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 the temperature deviation over the entire length of the coil during hot rolling is reduced by accelerated rolling, thereby improving the surface properties and magnetic properties. The method includes the steps of hot rolling a slab containing, by weight, 3.0 to 5.0% Si, 0.1 to 1.4% Mn, and 0.3 to 1.3% Al, with the balance being Fe and unavoidable impurities, to produce a hot rolled sheet, cold rolling the hot rolled sheet to produce a cold rolled sheet, and cold-rolling the cold rolled sheet, wherein in the step of producing the hot rolled sheet, the speed at which the front end of a rough rolled bar is charged into a hot finishing mill is 300 m / min to 800 m / min, and the speed at which the rear end of the rough rolled bar is charged relative to the front end is 1.25 times or more. The slab further contains one or more of P: 0.1% by weight or less (excluding 0%), Sn: 0.1% by weight or less (excluding 0%), and Sb: 0.1% by weight or less (excluding 0%), and the slab further contains one or more of C: 0.005% by weight or less (excluding 0%), N: 0.005% by weight or less (excluding 0%), S: 0.005% by weight or less (excluding 0%), Ti: 0.005% by weight or less (excluding 0%), Nb: 0.005% by weight or less (excluding 0%), and V: 0.005% by weight or less (excluding 0%).

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 temperature deviation over the entire coil length during hot rolling is reduced by accelerated rolling, thereby improving surface properties and 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 excellent magnetic properties are required for high efficiency in this process. In particular, with the recent rise in attention to environmentally friendly automobiles that are driven by motors instead of internal combustion engines, demand for non-oriented electrical steel sheets used as the core material of drive motors is increasing, leading to a demand for non-oriented electrical steel sheets that have both excellent magnetic properties and strength. 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 manufacture of more energy-efficient motors under the same conditions, while higher magnetic flux density allows for the manufacture of more compact motors and reduced copper loss. Therefore, non-oriented electrical steel sheets 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.

[0003] The characteristics of non-oriented electrical steel that should be considered 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 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.

[0004] A commonly used method to improve 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, 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 addition of alloying elements such as Si, Al, and Mn in large amounts reduces magnetic flux density and increases brittleness. Adding more than a certain amount makes cold rolling impossible, making commercial production impossible. While thinner electrical steel sheets offer superior high-frequency iron loss, the reduction in rollability due to brittleness is a critical issue. While there is a limit to the maximum total content of Si, Al, and Mn that can be commercially produced, optimizing the content of other trace elements can produce the highest-quality non-oriented electrical steel sheets with excellent magnetic properties and strength. On the other hand, the surface shape of the steel sheet also affects the magnetic properties, but no technology has been proposed to improve this. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides a non-oriented electrical steel sheet and a manufacturing method thereof, specifically, a non-oriented electrical steel sheet in which the temperature deviation over the entire coil length during hot rolling is reduced by accelerated rolling, thereby improving surface properties and magnetic properties, and a manufacturing method thereof. [Means for solving the problem]

[0006] The non-oriented electrical steel sheet of the present invention contains, by weight %, 3.0 to 5.0% Si, 0.1 to 1.4% Mn, 0.3 to 1.3% Al, and the balance being Fe and unavoidable impurities. When observing a 5 mm×5 mm area on the surface of the non-oriented electrical steel sheet of the present invention, the length of irregularities having a difference in height from the average height of 1.0 μm or more may be 3 mm or less. The magnetic flux density B50 is 1.603 + 0.96 × t for the thickness t (mm) of the steel plate2 (T) or more, and the iron loss W10 / 400 is 7.231 + 21.385 × t (W / kg) or less.

[0007] The non-oriented electrical steel sheet of the present invention may further contain one or more of P: 0.1% by weight or less (excluding 0%), Sn: 0.1% by weight or less (excluding 0%), and Sb: 0.1% by weight or less (excluding 0%).

[0008] The non-oriented electrical steel sheet of the present invention may further contain one or more of C: 0.005% by weight or less (excluding 0%), N: 0.005% by weight or less (excluding 0%), S: 0.005% by weight or less (excluding 0%), Ti: 0.005% by weight or less (excluding 0%), Nb: 0.005% by weight or less (excluding 0%), and V: 0.005% by weight or less (excluding 0%).

[0009] The non-oriented electrical steel sheet of the present invention may further contain one or more of Cu: 0.005 to 0.2 wt %, Cr: 0.01 to 0.5 wt %, Ni: 0.05 wt % or less (excluding 0%), and Zn: 0.01 wt % or less (excluding 0%).

