating temperature of the slab is not limited, but the slab can be heated to below 1200°C. If the heating temperature of the slab is too high, precipitates such as AlN and MnS present in the slab will redissolve and then precipitate finely during hot rolling and annealing, thereby inhibiting grain growth and possibly causing a decrease in magnetism.

[0085] Next, the slab is hot rolled to manufacture a hot-rolled sheet. The thickness of the hot-rolled sheet can be from 1.8 to 2.3 mm. In the step of manufacturing the hot-rolled sheet, the finish rolling temperature can be 800°C or higher. Specifically, it can be 800 to 1000°C. For the hot-rolled sheet, coiling can be performed at a temperature below 700°C.

[0086] After the step of manufacturing the hot-rolled sheet, hot-rolled sheet annealing is performed. Figure 1 is a graph schematically showing the thermal history over time in the hot-rolled sheet annealing process.

[0087] As Figure 1As shown, the annealing steps of the hot-rolled sheet include: 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 / second or more; a first soaking step of maintaining for 20 to 60 seconds within a range of 10°C of the first soaking temperature (T1); 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; a second soaking step of maintaining for 30 to 90 seconds within a range of 10°C of the second soaking temperature (T2).

[0088] At this time, the temperature of each step refers to the temperature of the surface of the steel sheet in each step.

[0089] 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 / second or more. For annealing of the hot-rolled sheet, rapid heating at a heating rate of 30°C / second or more helps to improve the texture. More specifically, the heating rate can be 35 to 150°C / second. It can also be cooled after heating to a temperature above the first soaking temperature (T1) and then adjusted to the first soaking temperature (T1).

[0090] The heating step can be carried out for 40 to 100 seconds starting from an initial temperature of 10 to 50°C. At this time, the heating rate can be the average heating rate per hour from the initial temperature to the end temperature. At a temperature below the initial temperature, after heating at a general heating rate of less than 30°C / second, rapid heating can be carried out.

[0091] Next, in the first soaking step, it is maintained for 20 to 60 seconds within a range of 10°C of the first soaking temperature (T1). The first soaking temperature (T1) can be any temperature between 980°C and 1100°C. Maintaining a certain temperature within a range of 10°C allows annealing for 20 to 60 seconds. If the first soaking temperature is too low or the time is too short, the grains will not grow sufficiently, and the development of the {111} / / ND orientation in the subsequent recrystallization annealing step after cold rolling will be significant, which may lead to deterioration of magnetism. If the first soaking temperature is too high or too long, the orientation development away from {001}<130> during recrystallization annealing after cold rolling may lead to magnetic deterioration. More specifically, the first soaking temperature (T1) is 1000°C to 1050°C and can be maintained for 30 to 50 seconds. It can be maintained within a range of 5°C from the first soaking temperature.

[0092] Next, in the cooling step, it passes from the first soaking temperature (T1) to a second soaking temperature (T2) of 750°C to 850°C within 30 seconds. At this time, if the time of the cooling step becomes too long, texture improvement may not be fully achieved. More specifically, the cooling step can be carried out for 5 to 20 seconds.

[0093] Next, in the second soaking step, it is maintained within a range of 10°C of the second soaking temperature (T2) 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, and thus the texture improvement effect may be reduced. If the second soaking temperature is too high or the time is too long, fine MgS precipitates are formed, which may lead to deterioration of 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 range of 5°C from the second soaking temperature.

[0094] After the second soaking step, cooling is performed as needed.

[0095] Next, the hot-rolled sheet is cold-rolled to manufacture a cold-rolled sheet. For cold rolling, the final thickness is rolled to 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, a thickness difference in the width direction of the steel sheet may occur.

[0096] Next, the cold-rolled sheet is annealed. The cold-rolled sheet annealing step can be performed in a mixed gas of hydrogen (H2) and nitrogen (N2) and an environment with a dew point temperature of -10°C or lower. By annealing in an environment with a low dew point temperature, surface oxidation can be suppressed and surface segregation of S can be promoted, thereby forming an excellent texture throughout the thickness. More specifically, the dew point temperature can be -10 to -50°C. More specifically, it can be -15 to -45°C. The mixed gas can contain 40% by volume or less of hydrogen and 60% by volume or more of nitrogen. This environment can also be applied to the following heating step and soaking step.

[0097] The cold-rolled sheet annealing step includes a heating step of heating from an initial temperature of 20 to 50°C to the soaking temperature at a heating rate of 25°C / second or more. By rapidly heating during cold-rolled sheet annealing, the texture can be improved. More specifically, the heating can be performed at a heating rate of 35 to 150°C / second.

[0098] The cold-rolled sheet annealing step can include a soaking step of soaking at a soaking temperature of 900 to 1100°C. If the soaking temperature is too low, the grains cannot grow sufficiently or the deformed structure remains, which may lead to poor iron loss. If the soaking temperature is too high, the eddy current loss increases and the {001}<130> orientation decreases, which may lead to deterioration of magnetic properties. More specifically, the soaking can be performed at a soaking temperature of 950 to 1050°C. It can be annealed at the soaking temperature for 30 to 50 seconds.

[0099] During the cold-rolled sheet annealing, all (i.e., 99% or more) of the processing structure formed in the cold rolling step can be recrystallized.

[0100] After annealing the cold-rolled sheet, an insulating coating film can be formed. The insulating coating film can be processed into an organic film, an inorganic film, and an organic-inorganic composite film, or can be processed with other insulating film-forming agents.