[0010] The non-oriented electrical steel sheet of the present invention may further contain one or more of Bi: 0.200% by weight or less (excluding 0%), Pb: 0.200% by weight or less (excluding 0%), Ge: 0.200% by weight or less (excluding 0%), and As: 0.200% by weight or less (excluding 0%).

[0011] The non-oriented electrical steel sheet of the present invention may further contain one or more of Mo: 0.03% by weight or less (excluding 0%), B: 0.0050% by weight or less (excluding 0%), Ca: 0.0050% by weight or less (excluding 0%), Zr: 0.005% by weight or less (excluding 0%), and Mg: 0.0050% by weight or less (excluding 0%).

[0012] The method for producing a non-oriented electrical steel sheet of the present invention includes the steps of hot rolling a slab containing, by weight, 3.0 to 5.0% Si, 0.1 to 1.4% Mn, and 0.3 to 1.3% Al, with the balance being Fe and unavoidable impurities, to produce a hot-rolled sheet, cold rolling the hot-rolled sheet to produce a cold-rolled sheet, and cold-rolling the cold-rolled sheet, wherein in the step of producing the hot-rolled sheet, the speed at which the front end of a rough-rolled bar is charged into a hot finishing mill is 300 m / min to 800 m / min, and the speed at which the rear end of the rough-rolled bar is charged relative to the front end is 1.25 times or more.

[0013] The slab may further contain one or more of P: 0.1% by weight or less (excluding 0%), Sn: 0.1% by weight or less (excluding 0%), and Sb: 0.1% by weight or less (excluding 0%).

[0014] The slab may further contain one or more of C: 0.005% by weight or less (excluding 0%), N: 0.005% by weight or less (excluding 0%), S: 0.005% by weight or less (excluding 0%), Ti: 0.005% by weight or less (excluding 0%), Nb: 0.005% by weight or less (excluding 0%), and V: 0.005% by weight or less (excluding 0%).

[0015] The slab may further contain one or more of Cu: 0.005 to 0.2 wt %, Cr: 0.01 to 0.5 wt %, Ni: 0.05 wt % or less (excluding 0%), and Zn: 0.01 wt % or less (excluding 0%).

[0016] The slab may further contain one or more of Bi: 0.200 wt% or less (excluding 0%), Pb: 0.200 wt% or less (excluding 0%), Ge: 0.200 wt% or less (excluding 0%), and As: 0.200 wt% or less (excluding 0%).

[0017] The slab may further contain one or more of Mo: 0.03% by weight or less (excluding 0%), B: 0.0050% by weight or less (excluding 0%), Ca: 0.0050% by weight or less (excluding 0%), Zr: 0.005% by weight or less (excluding 0%), and Mg: 0.0050% by weight or less (excluding 0%).

[0018] The method may further include a step of heating the slab to 1200°C or less before the step of producing the hot-rolled plate. The step of producing a hot-rolled sheet may include a step of rough rolling a slab to produce a bar, a step of finish rolling the bar, and a step of coiling the finish-rolled hot-rolled sheet, and at the start of the finish rolling step, the temperature deviation between a region from the forefront end of the bar to 50 m and a region from the rear end to 50 m may be 30°C or less.

[0019] The speed at which the slabs are charged into the hot roughing mill may be 40 m / min to 100 m / min.

[0020] After the step of producing the hot-rolled sheet, a step of annealing the hot-rolled sheet at 600 to 1100°C may be further included.

[0021] The step of manufacturing the cold-rolled sheet may include a step of first cold-rolling the hot-rolled sheet to manufacture a first cold-rolled sheet, a step of intermediate-annealing the first cold-rolled sheet, and a step of second cold-rolling the first cold-rolled sheet to manufacture a second cold-rolled sheet. [Effects of the Invention]

[0022] The non-oriented electrical steel sheet of the present invention is excellent in surface shape, magnetic flux density, and core loss. Ultimately, the non-oriented electrical steel sheet of the present invention contributes to the production of environmentally friendly motors for automobiles, highly efficient motors for home appliances, and super premium class electric motors. DETAILED DESCRIPTION OF THE INVENTION

[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 may 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 form includes the plural form unless the context clearly dictates otherwise. As used in the specification, the meaning of "comprising" embodies certain features, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components. When a part is referred to as being "on" another part, it may be directly on top of the other part, or there may be other parts between them. In contrast, when a part is referred to as being "directly on top" of another part, there are no other parts between them.

[0025] Unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight. In one embodiment of the present invention, the term "additionally containing an additional element" means that the remaining iron (Fe) is replaced by the additional amount of the additional element. 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] While the present invention may be embodied in various different forms, it is to be understood that the invention is not limited to the specific embodiments set forth herein, and that the invention may be embodied in various different forms, without departing from the spirit or scope of the present invention.

[0027] The non-oriented electrical steel sheet of the present invention contains, by weight %, 3.0 to 5.0% Si, 0.1 to 1.4% Mn, 0.3 to 1.3% Al, and the balance being Fe and inevitable impurities. The reasons for limiting the components of the non-oriented electrical steel sheet will be explained below.

[0028] Si:3.0~5.0wt% Silicon (Si) increases the resistivity of the material and reduces iron loss. If too little Si is added, the iron loss improvement effect may be 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 may form in the surface layer. More specifically, it may contain 3.2 to 4.5 wt. %. Even more specifically, it may contain 3.3 to 4.0 wt. %.

[0029] Mn:0.1~1.4wt% 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 sulfides are formed, causing a deterioration in magnetic properties. If too much Mn is added, fine MnS precipitates excessively, promoting the formation of a {111} texture that is unfavorable to magnetic properties and resulting in a rapid decrease in magnetic flux density. More specifically, Mn can be added in an amount of 0.3 to 1.0 wt%.

[0030] Al: 0.3 to 1.3% Aluminum (Al) increases the resistivity of the material, reducing 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 desired 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. More specifically, the Al content can be 0.5 to 1.0 wt. %. Even more specifically, the Al content can be 0.6 to 0.9 wt. %.

[0031] The non-oriented electrical steel sheet of the present invention may further contain one or more of P: 0.1% by weight or less (excluding 0%), Sn: 0.1% by weight or less (excluding 0%), and Sb: 0.1% by weight or less (excluding 0%).

[0032] P: 0.1% by weight or less Phosphorus (P) acts as a grain boundary segregating element, and if added in excessive amounts, it can delay recrystallization and deteriorate strength uniformity in the rolling direction and the direction perpendicular to the rolling direction. More specifically, P can be contained in an amount of 0.0001 to 0.05 wt %. Even more specifically, P can be contained in an amount of 0.001 to 0.01 wt %.

[0033] Sn: 0.1% by weight or less (excluding 0%) and / or Sb: 0.1% by weight or less (excluding 0%) Tin (Sn) and antimony (Sb) can be added to improve magnetic properties by segregating at grain boundaries and surfaces, improving the texture of the material and suppressing surface oxidation. Addition of excessive amounts of Sn and Sb can lead to severe grain boundary segregation, degrading surface quality, and increasing hardness, which can lead to breakage of the cold-rolled sheet and reduced rollability. Therefore, one or more of Sn and Sb can be added within the above-mentioned ranges. More specifically, the alloy can further contain one or more of 0.001 to 0.08 wt% Sn and 0.001 to 0.08 wt% Sb. Even more specifically, the alloy can further contain one or more of 0.01 to 0.05 wt% Sn and 0.01 to 0.05 wt% Sb.

[0034] The non-oriented electrical steel sheet of the present invention may further contain one or more of C: 0.005% by weight or less (excluding 0%), N: 0.005% by weight or less (excluding 0%), S: 0.005% by weight or less (excluding 0%), Ti: 0.005% by weight or less (excluding 0%), Nb: 0.005% by weight or less (excluding 0%), and V: 0.005% by weight or less (excluding 0%).

[0035] C: 0.0050% by weight or less Carbon (C) causes magnetic aging and combines with other impurity elements to form carbides, which degrade magnetic properties, and improves strength by hindering dislocation movement. If C is included in an excessive amount, the fraction of fine carbides may increase, resulting in a deterioration of magnetic properties. There is no particular lower limit for C, but considering productivity, it can contain 0.0005 wt% or more. In other words, it can contain 0.0005 to 0.0050 wt% C. More specifically, it can contain 0.0010 to 0.0030 wt% C.

[0036] 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 since N helps improve strength, the lower limit should be set at 0.0003 wt%. In other words, 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%.

[0037] S: 0.0050% by weight or less Sulfur (S) forms fine precipitates of MnS and CuS, which deteriorates magnetic properties and hot workability. However, in the present invention, S promotes the development of crystal grains with a specific orientation and helps improve magnetic flux density, so it can be added in an amount of 0.0005 wt% or more. More specifically, S can be contained in an amount of 0.0010 to 0.0030 wt%.

[0038] Ti: 0.0050% by weight or less Titanium (Ti) has a strong tendency to form precipitates in steel, forming fine carbides, nitrides, or sulfides inside the base material, which inhibit grain growth and domain wall motion, thereby deteriorating core loss. Therefore, the Ti content may be 0.0050 wt% or less. The lower limit is not particularly limited, but it may be set to 0.0003 wt% depending on steelmaking costs. In other words, Ti may be contained in an amount of 0.0003 to 0.0050 wt%. More specifically, Ti may be contained in an amount of 0.0003 to 0.0030 wt%.