[0101] Hereinafter, the present invention will be further described in detail by way of examples. However, the following examples are only for illustrating the present invention, and the present invention is not limited to the following examples.

[0102] Example 1

[0103] A slab is manufactured, which contains the components shown in Table 1 and Table 2 and the balance of Fe and inevitable impurities. The slab is heated to 1150 °C and hot-rolled at a finishing temperature of 880 °C to manufacture a hot-rolled sheet with a thickness of 2.0 m. After the first and second hot-rolled sheet annealings of the hot-rolled sheet under the conditions in Table 3 below, it is cold-rolled to a thickness of 0.25 mm. Then, cold-rolled sheet annealing is carried out under the conditions in Table 4.

[0104] For each specimen, the average grain diameter, the density of MgS precipitates below 100 nm, the {111} / / ND orientation fraction, and the angular difference of {001}<130> are shown in Table 4.

[0105] For the average grain size of the grains, the TD cross-section of the specimen is polished to an area of 100 mm 2 Above, after measuring by EBSD, it is merged through the Merge function of the OIM software, and the average number (Average Number) and area fraction (Area fraction) values obtained when calculating by the particle size (diameter) function are adopted.

[0106] The density of MgS precipitates below 100 nm is obtained as follows: The final annealed sheet is made into a TEM specimen by the replica method, and among the precipitates that appear when observing an area of 10000 μm 2 above, the number of precipitates in which the length of the longest line segment of the shape is below 100 nm and the peaks of Mg and S appear simultaneously when analyzing the composition by EDS is divided by the measured area.

[0107] The {111} / / ND orientation fraction is obtained as follows: The EBSD measurement data is partitioned in the OIM software so that when ND has a <111> direction within an error angle of 15 degrees, the fraction value that appears in the partition summary information.

[0108] The angular difference of {001}<130> is obtained as follows: Calculate the ODF from the EBSD data to calculate the orientation with the maximum intensity, and calculate the misorientation value between this orientation and the {001}<130> orientation.

[0109] For magnetic properties such as magnetic flux density and iron loss, five specimens with a width of 60 mm × a length of 60 mm were cut out. For each specimen, the iron loss was measured in the rolling direction and the direction perpendicular to the rolling direction using a single sheet tester, and the average value was represented. For the magnetic flux density, the measurement was carried out in a direction forming a 55-degree angle with the direction perpendicular to the rolling direction and the rolling direction.

[0110] At this time, W 10 / 400 is the iron loss when the magnetic flux density of 1.0 T is excited at a frequency of 400 Hz, and B 50 is the magnetic flux density induced under a magnetic field of 5000 A / m.

[0111]

Table 1

[0112]

[0113]

Table 2

[0114]

[0115]

Table 3

[0116]

[0117]

Table 4

[0118]

[0119]

Table 5

[0120]

[0121] As shown in Tables 1 to 5, when the hot-rolled sheet is annealed and the temperature and time are appropriately adjusted, the {001}<130> crystal orientation develops, and it can be confirmed that the magnetic flux density and iron loss are excellent, and the anisotropy of the magnetic flux density is excellent.

[0122] On the other hand, when the hot-rolled sheet is annealed and the temperature and time are not appropriately adjusted, the formation of the {001}<130> crystal orientation is less, and it can be confirmed that the magnetic flux density and iron loss are poor, and the anisotropy of the magnetic flux density is poor.

[0123] The present invention can be implemented in various different ways and is not limited to the above embodiments. Those of ordinary skill in the technical field to which the present invention pertains can understand that the present invention can be implemented in other specific ways without changing the technical idea or essential features of the present invention. Therefore, it should be understood that the above embodiments are exemplary in all aspects and not restrictive.

Claims

1. An non-oriented electrical steel sheet, wherein, by weight%, the non-oriented electrical steel sheet contains Si: 2.5 to 4.5%, Al: 0.1 to 1.5%, Mn: 0.1 to 0.5%, and the balance contains Fe and inevitable impurities, the {111} / / ND orientation fraction is 20 area% or less. Here, {111} / / ND refers to grains in which the {111} plane of the grains is parallel to the rolling plane (ND plane) within 15°, when the texture is represented by ODF, the orientation with the highest strength is within 10° from {001}<130>.

2. The non-oriented electrical steel sheet according to claim 1, wherein, the non-oriented electrical steel sheet further contains one or more of Sn, Sb, C, N, Ti, Nb, and V, and their contents are each 0.0050% by weight or less.

3. The non-oriented electrical steel sheet according to claim 1, wherein, the non-oriented electrical steel sheet further contains 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.

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

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

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

7. A method for manufacturing a non-oriented electrical steel sheet, which includes: a step of hot rolling a slab to manufacture a hot rolled sheet. By weight%, the slab contains Si: 2.5 to 4.5%, Al: 0.1 to 1.5%, Mn: 0.1 to 0.5%, and the balance contains Fe and inevitable impurities; a step of annealing the hot rolled sheet; a step of cold rolling the hot rolled sheet to manufacture a cold rolled sheet; and a step of annealing the cold rolled sheet; 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 / second or more; a first soaking step of holding for 20 to 60 seconds within a range of 10°C of the first soaking temperature (T1); 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; a second soaking step of holding for 30 to 90 seconds within a range of 10°C of the second soaking temperature (T2).

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 method for manufacturing a non-oriented electrical steel sheet according to claim 7, wherein, the cold rolled sheet annealing step is performed in an environment of a mixed gas of hydrogen (H2) and nitrogen (N2) and a dew point temperature of -10°C or lower.

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

11. The manufacturing method of the 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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