[0039] Nb: 0.0050% by weight or less Niobium (Nb) has a strong tendency to form precipitates in steel, forming fine carbides, nitrides, or sulfides inside the base material, which inhibit grain growth and domain wall motion, thereby deteriorating core loss. Therefore, the Nb content may be 0.0050 wt% or less. The lower limit is not particularly limited, but it may be set to 0.0003 wt% depending on steelmaking costs. In other words, Nb may be contained in an amount of 0.0003 to 0.0050 wt%. More specifically, Nb may be contained in an amount of 0.0003 to 0.0030 wt%.

[0040] V: 0.0050% by weight or less Vanadium (V) has a strong tendency to form precipitates in steel, forming fine carbides, nitrides, or sulfides inside the base material, which inhibit grain growth and domain wall motion, thereby deteriorating core loss. Therefore, the V content may be 0.0050 wt% or less. The lower limit is not particularly limited, but it may be set to 0.0003 wt% depending on steelmaking costs. In other words, V may be contained in an amount of 0.0003 to 0.0050 wt%. More specifically, V may be contained in an amount of 0.0003 to 0.0030 wt%.

[0041] The non-oriented electrical steel sheet according to the present invention may further contain one or more of Cu: 0.005 to 0.2 wt %, Cr: 0.01 to 0.5 wt %, Ni: 0.05 wt % or less (excluding 0%), and Zn: 0.01 wt % or less (excluding 0%).

[0042] Cu:0.005~0.2wt% Copper (Cu) plays a role in forming sulfides together with Mn. If Cu is added in an excessively small amount, fine CuMnS may precipitate, deteriorating magnetic properties. If Cu is added in an excessively large amount, high-temperature brittleness may occur, which may lead to crack formation during continuous casting or hot rolling. More specifically, Cu may be contained in an amount of 0.01 to 0.1 wt %.

[0043] Cr:0.01~0.50wt% Chromium (Cr) plays a role in increasing resistivity and improving iron loss. If too little Cr is added, the effect of increasing resistivity may be insufficient. If too much Cr is added, the magnetic flux density may decrease. More specifically, if Cr is further added, it may be contained in an amount of 0.05 to 0.30 wt %.

[0044] Ni: 0.05% by weight or less Nickel (Ni) reacts with impurity elements to form fine sulfides, carbides, and nitrides, which can have a detrimental effect on magnetic properties. More specifically, Ni can be contained in an amount of 0.0001 to 0.0500 wt %. Even more specifically, Ni can be contained in an amount of 0.0010 to 0.0100 wt %.

[0045] Zn: 0.01% by weight or less If the zinc (Zn) content is excessive, it may act as an impurity and deteriorate the magnetic properties. Therefore, Zn can be further added within the above-mentioned range. More specifically, it can be contained in an amount of 0.0001 to 0.0100% by weight. Even more specifically, it can be contained in an amount of 0.0005 to 0.0050% by weight.

[0046] The non-oriented electrical steel sheet according to the present invention may further contain one or more of Bi: 0.200% by weight or less (excluding 0%), Pb: 0.200% by weight or less (excluding 0%), Ge: 0.200% by weight or less (excluding 0%), and As: 0.200% by weight or less (excluding 0%).

[0047] When bismuth (Bi), lead (Pb), germanium (Ge) and arsenic (As) are added, they segregate at the grain boundaries, easing stress concentration at the grain boundaries during cold rolling and reducing the stress concentration during the subsequent recrystallization annealing process. <111> / / Improves magnetic flux density by suppressing recrystallization of ND-oriented crystal grains. When added appropriately, these elements can provide the aforementioned additional effects. However, excessive amounts can cause excessive segregation, inhibiting grain growth and actually degrading magnetic flux density and core loss. More specifically, the alloy may further contain one or more of Bi: 0.0001-0.200 wt%, Pb: 0.0001-0.200 wt%, Ge: 0.0001-0.200 wt%, and As: 0.0001-0.200 wt%. More specifically, the alloy may further contain one or more of Bi: 0.0010-0.100 wt%, Pb: 0.0010-0.100 wt%, Ge: 0.0010-0.100 wt%, and As: 0.0010-0.100 wt%.

[0048] The non-oriented electrical steel sheet of the present invention may further contain one or more of Mo: 0.03% by weight or less (excluding 0%), B: 0.0050% by weight or less (excluding 0%), Ca: 0.0050% by weight or less (excluding 0%), Zr: 0.005% by weight or less (excluding 0%), and Mg: 0.0050% by weight or less (excluding 0%). These react with the unavoidably contained C, S, N, etc. to form fine carbides, nitrides, or sulfides, which may adversely affect the magnetic properties, so the upper limit can be set as described above.

[0049] More specifically, it may further contain one or more of Mo: 0.0001 to 0.03 wt%, B: 0.0001 to 0.0050 wt%, Ca: 0.0001 to 0.0050 wt%, Zr: 0.0001 to 0.005 wt%, and Mg: 0. Even more specifically, it may further contain one or more of Mo: 0.001 to 0.01 wt%, B: 0.0005 to 0.0030 wt%, Ca: 0.0005 to 0.0030 wt%, Zr: 0.0005 to 0.0030 wt%, and Mg: 0.0005 to 0.0030 wt%.

[0050] Other impurities The balance is Fe. Other inevitable impurities may be included. The inevitable 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. In the present invention, the addition of elements other than the above-mentioned alloy components is not excluded, 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.

[0051] The non-oriented electrical steel sheet of the present invention has an excellent surface shape. If the surface shape is poor, the shape of the core when manufactured into a motor will be poor, resulting in reduced motor efficiency. The surface shape of a non-oriented electrical steel sheet is mainly determined during cold rolling, and one of the factors that influences cold rolling is the material quality of the hot-rolled sheet. Material variation in a hot-rolled sheet is mainly caused by temperature deviation between the front and rear ends during hot finish rolling, which can be corrected by accelerated rolling during hot rolling. More specific methods will be described in detail in the method for manufacturing a non-oriented electrical steel sheet of the present invention.

[0052] The non-oriented electrical steel sheet of the present invention may have an average crystal grain size of 25 to 125 μm. When an appropriate average crystal grain size is ensured, magnetic properties can be improved. In particular, high-frequency iron loss can be improved. In the present invention, the crystal grain size means the diameter of a virtual circle having the same area as the crystal grain. The average crystal grain size is calculated by 2 × (measured area ÷ number of crystal grains ÷ π). 0.5The grain size can be measured based on a plane parallel to the rolling perpendicular plane (TD plane). There are no particular limitations on the measurement position, but measurements can be made at a point 1 / 4 to 3 / 4 of the way through the steel sheet thickness. More specifically, the average grain size may be 60 to 95 μm.

[0053] Furthermore, the non-oriented electrical steel sheet of the present invention has an excellent surface shape. Specifically, when observing a 5 mm × 5 mm area on the surface of the non-oriented electrical steel sheet of the present invention, the length of irregularities where the difference in height from the average height is 1.0 μm or more may be 3 mm or less. If an insulating coating is present on the non-oriented electrical steel sheet, the insulating coating can be removed so that the surface characteristics of the non-oriented electrical steel sheet satisfy the above-mentioned conditions. There are no particular restrictions on the method for removing the insulating coating, and it can be removed by immersing the sheet in an NaOH solution at a temperature of 80°C for about 30 minutes. The average height refers to the average height relative to the total area (length) of the sheet being measured. The height difference may be + or -, and the length of the irregularities refers to the length in a specific direction where the length is the longest. The length of the irregularities can be measured using a method for measuring surface roughness, such as a method using a confocal laser.

[0054] Furthermore, the non-oriented electrical steel sheet of the present invention has excellent magnetic flux density and iron loss, which is advantageous in terms of output and energy efficiency when used to manufacture environmentally friendly automobile drive motors. Specifically, the magnetic flux density B of non-oriented electrical steel sheet 50 is 1.603 + 0.96 × t 2 (T) or more. In this case, t means the thickness of the steel plate (mm). B 50 means the magnetic flux density induced in a magnetic field of 5000 A / m. More specifically, the magnetic flux density B at 0.25 mm 50 is 1.67 to 1.70T, magnetic flux density B at 0.20mm 50 is 1.65 to 1.68T, magnetic flux density B at 0.15mm 50 is 1.63T~1.66T, magnetic flux density B at 0.10mm 50 may be 1.62T to 1.65T.

[0055] At the same time, the iron loss (W 10 / 400 ) may be 7.231 + 21.385 × t or less, where t means the thickness (mm) of the steel sheet. More specifically, the iron loss (W 10 / 400 ) is 12.3W / kg to 10.8W / kg, iron loss at 0.20mm (W 10 / 400 ) is 11.3W / kg to 9.8W / kg, iron loss at 0.15mm (W 10 / 400 ) is 10.1W / kg to 8.6W / kg, iron loss at 0.10mm (W 10 / 400 ) may be 9 W / kg to 7.5 W / kg.

[0056] 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, cold rolling the hot-rolled sheet to produce a cold-rolled sheet, and cold-rolling the 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.

[0057] Specifically, the slab contains, by weight, 3.0 to 5.0% Si, 0.1 to 1.4% Mn, and 0.3 to 1.3% Al, with the remainder being 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. 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 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, which may inhibit grain growth and reduce magnetic properties.

[0058] Next, the slab is hot rolled to produce a hot-rolled sheet. In the present invention, the speed at which the slab is charged into the hot roughing mill is 40 m / min to 100 m / min, the speed at which the front end of the rough-rolled bar is charged into the hot finishing mill is 300 m / min to 800 m / min, and the speed at which the front end of the rough-rolled bar is charged into the hot finishing mill is 1.25 times or more the speed at which the slab is charged into the hot roughing mill. In this case, the front end means the length from the front end of the bar to 50 m, and the rear end means the length from the rear end of the bar to 50 m.

[0059] If the speed is too slow, the time the slab is left standing after heating varies depending on its length, resulting in significant temperature deviation in the longitudinal direction of the slab, which manifests as surface defects in the final non-oriented electrical steel sheet. If the speed is too fast, the rolling mill is overloaded, and proper rolling may not be performed. More specifically, the speed at which the slab is charged into the hot roughing mill is 50 m / min to 900 m / min, the speed at which the front end of the rough-rolled bar is charged into the hot finishing mill is 350 m / min to 750 m / min, and the speed at which the front end of the rough-rolled bar is charged into the hot finishing mill is 1.25 to 2.0 times the speed at which the slab is charged into the hot roughing mill. The step of producing a hot-rolled sheet includes the steps of rough-rolling a slab to produce a bar, finish-rolling the bar, and coiling the finish-rolled hot-rolled sheet.

[0060] At the start of the finish rolling step, when the temperature is measured at any point between 1 / 4 and 3 / 4 of the way across the width of the bar, the temperature deviation between the region from the front end to 50 m of the bar and the region from the rear end to 50 m of the bar may be 30°C or less. If the temperature deviation is too large, the final non-oriented electrical steel sheet will have irregularities in the longitudinal direction, resulting in a poor surface shape.

[0061] The thickness of the hot-rolled sheet may be 1.8 to 2.5 mm. In the stage of producing the hot-rolled sheet, the finish rolling temperature may be 800°C or higher. If the finish rolling temperature of the hot rolling is excessively low, the rolling load increases and the hot-rolling workability decreases. Furthermore, a large amount of deformed structure remains in the hot-rolled steel sheet, which may cause an increase in the rolling load during the subsequent preliminary cold rolling process. In addition, the deformed structure may be removed during intermediate annealing. <111> / / Recrystallization of ND-oriented crystal grains is promoted, resulting in a deterioration in magnetic flux density. Specifically, the temperature may be 800 to 1000°C.

[0062] Hot-rolled steel sheets can be coiled at temperatures below 700°C. Controlling the coiling temperature too low can hinder recovery and recrystallization of the hot-rolled deformation structure. Rapid cooling of the steel sheet at a low temperature increases the cooling load, making it difficult to coil an overcooled coil. Conversely, excessively high temperatures can promote recovery and recrystallization, but can also cause additional oxidation due to atmospheric oxygen during coiling, leading to thicker scale formation and intergranular oxidation problems. Intergranular oxidation of hot-rolled steel sheets can promote grain boundary corrosion during the subsequent pickling process, potentially resulting in surface stripe defects and severe wear of the rolling rolls.

[0063] After the step of producing the hot-rolled sheet, the method may further include a step of annealing the hot-rolled sheet at a temperature in the range of 600 to 1100°C. If the annealing temperature of the hot-rolled sheet is too low, the recrystallized structure may not be formed or may grow finely, resulting in little effect in increasing magnetic flux density. If the annealing temperature is too high, the magnetic properties may deteriorate and the rolling workability may be impaired due to deformation of the sheet. More specifically, the hot-rolled sheet may be annealed at a temperature in the range of 850 to 1000°C. Annealing of the hot-rolled sheet is performed as necessary to increase the orientation advantageous for magnetic properties, and can be omitted. That is, the hot-rolled hot-rolled sheet can be cooled to 10 to 50°C and then cold-rolled. The annealing method is not particularly limited, and annealing can be performed in batch or continuous manner.

[0064] The hot-rolled sheet may be subjected to pickling as required.

[0065] Next, the hot-rolled sheet is cold-rolled. The step of producing the cold-rolled sheet may include the steps of: first cold-rolling the hot-rolled sheet to produce a first cold-rolled sheet; intermediate-annealing the first cold-rolled sheet; and second cold-rolling the first cold-rolled sheet to produce a second cold-rolled sheet. A single cold rolling is also possible. When cold-rolling is performed twice, the thickness of the first cold-rolled sheet may be 0.5 to 1.2 mm. If the thickness of the first cold-rolled sheet is too thin, the cold-rolling itself becomes difficult, and problems such as noticeable surface irregularities may occur. If the thickness of the first cold-rolled sheet is too thick, problems may occur in that it is difficult to ensure the magnetic properties of the final product. More specifically, the thickness of the first cold-rolled sheet may be 0.5 to 1.0 mm.

[0066] In the intermediate annealing step, the first cold-rolled sheet may be annealed at 950 to 1100°C for 60 to 150 seconds. If the intermediate annealing temperature is too low, it may be difficult to ensure the magnetic properties of the final product. If the intermediate annealing temperature is too high, it may be difficult to perform cold rolling. More specifically, in the intermediate annealing step, the sheet may be annealed at 950 to 1100°C for 60 to 150 seconds. After the intermediate annealing step, pickling can be carried out if necessary. In the step of producing a second cold-rolled sheet by second cold-rolling the first cold-rolled sheet, the thickness of the second cold-rolled sheet may be 0.10 to 0.30 mm, and the thickness of the second cold-rolled sheet may be the same as the thickness of the final produced non-oriented electrical steel sheet.

[0067] Next, the cold-rolled sheet is subjected to cold-rolled sheet annealing. When annealing the cold-rolled sheet, the soaking temperature is 900°C or higher. If the soaking temperature is too low, the grain growth may be insufficient. More specifically, the soaking temperature may be 900 to 1050°C. The soaking step may be performed for 45 to 100 seconds. During the soaking process, all (i.e., more than 99%) of the processed structure formed during the cold rolling stage can be recrystallized. After the soaking, an insulating coating can be formed. The insulating coating can be an organic, inorganic, or organic-inorganic composite coating, or it can be any other insulating coating agent. The present invention will be described in more detail with reference to the following examples, but these examples are merely for illustrative purposes and are not intended to limit the scope of the present invention. [Example]

[0068] Slabs were produced using the chemical compositions shown in Table 1, with the balance consisting of Fe and unavoidable impurities. They were heated to 1150°C and hot-rolled to a thickness of 2.0 mm. The slab speed when charging into the hot rolling mill was controlled as shown in Table 3 below, and the temperature deviation of the bar between the front and rear ends of the slab at the start of finish rolling was measured and summarized in Table 3 below. The hot-rolled sheet was then cooled to room temperature in air, first cold-rolled to a thickness of 0.8 mm, and intermediate annealed at 1050°C for 2 minutes. After annealing, the sheet was pickled and cold-rolled to a thickness of 0.25 mm.

[0069] The magnetic flux density and iron loss were measured using an Epstein test. The Epstein test specimens were 305mm x 30mm in size. The magnetic flux density B50 is the magnitude (Tesla) of the magnetic flux density induced in a magnetic field of 5000A / m, and the iron loss W10 / 400 is the loss (W / kg) when a magnetic flux density of 1.0 Tesla is induced at a frequency of 400Hz. The surface shape was measured using a Confocal laser measuring device capable of measuring roughness, a 3D surface roughness meter, etc. The maximum length of the irregularities on the test piece is summarized in Table 2 below.

[0070] [Table 1]

[0071] [Table 2]

[0072] [Table 3]

[0073] As shown in Tables 1 to 3, the inventive examples, in which the steel compositions were appropriately adjusted and the charging speed during charging into the hot rolling mill was appropriately adjusted, showed the development of a specific texture, resulting in excellent surface shape, iron loss, and magnetic flux density. On the other hand, if the steel composition is not properly adjusted, it can be seen that the core loss and magnetic flux density deteriorate. In addition, even if the steel composition is appropriately adjusted, if the charging speed at the time of charging into the hot rolling mill is not appropriately adjusted, it has been confirmed that a specific texture cannot be developed, resulting in deterioration of surface properties, iron loss, and magnetic flux density. [Example]

[0074] The magnetic properties were confirmed at various thicknesses using steel types 1, 3, 4, 10, and 13 of the invention examples.

[0075] [Table 4]

[0076] 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 will understand that the present invention can be embodied in other specific forms without changing the technical idea or essential characteristics of the present invention. Therefore, it should be understood that the above-described examples are illustrative in all respects and not limiting.

Claims

1. In weight percent, Si: 3.0 to 5.0%, Mn: 0.1 to 1.4%, Al: 0.3 to 1.3%, and the balance being Fe and inevitable impurities; A non-oriented electrical steel sheet characterized in that, when a 5 mm x 5 mm area on the surface is observed, the length of irregularities having a height difference from the average height of 1.0 μm or more is 3 mm or less.

2. The magnetic flux density B50 is 1.603 + 0.96 x t where t (mm) is the thickness of the steel plate. ２ 2. The non-oriented electrical steel sheet according to claim 1, wherein the tensile strength is 1.031 W / kg or more, and the iron loss W10 / 400 is 7.231 + 21.385 × t (W / kg) or less.

3. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of P: 0.1% by weight or less (excluding 0%), Sn: 0.1% by weight or less (excluding 0%), and Sb: 0.1% by weight or less (excluding 0%).

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

5. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of Cu: 0.005 to 0.2 wt %, Cr: 0.01 to 0.5 wt %, Ni: 0.05 wt % or less (excluding 0%), and Zn: 0.01 wt % or less (excluding 0%).

6. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of Bi: 0.200% by weight or less (excluding 0%), Pb: 0.200% by weight or less (excluding 0%), Ge: 0.200% by weight or less (excluding 0%), and As: 0.200% by weight or less (excluding 0%).

7. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of Mo: 0.03% by weight or less (except 0%), B: 0.0050% by weight or less (except 0%), Ca: 0.0050% by weight or less (except 0%), Zr: 0.005% by weight or less (except 0%), and Mg: 0.0050% by weight or less (except 0%).

8. A step of producing a hot-rolled sheet by hot-rolling a slab consisting of, in weight percent, 3.0 to 5.0% Si, 0.1 to 1.4% Mn, and 0.3 to 1.3% Al, with the balance being Fe and unavoidable impurities; cold-rolling the hot-rolled sheet to produce a cold-rolled sheet; annealing the cold-rolled sheet; In the step of producing the hot-rolled sheet, the speed at which the front end of the rough-rolled bar is charged into the hot finishing mill is 300 m / min to 800 m / min, and the speed at which the rear end of the rough-rolled bar is charged relative to the front end is 1.25 times or more.

9. 9. The method for producing a non-oriented electrical steel sheet according to claim 8, wherein the slab further contains one or more of P: 0.1% by weight or less (excluding 0%), Sn: 0.1% by weight or less (excluding 0%), and Sb: 0.1% by weight or less (excluding 0%).

10. 9. The method for producing a non-oriented electrical steel sheet according to claim 8, wherein the slab further contains one or more of C: 0.005% by weight or less (excluding 0%), N: 0.005% by weight or less (excluding 0%), S: 0.005% by weight or less (excluding 0%), Ti: 0.005% by weight or less (excluding 0%), Nb: 0.005% by weight or less (excluding 0%), and V: 0.005% by weight or less (excluding 0%).

11. 9. The method for producing a non-oriented electrical steel sheet according to claim 8, wherein the slab further contains one or more of Cu: 0.005 to 0.2 wt %, Cr: 0.01 to 0.5 wt %, Ni: 0.05 wt % or less (excluding 0%), and Zn: 0.01 wt % or less (excluding 0%).

12. 9. The method for producing a non-oriented electrical steel sheet according to claim 8, wherein the slab further contains one or more of Bi: 0.200% by weight or less (excluding 0%), Pb: 0.200% by weight or less (excluding 0%), Ge: 0.200% by weight or less (excluding 0%), and As: 0.200% by weight or less (excluding 0%).

13. 9. The method for producing a non-oriented electrical steel sheet according to claim 8, wherein the slab further contains one or more of Mo: 0.03% by weight or less (excluding 0%), B: 0.0050% by weight or less (excluding 0%), Ca: 0.0050% by weight or less (excluding 0%), Zr: 0.005% by weight or less (excluding 0%), and Mg: 0.0050% by weight or less (excluding 0%).

14. The method for manufacturing a non-oriented electrical steel sheet according to claim 8, further comprising the step of heating the slab to 1200°C or less before the step of manufacturing the hot-rolled sheet.

15. 9. The method for producing a non-oriented electrical steel sheet according to claim 8, wherein the step of producing the hot-rolled sheet comprises the steps of rough rolling the slab to produce a bar, finish rolling the bar, and coiling the finish-rolled hot-rolled sheet, and at the start of the finish rolling step, a temperature deviation between a region from a front end to 50 m of the bar and a region from a rear end to 50 m of the bar is 30° C. or less.

16. 9. The method of claim 8, wherein in the step of producing the hot-rolled sheet, the speed at which the slab is charged into the hot roughing mill is 40 m / min to 100 m / min.

17. The method for manufacturing a non-oriented electrical steel sheet according to claim 8, further comprising the step of annealing the hot-rolled sheet at 600 to 1100°C after the step of manufacturing the hot-rolled sheet.

18. The step of manufacturing the cold-rolled sheet includes: first cold-rolling the hot-rolled sheet to manufacture a first cold-rolled sheet; intermediately annealing the first cold-rolled sheet; The method of claim 8, further comprising: subjecting the first cold-rolled sheet to a second cold-rolling process to produce a second cold-rolled sheet.

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